Crustal architecture and tectonic evolution of the Cauvery Suture Zone, southern India

NASA Astrophysics Data System (ADS)

Chetty, T. R. K.; Yellappa, T.; Santosh, M.

2016-11-01

The Cauvery suture zone (CSZ) in southern India has witnessed multiple deformations associated with multiple subduction-collision history, with incorporation of the related accretionary belts sequentially into the southern continental margin of the Archaean Dharwar craton since Neoarchean to Neoproterozoic. The accreted tectonic elements include suprasubduction complexes of arc magmatic sequences, high-grade supracrustals, thrust duplexes, ophiolites, and younger intrusions that are dispersed along the suture. The intra-oceanic Neoarchean-Neoproterozoic arc assemblages are well exposed in the form of tectonic mélanges dominantly towards the eastern sector of the CSZ and are typically subjected to complex and multiple deformation events. Multi-scale analysis of structural elements with detailed geological mapping of the sub-regions and their structural cross sections, geochemical and geochronological data and integrated geophysical observations suggest that the CSZ is an important zone that preserves the imprints of multiple cycles of Precambrian plate tectonic regimes.

Petrography and geochemistry characteristics of the lower Cretaceous Muling Formation from the Laoheishan Basin, Northeast China: implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Song, Yu; Liu, Zhaojun; Meng, Qingtao; Wang, Yimeng; Zheng, Guodong; Xu, Yinbo

2017-06-01

The petrography, mineralogy and geochemistry of sedimentary rocks from the lower Cretaceous Muling Formation (K1ml) in the Laoheishan basin, northeast (NE) China are studied to determine the weathering intensity, provenance and tectonic setting of the source region. Petrographic data indicate the average quartz-feldspar-lithic fragments (QFL) of the sandstone is Q = 63 %, F = 22 %, and L = 15 %. Lithic fragments mainly contain volcanic clasts that derived from surrounding basement. X-ray diffraction (XRD) data reveal abundant clay and detrital minerals (e.g. quartz), as well as minor calcite in the fine-grained sediments. The Hf contents and element concentration ratios such as Al2O3/TiO2, Co/Th, La/Sc, and La/Th are comparable to sediments derived from felsic and intermediate igneous rocks. The strong genetic relationship with the igneous rocks from the northwest and northeast areas provides evidence that the sediments of the Muling Formation (K1ml) in the Laoheishan basin have been derived from this area. The chemical index of alteration (CIA) and index of chemical variability (ICV) reveal an intensive weathering in the source region of the sediments. The multidimensional tectonic discrimination diagrams indicate that the source rocks of K1ml are mainly derived from the collision system. However, they may also comprise sediments derived from the continental rift system. The results are consistent with the geology of the study area.

Perogenesis of granites, Sharm El-Sheikh area, South Sinai, Egypt: petrological constrains and tectonic evolution

NASA Astrophysics Data System (ADS)

Sherif, Mahmoud I.; Ghoneim, Mohamed F.; Heikal, Mohamed Th. S.; El Dosuky, Bothina T.

2013-10-01

Precambrian granites of the Sharm El-Sheikh area in south Sinai, Egypt belong to collisional and post-collisional Magmatism (610-580 Ma). The granites are widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield. South Sinai includes important components of successive multiple stages of upper crust granitic rocks. The earliest stages include monzogranite and syenogranites while the later stages produced alkali feldspar granites and riebeckite-bearing granites. Numerous felsic, mafic dikes and quartz veins traverse the study granites. Petrographically, the granitic rocks consist mainly of perthite, plagioclase, quartz, biotite and riebeckite. Analysis results portray monzogranites displaying calc-alkaline characteristics and emplaced in island-arc tectonic settings, whereas the syenogranites, alkali-feldspar granites and the riebeckite bearing-granites exhibit an alkaline nature and are enriched in HFSEs similar to granites within an extensional regime. Multi-element variation diagrams and geochemical characteristics reinforce a post-collision tectonic setting. REEs geochemical modeling reveals that the rocks were generated as a result of partial melting and fractionation of lower crust basaltic magma giving rise to A1 and A2 subtype granites. They were subsequently emplaced within an intraplate environment at the end of the Pan-African Orogeny.

Analysis of tectonic features in US southwest from Skylab photographs

NASA Technical Reports Server (NTRS)

Abdel-Gawad, M. (Principal Investigator); Tubbesing, L.

1975-01-01

The author has identified the following significant results. Skylab photographs were utilized to study faults and tectonic lines in selected areas of the U.S. Southwest. Emphasis was on elements of the Texas Zone in the Mojave Desert and the tectonic intersection in southern Nevada. Transverse faults believed to represent the continuation of the Texas Zone were found to be anomalous in strike. This suggests that the Mojave Desert block was rotated counterclockwise as a unit with the Sierra Nevada. Left-lateral strike-slip faults in Lake Mead area are interpreted as elements of the Wasatch tectonic zone; their anomalous trend indicates that the Lake Mead area has rotated clockwise with the Colorado Plateau. A tectonic model relating major fault zones to fragmentation and rotation of crustal blocks was developed. Detailed correlation of the high resolution S190B metric camera photographs with U-2 photographs and geologic maps demonstrates the feasibility of utilizing S190B photographs for the identification of geomorphic features associated with recent and active faults and for the assessment of seismic hazards.

Tectonic Origin of Serpentinites on Syros, Greece: Geochemical Signatures of Seafloor Serpentinization Preserved in the HP/LT Subduction Complex

NASA Astrophysics Data System (ADS)

Raia, N. H.; Cooperdock, E. H. G.; Barnes, J.; Stockli, D. F.; Schwarzenbach, E. M.

2016-12-01

Serpentinized ultramafic rocks are commonly found in exhumed HP/LT subduction complexes, but their tectonic origins (i.e., setting of serpentinization) are difficult to decipher due to extensive alteration. Growing literature and geochemical datasets demonstrate that immobile elements (REE, HFSE) in serpentinites can retain magmatic signatures indicative of the tectonic setting of parent peridotite, while fluid-mobile elements and stable isotopic signatures shed light on the fluids causing serpentinization. This study combines whole-rock trace and major element geochemistry, stable isotope (δD and δO) analyses with petrographic observation to determine the tectonic origin of ultramafic rocks in the HP/LT Aegean subduction complex. The best-preserved HP rocks of the Cycladic Blueschist Unit (CBU) are found on Syros, Greece, where serpentinized ultramafic rocks within the CBU are closely associated with metamorphosed remnants of subducted oceanic crust. All samples are completely serpentinized, lacking relict pyroxene or spinel grains, with typical assemblages consisting of serpentine, talc, chlorite, magnetite, and minor carbonate. The serpentinizing fluid was characterized using stable isotopes. δD and δO values of bulk-rock serpentinite powders and chips, respectively, suggest seafloor serpentinites hydrated by seawater at low T, typical of alteration at mid-ocean ridges and hyper-extended margins (δD = -64 to -33‰ and δO = 5.2 to 9.0‰). To fingerprint a tectonic origin, whole rock serpentinite REE patterns are compared to a global database of whole rock serpentinite analyses from fore-arc mantle wedge, mid-ocean ridge, and hyper-extended margin tectonic settings. Whole rock major element, trace element, and REE analyses are consistent with limited melt extraction, flat REE patterns (LaN/SmN = 0.2-2.6, SmN/YbN = 0.3-3.5; N= C1 normalized), and do not show pronounced Eu anomalies. These data are consistent with abyssal peridotites derived from hyper-extended margin settings, although some overlap with mid-ocean ridge serpentinites makes it difficult to rule out. In any case, the geochemical signatures retained in these serpentinites indicate they are unlikely sourced from the mantle wedge, as has been historically speculated.

Geochemistry and petrology of selected coal samples from Sumatra, Kalimantan, Sulawesi, and Papua, Indonesia

USGS Publications Warehouse

Belkin, H.E.; Tewalt, S.J.; Hower, J.C.; Stucker, J.D.; O'Keefe, J.M.K.

2009-01-01

Indonesia has become the world's largest exporter of thermal coal and is a major supplier to the Asian coal market, particularly as the People's Republic of China is now (2007) and perhaps may remain a net importer of coal. Indonesia has had a long history of coal production, mainly in Sumatra and Kalimantan, but only in the last two decades have government and commercial forces resulted in a remarkable coal boom. A recent assessment of Indonesian coal-bed methane (CBM) potential has motivated active CBM exploration. Most of the coal is Paleogene and Neogene, low to moderate rank and has low ash yield and sulfur (generally < 10 and < 1??wt.%, respectively). Active tectonic and igneous activity has resulted in significant rank increase in some coal basins. Eight coal samples are described that represent the major export and/or resource potential of Sumatra, Kalimantan, Sulawesi, and Papua. Detailed geochemistry, including proximate and ultimate analysis, sulfur forms, and major, minor, and trace element determinations are presented. Organic petrology and vitrinite reflectance data reflect various precursor flora assemblages and rank variations, including sample composites from active igneous and tectonic areas. A comparison of Hazardous Air Pollutants (HAPs) elements abundance with world and US averages show that the Indonesian coals have low combustion pollution potential.

Long term landscape evolution within central Apennines (Italy): Marsica and Peligna region morphotectonics and surface processes

NASA Astrophysics Data System (ADS)

Miccadei, E.; Piacentini, T.; Berti, C.

2010-12-01

The relief features of the Apennines have been developed in a complex geomorphological and geological setting from Neogene to Quaternary. Growth of topography has been driven by active tectonics (thrust-related crustal shortening and high-angle normal faulting related to crustal extension), regional rock uplift, and surface processes, starting from Late Miocene(?) - Early Pliocene. At present a high-relief landscape is dominated by morphostructures including high-standing, resistant Mesozoic and early Tertiary carbonates ridges (i.e. thrust ridges, faulted homocline ridges) and intervening, erodible Tertiary siliciclastics valleys (i.e. fault line valleys) and Quaternary continental deposits filled basins (i.e. tectonic valleys, tectonic basins). This study tries to identify paleo-uplands that may be linked to paleo-base levels and aims at the reconstruction of ancient landscapes since the incipient phases of morphogenesis. It analyzes the role of tectonics and morphogenic processes in the long term temporal scale landscape evolution (i.e. Mio?-Pliocene to Quaternary). It is focused on the marsicano-peligna region, located along the main drainage divide between Adriatic side and Tyrrhenian side of Central Apennines, one of the highest average elevation area of the whole chain. The work incorporates GIS-based geomorphologic field mapping of morphostructures and Quaternary continental deposits, and plano-altimetric analysis and morphometry (DEM-, map-based) of the drainage network (i.e. patterns, hypsometry, knick points, Ks). Field mapping give clues on the definition of paleo-landscapes related to different paleo-morpho-climatic environments (i.e. karst, glacial, slope, fluvial). Geomorphological evidence of tectonics and their cross-cutting relationships with morphostructures, continental deposits and faults, provide clues on the deciphering of the reciprocal relationship of antecedence of the paleo-landscapes and on the timing of morphotectonics. Morphotectonic features are related to Neogene thrusts, reactivated or displaced by complex kinematic strike slip and followed by extensional tectonic features (present surface evidence given by fault line scarps, fault line valleys, fault scarps, fault slopes, wind gaps, etc.). Geomorphic evidence of faults is provided also by morphometry of the drainage network: highest long slope of the main streams (knick points and Ks) are located where the streams cut across or run along recent faults. Correlation of tectonic elements, paleosurfaces, Quaternary continental deposits, by means of morphotectonic cross sections, lead to the identification, in the marsicano-peligna region, of areas in which morphotectonics acted in the same period, becoming younger moving from the West to the East. In conclusion, recognition of different morphotectonic features, identification of different paleo-landscapes, and reconstruction of their migration history, contribute to define the main phases of syn and post orogenic, Apennine chain landscape evolution: it results from the link of alternating morphotectonics and surface processes, due to migrating fault activity, rock uplift processes and alternating karst, glacial, slope, fluvial processes.

Geometric description and analysis of metamorphic tectonites (Pelagonian Zone, Internal Hellenides, Northern Greece)

NASA Astrophysics Data System (ADS)

Diamantopoulos, A.

2009-04-01

An assortment of alpine and pre-Permian metamorphic tectonites, belonging to the Pelagonian Zone of the Internal Hellenides, are analyzed from Askion, Vernon and Vorras mountains. They in fact compose the Upper plate of the Western Macedonia core complex, overlying Late Tertiary high-P rocks through large-scale detachment fautls (Diamantopoulos et al. 2007). This work wants to determine the architecture and the kinematic path of rocks in a 3D assumption. Field analysis concludes: a) Meta-sedimentary lithologies and amphibolites, meta-igneous lithologies, granitoid mylonites composed of augen fieldspar gneisses, Permo-Triassic fossiliferous rocks, meta-carbonates of Triassic-Jurassic age, a Jurassic mélange including meta-sedimentary lithologies, serpentinites and carbonate tectonic blocks, Mesozoic Ophiolites, Cretaceous limestones and conglomerates as well as flysch sediments compose the architecture of the study area, b) Multiple high and low-angle cataclastic zones of intense non-coaxial strain separate distinct pre-Permian lithologies, alpine from pre-alpine rocks, Triassic-Jurassic rocks from Permo-Triassic rocks, Jurassic mélange from flysch sediments, Jurassic mélange from Triassic-Jurassic rocks, Cretaceous rocks from the Jurassic mélange, Cretaceous limestones from flysch lithologies and Cretaceous rocks from serpentinites, c) Geometric analysis and description of asymmetric structures found in fault cores, damage zones and in the footwall-related rocks showed a prominent kinematic direction towards WSW in low-T conditions affected all the rock lithologies, d) Multiple S- and L- shape fabric elements in the pre-Permian and Permo-Triassic rocks appear an intricate orientation, produced by intense non-coaxial syn-metamorphic deformation, e) Sheath and isoclinal folds oriented parallel to the L-shape fabric elements as well as a major S-shape fabric element, producing macroscopic fold-like structures compose the main syn-metamorphic fabric elements in the pre-alpine tectonites, f) Discrete and distributed strain along the former boundaries and within footwall- and hangingwall rocks is connoted to control the bulk kinematic path of the involved sequences, g) Field evaluation of the structural geology and the tectonics connote the conjugate character of the cataclastically-deformed boundaries, causing overprinting of the pre-existed ductile-related geometries, h) For the age of the inferred WSW kinematic direction of the involved rocks we believe that it is closely associated with the tectonic superimposition of the Pelagonian Zone onto the Olympos tectonic window during post-Late Eocene times. Miocene to Quaternary faulting activity in all the scales overprint the above Late Tertiary perturbation, resulting a real complicated structural feature (Diamantopoulos 2006). Diamantopoulos A., 2006. Plio-Quaternary geometry and Kinematics of Ptolemais basin (Northern Greece). Implications for the intra-plate tectonics in Western Macedonia. Geologica Croatica 59/1, pages 85-96. Diamantopoulos A., Krohe A., Mposkos E., 2007. Structural asymmetry and distributed strain of low-T shear planes inducing evidence for orogen-scale kinematic partitioning during denudation of high-P rocks (Pelagonian Zone, Greece). Geophysical Research Abstracts, Vol. 9, 03622.

Weathering processes and the composition of inorganic material transported through the orinoco river system, Venezuela and Colombia

USGS Publications Warehouse

Stallard, R.F.; Koehnken, L.; Johnsson, M.J.

1991-01-01

The composition of river-borne material in the Orinoco River system is related primarily to erosion regime, which in turn is related to tectonic setting; especially notable is the contrast between material derived from tectonically active mountain belts and that from stable cratonic regions. For a particular morpho-tectonic region, the compositional suites of suspended sediment, bed material, overback deposits, and dissolved phases are fairly uniform are are typically distinct from whose of other regions. For each region, a consistent set of chemical weathering reactions can be formulated to explain the composition of dissolved and solid loads. In developing these formulations, erosion on slopes and storage of solids in soils and alluvial sediments are important considerations. Compositionally verymature sediment is derived from areas of thick soils where erosion is transport limited and from areas where sediments are stored for extended periods of time in alluvial deposits. Compositionally immature sediments are derived from tectonically active mountain belts where erosion is weathering limited. Weathering-limited erosion also is important in the elevated parts of the Guayana Shield within areas of sleep topography. Compared to the mountain belts, sediments derived from elevated parts of the Shield are more mature. A greater degree of chemical weathering seems to be needed to erode the rock types typical of the Shield. The major-element chemistry and mineral composition of sediment delivered by the Orinoco River to the ocean are controlled by rivers that have their headwaters in mountain belts and cross the Llanos, a region of alluvial plains within the foreland basin. The composition of sediments in rivers that drain the Shield seems to be established primarily at the site of soil formation, whereas for rivers that drain the mountain belts, additional weathering occurs during s episodes of storage on alluvial plains as sediments are transported across the Llanos to the main stem of the Orinoco. After mixing into the main stem, there seems to be little subsequent alteration of sediment. ?? 1991.

Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau

NASA Astrophysics Data System (ADS)

El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien

2015-04-01

While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a depleted mantle source. It is the first time that such a signature is observed in the Archean part of the West African craton, and would suggest a widespread bimodal distribution of trace elements signature in all Archean basalts.

Deformation patterns in the southwestern part of the Mediterranean Ridge (South Matapan Trench, Western Greece)

NASA Astrophysics Data System (ADS)

Andronikidis, Nikolaos; Kokinou, Eleni; Vafidis, Antonios; Kamberis, Evangelos; Manoutsoglou, Emmanouil

2017-12-01

Seismic reflection data and bathymetry analyses, together with geological information, are combined in the present work to identify seabed structural deformation and crustal structure in the Western Mediterranean Ridge (the backstop and the South Matapan Trench). As a first step, we apply bathymetric data and state of art methods of pattern recognition to automatically detect seabed lineaments, which are possibly related to the presence of tectonic structures (faults). The resulting pattern is tied to seismic reflection data, further assisting in the construction of a stratigraphic and structural model for this part of the Mediterranean Ridge. Structural elements and stratigraphic units in the final model are estimated based on: (a) the detected lineaments on the seabed, (b) the distribution of the interval velocities and the presence of velocity inversions, (c) the continuity and the amplitudes of the seismic reflections, the seismic structure of the units and (d) well and stratigraphic data as well as the main tectonic structures from the nearest onshore areas. Seabed morphology in the study area is probably related with the past and recent tectonics movements that result from African and European plates' convergence. Backthrusts and reverse faults, flower structures and deep normal faults are among the most important extensional/compressional structures interpreted in the study area.

Geochemical Analysis for Sedimentary Emerald Mineralization in Western Emerald belt, Colombia

NASA Astrophysics Data System (ADS)

Nino Vasquez, Gabriel Felipe; Song, Sheng-Rong

2017-04-01

1Gabriel Felipe Nino Vasquez and 1Sheng-Rong Song 1Department of Geosciences, National Taiwan University Colombia hosts a large quantity of mineral resources due to its complex tectonic arrangement, and emerald deposits are one of the most representatives for the country. Emeralds in Colombia occur mainly in black shale, and are located in eastern Andes Cordillera with two parallel belts separated by approximately 130 Km: the Western belt (WB) and the Eastern belt (EB). The geological, mineralogical and tectonic features from these belts are quite similar (Buenaventura 2002). Previous researchers concluded that emeralds in Colombia came from hydrothermal sedimentary processes without any magmatic influence, and suggested that the source of Cr, V and Be (which are important components of the beryl) was the host rock. According to their results, the process which allowed the shale to release these cations was the metasomatism (albitization and carbonization), which was resulted from the interaction between the rocks and the alkaline brines. Fractures and fault planes originated by these tectonic movements were fulfilled by enriched fluids, which they allowed emeralds and the other minerals precipitation with decreasing alkalinity and pressure (Giuliani et al. 1994). However, there were several pitfalls of conclusions drawn from previous researches. Firstly, Cr and V were widely distributed and come from mafic and ultramafic rocks, and Be was mostly found in pegmatites, finding these elements in sedimentary rocks suggest that probably the ultramafic rocks occurred not far from the deposits. Secondly, there was an inconsistency in the estimated temperatures of emeralds formation, i.e. temperature of hydrothermal sedimentary deposits was only 200° C, while laboratory analysis showed that the formation of emeralds was higher than 300° C. Therefore, there might still be an allocthonus influence on emerald formation that significantly increases the temperature. This research is going to contribute information in order to clarify these inconsistencies, We have done the O and C isotopes in calcite and S isotope in pyrite and shale from different mines along the (WB) in order to determine the main fluid source of the mineralization. Selected samples will also be analyzed with EDS, RAMAN and ICP-MS methods to obtain the exact compositions of elements with extremely low concentrations in host rock, metazomatized host rock and mineralization (productive and not productive veins); the main purpose is to measure how strong were the fluid-rock interaction to leach elements out from the black shale. Thin sections from the altered shale and vein have been analyzed with the purpose of identify paragenesis and microstructures in the mineralization. Finally, we would like to gather the results from different sectors and compare it with the previous studies.

Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

NASA Astrophysics Data System (ADS)

Cai, Da-wei; Tang, Yong; Zhang, Hui; Lv, Zheng-Hang; Liu, Yun-long

2017-06-01

Most Silurian-Devonian granites in South China are S- or I-type granites, which are suggested to be petrogenetically related to the Wuyi-Yunkai orogeny. In this paper, we present the detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical, and Nd-Hf isotopic data for Xiqin A-type granites in the northeastern Cathaysia Block, SE China. Zircon U-Pb dating results show that the Xiqin granites were emplaced at about 410 Ma, indicating that they were generated at the end of Wuyi-Yunkai orogeny. These granites are high in K2O + Na2O (6.31-8.79 wt%), high field strength elements (Zr + Nb + Ce + Y = 427-699 ppm), rare earth elements (total REE = 221-361 ppm) as well as high Ga/Al ratios (10,000 Ga/Al = 2.50-3.10), and show characteristics typical of A-type granites. εHf(t) values of the Xiqin granites mainly vary from -0.4 to -3.1 and yield Mesoproterozoic T2DM(Hf) (mainly ranging from 1.29 to 1.45 Ga). The εNd(t) values are from -1.23 to -2.11 and T2DM(Nd) vary from 1.25 to 1.32 Ga. These isotopic data suggest that the Xiqin granites were generated by partial melting of metavolcanic rocks with minor metasedimentary rocks in the lower crust. Our data on the Xiqin granites, coupled with previous studies of Silurian-Devonian magmatism, suggest that the tectonic regime had changed to a strongly post-collisional extension environment in the Wuyi-Yunkai orogen at least since 410 Ma, and that delamination, which accounts for the change in stress from the compression to extension and asthenospheric upwelling during the early Paleozoic, plays a significant role in the generation of Xiqin A-type granites.

Tectonic affinities of the accreted basalts in southern Taiwan

NASA Astrophysics Data System (ADS)

Chen, Hsin-Yu; Yang, Huai-Jen; Liu, Yung-Hsin; Huang, Kuo-Fang; Takazawa, Eiichi

2018-06-01

Tectonic affinities of accreted basalts provide constraints on mass transport in convergent boundaries, improving our understandings on the evolution of regional geology. In this study, nineteen accreted basalts from the southernmost tip of Taiwan Island, which is on the convergent boundary between the Eurasian and Philippine Sea Plates, were analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to investigate their tectonic affinities. All the samples contain > 3% LOI, reflecting post-magmatic alteration. LOI and Nb variation diagrams together with comparisons to oceanic basalt compositions indicated that the concentrations of most major elements and Rb, Sr, and Ba were modified by post-magmatic processes to varying extents, while P2O5, REE and HFSE remained immobile. Although some samples show Pb loss, most samples have Pb concentrations not affected by post-magmatic processes. Isotope ratios of Pb, Nd and Hf, generally reflect the mantle source characteristics. The εNd-εHf relationship and trace element abundance ratios indicated that the LREE-depleted samples were mostly scraped off the subducting South China Sea floor, reflecting the volumetric dominance of N-MORB on ocean floors. The overriding Philippine Sea Plate contributed both N-MORB and E-MORB to the accretionary prism. The tectonic affinities of the LREE-enriched samples, however, could not be unambiguously determined for the large geochemical variability of OIB from both subducting and overlying slabs. Based on our results, it is proposed that the tectonic affinity of the basalts in an accretionary prism can indicate the subduction polarity of the associated convergent boundary, providing a constraint for regional geology evolution.

Tectonic controls of a backarc trough-fill turbidite system: The Pliocene Tamugigawa Formation in the Niigata Shin'etsu inverted rift basin, Northern Fossa Magna, central Japan

NASA Astrophysics Data System (ADS)

Takano, Osamu; Tateishi, Masaaki; Endo, Masataka

2005-05-01

The Pliocene Tamugigawa Formation in the Niigata-Shin'etsu inverted rift basin, Northern Fossa Magna, located in the junction zone of the NE and SW Japan arcs, demonstrates a trough-fill turbidite system, which is topographically controlled in depositional style and shows notable contrasts in depositional architecture from sandy radial-fan-type turbidite systems. The Tamugigawa trough-fill turbidite system shows an elongated morphology parallel to the basin extent and facies associations consisting of trough-fill, lateral-supply and trough-side elements. The trough-fill elements comprise thick-bedded sheet sandstone and sheet-flow turbidite associations, which show sheet-like sedimentation configuration, instead of depositional lobes, without distinct upward fining and coarsening successions. The lateral-supply elements form an intra-trough small fan along a lateral sediment-supply system into the troughs, and consist mainly of coarser-grained distributary-channel fills and sheet sandstones. The trough-side elements consist of slope-mudstone and spillover associations, which were deposited on the structural highs beside the troughs. The Tamugigawa trough-fill turbidites were deposited through three phases: (a) initial ponding stage with thick, sheet sandstones provided by the lateral-supply system, (b) main filling stage with sheet-flow turbidites provided by the longitudinal supply system, and (c) filled-up stage characterized by minor-scale channel-levee systems. Basin-wide tectono-sedimentary studies reveal that the trough-fill turbidites were characteristically formed during the compressional-stress-field stage related to basin inversion. The compressional stress induced basin-floor syndepositional folding and coarse clastic supply from the uplifted provenance, resulting in topographically restricted turbidite deposition within the troughs. In contrast, turbidites of the post-rift stage, prior to basin inversion, show no topographical control because of the simple and wide rift-basin topography, relative to the amount of sediment supply. It is concluded that the trough-fill turbidites of the Niigata-Shin'etsu basin have been strongly affected by basin tectonics in their depositional architecture and formation phases.

Fracture mapping of lineaments and recognizing their tectonic significance using SPOT-5 satellite data: A case study from the Bajestan area, Lut Block, east of Iran

NASA Astrophysics Data System (ADS)

Ahmadirouhani, Reyhaneh; Rahimi, Behnam; Karimpour, Mohammad Hassan; Malekzadeh Shafaroudi, Azadeh; Afshar Najafi, Sadegh; Pour, Amin Beiranvand

2017-10-01

Syste'm Pour l'Observation de la Terre (SPOT) remote sensing satellite data have useful characteristics for lineament extraction and enhancement related to the tectonic evaluation of a region. In this study, lineament features in the Bajestan area associated with the tectonic significance of the Lut Block (LB), east Iran were mapped and characterized using SPOT-5 satellite data. The structure of the Bajestan area is affected by the activity of deep strike-slip faults in the boundary of the LB. Structural elements such as faults and major joints were extracted, mapped, and analyzed by the implementation of high-Pass and standard kernels (Threshold and Sobel) filters to bands 1, 2 and 3 of SPOT-5 Level 2 A scene product of the Bajestan area. Lineament map was produced by assigning resultant filter images to red-green-blue (RGB) colour combinations of three main directions such as N-S, E-W and NE-SW. Results derived from image processing technique and statistical assessment indicate that two main orientations, including NW-SE with N-110 azimuth and NE-SW with N-40 azimuth, were dominated in the Bajestan area. The NW-SE trend has a high frequency in the study area. Based on the results of remote sensing lineament analysis and fieldwork, two dextral and sinistral strike-slip components were identified as main fault trends in the Bajestan region. Two dextral faults have acted as the cause of shear in the south and north of the Bajestan granitoid mass. Furthermore, the results indicate that the most of the lineaments in this area are extensional fractures corresponding to both the dykes emplacement and hydrothermal alteration zones. The application of SPOT-5 satellite data for structural analysis in a study region has great capability to provide very useful information of a vast area with low cost and time-consuming.

Geochemistry of sandstones from the Pliocene Gabir Formation, north Marsa Alam, Red Sea, Egypt: Implication for provenance, weathering and tectonic setting

NASA Astrophysics Data System (ADS)

Zaid, Samir M.

2015-02-01

Petrographic, major and trace element compositions of sandstones from the Pliocene Gabir Formation, Central Eastern Desert, Egypt have been investigated to determine their provenance, intensity of paleo-weathering of the source rocks and their depositional tectonic setting. Gabir Formation is composed mainly of sandstones alternating with limestone and shale beds. The Gabir sandstone is yellowish gray to yellowish brown color, calcareous and fossiliferous. The composition of this formation refers to shallow warm agitated marine conditions. Texturally, Gabir sandstones are immature, poorly sorted and grain supported. Abundance of feldspars indicates rapid deposition of sediments from a nearby source rocks. Their average modal composition (Q71.35F16.6L12.05), classifies them as sublitharenite and arkose with subordinate litharenite and subarkose, which is also supported by geochemical study. Chemical analyses revealed that sandstones have high SiO2, K2O > Na2O, and low Fe2O3 values, which are consistent with the modal data. Also, sandstone samples are enriched in most trace elements such as Ba, Sr, Ni, Cr and Zr and depleted in U and Th. The petrography and geochemistry suggest that Gabir sandstones were deposited in an active continental margin basin. They were mainly derived from granitic and low grade metamorphic sources. The CIA values (41.69-74.84) of the Gabir sandstones indicate low to moderate degree of chemical weathering, which may reflect cold and/or arid climate conditions in the source area. The source rocks are probably identified to be Proterozoic granites, metagabbros and metavolcanics, which must have been exposed during rifting, initiated during Oligocene and continued till post Miocene.

Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.

1992-01-01

A combined isotopic and trace-element study of the Late Paleozoic Ouachita Orogenic belt has the following goals: (1) define changing provenance of Ouachita sedimentary systems throughout the Paleozoic; (2) constrain sources feeding into the Ouachita flysch trough during the Late Paleozoic; (3) isolate the geochemical signature of proposed colliding terranes to the south; (4) build a data base to compare with possible Ouachita System equivalents in Mexico. The ultimate aim is to constrain the tectonic setting of the southern margin of North America during the Paleozoic, with particular emphasis on collisional events leading to the final suturing of Pangea. Ndmore » isotopic data identify 3 distinct groups: (1) Ordovician passive margin sequence; (2) Carboniferous proto-flysch (Stanley Fm.), main flysch (Jackfork and Atoka Fms.) and molasse (foreland Atoka Fm.); (3) Mississippian ash-flow tuffs. The authors interpret the Ordovician signature to be essentially all craton-derived, whereas the Carboniferous signature reflects mixed sources from the craton plus orogenic sources to the east and possibly the south, including the evolving Appalachian Orogen. The proposed southern source is revealed by the tuffs to be too old and evolved to be a juvenile island arc terrane. They interpret the tuffs to have been erupted in a continental margin arc-type setting. Surprisingly, the foreland molasse sequence is indistinguishable from the main trough flysch sequence, suggesting the Ouachita trough and the craton were both inundated with sediment of a single homogenized isotopic signature during the Late Carboniferous. The possibility that Carboniferous-type sedimentary dispersal patterns began as early as the Silurian has important implications for the tectonics and paleogeography of the evolving Appalachian-Ouachita Orogenic System.« less

Topographic representation using DEMs and its applications to active tectonics research

NASA Astrophysics Data System (ADS)

Oguchi, T.; Lin, Z.; Hayakawa, Y. S.

2016-12-01

Identifying topographic deformations due to active tectonics has been a principal issue in tectonic geomorphology. It provides useful information such as whether a fault has been active during the recent past. Traditionally, field observations, conventional surveying, and visual interpretation of topographic maps, aerial photos, and satellite images were the main methods for such geomorphological investigations. However, recent studies have been utilizing digital elevation models (DEMs) to visualize and quantitatively analyze landforms. There are many advantages to the use of DEMs for research in active tectonics. For example, unlike aerial photos and satellite images, DEMs show ground conditions without vegetation and man-made objects such as buildings, permitting direct representation of tectonically deformed landforms. Recent developments and advances in airborne LiDAR also allow the fast creation of DEMs even in vegetated areas such as forested lands. In addition, DEMs enable flexible topographic visualization based on various digital cartographic and computer-graphic techniques, facilitating identification of particular landforms such as active faults. Further, recent progress in morphometric analyses using DEMs can be employed to quantitatively represent topographic characteristics, and objectively evaluate tectonic deformation and the properties of related landforms. This paper presents a review of DEM applications in tectonic geomorphology, with attention to historical development, recent advances, and future perspectives. Examples are taken mainly from Japan, a typical tectonically active country. The broader contributions of DEM-based active tectonics research to other fields, such as fluvial geomorphology and geochronology, will also be discussed.

Proterozoic low-Ti iron-oxide deposits in New York and New Jersey: relation to Fe-oxide (Cu-U-Au-rare earth element) deposits and tectonic implications

USGS Publications Warehouse

Foose, M.P.; McLelland, J.M.

1995-01-01

Low-Ti iron-oxide deposits in exposed Grenville-age rocks of New York and New Jersey belong to a distinct class of iron-oxide (Cu-U-Au-rare earth element [REE]) deposits that includes similar iron deposits in southeastern Missouri and the Kiruna district of Sweden, the giant Olympic Dam U-Cu-Au-Ag deposit (Australia), and the Bayan Obo REE-Nb deposit (China). Most of the New York-New Jersey deposits exhibit features consistent with a hydrothermal origin and define a regionally significant metallogenic event that provides important clues to the evolution of this part of the Grenville orogen. In the Adirondacks, the tectonic setting of these deposits is consistent with postorogenic uplift and extensive crustal melting at 1070-1050 Ma that was accompanied by late tectonic to posttectonic deposition of iron. -Authors

Hydrothermal fluids circulation and travertine deposition in an active tectonic setting: Insights from the Kamara geothermal area (western Anatolia, Turkey)

NASA Astrophysics Data System (ADS)

Brogi, Andrea; Alçiçek, M. Cihat; Yalçıner, Cahit Çağlar; Capezzuoli, Enrico; Liotta, Domenico; Meccheri, Marco; Rimondi, Valentina; Ruggieri, Giovanni; Gandin, Anna; Boschi, Chiara; Büyüksaraç, Aydin; Alçiçek, Hülya; Bülbül, Ali; Baykara, Mehmet Oruç; Shen, Chuan-Chou

2016-06-01

Coexistence of thermal springs, travertine deposits and tectonic activity is a recurring feature for most geothermal areas. Although such a certainty, their relationships are debated mainly addressing on the role of the tectonic activity in triggering and controlling fluids flow and travertine deposition. In this paper, we present the results of an integrated study carried out in a geothermal area located in western Anatolia (Turkey), nearby the well-known Pamukkale area (Denizli Basin). Our study focused on the relationships among hydrothermal fluids circulation, travertine deposition and tectonic activity, with particular emphasis on the role of faults in controlling fluids upwelling, thermal springs location and deposition of travertine masses. New field mapping and structural/kinematics analyses allowed us to recognize two main faults systems (NW- and NE-trending), framed in the Neogene-Quaternary extensional tectonic evolution of western Anatolia. A geo-radar (GPR) prospection was also provided in a key-area, permitting us to reconstruct a buried fault zone and its relationships with the development of a fissure-ridge travertine deposit (Kamara fissure-ridge). The integration among structural and geophysical studies, fluids inclusion, geochemical, isotopic data and 230 Th/238 U radiometric age determination on travertine deposits, depict the characteristics of the geothermal fluids and their pathway, up to the surface. Hydrological and seismological data have been also taken in account to investigate the relation between local seismicity and fluid upwelling. As a main conclusion we found strict relationships among tectonic activity, earthquakes occurrence, and variation of the physical/chemical features of the hydrothermal fluids, presently exploited at depth, or flowing out in thermal springs. In the same way, we underline the tectonic role in controlling the travertine deposition, making travertine (mainly banded travertine) a useful proxy to reconstruct the seismological history of an area, as well as the characteristics of the parent geothermal fluids, adding an effective tool for geothermal exploration tasks.

[Analysis of X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry of Pangxidong Composite Granitoid Pluton and Its Implications for Magmatic Differentiation].

PubMed

Zeng, Chang-yu; Ding, Ru-xin; Li, Hong-zhong; Zhou, Yong-zhang; Niu, Jia; Zhang, Jie-tang

2015-11-01

Pangxidong composite granitoid pluton located in the southwestern margin of Yunkai massif. The metamorphic grade of this pluton increases from outside to inside, that is, banded-augen granitic gneisses, gneissoid granites and granites distribute in order from edge to core. X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry are conducted to study the geochemical characteristics of the three types of rocks. The result shows that all the three types of rocks are peraluminous rocks and their contents of main elements and rare earth elements change gradually. From granitic gneisses to granites, the contents of Al₂O₃, CaO, MgO, TiO₂, total rare earth elements and light rare earth elements increase, but the contents of SiO₂ and heavy rare earth elements decrease. It is suggested that the phylogenetic relationship exists between granitic gneisses, gneissoid granites and granites during the multi-stage tectonic evolution process. Furthermore, the remelting of metamorphosed supracrustal rocks in Yunkai massif is probably an important cause of granitoid rocks forming. The evolutionary mechanism is probably that SiO₂ and heavy rare earth elements were melt out from the protolith and gradually enriched upward, but Al₂O₃, CaO, MgO, TiO₂ and light rare earth elements enriched downward.

Geology of photo linear elements, Great Divide Basin, Wyoming

NASA Technical Reports Server (NTRS)

Blackstone, D. L., Jr.

1973-01-01

The author has identified the following significant results. Ground examination of photo linear elements in the Great Divide Basin, Wyoming indicates little if any tectonic control. Aeolian aspects are more widespread and pervasive than previously considered.

High-Resolution Regional Phase Attenuation Models of the Iranian Plateau and Surrounding Regions

DTIC Science & Technology

2014-03-03

1 2.2. Tectonic and Geophysical Setting ..........................................................................2 2.3...superimposed with the major tectonic features across the Middle East. The major faults are depicted with black solid lines. The main continental boundary fault...zones and tectonic settings are abbreviated on the map and described here. The red triangles present the location of quaternary volcanoes. The dashed

Evolution Process and Structural Analysis of Precambrian Jirisan Metamorphic and Sancheong Anorthosite Complexes in the Jirisan Province, Yeongnam Massif, Korea

NASA Astrophysics Data System (ADS)

Kang, J. H.; Lee, D. S.

2016-12-01

The Jirisan metamorphic complex consists mainly of schist, blastoporphyritic granite gneiss, granitic gneiss, leucocratic gneiss, biotite gneiss, banded gneiss, migmatitic gneiss and granite gneiss. The Paleoproterozoic (1.87 1.79 Ga) Sancheong anorthosite complex, which intrude it, is classified into massive-type and foliation-type Sancheong anorthosite, Fe-Ti ore body, and mafic granulite which were formed from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma. These complexes went at least through three times of ductile deformation during Early Proterozoic Late Paleozoic. The D1 deformation formed sheath or "A" type folds and its characteristic orientation was uncertain due to the intensive multi-deformation superimposed after that. The D2 deformation occurred under the EW- or WNW-directed tectonic compression, and formed a regional NS or NNE trend of isoclinal and intrafolial folds and an extensive ductile shear zone accompanied by mylonitization. The D3 deformation occurred under the NS- or NNW-directed tectonic compression environment, and formed an EW or ENE trend of open and tight folds and a partial semibrittle shear zone accompanied by mylonitization, and rearranged the NS-trend pre-D3 structural elements into (E)NE or (W)NW direction. The D2 deformation generally increases from the center toward the margin of Sancheong anorthosite complex but is more intensive in the eastern than western parts of Sancheong anorthosite complex. While the D3 deformation is inversely more intensive in the its western than eastern parts. The D2 and D3 deformations are closely related to the distribution features of Sancheong anorthosite complex. These three tectonic events are expected to give important information in understanding and reconstructing the tectonic movement after the formation of Columbia Supercontinent as well as the present NS-trend tectonic frame of the Jirisan province of the Yeongnam massif, the Korean Peninsula.

Provenance of the Walash-Naopurdan back-arc-arc clastic sequences in the Iraqi Zagros Suture Zone

NASA Astrophysics Data System (ADS)

Ali, Sarmad A.; Sleabi, Rajaa S.; Talabani, Mohammad J. A.; Jones, Brian G.

2017-01-01

Marine clastic rocks occurring in the Walash and Naopurdan Groups in the Hasanbag and Qalander areas, Kurdistan region, Iraqi Zagros Suture Zone, are lithic arenites with high proportions of volcanic rock fragments. Geochemical classification of the Eocene Walash and Oligocene Naopurdan clastic rocks indicates that they were mainly derived from associated sub-alkaline basalt and andesitic basalt in back-arc and island arc tectonic settings. Major and trace element geochemical data reveal that the Naopurdan samples are chemically less mature than the Walash samples and both were subjected to moderate weathering. The seaway in the southern Neotethys Ocean was shallow during both Eocene and Oligocene permitting mixing of sediment from the volcanic arcs with sediment derived from the Arabian continental margin. The Walash and Naopurdan clastic rocks enhance an earlier tectonic model of the Zagros Suture Zone with their deposition occurring during the Eocene Walash calc-alkaline back-arc magmatism and Early Oligocene Naopurdan island arc magmatism in the final stages of intra-oceanic subduction before the Miocene closure and obduction of the Neotethys basin.

Geochemical and NdSr isotopic composition of deep-sea turbidites: Crustal evolution and plate tectonic associations

NASA Astrophysics Data System (ADS)

McLennan, S. M.; Taylor, S. R.; McCulloch, M. T.; Maynard, J. B.

1990-07-01

Petrographic, geochemical, and isotopic data for turbidites from a variety of tectonic settings exhibit considerable variability that is related to tectonic association. Passive margin turbidites (Trailing Edge, Continental Collision) display high framework quartz (Q) content in sands, evolved major element compositions (high Si/Al, K/Na), incompatible element enrichments (high Th/Sc, La/Sc, La/Yb), negative Eu-anomalies and variable Th/U ratios. They have low 143Nd /144Nd and high 87Sr /86Sr ( ɛNd = -26 to -10; 87Sr /86Sr = 0.709 to 0.734 ), indicating a dominance of old upper crustal sources. Active margin settings (Fore Arc, Continental Arc, Back Arc, Strike Slip) commonly exhibit quite different compositions. Th/Sc varies from <0.01 to 1.8, and ɛNd varies from -13.8 to +8.3. Eu-anomalies range from no anomaly ( Eu/Eu ∗ = 1.0 ) to Eu-depletions typical of post-Archean shales ( Eu/Eu ∗ = 0.65 ). Active margin data are explained by mixtures of young arc-derived material, with variable composition and old upper crustal sources. Major element data indicate that passive margin turbidites have experienced more severe weathering histories than those from active settings. Most trace elements are enriched in muds relative to associated sands because of dilution effects from quartz and calcite and concentration of trace elements in clays. Exceptions include Zr, Hf (heavy mineral influence) and Tl (enriched in feldspar) which display enrichments in sands. Active margin sands commonly exhibit higher Eu/Eu ∗ than associated muds, resulting from concentration of plagioclase during sorting. Some associated sands and muds, especially from active settings, have systematic differences in Th/Sc ratios and Nd-isotopic composition, indicating that various provenance components may separate into different grain-size fractions during sedimentary sorting processes. Trace element abundances of modern turbidites, from both active and passive settings, differ from Archean turbidites in several important ways. Modern turbidites have less uniformity, for example, in Th/Sc ratios. On average, modern turbidites have greater depletions in Eu (lower Eu/Eu ∗) than do Archean turbidites, suggesting that the processes of intracrustal differentiation (involving plagioclase fractionation) are of greater importance for crustal evolution at modern continental margins than they were during the Archean. Modern turbidites do not display HREE depletion, a feature commonly seen in Archean data. HREE depletion ( Gd N/Yb N > 2.0 ) in Archean sediments results from incorporation of felsic igneous rocks that were in equilibrium (or their sources were in equilibrium) with garnet sometime in their history. Absence of HREE depletion at modern continental margins suggests that processes of crust formation (or mantle source compositions) may have differed. Differences in trace element abundances for Archean and modern turbidites add support to suggestions that upper continental crust compositions and major processes responsible for continental crust differentiation differed during the Archean. Neodymium model ages, thought to approximate average provenance age, are highly variable ( TDMND = 0-2.6 Ga) in modern turbidites, in contrast with studies that indicate Nd-model ages of lithified Phanerozoic sediment are fairly constant at about 1.5-2.0 Ga. This variability indicates that continental margin sediments incorporate new mantle-derived components, as well as continental crust of widely varying age, during recycling. The apparent dearth of ancient sediments with Nd-model age similar to stratigraphic age supports the suggestion that preservation potential of sediments is related to tectonic setting. Many samples from active settings have isotopic compositions similar to or only slightly evolved from mantle-derived igneous rocks. Subduction of active margin turbidites should be considered in models of crust-mantle recycling. For short-term recycling, such as that postulated for island arc petrogenesis, arc-derived turbidites cannot be easily recognized as a source component because of the lack of time available for isotopic evolution. If turbidites were incorporated into the sources of ocean island volcanics, the isotopic signatures would be considerably more evolved since most models call for long mantle storage times (1.0-2.0 Ga), prior to incorporation. Four provenance components are recognized on the basis of geochemistry and Nd-isotopic composition: (1) Old Upper Continental Crust (old igneous/metamorphic terranes, recycled sediment); (2) Young Undifferentiated Arc (young volcanic/plutonic source that has not experienced plagioclase fractionation); (3) Young Differentiated Arc (young volcanic/plutonic source that has experienced plagioclase fractionation); (4) MORB (minor). Relative proportions of these components are influenced by the plate tectonic association of the provenance and are typically (but not necessarily) reflected in the depositional basin. Provenance of quartzose (mainly passive settings) and non-quartzose (mainly active settings) turbidites can be characterized by bulk composition (e.g., Th/Sc) and Nd-isotopic composition (reflecting age).

Tectonic map of Uruguay

NASA Astrophysics Data System (ADS)

Sanchez Bettucci, L.; Oyhantcabal, P.

2008-05-01

A compilation of available data about the geology of Uruguay allowed the definition of its main events and tectonic units. Based on a critical revision of different tectonic hypothesis found in the literature, a parsimonious tectonic evolution schema is presented, in the context of Western Gondwana. The tectonic map illustrates the general features of the structure and main tectonic units of Uruguay. The Precambrian shield, cropping out in the South and Southeast of the country is an Archean to Paleoprtoerozoic basement divided in three main tectonostratigraphic terrranes: the Piedra Alta (PAT) a juvenile Paleoproterozoic unit not reworked by later events; the Nico Pérez (NPT) a complex unit composed of several blocks where Archean to Mesoproterozoic events are recognised. The NPT was strongly reworked by Neoproterozoic (Brasiliano) orogeny. The Dom Feliciano Belt cropping out in eastern Uruguay is related to Western Gondwana amalgamation. Different tectonic settings are considered: pre-Brasiliano Basement inliers; supracrustal successions representing the evolution from a back- arc to a foreland basin; a magmatic arc; and post-collisional basins and related magmatism. In lower Paleozoic the Paraná foreland basin was generated as a consequence of orogenic events. The sedimentary successions in Uruguay include continental to shallow marine deposits where the influence of carboniferous to Permian glacial episode is recorded. The Mesozoic record is characterised by the influence of extension related to the break-up of Gondwana and the formation of the Atlantic Ocean: huge amounts of tholeiitic basalt were erupted (near 30.000 km3 in Uruguay), followed by cretaceous sediments in the northern area of the country while in the south-east, bimodal magmatism and sediments of the same age are associated to rift basins. The Cenozoic is characterised by tectonic quiescence. Subsidence is only observed in the western region (Chaco-Paraná Basin) and in the east (Laguna Merín Basin).

Microplate and shear zone models for oceanic spreading center reorganizations

NASA Technical Reports Server (NTRS)

Engeln, Joseph F.; Stein, Seth; Werner, John; Gordon, Richard

1988-01-01

The kinematics of rift propagation and the resulting goemetries of various tectonic elements for two plates is reviewed with no overlap zone. The formation and evolution of overlap regions using schematic models is discussed. The models are scaled in space and time to approximate the Easter plate, but are simplified to emphasize key elements. The tectonic evolution of overlap regions which act as rigid microplates and shear zones is discussed, and the use of relative motion and structural data to discriminate between the two types of models is investigated. The effect of propagation rate and rise time on the size, shape, and deformation of the overlap region is demonstrated.

Layers and Fractures in Ophir Chasma

NASA Image and Video Library

2015-11-05

Ophir Chasma forms the northern portion of Valles Marineris, and this image from NASA Mars Reconnaissance Orbiter spacecraft features a small part of its wall and floor. The wall rock shows many sedimentary layers and the floor is covered with wind-blown ridges, which are intermediate in size between sand ripples and sand dunes. Rocks protruding on the floor could be volcanic intrusions of once-molten magma that have pushed aside the surrounding sedimentary layers and "froze" in place. Images like this can help geologists study the formation mechanisms of large tectonic systems like Valles Marineris. (The word "tectonics" does not mean the same thing as "plate tectonics." Tectonics simply refers to large stresses and strains in a planet's crust. Plate tectonics is the main type of tectonics that Earth has; Mars does not have plate tectonics.) http://photojournal.jpl.nasa.gov/catalog/PIA20044

Progressive magmatism and evolution of the Variscan suture in southern Iberia

NASA Astrophysics Data System (ADS)

Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; Gladney, Evan R.; Dupuis, Nicolle

2018-04-01

Magmatic activity is an integral component of orogenic processes, from arc magmatism during convergence to post-collisional crustal melting. Southern Iberia exposes a Late Paleozoic suture zone within Pangea and where a crustal fragment of Laurussia (South Portuguese Zone) is juxtaposed with parautochthonous Gondwana (Ossa Morena Zone). Fault-bounded oceanic metasedimentary rocks, mélanges and ophiolite complexes characterize the suture zone and are intruded by plutonic rocks and mafic dykes. The generation and emplacement of these intrusive rocks and their relationship to development of the suture zone and the orogen are undetermined. Field evidence combined with U/Pb (zircon) geochronology reveals three main phases of plutonism, a pre-collisional unfoliated gabbroic phase emplaced at ca 354 Ma, crosscut by a syn-tectonic ca 345 Ma foliated granodiorite phase followed by a ca 335 Ma granitic phase. Geochemical analyses (major, trace, rare earth elements) indicate that the gabbro exhibits a calc-alkaline arc signature whereas the granodiorite and granite are typical of post-collisional slab break-off. Taken together, these data demonstrate a protracted development of the orogen and support a complex late stage evolution broadly similar to the tectonics of the modern eastern Mediterranean. In this scenario, the highly oblique closure of a small tract of oceanic lithosphere postdates the main collision event resulting in escape of parautochthonous and allochthonous terranes toward the re-entrant.

Occurrence of high-Al N-MORB along the Easternmost Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Meyzen, C. M.; Humler, E.; Ludden, J. N.

2017-12-01

One of the deepest and slowest part of the mid-ocean-ridge system lies within the easternmost part of the Southwest Indian Ridge between 61°E and 69° E. In this region, a distinctive sea-floor terrain characterized by high-relief segments separated by long, deep tectonized sections shows a predominance of tectonic over magmatic extensional processes, suggesting an unstable and weak, but locally focalized magma supply. Other features of this section include the absence of long-lived transforms, thick lithosphere, high upper mantle seismic wave velocities and thin oceanic crust (4-5 km). When compared to other ridge segments, most MORB erupted along this section distinguish themselves by their higher Na2O, Sr and Al2O3 compositions, very low CaO/Al2O3 ratios relative to TiO2 and depleted heavy rare-earth element (REE) distributions. Another peculiar feature is their subparallel LREE enriched patterns. The high-Al-MgO magma type erupted periodically around the ridge system is also found in this region at 61.93°E. These lavas are characterized by high Al2O3 (> 17 wt. %), MgO (> 8.8 wt. %) and FeO contents, low SiO2 (< 49 wt. %) and Na2O and very low TiO2 (< 1 wt. %), and a LREE depleted pattern compared to the main population. At slightly lower MgO, sporadically, two other dredges located at 63.36-63.66°E share some of these distinct compositional characteristics. As a whole, these lavas are the most depleted in highly incompatible elements, but are also characterized by an offset toward lower MREE/HREE ratios relative to the main population. These peculiar basalts are not parental to the more common lower MgO compositions and cannot be related to them by fractional crystallization alone. Instead, their major element features, and the occasional presence of positive Eu and Sr anomalies might indicate assimilation of plagioclase cumulates, while their offset in MREE/HREE might require a multistage melting evolution with an earlier event in the garnet stability field.

Tectonic evolution, structural styles, and oil habitat in Campeche Sound, Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angeles-Aquino, F.J.; Reyes-Nunez, J.; Quezada-Muneton, J.M.

1994-12-31

Campeche Sound is located in the southern part of the Gulf of Mexico. This area is Mexico`s most important petroleum province. The Mesozoic section includes Callovian salt deposits; Upper Jurassic sandstones, anhydrites, limestones, and shales; and Cretaceous limestones, dolomites, shales, and carbonate breccias. The Cenozoic section is formed by bentonitic shales and minor sandstones and carbonate breccias. Campeche Sound has been affected by three episodes of deformation: first extensional tectonism, then compressional tectonism, and finally extensional tectonism again. The first period of deformation extended from the middle Jurassic to late Jurassic and is related to the opening of the Gulfmore » of Mexico. During this regime, tilted block faults trending northwest-southwest were dominant. The subsequent compressional regime occurred during the middle Miocene, and it was related to northeast tangential stresses that induced further flow of Callovian salt and gave rise to large faulted, and commonly overturned, anticlines. The last extensional regime lasted throughout the middle and late Miocene, and it is related to salt tectonics and growth faults that have a middle Miocene shaly horizon as the main detachment surface. The main source rocks are Tithonian shales and shaly limestones. Oolite bars, slope and shelf carbonates, and regressive sandstones form the main reservoirs. Evaporites and shales are the regional seals. Recent information indicates that Oxfordian shaly limestones are also important source rocks.« less

Superposed ridges of the Hesperia Planum area on Mars

NASA Technical Reports Server (NTRS)

Raitala, Jouko

1988-01-01

Mare ridges of the Hesperia Planum area form linear, reticular and circular structures. The main factors effective in mare ridge formation have been: (1) a large areal, or maybe even global, shortening and compression, (2) major crustal tectonics, and (3) the moderation of tectonic movements by the megaregolith discontinuity layer(s) between surface lavas and the bedrock leaving the compressional thrust to dominate over other fault movements in surface tectonics.

Post-magmatic tectonic deformation of the outer Izu-Bonin-Mariana forearc system: initial results of IODP Expedition 352

NASA Astrophysics Data System (ADS)

Kurz, Walter; Ferré, Eric C.; Robertson, Alastair; Avery, Aaron; Christeson, Gail L.; Morgan, Sally; Kutterorf, Steffen; Sager, William W.; Carvallo, Claire; Shervais, John; Party IODP Expedition 352, Scientific

2015-04-01

IODP Expedition 352 was designed to drill through the entire volcanic sequence of the Bonin forearc. Four sites were drilled, two on the outer fore arc and two on the upper trench slope. Site survey seismic data, combined with borehole data, indicate that tectonic deformation in the outer IBM fore arc is mainly post-magmatic. Post-magmatic extension resulted in the formation of asymmetric sedimentary basins such as, for example, the half-grabens at sites 352-U1439 and 352-U1442 located on the upper trench slope. Along their eastern margins these basins are bounded by west-dipping normal faults. Sedimentation was mainly syn-tectonic. The lowermost sequence of the sedimentary units was tilted eastward by ~20°. These tilted bedding planes were subsequently covered by sub-horizontally deposited sedimentary beds. Based on biostratigraphic constraints, the minimum age of the oldest sediments is ~ 35 Ma; the timing of the sedimentary unconformities lies between ~ 27 and 32 Ma. At sites 352-U1440 and 352-U1441, located on the outer forearc, post-magmatic deformation resulted mainly in strike-slip faults possibly bounding the sedimentary basins. The sedimentary units within these basins were not significantly affected by post-sedimentary tectonic tilting. Biostratigraphic ages indicate that the minimum age of the basement-cover contact lies between ~29.5 and 32 Ma. Overall, the post-magmatic tectonic structures observed during Expedition 352 reveal a multiphase tectonic evolution of the outer IBM fore arc. At sites 352-U1439 and 352-U1442, shear with dominant reverse to oblique reverse displacement was localized along distinct subhorizontal cataclastic shear zones as well as steeply dipping slickensides and shear fractures. These structures, forming within a contractional tectonic regime, were either re-activated as or cross-cut by normal-faults as well as strike-slip faults. Extension was also accommodated by steeply dipping to subvertical mineralized veins and extensional fractures. Faults observed at sites 352-U1440 and 352-U1441 show mainly strike-slip. The sediments overlying the igneous basement, of maximum Late Eocene to Recent age, document ash and aeolian input, together with mass wasting of the fault-bounded sediment ponds.

Geochemistry of pillow lavas and sheeted dikes from Nain and Ashin ophiolites (Central Iran)

NASA Astrophysics Data System (ADS)

Saccani, Emilio; Pirnia Naeini, Tahmineh; Torabi, Ghodrat

2017-04-01

An extensive, worldwide database on the geochemistry of basalts from well-known tectonic settings is available. Knowing the chemistry of basalts on one hand, and the tectonic setting of their origin on the other hand, resulted in the development of tectonic discrimination diagrams. Recently developed discrimination diagrams allow us to determine the tectonic setting of volcanics with almost neglectable probability of misclassification (<1%). One major application of these diagrams lies in discriminating the tectonic setting of formation of ophiolites, particularly in poorly-known areas. A good example is the Inner ophiolite belt of Iran, located in Central Iran. The geodynamic significance of the inner ophiolites is still poorly known. From the Inner ophiolites, either no volcanic section is reported, or, the data are highly limited and poorly-reliable due the high degree of alteration of the studied samples. We have been able to overcome this problem by spotting relatively well-preserved outcrops of pillow lavas and sheeted dikes from two ophiolite mélanges of Central Iran, Nain and Ashin ophiolites. The two mélanges are located in the west of Central-East Iranian microplate. In total, 28 samples have been collected from the pillow lavas and sheeted dikes outcrops. The studied volcanic rocks consist mainly of basalts and minor ferrobasalts and basaltic andesites, all showing a clear subalkaline nature (e.g., Nb/Y = 0.03-0.21). Two samples from the Nain ophiolite are characterized by N-MORB normalized incompatible element patterns showing marked Th positive anomalies and Ta, Nb, Ti negative anomalies. Chondrite-normalized REE patterns show LREE/HREE (light REE/heavy REE) enrichment, with LaN/YbN=3.2-4.3. These rocks are chemically similar to the calc-alkaline basalts (CAB), as also highlighted by many discrimination diagrams. These rocks are interpreted to have generated in a cordilleran-type volcanic arc setting. All other samples from both the Nain and Ashin ophiolites display a wide range of chemical composition. However, the relatively less fractionated basalts are characterized by low TiO2 (0.60-1 wt%), P2O5 (0.03-0.08 wt%), Zr (23-75 ppm) and Y (9-27) contents. Cr (38-619 ppm) and Ni (22-220 ppm) contents show a wide range of variation. N-MORB normalized incompatible element patterns show rather flat trends and a general depletion (from 0.4 to 0.8 times N-MORB composition) coupled with a slight Th enrichment (1-3 times N-MORB). Chondrite-normalized REE patterns are generally flat and are characterized by either a slight depletion or a slight enrichment in LREE compared to HREE (LaN/YbN=0.7-1.2). These overall chemical features resemble those of island arc tholeiites from many ophiolitic complexes. The depletion in incompatible elements compared to N-MORB suggest that these rocks were derived from partial melting of a depleted mantle source. Th enrichment with respect to Nb (ThN/NbN = 2.6-12.4) suggests that mantle sources underwent enrichment in subduction-derived chemical components prior melting. Our data suggest that the Nain and Ashin ophiolites were formed in a subduction-related tectonic setting during the Late Cretaceous. The chemistry of the studied rocks is compatible with transition zone either from forearc to arc or from arc to backarc.

Geological nature of mineral licks and the reasons for geophagy among animals

NASA Astrophysics Data System (ADS)

Panichev, Alexander M.; Popov, Vladimir K.; Chekryzhov, Igor Yu.; Seryodkin, Ivan V.; Sergievich, Alexander A.; Golokhvast, Kirill S.

2017-06-01

In this paper, the reasons for geophagy (the eating of rocks by wild herbivores) in two regions of the eastern Sikhote-Alin volcanic belt are considered. The mineralogical and chemical features of the consumed rocks, as well as the geological conditions of their formation, are investigated. A comparative analysis of the mineral and chemical composition of the consumed rocks and the excrement of the animals, almost completely consisting of mineral substances, is carried out. It is established that the consumed rocks are hydrothermally altered rhyolitic tuffs located in the volcanic calderas and early Cenozoic volcano-tectonic depressions. They consist of 30-65 % from zeolites (mainly clinoptilolites) and smectites, possessing powerful sorption properties. According to the obtained data, the main reason for geophagy may be connected with the animals' urge to discard excessive and toxic concentrations of certain elements that are widespread in specific habitats and ingested with forage plants.

Transverse tectonic structural elements across Himalayan mountain front, eastern Arunachal Himalaya, India: Implication of superposed landform development on analysis of neotectonics

NASA Astrophysics Data System (ADS)

Bhakuni, S. S.; Luirei, Khayingshing; Kothyari, Girish Ch.; Imsong, Watinaro

2017-04-01

Structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern Arunachal sub-Himalaya. Mountain front sinuosity (Smf) index values close to one are indicative of the active nature of the mountain front all along the eastern Arunachal Himalaya, which can be directly attributed to the regional uplift along the Himalayan Frontal Thrust (HFT). However, the mountain front is significantly sinusoidal around junctions between HFT/MBT (Main Boundary Thrust) and active transverse faults. The high values of stream length gradient (SL) and stream steepness (Ks) indices together with field evidence of fault scarps, offset of terraces, and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults. This reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses, providing favourable sites for deposition of recent sediments. Tectonic interactions of these transverse faults with the Himalayan longitudinal thrusts (MBT/HFT) have segmented the mountain front marked with varying sinuosity. The net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements. Some distinctive examples are: in the eastern extremity of NE Himalaya across the Dibang River valley, the NW-SE trending mountain front is attenuated by the active Mishmi Thrust that has thrust the Mishmi crystalline complex directly over the alluvium of the Brahmaputra plains. The junction of the folded HFT and Mishmi Thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the Dibang River course. Similarly, the transverse faults cut the mountain front along the Sesseri, Siluk, Siku, Siang, Mingo, Sileng, Dikari, and Simen rivers. At some such junctions, landforms associated with the active right-lateral strike-slip faults are superposed over the earlier landforms formed by transverse normal faults. In addition to linear transverse features, we see evidence that the fold-thrust belt of the frontal part of the Arunachal Himalaya has also been affected by the neotectonically active NW-SE trending major fold known as the Siang antiform that again is aligned transverse to the mountain front. The folding of the HFT and MBT along this antiform has reshaped the landscape developed between its two western and eastern limbs running N-S and NW-SE, respectively. The transverse faults are parallel to the already reported deep-seated transverse seismogenic strike-slip fault. Therefore, a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the Himalayan region must take into account the role of transverse tectonics.

Petrography and geochemistry of Jurassic sandstones from the Jhuran Formation of Jara dome, Kachchh basin, India: Implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Periasamy, V.; Venkateshwarlu, M.

2017-06-01

Sandstones of Jhuran Formation from Jara dome, western Kachchh, Gujarat, India were studied for major, trace and rare earth element (REE) geochemistry to deduce their paleo-weathering, tectonic setting, source rock characteristics and provenance. Petrographic analysis shows that sandstones are having quartz grains with minor amount of K-feldspar and lithic fragments in the modal ratio of Q 89:F 7:L 4. On the basis of geochemical results, sandstones are classified into arkose, sub-litharenite, wacke and quartz arenite. The corrected CIA values indicate that the weathering at source region was moderate to intense. The distribution of major and REE elements in the samples normalized to upper continental crust (UCC) and chondrite values indicate similar pattern of UCC. The tectonic discrimination diagram based on the elemental concentrations and elemental ratios of Fe2O3 + MgO vs. TiO2, SiO2 vs. log(K2O/Na2O), Sc/Cr vs. La/Y, Th-Sc-Zr/10, La-Th-Sc plots Jhuran Formation samples in continental rift and collision settings. The plots of Ni against TiO2, La/Sc vs. Th/Co and V-Ni-Th ∗10 reveals that the sediments of Jhuran Formation were derived from felsic rock sources. Additionally, the diagram of (Gd/Yb) N against Eu/Eu ∗ suggest the post-Archean provenance as source possibly Nagar Parkar complex for the studied samples.

Petrogenesis of two Triassic A-type intrusions in the interior of South China and their implications for tectonic transition

NASA Astrophysics Data System (ADS)

Sun, Li-Qiang; Ling, Hong-Fei; Shen, Wei-Zhou; Wang, Kai-Xing; Huang, Guo-Long

2017-07-01

The evolution of the tectonic regime that was responsible for the Indosinian granitoids in the South China Block (SCB) is still controversial. Investigations on A-type granites can provide important information regarding this tectonic evolution. A detailed study that utilizes whole-rock elemental, Sr-Nd isotopic, in situ zircon U-Pb and Lu-Hf isotopic geochemistry is conducted on the Miantuwo biotite granite in northern Guangdong Province and the Pingtian biotite monzogranite in southern Jiangxi Province, South China. The new data indicate that both the Miantuwo and Pingtian granites were emplaced at 233 ± 2 Ma and show metaluminous to slightly peraluminous A-type granite affinity. The two granites are characterized by high amounts of rare earth elements (total REEs = 247 ppm-557 ppm and 251 ppm-342 ppm) and high field strength elements (Zr + Nb + Ce + Y = 325 ppm-605 ppm and 343 ppm-496 ppm) and high Ga/Al ratios (10,000 × Ga/Al = 2.50-2.98 and 2.62-2.70). Calculations from a zircon saturation thermometer and apatite saturation thermometer indicate that the magmatic temperatures were 800 °C-980 °C for both granites. Both the Miantuwo and Pingtian granites show relatively high initial 87Sr/86Sr ratios (0.7151-0.7185 and 0.7170-0.7189), low εNd(t) values (- 9.8 to - 8.6 and - 9.7 to - 9.1) and low to moderate zircon εHf(t) values (- 10.4 to - 6.6 and - 9.5 to - 4.6). Based on these data, we suggest that these two A-type granites were derived from the partial melting of existing mafic to intermediate rocks in the lower crust in response to the underplating and/or intraplating of mantle-derived magma. Our study on the Miantuwo and Pingtian granites, alongside previous studies on other Triassic A-type granites in South China, indicates an extensional tectonic environment during the Late Triassic in the interior of the Cathaysia Block. Alongside existing geological observations and the tectonic evolution in the SCB, we suggest that the interior of the SCB was dominated by a compressional tectonic environment during the Late Permian-Middle Triassic in response to the collisions between the SCB and ambient blocks, and then a tectonic transition from this compressional environment to a post-collisional extension environment began at approximately 233 Ma.

Tectonic control on the genesis of magmas in the New Hebrides arc (Vanuatu)

NASA Astrophysics Data System (ADS)

Beier, Christoph; Brandl, Philipp A.; Lima, Selma M.; Haase, Karsten M.

2018-07-01

We present here new bathymetric, petrological and geochemical whole rock, glass and mineral data from the submarine Epi volcano in the New Hebrides (Vanuatu) island arc. The structure has previously been interpreted to be part of a larger caldera structure but new bathymetric data reveal that the volcanic cones are aligned along shear zones controlled by the local tectonic stress field parallel to the recent direction of subduction. We aim to test if there is an interaction between local tectonics and magmatism and to what extent the compositions of island arc volcanoes may be influenced by their tectonic setting. Primitive submarine Epi lavas and those from the neighbouring Lopevi and Ambrym islands originate from a depleted mantle wedge modified by addition of subduction zone components. Incompatible element ratios sensitive to fluid input (e.g., Th/Nb, Ce/Yb) in the lavas are positively correlated with those more sensitive to mantle wedge depletion (e.g., Nb/Yb, Zr/Nb) amongst the arc volcanoes suggesting that fluids or melts from the subducting sediments have a stronger impact on the more depleted compositions of the mantle wedge. The whole rock, glass and mineral major and trace element compositions and the occurrence of exclusively normally zoned clinopyroxene and plagioclase crystals combined with the absence of inversely zoned crystals and water-bearing phases in both mafic and evolved lavas suggest that the erupted melt was relatively dry compared to other subduction zone melts and has experienced little disequilibrium modification by melt mixing or assimilation. Our data also imply that differentiation of amphibole is not required to explain the incompatible element patterns but may rather result from extensive clinopyroxene fractionation in agreement with petrographic observations. Thermobarometric calculations indicate that the melts fractionated continuously during ascent, contrasting with fractionation during stagnation in an established crustal magma reservoir. We interpret the occurrence of this fractional crystallisation end-member in a relatively thick island arc crust ( 30 km thickness) to result from isolated and relatively rapid ascent of melts, most likely through a complex system of dykes and sills that developed due to the tectonic positioning of Epi in a complex tectonic zone between a compressional environment in the north and an extensional setting in the south. We can show that the alignment of the cones largely depends on the local tectonic stress field at Epi that is especially influenced by a large dextral strike-slip zone, indicating that structural features have a significant impact on the location and composition of volcanic edifices.

Pn tomography of South China Sea, Taiwan Island, Philippine archipelago, and adjacent regions

NASA Astrophysics Data System (ADS)

Li, Xibing; Song, Xiaodong; Li, Jiangtao

2017-02-01

The South China Sea (SCS) and its surrounding areas are geologically highly heterogeneous from the interactions of multiple plates in Southeast Asia (Eurasian plate, Indian-Australian plate, Philippine Sea plate, and Pacific plate). To understand the tectonics at depth, here we combined bulletin and handpicked data to conduct Pn tomography of the region. The results show distinct features that are correlated with the complex geology at surface, suggesting a lithosphere-scale tectonics of the region. Low Pn velocities are found along a belt of the western Pacific transpressional system from the Okinawa Trough and eastern East China Sea, across central and eastern Taiwan orogeny, to the island arcs of the Luzon Strait and the entire Philippine Islands, as well as under the Palawan Island and part of the continental margin north of the Pearl River Basin. High velocities are found under Ryukyu subduction zone, part of the Philippine subduction zone, part of the Eurasian subduction beneath the southwestern Taiwan, and the continent-ocean boundary between the south China and the SCS basin. The Taiwan Strait, the Mainland SE coast, and the main SCS basin sea are relatively uniform with average Pn values. Crustal thicknesses show large variations in the study region but also coherency with tectonic elements. The Pn pattern in Taiwan shows linear trends of surface geology and suggests strongly lithosphere-scale deformation of the young Taiwan orogenic belt marked by the deformation boundary under the Western Foothill and the Western Coastal Plain at depth, and the crustal thickness shows a complex pattern from the transpressional collision. Our observations are consistent with rifting and extension in the northern margin of the SCS but are not consistent with mantle upwelling as a mechanism for the opening and the subsequent closing of the SCS. The Philippine island arc is affected by volcanisms from both the Asian and Philippine Sea subductions in the south but mainly from the Asian subduction in the north and under the Luzon Strait.

Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations

NASA Astrophysics Data System (ADS)

Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

2010-12-01

We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian Pacific Congress on Computational Mechanics, July 2010, iopscience.iop.org/1757-899X/10/1/012012. [4] G. Morra, P. Chatelain, P. Tackley and P. Koumoutzakos, 2007, Large scale three-dimensional boundary element simulation of subduction, in Proceeding International Conference on Computational Science - Part III, LNCS 4489, pp. 1122-1129. Interaction between two subducting slabs.

Geochemical signature of provenance, tectonics and chemical weathering in the Quaternary flood plain sediments of the Hindon River, Gangetic plain, India

NASA Astrophysics Data System (ADS)

Mondal, M. E. A.; Wani, H.; Mondal, Bulbul

2012-09-01

The Ganga basin in the Himalayan foreland is a part of the world's largest area of modern alluvial sedimentation. Flood plain sediments of the Hindon River of the Gangetic plain have been analyzed for sediment texture, major and trace elements including rare earth elements (REEs). The results have been used to characterize the source rock composition and to understand the intensity of chemical weathering, tectonics and their interplay in the Hindon flood plain. The sediments of the Hindon flood plain dominantly consist of sand sized particles with little silt and clay. The geochemistry of the Hindon sediments has been compared to the Siwalik mudstone of the Siwalik Group (Siwaliks). The Siwalik sedimentary rocks like sandstones, mudstones and conglomerates are the known source rocks for the Hindon flood plain sediments. Mudstone geochemistry has been considered best to represent the source rock characteristics. The UCC (Upper Continental Crust) normalized major and trace elements of the Hindon flood plain sediments are very similar to the Siwalik mudstone except for Th and Cr. Furthermore, the average chondrite normalized REE pattern of the Hindon flood plain sediments is similar to the Siwalik mudstone. Textural immaturity, K/Rb ratios and the average CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values of the Hindon flood plain sediments indicate that the sediments have not been affected by chemical weathering. Our study suggests that the active tectonics of the Himalayas and monsoon climate enhances only physical erosion of the source rocks (Siwaliks) rather than the chemical alteration. These factors help the Hindon sediments to retain their parental and tectonic signature even after recycling.

NATURAL ARSENIC CONTAMINATION OF HOLOCENE ALLUVIAL AQUIFERS BY LINKED TECTONIC, WEATHERING, AND MICROBIAL PROCESSES

EPA Science Inventory

Linked tectonic, geochemical, and biologic processes lead to natural arsenic contamination of groundwater in Holocene alluvial aquifers, which are the main threat to human health around the world. These groundwaters are commonly found a long distance from their ultimate source of...

Provenance and tectonic settings of sands from Puerto Peñasco, Desemboque and Bahia Kino beaches, Gulf of California, Sonora, México

NASA Astrophysics Data System (ADS)

Madhavaraju, J.; Tom, Milu; Lee, Yong IL; Balaram, V.; Ramasamy, S.; Carranza-Edwards, A.; Ramachandran, A.

2016-11-01

Textural, heavy minerals and geochemical (major, trace and rare earth elements) studies were undertaken on the sands from Puerto Peñasco, Desemboque and Bahia Kino beaches to determine the provenance and tectonic settings. Puerto Peñasco and Bahia Kino sands are coarse grained to fine grained, while Desemboque sands are fine grained. Geochemically, these sands are classified as arkose. The sands are depleted in most of the trace elements relative to upper continental crust (UCC), except for few trace elements (Sr, Rb and Ba), which are slightly enriched. High ΣREE content are observed in the Desemboque sands (94.43 ± 6.9) than in the Puerto Peñasco and Bahia Kino sands (51.58 ± 17.06; 72.38 ± 9.27; respectively). The chemical index of alteration (CIA) values of Puerto Peñasco, Desemboque and Bahia Kino sands (PP: 42 to 50; DE: 48 to 50; BK: 44 to 50: respectively) indicate the low intensity of chemical weathering in the source rocks. The tectonic discriminant-function-based multidimensional diagram shows arc and rift settings for Puerto Peñasco sands whereas rift setting for both Desemboque and Bahia Kino sands. The heavy mineral assemblage, immobile trace elements, REE patterns, elemental ratios such Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, various bivariate and ternary plots indicate the contribution of sediments from felsic composition. This interpretation is supported by the comparison of REE patterns of the Puerto Peñasco, Desemboque and Bahia Kino sands with the potential source rocks exposed nearby the study areas.

Overview of geology and tectonic evolution of the Baikal-Tuva area.

PubMed

Gladkochub, Dmitry; Donskaya, Tatiana

2009-01-01

This chapter provides the results of geological investigations of the main tectonic units of the Baikal-Tuva region (southwestern part of Siberia) during the last decades: the ancient Siberian craton and adjacent areas of the Central Asian Orogenic belt. In the framework of these main units we describe small-scale blocks (terranes) with focus on details of their inner structure and evolution through time. As well as describing the geology and tectonics of the area studied, we give an overview of underwater sediments, neotectonics, and some phenomena of history and development of the Baikal, Khubsugul, Chargytai, and Tore-Chol Lakes basins of the Baikal-Tuva region. It is suggested that these lakes' evolution was controlled by neotectonic processes, modern seismic activity, and global climate changes.

Necessity of electromagnetic emission network arrangement in Georgia

NASA Astrophysics Data System (ADS)

Turazashvili, Ioseb; Kachakhidze, Nino; Machavariani, Kakhaber; Kachakhidze, Manana; Gogoberidze, Vitali; Khazaradze, Giorgi

2015-04-01

The field of the tectonic stress has the hierarchical structure. The most characteristic features connected with the regional tectonic elements are determined by the geologic - tectonic data. It is established that in the young folded areas like the Caucasus the field of tectonic stress is characterized by the sharp anisotropy with the predominance of the compression perpendicular to the trend of folding. Spatial location of the main positive and negative geotectonic morphostructures of the Caucasus shows the existence of the wavy tectonic movements in the region. They are caused by the horizontal compression, provoked evidently by advancement of the Arabian lithosphere plate to the North and its re-approach with the Euro-Asian plate. All these cause considerable deformation of the lithosphere of the Caucasian region and its breaking up in separate blocks. This, in its turn, causes the concentration of stress along the boundaries of the blocks and rising of earthquakes focuses there. According to the instrumental data starting from 1899 at about 40 large earthquakes were fixed in the Caucasus. The rate of risks associated with these hazards increases every year in Georgia due to the appearance of new complicated technological construction: oil and gas pipelines large dams and hydropower plants and others. Modern ground-based and satellite methods of viewing enables to reveal those multiple anomalous geophysical phenomena which become evident in the period preceding earthquake and are directly connected with the process of its preparation. Lately special attention is attributed to the electromagnetic emission fixed during large earthquake and has already been successfully detected in Japan, America and Europe. Unfortunately there is no electromagnetic emission detection network in Georgia yet. The presented abstract concerns arrange of EM emission net and begin implementation of this vital task by arrangement of the one relevant station on the fault near Tbilisi. The work is carried out in the frame of grant (DI/21/9-140/13 "Pilot project of before earthquake detected Very Low Frequency/Low Frequency electromagnetic emission network installation in Georgia") by financial support of Shota Rustaveli National Science Foundation.

Statistically Correct Methodology for Compositional Data in New Discriminant Function Tectonomagmatic Diagrams and Application to Ophiolite Origin

NASA Astrophysics Data System (ADS)

Verma, Surendra P.; Pandarinath, Kailasa; Verma, Sanjeet K.

2011-07-01

In the lead presentation (invited talk) of Session SE05 (Frontiers in Geochemistry with Reference to Lithospheric Evolution and Metallogeny) of AOGS2010, we have highlighted the requirement of correct statistical treatment of geochemical data. In most diagrams used for interpreting compositional data, the basic statistical assumption of open space for all variables is violated. Among these graphic tools, discrimination diagrams have been in use for nearly 40 years to decipher tectonic setting. The newer set of five tectonomagmatic discrimination diagrams published in 2006 (based on major-elements) and two sets made available in 2008 and 2011 (both based on immobile elements) fulfill all statistical requirements for correct handling of compositional data, including the multivariate nature of compositional variables, representative sampling, and probability-based tectonic field boundaries. Additionally in the most recent proposal of 2011, samples having normally distributed, discordant-outlier free, log-ratio variables were used in linear discriminant analysis. In these three sets of five diagrams each, discrimination was successfully documented for four tectonic settings (island arc, continental rift, ocean-island, and mid-ocean ridge). The discrimination diagrams have been extensively evaluated for their performance by different workers. We exemplify these two sets of new diagrams (one set based on major-elements and the other on immobile elements) using ophiolites from Boso Peninsula, Japan. This example is included for illustration purposes only and is not meant for testing of these newer diagrams. Their evaluation and comparison with older, conventional bivariate or ternary diagrams have been reported in other papers.

DELP Symposium: Tectonics of eastern Asia and western Pacific Continental Margin

NASA Astrophysics Data System (ADS)

Eastern Asia and the western Pacific make up a broad region of active plate tectonic interaction. The area is a natural laboratory for studying the processes involved in the origin and evolution of volcanic island arcs, marginal basins, accretionary prisims, oceanic trenches, accreted terranes, ophiolite emplacement, and intracontinental deformation. Many of our working concepts of plate tectonics and intraplate deformation were developed in this region, even though details of the geology and geophysics there must be considered of a reconnaissance nature.During the past few years researchers have accumulated a vast amount of new and detailed information and have developed a better understanding of the processes that have shaped the tectonic elements in this region. To bring together scientists from many disciplines and to present the wide range of new data and ideas that offer a broader perspective on the interrelations of geological, geochemical, geophysical and geodetic studies, the symposium Tectonics of Eastern Asia and Western Pacific Continental Margin was held December 13-16, 1988, at the Tokyo Institute of Technology in Japan, under the auspicies of DELP (Dynamics and Evolution of the Lithosphere Project).

Orogenic, Ophiolitic, and Abyssal Peridotites

NASA Astrophysics Data System (ADS)

Bodinier, J.-L.; Godard, M.

2003-12-01

"Tectonically emplaced" mantle rocks include subcontinental, suboceanic, and subarc mantle rocks that were tectonically exhumed from the upper mantle and occur:(i) as dispersed ultramafic bodies, a few meters to kilometers in size, in suture zones and mountain belts (i.e., the "alpine," or "orogenic" peridotite massifs - De Roever (1957), Thayer (1960), Den Tex (1969));(ii) as the lower ultramafic section of large (tens of kilometers) ophiolite or island arc complexes, obducted on continental margins (e.g., the Oman Ophiolite and the Kohistan Arc Complex - Coleman (1971), Boudier and Coleman (1981), Burg et al. (1998));(iii) exhumed above the sea level in ocean basins (e.g., Zabargad Island in the Red Sea, St. Paul's islets in the Atlantic and Macquarie Island in the southwestern Pacific - Tilley (1947), Melson et al. (1967), Varne and Rubenach (1972), Bonatti et al. (1981)).The "abyssal peridotites" are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974; Prinz et al., 1976; Hamlyn and Bonatti, 1980).Altogether, tectonically emplaced and abyssal mantle rocks provide insights into upper mantle compositions and processes that are complementary to the information conveyed by mantle xenoliths (See Chapter 2.05). They provide coverage to vast regions of the Earth's upper mantle that are sparsely sampled by mantle xenoliths, particularly in the ocean basins and beneath passive continental margins, back-arc basins, and oceanic island arcs.Compared with mantle xenoliths, a disadvantage of some tectonically emplaced mantle rocks for representing mantle compositions is that their original geodynamic setting is not exactly known and their significance is sometimes a subject of speculation. For instance, the provenance of orogenic lherzolite massifs (subcontinental lithosphere versus upwelling asthenosphere) is still debated (Menzies and Dupuy, 1991, and references herein), as is the original setting of ophiolites (mid-ocean ridges versus supra-subduction settings - e.g., Nicolas, 1989). In addition, the mantle structures and mineralogical compositions of tectonically emplaced mantle rocks may be obscured by deformation and metamorphic recrystallization during shallow upwelling, exhumation, and tectonic emplacement. Metamorphic processes range from high-temperature recrystallization in the stability field of plagioclase peridotites ( Rampone et al., 1993) to complete serpentinization (e.g., Burkhard and O'Neill, 1988). Some garnet peridotites record even more complex evolutions. They were first buried to, at least, the stability field of garnet peridotites, and, in some cases to greater than 150 km depths ( Dobrzhinetskaya et al., 1996; Green et al., 1997; Liou, 1999). Then, they were exhumed to the surface, dragged by buoyant crustal rocks ( Brueckner and Medaris, 2000).Alternatively, several peridotite massifs are sufficiently well preserved to allow the observation of structural relationships between mantle lithologies that are larger than the sampling scale of mantle xenoliths. It is possible in these massifs to evaluate the scale of mantle heterogeneities and the relative timing of mantle processes such as vein injection, melt-rock reaction, deformation, etc… Detailed studies of orogenic and ophiolitic peridotites on centimeter- to kilometer-scale provide invaluable insights into melt transfer mechanisms, such as melt flow in lithospheric vein conduits and wall-rock reactions (Bodinier et al., 1990), melt extraction from mantle sources via channeled porous flow ( Kelemen et al., 1995) or propagation of kilometer-scale melting fronts associated with thermalerosion of lithospheric mantle ( Lenoir et al., 2001). In contrast, mantle xenoliths may be used to infer either much smaller- or much larger-scale mantle heterogeneities, such as micro-inclusions in minerals ( Schiano and Clocchiatti, 1994) or lateral variations between lithospheric provinces ( O'Reilly et al., 2001).The abyssal peridotites are generally strongly affected by oceanic hydrothermal alteration. Most often, their whole-rock compositions are strongly modified and cannot be used straightforwardly to assess mantle compositions (e.g., Baker and Beckett, 1999). However, even in the worst cases the samples generally contain fresh, relic minerals (mainly clinopyroxene) that represent the only available direct information on the oceanic upper mantle in large ocean basins, away from hot-spot volcanic centers. In situ trace-element data on clinopyroxenes from abyssal peridotites provide constraints on melting processes at mid-ocean ridges (Johnson et al., 1990).In this chapter, we review the main inferences on upper mantle composition and heterogeneity that may be drawn from geochemical analyses of the major elements, lithophile trace elements, and Nd-Sr isotopes in tectonically emplaced and abyssal mantle rocks. In addition we emphasize important insights into the mechanisms of melt/fluid transfer that can be deduced from detailed studies of these mantle materials.

From 2D to 3D modelling in long term tectonics: Modelling challenges and HPC solutions (Invited)

NASA Astrophysics Data System (ADS)

Le Pourhiet, L.; May, D.

2013-12-01

Over the last decades, 3D thermo-mechanical codes have been made available to the long term tectonics community either as open source (Underworld, Gale) or more limited access (Fantom, Elvis3D, Douar, LaMem etc ...). However, to date, few published results using these methods have included the coupling between crustal and lithospheric dynamics at large strain. The fact that these computations are computational expensive is not the primary reason for the relatively slow development of 3D modeling in the long term tectonics community, as compare to the rapid development observed within the mantle dynamic community, or in the short-term tectonics field. Long term tectonics problems have specific issues not found in either of these two field, including; large strain (not an issue for short-term), the inclusion of free surface and the occurence of large viscosity contrasts. The first issue is typically eliminated using a combined marker-ALE method instead of fully lagrangian method, however, the marker-ALE approach can pose some algorithmic challenges in a massively parallel environment. The two last issues are more problematic because they affect the convergence of the linear/non-linear solver and the memory cost. Two options have been tested so far, using low order element and solving with a sparse direct solver, or using higher order stable elements together with a multi-grid solver. The first options, is simpler to code and to use but reaches its limit at around 80^3 low order elements. The second option requires more operations but allows using iterative solver on extremely large computers. In this presentation, I will describe the design philosophy and highlight results obtained using a code from the second-class method. The presentation will be oriented from an end-user point of view, using an application from 3D continental break up to illustrate key concepts. The description will proceed point by point from implementing physics into the code, to dealing with specific issues related to solving the discrete system of non linear equations.

The Origin of The Piz Terri-Lunschania zone (Central Alps, Switzerland)

NASA Astrophysics Data System (ADS)

Galster, Federico; Stockli, Daniel

2017-04-01

The Piz Terri-Lunschania zone (PTLZ) represents a band of metasedimentary rocks embedded in a crucial knot at the NE border of the Lepontine dome, at the intersection of the Gotthard, Lucomagno, Simano, Adula and Grava nappes. Its origin and its position in the tectonostratigraphy of the Central Alps are still not completely understood. A better understanding of this sedimentary zone and its tectonic position could shed lights on the Helvetic-Penninic connection and facilitate the disentanglement of the Lepontine dome tectonics. In this study we combine structural and stratigraphic observations with detrital zircon (DZ) and detrital rutile (DR) U-Pb geochronology as well as mineral trace element data from Permian, Triassic and Jurassic sandstones. We compare these data with those from adjacent tectonic units and coeval strata in other portions of the Alpine chain. Maximal depositional ages, abrupt changes in provenances and stratigraphic correlations based on new DZ and DR U-Pb and trace element data allow for a better understanding of the sedimentary evolution of the Terri basin and its palaeogeographic position along the northern margin of the Alpine Tethys. In particular the DZ U-Pb signatures, with its abundant 260-280 Ma zircons and the scarcity of 290-350 Ma zircons, corroborates an Ultra-Adula origin of the PTLZ as proposed by Galster et al (2010; 2012) based on stratigraphic arguments and reinforces the notion of a Briançonnais influence on the stratigraphic record of this complex zone, a fact that has important tectonic and Palaeogeographic implications. Galster F, Cavargna-Sani M, Epard J-L, Masson H (2012) New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps. Tectonophysics 579:37-55. doi: 10.1016/j.tecto.2012.05.029 Galster F, Epard J-L, Masson H (2010) The Soja and Luzzone-Terri nappes: Discovery of a Briançonnais element below the front of the Adula nappe (NE Ticino, Central Alps). Bulletin de la Société Vaudoise des Sciences naturelles 92:61-75.

Present-Day Kinematics of the Dead Sea Transform and Internal Deformation within the Sinai and Arabian Plates

NASA Astrophysics Data System (ADS)

Gomez, F. G.; Yassminh, R.; Cochran, W. J.; Reilinger, R. E.; Barazangi, M.

2015-12-01

An updated GPS velocity field along the Dead Sea Fault (DSF) provides a basis for assessing off-transform strain within the Sinai and Arabian plates along entire length of this left-lateral, continental transform. As one of the main tectonic elements in the eastern Mediterranean region, an improved kinematic view of the DSF elucidates the broader understanding of the regional tectonic framework, as well as contributes to refining the earthquake hazard assessment. Reconciling short-term (geodetic) measurements of crustal strain with neotectonic data on fault movements can yield insight into the mechanical and rheological properties of crustal deformation associated with transform tectonics. In addition to regional continuous GPS stations, this study assembles results from campaign GPS networks in Syria, Lebanon, and Jordan spanning more than a decade. 1-sigma uncertainties on velocities range from less than 0.4 mm/yr (continuous stations and older GPS survey sites) to about 1.0 mm/yr (newer survey sites). Analyses using elastic block models suggest slip rates of 4.0 - 5.0 mm/yr along the southern and central DSF and slip rates of 2.0 - 3.0 mm/yr along the northern DSF, and fault locking depths also vary along strike of the transform. Furthermore, the spatial distribution of GPS observations permits analyzing residual strains within the adjacent plates, after plate boundary strain is removed. A key observation is horizontal stretching within the Sinai plate, which may be related to pull by the subducted slab of the Sinai plate. Within the Arabian plate, areas of horizontal stretching generally correlate with locations of Quaternary volcanism.

Global evaluation of erosion rates in relation to tectonics

NASA Astrophysics Data System (ADS)

Hecht, Hagar; Oguchi, Takashi

2017-12-01

Understanding the mechanisms and controlling factors of erosion rates is essential in order to sufficiently comprehend bigger processes such as landscape evolution. For decades, scientists have been researching erosion rates where one of the main objectives was to find the controlling factors. A variety of parameters have been suggested ranging from climate-related, basin morphometry and the tectonic setting of an area. This study focuses on the latter. We use previously published erosion rate data obtained mainly using 10Be and sediment yield and sediment yield data published by the United States Geological Survey. We correlate these data to tectonic-related factors, i.e., distance to tectonic plate boundary, peak ground acceleration ( PGA), and fault distribution. We also examine the relationship between erosion rate and mean basin slope and find significant correlations of erosion rates with distance to tectonic plate boundary, PGA, and slope. The data are binned into high, medium, and low values of each of these parameters and grouped in all combinations. We find that groups with a combination of high PGA (> 0.2.86 g) and long distance (> 1118.69 km) or low PGA (< 0.68 g) and short distance (< 94.34 km) are almost inexistent suggesting a strong coupling between PGA and distance to tectonic plate boundary. Groups with low erosion rates include long distance and/or low PGA, and groups with high erosion rates include neither of these. These observations indicate that tectonics plays a major role in determining erosion rates, which is partly ascribable to steeper slopes produced by active crustal movements. However, our results show no apparent correlation of slope with erosion rates, pointing to problems with using mean basin-wide slope as a slope indicator because it does not represent the complex slope distribution within a basin.

Off-axis volcano-tectonic activity during continental rifting: Insights from the transversal Goba-Bonga lineament, Main Ethiopian Rift (East Africa)

NASA Astrophysics Data System (ADS)

Corti, Giacomo; Sani, Federico; Agostini, Samuele; Philippon, Melody; Sokoutis, Dimitrios; Willingshofer, Ernst

2018-03-01

The Main Ethiopian Rift, East Africa, is characterized by the presence of major, enigmatic structures which strike approximately orthogonal to the trend of the rift valley. These structures are marked by important deformation and magmatic activity in an off-axis position in the plateaus surrounding the rift. In this study, we present new structural data based on a remote and field analysis, complemented with analogue modelling experiments, and new geochemical analysis of volcanic rocks sampled in different portions of one of these transversal structures: the Goba-Bonga volcano-tectonic lineament (GBVL). This integrated analysis shows that the GBVL is associated with roughly E-W-trending prominent volcano-tectonic activity affecting the western plateau. Within the rift floor, the approximately E-W alignment of Awasa and Corbetti calderas likely represent expressions of the GBVL. Conversely, no tectonic or volcanic features of similar (E-W) orientation have been recognized on the eastern plateau. Analogue modelling suggests that the volcano-tectonic features of the GBVL have probably been controlled by the presence of a roughly E-W striking pre-existing discontinuity beneath the western plateau, which did not extend beneath the eastern plateau. Geochemical analysis supports this interpretation and indicates that, although magmas have the same sub-lithospheric mantle source, limited differences in magma evolution displayed by products found along the GBVL may be ascribed to the different tectonic framework to the west, to the east, and in the axial zone of the rift. These results support the importance of the heterogeneous nature of the lithosphere and the spatial variations of its structure in controlling the architecture of continental rifts and the distribution of the related volcano-tectonic activity.

Comment on "Intermittent plate tectonics?".

PubMed

Korenaga, Jun

2008-06-06

Silver and Behn (Reports, 4 January 2008, p. 85) proposed that intermittent plate tectonics may resolve a long-standing paradox in Earth's thermal evolution. However, their analysis misses one important term, which subsequently brings their main conclusion into question. In addition, the Phanerozoic eustasy record indicates that the claimed effect of intermittency is probably weak.

Recent developments in understanding the tectonic evolution of the Southern California offshore area: Implications for earthquake-hazard analysis

USGS Publications Warehouse

Fisher, M.A.; Langenheim, V.E.; Nicholson, C.; Ryan, H.F.; Sliter, R.W.

2009-01-01

During late Mesozoic and Cenozoic time, three main tectonic episodes affected the Southern California offshore area. Each episode imposed its unique structural imprint such that early-formed structures controlled or at least influenced the location and development of later ones. This cascaded structural inheritance greatly complicates analysis of the extent, orientation, and activity of modern faults. These fault attributes play key roles in estimates of earthquake magnitude and recurrence interval. Hence, understanding the earthquake hazard posed by offshore and coastal faults requires an understanding of the history of structural inheritance and modifi-cation. In this report we review recent (mainly since 1987) findings about the tectonic development of the Southern California offshore area and use analog models of fault deformation as guides to comprehend the bewildering variety of offshore structures that developed over time. This report also provides a background in regional tectonics for other chapters in this section that deal with the threat from offshore geologic hazards in Southern California. ?? 2009 The Geological Society of America.

Tectonic evolution of Western Ishtar Terra, Venus

NASA Astrophysics Data System (ADS)

Marinangeli, Lucia

1997-03-01

A detailed geological mapping based on Magellan data has been done in Western Ishtar Terra from 300-330 deg W to 65-75 deg N. The area studied comprises three main phisiografic provinces, Atropos Tessera, Akna Montes and North-Western Lakshmi Planum. The purposes of this study are (1) to recognize the tectonism of this area and investigate its type, direction, intensity, distribution and age relationships, (2) to define the link between the formation of the Akna mountain belt and the tectonic deformation in adjacent Tessera and Lakshmi Planum.

Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that collided with the Sino-Korea plate towards the end of the Early Paleozoic or during the Devonian. A prominent feature in the detrital zircon age structure of the Huyoufang Formation is the Neoproterozoic detritus, which could be derived only from the Yangtze Craton. Reasonable interpretation of the two distinct source materials for the Huyoufang Formation is that the two plates were juxtaposed through collision before the late Carboniferous.

Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang

2016-04-01

Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

Aptian sedimentation in the Recôncavo-Tucano-Jatobá Rift System and its tectonic and paleogeographic significance

NASA Astrophysics Data System (ADS)

Freitas, Bernardo T.; Almeida, Renato P.; Carrera, Simone C.; Figueiredo, Felipe T.; Turra, Bruno B.; Varejão, Filipe G.; Assine, Mario L.

2017-12-01

This study, based on detailed sedimentologic and stratigraphic analysis of the Aptian succession preserved in the Recôncavo-Tucano-Jatobá Rift System (RTJ), present new elements for biostratigraphic correlation and paleogeographic reconstruction in the mid-Cretaceous South Atlantic realm, supporting novel interpretations on the tectonic and sedimentary evolution related to the W-Gondwana breakup. The Aptian sedimentary succession in the RTJ has been referred to as Marizal Formation, and interpreted as post-rift deposits. Detailed sedimentologic and stratigraphic studies of these deposits enabled the recognition and individualization of two distinctive sedimentary units that can be traced in the entire RTJ. These units are here described and named Banzaê and Cícero Dantas members of the Marizal Formation. Their contact is locally marked by the fossiliferous successions of the here proposed Amargosa Bed, lying at the top of the Banzaê Member. Both members of the Marizal Formation record large river systems captured by the Tucano Basin with the local development of eolian dune fields and fault-bounded alluvial fans. The Amargosa Bed represents a regional-scale base level change preserved between the Aptian fluvial successions along the RTJ. Hence, the studied sedimentary record presents important implications for the timing and direction of marine ingressions affecting NE-Brazil interior basins during the Aptian. A remarkable contrast in preserved fluvial architecture between the Banzaê Member, characterized by connected channel bodies, and the Cícero Dantas Member, characterized by isolated channel bodies within overbank fines, is here reported. The main interpreted control for the observed contrast in fluvial stratigraphy is sedimentary yield variation. The interval is also subject to the interpretation of a regional shift in the mechanism responsible for the subsidence of the basins formed during the Cretaceous break-up of the Central South Atlantic. This view is challenged by our results which reveal that basin forming extension continued throughout the Aptian. As a conclusion, the detailed stratigraphy of the Marizal Formation forward alternative geodynamic interpretations for the Aptian successions in northeastern Brazil, bringing new elements to the mid-Cretaceous biogeographical, paleogeographical and tectonic reconstructions of western Gondwana.

Research on Distribution Characteristics of Lunar Faults

NASA Astrophysics Data System (ADS)

Lu, T.; Chen, S.; Lu, P.

2017-12-01

Circular and linear tectonics are two major types of tectonics on lunar surface. Tectonic characteristics are of significance for researching about lunar geological evolution. Linear tectonics refers to those structures extending linearly on a lunar surface. Their distribution are closely related to the internal geological actions of the moon. Linear tectonics can integrally or locally express the structural feature and the stress status as well as showing the geological information of the interior of the moon. Faults are of the largest number and are of a certain distribution regularity among the linear tectonics, and are always the focus of domestic and overseas lunar tectonic research. Based on remote sensing geology and theory of traditional tectonic geology, We use a variety of remote sensing data processing to establish lunar linear tectonic interpretation keys with lunar spectral, terrain and gravity data. On this basis, interpretation of faults of the whole moon was primarily conducted from Chang'e-2 CCD image data and reference to wide-angle camera data of LROC, laser altimeter data of LOLA and gravity data of GRAIL. Statistical analysis of the number and distribution characteristics of whole lunar faults are counted from three latitude ranges of low, middle and high latitudes, then analyze the azimuth characteristics of the faults at different latitudes. We concluded that S-N direction is a relatively developed orientation at low latitudes. Middle latitudes reveal six preferred orientations of N-E, N-W, NN-E, NN-W, N-EE and N-WW directions. There are sparse faults of E-W direction distribution at low and middle latitudes. Meanwhile, the largest number of faults of E-W direction on lunar surface are mainly distributed along high latitudes with continuity and regularity. Analyzing faults of Mare Imbrium by the method of Euler deconvolution. The result show that there are two different properties of faults in Mare Imbrium. In conclusion, we suggest that the dynamics mechanism of the formation of the lunar faults is mainly affected by despinning, followed by tidal force and global contraction.

The importance of geological data and derived information in seismic response assessment for urban sites. An example from the Island of Crete, Greece

NASA Astrophysics Data System (ADS)

Tsangaratos, Paraskevas; Loupasakis, Constantinos; Rozos, Dimitrios; Rondoyianni, Theodora; Vafidis, Antonios; Savvaidis, Alexandros; Soupios, Pantelis; Papadopoulos, Nikos; Sarris, Apostolos

2015-04-01

The magnitude, frequency content and duration of an earthquake ground motion depends mainly on the surrounding geological, tectonic and geomorphological conditions. Numerous reports have been contacted illustrating the necessity of providing accurate geological information in order to estimate the level of seismic hazard. In this context, geological information is the outcome of processing primary, raw field data and geotechnical investigation data that are non - organized and associated with the geological model of the study area. In most cases, the geological information is provided as an advance element, a key component of the "function" that solves any geo-environmental problem and is primarily reflected on analogue or digital maps. The main objective of the present study is to illustrate the importance of accurate geological information in the thirteen (13) selected sites of the Hellenic Accelerometric Network (HAN) in the area of Crete Island, in order to estimate the seismic action according to Eurocode (EC8). As an example the detailed geological-geotechnical map of the area around HAN site in Rethymno city, Crete is presented. The research area covers a 250m radius surrounding the RTHE HAN-station at a scale of 1: 2000 with detail description of the geological and geotechnical characteristics of the formations as well as the tectonic features (cracks, upthrust, thrust, etc) of the rock mass. The field survey showed that the RTHE station is founded over limestones and dolomites formations. The formations exhibit very good geomechanical behaviour; however they present extensive fragmentation and karstification. At this particular site the identification of a fault nearby the station proved to be significant information for the geophysical research as the location and orientation of the tectonic setting provided new perspective on the models of seismic wave prorogation. So, the geological data and the induced information along with the tectonic structure of the area, revealed variations that could alter the seismic wave prorogation models as well as the ground type/soil category of the foundation formations. In conclusion, the produced geological-geotechnical maps are the main mean of communication and flow of geological information between different scientific disciplines providing the bases for defining the ground type at each HAN site and calibrating the corresponding code prescribed spectra. This study is part of the on-going project that has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES. Investing in knowledge society through the European Social Fund.

Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

NASA Astrophysics Data System (ADS)

Zhao, Pan; Jahn, Bor-ming; Xu, Bei

2017-09-01

The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The generation of this belt was ascribed to subduction of the Paleo-Pacific Plate.

Albari granodiorite - a typical calcalkaline diapir of volcanic arc stage from the Arabian Shield

NASA Astrophysics Data System (ADS)

Radain, Abdulaziz A.

Granodiorite rocks of the Arabian Shield are generally considered to be collision-related granitoids. However, there are some granodiorites that were formed during the volcanic arc stage. Major and trace elements studies are carried out on Albari diapiric granodiorite to reveal its tectonic environment. This intrusive rock type is common in the Taif arc province (Mahd adh Dhahab quadrangle) of the Asir microplate near the border of the southeast dipping subduction zone that ended up with arc-arc collision (Asir-Hijaz microplates) along the now known Bir Umq suture zone. The granodiorite exhibits a calcalkaline trend on ternary AFM and K 2ONa 2OCaO diagrams. Tectonic discrimination diagrams using multicationic parameters (R1 = 4Sill(Na+K)2(Fe+Ti); R2 = 6Ca+2Mg+Al), SiO 2-trace elements (Nb, Y, Rb), and Y versus Nb and Rb versus (Y+Nb) indicate a destructive active plate margin or volcanic arc stage tectonic environment. Albari calcalkaline granodiorite might have been derived directly from partial melting of subducted oceanic crust or overlying mantle contaminated with variable amounts of intermediate (quartz diorite, diorite, tonalite, trondhjemite) early and late volcanic arc-related plutonic country rocks.

Tectonic elements of the continental margin of East Antarctica, 38-164ºE

USGS Publications Warehouse

O'Brien, P.E.; Stagg, H.M.J.

2007-01-01

The East Antarctic continental margin from 38–164ºE is divided into western and eastern provinces that developed during the separation of India from Australia–Antarctica (Early Cretaceous) and Australia from Antarctica (Late Cretaceous). In the overlap between these provinces the geology is complex and bears the imprint of both extension/spreading episodes, with an overprinting of volcanism. The main rift-bounding faults appear to approximately coincide with the outer edge of the continental shelf. Inboard of these faults, the sedimentary cover thins above shallowing basement towards the coast where crystalline basement generally crops out. The continental slope and the landward flanks of the ocean basins, are blanketed by up to 9–10 km of mainly post-rift sediments in margin-parallel basins, except in the Bruce Rise area. Beneath this blanket, extensive rift basins are identified off Enderby and Wilkes Land/Terre Adélie; however, their extent and detailed structures are difficult to determine.

Earthquake Related Variation of Total Electron Content in Ionosphere over Chinese Mainland Derived from Observations of a Nationwide GNSS Network

NASA Astrophysics Data System (ADS)

Gan, Weijun

2016-07-01

Crustal Movement Observation Network of China (CMONOC) is a key national scientific infrastructure project carried out during 1997-2012 with 2 phases. The network is composed of 260 continuously observed GNSS stations (CORS) and 2081 campaign mode GNSS stations, with the main purpose to monitor the crustal movement, perceptible water vapor (PWV), total electron content (TEC), and many other tectonic and environmental elements around mainland China, by mainly using the Global Navigation Satellite System (GNSS) technology. Here, based on the GNSS data of 260 CORS of COMNOC for about 5 years, we investigated the characteristics of TEC in ionosphere over Chinese Mainland and discussed if there was any abnormal change of TEC before and after a big earthquake. our preliminary results show that it is hard to see any convincing precursor of TEC before a big earthquake. However, the huge energy released by a big earthquake can obviously disturb the TEC over meizoseismal area.

Geology and mineralization of the Jabalat alkali-feldspar granite, northern Asir region, Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Al Tayyar, Jaffar; Jackson, Norman J.; Al-Yazidi, Saeed

The Jabalat post-tectonic granite pluton is composed of albite- and oligoclase-bearing, low-calcium, F-, Sn- and Rb-rich subsolvus granites. These granites display evidence of late-magmatic, granitophile- and metallic-element specialization, resulting ultimately in the development of post-magmatic, metalliferous hydrothermal systems characterized by a Mo sbnd Sn sbnd Cu sbnd Pb sbnd Zn sbnd Bi sbnd Ag sbnd F signature. Two main types of mineralization are present within the pluton and its environs: (1) weakly mineralized felsic and aplitic dikes and veins enhanced in Mo, Bi, Ag, Pb and Cu; and (2) pyrite—molybdenite—chalcopyrite-bearing quartz and quartz—feldspar veins rich in Mo, Sn, Bi, Cu, Zn and Ag. A satellite stock, 3 km north of the main intrusion, is composed of fine-grained, miarolitic, muscovite—albite—microcline (microperthite) granite. The flanks of this intrusion and adjacent dioritic rocks are greisenized and highly enriched in Sn, Bi and Ag. Quartz veins which transect the satellite stock contain molybdenite and stannite.

Tectonic activity evolution of the Scotia-Antarctic Plate boundary from mass transport deposit analysis

NASA Astrophysics Data System (ADS)

Pérez, Lara F.; Bohoyo, Fernando; Hernández-Molina, F. Javier; Casas, David; Galindo-Zaldívar, Jesús; Ruano, Patricia; Maldonado, Andrés.

2016-04-01

The spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia-Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia-Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic-Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.

Petrogenesis and tectonic association of rift-related basic Panjal dykes from the northern Indian plate, North-Western Pakistan: evidence of high-Ti basalts analogous to dykes from Tibet

NASA Astrophysics Data System (ADS)

Sajid, Muhammad; Andersen, Jens; Arif, Mohammad

2017-10-01

Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (< 10), K/Ba ratios (20-40) and Hf-Ta-Th and FeO-MgO-Al2O3 discrimination diagrams. The compositional zoning in plagioclase and clinopyroxene, variation in olivine compositions and major elements oxide trends indicate a vital role of fractional crystallization in the evolution of dolerites, which also show depletion in rare earth elements (REEs) and other incompatible elements compared to the amphibolites. The equilibrium partial melting models from primitive mantle using Dy/Yb, La/Yb, Sm/Yb and La/Sm ratios show that amphibolite formed by smaller degrees (< 5%) of partial melting than the dolerites (< 10%). The trace elements ratios suggest the origination of dolerites from the subcontinental lithospheric mantle with some crustal contamination. This is consistent with a petrogenetic relationship with Panjal trap magmatism, reported from Kashmir and other parts of north western India. The amphibolites, in contrast, show affinity towards Ocean Island basalts (OIB) with a relatively deep asthenospheric mantle source and minimal crustal contribution and are geochemically similar to the High-Ti mafic dykes of southern Qiangtang, Tibet. These similarities combined with Permian tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean.

Petrogenesis and tectonic association of rift-related basic Panjal dykes from the northern Indian plate, North-Western Pakistan: evidence of high-Ti basalts analogous to dykes from Tibet

NASA Astrophysics Data System (ADS)

Sajid, Muhammad; Andersen, Jens; Arif, Mohammad

2018-06-01

Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (< 10), K/Ba ratios (20-40) and Hf-Ta-Th and FeO-MgO-Al2O3 discrimination diagrams. The compositional zoning in plagioclase and clinopyroxene, variation in olivine compositions and major elements oxide trends indicate a vital role of fractional crystallization in the evolution of dolerites, which also show depletion in rare earth elements (REEs) and other incompatible elements compared to the amphibolites. The equilibrium partial melting models from primitive mantle using Dy/Yb, La/Yb, Sm/Yb and La/Sm ratios show that amphibolite formed by smaller degrees (< 5%) of partial melting than the dolerites (< 10%). The trace elements ratios suggest the origination of dolerites from the subcontinental lithospheric mantle with some crustal contamination. This is consistent with a petrogenetic relationship with Panjal trap magmatism, reported from Kashmir and other parts of north western India. The amphibolites, in contrast, show affinity towards Ocean Island basalts (OIB) with a relatively deep asthenospheric mantle source and minimal crustal contribution and are geochemically similar to the High-Ti mafic dykes of southern Qiangtang, Tibet. These similarities combined with Permian tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean.

Castiglione (Oletta, Corsica): relationships between phenomena of calcification and tectonic fossiliferous fracture dating

NASA Astrophysics Data System (ADS)

Pereira, Elisabeth; Rouzaud, François; Salotti, Michelle; Dubois, Jean-Noël; Ferrandini, Jean; Ottaviani-Spella, Marie-Madeleine; Quinif, Yves

Six cavities have been discovered in the Oletta massif. The massif, today constitued of Schistes lustrés with several metres of calcareous layers above them, has undergone intense fracturing. The networks of cavities are organised along north-south and subequatorial directions, and form a narrow bayonnet-network. All the elements in the galleries appear to be karstic: stalagmites, stalactites and calcitic deposits along the walls; but no trace of dissolution or excavation was found. Thus, the origin of the galleries is only tectonic, while the calcitic deposits result from the dissolution of the old, thick calcareous layers above, which are no longer present. The thickness and the volume of the calcitic deposits, which is variable depending on the galleries, indicates the chronology of the different tectonic periods which have fractured the massif. Five tectonic and successsive events have been detected. Calcitic datings confirm the timing of successional fracturing, indicating also the variable age of the fossiliferous Middle Pleistocene deposits found in these cavities.

Genetic features of petroleum systems in rift basins of eastern China

USGS Publications Warehouse

Qiang, J.; McCabe, P.J.

1998-01-01

Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes nevessary for a petroleum system. A four stage evolution model is suggested for the controls in the rift basin. A rift basin may consist of sub-basins, depressions, sub-depressions, and major, moderate, and minor uplifts. A depression or sub-depression has its own depocentre (mainly occupied by source rock) and all kinds of lacustrine sediments, and thus has all the essential elements of a petroleum system. However, only those depressions or sub-depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems. Immature oil, another characteristic, complicates the petroleum system in the rift basins. Three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern China rift basins: uplifts between oil source centres are the most prospective areas for oil and gas accumulations, slopes connecting oil source centres and uplifts are the second, and the third type is subtle traps in the soil source centre.Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes necessary for a petroleum system. A four stage evolution model is suggested for the controls in the rift basin. A rift basin may consist of sub-basins, depressions, sub-depressions, and major, moderate, and minor uplifts. A depression or sub-depression has its own depocentre (mainly occupied by source rock) and all kinds of lacustrine sediments, and thus has all the essential elements of a petroleum system. However, only those depressions or sub-depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems. Immature oil, another characteristic, complicates the petroleum system in the rift basins. Three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern China rift basins: uplifts between oil source centres are the most prospective areas for oil and gas accumulations, slopes connecting oil source centres and uplifts are the second, and the third type is subtle traps in the oil source centre.

The Eocene-Miocene tectonic evolution of the Rif chain (Morocco): new data from the Jebha area

NASA Astrophysics Data System (ADS)

D'Assisi Tramparulo, Francesco; Ciarcia, Sabatino; El Ouaragli, Bilal; Vitale, Stefano; Najib Zaghloul, Mohamed

2016-04-01

Keywords: structural analysis, tectonics, shear bands, Miocene, Jebha Fault The Jebha area, located in the Central Rif, is a key sector to understand the orogenic evolution of the Rif chain. Here, the left lateral Jebha-Chrafate transfer fault, allowed, in the Miocene time, the westward migration of the internal thrust front. The structural analysis of the area revealed a complex tectonic history. The Eocene orogenic pulse produced the tectonic stacking of the Ghomaride thrust sheets. During the late Aquitanian and Langhian, under a dominant ENE-WSW shortening, imbrication of several Internal Dorsale Calcaire slices occurred. The following orogenic stage, characterized by a main SE tectonic transport, allowed the External Dorsale Calcaire to overthrust the Maghrebian Flysch Basin Units by means of a dominant thin-skinned tectonics. Synchronously with the buttressing following the collision of the allochthonous wedge against the External Rif domain, an out-of-sequence thrusting stage involved the Ghomaride and Dorsale Calcaire Units and a general back-thrusting deformed the entire tectonic pile. A renewal of the NE-SW shortening produced strike-slip faults and SW-verging folds and finally a radial extension affected the whole chain.

The "chessboard" classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium

NASA Astrophysics Data System (ADS)

Dill, Harald G.

2010-06-01

Economic geology is a mixtum compositum of all geoscientific disciplines focused on one goal, finding new mineral depsosits and enhancing their exploitation. The keystones of this mixtum compositum are geology and mineralogy whose studies are centered around the emplacement of the ore body and the development of its minerals and rocks. In the present study, mineralogy and geology act as x- and y-coordinates of a classification chart of mineral resources called the "chessboard" (or "spreadsheet") classification scheme. Magmatic and sedimentary lithologies together with tectonic structures (1 -D/pipes, 2 -D/veins) are plotted along the x-axis in the header of the spreadsheet diagram representing the columns in this chart diagram. 63 commodity groups, encompassing minerals and elements are plotted along the y-axis, forming the lines of the spreadsheet. These commodities are subjected to a tripartite subdivision into ore minerals, industrial minerals/rocks and gemstones/ornamental stones. Further information on the various types of mineral deposits, as to the major ore and gangue minerals, the current models and the mode of formation or when and in which geodynamic setting these deposits mainly formed throughout the geological past may be obtained from the text by simply using the code of each deposit in the chart. This code can be created by combining the commodity (lines) shown by numbers plus lower caps with the host rocks or structure (columns) given by capital letters. Each commodity has a small preface on the mineralogy and chemistry and ends up with an outlook into its final use and the supply situation of the raw material on a global basis, which may be updated by the user through a direct link to databases available on the internet. In this case the study has been linked to the commodity database of the US Geological Survey. The internal subdivision of each commodity section corresponds to the common host rock lithologies (magmatic, sedimentary, and metamorphic) and structures. Cross sections and images illustrate the common ore types of each commodity. Ore takes priority over the mineral. The minerals and host rocks are listed by their chemical and mineralogical compositions, respectively, separated from the text but supplemented with cross-references to the columns and lines, where they prevalently occur. A metallogenetic-geodynamic overview is given at the bottom of each column in the spreadsheet. It may be taken as the "sum" or the " mean" of a number of geodynamic models and ideas put forward by the various researchers for all the deposits pertaining to a certain clan of lithology or structure. This classical or conservative view of metallotects related to the common plate tectonic settings is supplemented by an approach taken for the first time for such a number of deposits, using the concepts of sequence stratigraphy. This paper, so as to say, is a "launch pad" for a new mindset in metallogenesis rather than the final result. The relationship supergene-hypogene and syngenetic-epigenetic has been the topic of many studies for ages but to keep them as separate entities is often unworkable in practice, especially in the so-called epithermal or near-surface/shallow deposits. Vein-type and stratiform ore bodies are generally handled also very differently. To get these different structural elements (space) and various mineralizing processes (time) together and to allow for a forward modeling in mineral exploration, architectural elements of sequence stratigraphy are adapted to mineral resources. Deposits are geological bodies which need accommodation space created by the environment of formation and the tectonic/geodynamic setting through time. They are controlled by horizontal to subhorizontal reference planes and/or vertical structures. Prerequisites for the deposits to evolve are thermal and/or mechanical gradients. Thermal energy is for most of the settings under consideration deeply rooted in the mantle. A perspective on how this concept might work is given in the text by a pilot project on mineral deposits in Central Europe and in the spreadsheet classification scheme by providing a color-coded categorization into 1. mineralization mainly related to planar architectural elements, e.g. sequence boundaries subaerial and unconformities 2. mineralization mainly related to planar architectural elements, e.g. sequence boundaries submarine, transgressive surfaces and maximum flooding zones/surfaces) 3. mineralization mainly controlled by system tracts (lowstand system tracts transgressive system tracts, highstand system tracts) 4. mineralization of subvolcanic or intermediate level to be correlated with the architectural elements of basin evolution 5. mineralization of deep level to be correlated with the deep-seated structural elements. There are several squares on the chessboard left blank mainly for lack of information on sequence stratigraphy of mineral deposits. This method has not found many users yet in mineral exploration. This review is designed as an "interactive paper" open, for amendments in the electronic spreadsheet version and adjustable to the needs and wants of application, research and training in geosciences. Metamorphic host rock lithologies and commodities are addressed by different color codes in the chessboard classification scheme.

Features structure of iron-bearing strata’s of the Bakchar deposit, Western Siberia

NASA Astrophysics Data System (ADS)

Asochakova, E. M.

2017-12-01

The ore-bearing strata’s of Bakchar deposit have complicated structural-textural heterogeneity and variable mineral composition. This deposit is one of the most promising areas of localization of sedimentary iron ore. The ore-bearing strata’s are composed mainly of sandstones (sometimes with ferruginous pebbles, less often conglomerates), siltstones and clays. The ironstones are classified according to their lithology and geochemistry into three types: goethite-hydrogoethitic oolitic, glauconite-chloritic and transitional (intermediate) type iron ores. The mineral composition includes many different minerals: terrigenous, authigenic and clayey. Ironstones are characterized by elevated concentrations of many rare and valuable metals present in them as trace elements, additionally alloying (Mn, V, Cr, Ti, Zr, Mo, etc.) and harmful impurities (S, As, Cu, Pb, Zn, P). There are prerequisites for the influence of numerous factors, such as prolonged transgression of the sea, swamping of paleo-river deltas, the appearance of a tectonic fracture zone associated with active bottom tectonics and unloading of catagenetic waters, regression and natural ore enrichment due to the re-washing of slightly-iron rocks. These factors are reflected in the structure of the ore-bearing strata in which rhythmic cycles of ore sedimentation with successive changes in them are distinguished by an association of different mineral composition.

Quantitative prediction of fractures using the finite element method: A case study of the lower Silurian Longmaxi Formation in northern Guizhou, South China

NASA Astrophysics Data System (ADS)

Liu, Jingshou; Ding, Wenlong; Yang, Haimeng; Jiu, Kai; Wang, Zhe; Li, Ang

2018-04-01

Natural fractures have long been considered important factors in the production of gas from shale reservoirs because they can connect pore spaces and enlarge transport channels, thereby influencing the migration, accumulation and preservation of shale gas. Industrial-level shale gas production has been initiated in the lower Silurian Longmaxi Formation in northern Guizhou, South China. However, it is important to quantitatively predict the distribution of natural fractures in the lower Silurian shale reservoirs to locate additional 'sweet spots' in northern Guizhou. In this study, data obtained from outcrops, cores, thin sections, field-emission scanning electron microscope (FE-SEM) images and X-ray diffraction (XRD) were used to determine the developmental characteristics and controlling factors of these fractures. Correlation analysis indicated that the mechanical parameters of the Longmaxi shale are mainly related to the total organic carbon (TOC), quartz, clay, calcite and dolomite contents. The spatial variations in the mechanical parameters of the Longmaxi shale were determined based on the spatial variations in the TOC and mineral contents. Then, a heterogeneous geomechanical model of the study area was established based on interpretations of the fault systems derived from seismic data and acoustic emission (AE) experiments performed on samples of the relevant rocks. The paleotectonic stress fields during the Yanshanian period were obtained using the finite element method (FEM). Finally, a fracture density calculation model was established to analyze the quantitative development of fractures, and the effects of faults and mechanical parameters on the development of fractures were determined. The results suggest that the main developmental period of tectonic fractures in the Longmaxi Formation was the Early Yanshanian period. During this time, the horizontal principal stress conditions were dominated by a SE-NW-trending (135-315°) compressional stress field, and the Longmaxi Formation experienced a maximum tectonic stress of 110-120 MPa. This simulated paleotectonic stress field was mainly controlled by faults and the contents of TOC, quartz, clay, calcite and dolomite; at different positions along the same fault, the degree of fracture development varies significantly. Overall, the distribution of fractures in the Longmaxi Formation can be used to optimize well deployment and provides a basis for the future exploration of shale gas.

CRUSTAL TECTONICS AND SEISMICITY OF THE MIDDLE EAST

NASA Astrophysics Data System (ADS)

Ghalib, H. A.; Gritto, R.; Sibol, M. S.; Herrmann, R. B.; Aleqabi, G. I.; Caron, P. F.; Wagner, R. A.; Ali, B. S.; Ali, A. A.

2009-12-01

The Arabian plate describes a geological entity and a dynamic system that has been in continuous interaction with the African plate to the west and south and the Eurasian plate to the north and east. The western and southern boundaries are distinguished by see floor spreading along the Gulf of Aden and Red Sea and transform faulting along the Dead Sea, whereas the northern and eastern boundaries are portrayed by compressional suture zones under thrusting the Turkish and Iranian plateaus. Despite this favorable juxtaposition of continental land masses and the plethora of national seismic networks in every country of the Middle East, the majority of published research on the Arabian plate and surrounding tectonic blocks still depends primarily on global seismographic stations and occasional local networks. Since 2005, we deployed a number of seismic stations, and more recently a five elements array, in close proximity to the northeastern boundary of the Arabian plate. The primary objective of the effort is to better understand the regional seismicity and seismotectonics of the Arabian plate and surrounding regions. To date over a terabyte of high quality 100 sps continuous three-component broadband data have been collected and being analyzed to derive models representative of the greater Middle East tectonic setting. This goal is, in part, achieved by estimating local and regional seismic velocity models using receiver function and surface wave dispersion analyses, and by using these models to obtain accurate hypocenter locations and event focal mechanisms. The resulting events distribution reveals a distinct picture of the interaction between the seismicity and tectonics of the region. The highest seismicity rate seems to be confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases again in the Bandar Abbas region. Spatial distribution of the events and stations provide thorough coverage of all the tectonic provinces in the region. Phases including Pn, Pg, Sn, Lg, as well as LR are clearly observed on recorded seismograms. Blockage or attenuation of some of the crustal body waves is observed along propagation paths crossing the Zagros-Bitlis zone. These findings are also in support of earlier tectonic models that suggest the existence of multiple parallel listric faults splitting off the main Zagros fault zone in east-west direction. Surface- and body wave results in support of these findings will be presented. Our initial structural models of the crust beneath north-eastern Iraq depict a thickness of 40-50 km in the foothills, which increases to 45-55 km beneath the Zagros-Bitlis zone.

Evidence for extreme mantle fractionation in early Archaean ultramafic rocks from northern Labrador

NASA Technical Reports Server (NTRS)

Collerson, Kenneth D.; Campbell, Lisa M.; Weaver, Barry L.; Palacz, Zenon A.

1991-01-01

Samarium-neodymium isotope data for tectonically interleaved fragments of lithospheric mantle and meta-komatiite from the North Atlantic craton provide the first direct record of mantle differentiation before 3,800 Myr ago. The results confirm the magnitude of light-rare-earth-element depletion in the early mantle, and also its depleted neodymium isotope composition. The mantle fragments were able to retain these ancient geochemical signatures by virtue of having been tectonically incorporated in buoyant felsic crust, thus escaping recycling and homogenization by mantle convection.

Mineralogy and crystallization history of a highly differentiated REE-enriched hypabyssal rhyolite: Round Top laccolith, Trans-Pecos, Texas

NASA Astrophysics Data System (ADS)

O'Neill, L. Christine; Elliott, Brent A.; Kyle, J. Richard

2017-09-01

The Round Top hypabyssal rhyolite laccolith is a highly evolved magmatic system, enriched in incompatible elements including REE [Rare Earth Element(s)], U, Be, and F. The Round Top intrusion is part of a series of Paleogene intrusions emplaced as the Sierra Blanca Complex. These intrusions are situated within long-lived, complex tectonic regimes that have been subjected to regional compression and subduction, punctuated by extensional bimodal volcanism. The enrichment in the rhyolite that comprises Round Top is the result of the prolonged removal of compatible elements from the source magma chamber through the emplacement of earlier magmatic events. With the emplacement of each sequential laccolith, the F-rich source magma became more enriched in incompatible elements, with increasing HREE [Heavy Rare Earth Elements(s)] concentrations. The emplacement of Round Top as a laccolith (versus that of an extrusive rhyolitic flow) facilitated the retention of the volatile-rich vapor phase within the magma, forming ubiquitous REE-bearing minerals, mainly yttrofluorite and yttrocerite. The high temperature mineral-vapor phase alteration of the feldspar groundmass was essential to the formation of REE minerals, where the pervasive open pore space was occupied by the late-crystallizing minerals. These late-forming REE-bearing minerals also occur as crystals associated with other accessory and trace phases, as inclusions within other phases, along grain boundaries, and along fractures and within voids. The rhyolite at Round Top and other laccolith intrusions in the Sierra Blanca Complex represent a new sub-type of magmatic rare earth element hosting system.

Temporal variation of tectonic tremor activity in southern Taiwan around the 2010 ML6.4 Jiashian earthquake

NASA Astrophysics Data System (ADS)

Chao, Kevin; Peng, Zhigang; Hsu, Ya-Ju; Obara, Kazushige; Wu, Chunquan; Ching, Kuo-En; van der Lee, Suzan; Pu, Hsin-Chieh; Leu, Peih-Lin; Wech, Aaron

2017-07-01

Deep tectonic tremor, which is extremely sensitive to small stress variations, could be used to monitor fault zone processes during large earthquake cycles and aseismic processes before large earthquakes. In this study, we develop an algorithm for the automatic detection and location of tectonic tremor beneath the southern Central Range of Taiwan and examine the spatiotemporal relationship between tremor and the 4 March 2010 ML6.4 Jiashian earthquake, located about 20 km from active tremor sources. We find that tremor in this region has a relatively short duration, short recurrence time, and no consistent correlation with surface GPS data. We find a short-term increase in the tremor rate 19 days before the Jiashian main shock, and around the time when the tremor rate began to rise one GPS station recorded a flip in its direction of motion. We hypothesize that tremor is driven by a slow-slip event that preceded the occurrence of the shallower Jiashian main shock, even though the inferred slip is too small to be observed by all GPS stations. Our study shows that tectonic tremor may reflect stress variation during the prenucleation process of a nearby earthquake.

Regional setting and characteristics of the Neoproterozoic Wadi Hamama Zn-Cu-Ag-Au prospect: evidence for an intra-oceanic island arc-hosted volcanogenic hydrothermal system

NASA Astrophysics Data System (ADS)

Abd El-Rahman, Yasser; Surour, Adel A.; El-Manawi, Abdel Hamid W.; El-Dougdoug, Abdel-Monem A.; Omar, Sayed

2015-04-01

The Wadi Hamama area is a volcanogenic Zn-Cu-Au-Ag prospect. It is hosted by a Neoproterozoic bimodal-mafic sequence, which comprises basalt, dacite and rhyolite along with volcaniclastic rocks. The rocks have a low-K tholeiitic affinity and are enriched in large ion lithophile elements over high field strength elements, which indicated their formation in an intra-oceanic island arc tectonic setting. The area was intruded by a tonalite-trondhjemite body, which has an intra-oceanic island arc affinity and later by diorite, which has a cordilleran-margin geochemical affinity. These rock units were intruded by post-tectonic granite dykes, which have a within-plate geochemical signature. There is a quartz-carbonate horizon extending along the contact between the basalt and the volcaniclastic rocks, mainly banded and lapilli tuffs. This horizon is of exhalative origin and is underlain by a mushroom-shaped alteration zone extending from the horizon down to the massive basalt. The footwall alteration is characterized by a silica-rich core surrounded by a thick chlorite sheath. Both the quartz-carbonate horizon and the footwall-altered rocks enclose historical trenches and pits. Sulfide-rich core samples are enriched in Zn, relative to Cu, and in Ag, which indicates the low-temperature nature of the hydrothermal system. The prospect was affected by supergene processes, which led to the widespread occurrence of secondary copper minerals and gold enrichment relative to the leached base metals, especially Zn. The prospect formed through a limited rifting of an intra-oceanic island arc which resulted in the formation of a small-scale volcanogenic Zn-Cu-Ag-Au prospect.

Dynamics of double-polarity subduction: application to the Western Mediterranean

NASA Astrophysics Data System (ADS)

Peral, M.; Zlotnik, S.; Fernandez, M.; Verges, J.; Jiménez-Munt, I.; Torne, M.

2015-12-01

The evolution of the Western Mediterranean is a highly debated question by geologists and geophysicists. Even though most scientists agree in considering slab roll-back to be the driving mechanism of the tectonic evolution of this area, there is still no consensus about the initial setup and its time evolution. A recent model proposed by Vergés and Fernàndez (2012) suggests a lateral change in subduction polarity of the Ligurian-Thetys oceanic domain to explain the formation and evolution of the Betic-Rif orogenic system and the associated Alboran back-arc basin. Such geodynamic scenario is also proposed for different converging regions. The aim of this study is to analyze the dynamic evolution of a double-polarity subduction process and its consequences in order to test the physical feasibility of this interaction and provide geometries and evolutions comparable to those proposed for the Western Mediterranean. The 3D numerical model of double-polarity subduction is carried out via the Underworld framework. Tectonic plate behavior is described by equations of fluid dynamics in the presence of several different phases. Underworld solves a non-linear Stokes flow problem using Finite Elements combined with particle-in-cell approach, thus the discretization combines a standard Eulerian Finite Element mesh with Lagrangian particles to track the location of the phases. The final model consists of two oceanic plates with viscoplastic rheology subducting into the upper mantle and the problem is driven by Rayleigh-Taylor instability. The main factors to be studied are the interaction between the two plates, the poloidal and toroidal mantle fluxes, the velocity variations of slabs, the stress distribution and the variations in the trench morphology.

Tectonic analysis of mine tremor mechanisms from the Upper Silesian Coal Basin

NASA Astrophysics Data System (ADS)

Sagan, Grzegorz; Teper, Lesław; Zuberek, Waclaw M.

1996-07-01

Fault network of the Upper Silesian Coal Basin (USCB) is built of sets of strike-slip, oblique-slip and dip-slip faults. It is a typical product of force couple which acts evenly with the parallel of latitude, causing horizontal and anti-clockwise movement of rock-mass. Earlier research of focal mechanisms of mine tremors, using a standard fault plane solution, has shown that some events are related to tectonic directions in main structural units of the USCB. An attempt was undertaken to analyze the records of mine tremors from the period 1992 1994 in the selected coal fields. The digital records of about 200 mine tremors with energy larger than 1×104 J ( M L >1.23) were analyzed with SMT software for seismic moment tensor inversion. The decomposition of seismic moment tensor of mine tremors was segmented into isotropic (I) part, compensated linear vector dipole (CLVD) part and double-couple (DC) part. The DC part is prevalent (up to 70%) in the majority of quakes from the central region of the USCB. A group of mine tremors with large I element (up to 50%) can also be observed. The spatial orientation of the fault and auxiliary planes were obtained from the computations for the seismic moment DC part. Study of the DC part of the seismic moment tensor made it possible for us to separate the group of events which might be acknowledged to have their origin in unstable energy release on surfaces of faults forming a regional structural pattern. The possible influence of the Cainozoic tectonic history of the USCB on the recent shape of stress field is discussed.

Strain transformation between tectonic extrusion and crustal thickening in the growth of the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Liu, M.; Li, Y.; Sun, Y.; Shen, X.

2017-12-01

The Indo-Eurasian continental collision since 50 Ma has thickened the crust to raise the Himalayan-Tibetan Plateau and driven lateral extrusion of Asian lithospheric blocks to affect Cenozoic tectonics in central and east Asia. The relative roles of crustal thickening and tectonic extrusion, and the strain partitioning between them over time and space, remain controversial. We have analyzed the strain rates using GPS velocities, and correlated the results with vertical motion derived from precise leveling. We found that tectonic extrusion largely transforms to crustal thickening near the margins of the Tibetan Plateau. Near the NW margin of the Tibetan Plateau, the shear stain transforms to compressive strain, consistent with neotectonic studies that indicate crustal shortening and uplift. Around the SE margin, shear stain largely terminates in the southern Yunnan province of China. The present-day crustal motion in SE Tibetan Plateau can be well explained by gravitational spreading without invoking plate-edge push as envisioned in the tectonic extrusion model. Using data collected from local seismic arrays, we derived receiver functions to image the lithospheric structures across the Tibetan Plateau and the Alashan block to its north and the Ordos block to its east. Our results indicate that the mantle lithosphere of these bounding Asian blocks has not been reworked by Tibetan tectonics; instead they have acted as restrictive walls to the growing Tibetan Plateau. Our finite element modeling shows that crustal deformation along the margins of the Tibetan Plateau are consistent with the notion that the east- and southeastward extrusion of the Tibetan lithosphere is largely confined to the Tibetan Plateau because of the restrictive bounding blocks of the Asian lithosphere. Thus the tectonic impact of the Indo-Eurasian collision on the Cenozoic Asian tectonics may not be as extensive as previously thought.

Fabric evolution across a discontinuity between lower and upper crustal domains from field, microscopic, and anisotropy of magnetic susceptibility studies in central eastern Eritrea, NE Africa

NASA Astrophysics Data System (ADS)

Ghebreab, W.; Kontny, A.; Greiling, R. O.

2007-06-01

In the Neoproterozoic East African Orogen (EAO) of Eritrea, lower to middle crustal high-grade metamorphic rocks are juxtaposed against low-grade upper crustal rocks along diffuse tectonic contact zones or discontinuities. In the central eastern part of Eritrea, such a tectonic zone is exposed as a low-angle shear zone separating two distinct high- and low-grade domains, the Ghedem and Bizen, respectively. Integrated field, microfabric, and anisotropy of magnetic susceptibility (AMS) studies show that this low-angle shear zone formed during late deformation, D2, with top-to-the-E/SE sense of motion. The hanging wall upper crustal volcanosedimentary schists are mainly paramagnetic and the footwall middle crustal mylonitized orthogneisses are mainly ferrimagnetic. Magnetic fabric studies revealed a good agreement between metamorphic/mylonitic and magnetic foliations (Kmin) and helped to explain fabric development in the shear zone. The magnetic lineations (Kmax) reflect stretching lineations where stretched mineral aggregates dominate fine-grained mylonitic matrices and intersection lineations where microstructural studies revealed two fabric elements. AMS directional plots indicate that the orientations of the magnetic lineation and of the pole to the magnetic foliation vary systematically across the shear zone. While Kmax axes form two broad maxima oriented approximately N-S and E-W, the Kmin axes change from subhorizontal, generally westward inclination in the west to moderate to steep inclination in the direction of tectonic movement to the east. Because there is a systematic change in inclination of Kmin for individual samples, all samples together form a fairly well defined cluster distribution. The distribution of Kmin in combination with the E-W scattered plot of the Kmax is in accordance with the E/SE flow of mylonites over exhumed Damas core complex in the late Neoproterozoic. During the Cenozoic, the Red Sea rift-related detachments exploited the late orogenic shear zone, indicating that the discontinuities between ductile middle and brittle upper crustal layers in the region are reactivated low-angle shear zones and possible sites of core complexes.

Modeling and Simulation of the Gonghe geothermal field (Qinghai, China) Constrained by Geophysical

NASA Astrophysics Data System (ADS)

Zeng, Z.; Wang, K.; Zhao, X.; Huai, N.; He, R.

2017-12-01

The Gonghe geothermal field in Qinghai is important because of its variety of geothermal resource types. Now, the Gonghe geothermal field has been a demonstration area of geothermal development and utilization in China. It has been the topic of numerous geophysical investigations conducted to determine the depth to and the nature of the heat source, and to image the channel of heat flow. This work focuses on the causes of geothermal fields used numerical simulation method constrained by geophysical data. At first, by analyzing and inverting an magnetotelluric (MT) measurements profile across this area we obtain the deep resistivity distribution. Using the gravity anomaly inversion constrained by the resistivity profile, the density of the basins and the underlying rocks can be calculated. Combined with the measured parameters of rock thermal conductivity, the 2D geothermal conceptual model of Gonghe area is constructed. Then, the unstructured finite element method is used to simulate the heat conduction equation and the geothermal field. Results of this model were calibrated with temperature data for the observation well. A good match was achieved between the measured values and the model's predicted values. At last, geothermal gradient and heat flow distribution of this model are calculated(fig.1.). According to the results of geophysical exploration, there is a low resistance and low density region (d5) below the geothermal field. We recognize that this anomaly is generated by tectonic motion, and this tectonic movement creates a mantle-derived heat upstream channel. So that the anomalous basement heat flow values are higher than in other regions. The model's predicted values simulated using that boundary condition has a good match with the measured values. The simulated heat flow values show that the mantle-derived heat flow migrates through the boundary of the low-resistance low-density anomaly area to the Gonghe geothermal field, with only a small fraction moving to other regions. Therefore, the mantle-derived heat flow across the tectonic channel to the cohesive continuous supply heat for Gonghe geothermal field, is the main the main causes of abundant geothermal resources.

Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis

NASA Astrophysics Data System (ADS)

Xue, Liang; Alemu, Tadesse; Gani, Nahid D.; Abdelsalam, Mohamed G.

2018-05-01

We use morphotectonic analysis to study the tectonic uplift history of the southeastern Ethiopian Plateau (SEEP). Based on studies conducted on the Northwestern Ethiopian Plateau, steady-state and pulsed tectonic uplift models were proposed to explain the growth of the plateau since 30 Ma. We test these two models for the largely unknown SEEP. We present the first quantitative morphotectonic study of the SEEP. First, in order to infer the spatial distribution of the tectonic uplift rates, we extract geomorphic proxies including normalized steepness index ksn, hypsometric integral HI, and chi integral χ from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). Second, we compare these rates with the thickness of flood basalt that we estimated from geological maps. Third, to constrain the timing of regional tectonic uplift, we develop a knickpoint celerity model. Fourth, we compare our results to those from the Northwestern Ethiopian Plateau to suggest a possible mechanism to explain regional tectonic uplift of the entire Ethiopian Plateau. We find an increase in tectonic uplift rates from the southeastern escarpments of the Afar Depression in the northeast to that of the Main Ethiopian Rift to the southwest. We identify three regional tectonic uplift events at 11.7, 6.5, and 4.5 Ma recorded by the development of regionally distributed knickpoints. This is in good agreement with ages of tectonic uplift events reported from the Northwestern Ethiopian Plateau.

The role of post-collisional strike-slip tectonics in the geological evolution of the late Neoproterozoic volcano-sedimentary Guaratubinha Basin, southern Brazil

NASA Astrophysics Data System (ADS)

Barão, Leonardo M.; Trzaskos, Barbara; Vesely, Fernando F.; de Castro, Luís Gustavo; Ferreira, Francisco J. F.; Vasconcellos, Eleonora M. G.; Barbosa, Tiago C.

2017-12-01

The Guaratubinha Basin is a late Neoproterozoic volcano-sedimentary basin included in the transitional-stage basins of the South American Platform. The aim of this study is to investigate its tectonic evolution through a detailed structural analysis based on remote sensing and field data. The structural and aerogeophysics data indicate that at least three major deformational events affected the basin. Event E1 caused the activation of the two main basin-bounding fault zones, the Guaratubinha Master Fault and the Guaricana Shear Zone. These structures, oriented N20-45E, are associated with well-defined right-lateral to oblique vertical faults, conjugate normal faults and vertical flow structures. Progressive transtensional deformation along the two main fault systems was the main mechanism for basin formation and the deposition of thick coarse-grained deposits close to basin-borders. The continuous opening of the basin provided intense intermediate and acid magmatism as well as deposition of volcaniclastic sediments. Event E2 characterizes generalized compression, recorded as minor thrust faults with tectonic transport toward the northwest and left-lateral activation of the NNE-SSW Palmital Shear Zone. Event E3 is related to the Mesozoic tectonism associated with the South Atlantic opening, which generated diabase dykes and predominantly right-lateral strike-slip faults oriented N10-50W. Its rhomboidal geometry with long axis parallel to major Precambrian shear zones, the main presence of high-angle, strike-slip or oblique faults, the asymmetric distribution of geological units and field evidence for concomitant Neoproterozoic magmatism and strike-slip movements are consistent with pull-apart basins reported in the literature.

The Middle Pleistocene evolution of the Molise intermontane basins: revision of the chrono-stratigraphic framework and new results inferred from a deep core of the Isernia - Le Piane basin

NASA Astrophysics Data System (ADS)

Amato, Vincenzo; Patrizio Ciro Aucelli, Pietro; Cesarano, Massimo; Rosskopf, Carmen Maria

2014-05-01

The Molise sector of the Apennine chain includes several Quaternary intermontane basins of tectonic origin (Venafro, Isernia-Le Piane, Carpino, Sessano, Boiano and Sepino basins). Since the Middle Pleistocene, the palaeoenvironmental evolution of these basins has been strongly conditioned by extensional tectonics, dominated by fault systems with a general NW-SE trend. This tectonics has produced important vertical displacements which are testified by the elevated thickness of basin fillings and the presence of several generations of palaeosurfaces, gentle erosion glacis and hanging valleys, the latter being generally located along the borders of the basins. Our research has focused, in the last years, on clarifying the infilling nature and the Quaternary evolution of the Boiano and Sessano basins and, more recently, of the Venafro and Isernia basins, the latter being investigated also by a new deep drilling. The present paper aims at presenting the results of the detailed, integrated analysis of the palaeoenvironmental and geomorphological evolution of these basins, that allowed for constraining the chronology of the basin infillings and for clarifying the significance and age of the ancient gentle surfaces, now hanging up to hundreds of meters above the basins floors. Furthermore, the main palaeoenvironmental changes and the tectonic phases are highlighted. The dating of several tephra layers interbedded within the investigated fluvial-marshy and lacustrine-palustrine successions, allowed to correlate different basin successions, and to refer the main sedimentary facies and some of the palaeosurface generations to the Middle Pleistocene. The obtained results confirm that the Middle Pleistocene evolution of the Molise Apennine was controlled by a polyphasic extensional tectonics, with periods of relative landscape stability alternating with periods of major landscape fragmentation, due to the variable interplay of tectonic and climate. They allow, furthermore, to better decipher the Middle Pleistocene tectonic evolution providing new data on the number of phases and their differences in length, intensity and related accommodation rates.

Structural features of northern Tarim basin: Implications for regional tectonics and petroleum traps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong Jia; Juafu Lu; Dongsheng Cai

1998-01-01

The rhombus-shaped Tarim basin in northwestern China is controlled mainly by two left-lateral strike-slip systems: the northeast-trending Altun fault zone along its southeastern side and the northeast-trending Aheqi fault zone along its northwestern side. In this paper, we discuss the northern Tarim basin`s structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the Tarim basin. Structural mapping in the Kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike-slip faulting. The amount of strike-slip displacement is estimated to be 148more » km by restoration of strike-slip structures in the uplift. The Kuqa depression is a Mesozoic-Cenozoic foredeep depression with well-developed flat-ramp structures and fault-related folds. The Baicheng basin, a Quaternary pull-apart basin, developed at the center of the Kuqa depression. Subsurface structures in the North Tarim uplift can be divided into the Mesozoic-Cenozoic and the Paleozoic lithotectonic sequences in seismic profiles. The Paleozoic litho-tectonic sequence exhibits the interference of earlier left-lateral and later right-lateral strike-slip structures. Many normal faults in the Mesozoic-Cenozoic litho-tectonic sequence form the negative flower structures in the North Tarim uplift; these structures commonly directly overlie the positive flower structures in the Paleozoic litho-tectonic sequence. The interference regions of the northwest-trending and northeast-trending folds in the Paleozoic tectonic sequence have been identified to have the best trap structures. Our structural analysis indicates that the Tarim basin is a transpressional foreland basin rejuvenated during the Cenozoic.« less

Petrography, geochemistry, and tectonics of a rifted fragment of Mainland Asia: evidence from the Lasala Formation, Mindoro Island, Philippines

NASA Astrophysics Data System (ADS)

Concepcion, R. A. B.; Dimalanta, C. B.; Yumul, G. P.; Faustino-Eslava, D. V.; Queaño, K. L.; Tamayo, R. A.; Imai, A.

2012-01-01

Petrological and geochemical investigations of the sedimentary Lasala formation in northwest Mindoro, Philippines, offer new insights into the origin of this geologically contentious region. Mindoro island's position at the boundary between Sundaland and the Philippine Mobile Belt has led to variable suggestions as to how much of it is continent derived or not. The Eocene Lasala formation overlies the Jurassic Halcon metamorphics, a regionally metamorphosed suite generally thought to have formed as a result of arc-continent collision processes. The sedimentary formation consists mainly of sandstones and shales interbedded with mudstones, basalt flows, and subordinate limestones and conglomerates. Petrographic information on the Lasala clastic rocks demonstrates a uniform framework composition that is predominantly quartzose. Major oxide, trace element abundances, and various elemental ratios similarly impart a strongly felsic signature. These characteristics are taken to indicate a chiefly continental, passive margin derivation and deposition of the Lasala sediments during the Eocene. The weak indication of active margin influence is suggested to be an inherited signature, supported by paleogeographic models of the southeastern Asian margin area during the pre-Cenozoic.

Present tectonics of the southeast of Russia as seen from GPS observations

NASA Astrophysics Data System (ADS)

Shestakov, N. V.; Gerasimenko, M. D.; Takahashi, H.; Kasahara, M.; Bormotov, V. A.; Bykov, V. G.; Kolomiets, A. G.; Gerasimov, G. N.; Vasilenko, N. F.; Prytkov, A. S.; Timofeev, V. Yu.; Ardyukov, D. G.; Kato, T.

2011-02-01

The present tectonics of Northeast Asia has been extensively investigated during the last 12 yr by using GPS techniques. Nevertheless, crustal velocity field of the southeast of Russia near the northeastern boundaries of the hypothesized Amurian microplate has not been defined yet. The GPS data collected between 1997 February and 2009 April at sites of the regional geodynamic network were used to estimate the recent geodynamic activity of this area. The calculated GPS velocities indicate almost internal (between network sites) and external (with respect to the Eurasian tectonic plate) stability of the investigated region. We have not found clear evidences of any notable present-day tectonic activity of the Central Sikhote-Alin Fault as a whole. This fault is the main tectonic unit that determines the geological structure of the investigated region. The obtained results speak in favour of the existence of a few separate blocks and a more sophisticated structure of the proposed Amurian microplate in comparison with an indivisible plate approach.

Tectonochemistry of the Brooks Range Ophiolite, Alaska

NASA Astrophysics Data System (ADS)

Biasi, J.; Asimow, P. D.; Harris, R. A.

2017-12-01

The Brooks Range Ophiolite (BRO), recently estimated to be 1800km2 in area, is the largest ophiolite in the Western Hemisphere. However, due to its remote location, it remains one of the least studied. Mineral exploration and reconnaissance-level mapping of the ophiolite were done in the 1970s and 1980s. Some chemical analyses were also performed, but since that time the BRO has received little attention. Over the subsequent 25+ years, the study of ophiolites has advanced greatly. These early studies found that the BRO lies in the structurally highest position in the Brooks Range, and its obduction probably coincided with the collision between the Koyukuk Arc and the Arctic-Alaska continental margin. It is therefore important to determine the tectonic setting in which the BRO formed if one wants to understand the tectonic history of the Northern Cordillera during the Jurassic/Cretaceous. Here we present new tectonochemistry data from the BRO. This includes whole-rock data (via XRF), trace element data (via XRF and ICP-MS), and mineral chemistries (via Electron Microprobe). Using immobile element fingerprinting, we constrain the tectonic setting in which the BRO formed and how this information ties in with other events in the Northern Cordillera's history. The fingerprinting results are supplemented by Cr-in-spinel data and Al-in-olivine thermometry.

The U.S. Geological Survey's Earthquake Summary Posters: A GIS-based Education and Communication Product for Presenting Consolidated Post-Earthquake Information

NASA Astrophysics Data System (ADS)

Tarr, A.; Benz, H.; Earle, P.; Wald, D. J.

2003-12-01

Earthquake Summary Posters (ESP's), a new product of the U.S. Geological Survey's Earthquake Program, are produced at the National Earthquake Information Center (NEIC) in Golden. The posters consist of rapidly-generated, GIS-based maps made following significant earthquakes worldwide (typically M>7.0, or events of significant media/public interest). ESP's consolidate, in an attractive map format, a large-scale epicentral map, several auxiliary regional overviews (showing tectonic and geographical setting, seismic history, seismic hazard, and earthquake effects), depth sections (as appropriate), a table of regional earthquakes, and a summary of the reional seismic history and tectonics. The immediate availability of the latter text summaries has been facilitated by the availability of Rapid, Accurate Tectonic Summaries (RATS) produced at NEIC and posted on the web following significant events. The rapid production of ESP's has been facilitated by generating, during the past two years, regional templates for tectonic areas around the world by organizing the necessary spatially-referenced data for the map base and the thematic layers that overlay the base. These GIS databases enable scripted Arc Macro Language (AML) production of routine elements of the maps (for example background seismicity, tectonic features, and probabilistic hazard maps). However, other elements of the maps are earthquake-specific and are produced manually to reflect new data, earthquake effects, and special characteristics. By the end of this year, approximately 85% of the Earth's seismic zones will be covered for generating future ESP's. During the past year, 13 posters were completed, comparable to the yearly average expected for significant earthquakes. Each year, all ESPs will be published on a CD in PDF format as an Open-File Report. In addition, each is linked to the special event earthquake pages on the USGS Earthquake Program web site (http://earthquake.usgs.gov). Although three formats are generated, the poster-size format is the most popular for display, outreach, and use as a working map for project scientists (JPEG format for web; PDF for download, editing, and printing) whereas the other (smaller) formats are suitable for briefing packages. We will soon make both GIS and PDF files of individual elements of the posters available online. ESP's provide an unprecedented opportunity for college earth-science faculty to take advantage of current events for timely lessons in global tectonics. They are also invaluable to communicate with the media and with government officials. ESP's will be used as a vehicle to present other products now under development under the auspices of NEIC and the ANSS, including rapid finite-fault models, global predictive ShakeMaps, "Did You Feel It?", and Rapid Assessments of Global Earthquakes (RAGE, Earle and others, this meeting).

Structural-tectonic zoning of the Arctic

NASA Astrophysics Data System (ADS)

Petrov, Oleg; Sobolev, Nikolay; Morozov, Andrey; Shokalsky, Sergey; Kashubin, Sergey; Grikurov, Garrik; Tolmacheva, Tatiana; Rekant, Pavel; Petrov, Evgeny

2017-04-01

Structural-tectonic zoning of the Arctic is based on the processing of geological and geophysical data and bottom sampling materials produced within the project "Atlas of Geological Maps of the Circumpolar Arctic." Zoning of the Arctic territories has been conducted taking into account the Earth's crust types, age of consolidated basement, and features of geological structure of the sedimentary cover. Developed legend for the zoning scheme incorporates five main groups of elements: continental and oceanic crust, folded platform covers, accretion-collision systems, and provinces of continental cover basalts. An important feature of the structural-tectonic zoning scheme is designation of continental crust in the central regions of the Arctic Ocean, the existence of which is assumed on the basis of numerous geological data. It has been found that most of the Arctic region has continental crust with the exception of the Eurasian Basin and the central part of the Canada Basin, which are characterized by oceanic crust type. Thickness of continental crust from seismic data varies widely: from 30-32 km on the Mendeleev Rise to 18-20 km on the Lomonosov Ridge, decreasing to 8-10 km in rift structures of the Podvodnikov-Makarov Basin at the expense of reduction of the upper granite layer. New data confirm similar basement structure on the western and eastern continental margins of the Eurasian oceanic basin. South to north, areas of Neoproterozoic (Baikalian) and Paleozoic (Ellesmerian) folding are successively distinguished. Neoproterozoic foldbelt is observed in Central Taimyr (Byrranga Mountains). Continuation of this belt in the eastern part of the Arctic is Novosibirsk-Chukchi fold system. Ellesmerian orogen incorporates the northernmost areas of Taimyr and Severnaya Zemlya, wherefrom it can be traced to the Geofizikov Spur of the Lomonosov Ridge and further across the De Long Archipelago and North Chukchi Basin to the north of Alaska Peninsula and in the Beaufort Sea. From the north, Ellesmerides are limited by the Precambrian continental blocks - North Kara and Mendeleev Rise, the sedimentary cover within which is represented by undisturbed Paleozoic and Mesozoic deposits. Analysis of the geological and tectonic maps and the map of the Arctic basement structure indicates that the heterogeneous crustal structure of the Arctic Ocean and its continental framing were formed as a result of simultaneous development and interaction of three large paleo-oceans in the Neoproterozoic and Phanerozoic - Paleo-Asian, Proto-Atlantic and Paleo-Pacific oceans. A conceptual model that represents our understanding of structural relationships and crustal types of the main Arctic Basin structures is quite simple. The Arctic Basin is bounded by continental margins with continental crust: relatively elevated Barents-Kara - in the west, and generally submerged Amerasia margin - in the east. The latter represents a continental "bridge" formed by thinned and stretched continental crust. It connects two opposite continents - Laurentia and Eurasia, and is essentially a fragmented, tectonically mobile structure.

How did Earth not End up like Venus?

NASA Astrophysics Data System (ADS)

Jellinek, M.; Lenardic, A.; Weller, M. B.

2017-12-01

Recent geodynamic calculations show that terrestrial planets forming with a chondritic initial bulk composition at order 1 AU can evolve to be either "Earth-like" or "Venus-like": Both mobile- and stagnant-lid tectonic regimes are permitted, neither solution is an explicitly stronger attractor and effects related to differences in Sun-Earth distance are irrelevant. What factors might then cause the thermal evolutionary paths of Earth and Venus to diverge dynamically at early times? At what point in Earth's evolution did plate tectonics emerge and when and how did this tectonic mode gain sufficient resilience to persist over much of Earth's evolution? What is the role of volatile cycling and climate: To what extent have the stable climate of Earth and the greenhouse runaway climate of Venus enforced their distinct tectonic regimes over time? In this talk I will explore some of the mechanisms potentially governing the evolutionary divergence of Earth and Venus. I will first review observational constraints that suggest that Earth's entry into the current stable plate tectonic mode was far from assured by 2 Ga. Next I will discuss how models have been used to build understanding of some key dynamical controls. In particular, the probability of "Earth-like" solutions is affected by: 1) small differences in the initial concentrations of heat producing elements (i.e., planetary initial conditions); 2) long-term climate change; and 3) the character of a planet's early evolutionary path (i.e., tectonic hysteresis).

Mesozoic to Cenozoic tectonic transition process in Zhanhua Sag, Bohai Bay Basin, East China

NASA Astrophysics Data System (ADS)

Cheng, Yanjun; Wu, Zhiping; Lu, Shunan; Li, Xu; Lin, Chengyan; Huang, Zheng; Su, Wen; Jiang, Chao; Wang, Shouye

2018-04-01

The Zhanhua sag is part of the Bohai Bay intracontinental basin system that has developed since the Mesozoic in East China. The timing of this basin system coincides with the final assembly of East Asia and the development of Western Pacific-type plate margin. Here we use 3-D seismic and core log data to investigate the evolution of this basin and discuss its broad tectonic settings. Our new structural study of Zhanhua sag suggests that there are four major tectonic transitions occurred in the Bohai Bay Basin during Mesozoic and Cenozoic: (1) The first tectonic transition was from stable Craton to thrusting during the Triassic, mainly caused by the South China Block's subduction northward beneath the North China Block, which induced the formation of the NW-striking thrust faults. (2) The second tectonic transition was mainly characterized by a change from compression to extension, which can be further divided into two-stages. At the first stage, two episodes of NW-SE shortening occurred in East Asia during Early-Middle Jurassic and Late Jurassic-earliest Cretaceous, respectively. At the second stage, the extension and left-lateral shearing took place during Early Cretaceous while compression occurred during Late Cretaceous. The NW-striking thrust faults changed to normal faults and the NNE-striking left-lateral strike-slip faults started to influence the eastern part of the basin. (3) The third transition occurred when the NW-SE extension and NNE-striking right-lateral shearing started to form during Paleogene, and the peak deformation happen around 40 Ma due to the change of the subduction direction of Pacific Plate relative to Eurasia Plate. The NE-striking normal faults are the main structure, and the pre-existing NNE-striking strike-slip faults changed from left-lateral to right-lateral. (4) The fourth transition saw the regional subsidence during Neogene, which was probably caused by the India-Asia "Hard collision" between 25 and 20 Ma.

Micro-seismicity and seismotectonic study in Western Himalaya-Ladakh-Karakoram using local broadband seismic data

NASA Astrophysics Data System (ADS)

Kanna, Nagaraju; Gupta, Sandeep; Prakasam, K. S.

2018-02-01

We document the seismic activity and fault plane solutions (FPSs) in the Western Himalaya, Ladakh and Karakoram using data from 16 broadband seismographs operated during June 2002 to December 2003. We locate 206 earthquakes with a local magnitude in the range of 1.5 to 4.9 and calculate FPSs of 19 selected earthquakes based on moment tensor solutions. The earthquakes are distributed throughout the study region and indicate active tectonics in this region. The observed seismicity pattern is quite different than a well-defined pattern of seismicity, along the Main Central Thrust zone, in the eastern side of the study region (i.e., Kumaon-Garhwal Himalaya). In the Himalaya region, the earthquakes are distributed in the crust and upper mantle, whereas in the Ladakh-Karakoram area the earthquakes are mostly confined up to crustal depths. The fault plane solutions show a mixture of thrust, normal and strike-slip type mechanisms, which are well corroborated with the known faults/tectonics of the region. The normal fault earthquakes are observed along the Southern Tibet Detachment, Zanskar Shear Zone, Tso-Morari dome, and Kaurik-Chango fault; and suggest E-W extension tectonics in the Higher and Tethys Himalaya. The earthquakes of thrust mechanism with the left-lateral strike-slip component are seen along the Kistwar fault. The right-lateral strike-slip faulting with thrust component along the bending of the Main Boundary Thrust and Main Central Thrust shows the transpressional tectonics in this part of the Himalaya. The observed earthquakes with right-lateral strike-slip faulting indicate seismically active nature of the Karakoram fault.

Tectonic escape in the evolution of the continental crust

NASA Technical Reports Server (NTRS)

Burke, K.; Sengor, C.

1986-01-01

The continental crust originated by processes similar to those operating today and continents consist of material most of which originated long ago in arc-systems that have later been modified, especially at Andean margins and in continental collisions where crustal thickening is common. Collision-related strike-slip motion is a general process in continental evolution. Because buoyant continental (or arc) material generally moves during collision toward a nearby oceanic margin where less buoyant lithosphere crops out, the process of major strike-slip dominated motion toward a 'free-face' is called 'tectonic escape'. Tectonic escape is and has been an element in continental evolution throughout recorded earth-history. It promotes: (1) rifting and the formation of rift-basins with thinning of thickened crust; (2) pervasive strike-slip faulting late in orogenic history which breaks up mountain belts across strike and may juxtapose unrelated sectors in cross-section; (3) localized compressional mountains and related foreland-trough basins.

Tectonic analysis of folds in the Colorado plateau of Arizona

NASA Technical Reports Server (NTRS)

Davis, G. H.

1975-01-01

Structural mapping and analysis of folds in Phanerozoic rocks in northern Arizona, using LANDSAT-1 imagery, yielded information for a tectonic model useful in identifying regional fracture zones within the Colorado Plateau tectonic province. Since the monoclines within the province developed as a response to differential movements of basement blocks along high-angle faults, the monoclinal fold pattern records the position and trend of many elements of the regional fracture system. The Plateau is divided into a mosaic of complex, polyhedral crustal blocks whose steeply dipping faces correspond to major fracture zones. Zones of convergence and changes in the trend of the monoclinal traces reveal the corners of the blocks. Igneous (and salt) diapirs have been emplaced into many of the designated zones of crustal weakness. As loci of major fracturing, folding, and probably facies changes, the fractures exert control on the entrapment of oil and gas.

Stratigraphy, geochemistry and tectonic significance of the Oligocene magmatic rocks of western Oaxaca, southern Mexico

USGS Publications Warehouse

Martiny, B.; Martinez-Serrano, R. G.; Moran-Zenteno, D. J.; MacIas-Romo, C.; Ayuso, R.A.

2000-01-01

In Western Oaxaca, Tertiary magmatic activity is represented by extensive plutons along the continental margin and volcanic sequences in the inland region. K-Ar age determinations reported previously and in the present work indicate that these rocks correspond to a relatively broad arc in this region that was active mainly during the Oligocene (~ 35 to ~ 25 Ma). In the northern sector of western Oaxaca (Huajuapan-Monte Verde-Yanhuitlan), the volcanic suite comprises principally basaltic andesite to andesitic lavas, overlying minor silicic to intermediate volcaniclastic rocks (epiclastic deposits, ash fall tuffs, ignimbrites) that were deposited in the lacustrine-fluvial environment. The southern sector of the volcanic zone includes the Tlaxiaco-Laguna de Guadalupe region and consists of intermediate to silicic pyroclastic and epiclastic deposits, with silicic ash fall tuffs and ignimbrites. In both sectors, numerous andesitic to dacitic hypabyssal intrusions (stocks and dikes) were emplaced at different levels of the sequence. The granitoids of the coastal plutonic belt are generally more differentiated than the volcanic rocks that predominate in the northern sector and vary in composition from granite to granodiorite. The studied rocks show large-ion lithophile element (LILE) enrichment (K, Rb, Ba, Th) relative to high-field-strength (HFS) elements (Nb, Ti, Zr) that is characteristic of subduction-related magmatic rocks. On chondrite-normalized rare earth element diagrams, these samples display light rare earth element enrichment (LREE) and a flat pattern for the heavy rare earth elements (HREE). In spite of the contrasting degree of differentiation between the coastal plutons and inland volcanic rocks, there is a relatively small variation in the isotopic composition of these two suites. Initial 87Sr/86Sr ratios obtained and reported previously for Tertiary plutonic rocks of western Oaxaca range from 0.7042 to 0.7054 and ??Nd values, from -3.0 to +2.4, and for the volcanic rocks, from 0.7042 to 0.7046 and 0 +2.6. The range of these isotope ratios and those reported for the basement rocks in this region suggest a relatively low degree of old crustal involvement for most of the studied rocks. The Pb isotopic compositions of the Tertiary magmatic rocks also show a narrow range [(206Pb/204Pb) = 18.67-18.75; (207Pb/204Pb) = 15.59-15.62; (208Pb/204Pb) = 38.44-38.59], suggesting a similar source region for the volcanic and plutonic rocks. Trace elements and isotopic compositions suggest a mantle source in the subcontinental lithosphere that has been enriched by a subduction component. General tectonic features in this region indicate a more active rate of transtensional deformation for the inland volcanic region than along the coastal margin during the main events of Oligocene magmatism. The lower degree of differentiation of the inland volcanic sequences, particularly the upper unit of the northern sector, compared to the plutons of the coastal margin, suggests that the differentiation of the Tertiary magmas in southern Mexico was controlled to a great extent by the characteristics of the different strain domains. (C) 2000 Elsevier Science B.V. All rights reserved.

Red Sea rift-related Quseir basalts, central Eastern Desert, Egypt: Petrogenesis and tectonic processes

NASA Astrophysics Data System (ADS)

Farahat, Esam S.; Ali, Shehata; Hauzenberger, Christoph

2017-01-01

Mineral and whole-rock chemistry of Red Sea rift-related Tertiary basalts from south Quseir city, central Eastern Desert of Egypt is presented to investigate their petrogenesis and relationship to tectonic processes. The south Quseir basalts (SQB) are classified as high-Ti (TiO2 >2 wt.%) subalkaline transitional lava emplaced in an anorogenic tectonic setting. Their Mg# varies from 48 to 53 indicating the evolved nature of the SQB. Pearce element ratios suggest that the SQB magmas evolved via fractional crystallization of olivine + clinopyroxene ± plagioclase, but the absence of Eu anomalies argues against significant plagioclase fractionation. Clinopyroxene compositions provide evidence for polybaric fractionation of the parental mafic magmas. Estimated temperatures of crystallization are 1015 to 1207 °C for clinopyroxene and 1076 to 1155 °C for plagioclase. These values are interpreted to result from early stage crystallization of clinopyroxene followed by concurrent crystallization of clinopyroxene and plagioclase. The incompatible trace element signatures of the SQB (La/Ba = 0.08-0.10 and La/Nb = 0.89-1.04) are comparable to those of ocean island basalts (OIB) generated from an asthenospheric mantle source unaffected by subduction components. Modeling calculations indicate that the SQB primary magmas were derived from 4-5% partial melting of a garnet-bearing lherzolite mantle source. The NE Egyptian basaltic volcanism is spatially and temporally related to Red Sea rifting and to the local E-W striking faults, confirming a relationship to tectonic activity. Our results suggest that the extensional regime associated with Red Sea rifting controlled the generation of the Egyptian basalts, likely as a result of passive upwelling of asthenospheric mantle.

Faulting, fracturing and in situ stress prediction in the Ahnet Basin, Algeria — a finite element approach

NASA Astrophysics Data System (ADS)

Beekman, Fred; Badsi, Madjid; van Wees, Jan-Diederik

2000-05-01

Many low-efficiency hydrocarbon reservoirs are productive largely because effective reservoir permeability is controlled by faults and natural fractures. Accurate and low-cost information on basic fault and fracture properties, orientation in particular, is critical in reducing well costs and increasing well recoveries. This paper describes how we used an advanced numerical modelling technique, the finite element method (FEM), to compute site-specific in situ stresses and rock deformation and to predict fracture attributes as a function of material properties, structural position and tectonic stress. Presented are the numerical results of two-dimensional, plane-strain end-member FEM models of a hydrocarbon-bearing fault-propagation-fold structure. Interpretation of the modelling results remains qualitative because of the intrinsic limitations of numerical modelling; however, it still allows comparisons with (the little available) geological and geophysical data. In all models, the weak mechanical strength and flow properties of a thick shale layer (the main seal) leads to a decoupling of the structural deformation of the shallower sediments from the underlying sediments and basement, and results in flexural slip across the shale layer. All models predict rock fracturing to initiate at the surface and to expand with depth under increasing horizontal tectonic compression. The stress regime for the formation of new fractures changes from compressional to shear with depth. If pre-existing fractures exist, only (sub)horizontal fractures are predicted to open, thus defining the principal orientation of effective reservoir permeability. In models that do not include a blind thrust fault in the basement, flexural amplification of the initial fold structure generates additional fracturing in the crest of the anticline controlled by the material properties of the rocks. The folding-induced fracturing expands laterally along the stratigraphic boundaries under enhanced tectonic loading. Models incorporating a blind thrust fault correctly predict the formation of secondary syn- and anti-thetic mesoscale faults in the basement and sediments of the hanging wall. Some of these faults cut reservoir and/or seal layers, and thus may influence effective reservoir permeability and affect seal integrity. The predicted faults divide the sediments across the anticline in several compartments with different stress levels and different rock failure (and proximity to failure). These numerical model outcomes can assist classic interpretation of seismic and well bore data in search of fractured and overpressured hydrocarbon reservoirs.

Easter microplate dynamics

NASA Astrophysics Data System (ADS)

Neves, M. C.; Searle, R. C.; Bott, M. H. P.

2003-04-01

We use two-dimensional elastic finite element analysis, supplemented by strength estimates, to investigate the driving mechanism of the Easter microplate. Modeled stresses are compared with the stress indicators compiled from earthquake focal mechanisms and structural observations. The objective is to constrain the tectonic forces that govern the Easter microplate rotation and to test the microplate driving hypothesis proposed by [1993]. We infer that the mantle basal drag cannot drive the microplate rotation but opposes it, and that the asthenospheric viscosity is no more than about 1 × 1018 Pa s. At most, the basal drag comprises 20% of the force resisting microplate rotation. The outward pull of the main plates can drive the rotation by shear drag applied along the northern and southern boundaries of the microplate. However, we propose an additional driving force which arises from the strong variation of the ridge resistance force along the east and west rifts, so that the main driving torques come from the pull of the major plates acting across the narrowing and slowing rifts. This requires the strength to increase substantially toward the rift tips due to thickening of the brittle lithosphere as the spreading rate slows.

Crustal subsidence, seismicity, and structure near Medicine Lake Volcano, California

USGS Publications Warehouse

Dzurisin, D.; Donnelly-Nolan, J. M.; Evans, J.R.; Walter, S.R.

1991-01-01

The pattern of historical ground deformation, seismicity, and crustal structure near Medicine Lake volcano illustrates a close relation between magmatism and tectonism near the margin of the Cascade volcanic chain and the Basin and Range tectonic province. Subsidence occurs mainly by aseismic creep within 25km of the summit, where the crust has been heated and weakened by intrusions, and by normal faulting during episodic earthquake swarms in surrounding, cooler terrain. -from Authors

Examples of Deep Seated Gravitational Slope Deformations in the central part of the Lower Beskids, (the Polish Flysch Carpathians)

NASA Astrophysics Data System (ADS)

Zatorski, Michał

2016-04-01

The Lower Beskids are located between the western and eastern parts of the Carpathian flysch belt, whereas the low altitudes of passes and ridges in this region have until now been identified mainly with the differences in bedrock resistance. In the light of contemporary information regarding the geology of this area, the hypothesis of the gravitational placement of large tectonic elements has become topical again. A particularly interesting area is the ridge and foreland of the Magura Wątkowska, bordering in the north with the Sanok-Jasło Pits (a denudation valley). This edge zone of the Lower Beskids has a complicated geological structure, i.e. it constitutes a tectonic contact of the Magura Unit and the Central Carpathian Depression (the depressed part of the Silesian nappe). During the field research and analyses regarding the identification of morphostructural elements, the important role of various kinds of lineaments was observed. Some of the inventoried lineaments were, e.g. large size faults or effects of the impact of tectonic processes on bedrock. Structures in the rock (cracks, faults) accompanying them are important in determining the type of macro scale gravitational movements. The outer part of fold structures in the foreland of the Magura Wątkowska shows the rotation around the longitudinal syncline axis, and is an excellent research field for a comprehensive analysis of gravitational movements, both of the basin type and the DSGSD (Deep Seated Gravitational Slope Deformations) type. Determining the types of tectonic lineaments was based on a review of selected directions in the context of the course of tectonic structures in the study area. On that basis, lineaments were classified into two morphogenetic groups, i.e. structures that do not result in visible movements relative to the analyzed rock massif (cracks), and those causing the displacement of the rock massif (faults, overthrust). Using the directional and contour diagrams generated by measuring the spatial orientation of joint planes, gravitational macrocomplexes with a characteristic joint system were singled out. Next, by correlating them with fault zones, a morphogenetic analysis was performed the result of which was a precise characterization of the type of gravitational morphogenetic processes in the meso scale (e.g. large rock landslides) as well as in the macro scale (the basin type or DSGSD). Ultimately, the research results were used to classify lineaments in the context of the structural control of the Carpathian Mountains (gravity development of macro scale landforms) and to reinterpret the spatial interdependence of landforms (e.g. ridge, ridge-top trenches and rifts) with the geological structure. The research conducted so far indicates a variety of macro scale movements in the edge zone of the research area. Based on the morphotectonic analysis performed so far, the following examples of displacement have been found: lateral spreading, toppling, and rotation movement. The effects of these movements are associated with both the basin phases and the DSGSD, so they play an important morphogenetic role, leading to the fragmentation of the morphological threshold of the Lower Beskids, and to the development of characteristic structural landforms.

Serpentinite-driven Exhumation of the UHP Lago di Cignana Unit in the Fossil Alpine Plate Interface

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Gilio, M.; Angiboust, S.; Godard, M.; Pettke, T.

2015-12-01

The Lago di Cignana Unit (LCU) is a coesite- [1] and diamond-bearing [2] slice of oceanic-derived eclogites and metasediments recording Alpine UHP metamorphism at 600 °C-3.2 GPa (~110 km depth) [3]. The LCU is tectonically sandwiched between the eclogitic Zermatt-Saas Zone (ZSZ; 540 °C-3.2 GPa) [4] and the blueschist Combin Zone (400 °C-0.9 GPa) [5] along a tectonic structure joining HP units recording a ~1.2 GPa (40 km) pressure difference. So far, the ZSZ has been attributed to normal HP conditions and the mechanism driving exhumation and accretion of the LCU in its present structural position is not fully understood.We performed petrography and bulk-rock trace element analyses of rocks from LCU and ZSZ serpentinites. We observed that, while serpentinites in the core of the ZSZ show normal subduction zone trace elements and REE's patterns, the Ol+Ti-chu+Chl veins and host serpentinites enveloping the LCU are strongly enriched in sediment-derived fluid-mobile elements (U, Th, Nb, Ta, Ce, Y, As, Sb) and REE's: their patterns well match those of the closely associated LCU-UHP rocks.The presence of extremely enriched Ol+Ti-chu+Chl veins in the serpentinites at direct contact with the UHP Lago di Cignana Unit suggests that fluid exchange between serpentinite and LCU crustal rocks occurred at peak metamorphic conditions. Their coupling therefore occurred during subduction burial and/or peak UHP conditions. As such, the buoyancy force originating from the relatively light serpentinites fuelled the exhumation of the Lago di Cignana Unit. In this contest, the tectonic contact between the Zermatt-Saas Zone and the Combin Zone evolved into a true tectonic plate interface surface.1. Reinecke (1998). Lithos 42(3), 147-189; 2. Frezzotti et al. (2011). Nat. Geosci. 4(10), 703-706; 3. Groppo et al. (2009). J. Metam. Geol. 27(3), 207-231; 4. Angiboust et al. (2009). Terra Nova 21(3), 171-180; 5. Reddy et al. (1999). J. Metam. Geol. 17, 573-590.

Chemistry of the subalkalic silicic obsidians

USGS Publications Warehouse

MacDonald, Ray; Smith, Robert L.; Thomas, John E.

1992-01-01

Nonhydrated obsidians are quenched magmatic liquids that record in their chemical compositions details of the tectonic environment of formation and of the differentiation mechanisms that affected their subsequent evolution. This study attempts to analyze, in terms of geologic processes, the compositional variations in the subalkalic silicic obsidians (Si02≥70 percent by weight, molecular (Na2O+K20)>Al2O3). New major- and trace-element determinations of 241 samples and a compilation of 130 published major-element analyses are reported and interpreted. Obsidians from five different tectonic settings are recognized: (1) primitive island arcs, (2) mature island arcs, (3) continental margins, (4) continental interiors, and (5) oceanic extensional zones. Tectonomagmatic discrimination between these groups is successfully made on Nb-Ta, Nb-FeOt and Th-Hf-Ta plots, and compositional ranges and averages for each group are presented. The chemical differences between groups are related to the type of crust in which magmas were generated. With increasingly sialic (continental type) crust, the obsidians show overall enrichment in F, Be, Li, Mo, Nb, Rb, Sn, Ta, U, W, Zn, and the rare-earth elements, and depletion in Mg, Ca, Ba, Co, Sc, Sr, and Zr. They become more potassic, have higher Fe/Mg and F/Cl ratios, and lower Zr/Hf, Nb/Ta, and Th/U ratios. Higher values of total rare-earth elements are accompanied by light rare-earth-element enrichment and pronounced negative Eu anomalies. An attempt is made to link obsidian chemistry to genetic mechanlism. Two broad groups of rocks are distinguished: one generated where crystal-liquid processes dominated (CLPD types), which are the products of crustal anatexis, possibly under conditions of low halogen fugacity, ± crystal fractionation ± magma mixing; and a second group represented by rocks formed in the upper parts of large magma chambers by interplays of crystal fractionation, volatile transfer, magma mixing, and possibly various liquid-state differentiation mechanisms, or in other words a complex interaction of petrogenetic processes (CIPP types). Such rocks may also form by volatile-fluxed partial melting of the wallrocks, and subsequent mixing into the magma reservoir. Compositional ranges and averages for CLPD and CIPP obsidians are given. It is shown by analogy with well-documented, zoned ash-flow ruffs that obsidians fractionated by CIPP have very low Mg, P, Ba, and Sr contents, flat rare-earth-element patterns with extensive Eu anomalies, low K/Rb and Zr/Nb ratios, and relatively high Na2O/K2O ratios. There is, however, considerable compositional overlap between CLPD and CIPP obsidians. The effects of magma mixing, assimilation, and vapor-phase transport in producing compositional variations in the obsidians are briefly assessed. The geochemistry of the subalkalic silicic obsidians is described on an element-by-element basis, in order to provide a database for silicic magma compositions that will hopefully contribute to studies of granitic rocks. Attempts are also made to isolate the geochemical effects of tectonic environment and genetic mechanism for each element, by comparison with data from crystal-liquid equilibria-controlled systems, from ash-flow sheets zoned by CIPP, and from mixed-magma series. A final tabulation relates the complexities of obsidian geochemistry to all the tectonic and genetic variables.

Active faulting at Delphi, Greece: Seismotectonic remarks and a hypothesis for the geologic environment of a myth

NASA Astrophysics Data System (ADS)

Piccardi, Luigi

2000-07-01

Historical data are fundamental to the understanding of the seismic history of an area. At the same time, knowledge of the active tectonic processes allows us to understand how earthquakes have been perceived by past cultures. Delphi is one of the principal archaeological sites of Greece, the main oracle of Apollo. It was by far the most venerated oracle of the Greek ancient world. According to tradition, the mantic proprieties of the oracle were obtained from an open chasm in the earth. Delphi is directly above one of the main antithetic active faults of the Gulf of Corinth Rift, which bounds Mount Parnassus to the south. The geometry of the fault and slip-parallel lineations on the main fault plane indicate normal movement, with minor right-lateral slip component. Combining tectonic data, archaeological evidence, historical sources, and a reexamination of myths, it appears that the Helice earthquake of 373 B.C. ruptured not only the master fault of the Gulf of Corinth Rift at Helice, but also the antithetic fault at Delphi, similarly to the Corinth earthquake of 1981. Moreover, the presence of an active fault directly below the temples of the oldest sanctuary suggests that the mythological oracular chasm might well have been an ancient tectonic surface rupture.

Ar/Ar geochronology in the western Tianshan (northwestern China): from Carboniferous (ultra)high-pressure metamorphism and thrusting to Permian strike-slip deformation and fluid ingress

NASA Astrophysics Data System (ADS)

de Jong, K.; Wang, B.; Ruffet, G.; Shu, L. S.; Faure, M.

2012-04-01

The Tianshan belt (northwestern China) is a major tectonic element of the southern Central Asian Orogenic Belt that contains a number of ophiolitic mélanges and (ultra)high-pressure metamorphic belts formed after closure of oceanic and back-arc basins that resulted in terrane collisions. Deciphering its tectonic evolution is thus crucial for understanding the amalgamation of Central Asia. We produce robust 40Ar/39Ar laser-probe evidence that the Tianshan is a Late Palaeozoic (ultra)high-pressure metamorphic collision belt, not a Triassic one, as suggested by some SHRIMP zircon ages in recent literature. Instead of trying to date the peak pressure conditions we focused on 40Ar/39Ar analysis of white mica formed during retrograde recrystallisation when the (ultra)high-pressure metamorphic rocks of the Changawuzi-Kekesu complex were exhumed. Exhumation was coeval with their northward thrusting over the southern margin of the Yili terrane, the easternmost element of the Kazakhstan composite super-terrane, which produced main phase tectonic structures. The Yili terrane comprises a Proterozoic basement covered by metasediments, intruded by Early Carboniferous granites when it formed part of a continental margin arc. During the Permian deformation was partitioned in vertical brittle-ductile strike-slip fault zones that reactivated these suture zones and in which bimodal magmatism was concentrated. We also investigate the effects of these events on the isotopic ages of mica. 40Ar/39Ar laser-probe dating of white mica reveals that the strongest retrogressed blueschists immediately above the basal thrust fault of the Changawuzi-Kekesu belt gave the youngest plateau age of 316 ± 2 Ma (1σ). White mica in greenschist-facies metamorphic quartzite from the ductilely deformed metasedimentary cover of the Yili terrane's crystalline basement, taken at about 1 km below the thrust contact with the overlying Changawuzi-Kekesu belt, yielded a plateau age of 323 ± 1 Ma (1σ). Elsewhere, such metasediments yielded plateau ages (1σ) of 253 ± 1 (muscovite) and 252 ± 1 (biotite) Ma, whereas biotite from an undeformed ca. 340 Ma-old granite intruding the Yili terrane's southern margin gave a 263 ± 1 Ma plateau age (1σ). The 263-252-Ma-old samples were taken between 2 and 5 km across strike from the Permian Qingbulak-Nalati strike-slip fault, and within the 15-20 km wide zone with steeply dipping tectonic fabrics used by intruding Permian granites, and associated mineralisations. We interpret these Permian ages by recrystallisation of the mica by (late magmatic?) fluid flow channeled into these steep zones. Laser-probe dating of mylonite whole-rock samples from the North Tianshan - Main Tianshan strike-slip fault zone yielded 40Ar/39Ar spectra with step ages in the 255-285 Ma range, which date the movement on this ductile shear zone. The picture is emerging that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation, leading to the erroneous view that the Tianshan is a Triassic orogenic belt.

Meso-Cenozoic tectonic evolution of the SE Brazilian continental margin: Petrographic, kinematic and dynamic analysis of the onshore Araruama Lagoon Fault System

NASA Astrophysics Data System (ADS)

Souza, Pricilla Camões Martins de; Schmitt, Renata da Silva; Stanton, Natasha

2017-09-01

The Ararauama Lagoon Fault System composes one of the most prominent set of lineaments of the SE Brazilian continental margin. It is located onshore in a key tectonic domain, where the basement inheritance rule is not followed. This fault system is characterized by ENE-WSW silicified tectonic breccias and cataclasites showing evidences of recurrent tectonic reactivations. Based on field work, microtectonic, kinematic and dynamic analysis, we reconstructed the paleostresses in the region and propose a sequence of three brittle deformational phases accountable for these reactivations: 1) NE-SW dextral transcurrence; 2) NNW-SSE dextral oblique extension that evolved to NNW-SSE "pure" extension; 3) ENE-WSW dextral oblique extension. These phases are reasonably correlated with the tectonic events responsible for the onset and evolution of the SE onshore rift basins, between the Neocretaceous and Holocene. However, based on petrographic studies and supported by regional geological correlations, we assume that the origin of this fault system is older, related to the Early Cretaceous South Atlantic rifting. This study provides significant information about one of the main structural trends of the SE Brazilian continental margin and the tectonic events that controlled its segmentation, since the Gondwana rifting, and compartmentalization of its onshore sedimentary deposits during the Cenozoic.

The Yilgarn Craton western Australia: A tectonic synthesis

NASA Technical Reports Server (NTRS)

Fripp, R. E. P.

1986-01-01

The Yilgarn Craton in Western Australia is one of the larger contiguous preserved Archaean crustal fragments, with an area of about 650,000 square kilometres. Of this, by area, about 70% is granitoid and 30% greenstone. The Craton is defined by the Darling Fault on its western margin, by Proterozoic deformation belts on its southern and northwestern margins, and by unconformable younger sediments on its eastern and northeastern margins. A regional geotectonic synthesis at a scale of 1:500,000 is being prepared. This is based largely upon the 1:250,000 scale mapping of the Geological Survey of Western Australia together with interpretation using geophysical data, mainly airborne magnetic surveys. On a regional basis the granitoids are classied as pre-, syn- and post-tectonic with respect to greenstone belt deformation. The post-tectonic granitoids yield Rb-Sr isochrons of about 2.6 b.y., close to Rb-Sr ages for the greenstones themselves which are up to about 2.8 b.y. old, although data for the latter is sparse. Contacts between earlier granitoids and greenstones which are not obscured by the post-tectonic granitoids are most commonly tectonic contacts, intensely deformed and with mylonitic fabrics. The general concensus however is that there is a pre-tectonic, pre-greenhouse sialic gneiss preserved in places. A discussion follows.

Mantle convection with plates and mobile, faulted plate margins.

PubMed

Zhong, S; Gurnis, M

1995-02-10

A finite-element formulation of faults has been incorporated into time-dependent models of mantle convection with realistic rheology, continents, and phase changes. Realistic tectonic plates naturally form with self-consistent coupling between plate and mantle dynamics. After the initiation of subduction, trenches rapidly roll back with subducted slabs temporarily laid out along the base of the transition zone. After the slabs have penetrated into the lower mantle, the velocity of trench migration decreases markedly. The inhibition of slab penetration into the lower mantle by the 670-kilometer phase change is greatly reduced in these models as compared to models without tectonic plates.

Tectonic evolution of the outer Izu-Bonin-Mariana fore arc system: initial results from IODP Expedition 352

NASA Astrophysics Data System (ADS)

Kurz, W.; Ferre, E. C.; Robertson, A. H. F.; Avery, A. J.; Kutterolf, S.

2015-12-01

During International Ocean Discovery Program (IODP) Expedition 352, a section through the volcanic stratigraphy of the outer fore arc of the Izu-Bonin-Mariana (IBM) system was drilled to trace magmatism, tectonics, and crustal accretion associated with subduction initiation. Structures within drill cores, borehole and site survey seismic data indicate that tectonic deformation in the outer IBM fore arc is mainly post-magmatic. Extension generated asymmetric sediment basins such as half-grabens at sites 352-U1439 and 352-U1442 on the upper trench slope. Along their eastern margins the basins are bounded by west-dipping normal faults. Deformation was localized along multiple sets of faults, accompanied by syn-tectonic pelagic and volcaniclastic sedimentation. The lowermost sedimentary units were tilted eastward by ~20°. Tilted beds were covered by sub-horizontal beds. Biostratigraphic constraints reveal a minimum age of the oldest sediments at ~ 35 Ma; timing of the sedimentary unconformities is between ~ 27 and 32 Ma. At sites 352-U1440 and 352-U1441 on the outer fore arc strike-slip faults are bounding sediment basins. Sediments were not significantly affected by tectonic tilting. Biostratigraphy gives a minimum age of the basement-cover contact between ~29.5 and 32 Ma. The post-magmatic structures reveal a multiphase tectonic evolution of the outer IBM fore arc. At sites 352-U1439 and 352-U1442, shear with dominant reverse to oblique reverse displacement was localized along subhorizontal fault zones, steep slickensides and shear fractures. These were either re-activated as or cut by normal-faults and strike-slip faults. Extension was also accommodated by steep to subvertical mineralized veins and extensional fractures. Faults at sites 352-U1440 and 352-U1441 show mainly strike-slip kinematics. Sediments overlying the igneous basement(maximum Late Eocene to Recent age), document ash and aeolian input, together with mass wasting of the fault-bounded sediment ponds.

Numerical validation of the 'Pop-Down tectonics' as a structural frame for hot lithospheres with particular reference to the Hearne craton (Canadian Shield)

NASA Astrophysics Data System (ADS)

Poh, Jonathan; Yamato, Philippe; Gapais, Denis; Duretz, Thibault; Ledru, Patrick

2017-04-01

The formation of the architecture of the main cratons of the Canadian Shield has been debated over the past three decades. Understanding the role of tangential Vs. vertical tectonics in the Rae craton is of great interest as the role of inherited structure is fundamental for the subsequent drainage of fluids and the formation of high to ultra-high grade unconformity-type uranium deposits. These deposits are located in the vicinity of the intersection between the unconformity at the base of the Paleoproterozoic Athabasca sedimentary basin (1.75-1.5 Ga) and the graphite-rich metasediments of the Wollaston-Mudjatik transition zone, one of the main fault system of the Rae Craton related to the Trans-Hudson orogeny (1.82-1.78 Ga). A new tectonic model, Pop-down tectonics, was proposed as the primary driving process to concentrate supracrustal materials, strains, fluid transfers and metal transport in permeability enhanced deformation zones. The sub-vertical structural patterns with regional horizontal shortening seen in the tectonic model appear to be consistent with field evidences and has the potential for sustaining strong fluid-rock interactions. In the light of previous analogue modelling studies, we test the viability of the Pop-down tectonics model in a thermo-mechanical framework. The numerical experiments are based on a series of 2D visco-elasto-plastic thermo-mechanical models. We employ various thermal and rheological parameters derived from laboratory experiments. The geometry, thermicity and kinematics of the models are further constrained by applying existing geophysical and geological data. We impose a fixed upper mantle temperature of 1330 °C and a thin crust ranging from 30 - 40 km. The outcome of the models will provide insights into the mechanical processes controlling the deformation of hot lithospheres in convergent settings.

Identification of new NE-trending deep-seated faults and tectonic pattern updating in northern Tunisia (Mogodos-Bizerte region), insights from field and seismic reflection data

NASA Astrophysics Data System (ADS)

Essid, El Mabrouk; Kadri, Ali; Inoubli, Mohamed Hedi; Zargouni, Fouad

2016-07-01

The northern Tunisia is occupied by the Tellian domain constituent the eastern end of the Maghrebides, Alpine fold-thrust belt. Study area includes partially the Tellian domain (Mogodos belt) and its foreland (Bizerte region). Most of this region outcrops consist of Numidian thrust sheet flysch attributed to the lower Oligocene-Burdigalian. In the study area, the major fault systems are still subject of discussion. The Numidian nappe structure, the distribution of basalt and Triassic outcrops within and at the front of this Tellian domain deserve more explanation. In this work we intend to update the structural scheme and the tectonic evolution of the northern Tunisia, taking into account salt tectonics and magmatism. The updated tectonic evolution will be integrated in the geodynamic framework of the Central Mediterranean. For this purpose, we have analyzed morphologic, seismic and structural data. The compilation of the results has allowed the identification of new regional NE-trending faults dipping towards the NW: the Bled el Aouana-Bizerte, the Sejnane-Ras Enjla and the Oued el Harka faults. They correspond to the reactivation of deep-seated normal faults splaying on the Triassic evaporites. This fault system constitutes the main component of the northern Tunisia structural scheme and has influenced its tectonic evolution marked by the main following stages. The Tellian thrust-sheets were immobilized at the uppermost Langhian. During the major Tortonian NW-trending compressive phase, these faults were reactivated with reverse kinematics and controlled the distribution of the post-nappes Neogene continental deposits. At the early Pleistocene, a compressive NNW-trending event has reactivated again these faults with sinistral-reverse movements and deformed the post-nappes Neogene series. Late Quaternary to Actual, the tectonic regime continues to be compressive with a NNW-trending maximum horizontal stress.

Pre-lithification tectonic foliation development in a clastic sedimentary rock sequence from SW Ireland

NASA Astrophysics Data System (ADS)

Meere, Patrick; Mulchrone, Kieran; McCarthy, David

2017-04-01

The current orthodoxy regarding the development of regionally developed penetrative tectonic cleavage fabrics in sedimentary rocks is that it postdates lithification of those rocks. It is well established that fabric development under these circumstances is achieved by a combination of grain rigid body rotation, crystal-plastic deformation and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal nature of cleavage development commonly observed in low grade metamorphic rocks. While there have been advocates for the development of tectonic cleavages before host rock lithification these are currently viewed as essentially local aberrations without regional significance. In this study we combine new field observations with strain analysis, element mapping and modelling to characterise Acadian (>50%) crustal shortening in a Devonian clastic sedimentary sequence from the Dingle Peninsula of south west Ireland. Fabrics in these rocks reflect significant levels of tectonic shortening are a product of grain translation, rigid body rotation and repacking of intra- and extra-formational clasts during deformation of an unconsolidated clastic sedimentary sequence. There is an absence of the expected domainal cleavage structure and intra-clast deformation expected with conventional cleavage formation. This study requires geologists to consider the possibility such a mechanism contributing to tectonic strain in a wide range of geological settings and to look again at field evidence that indicates early sediment mobility during deformation.

Evaluating influence of active tectonics on spatial distribution pattern of floods along eastern Tamil Nadu, India

NASA Astrophysics Data System (ADS)

Selvakumar, R.; Ramasamy, SM.

2014-12-01

Flooding is a naturally recurrent phenomenon that causes severe damage to lives and property. Predictions on flood-prone zones are made based on intensity-duration of rainfall, carrying capacity of drainage, and natural or man-made obstructions. Particularly, the lower part of the drainage system and its adjacent geomorphic landforms like floodplains and deltaic plains are considered for analysis, but stagnation in parts of basins that are far away from major riverine systems is less unveiled. Similarly, uncharacteristic flooding in the upper and middle parts of drainage, especially in zones of an anomalous drainage pattern, is also least understood. Even though topographic differences are attributed for such anomalous spatial occurrence of floods, its genetic cause has to be identified for effective management practice. Added to structural and lithological variations, tectonic movements too impart micro-scale terrain undulations. Because active tectonic movements are slow-occurring, long-term geological processes, its resultant topographical variations and drainage anomalies are least correlated with floods. The recent floods of Tamil Nadu also exhibit a unique distribution pattern emphasizing the role of tectonics over it. Hence a detailed geoinformatics-based analysis was carried out to envisage the relationship between spatial distribution of flood and active tectonic elements such as regional arches and deeps, block faults, and graben and drainage anomalies such as deflected drainage, compressed meander, and eyed drainages. The analysis reveals that micro-scale topographic highs and lows imparted by active tectonic movements and its further induced drainage anomalies have substantially controlled the distribution pattern of flood.

Confused about Fusion? Weed Your Science Collection with a Pro.

ERIC Educational Resources Information Center

O'Dell, Charli

1998-01-01

Provides guidelines on weeding science collections in junior high/high school libraries. Highlights include checking copyright dates, online sources, 13 science subject areas that deserve special consideration (plate tectonics, fission, fusion, radioactive dating, weather/climate, astronomy/space science, elements, integrated science,…

Jadeitites and Plate Tectonics

NASA Astrophysics Data System (ADS)

Harlow, George E.; Tsujimori, Tatsuki; Sorensen, Sorena S.

2015-05-01

Jadeitite is a relatively rare, very tough rock composed predominantly of jadeite and typically found associated with tectonic blocks of high-pressure/low-temperature metabasaltic rocks (e.g., eclogite, blueschist) in exhumed serpentinite-matrix mélanges. Studies over the past ˜20 years have interpreted jadeitite either as the direct hydrous fluid precipitate from subduction channel dewatering into the overlying mantle wedge or as the metasomatic replacement by such fluids of oceanic plagiogranite, graywacke, or metabasite along the channel margin. Thus, jadeitites directly sample and record fluid transport in the subduction factory and provide a window into this geochemical process that is critical to a major process in the Earth system. They record the remarkable transport of large ion lithophile elements, such as Li, Ba, Sr, and Pb, as well as elements generally considered more refractory, such as U, Th, Zr, and Hf. Jadeitite is also the precious form of jade, utilized since antiquity in the form of tools, adornments, and symbols of prestige.

On the effects of subsurface parameters on evaporite dissolution (Switzerland)

NASA Astrophysics Data System (ADS)

Zidane, Ali; Zechner, Eric; Huggenberger, Peter; Younes, Anis

2014-05-01

Uncontrolled subsurface evaporite dissolution could lead to hazards such as land subsidence. Observed subsidences in a study area of Northwestern Switzerland were mainly due to subsurface dissolution (subrosion) of evaporites such as halite and gypsum. A set of 2D density driven flow simulations were evaluated along 1000 m long and 150 m deep 2D cross sections within the study area that is characterized by tectonic horst and graben structures. The simulations were conducted to study the effect of the different subsurface parameters that could affect the dissolution process. The heterogeneity of normal faults and its impact on the dissolution of evaporites is studied by considering several permeable faults that include non-permeable areas. The mixed finite element method (MFE) is used to solve the flow equation, coupled with the multipoint flux approximation (MPFA) and the discontinuous Galerkin method (DG) to solve the diffusion and the advection parts of the transport equation.

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

Melting-induced crustal production helps plate tectonics on Earth-like planets

NASA Astrophysics Data System (ADS)

Lourenço, Diogo L.; Rozel, Antoine; Tackley, Paul J.

2016-04-01

Within our Solar System, Earth is the only planet to be in a mobile-lid regime. It is generally accepted that the other terrestrial planets are currently in a stagnant-lid regime, with the possible exception of Venus that may be in an episodic-lid regime (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around two. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2). Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question of whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour (plate tectonics). Our results show that melting-induced crustal production strongly influences plate tectonics on Earth-like planets by strongly enhancing the mobility of the lid, replacing a stagnant lid with an episodic lid, or greatly extending the time in which a smoothly evolving mobile lid is present in a planet. Finally, we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory, whether melting-induced crustal production is considered or not.

Hypsometry and relief analysis of the southern termination of the Calabrian arc, NE-Sicily (southern Italy)

NASA Astrophysics Data System (ADS)

Pavano, F.; Catalano, S.; Romagnoli, G.; Tortorici, G.

2018-03-01

Tectonic forcing causes the relief-building of mountain chains and enforces the surficial processes in a persistent dismantling of rock volumes, continuously modelling Earth's surface. Actually, we observe transient landscapes that have temporarily recorded tectonic forcing as a codified signal. The Late Quaternary tectonic evolution of northeastern Sicily, located along the Nubia-Eurasia plate boundary at the southern termination of the Calabrian arc, has been dominated by intense Plio-Pleistocene dynamics that severely modified the Late Miocene landscape. The present work aims to investigate geomorphically northeastern Sicily, essentially focusing on the hypsometric and relief analyses of the region in order to define how the topography responds to the post-Pliocene tectonic deformation. We apply different relief morphometric indices (Hypsometric Integral, Topographic Relief and Topographic Dissection) measured for each differently sized moving window, and we use different swath topographic profiles as well. Our analysis evidences differential morphological responses between distinct morphotectonic domains of the studied area, led by the combination of earlier morphological background and Late Quaternary tectonic deformation stages of the region. In addition, in the context of a constant and uniform tectonic uplift, the results define the general space- and time-relating pathways of the landscape geomorphic metrics. This enables us to bring out the controls of the vertical scale of landscape on hypsometry, exploring their mutual relationships. Finally, we reconstruct the Late Quaternary morphotectonic evolution of the region, defining the role played by the main tectonic alignments on the present geomorphic setting.

The Role of Long-Term Tectonic Deformation on the Distribution of Present-Day Seismic Activity in the Caribbean and Central America

NASA Astrophysics Data System (ADS)

Schobelock, J.; Stamps, D. S.; Pagani, M.; Garcia, J.; Styron, R. H.

2017-12-01

The Caribbean and Central America region (CCAR) undergoes the entire spectrum of earthquake types due to its complex tectonic setting comprised of transform zones, young oceanic spreading ridges, and subductions along its eastern and western boundaries. CCAR is, therefore, an ideal setting in which to study the impacts of long-term tectonic deformation on the distribution of present-day seismic activity. In this work, we develop a continuous tectonic strain rate model based on inter-seismic geodetic data and compare it with known active faults and earthquake focal mechanism data. We first create a 0.25o x 0.25o finite element mesh that is comprised of block geometries defined in previously studies. Second, we isolate and remove transient signals from the latest open access community velocity solution from UNAVCO, which includes 339 velocities from COCONet and TLALOCNet GNSS data for the Caribbean and Central America, respectively. In a third step we define zones of deformation and rigidity by creating a buffer around the boundary of each block that varies depending on the size of the block and the expected deformation zone based on locations of GNSS data that are consistent with rigid block motion. We then assign each node within the buffer a 0 for the deforming areas and a plate index outside the buffer for the rigid. Finally, we calculate a tectonic strain rate model for CCAR using the Haines and Holt finite element approach to fit bi-cubic Bessel splines to the the GNSS/GPS data assuming block rotation for zones of rigidity. Our model of the CCAR is consistent with compression along subduction zones, extension across the mid-Pacific Rise, and a combination of compression and extension across the North America - Caribbean plate boundary. The majority of CCAR strain rate magnitudes range from -60 to 60 nanostrains/yr. Modeling results are then used to calculate expected faulting behaviors that we compare with mapped geologic faults and seismic activity.

Temporal Variation of Tectonic Tremor Activity Associated with Nearby Earthquakes

NASA Astrophysics Data System (ADS)

Chao, K.; Van der Lee, S.; Hsu, Y. J.; Pu, H. C.

2017-12-01

Tectonic tremor and slow slip events, located downdip from the seismogenic zone, hold the key to recurring patterns of typical earthquakes. Several findings of slow aseismic slip during the prenucletion processes of nearby earthquakes have provided new insight into the study of stress transform of slow earthquakes in fault zones prior to megathrust earthquakes. However, how tectonic tremor is associated with the occurrence of nearby earthquakes remains unclear. To enhance our understanding of the stress interaction between tremor and earthquakes, we developed an algorithm for the automatic detection and location of tectonic tremor in the collisional tectonic environment in Taiwan. Our analysis of a three-year data set indicates a short-term increase in the tremor rate starting at 19 days before the 2010 ML6.4 Jiashian main shock (Chao et al., JGR, 2017). Around the time when the tremor rate began to rise, one GPS station recorded a flip in its direction of motion. We hypothesize that tremor is driven by a slow-slip event that preceded the occurrence of the shallower nearby main shock, even though the inferred slip is too small to be observed by all GPS stations. To better quantify what the necessary condition for tremor to response to nearby earthquakes is, we obtained a 13-year ambient tremor catalog from 2004 to 2016 in the same region. We examine the spatiotemporal relationship between tremor and 37 ML>=5.0 (seven events with ML>=6.0) nearby earthquakes located within 0.5 degrees to the active tremor sources. The findings from this study can enhance our understanding of the interaction among tremor, slow slip, and nearby earthquakes in the high seismic hazard regions.

Devonian magmatism in the Timan Range, Arctic Russia - subduction, post-orogenic extension, or rifting?

NASA Astrophysics Data System (ADS)

Pease, V.; Scarrow, J. H.; Silva, I. G. Nobre; Cambeses, A.

2016-11-01

Devonian mafic magmatism of the northern East European Craton (EEC) has been variously linked to Uralian subduction, post-orogenic extension associated with Caledonian collision, and rifting. New elemental and isotopic analyses of Devonian basalts from the Timan Range and Kanin Peninsula, Russia, in the northern EEC constrain magma genesis, mantle source(s) and the tectonic process(es) associated with this Devonian volcanism to a rift-related context. Two compositional groups of low-K2O tholeiitic basalts are recognized. On the basis of Th concentrations, LREE concentrations, and (LREE/HREE)N, the data suggest two distinct magma batches. Incompatible trace elements ratios (e.g., Th/Yb, Nb/Th, Nb/La) together with Nd and Pb isotopes indicate involvement of an NMORB to EMORB 'transitional' mantle component mixed with variable amounts of a continental component. The magmas were derived from a source that developed high (U,Th)/Pb, U/Th and Sm/Nd over time. The geochemistry of Timan-Kanin basalts supports the hypothesis that the genesis of Devonian basaltic magmatism in the region resulted from local melting of transitional mantle and lower crust during rifting of a mainly non-volcanic continental rifted margin.

Erratum to Dynamic stresses, Coulomb failure, and remote triggering and to Surface wave potential for triggering tectonic (nonvolcanic) tremor

USGS Publications Warehouse

Hill, David P.

2012-01-01

Hill (2008) and Hill (2010) contain two technical errors: (1) a missing factor of 2 for computed Love‐wave amplitudes, and (2) a sign error in the off‐diagonal elements in the Euler rotation matrix.

Effects of Caledonian tectonism in Arctic Canada

NASA Astrophysics Data System (ADS)

Miall, Andrew D.

1986-11-01

Several north-trending structures in the Canadian Arctic islands are interpreted as Caledonian in origin, in the sense that they probably represent intraplate tectonism triggered by the closing of the Iapetus Ocean along the Greenland-Scandinavia-Svalbard Caledonian suture. These structures include the Boothia uplift, Rens Fiord uplift, Inglefield uplift (redefined unit, replacing Bache Peninsula arch), and possibly several other structures, such as the Cornwall arch, which are now expressed mainly in Mesozoic-Cenozoic strata but may represent rejuvenated Caledonian lineaments.

Mineralogical, petrological and geochemical aspects of alkaline and alkaline-carbonatite associations from Brazil

NASA Astrophysics Data System (ADS)

Morbidelli, L.; Gomes, C. B.; Beccaluva, L.; Brotzu, P.; Conte, A. M.; Ruberti, E.; Traversa, G.

1995-12-01

A general description of Mesozoic and Tertiary (Fortaleza) Brazilian alkaline and alkaline-carbonatite districts is presented with reference to mineralogy, petrology, geochemistry and geochronology. It mainly refers to scientific results obtained during the last decade by an Italo-Brazilian research team. Alkaline occurrences are distributed across Brazilian territory from the southern (Piratini, Rio Grande do Sul State) to the northeastern (Fortaleza, Ceará State) regions and are mainly concentrated along the borders of the Paraná Basin generally coinciding with important tectonic lineaments. The most noteworthy characteristics of these alkaline and alkaline-carbonatite suites are: (i) prevalence of intrusive forms; (ii) abundance of cumulate assemblages (minor dunites, frequent clinopyroxenites and members of the ijolite series) and (iii) abundance of evolved rock-types. Many data demonstrate that crystal fractionation was the main process responsible for magma evolution of all Brazilian alkaline rocks. A hypothesis is proposed for the genesis of carbonatite liquids by immiscibility processes. The incidence of REE and trace elements for different major groups of lithotypes, belonging both to carbonatite-bearing and carbonatite-free districts, are documented. Sr and preliminary Nd isotopic data are indicative of a mantle origin for the least evolved magmas of all the studied occurrences. Mantle source material and melting models for the generation of the Brazilian alkaline magma types are also discussed.

Contrast of lithospheric dynamics across the southern and eastern margins of the Tibetan Plateau: a numerical study

NASA Astrophysics Data System (ADS)

Sun, Yujun; Fan, Taoyuan; Wu, Zhonghai

2018-05-01

Both of the southern and eastern margins of the Tibetan Plateau are bounded by the cratonic blocks (Indian plate and Sichuan basin). However, there are many differences in tectonic deformation, lithospheric structure and surface heat flow between these two margins. What dynamics cause these differences? With the constraints of the lithospheric structure and surface heat flow across the southern and eastern margins of Tibetan Plateau, we constructed 2-D thermal-mechanical finite-element models to investigate the dynamics across these two margins. The results show that the delamination of mantle lithosphere beneath the Lhasa terrane in Oligocene and the rheological contrast between the Indian and Tibetan crust are the two main factors that control the subduction of the Indian plate. The dynamics across the eastern margin of the Tibetan Plateau are different from the southern margin. During the lateral expansion of the Tibetan Plateau, pure shear thickening is the main deformation characteristic for the Songpan-Ganzi lithosphere. This thickening results in the reduction of geothermal gradient and surface heat flow. From this study, it can be seen that the delamination of the mantle lithosphere and the rheological contrast between the Tibetan Plateau and its bounding blocks are the two main factors that control the lithospheric deformation and surface heat flow.

The Role of Crustal Tectonics in Volcano Dynamics (ROCTEVODY) along the Southern Andes: seismological study with emphasis on Villarrica Volcano

NASA Astrophysics Data System (ADS)

Mora-Stock, Cindy; Tassara, Andrés

2016-04-01

The Southern Andean margin is intrinsically related to the Liquiñe-Ofqui Fault Zone (LOFZ), a 1000 km-long dextral strike-slip arc-parallel fault on which most of the volcanic centers of the Southern Volcanic Zone (SCVZ) of the Andes are emplaced. At large spatial (102 - 103 km) and temporal (105 - 107 yr) scales, regional tectonics linked to partitioning of the oblique convergence controls the distribution of magma reservoirs, eruption rates and style, as well as the magma evolution. At small scales in space (< 102 km) and time (10-1 - 102 yr), stress transfer mechanisms between magma reservoirs and seismically-active faults are though to transiently change the regional stress field, thus leading to eruptions and fault (re)activation. However, the mechanisms by which the interaction between (megathrust and crustal) earthquakes and volcanic eruptions actually occur, in terms of generating the relationships and characteristics verified at the long term, are still poorly understood. Since 2007, the Southern Andean margin has presented an increase of its tectonic and eruptive activity with several volcanic crisis and eruptions taking place in association with significant seismicity clusters and earthquakes both in the megathrust and the LOFZ. This increased activity offers a unique opportunity to improve our understanding of the physical relation between contemporary tectono-volcanic processes and the long-term construction of the LOFZ-SVZ system. Taking advantage of this opportunity by means of an integrated analysis of geodetic and seismological data through finite element numerical modeling at the scale of the entire margin and for selected cases is the main goal of project Active Tectonics and Volcanism at the Southern Andes (ACT&VO-SA, see Tassara et al. this meeting). Into the framework of the ACT&VO-SA project, the complementary ROCTEVODY-Villarrica project concentrates on the role that inherited crustal structures have in the volcano dynamics. The focus is on Villarrica volcano, which is emplaced at the intersection of the main NNE-branch of the LOFZ and the NW-SE inherited Mocha-Villarrica Fault (MVF). The extensional characteristics of previous eruptions at Villarrica contrasts with the dextral strike-slip motion of LOFZ and the compressive regime dominated by the subduction. Then, this projects aims to understand how the NW-SE inherited structures interacts with their intra-arc counterpart to allow the emplacement of volcanic edifices under the present day compressive stress regime. This goal will be achieved through the analysis of a seismic database for Villarrica volcano that combines data from a dense local network and the network of the Chilean volcanic observatory. These data will allow us to identify long period events and tremor signals from which we plan to perform a wave field characterization to extract information about fluid flow and seismic source, together with a precise location of tectonic crustal events. We will present preliminary results and a conceptual model to explain the role of the different structures at interplay in the region and their relation with volcano dynamics.

Lateral variations in geologic structure and tectonic setting from remote sensing data

NASA Astrophysics Data System (ADS)

Alexander, S. S.

1983-05-01

The principal objective of this study was: (1) to assess the usefulness of remote sensing digital imagery, principally LANDSAT multispectral scanning (MSS) data, for inferring lateral variations in geologic structure and tectonic setting; and (2) to determine the extent to which these inferred variations correlate with observed variations in seismic excitation from underground nuclear explosion test sites in the Soviet Union. Soviet, French and U.S. test sites have been investigated to compare their geologic and tectonic responses as seen by LANDSAT. The characteristics of "granite' intrusive bodies exposed at Semipalatinsk (Degelen), North Africa (Hoggar), NTS (Climax stock), and an analog site in Maine (Mt. Katahdin), have been studied in detail. The tectonic stress field inferred from the tectonic release portion of seismic signatures of explosions in these three areas is compared with local and regional fracture patterns discernable from imagery. The usefulness of satellite synthetic aperture radar (SAR) to determine geologic conditions and delineate fault (fracture) patterns is demonstrated by the analysis of SEASAT data for an area in the eastern United States. Algorithms to enhance structural boundaries and to use textures to identify rock types were developed and applied to several test sites.

Marine Terrace Deposits along the Mediterranean Coast on the Southeastern Turkey and Their Implications for Tectonic Uplift and Sea Level Change

NASA Astrophysics Data System (ADS)

Tari, U.; Tüysüz, O.; Blackwell, B. A. B.; Genç, Ş. C.; Florentin, J. A.; Mahmud, Z.; Li, G. L.; Blickstein, J. I. B.; Skinner, A. R.

2016-12-01

Tectonic movements among the African, Arabian and Anatolian Plates have deformed the eastern Mediterranean. These movements caused transtensional opening of the NE-trending Antakya Graben since the late Pliocene. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces along the Mediterranean coasts on the graben. Here, marine terrace deposits that sit on both flanks of the graben at elevations between 3 and 175 m were dated using electron spin resonance (ESR) method in order to calculate uplift rates. The ESR ages range from 12 ka in late MIS 2 to 457 ka in MIS 9-11, but most of the terraces contain molluscs reworked from several earlier deposits due to successive tectonic movements and sealevel fluctuations. By dating in situ fossils, along the basal contacts of the marine terraces, uplift rates were calculated on both sides of the Antakya Graben. Results indicate that these deposits were mainly uplifted by local active faults rather than regional movements.

Role of the Yakutat collision and upper mantle dynamics in the present-day tectonics of the North America Northern Cordillera

NASA Astrophysics Data System (ADS)

Mazzotti, S.; Tarayoun, A.; Marechal, A.; Audet, P.

2017-12-01

The Northern Cordillera of North America is a type example of present-day strain distribution across a wide orogeny. Several geodynamic models are proposed to explain this large-scale tectonic activity, with two main end-members: strain transfer from the Yakutat collision zone (orogenic float) and strain transfer from upper mantle convection (lithosphere basal traction). One of the main differences between these is the lithosphere vertical rheology profile: the former requires significant crust - mantle decoupling to allow far field strain transfer, whereas the latter requires a vertically coupled lithosphere. Here we combine recent data across the eastern region of the Northern Cordillera (eastern Alaska, Yukon, western Northwest Territories) to characterize its states of strain rate, stress, and crustal and lithospheric structure, in order to test the role of the Yakutat collision and upper mantle convection in its present-day tectonics. Recent GPS data confirm the radial, east- to northeastward motion of the central Yukon and foreland belt (Mackenzie and Richardson Mountains), albeit at a much lower velocity than previously proposed. This motion is primarily accommodated by E-W to NE-SW shortening, mainly in the foreland belt, and small to near-zero lateral motion on the major Denali and Tintina strike-slip faults. Seismic anisotropy data further suggest that these two major faults, like most of the Yukon Cordillera, have kept their early Cenozoic crustal and upper mantle structures, as shown by the fault-parallel (NW-SE) fast anisotropy orientation. We use these new data, combined with numerical models of strain distribution under various boundary conditions, to provide constraints on the respective role of the Yakutat collision and upper mantle convection in the present-day tectonics. Preliminary results suggest that, whichever the driving mechanism (or combination thereof), the total strain associated with the present-day tectonics must remain small in order to preserve the inherited crustal and mantle fabrics. Such small cumulative strain appears in contradiction with a thin decoupling layer (such as lower crust decoupling in the orogenic float model) and seems more suggestive of distributed shear across a large part of the lithosphere.

Large Sanjiang basin groups outside of the Songliao Basin Meso-Senozoic Tectonic-sediment evolution and hydrocarbon accumulation

NASA Astrophysics Data System (ADS)

Zheng, M.; Wu, X.

2015-12-01

The basis geological problem is still the bottleneck of the exploration work of the lager Sanjiang basin groups. In general terms, the problems are including the prototype basins and basin forming mechanism of two aspects. In this paper, using the field geological survey and investigation, logging data analysis, seismic data interpretation technical means large Sanjiang basin groups and basin forming mechanism of the prototype are discussed. Main draw the following conclusions： 1. Sanjiang region group-level formation can be completely contrasted. 2. Tension faults, compressive faults, shear structure composition and structure combination of four kinds of compound fracture are mainly developed In the study area. The direction of their distribution can be divided into SN, EW, NNE, NEE, NNW, NWW to other groups of fracture. 3. Large Sanjiang basin has the SN and the EW two main directions of tectonic evolution. Cenozoic basins in Sanjiang region in group formation located the two tectonic domains of ancient Paleo-Asian Ocean and the Pacific Interchange. 4. Large Sanjiang basin has experienced in the late Mesozoic tectonic evolution of two-stage and nine times. The first stage, developmental stage basement, they are ① Since the Mesozoic era and before the Jurassic; ② Early Jurassic period; The second stage, cap stage of development, they are ③ Late Jurassic depression developmental stages of compression; ④ Early Cretaceous rifting stage; ⑤ depression in mid-Early Cretaceous period; ⑥ tensile Early Cretaceous rifting stage; ⑦ inversion of Late Cretaceous tectonic compression stage; ⑧ Paleogene - Neogene; ⑨ After recently Ji Baoquan Sedimentary Ridge. 5. Large Sanjiang basin group is actually a residual basin structure, and Can be divided into left - superimposed (Founder, Tangyuan depression, Hulin Basin), residual - inherited type (Sanjiang basin), residual - reformed (Jixi, Boli, Hegang basin). there are two developed depression and the mechanism of rifting. 6. Sanjiang Basin Suibin Depression, Tangyuan depression, Jixi Cretaceous Tangyuan and Fangzheng rift is the key for further exploration. Yishu graben is a large core of Sanjiang region to find oil, and Paleogene basin is the focus of the external layer system exploration.

Plutonic-squishy lid and beyond: implications of intrusive magmatism and characterization of a new global-tectonic regime on Earth-like planets

NASA Astrophysics Data System (ADS)

Louro Lourenço, Diogo; Rozel, Antoine; Ballmer, Maxim; Tackley, Paul

2017-04-01

It is now well established that compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. Mechanisms that have been found to facilitate plate tectonics include: water circulation [Regenauer-Lieb et al., Science 2001; Dymkova and Gerya, GRL 2013], presence of continents [Rolf and Tackley, GRL 2011], and melting [Korenaga, GJI 2009; Armann and Tackley, JGR 2012]. In a recent work by Lourenço et al. [EPSL 2016], it has been shown that Earth-like plate tectonics is more likely to occur in planets that can produce a crust of variable thickness and density through melt extraction from the mantle. The authors employed a first-order approximation by assuming that all magmatism was extrusive. However, volumes of intruded magmas are observed to be around 4- 9 times more present on Earth than erupted magmas [Crisp, J. Volcanol. Geotherm. Res. 1984]. Therefore, intrusive magmatism is thought to play a role in the dynamics of the lithosphere on Earth [Cawood et al., Geol. Soc. Am. Bull. 2013] and other Earth-like planets. We extend the work of Lourenço et al. [2016] by taking into account intrusive magmatism, and systematically investigate the effect of plutonism, in conjugation with eruptive volcanism. We present a set of 2D spherical annulus simulations of thermo-compositional global mantle convection using StagYY [Tackley, PEPI 2008], which uses a finite-volume discretization of the governing compressible anelastic Stokes equations. Tracers are used to track composition and to allow for the treatment of partial melting and crustal formation. A direct solver is employed to obtain a solution of the Stokes and continuity equations, using the PETSc toolkit. The heat equation is solved in two steps: advection is performed using the MPDATA scheme and diffusion is then solved implicitly using a PETSc solver. Results show that three common convection regimes are usually reached in simulations when using a visco-plastic rheology: stagnant-lid regime (a one-plate planet), episodic lid (where the lithosphere is unstable and frequently overturns into the mantle), and mobile-lid regime (similar to plate tectonics). At high intrusion efficiencies, we observe and characterise a new additional regime called here "plutonic-squishy lid". This regime is characterised by a set of strong plates separated by warm and weak regions due to plutonism. Eclogitic drippings and lithospheric delaminations often occur around these weak regions. These processes lead to significant surface velocities, even if subduction is not active. The location of plate boundaries is strongly time-dependent and mainly occurs in magma intrusion regions. This regime is also distinctive because it generates a thin lithosphere, which results in high conductive heat fluxes and lower internal temperatures when compared to a stagnant lid. The plutonic-squishy-lid regime has the potential to be applicable to the Archean Earth and Venus, as it combines elements of both protoplate tectonic and vertical tectonic models, such as horizontal plate motion and reprocessing of the lithosphere for the former, and lithospheric diapirism, volcanism, and basal delamination for the later.

Attenuation in the Upper Mantle Beneath the Northern Apennines (Italy) from Teleseismic P- and S-Wave Spectra

NASA Astrophysics Data System (ADS)

Lucente, F. P.; Piccinini, D.; Dibona, M.; Levin, V.; Park, J.

2007-12-01

We present preliminary results for seismic attenuation in the mantle beneath the Italian region. We estimate P- and S-wave spectral ratios from teleseisms recorded at the temporary broadband seismic network deployed during the RETREAT (Retreating-TRrench, Extension, and Accretion Tectonics) project. We examine body-wave attenuation variation across the northern part of the Apennines mountain belt, which represents the accretionary wedge exposed during recent episodes of the subduction process in Italy. The data recorded during the three-year seismic campaign were analyzed using an ad hoc semi-automated procedure based on the cross-correlation analysis of a single phase across all the stations for each event. The seismic phases analyzed (P, S, SKS) display different patterns of seismic attenuation. Furthermore, we observe systematic variations in the distribution of the attenuation values as function of both the azimuth and the incidence angle of the seismic rays. Relatively high attenuation values are found on the Tyrrhenian side by seismic rays coming from the SW for both P- and S-phases. For NE-approaching rays the pattern of high attenuation values varies considerably, depending on the seismic phases: for P-waves it grossly corresponds to the mountain belt, while for S-waves it extends over almost the whole study area. By correlating attenuation estimates and the velocity structure from the existing tomographic models, we can make some inferences on the thermal state of the sublithospheric mantle, and on the physical properties of the tectonic elements which constitute the subduction system in the region. From the analysis of the P-phases we can clearly distinguish three main areas with different attenuation values, corresponding to the back-arc mantle (high attenuation), to the slab (low attenuation) and to the retro-slab mantle (high attenuation). The correspondence between the identified elements of the subduction system and the S- waves attenuation is not straightforward, and need to be further investigated.

Bathymetry of the Levant basin: interaction of salt-tectonics and surficial mass movements

NASA Astrophysics Data System (ADS)

Gvirtzman, Zohar; Reshef, Moshe; Buch-Leviatan, Orna; Groves-Gidney, Gavrielle; Karcz, Zvi; Makovsky, Yizhaq; Ben-Avraham, Zvi

2015-04-01

A new high resolution bathymetric map of the Levant Basin between Israel and the Eratosthenes Seamount reveals previously undetected folds, faults and channels. The map facilitates a regional map-view analysis of structures that were previously examined only in cross section. The systematic mapping of morpho-structural elements in the entire basin is followed by a kinematic interpretation that distinguished between two main processes sculpting the seabed from bottom and top: salt tectonics and sediment transport. We show that the contractional domain related to salt tectonics is far more complex than previously thought. Ridges, previously interpreted as contractional folds are, in fact, surficial undulations of the seabed reminiscent of sediment waves. Moreover, other folds previously interpreted as downdip contraction of the westward gliding Plio-Quaternary section are, in some parts of the basin, caused by updip climbing of this section eastwards as a result of the regional pattern of salt flow away from the Nile Cone. In the context of sediment transport, we show that the northern Sinai continental slope is covered by a dense net of turbidite channels, whereas the Levant slope has no channels at all. Particularly interesting is the Levant Turbidite Channel, described and named here for the first time. This feature begins at the southeastern corner of the Mediterranean at water depths of ~1100 m, continues along the valley between the Sinai and Levant slopes, and reaches the deepest part of the basin, in water depths of ~2500 m, northeast of the Eratosthenes seamount. However, this prominent feature cannot be explained by the current drainage, consisting of two minor rivers that enter the basin at that point, and thus most likely reflects periods of wetter climate and/or lower sea-level, when these rivers were more active and possibly connected to the submarine channel system.

Late Cretaceous infant intra-oceanic arc volcanism, the Central Pontides, Turkey: Petrogenetic and tectonic implications

NASA Astrophysics Data System (ADS)

Aygül, Mesut; Okay, Aral I.; Oberhänsli, Roland; Schmidt, Alexander; Sudo, Masafumi

2015-11-01

A tectonic slice of an arc sequence consisting of low-grade metavolcanic rocks and overlying metasedimentary succession is exposed in the Central Pontides north of the İzmir-Ankara-Erzincan suture separating Laurasia from Gondwana-derived terranes. The metavolcanic rocks mainly consist of basaltic andesite/andesite and mafic cognate xenolith-bearing rhyolite with their pyroclastic equivalents, which are interbedded with recrystallized pelagic limestone and chert. The metasedimentary succession comprises recrystallized micritic limestone with rare volcanogenic metaclastic rocks and stratigraphically overlies the metavolcanic rocks. The geochemistry of the metavolcanic rocks indicates an arc setting evidenced by depletion of HFSE (Ti, P and Nb) and enrichment of fluid mobile LILE. Identical trace and rare earth elements compositions of basaltic andesites/andesites and rhyolites suggest that they are cogenetic and derived from a common parental magma. The arc sequence crops out between an Albian-Turonian subduction-accretionary complex representing the Laurasian active margin and an ophiolitic mélange. Absence of continent derived detritus in the arc sequence and its tectonic setting in a wide Cretaceous accretionary complex suggest that the Kösdağ Arc was intra-oceanic. Zircons from two metarhyolite samples give Late Cretaceous (93.8 ± 1.9 and 94.4 ± 1.9 Ma) U/Pb ages. These ages are the same as the age of the supra-subduction ophiolites in western Turkey, which implies that that the Kösdağ Arc may represent part of the incipient arc formed during the generation of the supra-subduction ophiolites. The low-grade regional metamorphism in the Kösdağ Arc is constrained to 69.9 ± 0.4 Ma by 40Ar/39Ar muscovite dating indicating that the arc sequence became part of a wide Tethyan Cretaceous accretionary complex by the latest Cretaceous. Non-collisional cessation of the arc volcanism is possibly associated with southward migration of the magmatism as in the Izu-Bonin-Mariana arc system.

3D geodynamic models for the development of opposing continental subduction zones: The Hindu Kush-Pamir example

NASA Astrophysics Data System (ADS)

Liao, Jie; Gerya, Taras; Thielmann, Marcel; Webb, A. Alexander G.; Kufner, Sofia-Katerina; Yin, An

2017-12-01

The development of opposing continental subduction zones remains scantly explored in three dimensions. The Hindu Kush-Pamir orogenic system at the western end of the Himalayan orogen provides a rare example of continental collision linked to two opposing intra-continental subduction zones. The subducted plates feature a peculiar 3D geometry consisting of two distinct lithospheric fragments with different polarities, subduction angles and slab-curvatures beneath the Hindu Kush and Pamir, respectively. Using 3D geodynamic modeling, we simulate possible development of two opposing continental subduction zones to understand the dynamic evolution of the Hindu Kush-Pamir orogenic system. Our geodynamic model reproduces the major tectonic elements observed: (1) the deeper subduction depth, the steeper dip angle and the southward offset of the Hindu Kush subduction zone relative to the Pamir naturally occur if convergence direction of the subducting Indian plate and dip-direction of the Hindu Kush subduction zone match. (2) The formation of the highly asymmetrically curved Pamir region and the south-dipping subduction is promoted by the initial geometry of the indenting Indian lithosphere together with the existence of a major strike-slip fault on the eastern margin of the Pamir region. (3) Subduction of only the lower continental crust during continental collision can occur if the coupling between upper and lower crusts is weak enough to allow a separation of these two components, and that (4) the subduction of mainly lower crust then facilitates that conditions for intermediate-depth seismicity can be reached. (5) The secondary tectonic features modeled here such as strike-slip-fault growth, north-northwest striking extension zone, and lateral flow of the thickened ductile upper crust are comparable to the current tectonics of the region. (6) Model results are further compared to the potentially similar orogenic system, i.e., the Alpine orogen, in terms of the curved Western Alpine arc and the two opposing subducted slabs beneath the Alps and the Dinarides.

The Role of Wrench Tectonics In The Neogene-quaternary Evolution of The Western Hyblean Plateau (sicily)

NASA Astrophysics Data System (ADS)

Mattina, D.

This study focussed on the kinematics and temporal variations of neotectonic-to-active structures on the margin of the Southern Apennines thrust front. The border between the thrustbelt contractional terranes and continental plateau hosts a number of strike- slip and, secondarily, normal structures of still disputed geometry. Based on newly- acquired data, this research opened new issues with respect to present-day kinematics of these fault systems, suggesting a new interpretation for the tectonic mechanisms underpinning the Hyblean plateau. Given its geodynamic environs, the present-day structural configuration of this plateau reflects a long tectonic history involving both intraplate extension and plate margin deformation. As a consequence, the platform area has been dominated by a complex interplay between extensional, compressional and strike-slip tectonics, expressed by subvertical faults that can be brokendown into two main trends: NE-SW and NNE- SSW. Fieldwork, integrated by interpretation of aerial photos and SPOT images, con- tributed to constrain and enhance a structural model of the region. The main NNE- SSW fault system (Scicli - Ragusa - Giarratana) is well exposed in the western part of the Hyblean plateau, called Ragusa Platform. This is an important structural feature which affects all domains present here and is characterised by vertical slip rates with a lateral component of motion. Structural analysis was primarily concentrated in this zone. Notably, a large set of structural elements, associated with a principal rigth-lateral NNE-SSW and NE-SW fault zone, was documented in the area and local transpressive elements, associated with these faults, are shown on the basis of their morphological evidence. A large bending and elevated area characterises the northern edge of the Ragusa platform and unveils the presence of several N-S striking reverse faults, with dextral lateral component of movement, and anticlinal folds. The detailed meso-structural analysis conducted on the Ragusa platform revealed the presence of non-coaxial compressive deformations, which in turn generated folds, re- verse faults and rare thrusts, involving the Upper Miocene - Lower Pleistocene de- posits. The structural analysis was conducted at the 1:25.000 scale, using the dis- persion of bedding data to define the orientation of the main structures. These data display a certain scattering but nevertheless allow to recognise a common trend; the 1 main fold system is characterised by structures trending~N-S. Subordinately, another set of folds is present; these are less developed and continuous than the previous sys- tem, forming fold with an average trend of about N 140E. The scattering of these structures is summarized in the structural model developed, including diagrams of some meso-folds recognized in the field. The presence of reverse faults is interpreted as flower structures and push-up systems which developed in a transpressive stress regime. In order to devise a tectonic model of the Hyblean plateau, the structural dataset was supplemented with a comparative morphological analysis, as revealed by fieldwork, satellite images, aerial photos and topographic data. Drainage network has been thor- oughly ascertained. In the case that the preferential directions of rivers were statisti- cally significant and different from those expected from non-structural controls (e.g. topographic and geographic trend), they were deemed to be a diagnostic tool to iden- tify the deformation system. This is based on the assumption of a strict structural control on the local hydrographic network and its evolution. The close relationship between the structural and morphological features underline the recent activity of the main fault trends. This study indicates that widespread occurrence of folds and reverse faulting can be ascribed to the transpressive regime, as a consequence of regional active wrenching capable of generating push-up and positive flower structures. Consequently, transform systems and brittle/ductile deformation is herewith envisaged to pertain to a single ma- jor deformation event. Within the central Mediterranean framework, the Scicli shear zone represents the on-shore strand of a major dextral transform system, documented off-shore to be the triggering mechanism responsible for the opening of the Sicily Strait. Such system also splits the western and eastern sectors of the Hyblean plateau, as indicated by differing kinematic evolutions. Present-day opening of the Pantelleria Rift, connected to a NE-SW extensional axis (Illies etl., 1981; Finetti et al., 1982; Boccaletti et al., 1987), activated the NNE trans- form system, whose on-shore expressions are highlighted by Scicli and Chiaramonte structures. Inception of activity for these fault systems is synchronous with the one characterizing the Rift (5 Ma; Ben-Avraham et al., 1991). Such line of evidence would enable to substantiate the Plio-Pleistocene shear mechanisms documented along these faults, indicating its viability within a regional stress field. Its likely s1, triggering con- traction at the plate boundary and causative of the rifting transtensional regime, would therefore be oriented NW-SE. 2

The Role of Tectonic Stress in Triggering Large Silicic Caldera Eruptions

NASA Astrophysics Data System (ADS)

Cabaniss, Haley E.; Gregg, Patricia M.; Grosfils, Eric B.

2018-05-01

We utilize 3-D temperature-dependent viscoelastic finite element models to investigate the mechanical response of the host rock supporting large caldera-size magma reservoirs (volumes >102 km3) to local tectonic stresses. The mechanical stability of the host rock is used to determine the maximum predicted repose intervals and magma flux rates that systems may experience before successive eruption is triggered. Numerical results indicate that regional extension decreases the stability of the roof rock overlying a magma reservoir, thereby promoting early-onset caldera collapse. Alternatively, moderate amounts of compression (≤10 mm/year) on relatively short timescales (<104 years) increases roof rock stability. In addition to quantifying the affect of tectonic stresses on reservoir stability, our models indicate that the process of rejuvenation and mechanical failure is likely to take place over short time periods of hundreds to thousands of years. These findings support the short preeruption melt accumulation timescales indicated by U series disequilibrium studies.

Plate tectonics 2.5 billion years ago: evidence at kolar, South India.

PubMed

Krogstad, E J; Balakrishnan, S; Mukhopadhyay, D K; Rajamani, V; Hanson, G N

1989-03-10

The Archean Kolar Schist Belt, south India, is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources. The amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago (Ma) along a zone marked by the Kolar Schist Belt. This history of accretion of discrete crustal terranes resembles those of Phanerozoic convergent margins and thus suggests that plate tectonics operated on Earth by 2500 Ma.

Plate tectonics 2.5 billion years ago - Evidence at Kolar, south India

NASA Technical Reports Server (NTRS)

Krogstad, E. J.; Hanson, G. N.; Balakrishnan, S.; Rajamani, V.; Mukhopadhyay, D. K.

1989-01-01

The Archean Kolar Schist Belt, south India, is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accreted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics suggesting that their volcanic protoliths were derived from different mantle sources. The amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago (Ma) along a zone marked by the Kolar Schist Belt. This history of accretion of discrete crustal terranes resembles those of Phanerozoic convergent margins and thus suggests that plate tectonics operated on earth by 2500 Ma.

Seismic evidence for change of the tectonic regime in Messinian, northern Marmara Sea, Turkey

NASA Astrophysics Data System (ADS)

Alp, Hakan; Vardar, Denizhan; Alpar, Bedri; Ustaömer, Timur

2018-01-01

New Chirp seismic data collected from the northern margin of the Marmara Sea in June 2015 and previous Sparker seismic profiles recorded in 1999 suggest a change in tectonic regime in Messinian. New tectonic lineaments and fault segments were detected at offshore the Çekmece lagoons region that is located on one of the possible water corridors with the Paratethys. The faults only affect the older seismic unit (U1), which can be best outlined on the Chirp data. The E-W trending fault offshore Avcılar (OAF) borders the northern edge of a tightly folded sedimentary zone. The NNE-SSW trending fault, namely the Büyükçekmece Fault (BF), passing through the Büyükçekmece Bay, follows a buried valley. Its evolution must be related to the development of the Early Miocene - Early Pliocene Thrace-Eskişehir fault zone (TEFZ). BF and OAF indicate old tectonic activities in the region, which continued to the North Anatolian fault becoming the most dominant tectonic element in the region. The upper surface of the stratigraphic unit U1 and its terraces define the thickness of younger deposits (U2), which is thinner in the middle of the shelf. The morphology of the tightly folded zone controls those terraces, which correspond to the Bakırköy Formation and Kıraç member on land. The topmost parts of the terraces must have been eroded during sea level low-stands and cutting of the paleo-valleys. There is no evidence of any tectonic deformation or active fault in the younger seismic unit (U2).

An explicit plate kinematic model for the orogeny in the southern Uralides

NASA Astrophysics Data System (ADS)

Görz, Ines; Hielscher, Peggy

2010-10-01

The Palaeozoic Uralides formed in a three plate constellation between Europe, Siberia and Kazakhstan-Tarim. Starting from the first plate tectonic concepts, it was controversially discussed, whether the Uralide orogeny was the result of a relative plate motion between Europe and Siberia or between Europe and Kazakhstan. In this study, we use a new approach to address this problem. We perform a structural analysis on the sphere, reconstruct the positions of the Euler poles of the relative plate rotation Siberia-Europe and Tarim-Europe and describe Uralide structures by their relation to small circles about the two Euler poles. Using this method, changes in the strike of tectonic elements that are caused by the spherical geometry of the Earth's surface are eliminated and structures that are compatible with one of the relative plate motions can be identified. We show that only two Euler poles controlled the Palaeozoic tectonic evolution in the whole West Siberian region, but that they acted diachronously in different regions. We provide an explicit model describing the tectonism in West Siberia by an Euler pole, a sense of rotation and an approximate rotation angle. In the southern Uralides, Devonian structures resulted from a plate rotation of Siberia with respect to Europe, while the Permian structures were caused by a relative plate motion of Kazakhstan-Tarim with respect to Europe. The tectonic pause in the Carboniferous period correlates with a reorganization of the plate kinematics.

Provenance, tectonic setting and source-area weathering of the lower Cambrian sediments of the Parahio valley in the Spiti basin, India

NASA Astrophysics Data System (ADS)

Pandey, Shivani; Parcha, Suraj K.

2017-03-01

The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K2O/Al2O3 ratio and positive correlation of Co ( r=0.85), Ni ( r=0.86), Zn ( r=0.82), Rb ( r=0.98) with K2O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K2O/Na2O] vs. SiO2; [SiO2/Al2O3] vs. log[K2O/Na2O]; [SiO2/20] - [K2O+Na2O] - [TiO2+Fe2O3+MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A-CN-K diagram indicates that these sediments were generated from source rocks of the upper continental crust.

Morphotectonics of the Jamini River basin, Bundelkhand Craton, Central India; using remote sensing and GIS technique

NASA Astrophysics Data System (ADS)

Prakash, K.; Mohanty, T.; Pati, J. K.; Singh, S.; Chaubey, K.

2017-11-01

Morphological and morphotectonic analyses have been used to obtain information that influence hydrographic basins, predominantly these are modifications of tectonic elements and the quantitative description of landforms. Discrimination of morphotectonic indices of active tectonics of the Jamini river basin consists the analyses of asymmetry factor, ruggedness number, basin relief, gradient, basin elongation ratio, drainage density analysis, and drainage pattern analysis, which have been completed for each drainage basin using remote sensing and GIS techniques. The Jamini river is one of the major tributaries of the Betwa river in central India. The Jamini river basin is divided into five subwatersheds viz. Jamrar, Onri, Sainam, Shahzad and Baragl subwatershed. The quantitative approach of watershed development of the Jamini river basin, and its four sixth (SW1-SW4) and one fifth (SW5) order subwatersheds, was carried out using Survey of India toposheets (parts of 54I, 54K, 54L, 54O, and 54P), Landsat 7 ETM+, ASTER (GDEM) data, and field data. The Jamini river has low bifurcation index which is a positive marker of tectonic imprint on the hydrographic network. The analyses show that the geomorphological progression of the study area was robustly influenced by tectonics. The analysis demonstrates to extensional tectonics system with the following alignments: NE-SW, NW-SE, NNE-SSW, ENE-WSW, E-W, and N-S. Three major trends are followed by lower order streams viz. NE-SW, NW-SE, and E-W directions which advocate that these tectonic trends were active at least up to the Late Pleistocene. The assessment of morphotectonic indices may be used to evaluate the control of active faults on the hydrographic system. The analysis points out westward tilting of the drainage basins with strong asymmetry in some reaches, marked elongation ratio of subwatersheds, and lower order streams having close alignment with lineaments (active faults). The study facilitated to considerate the function of active tectonism in the advancement of the basin.

Accessory mineral records of tectonic environments? (Invited)

NASA Astrophysics Data System (ADS)

Storey, C.; Marschall, H. R.; Enea, F.; Taylor, J.; Jennings, E. S.

2010-12-01

Accessory mineral research continues to gather momentum as we seek to unleash their full potential. It is now widely recognised that robust accessory minerals, such as zircon, rutile, titanite, allanite and monazite, are archives of important trace elements that can help deduce metamorphic reaction history in metapelites, metabasites and other rock types. Moreover, they are important carriers of certain trace elements and govern or influence the products of partial melting and of fluid-rock interaction (e.g. magmas and mineralisation) in settings like subduction zones and hydrothermal systems. Perhaps most importantly, they can often be dated using the U-Th-Pb system. More recently, radiogenic (Lu-Hf, Sm-Nd, Rb-Sr) and stable (O) isotope systems have been applied and have further pushed the utility of accessory mineral research. In this talk I will discuss some of these advances towards one particular aim: the use of detrital accessory minerals for fingerprinting tectonic environments. This is a particularly laudable aim in Precambrian rocks, for which the preservation potential of orogenic belts and fossil subduction zones and their diagnostic metamorphic rocks is low. The implication is that our understanding of plate tectonics, particularly in the Archaean, is biased by the preserved in-tact rock record. An analogy is that Jack Hills zircons record evidence of Earth’s crust some 400 Ma before the preserved rock record begins. I will focus on some recent advances and new data from rutile and also the mineral inclusion record within zircon, which shows great promise for petrologic interpretation.

Geomorphology of the Iberian Continental Margin

NASA Astrophysics Data System (ADS)

Maestro, Adolfo; López-Martínez, Jerónimo; Llave, Estefanía; Bohoyo, Fernando; Acosta, Juan; Hernández-Molina, F. Javier; Muñoz, Araceli; Jané, Gloria

2013-08-01

The submarine features and processes around the Iberian Peninsula are the result of a complex and diverse geological and oceanographical setting. This paper presents an overview of the seafloor geomorphology of the Iberian Continental Margin and the adjacent abyssal plains. The study covers an area of approximately 2.3 million km2, including a 50 to 400 km wide band adjacent to the coastline. The main morphological characteristics of the seafloor features on the Iberian continental shelf, continental slope, continental rise and the surrounding abyssal plains are described. Individual seafloor features existing on the Iberian Margin have been classified into three main groups according to their origin: tectonic and/or volcanic, depositional and erosional. Major depositional and erosional features around the Iberian Margin developed in late Pleistocene-Holocene times and have been controlled by tectonic movements and eustatic fluctuations. The distribution of the geomorphological features is discussed in relation to their genetic processes and the evolution of the margin. The prevalence of one or several specific processes in certain areas reflects the dominant morphotectonic and oceanographic controlling factors. Sedimentary processes and the resulting depositional products are dominant on the Valencia-Catalán Margin and in the northern part of the Balearic Promontory. Strong tectonic control is observed in the geomorphology of the Betic and the Gulf of Cádiz margins. The role of bottom currents is especially evident throughout the Iberian Margin. The Galicia, Portuguese and Cantabrian margins show a predominance of erosional features and tectonically-controlled linear features related to faults.

Sequence and petrogenesis of the Jurassic volcanic rocks (Yeba Formation) in the Gangdese arc, southern Tibet: Implications for the Neo-Tethyan subduction

NASA Astrophysics Data System (ADS)

Liu, Zhi-Chao; Ding, Lin; Zhang, Li-Yun; Wang, Chao; Qiu, Zhi-Li; Wang, Jian-Gang; Shen, Xiao-Li; Deng, Xiao-Qin

2018-07-01

The Yeba Formation volcanic rocks in the Gangdese arc recorded important information regarding the early history of the Neo-Tethyan subduction. To explore their magmatic evolution and tectonic significance, we performed a systematic petrological, geochronological and geochemical study on these volcanic rocks. Our data indicated that the Yeba Formation documents a transition from andesite-dominated volcanism (which started before 182 Ma and continued until 176 Ma) to bimodal volcanism ( 174-168 Ma) in the earliest Middle Jurassic. The early-stage andesite-dominated volcanics are characterized by various features of major and trace elements and are interpreted as the products of interactions between mantle-derived arc magmas and lower crustal melts. Their positive εNd(t) and εHf(t) values suggest a significant contribution of asthenosphere-like mantle. The late-stage bimodal volcanism is dominated by felsic rocks with subordinate basalts. Geochemical signatures of the basalts indicate a composite magma source that included a "subduction component", an asthenosphere-like upper mantle domain and an ancient subcontinental lithospheric mantle component. The felsic rocks of the late stage were produced mainly by the melting of juvenile crust, with some ancient crustal materials also involved. We suggest that the occurrence and preservation of the Yeba Formation volcanic rocks were tied to a tectonic switch from contraction to extension in the Gangdese arc, which probably resulted from slab rollback of the subducting Neo-Tethyan oceanic slab during the Jurassic.

Characterization of Stream Channel Evolution Due to Extensional Tectonics Along the Western Margin of North Boulder Basin (Bull Mountain), SW Montana with the Use of Geologic Mapping and Thermochronologic (U-Th/He) Dating.

NASA Astrophysics Data System (ADS)

Cataldo, K.; Douglas, B. J.; Yanites, B.

2017-12-01

Landscape response to active tectonics, such as fault motion or regional uplift, can be recorded in river profiles as changes in slope (i.e. knickpoints) or topography. North Boulder basin region (SW Montana), experienced two separate phases of extension, from 45 - 35 Ma and again beginning 14 Ma to the present, producing basin-and-range style fault-blocks. Focusing on the Bull Mountain region, located on the western margin of the North Boulder basin, data is collected to test the hypothesis that Bull Mountain is located on the hanging wall of a half-graben. Our objective is to elucidate the active tectonics of the study area within a regional context by utilizing river profile analysis and thermochronometric data. High-resolution (< 5cm) river profile data is obtained from five of the main tributaries of Bull Mountain. Comprehensive geologic mapping along the main tributaries and topographic highs of the region allowed for the identification and measurement of knickpoints, composition of detailed lithologic descriptions, and analysis of key structural features. The absence of knickpoints within the four tributaries mapped on east Bull Mountain are consistent with a lack of tectonic activity. In contrast, Dearborn Creek, on western Bull Mountain, is located along an active normal fault and presents several knickpoints. Geologic mapping confirms that the primary lithologies of the region belong to the Elkhorn Mountain Volcanics. At lower elevations, there are massive plutonic intrusions of Quartz Monzonite and Diorite, both constituents of the Boulder batholith. These lithologies contain minerals suited for low-temperature thermochronology (U-Th/He) to constrain the timing of tectonic activity (i.e. uplift and exhumation) and erosion rates in the region. High-resolution stream profiles and a 10m DEM are used to delineate watersheds and produce steepness and concavity maps of major tributaries to investigate changes in slope or topography. The effects of extensional tectonic events can reshape drainage patterns of streams and their distribution of water, which is an important commodity in SW Montana for ranchers and farmers. Thus, the ability to discern the probability of recurring tectonic events and the effects on the regional watersheds, could help facilitate solutions before these events take place.

Basin deconstruction-construction: Seeking thermal-tectonic consistency through the integration of geochemical thermal indicators and seismic fault mechanical stratigraphy ​- Example from Faras Field, North Western Desert, Egypt

NASA Astrophysics Data System (ADS)

Pigott, John D.; Abouelresh, Mohamed O.

2016-02-01

To construct a model of a sedimentary basin's thermal tectonic history is first to deconstruct it: taking apart its geological elements, searching for its initial conditions, and then to reassemble the elements in the temporal order that the basin is assumed to have evolved. Two inherent difficulties implicit to the analysis are that most organic thermal indicators are cumulative, irreversible and a function of both temperature and time and the non-uniqueness of crustal strain histories which complicates tectonic interpretations. If the initial conditions (e.g. starting maturity of the reactants and initial crustal temperature) can be specified and the boundary conditions incrementally designated from changes in the lithospheric heat engine owing to stratigraphic structural constraints, then the number of pathways for the temporal evolution of a basin is greatly reduced. For this investigation, model input uncertainties are reduced through seeking a solution that iteratively integrates the geologically constrained tectonic subsidence, geochemically constrained thermal indicators, and geophysically constrained fault mechanical stratigraphy. The Faras oilfield in the Abu Gharadig Basin, North Western Desert, Egypt, provides an investigative example of such a basin's deconstructive procedure. Multiple episodes of crustal extension and shortening are apparent in the tectonic subsidence analyses which are constrained from the fault mechanical stratigraphy interpreted from reflection seismic profiles. The model was iterated with different thermal boundary conditions until outputs best fit the geochemical observations. In so doing, the thermal iterations demonstrate that general relationship that basin heat flow increases decrease vertical model maturity gradients, increases in surface temperatures shift vertical maturity gradients linearly to higher values, increases in sediment conductivities lower vertical maturities with depth, and the addition of ;ghost; layers (those layers removed) prior to the erosional event increase maturities beneath, and conversely. These integrated constraints upon the basin evolution model indicate that the principal source rocks, Khatatba and the lowest part of the Alam El Bueib formations, entered the oil window at approximately 95 Ma and the gas window at approximately 25 Ma. The upper part of the Alam El Bueib Formation is within the oil window at the present day. Establishing initial and boundary value conditions for a basin's thermal evolution when geovalidated by the integration of seismic fault mechanical stratigraphy, tectonic subsidence analysis, and organic geochemical maturity indicators provides a powerful tool for optimizing petroleum exploration in both mature and frontier basins.

Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique

NASA Astrophysics Data System (ADS)

Ibraimo, Daniel Luis; Larsen, Rune B.

2015-11-01

The Atchiza mafic and ultramafic-layered suite (hereafter, "Atchiza Suite) crops out in an area 330 km2 west of the Mozambican Tete province. In an early account of the geology of this intrusion, it was considered the continuation of the Great Dyke of Zimbabwe, an idea that was aborted after detailed studies. Nevertheless, the Ni concentrations in the Atchiza outcrop rocks are considerable. Our investigation used field evidence, hand specimens and petrography descriptions, mineral chemistry studies using electron microprobe analysis and tectonic analysis to arrive at a plausible mineralogical composition and understanding of the tectonic setting for the igneous evolution. The mineral composition from the Atchiza Suite indicates that these are cumulates. The magmatic segregation from the petrographic and mineral composition reasoning indicates that dunite-lherzolitic peridotite-olivine gabbro-gabbronorite-gabbro-pegmatitic gabbro is the rock formation sequence. Olivine and chromite were the first phases formed, followed by pyroxene and plagioclase. In addition, it is shown that these minerals are near-liquidus crystallization products of basaltic magma with olivine Fo: 87.06 in dunite, mean values of clinopyroxene are (Wo: 36.4, En: 48.0, Fs: 15.2), orthopyroxene (Wo: 2.95, En: 73.0, Fs: 24.2) and plagioclase An: 71.3, respectively. Opaque minerals comprise Fe-Ti oxides and (Fe, Cr) spinel up to 4.8 vol.%, but chromitite layers are not present. Most of the opaque minerals are interstitial to pyroxene. Sulphides are common in gabbros, with pyrrhotite, pentlandite, chalcopyrite, pyrite and covellite together comprising 0.4-2.0 vol.%. The whole rock Rare Earth Element (REE) concentrations are mainly a result of differentiation, but slight crustal contamination/assimilation contributed to the REE contents. In addition, they also show Eu enrichment, suggesting that plagioclase fractionation was important in the rock. The Atchiza Suite preserves a deep-seated plumbing system of the continental rift environment. The intrusion resulted from the emplacement of mafic magma in space created by extensional forces. Space was created through a connecting fault generated as a result of overall extensional, torsion and slab displacement in a rift system. The geometry of the body is tectonically controlled, and it agrees with the tectonic framework of the Zambezi Belt during the Rodinia breakup in the early Neoproterozoic.

Venus tectonic styles and crustal differentiation

NASA Technical Reports Server (NTRS)

Kaula, W. M.; Lenardic, A.

1992-01-01

Two of the most important constraints are known from Pioneer Venus data: the lack of a system of spreading rises, indicating distributed deformation rather than plate tectonics; and the high gravity/topography ratio, indicating the absence of an asthenosphere. In addition, the high depth/diameter ratios of craters on Venus indicate that Venus probably has no more crust than Earth. The problems of the character of tectonics and crustal formation and recycling are closely coupled. Venus appears to lack a recycling mechanism as effective as subduction, but may also have a low rate of crustal differentiation because of a mantle convection pattern that is more distributed, less concentrated, than Earth's. Distributed convection, coupled with the nonlinear dependence of volcanism on heat flow, would lead to much less magmatism, despite only moderately less heat flow, compared to Earth. The plausible reason for this difference in convective style is the absence of water in the upper mantle of Venus. We have applied finite element modeling to problems of the interaction of mantle convection and crust on Venus. The main emphasis has been on the tectonic evolution of Ishtar Terra, as the consequence of convergent mantle flow. The early stage evolution is primarily mechanical, with crust being piled up on the down-stream side. Then the downflow migrates away from the center. In the later stages, after more than 100 m.y., thermal effects develop due to the insulating influence of the thickened crust. An important feature of this modeling is the entrainment of some crustal material in downflows. An important general theme in both convergent and divergent flows is that of mixing vs. stratification. Models of multicomponent solid-state flow obtain that lower-density crustal material can be entrained and recycled, provided that the ration of low-density to high-density material is small enough (as in subducted slabs on Earth). The same considerations should apply in upflows; a small percent of partial melt may be carried along with its matrix and never escape to the surface. Models that assume melt automatically rising to the crust and no entrainment or other mechanism of recycling lower-density material obtain oscillatory behavior, because it takes a long time for heat to build up enough to overcome a Mg-rich low-density residuum. However, these models develop much thicker crust than consistent with estimates from crater depth/diameter ratios.

States of stress and slip partitioning in a continental scale strike-slip duplex: Tectonic and magmatic implications by means of finite element modeling

NASA Astrophysics Data System (ADS)

Iturrieta, Pablo Cristián; Hurtado, Daniel E.; Cembrano, José; Stanton-Yonge, Ashley

2017-09-01

Orogenic belts at oblique convergent subduction margins accommodate deformation in several trench-parallel domains, one of which is the magmatic arc, commonly regarded as taking up the margin-parallel, strike-slip component. However, the stress state and kinematics of volcanic arcs is more complex than usually recognized, involving first- and second-order faults with distinctive slip senses and mutual interaction. These are usually organized into regional scale strike-slip duplexes, associated with both long-term and short-term heterogeneous deformation and magmatic activity. This is the case of the 1100 km-long Liquiñe-Ofqui Fault System in the Southern Andes, made up of two overlapping margin-parallel master faults joined by several NE-striking second-order faults. We present a finite element model addressing the nature and spatial distribution of stress across and along the volcanic arc in the Southern Andes to understand slip partitioning and the connection between tectonics and magmatism, particularly during the interseismic phase of the subduction earthquake cycle. We correlate the dynamics of the strike-slip duplex with geological, seismic and magma transport evidence documented by previous work, showing consistency between the model and the inferred fault system behavior. Our results show that maximum principal stress orientations are heterogeneously distributed within the continental margin, ranging from 15° to 25° counter-clockwise (with respect to the convergence vector) in the master faults and 10-19° clockwise in the forearc and backarc domains. We calculate the stress tensor ellipticity, indicating simple shearing in the eastern master fault and transpressional stress in the western master fault. Subsidiary faults undergo transtensional-to-extensional stress states. The eastern master fault displays slip rates of 5 to 10 mm/yr, whereas the western and subsidiary faults show slips rates of 1 to 5 mm/yr. Our results endorse that favorably oriented subsidiary faults serve as magma pathways, particularly where they are close to the intersection with a master fault. Also, the slip of a fault segment is enhanced when an adjacent fault kinematics is superimposed on the regional tectonic loading. Hence, finite element models help to understand coupled tectonics and volcanic processes, demonstrating that geological and geophysical observations can be accounted for by a small number of key first order boundary conditions.

Application of laser ranging and VLBI data to a study of plate tectonic driving forces. [finite element method

NASA Technical Reports Server (NTRS)

Solomon, S. C.

1980-01-01

The measurability of changes in plate driving or resistive forces associated with plate boundary earthquakes by laser rangefinding or VLBI is considered with emphasis on those aspects of plate forces that can be characterized by such measurements. Topics covered include: (1) analytic solutions for two dimensional stress diffusion in a plate following earthquake faulting on a finite fault; (2) two dimensional finite-element solutions for the global state of stress at the Earth's surface for possible plate driving forces; and (3) finite-element solutions for three dimensional stress diffusion in a viscoelastic Earth following earthquake faulting.

Copernican tectonic activities in the northwestern Imbrium region of the Moon

NASA Astrophysics Data System (ADS)

Daket, Yuko; Yamaji, Atsushi; Sato, Katsushi

2015-04-01

Mare ridges and lobate scarps are the manifestations of horizontal compression in the shallow part of the Moon. Conventionally, tectonism within mascon basins has been thought to originate from mascon loading which is syndepositional tectonics (e.g., Solomon and Head, 1980). However, Ono et al. (2009) have pointed out that the subsurface tectonic structures beneath some mare ridges in Serenitatis appeared to be formed after the deposition of mare strata. Watters et al. (2010) also reported Copernican lobate scarps. Those young deformations cannot be explained by the mascon loading and are possibly ascribed to global cooling, orbital evolution and/or regional factors. Since mare ridges are topographically larger than lobate scarps, they might have large contribution to the recent contraction. In this study, we estimated until when the tectonic activities of mare ridges lasted in the northwestern Imbrium region. In order to infer the timing of the latest ages of tectonic activities, we used craters dislocated by the thrust faults that run along to the mare ridges in the study area. The ages of dislocated craters indicate the oldest estimate of the latest tectonic activity of the faults, because those craters must have existed during the tectonic activities. The ages of craters are inferred by the degradation levels classified by Trask (1971). We found ~450 dislocated craters in the study area. About 40 of them are smaller than 100 meter in diameter. Sub-hundred-meter-sized craters that still maintain their morphology sharp are classified into Copernican Period. Those small dislocated craters are interspersed all over the region, indicating that the most of the mare ridges in the study area were tectonically active in Copernican Period. In addition, we also found two sub-hundred-meter-sized craters dislocated by a graben at the west of Promontorium Laplace, indicating horizontal extension existed at Copernican Period. Consequently, tectonic activities in the study area lasted until recently. Those young tectonic activities are too young to be explained by mascon loading hypothesis. Tectonism induced by global cooling or orbital evolution are possible origins for the young horizontal compression. However, they cannot explain the recent extension. Our study area is located in PKT region where the heat-producing elements are more abundant than surrounding areas. Therefore, regional cooling would be a reasonable explanation for the young extensional tectonics. References Ono, T., A. Kumamoto, H. Nakagawa, Y. Yamaguchi, S. Oshigami, A. Yamaji, T. Kobayashi, Y. Kasahara, and H. Oya, 2009, Science, 323, 909--912. Solomon, S.C. and Head, J.W., 1980, Rev. Geophys., 18, 107--141. Trask, N.J., 1971, Geological Survey Research, U.S. Geol. Surv. Prof. Pap. 750-D, D138--D144. Watters, T.R., M.S. Robinson, M.E. Banks, T. Tran, and B.W. Denevi, 2012, Nature Geosci., 5, 181--185.

Unzipping of the volcano arc, Japan

USGS Publications Warehouse

Stern, R.J.; Smoot, N.C.; Rubin, M.

1984-01-01

A working hypothesis for the recent evolution of the southern Volcano Arc, Japan, is presented which calls upon a northward-progressing sundering of the arc in response to a northward-propagating back-arc basin extensional regime. This model appears to explain several localized and recent changes in the tectonic and magrnatic evolution of the Volcano Arc. Most important among these changes is the unusual composition of Iwo Jima volcanic rocks. This contrasts with normal arc tholeiites typical of the rest of the Izu-Volcano-Mariana and other primitive arcs in having alkaline tendencies, high concentrations of light REE and other incompatible elements, and relatively high silica contents. In spite of such fractionated characteristics, these lavas appear to be very early manifestations of a new volcanic and tectonic cycle in the southern Volcano Arc. These alkaline characteristics and indications of strong regional uplift are consistent with the recent development of an early stage of inter-arc basin rifting in the southern Volcano Arc. New bathymetric data are presented in support of this model which indicate: 1. (1) structural elements of the Mariana Trough extend north to the southern Volcano Arc. 2. (2) both the Mariana Trough and frontal arc shoal rapidly northwards as the Volcano Arc is approached. 3. (3) rugged bathymetry associated with the rifted Mariana Trough is replaced just south of Iwo Jima by the development of a huge dome (50-75 km diameter) centered around Iwo Jima. Such uplifted domes are the immediate precursors of rifts in other environments, and it appears that a similar situation may now exist in the southern Volcano Arc. The present distribution of unrifted Volcano Arc to the north and rifted Mariana Arc to the south is interpreted not as a stable tectonic configuration but as representing a tectonic "snapshot" of an arc in the process of being rifted to form a back-arc basin. ?? 1984.

Integration of remote sensing, geochemical and field data in the Qena-Safaga shear zone: Implications for structural evolution of the Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

El-Din, Gamal Kamal; Abdelkareem, Mohamed

2018-05-01

The Qena-Safaga shear zone (QSSZ) represents a significant structural characteristic in the Eastern Desert of Egypt. Remote Sensing, field and geochemical data were utilized in the present study. The results revealed that the QSSZ dominated by metamorphic complex (MC) that intruded by syn-tectonic granitoids. The low angle thrust fault brings calc-alkaline metavolcanics to overlie MC and its association. Subsequently, the area is dissected by strike-slip faults and the small elongated basins of Hammamat sediments of Precambrian were accumulated. The MC intruded by late-to post-tectonic granites (LPG) and Dokhan Volcanics which comprise felsic varieties forming distinctive columnar joints. Remote sensing analysis and field data revealed that major sub-vertical conspicuous strike-slip faults (SSF) including sinistral NW-SE and dextral ca. E-W shaped the study area. Various shear zones that accompanying the SSF are running NW-SE, NE-SW, E-W, N-S and ENE-WSW. The obtained shear sense presented a multiphase of deformation on each trend. i.e., the predominant NW-SE strike-slip fault trend started with sinistral displacement and is reactivated during later events to be right (dextral) strike slip cutting with dextral displacement the E-W trending faults; while NE-SW movements are cut by both the N-S and NNW - SSE trends. Remote sensing data revealed that the NW-SE direction that dominated the area is associated with hydrothermal alteration processes. This allowed modifying the major and trace elements of the highly deformed rocks that showed depletion in SiO2 and enrichments in Fe2O3, MnO, Al2O3, TiO2, Na2O, K2O, Cu, Zn and Pb contents. The geochemical signatures of major and trace elements revealed two types of granites including I-type calc-alkaline granites (late-to post-tectonic) that formed during an extensional regime. However, syn-tectonic granitoids are related to subduction-related environment.

Quantitative analysis of the tectonic subsidence in the Potiguar Basin (NE Brazil)

NASA Astrophysics Data System (ADS)

Lopes, Juliana A. G.; de Castro, David L.; Bertotti, Giovanni

2018-06-01

The Potiguar Basin, located in the Brazilian Equatorial Margin, evolved from a complex rifting process implemented during the Atlantic Ocean opening in the Jurassic/Cretaceous. Different driving mechanisms were responsible for the onset of an aborted onshore rift and an offshore rift that initiated crustal rupture and the formation of a continental transform margin. Therefore, we applied the backstripping method to quantify the tectonic subsidence during the rift and post-rift phases of Potiguar Basin formation and to analyze the spatial variation of subsidence during the two successive and distinct tectonic events responsible for the basin evolution. The parameters required to apply this methodology were extracted from 2D seismic lines and exploratory well data. The tectonic subsidence curves present periods with moderate subsidence rates (up to 300 m/My), which correspond to the evolution of the onshore Potiguar Rift (∼141 to 128 Ma). From 128-118 Ma, the tectonic subsidence curves show no subsidence in the onshore Potiguar Basin, whereas subsidence occurred at high rates (over 300 m/My) in the offshore rift. The post-rift phase began ca. 118 Ma (Aptian), when the tectonic subsidence drastically slowed to less than 35 m/My, probably related to thermal relaxation. The tectonic subsidence rates in the various sectors of the Potiguar Rift, during the different rift phases, indicate that more intense faulting occurred in the southern portion of the onshore rift, along the main border faults, and in the southeastern portion of the offshore rift. During the post-rift phase, the tectonic subsidence rates increased from the onshore portion towards the offshore portion until the continental slope. The highest rates of post-rift subsidence (up to 35 m/My) are concentrated in the central region of the offshore portion and may be related to lithospheric processes related to the continental crust rupture and oceanic seafloor spreading. The variation in subsidence rates and the pattern of tectonic subsidence curves allowed us to interpret the tectonic signature recorded by the sedimentary sequences of the Potiguar Basin during its evolution. In the onshore rift area, the tectonic subsidence curves presented subsidence rates up to 300 m/My during a long-term rift phase (13 Ma), which confirmed that this portion had an extensional tectonic regime. In the offshore rift, the curves presented high subsidence rates of over 300 m/My in a shorter period (5-10 My), typical of basins formed in a transtensional tectonic regime.

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

Thermal Evolution of the Earth from a Plate Tectonics Point of View

NASA Astrophysics Data System (ADS)

Grigne, C.; Combes, M.; Le Yaouanq, S.; Husson, L.; Conrad, C. P.; Tisseau, C.

2011-12-01

Earth's thermal history is classically studied using scaling laws that link the surface heat loss to the temperature and viscosity of the convecting mantle. When such a parameterization is used in the global heat budget of the Earth to integrate the mantle temperature backwards in time, a runaway increase of temperature is obtained, leading to the so-called "thermal catastrophe". We propose a new approach that does not rely on convective scaling laws but instead considers the dynamics of plate tectonics, including temperature-dependent surface processes. We use a multi-agent system to simulate time-dependent plate tectonics in a 2D cylindrical geometry with evolutive plate boundaries. Plate velocities are computed using local force balance and explicit parameterizations for plate boundary processes such as trench migration, subduction initiation, continental breakup and plate suturing. The number of plates is not imposed but emerges naturally. At a given time step, heat flux is integrated from the seafloor age distribution and a global heat budget is used to compute the evolution of mantle temperature. This approach has a very low computational cost and allows us to study the effect of a wide range of input parameters on the long-term thermal evolution of the system. For Earth-like parameters, an average cooling rate of 60-70K per billion years is obtained, which is consistent with petrological and rheological constraints. Two time scales arise in the evolution of the heat flux: a linear long-term decrease and high-amplitude short-term fluctuations due to tectonic rearrangements. We show that the viscosity of the mantle is not a key parameter in the thermal evolution of the system and that no thermal catastrophe occurs when considering tectonic processes. The cooling rate of the Earth depends mainly on its ability to replace old insulating seafloor by young thin oceanic lithosphere. Therefore, the main controlling factors are parameters such as the resistance of continental lithosphere to breakup or the critical age for subduction initiation. We infer that simple convective considerations alone cannot account for the complex nature of mantle heat loss and that tectonic processes dictate the thermal evolution of the Earth.

Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times.

PubMed

Bernardini, Federico; Vinci, Giacomo; Forte, Emanuele; Furlani, Stefano; Pipan, Michele; Biolchi, Sara; De Min, Angelo; Fragiacomo, Andrea; Micheli, Roberto; Ventura, Paola; Tuniz, Claudio

2018-01-01

Sinkholes are a well-known geologic hazard but their past occurrence, useful for subsidence risk prediction, is difficult to define, especially for ancient historic times. Consequently, our knowledge about Holocene carbonate landscapes is often limited. A multidisciplinary study of Trieste Karst (Italy), close to early Roman military fortifications, led to the identification of possible ancient road tracks, cut by at least one sinkhole. Electrical Resistivity Tomography through the sinkhole has suggested the presence of a cave below its bottom, possibly responsible of the sinkhole formation, while Ground Penetrating Radar has detected no tectonic disturbances underneath the tracks. Additionally, archaeological surveys led to the discovery of over 200 Roman shoe hobnails within or close to the investigated route. According to these data, the tracks are interpreted as the remains of a main Roman road, whose itinerary has been reconstructed for more than 4 km together with other elements of ancient landscape. Our results provide the first known evidence of a Roman main road swallowed by sinkholes and suggest that Holocene karst landscapes could be much different from what previously believed. In fact, sinkholes visible nowadays in the investigated region could have been flat areas filled by sediments up to the Roman time.

Crustal deformations in the Central Mediterranean derived from the WHAT A CAT GPS project.

NASA Astrophysics Data System (ADS)

Kaniuth, K.; Drewes, H.; Stuber, K.; Tremel, H.; Kahler, H.-G.; Peter, Y.; Zerbini, S.; Tonti, G.; Veis, G.; Fagard, H.

1999-03-01

The West Hellenic Arc Tectonics and Calabrian Arc Tectonics (WHAT A CAT) project aimes at monitoring crustal deformations in the Central Mediterranean by repeated GPS campaigns. The data set acquired so far is rather heterogeneous in terms of availability of GPS satellites, performance of the involved receiver systems and quality of the satellites' orbits. The paper presents the velocity estimates achieved using a modified version of the Bernese GPS software. Main characteristic of the solution strategy is the definition of station velocity parameters already on theobservation equation level.

Calculation of Tectonic Strain Release from an Explosion in a Three-Dimensional Stress Field

NASA Astrophysics Data System (ADS)

Stevens, J. L.; O'Brien, M. S.

2012-12-01

We have developed a 3D nonlinear finite element code designed for calculation of explosions in 3D heterogeneous media and have incorporated the capability to perform explosion calculations in a prestressed medium. The effect of tectonic prestress on explosion-generated surface waves has been discussed since the 1960's. In most of these studies tectonic release was described as superposition of a tectonic source modeled as a double couple, multipole or moment tensor, plus a point explosion source. The size of the tectonic source was determined by comparison with the observed Love waves and the Rayleigh wave radiation pattern. Day et al. (1987) first attempted to perform numerical modeling of tectonic release through an axisymmetric calculation of the explosion Piledriver. To the best of our knowledge no one has previously performed numerical calculations for an explosion in a three-dimensional stress field. Calculation of tectonic release depends on a realistic representation of the stress state in the earth. In general the vertical stress is equal to the overburden weight of the material above at any given point. The horizontal stresses may be larger or smaller than this value up to the point where failure due to frictional sliding relieves the stress. In our calculations, we use the normal overburden calculation to determine the vertical stress, and then modify the horizontal stresses to some fraction of the frictional limit. This is the initial stable state of the calculation prior to introduction of the explosion. Note that although the vertical stress is still equivalent to the overburden weight, the pressure is not, and it may be either increased or reduced by the tectonic stresses. Since material strength increases with pressure, this also can substantially affect the seismic source. In general, normal faulting regimes will amplify seismic signals, while reverse faulting regimes will decrease seismic signals; strike-slip regimes may do either. We performed a 3D calculation of the Shoal underground nuclear explosion including tectonic prestress. Shoal was a 12.5 kiloton nuclear explosion detonated near Fallon, Nevada. This event had strong heterogeneity in near field waveforms and is in a region under primarily extensional tectonic stress. There were three near-field shot level recording stations located in three directions each at about 590 meters from the shot. Including prestress consistent with the regional stress field causes variations in the calculated near-field waveforms similar to those observed in the Shoal data.

Differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes

USGS Publications Warehouse

Draut, Amy; Clift, Peter D.

2013-01-01

Records of ancient intraoceanic arc activity, now preserved in continental suture zones, are commonly used to reconstruct paleogeography and plate motion, and to understand how continental crust is formed, recycled, and maintained through time. However, interpreting tectonic and sedimentary records from ancient terranes after arc–continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others. In this synthesis we examine what is lost, and what is preserved, in the translation from modern processes to the ancient record of intraoceanic arcs. Composition of accreted arc terranes differs as a function of arc–continent collision geometry. ‘Forward-facing’ collision can accrete an oceanic arc on to either a passive or an active continental margin, with the arc facing the continent and colliding trench- and forearc-side first. In a ‘backward-facing’ collision, involving two subduction zones with similar polarity, the arc collides backarc-first with an active continental margin. The preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case. Preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision, rather than tectonic erosion. The prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent. Arc systems are most likely to undergo tectonic accretion shortly before forward-facing collision with a continent, and thus most forearc and accretionary-prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity, when sediment flux to the trench was greatest and tectonic accretion prevailed. Collision geometry and tectonic erosion vs. accretion are important controls on the ultimate survival of material from the trench, forearc, arc massif, intra-arc basins, and backarc basins, and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts, oblique plate convergence, and arc rifting. Forward-facing collision involves substantial recycling, melting, and fractionation of continent-derived material during and after collision, and so produces melts rich in silica and incompatible trace elements. As a result, forward-facing collision can drive the composition of accreted arc crust toward that of average continental crust.

The Stress-Strain State of Recent Structures in the Northeastern Sector of the Russian Arctic Region

NASA Astrophysics Data System (ADS)

Imaeva, L. P.; Imaev, V. S.; Mel'nikova, V. I.

2018-03-01

Complex research to determine the stress-strain state of the Earth's crust and the types of seismotectonic destruction for the northeastern sector of the Russian Arctic was conducted. The principles of regional ranking of neotectonic structures were developed according to the activity of geodynamic processes, and argumentation for their class differentiation is presented. The structural-tectonic position, the parameters of the deep structure, the system of active faults, and the tectonic stress fields, calculated on the basis of both tectonophysical analysis of discontinuous and folded late Cenozoic deformations and seismological data, were analyzed. This complex of investigations made it possible to determine the directions of the main axes of deformations of the stress-strain state of the Earth's crust and to reveal the regularity in the change of tectonic regimes.

Petrogenesis of Jurassic granitoids at the northeastern margin of the North China Craton: New geochemical and geochronological constraints on subduction of the Paleo-Pacific Plate

NASA Astrophysics Data System (ADS)

Liu, Jin; Zhang, Jian; Liu, Zhenghong; Yin, Changqing; Zhao, Chen; Peng, Youbo

2018-06-01

At the junction between the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB), northern Liaoning province, NE China, there are widespread Jurassic igneous rocks. The tectonic setting and petrogenesis of these rocks are unresolved. Zircon U-Pb dating, whole-rock geochemistry, and Hf isotopic compositions of Jurassic granitoids were investigated to constrain their ages and petrogenesis in order to understand the tectonic evolution of the Paleo-Pacific Ocean along the northeastern margin of the NCC. Geochronological data indicate that magmatism occurred between the early and late Jurassic (180-156 Ma). Despite the wide range in ages of the intrusions, Jurassic granitoids were likely derived from a similar or common source, as inferred from their geochemical and Hf isotopic characteristics. Compared to the island arc andesite-dacite-rhyolite series, the Jurassic granitoids are characterized by higher SiO2, Al2O3, and Sr contents, and lower MgO, FeOT, Y, and Yb contents, indicating that the primary magmas show typical characteristics of adakitic magmas derived from partial melting of thickened lower crust. These findings, combined with their εHf(t) values (+1.4 to +5.4) and two-stage model ages (1515-1165 Ma), indicate the primary magmas originated from partial melting of juvenile crustal material accreted during the Mesoproterozoic. They are enriched in large-ion lithophile elements (e.g., Rb, K, Th, Ba, and U) and light rare-earth elements (REE), and depleted in high-field-strength elements (e.g., Nb, Ta, Ti, and P) and heavy REE. Based on these findings and previous studies, we suggest that the Jurassic adakitic granitoids (180-156 Ma) were formed in an active continental margin and compressive tectonic setting, related to subduction of the Paleo-Pacific Plate.

Can tract element distributions reclaim tectonomagmatic facies of basalts in greenstone assemblages?

NASA Technical Reports Server (NTRS)

Butler, J. C.

1986-01-01

During the past two decades many words have been written both for and against the hypothesis that the tectonic setting of a suite of igneous rocks is retained by the chemical variability within the suite. For example, it is argued that diagrams can be constructed from modern/recent basalt subcompositions within the system Ti-Zr-Y-Nb-Sr such that tectonomagmatic settings can be reclaimed. If one accepts this conclusion, it is tempting to inquire as to how far this hypothesis can be extended into other petrological realms. If chemical variations of metabasalts retain information relating to their genesis (tectonic setting), for example, this would be most helpful in reconstructing the history of basalts from greenstone belts. A discussion follows.

Rare earth element patterns in Archean high-grade metasediments and their tectonic significance

NASA Technical Reports Server (NTRS)

Taylor, Stuart Ross; Rudnick, Roberta L.; Mclennan, Scott M.; Eriksson, Kenneth A.

1986-01-01

REE data on metasedimentary rocks from two different types of high-grade Archean terrains are presented and analyzed. The value of REEs as indicators of crustal evolution is explained; the three geologic settings (in North America, Southern Africa, and Australia) from which the samples were obtained are described; and the data are presented in extensive tables and graphs and discussed in terms of metamorphic effects, the role of accessory phases, provenance, and tectonic implications (recycling, the previous extent of high-grade terrains, and a model of Archean crustal growth). The diversity of REE patterns in shallow-shelf metasediments is attributed to local provenance, while the Eu-depleted post-Archean patterns are associated with K-rich plutons from small, stable early Archean terrains.

A PILOT SEARCH FOR EVIDENCE OF EXTRASOLAR EARTH-ANALOG PLATE TECTONICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jura, M.; Klein, B.; Xu, S.

Relative to calcium, both strontium and barium are markedly enriched in Earth's continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets,more » this search should be extended to additional targets.« less

Tectonics of the Scotia-Antarctica plate boundary constrained from seismic and seismological data

NASA Astrophysics Data System (ADS)

Civile, D.; Lodolo, E.; Vuan, A.; Loreto, M. F.

2012-07-01

The plate boundary between the Scotia and Antarctic plates runs along the broadly E-W trending South Scotia Ridge. It is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs. Seismic profiles and regional-scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern Scotia Sea, and focal solutions from recent earthquakes help to understand the present-day geodynamic setting. The northern edge of the western South Scotia Ridge is marked by a sub-vertical, left-lateral master fault. Locally, a narrow wedge of accreted sediments is present at the base of the slope. This segment represents the boundary between the Scotia plate and the independent South Shetland continental block. Along the northern margin of the South Orkney microcontinent, the largest fragment of the South Scotia Ridge, an accretionary prism is present at the base of the slope, which was possibly created by the eastward drift of the South Orkney microcontinent and the consequent subduction of the transitional crust present to the north. East of the South Orkney microcontinent, the physiography and structure of the plate boundary are less constrained. Here the tectonic regime exhibits mainly strike-slip behavior with some grade of extensional component, and the plate boundary is segmented by a series of NNW-SSE trending release zones which favored the fragmentation and dispersion of the crustal blocks. Seismic data have also identified, along the north-western edge of the South Scotia Ridge, an elevated region - the Ona Platform - which can be considered, along with the Terror Rise, as the conjugate margin of the Tierra del Fuego, before the Drake Passage opening. We propose here an evolutionary sketch for the plate boundary (from the Late Oligocene to the present) encompassing the segment from the Elephant Island platform to the Herdman Bank.

Rapid Ice Mass Loss: Does It Have an Influence on Earthquake Occurrence in Southern Alaska?

NASA Technical Reports Server (NTRS)

Sauber, Jeanne M.

2008-01-01

The glaciers of southern Alaska are extensive, and many of them have undergone gigatons of ice wastage on time scales on the order of the seismic cycle. Since the ice loss occurs directly above a shallow main thrust zone associated with subduction of the Pacific-Yakutat plate beneath continental Alaska, the region between the Malaspina and Bering Glaciers is an excellent test site for evaluating the importance of recent ice wastage on earthquake faulting potential. We demonstrate the influence of cumulative glacial mass loss following the 1899 Yakataga earthquake (M=8.1) by using a two dimensional finite element model with a simple representation of ice fluctuations to calculate the incremental stresses and change in the fault stability margin (FSM) along the main thrust zone (MTZ) and on the surface. Along the MTZ, our results indicate a decrease in FSM between 1899 and the 1979 St. Elias earthquake (M=7.4) of 0.2 - 1.2 MPa over an 80 km region between the coast and the 1979 aftershock zone; at the surface, the estimated FSM was larger but more localized to the lower reaches of glacial ablation zones. The ice-induced stresses were large enough, in theory, to promote the occurrence of shallow thrust earthquakes. To empirically test the influence of short-term ice fluctuations on fault stability, we compared the seismic rate from a reference background time period (1988-1992) against other time periods (1993-2006) with variable ice or tectonic change characteristics. We found that the frequency of small tectonic events in the Icy Bay region increased in 2002-2006 relative to the background seismic rate. We hypothesize that this was due to a significant increase in the rate of ice wastage in 2002-2006 instead of the M=7.9, 2002 Denali earthquake, located more than 100km away.

Continental crust formation on early Earth controlled by intrusive magmatism

NASA Astrophysics Data System (ADS)

Rozel, A. B.; Golabek, G. J.; Jain, C.; Tackley, P. J.; Gerya, T.

2017-05-01

The global geodynamic regime of early Earth, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean mantle temperature and more intense juvenile magmatism than in the present-day Earth, two crust-mantle interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the “Plutonic squishy lid” tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce Earth-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean Earth operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.

Continental crust formation on early Earth controlled by intrusive magmatism.

PubMed

Rozel, A B; Golabek, G J; Jain, C; Tackley, P J; Gerya, T

2017-05-18

The global geodynamic regime of early Earth, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean mantle temperature and more intense juvenile magmatism than in the present-day Earth, two crust-mantle interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the "Plutonic squishy lid" tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce Earth-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean Earth operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.

Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

NASA Astrophysics Data System (ADS)

Fernandes, A. J.; Amaral, G.

2002-03-01

In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo. The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map. The study area, during the Cenozoic, has been affected by five strike-slip tectonic events, which generated mainly strike-slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE-SW, E-W, NW-SE, N-S, and NNE-SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike-slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.

Relations between tectonics and sedimentation along the Eastern Sardinian margin (Western Tyrrhenian Sea) : from rifting to reactivation

NASA Astrophysics Data System (ADS)

Gaullier, Virginie; Chanier, Frank; Vendeville, Bruno; Lymer, Gaël; Maillard, Agnès; Thinon, Isabelle; Lofi, Johanna; Sage, Françoise; Giresse, Pierre; Bassetti, Maria-Angela

2014-05-01

The offshore-onshore project "METYSS-METYSAR" aims at better understand the Miocene-Pliocene relationships between crustal tectonics, salt tectonics, and sedimentation along the Eastern Sardinian margin, Western Tyrrhenian Sea. In this key-area, the Tyrrhenian back-arc basin underwent recent rifting (9-5 Ma), pro parte coeval with the Messinian Salinity Crisis (MSC, 5.96-5.33 Ma), sea-floor spreading starting during Pliocene times. Thereby, the Tyrrhenian basin and the Eastern Sardinian margin are excellent candidates for studying the mechanisms of extreme lithospheric stretching and thinning, the role of pre-existing structural fabric during and after rifting, and the reactivation of a passive margin and the associated deformation and sedimentation patterns during the MSC. We looked at the respective contributions of crustal and salt tectonics in quantifying vertical and horizontal movements, using especially the seismic markers of the MSC. Overall, we delineate the history of rifting and tectonic reactivation in the area. The distribution maps respectively of the Messinian Erosion Surface and of Messinian units (Upper Unit and Mobile Unit) show that a rifted basin already existed by Messinian time. This reveals a major pre-MSC rifting across the entire domain. Because salt tectonics can create fan-shaped geometries in sediments, syn-rift deposits have to be carefully re-examined in order to decipher the effects of crustal tectonics (rifting) and thin-skinned salt tectonics. Our data surprisingly show that there are no clues for Messinian syn-rift sediments along the East-Sardinia Basin and Cornaglia Terrace, hence no evidence for rifting after Late Tortonian times. Nevertheless, widespread deformation occurred during the Pliocene and can only be attributed to post-rift reactivation. This reactivation is characterized not only by normal faulting but also by contractional structures. Some Pliocene vertical movements caused localized gravity gliding of the mobile salt and its Late Messinian and Early Pliocene brittle overburden. "METYSAR" fieldwork onshore was conducted in the Orosei region and showed that the main present-day Cedrino river follows the trend of a paleo-valley that cuts through the underlying granitic basement and alterites. These deposits, along with the basement, were likely eroded during Messinian times, then reworked during a marine transgression. Micro-fauna in these fine-grained marine sediments are of Upper Pliocene age. The strata dip by 20° to 30° and trend NNE-SSW, a direction which is sub-parallel to the main tectonic structures involved in the rifting of the margin. The tilted Pliocene strata were overlain by volcanic flows, some dating from Upper Pliocene time. Field mapping has evidenced that there was a paleo-topographic relief, trending NNE-SSW, that controlled the sediment deposition. These results indicate that the post-Messinian tectonic activity, which is also visible offshore, controlled the sedimentary architecture and the paleogeography of this area. Onshore, there are signs of neither Lower-Pliocene marine deposits nor Gilbert deltas. The absence of such sedimentary edifices, which are characteristic of the Pliocene refilling of the Mediterranean basin are clues about significant post-rift vertical movements in the Tyrrhenian sea.

Numerical investigation of the triggering mechanisms of the Piz Dora sackung system (Val Mustair, Switzerland)

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Crosta, Giovanni B.; Zanchi, Andrea

2015-04-01

Deep-Seated Gravitational Slope Deformations (DSGSD) are widespread phenomena in alpine environments, where they affect entire high-relief valley flanks involving huge rock volumes. Slope scale inherited structures related to ductile and brittle tectonic deformation can control the onset and development of DSGSD and the localization of strain in deep gravitational shear zones. Slope unloading, rock mass damage and hydrological perturbations related to deglaciation are considered important triggers of these phenomena in formerly glaciated areas. Furthermore, earthquake shaking and the long-term effects of seismicity in active tectonic areas might provide an additional triggering component. Nevertheless, the role played by these different processes and their interplay is not obvious, especially in geological context less typically favourable to DSGSD and in low-magnitude seismicity settings as the axial European Alps. We analysed the Piz Dora sackung system (Val Mustair, Switzerland), which affects conglomerates, meta-conglomerates and phyllites of the Austroalpine S-Charl nappe, involved in a slope-scale, WNW trending closed anticline fold. The area is actively uplifting, seismically active (maximum Mw>5) and experienced extensive glaciation during the LGM. The slope is affected by sharp gravitational morphostructures associated to the deep-seated sliding of 1.85 km3 of rock along a basal shear zone up to 300 m deep (Agliardi et al., 2014; Barbarano et al., 2015). We investigated the controlling role of inherited tectonic features and the relative influence of different candidate triggering processes (post-glacial debuttressing, related changes in slope hydrology, seismicity) through a series of 2D Distinct Element (DEM) numerical models set up using the code UDEC (ItascaTM). Based on field structural and geomechanical data, we discretized the slope into an ensemble of discontinuum domains, accounting for the slope-scale folded structure and characterised by unique combinations of rock mass properties and persistent brittle structural patterns related to folding or regional stress fields. We analysed the processes leading to DSGSD onset and evolution by testing combinations of: a) rock mass constitutive models; b) in situ stress fields; c) hydro-mechanical coupling; d) dynamic loadings. DEM results, validated using field evidence and discussed against the results of continuum-based Finite-Element models (Agliardi et al., 2014; Barbarano et al., 2015), suggest that DSGSD failure mechanisms are constrained by fold-related brittle structures, and stress and hydrologic conditioning of deglaciation were key triggers modulated by active tectonic processes. References: - Agliardi F., Barbarano M., Crosta G.B., Riva F. & Zanchi A. (2014). Inherited and active tectonic controls on the Piz Dora sackung system (Val Mustair). In 3rd Slope Tectonic Conference proceedings, NGU Report 2014.030. - Barbarano M., Agliardi F., Crosta G. B., & Zanchi A. (2015). Inherited and Active Tectonic Controls on the Piz Dora DSGSD (Val Müstair, Switzerland). In Engineering Geology for Society and Territory-Volume 2 (pp. 605-608). Springer International Publishing.

Late Jurassic rhyolites from the Wuchagou region in the central Great Xing'an Range, NE China: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Ji, Zheng; Ge, Wen-Chun; Yang, Hao; Wang, Qing-hai; Zhang, Yan-long; Wang, Zhi-hui; Bi, Jun-Hui

2018-06-01

We report geochronological, whole-rock geochemical, and zircon Hf isotopic data for Late Jurassic rhyolites in the central Great Xing'an Range of northeastern China, to determine their petrogenesis, source, and tectonic setting. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb ages indicate that the rhyolites previously mapped as the lower Permian Dashizhai Formation in the Wuchagou region formed during the Late Jurassic (162-154 Ma). Geochemically, these rhyolites belong to the mid- to high-K calc-alkaline series and show peraluminous characteristics and consistent correlations between major elements and SiO2. They are characterized by enrichments in large ion lithophile elements (LILEs; e.g., Rb and K) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs). In situ Hf isotopic analyses of zircons from the rhyolites reveal relatively homogeneous Hf isotopic compositions, with εHf(t) values of +4.84 to +9.44, and two-stage model ages of 606-895 Ma. Based on their eruption ages, geochemical characteristics, and Hf isotopic compositions, we conclude that the magmas that formed the Late Jurassic rhyolites were produced during partial melting of a Neoproterozoic quartz-bearing amphibolite-facies mafic crust. These magmas subsequently underwent extensive fractional crystallization of plagioclase, hornblende, Ti-bearing phases, monazite, and apatite. Combined with previous data, our results demonstrate that the Late Jurassic volcanic rocks in the Great Xing'an Range were formed in a post-collisional extensional setting. The gravitational collapse of the orogenically thickened crust was caused by break-off of the subducted oceanic slab and upwelling of asthenosphere after closure of the Mongol-Okhotsk Ocean.

Modes of occurrence of mercury and other trace elements in coals from the warrior field, Black Warrior Basin, Northwestern Alabama

USGS Publications Warehouse

Diehl, S.F.; Goldhaber, M.B.; Hatch, J.R.

2004-01-01

The mineralogic residence and abundance of trace metals is an important environmental issue. Data from the USGS coal quality database show that potentially toxic elements, including Hg, As, Mo, Se, Cu, and Tl are enriched in a subset of coal samples in the Black Warrior Basin of Alabama, USA. Although the coal as-mined typically is low in these elements, localized enrichments occur in high-pyrite coals and near faults. Microscopic analyses demonstrate that the residence of these elements is dominantly in a late-stage pyrite associated with structurally disrupted coal. Further, our data suggest addition of Hg to the coal matrix as well. The source of these trace elements was hydrothermal fluids driven into the Black Warrior Basin by Alleghanian age tectonism. ?? 2004 Published by Elsevier B.V.

Late-Variscan Tectonic Inheritance and Salt Tectonics Interplay in the Central Lusitanian Basin

NASA Astrophysics Data System (ADS)

Nogueira, Carlos R.; Marques, Fernando O.

2017-04-01

Tectonic inheritance and salt structures can play an important role in the tectono-sedimentary evolution of basins. The Alpine regional stress field in west Iberia had a horizontal maximum compressive stress striking approximately NNW-SSE, related to the Late Miocene inversion event. However, this stress field cannot produce a great deal of the observed and mapped structures in the Lusitanian Basin. Moreover, many observed structures show a trend similar to well-known basement fault systems. The Central Lusitanian basin shows an interesting tectonic structure, the Montejunto structure, generally assigned to this inversion event. Therefore, special attention was paid to: (1) basement control of important observed structures; and (2) diapir tectonics (vertical maximum compressive stress), which can be responsible for significant vertical movements. Based on fieldwork, tectonic analysis and interpretation of geological maps (Portuguese Geological Survey, 1:50000 scale) and geophysical data, our work shows: (1) the Montejunto structure is a composite structure comprising an antiform with a curved hinge and middle Jurassic core, and bounding main faults; (2) the antiform can be divided into three main segments: (i) a northern segment with NNE-SSW trend showing W-dipping bedding bounded at the eastern border by a NNE-SSW striking fault, (ii) a curved central segment, showing the highest topography, with a middle Jurassic core and radial dipping bedding, (iii) a western segment with ENE-WSW trend comprising an antiform with a steeper northern limb and periclinal termination towards WSW, bounded to the south by ENE-WSW reverse faulting, (3) both fold and fault trends at the northern and western segments are parallel to well-known basement faults related to late-Variscan strike-slip systems with NNE-SSW and ENE-WSW trends; (4) given the orientation of Alpine maximum compressive stress, the northern segment border fault should be mostly sinistral strike-slip and the western segment border fault should be a pure thrust; (5) uplift along the northern and central segments may point out to the presence of a salt diapir at depth, aiding vertical movement and local uplift of the structure; (6) geometry of seismic units of the neighboring basins is consistent with halokinesis related to the antiform growth during the Jurassic; (7) sedimentary filling of the neighbouring basins shows relationship to antiform development and growth into a structural high before the Late Miocene Alpine event. These data suggest that: (1) pre-existing basement faults and their reactivation played important role on the development of Montejunto complex tectonic structure; (2) important vertical movements occurred as the result of regional and local (diapir) tectonics; (3) subsidence in neighbouring basins may have promoted maturation, and possible targets with strong potential for hydrocarbon trapping and accumulation may have also developed; (4) diapir tectonics initiated before the Cretaceous; (5) given the topography, and the geometry and inferred kinematics of all segments, it seems that the Montejunto structure formed in a restraining bend controlled by inherited late-Variscan basement faults.

A review of structural patterns and melting processes in the Archean craton of West Greenland: Evidence for crustal growth at convergent plate margins as opposed to non-uniformitarian models

NASA Astrophysics Data System (ADS)

Polat, Ali; Wang, Lu; Appel, Peter W. U.

2015-11-01

The Archean craton of West Greenland consists of many fault-bounded Eoarchean to Neoarchean tectonic terranes (crustal blocks). These tectonic terranes are composed mainly of tonalite-trondhjemite-granodiorite (TTG) gneisses, granitic gneisses, metavolcanic-dominated supracrustal belts, layered anorthositic complexes, and late- to post-tectonic granites. Rock assemblages and geochemical signatures in these terranes suggest that they represent fragments of dismembered oceanic island arcs, consisting mainly of TTG plutons, tholeiitic to calc-alkaline basalts, boninites, picrites, and cumulate layers of ultramafic rocks, gabbros, leucogabbros and anorthosites, with minor sedimentary rocks. The structural characteristics of the terrane boundaries are consistent with the assembly of these island arcs through modern style of horizontal tectonics, suggesting that the Archean craton of West Greenland grew at convergent plate margins. Several supracrustal belts that occur at or near the terrane boundaries are interpreted as relict accretionary prisms. The terranes display fold and thrust structures and contain numerous 10 cm to 20 m wide bifurcating, ductile shear zones that are characterized by a variety of structures including transposed and redistributed isoclinal folds. Geometrically these structures are similar to those occurring on regional scales, suggesting that the Archean craton of West Greenland can be interpreted as a continental scale accretionary complex, such as the Paleozoic Altaids. Melting of metavolcanic rocks during tectonic thickening in the arcs played an important role in the generation of TTGs. Non-uniformitarian models proposed for the origin of Archean terranes have no analogs in the geologic record and are inconsistent with structural, lithological, petrological and geochemical data collected from Archean terranes over the last four decades. The style of deformation and generation of felsic rocks on outcrop scales in the Archean craton of West Greenland and the Mesozoic Sulu orogenic belt of eastern China are similar, consistent with the formation of Archean continental crust by subduction zone processes.

Facies architecture of the fluvial Missão Velha Formation (Late Jurassic-Early Cretaceous), Araripe Basin, Northeast Brazil: paleogeographic and tectonic implications

NASA Astrophysics Data System (ADS)

Fambrini, Gelson Luís; Neumann, Virgínio Henrique M. L.; Menezes-Filho, José Acioli B.; Da Silva-Filho, Wellington F.; De Oliveira, Édison Vicente

2017-12-01

Sedimentological analysis of the Missão Velha Formation (Araripe Basin, northeast Brazil) is the aim of this paper through detailed facies analysis, architectural elements, depositional systems and paleocurrent data. The main facies recognized were: (i) coarse-grained conglomeratic sandstones, locally pebbly conglomerates, with abundant silicified fossil trunks and several large-to-medium trough cross-stratifications and predominantly lenticular geometry; (ii) lenticular coarse-to-medium sandstones with some granules, abundant silicified fossil wood, and large-to-medium trough cross-stratifications, cut-and fill features and mud drapes on the foresets of cross-strata, (iii) poorly sorted medium-grained sandstones with sparse pebbles and with horizontal stratification, (iv) fine to very fine silty sandstones, laminated, interlayered with (v) decimetric muddy layers with horizontal lamination and climbing-ripple cross-lamination. Nine architectural elements were recognized: CH: Channels, GB: Gravel bars and bed forms, SB: Sand bars and bedforms, SB (p): sand bedform with planar cross-stratification, OF: Overbank flow, DA: Downstream-accretion macroforms, LS: Laminated sandsheet, LA: Lateral-accretion macroforms and FF: Floodplain fines. The lithofacies types and facies associations were interpreted as having been generated by alluvial systems characterized by (i) high energy perennial braided river systems and (ii) ephemeral river systems. Aeolian sand dunes and sand sheets generated by the reworking of braided alluvial deposits can also occur. The paleocurrent measurements show a main dispersion pattern to S, SE and SW, and another to NE/E. These features imply a paleodrainage flowing into the basins of the Recôncavo-Tucano-Jatobá.

Hot-field tectonics

NASA Astrophysics Data System (ADS)

Zonenshain, L. P.; Kuzmin, M. I.; Bocharova, N. Yu.

1991-12-01

Intraplate, hot spot related volcanic occurrences do not have a random distribution on the Earth's surface. They are concentrated in two large regions (up to 10,000 km in diameter), the Pacific and the African, and two smaller areas (2000-3000 km in diameter), the Central Asian and the Tasmanian. These regions are considered as manifestations of hot fields in the mantle, whereas the regions lying in between are expressions of cold fields in the mantle. Large-scale anomalies coincide with the hot fields: topographic swells, geoid highs, uplifts of the "asthenospheric table", inferred heated regions in the lowermost mantle according to seismic tomographic images, geochemical anomalies showing the origin of volcanics from undepleted mantle sources. Hot fields are relatively stable features, having remained in the same position on the Earth's surface during the last 120 Ma, although they have other configurations and other positions in the Late Paleozoic and Early Mesozoic. Available data show that two main hot fields (Pacific and African) are possibly moving one with respect to the other, converging along the Eastern Pacific subduction system and diverging along that of the Western Pacific. If so, well-known differences between these subduction systems can also be connected with related displacement of the hot fields. Hot fields are assumed to correspond to upwelling branches of mantle and rather deep mantle convection, and cold fields to downwelling branches. Thus, hot fields can be regarded as expressions of deeper tectonics, comparative to the plate tectonics, which is operating in the upper layers of the Earth. We call it hot-field tectonics. Plate tectonics is responsible for the opening and closure of oceans and for the formation of orogenic belts, whereas hot-field tectonics accounts for a larger cyclicity of the Earth's evolution and for amalgamation and break up of Pangea-type supercontinents. Hot-field tectonics seems to be the only process to have existed on all of the terrestrial planets. We speculate that hot-field tectonics governs the global geodynamics of the Earth.

Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley

NASA Astrophysics Data System (ADS)

Olen, Stephanie M.; Bookhagen, Bodo; Hoffmann, Bernd; Sachse, Dirk; Adhikari, D. P.; Strecker, Manfred R.

2015-10-01

Understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution. Denudation rates derived from terrestrial cosmogenic nuclides (TCNs) are commonly used to quantify erosion and bridge tectonic (Myr) and climatic (up to several kiloyears) time scales. However, how the processes of erosion in active orogens are ultimately reflected in 10Be TCN samples remains a topic of discussion. We investigate this problem in the Arun Valley of eastern Nepal with 34 new 10Be-derived catchment-mean denudation rates. The Arun Valley is characterized by steep north-south gradients in topography and climate. Locally, denudation rates increase northward, from <0.2 mm yr-1 to ~1.5 mm yr-1 in tributary samples, while main stem samples appear to increase downstream from ~0.2 mm yr-1 at the border with Tibet to 0.91 mm yr-1 in the foreland. Denudation rates most strongly correlate with normalized channel steepness (R2 = 0.67), which has been commonly interpreted to indicate tectonic activity. Significant downstream decrease of 10Be concentration in the main stem Arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample. This results in 10Be concentrations and denudation rates that do not uniformly represent the upstream catchment area. We observe strong impacts on 10Be concentrations from local, nonfluvial geomorphic processes, such as glaciation and landsliding coinciding with areas of peak rainfall rates, pointing toward climatic modulation of predominantly tectonically driven denudation rates.

Geochemical and Morphologic Evolution of Soil-Covered Hillslopes in the Feather River Basin, California: Responses to Channel Incision

NASA Astrophysics Data System (ADS)

Weinman, B.; Yoo, K.; Mudd, S. M.; Hurst, M. D.; Mayer, K.; Maher, K.

2009-12-01

Tectonically driven changes in channel incision rates lead to changes in hillslope erosion rates that propagate upslope. In an effort to understand how these changes affect soil geochemistry, this study theoretically and empirically integrates sediment transport and chemical weathering. Here, we focus on a tributary basin of the Middle Folk Feather River (FR) in Sierra Nevada, California. This basin is adjusting to an increase in main stem channel incision that has resulted in rapidly eroding, steep hillslopes near the main stem channel and gentler, more slowly eroding slopes further upstream. To constrain how geomorphic signals (i.e., knickpoint) propagate upslope and affect soil geochemistry, soils were sampled in July 2009 along three hillslope transects within the FR basin: transect POMD (40% slope at 780m elevation), FTA (70% slope at 680m elevation), and BRC (90% slope at 630m elevation). To capture and bracket a coupled change in soil geochemistry upslope, transects were specifically chosen so that POMD is downstream of the knickpoint of the main channel, FTA in a transitional region, and BRC upstream of the knickpoint. Along each ~50 m transect, soil pits were dug <10 m apart of each other to depths of about 1m. CRN samples were collected from the upper saprolite and undisturbed B horizons to determine the soil production rates. For constraining soil mixing, sediment ages, and chemical weathering, OSL and geochemistry samples were collected every ~10 cm in the A, B, and saprolite horizons. Judging from the soil color, the abundances of pedogenic iron oxides systematically are greater in the less steep hillslopes. This is consistent with a preliminary view that the soils have briefer residence times in the steeper hillslopes, which have greater rates of channel incision at their lower boundaries. One contrast to our expectations, however, was that the soils were not consistently thicker in the gentler hillslopes, which presumably undergo reduced rates of soil erosion. Additionally, within each hillslope, soil thicknesses were largely constant, ~50-70 cm thick. Therefore, tree throw, which appears to be dominant soil production mechanism at the site, may be capable of buffering soil thickness against the variation of soil erosion rate. While we are still in the preliminary stages of the OSL and CRN work, transect profiles of major oxide elements Si, Al, Fe, Ca, Mg, Na, K, P, and Mn versus potentially immobile elements such as Zr and Ti in the soils are used to infer how channel incision affects soil geochemistry in the three hillslopes. In the future, these results will be coupled with LiDAR, OSL, CRN, and pore-water chemistry work for a more holistic view of how the morphology and geochemistry of hillslopes evolve together in their responses to tectonic forcing.

GLOBE (Global Oceanographic Bathymetry Explorer) : an innovative and generic software combining all necessary functionalities for cruise preparation, for collection, linking, processing and display of scientific data acquired during sea cruises, and for exporting data and information to the main marine data centers and networks.

NASA Astrophysics Data System (ADS)

Sinquin, J. M.; Sorribas, J.

2014-12-01

Within the EUROFLEETS project, and linked to the EMODNet and Geo-Seas European projects, GLOBE (Global Oceanographic Bathymetry Explorer) is an innovative and generic software. I. INTRODUCTION The first version can be used onboard during the survey to get a quick overview of acquired data, or later, to re-process data with accurate environmental data. II. MAIN FUNCTIONALITIES The version shown at AGU-2014 will present several key items : - 3D visualization: DTM multi-layers from EMODNet, - Water Column echogram, Seismic lines, ... - Bathymetry Plug-In: manual and automatic data cleaning, integration of EMODNet methodology to introduce CDI concept, filtering, spline, data gridding, ... - Backscatter with compensation, - Tectonic toolset, - Photo/Video Plug-In - Navigation 3D including tide correction, MRU corrections, GPS offsets correction, - WMS/WFS interfaces. III. FOCUS ON EMODNET One of the main objectives of the EMODNet European project is to elaborate a common processing flow for gridding the bathymetry data and for generating harmonized digital terrain model (DTM) : this flow includes the definition of the DTM characteristics (geodetic parameters, grid spacing, interpolation and smoothing parameters…) and also the specifications of a set of layers which enrich the basic depth layer : statistical layers (sounding density, standard deviation,…) and an innovative data source layer which indicates the source of the soundings and and which is linked and collects to the associated metadata. GLOBE Software provides the required tools for applying this methodology and is offered to the project partners. V. FOCUS ON THE TECTONIC TOOLSET The tectonic toolset allows the user to associate any DTM to 3D rotation movements. These rotations represent the movement of tectonic plates along discrete time lines (from 200 million years ago to now). One rotation is described by its axes, its value angle and its date. GLOBE can display the movement of tectonic plates, represented by a DTM, at different geological times. The same movements can be operated for geotiff images or GMT files representing grids for any kind of data. The free software GLOBE3D is a product of Ifremer and is funded by Carnot-Edrome

Oceanic Remnants In The Caribbean Plate: Origin And Loss Of Related LIPs.

NASA Astrophysics Data System (ADS)

Giunta, G.

2005-12-01

The modern Caribbean Plate is an independent lithospheric entity, occupying more than 4 Mkm2 and consisting of the remnants of little deformed Cretaceous oceanic plateau of the Colombia and Venezuela Basins (almost 1 Mkm2) and the Palaeozoic-Mesozoic Chortis continental block (about 700,000 km2), both bounded by deformed marginal belts. The northern (Guatemala and Greater Antilles) and the southern (northern Venezuela) plate margins are marked by collisional zones, whereas the western (Central America Isthmus) and the eastern (Lesser Antilles) margins are represented by convergent boundaries and their magmatic arcs, all involving ophiolitic terranes. The evolutionary history of the Caribbean Plate since the Jurassic-Early Cretaceous encompasses plume, accretionary, and collisional tectonics, the evidence of which has been recorded in the oceanic remnants of lost LIPs, as revealed in: i) the MORB to OIB thickened crust of the oceanic plateau, including its un-deformed or little deformed main portion, and scattered deformed tectonic units; ii) ophiolitic tectonic units of MORB affinity and the rock blocks in ophiolitic melanges; iii) intra-oceanic, supra subduction magmatic sequences with IAT and CA affinities. The Mesozoic oceanic LIPs, from which the remnants of the Caribbean Plate have been derived, have been poorly preserved during various episodes of the intra-oceanic convergence, either those related to the original proto-Caribbean oceanic realm or those connected with two eo-Caribbean stages of subduction. The trapped oceanic plateau of the Colombia and Venezuela Basins is likely to be an unknown portion of a bigger crustal element of a LIP, similar to the Ontong-Java plateau. The Jurassic-Early Cretaceous proto-Caribbean oceanic domain consists of oceanic crust generated at multiple spreading centres; during the Cretaceous, part of this crust was thickened to form an oceanic plateau with MORB and OIB affinities. At the same time, both South and North American continental margins, inferred to be close to the oceanic realm, were affected by rifting and within-plate tholeiitic magmatism (WPT); this interpretation supports a near mid-America original location of the "proto-Caribbean" LIP. The MORB magmatic sections and rock blocks in the ophiolitic melanges are interpreted as exhumed tectonic sheets of the normal proto-Caribbean oceanic lithosphere, or part of a back-arc crust, both deformed in the eo-Caribbean stages. The SSZ complexes, considered as Cordilleran-type deformed ophiolites, were derived from a LIP that experienced two superimposed eo-Caribbean stages of intra-oceanic subduction. The older (Mid-Cretaceous) stage involved the eastward subduction of the un-thickened proto-Caribbean lithosphere, resulting in IAT and CA magmatism accompanied by HP-LT metamorphism and melange formation. The second, Late Cretaceous stage involved a westward dipping intra-oceanic subduction, which generated tonalitic arc magmatism. The eastward wedging of the Caribbean Plateau between the North and South American plates progressively trapped remnants of the Colombia and Venezuela Basins between the Atlantic and Pacific subduction zones and their new volcanic arcs (Aves-Lesser Antilles and Central American Isthmus). Unlike the proto-Caribbean, it appears that this LIP did not involve the main continental margins, even though the northern and southern Caribbean borders experienced different evolutionary paths. It was largely lost by superimposed accretionary and collisional events producing the marginal belts of the Caribbean Plate; its evolution has been dominated by a strongly oblique tectonic regime, constraining seafloor spreading, subduction, crustal exhumation, emplacement, and dismembering processes.

Tectonics and metallogenesis of Proterozoic rocks of the Reading Prong

USGS Publications Warehouse

Gundersen, L.C.S.

2004-01-01

Detailed geologic mapping, petrography, and major and trace-element analyses of Proterozoic rocks from the Greenwood Lake Quadrangle, New York are compared with chemical analyses and stratigraphic information compiled for the entire Reading Prong. A persistent regional stratigraphy is evident in the mapped area whose geochemistry indicates protoliths consistent with a back-arc marginal basin sequence. The proposed marginal basin may have been floored by an older sialic basement and overlain by a basin-fill sequence consisting of a basal tholeiitic basalt, basic to intermediate volcanic or volcaniclastic rocks and carbonate sediments, a bimodal calc-alkaline volcanic sequence, and finally volcaniclastic, marine, and continental sediments. The presence of high-chlorine biotite and scapolite may indicate circulation of brine fluids or the presence of evaporite layers in the sequence. Abundant, stratabound magnetite deposits with a geologic setting very unlike that of cratonic, Proterozoic banded-iron formations are found throughout the proposed basin sequence. Associated with many of the magnetite deposits is unusual uranium and rare-earth element mineralization. It is proposed here that these deposits formed in an exhalative, volcanogenic, depositional environment within an extensional back-arc marginal basin. Such a tectonic setting is consistent with interpretations of protoliths in other portions of the Reading Prong, the Central Metasedimentary Belt of the Canadian Grenville Province, and recent interpretation of the origin of the Franklin lead-zinc deposits, suggesting a more cohesive evolving arc/back-arc tectonic model for the entire Proterozoic margin of the north-eastern portion of the North American craton. Published by Elsevier Ltd.

Carboniferous rifted arcs leading to an archipelago of multiple arcs in the Beishan-Tianshan orogenic collages (NW China)

NASA Astrophysics Data System (ADS)

Tian, Zhonghua; Xiao, Wenjiao; Windley, Brian F.; Zhang, Ji'en; Zhang, Zhiyong; Song, Dongfang

2017-10-01

The Beishan and East Tianshan Orogenic Collages in the southernmost Central Asian Orogenic Belt (CAOB) record the final stages of evolution of the Paleo-Asian Ocean. These collages and their constituent arcs have an important significance for resolving current controversies regarding their tectonic setting and age, consequent accretionary history of the southern CAOB, and the closure time of the Paleo-Asian Ocean. In this paper, we present our work on the southern Mazongshan arc and the northern Hongyanjing Basin in the Beishan Orogenic Collage (BOC), and our comparison with the Bogda arc and associated basins in the East Tianshan Orogenic Collage. Field relationships indicate that the Pochengshan fault defines the boundary between the arc and basin in the BOC. Volcanic rocks including basalts and rhyolites in the Mazongshan arc have bimodal calc-alkaline characteristics, an enrichment in large ion lithophile elements such as Rb, Ba, and Pb and depletion in high field-strength elements (e.g., Nb and Ta), which were probably developed in a subduction-related tectonic setting. We suggest that these bimodal calc-alkaline volcanic rocks formed in rifted arcs instead of post-orogenic rifts with mantle plume inputs. By making detailed geochemical comparisons between the Mazongshan arc and the Bogda arc to the west, we further propose that they are similar and both formed in arc rifts, and helped generate a Carboniferous archipelago of multiple arcs in the southern Paleo-Asian Ocean. These data and ideas enable us to postulate a new model for the tectonic evolution of the southern CAOB.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roy, D.W.; Schmitt, L.; Woussen, G.

Airborne SAR images provided essential clues to the tectonic setting of (1) the MbLg 6.5 Saguenay earthquake of 25 November 1988, (2) the Charlevoix-Kamouraska seismic source zone, and (3) some of the low *eve* seismic activity in the Eastern seismic background zone of Canada. The event occurred in the southeastern part of the Canadian Shield in an area where the boundary between the Saguenay graben and the Jacques Cartier horst is not well defined. These two tectonic blocks are both associated with the Iapetan St-Lawrence rift. These blocks exhibit several important structural breaks and distinct domains defined by the lineamentmore » orientations, densities, and habits. Outcrop observations confirm that several lineament sets correspond to Precambrian ductile shear zones reactivated as brittle faults during the Phanerozoic. In addition, the northeast and southwest limits of recent seismic activity in the Charlevoix-Kamouraska zone correspond to major elements of the fracture pattern identified on the SAR images. These fractures appear to be related to the interaction of the Charlevoix astrobleme with the tectonic features of the area. 20 refs.« less

Item Description: ISS TransHab Restraint Sample and Photo Documentation

NASA Technical Reports Server (NTRS)

Adams, Constance

2000-01-01

The yellow strap seen in the display is a piece of the main restraint layer of a test article for the ISS TransHab spacecraft, First conceived as a technology which is capable of supporting a [human] crew of six on an extended space journey such as the six-month trip to Mars, TransHab (short for "Transit habitat") is the first space inflatable module ever designed. As this text is written it is being considered as a replacement for the Habitation module on the International Space Station (ISS). It constitutes a major breakthrough both in technology and in tectonics: capable of tight packaging at light weight for efficient launch, the vehicle can then be inflated to its full size on orbit via its own inflation tanks. This is made possible by the separation of its main structural elements from its pressure-shell. In other words, all spacecraft flown to date have been of an exoskeletal type---i.e., its hard outer shell acts both as a pressure container and as its main channel for structural loading This includes the ISS, which is currently under construction in Low Earth Orbit [275 miles above the Earth]. By contrast TransHab is the first endoskeletal space Habitat, consisting of a dual system: a light, reconfigurable central structure of graphite composite and a multilayered, deployable pressure shell.

Holocene vertical tectonic movements of the Taipei Basin, northern Taiwan and its implications

NASA Astrophysics Data System (ADS)

Chen, B.; Hsieh, M.; Lai, T.; Liew, P.

2007-12-01

Many geological data of the Taipei Basin, although, have been published by various studies in past decades, however, vertical tectonic movement rate of the Basin was not well understood so far. This study, therefore, used radiocarbon dates, obtained from fifteen boreholes in the Basin, to calculate the Holocene vertical tectonic movement rate. In addition to the derived tectonic movement rate, this study also discussed the causes of the tectonic patterns of the Taipei Basin. The Taipei Basin, located in the northern Taiwan, was a half graben subsided and extended along the western boundary, the Shangiao Normal Fault, of the Basin. The Holocene vertical tectonic movement rate of the Basin were calculated based on 94 radiocarbon dates in fifteen boreholes, the elevations of the radiocarbon dating samples, and the eustatic sea-level curve of the past 15 ka. The results showed the rate in the western part of the Basin, was -2.2 -- -0.9 mm/yr (negative value indicates subsiding, and positive value indicates uplifting). In the central part of the Basin, the rate was ca. -1 -- 1 mm/yr while in the eastern part of the Basin, the rate was 0.1 -- 1.6 mm/yr. Along the Shiangiao Fault, the rate of the hanging-wall was ca. -1.6 -- -0.4 mm/yr and the rate of the footwall was ca. 0 mm/yr. According to the results of this study, the present territory of the Taipei Basin was not actually consistent with the tectonic subsiding region. The vertical tectonic movement pattern demonstrated subsidence in the western part and uplift in the eastern part of the Taipei Basin. The subsidence of the western part was controlled by the extension of the Shangiao Faul. The uplift of the eastern part might be ascribed to the roll-over of the Fault. Another possibility is that the uplift of the east was controlled by the same behavior as the Western Foothills.Consequently, the deposition of the eastern part of the Basin, wass mainly related to the accommodations due to sea-level rise but not tectonic subsidence.

Late Miocene-Early Pliocene reactivation of the Main Boundary Thrust: Evidence from the seismites in southeastern Kumaun Himalaya, India

NASA Astrophysics Data System (ADS)

Mishra, Anurag; Srivastava, Deepak C.; Shah, Jyoti

2013-05-01

Tectonic history of the Himalaya is punctuated by successive development of the faults that run along the boundaries between different lithotectonic terrains. The Main Boundary Fault, defining the southern limit of the Lesser Himalayan terrain, is tectonically most active. A review of published literature reveals that the nature and age of reactivation events on the Main Boundary Fault is one of the poorly understood aspects of the Himalayan orogen. By systematic outcrop mapping of the seismites, this study identifies a Late Miocene-Early Pliocene reactivation on the Main Boundary Thrust in southeast Kumaun Himalaya. Relatively friable and cohesionless Neogene sedimentary sequences host abundant soft-sediment deformation structures in the vicinity of the Main Boundary Thrust. Among a large variety of structures, deformed cross-beds, liquefaction pockets, slump folds, convolute laminations, sand dykes, mushroom structures, fluid escape structures, flame and load structures and synsedimentary faults are common. The morphological attributes, the structural association and the distribution pattern of the soft-sediment deformation structures with respect to the Main Boundary Fault strongly suggest their development by seismically triggered liquefaction and fluidization. Available magnetostratigraphic age data imply that the seismites were developed during a Late Miocene-Early Pliocene slip on the Main Boundary Thrust. The hypocenter of the main seismic event may lie on the Main Boundary Thrust or to the north of the study area on an unknown fault or the Basal Detachment Thrust.

Plate tectonics and continental basaltic geochemistry throughout Earth history

NASA Astrophysics Data System (ADS)

Keller, Brenhin; Schoene, Blair

2018-01-01

Basaltic magmas constitute the primary mass flux from Earth's mantle to its crust, carrying information about the conditions of mantle melting through which they were generated. As such, changes in the average basaltic geochemistry through time reflect changes in underlying parameters such as mantle potential temperature and the geodynamic setting of mantle melting. However, sampling bias, preservation bias, and geological heterogeneity complicate the calculation of representative average compositions. Here we use weighted bootstrap resampling to minimize sampling bias over the heterogeneous rock record and obtain maximally representative average basaltic compositions through time. Over the approximately 4 Ga of the continental rock record, the average composition of preserved continental basalts has evolved along a generally continuous trajectory, with decreasing compatible element concentrations and increasing incompatible element concentrations, punctuated by a comparatively rapid transition in some variables such as La/Yb ratios and Zr, Nb, and Ti abundances approximately 2.5 Ga ago. Geochemical modeling of mantle melting systematics and trace element partitioning suggests that these observations can be explained by discontinuous changes in the mineralogy of mantle partial melting driven by a gradual decrease in mantle potential temperature, without appealing to any change in tectonic process. This interpretation is supported by the geochemical record of slab fluid input to continental basalts, which indicates no long-term change in the global proportion of arc versus non-arc basaltic magmatism at any time in the preserved rock record.

Tectonic and climatic control on river profiles for rivers draining northwards from the Pamir and Kunlun (Central Asia).

NASA Astrophysics Data System (ADS)

Brookfield, M. E.

2004-12-01

Collision orogens developed between two plates result not only in shortening, uplift and erosion of the rocks, but also compression, uplift and modification of the drainage systems.Many studies now relate orogenic uplifts to the interaction of plate compression with isostatic changes due to active denudation (England and Molnar, 1990). In this paper I outline the relationships between river profiles, drainage patterns, tectonics and climate during the indentation of Asia in the Pamir range and adjacent areas: it extends a previous study of rivers draining south (Brookfield, 1998). The reasons for choosing the Pamir and Kunlun are the following. a) The indentation is relatively simple and can thus be modelled with a relatively simple rigid indentation model. The major complication is due to the different behaviour of the western and eastern edges of the indenter. The western edge involves mostly ductile deformation of the Tadjik back-arc basin to form a fold and thrust belt. The eastern edge involves strong shearing between continental crust of the Pamir and Tarim basins to form a complex collisional transform zone (marked by the Karakoram and associated faults) linking the Pamir arc with the Kunlun and Himalaya. b) The compression pattern is relatively simple and various tectonic units can mostly be traced from west to east across the Pamir indenter. Individual tectonic elements and ancient sedimentary basins can be followed almost continuously from the hardly compressed Afghan area through the highly compressed Pamir indent into the less compressed Kunlun and Tibetan plateau area. c) The displacements are enormous, relatively recent, and measurable. The Pamir arc only started developing in the Miocene around 20 ma. Since then over 800 km of internal shortening has occurred between the Indian shield and the Tien Shan(Dewey et al., 1989). Most of this post-Oligocene shortening occurred in the Pamir arc itself. And because of this, the earlier progressive Paleocene - Oligocene collisions of India with magmatic arcs south of Asia can be followed in some detail in the Pakistan Himalaya though not in the Indian Himalaya. d) The river profiles and courses can be directly related to the major tectonic development of the arc, modified by the influence of Quaternary climatic change (Molnar and England, 1990). The main drainage divide is along the crest of the fundamentally Mesozoic Hindu Kush and Karakoram ranges and extensions. Despite the late Cenozoic uplift of the Pamir, only the Pyandzh river cuts across the Pamir range in a course that corresponds with a geophysical but not a geological boundary. The rest of the rivers, with a few exceptions, tend to run in valleys parallel to the arc, except to the west and east. To the west, in northern Afghanistan the rivers still run northward from the westward extension of the Hindu Kush. To the east the main rivers have headwaters far within the Tibetan plateau and cut, with incredibly steep gradients across the Kun Lun and related ranges - testifying to the latest Tertiary development of this range. REFERENCES Brookfield, 1998. The evolution of the great river systems of southern Asia during the Cenozoic India-Asia collision: rivers draining southwards. Geomorphology, 22: 285-312. Dewey, J.F., Cande, S. and Pitman III, W.C., 1989. Tectonic evolution of the India/Eurasia collision zone. Eclogae geologica Helvetica, 82: 717-734. England, P. and Molnar, P., 1990. Surface uplift, uplift of rocks and exhumation of rocks. Geology, 18: 1173-1177. Molnar, P. and England, P., 1990. Late Cenozoic uplift of mountain ranges and global climatic change: chicken or egg? Nature, 346: 29-34.

Metamorphozed Hercynian granitoids in the Alpine structures of the Central Rhodope, Bulgaria: geotectonic position and geochemistry

NASA Astrophysics Data System (ADS)

Cherneva, Zlatka; Georgieva, Milena

2005-05-01

Orthogneisses of late-Hercynian protolith age crop out in the Central Rhodope high-grade metamorphic complex, which is part of the Alpine orogen in south-eastern Europe. They compose a tectonic unit bordered by late-Alpine extensional shear zones. These rocks reflect Eocene amphibolite facies migmatization (<750 °C/0.9-0.5 GPa). The low-temperature melting favored zircon inheritance and disturbed mainly the LILE protolith compositions. Despite the intense Alpine metamorphic overprint, the major elements, HFSE and REE reflect the initial composition of the Hercynian protolith. A geochemical data set summarizing 200 whole rock analyses testifies to a calc-alkaline magma differentiation producing a compositional range of tonalite and/or granodiorite to granite and leucocratic granite. Geochemical compositions combined with published isotope and age data suggest dominant I-type protoliths and mixed magma sources including crustal and mantle material, and distinguish between older granitoids of volcanic-arc affinity and probably younger ones of late or post-collision origin.

Tectonic origin of serpentinites on Syros, Greece: Geochemical signatures of abyssal origin preserved in a HP/LT subduction complex

NASA Astrophysics Data System (ADS)

Cooperdock, Emily H. G.; Raia, Natalie H.; Barnes, Jaime D.; Stockli, Daniel F.; Schwarzenbach, Esther M.

2018-01-01

This study combines whole rock trace and major element geochemistry, and stable isotope (δD and δ18O) analyses with petrographic observations to deduce the origin and tectonic setting of serpentinization of ultramafic blocks from the exhumed HP/LT Aegean subduction complex on Syros, Greece. Samples are completely serpentinized and are characterized by mineral assemblages that consist of variable amounts of serpentine, talc, chlorite, and magnetite. δD and δ18O values of bulk rock serpentinite powders and chips (δD = - 64 to - 33‰ and δ18O = + 5.2 to + 9.0‰) reflect hydration by seawater at temperatures < 250 °C in an oceanic setting pre-subduction, or by fluids derived from dehydrating altered oceanic crust during subduction. Fluid-mobile elements corroborate the possibility of initial serpentinization by seawater, followed by secondary fluid-rock interactions with a sedimentary source pre- or syn-subduction. Whole rock major element, trace element, and REE analyses record limited melt extraction, exhibit flat REE patterns, and do not show pronounced Eu anomalies. The geochemical signatures preserved in these serpentinites argue against a mantle wedge source, as has been previously speculated for ultramafic rocks on Syros. Rather, the data are consistent with derivation from abyssal peridotites in a hyper-extended margin setting or mid-ocean ridge and fracture zone environment. In either case, the data suggest an extensional and/or oceanic origin associated with the Cretaceous opening of the Pindos Ocean and not a subduction-related derivation from the mantle wedge.

Basement and crustal structure of the Davis Sea region (East Antarctica): implications for tectonic setting and continent to oceanic boundary definition

USGS Publications Warehouse

Guseva, Y.B.; Leitchenkov, G.L.; Gandyukhin, V.V.; Ivanov, S.V.

2007-01-01

This study is based on about 8400 km of MCS, magnetic and gravity data as well as 20 sonobuoys collected by the Russian Antarctic Expedition during 2003 and 2004 in the Davis Sea and adjacent areas between 80°E and 102°E. Major tectonic provinces and features are identified and mapped in the study region including: 1) A marginal rift with a the extended continental crust ranging 130 to more than 200 km in width; 2) The marginal volcanic plateau of the Bruce Bank consisting of the Early Cretaceous igneous rocks; 3) The Early Cretaceous and Late Cretaceous−Paleogene oceanic basins; and 4) The Early Cretaceous igneous province of the Kerguelen Plateau. Four major horizons identified in the sedimentary cover of the Davis Sea region are attributed to main tectonic events and/or paleoenvironmental changes.

New maps of Lakshmi Planum and eastern Aphrodite, Venus

NASA Technical Reports Server (NTRS)

Mcgill, G. E.

1984-01-01

Interest on Venus has centered on three regions; (1) Aphrodite Terra, especially east of the main uplant portion, (2) Ishtar Terra, especially Lakshmi Planum and its bounding scarp and massifs, and (3) Beta Regio-Phoebe Regio. The last region is topographically similar to the East African rift system, and has been inferred to have a similar tectonic origin. The Aphrodite region is part of a 21,000 km long tectonic zone that seems best explained as due to extension, and that may represent hot spots clustered along an incipient divergent plate boundary. The most interesting and complex portion of this tectonic zone is that part of eastern Aphrodite between Thetis Regio and Atla Regio. In contrast, the Lakshmi Planum region has many topographic characteristics suggesting that it is a true continent, and thus indicative of convergence and a thick crust. Detailed topographic contour maps of eastern Aphrodite Terra and of Lakshmi Planum are included.

Tharsis block tectonics on Mars

NASA Technical Reports Server (NTRS)

Raitala, Jouko T.

1988-01-01

The concept of block tectonics provides a framework for understanding many aspects of Tharsis and adjoining structures. This Tharsis block tectonics on Mars is manifested partly by mantle-related doming and partly by response to loading by subsequent volcanic construction. Although the origin of the volcanism from beneath Tharsis is a subject of controversy explanations have to include inhomogeneities in Martian internal structure, energy distribution, magma accumulation and motion below the lithosphere. Thermal convection can be seen as a necessary consequence for transient initial phase of Martian cooling. This produced part of the elevated topography with tensional stresses and graben systems radial to the main bulge. The linear grabens, radial to the Tharsis center, can be interpreted to indicate rift zones that define the crustal block boundaries. The load-induced stresses may then have contributed on further graben and ridge formation over an extended period of time.

Tectonic stratification and seismicity of the accretionary prism of the Azerbaijani part of Greater Caucasus

NASA Astrophysics Data System (ADS)

Alizade, Akif; Kangarli, Talat; Aliyev, Fuad

2013-04-01

The Greater Caucasus has formed during last stage of the tectogenesis in a geodynamic condition of the lateral compression, peculiar to the zone pseudo-subduction interaction zone between Northern and Southern Caucasian continental microplates. Its present day structure formed as a result of horizontal movements of the different phases and sub-phases of Alpine tectogenesis (from late Cimmerian to Valakhian), and is generally regarded as zone where, along Zangi deformation, the insular arc formations of the Northern edge of South Caucasian microplate thrust under the Meso-Cenozoic substantial complex contained in the facials of marginal sea of Greater Caucasus. The last, in its turn, has been pushed beneath the North-Caucasus continental margin of the Scythian plate along Main Caucasus Thrust fault. Data collected from the territory of Azerbaijan and its' sector of the Caspian area stands for pseudo-subduction interaction of microplates which resulted in the tectonic stratification of the continental slope of Alpine formations, marginal sea and insular arc into different scale plates of south vergent combined into napping complexes. In the orogeny's present structure, tectonically stratified Alpine substantial complex of the marginal sea of Greater Caucasus bordered by Main Caucasus and Zangi thrusts, is represented by allochthonous south vergent accretionary prism in the front of first deformation with its' root buried under the southern border of Scythian plate. Allocated beneath mentioned prism, the autochthonous bedding is presented by Meso-Cenosoic complex of the Northern flank of the South-Caucasian miroplate, which is in its' turn crushed and lensed into southward shifted tectonic microplates gently overlapping the northern flank of Kura flexure along Ganykh-Ayrichay-Alyat thrust. Data of real-time GPS measurement of regional geodynamics indicates that pseudo-subduction of South Caucasian microplate under the North Caucasian microplate still continues during present stage of alpine tectogenesis. Among others, ongoing pseudo-subduction is indicated by data of regional seismicity which is irregularly distributed by depth (foci levels 2-6; 8-12; 17-22; 25-45 km). Horizontal and vertical seismic zoning is explained by Earth crust's block divisibility and tectonic stratification, within the structure of which the earthquake focuses are mainly confined to the crossing nodes of differently oriented ruptures, or to the planes of deep tectonic disruptions and lateral displacements along unstable contacts of the substantial complexes with various degree of competence. At present stage of tectogenesis, seismically most active are the structures of the northern flank of South Caucasian microplate, controlled by Ganyx-Ayrichay-Alyat deep thrust with "General Caucasus" spread in the west, and sub-meridian right-lateral strike slip zone of the Western Caspian fault in the east of Azerbaijani part of Greater Caucasus.

Magma Chamber of the 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand

NASA Astrophysics Data System (ADS)

Liu, Y.; Anderson, A. T.; Wilson, C. J.; Davis, A. M.

2004-12-01

We have investigated melt inclusions and their host quartz crystals from the Bishop-Tuff-sized 26.5 ka Oruanui eruption at Taupo volcano, New Zealand. Compositions (major and trace elements, H2O and CO2) of melt inclusions and cathodoluminescence (CL) images of quartz were obtained for eight individual pumices from early, middle and late depositional units. All melt inclusions are high-silica weakly peraluminous rhyolites. Melt inclusions for different eruptive phases have similar ranges of H2O contents (3.8-5.2 wt %), but late-erupted samples have higher CO2 contents (mostly > 140 ppm). A positive correlation between CO2 and compatible trace elements such as Sr suggests that crystallization and melt entrapment occurred under gas-saturated conditions. Trace elements variations in melt inclusions are consistent with fractionation of 30-40 wt % crystals (plagioclase+quartz+pyroxene+amphibole). Crystal contents in pumices, trace-element contents in melt inclusions, and CL zoning patterns of quartz show no correlation with eruptive phases, suggesting that the Oruanui magma was well mixed before eruption. Some Oruanui quartz crystals contain distinctive CL zonings with a jagged ('restitic') core mantled by a black CL zone. Trace element variations in melt inclusions in the 'restitic' cores are consistent with fractionation of Ba-bearing minerals such as sanidine and/or biotite, both of which are rare or absent in rocks erupted from Taupo volcanic center. The above evidence suggests that Oruanui rhyolite is generated by assimilation of previous intruded rocks or country rocks, differentiated by crystal fractionation, and then mixed prior to eruption. Despite the differences in trace element and volatile contents, and crystal assemblages, both Bishop Tuff and Oruanui magmas involve crystal fractionation as one of the main differentiation mechanisms during their evolution. However, there are pronounced differences in the pre-eruptive stratification of the two chambers, which may reflect the tectonic settings, eruption rates, and ages of the systems.

Drainage basin and topographic analysis of a tropical landscape: Insights into surface and tectonic processes in northern Borneo

NASA Astrophysics Data System (ADS)

Mathew, Manoj Joseph; Menier, David; Siddiqui, Numair; Ramkumar, Mu.; Santosh, M.; Kumar, Shashi; Hassaan, Muhammad

2016-07-01

We investigated the recent landscape development of Borneo through geomorphic analysis of two large drainage basins (Rajang and Baram basins). The extraction of morphometric parameters utilizing digital terrain data in a GIS environment, focusing on hydrography (stream length-gradient index, ratio of valley floor width to valley height, and transverse topographic symmetry factor) and topography (local relief and relief anomaly), was carried out in order to elucidate processes governing drainage and landscape evolution. Anomalously high and low values of stream length-gradient indices of main tributary streams associated with faults and multiple knick-points along the channel profiles are linked to deformation events. The development of deeply incised V-shaped valleys show enhanced incision capability of streams in response to steepening of hillslope gradients following tectonic inputs. Deflection of streams and probable dynamic reorganization of the drainage system through stream capture processes as feedbacks to tectonic uplift and orographic effect are observed. Local relief and relief anomaly maps highlight the presence of preserved elevation-accordant relict portions of landscapes characterized by low amplitude relief, nested between ridgelines in regions of complex folding. Our results reveal dynamic geomorphic adjustment of the landscape due to perturbations in tectonic and climatic boundary conditions. The implication is that the landscape of north Borneo experienced a tectonic phase of rapid uplift after 5 Ma and undergoes active folding of the Rajang Group thrust belts in the present-day. Active shortening combined with high rates of denudation in Sarawak, demonstrates transience emphasized by the drainage system attempting to adjust to tectonic and climatic forcing.

Identifying tectonic parameters that affect tsunamigenesis

NASA Astrophysics Data System (ADS)

van Zelst, I.; Brizzi, S.; Heuret, A.; Funiciello, F.; van Dinther, Y.

2016-12-01

The role of tectonics in tsunami generation is at present poorly understood. However, the fact thatsome regions produce more tsunamis than others indicates that tectonics could influencetsunamigenesis. Here, we complement a global earthquake database that contains geometrical,mechanical, and seismicity parameters of subduction zones with tsunami data. We statisticallyanalyse the database to identify the tectonic parameters that affect tsunamigenesis. The Pearson'sproduct-moment correlation coefficients reveal high positive correlations of 0.65 between,amongst others, the maximum water height of tsunamis and the seismic coupling in a subductionzone. However, these correlations are mainly caused by outliers. The Spearman's rank correlationcoefficient results in statistically significant correlations of 0.60 between the number of tsunamisin a subduction zone and subduction velocity (positive correlation) and the sediment thickness atthe trench (negative correlation). Interestingly, there is a positive correlation between the latter andtsunami magnitude. These bivariate statistical methods are extended to a binary decision tree(BDT) and multivariate analysis. Using the BDT, the tectonic parameters that distinguish betweensubduction zones with tsunamigenic and non-tsunamigenic earthquakes are identified. To assessphysical causality of the tectonic parameters with regard to tsunamigenesis, we complement ouranalysis by a numerical study of the most promising parameters using a geodynamic seismic cyclemodel. We show that the inclusion of sediments on the subducting plate results in an increase insplay fault activity, which could lead to larger vertical seafloor displacements due to their steeperdips and hence a larger tsunamigenic potential. We also show that the splay fault is the preferredrupture path for a strongly velocity strengthening friction regime in the shallow part of thesubduction zone, which again increases the tsunamigenic potential.

Erosion-tectonics feedbacks in shaping the landscape: An example from the Mekele Outlier (Tigray, Ethiopia)

NASA Astrophysics Data System (ADS)

Sembroni, Andrea; Molin, Paola; Dramis, Francesco; Faccenna, Claudio; Abebe, Bekele

2017-05-01

An outlier consists of an area of younger rocks surrounded by older ones. Its formation is mainly related to the erosion of surrounding rocks which causes the interruption of the original continuity of the rocks. Because of its origin, an outlier is an important witness of the paleogeography of a region and, therefore, essential to understand its topographic and geological evolution. The Mekele Outlier (N Ethiopia) is characterized by poorly incised Mesozoic marine sediments and dolerites (∼2000 m in elevation), surrounded by strongly eroded Precambrian and Paleozoic rocks and Tertiary volcanic deposits in a context of a mantle supported topography. In the past, studies about the Mekele outlier focused mainly in the mere description of the stratigraphic and tectonic settings without taking into account the feedback between surface and deep processes in shaping such peculiar feature. In this study we present the geological and geomorphometric analyses of the Mekele Outlier taking into account the general topographic features (slope map, swath profiles, local relief), the river network and the principal tectonic lineaments of the outlier. The results trace the evolution of the study area as related not only to the mere erosion of the surrounding rocks but to a complex interaction between surface and deep processes where the lithology played a crucial role.

Parallel Extension Tectonics (PET): Early Cretaceous tectonic extension of the Eastern Eurasian continent

NASA Astrophysics Data System (ADS)

Liu, Junlai; Ji, Mo; Ni, Jinlong; Guan, Huimei; Shen, Liang

2017-04-01

The present study reports progress of our recent studies on the extensional structures in eastern North China craton and contiguous areas. We focus on characterizing and timing the formation/exhumation of the extensional structures, the Liaonan metamorphic core complex (mcc) and the Dayingzi basin from the Liaodong peninsula, the Queshan mcc, the Wulian mcc and the Zhucheng basin from the Jiaodong peninsula, and the Dashan magmatic dome within the Sulu orogenic belt. Magmatic rocks (either volcanic or plutonic) are ubiquitous in association with the tectonic extension (both syn- and post-kinematic). Evidence for crustal-mantle magma mixing are popular in many syn-kinematic intrusions. Geochemical analysis reveals that basaltic, andesitic to rhyolitic magmas were generated during the tectonic extension. Sr-Nd isotopes of the syn-kinematic magmatic rocks suggest that they were dominantly originated from ancient or juvenile crust partly with mantle signatures. Post-kinematic mafic intrusions with ages from ca. 121 Ma to Cenozoic, however, are of characteristic oceanic island basalts (OIB)-like trace element distribution patterns and relatively depleted radiogenic Sr-Nd isotope compositions. Integrated studies on the extensional structures, geochemical signatures of syn-kinematic magmatic rocks (mostly of granitic) and the tectono-magmatic relationships suggest that extension of the crust and the mantle lithosphere triggered the magmatisms from both the crust and the mantle. The Early Cretaceous tectono-magmatic evolution of the eastern Eurasian continent is governed by the PET in which the tectonic processes is subdivided into two stages, i.e. an early stage of tectonic extension, and a late stage of collapse of the extended lithosphere and transformation of lithospheric mantle. During the early stage, tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mccs, and triggered plutonic emplacement and volcanic eruptions of hybrid magmas. During the late stage, the nature of mantle lithosphere in North China was changed from the ancient SCLM to the juvenile SCLM. Extensional structures in eastern Eurasian continent provide a general architecture of the extensional tectonics of a rifted continent. Progressive extension resulted a sudden collaps of the crust (lithosphere) at ca. 130 to 120 Ma, associated with exhumation of mcc's and giant syn-kinematic magmatism, and post-kinematic magmatism. Parallel extension of both the crust and the mantle resulted in detachment faulting and magmatism, and also contributed to inhomogeneous thinning of the NCC lithosphere. Paleo-Pacific plate subduction and roll-back of the subducting oceanic plate contributed to the PET tectonic processes.

A coupling between geometry of the main geomagnetic field tectonic margins and seismicity

NASA Astrophysics Data System (ADS)

Khachikyan, Galina

2013-04-01

Integrated studies involving geomagnetism, geodynamics, and seismology are essential for advances in understanding the Earth dynamics. This work presents recent results based of the International Geomagnetic Reference Field (IGRF-10) model, Digital Tectonic Activity Map (DTAM-1), and the global seismological catalogue (173477 events for 1973-2010 with ?≥4.5). It will be shown that: 1. The geometry of the main geomagnetic field controls a spatial distribution of seismicity around the globe. This becomes apparent when geomagnetic field components are analyzed using the geocentric solar magnetospheric (GSM) coordinate system. Earthquakes prefer occur in the regions where geomagnetic Z_GSM component reaches large positive value, that takes place at low and middle latitudes. In the areas of strongest seismicity, that takes place at low and mid latitudes in the eastern hemisphere, the Z_GSM values are largest compared to all other regions of the planet. The possible maximal magnitude of earthquake (Mmax) has a linear dependence on the logarithm of absolute Z_GSM value in the epicenter in the moment of earthquake occurrence. 2. There is a geomagnetic conjugacy between certain tectonic structures. In particular, the middle ocean ridges located in the southern hemisphere along the boundary of the Antarctic tectonic plate are magnetically conjugate with the areas of junction of continental orogens and platforms in the northern hemisphere. Close magnetic conjugacy exists between southern boundary of the Nazca tectonic plate and northern boundaries of the Cocos and Caribbean plates. 3. Variations in the total strength of the main geomagnetic field could be associated, to some extent, with the earthquake occurrence. In particular, the IGRF-10 model shows that in the area of the major 2004 Sumatra earthquake (epicenter 3.3N; 95.98E), the strength of the main geomagnetic field steadily increased from ~ 41338 nT in 1980 to ~ 41855 nT in 2004 with a mean change per year of about 21.6 nT. After the M=9.1 earthquake on December 26 2004, an increase in the geomagnetic field in this area slowed down: from 2005 to 2010, the mean change in geomagnetic field was only 4.7 nT per year. Another example, in the area of a major M=8.0 earthquake in 1995 (epicenter 19.060N; 104.210W) in the Mexican Manzanillo region, the strength of the main geomagnetic field systematically decreased from ~ 42369 nT in 1980 to ~ 41695 nT in 1994 with the mean change of about - 48.1 nT per year. After the earthquake on October 9 1995, the decrease in geomagnetic field speeded up, and from 1995 to 2010, the mean change per year was -77.1 nT. Possible reasons for the observed effects and future research directions in this area will be discussed.

Petrogenesis of Oxidized Arfvedsonite Granite Gneiss from Dimra Pahar, Hazaribagh, Eastern India: Constraints from Mineral Chemistry and Trace Element Geochemistry

NASA Astrophysics Data System (ADS)

Basak, Ankita; Goswami, Bapi

2017-04-01

The arfvedsonite granite gneiss of Dimra Pahar occurs along the North Purulia Shear Zone (NPSZ) which pivots the Proterozoic Chotannagpur Gneissic Complex (CGC), Eastern India. Although minerals like arfvedsonite and aegirine depict the peralkaline nature of the pluton, the geochemistry of the rock reflects its composition varying from peralkaline to mildly peraluminous. K-feldspar, quartz, arfvedsonite, albite with accessory aegirine, titaniferous iron oxides and zircon form the dominant mineralogy of this alkali feldspar granite (IUGS, 2000) gneiss. The zircon saturation temperature corresponds to 747oC-1066oC. The granitic magma contains low water content evidenced by the absence of any pegmatite associated with this pluton. Geochemically these granites are classified as ferroan and alkalic (cf. Frost et al., 2001). These highly evolved granites possess enrichment of SiO2, Na2O + K2O, FeO(t)/MgO, Ga/Al, Zr, Nb, Ga, Y, Ce and rare earth elements (REE) with low abundance of CaO, MgO, Ba and Sr which characterize their A-type nature while standard discrimination diagrams ( cf. Eby, 1992; Grebennikov, 2014) help to further discriminate them as A1 type. Tectonic discriminations diagrams (Pearce et al., 1984; Maniar and Piccoli, 1989; Batchelor and Bowden, 1985) constrain the tectonic setting of the magma to be anorogenic, within plate, rift-related one. The REE compositions show moderately fractionated patterns with (La/Yb)N 2.57-10.5 and Eu/Eu* 0.16-0.70. Multielement spider diagram and various trace element ratio together with oxidized nature (ΔNNO: +2) of these granites further suggest that these have been derived from OIB-type parental magma. The peralkaline nature of the granite and its lack of subduction- related geochemical features are consistent with an origin in a zone of regional extension. The extremely high Rb/Sr ratios combined with the extreme Sr, Ba, P, Ti and Eu depletions clearly indicate that these A-type granites were highly evolved and require advanced fractional crystallization in upper crustal conditions. Major element mass-balance models that use observed phases are consistent with an origin by fractional crystallization from a basaltic parent. The high Sr, Eu and Ba anomalies strongly suggest plagioclase and alkali feldspar fractionation. The abundance of Nb relative to Y reflects pyroxene and amphibole fractionation during differentiation process. EPMA studies of arfvedsonite, aegirine, k-feldspar and albite reveal the pure end-member composition of all the minerals which in turn reflects metamorphism has superimposed on the pluton. The elongated nature of the pluton, metamorphism together with the shear- related deformation as evidenced from the petrographic studies of the rocks suggest syn-tectonic emplacement of the pluton in relation to the kinematics of the North Purulia Shear Zone during 1000Ma (Goswami and Bhattacharyya, 2014). Derivation from basaltic parental magmas indicates that the Dimrapahar pluton represents addition of juvenile material to the crust. References Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J. and Frost, C.D., (2001): A geochemical classification for granitic rocks. Journal of petrology, 42(11):2033-2048. Eby, G.N (1992): Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology, 20(7): 641-644. Le Bas, M. J. (2000). IUGS reclassification of the high-Mg and picritic volcanic rocks. Journal of Petrology, 41(10): 1467-1470. Grebennikov, A. V. (2014): A-type granites and related rocks: petrogenesis and classification. Russian Geology and Geophysics, 55.(11): 1353-1366. Pearce, J.A., Harris, N.B. and Tindle, A.G. (1984): Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of petrology, 25(4): 956-983. Maniar, P.D. and Piccoli, P.M. (1989): Tectonic discrimination of granitoids. Geological society of America bulletin, 101(5): 635-643. Batchelor, R.A. and Bowden, P. (1985): Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chemical geology, 48(1-4): 43-55. Goswami, B. and Bhattacharyya, C. (2014): Petrogenesis of shoshonitic granitoids, eastern India: implications for the late Grenvillian post-collisional magmatism. Geoscience Frontiers, 5(6): 821-843.

An evaporite-bearing accretionary complex in the northern front of the Betic-Rif orogen

NASA Astrophysics Data System (ADS)

Pérez-Valera, Fernando; Sánchez-Gómez, Mario; Pérez-López, Alberto; Pérez-Valera, Luis Alfonso

2017-06-01

The Guadalquivir Accretionary Complex forms a largely oblique prism at the northern edge of the Betic-Rif orogen, where Miocene sediments plus allochthonous evaporite-bearing units were accreted during the displacement of the Alborán Domain toward the west. Traditional interpretations end the tectonic structuring of the Betic Cordillera at the present topographic front, beyond which gravitational and/or diapiric processes would predominate. However, this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics, which is achieved through an alternation of roughly N-S arcuate thrust systems connected by E-W transfer fault zones. These structures accord well with the geophysical models that propose westward rollback subduction. The main stage of tectonic activity occurred in the early-middle Miocene, but deformation lasted until the Quaternary with the same kinematics. Evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area. S- and L- gypsum tectonites, scaly clay fabrics, and brittle fabrics coexist and consistently indicate westward motion (top to 290°), with subordinate N-S contraction almost perpendicular to the transfer zones. This work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic mélanges involving evaporites above the décollement level of accretionary wedges.

An AMS study of the Takidani pluton (Japan)

NASA Astrophysics Data System (ADS)

Hartung, Eva; Caricchi, Luca; Floess, David; Wallis, Simon; Harayama, Satoru

2016-04-01

Large plutonic bodies are typically constructed incrementally often by under-accretion of distinct successive magma pulses. Petrography and geochemistry of the Takidani Pluton (1.54 Ma ± 0.23 Ma) in the Northern Japanese Alps show that the chemical and textural variability observed at the roof of this intrusion is best explained by the segregation of residual melt from a crystallising magma body. We carried out a magnetic susceptibility survey (bulk susceptibility and anisotropy of magnetic susceptibility) to identify the structures associated with the emplacement and extraction of residual melts from a magmatic mush. Additionally, we determined shape preferred orientations (SPO) of amphibole at several locations within the Takidani pluton. From bottom to top of the intrusion, the bulk susceptibility is about constant in the main granodioritic part, decreases roofwards within the porphyritic unit, before increasing again within the marginal granodiorite close to the contact with the overlaying Hotaka Andesite. Such variability mimics the major and trace elements compositional variability measured in the whole rock samples. Magnetic foliations are observed at the western tectonic contact of the pluton potentially indicating overprint, while most other magnetic fabrics across the pluton are characterised by triaxial ellipsoids of magnetic susceptibility or magnetic lineations. Our preliminary data and the lack of internal contacts indicate that Takidani Pluton was likely emplaced as a series of successive magma pulses finally merging to produce a large connected magma body. While amphibole foliations may likely be the results of super-solidus tectonic overprint, anisotropy of magnetic susceptibility data may be related to post-emplacement melt segregation.

The Western Carpathians fold and thrust belt and its relationships with the inner zone of the orogen: constraints from sequentially restored, balanced cross-sections integrated with low-temperature thermochronometry

NASA Astrophysics Data System (ADS)

Mazzoli, Stefano; Castelluccio, Ada; Andreucci, Benedetta; Jankowski, Leszek; Ketcham, Richard A.; Szaniawski, Rafal; Zattin, Massimiliano

2017-04-01

The Western Carpathians are the northernmost, W-E-trending branch of a more than 1500 km long, curved orogen. Traditionally, the Western Carpathians have been divided into two distinct parts, namely the Inner Carpathians (including basement nappes) and the Outer Carpathians fold and thrust belt. These two major domains are separated by the so-called 'Pieniny Klippen Belt', a narrow zone of intensely deformed and sheared Mesozoic to Palaeogene rocks. In this contribution, a new interpretation for the tectonic evolution of the Western Carpathians is provided based on: (i) the analysis of the stratigraphy of the Mesozoic-Tertiary successions across the different orogenic domains; (ii) the construction of a series of balanced and restored cross-sections, validated by 2D forward modeling; and (iii) the integration of a large thermochronometric dataset (apatite fission tracks and apatite and zircon (U-Th-(Sm))/He ages). The latter work included thermo-kinematic modeling using FetKin, a finite element solver that takes as input a series of balanced cross-sections. The software solves the heat flow equations in 2D together with the predicted thermochronometric ages, which can be compared with the measured data. Moreover, the spatial distribution of burial depths, cooling ages and the rate of exhumation were correlated with heat flow, topographic relief, crustal and lithospheric thickness. This process allowed us to obtain the cooling history along each section and test the response of low-temperature thermochronometers to the changes in the thrust belt geometry produced by fault activity and topography evolution. Our sequentially restored, balanced cross-sections, showing a mix of thin-skinned thrusting and thick-skinned tectonic inversion involving the reactivation of pre-existing basement normal faults, effectively unravel the tectonic evolution of the thrust belt-foreland basin system. Our analysis provides a robust correlation of the stratigraphy from the Outer to the Inner Carpathians, independently of the occurrence of oceanic lithosphere in the area; it also allows for the reinterpretation of the tectonic relationships between the two major tectonic domains of the orogen, and the exhumation mechanisms affecting them. The interplay between thick- and thin-skinned thrusting had a relevant effect on the distribution of cooling ages. The non-homogeneous burial and exhumation history unravelled by our work suggests that different exhumation processes controlled the Neogene stages of the Carpathian evolution. In particular, the data point out a significant along-strike variation of exhumation mechanisms in the Outer Carpathian domain, ranging from Early Miocene syn-thrusting erosion to the west, to post-thrusting tectonic denudation in the central sector, to post-thrusting exhumation associated with uplift of the accretionary wedge to the east. Relatively young cooling ages (13 to 4 Ma) obtained for the Inner Carpathian domain were mainly associated with a later uplift, partly controlled by high-angle faulting, and coeval erosion. The effective integration of structural and thermochronometric methods carried out in this study provided, for the first time, a high-resolution thermo-kinematic model of the Western Carpathians from the Early Cretaceous onset of shortening to the present-day.

Constraints on the depth and geometry of the magma chamber of the Olympus Mons Volcano, Mars

NASA Technical Reports Server (NTRS)

Zuber, Maria T.; Mouginis-Mark, Peter J.

1990-01-01

The summit caldera of the Olympus Mons volcano exhibits one of the clearest examples of tectonic processes associated with shield volcanism on Mars. The radial distance from the center of the transition from concentric ridges to concentric graben within the oldest crater provides a constraint on the geometry and depth of the subsurface magmatic reservoir at the time of subsidence. Here, researchers use this constraint to investigate the size, shape, and depth of the reservoir. Their approach consists of calculating radial surface stresses corresponding to the range of subsurface pressure distributions representing an evacuating magma chamber. They then compare stress patterns to the observed radial positions of concentric ridges and graben. The problem is solved by employing the finite element approach using the program TECTON.

Across and along arc geochemical variations in altered volcanic rocks: Evidence from mineral chemistry of Jurassic lavas in northern Chile, and tectonic implications

NASA Astrophysics Data System (ADS)

Rossel, Pablo; Oliveros, Verónica; Ducea, Mihai N.; Hernandez, Laura

2015-12-01

Postmagmatic processes mask the original whole-rock chemistry of most Mesozoic igneous rocks from the Andean arc and back-arc units preserved in Chile. Mineral assemblages corresponding to subgreenschist metamorphic facies and/or propylitic hydrothermal alteration are ubiquitous in volcanic and plutonic rocks, suggesting element mobility at macroscopic and microscopic scale. However, fresh primary phenocrysts of clinopyroxene and plagioclase do occur in some of the altered rocks. We use major and trace element chemistry of such mineral phases to infer the geochemical variations of four Jurassic arc and four back-arc units from northern Chile. Clinopyroxene belonging to rocks of the main arc and two units of the bark-arc are augites with low contents of HFSE and REE; they originated from melting of an asthenospheric mantle source. Clinopyroxenes from a third back-arc unit show typical OIB affinities, with high Ti and trace element contents and low Si. Trace elemental variations in clinopyroxenes from these arc and back-arc units suggest that olivine and clinopyroxene were the main fractionating phases during early stages of magma evolution. The last back-arc unit shows a broad spectrum of clinopyroxene compositions that includes depleted arc-like augite, high Al and high Sr-Ca diopside (adakite-like signature). The origin of these lavas is the result of melting of a mixture of depleted mantle plus Sr-rich sediments and subsequent high pressure fractionation of garnet. Thermobarometric calculations suggest that the Jurassic arc and back-arc magmatism had at least one crustal stagnation level where crystallization and fractionation took place, located at ca. ~ 8-15 km. The depth of this stagnation level is consistent with lower-middle crust boundary in extensional settings. Crystallization conditions calculated for high Al diopsides suggest a deeper stagnation level that is not consistent with a thinned back-arc continental crust. Thus minor garnet fractionation occurred before these magmas reached the base of the crust. The presented data support the existence of a heterogeneous sub arc mantle and complex magmatic processes in the early stages of the Andean subduction.

Mineralogical and geochemical evidence for hydrothermal activity at the west wall of 12°50′N core complex (Mid-Atlantic ridge): a new ultramafic-hosted seafloor hydrothermal deposit?

USGS Publications Warehouse

Dekov, Vesselin; Boycheva, Tanya; Halenius, Ulf; Billstrom, Kjell; Kamenov, George D.; Shanks, Wayne C.; Stummeyer, Jens

2011-01-01

Dredging along the west wall of the core complex at 12°50′N Mid-Atlantic Ridge sampled a number of black oxyhydroxide crusts and breccias cemented by black and dark brown oxyhydroxide matrix. Black crusts found on top of basalt clasts (rubble) are mainly composed of Mn-oxides (birnessite, 10-Å manganates) with thin films of nontronite and X-ray amorphous FeOOH on their surfaces. Their chemical composition (low trace- and rare earth-element contents, high Li and Ag concentrations, rare earth element distribution patterns with negative both Ce and Eu anomalies), Sr–Nd–Pb-isotope systematic and O-isotope data suggest low-temperature (~ 20 °C) hydrothermal deposition from a diffuse vent area on the seafloor. Mineralogical, petrographic and geochemical investigations of the breccias showed the rock clasts were hydrothermally altered fragments of MORBs. Despite the substantial mineralogical changes caused by the alteration the Sr–Nd–Pb-isotope ratios have not been significantly affected by this process. The basalt clasts are cemented by dark brown and black matrix. Dark brown cement exhibits geochemical features (very low trace- and rare earth- element contents, high U concentration, rare earth element distribution pattern with high positive Eu anomaly) and Nd–Pb-isotope systematics (similar to that of MORB) suggesting that the precursor was a primary, high-temperature Fe-sulfide, which was eventually altered to goethite at ambient seawater conditions. The data presented in this work points towards the possible existence of high- and low-temperature hydrothermal activity at the west wall of the core complex at 12°50′N Mid-Atlantic Ridge. Tectonic setting at the site implies that the proposed hydrothermal field is possibly ultramafic-hosted.

Elemental and Sr-Nd isotopic geochemistry of the Uradzhongqi magmatic complex in western Inner Mongolia, China: A record of early Permian post-collisional magmatism

NASA Astrophysics Data System (ADS)

Qiao, Xueyuan; Li, Wenbo; Zhong, Richen; Hu, Chuansheng; Zhu, Feng; Li, Zhihua

2017-08-01

The magmatic complex in Uradzhongqi, Inner Mongolia, is located in the western segment of the northern margin of the North China Craton (NCC). The dominant components in the complex include syenogranite, monzogranite, granodiorite, diorite and gabbro. Mafic microgranular enclaves (MMEs) are common in syenogranite and granodiorite. Zircon U-Pb dating shows that the ages of these rocks range from 283 to 270 Ma, suggesting an early Permian emplacement. The syenogranite and monzogranite are peraluminous I-type granites, exhibiting conspicuous negative Eu anomaly, enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in high field strength elements (HFSE). The granodiorites, diorites and MMEs are metaluminous in composition, show high Al2O3, MgO and Fe2O3T contents and weak negative Eu anomaly, as well as LREE and LILE enrichment and HFSE depletion. The gabbros show weak positive Eu anomaly and slight REE differentiation. The Sr-Nd isotope compositions show that the source of mafic magma was depleted mantle (DM) with possible involvement of enriched mantle II (EM II), whereas the felsic magma was derived from the Archean lower crust. Petrographic observation and analytical results of mineralogy, geochronology, geochemistry and Sr-Nd isotopes indicate that the main petrogenesis of these magmatic rocks is the mixing of underplating mafic magma and felsic magma. Tectonically, the complex pluton was formed within a post-collisional regime, and the underplating in this area provides another piece of evidence for the vertical growth of the western segment of the northern margin of the NCC.

Phanerozoic tectonic evolution of the Circum-North Pacific

USGS Publications Warehouse

Nokleberg, Warren J.; Parfenov, Leonid M.; Monger, James W.H.; Norton, Ian O.; Khanchuk, Alexander I.; Stone, David B.; Scotese, Christopher R.; Scholl, David W.; Fujita, Kazuya

2000-01-01

The Phanerozoic tectonic evolution of the Circum-North Pacific is recorded mainly in the orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern part of the North Asian Craton and the western part of the North American Craton. These collages consist of tectonostratigraphic terranes that are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons; they are overlapped by continental-margin-arc and sedimentary-basin assemblages. The geologic history of the terranes and overlap assemblages is highly complex because of postaccretionary dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins.We analyze the complex tectonics of this region by the following steps. (1) We assign tectonic environments for the orogenic collages from regional compilation and synthesis of stratigraphic and faunal data. The types of tectonic environments include cratonal, passive continental margin, metamorphosed continental margin, continental-margin arc, island arc, oceanic crust, seamount, ophiolite, accretionary wedge, subduction zone, turbidite basin, and metamorphic. (2) We make correlations between terranes. (3) We group coeval terranes into a single tectonic origin, for example, a single island arc or subduction zone. (4) We group igneous-arc and subduction- zone terranes, which are interpreted as being tectonically linked, into coeval, curvilinear arc/subduction-zone complexes. (5) We interpret the original positions of terranes, using geologic, faunal, and paleomagnetic data. (6) We construct the paths of tectonic migration. Six processes overlapping in time were responsible for most of the complexities of the collage of terranes and overlap assemblages around the Circum-North Pacific, as follows. (1) During the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in the fragmentation of each continent and the formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. (2) From about the Late Triassic through the mid-Cretaceous, a succession of island arcs and tectonically paired subduction zones formed near the continental margins. (3) From about mainly the mid-Cretaceous through the present, a succession of igneous arcs and tectonically paired subduction zones formed along the continental margins. (4) From about the Jurassic to the present, oblique convergence and rotations caused orogenparallel sinistral and then dextral displacements within the upper-plate margins of cratons that have become Northeast Asia and North America. The oblique convergences and rotations resulted in the fragmentation, displacement, and duplication of formerly more nearly continuous arcs, subduction zones, and passive continental margins. These fragments were subsequently accreted along the expanding continental margins. (5) From the Early Jurassic through Tertiary, movement of the upper continental plates toward subduction zones resulted in strong plate coupling and accretion of the former island arcs and subduction zones to the continental margins. Accretions were accompanied and followed by crustal thickening, anatexis, metamorphism, and uplift. The accretions resulted in substantial growth of the North Asian and North American Continents. (6) During the middle and late Cenozoic, oblique to orthogonal convergence of the Pacifi c plate with present-day Alaska and Northeast Asia resulted in formation of the modern-day ring of volcanoes around the Circum-North Pacific. Oblique convergence between the Pacific plate and Alaska also resulted in major dextral-slip faulting in interior and southern Alaska and along the western p

Genesis of giant Early Proterozoic magnesite and related talc deposits in the Mafeng area, Liaoning Province, NE China

NASA Astrophysics Data System (ADS)

Misch, David; Pluch, Hannes; Mali, Heinrich; Ebner, Fritz; Huang, Hui

2018-07-01

This study aims to understand the origin of giant magnesite and talc deposits in the Liaohe Group (Liaoning Province, NE China). Magnesite stromatolites and the composition of fluid inclusions suggest that magnesite or high-Mg calcite precipitated directly from strongly restricted seawater pools with meteoric influx. A primary evaporitic origin is also indicated for parts of the investigated dolomites by comparably heavy δ18O values. Later, intense metasomatic activity led to the formation of a magnesite/dolomite succession with irregular contacts and a lighter isotopic signature of oxygen. A slight shift in δ18O to more positive values was observed for talc-hosting magnesite, which can be explained by the incorporation of isotopically light oxygen into talc. This highlights that the hydrothermal processes that led to talc formation influenced the hosting carbonates as well, which is also documented by a tendency to smaller crystal sizes, a higher whiteness and lower trace element concentrations in samples from locations nearby large talc bodies. Although δ13C is suggested to be less sensitive to hydrothermal activity, comparably light δ13C values were determined for magnesite sinters, as well as for remobilized magnesites. In general, the δ13C signature of the investigated magnesites is lighter than expected for Proterozoic carbonates. A single-stage generation of the giant talc deposit in the study area is suggested based on elemental and isotopic data. Later deformation led to a (iso-chemical) re-location of talc at least once. During this process, irregularly distributed, cloudy/massive talc bodies acted as weak zones and were incorporated into shear bands up to several meters in thickness, which form the actually present, structurally controlled deposit. The original ore type is preserved only in areas with minor deformation. Lamprophyre dykes prove Jurassic volcanism and are clearly younger than the main phase of talc generation. A younger (post-Jurassic?), intense tectonic event is indicated by strongly tectonized dyke material that is re-worked into strike-slip faults and shows siliceous contact zones to the surrounding magnesite. These faults occasionally cross-cut the older, deposit-forming talc shear bands, indicating that the event that led to the deformation of lamprophyre dykes was younger than the main phase of talc re-location. However, this younger event did not lead to a second phase of major talc generation or affect the quality of the initial deposit to a large extent.

Location-Based Critical Infrastructure Interdependency (LBCII)

DTIC Science & Technology

2010-04-01

Effective disaster management reduces devastation and cost . This section describes the processes of disaster management, including the elements of CEM...it has reasonable probability, based on the tectonic geology and the history of the region. The case highlights the usability of network- centric...of earthquake risk assessment in Cartago, Costa Rica . International Institute for Geo-Information Science and Earth Observation (ITC): Enschede

The mafic-ultramafic complex of Aniyapuram, Cauvery Suture Zone, southern India: Petrological and geochemical constraints for Neoarchean suprasubduction zone tectonics

NASA Astrophysics Data System (ADS)

Yellappa, T.; Venkatasivappa, V.; Koizumi, T.; Chetty, T. R. K.; Santosh, M.; Tsunogae, T.

2014-12-01

Several Precambrian mafic-ultramafic complexes occur along the Cauvery Suture Zone (CSZ) in Southern Granulite Terrain, India. Their origin, magmatic evolution and relationship with the associated high-grade rocks have not been resolved. The Aniyapuram Mafic-Ultramafic Complex (AMUC), the focus of the present study in southern part of the CSZ, is dominantly composed of peridotites, pyroxenites, gabbros, metagabbros/mafic granulites, hornblendites, amphibolites, plagiogranites, felsic granulites and ferruginous cherts. The rock types in the AMUC are structurally emplaced within hornblende gneiss (TTG) basement rocks and are highly deformed. The geochemical signature of the amphibolites indicates tholeiitic affinity for the protolith with magma generation in island arc-setting. N-MORB normalized pattern of the amphibolites show depletion in HFS-elements (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Rb, Ba, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. Our new results when correlated with the available age data suggest that the lithological association of AMUC represent the remnants of the Neoarchean oceanic lithosphere.

A global geochemical model for the evolution of the mantle

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1979-01-01

It is proposed that the upper mantle transition region, 220 to 670 km, is composed of eclogite which has been derived from primitive mantle by about 20 percent partial melting and that this is the source and sink of oceanic crust. The remainder of the upper mantle is garnet peridotite which is the source of continental basalts and hotspot magmas. This region is enriched in incompatible elements by hydrous and CO2 rich metasomatic fluids which have depleted the underlying layers in the L.I.L. elements and L.R.E.E. The volatiles make this a low-velocity, high attenuation, low viscosity region. The eclogite layer is internally heated and its controls the convection pattern in the upper mantle. Plate tectonics is intermittent. The continental thermal anomaly at a depth of 150-220 km triggers kimberlite and carbonatite activity, alkali and flood basalt volcanism, vertical tectonics and continental breakup. Hot spots remain active after the continents leave and build the oceanic islands. Mantle plumes rise from a depth of about 220 km. Midocean ridge basalts rise from the depleted layer below this depth. Material from this layer can also be displaced upwards by subducted oceanic lithosphere to form back-arc basins.

Spreading vs. Rifting as modes of extensional tectonics on the globally expanded Ganymede

NASA Astrophysics Data System (ADS)

Pizzi, Alberto; Domenica, Alessandra Di; Komatsu, Goro; Cofano, Alessandra; Mitri, Giuseppe; Bruzzone, Lorenzo

2017-05-01

The formation of Ganymede's sulci is likely related to extensional tectonics that affected this largest icy satellite of Jupiter. Through geometric and structural analyses we reconstructed the pre-deformed terrains and we recognized two different modes of extension associated with sulci. In the first mode, smooth sulci constitute spreading centers between two dark terrain plates, similar to the fast oceanic spreading centers on Earth. Here extension is primarily accommodated by crustal accretion of newly formed icy crust. In the second mode, dark terrain extension is mainly accommodated by swaths of normal fault systems analogous to Earth's continental crustal rifts. A comparison with terrestrial extensional analogues, based on the fault displacement/length (Dmax/L) ratio, spacing and morphology, showed that magmato-tectonic spreading centers and continental crustal rifts on Earth follow the same relative patterns observed on Ganymede. Our results suggest that the amount of extensional strain may have previously been underestimated since the occurrence of spreading centers may have played a major role in the tectonic evolution of the globally expanded Ganymede. We also discuss a possible model for the origin of the different modes of extension in the context of the global expansion of the satellite.

Active tectonics and drainage evolution in the Tunisian Atlas driven by interaction between crustal shortening and slab pull

NASA Astrophysics Data System (ADS)

Camafort, Miquel; Booth-Rea, Guillermo; Pérez-Peña, Jose Vicente; Melki, Fetheddine; Gracia, Eulalia; Azañón, Jose Miguel; Ranero, César R.

2017-04-01

Active tectonics in North Africa is fundamentally driven by NW-SE directed slow convergence between the Nubia and Eurasia plates, leading to a region of thrust and strike-slip faulting. In this paper we analyze the morphometric characteristics of the little-studied northern Tunisia sector. The study aimed at identifying previously unknown active tectonic structures, and to further understand the mechanisms that drive the drainage evolution in this region of slow convergence. The interpretation of morphometric data was supported with a field campaign of a selection of structures. The analysis indicates that recent fluvial captures have been the main factor rejuvenating drainage catchments. The Medjerda River, which is the main catchment in northern Tunisia, has increased its drainage area during the Quaternary by capturing adjacent axial valleys to the north and south of its drainage divide. These captures are probably driven by gradual uplift of adjacent axial valleys by reverse/oblique faults or associated folds like El Alia-Teboursouk and Dkhila faults. Our fieldwork found that these faults cut Holocene colluvial fans containing seismites like clastic dikes and sand volcanoes, indicating recent seismogenic faulting. The growth and stabilization of the axial Medjerda River against the natural tendency of transverse drainages might be caused by a combination of dynamic topography and transpressive tectonics. The orientation of the large axial Medjerda drainage that runs from eastern Algeria towards northeastern Tunisia into the Gulf of Tunis, might be the associated to negative buoyancy caused by the underlying Nubia slab at its mouth, together with uplift of the Medjerda headwaters along the South Atlassic dextral transfer zone.

Three-dimensional Gravity Modeling of Ocean Core Complexes at the Central Indian Ridge

NASA Astrophysics Data System (ADS)

Kim, S. S.; Chandler, M. T.; Pak, S. J.; Son, S. K.

2017-12-01

The spatial distribution of ocean core complexes (OCCs) on mid-ocean ridge flanks can indicate the variation of magmatism and tectonic extension at a given spreading center. A recent study revealed 11 prominent OCCs developed along the middle portion of the Central Indian Ridge (CIR) based on the high-resolution shipboard bathymetry. The CIR is located between the Carlsberg Ridge and the Indian Ocean triple junction. The detailed morphotectonic interpretations from the recent study suggested that the middle ridge segments of the CIR were mainly developed through tectonic extension with little magmatism. Furthermore, the OCCs exposed by detachment faults appear to the main host for active off-axis hydrothermal circulations. Here we form a three-dimensional gravity model to investigate the crustal structures of OCCs developed between 12oS and 14oS at the CIR. These OCCs exhibit domal topographic highs with corrugated surface. The rock samples from these areas include deep-seated rocks such as serpentinized harzburgite and gabbro. A typical gravity study on mid-ocean ridges assumes a constant density contrast along the water-crust interface and constant crustal thickness and removes its gravitational contributions and thermal effects of lithospheric cooling from the free-air gravity anomaly. This approach is effective to distinguish anomalous regions that deviate from the applied crustal and thermal models. The oceanic crust around the OCCs, however, tends to be thinned due to detachment faulting and tectonic extension. In this study, we include multi-layers with different density contrast and variable thickness to approximate gravity anomalies resulting from the OCCs. In addition, we aim to differentiate the geophysical characteristics of the OCCs from the nearby ridge segments and infer tectonic relationship between the OCCs and ridges.

Dike orientations in the late jurassic independence dike swarm and implications for vertical-axis tectonic rotations in eastern California

USGS Publications Warehouse

Hopson, R.F.; Hillhouse, J.W.; Howard, K.A.

2008-01-01

Analysis of the strikes of 3841 dikes in 47 domains in the 500-km-long Late Jurassic Independence dike swarm indicates a distribution that is skewed clockwise from the dominant northwest strike. Independence dike swarm azimuths tend to cluster near 325?? ?? 30??, consistent with initial subparallel intrusion along much of the swarm. Dike azimuths in a quarter of the domains vary widely from the dominant trend. In domains in the essentially unrotated Sierra Nevada block, mean dike azimuths range mostly between 300?? and 320??, with the exception of Mount Goddard (247??). Mean dike azimuths in domains in the Basin and Range Province in the Argus, Inyo, and White Mountains areas range from 291?? to 354?? the mean is 004?? in the El Paso Mountains. In the Mojave Desert, mean dike azimuths range from 318?? to 023??, and in the eastern Transverse Ranges, they range from 316?? to 051??. Restoration for late Cenozoic vertical-axis rotations, suggested by paleodeclinations determined from published studies from nearby Miocene and younger rocks, shifts dike azimuths into better agreement with azimuths measured in the tectonically stable Sierra Nevada. This confirms that vertical-axis tectonic rotations explain some of the dispersion in orientation, especially in the Mojave Desert and eastern Transverse Ranges, and that the dike orientations can be a useful if imperfect guide to tectonic rotations where paleomagnetic data do not exist. Large deviations from the main trend of the swarm may reflect (1) clockwise rotations for which there is no paleomagnetic evidence available, (2) dike intrusions of other ages, (3) crack filling at angles oblique or perpendicular to the main swarm, (4) pre-Miocene rotations, or (5) unrecognized domain boundaries between dike localities and sites with paleomagnetic determinations. ?? 2008 The Geological Society of America.

An Integrated View of Tectonics in the North Pacific Derived from GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J.; Marechal, A.; Larsen, C.; Perea Barreto, M. A.

2015-12-01

Textbooks show a simple picture of the tectonics of the North Pacific, with discrete deformation along the boundary between the Pacific and North American plates along the Aleutian megathrust and Fairweather/Queen Charlotte fault system. Reality is much more complex, with a pattern of broadly distributed deformation. This is in part due to a number of studies and initiatives (such as PBO) in recent years that have greatly expanded the density of GPS data throughout the region. We present an overview of the GPS data acquired and various tectonic interpretations developed over the past decade and discuss a current effort to integrate the available data into a regional tectonic model for Alaska and northwestern Canada. Rather than discrete plate boundaries, we observe zones of concentrated deformation where the majority of the relative plate motion is accommodated. Within these zones, there are major fault systems, such as the Fairweather-Queen Charlotte transform and the Aleutian megathrust, where most of the deformation occurs along a main structure, but often motion is instead partitioned across multiple faults, such as the fold-and-thrust belt of the eastern St. Elias orogen. In zones of particular complexity, such as the eastern syntaxis of the St. Elias orogen, the deformation is better described by continuum deformation than localized strain along crustal structures. Strain is transferred far inboard, either by diffuse deformation or along fault system such as the Denali fault, and outboard of the main zones of deformation. The upper plate, if it can be called such, consists of a number of blocks and deforming zones while the lower plate is segmented between the Yakutat block and Pacific plate and is also likely undergoing internal deformation.

Stress state reconstruction and tectonic evolution of the northern slope of the Baikit anteclise, Siberian Craton, based on 3D seismic data

NASA Astrophysics Data System (ADS)

Moskalenko, A. N.; Khudoley, A. K.; Khusnitdinov, R. R.

2017-05-01

In this work, we consider application of an original method for determining the indicators of the tectonic stress fields in the northern Baikit anteclise based on 3D seismic data for further reconstruction of the stress state parameters when analyzing structural maps of seismic horizons and corresponded faults. The stress state parameters are determined by the orientations of the main stress axes and shape of the stress ellipsoid. To calculate the stress state parameters from data on the spatial orientations of faults and slip vectors, we used the algorithms from quasiprimary stress computation methods and cataclastic analysis, implemented in the software products FaultKinWin and StressGeol, respectively. The results of this work show that kinematic characteristics of faults regularly change toward the top of succession and that the stress state parameters are characterized by different values of the Lode-Nadai coefficient. Faults are presented as strike-slip faults with normal or reverse component of displacement. Three stages of formation of the faults are revealed: (1) partial inversion of ancient normal faults, (2) the most intense stage with the predominance of thrust and strike-slip faults at north-northeast orientation of an axis of the main compression, and (3) strike-slip faults at the west-northwest orientation of an axis of the main compression. The second and third stages are pre-Vendian in age and correlate to tectonic events that took place during the evolution of the active southwestern margin of the Siberian Craton.

Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) Model - An Unified Concept for Earthquake Precursors Validation

NASA Technical Reports Server (NTRS)

Pulinets, S.; Ouzounov, D.

2010-01-01

The paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short-term earthquake precursors observed in atmosphere, atmospheric electricity and in ionosphere and magnetosphere. Our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes. Different kind of gases: methane, helium, hydrogen, and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults. Radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere: it is the air ionization and formation by ions the nucleus of water condensation. Condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies. Formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults. Variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors. A newly developed approach of Interdisciplinary Space-Terrestrial Framework (ISTF) can provide also a verification of these precursory processes in seismically active regions. The main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory.

Petroleum geology of Azov-Black Sea region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lukin, A.; Trofimenko, G.

1995-08-01

The main features of tectonics, stratigraphy, paleogeography, lithology, hydrogeology, geothermics and hydrocarbon-bearingness of Azov-Black Sea Region are characterized on the basis of present-day data. Among the most prospective petroliferous complexes one ought to mention: Paleozoic (S - D - C{sub 1}) of Near-Dobrudga foredeep, Triassic - Jurassic of the Black Sea (shelf and continental slope); Lower Cretaceous of the various parts of the Region; Upper Cretaceous of the Black Sea shelf; Paleocene-Eocene of Azov Sea. In addition certain prospects are connected with Precambrian and Paleozoic basements within conjunction zone between Eastern-Europe platform and Scythian plate. Geodynamic evolution of the Regionmore » is considered with determination of tension and compression stages and characteristic of the main regularities of diapirs, mud volcanos, swells, horsts and grabens distribution. There determined the most interesting types of hydrocarbon traps connected with various tectonic forms, river and deltaic channels, bars, conturites, carbonate reefs, etc. Paleogeothermic and paleogeodynamic reconstructions allow to determine the main phases of oil and gas accumulation. The most prospective oil-gas-bearing zones and areas are mapped.« less

Shear-wave polarization analysis of the seismic swarm following the July 9th 1998 Faial (Azores) earthquake

NASA Astrophysics Data System (ADS)

Dias, N. A.; Matias, L.; Tellez, J.; Senos, L.; Gaspar, J. L.

2003-04-01

The Azores Islands, located at a tectonic triple Junction, geodynamically are a highly active place. The seismicity in this region occurs mainly in the form of two types of seismic swarms with tectonic and/or volcanic origins, lasting from hours to years. In some cases the swarm follows a main stronger shock, while in others the more energetic event occurs sometime after the beginning of the swarm. In order to understand the complex phenomena of this region, a multidisciplinary approach is needed, involving geophysical, geological and geochemical studies such as the one being carried under the MASHA project (POCTI/CTA/39158/2001), On July 9th 1998 an Mw=6.2 earthquake stroked the island of Faial, in the central group of the Azores archipelago, followed by a seismic swarm still active today. We will present some preliminary results of the shear-wave polarization analysis of a selected dataset of events of this swarm. These correspond to the 112 best- constrained events, record during the first 2 weeks by the seismic network deployed on the 3 islands surrounding the area of the main shock. The objective was to analyse the behaviour of the S wave polarization and the eventual relationship with the presence of seismic anisotropy under the seismic stations, and to correlate this with the regional structure and origin of the Azores plateau. Two main tectonic features are observable on the islands, one primarily orientated SE-NW and the other crossing it roughly with the WNW-ESE direction. The polarization direction observed in the majority of the seismic stations is not stable, varying from SE-NW to WSW-ENE, and showing also the presence in same cases of shear-wave splitting, indicating the presence of anisotropy. Part of the polarization seems to be coherent with the direction of the local tectonic features, but its instability suggest a more complex seismic anisotropy than that proposed by the model EDA of Crampin. Furthermore, the dataset revealed some limitations to be corrected, such us: the poor azimuthal coverage, the focal mechanism of some events unknown, and the presence of a precursor to the shear-wave marked as an S-wave and affecting the polarization interpretation

Nature and tectonic implications of uneven sedimentary filling of the South China Sea oceanic basin

NASA Astrophysics Data System (ADS)

Yin, Shaoru; Li, Jiabiao; Ding, Weiwei; Fang, Yinxia

2017-04-01

The IODP Expedition 349 in 2014, for the first time, illustrated significant differences of sediment rate and lithology in the central South China Sea (SCS) oceanic basin. Based on seismic reflection profiles tied to IODP349 drilling data, we investigated characteristics of sedimentary filling of the whole SCS oceanic basin, and examined their implications for tectonics. Results show that sediments fill the SCS oceanic basin mainly in three depositional patterns. Firstly, during the Oligocene to middle Miocene, sediments amassed almost solely and then connected like a band parallel to the continent in a low average sediment rate (<10 m/Myr) in the northern oceanic basin. These sediments were deposited mainly in the form of submarine fans and mass transport deposits. Sediments were predominately supplied by the Red and Pearl Rivers and the Dongsha Islands. The sedimentary characteristics likely reflect the latest early Miocene end of seafloor spreading of the SCS and the first-phase rapid uplift of the Tibetan Plateau. Secondly, during the late Miocene, deposition mainly occurred in the Northwest Sub-basin and extended southeastward with a middle average sediment rate ( 30 m/Myr). Sediments were mostly transported by the Red River and Xisha Trough and deposited in the form of submarine fans. The abnormal increase of sediment rate in the Northwest Sub-basin reflects late Miocene slip reversal of the Red River Fault. Finally, since the Pliocene, sediments gradually propagated northeastward in the Southwestern Sub-basin, and accumulated rapidly in the southeastern and northeastern basin, especially in the northern Manila Trench during the Quaternary, in an average sediment rate about 60-80 m/Myr. These sediments were transported mainly by submarine canyons and settled in the form of submarine fans and canyon-overbank deposition. Sediments came from four major sources, including Taiwan, Dongsha Islands, Mekong River, and northern Palawan. The Pliocene to Quaternary explosion of uneven sedimentary filling in the SCS oceanic basin points to the combined action of local and regional tectonics, including the two-phase rapid uplift of the Tibetan Plateau, the Pliocene to Quaternary increased northwestward movement of the Philippine Sea plate and Dongsha event. This study exhibits hitherto most completed observation of sedimentary filling of the SCS oceanic basin and provides new geophysical evidences for the local and regional important tectonics.

Structural analysis and thermal remote sensing of the Los Humeros Volcanic Complex: Implications for volcano structure and geothermal exploration

NASA Astrophysics Data System (ADS)

Norini, G.; Groppelli, G.; Sulpizio, R.; Carrasco-Núñez, G.; Dávila-Harris, P.; Pellicioli, C.; Zucca, F.; De Franco, R.

2015-08-01

The Los Humeros Volcanic Complex (LHVC) is an important geothermal target in the Trans-Mexican Volcanic Belt. Understanding the structure of the LHVC and its influence on the occurrence of thermal anomalies and hydrothermal fluids is important to get insights into the interplay between the volcano-tectonic setting and the characteristics of the geothermal resources in the area. In this study, we present a structural analysis of the LHVC, focused on Quaternary tectonic and volcano-tectonic features, including the areal distribution of monogenetic volcanic centers. Morphostructural analysis and structural field mapping revealed the geometry, kinematics and dynamics of the structural features in the study area. Also, thermal infrared remote sensing analysis has been applied to the LHVC for the first time, to map the main endogenous thermal anomalies. These data are integrated with newly proposed Unconformity Bounded Stratigraphic Units, to evaluate the implications for the structural behavior of the caldera complex and geothermal field. The LHVC is characterized by a multistage formation, with at least two major episodes of caldera collapse: Los Humeros Caldera (460 ka) and Los Potreros Caldera (100 ka). The study suggests that the geometry of the first collapse recalls a trap-door structure and impinges on a thick volcanic succession (10.5-1.55 Ma), now hosting the geothermal reservoir. The main ring-faults of the two calderas are buried and sealed by the widespread post-calderas volcanic products, and for this reason they probably do not have enough permeability to be the main conveyers of the hydrothermal fluid circulation. An active, previously unrecognized fault system of volcano-tectonic origin has been identified inside the Los Potreros Caldera. This fault system is the main geothermal target, probably originated by active resurgence of the caldera floor. The active fault system defines three distinct structural sectors in the caldera floor, where the occurrence of hydrothermal fluids is controlled by fault-induced secondary permeability. The resurgence of the caldera floor could be induced by an inferred magmatic intrusion, representing the heat source of the geothermal system and feeding the simultaneous monogenetic volcanic activity around the deforming area. The operation of the geothermal field and the plans for further exploration should focus on, both, the active resurgence fault system and the new endogenous thermal anomalies mapped outside the known boundaries of the geothermal field.

Localized Failure Promoted by Heterogeneous Stresses in Tectonic Mélanges

NASA Astrophysics Data System (ADS)

Phillips, N. J.; Rowe, C. D.; Ujiie, K.

2017-12-01

Within the shallow (<10 km depth) portion of subduction zones, tectonic mélanges are produced by distributed shear within downgoing sediments above the oceanic plate. Basaltic slabs (incorporated into the sediments through plucking and underplating) and sandstone layers form boudins within a shale dominated matrix due to strength contrasts within this zone of distributed shear. These tectonic mélanges are the host rocks of seismicity in subduction zones at shallow depths. Fluidized gouge and pseudotachylytes are evidence for paleoseismicity within exposures of mélanges, and occur preferentially along the contacts between shale matrix mélange and sandstone or basaltic layers. Detailed mapping within the Mugi Mélange, Japan has revealed basalt boudins enclosed by a cataclasite matrix derived from basalt. We model the stress concentrations around the strong basaltic boudins and slabs using the Power-Law Creep (PLC) toolbox developed at the University of Maine, which uses Asymptotic Expansion Homogenization (AEH) over a finite element mesh to determine the instantaneous stress distributions in a multiphase system. We model the shale matrix mélange to be deforming through a modified flow law for viscous creep based on coupled frictional sliding and pressure solution, where at a strain rate of 10-12 s-1 the flow stress is 10 MPa under the temperature (190 ºC) and pressure ( 100 MPa) conditions during deformation, and describe the behaviour of the basaltic blocks using experimentally-derived power law flow laws. The results show that at the strain rates calculated based on plate-rate motion, differential stresses high enough to cause comminution of the basalts ( 300 MPa) correspond strongly to areas around the blocks with basalt derived cataclasites. Within the basalt derived cataclasites, thin zones of ultracataclasite record localized slip. We hypothesize that the heterogeneous stress distributions within subduction mélanges: 1) fractures the strong basalt thereby facilitating weakening through fluid-rock interactions, and 2) promotes localized slip (and occasionally seismicity) within these zones of altered basalt along the margins of strong intact basalt.

Permian arc-back-arc basin development along the Ailaoshan tectonic zone: Geochemical, isotopic and geochronological evidence from the Mojiang volcanic rocks, Southwest China

NASA Astrophysics Data System (ADS)

Fan, Weiming; Wang, Yuejun; Zhang, Aimei; Zhang, Feifei; Zhang, Yuzhi

2010-10-01

This paper presents a set of new SHRIMP zircon U-Pb geochronological, elemental and Sr-Nd-Pb isotopic data for the Wusu and Yaxuanqiao basaltic rocks (the Mojiang area) along the Ailaoshan tectonic zone. The Wusu basaltic sequence is dominated by SiO 2-poor, MgO- and TiO 2-rich basalts with a major mineral assemblage of plagioclase + clinopyroxene. These rocks gave a SHRIMP zircon U-Pb age of 287 ± 5 Ma (MSWD = 0.58). In contrast, the Yaxuanqiao basaltic sequence is predominantly composed of high-Al basaltic andesite, which gave a SHRIMP zircon U-Pb age of 265 ± 7 Ma (MSWD = 0.34). The analyzed samples for both sequences exhibit significant enrichment in LILEs and depletion in HFSEs with (Nb/La)n of 0.38-0.81, similar to arc-like volcanics. They have positive ɛNd(t) values (+ 3.52 to + 5.54). In comparison with MORB-derived magmatic rocks, the Wusu basalts are more enriched in LILEs and REEs, and the Yaxuanqiao samples are more enriched in LILEs but variably depleted in Ti, Y and HREE. The Wusu samples show high Pb isotopic ratios, similar to the Tethyan basalts, whereas the Yaxuanqiao samples plot in the field of the global pelagic sediments. The geochemical and Sr-Nd-Pb isotopic characteristics suggest that the Wusu basalts originated from a MORB-like source metasomatised by slab-derived fluids, while the Yaxuanqiao rocks have a fluid-modified MORB source with the input of subducted sediments. The geochemical affinity to both MORB- and arc-like sources, together with other geological observations, appears to support the development of a Permian arc-back-arc basin along the Ailaoshan-Song Ma tectonic zone in response to the northward subduction of the Paleotethys main Ocean. The final closure of the arc-back-arc basin took place in the uppermost Triassic due to the diachronous amalgamation between the Yangtze and Simao-Indochina Blocks.

Tectonic setting of Jurassic basins in Central Mongolia: Insights from the geochemistry of Tsagaan-Ovoo oil shale

NASA Astrophysics Data System (ADS)

Erdenetsogt, B. O.; Hong, S. K.; Choi, J.; Odgerel, N.; Lee, I.; Ichinnorov, N.; Tsolmon, G.; Munkhnasan, B.

2017-12-01

Tsagaan-Ovoo syncline hosting Lower-Middle Jurassic oil shale is a part of Saikhan-Ovoo the largest Jurassic sedimentary basin in Central Mongolia. It is generally accepted that early Mesozoic basins are foreland basins. In total, 18 oil shale samples were collected from an open-pit mine. The contents of organic carbon, and total nitrogen and their isotopic compositions as well as major element concentrations were analyzed. The average TOC content is 12.4±1.2 %, indicating excellent source rock potential. C/N ratios show an average of 30.0±1.2, suggesting terrestrial OM. The average value of δ15N is +3.9±0.2‰, while that of δ13Corg is -25.7±0.1‰. The isotopic compositions argue for OM derived dominantly from land plant. Moreover, changes in δ15N values of analyzed samples reflect variations in algal OM concentration of oil shale. The lowest δ15N value (+2.5‰) was obtained from base section, representing the highest amount of terrestrial OM, whereas higher δ15N values (up to +5.2‰) are recorded at top section, reflecting increased amount of algal OM. On the other hand, changes in δ15N value may also represent changes in redox state of water column in paleolake. The oil shale at bottom of section with low δ15N value was accumulated under oxic condition, when the delivery of land plant OM was high. With increase in subsidence rate through time, lake was deepened and water column was depleted in oxygen probably due to extensive phytoplankton growth, which results increase in algae derived OM contents as well as bulk δ15N of oil shale. The average value of CAI for Tsagan-Ovoo oil shale is 81.6±1.3, reflecting intensive weathering in the source area. The plotted data on A-CN-K diagram displays that oil shale was sourced mainly from Early Permian granodiorite and diorite, which are widely distributed around Tsagaan-Ovoo syncline. To infer tectonic setting, two multi-dimensional discrimination diagrams were used. The results suggest that the tectonic setting of Tsagaan-Ovoo syncline, in which the studied oil shale was deposited, was continental rift. This finding contradicts with generally accepted contractile deformation during early Mesozoic in Mongolia and China. Further detailed study is required to decipher the tectonic settings of central Mongolian Jurassic basins.

Geochemistry, geochronology, and tectonic setting of Early Cretaceous volcanic rocks in the northern segment of the Tan-Lu Fault region, northeast China

NASA Astrophysics Data System (ADS)

Ling, Yi-Yun; Zhang, Jin-Jiang; Liu, Kai; Ge, Mao-Hui; Wang, Meng; Wang, Jia-Min

2017-08-01

We present new geochemical and geochronological data for volcanic and related rocks in the regions of the Jia-Yi and Dun-Mi faults, in order to constrain the late Mesozoic tectonic evolution of the northern segment of the Tan-Lu Fault. Zircon U-Pb dating shows that rhyolite and intermediate-mafic rocks along the southern part of the Jia-Yi Fault formed at 124 and 113 Ma, respectively, whereas the volcanic rocks along the northern parts of the Jia-Yi and Dun-Mi faults formed at 100 Ma. The rhyolite has an A-type granitoid affinity, with high alkalis, low MgO, Ti, and P contents, high rare earth element (REE) contents and Ga/Al ratios, enrichments in large-ion lithophile (LILEs; e.g., Rb, Th, and U) and high-field-strength element (HFSEs; e.g., Nb, Ta, Zr, and Y), and marked negative Eu anomalies. These features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment. The basaltic rocks are enriched in light REEs and LILEs (e.g., Rb, K, Th, and U), and depleted in heavy REEs, HFSEs (e.g., Nb, Ta, Ti, and P), and Sr. These geochemical characteristics indicate that these rocks are calc-alkaline basalts that formed in an intraplate extensional tectonic setting. The dacite is a medium- to high-K, calc-alkaline, I-type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc. Therefore, the volcanic rocks along the Jia-Yi and Dun-Mi faults were formed in an extensional regime at 124-100 Ma (Early Cretaceous), and these faults were extensional strike-slip faults at this time.

The Middlesex Fells Volcanic Complex: A Revised Tectonic Model based on Geochronology, Geochemistry, and Field Data

NASA Astrophysics Data System (ADS)

Hampton, R.

2017-12-01

The Boston Bay area is composed of several terranes originating on the paleocontinent of Avalonia, an arc terrane that accreted onto the continent of Laurentia during the Devonian. Included in these terranes is the Middlesex Fells Volcanic Complex, a bimodal complex composed of both intrusive and extrusive igneous rocks. Initial studies suggested that this volcanic complex formed during a rift event as the Avalonian continent separated from its parent continent 700-900 Ma. New geochemical and geochronological data and field relationships observed in this study establishes a new tectonic model. U-Pb laser ablation zircon data on four samples from different units within the complex reveal that the complex erupted 600 Ma. ICP-MS geochemical analysis of the metabasalt member of the complex yield a trace element signature enriched in Rb, Pb, and Sr and depleted in Th, indicating a subduction component to the melt and interpreted as an eruption into a back-arc basin. The felsic units similarly have an arc related signature when plotted on trace element spider diagrams and tectonic discrimination diagrams. Combined with the field relationships, including an erosional unconformity, stratigraphic and intrusional relationships and large faults from episodic extension events, this data suggests that the Middlesex Fells Volcanic Complex was erupted as part of the arc-sequence of Avalonia and as part of the formation of a back-arc basin well after Avalonia separated from its parent continent. This model presents a significantly younger eruption scenario for the Middlesex Fells Volcanics than previously hypothesized and may be used to study and compare to other volcanics from Avalon terranes in localities such as Newfoundland and the greater Boston area.

Provenance and tectonic setting of siliciclastic rocks associated with the Neoproterozoic Dahongliutan BIF: Implications for the Precambrian crustal evolution of the Western Kunlun orogenic belt, NW China

NASA Astrophysics Data System (ADS)

Hu, Jun; Wang, He; Wang, Min

2017-10-01

The Late Neoproterozoic Dahongliutan BIF is associated with siliciclastic rocks in the Tianshuihai terrane of the Western Kunlun orogenic belt (WKO), NW China. The sedimentary rocks have various weathering indices (e.g., CIA = 57-87, PIA = 61-96 and Th/U = 4.85-12.45), indicative of varying degrees of weathering in the source area. The rocks have trace element ratios, such as Th/Sc = 0.60-1.21 and Co/Th = 0.29-1.67, and light rare earth element (LREE) enriched chondrite-normalized REE patterns, suggesting that they were mainly sourced from intermediate and felsic rocks. Available U-Pb ages of detrital zircon from these rocks reveal that the detrital sources may have been igneous and metamorphic rocks from the WKO and the Tarim Block. Our study suggests that the Dahongliutan BIF and hosting siliciclastic rocks may have deposited in a setting transitional from a passive to active continental margin, probably related to the Late Neoproterozoic-Early Cambrian seafloor spreading and subduction of the Proto-Tethys Ocean. U-Pb dating of 163 detrital zircons defines five major age populations at 2561-2329 Ma, 2076-1644 Ma, 1164-899 Ma, 869-722 Ma and 696-593 Ma. These age groups broadly correspond to the major stages of supercontinent assembly and breakup events widely accepted for Columbia, Rodinia and Gondwana. Some zircons have TDM2 model ages of 3.9-1.8 Ga and negative εHf(t) values, suggesting that the Archean to Paleoproterozoic (as old as Eoarchean) crustal materials were episodically reworked and incorporated into the late magmatic process in the WKO. Some Neoproterozoic zircons have TDM2 model ages of 1.47-1.07 Ga and 1.81-1.53 Ga and positive εHf(t) values, indicating juvenile crustal growth during the Mesoproterozoic. Our new results, combined with published data, imply that both the Tianshuihai terrane in the WKO and the Tarim Block share the same Precambrian tectonic evolution history.

Similarity in Evolutionary Histories of Eocene Sediments from Subathu and Cambay Basins: Geochemical and Palaeontological Studies

NASA Astrophysics Data System (ADS)

Chaudhuri, S.; Halder, K.; Sarkar, S.

2017-12-01

A systematic comparative study of microfaunal assemblage and representative geochemical elements from two Cenozoic basins of India, Mangrol-Valia Lignite Mine section (21°30'52''N:73°12'20.5''E) of Cambay Shale Formation, western India and Jigni section (33°14'45"N:74°22'0"E) from Subathu Formation in northern India was undertaken to infer the paleoenvironment, palaeobathymetry and paleoclimate of these successions. Despite a gamut of work already carried out in these two basins, the sedimentary successions still await a correlative-detailed process-based facies, geochemical characterization and paleoenvironmental analysis. With a view to fulfill this gap, the present work was carried out by studying bulk rock XRD, XRF, clay mineralogy and analyzing calcareous microfossil foraminifera from samples at equivalent depth of these two basins which are situated thousands of kilometers apart and in different tectonic settings. The faunal assemblage of Eocene sediments of Mangrol-Valia section is indicative of shallow marine and inner shelf deposition with medium oxygen supply, while that of the Jigni section suggests primarily a shallow marine condition, which gradually changes to open marine condition with time. It is pertinent to note that the two basins of Cenozoic India started their lithosuccession with coal bearing strata. Well preserved pectin aragonite shells also indicate that primarily these two basins experienced low energy lagoonal environment. The fossil assemblage in both basins also suggests a tropical moist to terrestrial lowland environment. Geochemical analysis shows that the Mangrol-Valia section mineralogically comprises of kaolinite, siderite, quartz, smectite and kaolinite with higher abundance throughout the succession indicating chemical weathering of Deccan basement and high erosional environment. Calcite is the main constituent of Jigni section that indicates intracratonic rift settings. Medium to high quartz content and other detrital elements may support increased erosional power, manifested as a quantitative increase in detrital flux for both the basins. So the geochemical and paleontological studies of Subathu and Cambay Shale Formations reveal similar evolutionary history in spite of their different tectonic scenario.

The Late Jurassic Panjeh submarine volcano in the northern Sanandaj-Sirjan Zone, northwest Iran: Mantle plume or active margin?

NASA Astrophysics Data System (ADS)

Azizi, Hossein; Lucci, Federico; Stern, Robert J.; Hasannejad, Shima; Asahara, Yoshihiro

2018-05-01

The tectonic setting in which Jurassic igneous rocks of the Sanandaj-Sirjan Zone (SaSZ) of Iran formed is controversial. SaSZ igneous rocks are mainly intrusive granodiorite to gabbroic bodies, which intrude Early to Middle Jurassic metamorphic basement; Jurassic volcanic rocks are rare. Here, we report the age and petrology of volcanic rocks from the Panjeh basaltic-andesitic rocks complex in the northern SaSZ, southwest of Ghorveh city. The Panjeh magmatic complex consists of pillowed and massive basalts, andesites and microdioritic dykes and is associated with intrusive gabbros; the overall sequence and relations with surrounding sediments indicate that this is an unusually well preserved submarine volcanic complex. Igneous rocks belong to a metaluminous sub-alkaline, medium-K to high-K calc-alkaline mafic suite characterized by moderate Al2O3 (13.7-17.6 wt%) and variable Fe2O3 (6.0-12.6 wt%) and MgO (0.9-11.1 wt%) contents. Zircon U-Pb ages (145-149 Ma) define a Late Jurassic (Tithonian) age for magma crystallization and emplacement. Whole rock compositions are enriched in Th, U and light rare earth elements (LREEs) and are slightly depleted in Nb, Ta and Ti. The initial ratios of 87Sr/86Sr (0.7039-0.7076) and εNd(t) values (-1.8 to +4.3) lie along the mantle array in the field of ocean island basalts and subcontinental metasomatized mantle. Immobile trace element (Ti, V, Zr, Y, Nb, Yb, Th and Co) behavior suggests that the mantle source was enriched by fluids released from a subducting slab (i.e. deep-crustal recycling) with some contribution from continental crust for andesitic rocks. Based the chemical composition of Panjeh mafic and intermediate rocks in combination with data for other gabbroic to dioritic bodies in the Ghorveh area we offer two interpretations for these (and other Jurassic igneous rocks of the SaSZ) as reflecting melts from a) subduction-modified OIB-type source above a Neo-Tethys subduction zone or b) plume or rift tectonics involving upwelling metasomatized mantle (mostly reflecting the 550 Ma Cadomian crust-forming event).

Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times

PubMed Central

Vinci, Giacomo; Forte, Emanuele; Furlani, Stefano; Pipan, Michele; Biolchi, Sara; De Min, Angelo; Fragiacomo, Andrea; Micheli, Roberto; Ventura, Paola; Tuniz, Claudio

2018-01-01

Sinkholes are a well-known geologic hazard but their past occurrence, useful for subsidence risk prediction, is difficult to define, especially for ancient historic times. Consequently, our knowledge about Holocene carbonate landscapes is often limited. A multidisciplinary study of Trieste Karst (Italy), close to early Roman military fortifications, led to the identification of possible ancient road tracks, cut by at least one sinkhole. Electrical Resistivity Tomography through the sinkhole has suggested the presence of a cave below its bottom, possibly responsible of the sinkhole formation, while Ground Penetrating Radar has detected no tectonic disturbances underneath the tracks. Additionally, archaeological surveys led to the discovery of over 200 Roman shoe hobnails within or close to the investigated route. According to these data, the tracks are interpreted as the remains of a main Roman road, whose itinerary has been reconstructed for more than 4 km together with other elements of ancient landscape. Our results provide the first known evidence of a Roman main road swallowed by sinkholes and suggest that Holocene karst landscapes could be much different from what previously believed. In fact, sinkholes visible nowadays in the investigated region could have been flat areas filled by sediments up to the Roman time. PMID:29570732

Quantitative morphometric analysis for the tectonic characterisation of northern Tunisia.

NASA Astrophysics Data System (ADS)

Camafort, Miquel; Pérez-Peña, José Vicente; Booth-Rea, Guillermo; Ranero, César R.; Gràcia, Eulàlia; Azañón, José Miguel; Melki, Fetheddine; Ouadday, Mohamed

2016-04-01

Northern Tunisia is characterized by low deformation rates and low to moderate seismicity. Although instrumental seismicity reaches maximum magnitudes of Mw 5.5, some historical earthquakes have occurred with catastrophic consequences in this region. Aiming to improve our knowledge of active tectonics in Tunisia, we carried out both a quantitative morphometric analysis and field study in the north-western region. We applied different morphometric tools, like river profiles, knickpoint analysis, hypsometric curves and integrals and drainage pattern anomalies in order to differentiate between zones with high or low recent tectonic activity. This analysis helps identifying uplift and subsidence zones, which we relate to fault activity. Several active faults in a sparse distribution were identified. A selected sector was studied with a field campaign to test the results obtained with the quantitative analysis. During the fieldwork we identified geological evidence of recent activity and a considerable seismogenic potential along El Alia-Teboursouk (ETF) and Dkhila (DF) faults. The ETF fault could be responsible of one of the most devastating historical earthquakes in northern Tunisia that destroyed Utique in 412 A.D. Geological evidence include fluvial terraces folded by faults, striated and cracked pebbles, clastic dikes, sand volcanoes, coseismic cracks, etc. Although not reflected in the instrumental seismicity, our results support an important seismic hazard, evidenced by the several active tectonic structures identified and the two seismogenic faults described. After obtaining the current active tectonic framework of Tunisia we discuss our results within the western Mediterranean trying to contribute to the understanding of the western Mediterranean tectonic context. With our results, we suggest that the main reason explaining the sparse and scarce seismicity of the area in contrast with the adjacent parts of the Nubia-Eurasia boundary is due to its extended continental platform and its lack of proto-oceanic crust northward.

The Roles of Tectonics and Climate in Driving Erosion Rates in the Eastern Himalaya

NASA Astrophysics Data System (ADS)

Larsen, I. J.; Montgomery, D.; Stone, J. O.

2016-12-01

Landslide erosion governs the flux of sediment from non-glaciated mountains. Hence patterns in landslide erosion rates have the potential to reveal how such landscapes respond to spatially-varying climatic and tectonic forcing. Across strong spatial gradients in precipitation and exhumation rates in the eastern Himalaya, we mapped 27,611 landslides and measured 10Be in river sediment in a swath spanning from the Himalayan mountain front northward to the Yarlung Tsangpo Gorge. For the entire landscape, landslide erosion and 10Be-based denudation rates are not correlated with mean annual precipitation. However, erosion and denudation rates increase non-linearly as a function of mean hillslope angles, which is diagnostic of tectonic-driven landslide erosion on threshold hillslopes. Dividing the landscape into distinct geologic-tectonic terranes reveals that erosion rates scale positively with both mean hillslope angles and exhumation rates, but also that threshold topography has not developed throughout the region. Mean annual precipitation rates range from 0.5 to 3 m across the terranes, and erosion rates are highest in the relatively dry Yarlung Tsangpo Gorge, which receives 1.5 m of precipitation annually. However, for areas south of the Gorge, where moisture sources from the south first interact with the orographic barrier of the Himalaya, there is a modest linear increase in erosion rate with increasing mean annual rainfall. These results indicate that tectonics is the main control on spatial patterns of erosion in the eastern Himalaya, but that climate may play a modulating role. Hence the relative roles tectonics and climate play in driving erosion rates likely vary at the sub-orogen scale.

Regional tectonic evaluation of the Tuscan Apenine, vulcanism, thermal anomalies and the relation to structural units

NASA Technical Reports Server (NTRS)

Bodechtel, J. (Principal Investigator)

1975-01-01

The author has identified the following significant results. The geological interpretation on data exhibiting the Italian peninsula led to the recognition of tectonic features which are explained by a clockwise rotation of various blocks along left-handed transform faults. These faults can be interpreted as resulting from shear due to main stress directed north-eastwards. A land use map of the mountainous regions of Italy was produced on a scale of 1:250,000. For the digital treatment of MSS-CCTs an image processing software was written in FORTRAN 4. The software package includes descriptive statistics and also classification algorithms.

Le graben de l'Anti-Atlas occidental (Maroc) : contrôle tectonique de la paléogéographie et des séquences au Cambrien inférieurThe Lower-Cambrian western Anti-Atlasic graben: tectonic control of palaeogeography and sequential organisation

NASA Astrophysics Data System (ADS)

Benssaou, Mohammed; Hamoumi, Naı̈ma

2003-03-01

In the Moroccan western Anti-Atlas, the combined extensive tectonic events with a long-term sea-level rise is the main factor on building vertical stacking transgressive-regressive sequences. In the Ait Abdallah-Boussafene axis, the subsidence processes, relayed by a brutal platform tilting generated an elongated NE-SW graben. This is an evidence of the persistence of the Anti-Atlasic rifting process during the last part of the Lower-Cambrian succession.

Comments on the paper of Bodin et al. (2010). Journal of African Earth Sciences, 58, pp. 489-506

NASA Astrophysics Data System (ADS)

Tlig, Saïd

2016-06-01

Bodin et al. (2010) produced an important paper in the Journal of African Earth Sciences. The main goals of this paper were: (1) the petrological and sedimentological treatment of the upper Jurassic and Cretaceous series in southern Tunisia and northern Ghadames Basin including the Hamada El Hamra area and Nafussah Mountain of Libya; (2) the reconstruction of tectonic controls on deposition and basin-fill; (3) the correlation of poorly dated lithostratigraphic columns, poor in diagnostic fauna, from northwestern Libya to southern Tunisia; and (4) the comparison between the authors' findings and assignments of global eustatic and plate tectonic events.

Tectonic wedging in the forearc basin - Accretionary prism transition, Lesser Antilles forearc

NASA Technical Reports Server (NTRS)

Torrini, Rudolph, Jr.; Speed, Robert C.

1989-01-01

This paper describes regional structure of the inner forearc of the southern Lesser Antilles, which contains an extensive 50-70 km wide inner forearc deformation belt (IFDB) developed above crystalline basement of the undeformed forearc basin (FAB), close to and perhaps above its probable subduction trace with Atlantic lithosphere. The IFDB is analyzed, with emphasis placed on five transects across the belt, using mainly migrated seismic sections and balanced model cross sections. The IFDB features and its evolution are discussed, with special attention given to the major structures divided by early and late stages of development, paleobathymetric history, event timing, displacement and strain, and alternative tectonic explanations.

Boron Isotopes as Tracers of the Tectonic Origin and Geological History of Serpentinites in Subduction and Suture Zones.

NASA Astrophysics Data System (ADS)

Martin, C.; Harlow, G. E.; Flores, K. E.; Angiboust, S.

2017-12-01

Serpentinites are known to play a key role in subduction, because they contain significant water content and can be enriched in elements such as As, B, Li, Sb, and U. They originate by hydration of peridotite by two different processes: (i) by a seawater source reacting with peridotite beneath the ocean crust and (ii) by reaction of peridotite at the base of the mantle-wedge with fluids released from the slab during subduction. In suture zones, it is relatively common to find serpentinite from both exhumed subduction channel mélange (from the mantle wedge) and ophiolite (from the oceanic crust), but recognizing them and their tectonic origin can be difficult. A recent study based on samples from the Guatemala Suture Zone demonstrated that boron (B) isotopes can be used as a probe of the fluid from which serpentinites form. Serpentinites from an ophiolite complex have positive δ11B, as expected for peridotites hydrated by seawater-derived fluid, whereas serpentinite samples from the matrix of the mélange (coming from the roof of the subducting channel) have negative δ11B, in agreement with hydration of mantellic peridotites by fluids released at 30-70 km depth from metamorphic rocks. Serpentinites from tectonically well-constrained locations were selected to extend our knowledge of metasomatism in subduction-related areas. The trace-element contents and B isotopes were measured in situ, respectively by LA-ICP-MS and LA-MC-ICP-MS on samples from the oceanic crust (ophiolite = Guatemala, Iran, Cuba), the subduction forearc (Nicaragua), and the mantle wedge (Guatemala, Iran, Japan, Myanmar). The spider diagrams and REE patterns, as well as a B/La vs. As/La diagram do not show any reliable difference to distinguish the tectonic origin of the serpentinite. However, in a δ11B vs. B content diagram, the serpentinites seem to plot in a triangle with fluid endmembers representing (i) seawater (δ11B = 40‰, [B] = 5ppm), (ii) metabasite-issued metamorphic fluids, and (iii) metasediments-issued metamorphic fluids (δ11B varies with temperature from +19 to - 15‰, [B] badly constrained but likely varies with depth (i.e., T) from hundreds (in metasediments) to few (in metabasites) ppm). Thus, the tectonic origin of serpentinites encountered in suture areas as well as the fluid(s) responsible of it might be defined in a δ11B vs. B diagram.

Age and tectonic implications of Paleoproterozoic Deo Khe Granitoids within the Phan Si Pan Zone, Vietnam

NASA Astrophysics Data System (ADS)

Anh, Hoang Thi Hong; Hieu, Pham Trung; Tu, Vu Le; Son, La Mai; Choi, Sung Hi; Yu, Yongjae

2015-11-01

We report the first U-Pb zircon ages of 1855-1873 Ma for the Deo Khe Granitoids (DKG) in the Phan Si Pan Zone (PSPZ) of northern Vietnam. The DKG are medium-grained two-mica granitoids predominantly composed of quartz, K-feldspar, and muscovite. Trace element analyses indicate that the DKG are enriched in large ion lithophile elements but depleted in high field strength elements. Zircons from the granitoids have negative εHf(t) values ranging from -23.6 to -17.5. The magmatic zircons from the DKG have single-stage Hf model ages (TDM1) that range from 3.3 to 2.8 Ga and their εHf(t) data all plot well below the evolution trend of 2800 Ma average juvenile mantle. Observed Hf model ages are contemporaneous with the emplacement of 2.90-2.84 Ga tonalite-trondhjemite-granodiorite (TTG) gneiss observed in a nearby Ca Vinh Complex, suggesting that PSPZ in northern Vietnam is a product of partial melting of Archean crust. A sequence of similar tectonic events including initial emplacement of TTG protolith at 2.8-2.9 Ga, metamorphic development of TTG gneiss at 1.9-2.0 Ga, and magmatic activity at 1.8-2.0 Ga are now recognized both in northern Vietnam and Yangtze block which we interpret to indicate basement rocks in northern Vietnam are similar to those found along southern China.

On the role of fluids in stick-slip dynamics of saturated granular fault gouge using a coupled computational fluid dynamics-discrete element approach

NASA Astrophysics Data System (ADS)

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul A.; Marone, Chris; Carmeliet, Jan

2017-05-01

The presence of fault gouge has considerable influence on slip properties of tectonic faults and the physics of earthquake rupture. The presence of fluids within faults also plays a significant role in faulting and earthquake processes. In this paper, we present 3-D discrete element simulations of dry and fluid-saturated granular fault gouge and analyze the effect of fluids on stick-slip behavior. Fluid flow is modeled using computational fluid dynamics based on the Navier-Stokes equations for an incompressible fluid and modified to take into account the presence of particles. Analysis of a long time train of slip events shows that the (1) drop in shear stress, (2) compaction of granular layer, and (3) the kinetic energy release during slip all increase in magnitude in the presence of an incompressible fluid, compared to dry conditions. We also observe that on average, the recurrence interval between slip events is longer for fluid-saturated granular fault gouge compared to the dry case. This observation is consistent with the occurrence of larger events in the presence of fluid. It is found that the increase in kinetic energy during slip events for saturated conditions can be attributed to the increased fluid flow during slip. Our observations emphasize the important role that fluid flow and fluid-particle interactions play in tectonic fault zones and show in particular how discrete element method (DEM) models can help understand the hydromechanical processes that dictate fault slip.

Hot-spot tectonics of Eistla Regio, Venus: Results from Magellan images and Pioneer Venus gravity

NASA Technical Reports Server (NTRS)

Grimm, Robert E.; Phillips, Roger J.

1991-01-01

Eistla Regio (ER) is a broad, low, discontinuous topographic rise striking roughly EW at low northern latitudes of Venus. Some 2000 x 7000 km in dimensions, it is the third largest rise in planform on Venus after Aphrodite Terra and Beta Phoebe Regiones. These rises are the key physiographic elements in a hot spot model of global tectonics including transient plume behavior. Since ER is the first such rise viewed by Magellan and the latitude is very favorable for Pioneer Venus gravity studies, some of the predictions of a time dependent hot spot model are tested. Western ER is defined as the rise including Gula and Sif Mons and central ER as that including Sappho Patera. Superior conjunction prevented Magellan from returning data on eastern ER (Pavlova) during the first mapping cycle. It is concluded that the western and central portions of ER, while part of the same broad topographic rise and tectonic framework, have distinctly different surface ages and gravity signatures. The western rise, including Gula and Sif Mons, is the expression of deep seated uplift with volcanism limited to the individual large shields. The eastern portion has been widely resurfaced more recently by thermal anomalies in the mantle.

Erosion distribution in Central Nepal Himalaya from late Pleistocene to present : evidence for recent anthropic forcing of erosion of the Lesser Himalaya

NASA Astrophysics Data System (ADS)

France-Lanord, C.; Lave, J.; Morin, G. P.; Gajurel, A.; Galy, A.; Bosia, C.; Sinha, R.

2016-12-01

Evolution of the erosion of continental surfaces through geologic times provides key evidences to assess the interplay of controls exerted by tectonic, topography, climate, and lately, human activities. Mountains belts, and particularly the Himalaya, present intense tectonic activity, contrasted seasonality marked by the monsoon, steep topography and recent socio-economic development, which makes it a laboratory to assess main issues on these complex interactions.Taking advantage of the large Sr and Nd isotopic contrasts of the main geological and physiographic Himalayan units, this study explores the time variations of the spatial distribution of erosion in Central Nepal Himalaya. Compiling Sr and Nd isotopic compositions of rivers sediments from many tributaries within the Narayani Basin in central Nepal, we first define the mean Sr and Nd isotopic compositions of the three main Himalayan geological units in this region. Then, we present isotopic chronicles of river sediments sampled at the outlet of the Narayani Basin during 21 years, and 50-kyr-long sedimentary archives drilled in the foreland basin.Using Sr and Nd isotopic compositions to trace relative geological provenances and contributions, we show that erosion distribution in the Narayani Basin remained stable for 50 kyr until the end of the 20th century. Sediment fluxes were primarily derived from erosion of the High Himalayan regions (Tethys H. and HHC) ( 80 %), i.e. from the areas presenting high reliefs and steep slopes. Erosion distribution stability during the Pleistocene-Holocene climatic transition provides new evidence for a primary control of erosion by tectonic forcing rather than climatic forcing in the Himalayas. Since 2000s, a shift of the sediment isotopic compositions reveals an intensification of erosion in the Lesser Himalaya (from 15-25% to 30-45% of the sediment budget) despite unchanged tectonic or climatic conditions. We propose that this strong increase by 2-3 fold of erosion of the Lesser Himalayan region is a consequence of recent human activities, and likely roads constructions in the Middle Hills of Nepal, highlighting the role of anthropic activities as erosion agents on sensitive environments such as can be mountain ranges.

Rescaled Range analysis of Induced Seismicity: rapid classification of clusters in seismic crisis

NASA Astrophysics Data System (ADS)

Bejar-Pizarro, M.; Perez Lopez, R.; Benito-Parejo, M.; Guardiola-Albert, C.; Herraiz, M.

2017-12-01

Different underground fluid operations, mainly gas storing, fracking and water pumping, can trigger Induced Seismicity (IS). This seismicity is normally featured by small-sized earthquakes (M<2.5), although particular cases reach magnitude as great as 5. It has been up for debate whether earthquakes greater than 5 can be triggered by IS or this level of magnitude only corresponds to tectonic earthquakes caused by stress change. Whatever the case, the characterization of IS for seismic clusters and seismic series recorded close but not into the gas storage, is still under discussion. Time-series of earthquakes obey non-linear patterns where the Hurst exponent describes the persistency or anti-persistency of the sequence. Natural seismic sequences have an H-exponent close to 0.7, which combined with the b-value time evolution during the time clusters, give us valuable information about the stationarity of the phenomena. Tectonic earthquakes consist in a main shock with a decay of time-occurrence of seismic shocks obeying the Omori's empirical law. On the contrary, IS does not exhibit a main shock and the time occurrence depends on the injection operations instead of on the tectonic energy released. In this context, the H-exponent can give information about the origin of the sequence. In 2013, a seismic crisis was declared from the Castor underground gas storing located off-shore in the Mediterranean Sea, close to the Northeastern Spanish cost. The greatest induced earthquake was 3.7. However, a 4.2 earthquake, probably of tectonic origin, occurred few days after the operations stopped. In this work, we have compared the H-exponent and the b-value time evolution according to the timeline of gas injection. Moreover, we have divided the seismic sequence into two groups: (1) Induced Seismicity and (2) Triggered Seismicity. The rescaled range analysis allows the differentiation between natural and induced seismicity and gives information about the persistency and long-term memory of the seismic crisis. These results are a part of the Spanish project SISMOSIMA (CGL2013-47412-C2-2P).

Apatite Fission-Track Analysis of the Middle Jurassic Todos Santos Formation from Chiapas, Mexico.

NASA Astrophysics Data System (ADS)

Abdullin, Fanis; Solé, Jesús; Shchepetilnikova, Valentina; Solari, Luigi; Ortega-Obregón, Carlos

2014-05-01

The Sierra de Chiapas (SCH), located in the south of Mexico, is a complex geological province that can be divided on four different lithological or tectonic areas: (1) the Chiapas Massif Complex (CMC); (2) the Central Depression; (3) the Strike-slip Fault Province, and (4) the Chiapas Fold-and-thrust Belt. The CMC mostly consists of Permian granitoids and meta-granitoids, and represents the basement of the SCH. During the Jurassic period red beds and salt were deposited on this territory, related to the main pulse of rifting and opening of the Gulf of Mexico. Most of the Cretaceous stratigraphy contains limestones and dolomites deposited on a marine platform setting during the postrift stage of the Gulf of Mexico rift. During the Cenozoic Era took place the major clastic sedimentation along the SCH. According the published low-temperature geochronology data (Witt et al., 2012), SCH has three main phases of thermo-tectonic history: (1) slow exhumation between 35 and 25 Ma, that affected mainly the basement (CMC) and is probably related to the migration of the Chortís block; (2) fast exhumation during the Middle-Late Miocene caused by strike-slip deformation that affects almost all Chiapas territory; (3) period of rapid cooling from 6 to 5 Ma, that affects the Chiapas Fold-and-thrust Belt, coincident with the landward migration of the Caribbean-North America plate boundaries. The two last events were the most significant on the formation of the present-day topography of the SCH. However, the stratigraphy of the SCH shows traces of the existence of earlier tectonic events. This study presents preliminary results of apatite fission-track (AFT) dating of sandstones from the Todos Santos Formation (Middle Jurassic). The analyses are performed with in situ uranium determination using LA-ICP-MS (e.g., Hasebe et al., 2004). The AFT data indicate that this Formation has suffered high-grade diagenesis (probably over 150 ºC) and the obtained cooling ages, about 70-60 Ma, correspond to a Late Cretaceous event. This tectonic event is contemporaneous with a startup of the Laramide Orogeny occurred in North America. The constructed time-temperature paths show the rapid cooling during the Middle-Late Miocene (15-10 Ma), like other published data. References: Hasebe et al. (2004) Chemical Geology, 207, 135-145 Witt et al. (2012) Tectonics, 31, TC6001, doi:10.1029/2012TC003141

Deep Landslides in flysch formations

NASA Astrophysics Data System (ADS)

Marinos, Vassilis

2017-04-01

Flysch, linked with the tectonic development of an area, has suffered from compressional forces being highly deformed by thrust faults and folds, containing thus often tectonically pre-sheared zones of various size. These geological characteristics may produce weak to very weak rock masses which may present instability and landslides in both mountain and local slope scale. The paper mainly discusses the "mountain" scale phenomena. The size of these masses can reach hundreds of meters in both depth and width on the valley sides. A brief presentation of the flysch formation is presented. A typology is presented with 11 types of flysch, depending on the persistence and participation or not of the strong members (as sandstones) against the weak ones (as siltstones, shales) and the degree and scale of tectonic disturbance. These rock mass types are connected with the landslide mechanism. In all cases the tectonic conditions of a broader area are responsible and the establishment of the tectonic-paleogeographic model is necessary before the conceptual study and design of any major infrastructure work and the choice of its alignment or location. Given the size of such instability areas remedial measures are in most cases not feasible and the realignment or relocation from the initial plans are often the only solution. Cases from highways and pipelines in Greek and Albanian territory are presented. A large number of information from lab tests, geotechnical classifications and back analyses collected from a wide variety of flysch formations is presented and discussed.

Paleogeographic evolution of the western Maghreb (Berberids) during the Jurassic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmi, S.

1988-08-01

Several basins of the western Maghreb (northwest Africa) have been studied, taking into account their sedimentological and structural evolutions. Special attention is given to paleontological data (biostratigraphy, paleobiology, paleobiogeography). The paleogeographic pattern was the result of the differentiation in four stable blocks (Moroccan Meseta, Oran High Plains, Constantine block, Tunisian north-south ridge) which were developed between the Sahara craton and median strike-slips of the Tethys. This area, called the Berberids, was split by basins and furrows evolving during the Jurassic. Large, shallow, heterochronous initial carbonate platforms (Early Jurassic) were broken by local tectonic movements (tilting and rifting). A mature progradationmore » resulted from a rupture in the balance between carbonate production and subsidence. The result was the growth of more-or-less extended carbonate platforms along the basins margins during the Aalenian and Bajocia. From the late Bajocian, a large deltaic system prograded from the southwest and the west. Terrigenous input and large-scale tectonics provoked the filling of many basins. The southern and western areas became continental. In the north, carbonate series prograded on deltaic formations. A large, shallow platform developed on the southern rim of the Alpine Tethys. The tectonics of the basement on the southern rim of the Alpine Tethys. The tectonics of the basement became less important and sea level changes controlled the sedimentologic evolution. Bio- and chronostratigraphic correlations allow us to chart the main tectonic and eustatic events which occurred in the western Maghreb during the Jurassic.« less

Space geodesy validation of the global lithospheric flow

NASA Astrophysics Data System (ADS)

Crespi, M.; Cuffaro, M.; Doglioni, C.; Giannone, F.; Riguzzi, F.

2007-02-01

Space geodesy data are used to verify whether plates move chaotically or rather follow a sort of tectonic mainstream. While independent lines of geological evidence support the existence of a global ordered flow of plate motions that is westerly polarized, the Terrestrial Reference Frame (TRF) presents limitations in describing absolute plate motions relative to the mantle. For these reasons we jointly estimated a new plate motions model and three different solutions of net lithospheric rotation. Considering the six major plate boundaries and variable source depths of the main Pacific hotspots, we adapted the TRF plate kinematics by global space geodesy to absolute plate motions models with respect to the mantle. All three reconstructions confirm (i) the tectonic mainstream and (ii) the net rotation of the lithosphere. We still do not know the precise trend of this tectonic flow and the velocity of the differential rotation. However, our results show that assuming faster Pacific motions, as the asthenospheric source of the hotspots would allow, the best lithospheric net rotation estimate is 13.4 +/- 0.7 cm yr-1. This superfast solution seems in contradiction with present knowledge on the lithosphere decoupling, but it matches remarkably better with the geological constraints than those retrieved with slower Pacific motion and net rotation estimates. Assuming faster Pacific motion, it is shown that all plates move orderly `westward' along the tectonic mainstream at different velocities and the equator of the lithospheric net rotation lies inside the corresponding tectonic mainstream latitude band (~ +/-7°), defined by the 1σ confidence intervals.

Role of tectonic inheritance in the instauration of Tunisian Atlassic fold-and-thrust belt: Case of Bouhedma - Boudouaou structures

NASA Astrophysics Data System (ADS)

Ghanmi, Mohamed Abdelhamid; Ghanmi, Mohamed; Aridhi, Sabri; Ben Salem, Mohamed Sadok; Zargouni, Fouad

2016-07-01

Tectonic inversion in the Bouhedma-Boudouaou Mountains was investigated through recent field work and seismic lines interpretation calibrated with petroleum well data. Located to the Central-Southern Atlas of Tunisia, this area signed shortened intra-continental fold-and-thrust belts. Two dissymmetric anticlines characterize Bouhedma - Boudouaou major fold. These structures show a strong virgation respectively from E-W to NNE-SSW as a response to the interference between both tectonic inversion and tectonic inheritance. This complex geometry is driven by Mesozoic rifting, which marked an extensional inherited regime. A set of late Triassic-Early Jurassic E-W and NW-SE normal faults dipping respectively to the North and to the East seems to widely affect the overall geodynamic evolution of this domain. They result in major thickness changes across the hanging wall and the footwall blocks in response with the rifting activity. Tectonic inversion is inferred from convergence between African and European plates since late Cretaceous. During Serravalian - Tortonian event, NW-SE trending paroxysm led to: 1) folding of pre-inversion and syn-inversion strata, 2) reactivation of pre-existing normal faults to reverse ones and 3) orogeny of the main structures with NE-SW and E-W trending. The compressional feature still remains active during Quaternary event (Post-Villafranchian) with N-S trending compression. Contraction during inversion generates folding and internal deformation as well as Fault-Propagation-Fold and folding related strike.

Tectonics of Lakshmi Planum, Venus - Tests for Magellan

NASA Technical Reports Server (NTRS)

Grimm, Robert E.; Phillips, Roger J.

1990-01-01

The origin of Lakshmi Planum and its surrounding mountain belts remains an important unresolved element in the global tectonic framework of Venus. From the perspective of gravity signature and potential driving forces, the mantle upwelling model is the simplest, and its principal failure, that it cannot produce radial shortening on the uplift periphery, may be resolved if the lithosphere is laterally heterogeneous. The preferred model consists of a hot mantle plume rising beneath a preexisting block of tessera. The lithosphere is weakened at this hotter and presumably thicker crust, and the outward near-surface flow is attenuated at the peripheral discontinuity in lithospheric strength. Crustal thickening and mountain belt formation occur there. Several criteria are proposed to test this 'tessera-plume' model together with its competitors at the higher resolution in both imaging and gravity afforded by the Magellan mission.

Tectonics of Lakshmi Planum, Venus - Tests for Magellan

NASA Astrophysics Data System (ADS)

Grimm, Robert E.; Phillips, Roger J.

1990-08-01

The origin of Lakshmi Planum and its surrounding mountain belts remains an important unresolved element in the global tectonic framework of Venus. From the perspective of gravity signature and potential driving forces, the mantle upwelling model is the simplest, and its principal failure, that it cannot produce radial shortening on the uplift periphery, may be resolved if the lithosphere is laterally heterogeneous. The preferred model consists of a hot mantle plume rising beneath a preexisting block of tessera. The lithosphere is weakened at this hotter and presumably thicker crust, and the outward near-surface flow is attenuated at the peripheral discontinuity in lithospheric strength. Crustal thickening and mountain belt formation occur there. Several criteria are proposed to test this 'tessera-plume' model together with its competitors at the higher resolution in both imaging and gravity afforded by the Magellan mission.

Geochronology and geochemistry of the Huilvshan gabbro in west Junggar (NW China): Implications for magma process and tectonic regime

NASA Astrophysics Data System (ADS)

Zhang, Huichao; Zhu, Yongfeng

2018-06-01

Gabbro plutons, consisting of clinopyroxene and plagioclase with trace amounts of magnetite, titanite, and apatite, intruded into Early Carboniferous volcanic-sedimentary strata in the Huilvshan gold mining region (west Junggar, China). Samples collected from two gabbro bodies are tholeiitic in composition with low concentrations of Na2O + K2O, showing weak depletions of light rare earth elements with insignificant Eu, Nb, and Ti anomalies. Zircon U-Pb analyses yield a weighted average U-Pb age of 296.1 ± 2.7 Ma (MSWD = 0.98), which could represent the time corresponding to mafic magma emplacement in the Huilvshan region. Geochemical calculations suggest that this mafic magma was derived from a depleted mantle source in a post-collisional tectonic setting corresponding to 4% partial melting of spinel lherzolite.

Α Deformation study in Central Greece using 20 years of GPS data

NASA Astrophysics Data System (ADS)

Marinou, Aggeliki; Papazissi, Kaliopi; Mitsakaki, Christiana; Paradissis, Demitris; Papanikolaou, Xanthos; Anastasiou, Demitris

2015-04-01

Central Greece is a region recognized for its intense tectonic activity with the main characterics being the extension in the North-South direction. This extension is revealed mainly in the form of large parallel grabens. Among these rifts is the Corinth Gulf, which is the most active tectonically, the basin between Parnassos and Kallidromo Mt, the Locris basin and the graben of North Evoikos Gulf, while in the south lays the Thebes basin and the South Evoikos Gulf. Since the late eighties the Laboratory of Higher Geodesy and the Dionysos Satellite Observatory of the National Technical University of Athens, in cooperation with several National and International Universities and Institutions have established, in various Greek areas, of high seismic activity, geodetic networks in order to monitor tectonic displacements. These geodetic networks were observed periodically using Satellite Geodesy techniques and in recent years almost entirely GPS. In this study all the available GPS data, referring to the broader area of Evia, Attiki and Viotia, for the years 1989 to 2008, are analyzed. The displacement field and its temporal changes for the area between the two major geological features, the Corinth Gulf and the Evoikos Gulf, are investigated. Αll the kinematic models that were used do not confirm that the area of study is deforming homogeneously, while an indication of a discontinuity has been detected.

Petrography and geochemistry of the Middle Miocene Gebel El Rusas sandstones, Eastern Desert, Egypt: Implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Zaid, Samir M.

2017-10-01

Petrography and bulk rock geochemistry of the Middle Miocene sandstones of the lower and upper members of Gebel El Rusas Formation along the Egyptian Red Sea Coastal plain, have been investigated to determine the provenance, tectonic setting, and weathering condition of this formation. The Lower Member is formed mainly of sandstones and conglomerates with clay interbeds. The Upper Member is more calcareous and formed mainly of sandstones and limestones with marls and clays intercalations. Petrographically, the Lower Member sandstones are mostly immature and classified as arkoses with an average framework composition of Q_{66}F_{29}R5, and the Upper Member sandstones are partly submature (more quartzose, less feldspathic) and classified as subarkoses with an average framework composition of Q_{80}F_{17}R3. The Gebel El Rusas sandstones are enriched in Sr, Ba, Zr and Rb and depleted in Co and U, as compared to UCC. The chemical index of alteration (CIA) values suggest moderate weathering conditions. The geochemistry results revealed that the Gebel El Rusas sandstones were derived from felsic-granitic source rocks and deposited in a passive margin of a synrift basin. The inferred tectonic setting for Middle Miocene Gebel El Rusas sandstones in the study area is consistent with the regional geology of the Eastern Desert of Egypt during Middle Miocene.

Gliding Box method applied to trace element distribution of a geochemical data set

NASA Astrophysics Data System (ADS)

Paz González, Antonio; Vidal Vázquez, Eva; Rosario García Moreno, M.; Paz Ferreiro, Jorge; Saa Requejo, Antonio; María Tarquis, Ana

2010-05-01

The application of fractal theory to process geochemical prospecting data can provide useful information for evaluating mineralization potential. A geochemical survey was carried out in the west area of Coruña province (NW Spain). Major elements and trace elements were determined by standard analytical techniques. It is well known that there are specific elements or arrays of elements, which are associated with specific types of mineralization. Arsenic has been used to evaluate the metallogenetic importance of the studied zone. Moreover, as can be considered as a pathfinder of Au, as these two elements are genetically associated. The main objective of this study was to use multifractal analysis to characterize the distribution of three trace elements, namely Au, As, and Sb. Concerning the local geology, the study area comprises predominantly acid rocks, mainly alkaline and calcalkaline granites, gneiss and migmatites. The most significant structural feature of this zone is the presence of a mylonitic band, with an approximate NE-SW orientation. The data set used in this study comprises 323 samples collected, with standard geochemical criteria, preferentially in the B horizon of the soil. Occasionally where this horizon was not present, samples were collected from the C horizon. Samples were taken in a rectilinear grid. The sampling lines were perpendicular to the NE-SW tectonic structures. Frequency distributions of the studied elements departed from normal. Coefficients of variation ranked as follows: Sb < As < Au. Significant correlation coefficients between Au, Sb, and As were found, even if these were low. The so-called ‘gliding box' algorithm (GB) proposed originally for lacunarity analysis has been extended to multifractal modelling and provides an alternative to the ‘box-counting' method for implementing multifractal analysis. The partitioning method applied in GB algorithm constructs samples by gliding a box of certain size (a) over the grid map in all possible directions. An "up-scaling" partitioning process will begin with a minimum size or area box (amin) up to a certain size less than the total area A. An advantage of the GB method is the large sample size that usually leads to better statistical results on Dq values, particularly for negative values of q. Because this partitioning overlaps, the measure defined on these boxes is not statistically independent and the definition of the measure in the gliding boxes is different. In order to show the advantages of the GB method, spatial distributions of As, Sb, and Au in the studied area were analyzed. We discussed the usefulness of this method to achieve the numerical characterization of anomalies and its differentiation from the background from the available data of the geochemistry survey.

Geochronology and geochemistry of the Niujuanzi ophiolitic mélange, Gansu Province, NW China: implications for tectonic evolution of the Beishan Orogenic Collage

NASA Astrophysics Data System (ADS)

Wang, Shengdong; Zhang, Kexin; Song, Bowen; Li, Shucai; Li, Ming; Zhou, Jie

2018-01-01

The Niujuanzi ophiolitic mélange (NOM), located in the Beishan Orogenic Collage, marks the termination between the Huaniushan arc and Mingshui-Hanshan Massifs. The NOM is mainly composed of gabbros, diabases, plagiogranites, basalts, and greywacke. Two gabbros have ages of 433.8 ± 3.1 and 354.0 ± 3.3 Ma, two plagiogranites have ages of 429.8 ± 2 and 448.7 ± 2.0 Ma, and a diabase has an age of 433.4 ± 3.2 Ma. The gabbros and diabases are calc-alkaline and tholeiitic, with high Al2O3, CaO, and TiO2 contents and low FeOT contents. The gabbros have high Mg# values (49-82), while the diabases have relatively low Mg# values (46-61). The plagiogranites are calc-alkaline and metaluminous, with high SiO2 and Na2O contents and low Al2O3 and K2O contents. The gabbros and diabases are enriched in large iron lithophile elements and slightly depleted in high field strength elements relative to N-MORB and their trace element characteristics are similar to E-MORB. With respect to rare earth element (REE), they have slightly enriched LREEs relative to HREEs. The majority of the plagiogranite trace elements approximate those of the volcanic arc granite. The plagiogranites have obviously enriched LREEs relative to HREEs, with a slightly to strongly negative Eu anomaly, which is similar to ORG but distinct from volcanic arc and within plate granite. The NOM was formed from the Ordovician to the Carboniferous, representing the expansion period of the Niujuanzi Ocean. The gabbros, diabases, and plagiogranites were formed in a mid-ocean ridge environment. The gabbros and diabases were generated by different degrees of partial melting of the mantle, and the plagiogranites derived from both the crystallization differentiation of basaltic magma and the partial melting of amphibolites in the crust.

The alternative concept of global tectonics

NASA Astrophysics Data System (ADS)

Anokhin, Vladimir; Kholmyansky, Mikhael

2016-04-01

The existing plate tectonic paradigm becomes more questionable in relation to the new facts of the Earth. The most complete to date criticism of plate tectonics provisions contained in the article (Pratt, 2000). Authors can recall a few facts that contradict the idea of long-range movement of plates: - The absence of convection cells in the mantle, detected by seismic tomography; - The presence of long-lived deep regmatic network in the crust, not distorted by the movement of plates; - The inability of linking the global geometry of the of mutual long-distance movement of plates. All this gives reason to believe that correct, or at least a satisfactory concept of global tectonics are not exist now. After overcoming the usual inertia of thinking the plate paradigm in the foreseeable future will replace by different concept, more relevant as the observable facts of the Earth and the well-known physical laws. The authors suggest that currently accumulated sufficient volume of facts and theoretical ideas for the synthesis of a new general hypothesis of the structure and dynamics of the Earth. Analysis of the existing tectonic theory suggests that most of their provisions are mutually compatible. Obviously, plume tectonics perfectly compatible with any of classical models. It contradicts the only plate tectonics (movement of hot spots in principle not linked either with each other or with the general picture of the plate movements, the presence of mantle convection and mantle streams are mutually exclusive, and so on). The probable transfer of the heated material down up within the Earth may occur in various forms, the simplest of which (and, consequently, the most probable) are presented plumes. The existence in the mantle numerous large volumes of decompressed substances (detected seismic tomography), can be correlated with the bodies of plumes at different stages of uplift. Plumes who raise to the bottom of the lithosphere, to spread out to the sides and form a set of lenses partially molten mantle material - asthenolithes previously mistaken for ubiquitous asthenosphere. Interaction between a plumes and their impact on the crust gives rise to all of the observed tectonic processes, including geosynclinal. This scheme is well complemented by some of the elements of plate tectonics, such as the separation of the crust for large plates across the present seismic belts, regional tension along the "divergence" borders, regional compression and collisions along the "convergence" borders. It is necessary to reject the dogmatic, contrary to the facts and unnecessary assumptions about the far moving plates, terraines, "hidden" boundaries, etc. The proposed scheme is contained not so much a new idea as a synthesis of already known ideas. The authors believe that in this way it is possible to construct a general geotectonic concept that would match the best of our knowledge in the earth sciences. Reference: David Pratt, Plate Tectonics: A Paradigm Under Threat - Journal of Scientific Exploration, vol. 14, no. 3, pp. 307-352, 2000.

Cenozoic basin thermal history reconstruction and petroleum systems in the eastern Colombian Andes

NASA Astrophysics Data System (ADS)

Parra, Mauricio; Mora, Andres; Ketcham, Richard A.; Stockli, Daniel F.; Almendral, Ariel

2017-04-01

Late Mesozoic-Cenozoic retro-arc foreland basins along the eastern margin of the Andes in South America host the world's best detrital record for the study of subduction orogenesis. There, the world's most prolific petroleum system occur in the northernmost of these foreland basin systems, in Ecuador, Colombia and Venezuela, yet over 90% of the discovered hydrocarbons there occur in one single province in norteastern Venezuela. A successful industry-academy collaboration applied a multidisciplinary approach to the study of the north Andes with the aim of investigating both, the driving mechanisms of orogenesis, and its impact on hydrocarbon accumulation in eastern Colombia. The Eastern Cordillera is an inversion orogen located at the leading edge of the northern Andes. Syn-rift subsidence favored the accumulation of km-thick organic matter rich shales in a back-arc basin in the early Cretaceous. Subsequent late Cretaceous thermal subsidence prompted the accumulation of shallow marine sandstones and shales, the latter including the Turonian-Cenomanian main hydrocarbon source-rock. Early Andean uplift since the Paleocene led to development of a flexural basin, filled with mainly non-marine strata. We have studied the Meso-Cenozoic thermal evolution of these basins through modeling of a large thermochronometric database including hundreds of apatite and zircon fission-track and (U-Th)/He data, as well as paleothermometric information based on vitrinite reflectance and present-day temperatures measured in boreholes. The detrital record of Andean construction was also investigated through detrital zircon U-Pb geochronometry in outcrop and borehole samples. A comprehensive burial/exhumation history has been accomplished through three main modeling strategies. First, one-dimensional subsidence was used to invert the pre-extensional lithospheric thicknesses, the magnitude of stretching, and the resulting heat flow associated to extension. The amount of eroded section and the maximum temperatures for various stratigraphic units at each locality were calibrated with thermochronometry. Subsequently, two-dimensional thermal models were constructed using thermokinematic modeling of sequentially restored structural cross-sections, for which abundant thermochronometric data was inverse modeled using FETKIN, a software developed within this collaborative project. Finally, the spatial and temporal distribution of source rock exhumation was documented with quantitative modeling of U-Pb data. The results reveal that early Cretaceous back-arc development occurred along a pre-stretched, 90 km thick lithosphere with stretching factors of up to 1.8. Such conditions led to an early Cretaceous high heat flux which, along with rapid syn-rift subsidence, resulted in an early maturation of the potential early Cretaceous source rocks, limiting their ability to expulse hydrocarbons later on, during the petroleum system's critical moment. Our results reveal the competing roles of tectonic inheritance and climate-tectonic feedbacks in the construction of the North Andes and, importantly, illustrate that the Oligocene main inversion of the Eastern Cordillera was a key element for assessing the size of active hydrocarbon kitchens and is a decisive element to consider for volumetric calculations of yet-to-find resources. Our work in the northern Andes demonstrated that thermal and structural kinematic modeling in thrust-belts is greatly improved by a careful usage of geochronological data, which involves robust modeling strategies.

Global Patterns of Tectonism on Titan from Mountain Chains and Virgae

NASA Technical Reports Server (NTRS)

Cook, C.; Barnes, J. W.; Radebaugh, J.; Hurford, T.; Ktatenhorn, S. A.

2012-01-01

This research is based on the exploration of tectonic patterns on Titan from a global perspective. Several moons in the outer solar system display patterns of surface tectonic features that imply global stress fields driven or modified by global forces. Patterns such as these are seen in Europa's tidally induced fracture patterns, Enceladus's tiger stripes, and Ganymede's global expansion induced normal fault bands. Given its proximity to Saturn, as well as its eccentric orbit, tectonic features and global stresses may be present on Titan as well. Titan displays possible tectonic structures, such as mountain chains along its equator (Radebaugh et al. 2007), as well as the unexplored dark linear streaks termed virgae by the IAU. Imaged by Cassini with the RADAR instrument, mountain chains near the equator are observed with a predominante east-west orientation (Liu et al. 2012, Mitri et al. 2010). Orientations such as these can be explained by modifications in the global tidal stress field induced by global contraction followed by rotational spin-up. Also, due to Titan's eccentric orbit, its current rotation rate may be in an equilibrium between tidal spin-up near periapsis and spin-down near apoapsis (Barnes and Fortney 2003). Additional stress from rotational spin-up provides an asymmetry to the stress field. This, combined with an isotropic stress from radial contraction, favors the formation of equatorial mountain chains in an east-west direction. The virgae, which have been imaged by Cassini with both the Visual and Infrared Mapping Spectrometer (VIMS) and Imaging Science Subsystem (ISS) instruments, are located predominately near 30 degrees latitude in either hemisphere. Oriented with a pronounced elongation in the east-west direction, all observed virgae display similar characteristics: similar relative albedos as the surrounding terrain however darkened with an apparent neutral absorber, broken-linear or rounded sharp edges, and connected, angular elements with distinct, linear edges. Virgae imaged during northern latitude passes are oriented with their long dimensions toward Titan's antiSaturn point. If the virgae are of tectonic origin, for instance if the turn out to be i.e. grabens, they could serve as markers to Titan's global stress field. Using them in this way allows for a mapping of global tectonic patterns. These patterns will be tested for consistency against the various sources of global stress and orientations of mountain chains. By determining what drives Titan's tectonics globally, we will be able to place Titan within the context of the other outer planet icy satellites.

Regional and contact metamorphism within the Moy Intrusive Complex, Grampian Highlands, Scotland

NASA Astrophysics Data System (ADS)

Zaleski, E.

1985-04-01

In central Scotland, the Moy Intrusive Complex consists of (1) the Main Phase — syntectonic peraluminous granodiorite to granite emplaced at c. 455 Ma, intruded by (2) the Finglack Alaskite — post-tectonic leucocratic granite emplaced at 407+/-5 Ma. The Main Phase was emplaced into country rocks at amphibolite facies temperatures. Rb-Sr dates and a compositional spectrum of decreasing celadonite content in Main Phase muscovite suggest the persistence of c. 550° C temperatures for c. 30 Ma but with a declining pressure regime, i.e. isothermal uplift. The Finglack Alaskite was intruded at high structural level, leading to the development of a contact metamorphic aureole in the Main Phase. The thermal effects of contact metamorphism include intergrowths of andalusite, biotite and feldspar in pseudomorphs after muscovite. This is associated with recrystallized granoblastic quartz. Muscovite breakdown and reaction with adjacent biotite, quartz and feldspar, i.e. a function of local mineral assemblage rather than bulk rock composition, is postulated to explain the occurrence of metamorphic andalusite in a granitoid rock. The Main Phase pluton of the Moy Intrusive Complex lies within a NNE trending belt of c. 450 Ma Caledonian tectonic and magmatic activity paralleling the Moine Thrust, and extending from northern Scotland to the Highland Boundary Fault. Syntectonic ‘S-type’ magmatism with upper crustal source areas implies crustal thickening and suggests an intracratonic orogeny.

Geochemical element mobility during the hydrothermal alteration in the Tepeoba porphyry Cu-Mo-Au deposits at Balikesir, NW Turkey

NASA Astrophysics Data System (ADS)

Abdelnasser, Amr; Kiran Yildirim, Demet; Doner, Zeynep; Kumral, Mustafa

2016-04-01

The Tepeoba porphyry Cu-Mo-Au deposit represents one of the important copper source and mineral deposits in the Anatolian tectonic belt at Balikesir province, NW Turkey. It considered as a vein-type deposit locally associated with intense hydrothermal alteration within the brecciation, quartz stockwork veining, and brittle fracture zones in the main host rock that represented by hornfels, as well as generally related to the shallow intermediate to silicic intrusive Eybek pluton. Based on the field and geologic relationships and types of ore mineral assemblages and the accompanied alteration types, there are two mineralization zones; hypogene (primary) and oxidation/supergene zones are observed associated with three alteration zones; potassic, phyllic, and propylitic zones related to this porphyry deposit. The phyllic and propylitic alterations locally surrounded the potassic alteration. The ore minerals related to the hypogene zone represented by mostly chalcopyrite, Molybdenite, and pyrite with subordinate amount of marcasite, enargite, and gold. On the other hand they include mainly cuprite with chalcopyrite, pyrite and gold as well as hematite and goethite at the oxidation/supergene zone. This study deals with the quantitative calculations of the mass/volume changes (gains and losses) of the major and trace elements during the different episodes of alteration in this porphyry deposit. These mass balance data reveal that the potassic alteration zone that the main Cu- and Mo-enriched zone, has enrichment of K, Si, Fe, and Mg, and depletion of Na referring to replacement of plagioclase and amphibole by K-feldspar, sericite and biotite. While the propylitic alteration that is the main Mo- and Au-enriched zone is accompanied with K and Na depletion with enrichment of Si, Fe, Mg, and Ca forming chlorite, epidote, carbonate and pyrite. On the other hand the phyllic alteration that occurred in the outer part around the potassic alteration, characterized by less amount of Cu and Mo mineralization having addition of Si and K with removal of Fe, Mg, Ca, and Na. Keywords: Mass balance calculation; Tepeoba porphyry Cu-Mo-Au deposits; Balikesir; Turkey

Morphometric and magmatic evolution at the Boset-Bericha Volcanic Complex in the Main Ethiopian Rift

NASA Astrophysics Data System (ADS)

Siegburg, Melanie; Gernon, Thomas; Bull, Jonathan; Keir, Derek; Taylor, Rex; Nixon, Casey; Abebe, Bekele; Ayele, Atalay

2017-04-01

Tectono-magmatic interactions are an intrinsic feature of continental rifting and break up in the Main Ethiopian Rift (MER). The Boset-Bericha volcanic complex (BBVC) is one of the largest stratovolcanoes in the MER (with a total area of ˜870 km2), with volcanism largely occurring over the last ˜2 Myr. Despite the fact that 4 million people live within 100 km of the volcano, little is known about its eruptive history and how the volcanic system interacts with rift valley tectonics. Here, we present a detailed relative eruption chronology combined with morphometric analyses of different elements of the volcanic complex and petrological analyses to constrain morphometric and magmatic evolution at the BBVC. Additionally, tectonic activity has been characterised around the BBVC, all based on field observations and mapping using high-resolution digital elevation data. The BBVC consists of the Gudda Volcano and the younger Bericha Volcano, two silicic eruption centres located along the NNE-SSW trending rift axis. The fault population predominantly comprises distributed extensional faults parallel to the rift axis, as well as localised discrete faults with displacements of up to 50 m in the rift centre, and up to 200 m in the NE-SW trending border fault system. Multiple cones, craters and fissure systems are also oriented parallel to the rift axis, i.e. perpendicular to the minimum compressive stress. The eruption history of BBVC can be differentiated into 5 main eruption stages, subdivided into at least 12 eruptive phases with a total of 128 mappable lava flows. Crosscutting relationships of lava flows provide a relative chronology of the eruptive history of the BBVC, starting with pre-BBVC rift floor basalts, pre-caldera and caldera activity, three post-caldera phases at the Gudda Volcano and two phases forming the Bericha Volcano. At least four fissure eruption phases occurred along the rift axis temporally in between the main eruptive phases. Morphometric analyses indicate a total corrected volume of eruptive material at the BBVC of ˜36 km3. The magmatic and morphometric evolution of the BBVC is spatially and temporally complex, showing a bimodal distribution of effusive basalts towards explosive peralkaline trachytic and rhyolitic lavas for the Gudda and Bericha Volcano, respectively, with rare intermediate lavas from fissure eruptions. Preliminary geochemical data suggest that fractional crystallisation may have played an important role in driving magmatic evolution the BBVC. This study emphasises the important role of tectono-magmatic interactions in the evolution of a continental rift system.

Tectonics of Europa

NASA Astrophysics Data System (ADS)

Kattenhorn, S. A.; Hurford, T. A.

2007-12-01

This review of Europan tectonics previews a chapter of the forthcoming text "Europa". After the Voyager flyby of the icy moon Europa in 1979, models were developed that attributed pervasive surface fracturing to the effects of tidal forcing due to the gravitational pull of Jupiter. The late 1990s Galileo mission returned high resolution coverage of the surface, allowing a diverse range of tectonic features to be identified. Subsequent description, interpretation, and modeling of these features has resulted in significant developments in five key themes: (1) What drives the tectonics? (2) What are the formation mechanisms of the various types of tectonic features? (3) What are the implications for a subsurface ocean? (4) What is the nature and thickness of the ice shell? (5) Is Europa currently tectonically active? We highlight key developments pertaining to these fundamental issues, focusing on the following elements: (1) Many fracture patterns can be correlated with theoretical stress fields induced by diurnal tidal forcing and long-term effects of nonsynchronous rotation of the ice shell; however, these driving mechanisms alone cannot explain all fracturing. The tectonic fabric has likely been affected by additional contributing effects: tidal despinning, orbital evolution, interior differentiation, polar wander, finite obliquity, stresses due to shell thickening, endogenic forcing by convection and diapirism, and secondary effects driven by strike-slip faulting and plate flexure. (2) Due to the prevalence of global tension, a low lithostatic gradient, and the inherent weakness of ice, tectonic features likely have predominantly extensional primary formation mechanisms (e.g. surface fractures, ridges, and normal faults). There has been no categorical documentation of fracture development by compressive shearing. Even so, the constantly changing nature of the tidal stress field results in shearing reactivation of cracks being important for the morphologic and mechanical development of tectonic features. Hence, strike-slip faults are relatively common. Also, frictional shearing and heating has likely contributed to the construction of edifices along crack margins (i.e., ridges). If Europa has not recently expanded, crustal convergence (although elusive in Galileo images) is required to balance out new surface material created at spreading bands and may be accommodated locally along ridges or convergence bands. (3) Chains of concatenated curved cracks called cycloids provide convincing evidence of a subsurface ocean in that they must be the result of diurnal forcing of sufficient tidal amplitude to break the ice during a large portion of the Europan orbit, suggesting a tidally responding ocean beneath the ice shell. (4) Fracture mechanics reveals that the brittle portion of the ice shell is likely no more than a few km thick, but convection driven diapirism and crater morphologies necessitate a thicker shell overall (up to about 30 km). It is not known if fractures are able to penetrate this entire shell thickness. The brittle layer acts as a stagnant lid to plastic deformation in the ductile portion of the ice shell, resulting in localized brittle deformation. (5) Tectonic resurfacing has dominated the <70 my of visible geologic history. No evidence exists that Europa is currently tectonically active; however, this may be more a failing of the current state of the science rather than a lack of probability. A tectonically based answer to this question lies in a thorough analysis of geologically young surface fractures but would benefit from far more extensive coverage of the surface via a return mission to Europa.

From P-T-age to secular change and global tectonic regimes (or Essene in reverse - from granulites to blueschists and eclogites over time)

NASA Astrophysics Data System (ADS)

Brown, M.

2006-12-01

Essene's contributions began pre-plate tectonics more than 40 years ago; they range from mineralogy to tectonics, from experiments and thermobarometry to elements and isotopes, and from the Phanerozoic to the Precambrian. Eric is a true polymath! Assessing the P-T conditions and age distribution of crustal metamorphism is an important step in evaluating secular change in tectonic regimes and geodynamics. In general, Archean rocks exhibit moderate-P - moderate-to-high-T facies series metamorphism (greenstone belts and granulite terranes); neither blueschists nor any record of deep continental subduction and return are documented and only one example of granulite facies ultrahigh-temperature metamorphism is reported. Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian, although G-UHTM facies series rocks may be inferred at depth in younger orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the formation and breakup of supercontinents, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those around the modern Pacific rim. Medium-temperature eclogite - high-pressure granulite metamorphism (E-HPGM) also is first recognized in the Neoarchean rock record, and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E- HPGM belts are complementary to G-UHTM belts, and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; lawsonite blueschists and eclogites (high-pressure metamorphism, HPM), and ultrahigh pressure metamorphism (UHPM) characterized by coesite or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts - reflecting a duality of thermal regimes - appears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both G- UHTM and E-HPGM belts since the Neoarchean manifests the onset of a `Proterozoic plate tectonics regime', although the style of tectonics likely involved differences from modern Earth. Although the style of Proterozoic subduction remains cryptic, the change in tectonic regime whereby interactions between discrete lithospheric plates generated tectonic settings with contrasting thermal regimes was a landmark event in Earth history. The `Proterozoic plate tectonics regime' evolved during a Neoproterozoic transition to the `modern plate tectonics regime' characterized by colder subduction, and subduction of continental crust deep into the mantle and its (partial) return from depths of up to 300 km, as chronicled by the appearance of blueschists and HPM-UHPM in the rock record.

Beginning the Modern Regime of Subduction Tectonics in Neoproterozoic time: Inferences from Ophiolites of the Arabian-Nubian Shield

NASA Astrophysics Data System (ADS)

Stern, R.

2003-04-01

It is now clear that the motive force for plate tectonics is provided by the sinking of dense lithosphere in subduction zones. Correspondingly, the modern tectonic regime is more aptly called ``subduction tectonics" than plate tectonics, which only describes the way Earth's thermal boundary layer adjusts to subduction. The absence of subduction tectonics on Mars and Venus implies that special circumstances are required for subduction to occur on a silicate planet. This begs the question: When did Earth's oceanic lithosphere cool sufficiently for subduction to began? This must be inferred from indirect lines of evidence; the focus here is on the temporal distribution of ophiolites. Well-preserved ophiolites with ``supra-subduction zone" (SSZ) affinities are increasingly regarded as forming when subduction initiates as a result of lithospheric collapse (± a nudge to get it started), and the formation of ophiolitic lithosphere in evolving forearcs favors their emplacement and preservation. The question now is what percentage of ophiolites with ``supra-subduction zone" (SSZ) chemical signatures formed in forearcs during subduction initiation events? Most of the large, well-preserved ophiolites (e.g., Oman, Cyprus, California, Newfoundland) may have this origin. If so, the distribution in space and time of such ophiolites can be used to identify ``subduction initiation" events, which are important events in the evolution of plate tectonics. Such events first occurred at the end of the Archean (˜2.5Ga) and again in the Paleoproterozoic (˜1.8 Ga), but ophiolites become uncommon after this. Well-preserved ophiolites become abundant in Neoproterozoic time, at about 800±50 Ma. Ophiolites of this age are common and well-preserved in the Arabian-Nubian Shield (ANS) of Egypt, Sudan, Ethiopia, Eritrea, and Saudi Arabia. ANS ophiolites mostly contain spinels with high Cr#, indicating SSZ affinities. Limited trace element data on pillowed lavas supports this interpretation. Boninites are unusual melts of harzburgite that result from asthenospheric upwelling interactng with slab-derived water. This environment is only common during subduction initiation events. Boninites associated with ophiolites have been reported from Egypt, Ethiopia and Eritrea, but most of the geochemical studies of ANS ophiolitic basalts are based on studies that are a decade or more old. The abundance of ANS ophiolites implies an episode of subduction initiation occurred in Neoproterozoic time.

Tectonic state: its significance and characterization in the assessment of seismic effects associated with reservoir impounding

USGS Publications Warehouse

Castle, R.O.; Clark, M.M.; Grantz, A.; Savage, J.C.

1980-01-01

Any analysis of seismicity associated with the filling of large reservoirs requires an evaluation of the natural tectonic state in order to determine whether impoundment is the basic source, a mechanically unrelated companion feature, or a triggering stimulus of the observed seismicity. Several arguments indicate that the associated seismicity is usually a triggered effect. Among the elements of tectonic state considered here (existing fractures, accumulated elastic strain, and deformational style), deformational style is especially critical in forecasting the occurrence of impoundment-induced seismicity. The observational evidence indicates that seismicity associated with impounding generally occurs in areas that combine steeply dipping faults, relatively high strain rates, and either extensional or horizontal-shear strain. Simple physical arguments suggest: (1) that increased fluid pressures resulting from increased reservoir head should enhance the likelihood of seismic activity, whatever the tectonic environment; (2) that stress changes resulting from surface loading may increase the likelihood of crustal failure in areas of normal and transcurrent faulting, whereas they generally inhibit failure in areas of thrust faulting. Comparisons with other earthquake-producing artificial and natural processes (underground explosions, fluid injection, underground mining, fluid extraction, volcanic emissions) indicate that reservoir loading may similarly modify the natural tectonic state. Subsurface loading resulting from fluid extraction may be a particularly close analogue of reservoir loading; "seismotectonic" events associated with fluid extraction have been recognized in both seismically active and otherwise aseismic regions. Because the historic record of seismicity and surface faulting commonly is short in comparison with recurrence intervals of earthquake and fault-slip events, tectonic state is most reliably appraised through combined studies of historic seismicity and faulting, instrumentally measured strain, and the geological record, especially that of the Quaternary. Experience in California and elsewhere demonstrates that the character and activity of recognized faults can be assessed by means of: instrumental earthquake investigations, repeated geodetic measurements, written history, archeological studies, fault topography, and local stratigraphic relations. Where faults are less easily distinguished, appraisals of tectonic state may be based on both the regional seismicity and the regional history of vertical movement as shown by: repeated levelling and sea-level measurements, written history, archeologic investigations, terrace and shoreline deformation, and denudation and sedimentation studies. ?? 1980.

Structural control on geothermal circulation in the Cerro Tuzgle-Tocomar geothermal volcanic area (Puna plateau, Argentina)

NASA Astrophysics Data System (ADS)

Giordano, Guido; Pinton, Annamaria; Cianfarra, Paola; Baez, Walter; Chiodi, Agostina; Viramonte, José; Norini, Gianluca; Groppelli, Gianluca

2013-01-01

The reconstruction of the stratigraphical-structural framework and the hydrogeology of geothermal areas is fundamental for understanding the relationships between cap rocks, reservoir and circulation of geothermal fluids and for planning the exploitation of the field. The Cerro Tuzgle-Tocomar geothermal volcanic area (Puna plateau, Central Andes, NW Argentina) has a high geothermal potential. It is crossed by the active NW-SE trans-Andean tectonic lineament known as the Calama-Olacapato-Toro (COT) fault system, which favours a high secondary permeability testified by the presence of numerous springs. This study presents new stratigraphic and hydrogeological data on the geothermal field, together with the analysis from remote sensed image analysis of morphostructural evidences associated with the structural framework and active tectonics. Our data suggest that the main geothermal reservoir is located within or below the Pre-Palaeozoic-Ordovician basement units, characterised by unevenly distributed secondary permeability. The reservoir is recharged by infiltration in the ridges above 4500 m a.s.l., where basement rocks are in outcrop. Below 4500 m a.s.l., the reservoir is covered by the low permeable Miocene-Quaternary units that allow a poor circulation of shallow groundwater. Geothermal fluids upwell in areas with more intense fracturing, especially where main regional structures, particularly NW-SE COT-parallel lineaments, intersect with secondary structures, such as at the Tocomar field. Away from the main tectonic features, such as at the Cerro Tuzgle field, the less developed network of faults and fractures allows only a moderate upwelling of geothermal fluids and a mixing between hot and shallow cold waters. The integration of field-based and remote-sensing analyses at the Cerro Tuzgle-Tocomar area proved to be effective in approaching the prospection of remote geothermal fields, and in defining the conceptual model for geothermal circulation.

Updating of the geological and geothermal research on Milos island

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fytikas, M.

1989-01-01

The oldest geologic formations outcropping in Milos are an Alpine age crystalline basement and a transgressive marine Neogene sequence. The island is mainly volcanic. It belongs to the Aegean Active Arc, within which the Milos archipelago shows the most important volcanism in terms of quantity, variety of products and duration of activity (3.5-0.8 M.a.). There are no large central volcanic edifices but different, frequently coeval eruption centres. The initial and intermediate phases of activity were mainly pyroclastic and submarine, whereas the last one (0.1 M.a.) was subaerial and formed tuff rings, surge deposits and lava flows, all of homogenous rhyoliticmore » composition. Recent detailed studies have addressed the mechanism of feeding and the type of magmatic chambers beneath Milos. Distention tectonics have two main phases: an earlier one (Pliocene) with NE-SW direction and a much more intense recent (Quaternary) one, trending NW-SE. The geological, tectonic and magmatic activity favoured the formation of a high enthalpy geothermal field. Many fossil and active thermal manifestations exist: hot springs, fumaroles, hot grounds, phreatic explosion craters. The hydrothermal alteration of the volcanites produced, by self sealing, a perfect cover for the geothermal fluids. Geothermometry of the surface fluids indicated high values for the source temperatures and very high geothermal gradients in central and eastern Milos. Geothermally anomalous zones, defined by two different methods, together with superficial geological and tectonic information, permitted the location of sites for deep drilling. Five exploratory wells 1000-1400m deep gave satisfactory results of flow rate (40-120 t/h), temperature (300-320{sup 0}C) and enthalpy.« less

Application of multi-dimensional discrimination diagrams and probability calculations to Paleoproterozoic acid rocks from Brazilian cratons and provinces to infer tectonic settings

NASA Astrophysics Data System (ADS)

Verma, Sanjeet K.; Oliveira, Elson P.

2013-08-01

In present work, we applied two sets of new multi-dimensional geochemical diagrams (Verma et al., 2013) obtained from linear discriminant analysis (LDA) of natural logarithm-transformed ratios of major elements and immobile major and trace elements in acid magmas to decipher plate tectonic settings and corresponding probability estimates for Paleoproterozoic rocks from Amazonian craton, São Francisco craton, São Luís craton, and Borborema province of Brazil. The robustness of LDA minimizes the effects of petrogenetic processes and maximizes the separation among the different tectonic groups. The probability based boundaries further provide a better objective statistical method in comparison to the commonly used subjective method of determining the boundaries by eye judgment. The use of readjusted major element data to 100% on an anhydrous basis from SINCLAS computer program, also helps to minimize the effects of post-emplacement compositional changes and analytical errors on these tectonic discrimination diagrams. Fifteen case studies of acid suites highlighted the application of these diagrams and probability calculations. The first case study on Jamon and Musa granites, Carajás area (Central Amazonian Province, Amazonian craton) shows a collision setting (previously thought anorogenic). A collision setting was clearly inferred for Bom Jardim granite, Xingú area (Central Amazonian Province, Amazonian craton) The third case study on Older São Jorge, Younger São Jorge and Maloquinha granites Tapajós area (Ventuari-Tapajós Province, Amazonian craton) indicated a within-plate setting (previously transitional between volcanic arc and within-plate). We also recognized a within-plate setting for the next three case studies on Aripuanã and Teles Pires granites (SW Amazonian craton), and Pitinga area granites (Mapuera Suite, NW Amazonian craton), which were all previously suggested to have been emplaced in post-collision to within-plate settings. The seventh case studies on Cassiterita-Tabuões, Ritápolis, São Tiago-Rezende Costa (south of São Francisco craton, Minas Gerais) showed a collision setting, which agrees fairly reasonably with a syn-collision tectonic setting indicated in the literature. A within-plate setting is suggested for the Serrinha magmatic suite, Mineiro belt (south of São Francisco craton, Minas Gerais), contrasting markedly with the arc setting suggested in the literature. The ninth case study on Rio Itapicuru granites and Rio Capim dacites (north of São Francisco craton, Serrinha block, Bahia) showed a continental arc setting. The tenth case study indicated within-plate setting for Rio dos Remédios volcanic rocks (São Francisco craton, Bahia), which is compatible with these rocks being the initial, rift-related igneous activity associated with the Chapada Diamantina cratonic cover. The eleventh, twelfth and thirteenth case studies on Bom Jesus-Areal granites, Rio Diamante-Rosilha dacite-rhyolite and Timbozal-Cantão granites (São Luís craton) showed continental arc, within-plate and collision settings, respectively. Finally, the last two case studies, fourteenth and fifteenth showed a collision setting for Caicó Complex and continental arc setting for Algodões (Borborema province).

Geodynamic control on melt production in the central Azores : new insights from major and trace elements, Sr, Nd, Pb, Hf isotopic data and K/Ar ages on the islands of Terceira, Sao Jorge and Faial

NASA Astrophysics Data System (ADS)

Hildenbrand, A.; Weis, D. A.; Madureira, P.; Marques, F. O.

2012-12-01

A combined geochronological and geochemical study has been carried out on the volcanic islands of Terceira, São Jorge, and Faial (central Azores) to examine the relationships between mantle dynamics, melt production and regional deformation close to the triple junction between the American, the Eurasian and the Nubian lithospheric plates. The lavas analyzed span the last 1.3 Myr, and have been erupted during two main periods prior to 800 ka and after 750 ka, respectively. They range in composition from alkaline basalts/basanites to trachytes, and overall exhibit a strong enrichment in highly incompatible elements. The whole range of isotopic compositions here reported (87Sr/86Sr: 0.703508-0.703913; 143Nd/144Nd: 0.512882-0.513010; 206Pb/204Pb: 19.0840- 20.0932; 207Pb/204Pb: 15.5388-15.6409; 208Pb/204Pb: 38.7416-39.3921; 176Hf/177Hf: 0.282956-0.283111) suggests the involvement of three components: (1) a weakly radiogenic component reflecting the source of regional MORBs, (2) a main HIMU-type component represented in the three islands, and (3) an additional component in Faial recent lavas, which appears similar to the EM type end-member previously recognized on other Azores eruptive complexes. The geographical distribution of the enriched components and the synchronous construction of various islands at the regional scale rules out a single narrow active plume. They suggest in turn the presence of dispersed residual enriched mantle blobs, interpreted as remnants from a large heterogeneous plume probably responsible for edification of the Azores plateau several Myr ago. The lavas erupted in São Jorge and Faial prior to 800 ka have similar and homogeneous isotopic ratios, which partly overlap the compositional field of MORBs from the adjacent portion of the Mid-Atlantic Ridge (MAR). Their genesis can be explained by the regional development of N150 transtensive tectonic structures, which promoted significant decompression melting of the upper mantle, with correlative dilute expression of the enriched components. In contrast, the youngest lavas (< 750 ka) erupted along the N110 main structural direction on the three islands are significantly enriched in LILE and LREE, and generally have variable but more radiogenic isotopic compositions. Such characteristics suggest low-degree partial melting and greater incorporation of fertile residual mantle anomalies during passive tectonic reactivation of pre-existing transform faults promoted by recent ridge-push at the MAR. We propose that sub-aerial volcanism over the last 1.3 Myr in the central Azores recorded a sudden change in the conditions of melt generation which most probably reveals a major reconfiguration of regional deformation accompanying the recent geodynamic reorganization of the Eurasia-Nubia plate boundary.

Beneath the scaly clay and clay breccia of Karangsambung area

NASA Astrophysics Data System (ADS)

Arisbaya, Ilham; Handayani, Lina

2018-02-01

Karangsambung area, Central Java-Indonesia, records tectonic evolution of the western part of Sundaland margin. The area is thought to have undergone a long tectonic evolution from palaeosubduction, collision with the continental fragments of Gondwana, to the formation of the recent subduction zone. An interesting phenomenon in this area is the presence of the Late Cretaceous ophiolitic blocks with an east northeast (ENE) trending-direction surrounded by the east trend of Eocene - Oligocene sedimentary melange formation. There was also an ENE trending Dakah volcanic rocks unit found in this area, with approximately equivalent age with the sedimentary mélange formation. There are two main interpretations regarding this volcanic unit, as an olistostrome and as an insitu shallow subduction magmatic product. Detailed mechanism of the emplacement of the Late Cretaceous ophiolite and the genesis of the volcanic rocks unit and their implications to the regional tectonic model is still open for discussion. Geophysical research in this key area may help to reveal the geometry, relationship among rocks units, and tectonic evolution. Unfortunately, geophysical studies in this area are still lacking. Previous geophysical work in Karangsambung still leaves uncertainty, especially in depth control and spatial resolution issue. Here we describe the results of previous works in Karangsambung as basic knowledge for the upcoming geophysical study.

Evolution of the Mazatzal province and the timing of the Mazatzal orogeny: Insights from U-Pb geochronology and geochemistry of igneous and metasedimentary rocks in southern New Mexico

USGS Publications Warehouse

Amato, J.M.; Boullion, A.O.; Serna, A.M.; Sanders, A.E.; Farmer, G.L.; Gehrels, G.E.; Wooden, J.L.

2008-01-01

New U-Pb zircon ages, geochemistry, and Nd isotopic data are presented from three localities in the Paleoproterozoic Mazatzal province of southern New Mexico, United States. These data help in understanding the source regions and tectonic setting of magmatism from 1680 to 1620 Ma, the timing of the Mazatzal orogeny, the nature of postorogenic maginatism, Proterozoic plate tectonics, and provide a link between Mazatzal subblocks in Arizona and northern New Mexico. The data indicate a period from 1680 to 1650 Ma in which juvenile felsic granitoids were formed, and a later event between 1646 and 1633 Ma, when these rocks were deformed together with sedimentary rocks. No evidence of pre-1680 Ma rocks or inherited zircons was observed. The igneous rocks have ENd(t) from -1.2 to +4.3 with most between +2 and +4, suggesting a mantle source or derivation from similar-aged crust. Nd isotope and trace element concentrations are consistent with models for typical are magmatism. Detrital zircon ages from metasedimentary rocks indicate that sedimentation occurred until at least 1646 Ma. Both local and Yavapai province sources contributed to the detritus. All of the samples older than ca. 1650 Ma are deformed, whereas undeformed porphyroblasts were found in the contact aureole of a previously dated 1633 Ma gabbro. Regionally, the Mlazatzal orogeny occurred mainly between 1654 and 1643 Ma, during final accretion of a series of island arcs and intervening basins that may have amalgamated offshore. Rhyolite magmatism in the southern Mazatzal province was coeval with gabbro intrusions at 1633 Ma and this bimodal magmatism may have been related to extensional processes following arc accretion. ?? 2007 Geological Society of America.

Magnesium Isotopic Compositions of Continental Basalts From Various Tectonic Settings

NASA Astrophysics Data System (ADS)

Yang, W.; Li, S.; Tian, H.; Ke, S.

2016-12-01

Recycled sedimentary carbonate through subduction is the main light Mg isotopic reservoir in Earth's deep interior, thus Mg isotopic variation of mantle-derived melts provides a fresh perspective on investigating deep carbon cycling. Here we investigate Mg isotopic compositions of continental basalts from various tectonic settings: (1) The Cenozoic basalts from eastern China, coinciding with the stagnant Pacific slab in the mantle transition zone revealed by seismic tomography; (2) The Cenozoic basalts from Tengchong area, southwestern China, which comprises a crucial part of the collision zone between the Indian and Eurasian plates; (3) The Permian basalts from Emeishan large igneous province, related to a mantle plume. The Cenozoic basalts from both eastern China and Tengchong area exhibit light Mg isotopic compositions (δ26Mg = -0.60 to -0.30‰ and -0.51 to -0.33‰), suggesting recycled sedimentary carbonates in their mantle sources. This is supported by their low Fe/Mn, high CaO/Al2O3, low Hf/Hf* and low Ti/Ti* ratios, which are typical features of carbonated peridotite-derived melt. The Tengchong basalts also show high 87Sr/86Sr, high radiogenic Pb and upper crustal-like trace element pattern, indicating contribution of recycled continental crustal materials. By contrast, all Emeishan basalts display a mantle-like Mg isotopic composition, with δ26Mg ranging from -0.35 to -0.19‰. Since the Emeishan basalts derived from a mantle plume, their mantle-like Mg isotopic composition may indicate limited sedimentary carbonated recycled into the lower mantle. This is consistent with a recent experimental study which concluded that direct recycling of carbon into the lower mantle may have been highly restricted throughout most of the Earth's history.

The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

NASA Astrophysics Data System (ADS)

Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

2016-04-01

The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

DEM Simulated Results And Seismic Interpretation of the Red River Fault Displacements in Vietnam

NASA Astrophysics Data System (ADS)

Bui, H. T.; Yamada, Y.; Matsuoka, T.

2005-12-01

The Song Hong basin is the largest Tertiary sedimentary basin in Viet Nam. Its onset is approximately 32 Ma ago since the left-lateral displacement of the Red River Fault commenced. Many researches on structures, formation and tectonic evolution of the Song Hong basin have been carried out for a long time but there are still remained some problems that needed to put into continuous discussion such as: magnitude of the displacements, magnitude of movement along the faults, the time of tectonic inversion and right lateral displacement. Especially the mechanism of the Song Hong basin formation is still in controversy with many different hypotheses due to the activation of the Red River fault. In this paper PFC2D based on the Distinct Element Method (DEM) was used to simulate the development of the Red River fault system that controlled the development of the Song Hong basin from the onshore to the elongated portion offshore area. The numerical results show the different parts of the stress field such as compress field, non-stress field, pull-apart field of the dynamic mechanism along the Red River fault in the onshore area. This propagation to the offshore area is partitioned into two main branch faults that are corresponding to the Song Chay and Song Lo fault systems and said to restrain the east and west flanks of the Song Hong basin. The simulation of the Red River motion also showed well the left lateral displacement since its onset. Though it is the first time the DEM method was applied to study the deformation and geodynamic evolution of the Song Hong basin, the results showed reliably applied into the structural configuration evaluation of the Song Hong basin.

The Tethys Sea and the Alpine-Himalayan orogenic belt; mega-elements in a new global tectonic system

NASA Astrophysics Data System (ADS)

Storetvedt, K. M.

Analysis of Meso-Cainozoic palaeomagnetic data for Africa, India and Eurasia has led to the development of a new mobilistic Alpine plate tectonic model characterized by a hierarchical system of plates in relative rotation. The new model, which discounts seafloor spreading, implies that there have been no significant palaeogeographic changes in the overall distribution of continental and oceanic regions. The mid-oceanic ridges are interpreted as transpressive tectonic features caused by rotation of megaplates (containing both continental and oceanic crust), the isostatic uplift due to crustal/lithospheric thickening giving rise to the general ridge topography as well as to the ridge-parallel structural grain. The new plate tectonic theory gains strong support from a variety of geophysical, geological and palaeoclimatological evidence, and several observations that have remained enigmatic or awkward within the context of the orthodox model can be readily accounted for in the new tectonic framework. The model maintains the Tethys as a relatively narrow epicontinental sea which, during its maximum extent, stretched latitudinally from the Caribbean, across the Central Atlantic to SE Asia. The Alpine-Himalayan orogenic belt developed along the boundary of two megaplates in relative rotation, which provided a transpressive tectonic regime. The location of the plate boundary to the north of the Mediterranean has important implications for discussion of Mediterranean microplates. For example, it now seems that Italy has been subjected to 10-15° of clockwise microplate rotation; previous conclusions in favour of 30-40° of anticlockwise rotation are regarded as artefacts which arise from incorrectly linking the Mediterranean region to the European palaeomagnetic frame instead of to the African one. The model suggests further that the Indo-Pakistani plate was closely tied to Eurasia; this challenges the conventional view that the Peninsula was part of an alleged Gondwanaland. The new pre-drift configuration implies that the Indo-Pakistani plate rotated ˜ 135° clockwise at around the Cretaceous-Tertiary boundary before redocking with Asia in approximately its present relative orientation.

Petrographic and Geochemical Characterization of the Cambumbia STOCK in Andean Central Cordillera, Colombia

NASA Astrophysics Data System (ADS)

Rojas Lequerica, S.; Jaramillo Mejía, J.; Concha Perdomo, A.

2012-12-01

The Cambumbia Stock is located on the western flank of the Central Cordillera of the northern Andes. The goals of this study were to petrographic and geochemically characterize the Cambumbia igneous body and to establish its petrogenetic history. 41 samples were collected, 28 for petrographic analysis and 14 for elementary chemical determination by ICP-MS. Petrographically the samples were classified as hornblende and pyroxene-gabbros varying to diorites, gabbronorites and tonalites, the rock texture varies from medium to coarse granular grain, with local microporfiritic texture. It was concluded from the major elements analysis that the samples correspond to the sub-alkaline series with low K content, mainly in the calc-alkaline series, within the gabbros and diorites fields. By using the SiO2 vs TiO2 (Jaramillo, 1980), Th/Yb vs Ta/Yb (Pearce, 1984) (Fig. 1) and Zr/117-Th-Nb/16 (Wood, 1979) diagrams it was determined that these rocks were generated in two geotectonic environments: one type MOR (extension) and other island arc (subduction, compression). Petrographic and geochemical comparisons between the rocks of Cambumbia Stock and Diorite and Gabbro El Pueblito (Giraldo, 2009) (located about 25 km to the north-west) may postulate a possible genetic link between them. Recently, a U/Pb age was obtained by the Universidad de Caldas in zircon in 2009 (not published data), yielded an age of 233.41 ± 3.4 Ma (Middle Triassic). This age is consistent with the global event of the extension and fragmentation of Pangea supercontinent. In addition, the mantle nature of the source and the petrogenetic evolution of the magmatic system were established. References GIRALDO, M.I., (2009): Esquema geodinámica de la parte noroccidental de la cordillera Central de Colombia. (Thesis). p.56-68. Universidad Nacional de Colombia, Medellín. JARAMILLO, J.M. (1980): Petrology and geochemistry of the Nevado del Ruiz Volcano northern Andes, Colombia (Thesis). 167 p. University of Houston, Faculty of the Department of Geology, Houston. PEARCE, J.A., HARRIS, N.B.W., and TINDLE, A.G., (1984), Trace element discrimination diagrams for the tectonic interpretation: Journal of Petrology, v. 25, p. 956-983. WOOD, D., JORON, J.L., & TREUIL, M. (1979): A re-appaisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings. Earth Planet Sci. Lett., 326-336. Th/Yb Vs Ta/Yb diagram

Tectonic and metamorphic discontinuities in the Greater Himalayan Sequence in Central Himalaya: in-sequence shearing by accretion from the Indian plate

NASA Astrophysics Data System (ADS)

Carosi, Rodolfo

2016-04-01

The Greater Himalayan Sequence (GHS) is the main metamorphic unit of the Himalayas, stretching for over 2400 km, bounded to the South by the Main Central Thrust (MCT) and to the North by the South Tibetan Detachment (STD) whose contemporanous activity controlled its exhumation between 23 and 17 Ma (Godin et al., 2006). Several shear zones and/or faults have been recognized within the GHS, usually regarded as out of sequence thrusts. Recent investigations, using a multitechnique approach, allowed to recognize a tectonic and metamorphic discontinuity, localized in the mid GHS, with a top-to-the SW sense of shear (Higher Himalayan Discontinuity: HHD) (Carosi et al., 2010; Montomoli et al., 2013). U-(Th)-Pb in situ monazite ages provide temporal constraint of the acitivity of the HHD from ~ 27-25 Ma to 18-17 Ma. Data on the P and T evolution testify that this shear zone affected the tectono-metamorphic evolution of the belt and different P and T conditions have been recorded in the hanging-wall and footwall of the HHD. The HHD is a regional tectonic feature running for more than 700 km, dividing the GHS in two different portions (Iaccarino et al., 2015; Montomoli et al., 2015). The occurrence of even more structurally higher contractional shear zone in the GHS (above the HHD): the Kalopani shear zone (Kali Gandaki valley, Central Nepal), active from ~ 41 to 30 Ma (U-Th-Pb on monazite) points out to a more complex deformation pattern in the GHS characterized by in sequence shearing. The actual proposed models of exhumation of the GHS, based exclusively on the MCT and STD activities, are not able to explain the occurrence of the HHD and other in-sequence shear zones. Any model of the tectonic and metamorphic evolution of the GHS should account for the occurrence of the tectonic and metamorphic discontinuities within the GHS and its consequences on the metamorphic paths and on the assembly of Himalayan belt. References Godin L., Grujic D., Law, R. D. & Searle, M. P. 2006. Geol. Soc. London Sp. Publ., 268, 1-23. Carosi R., Montomoli C., Rubatto D. & Visonà D. 2010. Tectonics, 29, TC4029. Iaccarino S., Montomoli C., Carosi R., Massonne H-J., Langone A., Visonà D. 2015. Lithos, 231, 103-121. Montomoli C., Iaccarino S., Carosi R., Langone A. & Visonà D. 2013. Tectonophysics 608, 1349-1370, doi:10.1016/j.tecto.2013.06.006. Montomoli C., Carosi R., Iaccarino S. 2015. Geol. Soc. London Sp. Publ., 412, 25-41.

Models of convection-driven tectonic plates - A comparison of methods and results

NASA Technical Reports Server (NTRS)

King, Scott D.; Gable, Carl W.; Weinstein, Stuart A.

1992-01-01

Recent numerical studies of convection in the earth's mantle have included various features of plate tectonics. This paper describes three methods of modeling plates: through material properties, through force balance, and through a thin power-law sheet approximation. The results obtained are compared using each method on a series of simple calculations. From these results, scaling relations between the different parameterizations are developed. While each method produces different degrees of deformation within the surface plate, the surface heat flux and average plate velocity agree to within a few percent. The main results are not dependent upon the plate modeling method and herefore are representative of the physical system modeled.

Geodynamic Implications of Himu Mantle In The Source of Tertiary Volcanics From The Veneto Region (south Eastern Alps)

NASA Astrophysics Data System (ADS)

Macera, P.; Gasperini, D.; Blichert-Toft; Bosch, D.; del Moro, A.; Dini, G.; Martin, S.; Piromallo, C.

DuringTertiary times extensive mafic volcanism took place in the South-Eastern Alps, along a half-graben structure bounded by the Schio-Vicenza main fault. This mag- matism gave rise to four main volcanic centers: Lessini, Berici, Euganei, and Maros- tica. The dominating rock types are alkali basalts, basanites and transitional basalts, with hawaiites, trachybasalts, tephrites, basaltic andesites, and differentiated rocks be- ing less common. Major and trace element and Sr-Nd-Hf-Pb isotopic data for the most primitive lavas from each volcanic center show the typical features of HIMU hotspot volcanism, variably diluted by a depleted asthenospheric mantle component (87Sr/86Sr48Ma = 0.70314-0.70321; eNd48Ma = +6.4 to +6.5; eHf48Ma = +6.4 to +8.1, 206Pb/204Pb48Ma = 18.786-19.574). Since the HIMU component is consid- ered to be of deep mantle origin, its presence in a tectonic environment dominated by subduction (the Alpine subduction of the European plate below the Adria plate) has significant geodynamic implications. Slab detachment and ensuing rise of deep man- tle material into the lithospheric gap is proposed to be a viable mechanism of hotspot magmatism in a subduction zone setting. Interaction between deep-seated plume ma- terial and shallow depleted asthenospheric mantle may account for the geochemical features of the Veneto volcanics, as well as those of the so-called enriched astheno- spheric reservoir (EAR) component. Ascending counterflow of deep mantle material through the lithospheric gap to the top of the subducting slab further may induce heat- ing of the overriding plate and trigger it to partially melt. Upwelling of the resulting mafic magmas and their subsequent underplating at the mantle-lower crust bound- ary would favor partial melting of the lower crust, thereby giving rise to the bimodal mafic-felsic magmatism that characterizes the whole Periadriatic province. According to this model, the HIMU-like magmatism of the Alpine foreland is therefore closely related to the calc-alkaline magmatism of the Periadriatic Lineament, and caused by the same mechanism of Tertiary Alpine convergence tectonics.

A contribution to regional stratigraphic correlations of the Afro-Brazilian depression - The Dom João Stage (Brotas Group and equivalent units - Late Jurassic) in Northeastern Brazilian sedimentary basins

NASA Astrophysics Data System (ADS)

Kuchle, Juliano; Scherer, Claiton Marlon dos Santos; Born, Christian Correa; Alvarenga, Renata dos Santos; Adegas, Felipe

2011-04-01

The Dom João Stage comprises an interval with variable thickness between 100 and 1200 m, composed of fluvial, eolian and lacustrine deposits of Late Jurassic age, based mainly on the lacustrine ostracod fauna (although the top deposits may extend into the Early Cretaceous). These deposits comprise the so-called Afro-Brazilian Depression, initially characterized as containing the Brotas Group of the Recôncavo Basin (which includes the Aliança and the Sergi Formations) and subsequently extended into the Tucano, Jatobá, Camamu, Almada, Sergipe, Alagoas and Araripe Basins in northeastern Brazil, encompassing the study area of this paper. The large occurrence area of the Dom João Stage gives rise to discussions about the depositional connectivity between the basins, and the real extension of sedimentation. In the first studies of this stratigraphic interval, the Dom João Stage was strictly associated with the rift phase, as an initial stage (decades of 1960-70), but subsequent analyses considered the Dom João as an intracratonic basin or pre-rift phase - without any relation to the active mechanics of a tectonic syn-rift phase (decades of 1980-2000). The present work developed an evolutionary stratigraphic and tectonic model, based on the characterization of depositional sequences, internal flooding surfaces, depositional systems arrangement and paleoflow directions. Several outcrops on the onshore basins were used to build composite sections of each basin, comprising facies, architectural elements, depositional systems, stratigraphic and lithostratigraphic frameworks, and paleocurrents. In addition to that, over a hundred onshore and offshore exploration wells were used (only 21 of which are showed) to map the depositional sequences and generate correlation sections. These show the characteristics and relations of the Dom João Stage in each studied basin, and they were also extended to the Gabon Basin. The results indicate that there were two main phases during the Dom João Stage, in which distinctive sedimentary environments were developed, reflecting depositional system arrangements, paleoflow directions were diverse, and continuous or compartmented basins were developed.

The origin of alkaline magmas in an intraplate setting near a subduction zone: the Ngatutura Basalts, North Island, New Zealand

NASA Astrophysics Data System (ADS)

Briggs, R. M.; Utting, A. J.; Gibson, I. L.

1990-01-01

The Ngatutura Basalts are one of a series of Pliocene-Quaternary alkalic basalt volcanic fields in North Island, New Zealand. They are situated in an intraplate tectonic setting behind the currently active Taupo Volcanic Zone, and 300 km above the subducting slab. The volcanic field consists of 16 small-volume monogenetic volcanic centres composed mainly of eroded scoria cones and lava flows, that occupy an extensional tectonic environment characterized by NE-striking block faulting. In some cases the faults have controlled the localization of volcanic vents. The lavas have restricted compositions, ranging from hawaiites to nepheline hawaiites, and are characterized by enriched LILE, LREE, and HFS elements, with particularly high Nb and Ta, low Ba/Nb, and high Zr/Y and Ce N/Yb N ratios. Nepheline hawaiites are slightly more differentiated than hawaiites and have higher Ce N/Yb N ratios. Petrogenetic modelling suggests that the range in composition was mainly controlled by fractional crystallization of olivine, clinopyroxene, and minor plagioclase and titanomagnetite, which is consistent with the modal phenocryst abundances. Fractionation is explained by side-wall crystallization and flowage differentiation during rapid ascent, rather than gravitative settling in a magma chamber. Ngatutura magmas were probably derived from an enriched garnet lherzolite source within the low-velocity mantle. The process of source enrichment is speculative but our preferred model calls on metasomatizing fluids in the low-velocity zone. There is no geochemical evidence for any influence of the subducted slab on their composition, even though they overlie the Pacific plate subduction zone. This implies that the extent of subduction-related contamination in the mantle wedge is not pervasive, but is confined to a limited region overlying the subducted slab. Also, the "deep mantle plume" responsible for alkalic magmatism must have originated above the slab, because it seems unlikely that such a plume could have occurred at a deeper level and penetrate the slab without some evidence. This therefore limits the depth of origin of these "deep mantle plumes" to less than 300 km.

Plate Like Convection with Viscous Strain Weakening and Corresponding Surface Deformation Pattern

NASA Astrophysics Data System (ADS)

Fuchs, L.; Becker, T. W.

2017-12-01

How plate tectonic surface motions are generated by mantle convection on Earth and possibly other terrestrial type planets has recently become more readily accessible with fully dynamic convection computations. However, it remains debated how plate-like the behavior in such models truly is, and in particular how the well plate boundary dynamics are captured in models which typically exclude the effects of deformation history and memory. Here, we analyze some of the effects of viscous strain weakening on plate behavior and the interactions between interior convection dynamics and surface deformation patterns. We use the finite element code CitcomCU to model convection in a 3D Cartesian model setup. The models are internally heated, with an Arrhenius-type temperature dependent viscosity including plastic yielding and viscous strain weakening (VSW) and healing (VSWH). VSW can mimic first order features of more complex damage mechanisms such as grain-size dependent rheology. Besides plate diagnostic parameters (Plateness, Mobility, and Toroidal: Poloidal ratio) to analyze the tectonic behavior our models, we also explore how "plate boundaries" link to convective patterns. In a first model series, we analyze general surface deformation patterns without VSW. In the early stages, deformation patterns are clearly co-located with up- and downwelling limbs of convection. Along downwellings strain-rates are high and localized, whereas upwellings tend to lead to broad zones of high deformation. At a more advanced stage, however, the plates' interior is highly deformed due to continuous strain accumulation and resurfaced inherited strain. Including only VSW leads to more localized deformation along downwellings. However, at a more advanced stage plate-like convection fails due an overall weakening of the material. This is prevented including strain healing. Deformation pattern at the surface more closely coincide with the internal convection patterns. The average surface deformation is reduced significantly and mainly governed by the location of the up- and downwellings. VSWH thereby affects plate dynamics due to two main properties: the intensity of weakening with increasing strain and the strain healing rate. As both increase, mobility increases as well and strain becomes more localized at the downwellings.

Timing of tectonic evolution of the East Kunlun Orogen, Northern Tibet Plateau

NASA Astrophysics Data System (ADS)

Dong, Yunpeng

2017-04-01

The East Kunlun Orogen, located at the northern Tibet Plateau, represents the western segment of the Central China Orogenic Belt which was formed by amalgamation of the North China blocks and South China blocks. It is a key to understanding the formation of Eastern Asian continent as well as the evolution of the Pangea supercontinent. Based on detailed geological mapping, geochemical and geochronological investigations, the orogen is divided into three main tectonic belts, from north to south, including the Northern Qimantagh, Central Kunlun and Southern Kunlun Belts by the Qimantagh suture, Central Kunlun suture and South Kunlun fault. The Qimantagh suture is marked by the Early Paleozoic ophiolites outcropped in the Yangziquan, Wutumeiren, and Tatuo areas, which consist mainly of peridotites, gabbros, diabases and basalts. Besides, the ophiolite in the Wutumeiren is characterized by occurring anorthosite while the ophiolite in the Tatuo occurring chert. The basalts and diabases from both Yaziquan and Tatuo areas display depletion of Nb, Ta, P and Ti, and enrichment of LILE, suggesting a subduction related tectonic setting. LA-ICP-MS zircon U-Pb age of 421 Ma for the diabase represents the formation age of the Yaziquan ophiolite, while the U-Pb ages of 490 Ma and 505 Ma for gabbro and anorthosite, respectively, constrain the formation age of the Tatuo ophiolite. The basaltic rocks in the Wutumeiren area display flat distribution of HFSEs (such as Nb, Ta, K, La, Ce, Pr, Nd, Zr, Sm, Eu, Ti, Dy, Y, Yb and Lu) and slightly enrichment in LREEs, while the peridotites showing depletion in MREEs. The LA-ICP-MS zircon U-Pb age of 431 Ma for the gabbro represents the formation age of the Wutumeiren ophiolite. Together with regional geology, we suggest herewith a back-arc basin tectonic setting during ca. 505-421 Ma at least for the Qimantagh suture. The Central Kunlun suture is represented by the ophiolite in the Wutuo area, which is characterized by depletion of Nb, Ta, P and Ti, and enrichment of LILEs, LREEs, K, Pb, Sr and Nd, accounting for a subduction relation setting. The gabbro yields a LA-ICP-MS zircon U-Pb age of 243 Ma, representing the formation age of the ophiolite. Taking into account of evidence from the Early Paleozoic ophiolites in the Buqinshan ( Bian Qiantao et al., 2001, 2007; Li Zuochen et al., 2013; Li Ruibao et al., 2014; Liu Zhanqing et al., 2011) and the Derni areas (Chen Liang et al., 2001, 2003), the Central Kunlun ocean might be existed from Early Paleozoic to Middle Triassic time. The Northern Qimantagh tectonic belt, to the north of the Qimantagh suture, exposes a large volume of Early Paleozoic granitic plutons and volcanic rocks. Geochemistry of the granites suggests an arc setting. LA-ICP-MS zircon U-Pb ages ranging from ca. 440 to 402 Ma constrain the time of the subduction and arc setting. The Central Kunlun tectonic belt is characterized by occurring of Paleo-Proterozoic basement which was intruded by large amounts of Triassic granitoids. The basement represented by the Jinshuikou Group including gneisses, amphibolites and marbles, yields a protolith formation age of 2.2 Ga which was overprinted by Neoproterozoic tectono-thermal event. The plutonic intrusions display LA-ICP-MS zircon ages mainly of 260-200 Ma with minor ages of 470-400 Ma, revealing a long-lived subduction from Early Paleozoic to Late Triassic. Taken into together all above evidence, trench-arc-back arc basin tectonics were suggested here accounting for the tectonic evolution of the East Kunlun Orogeny during Early Paleozoic to Triassic time.

Mesozoic units in SE Rhodope (Bulgaria): new structural and petrologic data and geodynamic implications for the Early Jurassic to Mid-Cretaceous evolution of the Vardar ocean basin

NASA Astrophysics Data System (ADS)

Bonev, N.; Stampfli, G.

2003-04-01

In the southeastern Rhodope, both in southern Bulgaria and northern Greece, Mesozoic low-grade to non-metamorphic units, together with similar units in the eastern Vardar zone, were designated as the Circum-Rhodope Belt (CRB) that fringes the Rhodope high-grade metamorphic complex. In the Bulgarian southeastern Rhodope, Mesozoic units show a complicated tectono-stratigraphy underlaid by amphibolite-facies basement units. The basement sequence includes a lower orthogneiss unit with eclogite and meta-ophiolite lenses overlain by an upper marble-schist unit, presumably along a SSW-directed detachment fault as indicated by shear sense indicators. The Mesozoic sequence starts with greenschist units at the base, overlaying the basement along the tectonic contact. Mineral assemblages such as actinolite-chlorite-white mica ± garnet in schists and phyllites indicate medium greenschist facies metamorphism. Kinematic indicators in the same unit demonstrate a top-to-the NNW and NNE shear deformation coeval with metamorphism, subparallel to NW-SE to NE-SW trending mineral elongation lineation and axis of NW vergent small-scale folds. The greenschist unit is overlain by tectonic or depositional contact of melange-like unit that consists of diabases with Lower Jurassic radiolarian chert interlayers, Upper Permian siliciclastics and Middle-Upper Triassic limestones found as blocks in olistostromic member, embedded in Jurassic-Lower Cretaceous turbiditic matrix. The uppermost sedimentary-volcanogenic unit is represented by andesito-basalt lavas and gabbro-diorites, interbedded with terrigeneous-marl and tufaceous sediments that yield Upper Cretaceous (Campanian) fossils, related to the Late Cretaceous back-arc magmatic activity to the north in Sredna Gora zone. Petrologic and geochemical data indicates sub-alkaline and tholeiitic character of the greenschists and ophiolitic basaltic lavas, and the latter are classified as low-K and very low-Ti basalts with some boninitic affinity. Immobile trace element discrimination of both rock types constrains the volcanic (oceanic)-arc origin. They generally show low total REE concentrations (LREE>HREE) with enrichment of LIL elements relative to the HFS elements, and also very low Nb and relatively high Ce content consistent with an island-arc tectonic setting. We consider that the Meliata-Maliac ocean northern passive margin could be the source provenance for the Upper Permian clastics and Middle-Upper Triassic limestone blocks within the olistostromic melange-like unit, whereas turbidites and magmatic blocks may originate in an island arc-accretionary complex that relates to the southward subduction of the Maliac ocean under the supra-subduction back-arc Vardar ocean/island arc system. These new structural and petrologic data allow to precise the tectonic setting of the Mesozoic units and their geodynamic context in the frame of the Early Jurassic to Late Cretaceous evolution of the Vardar ocean.

Inversion for the driving forces of plate tectonics

NASA Technical Reports Server (NTRS)

Richardson, R. M.

1983-01-01

Inverse modeling techniques have been applied to the problem of determining the roles of various forces that may drive and resist plate tectonic motions. Separate linear inverse problems have been solved to find the best fitting pole of rotation for finite element grid point velocities and to find the best combination of force models to fit the observed relative plate velocities for the earth's twelve major plates using the generalized inverse operator. Variance-covariance data on plate motion have also been included. Results emphasize the relative importance of ridge push forces in the driving mechanism. Convergent margin forces are smaller by at least a factor of two, and perhaps by as much as a factor of twenty. Slab pull, apparently, is poorly transmitted to the surface plate as a driving force. Drag forces at the base of the plate are smaller than ridge push forces, although the sign of the force remains in question.

Integrated geophysical investigations in a fault zone located on southwestern part of İzmir city, Western Anatolia, Turkey

NASA Astrophysics Data System (ADS)

Drahor, Mahmut G.; Berge, Meriç A.

2017-01-01

Integrated geophysical investigations consisting of joint application of various geophysical techniques have become a major tool of active tectonic investigations. The choice of integrated techniques depends on geological features, tectonic and fault characteristics of the study area, required resolution and penetration depth of used techniques and also financial supports. Therefore, fault geometry and offsets, sediment thickness and properties, features of folded strata and tectonic characteristics of near-surface sections of the subsurface could be thoroughly determined using integrated geophysical approaches. Although Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT) methods are commonly used in active tectonic investigations, other geophysical techniques will also contribute in obtaining of different properties in the complex geological environments of tectonically active sites. In this study, six different geophysical methods used to define faulting locations and characterizations around the study area. These are GPR, ERT, SRT, Very Low Frequency electromagnetic (VLF), magnetics and self-potential (SP). Overall integrated geophysical approaches used in this study gave us commonly important results about the near surface geological properties and faulting characteristics in the investigation area. After integrated interpretations of geophysical surveys, we determined an optimal trench location for paleoseismological studies. The main geological properties associated with faulting process obtained after trenching studies. In addition, geophysical results pointed out some indications concerning the active faulting mechanism in the area investigated. Consequently, the trenching studies indicate that the integrated approach of geophysical techniques applied on the fault problem reveals very useful and interpretative results in description of various properties of faulting zone in the investigation site.

Mars channel observations 1877-90, compared with modern Orbiter data

NASA Astrophysics Data System (ADS)

Gerstbach, G.

2003-10-01

The astronomic sensation of 1877, Schiaparelli's Canali, were a main research topic for 80 years (in a way they are it now again). Up to Mariner 4 (1965) many institutes believed in melted ice and periodic vegetation along the gray or green linear structures. Mars mapping reached a 2nd summit by Antoniadi, whose map 1936 was the basis of the US Mariner program. But ~1915 the shift from linear to area drawing caused some quality losses in planetography. In the fifties the Canali were mostly interpreted as optical illusions or contrast effects. The rivers and tectonics seen by Orbiters encouraged me to special studies: 60% of Schiaparelli channels correlate with: Albedo patterns, terrace-shadow structures, broad valley systems (e.g. Valles Marineris) and rows of craters or clouds. Experienced observers know that linear structures can be "seen" even if their elements are below the resolution. Feedback of this fact to space-born Remote Sensing is recommended - for maximal use of the modern planet Orbiters and special studies of geology, dust storms and clouds.

Lithium brines: A global perspective: Chapter 14

USGS Publications Warehouse

Munk, LeeAnn; Hynek, Scott; Bradley, Dwight C.; Boutt, David; Labay, Keith A.; Jochens, Hillary; Verplanck, Philip L.; Hitzman, Murray W.

2016-01-01

Lithium is a critical and technologically important element that has widespread use, particularly in batteries for hybrid cars and portable electronic devices. Global demand for lithium has been on the rise since the mid-1900s and is projected to continue to increase. Lithium is found in three main deposit types: (1) pegmatites, (2) continental brines, and (3) hydrothermally altered clays. Continental brines provide approximately three-fourths of the world’s Li production due to their relatively low production cost. The Li-rich brine systems addressed here share six common characteristics that provide clues to deposit genesis while also serving as exploration guidelines. These are as follows: (1) arid climate; (2) closed basin containing a salar (salt crust), a salt lake, or both; (3) associated igneous and/or geothermal activity; (4) tectonically driven subsidence; (5) suitable lithium sources; and (6) sufficient time to concentrate brine. Two detailed case studies of Li-rich brines are presented; one on the longest produced lithium brine at Clayton Valley, Nevada, and the other on the world’s largest producing lithium brine at the Salar de Atacama, Chile.

Miocene calc-alkaline heritage in the pliocene postcollisional volcanism of monte arci (Sardinia, Italy)

NASA Astrophysics Data System (ADS)

Cioni, Roberto; Clocchiatti, Robert; Di Paola, Giovanni M.; Santacroce, Roberto; Tonarini, Sonia

1982-10-01

At Monte Arci alkaline (hawaiites to trachytes), subalkaline with a marked calc-alkaline character (basalts to dacites) and rhyolitic lavas were erupted almost simultaneously in Late Pliocene time. Major- and trace-element chemistry, microprobe mineralogy and isotopic data suggest a partial melting origin for both rhyolites and subalkaline rocks. Different sources are however inferred for two rock series: homogeneous, calc-alkaline in nature for subalkaline rocks; unhomogeneous, richer in 87Sr, for rhyolitic ones. Crystal fractionation differentiation from subcrustal alkali-basalts should have been the main process in the genesis of alkaline rocks. Large-scale contaminations with rhyolitic and/or alkaline rocks are evident in many of these lavas. Such a complicated magmatic association characterizes an area where volcanism related to post-collisional tensional movements in Pliocene time superimposes to Middle Miocene calc-alkaline basic volcanism related to previous subduction processes. The Pliocene volcanic history of Monte Arci emphasizes the influence of the paleogeodynamic environment on the nature of magmas erupted in post-continental collision areas, that are frequently difficult to arrange in the usual schemas connecting magma composition with tectonic setting.

A basic tool for post-seismic rebuilding: the new 1:5.000 scale geological map of Amatrice town

NASA Astrophysics Data System (ADS)

Mancini, Marco; Vignaroli, Gianluca; Ardizzone, Francesca; Bucci, Francesco; Cardinali, Mauro; Cavinato, Gian Paolo; Cosentino, Giuseppe; Di Salvo, Cristina; Fiorucci, Federica; Gaudiosi, Iolanda; Giallini, Silvia; Peronace, Edoardo; Polpetta, Federica; Putignano, Maria Luisa; Reichenbach, Paola; Santangelo, Michele; Scionti, Veronica; Simionato, Maurizio; Sirianni, Pietro; Stigliano, Francesco

2017-04-01

A geological survey has been carried out in the area of Amatrice, the most damaged town after the 24 August 2016 event, to provide a basic reference for geophysical and geotechnical data useful for seismic response analyses and microzonation studies. The morphologies and the stratigraphic-structural setting of the investigated area are detailed on a 1:5000 scale geological map and cross sections, which derive from the integration of field-based observations and photo-geological interpretation. The Amatrice basin is filled by the one km-thick Laga Formation, composed of Messinian syn-orogenic marine sandstones and siltstones (Marini et al., 2015) and covered with disconformity by Quaternary conglomerates and sands, referred to alluvial fans, fluvial terraces and landslides. Presently, the Amatrice basin is a structurally-controlled depression bounded eastward by the Gorzano Mt ridge, and westward by the Sibillini Mts thrust front (Koopman, 1983). Our observations focus on (i) relationships between geometry and extent of cover deposits, (ii) bedding of the substratum, and (iii) areal arrangement and distribution of the main fault systems. Amatrice is located on a N-S trending mesa bounded by steep escarpments. The siliciclastic substratum was folded by syn-orogenic movements, broadly forming a NW-SE-trending synform, and is dissected by two main fault systems of the Plio-Quaternary post-orogenic tectonics. The first system consists of N-S striking high angle normal fault segments, each one having continuous length of up to 2 km; the second consists of E-W-striking normal-to-strike slip fault systems dissecting the first one. N-S-striking faults are morphologically expressed by fault plane scarps and triangular facets, and control the areal distribution of the Quaternary fluvial deposits. These are up to 50 m thick below Amatrice and thin to few metres along the north west direction. East of Amatrice, the stratigraphic setting is dominated by SW-prograding alluvial fans, downlapping the substratum, while on the West the stratigraphic setting is strongly complicated by large scale deformations (folding and tectonic repetitions) produced by shortening mechanisms. The recognized morphological irregularities, stratigraphic heterogeneities, and structural alignments are considered critical elements to define, at local scale, subsoil models useful for evaluating seismic amplification effects. References Koopman, A., (1983) Detachment tectonics in the central Apennines, Italy. Geol. Ultraiectina, 30, 1-155. Marini M., Milli S., Ravnås R., Moscatelli M. (2015) A comparative study of confined vs. semi-confined turbidite lobes from the Lower Messinian Laga Basin (Central Apennines, Italy): Implications for assessment of reservoir architecture. Mar. and Petrol. Geol., 63, 142-165.

Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

2018-05-01

The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid-ocean-ridge-basalt mantle and enriched-mantle I components. The Permian mafic-ultramafic intrusions in North Xinjiang were formed from tholeiitic basaltic magmas derived from decompression partial melting of the metasomatized mantle in a post-collision extensional tectonic setting. The tholeiitic basaltic magmas are equivalent to the voluminous underplated basaltic magmas that formed during vertical crustal growth of the Central Asian Orogenic Belt in the later Paleozoic.

Erosion and landscape development decouple strontium and sulfur in the transition to dominance by atmospheric inputs

USGS Publications Warehouse

Bern, C.R.; Porder, S.; Townsend, A.R.

2007-01-01

Weathering and leaching can progressively deplete the pools of soluble, rock-derived elements in soils and ecosystems over millennial time-scales, such that productivity increasingly relies on inputs from atmospheric deposition. This transition has been explored using strontium isotopes, which have been widely assumed to be a proxy for the provenance of other rock-derived elements. We compared rock versus atmospheric proportions of strontium to those for sulfur, a plant macronutrient, at several tropical forest sites in Hawaii and Costa Rica. Isotopic analyses reveal that sulfur is often decoupled from strontium in the transition to atmospheric dependence. Decoupling is likely the result of differences in chemical factors such as atmospheric input rates, mobility in the soil environment, and mineral weathering susceptibility. Strontium and sulfur decoupling appears to be accentuated by the physical process of erosion. Erosion rates are presumed to be high on the Osa Peninsula of Costa Rica, where the recent onset of rapid tectonic uplift has placed the landscape in a transient state. Decoupling is strong there, as erosion has rejuvenated the supply of rock-derived strontium but not sulfur. The landscape response to changes in tectonic uplift on the Osa Peninsula has produced decoupling at the landscape scale. Decoupling is more variable along a Hawaiian catena, presumably due to smaller scale variations in erosion rates and their influence on rejuvenation of rock-strontium inputs. These results illustrate how chemical and physical processes can interact to produce contrasting origins for different nutrient elements in soils and the ecosystems they support. ?? 2007 Elsevier B.V. All rights reserved.

On the role of fluids in stick-slip dynamics of saturated granular fault gouge using a coupled computational fluid dynamics-discrete element approach: STICK-SLIP IN SATURATED FAULT GOUGE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul A.

The presence of fault gouge has considerable influence on slip properties of tectonic faults and the physics of earthquake rupture. The presence of fluids within faults also plays a significant role in faulting and earthquake processes. In this study, we present 3-D discrete element simulations of dry and fluid-saturated granular fault gouge and analyze the effect of fluids on stick-slip behavior. Fluid flow is modeled using computational fluid dynamics based on the Navier-Stokes equations for an incompressible fluid and modified to take into account the presence of particles. Analysis of a long time train of slip events shows that themore » (1) drop in shear stress, (2) compaction of granular layer, and (3) the kinetic energy release during slip all increase in magnitude in the presence of an incompressible fluid, compared to dry conditions. We also observe that on average, the recurrence interval between slip events is longer for fluid-saturated granular fault gouge compared to the dry case. This observation is consistent with the occurrence of larger events in the presence of fluid. It is found that the increase in kinetic energy during slip events for saturated conditions can be attributed to the increased fluid flow during slip. Finally, our observations emphasize the important role that fluid flow and fluid-particle interactions play in tectonic fault zones and show in particular how discrete element method (DEM) models can help understand the hydromechanical processes that dictate fault slip.« less

On the role of fluids in stick-slip dynamics of saturated granular fault gouge using a coupled computational fluid dynamics-discrete element approach: STICK-SLIP IN SATURATED FAULT GOUGE

DOE PAGES

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul A.; ...

2017-05-01

The presence of fault gouge has considerable influence on slip properties of tectonic faults and the physics of earthquake rupture. The presence of fluids within faults also plays a significant role in faulting and earthquake processes. In this study, we present 3-D discrete element simulations of dry and fluid-saturated granular fault gouge and analyze the effect of fluids on stick-slip behavior. Fluid flow is modeled using computational fluid dynamics based on the Navier-Stokes equations for an incompressible fluid and modified to take into account the presence of particles. Analysis of a long time train of slip events shows that themore » (1) drop in shear stress, (2) compaction of granular layer, and (3) the kinetic energy release during slip all increase in magnitude in the presence of an incompressible fluid, compared to dry conditions. We also observe that on average, the recurrence interval between slip events is longer for fluid-saturated granular fault gouge compared to the dry case. This observation is consistent with the occurrence of larger events in the presence of fluid. It is found that the increase in kinetic energy during slip events for saturated conditions can be attributed to the increased fluid flow during slip. Finally, our observations emphasize the important role that fluid flow and fluid-particle interactions play in tectonic fault zones and show in particular how discrete element method (DEM) models can help understand the hydromechanical processes that dictate fault slip.« less

Comparative analysis of geodynamic activity of the Caucasian and Eastern Mediterranean segments of the Alpine-Himalayan convergence zone

NASA Astrophysics Data System (ADS)

Chelidze, Tamaz; Eppelbaum, Lev

2013-04-01

The Alpine-Himalayan convergence zone (AHCZ) underwent recent transverse shortening under the effect of collisional compression. The process was accompanied by rotation of separate microplates. The Caucasian and Eastern Mediterranean regions are segments of the of the AHCZ and are characterized by intensive endogenous and exogenous geodynamic processes, which manifest themselves in occurrence of powerful (with magnitude of 8-9) earthquakes accompanied by development of secondary catastrophic processes. Large landslides, rock falls, avalanches, mud flows, etc. cause human deaths and great material losses. The development of the aforesaid endogenous processes is set forth by peculiarities of the deep structure of the region and an impact of deep geological processes. The Caucasus is divided into several main tectonic terranes: platform (sub-platform, quasi-platform) and fold-thrust units. Existing data enable to perform a division of the Caucasian region into two large-scale geological provinces: southern Tethyan and northern Tethyan located to the south of and to the north of the Lesser Caucasian ophiolite suture, respectively. The recent investigations show that the assessments of the seismic hazard in these regions are not quite correct - for example in the West Caucasus the seismic hazard can be significantly underestimated, which affects the corresponding risk assessments. Integrated analysis of gravity, magnetic, seismic and thermal data enables to refine the assessment of the seismic hazard of the region, taking into account real rates of the geodynamic movements. Important role play the last rheological constructions. According to Reilinger et al. (2006) tectonic scheme, the West flanking of the Arabian Plate manifests strike-slip motion, when the East Caucasian block is converging and shortening. The Eastern Mediterranean is a tectonically complex region located in the midst of the progressive Afro-Eurasian collision. The recent increasing geotectonic activity in this region highlights the need for combined analysis of seismo-neotectonic signatures. For this purpose, this article presents the key features of the tectonic zonation of the Eastern Mediterranean. Map of derivatives of the gravity field retracked from the Geosat satellite and novel map of the Moho discontinuity illustrate the most important tectonic features of the region. The Post-Jurassic map of the deformation of surface leveling reflects the modern tectonic stage of Eastern Mediterranean evolution. The developed tectono-geophysical zonation map integrates the potential geophysical field analysis and seismic section utilization, as well as tectonic-structural, paleogeographical and facial analyses. Tectonically the map agrees with the earlier model of continental accretion (Ben-Avraham and Ginzburg, 1990). Overlaying the seismicity map of the Eastern Mediterranean tectonic region (for the period between 1900 and 2012) on the tectonic zonation chart reveals the key features of the seismo-neotectonic pattern of the Eastern Mediterranean. The results have important implications for tectonic-seismological analysis in this region (Eppelbaum and Katz, 2012). A difference in the geotectonic patterns makes interesting comparison of geodynamic activity and seismic hazard of the Caucasian and Eastern Mediterranean segments of the AHCZ.

From Geodynamics to Simplicity

NASA Astrophysics Data System (ADS)

Anderson, D. L.

2002-12-01

Mantle convection and plate tectonics are often thought as synonymous. Convection is sometimes treated as the driver or plate tectonics is viewed as simply a manifestation of mantle convection. Mantle plumes are regarded as supplying some of the elements missing in the plate tectonic and mantle convection paradigms, such as island chains, swells and large igneous provinces. An alternate view is motivated by Prigogine's concept of far-from-equilibrium self-organization ( SOFFE), not to be confused with Bak's self-organized criticality ( SOC) . In a SOFFE system the components interact, and the system is small compared to the outside world to which it is open. There must be multiple possible states and dissipation is important. Such a system is sensitive to small changes. Rayleigh-Benard convection in a container with isothermal walls is such a self-organizing system ; the driving bouyancy and the dissipation ( viscosity ) are in the fluid. In Marangoni convection the driving forces ( surface tension ) and dissipation are in the surface film and this organizes the surface and the underlying fluid. The mantle provides energy and matter to the interacting plate system but forces in the plates drive and dissipate the energy. Thus, plate tectonics may be a SOFFEE system that drives convection,as are systems cooled from above, in general. If so, plates will reorganize as boundary conditions change ; incipient plate boundaries will emerge as volcanic chains at tensile regions. Plates are defined as regions of lateral compression ( force chains ), rather than strength, and they are ephemeral. The plate system, rather than mantle viscosity, will modulate mantle cooling. The supercontinent cycle, with episodes of reorganization and massive magmatism, may be a manifestation of this far-from-equilibrium, driven from above, system. Geodynamics may be simpler than we think. Plate tectonics is certainly a more powerful concept once the concepts of rididity, elasticity, homogeneity, steady-state, equilibrium and uniformity are dropped or modified, as qualifiers of the system,as recommended in Occam's philosophy.

The effect of plate-scale rheology and plate interactions on intraplate seismicity

NASA Astrophysics Data System (ADS)

So, Byung-Dal; Capitanio, Fabio A.

2017-11-01

We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ =ηI /ηL, the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ =σY /σL the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ, illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic plates.

Numerical modeling of intraplate seismicity with a deformable loading plate

NASA Astrophysics Data System (ADS)

So, B. D.; Capitanio, F. A.

2017-12-01

We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ = ηI/ηL the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ = σY/σL the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ, illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic plates.

Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

NASA Astrophysics Data System (ADS)

Maffione, Marco; Hernandez-Moreno, Catalina; Ghiglione, Matias C.; Speranza, Fabio; van Hinsbergen, Douwe J. J.; Lodolo, Emanuele

2015-12-01

The southernmost segment of the Andean Cordillera underwent a complex deformation history characterized by alternation of contractional, extensional, and strike-slip tectonics. Key elements of southern Andean deformation that remain poorly constrained, include the origin of the orogenic bend known as the Patagonian Orocline (here renamed as Patagonian Arc), and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in Cordillera Darwin. Here, we present results of anisotropy of magnetic susceptibility (AMS) from 22 sites in Upper Cretaceous to upper Eocene sedimentary rocks within the internal structural domain of the Magallanes fold-and-thrust belt in Tierra del Fuego (Argentina). AMS parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric, which was likely acquired upon layer-parallel shortening soon after sedimentation. Magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous N-S contraction. Our data, combined with the existing AMS database from adjacent areas, show that the Early Cretaceous-late Oligocene tectonic phases in the Southern Andes yielded continuous contraction, variable from E-W in the Patagonian Andes to N-S in the Fuegian Andes, which defined a radial strain field. A direct implication is that the exhumation of the Cordillera Darwin metamorphic complex occurred under compressive, rather than extensional or strike-slip tectonics, as alternatively proposed. If we agree with recent works considering the curved Magallanes fold-and-thrust belt as a primary arc (i.e., no relative vertical-axis rotation of the limbs occurs during its formation), then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field. We tentatively propose a kinematic model in which reactivation of variably oriented Jurassic faults at the South American continental margin controlled the Late Cretaceous to Cenozoic evolution of the Magallanes fold-and-thrust belt, yielding the observed deformation pattern.

Fluvial archives, a valuable record of vertical crustal deformation

NASA Astrophysics Data System (ADS)

Demoulin, A.; Mather, A.; Whittaker, A.

2017-06-01

The study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms, but also for identifying the nature of crustal deformation and its history. In recent decades, geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens. Here, we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions (the effects of horizontal deformation are not addressed). Channel long profiles have received considerable attention in the literature, and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives, before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady-state characteristics. Then, we review the literature dealing with the transient response of rivers to tectonic perturbation, through the production of knickpoints propagating through the drainage network. Inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories. Finally, we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes. As well as the erosional imprint of tectonic forcing, sedimentary deposits, such as fluvial terrace staircases, are also considered as a classical component of tectonic geomorphology. We show that these studies have recently benefited from rapid advances in dating techniques, allowing more reliable reconstruction of incision histories and estimation of incision rates. The combination of progress in the understanding of transient river profiles and larger, more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation, i.e., extrapolation of local data to entire profiles. Finally, planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation. Examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the (dis)equilibrium state of drainage systems across regional drainage divides.

Late Quaternary river channel migrations of the Kura River in Transcaucasia - tectonic versus climatic causes

NASA Astrophysics Data System (ADS)

von Suchodoletz, Hans; Gärtner, Andreas; Hoth, Silvan; Umlauft, Josefine; Godoladze, Tea; Faust, Dominik

2015-04-01

Large-scale river channel migrations either in the form of avulsions or combing, i.e. progressive lateral migrations, are global phenomena during the Late Quaternary. Such channel migrations were triggered by tectonics, climate change, human activity or a combination of those factors. River channel migrations have the potential to cause significant human and economic losses. Thus, a more thorough knowledge about underlying causes and process rates is essential. Furthermore, such studies will elucidate the sensitivity or robustness of rivers to different external and internal forcing-agents, i.e. they help to identify the dominant drivers of regional landscape evolution. The Caucasus region is part of the active collision zone between the Africa-Arabian and the Eurasian plates, and is characterized by high current tectonic activity. Furthermore, significant environmental changes took place during the Late Quaternary, i.e. the shrinking or even disappearance of glaciers in the Greater and Lesser Caucasus or fundamental changes of the vegetation cover varying between woodland and grassland-dominated vegetation. The Kura River is the main gaining stream of the Transcaucasian Depression located between the Greater Caucasus Mountains in the north and the Lesser Caucasus Mountains in the south, and receives several tributaries from both mountain ranges. This study focusses on the middle course of the Kura River in eastern Georgia, SE of the city of Tbilisi. Integration of fluvial geomorphology, geochronology, heavy mineral analyses and seismo-tectonic analyses demonstrates that this part of the Kura River underwent large-scale channel migrations up to >10 km during Late Pleistocene and Holocene. It is interpreted that these movements followed both tectonic and climatic triggers: Whereas SW-ward migrations were caused by tectonic uplift in and SW-directed advance of the Kura fold and thrust belt as part of the Greater Caucasus, NE-ward migrations occurred during cold glacial periods with intensive sediment supply and strong vertical sedimentation of tributaries originating from a westerly direction. Thus, the middle course of the Kura River shows a dynamic equilibrium between competing tectonic and climatic processes.

Geometry and kinematics of Majiatan Fold-and-thrust Belt, Western Ordos Basin: implication for Tectonic Evolution of North-South Tectonic Belt

NASA Astrophysics Data System (ADS)

He, D.

2017-12-01

The Helan-Chuandian North-South Tectonic Belt crossed the central Chinese mainland. It is a boundary of geological, geophysical, and geographic system of Chinese continent tectonics from shallow to deep, and a key zone for tectonic and geomorphologic inversion during Mesozoic to Cenozoic. It is superimposed by the southeastward and northeastward propagation of Qinghai-Tibet Plateau in late Cenozoic. It is thus the critical division for West and East China since Mesozoic. The Majiatan fold-and-thrust belt (MFTB), locating at the central part of HCNSTB and the western margin of Ordos Basin, is formed by the tectonic evolution of the Helan-Liupanshan Mountains. Based on the newly-acquired high-resolution seismic profiles, deep boreholes, and surface geology, the paper discusses the geometry, kinematics, and geodynamic evolution of MFTB. With the Upper Carboniferous coal measures and the pre-Sinian ductile zone as the detachments, MFTB is a multi-level detached thrust system. The thrusting was mainly during latest Jurassic to Late Cretaceous, breaking-forward in the foreland, and resulting in a shortening rate of 25-29%. By structural restoration, this area underwent extension in Middle Proterozoic to Paleozoic, which can be divided into three phases of rifting such as Middle to Late Proterozoic, Cambiran to Ordovician, and Caboniferous to early Permian. It underwent compression since Late Triassic, including such periods as Latest Triassic, Late Jurassic to early Cretaceous, Late Cretaceous to early Paleogene, and Pliocene to Quaternary, with the largest shortening around Late Jurassic to early Cretaceous period (i.e. the mid-Yanshanian movement by the local name). However, trans-extension since Eocene around the Ordos Basin got rise to the formation the Yingchuan, Hetao, and Weihe grabens. It is concluded that MFTB is the leading edge of the intra-continental Helan orogenic belt, and formed by multi-phase breaking-forward thrusting during Late Jurassic to Cretaceous. During Cenozoic, MFTB is moderately modified by the northeastward compression due to the NE propagation of Qinghai-Tibet Plateau, and distinctly superimposed by the Yingchuan half-graben. North-South Tectonic Belt underwent a full cycle from extension during Middle Proterozoic to Paleozoic to compression since late Triassic.

Analytically based forward and inverse models of fluvial landscape evolution during temporally continuous climatic and tectonic variations

NASA Astrophysics Data System (ADS)

Goren, Liran; Petit, Carole

2017-04-01

Fluvial channels respond to changing tectonic and climatic conditions by adjusting their patterns of erosion and relief. It is therefore expected that by examining these patterns, we can infer the tectonic and climatic conditions that shaped the channels. However, the potential interference between climatic and tectonic signals complicates this inference. Within the framework of the stream power model that describes incision rate of mountainous bedrock rivers, climate variability has two effects: it influences the erosive power of the river, causing local slope change, and it changes the fluvial response time that controls the rate at which tectonically and climatically induced slope breaks are communicated upstream. Because of this dual role, the fluvial response time during continuous climate change has so far been elusive, which hinders our understanding of environmental signal propagation and preservation in the fluvial topography. An analytic solution of the stream power model during general tectonic and climatic histories gives rise to a new definition of the fluvial response time. The analytic solution offers accurate predictions for landscape evolution that are hard to achieve with classical numerical schemes and thus can be used to validate and evaluate the accuracy of numerical landscape evolution models. The analytic solution together with the new definition of the fluvial response time allow inferring either the tectonic history or the climatic history from river long profiles by using simple linear inversion schemes. Analytic study of landscape evolution during periodic climate change reveals that high frequency (10-100 kyr) climatic oscillations with respect to the response time, such as Milankovitch cycles, are not expected to leave significant fingerprints in the upstream reaches of fluvial channels. Linear inversion schemes are applied to the Tinee river tributaries in the southern French Alps, where tributary long profiles are used to recover the incision rate history of the Tinee main trunk. Inversion results show periodic, high incision rate pulses, which are correlated with interglacial episodes. Similar incision rate histories are recovered for the past 100 kyr when assuming constant climatic conditions or periodic climatic oscillations, in agreement with theoretical predictions.

Volcano-tectonics of the Al Haruj Volcanic Province, Central Libya

NASA Astrophysics Data System (ADS)

Elshaafi, Abdelsalam; Gudmundsson, Agust

2016-10-01

The Al Haruj intra-continental Volcanic Province (AHVP), located at the south-western margin of the Sirt Basin, hosts the most extensive and recent volcanic activity in Libya - which is considered typical for plate interiors. From north to south the AHVP is divided into two subprovinces, namely Al Haruj al Aswad and Al Haruj al Abiyad. The total area of the AHVP is around 42,000 km2. Despite the great size of the AHVP, its volcano-tectonic evolution and activity have received very little attention and are poorly documented and understood. Here we present new field data, and analytical and numerical results, on the volcano-tectonics of the AHVP. The length/thickness ratio of 47 dykes and volcanic fissures were measured to estimate magmatic overpressure at the time of eruption. The average dyke (length/thickness) ratio of 421 indicates magmatic overpressures during the associate fissure eruptions of 8-19 MPa (depending on host-rock elastic properties). Spatial distributions of 432 monogenetic eruptions sites/points (lava shields, pyroclastic cones) in the AHVP reveal two main clusters, one in the south and another in the north. Aligned eruptive vents show the dominating strike of volcanic fissures/feeder-dykes as WNW-ESE to NW-SE, coinciding with the orientation of one of main fracture/fault zones. Numerical modelling and field observations suggest that some feeder-dykes may have used steeply dipping normal-fault zones as part of their paths to the surface.

Terrace sequence along the Yushanguxi River in the southern piedmont of Tian Shan and its relationship to climate and tectonics in northwestern China

NASA Astrophysics Data System (ADS)

Wu, Chuanyong; Zheng, Wenjun; Zhang, Zhuqi; Jia, Qichao; Yu, Jingxing; Zhang, Huiping; Han, Guihong; Yao, Yuan

2018-07-01

Controversies persist regarding the formation of terraces under the control of tectonic factors or climatic changes. This work focuses on the Yushanguxi River in the southern piedmont of Tian Shan, which is an intense tectonic uplift area where the terraces are very developed and the river has deeply downcut. Nine main terraces are distinguished (labelled T1 to Th, from youngest to oldest) based on the interpretation of a high-resolution remote sensing image, field investigations and detailed surveying with differential GPS. The results of the determination of 10Be exposure and 14C show abandoned ages of 2.1 ka for T1, 4.1 ka for T2, 4.2 ka for T3, 8.2 ka for T4, 18.1 ka for T5, 18.8 ka for T6, 102.1 ka for T7, 100.6 ka for T81, 113.9 ka for T82, 144.6 ka for Th1, 210.7 ka for Th2, and 284.3 ka for Th3. Since 18 ka, the incision rate began to increase from 0.6 mm a-1 to 12 mm a-1, which is obviously higher than the fault slip rate of 0.7 mm a-1. We suggest that the rapid downcutting along the Yushanguxi River during the Holocene has mainly been caused by frequent climate fluctuations.

Tectonosedimentary framework of Upper Cretaceous -Neogene series in the Gulf of Tunis inferred from subsurface data: implications for petroleum exploration

NASA Astrophysics Data System (ADS)

Dhraief, Wissem; Dhahri, Ferid; Chalwati, Imen; Boukadi, Noureddine

2017-04-01

The objective and the main contribution of this issue are dedicated to using subsurface data to delineate a basin beneath the Gulf of Tunis and its neighbouring areas, and to investigate the potential of this area in terms of hydrocarbon resources. Available well data provided information about the subsurface geology beneath the Gulf of Tunis. 2D seismic data allowed delineation of the basin shape, strata geometries, and some potential promising subsurface structures in terms of hydrocarbon accumulation. Together with lithostratigraphic data obtained from drilled wells, seismic data permitted the construction of isochron and isobath maps of Upper Cretaceous-Neogene strata. Structural and lithostratigraphic interpretations indicate that the area is tectonically complex, and they highlight the tectonic control of strata deposition during the Cretaceous and Neogene. Tectonic activity related to the geodynamic evolution of the northern African margin appears to have been responsible for several thickness and facies variations, and to have played a significant role in the establishment and evolution of petroleum systems in northeastern Tunisia. As for petroleum systems in the basin, the Cretaceous series of the Bahloul, Mouelha and Fahdene formations are acknowledged to be the main source rocks. In addition, potential reservoirs (Fractured Abiod and Bou Dabbous carbonated formations) sealed by shaly and marly formations (Haria and Souar formations respectively) show favourable geometries of trap structures (anticlines, tilted blocks, unconformities, etc.) which make this area adequate for hydrocarbon accumulations.

Geomorphology and Neogene tectonic evolution of the Palomares continental margin (Western Mediterranean)

NASA Astrophysics Data System (ADS)

Gómez de la Peña, Laura; Gràcia, Eulàlia; Muñoz, Araceli; Acosta, Juan; Gómez-Ballesteros, María; R. Ranero, César; Uchupi, Elazar

2016-10-01

The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike-slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw < 5.2) shallow instrumental earthquakes, although large historical events have also occurred. To understand the recent tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero-Balearic Basin is affected by surficial processes, associated to halokinesis of Messinian evaporites.

The impact of a pressurized regional sea or global ocean on stresses on Enceladus

NASA Astrophysics Data System (ADS)

Johnston, Stephanie A.; Montési, Laurent G. J.

2017-06-01

Liquid water is likely present in the interior of Enceladus, but it is still debated whether this water forms a global ocean or a regional sea and whether the present-day situation is stable. As the heat flux of Enceladus exceeds most heat source estimates, the liquid water is likely cooling and crystallizing, which results in expansion and pressurization of the sea or ocean. We determine, using an axisymmetric Finite Element Model, the tectonic patterns that pressurization of a regional sea or global ocean might produce at the surface of Enceladus. Tension is always predicted above where the ice is thinnest and generates cracks that might be at the origin of the Tiger Stripes. Tectonic activity is also expected in an annulus around the sea if the ice shell is in contact with but slips freely along the rocky core of the satellite. Cracks at the north pole are expected if the shell slips along the core or if there is a global ocean with thin ice at the pole. Water is likely injected along the base of the ice when the shell is grounded, which may lead to cycles of tectonic activity with the shell alternating between floating and grounded states and midlatitude faulting occurring at the transition from a grounded to a floating state.

Geologic setting of the Fortymile River area - Polyphase deformational history within part of the eastern Yukon-Tanana uplands of Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Day, Warren C.; Gamble, Bruce M.; Henning, Mitchell W.; Smith, Bruce D.

2000-01-01

The Fortymile River area lies within the Yukon-Tanana lithotectonic terrane of east-central Alaska. This terrane is a mosaic of several lithotectonic assemblages, each with a coherent lithologic, metamorphic, and deformational history. Previous workers have shown that the Fortymile River area is underlain by rocks of the Seventymile, Taylor Mountain, and Nisutlin assemblages. The Taylor Mountain tectonostratigraphic assemblage is the most widespread within study area and is made up of amphibolite-grade Paleozoic(?) metamorphosed supracrustal rocks that have been intruded by plutonic rocks. The protoliths for the supracrustal rocks include mafic volcanic(?) rocks, graywacke, sulfide-rich siliciclastic sediments, quartz-rich sandstone, pelite, and marble, all of which are cut by late sulfide-bearing quartz veins. The mafic metavolcanic(?) rocks are of both tholeiitic and calc-alkalic affinity and have distinctly different rare-earth-element abundances. The supracrustal rocks are interpreted to have been deposited on a continental margin and (or) distal to an island-arc complex in a back-arc basin.The Steele Creek Dome Tonalite is defined herein as a composite body of foliated biotite-hornblende tonalitic orthogneiss containing country-rock rafts of paragneiss. The complex lies within the Taylor Mountain assemblage and has been tectonized and presumably recrystallized during regional Early Jurassic ductile deformation. The tonalite is compositionally similar to other volcanic-arc granites. The entire sequence was intruded by a Early Jurassic(?) hornblende monzodioritediorite-quartz diorite suite.The area has been subjected to at least three phases of deformation. The first (D1) produced a strong regional S1 schistosity and local mineral lineations. The second (D2) deformation generated tight to isoclinal F2 folds, folding the S1 schistosity and L1 mineral lineations, and was accompanied by a weak axial-planar S2 cleavage and both L2 mineral and stretching lineations. The question remains if the D1 and D2 tectonic fabrics either (1) record end members of a continuous, relatively long lived, progressive ductile deformation associated with the peak regional metamorphism and northward-directed thrusting; or (2) were separate and distinct pulses of tectonism. The youngest deformation recognized (D3) folded the ductile fabric elements about south-plunging, east-vergent, open folds and records east-west-directed tectonic shortening.

Evaluation of the Interplate and Intraplate Deformations of the African Continent Using cGNSS Data

NASA Astrophysics Data System (ADS)

Apolinário, J. P.; Fernandes, R. M. S.; Bos, M. S.; Meghraoui, M.; Miranda, J. M. A.

2014-12-01

Two main plates, Nubia and Somalia, plus some few more tectonic blocks in the East African Rift System (EARS) delimit the African continent. The major part of the external plate boundaries of Africa is well defined by oceanic ridge systems with the exception of the Nubia-Eurasia complex convergence-collision tectonic zone. In addition, the number and distribution of the tectonic blocks along the EARS region is a major scientific issue that has not been completely answered so far. Nevertheless, the increased number of cGNSS (continuous Global Navigation Satellite Systems) stations in Africa with sufficient long data span is helping to better understand and constrain the complex sub-plate distribution in the EARS as well as in the other plate boundaries of Africa. This work is the geodetic contribution for the IGCP-Project 601 - "Seismotectonics and Seismic Hazards in Africa". It presents the current tectonic relative motions of the African continent based on the analysis of the estimated velocity field derived from the existing network of cGNSS stations in Africa and bordering plate tectonics. For the majority of the plate pairs, we present the most recent estimation of their relative velocity using a dedicated processing. The velocity solutions are computed using HECTOR, a software that takes into account the existing temporal correlations between the daily solutions of the stations. It allows to properly estimate the velocity uncertainties and to detect any artifacts in the time-series. For some of the plate pairs, we compare our solutions of the angular velocities with other geodetic and geophysical models. In addition, we also study the sensitivity of the derived angular velocity to changes in the data (longer data-span for some stations) for tectonic units with few stations, and in particular for the Victoria and Rovuma blocks of the EARS. Finally, we compute estimates of velocity fields for several sub-regions correlated with the seismotectonic provinces and discuss the level of interplate and intraplate deformations in Africa.

Present-day geothermal characteristics of the Ordos Basin, western North China Craton: new findings from deep borehole steady-state temperature measurements

NASA Astrophysics Data System (ADS)

Gao, Peng; Qiu, Qianfeng; Jiang, Guangzheng; Zhang, Chao; Hu, Shengbiao; Lei, Yuhong; Wang, Xiangzeng

2018-03-01

Heat flow and associated thermal regimes are related to the tectonic evolution and geophysical properties of the lithosphere. The Ordos Basin is located in a tectonic transitional zone: areas to the east of the basin are characterized as tectonically active, while regions to the west of the basin are characterized as tectonically stable. It is of general interest to learn the geothermal characteristics of the basin in such tectonic conditions. To clarify the spatial variability of the present-day geothermal field across the basin and its implications, we report 13 terrestrial heat flow points based on the first systematic steady-state deep borehole temperature measurements in the basin. The new data together with existing data show that the geothermal gradients in the basin range from 12.6 to 42.3° C km-1 with a mean of 27.7 ± 5.3° C km-1; the terrestrial heat flow values range from 43.3 to 88.7 mW/m2 with a mean of 64.7 ± 8.9 mW/m2. Such values are higher than those of typical cratonic basins and lower than those of tectonically active areas. By using all these data in the basin and adjacent areas, we plot geothermal gradient and heat flow distribution maps. The maps reveal that the basin is cooling westward and northward. The distribution pattern of the geothermal field is consistent with the lithospheric thickness variation in the basin. This similarity suggests that the geothermal spatial variability of the Ordos Basin is mainly influenced by heat from the deep mantle. In the southeastern basin, we locate a positive geothermal anomaly caused by the convergence of heat flow in basement highs and the high radiogenic heat production. In addition, the high heat flow in the eastern basin is related to the intense uplift during the Cenozoic Era.

Present-day geothermal characteristics of the Ordos Basin, western North China Craton: new findings from deep borehole steady-state temperature measurements

NASA Astrophysics Data System (ADS)

Gao, Peng; Qiu, Qianfeng; Jiang, Guangzheng; Zhang, Chao; Hu, Shengbiao; Lei, Yuhong; Wang, Xiangzeng

2018-07-01

Heat flow and associated thermal regimes are related to the tectonic evolution and geophysical properties of the lithosphere. The Ordos Basin is located in a tectonic transitional zone: areas to the east of the basin are characterized as tectonically active, while regions to the west of the basin are characterized as tectonically stable. It is of general interest to learn the geothermal characteristics of the basin in such tectonic conditions. To clarify the spatial variability of the present-day geothermal field across the basin and its implications, we report 13 terrestrial heat flow points based on the first systematic steady-state deep borehole temperature measurements in the basin. The new data together with existing data show that the geothermal gradients in the basin range from 12.6 to 42.3 °C km-1 with a mean of 27.7 ± 5.3 °C km-1; the terrestrial heat flow values range from 43.3 to 88.7 mW m-2 with a mean of 64.7 ± 8.9 mW m-2. Such values are higher than those of typical cratonic basins and lower than those of tectonically active areas. By using all these data in the basin and adjacent areas, we plot geothermal gradient and heat flow distribution maps. The maps reveal that the basin is cooling westwards and northwards. The distribution pattern of the geothermal field is consistent with the lithospheric thickness variation in the basin. This similarity suggests that the geothermal spatial variability of the Ordos Basin is mainly influenced by heat from the deep mantle. In the southeastern basin, we locate a positive geothermal anomaly caused by the convergence of heat flow in basement highs and the high radiogenic heat production. In addition, the high heat flow in the eastern basin is related to the intense uplift during the Cenozoic Era.

Triassic structural and stratigraphic evolution of the Central German North Sea sector

NASA Astrophysics Data System (ADS)

Wolf, Marco; Jähne-Klingberg, Fabian

2017-04-01

The subsurface of the Central German North Sea sector is characterized by a complex sequence of tectonic events that span from the Permo-Carboniferous initiation of the Southern Permian Basin to the present day. The Triassic period is one of the most prominent stratigraphic intervals in this area due to alternating phases of relatively tectonic quiescence and intense tectonic activity with the development of grabens, salt-tectonics movements, various regional and local erosional events and strong local and regional changes in subsidence over time. The heterogeneous geological history led to complex structural and lithological patterns. The presented results are part of a comprehensive investigation of the Central German North Sea sector. It was carried out within the scope of the project TUNB (www.bgr.bund.de). The main goal was to enhance the understanding of the Triassic geological development in the area of interest due to detailed seismic interpretation of several hundred 2D seismic lines and as well 3D seismic data sets. A seismostratigraphic concept was used to interpret most formations of the Triassic resulting in a detailed subdivision of the Triassic unit. Depth and thickness maps for every stratigraphic unit and geological cross sections provided new insights regarding an overall basin evolution as well as the timing and mechanisms of rifting and salt-tectonics. New results concerning the evolution of the Keuper in the German North Sea and especially the Triassic evolution of the Horn Graben, as one of the major Triassic rift-structures in the North Sea, will be highlighted. We will show aspects of strong tectonic subsidence in the Horn Graben in the Lower Triassic. In parts of the study area, halotectonic movements started in the Upper Triassic, earlier than previously proposed. Besides mapping of regional seismic reflectors, distinct sedimentary features like fluvial channel systems of the Stuttgart formation (Middle Keuper) or subrosion-like structures along the major Upper Jurassic to Lower Cretaceous unconformity, which are related to erosion of Triassic evaporitic formations, will be shown.

Recurrent intraplate tectonism in the New Madrid seismic zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zoback, M.D.; Hamilton, R.M.; Crone, A.J.

1980-08-29

For the first time, New Madrid seismicity can be linked to specific structural features that have been reactivated through geologic time. Extensive seismic reflection profiling reveals major faults coincident with the main earthquake trends in the area and with structural deformation apparently caused by repeated episodes of igneous activity.

Learning Geomorphology Using Aerial Photography in a Web-Facilitated Class

ERIC Educational Resources Information Center

Palmer, R. Evan

2013-01-01

General education students taking freshman-level physical geography and geomorphology classes at Arizona State University completed an online laboratory whose main tool was Google Earth. Early in the semester, oblique and planimetric views introduced students to a few volcanic, tectonic, glacial, karst, and coastal landforms. Semi-quantitative…

Satellite Gravity Transforms Unmask Tectonic Pattern of Arabian-African Region

NASA Astrophysics Data System (ADS)

Eppelbaum, Lev; Katz, Youri

2017-04-01

Satellite derived geophysical gravity data are the modern powerful tool of regional tectono-geophysical examination of the Earth's crust and upper mantle. It is well known that regional long-term seismological prognosis, strategy of searching economic deposits and many other important geological-geophysical problems are based mainly on constructions derived from the combined tectono-geophysical zonation. Some authors' experience of the tectono-geophysical zonation in the Eastern Mediterranean (both sea and land) with satellite derived gravity field (Eppelbaum and Katz, 2015a, 2015b) indicates a high effectiveness of the data employment for delineation of different tectono-structural units. Therefore, on the basis of the previous successive application, satellite derived gravity field analysis was applied for a giant (covering > 10 mln. km2) and complex Arabian-African region (including Zagros Mts.). The gravity field retracked from the Geosat and ERS-1 altimetry (e.g., Sandwell and Smith, 2009) was processed by the use of different mathematical apparatus employment enabling to underline these or those tectonic (geodynamic) features of the region under study. The main goals of present investigation are following: (1) employment of a new powerful regional geophysical tool - satellite derived gravity data and its transforms for unmasking some buried tectonic and geodynamic peculiarities of the study area, (2) finding definite relationships between the novel tectonic map and the gravity field transformations, (3) development of a novel tectonic map of this area (on the basis of careful examination of and generalization of available geological and geophysical (mostly satellite gravity) data). The compiled gravity map (for the map compiling more than 4 mln. observations were utilized) with the main tectonic features shows the intricate gravity pattern of the investigated area. An initial analysis of the gravity field behavior enabled to separate two main types of tectonic structures: (1) stable zones of continental and oceanic crust, and (2) mobile geotectonic belts. First type is characterized by homogeneous character of gravity field pattern (for instance, East Arabian Craton), whereas second type is characterized by mosaic and variable behavior of gravity field (especially, active rift zones). It should be noted that 'youngest' mobile structure (Alpine-Himalayan orogenic belt and active rift systems of the Red Sea - East Africa) significantly differs in the gravity field pattern from the Mesozoic terrane belt and Neoproterozoic belt. In this investigation six satellite gravity transforms (SGT) are described: multidimensional statistical analysis (MSA) by the use of sliding window, low-pass filtering, informational approach, gradient operator, entropy processing by sliding window of adaptive form, and 3D inverse methods. Application of the MSA enabled not only to delineate geodynamical parameters of the studied region (collision zone at the boundary between the Arabian and Eurasian Plates, and active rift zones between the Arabian, Nubian and Somalian Plates, etc.), but also to estimate generalized properties of the Earth's crust. Results of MSA employment clearly show zone of development of the oceanic crust of the Easternmost Mediterranean and zone of oceanic crust of the Gulf of Aden and eastern (oceanic) part of the Somalian Plate. Besides this, in this map the Arabian and East African active rift zones and collision zone between the Arabian and Eurasian Plates are visibly traced. Applied low-pass gravity field filtering enabled to recognize the most contrast crust-mantle structures. For example, the Afar triangle zone is clearly detected. Zones of the Neotethys closing Eastern Mediterranean, Persian Gulf, Zagros Fault Zone and South Caspian Basin can be easily identified. Subduction zones associated with the plate boundaries are reflected by elongated gradient pattern. These nonstable zones are conjugated with large mobile belts: Alpine-Himalayan belt and Mesozoic terrane belt. The zone of active rifting of the Red Sea, Gulf of Aden and complex structure of Afar triangle as well as East African rift system are noticeably fixed. The boundary between the continental and crust in the SE part of the region (where occurs a transfer zone between the Gulf of Aden and Arabian Sea) is visibly detected. Application of informational approach (Eppelbaum and Khesin, 2012) enabled to reliably fix both continental and oceanic cratons and all belts. To south-east of the Horn of Africa the Arabian Sea Basin with oceanic crust is clearly distinguished. The East Arabian Craton (platform) as well as its framing are noticeably detected. Computation of entropy map from the satellite derived gravity field was earlier successfully tested by the authors in the Eastern Mediterranean (Eppelbaum and Katz, 2015a). Application of the adaptive form sliding window enables to receive the most reliable entropy estimations in conditions of complex field caused by superimposed influence of targets of different order. Obviously, computation of an entropial map by the same method for the region under study reproduces mainly deep tectonic units (elements) of the region. Complex pattern of entropial field in the SE part of the region reflects transfer from the Somalian Plate to Indian Plate (this area is characterized by the most mosaic pattern). This map nicely indicates position of the Mesozoic terrane belt and transition zone between the Victorian and Tanzanian plates. On the basis of advanced inverse method employment, the map indicating the most density contrast surface (discontinuity) in the upper mantle was developed. This map presents an intricate density-tectonic depth pattern of the region. Here such important tectonic features as the Afar Triple Junction and collision zone between the Arabian and Eurasian lithospheric plates are noticeably recognized. Besides this, we can note increasing of lithospheric thickness in central parts of the Arabian and Somalian plates. Both these plates are countered by low-thickness lithospheric zones corresponding to the active rift zones. As it is indicated in the map, the thick lithospheric zones are associated with collisional zones at boundaries between the cratons and mobile belts. We suggest that the lowered values in the northern boundaries of the Arabian Plate correspond to subduction zones. The zones of lowered values in the middle of western part of the region correspond to the Neoproterozoic belt where ophiolitic and back-arc complexes with a thinned crust (e.g., Stern et al., 2004) are developed. Compiled satellite derived gravity field and a set of SGT were utilized for development of a novel tectono-geophysical zonation map of the Arabian-African region. Structurally- geodynamically this region is one of the key Earth's megastructures where are closely disposed remain elements of the Tethys Ocean crust (Ben-Avraham et al., 2002; Robertson, 2004), most ancient Early Permian reversly magnetized Kiama zone (Eppelbaum and Katz, 2012b; Eppelbaum et al., 2014), and the youngest modern oceanic crust of the Afar triangle developed among the continental lumps (Yirgu et al., 2006; Bastow et al., 2011). The tectonic zonation was carried out with application of three main principles of tectonic analysis: (1) classic basis of space-temporary reflection of structural complexes, (2) modern structural-geodynamic approach derived from the plate tectonic reconstructions where essential role plays analysis of rift, tectonic transform and collision forms of Earth's development, (3) revealing of intricate correlation between the mapped tectono-structural elements and lithospheric-mantle complexes delineated by using both conventional geophysical methods (seismic, seismological, thermal data, etc.) and comprehensive analysis of satellite derived gravity data. Compiled tectonic map of the region (00 - 35.60 north, and 300 - 570 east) indicates that Precambrian basement and Mesozoic-Cenozoic structures play dominating structural- geodynamic role in this region. Precambrian generations include two main structural elements: (1) Archean platforms (Eastern Arabian, Tanzanian and Eastern Saharan cratons), and (2) Neoproterozoic belt. In the Neoproterozoic belt we distinguish: (a) final Proterozoic back-arc belts with ophiolites, and (b) more ancient Early/Middle Proterozoic massifs (detected both in some previous works of various authors and recognized by the authors of the present investigation using a set of geological-geophysical indicators). In the areas of development of sedimentary Phanerozoic cover in the northern part of Arabian and African (Nubian) Plates, boundaries of Early/Middle Proterozoic massifs (Tabuk, Haif-Rutfah, Widyan and Nile Cone) and Neoproterozoic belts (Azraq-Sirhan, Ga'ara and Northern Western Desert) were delineated by analysis of: (1) land and airborne geophysical data, and (2) satellite derived gravity data. Meso-Cenozoic structures of the region contain two tectonic complexes of its forming. 1st complex (from Permian to present) is associated with the Neotethys Ocean evolution. 2nd complex (from Oligocene to present) is associated with initial phases of spreading in the Arabian-African segment of Earth's crust. 1st complex structurally and geodynamically is a multiple generation since the Neotethys Ocean evolution was accompanied by processes of spreading, movements of some giant blocks along tectonic transforms, and collisions. These processes have formed structures of three types: (1) Mesozoic terrane belt, (2) Cenozoic orogenic belt, and (3) remain depressions of the Neotethys with oceanic crust. Western (Levantine) part of the Mesozoic terrane belt is characterized by more ancient (Hauterive) age of consolidation comparing with the eastern part of the belt (Persian-Oman). Its terranes (from Zagros to Makran) and ophiolites were joined to Arabian platform in the Middle Cretaceous (Senomanian-Turonian). Many authors note an important role of Zagros terrane in the region under study and within the Caucasian-Arabian Sintaxis (e.g., Reilinger et al., 2006; Bordenave, 2008; Agard et al., 2011; Verges et al., 2011; Sharkov et al., 2015; Tunini et al., 2015). We propose that present study will unmask some tectono-geodynamic peculiarities of this complex tectonic unit. The Mesozoic terrane belt was delineated in the Eastern Mediterranean by the use of variety of geological and geophysical methods (multilevel gravity and magnetic data examination, thermal data analysis, seismic and seismological data) application (Ben- Avraham et al., 2002; Eppelbaum et al., 2012; Eppelbaum, 2015; Eppelbaum and Katz, 2015a, 2015b, 2016). At the same time, eastern Zagros-Makran part of the Mesozoic terrane belt never was analyzed as a separately developing structural part (unit) of the Arabian craton. In all known paleogeographical reconstructions the Zagros-Makran structure is shown as a part of its northern periphery. However, analysis of facial, sedimentary and structural data (presented in Bordenave, 2008) indicates that there is a sharp discordant joining between the Arabian craton and Zagros belt. Axes of anticline structures of the Arabian craton have a meridional strike, while axes of the Zagros anticline structures are disposed discordantly to them at SW 35 - 500. Besides this, paleogeological maps of Paleozoic (Bordenave, 2008) indicate that Devonian and Carboniferous deposits widely developed within the Arabian craton, do not presented in the Zagros belt. It testifies an uplift of Zagros structure and its isolated evaluation in the post-Carboniferous time when the Tethys Ocean began to form. Geological factors of Zagros structure isolation indicate that it was possibly a part of terrane belt in the southern part of the Neothetys Ocean forming. It is necessary to take into account that Zagros structure most likely occupied different tectonic positions at different periods of geological time: (1) up to Carboniferous period Zagros was a part of the Eastern Arabian Craton, (2) in the interval between Permian and Middle Cretaceous it was a part of the terrane belt within Neotethys, (3) at present it is a marginal part of the Arabian lithospheric plate. All three aforementioned items find a direct reflection in the compiled gravity and SGT maps: (1) Common structural-geophysical properties of Zagros structure and Arabian craton can be recognized in informational and gradient gravity field transformations; (2) Examination of initial gravity map, entropial transformation map and deep structure map testify that Zagros is an independent structural unit within the Mesozoic terrane belt. Presence of thick Cenozoic sediments in the eastern part of Arabian Plate essentially limits application of conventional geological methods; therefore, contouring of boundaries between the Mesozoic terrane belt and Precambrian platform is possible mainly by regional geophysical data analysis. Sharp changing of gravity pattern in all three afore- mentioned maps enables to utilize this property as criterion for delineation of southern boundary of the Mesozoic terrane belt; (3) Examination of the MSA map unambiguously indicates that Zagros suture is a marginal part of the Arabian lithospheric plate. REFERENCES Agard, P., Omrani, G., Jolivet, L., Whitechurch, H., Vrielynck, B., Spakman, W., Monie, P., Meyer, B. and Wortel, R., 2011. Zagros orogeny: A subduction-dominated process. Geological Magazine, 148, Nos. 5-6, 692-725. Bastow, I. D., Keir, D. and Daly, E., 2011. The Ethiopia Afar Geoscientific Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading, In: (L. Beccaluva, G. Bianchini, and M. Wilson, Eds.), Volcanism and Evolution of the African Lithosphere. The Geol. Society of America, Spec. Paper 478, 51-76. Ben-Avraham, Z., Ginzburg, A., Makris, J. and Eppelbaum, L., 2002. Crustal structure of the Levant basin, Eastern Mediterranean. Tectonophysics, 346, 23-43. Bordenave, M. L., 2008. The origin of the Permo-Triassic gas accumulations in the Iranian Zagros foldbelt and contiguous offshore areas: A review of the Paleozoic petroleum system. Jour. of Petroleum Geology, 31, No. 1, 3-42. Eppelbaum, L.V., 2015. Comparison of 3D integrated geophysical modeling in the South Caucasian and Eastern Mediterranean segments of the Alpine-Himalayan tectonic belt. Izv. Acad. Sci. Azerb. Rep., Ser.: Earth Sciences, No. 3, 25-45. Eppelbaum, L. V. and Katz, Y. I., 2012. Key features of seismo-neotectonic pattern of the Eastern Mediterranean. Izvestiya Acad. Sci. Azerb. Rep., Ser.: Earth Sciences, No. 3, 29-40. Eppelbaum, L. V. and Katz, Yu. I., 2015a. Newly Developed Paleomagnetic Map of the Easternmost Mediterranean Unmasks Geodynamic History of this Region. Central European Jour. of Geosciences (Open Geosciences), 7, No. 1, 95-117. Eppelbaum, L. V. and Katz, Yu. I., 1915b. Eastern Mediterranean: Combined geological- geophysical zonation and paleogeodynamics of the Mesozoic and Cenozoic structural- sedimentation stages. Marine and Petroleum Geology, 65, 198-216. Eppelbaum, L. V. and Katz, Yu. I., 2016. Tectono-Geophysical Zonation of the Near and Middle East and Eastern Africa. International Journal of Geology, 10, 1-10. Eppelbaum, L. V., Katz, Y. I. and Ben-Avraham, Z., 2012. Israel - Petroleum Geology and Prospective Provinces. AAPG European Newsletter, No. 4, 4-9. Eppelbaum, L. V. and Khesin, B. E., 2012. Geophysical Studies in the Caucasus. Springer, Heidelberg - N.Y. - London. Eppelbaum, L.V., Nikolaev, A.V. and Katz, Y.I., 2014. Space location of the Kiama paleomagnetic hyperzone of inverse polarity in the crust of the eastern Mediterranean. Doklady Earth Sciences (Springer), 457, No. 6, 710-714. Reilinger, R. E., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Cakmak, R., Ozener, H., Kadirov, F., Guliev, I., Stepanyan, R., Nadariya, M., Hahubia, G., Mahmoud, S., Sakr, K., ArRajehi, A., Paradissis, D., Al-Aydrus, A., Prilepin, M., Guseva, T., Evren, E., Dmitrotsa, A. Filikov, S.V., Gomez, F., Al-Ghazzi, R. and Karam, G., 2006. GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions. Jour. of Geophysical Research, BO5411, doi: 10.1029/2005JB004051, 1-26. Robertson, A., 2004. Development of concepts concerning the genesis and emplacement of Tethyan ophiolites in the Eastern Mediterranean and Oman regions. Tectonophysics, 66, 331-387. Sandwell, D. T. and Smith, W. H. F., 2009. Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge Segmentation versus spreading rate. Journal of Geophysical Research, 114, B01411, 1-18. Sharkov, E., Lebedev, V., Chugaev, A., Zabarinskaya, L., Rodnikov, A., Sergeeva, N. and Safonova, I., 2015. The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt: Geology, volcanism and neotectonics. Geoscience Frontiers, 6, 513-522. Stern, R. J., Johnson, P. R., Kroner, A. and Yibas, B., 2004. Neoproterozoic ophiolites of the Arabian-Nubian Shield. Developments in Precambrian Geology, 13, 95-128. Tunini, L., Jimenez-Munt, I., Fernandes, M., Verges, J. and Villasenor, A., 2015. Lithospheric mantle heterogeneities beneath the Zagros Mountains and the Iranian Plateau: A petrological-geophysical study. Geophysical Jour. International, 200, 596-614. Verges, J., Saura, E., Casciello, E., Fernandez, M., Villasenor, A., Jimenez-Munt, I. and Garsia- Castellanos, D., 2011. Crustal-scale cross-sections across the NW Zagros belt: implications for the Arabian margin reconstruction. Geological Magazine, doi: 10.1017/S0016756811000331, 1-23. Yirgu, G., Ebinger, C. J. and Maguire, P. K. H., 2006. The Afar volcanic province within the East African Rift System: Introduction. In: (Yirgu, G., Ebinger, C. J. and Maguire, P. K. H., Eds.), The Afar Volcanic Province within the East African Rift System. Geological Society, London, Special Publications, 259, 1-6.

The analysis of the Tectonics - SSS - Seismicity System in the 3D-model of the Rasvumchorr Mine - Central Open Pit Natural and Technical System (Khibiny)

NASA Astrophysics Data System (ADS)

Zhirov, Dmitry; Klimov, Sergey; Zhirova, Anzhela; Panteleev, Alexey; Rybin, Vadim

2017-04-01

Main hazardous factors during the operation of deposits represent tectonics (structural dislocation), strain and stress state (SSS), and seismicity. The cause and effect relationships in the Fault Tectonics - SSS - Seismicity system were analyzed using a 3D geological and structural Rasvumchorr Mine - Central Open Pit model. This natural and technical system (NTS) has resulted from the development of the world-class apatite-nepheline deposits the Apatite Circus and Rasvumchorr Plateau. The 3D model integrates various spatial data on the earth's surface topography before and after mining, geometry of mines and dumps, SSS measurements and rock pressure, seismicity, fault tectonics and etc. The analysis of the 3D model has clearly demonstrated the localization of three main seismic emanation zones in the areas of maximum anthropogenic variation of the initial rock state, and namely: ore pass zone under the Southern edge of the Central open pit, collapse and joining zone of the Rasvumchorr Mine and NW edge of the open pit, and zone under the Apatite Circus plate - collapse console. And, on the contrary, in the area of a large dump under the underground mine, a perennial seismic minimum zone was identified. The relation of the seismicity and fault tectonics was revealed only in three local sectors near come certain echelon fissures of the Main Fault(MF). No confinement of increased seismicity areas to the MF and other numerous echelon fissures is observed. The same picture occurs towards manifestations of rock pressure. Only an insignificant part of echelon fissures (including low rank of hierarchy) controls hazardous manifestations of rock pressure (dumps, strong deformations of the mine contour, etc.). It is shown that the anthropogenic factor (explosive, geometry and arrangement of mined spaces and collapse console), as well as the time factor significantly change orientation and structure (contrast and heterogeneity) of the stress fields. Time series of natural geophysical field fluctuations were additionally analyzed in order to find relationships with the seismicity. A sustainable regular relationship between the seismicity and solar and lunar tides has been observed; though, medium (classes 3 to 6) and high (class 7 and above) energy values of the events reveal various symmetry towards the Lunar cycle phases. The relationship of seismicity with other geophysical fields, e.g., geomagnetic disturbances, is defined as weak to very weak. The anthropogenic (man-induced) factor mostly influences the seismicity in the NTS rock masses. A law for shifting of maximum seismicity zones following the advance of the mining front has been found. The 3D model integrates various spatial data on the earth's surface topography before and after mining, geometry of mines and dumps, SSS measurements, and rock pressure, seismicity, fault tectonics, and other manifestations. The study is made within R&D topic No. 0231-2015-0013. The collection, processing, and analysis of data for natural stress fields became possible due to the support from RSF grant 14-17-00751.

Preliminary investigation on the deformation rates of the Nazimiye Fault (Eastern Turkey)

NASA Astrophysics Data System (ADS)

Sançar, Taylan

2016-04-01

The complex tectonic setting of the eastern Mediterranean is mainly shaped by the interaction between three major plates, Eurasian, African, and Arabian plates, with additional involvement from the smaller Anatolian Scholle. The internal deformation of the Anatolian Scholle is mainly accommodated along NW-striking dextral and NE-striking sinistral faults, which are explained by the Prandtl Cell model by Şengör (1979). Although some of these strike-slip faults, such as Tuzgölü, Ecemiş and Malatya-Ovacık faults, have long been documented, the Nazimiye Fault (NF) is only presented in very recent studies (Kara et al. 2013; Emre et al. 2012). The aim of the study is to understand intra-plate deformation of the Anatolian Scholle, by studying the morphotectonic structures along the NF. The study area located close to the eastern boundary of Anatolia, roughly on the wedge that is delimited by the North and East Anatolian shear zones and the Malatya-Ovacık Fault Zone. After the preliminary remote sensing analyses and field observations, I mapped the locations of the different terrace treads along the Pülümür River, which is strongly deflected by the activity of the NF. This dextral strike-slip fault, is not only characterized with the deformation of the Pülümür River, but also it shows many beheaded streams, pressure ridges, hot springs and travertines along its course. I sampled one of the alluvial fans for cosmogenic dating at the eastern section of the NF, where about 20 m of dextral offset was measured at the margins of the incised stream. Moreover, additional sampling was performed from different terrace levels along the Pülümür River, in order not only to estimate the min. horizontal rate, but also to quantify the vertical deformation. Moreover, I applied morphometric indices to understand the tectonic control on the local morphology along the NF. Transverse Topographic Symmetry Factor was used to show the relative degree of tectonic activity along the fault-bounded mountain fronts. In addition to that I also extracted hypsometric curves, hypsometric integrals and stream length gradient index to understand the relationship between characteristics of the drainage basins and tectonic activity. As preliminary results, I conclude that the southern segment of the NF is tectonically quiescent, whereas the deformation is mainly accommodated on the northern branch. References Emre, Ö., Duman, T.Y., Kondo, H., Olgun, Ş., Özalp, S., Elmacı, H., 2012. 1:250.000 Ölçekli Türkiye Diri Fay Haritası Serisi, Erzincan (NJ37-3) Paftası, Seri No:44, Maden Tetkik ve Arama Genel Müdürlüǧü, Ankara-Türkiye. Kara, K., Sançar, T., Zabci, C., 2013. Morphologic and Morphotectonic Characteristics of the Nazimiye Fault Zone, Eastern Turkey. EGU2013-8105, EGU General Assembly Vienna, Austria. Şengör, A.M.C., 1979. The North Anatolian transform fault; its age, offset and tectonic significance. Journal of the Geological Society of London 136, Part 3, 269-282.

Active control of multi-element rotor blade airfoils

NASA Technical Reports Server (NTRS)

Torok, Michael S. (Inventor); Moffitt, Robert C. (Inventor); Bagai, Ashish (Inventor)

2005-01-01

A multi-element rotor blade includes an individually controllable main element and fixed aerodynamic surface in an aerodynamically efficient location relative to the main element. The main element is controlled to locate the fixed aerodynamic surface in a position to increase lift and/or reduce drag upon the main element at various azimuthal positions during rotation.

The Trans-Rocky Mountain Fault System - A Fundamental Precambrian Strike-Slip System

USGS Publications Warehouse

Sims, P.K.

2009-01-01

Recognition of a major Precambrian continental-scale, two-stage conjugate strike-slip fault system - here designated as the Trans-Rocky Mountain fault system - provides new insights into the architecture of the North American continent. The fault system consists chiefly of steep linear to curvilinear, en echelon, braided and branching ductile-brittle shears and faults, and local coeval en echelon folds of northwest strike, that cut indiscriminately across both Proterozoic and Archean cratonic elements. The fault system formed during late stages of two distinct tectonic episodes: Neoarchean and Paleoproterozoic orogenies at about 2.70 and 1.70 billion years (Ga). In the Archean Superior province, the fault system formed (about 2.70-2.65 Ga) during a late stage of the main deformation that involved oblique shortening (dextral transpression) across the region and progressed from crystal-plastic to ductile-brittle deformation. In Paleoproterozoic terranes, the fault system formed about 1.70 Ga, shortly following amalgamation of Paleoproterozoic and Archean terranes and the main Paleoproterozoic plastic-fabric-producing events in the protocontinent, chiefly during sinistral transpression. The postulated driving force for the fault system is subcontinental mantle deformation, the bottom-driven deformation of previous investigators. This model, based on seismic anisotropy, invokes mechanical coupling and subsequent shear between the lithosphere and the asthenosphere such that a major driving force for plate motion is deep-mantle flow.

Fluid-rock interaction during a large earthquake recorded in fault gouge: A case study of the Nojima fault, Japan

NASA Astrophysics Data System (ADS)

Bian, D.; Lin, A.

2016-12-01

Distinguishing the seismic ruptures during the earthquake from a lot of fractures in borehole core is very important to understand rupture processes and seismic efficiency. In particular, a great earthquake like the 1995 Mw 7.2 Kobe earthquake, but again, evidence has been limited to the grain size analysis and the color of fault gouge. In the past two decades, increasing geological evidence has emerged that seismic faults and shear zones within the middle to upper crust play a crucial role in controlling the architectures of crustal fluid migration. Rock-fluid interactions along seismogenic faults give us a chance to find the seismic ruptures from the same event. Recently, a new project of "Drilling into Fault Damage Zone" has being conducted by Kyoto University on the Nojima Fault again after 20 years of the 1995 Kobe earthquake for an integrated multidisciplinary study on the assessment of activity of active faults involving active tectonics, geochemistry and geochronology of active fault zones. In this work, we report on the signature of slip plane inside the Nojima Fault associated with individual earthquakes on the basis of trace element and isotope analyses. Trace element concentrations and 87Sr/86Sr ratios of fault gouge and host rocks were determined by an inductively coupled plasma mass spectrometer (ICP-MS) and thermal ionization mass spectrometry (TIMS). Samples were collected from two trenches and an outcrop of Nojima Fault which. Based on the geochemical result, we interpret these geochemical results in terms of fluid-rock interactions recorded in fault friction during earthquake. The trace-element enrichment pattern of the slip plane can be explained by fluid-rock interactions at high temperature. It also can help us find the main coseismic fault slipping plane inside the thick fault gouge zone.

Paleostress maps and structural evolution of the Pontides

NASA Astrophysics Data System (ADS)

Hippolyte, Jean-Claude; Espurt, Nicolas; Kaymakci, Nuretdin; Sangu, Ercan; Müller, Carla

2014-05-01

In the frame of DARIUS programme we worked from 2010 to 2012 in the central and eastern Pontides. We aimed at understanding the timing and the characteristics of the extensional and compressional episodes that occurred along the southern margin of the Black Sea (Pontides belt). We used stress inversion technique (Angelier's softwares) for analyzing fault kinematics and characterizing the successive tectonic episodes in terms of paleostresses. The age of the tectonic episodes was constrained by combining structural analysis with nannoplankton dating of the sedimentary units. 1) In the central Pontides, structural analysis shows that deposition of the Barremian-Albian terrigenous sediments of the "syn-rift" Çaglayan Group was controlled by large normal faults under an ESE-WNW extension probably related to the SE-directed opening of the western Black Sea Basin. In contrast, the Coniacian-Santonian and the Paleocene "post-rift" sequences were deposited under NE-SW extension probably related to the SW-directed opening of the eastern Black Sea Basin. At the beginning of Eocene the stress regime changed from extensional to compressional which resulted in the formation of syn-compressional basins. In order to illustrate the two-dimensional structural evolution of the central Pontides we built a NNE-trending 75 km long balanced and restored cross section between Boyabat and Sinop cities. The section is constrained by 183 sites of field data, 5 seismic lines and 8 wells. We model the Pontides as a bi-vergent structure resulting from the structural inversion of Cretaceous normal faults of the southern Black Sea margin. Apatite fission track data along this section suggest that inversion started in the earliest Eocene (~55 Ma). Eocene-Miocene shortening reached ~28 km. 2) In the eastern Pontides, an early Campanian to late Paleocene NW-SE extension was followed by three successive compressional events. A Paleocene to early Eocene NW-SE compression resulted in the formation of the main structural elements of the eastern Pontides. This compression is probably the consequence of the oblique collision of the Tauride block in the South. Paleogene sediments in the Tercan region are interpreted as remnants of a flexural basin related to this collision. A more recent NE-SW compression created interference fold structures in particular in the easternmost Pontides. It may be related to the middle Miocene collision of the Arabian plate. The last event is a N-S to NW-SE compressional to transcurrent tectonics that uplifted the Tercan foreland basin. The change from the Miocene NE-SW compression to the modern stress field is correlated with the change from shortening to escape related strike-slip tectonics that occurred in the Zagros Belt and gave way to the inception of the North Anatolian Fault Zone along the southern margin of the Pontides Belt.

Stress field sensitivity analysis within Mesozoic successions in the Swiss Alpine foreland using 3-D-geomechanical-numerical models

NASA Astrophysics Data System (ADS)

Reiter, Karsten; Hergert, Tobias; Heidbach, Oliver

2016-04-01

The in situ stress conditions are of key importance for the evaluation of radioactive waste repositories. In stage two of the Swiss site selection program, the three siting areas of high-level radioactive waste are located in the Alpine foreland in northern Switzerland. The sedimentary succession overlays the basement, consisting of variscan crystalline rocks as well as partly preserved Permo-Carboniferous deposits in graben structures. The Mesozoic sequence represents nearly the complete era and is covered by Cenozoic Molasse deposits as well as Quaternary sediments, mainly in the valleys. The target horizon (designated host rock) is an >100 m thick argillaceous Jurassic deposit (Opalinus Clay). To enlighten the impact of site-specific features on the state of stress within the sedimentary succession, 3-D-geomechanical-numerical models with elasto-plastic rock properties are set up for three potential siting areas. The lateral extent of the models ranges between 12 and 20 km, the vertical extent is up to a depth of 2.5 or 5 km below sea level. The sedimentary sequence plus the basement are separated into 10 to 14 rock mechanical units. The Mesozoic succession is intersected by regional fault zones; two or three of them are present in each model. The numerical problem is solved with the finite element method with a resolution of 100-150 m laterally and 10-30 m vertically. An initial stress state is established for all models taking into account the depth-dependent overconsolidation ratio in Opalinus Clay in northern Switzerland. The influence of topography, rock properties, friction on the faults as well as the impact of tectonic shortening on the state of stress is investigated. The tectonic stress is implemented with lateral displacement boundary conditions, calibrated on stress data that are compiled in Northern Switzerland. The model results indicate that the stress perturbation by the topography is significant to depths greater than the relief contrast. The impact of fault geometry and frictional properties is observed within a distance of <1 km. The major impact on the stress state is caused by the variability of the geomechanical stratigraphy. The stress anisotropy increases when tectonic shortening is applied to the models. Stress magnitudes and anisotropy are largest within the stiff formations such as limestone. These stiff formations carry the load due to far field tectonic forces, whereas weak formations, like the argillaceous target horizon for the waste disposal, exhibits smaller stress magnitudes. Using the fracture potential as a more unambiguous indicator, the stiff overburden rocks are closer to failure than the target horizon for the repository, whereas stiff formations below the target rocks are far from failure.

Changes in Eocene-Miocene shallow marine carbonate factories along the tropical SE Circum-Caribbean responded to major regional and global environmental and tectonic events

NASA Astrophysics Data System (ADS)

Silva-Tamayo, Juan Carlos

2015-04-01

Changes in the factory of Cenozoic tropical marine carbonates have been for long attributed to major variations on climatic and environmental conditions. Although important changes on the factories of Cenozoic Caribbean carbonates seem to have followed global climatic and environmental changes, the regional impact of such changes on the factories of shallow marine carbonate along the Caribbean is not well established. Moreover, the influence of transpressional tectonics on the occurrence, distribution and stratigraphy of shallow marine carbonate factories along this area is far from being well understood. Here we report detailed stratigraphic, petrographic and Sr-isotope chemostratigraphic information of several Eocene-Miocene carbonate successions deposited along the equatorial/tropical SE Circum-Caribbean (Colombia and Panama) from which we further assess the influence of changing environmental conditions, transtentional tectonics and sea level change on the development of the shallow marine carbonate factories. Our results suggest that during the Eocene-early Oligocene interval, a period of predominant high atmospheric pCO2, coralline algae constitute the principal carbonate builders of shallow marine carbonate successions along the SE Circum-Caribbean. Detailed stratigraphic and paragenetic analyses suggest the developed of laterally continuous red algae calcareous build-ups along outer-rimmed carbonate platforms. The predominance of coralline red algae over corals on the shallow marine carbonate factories was likely related to high sea surface temperatures and high turbidity. The occurrence of such build-ups was likely controlled by pronounce changes in the basin paleotopography, i.e. the occurrence of basement highs and lows, resulting from local transpressional tectonics. The occurrence of these calcareous red algae dominated factories was also controlled by diachronic opening of different sedimentary basins along the SE Circum Caribbean resulting from transpressional tectonics. Calcareous algae persisted as the main constituents of the shallow marine carbonate factories until the middle Oligocene; a period when atmospheric pCO2 dropped significantly. The drop in atmospheric pCO2 allowed the onset of global icehouse conditions, which likely resulted in a decrease in sea surface temperatures along the Caribbean. This drop allowed the appearance of corals as the main constituents of the shallow marine carbonate factories along the SE Circum-Caribbean by late Oligocene times.

Seismo-stratigraphic evolution of the northern Austral Basin and its possible relation to the Andean tectonics, onshore Argentina.

NASA Astrophysics Data System (ADS)

Sachse, Victoria; Anka, Zahie; Pagan, Facundo; Kohler, Guillermina; Cagnolatti, Marcelo; di Primio, Rolando; Rodriguez, Jorge

2013-04-01

The Austral Basin is situated in a formerly and recently high active tectonic zone in southern Argentina. The opening of the South Atlantic to the east, the opening of the Drake Passage in the south, and the subduction related to the rise of the Andes to the west, had major influence on the study area. To identify the impact of the tectonic events on basin geometry, sediment thickness and depocenter migration through time, 2D seismic interpretation was performed for an area of approx. 180.000 km² covering the onshore northern Austral Basin. A total of 10 seismic horizons were mapped and tied to the stratigraphy from well reports, representing 9 syn- and post- rift sequences. The main units are: Basement (U1), Jurassic Tobifera Formation (U2), Early Cretaceous (U3), Late Cretaceous (U4), sub-unit Campanian (U4A), Paleocene (U5), Eocene (U6), Oligocene (U7), Miocene (U8), and Plio-Pleistocene (U9). Main tectonic events are identified representing the break-up phase forming graben systems and the evolution from the ancient backarc Rocas Verdes Basin to the foreland Austral Basin. Inversion and changes in the tectonic regime are concomitant with onlapping and thinning of the base of the Upper Cretaceous to Campanian sediments, while the Top of the Upper Cretaceous represents a Maastrichtian unconformity. Units depth maps show a triangular geometry since the Jurassic, tracing the north-eastern basement high and deepening to the south. Since the Campanian the former geometry of basin fill changed and deepening to the south stopped. Beginning of the foreland phase is assigned to this time as well as changes in the stress regime. Paleogene times are marked by a relatively high sedimentation rate coupled with enduring thermal subsidence, on-going rise of the Andes and changes in the convergence rates of the Nazca relative to the South American plate. Onset of sediment supply from the Andes (Incaic phase) resulted in enhanced sedimentation rates during the Paleocene, coupled with important basin subsidence at Andes foothills. An E-W transpressive deformation occurred during late Oligocene and Miocene, initiated by significant changes of plate motion between Nazca and South American plate, driving the Quechua phase of the Andean uplift. Hence, enhanced sedimentation from the rising Andes was renewed since a late Miocene unconformity.

The crustal structure of the eastern Fennoscandian Shield and central part of the East-European platform based on seismic, regional geophysic and geological data

NASA Astrophysics Data System (ADS)

Mints, M. V.; Berzin, R. G.; Babayants, P. S.; Konilov, A. N.; Suleimanov, A. K.; Zamozhniaya, N. G.; Zlobin, V. L.

2003-04-01

The 1-EU and 4B CDP transects worked out during 1998-2002 years by "Spetsgeophyzica", together with previously developed CDP profiles, have crossed most of the main tectonic units of the eastern Fennoscandian Shield and central part of the East-European platform. They provide seismic images of the Early Precambrian crust and upper mantle from the surface to about 80 km depth (25 s). The Neoarchaean granite-greenstone complexes of the Karelia craton along the 4B profile form a series of the tectonic slices descending eastward, some of which can be traced to the Moho. The Palaeoproterozoic structures presented by two main types: (1) volcano-sedimentary (VS) and (2) granulite-gneiss (GN) belts. The Pechenga-Varzuga VS belt has been identified as overthrust-underthrust southward-dipping package. Tectonic slices formed by the Palaeoproterozoic VS belts alternating with slices of the Neoarchaean granite-gneisses form the imbricated crustal unit that extends along the eastern margin of the Neoarchaean Karelia craton. The slices dip steeply northeastward flattening and partially juxtaposing at 20 km depth at the 1-EU cross-section. This level, which can be understood as the surface of main detachment, ascends westward. An imbrication and related thickening of the crust was caused by displacement of crustal slices in western and southwestern directions because of the Palaeoproterozoic collision event. The Palaeoproterozoic Onega unit comprising VS assemblages originated in a setting of the rifted passive margin forms the northwestward displaced thrust nappe complex. It is considered initially belonging to the southern edge of the Svecofennian passive margin. The Lapland GN belt has been transected by the Polar and EGGI profiles. Both cross-sections demonstrated that it constitutes thick composite crustal-scale tectonic slice. According to geophysical data, the continuation of the Lapland GN belt beneath the platform cover of the East European Craton forms an extended arch-shaped system of the belts approximately 2000 km long. In the vicinity of Moscow the thrust-nappe structure of these belts was recently recognized from reflection seismic profiling along 1-EU profile. The work has been developed in frames of the MPR RF Program and The SVEKALAPKO project and supported by the RFBR, grant No.00-05-64241.

Seafloor Tectonic Fault Fabric and the Evolution of the Walvis Ridge-Rio Grande Rise Hot Spot Twins in the South Atlantic

NASA Astrophysics Data System (ADS)

Sager, W. W.; Engfer, D.; Thoram, S.; Koppers, A. A. P.; Class, C.

2015-12-01

Walvis Ridge (WR) and Rio Grande Rise (RGR) are Cretaceous-Cenozoic large igneous provinces (LIPs) formed by the Tristan-Gough hot spot interacting with the Mid-Atlantic Ridge (MAR). Although hot spot-ridge interaction has long been considered a primary factor controlling WR-RGR morphology, details are fuzzy owing to sparse geophysical data. We examined tectonic fabric revealed in satellite altimetry-derived gravity data to infer details about RGR-WR evolution. Plate tectonic reconstructions indicate that the main RGR plateau and large N-S plateau in the eastern WR erupted at the same point at ~90 Ma. Over the next ~8 Myr, these conjunct LIPs formed a "V" shape with a basin in between. Curved fracture zones within the basin imply the two LIPs formed around a microplate. The prominent rift in the middle of RGR formed nearly perpendicular to the RGR-WR intersection, suggesting an extensional microplate boundary. Hot spot eruptions continued at the MAR, emplacing the eastern WR and two main RGR plateaus until ~60 Ma. During this period, the N-S trending Eastern Rio Grande Rise (ERGR) was erupted along the MAR. Both the ERGR and WR formed bathymetric lineaments parallel to seafloor fault fabric and were likely connected. This resulted in WR seamounts with a "tadpole" shape, the head being small to medium seamounts on the WR track and the tails being low, spreading-fabric-parallel ridges extending up to ~150 km northward. Similar, small seamounts are found in the contemporaneous ERGR. Another critical observation is that the WR-RGR formed at a large crustal discontinuity (~700 km at anomaly C33, ~84 Ma) at one or more fracture zone offsets. By late Cenozoic time (anomaly C5, ~10 Ma), the offset was reduced by half while several new fracture zones formed at the junction between RGR and WR. This implies a connection between ridge reorganization and RGR-WR volcanism that may have resulted from the fracture zones becoming oblique to the spreading direction as Euler poles for South America - Africa shifted. Finally, after ~60 Ma, volcanism emplaced seamounts mainly on the African plate and hot spot volcanism at the MAR was greatly reduced. Results from the present study augment recently published findings of a strong link between the formation of the RGR-WR LIP and spreading ridge tectonics.

Crustal Structure and Deformation of the Sichuan-Yunnan Region Revealed by receiver Function Data

NASA Astrophysics Data System (ADS)

Zeng, S.; Zheng, Y.

2017-12-01

Sichuan-Yunnan and its surrounding areas locates in the southeast side to the Tibetan Plateau, due to the intrusion of the Indian Plate under the Tibetan Plateau, materials escape from the Tibetan Plateau and flow southward to southeastward. Because of such tectonic environment, the Sichuan-Yunnan region is experiencing high tectonic movement, and is capable of highly diffused seismicity. Based on dynamic simulation and field survey investigations, tectonic and geological studies proposed a decoupling model in this region and lower crustal flow may inflate in the crust. However, this idea needs more evidences, especially anisotropic structures to support it, since the anisotropic structures are usually directly related to the movement of materials, or to the tectonic distributions. In the past several years, a number of works have been done on the anisotropic structures in the Tibetan Plateau and its surroundings. In usually, previous studies were mainly carried out by two kinds of methods. First, the shear wave splitting of SKS, which mainly reflects the accumulation effect of the anisotropy of the crust to the mantle; the other way is use surface wave to investigate the anisotropic features at different azimuths and depths. In the recent years, receiver function is used to determine the inclination and anisotropy of the subsurface structure, comparing with the other two methods, receiver functions can provide higher resolution and reliable anisotropic features in the crust. Following the method of Liu and Niu(2012), we collected teleseismic data from the Himalayan first term network, and picked out high quality data based on the waveform SNR ratio, as well as the azimuthal distributions. Comparing with previous work (e.g., Sun et al.,2012), our work can provide more receiver functions results with higher reliability. We find that the crust beneath the Sichuan-Yunnan region has a thickness of 30-60 km and Vp/Vs ratio of 1.70-1.80. The Moho depth from northwest to southeast showed a trend of gradual thinning. We also find that the crust beneath this area is highly anisotropic, and align with the main fault. Crustal anisotropy is present at most stations with a fast axis trending N-S to NW-SE from west side to east side of this region.

Recognized Multiple Rifts of the Neoproterozoic in the Initiation of the Tarim Craton (NW China) and Their Tectonic Implications

NASA Astrophysics Data System (ADS)

He, B.; Jiao, C.; Huang, T.; Zhou, X.; Cai, Z.; Cao, Z.; Jiang, Z.; Cui, J.; Yu, Z.; Chen, W.

2017-12-01

The Tarim Basin is the largest, oil-bearing and superimposed basin in the northwest of China. The development and tectonic property of the initial Tarim basin have been acutely disputed and remain enigmatic. Urgently need to reveal the origin and formation dynamics of the Tarim Carton and evaluate the potential of the deep energy resources. However, covered by vast desert and huge-thickness sedimentary strata, suffered by multiple tectonic movements, seismic data with low signal- to- noise ratio in the deep are the critical difficulties. We analyse 4 field outcrops, 18 wells, 27 reprocessed seismic reflection profiles with high SNR across the basin and many ancillary ones and aeromagnetic data. We find about 20 normal fault-controlled rift depressions of the Cryogenian and Ediacaran scattered in the Tarim basin, which developed on the Precambrian metamorphic and crystalline basements and covered by the epeiric sea and basin facies sediments of the Lower Cambrian. The structural styles of the rifts are mainly half grabens, symmetrical troughs and horst-grabens. The regional differences exist obviously in spatial and temporal. The WNW-ESE-trending faults occur in the central part and northern of the basin and the NE, and the NEE-trending faults occur in the southern parts, which response with the anomaly of aeromagnetic. Some main faults of the Ediacaran inherited from the Cryogenian and some occurred newly, the more rifting depressions occurred during the Ediacaran. The extensional NNW-SSE-oriented and NNE-SSW-oriented paleostress field occurred simultaneously during rifting, and accompanied with the clockwise shearing. According to the activities of syn-sedimentary faults, magmatic events and sediments, the tectonic properties of the rifts are different depending on their locations in the Tarim craton. The rifting phases mainly occurred from 780 Ma to 615 Ma. The formation of rifts were associated with the opening of the South Tianshan Ocean and the South Altun-West Kunlun Oceans, which located at the north and south margin of the Tarim block, respectively, in response to break-up of the Rodinia supercontinent. The multiple rifts recognized reflect the fine-scale structure of the initiation of the Tarim craton and is the significant for understanding of the plate system and formation dynamics.

Neoproterozoic Evolution and Najd‒Related Transpressive Shear Deformations Along Nugrus Shear Zone, South Eastern Desert, Egypt (Implications from Field‒Structural Data and AMS‒Technique)

NASA Astrophysics Data System (ADS)

Hagag, W.; Moustafa, R.; Hamimi, Z.

2018-01-01

The tectonometamorphic evolution of Nugrus Shear Zone (NSZ) in the south Eastern Desert of Egypt was reevaluated through an integrated study including field-structural work and magnetofabric analysis using Anisotropy of Magnetic Susceptibility (AMS) technique, complemented by detailed microstructural investigation. Several lines of evidence indicate that the Neoproterozoic juvenile crust within this high strain zone suffered an impressive tectonic event of left-lateral transpressional regime, transposed the majority of the earlier formed structures into a NNW to NW-directed wrench corridor depicts the northwestern extension of the Najd Shear System (NSS) along the Eastern Desert of Egypt. The core of the southern Hafafit dome underwent a high metamorphic event ( M 1) developed during the end of the main collisional orogeny in the Arabian-Nubian Shield (ANS). The subsequent M 2 metamorphic event was retrogressive and depicts the tectonic evolution and exhumation of the Nugrus-Hafafit area including the Hafafit gneissic domes, during the origination of the left-lateral transpressive wrench corridor of the NSS. The early tectonic fabric within the NSZ and associated highly deformed rocks was successfully detected by the integration of AMS-technique and microstructural observations. Such fabric grain was checked through a field-structural work. The outcomes of the present contribution advocate a complex tectonic evolution with successive and overlapped deformation events for the NSZ.

Integrated geophysical and geological study and petroleum appraisal of Cretaceous plays in the Western Gulf of Gabes, Tunisia

NASA Astrophysics Data System (ADS)

Dkhaili, Noomen; Bey, Saloua; El Abed, Mahmoud; Gasmi, Mohamed; Inoubli, Mohamed Hedi

2015-09-01

An integrated study of available seismic and calibrated wells has been conducted in order to ascertain the structural development and petroleum potential of the Cretaceous Formations of the Western Gulf of Gabes. This study has resulted in an understanding of the controls of deep seated Tethyan tectonic lineaments by analysis of the Cretaceous deposits distribution. Three main unconformities have been identified in this area, unconformity U1 between the Jurassic and Cretaceous series, unconformity U2 separating Early from Late Cretaceous and known as the Austrian unconformity and the major unconformity U3 separating Cretaceous from Tertiary series. The seismic analysis and interpretation have confirmed the existence of several features dominated by an NE-SW extensive tectonic regime evidenced by deep listric faults, asymmetric horst and graben and tilted blocks structures. Indeed, the structural mapping of these unconformities, displays the presence of dominant NW-SE fault system (N140 to N160) bounding a large number of moderate sized basins. A strong inversion event related to the unconformity U3 can be demonstrated by the mapping of the unconformities consequence of the succession of several tectonic manifestations during the Cretaceous and post-Cretaceous periods. These tectonic events have resulted in the development of structural and stratigraphic traps further to the porosity and permeability enhancement of Cretaceous reservoirs.

Tectonics earthquake distribution pattern analysis based focal mechanisms (Case study Sulawesi Island, 1993–2012)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ismullah M, Muh. Fawzy, E-mail: mallaniung@gmail.com; Lantu,; Aswad, Sabrianto

Indonesia is the meeting zone between three world main plates: Eurasian Plate, Pacific Plate, and Indo – Australia Plate. Therefore, Indonesia has a high seismicity degree. Sulawesi is one of whose high seismicity level. The earthquake centre lies in fault zone so the earthquake data gives tectonic visualization in a certain place. This research purpose is to identify Sulawesi tectonic model by using earthquake data from 1993 to 2012. Data used in this research is the earthquake data which consist of: the origin time, the epicenter coordinate, the depth, the magnitude and the fault parameter (strike, dip and slip). Themore » result of research shows that there are a lot of active structures as a reason of the earthquake in Sulawesi. The active structures are Walannae Fault, Lawanopo Fault, Matano Fault, Palu – Koro Fault, Batui Fault and Moluccas Sea Double Subduction. The focal mechanism also shows that Walannae Fault, Batui Fault and Moluccas Sea Double Subduction are kind of reverse fault. While Lawanopo Fault, Matano Fault and Palu – Koro Fault are kind of strike slip fault.« less

Kinematics of the asal rift (djibouti) determined from the deformation of fieale volcano.

PubMed

De Chabalier, J B; Avouac, J P

1994-09-16

Because of its subaerial exposure the Asal rift segment provides an exceptional opportunity to quantify the deformation field of an active rift and assess the contribution of tectonics and volcanism to rifting processes. The present topography of the Asal rift results from the tectonic dismemberment during the last 100,000 years of a large central volcanic edifice that formed astride the rift zone 300,000 to 100,000 years ago. Three-dimensional deformation of this volcano has been quantified from the combined analysis of the topography and geology. The analysis indicates that spreading at 17 to 29 millimeters per year in a N40 degrees +/- 5 degrees E direction accounts for most of the separation between Arabia and Somalia. The small topographic subsidence relative to extension suggests that tectonic thinning of the crust has been balanced by injection and underplating of magmatic material of near crustal density. The methodology developed in this study could also be applied to quantify deformation in relatively inaccessible areas where the main available information is topography or bathymetry.

Report of the panel on the land surface: Process of change, section 5

NASA Technical Reports Server (NTRS)

Adams, John B.; Barron, Eric E.; Bloom, Arthur A.; Breed, Carol; Dohrenwend, J.; Evans, Diane L.; Farr, Thomas T.; Gillespie, Allan R.; Isaks, B. L.; Williams, Richard S.

1991-01-01

The panel defined three main areas of study that are central to the Solid Earth Science (SES) program: climate interactions with the Earth's surface, tectonism as it affects the Earth's surface and climate, and human activities that modify the Earth's surface. Four foci of research are envisioned: process studies with an emphasis on modern processes in transitional areas; integrated studies with an emphasis on long term continental climate change; climate-tectonic interactions; and studies of human activities that modify the Earth's surface, with an emphasis on soil degradation. The panel concluded that there is a clear requirement for global coverage by high resolution stereoscopic images and a pressing need for global topographic data in support of studies of the land surface.

The San Andreas fault experiment. [gross tectonic plates relative velocity

NASA Technical Reports Server (NTRS)

Smith, D. E.; Vonbun, F. O.

1973-01-01

A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

Terrain classification and land hazard mapping in Kalsi-Chakrata area (Garhwal Himalaya), India

NASA Astrophysics Data System (ADS)

Choubey, Vishnu D.; Litoria, Pradeep K.

Terrain classification and land system mapping of a part of the Garhwal Himalaya (India) have been used to provide a base map for land hazard evaluation, with special reference to landslides and other mass movements. The study was based on MSS images, aerial photographs and 1:50,000 scale maps, followed by detailed field-work. The area is composed of two groups of rocks: well exposed sedimentary Precambrian formations in the Himalayan Main Boundary Thrust Belt and the Tertiary molasse deposits of the Siwaliks. Major tectonic boundaries were taken as the natural boundaries of land systems. A physiographic terrain classification included slope category, forest cover, occurrence of landslides, seismicity and tectonic activity in the area.

Three-Dimensional Structural and Hydrologic Evolution of Sant Corneli Anticline, a Fault-Cored Fold in the Central Spanish Pyrenees

NASA Astrophysics Data System (ADS)

Shackleton, J. R.; Cooke, M. L.

2005-12-01

The Sant Corneli Anticline is a well-exposed example of a fault-cored fold whose hydrologic evolution and structural development are directly linked. The E-W striking anticline is ~ 5 km wide with abrupt westerly plunge, and formed in response to thrusting associated with the upper Cretaceous to Miocene collision of Iberia with Europe. The fold's core of fractured carbonates contains a variety of west dipping normal faults with meter to decameter scale displacement and abundant calcite fill. This carbonate unit is capped by a marl unit with low angle, calcite filled normal faults. The marl unit is overlain by clastic syn-tectonic strata whose sedimentary architecture records limb rotation during the evolution of the fold. The syn-tectonic strata contain a variety of joint sets that record the stresses before, during, and possibly after fold growth. Faulting in the marl and calcite-filled joints in the syn-tectonic strata suggest that normal faults within the carbonate core of the fold eventually breached the overlying marl unit. This breach may have connected the joints of the syn-tectonic strata to the underlying carbonate reservoir and eliminated previous compartmentalization of fluids. Furthermore, breaching of the marl units probably enhanced joint formation in the overlying syn-tectonic strata. Future geochemical studies of calcite compositions in the three units will address this hypothesis. Preliminary mapping of joint sets in the syn-tectonic strata reveal a multistage history of jointing. Early bed-perpendicular joints healed by calcite strike NE-SW, parallel to normal faults in the underlying carbonates, and may be related to an early regional extensional event. Younger healed bed-perpendicular joints cross cut the NE-SW striking set, and are closer to N-S in strike: these joints are interpreted to represent the initial stages of folding. Decameter scale, bed perpendicular, unfilled fractures that are sub-parallel to strike probably represent small joints and faults that formed in response to outer arc extension during folding. Many filled, late stage joints strike sub-parallel to, and increase in frequency near, normal faults and transverse structures observed in the carbonate fold core. This suggests that faulting in the underlying carbonates and marls significantly affected the joint patterns in the syn-tectonic strata. Preliminary three-dimensional finite element restorations using Dynel have allowed us to test our hypotheses and constrain the timing of jointing and marl breach.

The Maritsa strike-slip shear zone between Kostenets and Krichim towns, South Bulgaria — Structural, petrographic and isotope geochronology study

NASA Astrophysics Data System (ADS)

Naydenov, Kalin; Peytcheva, Irena; von Quadt, Albrecht; Sarov, Stoyan; Kolcheva, Krastina; Dimov, Dimo

2013-06-01

The present study describes the characteristics of the Maritsa Shear Zone (MSZ), a major tectonic element in the Balkanides in South Central Bulgaria. Metamorphic rocks of four lithotectonic units — Madan, Chepinska, Asenitsa and Thrace units crop out in the study area. Strike-slip ductile deformation in MSZ affects the Thrace Lithotectonic Unit (TLU) for up to 15 km. The stratigraphy of this unit is divided in two: Parvenets succession and variegated succession. U-Pb zircon dating reveals Late Jurassic protolith age for metagranitoids and metagabbros of the variegated succession. For its metasedimentary part Triassic to Upper Jurassic age is suggested based on the strontium isotope signature of the marbles. The Parvenets succession affiliates to the Variscan metamorphic basement of Europe. The metamorphic evolution of the zone is subdivided into synmetamorphic strike-slip deformations and annealing stages. The ductile shearing occurred in greenschist to lower amphibolite facies between 130 Ma (discordant U-Pb ages) and 82-78 Ma (late-syntectonic granites). This stage is connected with the oblique collision of the Rhodope Late Jurassic arc with the European platform. With the docking of the arc and the triggering of the strike-slip movements, MSZ represents an orogen-scale border between the Rhodope south-vergent thrust complex and the north-vergent deformations in the Srednogorie and Sakar-Strandzha zones. During the Late Cretaceous MSZ is the contact between the Srednogorie magmatic arc (part of the Apuseni-Banat-Timok-Srednogorie Belt) and the Rhodopean metamorphic core complexes. NW-SE dextral faulting characterized the brittle tectonics along the zone. Strike-slip faults of the southern border of the TLU are transferred into reverse faults, along which the TLU overthrusted Oligocene sediments. MSZ is an orogen-scale transpressional shear zone and an important border in the structure of the Balkanides. This multidisciplinary research emphasizes its role as a major tectonic element by presenting new structural, petrographic and isotope geochronology data.

The electrical structure of lithosphere beneath Northeast China —Preliminary results from SinoProbe-01-04

NASA Astrophysics Data System (ADS)

Hui, F.; Qing, Z.; Gengen, Q.; Fagen, P.; Dawei, B.; Baotun, G.; Jingqi, L.; Changwang, L.; Xiaochang, L.; Meixing, H.; Bingrui, D.

2012-12-01

Being constituted by the Seberia, Northern China fossil plate and Pacific Plate, the tectonics of Northeast China are very complicated. In order to study the electrical structure in these areas, the project SinoProbe-01-04 'Experimental study of 'standard monitoring network' of continental EM parameters in Northeast China' have established a 4°×4°regional MT array covering the whole Northeast China(Fig. 1). To make sure that MT data observed on each standard point representatively, a cross profile with the standard point being center and eight auxiliary measuring points around has been designed in practical work, and the same direction of the physical measuring point should have 20 km space, the observation time should be more than 120 hours in standard point and more than 24 hours in each auxiliary station. Both broadband MT equipment (V5-2000) and long-period MT equipment (LEMI-417M) have been used together in standard point, then the ultra-wideband electromagnetic signals at 320HZ-1/10000Hz can be acquired by combining the field data observed by each equipment. Eleven MT standard network control point with total 99 physical measuring points have been finished in 2010, then those works were repeated again in 2011 to make sure observed result reliable. Based on the observed result, this article preliminary analysis the electrical structure of each major tectonic element in Northeast China, which including the regularity of distribution of regional electrical spindle, the distribution characteristics of vertical conductivity, development status of the low resistivity layer in the crust, and the depth of the high conductivity layer in upper mantle. It has been founded that the electrical features of the major tectonic element in Northeast China are different and appear electrical-heterogeneous in cross direction. Fig.1 MT array observed site

Tracking the Progress of EarthScope/USArray: The crust and upper mantle beneath the transition region between tectonic western US and cratonic eastern US

NASA Astrophysics Data System (ADS)

Shen, W.; Lin, F.; Ritzwoller, M. H.

2010-12-01

The transition region between the tectonic western US and the cratonic eastern US contains numerous significant geological regions (e.g., the Rocky Mountains, the Colorado Plateau, and the Rio Grande Rift), and also, unknowns (e.g, the location or extent of the east-west US dichotomy, the compensation of the high topography of the western Great Plains, the extensional mechanics of the Rio Grande Rift, and the structure of the mantle beneath the Colorado Plateau). The answers to these questions and others are critical to an understanding of the tectonics and tectonic history of this region and its impact on the cratonic eastern US. The recent deployments of seismic stations, particularly the EarthScope USArray Transportable Array (TA), provide an opportunity to construct a detailed 3-D structural model of the crust and upper mantle beneath this transition region, and thus allow us to address some of the questions listed above. We present results from ambient noise tomography (ANT) and teleseismic earthquake tomography by using data from TA stations within the western and central US. We processed continuous seismic noise data from ~600 TA stations from August 2008 to March 2010, which after data selection produces a data set with ~100,000 inter-station paths. Rayleigh wave phase speed maps between 6 and 40 sec period and Love wave phase speed maps between 8 and 30 sec with a resolution of ~60 km are constructed using eikonal tomography. In addition, we applied eikonal tomography (ET) to about 300 teleseismic earthquakes to obtain long-period (30 - 100 sec) Rayleigh wave phase speed maps and Love wave phase speeds maps (30 - 60 sec). By jointly inverting Rayleigh and Love phase speeds maps from ANT and earthquake tomography, we constructed a 3-D isotropic and radially anisotropic shear velocity model of the crust and upper mantle to ~150 km depth together with model uncertainties constrained by a Monte-Carlo inversion. The 3-D isotropic model reveals a variety of robust features in this transition region. In the uppermost crust, the main sedimentary basins (e.g., Green River, Uinta, Washakie, Powder River, Denver, Albuquerque, Permian, and Anadarko) are imaged. In the middle and lower crust where the low shear velocities from basins diminish, the Yellowstone hot spot becomes the main slow anomaly. In the uppermost mantle, high velocity anomalies are observed beneath the Colorado Plateau, the Wyoming craton, and the Great Plains. Although the Colorado Plateau shows more or less homogeneous shear velocity in its middle and towards its northern boundary, the other two main fast anomalies reveal inhomogeneous structures at depths deeper than 100 km. Two main low velocity anomalies are observed: one underlying the Snake River Plain which broadens and dips to the northeast and another U-shaped anomaly on the eastern margin of the Colorado Plateau. These velocity anomalies add to complexities at the transition between the tectonic western US and the stable eastern US. The location and uncertainty of the east-west shear velocity dichotomy also is constrained by this model.

Igneous and tectonic evolution of the Batchawana Greenstone Belt, Superior Province: a U-Pb zircon and titanite study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corfu, F.; Grunsky, E.C.

1987-01-01

U-Pb isotopic dating of zircon and titanite from all the major litho-tectonic units of the Batchawana belt, an Archean greenstone belt of the Abitibi Subprovince of the Superior Province in Canada, shows that the belt evolved during a period of about 60 Ma between about 2730 and 2670 Ma ago. Subsequent deformation of the supracrustal sequences produced isoclinal folding and culminated in metamorphism ranging from lower greenschist to amphibolite facies and anatexis related to the intrusion of syn- to late-tectonic plutons, four phases of which have ages of 2678 +4/-2 Ma, 2677 +/- 2 Ma, 2677 +/- 3 Ma, andmore » 2676 +/- 2 Ma. Two post-tectonic granitoid plutons in the center of the belt were intruded 2674 +/- 3 Ma and 2673 +/- 5 Ma ago and were followed by the emplacement of a composite mafic to felsic intrusion; a monzonite and a hornblendite from this intrusion yield identical ages of 2668 +/- 2 Ma. Titanite ages are identical or younger than the ages of coexisting zircons and reflect regional metamorphism and post-tectonic plutonism, but in a few cases they are younger and may record increased fluid activity along faults and the intrusion of mafic dikes. U-Pb zircon systematics, together with age and lithological relationships, suggests that the greenstone belt formed in an oceanic environment from material derived initially mainly from the mantle. Subsequent melting at the base of the thickening volcanic succession produced intermediate to felsic volcanic rocks, tonalites, and later granodioritic to granitic plutons leading to the final consolidation of the granite-greenstone terrain. 47 references.« less

Late Quaternary tectonic activity and lake level change in the Rukwa Rift Basin

NASA Astrophysics Data System (ADS)

Delvaux, D.; Kervyn, F.; Vittori, E.; Kajara, R. S. A.; Kilembe, E.

1998-04-01

Interpretation of remotely sensed images and air photographs, compilation of geological and topographical maps, morphostructural and fault kinematic observations and 14C dating reveal that, besides obvious climatic influences, the lake water extent and sedimentation in the closed hydrological system of Lake Rukwa is strongly influenced by tectonic processes. A series of sandy ridges, palaeolacustrine terraces and palaeounderwater delta fans are related to an Early Holocene high lake level and subsequent progressive lowering. The maximum lake level was controlled by the altitude of the watershed between the Rukwa and Tanganyika hydrological systems. Taking as reference the present elevation of the palaeolacustrine terraces around Lake Rukwa, two orders of vertical tectonic movement are evidenced: i) a general uplift centred on the Rungwe Volcanic Province between the Rukwa and Malawi Rift Basins; and ii) a tectonic northeastward tilting of the entire Rukwa Rift Basin, including the depression and rift shoulders. This is supported by the observed hydromorphological evolution. Local uplift is also induced by the development of an active fault zone in the central part of the depression, in a prolongation of the Mbeya Range-Galula Fault system. The Ufipa and Lupa Border Faults, bounding the Rukwa depression on the southwestern and northeastern sides, respectively, exert passive sedimentation control only. They appear inactive or at least less active in the Late Quaternary than during the previous rifting stage. The main Late Quaternary tectonic activity is represented by dextral strike-slip movement along the Mbeya Range-Galula Fault system, in the middle of the Rukwa Rift Basin, and by normal dip-slip movements along the Kanda Fault, in the western rift shoulder.

Vertical and Horizontal Analysis of Crustal Structure of Southeastern Mediterranean and the Egyptian Coastal Zone, from Bouguer and Satellite Mission Data

NASA Astrophysics Data System (ADS)

Saleh, Salah

2016-07-01

The present Tectonic system of Southeastern Mediterranean is driven by the collision of the African and Eurasian plates, the Arabian Eurasian convergence and the displacement of the Anatolian Aegean microplate, which generally represents the characteristic of lithospheric structure of the region. In the scope of this study, Bouguer and the satellite gravity (satellite altimetry) anomalies of southeastern Mediterranean and North Eastern part of Egypt were used for investigating the lithospheric structures. Second order trend analyses were applied firstly to Bouguer and satellite altimetry data for examining the characteristic of the anomaly. Later, the vertical and horizontal derivatives applications were applied to the same data. Generally, the purpose of the applying derivative methods is determining the vertical and horizontal borders of the structure. According to the results of derivatives maps, the study area could mainly divided into important four tectonic subzones depending on basement and Moho depth maps. These subzones are distributed from south to the north as: Nile delta-northern Sinai zone, north Egyptian coastal zone, Levantine basin zone and northern thrusting (Cyprus and its surroundings) zone. These zones are separated from each other by horizontal tectonic boundaries and/or near-vertical faults that display the block-faulting tectonic style of this belt. Finally, the gravity studies were evaluated together with the seismic activity of the region. Consequently, the geodynamical structure of the region is examined with the previous studies done in the region. Thus, the current study indicates that satellite gravity mission data is a valuable source of data in understanding the tectonic boundary behavior of the studied region and that satellite gravity data is an important modern source of data in the geodynamical studies.

Palaeohydrological evolution of the late Cenozoic saline lake in the Qaidam Basin, NE Tibetan Plateau: Tectonic vs. climatic control

NASA Astrophysics Data System (ADS)

Guo, Pei; Liu, Chiyang; Huang, Lei; Yu, Mengli; Wang, Peng; Zhang, Guoqing

2018-06-01

As the largest Cenozoic terrestrial intermountain basin on the Tibetan Plateau, the Qaidam Basin is an ideal setting to understand the coupled controls of tectonics and climate on hydrological evolution. In this study, we used 47,846 data of carbonate and chloride contents from 146 boreholes to reconstruct the Neogene-Quaternary basin-wide hydrological evolution of the Qaidam Basin. Our results show that during the early Miocene (22-15 Ma), the palaeolake in the Qaidam Basin was mainly situated in the southwestern part of the basin, and its water was mostly brackish. From then on, this palaeolake progressively migrated southeastward, and its salinity increased from late Miocene saline water to Quaternary brines. This generally increasing trend of the water palaeosalinity during the late Cenozoic corresponded with regional and global climate changes at that time, suggesting the dominance of climatic control. However, the paces of the salinity increase from sediments in front of the three basin-bounding ranges were not the same, indicating that extra tectonic controls occurred. Sediments in front of the Eastern Kunlun Shan to the southwest and the Altyn Shan to the northwest showed an abrupt, dramatic increase in salinity at 15 Ma and 8 Ma, respectively; sediments in front of the Qilian Shan to the northeast showed steady increase without prominent, abrupt changes, indicating the occurrence of asynchronous tectonic controls from the basin-bounding ranges. The late Miocene depocentre migration was synchronous with the hydrological changes in front of the Altyn Shan, while the more significant migration during the Quaternary was consistent with the pulsing, intense extrabasinal and intrabasinal tectonic movements along the Tibetan Plateau.

Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan-Mufushan Batholith in Southeast China and Its Tectonic Significance: 1. Structural Analysis and Geochronological Constraints

NASA Astrophysics Data System (ADS)

Ji, Wenbin; Faure, Michel; Lin, Wei; Chen, Yan; Chu, Yang; Xue, Zhenhua

2018-01-01

The South China Block (SCB) experienced a polyphase reworking by the Phanerozoic tectonothermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan-Mufushan composite batholith in the north-central SCB. This batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the batholith, characterized by a top-to-the-SW ductile shearing in the early-stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by farfield compression from the northern Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the batholith where the syntectonic late-stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top-to-the-NW kinematics; and (2) subsequent brittle faulting (D2b) further exhumed the entire batholith that behaved as rift shoulder with half-graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132-95 Ma. Such a Cretaceous NW-SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so-called "southeast China basin and range tectonics."

New seismo-stratigraphic and marine magnetic data of the Gulf of Pozzuoli (Naples Bay, Tyrrhenian Sea, Italy): inferences for the tectonic and magmatic events of the Phlegrean Fields volcanic complex (Campania)

NASA Astrophysics Data System (ADS)

Aiello, Gemma; Marsella, Ennio; Fiore, Vincenzo Di

2012-06-01

A detailed reconstruction of the stratigraphic and tectonic setting of the Gulf of Pozzuoli (Naples Bay) is provided on the basis of newly acquired single channel seismic profiles coupled with already recorded marine magnetics gathering the volcanic nature of some seismic units. Inferences for the tectonic and magmatic setting of the Phlegrean Fields volcanic complex, a volcanic district surrounding the western part of the Gulf of Naples, where volcanism has been active since at least 50 ka, are also discussed. The Gulf of Pozzuoli represents the submerged border of the Phlegrean caldera, resulting from the volcano-tectonic collapse induced from the pyroclastic flow deposits of the Campanian Ignimbrite (35 ka). Several morpho-depositional units have been identified, i.e., the inner continental shelf, the central basin, the submerged volcanic banks and the outer continental shelf. The stratigraphic relationships between the Quaternary volcanic units related to the offshore caldera border and the overlying deposits of the Late Quaternary depositional sequence in the Gulf of Pozzuoli have been highlighted. Fourteen main seismic units, both volcanic and sedimentary, tectonically controlled due to contemporaneous folding and normal faulting have been revealed by geological interpretation. Volcanic dykes, characterized by acoustically transparent sub-vertical bodies, locally bounded by normal faults, testify to the magma uprising in correspondence with extensional structures. A large field of tuff cones interlayered with marine deposits off the island of Nisida, on the western rim of the gulf, is related to the emplacement of the Neapolitan Yellow Tuff deposits. A thick volcanic unit, exposed over a large area off the Capo Miseno volcanic edifice is connected with the Bacoli-Isola Pennata-Capo Miseno yellow tuffs, cropping out in the northern Phlegrean Fields.

Identifying tectonic parameters that influence tsunamigenesis

NASA Astrophysics Data System (ADS)

van Zelst, Iris; Brizzi, Silvia; van Dinther, Ylona; Heuret, Arnauld; Funiciello, Francesca

2017-04-01

The role of tectonics in tsunami generation is at present poorly understood. However, the fact that some regions produce more tsunamis than others indicates that tectonics could influence tsunamigenesis. Here, we complement a global earthquake database that contains geometrical, mechanical, and seismicity parameters of subduction zones with tsunami data. We statistically analyse the database to identify the tectonic parameters that affect tsunamigenesis. The Pearson's product-moment correlation coefficients reveal high positive correlations of 0.65 between, amongst others, the maximum water height of tsunamis and the seismic coupling in a subduction zone. However, these correlations are mainly caused by outliers. The Spearman's rank correlation coefficient results in more robust correlations of 0.60 between the number of tsunamis in a subduction zone and subduction velocity (positive correlation) and the sediment thickness at the trench (negative correlation). Interestingly, there is a positive correlation between the latter and tsunami magnitude. In an effort towards multivariate statistics, a binary decision tree analysis is conducted with one variable. However, this shows that the amount of data is too scarce. To complement this limited amount of data and to assess physical causality of the tectonic parameters with regard to tsunamigenesis, we conduct a numerical study of the most promising parameters using a geodynamic seismic cycle model. We show that an increase in sediment thickness on the subducting plate results in a shift in seismic activity from outerrise normal faults to splay faults. We also show that the splay fault is the preferred rupture path for a strongly velocity strengthening friction regime in the shallow part of the subduction zone, which increases the tsunamigenic potential. A larger updip limit of the seismogenic zone results in larger vertical surface displacement.

Assessment of metal pollution associated with an alteration area: Old Gümüşhane, NE Black Sea.

PubMed

Vural, Alaaddin

2015-03-01

The objective of this study was to determine the potential environmental risks associated with the Kirkpavli (Old Gümüşhane in northern Turkey) alteration area by quantifying pollution in soil. The Kirkpavli (Old Gümüşhane) alteration area is situated at the south of the deposit with the same name of gold-silver-bearing lead, zinc, and copper in the southern part of the Black Sea Tectonic Unit (Eastern Pontides). In this study, 28 soil samples acquired from the alteration area were analyzed for contents of some main elements including lead (Pb), copper (Cu), zinc (Zn), cadmium (Cd), cobalt (Co), manganese (Mn), nickel (Ni), and arsenic (As). Contents of the elements in the area were determined, and high values were obtained such as 1,171 mg/kg for As, 12.4 mg/kg for Cd, 77.3 mg/kg for Co, 341 mg/kg for Cu, 1,172 mg/kg for Mn, 51.9 mg/kg for Ni, 3,725 mg/kg for Pb, and 880 mg/kg for Zn. Soil contamination was appraised on the basis of Geoaccumulation Index (I geo), Enrichment Factor (EF), Pollution Index, and Integrated Pollution Index. The calculated results of I geo, EF, and PI of the elements can be shown in descending order of parameters as As > Pb > Cd > Zn > Cu > Co > Mn. The parameters for some of these elements indicated extremely high contamination (I geo > 5), extremely high enrichment (EF > 40), and high pollution (PI > 3). High I geo, EF, and PI values of As, Pb, and Cd in the soil samples mean that soil pollution is typically associated with alteration area. Considering its location and the results of this study, the Kirkpavli alteration area is a significant source of pollution and may have ecotoxicological effects on terrestrial, groundwater, and aquatic ecosystems in the region.

Search for a meteoritic component at the Beaverhead impact structure, Montana

NASA Technical Reports Server (NTRS)

Lee, Pascal; Kay, Robert W.

1992-01-01

The Beaverhead impact structure, in southwestern Montana, was identified recently by the presence of shatter cones and impactites in outcrops of Proterozoic sandstones of the Belt Supergroup. The cones occur over an area greater than 100 sq km. Because the geologic and tectonic history of this region is long and complex, the outline of the original impact crater is no longer identifiable. The extent of the area over which shatter cones occur suggests, however, that the feature may have been at least 60 km in diameter. The absence of shatter cones in younger sedimentary units suggests that the impact event occurred in late Precambrian or early Paleozoic time. We have collected samples of shocked sandstone from the so-called 'Main Site' of dark-matrix breccias, and of impact breccias and melts from the south end of Island Butte. The melts, occurring often as veins through brecciated sandstone, exhibit a distinctive fluidal texture, a greenish color, and a cryptocrystalline matrix, with small inclusions of deformed sandstone. Samples of the same type, along with country rock, were analyzed previously for major- and trace-element abundances. It was found that, although the major-element composition as relatively uniform, trace-element composition showed variations between the melt material and the adjacent sandstone. These variations were attributed to extensive weathering and hydrothermal alteration. In a more specific search for a possible meteoritic signature in the breccia and the melt material we have conducted a new series of trace-element analyses on powders of our own samples by thermal neutron activation analysis. Our results indicate that Ir abundances in the breccia, the melts, and the adjacent sandstone clasts are no greater than about 0.1 ppb, suggesting no Ir enrichment of the breccia or the melts relative to the country rock. However, both the breccia and the melt material exhibit notable enrichments in Cr (8- and 10-fold), in U (9- and 5-fold), and in the heavy REE's (1.5- and 3-fold), respectively.

Geochemical behavior of rare earth elements of the hydrothermal alterations within the Tepeoba porphyry Cu-Mo-Au deposits at Balikesir, NW Turkey

NASA Astrophysics Data System (ADS)

Doner, Zeynep; Abdelnasser, Amr; Kiran Yildirim, Demet; Kumral, Mustafa

2016-04-01

This work reports the geochemical characteristics and behavior of the rare earth elements (REE) of the hydrothermal alteration of the Tepeoba porphyry Cu-Mo-Au deposit located in the Anatolian tectonic belt at Biga peninsula (Locally Balikesir province), NW Turkey. The Cu-Mo-Au mineralization at this deposit hosted in the hornfels rocks and related to the silicic to intermediate intrusion of Eybek pluton. It locally formed with brecciated zones and quartz vein stockworks, as well as the brittle fracture zones associated with intense hydrothermal alteration. Three main alteration zones with gradual boundaries formed in the mine area in the hornfels rock that represents the host rock, along that contact the Eybek pluton; potassic, propylitic and phyllic alteration zones. The potassic alteration zone that formed at the center having high amount of Cu-sulfide minerals contains biotite, muscovite, and sericite with less amount of K-feldspar and associated with tourmalinization alteration. The propylitic alteration surrounds the potassic alteration having high amount of Mo and Au and contains chlorite, albite, epidote, calcite and pyrite. The phyllic alteration zone also surrounds the potassic alteration containing quartz, sericite and pyrite minerals. Based on the REE characteristics and content and when we correlate the Alteration index (AI) with the light REEs and heavy REEs of each alteration zone, it concluded that the light REEs decrease and heavy REEs increase during the alteration processes. The relationships between K2O index with Eu/Eu* and Sr/Sr* reveals a positive correlation in the potassic and phyllic alteration zones and a negative correlation in the propylitic alteration zone. This refers to the hydrothermal solution which is responsible for the studied porphyry deposits and associated potassic and phyllic alterations has a positive Eu and Sr anomaly as well as these elements were added to the altered rock from the hydrothermal solution. Keywords: Rare earth elements geochemistry; Tepeoba porphyry Cu-Mo-Au deposits; Balikesir; Turkey

Prospects of application of survey satellite image for meteorology

NASA Astrophysics Data System (ADS)

Kapochkina, A. B.; Kapochkin, B. B.; Kucherenko, N. V.

The maximal interest is represented with the information from geostationary satellites. These satellites repeat shootings the chosen territories, allowing to study dynamics of images. Most interesting shootings in IR a range. Studying of survey image is applied to studying linear elements of clouds (LEC). It is established, that "LEC " arise only above breaks of an earth's crust. In research results of the complex analysis of the satellite data, hydrometeorological supervision, seismicity, supervision over deformations of a surface of the Earth are used. It is established that before formation "LEC " in a ground layer arise anomalies of temperature and humidity. The situation above Europe 16 May, 2001 is considered. "LEC " in Europe block carry of air weights from the west to the east. Synoptic conditions above the Great Britain July, 7-10, 2000 is considered. Moving "LEC" trace distribution of deformation waves to an earth's crust. Satellite shootings Europe before earthquake in Greece 14.08.2003 are considered. These days ground supervision were conducted and the data of the geostationary satellite were analyzed. During moving "LEC " occur failures (destruction houses & of gas mains), earthquake. The situation above Iberian peninsula 12-16.11.2001 is considered. "LEC" arose before flooding in Europe. The situation before flooding in Germany June, 6-8, 2002 and flooding on the river Kuban June, 16-23, 2002 is considered. In case of occurrence of tectonic compression of an earth's crust there are "LEC ", tracer intensive movements of air upwards and downwards above negative and positive anomalies of the form of a terrestrial surface, accordingly. Such meteorological situations are dangerous to flights of aircraft, the fast gravitational anomalies influencing into orbits of movement of satellites trace. The situation above equatorial Atlantic 26.03.2003 years is considered. At tectonic compression of continental scale overcast covers the whole continents for more than for 2 months that results in change of climatic conditions. Synoptic conditions above the African continent is considered from 13.11.2001 till 20.01.2002 during intensive movement of tectonic plates. The synoptic situation has come to norm after eruption of a volcano in Congo. The data of researches are published in scientific editions on Ukraine and in Russia. Some methods are patented on Ukraine. Results of researches were discussed at conference on satellite methods in Moscow November, 26-28, 2004.

Jurassic metabasic rocks in the Kızılırmak accretionary complex (Kargı region, Central Pontides, Northern Turkey)

NASA Astrophysics Data System (ADS)

Çelik, Ömer Faruk; Chiaradia, Massimo; Marzoli, Andrea; Özkan, Mutlu; Billor, Zeki; Topuz, Gültekin

2016-03-01

The Kızılırmak accretionary complex near Kargı is tectonically bounded by the Jurassic and Early Cretaceous metamorphic massives of the Central Pontides. It consists mainly of serpentinite, serpentinized peridotite, gabbro, basalt, metabasite and deep-marine sedimentary rocks. The metabasites in the Kızılırmak accretionary complex are tectonically located within a serpentinite, radiolarian chert, spilitized basalt, gabbro association and commonly display a steep contact with serpentinites. Amphiboles from metabasites yielded robust 40Ar/39Ar plateau ages ranging between 159.4 ± 0.4 Ma and 163.5 ± 0.8 Ma. These are interpreted as cooling ages of the metabasites. The metabasites have 87Sr/86Sr(i) between 0.7035 and 0.7044 and 206Pb/204Pb(i) ranging between 18.18 and 18.92. The gabbros have higher 87Sr/86Sr(i) between 0.7044 and 0.7060 and 206Pb/204Pb(i) ranging between 17.98 and 18.43. Three basalt samples display 87Sr/86Sr(i) between 0.7040 and 0.7059. Their 206Pb/204Pb(i) are unrealistically low (15.42 and 15.62), suggesting, most likely, Pb loss which results in over-corrected values for decay through time. Pb-Sr-Nd isotopic compositions for all samples consistently plot between the fields of MORB or the Depleted MORB Mantle reservoirs and enriched mantle reservoirs (EMII rather than EMI). All the samples (except one dolerite dike) have negative ɛNdDM(t = 160 Ma) values, suggesting derivation from a reservoir more enriched than the depleted mantle. The protoliths of metabasites correspond to diverse sources (N-MORB, E-MORB, OIB and IAT) based on whole rock major and trace element composition. An IAT-like protolith for the metabasites indicates that the İzmir-Ankara-Erzincan ocean domain was subducting and the tectonic regime was compressional during Late Jurassic and before. The protoliths of these rocks were metamorphosed during the subduction/accretion processes, as observed in the metamorphic rocks located along the Balkan, Northern Turkey and Armenia/Iran ophiolites and/or accretionary complexes. IAT-like geochemistry for the gabbro/dolerites indicates that the non-metamorphosed basaltic rocks occurred in a supra-subduction tectonomagmatic environment and is in agreement with their radiogenic isotope compositions.

Volcanic evolution of an active magmatic rift segment on a 100 Kyr timescale: exposure dating of lavas from the Manda Hararo/Dabbahu segment of the Afar Rift

NASA Astrophysics Data System (ADS)

Medynski, S.; Williams, A.; Pik, R.; Burnard, P.; Vye, C.; France, L.; Ayalew, D.; Yirgu, G.

2012-12-01

In the Afar depression (Ethiopia), extension is already organised along rift segments which morphologically resemble oceanic rifts. Segmentation here results from interactions between dyke injection and volcanism, as observed during the well documented 2005 event on the Dabbahu rift segment. During this tectono-volcanic crisis, a megadyke was injected, followed by 12 subsequent dike intrusions, sometimes associated with fissure flow eruptions. Despite the accurate surveying of the magmatic and tectonic interplay during this event via remote sensing techniques, there is a lack of data on timescales of 1 to 100 kyr, the period over which the main morphology of a rift is acquired. The Dabbahu rift segment represents an ideal natural laboratory to study the evolution of rift morphology as a response to volcanic and tectonic influences. It is possible to constrain the timing of fault growth relative to the infilling of the rift axial depression by lava flows, and to assess the influence of the different magma bodies involved in lava production along the rift-segment. We use cosmogenic nuclides (3He) to determine the ages of young (<100 kyr) lava flows and to date the initiation and movement of fault scarps which cut the lavas. Combined with major & trace element compositions, field mapping and digital cartography (Landsat, ASTER and SPOT imagery), the rift geomorphology can be linked to the magmatic and tectonic history defined by surface exposure dating. The results show that over the last 100 ka the Northern part of the Dabbahu segment was supplied by two different magma reservoirs which can be identified based on their distinctive chemistries. The main reservoir is located beneath Dabbahu volcano, and has been supplied with magma for at least 72 ka. This magmatic centre supplies magma to most of the northern third of the rift segment. The second reservoir is located further south, on the axis, close to the current mid-segment magma chamber, which was responsible for the 2005 rifting episode. This second magmatic centre supplies magma to the remaining 2/3 of the segment, but scarcely impacts its Northern termination (where the Dabbahu activity predominates) - except during extraordinary events when dykes are long enough to reach those parts, as in 2005. The eruption ages of the different lava units correlates with their degrees of differentiation, allowing different magmatic cycles of about a few tens of years each to be distinguished. During the first recorded magmatic cycle (~70 ka to ~55 ka), Dabbahu is built of wide-spreading pāhoehoe flows around localised eruptive centres. The resulting topography of the volcanic edifice remains low, and is only slightly affected by rift-related fault activity, with the development of minor scarps. The second recorded magmatic cycle (~50 ka to ~20 ka) coincides with a strong development of Dabbahu topography - underlined by the change in lava morphology with well channelized 'a'ā flows since 50 ka. Tectonic activity also clearly increases over this period, with the initiation of the major fault scarps of the rift, which have been dated at around 35 ka. Our study underlines the role of the magma supply and availability beneath Dabbahu in the evolution both topographies of Dabbahu volcano and of the rift depression morphology.

New constraints on the active tectonic deformation of the Aegean

USGS Publications Warehouse

Nyst, M.; Thatcher, W.

2004-01-01

Site velocities from six separate Global Positioning System (GPS) networks comprising 374 stations have been referred to a single common Eurasia-fixed reference frame to map the velocity distribution over the entire Aegean. We use the GPS velocity field to identify deforming regions, rigid elements, and potential microplate boundaries, and build upon previous work by others to initially specify rigid elements in central Greece, the South Aegean, Anatolia, and the Sea of Marmara. We apply an iterative approach, tentatively defining microplate boundaries, determining best fit rigid rotations, examining misfit patterns, and revising the boundaries to achieve a better match between model and data. Short-term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long-term kinematics. We find that present day Aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them. The RMS misfit of model to data is about 2-sigma, very good when compared to the typical match between coseismic fault models and GPS data. The simplicity of the microplate description of the deformation and its good fit to the GPS data are surprising and were not anticipated by previous work, which had suggested either many rigid elements or broad deforming zones that comprise much of the Aegean region. The isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions. Strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain/year (nstrain/year, 10-9/year), 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries. Lower strain rates may exist elsewhere withi the microplates but are only resolved in Anatolia, where extension of 13 ?? 4 nstrain/ year is required by the data. Our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity, active faulting, fault geomorphology, and earthquake fault plane solutions, continental tectonics, at least in the Aegean, is to first order very similar to global plate tectonics and obeys the same simple kinematic rules. Although the widespread distribution of Aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard, the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized.

Precambrrian crustal evolution in the great falls tectonic zone

NASA Astrophysics Data System (ADS)

Gifford, Jennifer N.

The Great Falls Tectonic Zone (GFTZ) is a zone of northeast trending geological structures in central Montana that parallel structures in the underlying basement. U-Pb zircon and Nd isotopic data from the Little Belt Mountains (LBM) suggest that the GFTZ formed at ~1.86 to 1.80 Ga due to ocean subduction followed by collision between the Archean Wyoming Province (WP) and Medicine Hat Block (MHB). This study characterizes the GFTZ basement by geochronological and geochemical analysis of crustal xenoliths collected from Montana Alkali Province volcanics and exposed basement rock in the Little Rocky Mountains (LRM). Xenoliths collected from the Grassrange and Missouri Breaks diatremes and volcanics in the Bearpaw and Highwood Mountains have igneous crystallization ages from ~1.7 Ga to 1.9 Ga and 2.4 Ga to 2.7 Ga, and metamorphic ages from ~1.65 Ga to 1.84 Ga. Zircon Lu-Hf and whole-rock Sm-Nd data indicate that the xenoliths originated from reworked older continental crust mixed with mantle-derived components in all cases. Trace element patterns show fluid mobile element enrichments and fluid immobile element depletions suggestive of a subduction origin. Igneous ages in the LRM range older, from ~2.4 Ga to 3.2 Ga. Geochemical evidence suggests that the LRM meta-igneous units also formed in a subduction setting. Detrital zircon ages span the early Paleoproterozoic to Mesoarchean, with abundant 2.8 Ga ages. Zircon U-Pb igneous crystallization age data from xenoliths and the LRM are consistent with U-Pb zircon igneous crystallization ages from the MHB, suggesting that this segment of the GFTZ shares an affinity with concealed MHB crust. Published detrital zircon ages from the northern Wyoming Province reveal more abundant >3.0 Ga ages than the MHB or GFTZ samples. These geochronologic and geochemical data from the xenoliths and LRM samples allow for a refined model for crustal evolution in the GFTZ. Subduction under the Neoarchean to Paleoproterozoic crust of the MHB formed an igneous arc followed by metamorphism during the MHB-WP collision. Later Paleoproterozoic tectonothermal activity represents post-orogenic collapse after the terminal collision. Tectonic activity in the Cenozoic led to basement uplift and the formation of xenolith bearing volcanic units sampled for this study.

B, Sr and Pb isotope geochemistry of high-pressure Alpine metaperidotites monitors fluid-mediated element recycling during serpentinite dehydration in subduction mélange (Cima di Gagnone, Swiss Central Alps)

NASA Astrophysics Data System (ADS)

Cannaò, E.; Agostini, S.; Scambelluri, M.; Tonarini, S.; Godard, M.

2015-08-01

Tectonic mixing of slab- and mantle-derived materials at the interface between converging plates highly enhances fluid-mediated mass transfer from the slab to the overlying mantle. Subduction mélanges can provide information about the interaction among different slices accreted at plate interface domains, with implications on the tectonic and geochemical evolution of the plate-interface itself. At Cima di Gagnone, pelitic schists and gneiss enclose chlorite harzburgite and garnet peridotite lenses, like in subduction mélanges located in-between downgoing slabs and overlying mantle. These peridotites host MORB-type eclogite and metarodingite, and derive from dehydration of serpentinized mantle protoliths. Their enrichment in fluid-mobile B, As, Sb, U, Th is the result of an early-stage oceanic serpentinization, followed by interaction with host metasediments during subduction burial. Here we define the element exchange process in the Gagnone mélange by means of the B, Sr and Pb isotope analysis of its main lithologies (ultramafic, mafic rocks and paragneiss). The 87Sr/86Sr and 206Pb/204Pb ratios of ultramafic rocks (0.7090-0.7124 and 18.292-18.837, respectively) show enrichments in radiogenic Sr and Pb after exchange with the host paraschist (up to 0.7287 87Sr/86Sr; 18.751 206Pb/204Pb). The δ11B values of peridotites (down to -10‰) point to a combined effect of (1) 11B release to deserpentinization fluids (serpentinized protoliths likely had positive δ11B and lower radiogenic Sr, Pb), and of (2) exchange with fluids from the surrounding metasediments. The whole Gagnone rock-suite is finally overprinted by retrograde fluids that essentially bring to an increase in radiogenic Pb (about 19.0 206Pb/204Pb) and to values of 0.710 87Sr/86Sr and of -10‰ δ11B. The recognition of different stages of interaction between mantle rocks and sedimentary/crustal reservoirs allows us to define the geochemical effects related to the early coupling of such rocks along the plate-interface. Our study shows that ultramafic rocks involved in subduction-zone metamorphism and serpentinization uptake radiogenic Pb and Sr released by associated sedimentary reservoirs. The exchange process envisioned here is not only representative of subduction mélanges: it can also be a proxy of mass transfer between slab and serpentinized supra-subduction mantle, as occurs in forearcs. Dehydration of the Gagnone-type serpentinized mantle releases crust-derived components to arcs, without direct involvement of metasediment dehydration and/or melting in subarc environments. The retention of appreciable amounts of fluid-mobile elements, radiogenic Pb and Sr in dehydrated Gagnone peridotites has implications on element recycling in the deep Earth's mantle.

Mid-Cretaceous transtension in the Canadian Cordillera: Evidence from the Rocky Ridge volcanics of the Skeena Group

NASA Astrophysics Data System (ADS)

Bassett, Kari N.; Kleinspehn, Karen L.

1996-08-01

The age relations, geochemistry, and sedimentology of the Rocky Ridge Formation of the Skeena Group are used to test competing tectonic reconstructions for the mid-Cretaceous Canadian Cordillera as well as the timing and location of the accretion of the Insular Superterrane. Pollen and macrofossil assemblages indicate that these intrabasinal basalts were erupted along the southern margin of the Bowser basin in the Early Albian to Early Cenomanian. Single-crystal fusion and step-heating 40Ar/39Ar dating of hornblendes in one basalt flow from the uppermost part of the formation yielded Middle Cenomanian ages of 94.3 ± 0.4, 95.6 ± 1.6, and 95.0 ± 1.6 Ma. Vesicular basalt flows interbedded with crystal-rich tuff breccias contain evidence for hot emplacement as pyroclastic flows. Individual eruptive centers are identified by their proximal facies, paleoflow indicators within the lava flows, paleoflow indicators within interbedded volcaniclastic fluvial deposits, geochemical differences, and geographic isolation of volcanic deposits. Major and trace-element geochemistry from 20 sampled lava flows indicates an alkali basalt composition for the volcanics. The basalts of the northern Rocky Ridge volcanic center show enrichment of light rare earth and large ion lithophile elements with strong negative Nb-Ta anomalies whereas the basalts of the southern Tahtsa Lake volcanic center show depletion to slight enrichment of light rare earth elements, slight enrichment of large ion lithophile elements with minimal negative Nb-Ta anomalies. The geochemistry combined with paleogeographic and regional tectonic reconstruction suggests a continental arc setting with intraarc extension. The presence of deeper marine facies to the west and the lack of a western sediment source in the Skeena Group indicate that the technically active Insular Superterrane was not west of the study area during mid-Cretaceous time. Thus we reconsider the Omineca Belt as the main axis of a mid-Cretaceous continental arc, placing the Intermontane Superterrane in the intraarc to forearc position with the Rocky Ridge volcanics erupted along the forearc side of the Omineca arc. Coeval regional strike-slip faulting and reconstructed oblique plate convergence suggest a transtensional setting for Rocky Ridge intraarc extension. An electronic supplement of Tables A1-A2 may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95TC03496, Mid-Cretaceous transtension in the Canadian Cordillera: Evidence from the Rocky Ridge volcanics of the Skeena Group, Kari N. Bassett and Karen L. Kleinspehn). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.

A generalized geologic map of Mars.

NASA Technical Reports Server (NTRS)

Carr, M. H.; Masursky, H.; Saunders, R. S.

1973-01-01

A geologic map of Mars has been constructed largely on the basis of photographic evidence. Four classes of units are recognized: (1) primitive cratered terrain, (2) sparsely cratered volcanic eolian plains, (3) circular radially symmetric volcanic constructs such as shield volcanoes, domes, and craters, and (4) tectonic erosional units such as chaotic and channel deposits. Grabens are the main structural features; compressional and strike slip features are almost completely absent. Most grabens are part of a set radial to the main volcanic area, Tharsis.

The Main Shear Zone in Sør Rondane, East Antarctica: Implications for the late-Pan-African tectonic evolution of Dronning Maud Land

NASA Astrophysics Data System (ADS)

Ruppel, Antonia S.; Läufer, Andreas; Jacobs, Joachim; Elburg, Marlina; Krohne, Nicole; Damaske, Detlef; Lisker, Frank

2015-06-01

Structural investigations in western Sør Rondane, eastern Dronning Maud Land (DML), provide new insights into the tectonic evolution of East Antarctica. One of the main structural features is the approximately 120 km long and several hundred meters wide WSW-ENE trending Main Shear Zone (MSZ). It is characterized by dextral high-strain ductile deformation under peak amphibolite-facies conditions. Crosscutting relationships with dated magmatic rocks bracket the activity of the MSZ between late Ediacaran to Cambrian times (circa 560 to 530 Ma). The MSZ separates Pan-African greenschist- to granulite-facies metamorphic rocks with "East African" affinities in the north from a Rayner-age early Neoproterozoic gabbro-tonalite-trondhjemite-granodiorite complex with "Indo-Antarctic" affinities in the south. It is interpreted to represent an important lithotectonic strike-slip boundary at a position close to the eastern margin of the East African-Antarctic Orogen (EAAO), which is assumed to be located farther south in the ice-covered region. Together with the possibly coeval left-lateral South Orvin Shear Zone in central DML, the MSZ may be related to NE directed lateral escape of the EAAO, whereas the Heimefront Shear Zone and South Kirwanveggen Shear Zone of western DML are part of the south directed branch of this bilateral system.

Tectonic setting and hydrocarbon habitat of external Carpathian basins in Romania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dicea, O.; Morariu, D.C.

1993-09-01

During the Alpine evolution of Romania, two distinct depositional areas evolved in the external zones of the Carpathians: the Paleogene flysch and Neogene Molasse basin of the eastern Carpathians, and the Paleogene and Neogene Molasse basin of the southern Carpathians. Both basins were compressionally deformed during the Neogene, giving rise to the development of a succession of nappes and thrust sheets. The internal elements of the external Carpathians corresponding to the Tarcau and marginal folds nappes and the external elements forming the sub-carpathian nappe and foredeep were thrusted over significant distances onto the European platform. Intense exploration of the externalmore » Carpathian thrustbelt has led to the discovery of more than 100 oil and gas pools. Reservoirs are provided by Oligocene, Burdigalian, Sarmatian, and Pliocene clastic rocks. A prolific hydrocarbon charge is derived from regionally distributed Oligocene oil source rocks. Traps are mainly of the structural type and involve faulted anticlines, [open quotes]scale folds,[close quotes] and compressional structures modified by salt; stratigraphic pinch-out and unconformity related traps play a secondary role. On the basis of selected examples, the development and distribution of hydrocarbon pools will be discussed in terms of thrust kinematics and the structure of different platform blocks. The philosophy of past exploration activities will be reviewed, and both success cases and failures will be discussed. Remaining oil and gas plays, aimed at shallow as well as at deep objectives, will be highlighted.« less

Numerical Modeling on Co-seismic Influence of Wenchuan 8.0 Earthquake in Sichuan-Yunnan Area, China

NASA Astrophysics Data System (ADS)

Chen, L.; Li, H.; Lu, Y.; Li, Y.; Ye, J.

2009-12-01

In this paper, a three dimensional finite element model for active faults which are handled by contact friction elements in Sichuan-Yunnan area is built. Applying the boundary conditions determined through GPS data, a numerical simulations on spatial patterns of stress-strain changes induced by Wenchuan Ms8.0 earthquake are performed. Some primary results are: a) the co-seismic displacements in Longmen shan fault zone by the initial cracking event benefit not only the NE-direction expanding of subsequent fracture process but also the focal mechanism conversions from thrust to right lateral strike for the most of following sub-cracking events. b) tectonic movements induced by the Wenchuan earthquake are stronger in the upper wall of Longmen shan fault belt than in the lower wall and are influenced remarkably by the northeast boundary faults of the rhombic block. c) the extrema of stress changes induced by the main shock are 106Pa and its spatial size is about 400km long and 100km wide. The total stress level is reduced in the most regions in Longmen shan fault zone, whereas stress change is rather weak in its southwest segment and possibly result in fewer aftershocks in there. d) effects induced by the Wenchuan earthquake to the major active faults are obviously different from each other. e) triggering effect of the Wenchuan earthquake to the following Huili 6.1 earthquake is very weak.

Turbidite systems: State of the art and future directions

USGS Publications Warehouse

Normark, W.R.; Posamentier, H.; Mutti, E.

1993-01-01

The study of turbidite systems covering a wide range of physical scales has led to confus ion regarding the use of certain key terms and hence a breakdown in communication between workers involved in turbidite research. There are three fundamentally different scales and types of observations derived from the study of outcrop data (ancient systems), high-resolution seismic reflection and side scan sonar data (modern systems), and multichannel seismic reflection data (modern and older buried systems). Despite the variability of scale the same terms are used to describe features that may have little in common. Consequently, turbidite system terminology has become imprecise and even misleading in some cases, thus providing impediments to developing useful predictive models for processes, depositional environments, and lateral and vertical distribution of sand bodies within turbidite systems. To address this concern, we review the principal elements critical to deepwater systems: slump scars, submarine canyons, channels, channel fill deposits, overbank deposits, and lobes and discuss some of their recognition criteria with each different type of data base. Local and regional tectonic setting, relative sea level variations, and bottom current activity are probably the main factors that control size, external geometry, internal stratal configuration, and facies characteristics of both modern and ancient turbidite systems. These factors ultimately control the timing and bounding characteristics between stages of growth of deepwater systems. If comparison of elements from different turbidite deposits using various data types is carried out at similar physical and temporal scales, predictive models eventually may be improved.

Fingerprints of the Paleotethyan back-arc basin in Central Hainan, South China: geochronological and geochemical constraints on the Carboniferous metabasites

NASA Astrophysics Data System (ADS)

He, Huiying; Wang, Yuejun; Zhang, Yanhua; Qian, Xin; Zhang, Yuzhi

2018-03-01

Hainan of Southeast Asia has been regarded as a key area for understanding the Late Paleozoic tectonic regime and amalgamation process of the Indochina with South China Blocks that are not well constrained. This paper presents a set of new geochronological, elemental, and Sr-Nd isotopic data for the Paleozoic Bangxi and Chenxing metabasites in Central Hainan. The geochronological data show that the representative samples yield the 40Ar/39Ar plateau age of 328.1 ± 2.6 Ma and zircon U-Pb age of 330.7 ± 4.4 Ma, respectively. They are SiO2- and TiO2-poor, Al2O3-rich mafic rocks. The Chenxing samples are characterized by left-sloping chondrite-normalized REE and N-MORB-like multi-elemental patterns. The Bangxi samples have the E-MORB-like geochemical affinity. All samples show high ɛ Nd(t) values ranging from +5.61 to +9.85. Such signatures suggest their origination of a MORB-like source with the input of subduction-derived components. Our investigation has verified the presence of the Carboniferous metabasites with both MORB- and arc- like geochemical affinities at the Bangxi-Chenxing area in Central Hainan. In combination with the available data from the Jinshajiang, Ailaoshan, and Song Ma suture zones, it is proposed for the development of a Carboniferous back-arc basin along the Ailaoshan-Song Ma and Central Hainan suture zones in response to the subduction of the Paleotethyan main Ocean.

Using the salt tectonics as a proxy to reveal post-rift active crustal tectonics: The example of the Eastern Sardinian margin

NASA Astrophysics Data System (ADS)

Lymer, Gaël; Vendeville, Bruno; Gaullier, Virginie; Chanier, Frank; Gaillard, Morgane

2017-04-01

The Western Tyrrhenian Basin, Mediterranean Sea, is a fascinating basin in terms of interactions between crustal tectonics, salt tectonics and sedimentation. The METYSS (Messinian Event in the Tyrrhenian from Seismic Study) project is based on 2100 km of HR seismic data acquired in 2009 and 2011 along the Eastern Sardinian margin. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigate the thinning processes of the continental crust and the timing of crustal vertical motions across this complex domain. Our first results allowed us to map the MSC seismic markers and to better constrain the timing of the rifting, which ended before the MSC across the upper and middle parts of the margin. We also evidenced that crustal activity persisted long after the end of rifting. This has been particularly observed on the upper margin, where several normal faults and a surprising compressional structure were recently active. In this study we investigate the middle margin, the Cornaglia Terrace, where the Mobile Unit (MU, mobile Messinian salt) accumulated during the MSC and acts as a décollement. Our goal is to ascertain whether or not crustal tectonics existed after the pre-MSC rift. This is a challenge where the MU is thick, because potential basement deformations could be first accommodated by the MU and therefore would not find any expression in the supra-salt layers (Upper Unit, UU and Plio-Quaternary, PQ). However our investigations clearly reveal interactions between crustal and salt tectonics along the margin. We thus evidence gravity gliding of the salt and its brittle sedimentary cover along basement slopes generated by the post-MSC tilting of some basement blocks bounded by crustal normal faults, formerly due to the rifting. Another intriguing structure also got our interest. It corresponds to a wedge-shaped of MU located in a narrow N-S half graben bounded to the west by a major, east-verging, crustal normal fault. Below the MU, the sediments thicken toward the fault. The top of the MU is sub-horizontal and the supra-salt layers are sub-horizontal. At a first glance this geometry would suggest that the pre-salt unit and the MU are syn-tectonic and that nothing happened after Messinian times. However some subtle evidence of deformations in the UU and PQ (an anticline to the west and a small west-verging normal fault in the east) imply that some crustal tectonics activity persisted after the end of the rifting. To understand why the salt unit is wedge-shaped, we considered several scenarii that we tested with physical modelling. We demonstrate that this structure is related to the post-rift activity of the major crustal normal fault, whose vertical motion has been cushioned by lateral flow of an initially tabular salt layer, which thinned upslope and inflated downslope, keeping the overlying sediments remained sub-horizontal. Such interactions between thin-skinned and thick-skinned tectonics highlight how the analysis of the salt tectonics is a powerful tool to reveal recent deep crustal tectonics in the Western Mediterranean Basin.

Geochronology and geochemistry of late Paleozoic-early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng

2017-08-01

We undertook geochemical and geochronological studies on late Paleozoic-early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol-Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral-subhedral, display oscillatory growth zoning, and have Th/U values of 0.14-6.48, indicating a magmatic origin. U-Pb dating of zircon using SIMS and LA-ICP-MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early-Middle Triassic (246-238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe-Nenjiang oceanic plate. Their positive εHf(t) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444-827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf(t) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500-607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna-Xing'an and Songnen-Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol-Okhotsk oceanic plate was subducting beneath the Erguna Massif.

Thickness of Weathering Profiles:Relaying Tectonic Signal to Biogeochemical Cycles

NASA Astrophysics Data System (ADS)

Yoo, K.; Weinman, B. A.; Hurst, M. D.; Mudd, S. M.; Gabet, E. J.; Attal, M.; Maher, K.

2011-12-01

Generation and transport of sediment across hillslopes and rivers are closely tied to mechanisms that produce and remove weathered material; in uplands this production and transport controls the thicknesses of weathering profiles. These processes, by controlling the residence time of minerals in the weathering profiles, further regulate the interactions between these minerals and largely biologically cycled elements like carbon and calcium. Here, we present and discuss the thicknesses of colluvial soils and underlying saprolites along three hillslopes that are subject to different rates of basal channel incision. Our field site is within a tributary basin to the Middle Folk Feather River in the Northern Sierra Nevada of California where the river has been down cutting through an uplifting granitic batholith over the past five to ten million years. Conventional modeling predicts that colluvial soil thickness declines with increasing denudation rates. Contrary to this expectation, intensive measurements of colluvial soil thickness show largely consistent values across the three hillslopes examined. This finding, in combination with the abrupt transitions to partial or full bare-rock landscapes with further increase in slope curvature or greater proximity to the Middle Folk Feather River, suggests that the mechanisms of soil production are capable of keeping pace with physical erosion rate until a certain threshold erosion rate is reached. We observe, however, that thicknesses of the underlying saprolite and the morphology (eg., color and texture) and geochemistry (eg., elemental concentration and extraction chemistry of iron) of both colluvial soil and saprolite materials vary systematically with the total denudation rates. This finding further allows us to build a simple relationship to describe and predict how the changes in erosion rates translate to the soils' capacity to store biologically cycled elements within rooting depths. Therefore, geomorphic and geochemical processes that control the thicknesses of weathering profiles, by determining their turn over time as well, relay the tectonic signal to the cycles of biologically relevant elements.

Mars: Lithospheric Flexure of the Tharsis Montes Volcanoes and the Evolutionary Relationship to Their Tectonic History

NASA Astrophysics Data System (ADS)

Chute, H.; Dombard, A. J.; Byrne, P. K.

2017-12-01

Lithospheric flexure associated with Arsia, Pavonis, and Ascraeus Montes has been previously studied to constrain the timeline and breadth of endogenic surface features surrounding these volcanoes. Here, we simulate the radial extent of two specific load-related features: annular graben and flank terraces. Detailed mapping of Ascraeus Mons (the youngest of the three volcanoes) showed a phase of compression of the edifice, forming the terraces and an annulus of graben immediately off the flanks, followed by a period of extension that formed additional graben superposed on the terraces on the lower flanks of the edifice. This transition from compression to extension on the lower flanks has been difficult to reconcile in mechanical models. We explore, with finite-element simulations, the effects of a thermal anomaly associated with an intrusive crustal underplate, which results in locally thinning the lithosphere (in contrast to past efforts that assumed a constant-thickness lithosphere). We find that it is primarily the horizontal extent of this thermal anomaly that governs how the lithosphere flexes under a volcano, as well as the transition from flank compression to a tight annulus of extensional stresses. Specifically, we propose that the structures on Ascraeus may be consistent with an early stage of volcanic growth accompanied by an underplate about the same width as the edifice that narrowed as volcanism waned, resulting in an inward migration of the extensional horizontal stresses from the surrounding plains onto the lower flanks. By linking the surface strains on the volcano with the volcano-tectonic evolution predicted by our flexure model, we can further constrain a more accurate timeline for the tectonic history of Ascraeus Mons. More broadly, because these tectonic structures are commonly observed, our results provide a general evolutionary model for large shield volcanoes on Mars.

Impact of slab pull and incipient mantle delamination on active tectonics and crustal thickening in the Betic-Alboran-Rif system

NASA Astrophysics Data System (ADS)

Mazzotti, Stephane; Baratin, Laura-May; Chéry, Jean; Vernant, Philippe; Gueydan, Frédéric; Tahayt, Abdelilah; Mourabit, Taoufik

2017-04-01

In Western Mediterranean, the Betic-Alboran-Rif orocline accommodates the WNW-ESE convergence between the Nubia and Eurasia plates. Recent geodetic data show that present-day tectonics in northern Morocco and southernmost Spain are not compatible with this simple two-plate-convergence model: GPS observations indicate significant (2-4 mm/a) deviations from the expected plate motion, and gravity data define two major negative Bouguer anomalies beneath the Betic and south of the Rif, interpreted as a thickened crust in a state of non-isostatic equilibrium. These anomalous geodetic patterns are likely related to the recent impact of the sub-vertical Alboran slab on crustal tectonics. Using 2-D finite-element models, we study the first-order behavior of a lithosphere affected by a downward normal traction, representing the pull of a high-density body in the upper mantle (slab pull or mantle delamination). We show that a specific range of lower crust and upper mantle viscosities allow a strong coupling between the mantle and the base of the brittle crust, thus enabling (1) the efficient conversion of vertical movement (resulting from the downward traction) to horizontal movement and (2) shortening and thickening on the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to the Alboran slab pull, can explain the present-day abnormal tectonics and non-isostatic equilibrium in northern Morocco. Similar processes may be at play in the whole Betic-Alboran-Rif region, although the fast temporal evolution of the slab - upper plate interactions needs to be taken into account to better understand this complex system.

Initial Results from the New Stress Map of Texas Project

NASA Astrophysics Data System (ADS)

Lund Snee, J. E.; Zoback, M. D.

2015-12-01

Modern techniques for characterizing tectonic stress orientation and relative magnitude have been successfully used for more than 35 years. Nevertheless, large areas of North America lack high spatial resolution maps of stress orientation, magnitude, and faulting regime. In Texas, for example, <30 A-C-quality stress orientations are currently registered on the World Stress Map and only 7 of these points also describe the stress regime. Stress data are foundational elements of attempts to characterize tectonic driving forces, understand hazards associated with induced seismicity, and optimize production of oil, gas, and geothermal resources. This year, we launched the Texas Stress Map project to characterize tectonic stress patterns at higher spatial resolution across Texas and nearby areas. Following a successful effort just completed in Oklahoma, we will evaluate borehole breakouts, drilling-induced tensile fractures, shear wave anisotropy, and earthquake data. The principal data source will be FMI (fullbore formation microimager), UBI (ultrasonic borehole imager), cross-dipole sonic, density, and caliper logs provided by private industry. Earthquake moment tensor solutions from the U.S. Geological Survey, Saint Louis University and other sources will also be used. Our initial focus is on the Permian Basin and Barnett Shale petroleum plays due to the availability of data, but we will expand our analysis across the state as the project progresses. In addition, we hope to eventually apply the higher spatial resolution data coverage to understanding tectonic and geodynamic characteristics of the southwestern United States and northeastern Mexico. Here we present early results from our work to constrain stress orientations and faulting regime in and near Texas, and we also provide a roadmap for the ongoing research.

Modeling Archean Subduction Initiation from Continental Spreading with a Free-Surface

NASA Astrophysics Data System (ADS)

Adams, A.; Thielmann, M.; Golabek, G.

2017-12-01

Earth is the only planet known to have plate tectonics, however the onset of plate tectonics and Earth's early tectonic environment are highly uncertain. Modern plate tectonics are characterized by the sinking of dense lithosphere at subduction zones; however this process may not have been feasible if Earth's interior was hotter in the Archean, resulting in thicker and more buoyant oceanic lithosphere than observed at present [van Hunen and van den Berg, 2008]. Previous studies have proposed gravitational spreading of early continents at passive margins as a mechanism to trigger early episodes of plate subduction using numerical simulations with a free-slip upper boundary condition [Rey et al., 2014]. This study utilizes 2D thermo-mechanical numerical experiments using the finite element code MVEP2 [Kaus, 2010; Thielmann et al., 2014] to investigate the viability of this mechanism for subduction initiation in an Archean mantle for both free-slip and free-surface models. Radiogenic heating, strain weakening, and eclogitization were systematically implemented to determine critical factors for modeling subduction initiation. In free-slip models, results show episodes of continent spreading and subduction initiation of oceanic lithosphere for low limiting yield stresses (100-150 MPa) and increasing continent width with no dependency on radiogenic heating, strain weakening, or eclogitization. For models with a free-surface, subduction initiation was observed at low limiting yield stresses (100-225 MPa) with increasing continent width and only in models with eclogitization. Initial lithospheric stress states were studied as a function of density and viscosity ratios between continent and oceanic lithosphere, and results indicate the magnitude of lithospheric stresses increases with increasing continental buoyancy. This work suggests continent spreading may trigger episodes of subduction in models with a free-surface with critical factors being low limiting yield stresses and eclogitization.

The acid and alkalinity budgets of weathering in the Andes-Amazon system: Insights into the erosional control of global biogeochemical cycles

NASA Astrophysics Data System (ADS)

Torres, Mark A.; West, A. Joshua; Clark, Kathryn E.; Paris, Guillaume; Bouchez, Julien; Ponton, Camilo; Feakins, Sarah J.; Galy, Valier; Adkins, Jess F.

2016-09-01

The correlation between chemical weathering fluxes and denudation rates suggests that tectonic activity can force variations in atmospheric pCO2 by modulating weathering fluxes. However, the effect of weathering on pCO2 is not solely determined by the total mass flux. Instead, the effect of weathering on pCO2 also depends upon the balance between 1) alkalinity generation by carbonate and silicate mineral dissolution and 2) sulfuric acid generation by the oxidation of sulfide minerals. In this study, we explore how the balance between acid and alkalinity generation varies with tectonic uplift to better understand the links between tectonics and the long-term carbon cycle. To trace weathering reactions across the transition from the Peruvian Andes to the Amazonian foreland basin, we measured a suite of elemental concentrations (Na, K, Ca, Mg, Sr, Si, Li, SO4, and Cl) and isotopic ratios (87Sr/86Sr and δ34S) on both dissolved and solid phase samples. Using an inverse model, we quantitatively link systematic changes in solute geochemistry with elevation to downstream declines in sulfuric acid weathering as well as the proportion of cations sourced from silicates. With a new carbonate-system framework, we show that weathering in the Andes Mountains is a CO2 source whereas foreland weathering is a CO2 sink. These results are consistent with the theoretical expectation that the ratio of sulfide oxidation to silicate weathering increases with increasing erosion. Altogether, our results suggest that the effect of tectonically-enhanced weathering on atmospheric pCO2 is strongly modulated by sulfide mineral oxidation.

Early to Middle Ordovician back-arc basin in the southern Appalachian Blue Ridge: characteristics, extent, and tectonic significance

USGS Publications Warehouse

Tull, James; Holm-Denoma, Christopher S.; Barineau, Clinton I.

2014-01-01

Fault-dismembered segments of a distinctive, extensive, highly allochthonous, and tectonically significant Ordovician (ca. 480–460 Ma) basin, which contains suites of bimodal metavolcanic rocks, associated base metal deposits, and thick immature deep-water (turbiditic) metasediments, occur in parts of the southern Appalachian Talladega belt, eastern Blue Ridge, and Inner Piedmont of Alabama, Georgia, and North and South Carolina. The basin's predominantly metasedimentary strata display geochemical and isotopic evidence of a mixed provenance, including an adjacent active volcanic arc and a provenance of mica (clay)-rich sedimentary and felsic plutonic rocks consistent with Laurentian (Grenvillian) upper-crustal continental rocks and their passive-margin cover sequences. Geochemical characteristics of the subordinate intercalated bimodal metavolcanic rocks indicate formation in a suprasubduction environment, most likely a back-arc basin, whereas characteristics of metasedimentary units suggest deposition above Neoproterozoic rift and outer-margin lower Paleozoic slope and rise sediments within a marginal basin along Ordovician Laurentia's Iapetus margin. This tectonic setting indicates that southernmost Appalachian Ordovician orogenesis (Taconic orogeny) began as an extensional accretionary orogen along the outer margin of Laurentia, rather than in an exotic (non-Laurentian) arc collisional setting. B-type subduction polarity requires that the associated arc-trench system formed southeast of the palinspastic position of the back-arc basin. This scenario can explain several unique features of the southern Appalachian Taconic orogen, including: the palinspastic geographic ordering of key tectonic elements (i.e., back-arc, arc, etc.), and a lack of (1) an obducted arc sensu stricto on the Laurentian margin, (2) widespread Ordovician regional metamorphism, and (3) Taconic klippen to supply detritus to the Taconic foreland basin.

Present-day plate motions: Retrieval from the TOPEX/Poseidon orbitography network (DORIS system)

NASA Technical Reports Server (NTRS)

Souriau, Annie; Cazenave, Anny; Biancale, R.; Balmino, G.; Dominh, K.; Mazzega, P.; Lemoine, J.-M.; Boucher, Claude; Willis, P.; Kasser, M.

1991-01-01

The goal of the proposal is to determine the present motion of the main tectonic plates from the Doppler data of the Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) orbitography system, which includes in its final configuration about 50 tracking stations with a world-wide distribution.

Structural evolution of Arsia Mons, Pavonis Mons, and Ascreus Mons Tharsis region of Mars

NASA Technical Reports Server (NTRS)

Crumpler, L. S.; Aubele, J. C.

1978-01-01

Analysis of Viking Orbiter data suggests that Arsia Mons, Pavonis Mons, and Ascreus Mons, three large shield volcanoes of the Tharsis volcanoes of Mars, have had similar evolutionary trends. Arsia Mons appears to have developed in the following sequence: (1) construction of a main shield volcano, (2) outbreak of parasitic eruption centers on the northeast and southwest flanks, (3) volcano-tectonic subsidence of the summit and formation of concentric fractures and grabens, possibly by evacuation of an underlying magma chamber during eruption of copious lavas from parasitic eruption centers on the northeast and southwest flanks, and (4) continued volcanism along a fissure or rift bisecting the main shield, resulting in flooding of the floor of the volcano-tectonic depression and inundation of the northeast and southwest flanks by voluminous lavas locally forming parasitic shields. In terms of this sequence Pavonis Mons has developed to stage (3) and Ascreus Mons has evolved to stage (2). This interpretation is supported by crater frequency-diameter distributions in the 0.1- to 3.0-km diameter range.

Diagenetic history of late Oligocene-early Miocene carbonates in East Sabah, Malaysia

NASA Astrophysics Data System (ADS)

Zainal Abidin, N. S.; Raymond, R. R.; Bashah, N. S. I.

2017-10-01

Limestones are particularly susceptible to drastic early diagenesis modifications, mainly cementation and dissolution. During the early Miocene, a major tectonic deformation has caused a widespread of uplift in Sabah. This has resulted change in depositional environment from deep to shallow marine, which favours the deposition of Gomantong Limestone. This study aims to investigate the diagenetic history of Gomantong Limestone in East Sabah. Thorough understanding of the diagenetic processes may provide data to unravel the tectonic activities which affected the reservoir quality of the carbonates. Combining the data from comprehensive petrographic analysis, and Scanning Electron Microscopy (SEM) of 30 samples, two main cements type were identified. These are microcrystalline cement and Mg-calcite cement of granular and blocky mosaics which are dominantly seen in all samples. The sequence of diagenesis events are determined as (1) micritization; (2) grain scale compaction; (3) cementation (pore-filling); (4) mechanical compaction and cementation infilling fractures and (5) chemical compaction. These diagenetic events are interpreted as reflection of changes in diagenetic environment from shallow marine to deep burial. The massive cementation in the Gomantong Limestone has resulted into a poor reservoir quality.

Soft sediment deformation structures in the Maastrichtian Ajali Formation Western Flank of Anambra Basin, Southern Nigeria

NASA Astrophysics Data System (ADS)

Olabode, Solomon Ojo

2014-01-01

Soft sediment deformation structures were recognized in the Maastrichtian shallow marine wave to tide influenced regressive sediments of Ajali Formation in the western flank of Anambra basin, southern Nigerian. The soft sediment deformation structures were in association with cross bedded sands, clay and silt and show different morphological types. Two main types recognised are plastic deformations represented by different types of recumbent folds and injection structure represented by clastic dykes. Other structures in association with the plastic deformation structures include distorted convolute lamination, subsidence lobes, pillars, cusps and sand balls. These structures are interpreted to have been formed by liquefaction and fluidization mechanisms. The driving forces inferred include gravitational instabilities and hydraulic processes. Facies analysis, detailed morphologic study of the soft sediment deformation structures and previous tectonic history of the basin indicate that the main trigger agent for deformation is earthquake shock. The soft sediment deformation structures recognised in the western part of Anambra basin provide a continuous record of the tectonic processes that acted on the regressive Ajali Formation during the Maastrichtian.

Proterozoic orogens in southern Peninsular India: Contiguities and complexities

NASA Astrophysics Data System (ADS)

Chetty, T. R. K.; Santosh, M.

2013-12-01

The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4 Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents - Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ˜400 km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P-T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale "flower structures", transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics. Our synthesis of the spatial distribution, geometry, kinematics and the transpressional strain of the shear zone systems provides insights into the tectono-metamorphic history of the Proterozoic orogens of southern India and their contiguity and complexities. Recent understanding of subduction, accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in Earth history, although the major and common structural architecture was built during the final assembly of the Gondwana supercontinent.

Geochemical fingerprinting of ∼2.5 Ga forearc-arc-backarc related magmatic suites in the Bastar Craton, central India

NASA Astrophysics Data System (ADS)

Asthana, Deepanker; Kumar, Sirish; Vind, Aditya Kumar; Zehra, Fatima; Kumar, Harshavardhan; Pophare, Anil M.

2018-05-01

The Pitepani volcanic suite of the Dongargarh Supergroup, central India comprises of a calc-alkaline suite and a tholeiitic suite, respectively. The rare earth element (REE) patterns, mantle normalized plots and relict clinopyroxene chemistry of the Pitepani calc-alkaline suite are akin to high-Mg andesites (HMA) and reveal remarkable similarity to the Cenozoic Setouchi HMA from Japan. The Pitepani HMAs are geochemically correlated with similar rocks in the Kotri-Dongargarh mobile belt (KDMB) and in the mafic dykes of the Bastar Craton. The rationale behind lithogeochemical correlations are that sanukitic HMAs represent fore-arc volcanism over a very limited period of time, under abnormally high temperature conditions and are excellent regional and tectonic time markers. Furthermore, the tholeiitic suites that are temporally and spatially associated with the HMAs in the KDMB and in the mafic dykes of the Bastar Craton are classified into: (a) a continental back-arc suite that are depleted in incompatible elements, and (b) a continental arc suite that are more depleted in incompatible elements, respectively. The HMA suite, the continental back-arc and continental arc suites are lithogeochemically correlated in the KDMB and in the mafic dykes of the Bastar Craton. The three geochemically distinct Neoarchaean magmatic suites are temporally and spatially related to each other and to an active continental margin. The identification of three active continental margin magmatic suites for the first time, provides a robust conceptual framework to unravel the Neoarchaean geodynamic evolution of the Bastar Craton. We propose an active continental margin along the Neoarchaen KDMB with eastward subduction coupled with slab roll back or preferably, ridge-subduction along the Central Indian Tectonic Zone (CITZ) to account for the three distinct magmatic suites and the Neoarchean geodynamic evolution of the Bastar Craton.

A new subdivision of the central Sesia Zone (Aosta Valley, Italy)

NASA Astrophysics Data System (ADS)

Giuntoli, Francesco; Engi, Martin; Manzotti, Paola; Ballèvre, Michel

2015-04-01

The Sesia Zone in the Western Alps is a continental terrane probably derived from the NW-Adriatic margin and polydeformed at HP conditions during Alpine convergence. Subdivisions of the Sesia Zone classically have been based on the dominant lithotypes: Eclogitic Micaschist Complex, Seconda Zona Diorito-Kinzigitica, and Gneiss Minuti Complex. However, recent work (Regis et al., 2014) on what was considered a single internal unit has revealed that it comprises two or more tectonic slices that experienced substantially different PTDt-evolutions. Therefore, detailed regional petrographic and structural mapping (1:3k to 1:10k) was undertaken and combined with extensive sampling for petrochronological analysis. Results allow us to propose a first tectonic scheme for the Sesia Zone between the Aosta Valley and Val d'Ayas. A set of field criteria was developed and applied, aiming to recognize and delimit the first order tectonic units in this complex structural and metamorphic context. The approach rests on three criteria used in the field: (1) Discontinuously visible metasedimentary trails (mostly carbonates) considered to be monocyclic (Permo-Mesozoic protoliths); (2) mappable high-strain zones; and (3) visible differences in the metamorphic imprint. None of these key features used are sufficient by themselves, but in combination they allow us to propose a new map that delimits main units. We propose an Internal Complex with three eclogitic sheets, each 0.5-3 km thick. Dominant lithotypes include micaschists associated with mafic rocks and minor orthogneiss. The main foliation is of HP, dipping moderately NW. Each of these sheets is bounded by (most likely monometamorphic) sediments, <10-50 m thick. HP-relics (of eclogite facies) are widespread, but a greenschist facies overprint locally is strong close to the tectonic contact to neighbouring sheets. An Intermediate Complex lies NW of the Internal Complex and comprises two thinner, wedge-shaped units termed slices. These are composed of siliceous dolomite marbles, meta-granites and -diorites with few mafic boudins. The main foliation dips SE and is of greenschist facies, but omphacite, glaucophane, and garnet occur as relics. Towards the SW, the width of the Intermediate Complex is reduced from 0.5 km to a few meters. In the External Complex several discontinuous lenses occur; these comprise 2DK-lithotypes and are aligned with greenschist facies shear zones mapped within Gneiss Minuti. By combining these features, three main sheets were delimited in the External Complex, with the main foliation being of greenschist facies and dipping moderately SE. Petrological work and in situ U-Th-Pb dating of accessory phases is underway in several of these subunits of the Sesia Zone to constrain their PTDt-history and thus their Alpine assembly. REFERENCE Regis, D., Rubatto, D., Darling, J., Cenki-Tok, B., Zucali, M., Engi, M., 2014. Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology. J.Petrol. 55, 1429-1456.

Petrogenesis of the granitic Donkerhuk batholith in the Damara Belt of Namibia: protracted, syntectonic, short-range, crustal magma transfer

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Buick, I. S.; Kisters, A. F. M.; Frei, D.

2017-07-01

The areally extensive (>5000 km2), syn-tectonic, ca. 520 Ma, mainly S-type Donkerhuk batholith was constructed through injection of thousands of mainly sheet-like magma pulses over 20-25 Myr. It intruded schists of the Southern Zone accretionary prism in the Damara Belt of Namibia. Each magma pulse had at least partly crystallised prior to the arrival of the following batch. However, much of the batholith may have remained partially molten for long periods, close to the H2O-saturated granite solidus. The batholith shows extreme variation in chemistry, while having limited mineralogical variation, and seems to be the world's most heterogeneous granitic mass. The Nd model ages of 2 Ga suggest that Eburnean rocks of the former magmatic arc, structurally overlain by the accretionary wedge, are the most probable magma sources. Crustal melting was initiated by mantle heat flux, probably introduced by thermal diffusion rather than magma advection. The granitic magmas were transferred from source to sink, with minimal intermediate storage; the whole process having occurred in the middle crust, resulting in feeble crustal differentiation despite the huge volume of silicic magma generated. Source heterogeneity controlled variation in the magmas and neither mixing nor fractionation was prominent. However, due to the transpressional emplacement régime, local filter pressing formed highly silicic liquids, as well as felsic cumulate rocks. The case of the Donkerhuk batholith demonstrates that emplacement-level tectonics can significantly influence compositional evolution of very large syn-tectonic magma bodies.

Magnetotelluric survey of Ischia resurgent caldera (Southern Italy): inference for volcano-tectonics and dynamic

NASA Astrophysics Data System (ADS)

Carlino, S.; Di Giuseppe, M. G.; Troiano, A.

2017-12-01

The island of Ischia (located in the Bay of Naples) represents a peculiar case of well-exposed caldera that has experienced a large (>800m) and rapid resurgence, until recent time. It gives us the possibility for a better understanding of caldera resurgence process, by integrating the available geological information with new geophysical data of the deeper structures associated to the resurgence. To this aim, a magnetotelluric survey of the island, has been performed along two main profiles of the central-western sector, obtaining the first electrical resistivity map down to a depth of 3km. The resurgence is tough to be associated to a shallow magma intrusion, which also produced a vigorous hot fluids circulation with high geothermal gradients (>150°Ckm-1) in the southern and western sector. The interpretation of resistivity variations allow us to recognize the main volcano-tectonic features of central-western part of the island, along the two profiles, such as the presence of a possible very shallow magmatic intrusion to a depth of about 1km, the tectonic structures bordering the resurgent area and the occurrence of large thermal anomaly of the western sector. All these data are fundamental for the assessment of volcano-dynamic of the island and associated hazard. Furthermore, this study show a not common example of a large resurgence that is likely generated by a laccolith intrusion. This process is generally associated to the arrival of fresh magma into the system that, in turn, may imply imminent eruption and high volcanic hazard.

Tectonic evolution and provenance of the Santa Bárbara Group, Camaquã Mines region, Rio Grande do Sul, Brazil

NASA Astrophysics Data System (ADS)

Bicca, Marcos Müller; Chemale, Farid; Jelinek, Andrea Ritter; de Oliveira, Christie Helouise Engelmann; Guadagnin, Felipe; Armstrong, Richard

2013-12-01

Cu- and Pb-Zn-hosting sedimentary units of the upper part of the Camaquã Basin (Ediacaran-Lower Ordovician) in the Dom Feliciano Belt of southernmost Brazil were formed during the late stages of the West Gondwana amalgamation and were controlled by large left-handed strike-slip shear zones. Integration of structural geology, stratigraphy and thermochronology allow recognition of five structural events (D1, Ediacaran-Lower Cambrian, through D5, Cretaceous). D1 structures are related to a N30E-trending, sinistral strike-slip shear zone that controlled the deposition of the mineralized sedimentary unit and its overlying units, the Santa Barbara and Guaritas Groups, respectively, in a transtensional setting. Based on U-Pb in situ methods, it is possible (a) to establish a maximum depositional age of 566 ± 6.9 Ma for the basal section of the Santa Barbara Group and, therefore, a minimum age of ca. 566 Ma for D1, and (b) to recognize two main zircon populations, Neoproterozoic and Paleoproterozoic, with sources from the eastern and southern parts of the Dom Feliciano Belt and reworking of older units of the Camaquã Basin. The D2 structures are mainly N-trending shear zones that developed after the deposition of the Guaritas Group during the Cambrian. During the Phanerozoic (post-Cambrian), the recognized structures were connected to compressional and extensional events that affected West Gondwana and the South America Platform. Thermochronological fission track analyses on apatite revealed four main age populations. The first three are interpreted to have formed during tectonic processes at the Gondwana Margin, namely the Famatinian and Gondwanides orogenies, and can be related to the D3 and D4 tectonic events in the basin. The last age population formed from thermal heating by the Upper Cretaceous continental flood basalts, which are represented in the area by volcanic intrusions, that were related to the separation of Africa and South America.

Active Tectonics of Himalayan Faults/Thrusts System in Northern India on the basis of recent & Paleo earthquake Studies

NASA Astrophysics Data System (ADS)

Kumar, S.; Biswal, S.; Parija, M. P.

2016-12-01

The Himalaya overrides the Indian plate along a decollement fault, referred as the Main Himalayan Thrust (MHT). The 2400 km long Himalayan mountain arc in the northern boundary of the Indian sub-continent is one of the most seismically active regions of the world. The Himalayan Frontal Thrust (HFT) is characterized by an abrupt physiographic and tectonic break between the Himalayan front and the Indo-Gangetic plain. The HFT represents the southern surface expression of the MHT on the Himalayan front. The tectonic zone between the Main Boundary Thrust (MBT) and the HFT encompasses the Himalayan Frontal Fault System (HFFS). The zone indicates late Quaternary-Holocene active deformation. Late Quaternary intramontane basin of Dehradun flanked to the south by the Mohand anticline lies between the MBT and the HFT in Garhwal Sub Himalaya. Slip rate 13-15 mm/yr has been estimated on the HFT based on uplifted strath terrace on the Himalyan front (Wesnousky et al. 2006). An out of sequence active fault, Bhauwala Thrust (BT), is observed between the HFT and the MBT. The Himalayan Frontal Fault System includes MBT, BT, HFT and PF active fault structures (Thakur, 2013). The HFFS structures were developed analogous to proto-thrusts in subduction zone, suggesting that the plate boundary is not a single structure, but series of structures across strike. Seismicity recorded by WIHG shows a concentrated belt of seismic events located in the Main Central Thrust Zone and the physiographic transition zone between the Higher and Lesser Himalaya. However, there is quiescence in the Himalayan frontal zone where surface rupture and active faults are reported. GPS measurements indicate the segment between the southern extent of microseismicity zone and the HFT is locked. The great earthquake originating in the locked segment rupture the plate boundary fault and propagate to the Himalaya front and are registered as surface rupture reactivating the fault in the HFFS.

Interpretation of remagnetization directions by Small Circle methods. Application to various tectonic problems

NASA Astrophysics Data System (ADS)

José Villalaín, Juan; Casas, Antonio; Calvín, Pablo; Soto-Marín, Ruth; Torres, Sara; Moussaid, Bennacer

2017-04-01

Secondary magnetizations have been used to constraint geological models in spite of the difficulties of dating the remanence age and the uncertainty in applying the valid tectonic correction, specially if the remagnetization is syntectonic. The fold test is the main tool used traditionally to identify and interpret remagnetization. In particular, the incremental fold test has been applied to attempt calculating the appropriate tectonic correction in synfolding remanences. However the fold test assumes symmetrical deformation giving erroneous solutions when dealing with asymmetrical folding. This strongly limits the use of the fold test because asymmetric tectonic evolution is very common in different geological processes. Therefore, it is necessary to use alternative techniques for analyzing remagnetization directions. In this sense, the use of small circles (SC) represents a very interesting option because it allows considering asymmetric deformations and degrees of freedom which fold test restricts. A SC is defined by a complete rotation of the in situ site mean paleomagnetic direction about the strike of bedding (i.e. the apical angle of its cone is the angle between the paleomagnetic vector and the strike of beds). In this presentation we analyze the use of SC for analysis of remagnetization directions in two phases: a) determination of the magnetic field direction at the remagnetization acquisition time by calculating the SC intersection (SCI) by methods described by Shipunov (1997) or Waldhör and Appel (2006). This obtained direction can be used to date the remagnetization by comparison with the APWP, but also as reference direction for restoration of the rotated remagnetization directions. And b) calculation of the bedding plane at the moment of the acquisition of the remagnetization (paleodip) by restoring the in situ remagnetization directions using each SC as described Villalaín et al. (2003), Henry et al. (2004) and Villalaín et al. (2015). In this work we discuss about the methodological problems observed when using SC analysis, such as the effect of the degree of coaxiality of different tectonic events on the uncertainty of the SCI solution and tectonic corrections, the presence of vertical axis rotation, etc. In addition we analyze different examples of application of SC techniques to solve different tectonic problems in areas affected by widespread remagnetizations, such as palinspastic reconstructions of inverted sedimentary basins, distinction of overlapped deformation events, identification of intra-Mesozoic stages in alpine chains, etc.

2D seismic interpretation and characterization of the Hauterivian-Early Barremian source rock in Al Baraka oil field, Komombo Basin, Upper Egypt

NASA Astrophysics Data System (ADS)

Ali, Moamen; Darwish, M.; Essa, Mahmoud A.; Abdelhady, A.

2018-03-01

Komombo Basin is located in Upper Egypt about 570 km southeast of Cairo; it is an asymmetrical half graben and the first oil producing basin in Upper Egypt. The Six Hills Formation is of Early Cretaceous age and subdivided into seven members from base to top (A-G); meanwhile the B member is of Hauterivian-Early Barremian and it is the only source rock of Komombo Basin. Therefore, a detailed study of the SR should be carried out, which includes the determination of the main structural elements, thickness, facies distribution and characterization of the B member SR which has not been conducted previously in the study area. Twenty 2D seismic lines were interpreted with three vertical seismic profiles (VSP) to construct the depth structure-tectonic map on the top of the B member and to highlight the major structural elements. The interpretation of depth structure contour map shows two main fault trends directed towards the NW-SE and NE to ENE directions. The NW-SE trend is the dominant one, creating a major half-graben system. Also the depth values range from -8400 ft at the depocenter in the eastern part to -4800 ft at the shoulder of the basin in the northwestern part of the study area. Meanwhile the Isopach contour map of the B member shows a variable thickness ranging between 300 ft to 750 ft. The facies model shows that the B member SR is composed mainly of shale with some sandstone streaks. The B member rock samples were collected from Al Baraka-1 and Al Baraka SE-1 in the eastern part of Komombo Basin. The results indicate that the organic matter content (TOC) has mainly good to very good (1-3.36 wt %), The B member samples have HI values in the range 157-365 (mg HC/g TOC) and dominated by Type II/III kerogen, and is thus considered to be oil-gas prone based on Rock-Eval pyrolysis, Tmax values between 442° and 456° C therefore interpreted to be mature for hydrocarbon generation. Based on the measured vitrinite equivalent reflectance values, the B member SR samples have a range 0.7-1.14%Ro, in the oil generation window.

Incipient mantle delamination, active tectonics and crustal thickening in Northern Morocco: Insights from gravity data and numerical modeling

NASA Astrophysics Data System (ADS)

Baratin, Laura-May; Mazzotti, Stéphane; Chéry, Jean; Vernant, Philippe; Tahayt, Abdelilah; Mourabit, Taoufik

2016-11-01

The Betic-Rif orocline surrounding the Alboran Sea, the westernmost tip of the Mediterranean Sea, accommodates the NW-SE convergence between the Nubia and Eurasia plates. Recent GPS observations indicate a ∼4 mm/yr SW motion of the Rif Mountains, relative to stable Nubia, incompatible with a simple two-plate model. New gravity data acquired in this study define a pronounced negative Bouguer anomaly south of the Rif, interpreted as a ∼40 km-thick crust in a state of non-isostatic equilibrium. We study the correlation between these present-day kinematic and geodynamic processes using a finite-element code to model in 2-D the first-order behavior of a lithosphere affected by a downward normal traction (representing the pull of a high-density body in the upper mantle). We show that intermediate viscosities for the lower crust and uppermost mantle (1021-1022Pas) allow an efficient coupling between the mantle and the base of the brittle crust, thus enabling (1) the conversion of vertical movement, resulting from the downward traction, to horizontal movement and (2) shortening in the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to slab pull, can explain the present-day abnormal tectonics, contribute to the gravity anomaly observed in northern Morocco, and give insight into recent tectonics in the Western Mediterranean region.

Tectonic and hydrological controls on multiscale deformations in the Levant: numerical modeling and theoretical analysis

NASA Astrophysics Data System (ADS)

Belferman, Mariana; Katsman, Regina; Agnon, Amotz; Ben Avraham, Zvi

2016-04-01

Understanding the role of the dynamics of water bodies in triggering deformations in the upper crust and subsequently leading to earthquakes has been attracting considerable attention. We suggest that dynamic changes in the levels of the water bodies occupying tectonic depressions along the Dead Sea Transform (DST) cause significant variations in the shallow crustal stress field and affect local fault systems in a way that eventually leads to earthquakes. This mechanism and its spatial and temporal scales differ from those in tectonically-driven deformations. In this study we present a new thermo-mechanical model, constructed using the finite element method, and extended by including a fluid flow component in the upper crust. The latter is modeled on a basis of two-way poroelastic coupling with the momentum equation. This coupling is essential for capturing fluid flow evolution induced by dynamic water loading in the DST depressions and to resolve porosity changes. All the components of the model, namely elasticity, creep, plasticity, heat transfer, and fluid flow, have been extensively verified and presented in the study. The two-way coupling between localized plastic volumetric deformations and enhanced fluid flow is addressed, as well as the role of variability of the rheological and the hydrological parameters in inducing deformations in specific faulting environments. Correlations with historical and contemporary earthquakes in the region are discussed.

Evaluation of mineral resource potential, caldera geology, and volcano-tectonic framework at and near Yucca Mountain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, S.I.; Noble, D.C.; Larson, L.T.

1992-09-30

This report summarizes the result of Task 3 work initially discussed in our monthly reports for the period October 1, 1991 through September 30, 1992, and contained in our various papers and abstracts, both published and currently in press or review. Our work during this period has involved (a) the continuation of studies begun prior to October, 1991, focussed mainly on aspects of the caldera geology, volcanic stratigraphy, magmatic activity, hydrothermal mineralization and extensional tectonics of the western and northwestern parts of the southwestern Nevada volcanic field (SWNVF), and (b) new studies of the alteration and trace-metal geochemistry of subsurfacemore » rocks at Yucca Mountain utilizing drill hole samples obtained in late 1991 and early 1992.« less

Géodynamique et évolution thermique de la matière organique: exemple du bassin de Qasbat-Tadla, Maroc centralBasin geodynamics and thermal evolution of organic material: example from the Qasbat-Tadla Basin, central Morocco

NASA Astrophysics Data System (ADS)

Er-Raïoui, H.; Bouabdelli, M.; Bélayouni, H.; Chellai, H.

2001-05-01

Seismic data analysis of the Qasbat-Tadla Basin allows the deciphering of the main tectonic and sedimentary events that characterised the Hercynian orogen and its role in the basin's structural development. The global tectono-sedimentary framework involves structural evolution of an orogenic foreland basin and was the source of rising geotherms in an epizonal metamorphic environment. The complementary effects of these parameters has led to different source rock maturity levels, ranging from oil producing to graphite domains. Different maturity levels result from three distinct structural domains within the basin, each of which exhibit characteristic geodynamic features (tectonic contraints, rate of subsidence, etc.).

Crustal structure of Yunnan province, People's Republic of China, from seismic refraction profiles

USGS Publications Warehouse

Kan, R.-J.; Hu, H.-X.; Zeng, R.-S.; Mooney, W.D.; McEvilly, T.V.

1986-01-01

Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics, on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile, but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

Crustal Structure of Yunnan Province, People's Republic of China, from Seismic Refraction Profiles.

PubMed

Kan, R J; Hu, H X; Zeng, R S; Mooney, W D; McEvilly, T V

1986-10-24

Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

Tectonics and hydrocarbon potential of the Barents Megatrough

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baturin, D.; Vinogradov, A.; Yunov, A.

1991-08-01

Interpretation of geophysical data shows that the geological structure of the Eastern Barents Shelf, named Barents Megatrough (BM), extends sublongitudinally almost from the Baltic shield to the Franz Josef Land archipelago. The earth crust within the axis part of the BM is attenuated up to 28-30 km, whereas in adjacent areas its thickness exceeds 35 km. The depression is filled with of more than 15 km of Upper Paleozoic, Mesozoic, and Cenozoic sediments overlying a folded basement of probable Caledonian age. Paleozoic sediments, with exception of the Upper Permian, are composed mainly of carbonates and evaporites. Mesozoic-Cenozoic sediments are mostlymore » terrigenous. The major force in the development of the BM was due to extensional tectonics. Three rifting phases are recognizable: Late Devonian-Early Carboniferous, Early Triassic, and Jurassic-Early Cretaceous. The principal features of the geologic structure and evolution of the BM during the late Paleozoic-Mesozoic correlate well with those of the Sverdup basin, Canadian Arctic. Significant quantity of Late Jurassic-Early Cretaceous basaltic dikes and sills were intruded within Triassic sequence during the third rifting phase. This was probably the main reason for trap disruption and hydrocarbon loss from Triassic structures. Lower Jurassic and Lower Cretaceous reservoir sandstones are most probably the main future objects for oil and gas discoveries within the BM. Upper Jurassic black shales are probably the main source rocks of the BM basin, as well as excellent structural traps for hydrocarbon fluids from the underlying sediments.« less

Mio-Pliocene to Pleistocene paleotopographic evolution of Brittany (France) from a sequence stratigraphic analysis: relative influence of tectonics and climate

NASA Astrophysics Data System (ADS)

Brault, N.; Bourquin, S.; Guillocheau, F.; Dabard, M.-P.; Bonnet, S.; Courville, P.; Estéoule-Choux, J.; Stepanoff, F.

2004-01-01

The Mio-Pliocene in Western Europe is a period of major climatic and tectonic change with important topographic consequences. The aim of this paper is to reconstruct these topographic changes (based on sedimentological analysis and sequence stratigraphy) for the Armorican Massif (western France) and to discuss their significance. The Mio-Pliocene sands of the Armorican Massif (Red Sands) are mainly preserved in paleovalleys and are characterized by extensive fluvial sheetflood deposits with low-preservation and by-pass facies. This sedimentological study shows that the Red Sands correspond to three main sedimentary environments: fluvial (alluvial fan, low-sinuosity rivers and braided rivers), estuarine and some rare open marine deposits (marine bioclastic sands: "faluns" of French authors). Two orders of sequences have been correlated across Brittany with one or two minor A/ S cycles comprised within the retrogradational trend of a major cycle. The unconformity at the base of the lower cycle is more marked than the unconformity observed at the top, which corresponds to a re-incision of the paleovalley network. A comparison of the results of the sequence stratigraphy analysis with eustatic variations and tectonic events during the Mio-Pliocene allows (1) to discuss their influence on the evolution of the Armorican Massif and (2) to compare the stratigraphic record with other west-European basins. The unconformity observed at the base of the first minor cycle may be attributed to Serravallian-Tortonian tectonic activity and/or eustatic fall, and the unconformity of the second minor cycle may be attributed to Late Tortonian-Early Messinian tectonic activity. The earlier unconformity is coeval with the development of a "smooth" paleovalley network compared to the jagged present-day relief. A single episode of Mio-Pliocene deformation recorded in Brittany may be dated as Zanclean, thus explaining the lack of the maximum flooding surface except in isolated areas. From this study, five paleogeographic maps were drawn up also indicating paleocurrent directions: three maps for the lower cycle (Tortonian retrogradational trend, Late Tortonian to Early Messinian maximum flooding surface and Messinian progradational trend) and two for the upper cycle (Pliocene retrogradational trend and Piacenzian maximum flooding surface). These maps show (1) the variations of paleocurrent directions during the Mio-Pliocene, (2) the extent of estuarine environments during the maximum flooding intervals and (3) a paleodrainage watershed oriented NNW-SSE following the regional Quessoy/Nort-sur-Erdre Fault during the retrogradational trend of the upper cycle and possibly during the progradational trend of the lower cycle. The present-day morphology of the Armorican Massif is characterized by (1) incised valleys and jagged topography, in contrast with the "smooth" morphology described for Mio-Pliocene times and (2) a main East-West drainage watershed, located to the north, separating rivers flowing towards the English Channel from rivers flowing towards the Atlantic Ocean. The Mio-Pliocene/Pleistocene paleotopographic changes seem to be controlled by climatic effects. These can be related to the change in runoff associated with warmer and wetter conditions during the Mio-Pliocene, which control the river discharge and lead to the development of extensive fluvial sheetflood deposits. Tectonic or eustatic factors exert a second-order control.

Stress field models from Maxwell stress functions: southern California

NASA Astrophysics Data System (ADS)

Bird, Peter

2017-08-01

The lithospheric stress field is formally divided into three components: a standard pressure which is a function of elevation (only), a topographic stress anomaly (3-D tensor field) and a tectonic stress anomaly (3-D tensor field). The boundary between topographic and tectonic stress anomalies is somewhat arbitrary, and here is based on the modeling tools available. The topographic stress anomaly is computed by numerical convolution of density anomalies with three tensor Green's functions provided by Boussinesq, Cerruti and Mindlin. By assuming either a seismically estimated or isostatic Moho depth, and by using Poisson ratio of either 0.25 or 0.5, I obtain four alternative topographic stress models. The tectonic stress field, which satisfies the homogeneous quasi-static momentum equation, is obtained from particular second derivatives of Maxwell vector potential fields which are weighted sums of basis functions representing constant tectonic stress components, linearly varying tectonic stress components and tectonic stress components that vary harmonically in one, two and three dimensions. Boundary conditions include zero traction due to tectonic stress anomaly at sea level, and zero traction due to the total stress anomaly on model boundaries at depths within the asthenosphere. The total stress anomaly is fit by least squares to both World Stress Map data and to a previous faulted-lithosphere, realistic-rheology dynamic model of the region computed with finite-element program Shells. No conflict is seen between the two target data sets, and the best-fitting model (using an isostatic Moho and Poisson ratio 0.5) gives minimum directional misfits relative to both targets. Constraints of computer memory, execution time and ill-conditioning of the linear system (which requires damping) limit harmonically varying tectonic stress to no more than six cycles along each axis of the model. The primary limitation on close fitting is that the Shells model predicts very sharp shallow stress maxima and discontinuous horizontal compression at the Moho, which the new model can only approximate. The new model also lacks the spatial resolution to portray the localized stress states that may occur near the central surfaces of weak faults; instead, the model portrays the regional or background stress field which provides boundary conditions for weak faults. Peak shear stresses in one registered model and one alternate model are 120 and 150 MPa, respectively, while peak vertically integrated shear stresses are 2.9 × 1012 and 4.1 × 1012 N m-1. Channeling of deviatoric stress along the strong Great Valley and the western slope of the Peninsular Ranges is evident. In the neotectonics of southern California, it appears that deviatoric stress and long-term strain rate have a negative correlation, because regions of low heat flow are strong and act as stress guides, while undergoing very little internal deformation. In contrast, active faults lie preferentially in areas with higher heat flow, and their low strength keeps deviatoric stresses locally modest.

State of stress, faulting, and eruption characteristics of large volcanoes on Mars

NASA Technical Reports Server (NTRS)

Mcgovern, Patrick J.; Solomon, Sean C.

1993-01-01

The formation of a large volcano loads the underlying lithospheric plate and can lead to lithospheric flexure and faulting. In turn, lithospheric stresses affect the stress field beneath and within the volcanic edifice and can influence magma transport. Modeling the interaction of these processes is crucial to an understanding of the history of eruption characteristics and tectonic deformation of large volcanoes. We develop models of time-dependent stress and deformation of the Tharsis volcanoes on Mars. A finite element code is used that simulates viscoelastic flow in the mantle and elastic plate flexural behavior. We calculate stresses and displacements due to a volcano-shaped load emplaced on an elastic plate. Models variously incorporate growth of the volcanic load with time and a detachment between volcano and lithosphere. The models illustrate the manner in which time-dependent stresses induced by lithospheric plate flexure beneath the volcanic load may affect eruption histories, and the derived stress fields can be related to tectonic features on and surrounding martian volcanoes.

The Role of Deformation Energetics in Long-Term Tectonic Modeling

NASA Astrophysics Data System (ADS)

Ahamed, S.; Choi, E.

2017-12-01

The deformation-related energy budget is usually considered in the simplest form or even entirely omitted from the energy balance equation. We derive a full energy balance equation that accounts not only for heat energy but also for mechanical (elastic, plastic and viscous) work. The derived equation is implemented in DES3D, an unstructured finite element solver for long-term tectonic deformation. We verify the implementation by comparing numerical solutions to the corresponding semi-analytic solutions in three benchmarks extended from the classical oedometer test. We also investigate the long-term effects of deformation energetics on the evolution of large offset normal faults. We find that the models considering the full energy balance equation tend to produce more secondary faults and an elongated core complex. Our results for the normal fault system confirm that persistent inelastic deformation has a significant impact on the long-term evolution of faults, motivating further exploration of the role of the full energy balance equation in other geodynamic systems.

Water and the oxidation state of subduction zone magmas.

PubMed

Kelley, Katherine A; Cottrell, Elizabeth

2009-07-31

Mantle oxygen fugacity exerts a primary control on mass exchange between Earth's surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/SigmaFe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/SigmaFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.

A model of convergent plate margins based on the recent tectonics of Shikoku, Japan

NASA Technical Reports Server (NTRS)

Bischke, R. E.

1974-01-01

A viscoelastic finite element plate tectonic model is applied to displacement data for the island of Shikoku, Japan. The flow properties and geometry of the upper portions of the earth are assumed known from geophysical evidence, and the loading characteristics are determined from the model. The nature of the forces acting on the Philippine Sea plate, particularly in the vicinity of the Nankai trough, is determined. Seismic displacement data related to the 1946 Nankaido earthquake are modeled in terms of a thick elastic plate overlying a fluidlike substratum. The sequence of preseismic and seismic displacements can be explained in terms of two independent processes operating on elastic lithospheric plates: a strain accumulation process caused by vertical downward forces acting on or within the lithosphere in the vicinity of the trench, and a strain release process caused by plate failure along a preexisting zone on weakness. This is a restatement of Reid's elastic rebound theory in terms of elastic lithospheric plates.

Immobile Trace Element Discrimination of Near-cogenetic Eruptions

NASA Astrophysics Data System (ADS)

Villa, I. M.

2015-12-01

A chemical diagram to discriminate individual magma batches in composite plutonic/volcanic complexes is proposed here: x = Y/Al, y = Zr/Ti. Both ratios are stable during weathering and low-grade metamorphism. Y/Al only depends on fractional crystallization of garnet, xenotime and monazite during magmatogenesis and the degree of partial melting. This already distinguishes individual magmas. Zr/Ti is modified by other phases (rutile, titanite, zircon, ilmenite, biotite, etc) that neither accommodate nor fractionate trivalent cations and provides a totally independent perspective on magmatogenesis. The Y/Al-Zr/Ti plot has no relation to tectonic setting (convergent, rift, intraplate, etc) and is not designed to distinguish lines of descent (calc-alkaline, transitional, etc). Instead, it can discriminate at a very fine scale lavas that share a common regional origin and are therefore confused in classic tectonic discrimination plots. Disentangling individual magma batches is inaccessible to global modeling but important to chronostratigraphers. Application to two well studied examples, Adamello (Alps) and North Anatolia, reproduces known consanguinity and rejects a few dubious ones.

Before Biology: Geologic Habitability and Setting the Chemical and Physical Foundations for Life

NASA Astrophysics Data System (ADS)

Unterborn, Cayman Thomas

The Earth is a habitable, dynamic planet, with plate tectonics creating a deep water and carbon cycle. These cycles regulate surface and atmospheric C and water abundances, and therefore long-term climate, which is vital to Earths habitability. The driving force behind plate tectonics is the convection of the mantle. The fact that the Earth transports its interior heat via convection instead of conduction is a result of a confluence of factors that include the internal energy budget as well as mantle size and composition. Relative to the Sun stars that host extrasolar planets vary in their refractory rock-building element proportions relative to Si by an order of magnitude. This variation will create terrestrial planets with unique mineralogies and dynamical behavior. How similar these planets are to Earth, chemically and physically, is the focus of this proposal with the end goal being to answer: "What variation in planetary chemical composition is capable of supporting the geochemical cycles necessary for life?".

Classifying seismic noise and sources from OBS data using unsupervised machine learning

NASA Astrophysics Data System (ADS)

Mosher, S. G.; Audet, P.

2017-12-01

The paradigm of plate tectonics was established mainly by recognizing the central role of oceanic plates in the production and destruction of tectonic plates at their boundaries. Since that realization, however, seismic studies of tectonic plates and their associated deformation have slowly shifted their attention toward continental plates due to the ease of installation and maintenance of high-quality seismic networks on land. The result has been a much more detailed understanding of the seismicity patterns associated with continental plate deformation in comparison with the low-magnitude deformation patterns within oceanic plates and at their boundaries. While the number of high-quality ocean-bottom seismometer (OBS) deployments within the past decade has demonstrated the potential to significantly increase our understanding of tectonic systems in oceanic settings, OBS data poses significant challenges to many of the traditional data processing techniques in seismology. In particular, problems involving the detection, location, and classification of seismic sources occurring within oceanic settings are much more difficult due to the extremely noisy seafloor environment in which data are recorded. However, classifying data without a priori constraints is a problem that is routinely pursued via unsupervised machine learning algorithms, which remain robust even in cases involving complicated datasets. In this research, we apply simple unsupervised machine learning algorithms (e.g., clustering) to OBS data from the Cascadia Initiative in an attempt to classify and detect a broad range of seismic sources, including various noise sources and tremor signals occurring within ocean settings.

Formation and tectonic evolution of the Cretaceous Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites

NASA Astrophysics Data System (ADS)

Khan, Mehrab; Kerr, Andrew C.; Mahmood, Khalid

2007-10-01

The Muslim Bagh ophiolitic complex Balochistan, Pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the Indian and Eurasian plates. These ophiolites were obducted onto the Indian continental margin around the Late Cretaceous, prior to the main collision between the Indian and Eurasian plates. The upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes. Each pluton has a transitional dunite-rich zone at its base, and new geochemical data suggest a similar mantle source region for both the plutons and dykes. In contrast, the lower nappe consists of pillow basalts, deep-marine sediments and a mélange of ophiolitic rocks. The rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid-ocean ridge. The basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the Indian plate. The two nappes of the Muslim Bagh ophiolitic complex are thus distinctively different in terms of their age, lithology and tectonic setting. The recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved.

What can we learn about impact mechanics from large craters on Venus?

NASA Technical Reports Server (NTRS)

Mckinnon, William B.; Alexopoulos, J. S.

1992-01-01

More than 50 unequivocal peak-ring craters and multiringed impact basins have been identified on Venus from Earth-based Arecibo, Venera 15/16, and Magellan radar images. These ringed craters are relatively pristine, and so serve as an important new dataset that will further understanding of the structural and rheological properties of the venusian surface and of impact mechanics in general. They are also the most direct analogues for craters formed on the Earth in Phanerozoic time. Finite-element simulations of basin collapse and ring formation were undertaken in collaboration with V. J. Hillgren (University of Arizona). These calculations used an axisymmetric version of the viscoelastic finite element code TECTON, modeled structures on the scale of Klenova or Meitner, and demonstrated two major points. First, viscous flow and ring formation are possible on the timescale of crater collapse for the sizes of multiringed basins seen on Venus and heat flows appropriate to the plant. Second, an elastic lithosphere overlying a Newtonian viscous asthenosphere results mainly in uplift beneath the crater. Inward asthenospheric flow mainly occurs at deeper levels. Lithospheric response is dominantly vertical and flexural. Tensional stress maxima occur and ring formation by normal faulting is predicted in some cases, but these predicted rings occur too far out to explain observed ring spacings on Venus (or on the Moon). Overall, these estimates and models suggest that multiringed basin formation is indeed possible at the scales observed on Venus. Furthermore, due to the strong inverse dependence of solid-state viscosity on stress, the absence of Cordilleran-style ring faulting in craters smaller than Meitner or Klenova makes sense. The apparent increase in viscosity of shock-fluidized rock with crater diameter, greater interior temperatures accessed by larger, deeper craters, and decreased non-Newtonian viscosity associated with larger craters may conspire to make the transition with diameter from peak-ring crater to Orientale-type multiringed basin rather abrupt.

Italian Present-day Stress Indicators: IPSI Database

NASA Astrophysics Data System (ADS)

Mariucci, M. T.; Montone, P.

2017-12-01

In Italy, since the 90s of the last century, researches concerning the contemporary stress field have been developing at Istituto Nazionale di Geofisica e Vulcanologia (INGV) with local and regional scale studies. Throughout the years many data have been analysed and collected: now they are organized and available for an easy end-use online. IPSI (Italian Present-day Stress Indicators) database, is the first geo-referenced repository of information on the crustal present-day stress field maintained at INGV through a web application database and website development by Gabriele Tarabusi. Data consist of horizontal stress orientations analysed and compiled in a standardized format and quality-ranked for reliability and comparability on a global scale with other database. Our first database release includes 855 data records updated to December 2015. Here we present an updated version that will be released in 2018, after new earthquake data entry up to December 2017. The IPSI web site (http://ipsi.rm.ingv.it/) allows accessing data on a standard map viewer and choose which data (category and/or quality) to plot easily. The main information of each single element (type, quality, orientation) can be viewed simply going over the related symbol, all the information appear by clicking the element. At the same time, simple basic information on the different data type, tectonic regime assignment, quality ranking method are available with pop-up windows. Data records can be downloaded in some common formats, moreover it is possible to download a file directly usable with SHINE, a web based application to interpolate stress orientations (http://shine.rm.ingv.it). IPSI is mainly conceived for those interested in studying the characters of Italian peninsula and surroundings although Italian data are part of the World Stress Map (http://www.world-stress-map.org/) as evidenced by many links that redirect to this database for more details on standard practices in this field.

Chelyabinsk fireball and Dyatlov pass tragedy

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2013-09-01

The Chelyabinsk bolide as well as the Kunashak meteorite in 1949 (Fig. 3, black square) hit ground in ectonically peculiar place in the Ural Mountains. The main explosion was followed by a series of weaker bangs. The long Uralian fold belt (Pz) separates two subsectors (1 & 2, Fig. 1) of the Eurasian sector (1+2) of the Eastern hemisphere sectoral structure (Fig. 1). At the Pamirs-Hindukush massif (the "Pamirs' cross") meet four tectonic sectors of this structure: two opposite differently uplifted (Africa-Mediterranean ++ and Asian +) and separating them two opposite differently subsided (Eurasian - and Indooceanic - -). Tectonic bisectors divide the sectors into two differently tectonically elevated subsectors. The Ural Mountains is one of these bisectors dividing the somewhat risen East-European subsector and the relatively fallen West-Siberian one. Even more important is the sharp tectonic boundary between subsided Eurasian sector and uplifted Asian one (between 2 and 3, Fig. 1). Fig. 3 shows distribution of electrophonic bolides over USSR [1]. Observations numbers are in circles. The total of 343 observations is distributed at relevant districts; accompanied meteorites were found only in 23-24 cases; in the chart are excluded background values of 1-2 observations per district. Two areas are obviously anomalous. These of the Urals, and the Eurasia-Asia sectoral contact (Novosibirsk - Yenisei R. - Tunguska). A location in the long Uralian belt is determined by its intersection with the Timan fold belt coming from the northwest (Fig. 3). The catastrophic Dyatlov pass where nine people mysteriously died at once occurs there (triangle in Fig. 3). Mancy aborigines know this place as deadly where killing white shining spheres appear. Moreover this belt intersection is well known among hunters for UFO as the Permian triangle (Fig. 2). They meet there to observe unusual atmospheric shining and other anomalous phenomena. In the Yenisei-Tunguska-Baikal region lightning balls appear regularly causing broken trees [2]. In conclusion, these two tectonically distinctive regions are famous by anomalously often appearance of bolides part of which is accompanied by meteorite falls. Out of 343 observations meteorites accompanied less than 10 %. Unclear remains a strange attraction of bolides by very pronounced tectonic features.

Understanding the Tectonic Features in the South China Sea By Analyzing Magnetic Anomalies

NASA Astrophysics Data System (ADS)

Guo, L.; Meng, X.; Shi, L.; Yao, C.

2011-12-01

The South China Sea (SCS) is surrounded by the Eurasia, Pacific and India-Australia plates. It formed during Late Oligocene-Early Miocene, and is one of the largest marginal seas in the Western Pacific. The collision of Indian subcontinent and Eurasian plate in the northwest, back-arc spreading in the centre and subduction beneath the Philippine plate along Manila trench in the east and along Palawan trough in the south had produced the complex tectonic features in the SCS that we can see today. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of the SCS. Here, we analyzed the magnetic data of this area using new data enhancement techniques to understand the regional tectonic features. We assembled the magnetic anomalies data with a resolution of two arc-minute from the World Digital Magnetic Anomaly Map, and then gridded the data on a regular grid. Then we used the method of reduction to the pole at low latitude with varying magnetic inclinations to stably reduce the magnetic anomalies. Then we used the preferential continuation method based on Wiener filtering and Green's equivalence principle to separate the reduced-to-pole (RTP) magnetic anomalies, and subsequently analyze the regional and residual anomalies. We also calculated the directional horizontal derivatives and the tilt-angle derivative of the data to derive clearer geological structures with more details. Then we calculated the depth of the magnetic basement surface in the area by 3D interface inversion. From the results of the preliminary processing, we analyzed the main faults, geological structures, magma distribution and tectonic features in the SCS. In the future, the integrated interpretation of the RTP magnetic anomalies, Bouguer gravity anomalies and other geophysical methods will be performed for better understanding the deep structure , the tectonic features and evolution of the South China Sea. Acknowledgment: We acknowledge the financial support of the SinoProbe project (201011039), the Fundamental Research Funds for the Central Universities (2010ZY26, 2011PY0184), and the National Natural Science Foundation of China (40904033, 41074095).

Structure and tectonic evolution of the southwestern Trinidad dome, Escambray complex, Central Cuba: Insights into deformation in an accretionary wedge

NASA Astrophysics Data System (ADS)

Despaigne-Díaz, Ana Ibis; García Casco, Antonio; Cáceres Govea, Dámaso; Wilde, Simon A.; Millán Trujillo, Guillermo

2017-10-01

The Trinidad dome, Escambray complex, Cuba, forms part of an accretionary wedge built during intra-oceanic subduction in the Caribbean from the Late Cretaceous to Cenozoic. The structure reflects syn-subduction exhumation during thickening of the wedge, followed by extension. Field mapping, metamorphic and structural analysis constrain the tectonic evolution into five stages. Three ductile deformation events (D1, D2 and D3) are related to metamorphism in a compressional setting and formation of several nappes. D1 subduction fabrics are only preserved as relict S1 foliation and rootless isoclinal folds strongly overprinted by the main S2 foliation. The S2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts, suggesting thrust stacks and underthrusting at mantle depths. Thrusting caused an inverted metamorphic structure with higher-grade on top of lower-grade nappes. Exhumation started during D2 when the units were incorporated into the growing accretionary wedge along NNE-directed thrust faults and was accompanied by substantial decompression and cooling. Folding and thrusting continued during D3 and marks the transition from ductile to brittle-ductile conditions at shallower crustal levels. The D4-5 events are related to extension and contributed to the final exhumation (likely as a core complex). D4 is associated with a regional spaced S4 cleavage, late open folds, and numerous extension veins, whereas D5 is recorded by normal and strike-slip faults affecting all nappes. The P-t path shows rapid exhumation during D2 and slower rates during D3 when the units were progressively incorporated into the accretionary prism. The domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development. These results support tectonic models of SW subduction of the Proto-Caribbean crust under the Caribbean plate during the latest Cretaceous and provide insights into the tectonic evolution of accretionary wedges in an intra-arc setting.

Response: Discussion of 'Morphotectonic records of neotectonic activity in the vicinity of North Almora Thrust Zone, Central Kumaun Himalaya' by Kothyari et al. (2017), Geomorphology (285), 272-286

NASA Astrophysics Data System (ADS)

Kothyari, Girish Ch.; Kandregula, Raj Sunil; Luirei, Khayingshing

2018-01-01

Rana and Sharma (2017) dispute our tectonic interpretation mainly on the basis of what they believe (climate?). However, we welcome their comments, as this gives us a chance to highlight the ambiguity inherent in discriminating the climate-tectonic imprints in morphotectonic records that are prevalent in current research. We should note that the paper published by Kothyari et al. (2017) was reviewed by national/international reviewers. We would like to emphasize the fact that the paper does not rule out the role of climate. However, most importantly, it presents significant features and observations that collection/assemblage points toward the dominant role of tectonics in their shaping, and not solely climate, as postulated by Rana and Sharma (2017). The objective of this paper is to identify tectonic signatures (geomorphology) in a monsoon - dominated, tectonically active terrain like the North Almora Thrust (NAT). These faults are marked by previous workers based on field evidence such as folding and faulting of lithological units; presence of slickensides parallel to the fault; offset of NAT owing to a transverse fault; and offset of drainage, drainage basin analysis, strath terraces, fluviolacustrine terraces, development of scarp, narrow river course, and deeply incised valleys. However, we disagree with the comments raised by Rana and Sharma (2017), because they are highly skewed toward the climate school of thought, and did not perceive the setting as a collection of landforms. Instead, they attempted to view them in isolation. Because these comments are important, we will try to further our research incorporating issues related to isolation of climate and tectonics imprints in the immediate future. We would like to thank Rana and Sharma (2017) for raising some basic questions on our work as this gave us an excellent opportunity to summarize and present the dominance of various processes and related landforms as earlier reported by Kothyari et al. (2017). A point-by-point detailed rebuttal/explanation of their queries is provided below.

Implications for the tectonic transition zone of active orogeny in Hoping drainage basin, by landscape evolution at the multi-temporal timescale

NASA Astrophysics Data System (ADS)

Chang, Q.; Chen, R. F.; Lin, W.; Hsieh, P. S.

2015-12-01

In an actively orogeny the landscape are transient state of disequilibrium in response to climatic and tectonic inputs. At the catchment scale, sensitivity of river systems plays an important role in landscape evolution. Hoping drainage basin is located at the tectonic transition zone in the north-eastern Taiwan, where the behavior of Philippine Sea plate switches from overriding above the east-dipping Eurasian Continental plate to northward subducting under the Ryukyu arc. However, extensive deep-seated landslides, debris flow, and numerous large alluvial terraces can be observed, suggesting strong surface processes in this watershed. This effect on regional climate fundamentally changed the landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. In this study we review the morphological evidence from multi-temporal timescale, including in-situ cosmogenic nuclides denudation rate and suspension load data, coupled with the analysis of the longitudinal profiles. The main goal of this study is to compare Holocene erosion rates with thermochronology and radiometric dating of river terraces to investigate the erosion history of Hoping area. The result shows that short-term erosion rate is around twice as large as the long-term denudation rate, which might due to the climate-driven erosion events such as typhoon-induced landslide. We've also mapped detail morphological features by using the high-resolution LiDAR image, which help us to identify not only the landslide but also tectonic features such as lineation, fault scarps, and fracture zones. The tectonic surface features and field investigation results show that the drainage basin is highly fractured, suggesting that even though the vertical tectonic activity rate is small, the horizontal shortening influenced by both southward opening of the back-arc Okinawa trough and the north-western collision in this area is significant. This might cause the reducing in rock strength and increase the hillslope erosion during heavy rainfall. By studying the erosion rate of Hoping River watershed we can understand more about surface processes in dynamic landscape, and more over, to establish a comprehensive understanding about the evolution of the ongoing Taiwan arc-continental collision process.

Investigation of Tectonic Boundaries in Taiwan Obtained with a Hierarchical Clustering of Dense GNSS Data

NASA Astrophysics Data System (ADS)

Takahashi, A.; Hashimoto, M.; Hu, J. C.; Fukahata, Y.

2017-12-01

Taiwan Island is composed of many geological structures. The main tectonic feature is the collision of the Luzon volcanic arc with the Eurasian continent, which propagates westward and generates complicated crustal deformation. One way to model crustal deformation is to divide Taiwan island into man rigid blocks that moves relatively each other along the boundaries (deformation zones) of the blocks. Since earthquakes tend to occur in the deformation zones, identification of such tectonic boundaries is important. So far, many tectonic boundaries have been proposed on the basis of geology, geomorphology, seismology and geodesy. However, which is the most significant boundary depends on disciplines and there is no way to objectively classify them. Here, we introduce an objective method to identify significant tectonic boundaries with a hierarchical representation proposed by Simpson et al. [2012].We apply a hierarchical agglomerative clustering algorithm to dense GNSS horizontal velocity data in Taiwan. One of the significant merits of the hierarchical representation of the clustering results is that we can consistently explore crustal structures from larger to smaller scales. This is because a higher hierarchy corresponds to a larger crustal structure, and a lower hierarchy corresponds to a smaller crustal structure. Relative motion between clusters can be obtained from this analysis.The first major boundary is identified along the eastern margin of the Longitudinal Valley, which corresponds to the separation of the Philippine Sea plate and the Eurasian continental margin. The second major boundary appears along the Chaochou fault and the Chishan fault in southwestern Taiwan. The third major boundary appears along the eastern margin of the coastal plane. The identified major clusters can be divided into several smaller blocks without losing consistency with geological boundaries. For example, the Fengshun fault, concealed beneath thick sediment layers, is identified. Furthermore, obtained relative motion between clusters demands a reverse fault or a left lateral fault in the off shore of the coastal range.Our clustering based block modeling is consistent with tectonics of Taiwan, implying that observed crustal deformation in Taiwan can be attributed to motion or deformation of shallow structures.

Reconstruction of the strain pattern in the Somma-Vesuvius area: field and remote sensing analyses

NASA Astrophysics Data System (ADS)

D'Assisi Tramparulo, Francesco; Bisson, Marina; Isaia, Roberto; Tadini, Alessandro; Vitale, Stefano

2016-04-01

Keywords: Somma-Vesuvio, structural analysis, volcano-tectonics. This study present a detailed structural analysis of the Somma-Vesuvio (SV) volcanic complex that couples field data about faults, fractures and dykes with the analysis of lineaments identified from high-resolution (1m) DTM deriving from LiDAR data. Field data were collected within the SV caldera,in some quarries along the volcano flanks, and in few outcrops along the carbonate reliefs bounding the southern sector of the Campania plain. A total of 8,500 orientation data have been analyzed through rose diagrams and inversion methods while a total of more than 4,000 lineaments were identified after the analyses of multiple hill shades obtained by applying different pseudo-illuminations (from NW, NE, SE and SW) and appropriate filters to the original DTM. Results indicate a complex interaction between volcanic (local) and tectonic (regional) stress fields. The preliminary analysis of lineaments indicate that most of them are radial with respect to the center of the caldera, however a "tectonic" component is present, mainly represented by the NNE-SSW, ENE-WSW and the well-known Apenninic (NW-SE) direction.

Kinematic evidence for the effect of changing plate boundary conditions on the tectonics of the northern U.S. Rockies

NASA Astrophysics Data System (ADS)

Schmeelk, Dylan; Bendick, Rebecca; Stickney, Michael; Bomberger, Cody

2017-06-01

We derive surface velocities from GPS sites in the interior Northwest U.S. relative to a fixed North American reference frame to investigate surface tectonic kinematics from the Snake River Plain (SRP) to the Canadian border. The Centennial Tectonic Belt (CTB) on the northern margin of the SRP exhibits west directed extensional velocity gradients and strain distributions similar to the main Basin and Range Province (BRP) suggesting that the CTB is part of the BRP. North of the CTB, however, the vergence of velocities relative to North America switches from westward to eastward along with a concomitant rotation of the principal stress axes based on available seismic focal mechanisms, revealing paired extension in the northern Rockies and shortening across the Rocky Mountain Front. This change in orientation of surface velocities suggests that the change in the boundary conditions on the western margin of North America influences the direction of gravitational collapse of Laramide thickened crust. Throughout the study region, fault slip rate estimates calculated from the new geodetic velocity field are consistently larger than previously reported fault slip rates determined from limited geomorphic and paleoseismic studies.

Extrusional Tectonics over Plate Corner: an Example in Northern Taiwan

NASA Astrophysics Data System (ADS)

Lu, Chia-Yu; Lee, Jian-Cheng; Li, Zhinuo; Lee, Ching-An; Yeh, Chia-Hung

2016-04-01

In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter, retreat of Ryukyu trench and opening of the Okinawa trough.

Extrusional Tectonics at Plate Corner: an Example in Northern Taiwan

NASA Astrophysics Data System (ADS)

Lu, C. Y.; Lee, J. C.; Li, Z.; Yeh, C. H.; Lee, C. A.

2015-12-01

In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter and opening of the Okinawa trough at plate corner.

An ArcGIS approach to include tectonic structures in point data regionalization.

PubMed

Darsow, Andreas; Schafmeister, Maria-Theresia; Hofmann, Thilo

2009-01-01

Point data derived from drilling logs must often be regionalized. However, aquifers may show discontinuous surface structures, such as the offset of an aquitard caused by tectonic faults. One main challenge has been to incorporate these structures into the regionalization process of point data. We combined ordinary kriging and inverse distance weighted (IDW) interpolation to account for neotectonic structures in the regionalization process. The study area chosen to test this approach is the largest porous aquifer in Austria. It consists of three basins formed by neotectonic events and delimited by steep faults with a vertical offset of the aquitard up to 70 m within very short distances. First, ordinary kriging was used to incorporate the characteristic spatial variability of the aquitard location by means of a variogram. The tectonic faults could be included into the regionalization process by using breaklines with buffer zones. All data points inside the buffer were deleted. Last, IDW was performed, resulting in an aquitard map representing the discontinuous surface structures. This approach enables one to account for such surfaces using the standard software package ArcGIS; therefore, it could be adopted in many practical applications.

Birth of an oceanic spreading center at a magma-poor rift system.

PubMed

Gillard, Morgane; Sauter, Daniel; Tugend, Julie; Tomasi, Simon; Epin, Marie-Eva; Manatschal, Gianreto

2017-11-08

Oceanic crust is continuously created at mid-oceanic ridges and seafloor spreading represents one of the main processes of plate tectonics. However, if oceanic crust architecture, composition and formation at present-day oceanic ridges are largely described, the processes governing the birth of a spreading center remain enigmatic. Understanding the transition between inherited continental and new oceanic domains is a prerequisite to constrain one of the last major unsolved problems of plate tectonics, namely the formation of a stable divergent plate boundary. In this paper, we present newly released high-resolution seismic reflection profiles that image the complete transition from unambiguous continental to oceanic crusts in the Gulf of Guinea. Based on these high-resolution seismic sections we show that onset of oceanic seafloor spreading is associated with the formation of a hybrid crust in which thinned continental crust and/or exhumed mantle is sandwiched between magmatic intrusive and extrusive bodies. This crust results from a polyphase evolution showing a gradual transition from tectonic-driven to magmatic-driven processes. The results presented in this paper provide a characterization of the domain in which lithospheric breakup occurs and enable to define the processes controlling formation of a new plate boundary.

Microclimate and architectural tectonic: vernacular floating house resilience in Seberang Ulu 1, Palembang

NASA Astrophysics Data System (ADS)

Puspitasari, P.; Kadri, T.; Indartoyo, I.; Kusumawati, L.

2018-01-01

This paper aims to describe the results of preliminary research on floating houses on the Musi River, Seberang Ulu 1, Palembang, focused on studying the influence of microclimates to the tectonics of Rumah Rakit (Floating House). The increase of water surface due to global warming will increase the need of using floating house typology in the future. The description of the inhabitants’ experiences on applying technics to create vernacular floating houses is considered as significant knowledge to develop advance technology on the basis of local characteristic. Vernacular floating houses resilience consists of natural experiences of inhabitants in adapting their daily activities to the characteristic of local climate. By using qualitative approach, the Rumah Rakit inhabitants’ verbal information in this article becomes the main aspect in exploring local knowledge. At the end, the conceptual model of vernacular Rumah Rakit in Seberang Ulu 1, Palembang is formulated, in terms of building architectural tectonic that is closely related to the local climate characteristic. The knowledge can be utilized in the context of rehabilitation or preservation of such architectural objects that are their existences tend to be extinct at this time.

Zircon U-Pb chronology, geochemistry and Sr-Nd-Pb isotopic compositions of the Volcanic Rocks in the Elashan area, NW China: petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Zhou, H.; Wei, J.; Shi, W.; Li, P.; Chen, M.; Zhao, X.

2017-12-01

Elashan area is located in the intersection of the East Kunlun Orogenic Belt (EKOB) and the West Qinling Orogenic (WQOB). We present petrology, zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Pb isotopic compositions from the andesite and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in Elashan group volcanic rock. The LA-ICP-MS zircon U-Pb age data indicate that the volcanic rocks are emplaced at 250 247 Ma. The volcanic rocks have high -K and aluminum - peraluminous characteristics, A/CNK = 1.07 1.82, δ ranges from 1.56 2.95, the main body is calc-alkaline rock. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in some high field strength elements (HFSEs, e.g., Nb, Ta, P and Ti), while having a flat heavy REE (HREEs) pattern. The ∑REE values of 178.68 to 298.11 ppm, average 230.50 ppm. The LREE/HREE values of 4.39 to 11.78 ppm, average 6.77 ppm. REE fractionation is obvious, REE distribution curve was right smooth, and have slightly negative Eu anomalies (Eu/Eu*=0.44-0.80, average 0.60), which as similar to the island arc volcanic rocks. The volcanic rocks have initial 87Sr/86Sr ratios of 0.71028-0.71232, ɛNd(t) values of -6.7 to -7.6, with T2DM-Nd ranging from 1561 to 1640 Ma. Pb isotopic composition (206 Pb / 204 Pb)t = 18.055 18.330, (207 Pb / 204 Pb)t = 15.586 15.618, (208 Pb / 204 Pb)t = 37.677 38.332. Geochemical and Sr-Nd-Pb isotopes indicates that Elashan group volcanic magma derived mainly from the lower crust. Elashan group volcanic rocks is the productive East Kunlun block and West Qinling block collision, which makes the thicken crust caused partial melting in the study area. The source rocks is probably from metamorphic sandstone of Bayankala. But with Y-Nb and Rb-(Y+Nb), R1-R2 and Rb/10-Hf-Ta*3 diagrams showing that intermediate-acid rocks mainly formed in volcanic arc-collision environment, probably the collision event is short , therefore rocks retain the original island arc properties. The formation age of intermediate -acidic volcanic rock can represent the time in which the end of transgressive and the beginning of intercontinental evolution in the northeastern Tibetan Plateau.

Late Alpine to recent thick-skinned tectonics of the central Swiss Molasse Basin, Canton of Bern, Switzerland

NASA Astrophysics Data System (ADS)

Mock, Samuel; Allenbach, Robin; Wehrens, Philip; Reynolds, Lance; Kurmann-Matzenauer, Eva; Michael, Salomè; Herwegh, Marco

2017-04-01

The Swiss Molasse Basin (SMB) forms part of the North Alpine Foreland Basin. It is a typical peripheral foreland basin, which developed in Paleogene and Neogene times in response to flexural bending of the European lithosphere induced by the orogenic loading of the advancing Alpine thrust wedge. The tectonics of the SMB and the role of Paleozoic and Mesozoic structures are still poorly understood. It is widely accepted that during the main deformation phase of the Jura fold-and-thrust belt, the SMB was riding piggy-back above a major detachment horizon situated within Triassic evaporites. In recent years it has been observed that the Jura fold-and-thrust belt is today deforming in a thick-skinned tectonic style. As for the western and central SMB, most authors still argue in favor of a classical foreland type, thin-skinned style of deformation. Based on the geological 3D modeling of seismic interpretations, we present new insights into the structural configuration of the central SMB. Revised and new interpretations of 2D reflection seismic data from the 1960s to the 1980s reveal a major strike-slip fault zone affecting not only the Mesozoic and Cenozoic cover, but also the crystalline basement beneath. The fault zone reactivated late Paleozoic synsedimentary normal faults bounding a Permo-Carboniferous trough. Basement-involved thrusting observed in the southern part of the SMB seems to be controlled by the presence of slightly inverted Permo-Carboniferous troughs as well. These observations, combined with a compiled structural map and the distribution of recent earthquake hypocenters suggest a late stage, NNW-SSE directed, compressional thick-skinned and strike-slip dominated tectonic activity of the central SMB, post-dating the main deformation phase of the Jura fold-and-thrust belt. This still ongoing deformation might be related to the slab rollback of the European plate and the associated lower crustal delamination as recently suggested by Singer et al. (2014). References: Singer, J., Diehl, T., Husen, S., Kissling, E., Duretz, T., 2014. Alpine lithosphere slab rollback causing lower crustal seismicity in northern foreland. Earth Planet. Sci. Lett. 397, 42-56. doi:10.1016/j.epsl.2014.04.002

Factors that affect coseismic folds in an overburden layer

NASA Astrophysics Data System (ADS)

Zeng, Shaogang; Cai, Yongen

2018-03-01

Coseismic folds induced by blind thrust faults have been observed in many earthquake zones, and they have received widespread attention from geologists and geophysicists. Numerous studies have been conducted regarding fold kinematics; however, few have studied fold dynamics quantitatively. In this paper, we establish a conceptual model with a thrust fault zone and tectonic stress load to study the factors that affect coseismic folds and their formation mechanisms using the finite element method. The numerical results show that the fault dip angle is a key factor that controls folding. The greater the dip angle is, the steeper the fold slope. The second most important factor is the overburden thickness. The thicker the overburden is, the more gradual the fold. In this case, folds are difficult to identify in field surveys. Therefore, if a fold can be easily identified with the naked eye, the overburden is likely shallow. The least important factors are the mechanical parameters of the overburden. The larger the Young's modulus of the overburden is, the smaller the displacement of the fold and the fold slope. Strong horizontal compression and vertical extension in the overburden near the fault zone are the main mechanisms that form coseismic folds.

The Genesis of tectonically and hydrothermally controlled industry mineral deposits: A geochemical and structural study

NASA Astrophysics Data System (ADS)

Wölfler, Anke; Prochaska, Walter; Henjes-Kunst, Friedhelm; Fritz, Harald

2010-05-01

The study aims to investigate the role of hydrothermal fluids in the formation of talc and magnesite deposits. These deposits occur in manifold geological and tectonical settings such as stockworks and veins within ultramafite hostrocks and monomineralic lenses within marine platform sediments. Along shear zones talc mineralizations may occur as a result of tectonical and hydrothermal activity. To understand the role of the fluids for the genesis of the mineralization, deposits in different geological and tectonical settings are investigated: Talc mineralization within in magnesite in low-grade palaeozoic nappe complexes (Gemerska Poloma, Slovakia): The magnesite body lies within the Gemer unit of the Inner Carpathians consisting of Middle Triassic metacarbonates and Upper Triassic pelagic limestones and radiolarites. The talc mineralization is bound to crosscutting veins. Two metamorphic events can be distinguished, one during Variscan orogeny and one related to the Alpine orogeny leading to the formation of talc along faults in an Mg carbonate body (Radvanec et al, 2004).The origin of the fluids as well as the tectonic events leading to the mineralization is still widely unknown. Talc mineralization in shearzones within Palaeozoic meta sedimentary rocks (Sa Matta, Sardinia): Variscan granitoids intruded Palaeozoic meta sedimentary rocks and were overprinted be NE striking tectonic structures that host talc mineralizations. The origin of Mg and fluids leading to the mineralization is still not answered satisfactorily (Grillo and Prochaska, 2007) and thus a tectonic model for the genesis of the talc deposit is missing. Talc mineralization within UHP pre-Alpine continental crust (Val Chisone, Italy): The talc deposit forms part of the Dora-Maira Massif. Geologicaly the massif derived from a Variscan basement that includes post-Variscan intrusions. The talc mineralization occurs as a sheetlike, conformable body. A possible tectonic emplacement of talc along shear surfaces was proposed by Sandrone & Zucchetti, 1988. Magnesite and talc bearing shearzones in ultramafic hostrocks (Lahnaslampi & Horsmanaho, Finland): Both deposits are situated in the Proterozoic schist belt where the talc-magnesite rocks at Lahnaslampi are associated with minor serpentine breccias. The steatitization took place in two different stages: During prograde metamorphism with H2O-dominated solutions and at declining temperature and pressure in the presence of CO2-bearing fluids that resulted in the main steatitization along tectonic structures. A combined geological, petrological and geochronological is chosen to resolve mechanism of mineralisation within the different tectonic setting. Different phases of mineral formation are first distinguished by pertrological and structural field work and then dated by radiometric techniques. Fluid species and chemical environment during mineralisation is resolved by geochemical techniques and stable isotope studies. References Grillo, S., Prochaska, W. (2007): Fluid Chemistry and Stable Isotope Evidence of Shearzone related Talc and Chlorite Mineralizations in Central Sardinia-Italy, In: Conference Abstracts SGA-Meeting. Radvanec, M., Koděra, P., Prochaska, W. (2004): Mg replacement of the Gemerska Poloma talk-magnesite deposit, Western Carpathians, Slovakia. Acta Petrologica Sinica, 20, 773-790. Sandrone, Zucchetti (1988): Geology of the Italian high-quality cosmetic talc from the Pinerolo district (Western Alps). Zuffar' Days - Symposium held in Cagliari, 10-15

Geologic map of Mészáros revisited: Pioneering tectonic mapping of the Transdanubian Range in the early 1980s

NASA Astrophysics Data System (ADS)

Zámolyi, A.; Horváth, F.; Kovács, G.; Timár, G.; Székely, B.

2009-04-01

Rocks, even in tectonically active areas are very solid compared to the changes within the scientific theories that occured especially in Eastern Europe as the political landscape changed and the separation into socialist and capitalist countries started to fade. While in Western Europe, Wegener's mobilistic approach gained widespread acceptance in the 1960-ies, in the countries of Eastern Europe (partly due to political reasons) fixistic ideas were supported. Despite the fact that most important early concepts in Hungarian tectonics were born about a century ago as a results of exploration of the Lake Balaton and its surroundings conducted by Lajos Lóczy, initiatives to integrate various geodynamic observations were rare exceptions in the second half of the 20th century. The high priority of economic geologic prospection in order to find raw materials resulted in an enormous amount of observations. In the central Transdanubian Range (TR), hosting bauxite, coal and manganese deposits, extensive surveying was carried out according to fixistic tectonic concepts. Although the recognition of faults was of vital importance in mining, mapped faults were rarely integrated into a global geodynamic model. A pioneering approach was presented by Mészáros (1983), who compiled a 1: 100 000 scale structural and economic-geologic map of large parts of TR. The map focuses on the Bakony hills that are of key importance for the geodynamic understanding of the formation of PB. TR forms inselbergs with well preserved outcrops, which is rare in PB, thus allowing for direct measurements of fault striations and fault plane orientations. Prinz (1926) maintained the theory that the TR is a rigid block and named it Tisia block. An alternative to this approach was the monograph of Uhlig (1907) proposing mobilistic concepts. Csontos et al (1991) reviewed the evolution of neogene stress-fields in the Carpatho-Pannonian region observing microtectonic faults in TR. The authors conclude that the faults mapped by Mészáros (1983) coincide fairly well with their microtectonic measurements. TR is nowadays interpreted as the uppermost Cretaceous thrust sheet of the Alpine nappes based on the interpretation of seismic surveys (Rumpler & Horváth, 1988; Horváth, 1993) and microtectonic measurements (Kiss & Fodor, 2007). We integrated the map into a GIS environment in order to evaluate the spatial accuracy of tectonic features and deformation style in the study area. Georeferencing was based upon control points applying rubber sheeting. Geological formations were digitized as polygons with their respective attributes (colour- or numerically coded). Three different categories of bounding elements are represented on the map: established, supposed and covered by younger geologic formations. Mészáros put a major emphasis on tectonic features, using 21 different line-types for representation. Digital terrain analysis methods using a 10 m DTM reveal a good correlation of the fault pattern with geomorphologic features, especially in the category of confirmed strike-slip faults. The connection of tectonic elements with the topography is a very anticipatory way of thinking for the early 1980s that became widely accepted by the end of the century. Csontos, L., Tari, G., Bergerat, F., Fodor, L. 1991. Tectonophysics, 199, 73-91. Horváth, F. 1993. In: Cloething, S., Sassi, W. & Horváth, F. (eds.) Tectonophysics, 226, 333-358. Kiss, A., Fodor, L. I. 2007. Geologica Carpathica, 58(5), 465-475. Mészáros, J. 1983. Ann. Rep. Hung. Geol. Inst. 1981, 485-502. Prinz, Gy. 1926. Danubia könyvkiadó, Pécs, 202 p. Rumpler, J., Horváth, F. 1988. In: L.H. Royden and F. Horváth (eds.) AAPG Mem. 45, Tulsa, Okl., 153-169p. Uhlig, V. 1907. Sitz. Ber. Akad. Wiss., math.- nat., Kl. 116(1), 871-982.

Anatomy of landslides along the Dead Sea Transform Fault System in NW Jordan

NASA Astrophysics Data System (ADS)

Dill, H. G.; Hahne, K.; Shaqour, F.

2012-03-01

In the mountainous region north of Amman, Jordan, Cenomanian calcareous rocks are being monitored constantly for their mass wasting processes which occasionally cause severe damage to the Amman-Irbid Highway. Satellite remote sensing data (Landsat TM, ASTER, and SRTM) and ground measurements are applied to investigate the anatomy of landslides along the Dead Sea Transform Fault System (DSTFS), a prominent strike-slip fault. The joints and faults pertinent to the DSTFS match the architectural elements identified in landslides of different size. This similarity attests to a close genetic relation between the tectonic setting of one of the most prominent fault zones on the earth and modern geomorphologic processes. Six indicators stand out in particular: 1) The fractures developing in N-S and splay faults represent the N-S lateral movement of the DSTFS. They governed the position of the landslides. 2) Cracks and faults aligned in NE-SW to NNW-SSW were caused by compressional strength. They were subsequently reactivated during extensional processes and used in some cases as slip planes during mass wasting. 3) Minor landslides with NE-SW straight scarps were derived from compressional features which were turned into slip planes during the incipient stages of mass wasting. They occur mainly along the slopes in small wadis or where a wide wadi narrows upstream. 4) Major landslides with curved instead of straight scarps and rotational slides are representative of a more advanced level of mass wasting. These areas have to be marked in the maps and during land management projects as high-risk area mainly and may be encountered in large wadis with steep slopes or longitudinal slopes undercut by road construction works. 5) The spatial relation between minor faults and slope angle is crucial as to the vulnerability of the areas in terms of mass wasting. 6) Springs lined up along faults cause serious problems to engineering geology in that they step up the behavior of marly interbeds to accelerate sliding during mass wasting. The most vulnerable areas prone to slope instabilities are those with compressional tectonics followed by extensional movements, with fault bound springs and smectite-bearing marly layers interbedded with pure massive limestones. The semi-arid to arid climate with periodic rainfalls combined with subsurface water circulation along the joints and faults can trigger mass wasting.

Structure and tectonics of the Main Himalayan Thrust and associated faults from recent earthquake and seismic imaging studies using the NAMASTE array

NASA Astrophysics Data System (ADS)

Karplus, M. S.; Pant, M.; Velasco, A. A.; Nabelek, J.; Kuna, V. M.; Sapkota, S. N.; Ghosh, A.; Mendoza, M.; Adhikari, L. B.; Klemperer, S. L.

2017-12-01

The India-Eurasia collision zone presents a significant earthquake hazard, as demonstrated by the recent, devastating April 25, 2015 M=7.8 Gorkha earthquake and the following May 12, 2015 M=7.3 earthquake. Important questions remain, including distinguishing possible geometries of the Main Himalayan Thrust (MHT), the role of other regional faults, the crustal composition and role of fluids in faulting, and the details of the rupture process, including structural causes and locations of rupture segmentation both along-strike and down-dip. These recent earthquakes and their aftershocks provide a unique opportunity to learn more about this collision zone. In June 2015, funded by NSF, we deployed the Nepal Array Measuring Aftershock Seismicity Trailing Earthquake (NAMASTE) array of 46 seismic stations distributed across eastern and central Nepal, spanning the region with most of the aftershocks. This array remained in place for 11 months from June 2015 to May 2016. We combine new results from this aftershock network in Nepal with previous geophysical and geological studies across the Himalaya to derive a new understanding of the tectonics of the Himalaya and southern Tibet in Nepal and surrounding countries. We focus on structure and composition of the Main Himalayan Thrust and compare this continent-continent subduction megathrust with megathrusts in other subduction zones.

Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic Rift System

NASA Astrophysics Data System (ADS)

Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.

2012-12-01

We collected samples from subaerial lava flows and dredged some Neogene basanitic lavas from seven volcanic edifices in the Ross Sea, Antarctica - a part of the West Antarctic Rift System (WARS) and one of the world's largest alkaline magmatic provinces - for a study aimed at two principal objectives: (1) Geochemical interrogation of the most primitive magmatic rocks to try and understand the nature of the seismically abnormal mantle domain recently identified beneath the shoulder of the Transantarctic Mountains (TAM), the Ross Sea Embayment and Marie Byrd Land; and (2) Using 40Ar/39Ar geochronology to establish a temporal link between magmatism and tectonism, particularly in the Terror Rift. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether rifting in the area triggered magmatic activity or vice versa. Results show that the area does not have an age-progressive hotspot track, and the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. In fact, preliminary volatile measurements on olivine-hosted melt inclusions have yielded water concentrations in excess of 2 wt%, indicating that flux melting was an important complementary process to decompression melting. The major oxide compositions of lavas in the WARS are best matched to experimental melts of carbonated peridotite, though garnet pyroxenite can also be a minor source. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along the Paleo-Pacific margin of Gondwana. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 ± 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.

Role of structural inheritance on present-day deformation in intraplate domains

NASA Astrophysics Data System (ADS)

Tarayoun, A.; Mazzotti, S.; Gueydan, F.

2017-12-01

Understanding the role of structural inheritance on present day surface deformation is a key element for better characterizing the dynamism of intraplate earthquakes. Current deformation and seismicity are poorly understood phenomenon in intra-continental domains. A commonly used hypothesis, based on observations, suggests that intraplate deformation is related to the reactivation of large tectonic paleo-structures, which can act as locally weakened domains. The objective of our study is to quantify the impact of these weakened areas on present-day strain localizations and rates. We combine GPS observations and numerical modeling to analyze the role of structural inheritance on strain rates, with specific observations along the St. Lawrence Valley of eastern Canada. We processed 143 GPS stations from five different networks, in particular one dense campaign network situated along a recognized major normal faults system of the Iapetus paleo-rift, in order to accurately determine the GPS velocities and strain rates. Results of strain rates show magnitude varying from 1.5x10-10 to 6.8x10-9 yr-1 in the St Lawrence valley. Weakened area strain rates are up to one order of magnitude higher than surrounding areas. We compare strain rates inferred from GPS and the new postglacial rebound model. We found that GPS signal is one order of magnitude higher in the weakened zone, which is likely due to structural inheritance. The numerical modeling investigates the steady-state deformation of the continental lithosphere with presence of a weak area. Our new approach integrates ductile structural inheritance using a weakening coefficient that decreases the lithosphere strength at different depths. This allows studying crustal strain rates mainly as a function of rheological contrast and geometry of the weakened domains. Comparison between model predictions and observed GPS strain rates will allow us to investigate the respective role of crustal and mantle tectonic inheritance.

Tertiary sedimentary history and structure of the Valencia trough (western Mediterranean)

NASA Astrophysics Data System (ADS)

Maillard, A.; Mauffret, A.; Watts, A. B.; Torné, M.; Pascal, G.; Buhl, P.; Pinet, B.

1992-03-01

We present here main results of the Common Depth Point (CDP) data acquired during the Valsis 2 Cruise in 1988 in the Valencia trough. The profiles are tied in with industrial well data and this correlation allows the sedimentary and structural history of the region to be deduced. The Valsis Cruise seismic profiles have been supplemented by a very dense grid of industrial seismic lines and these data permit us to establish an accurate depth to basement map. The formation of the initial grabens, coeval with those of the Gulf of Lions, is related to the Early Miocene opening of the northwestern Mediterranean basin and the Barcelona graben is filled by the same sedimentary layers, including evaporites, as that of the Provençal region. Nevertheless, the Valencia-Catalan grabens have been reactivated by young extensional tectonics which could be a consequence of the convergence of Africa relative to Europe. The Valencia trough is segmented by transfer faults which trend NW-SE. These faults, which have a more accentuated structural expression than the Valencia and Catalonia grabens, may act as transform faults separating the individual Balearic Islands. The transfer faults are in strike with volcanic ridges which have been sampled during the DSDP Leg 13. The dense seismic grid allows us to delineate several widespread volcanic features in the Valencia trough which have been active from the Early Miocene to the Pleistocene. However, we note that the volcanic features are mainly Miocene in age whereas the recent volcanism is restricted to a narrow zone (Columbretes Islands). The compressional tectonics which deformed the Balearic Islands does not appear to extend far towards the North. We delineate the compressional front north of Ibiza, but we failed to determine any thrust or fold north of Mallorca, whereas an extensional tectonics is evident.

Stenian Estuarine System and Early Neoproterozoic Microbial Records of Capiru Formation, Southern Ribeira Belt.

NASA Astrophysics Data System (ADS)

Cury, L. F.; Santos, L. D. R.; Leandro, R.; Lange, L.; Bahniuk Rumbelsperger, A.

2017-12-01

The Capiru formation is a low-grade metasedimentary sequence composed by slates, rhythmic phyllites, quartzites and marbles, disposed and disrupted in tectonic blocks delimited by thrust and strike-slip faults related to oblique collisions in the southern Ribeira Belt, Curitiba terrane, southern Brazil. The rocks of the Capiru formation crops out as a thrust-folded belt, delimited on the north by the transcurrent faults of Lancinha Shear Zone (LSZ), and to the south by thrust faults with large isograde variation. Three lithological sequences are recognized mainly by their compositional and stratigraphic records, including a (i) ferruginous sequence with quartzites, metasandstones and metaconglomerates with goethite/hematite cements and phyllites with magnetite; ii) metadolomites with stromatolites, interbeded with pelitic layers and iii) a metapelitic sequence with metarhythmites and metasandstones with well preserved organic-rich material. The records of two tectonic-metamorphic events related to thrust and transpressive tectonics are heterogeneously developed in all sequences, still been recognized sections with the original stratigraphic succession. The stratigraphic record suggests an estuarine environment with rising sea level developing tidal flats and tidal channels. U-Pb detrital zircon analyses characterizes Rhyacian ages (between 2.2-2.1 Ga) as the main sources, and Stenian ages (between 1.08-1.20 Ga) as maximum age for sedimentation. The metapelites mineral assemblage is composed by quartz, muscovite, sericite, illite, kaolinite, sepiolite, magnetite, goethite, hematite and carbonaceous material with bulk organic carbon content (BOC) ranging from 0.09 to 1.21 (%), a precambrian microbial activity record. The metadolomites are characterized by the presence of stromatolites in different types and dimensions, with microbial activity records supported by SEM-EDS (up to 91% C), with EPS-like morphologies within microporosity, NaCl compounds and clay minerals, probably indicative of microorganism contribution during the deposition.

Escape tectonism in the Gulf of Thailand: Paleogene left-lateral pull-apart rifting in the Vietnamese part of the Malay Basin

NASA Astrophysics Data System (ADS)

Fyhn, Michael B. W.; Boldreel, Lars O.; Nielsen, Lars H.

2010-03-01

The Malay Basin represents one of the largest rift basins of SE Asia. Based on a comprehensive 2-D seismic database tied to wells covering mainly Vietnamese acreage, the evolution of the Vietnamese part of the basin is outlined and a new tectonic model is proposed for the development of the basin. The Vietnamese part of the Malay Basin comprises a large and deep Paleogene pull-apart basin formed through Middle or Late Eocene to Oligocene left-lateral strike-slip along NNW-trending fault zones. The Tho Chu Fault Zone constitutes a significant Paleogene left-lateral strike-slip zone most likely associated with SE Asian extrusion tectonism. The fault zone outlines a deep rift that widens to the south and connects with the main Malay Basin. In the central northern part of the basin, a series of intra-basinal left-lateral fracture zones are interconnected by NW to WNW-trending extensional faults and worked to distribute sinistral shearing across the width of the basin. Extensive thermal sagging throughout the Neogene has led to the accommodation of a very thick sedimentary succession. Moderate rifting resumed during the Early Miocene following older structural fabric. The intensity of rifting increases towards the west and was probably related to coeval extension in the western part of the Gulf of Thailand. Neogene extension culminated before the Pliocene, although faults in places remains active. Late Neogene basin inversion has been attributed to c. 70 km of right-lateral movement across major c. N-S-trending faults in the central part of the basin. However, the lack of inversion in Vietnamese territory only seems to merit a few kilometers of dextral inversion.

Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan-Mufushan Batholith in Southeast China and Its Tectonic Significance: 2. Magnetic Fabrics and Gravity Survey

NASA Astrophysics Data System (ADS)

Ji, Wenbin; Chen, Yan; Chen, Ke; Wei, Wei; Faure, Michel; Lin, Wei

2018-01-01

The Late Mesozoic magmatic province is a prominent feature of the South China Block (SCB). However, the tectonic regimes associated with the magmatism are still elusive. A combined anisotropy of magnetic susceptibility and gravity study has been carried out to determine the fabric patterns and shape at depth of the Dayunshan-Mufushan composite batholith in the north-central SCB. This is a companion paper to Part 1 that presented the structural and geochronological data of this batholith. The magnetic fabrics in the batholith interior predominantly reflect magma flow structures. Two distinct patterns of the magnetic lineations are defined, around NNE-SSW and WNW-ESE trends for the early-stage and late-stage intrusions of the batholith, respectively. The gravity survey reveals that the early-stage intrusion has a main feeder zone located below its northern part, while several linear feeder zones trending NNE-SSW are inferred for the late-stage intrusion. Integrating all results, a two-stage construction of the batholith with distinct tectonic regimes has been established. It is concluded that the early-stage intrusion experienced a southward magma transport during its emplacement, partially assisted by far-field compression from the north at ca. 150 Ma. Conversely, the emplacement and exhumation of the late-stage intrusion was accommodated by a NW-SE crustal stretching involving a lateral magma expansion above the multiple feeder zones (likely corresponding to extensional fractures) and ductile shearing during 132-95 Ma localized mainly along the Dayunshan detachment fault. Finally, we discuss the geodynamic linkage between the paleo-Pacific subduction and the Late Mesozoic tectonomagmatism in the SCB.

Geochemistry of mineral waters and associated gases of the Sakhalin Island (Far East of Russia)

NASA Astrophysics Data System (ADS)

Chelnokov, George A.; Bragin, Ivan V.; Kharitonova, Natalia A.

2018-04-01

Isotopic and chemical data on the mineral water, mud volcanoes fluid and associated gases from the biggest Russian island Sakhalin, together with previous stable isotope data (d18O, dD, 13C), allow elucidation of their origin and general evolution. The water fluid circulation is mainly related to marine environment inducing three distinct types: Na-HCO3-Cl alkali carbonate groundwaters, Na-Cl-HCO3 highly evolved saline and Na-Cl mature groundwaters, indicating different evolution. Chemical evolution of groundwater on Sakhalin Island demonstrated cation exchange and salinization as dominant evolutionary pathways. Isotopic composition of groundwaters varies from meteoric to metamorphic waters. These metamorphic waters consist of water hydration from the clay and seawater are traced in fluids of Yuzhno-Sakhalin mud volcano despite modification by mixing with meteoric waters and water-rock interaction processes. Fault systems that define the areas of highly mineralized water circulation appear to play a major role in the CO2 migration to the surface and CH4 generation. The δ13C(CO2) values have pointed that gas phase in high-pCO2 waters mostly consists of mantle-derived CO2. The carbon isotope signature of methane δ13C(CH4) and δD(CH4) indicates its distinct origin which is specified by tectonics. Methane manifestation in the south of the Sakhalin Island is mainly related to thermogenic reservoirs as they are more often dislocate by tectonics, and crossed by active and permeable faults. The sources of biogenous methane in the north of Sakhalin Island is related to younger and shallower reservoirs, and less affected by tectonic processes. The determinations of 222Rn have allowed observing that maximal radon flux is associated with high pCO2 waters.

The mechanism of post-rift fault activities in Baiyun sag, Pearl River Mouth basin

NASA Astrophysics Data System (ADS)

Sun, Zhen; Xu, Ziying; Sun, Longtao; Pang, Xiong; Yan, Chengzhi; Li, Yuanping; Zhao, Zhongxian; Wang, Zhangwen; Zhang, Cuimei

2014-08-01

Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east.

Early cretaceous rift sediments of the Gabon-Congo margin: lithology and organic matter; tectonic and paleogeothermal evolution

NASA Astrophysics Data System (ADS)

Robert, P.; Yapaudjian, L.

The active troughs of the western Gabon-Congo margin which are part of the South Atlantic rift contain a Neocomian to barremian-aged fluvial-lacustrine series. The lithological sequence of interbedded clastic and pelitic formations constitutes a well-defined cycle. This cycle is divided into: a fluvial or piedmont stage, a lacustrine turbidite-stage corresponding to the distension paroxysm of the basin, and finally, a lacustrine deltaic stage of infilling and tectonic quiescence. The organic matter included in the shale layers is abundant and originates mainly from lacustrine Botryococcus algae and their alteration and secretion products. The geothermal history of the basin, demonstrated by the evolution of the organic matter indicates a strong hyperthermy located in the active, more subsiding part of the basin, and contemporaneous with sedimentation.

The origin and development of plains-type folds during the cretaceous in Central and western Kansas

USGS Publications Warehouse

Merriam, D.F.; Forster, A.

2000-01-01

Kansas is part of the Central Stable Region of North America. Structural movement on this part of the craton has been mainly the result of tectonism in nearby areas. Response to the outside tectonic forces, transmitted through the rigid Precambrian basement, has been vertical adjustment. Differential movement along an indigenous fault/fracture pattern in the basement created displaced blocks over which the later sediments were draped by differential compaction. After initial formation of this structural regimen in late Mississippian-early Pennsylvanian time, continued movement of the basement blocks gave rise to the plains-type folds so prevalent in the U.S. Midcontinent. The incremental movement continues through the late Paleozoic, Mesozoic, and Tertiary until today. This paper demonstrates the Cretaceous development of some of these structures in central and western Kansas.

Geology and tectonics of the Archean Superior Province, Canadian Shield

NASA Technical Reports Server (NTRS)

Card, K. D.

1986-01-01

Superior Province consists mainly of Late Archean rocks with Middle Archean gneisses in the south, and possibly in the north. The Late Archean supracrustal sequences are of island arc and interarc affinity and are cut by abundant plutonic rocks, including early arc-related intrusions, late synorogenic intrusions, and post-orogenic plutons that are possibly the product of crustal melting caused by thermal blanketing of newly-thickened continental crust combined with high mantle heat flux. The contemporaneity of magmatic and deformational events along the lengths of the belts is consistent with a subduction-dominated tectonic regime for assembly of the Kenoran Orogen. Successive addition of volcanic arcs accompanied and followed by voluminous plutonism resulted in crustal thickening and stabilization of the Superior craton prior to uplift of Kapuskasing granulites, emplacement of the Matachewan diabase dykes, and Early Proterozoic marginal rifting.

Tectonics of Tharsis Dorsa on Mars

NASA Technical Reports Server (NTRS)

Raitala, J.

1987-01-01

The tectonics of the Tharsis and adjoining areas is considered to be associated with the convection in the Martian mantle. Convection and mantle plume have been responsible for the primary uplift and volcanism of the Tharsis area. The radial compressional forces generated by the tendency for downslope movement of surface strata, vertical volcanic intrusions, and traction of mantle spreading beneath Tharsis were transmitted through the lithosphere to form peripheral mare ridge zones. The locations of mare ridges were thus mainly controlled by the Tharsis-radial compression. The load-induced stresses then contributed to further ridge formation over an extended period of time by the isostatic readjustment, which was responsible for long-term stresses in the adjoining areas. Extrusions, changes in internal temperature, and possible phase changes may also have caused changes in mantle volume, giving rise to additional compressional forces and crustal deformations.

Adakite petrogenesis

NASA Astrophysics Data System (ADS)

Castillo, Paterno R.

2012-03-01

Adakite was originally proposed as a genetic term to define intermediate to high-silica, high Sr/Y and La/Yb volcanic and plutonic rocks derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs. It was also initially believed that adakite only occurs in convergent margins where young and, thus, still hot oceanic slabs are being subducted. Currently, adakite covers a range of arc rocks ranging from primary slab melt, to slab melt hybridized by peridotite, to melt derived from peridotite metasomatized by slab melt. Adakites can occur in arc settings where unusual tectonic conditions can lower the solidi of even older slabs and their source also includes subducted sediments. Results of adakite studies have generated controversies due to (1) the specific genetic definition of adakite but its reliance on trace element chemistry for its distinguishing characteristics, (2) curious association of adakite with alkalic rocks enriched in high field-strength elements and Cu-Au mineral deposits and (3) existence of adakitic rocks produced through other petrogenetic processes. Other studies have shown that adakitic rocks and a number of the previously reported adakites are produced through melting of the lower crust or ponded basaltic magma, high pressure crystal fractionation of basaltic magma and low pressure crystal fractionation of water-rich basaltic magma plus magma mixing processes in both arc or non-arc tectonic environments. Thus, although adakite investigations enrich our understanding of material recycling and magmatic processes along convergent margins, economic deposits and crustal evolutionary processes, the term adakite should be used with extreme caution.

MaRGEE: Move and Rotate Google Earth Elements

NASA Astrophysics Data System (ADS)

Dordevic, Mladen M.; Whitmeyer, Steven J.

2015-12-01

Google Earth is recognized as a highly effective visualization tool for geospatial information. However, there remain serious limitations that have hindered its acceptance as a tool for research and education in the geosciences. One significant limitation is the inability to translate or rotate geometrical elements on the Google Earth virtual globe. Here we present a new JavaScript web application to "Move and Rotate Google Earth Elements" (MaRGEE). MaRGEE includes tools to simplify, translate, and rotate elements, add intermediate steps to a transposition, and batch process multiple transpositions. The transposition algorithm uses spherical geometry calculations, such as the haversine formula, to accurately reposition groups of points, paths, and polygons on the Google Earth globe without distortion. Due to the imminent deprecation of the Google Earth API and browser plugin, MaRGEE uses a Google Maps interface to facilitate and illustrate the transpositions. However, the inherent spatial distortions that result from the Google Maps Web Mercator projection are not apparent once the transposed elements are saved as a KML file and opened in Google Earth. Potential applications of the MaRGEE toolkit include tectonic reconstructions, the movements of glaciers or thrust sheets, and time-based animations of other large- and small-scale geologic processes.

Numerical Modeling of 3D Seismic Wave Propagation around Yogyakarta, the Southern Part of Central Java, Indonesia, Using Spectral-Element Method on MPI-GPU Cluster

NASA Astrophysics Data System (ADS)

Sudarmaji; Rudianto, Indra; Eka Nurcahya, Budi

2018-04-01

A strong tectonic earthquake with a magnitude of 5.9 Richter scale has been occurred in Yogyakarta and Central Java on May 26, 2006. The earthquake has caused severe damage in Yogyakarta and the southern part of Central Java, Indonesia. The understanding of seismic response of earthquake among ground shaking and the level of building damage is important. We present numerical modeling of 3D seismic wave propagation around Yogyakarta and the southern part of Central Java using spectral-element method on MPI-GPU (Graphics Processing Unit) computer cluster to observe its seismic response due to the earthquake. The homogeneous 3D realistic model is generated with detailed topography surface. The influences of free surface topography and layer discontinuity of the 3D model among the seismic response are observed. The seismic wave field is discretized using spectral-element method. The spectral-element method is solved on a mesh of hexahedral elements that is adapted to the free surface topography and the internal discontinuity of the model. To increase the data processing capabilities, the simulation is performed on a GPU cluster with implementation of MPI (Message Passing Interface).

It's "Your" Fault!: An Investigation into Earthquakes, Plate Tectonics, and Geologic Time

ERIC Educational Resources Information Center

Clary, Renee; Wandersee, James

2011-01-01

Earthquakes "have" been in the news of late--from the disastrous 2010 Haitian temblor that killed more than 300,000 people to the March 2011 earthquake and devastating tsunami in Honshu, Japan, to the unexpected August 2011 earthquake in Mineral, Virginia, felt from Alabama to Maine and as far west as Illinois. As expected, these events…

Alkaline magmatism in the Amambay area, NE Paraguay: The Cerro Sarambí complex

NASA Astrophysics Data System (ADS)

Gomes, C. B.; Velázquez, V. F.; Azzone, R. G.; Paula, G. S.

2011-07-01

The Early Cretaceous alkaline magmatism in the northeastern region of Paraguay (Amambay Province) is represented by stocks, plugs, dikes, and dike swarms emplaced into Carboniferous to Triassic-Jurassic sediments and Precambrian rocks. This magmatism is tectonically related to the Ponta Porã Arch, a NE-trending structural feature, and has the Cerro Sarambí and Cerro Chiriguelo carbonatite complexes as its most significant expressions. Other alkaline occurrences found in the area are the Cerro Guazú and the small bodies of Cerro Apuá, Arroyo Gasory, Cerro Jhú, Cerro Tayay, and Cerro Teyú. The alkaline rocks comprise ultramafic-mafic, syenitic, and carbonatitic petrographic associations in addition to lithologies of variable composition and texture occurring as dikes; fenites are described in both carbonatite complexes. Alkali feldspar and clinopyroxene, ranging from diopside to aegirine, are the most abundant minerals, with feldspathoids (nepheline, analcime), biotite, and subordinate Ti-rich garnet; minor constituents are Fe-Ti oxides and cancrinite as the main alteration product from nepheline. Chemically, the Amambay silicate rocks are potassic to highly potassic and have miaskitic affinity, with the non-cumulate intrusive types concentrated mainly in the saturated to undersaturated areas in silica syenitic fields. Fine-grained rocks are also of syenitic affiliation or represent more mafic varieties. The carbonatitic rocks consist dominantly of calciocarbonatites. Variation diagrams plotting major and trace elements vs. SiO 2 concentration for the Cerro Sarambí rocks show positive correlations for Al 2O 3, K 2O, and Rb, and negative ones for TiO 2, MgO, Fe 2O 3, CaO, P 2O 5, and Sr, indicating that fractional crystallization played an important role in the formation of the complex. Incompatible elements normalized to primitive mantle display positive spikes for Rb, La, Pb, Sr, and Sm, and negative for Nb-Ta, P, and Ti, as these negative anomalies are considerably more pronounced in the carbonatites. Chondrite-normalized REE patterns point to the high concentration of these elements and to the strong LRE/HRE fractionation. The Amambay rocks are highly enriched in radiogenic Sr and have TDM model ages that vary from 1.6 to 1.1 Ga, suggesting a mantle source enriched in incompatible elements by metasomatic events in Paleo-Mesoproterozoic times. Data are consistent with the derivation of the Cerro Sarambí rocks from a parental magma of lamprophyric (minette) composition and suggest an origin by liquid immiscibility processes for the carbonatites.

Geochemical, modal, and geochronologic data for 1.4 Ga A-type granitoid intrusions of the conterminous United States

USGS Publications Warehouse

du Bray, Edward A.; Holm-Denoma, Christopher S.; San Juan, Carma A.; Lund, Karen; Premo, Wayne R.; DeWitt, Ed

2015-08-10

In addition, Kisvarsanyi (1972) suggests that iron-copper deposits in the St. Francois Mountains of southeastern Missouri are petrogenetically associated with 1.4 Ga A-type granitoids that occur in that region. Similarly, Dall’Agnol and others (2012) summarize important global associations between A-type granitoid rocks and a variety of important ore deposit types, particularly tin, high-field-strength elements (Zr, Hf, Nb, Ta), rare-earth elements, and iron oxide-copper-gold deposits. Consequently, the need to better understand relations between A-type granitoid rocks, tectonic setting, and magma petrogenesis, as well as their genetic associations with important types of ore deposits, suggests that developing a definitive geochemical, modal, and geochronologic database for these rocks in the conterminous United States is of considerable value.

The Schlema-Alberoda five-element uranium deposit, Germany: An example of self-organizing hydrothermal system

NASA Astrophysics Data System (ADS)

Naumov, G. B.; Vlasov, B. P.; Golubev, V. N.; Mironova, O. F.

2017-01-01

As a result of integrating geological, mineralogical, and geochemical data on the unique Schlema-Alberoda five-element uranium deposit situated in Federal Republic of Germany and explored in detail down to a depth of 2 km, it has been shown that its formation for more than 100 Ma has been caused by combination of internal and external factors. The latter comprise favorable metallogenic specialization of the region, injection of intrusive bodies bearing the necessary stock of energy, and periodic pulses of tectonic reactivation. The internal factors of self-development involve evolutionary processes, which occur in host rocks at the consecutive stages of prograde and retrograde metamorphism giving rise to alteration of rocks in consistence with physical and chemical laws at variable temperature and degree of system opening.

Geology and geochemistry of the Arctic prospect, Ambler District, Alaska

NASA Astrophysics Data System (ADS)

Schmidt, J. M.

The Arctic volcanogenic massive sulfide prospect is the largest known (40 million ton) deposit hosted by the low greenschist grade, latest Devonian Ambler Sequence of bimodal, basaltic and rhyolitic volcanic and volcanoclastic rocks, pelitic, graphitic and calcareous metasediments. Detailed field mapping, core logging, petrography, X-ray diffractometry, electron microprobe analyses and whole-rock major element analyses of hydrothermally altered rocks were used to determine the emplacement history and setting of sulfide deposition. Low greenschist grade metamorphism was essentially isochemical on a macroscopic scale, and preserved volcanic compositions, the major element chemistry of alteration and the compositions of individual metamorphic, alteration and relict igneous minerals. Mineralization at Arctic was formed along a synvolcanic fault in a tectonically and volcanically active basin within a rifted continental margin, possibly related to an actively spreading oceanic rift.

Characterization of the Sukinda and Nausahi ultramafic complexes, Orissa, India by platinum-group element geochemistry

USGS Publications Warehouse

Page, N.J.; Banerji, P.K.; Haffty, J.

1985-01-01

Samples of 20 chromitite, 14 ultramafic and mafic rock, and 9 laterite and soil samples from the Precambrian Sukinda and Nausahi ultramafic complexes, Orissa, India were analyzed for platinum-group elements (PGE). The maximum concentrations are: palladium, 13 parts per billion (ppb); platinum, 120 ppb; rhodium, 21 ppb; iridium, 210 ppb; and ruthenium, 630 ppb. Comparison of chondrite-normalized ratios of PGE for the chromitite samples of lower Proterozoic to Archean age with similar data from Paleozoic and Mesozoic ophiolite complexes strongly implies that these complexes represent Precambrian analogs of ophiolite complexes. This finding is consistent with the geology and petrology of the Indian complexes and suggests that plate-tectonic and ocean basin developement models probably apply to some parts of Precambrian shield areas. ?? 1985.

Seismological and structural constraints on the 2011-2013, Mmax 4.6 seismic sequence at the south-eastern edge of the Calabrian arc (North-eastern Sicily, Italy)

NASA Astrophysics Data System (ADS)

Cammarata, Laura; Catalano, Stefano; Gambino, Salvatore; Palano, Mimmo; Pavano, Francesco; Romagnoli, Gino; Scaltrito, Antonio; Tortorici, Giuseppe

2018-01-01

Between June 2011 and September 2013, the Nebrodi Mountains region was affected by a seismic swarm consisting of > 2700 events with local magnitude 1.3 ≤ ML ≤ 4.6 and located in the 5-9 km depth interval. The seismic swarm defines a seismogenetic volume elongated along the E-W direction and encompasses the NW-SE-oriented tectonic boundary between the Calabrian arc (north-eastward) and the Sicilide units (south-westward). By exploring the recent tectonic deformation and the seismic behavior of the region, this study aims at providing additional constraints on the seismogenetic faults at the southern termination of the Calabrian arc. Waveform similarities analysis allowed observing that 45% of the whole dataset can be grouped into six different families of seismic events. Earthquake multiplet families are mainly located in the eastern part of the seismogenetic volume. We suggest that such a feature is responsive to the lateral lithological variations as highlighted by geology (at the surface) and P-wave seismic tomography (at depth of 10 km). Stress tensor inversions performed on FPSs indicate that the investigated region is currently subject to a nearly biaxial stress state in an extensional regime, such that crustal stretching occurs along both NW-SE and NE-SW directions. Accordingly, mesoscale fault geometries and kinematics analyses evidence that a younger normal faulting stress regime led to a tectonic negative inversion by replacing the pre-existing strike-slip one. Based on our results and findings reported in recent literature, we refer such a crustal stretching to mantle upwelling process (as evidenced by diffuse mantle-derived gas emissions) coupled with a tectonic uplift involving north-eastern Sicily since Middle Pleistocene. Moreover, seismic swarms striking the region would be related to the migration of mantle and sub-crustal fluids toward the surface along the complex network of tectonic structures cutting the crust and acting as pathways.

Devonian post-orogenic extension-related volcano-sedimentary rocks in the northern margin of the Tibetan Plateau, NW China: Implications for the Paleozoic tectonic transition in the North Qaidam Orogen

NASA Astrophysics Data System (ADS)

Qin, Yu; Feng, Qiao; Chen, Gang; Chen, Yan; Zou, Kaizhen; Liu, Qian; Jiao, Qianqian; Zhou, Dingwu; Pan, Lihui; Gao, Jindong

2018-05-01

The Maoniushan Formation in the northern part of the North Qaidam Orogen (NQO), NW China, contains key information on a Paleozoic change in tectonic setting of the NQO from compression to extension. Here, new zircon U-Pb, petrological, and sedimentological data for the lower molasse sequence of the Maoniushan Formation are used to constrain the timing of this tectonic transition. Detrital zircons yield U-Pb ages of 3.3-0.4 Ga with major populations at 0.53-0.4, 1.0-0.56, 2.5-1.0, and 3.3-2.5 Ga. The maximum depositional age of the Maoniushan Formation is well constrained by a youngest detrital zircon age of ∼409 Ma. Comparing these dates with geochronological data for the region indicates that Proterozoic-Paleozoic zircons were derived mainly from the NQO as well as the Oulongbuluk and Qaidam blocks, whereas Archean zircons were probably derived from the Oulongbuluk Block and the Tarim Craton. The ∼924, ∼463, and ∼439 Ma tectonothermal events recorded in this region indicate that the NQO was involved in the early Neoproterozoic assembly of Rodinia and early Paleozoic microcontinental convergence. A regional angular unconformity between Devonian and pre-Devonian strata within the NQO suggests a period of strong mountain building between the Oulongbuluk and Qaidam blocks during the Silurian, whereas an Early Devonian post-orogenic molasse, evidence of extensional collapse, and Middle to Late Devonian bimodal volcanic rocks and Carboniferous marine carbonate rocks clearly reflect long-lived tectonic extension. Based on these results and the regional geology, we suggest that the Devonian volcano-sedimentary rocks within the NQO were formed in a post-orogenic extensional setting similar to that of the East Kunlun Orogen, indicating that a major tectonic transition from compression to extension in these two orogens probably commenced in the Early Devonian.

Evidences of Neotectonic Movements Recorded in Fluvial and Lacustrine Deposits of the Niger River in Bamako, Mali

NASA Astrophysics Data System (ADS)

Dembele, N. D. J.

2015-12-01

Two alluvial profiles showing evidences of tectonic movements were discovered along the right bank of the Niger River at Bamako. The first profile of 25 meters thick is composed of a laminated silt layer of about 22 meters, of a gray sand layer of 25 cm and a pebble layer of 2 meters. A layer of 80 cm wide, an intrusive body, crosscuts the silt layers. The Grain size and heavy minerals analysis showed that this vertical layer is different in structure, texture and composition from the other layers. The second profile of about 20 meters is composed of interbedded fluvial gravel and sand deposits. The tectonic evidences found on those layers are of three types: faults and fractures, folds and the intrusion between silts deposits of the sand layers previously presented. The faults and fractures are located mainly on the fluvial gravel and sand deposits, whereas the silts deposits are folded and show some microfaults. The intrusion of a sand layer between the silt layer is a geological process that is not yet well understood but it is believed that this phenomena occurs during earthquakes as the sand layer during such event behave as a liquid. The discovery of such layer testifies that earthquakes used to happen in the area. As they concern only the alluvial deposits, their age should be no more than the Quaternary period. The presence of such tectonic evidences is surprising as Bamako like all the Republic of Mali is located on the west African craton that is supposed to be tectonically stable and their occurrence on Quaternary unconsolidated sediments shows that tectonic movements used to occur on that area during the last 2 millions years or may be less whereas people continue to build houses and other social infrastructures on them without any caution.

Crustal structure of the southeastern Brazilian margin, Campos Basin, from aeromagnetic data: New kinematic constraints

NASA Astrophysics Data System (ADS)

Stanton, N.; Schmitt, R.; Galdeano, A.; Maia, M.; Mane, M.

2010-07-01

The continental and adjacent marginal features along southeast Brazil were investigated, focusing on the basement structural relationships between onshore and offshore provinces. Lateral and vertical variations in the magnetic anomalies provided a good correlation with the regional tectonic features. The sin-rift dykes and faults are associated with the magnetic lineaments and lie sub parallel to the Precambrian N45E-S45W basement structure of the Ribeira Belt, but orthogonally to the Cabo Frio Tectonic Domain (CFTD) basement, implying that: (1) the upper portion of the continental crust was widely affected by Mesozoic extensional deformation; and (2) tectonic features related to the process of break up of the Gondwana at the CFTD were form regardless of the preexisting structural basement orientation being controlled by the stress orientation during the rift phase. The deep crustal structure (5 km depth) is characterized by NE-SW magnetic "provinces" related to the Ribeira Belt tectonic units, while deep suture zones are defined by magnetic lows. The offshore Campos structural framework is N30E-S30W oriented and resulted from a main WNW-ESE direction of extension in Early Cretaceous. Transfer zones are represented by NW-SE and E-W oriented discontinuities. A slight difference in orientation between onshore (N45E) and offshore (N30E) structural systems seems to reflect a re-orientation of stress during rifting. We proposed a kinematical model to explain the structural evolution of this portion of the margin, characterized by polyphase rifting, associated with the rotation of the South American plate. The Campos Magnetic High (CMH), an important tectonic feature of the Campos Basin corresponds to a wide area of high crustal magnetization. The CMH wass interpreted as a magmatic feature, mafic to ultramafic in composition that extends down to 14 km depth and constitutes an evidence of intense crustal extension at 60 km from the coast.

Seismic stratigraphy, tectonics and depositional history in the Halk el Menzel region, NE Tunisia

NASA Astrophysics Data System (ADS)

Sebei, Kawthar; Inoubli, Mohamed Hédi; Boussiga, Haïfa; Tlig, Said; Alouani, Rabah; Boujamaoui, Mustapha

2007-01-01

In the Halk el Menzel area, the proximal- to pelagic platform transition and related tectonic events during the Upper Cretaceous-Lower Miocene have not been taken into adequate consideration. The integrated interpretation of outcrop and subsurface data help define a seismic stratigraphic model and clarify the geodynamic evolution of the Halk el Menzel block. The sedimentary column comprises marls and limestones of the Campanian to Upper Eocene, overlain by Oligocene to Lower Miocene aged siliciclastics and carbonates. Well to well correlations show sedimentary sequences vary considerably in lithofacies and thicknesses over short distances with remarkable gaps. The comparison of sedimentary sequences cut by borehole and seismic stratigraphic modelling as well help define ten third order depositional sequences (S1-S10). Sequences S1 through S6 (Campanian-Paleocene) are mainly characterized by oblique to sigmoid configurations with prograding sedimentary structures, whereas, sequences S7-S10 (Ypresian to Middle Miocene) are organized in shallow water deposits with marked clinoform ramp geometry. Sedimentary discontinuities developed at sequence boundaries are thought to indicate widespread fall in relative sea level. Angular unconformities record a transpressive tectonic regime that operated from the Campanian to Upper Eocene. The geometry of sequences with reduced thicknesses, differential dipping of internal seismic reflections and associated normal faulting located westerly in the area, draw attention to a depositional sedimentary system developed on a gentle slope evolving from a tectonically driven steepening towards the Northwest. The seismic profiles help delimit normal faulting control environments of deposition. In contrast, reef build-ups in the Eastern parts occupy paleohighs NE-SW in strike with bordering Upper Maastrichtian-Ypresian seismic facies onlapping Upper Cretaceous counterparts. During the Middle-Upper Eocene, transpressive stress caused reactivation of faults from normal to reverse play. This has culminated in propagation folds located to the west; whereas, the eastern part of the block has suffered progressive subsidence. Transgressive carbonate depositional sequences have predominated during the Middle Miocene and have sealed pre-existing tectonic structures.

Incorporation of New and Old Tectonics Concepts Into a Modern Course in Tectonics.

ERIC Educational Resources Information Center

Hatcher, Robert D., Jr.

1983-01-01

Describes a graduate-level tectonics course which includes the historical basis for modern tectonics concepts and an in-depth review of pros/cons of plate tectonics. Tectonic features discussed include: ocean basins; volcanic arcs; continental margins; continents; orogenic belts; foreland fold and thrust belts; volcanic/plutonic belts of orogens;…

Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

NASA Astrophysics Data System (ADS)

Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

2017-04-01

The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly reflects basic frame work of the regional crust structure. The earth's crust basically present three layer structure, nearly horizontally distributes, undulation of Moho is obvious, which is consistent with the results of seismic sounding and seismic array detection; in the local area, there are lower density layer zonal distribution in the earth's crust what accelerates the lateral movement in up and middle crust; when the substance of the Tibetan plateau spreads around, the integrity in up and middle crust is well, and it is basically a coupling movement together; in the lower crust, the thickness of the Tibetan plateau is outward gradually thinning, there is decoupling phenomenon in crust-mantle; The results of the gravity and the crustal density structure show that the research area can be divided into several part such as Qinghai-Tibet Plateau, Sichuan-Yunnan block, Ordos block and Alxa block, the transitional zones of the Qinghai-Tibet Plateau and Sichuan basin, and Alxa and Ordos are complex, and Moho slope is bigger, where is the part of strong tectonic activity and strong earthquakes occur easily. The research is of great significance for study the crustal deep structure, geodynamic evolution process and environment of earthquake gestation of the NSSB region.

The Use of Multi-Component Statistical Techniques in Understanding Subduction Zone Arc Granitic Geochemical Data Sets

NASA Astrophysics Data System (ADS)

Pompe, L.; Clausen, B. L.; Morton, D. M.

2015-12-01

Multi-component statistical techniques and GIS visualization are emerging trends in understanding large data sets. Our research applies these techniques to a large igneous geochemical data set from southern California to better understand magmatic and plate tectonic processes. A set of 480 granitic samples collected by Baird from this area were analyzed for 39 geochemical elements. Of these samples, 287 are from the Peninsular Ranges Batholith (PRB) and 164 from part of the Transverse Ranges (TR). Principal component analysis (PCA) summarized the 39 variables into 3 principal components (PC) by matrix multiplication and for the PRB are interpreted as follows: PC1 with about 30% of the variation included mainly compatible elements and SiO2 and indicates extent of differentation; PC2 with about 20% of the variation included HFS elements and may indicate crustal contamination as usually identified by Sri; PC3 with about 20% of the variation included mainly HRE elements and may indicate magma source depth as often diplayed using REE spider diagrams and possibly Sr/Y. Several elements did not fit well in any of the three components: Cr, Ni, U, and Na2O.For the PRB, the PC1 correlation with SiO2 was r=-0.85, the PC2 correlation with Sri was r=0.80, and the PC3 correlation with Gd/Yb was r=-0.76 and with Sr/Y was r=-0.66 . Extending this method to the TR, correlations were r=-0.85, -0.21, -0.06, and -0.64, respectively. A similar extent of correlation for both areas was visually evident using GIS interpolation.PC1 seems to do well at indicating differentiation index for both the PRB and TR and correlates very well with SiO2, Al2O3, MgO, FeO*, CaO, K2O, Sc, V, and Co, but poorly with Na2O and Cr. If the crustal component is represented by Sri, PC2 correlates well and less expesively with this indicator in the PRB, but not in the TR. Source depth has been related to the slope on REE spidergrams, and PC3 based on only the HREE and using the Sr/Y ratios gives a reasonable correlation for both PRB and TR, but the Gd/Yb ratio gives a reasonable correlation for only the PRB. The PRB data provide reasonable correlation between principal components and standard geochemical indicators, perhaps because of the well-recognized monotonic variation from SW to NE. Data sets from the TR give similar results in some cases, but poor correlation in others.

Active tectonics around the Yakutat indentor: New geomorphological constraints on the eastern Denali, Totschunda and Duke River Faults

NASA Astrophysics Data System (ADS)

Marechal, Anaïs; Ritz, Jean-François; Ferry, Matthieu; Mazzotti, Stephane; Blard, Pierre-Henri; Braucher, Régis; Saint-Carlier, Dimitri

2018-01-01

The Yakutat collision in SE Alaska - SW Yukon is an outstanding example of indentor tectonics. The impinging Yakutat block strongly controls the pattern of deformation inland. However, the relationship between this collision system and inherited tectonic structures such as the Denali, Totschunda, and Duke River Faults remains debated. A detailed geomorphological analysis, based on high-resolution imagery, digital elevation models, field observations, and cosmogenic nuclide dating, allow us to estimate new slip rates along these active structures. Our results show a vertical motion of 0.9 ± 0.3 mm/yr along the whole eastern Denali Fault, while the dextral component of the fault tapers to less than 1 mm/yr ∼80 km south of the Denali-Totschunda junction. In contrast, the Totschunda Fault accommodates 14.6 ± 2.7 mm/yr of right-lateral strike-slip along its central section ∼100 km south of the junction. Further south, preliminary observations suggest a slip rate comprised between 3.5 and 6.5 mm/yr along the westernmost part of the Duke River thrust fault. Our results highlight the complex partitioning of deformation inland of the Yakutat collision, where the role and slip rate of the main faults vary significantly over distances of ∼100 km or less. We propose a schematic model of present-day tectonics that suggests ongoing partitioning and reorganization of deformation between major inherited structures, relay zones, and regions of distributed deformation, in response to the radial stress and strain pattern around the Yakutat collision eastern syntaxis.

Global Models of Ridge-Push Force, Geoid, and Lithospheric Strength of Oceanic plates

NASA Astrophysics Data System (ADS)

Mahatsente, Rezene

2017-12-01

An understanding of the transmission of ridge-push related stresses in the interior of oceanic plates is important because ridge-push force is one of the principal forces driving plate motion. Here, I assess the transmission of ridge-push related stresses in oceanic plates by comparing the magnitude of the ridge-push force to the integrated strength of oceanic plates. The strength is determined based on plate cooling and rheological models. The strength analysis includes low-temperature plasticity (LTP) in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from the thermal state of oceanic lithosphere, seafloor depth and crustal age data. The results of modeling show that the transmission of ridge-push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions. If a lithosphere has dry rheology, the estimated strength is higher than the ridge-push force at all ages for compressional tectonics and at old ages (>75 Ma) for extension. Therefore, under such conditions, oceanic plates may not respond to ridge-push force by intraplate deformation. Instead, the plates may transmit the ridge-push related stress in their interior. For a wet rheology, however, the strength of young lithosphere (<75 Ma) is much less than the ridge-push force for both compressional and extensional tectonics. In this case, the ridge-push related stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation. The state of stress within a plate depends on the balance of far-field and intraplate forces.

Impact of Neotectonic activities on coral reef Red Sea Egypt; Case study Jubal Island

NASA Astrophysics Data System (ADS)

Hamouda, A.

2016-12-01

Abstract:The Red Sea considered the youngest oceanic basin of the world. It separates the Arabian sub-plate from the African plate. Neotectonic activity is a fundamental issue at the northern Red Sea for our understanding of the tectonic hazards at this region. The tectonic activity research will thus be geared to understand how a single tectonic process works and how a group of processes work together as a part of larger system ultimately leading to the formation of mountain systems and evolution of the solid earth. The recent seismic activity in the northern Red Sea has been impact on surface geology and coral reef. The most major earthquake swarm sequence around Jubal Island is the migration of epicenters northward in diameter circle about 50 km with focal depths less than 2 to 15 km. This swarm may release energy that can be accumulated to cause larger events in the future. This affects the accumulation of oil and gas reservoir causing natural seepage on the seafloor. The main aim of this study represents the impact of this seepage which is related to tectonic activity on the coral reef states at the northern part of Red Sea. The greatest impact of crude oil on marine organisms are categorized as: direct lethal toxicity, sub-lethal disruption of physiological behavioral activities, effects of direct coating, incorporation of hydrocarbons and alteration of habitat, especially substrate character. Adult marine organisms may exhibit lethal toxic and Sub-lethal effects from exposures to soluble aromatic derivative hydrocarbons. Keywords: Neotectonic activity, earthquakes, hydrocarbon seepage, coral reef, Red Sea.

Permeability changes induced by microfissure closure and opening in tectonized materials. Effect on slope pore pressure regime.

NASA Astrophysics Data System (ADS)

De la Fuente, Maria; Vaunat, Jean; Pedone, Giuseppe; Cotecchia, Federica; Sollecito, Francesca; Casini, Francesca

2015-04-01

Tectonized clays are complex materials characterized by several levels of structures that may evolve during load and wetting/drying processes. Some microstructural patterns, as microfissures, have a particular influence on the value of permeability which is one of the main factors controlling pore pressure regime in slopes. In this work, the pore pressure regime measured in a real slope of tectonized clay in Southern Italy is analyzed by a numerical model that considers changes in permeability induced by microfissure closure and opening during the wetting and drying processes resulting from climatic actions. Permeability model accounts for the changes in Pore Size Distribution observed by Microscopy Intrusion Porosimetry. MIP tests are performed on representative samples of ground in initial conditions ("in situ" conditions) and final conditions (deformed sample after applying a wetting path that aims to reproduce the saturation of the soil under heavy rains). The resulting measurements allow for the characterization at microstructural level of the soil, identifying the distribution of dominant families pores in the sample and its evolution under external actions. Moreover, comparison of pore size density functions allows defining a microstructural parameter that depends on void ratio and degree of saturation and controls the variation of permeability. Model has been implemented in a thermo-hydro-mechanical code provided with a special boundary condition for climatic actions. Tool is used to analyze pore pressure measurements obtained in the tectonized clay slope. Results are analyzed at the light of the effect that permeability changes during wetting and drying have on the pore pressure regime.

Age and geochemistry of Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Luan, Jin-Peng; Xu, Wen-Liang; Wang, Feng; Wang, Zhi-Wei; Guo, Peng

2017-10-01

This study presents new zircon U-Pb ages and geochemical data for Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif (SZRM) of NE China. This dataset provides insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent. The zircon U-Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages: (1) a ∼917-911 Ma suite of syenogranites and monzogranites, and (2) an ∼841 Ma suite of granodiorites. The 917-911 Ma granitoids contain high concentrations of SiO2 (67.89-71.18 wt.%), K2O (4.24-6.91 wt.%), and Al2O3 (14.89-16.14 wt.%), and low concentrations of TFe2O3 (1.63-3.70 wt.%) and MgO (0.53-0.88 wt.%). They are enriched in the light rare earth elements (LREE) and the large ion lithophile elements (LILE), are depleted in the heavy REE (HREE) and the high field strength elements (HFSE; e.g., Nb, Ta, and Ti), and have slightly positive Eu anomalies, indicating that they are geochemically similar to high-K adakitic rocks. They have zircon εHf (t) values and TDM2 ages from -4.4 to +1.5 and 1915 Ma to 1592 Ma, respectively, suggesting that they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material. In comparison, the 841 Ma granodiorites contain relatively low concentrations of Al2O3 (14.50-14.58 wt.%) and K2O (3.27-3.29 wt.%), relatively high concentrations of TFe2O3 (3.78-3.81 wt.%) and the HREE, have negative Eu anomalies, and have zircon εHf (t) values and TDM2 ages from -4.7 to +1.0 and 1875 to 1559 Ma, respectively. These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material. The ∼917-911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting, whereas the ∼841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic continental rifting. It is proposed that the microcontinental massifs within the eastern central Asian orogenic belt of NE China formed during or following the final stage of assembly of Rodinia before rifting away from the Tarim Craton in response to the Rodinia breakup.

Fluvial geomorphic elements in modern sedimentary basins and their potential preservation in the rock record: A review

NASA Astrophysics Data System (ADS)

Weissmann, G. S.; Hartley, A. J.; Scuderi, L. A.; Nichols, G. J.; Owen, A.; Wright, S.; Felicia, A. L.; Holland, F.; Anaya, F. M. L.

2015-12-01

Since tectonic subsidence in sedimentary basins provides the potential for long-term facies preservation into the sedimentary record, analysis of geomorphic elements in modern continental sedimentary basins is required to understand facies relationships in sedimentary rocks. We use a database of over 700 modern sedimentary basins to characterize the fluvial geomorphology of sedimentary basins. Geomorphic elements were delineated in 10 representative sedimentary basins, focusing primarily on fluvial environments. Elements identified include distributive fluvial systems (DFS), tributive fluvial systems that occur between large DFS or in an axial position in the basin, lacustrine/playa, and eolian environments. The DFS elements include large DFS (> 30 km in length), small DFS (< 30 km in length), coalesced DFS in bajada or piedmont plains, and incised DFS. Our results indicate that over 88% of fluvial deposits in the evaluated sedimentary basins are present as DFS, with tributary systems covering a small portion (1-12%) of the basin. These geomorphic elements are commonly arranged hierarchically, with the largest transverse rivers forming large DFS and smaller transverse streams depositing smaller DFS in the areas between the larger DFS. These smaller streams commonly converge between the large DFS, forming a tributary system. Ultimately, most transverse rivers become tributary to the axial system in the sedimentary basin, with the axial system being confined between transverse DFS entering the basin from opposite sides of the basin, or a transverse DFS and the edge of the sedimentary basin. If axial systems are not confined by transverse DFS, they will form a DFS. Many of the world's largest rivers are located in the axial position of some sedimentary basins. Assuming uniformitarianism, sedimentary basins from the past most likely had a similar configuration of geomorphic elements. Facies distributions in tributary positions and those on DFS appear to display specific morphologic patterns. Tributary rivers tend to increase in size in the downstream direction. Because axial tributary rivers are present in confined settings in the sedimentary basin, they migrate back and forth within a relatively narrow belt (relative to the overall size of the sedimentary basin). Thus, axial tributary rivers tend to display amalgamated channel belt form with minimal preservation potential of floodplain deposits. Chute and neck cutoff avulsions are also common on meandering rivers in these settings. Where rivers on DFS exit their confining valley on the basin margin, sediment transport capacity is reduced and sediment deposition occurs resulting in development of a 'valley exit' nodal avulsion point that defines the DFS apex. Rivers may incise downstream of the basin margin valley because of changes in sediment supply and discharge through climatic variability or tectonic processes. We demonstrate that rivers on DFS commonly decrease in width down-DFS caused by infiltration, bifurcation, and evaporation. In proximal areas, channel sands are amalgamated through repeated avulsion, reoccupation of previous channel belts, and limited accumulation space. When rivers flood on the medial to distal portions of a DFS, the floodwaters spread across a large area on the DFS surface and typically do not re-enter the main channel. In these distal areas, rivers on DFS commonly avulse, leaving a discrete sand body and providing high preservation potential for floodplain deposits. Additional work is needed to evaluate the geomorphic character of modern sedimentary basins in order to construct improved facies models for the continental sedimentary rock record. Specifically, models for avulsion, bifurcation, infiltration, and geomorphic form on DFS are required to better define and subsequently predict facies geometries. Studies of fluvial systems in sedimentary basins are also important for evaluating flood patterns and groundwater distributions for populations in these regions.

Subduction and exhumation of a continental margin in the Scandinavian Caledonides: Insights from ultrahigh pressure metamorphism, late orogenic basins and 3D numerical modelling

NASA Astrophysics Data System (ADS)

Cuthbert, Simon

2017-04-01

The Scandinavian Caledonides (SC) represents a plate collision zone of Himalayan style and scale. Three fundamental characteristics of this orogen are: (1) early foreland-directed, tectonic transport and stacking of nappes; (2) late, wholesale reversal of tectonic transport; (3) ultrahigh pressure metamorphism of felsic crust derived from the underthrusting plate at several levels in the orogenic wedge and below the main thrust surface, indicating subduction of continental crust into the mantle. The significance of this for crustal evolution is the profound remodeling of continental crust, direct geochemical interaction of such crust and the mantle and the opening of accommodation space trapping large volumes of clastic detritus within the orogen. The orogenic wedge of the SC was derived from the upper crust of the Baltica continental margin (a hyper-extended passive margin), plus terranes derived from an assemblage of outboard arcs and intra-oceanic basins and, at the highest structural level, elements of the Laurentian margin. Nappe emplacement was driven by Scandian ( 430Ma) collision of Baltica with Laurentia, but emerging Middle Ordovician ages for diamond-facies metamorphism for the most outboard (or rifted) elements of Baltica suggest prior collision with an arc or microcontinent. Nappes derived from Baltica continental crust were subducted, in some cases to depths sufficient to form diamond. These then detached from the upper part of the down-going plate along major thrust faults, at which time they ceased to descend and possibly rose along the subduction channel. Subduction of the remaining continental margin continued below these nappes, possibly driven by slab-pull of the previously subducted Iapetus oceanic lithosphere and metamorphic densification of subducted felsic continental margin. 3D numerical modelling based upon a Caledonide-like plate scenario shows that if a continental corner or promontory enters the subduction zone, the continental margin descends to greater depths than for a simple orthogonal collision and its modelled thermal evolution is consistent with UHP metamorphic assemblages recorded in the southern part of the SC. Furthermore, a tear initiates at the promontary tip along the ocean-continent junction and propagates rapidly along the orogen. The buoyant upthrust of the subducted margin can then lead to reversal of the motion vector of the entire subducting continent, which withdraws the subducted lithospheric margin out of the subduction channel ("eduction"). Because of the diachroneity of slab failure, the continent also rotates, which causes the eduction vector to change azimuth over time. These model behaviours are consistent with the late orogenic structural evolution of the southern SC. However, during the final exhumation stage the crust may not have acted entirely coherently, as some eduction models propose: There is evidence that some inboard Baltica crust experienced late, shallow subduction before detaching as giant "flakes" that carried the orogenic wedge piggyback, forelandwards. Eduction and flake-tectonics could have operated coevally; the model system does not preclude this. Finally, the traction of a large educting (or extruding) mass of continental margin against the overlying orogenic wedge may have stretched and ruptured the wedge, resulting in opening of the late-orogenic Old Red Sandstone molasse basins.

Petrogenesis and tectonic implications of Late Carboniferous A-type granites and gabbronorites in NW Iran: Geochronological and geochemical constraints

NASA Astrophysics Data System (ADS)

Moghadam, Hadi Shafaii; Li, Xian-Hua; Ling, Xiao-Xiao; Stern, Robert J.; Santos, Jose F.; Meinhold, Guido; Ghorbani, Ghasem; Shahabi, Shirin

2015-01-01

Carboniferous igneous rocks constitute volumetrically minor components of Iranian crust but preserve important information about the magmatic and tectonic history of SW Asia. Ghushchi granites and gabbronorites in NW Iran comprise a bimodal magmatic suite that intruded Ediacaran-Cambrian gneiss and are good representatives of carboniferous igneous activity. Precise SIMS U-Pb zircon ages indicate that the gabbronorites and granites were emplaced synchronously at ~ 320 Ma. Ghushchi granites show A-type magmatic affinities, with typical enrichments in alkalis, Ga, Zr, Nb and Y, depletion in Sr and P and fractionated REE patterns showing strong negative Eu anomalies. The gabbronorites are enriched in LREEs, Nb, Ta and other incompatible trace elements, and are similar in geochemistry to OIB-type rocks. Granites and gabbronorites have similar εNd(t) (+ 1.3 to + 3.4 and - 0.1 to + 4.4, respectively) and zircon εHf(t) (+ 1.7 to + 6.2 and + 0.94 to + 6.5, respectively). The similar variation in bulk rock εNd(t) and zircon εHf(t) values and radiometric ages for the granites and gabbronorites indicate a genetic relationship between mafic and felsic magmas, either a crystal fractionation or silicate liquid immiscibility process; further work is needed to resolve petrogenetic details. The compositional characteristics of the bimodal Ghushchi complex are most consistent with magmatic activity in an extensional tectonic environment. This extension may have occurred during rifting of Cadomian fragments away from northern Gondwana during early phases of Neotethys opening.

Sand fairway mapping as a tool for tectonic restoration in orogenic belts

NASA Astrophysics Data System (ADS)

Butler, Rob

2016-04-01

The interplay between regional subsidence mechanisms and local deformation associated with individual fold-thrust structures is commonly investigated in neotectonic subaerial systems using tectonic geomorphology. Taking these approaches back into the early evolution of mountain belts is difficult as much of the key evidence is lost through erosion. The challenge is to develop appropriate tools for investigating these early stages of orogenesis. However, many such systems developed under water. In these settings the connections between regional and local tectonics are manifest in complex bathymetry. Turbidity currents flowing between and across these structures will interact with their substrate and thus their deposits, tied to stratigraphic ages, can chart tectonic evolution. Understanding the depositional processes of the turbidity currents provides substantial further insight on confining seabed geometry and thus can establish significant control on the evolution of bathymetric gradients and continuity through basins. However, reading these records commonly demands working in structurally deformed terrains that hitherto have discouraged sedimentological study. This is now changing. Sand fairway mapping provides a key approach. Fairway maps chart connectivity between basins and hence their relative elevation through time. Larger-scale tectonic reconstructions may be tested by linking fairway maps to sand composition and other provenance data. More detailed turbidite sedimentology provides substantial further insight. In confined turbidite systems, it is the coarser sand component that accumulates in the deeper basin with fines fractionated onto the flanks. Flow bypass, evidenced by abrupt breaks in grading within individual event beds, can be used to predict sand fraction distribution down fairways. Integrating sedimentology into fairway maps can chart syntectonic slope evolution and thus provide high resolution tools equivalent to those in subaerial tectonic geomorphology. The stratigraphic records are preserved in many parts of the Alpine-Mediterranean region. Examples are drawn from the Eo-Oligocene of the western Alps and the early Miocene of the Maghreb-Apennine system to illustrate how turbidite sedimentology, linked to studies of basin structure, can inform understanding of tectonic processes on regional and local scales. In both examples, sediment was delivered across deforming basin arrays containing contractional structures, sourced from beyond the immediate orogenic segments. The depositional systems show that multiple structures were active in parallel, rather than develop in any particular sequence. Both systems show that significant deformation occurs, emerging to the syn-orogenic surface ahead of the main orogenic wedge. The cycling of uplift and subsidence of "massifs" can be significantly more complex that the histories resolved from thermochronological data alone.

Generation of felsic crust in the Archean: a geodynamic modeling perspective

NASA Astrophysics Data System (ADS)

Sizova, Elena; Gerya, Taras; Stüwe, Kurt; Brown, Michael

2015-04-01

The relevance of contemporary tectonics to the formation of the Archean terrains is a matter of vigorous debate. Higher mantle temperatures and higher radiogenic heat production in the past would have impacted on the thickness and composition of the oceanic and continental crust. As a consequence of secular cooling, there is generally no modern analog to assist in understanding the tectonic style that may have operated in the Archean. For this reason, well-constrained numerical modeling, based on the fragmentary evidence preserved in the geological record, is the most appropriate tool to evaluate hypotheses of Archean crust formation. The main lithology of Archean terrains is the sodic tonalite-trondhjemite-granodiorite (TTG) suite. Melting of hydrated basalt at garnet-amphibolite to eclogite facies conditions is considered to be the dominant process for the generation of the Archean TTG crust. Taking into account geochemical signatures of possible mantle contributions to some TTGs, models proposed for the formation of Archean crust include subduction, melting at the bottom of thickened continental crust and fractional crystallization of mantle-derived melts under water-saturated conditions. We evaluated these hypotheses using a 2D coupled petrological-thermomechanical numerical model with initial conditions appropriate to the Eoarchean-Mesoarchean. As a result, we identified three tectonic settings in which intermediate to felsic melts are generated by melting of hydrated primitive basaltic crust: 1) delamination and dripping of the lower primitive basaltic crust into the mantle; 2) local thickening of the primitive basaltic crust; and, 3) small-scale crustal overturns. In addition, we consider remelting of the fractionated products derived from underplated dry basalts as an alternative mechanism for the formation of some Archean granitoids. In the context of a stagnant lid tectonic regime which is intermittently terminated by short-lived subduction, we identified two distinct types of continent crust. The first type is a pristine granite-greenstone-like crust with dome-and-keel geometry formed over delaminating-upwelling mantle which is mostly subjected to vertical tectonics processes. By contrast, the second type is a reworked (accreted) crust comprising strongly deformed granite-greenstone and subduction-related sequences and subjected to both strong horizontal compression and vertical tectonics processes. Thus, our study has identified a possible spatial and temporal transition from the lower-grade granite-greenstone terrains to higher-grade gneiss terrains in the Archean as each tectonic cycle is terminated by short-lived subduction. We suggest that the contemporaneity of the proposed mechanisms for the generation of TTGs explains the variety and complexity of the Archean geological record.

Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin

USGS Publications Warehouse

Liu, M.; Mooney, W.D.; Li, S.; Okaya, N.; Detweiler, S.

2006-01-01

The 1000-km-long Darlag-Lanzhou-Jingbian seismic refraction profile is located in the NE margin of the Tibetan plateau. This profile crosses the northern Songpan-Ganzi terrane, the Qinling-Qilian fold system, the Haiyuan arcuate tectonic region, and the stable Ordos basin. The P-wave and S-wave velocity structure and Poisson's ratios reveal many significant characteristics in the profile. The crustal thickness increases from northeast to southwest. The average crustal thickness observed increases from 42??km in the Ordos basin to 63??km in the Songpan-Ganzi terrane. The crust becomes obviously thicker south of the Haiyuan fault and beneath the West-Qinlin Shan. The crustal velocities have significant variations along the profile. The average P-wave velocities for the crystalline crust vary between 6.3 and 6.4??km/s. Beneath the Songpan-Ganzi terrane, West-Qinling Shan, and Haiyuan arcuate tectonic region P-wave velocities of 6.3??km/s are 0.15??km/s lower than the worldwide average of 6.45??km/s. North of the Kunlun fault, with exclusion of the Haiyuan arcuate tectonic region, the average P-wave velocity is 6.4??km/s and only 0.5??km/s lower than the worldwide average. A combination of the P-wave velocity and Poisson's ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base. A mafic lower crust is absent in the NE margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin. There are low velocity zones in the West-Qinling Shan and the Haiyuan arcuate tectonic region. The low velocity zones have low S-wave velocities and high Poisson's ratios, so it is possible these zones are due to partial melting. The crust is divided into two layers, the upper and the lower crust, with crustal thickening mainly in the lower crust as the NE Tibetan plateau is approached. The results in the study show that the thickness of the lower crust increases from 22 to 38??km as the crustal thickness increases from 42??km in the Ordos basin to 63??km in the Songpan-Ganzi terrane south of the Kunlun fault. Both the Conrad discontinuity and Moho in the West-Qinling Shan and in the Haiyuan arcuate tectonic region are laminated interfaces, implying intense tectonic activity. The arcuate faults and large earthquakes in the Haiyuan arcuate tectonic region are the result of interaction between the Tibetan plateau and the Sino-Korean and Gobi Ala Shan platforms. ?? 2006.

Mantle structure and tectonic history of SE Asia

NASA Astrophysics Data System (ADS)

Hall, Robert; Spakman, Wim

2015-09-01

Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs that detached in the Early Miocene such as the Sula slab, now found in the lower mantle north of Lombok, and the Proto-South China Sea slab now at depths below 700 km curving from northern Borneo to the Philippines. Based on our tectonic model we interpret virtually all features seen in upper mantle and lower mantle to depths of at least 1200 km to be the result of Cenozoic subduction.

The imprint of Late Holocene tectonic reactivation on a megafan landscape in the northern Amazonian wetlands

NASA Astrophysics Data System (ADS)

Rossetti, D. F.; Valeriano, M. M.; Gribel, R.; Cohen, M. C. L.; Tatumi, S. H.; Yee, M.

2017-10-01

The modern Amazonian ecosystem outcomes from the complex interplay of different factors performed over the geological history, with tectonics being long speculated as perhaps a fundamental one. Nevertheless, areas where tectonic activity can be fully characterized are still scarce in view of the large dimension of this region. In this work, we investigate the signature of neotectonics in one megafan paleolandform that typifies a large sector of the Negro-Branco basin in northern Amazonia. The approach joined regional morphostructural descriptions of the Viruá megafan surface and the acquisition of topographic, sedimentological, and chronological data focusing on the central sector of the megafan. The results revealed an abundance of rivers that form dendritic, subdendritic, and trellis patterns. These rivers also have numerous straight segments, orthogonal junctions, and orthogonal shifts in courses. Structural lineaments, defined by straight channels and also straight lake margins, are aligned along the NW-SE and NE-SW directions that are coincidental with the main regional structural pattern in Amazonia. This study also led to recognize two large areas of lower topography in the south-central part of the megafan that consist of rectangular depressions parallel to the morphostructural lineaments. A sedimentological survey indicated that cores extracted external to the largest depression have only distributary channel and overbank sand sheet megafan deposits. Optically stimulated luminescence (OSL) ages ranged from 17.5 ± 2.0 to 46.9 ± 3.4 ky and radiocarbon ages ranged from 5.9-5.7 to 20.1-19.6 cal ky BP. In contrast, cores extracted within the depression consisted of fluvial deposits younger than 2.1-1.9 cal ky BP that increased in thickness toward the central part of the depression. We propose that the studied megafan was affected by tectonic reactivation until at least a couple thousand years ago. Tectonics would have produced subsiding areas more prone to flooding than adjacent terrains, which constituted sites for renewed deposition of fluvial sediments reworked from the megafan surface following its abandonment. A comparison of our data with those from other Amazonian areas with similar records of late Holocene tectonics suggests a landscape imprinted by faulting, probably of strike-slip motion. This finding increases the record of neotectonic activity in the Amazonian wetlands and may be useful in studies aiming at discussing the origin and extension of late Holocene deformation in the South American intraplate. In addition, we present a megafan with an unusual development in a cratonic region under the combined effect of climate and tectonics.