Science.gov

Sample records for alpine tectonic evolution

  1. Complex tectonic and tectonostratigraphic evolution of an Alpine foreland basin: The western Duero Basin and the related Tertiary depressions of the NW Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Martín-González, F.; Heredia, N.

    2011-04-01

    The tectonic and tectonostratigaphic evolution of foreland basins and related Tertiary depressions are the key to investigate deformation history and the uplifting of the continental lithosphere of the Alpine-Pyrenean Orogeny. The northern part of the Duero basin is the foreland basin of the Cantabrian Mountains, which are, in turn, the western part of the Pyrenean Orogen. We have studied the western sharp end of the Duero foreland basin, and its relation to the Tertiary deposits of the NW Iberian Peninsula and the topography evolution. In order to propose a coherent tectonic and tectonosedimentary model that could explain all Tertiary deposits, we have analysed the depositional environment, stratigraphic sequences, paleocurrents and established a correlation of the main outcrops. Besides, a detailed structural mapping of the Alpine structures that limit and affect the main Tertiary outcrops has been carried out. The Tertiary deposits of the NW Iberian Peninsula depressions are affected and fragmented by Alpine structures that limit their extensions and locations. The stratigraphic succession is similar in the NW Tertiary outcrops; they are mainly terrigenous and carbonated continental deposits formed by assemblage of alluvial fans developed at the mountains front, in arid or semiarid conditions. Three formations can be identified in the main depressions: Toral Fm, Santalla Fm and Médulas Fm. The NW Tertiary outcrops were the western deposits of the Duero foreland basin that surrounded the lateral termination of the Pyrenean Orogen. These deposits were fragmented and eroded by the subsequent uplift of the Galaico-Leoneses Mountains and the NE-SW strike-slip faults activity (broken foreland basin). Only the latest stages of some of these outcrops can be considered as intramontane basins as traditionally have been interpreted. The sedimentation started in the northeast (Oviedo-Infiesto) during the Eocene and migrated to the west (As Pontes) during the Late Oligocene

  2. Magnetic fabric study of rock deformation during alpine tectonic evolution on a cross section through the Eastern Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Gruber, K.; Scholger, R.; Pueyo, E. L.

    2010-05-01

    Measurements of anisotropy of magnetic susceptibility (AMS) were carried out on samples from more than seventy sites collected in the Eastern Alps. The sites were taken alongside a North-South transect (about 15°30` East Longitude) from Scheibbs in the North to Kapfenberg in the South, comprising most of the Northern Calcareous Alps (NCA) nappes, Helvetic and Penninic Flysh units as well as the greywacke zone. Samples were taken in detail mostly in Mesozoic rocks of the NCA, from North to South: Bajuvaric (Frankenfels, Lunz, Sulzbach and Reisalpen nappes), Tirolic (Ötscher, Göller, Rotwald-Gindelstein nappes) and Juvavic (Mürzalpen nappe) system. Two to six sites per thrust sheet or nappe were analysed for a structural investigation of the relationship between magnetic fabric and tectonic strain. Standard paleomagnetic drill cores were taken. All measurements were performed in the Petrophysics and Paleomagnetic laboratories of the University of Leoben using AGICO MFK1-Kappabridge susceptibility system and a 2-G cryogenic magnetometer. Statistical evaluation of the AMS data was perfomed using the software package AGICO ANISOFT 4.2. (Chadima et al., 2009). Throughout the Eastern Alps transect distinct changes of the magnetic fabric are observed. Primary sedimentary fabrics and very low susceptibility values are dominant in most cases in the northernmost and southernmost part of the transect. Some inverse fabrics were found in few sites of the nappes and the percentage increases towards the south which might be related to tectonic events. Contrastingly, isotropic fabrics dominate in the middle part. The Helvetic and Penninic Flysh units yield in general weak oblate fabrics. A few sites show a tendency to inverse fabrics which indicate the presence of a certain amount of strain within this unit. The oblate fabrics of the Helvetic and Flysh units show either shallow NE dipping or slightly steeper SW dipping k1-axis orientation. Within the inverse fabrics, even

  3. Tectonic Evolution of Mars

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.

    1992-01-01

    The Final Technical Report on tectonic evolution of Mars is presented. Two papers and an abstract are included. Topics addressed include: scientific rationale and requirements for a global seismic network on Mars, permanent uplift in magmatic systems with application to the Tharsis Region of Mars, and the geophysical signal of the Martian global dichotomy.

  4. Alpine topography in the light of tectonic uplift and glaciation

    NASA Astrophysics Data System (ADS)

    Robl, Jörg; Prasicek, Günther; Hergarten, Stefan; Stüwe, Kurt

    2015-04-01

    In steady-state orogens, topographic gradients are expected to increase with elevation whereas the European Alps feature a transition from increasing to decreasing slopes. This peculiar pattern has been interpreted to reflect either the critical slope stability angle or a premature fluvial landscape but is also consistent with the glacial buzz-saw hypothesis. To disentangle the contributions of each of these principles we split the Alps into contiguous domains of structural units and analyze their slope-elevation distributions emphasizing glaciated and non-glaciated realms. In comparable structural units within the extent of the last glacial maximum (LGM) the transition from increasing to decreasing slopes is located at the equilibrium line altitude (ELA) of the LGM and we interpret this to be evidence for the impact of glacial erosion. Decay rates of glacial landforms towards steady-state slopes depend on lithological properties leading to a landscape characterized by different transient states. Beyond the LGM limits the slope-elevation distributions show local maxima as well, but these are located at varying altitudes implying a tectonic driver. This observation and data from surrounding basins suggests that at least parts of the European Alps experienced a pre-Pleistocene pulse of tectonic uplift. The resulting presence of premature low-gradient terrain above the ELA during the global cooling in Plio-Pleistocene times would have heavily influenced the onset and the extent of an alpine ice cap.

  5. Venus magmatic and tectonic evolution

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Hansen, V. L.

    1993-01-01

    Two years beyond the initial mapping by the Magellan spacecraft, hypotheses for the magmatic and tectonic evolution of Venus have become refined and focused. We present our view of these processes, attempting to synthesize aspects of a model for the tectonic and magmatic behavior of the planet. The ideas presented should be taken collectively as an hypothesis subject to further testing. The quintessence of our model is that shear and buoyancy forces in the upper boundary layer of mantle convection give rise to a spatially and temporally complex pattern of strain in a one-plate Venusian lithosphere and modulate the timing and occurrence of magmatism on a global basis.

  6. Tectonic evolution and paleogeography of Europe

    SciTech Connect

    Yilmaz, P.O.; Norton, I.O.; Chuchla, R.J. ); Leary, D.A. )

    1993-09-01

    The goal of this study was to use the tectonic framework of European craton to constrain our understanding of the sedimentary basins of Europe. An understanding of the amalgamation of the crustal blocks of Europe during the Caledonian, Hercynian, and Alpine orogenies was accomplished using an Evans and Sutherland system. Paleogeographic maps were ;made and integrated with the plate reconstruction with an eye toward how regional plate-scale events affect play elements in the basins. Europe is an artifact of Phanerozoic tectonic history, an amalgamation of crustal blocks without a precambrian nucleus of it own. This is in direct contrast of Africa, Asia, and North America. Multiple riftings and collisions created extremely complex mountain building during the Caledonian, Hercynian, Cimmerian, and Alpine orogenies. Basins are diverse, superimposed, and have long-lived tectonic histories with complex structuring and highly variable play elements. The Hercynian orogene set up the framework for northern European hydrocarbon systems. Its collapse set up the Apulian Mesozoic hydrocarbon system. Alpine deformation and tectonically related extension in turn set up the Neogene hydrocarbon systems of the Carpathians Pannonian basin and the Apennines. Eleven paleogeographic maps were completed at a scale of 1:5,000,000. There are four for the Paleozoic to show the Hercynian orogeny and its subsequent foredeeps, and four for the Mesozoic, showing Tethyan rifting and associated subsidence, as well as the Cimmerian orogenies and start of Alpine deformation. The three time slices in the Cenozoic show the Alpine orogene and its foredeeps and the tectonically related extensional basins.

  7. Subglacial extensional fracture development and implications for Alpine Valley evolution

    NASA Astrophysics Data System (ADS)

    Leith, Kerry; Moore, Jeffrey R.; Amann, Florian; Loew, Simon

    2014-01-01

    stresses induced through exhumation and tectonic processes play a key role in the topographic evolution of alpine valleys. Using a finite difference model combining the effects of tectonics, erosion, and long-term bedrock strength, we assess the development of near-surface in situ stresses and predict bedrock behavior in response to glacial erosion in an Alpine Valley (the Matter Valley, southern Switzerland). Initial stresses are derived from the regional tectonic history, which is characterized by ongoing transtensional or extensional strain throughout exhumation of the brittle crust. We find that bedrock stresses beneath glacial ice in an initial V-shaped topography are sufficient to induce localized extensional fracturing in a zone extending laterally 600 m from the valley axis. The limit of this zone is reflected in the landscape today by a valley "shoulder," separating linear upper mountain slopes from the deep U-shaped inner valley. We propose that this extensional fracture development enhanced glacial quarrying between the valley shoulder and axis and identify a positive feedback where enhanced quarrying promoted valley incision, which in turn increased in situ stress concentrations near the valley floor, assisting erosion and further driving rapid U-shaped valley development. During interglacial periods, these stresses were relieved through brittle strain or topographic modification, and without significant erosion to reach more highly stressed bedrock, subsequent glaciation caused a reduction in differential stress and suppressed extensional fracturing. A combination of stress relief during interglacial periods, and increased ice accumulation rates in highly incised valleys, will reduce the likelihood of repeat enhanced erosion events.

  8. In Review (Geology): Alpine Landscape Evolution Dominated by Cirque Retreat

    NASA Technical Reports Server (NTRS)

    Oskin, Michael; Burbank, Doug

    2005-01-01

    Despite the abundance in alpine terrain of glacially dissected landscapes, the magnitude and geometry of glacial erosion can rarely be defined. In the eastern Kyrgyz Range, a widespread unconformity exhumed as a geomorphic surface provides a regional datum with which to calibrate erosion. As tectonically driven surface uplift has progressively pushed this surface into the zone of ice accumulation, glacial erosion has overprinted the landscape. With as little as 500 m of incision into rocks underlying the unconformity, distinctive glacial valleys display their deepest incision adjacent to cirque headwalls. The expansion of north-facing glacial cirques at the expense of south-facing valleys has driven the drainage divide southwards at rates up to 2 to 3 times the rate of valley incision. Existing ice-flux-based glacial erosion rules incompletely model expansion of glacial valleys via cirque retreat into the low-gradient unconformity remnants. Local processes that either directly sap cirque headwalls or inhibit erosion down-glacier appear to control, at least initially, alpine landscape evolution.

  9. Plio-Pleistocene evolution of the north Alpine drainage system: new constraints from detrital thermochronology of foreland deposits

    NASA Astrophysics Data System (ADS)

    Reiter, Wolfgang; Elfert, Simon; Glotzbach, Christoph; Spiegel, Cornelia

    2015-04-01

    The evolution of drainage systems in and around active orogens may be strongly affected by climatic or tectonic processes. Information on the drainage evolution is stored in the sediments of the foreland depocentres. We investigated the provenance of two key deposits adjacent to the Central Alps, the Pliocene Sundgau gravels and the Pleistocene Höhere Deckenschotter by applying detrital thermochronology. Combined with provenance information from Rhine Graben deposits, we propose a reconstruction of the north Alpine drainage system since the middle Pliocene and discuss potential controlling mechanisms. Our data show that the Rhine Graben received detritus from the Alpine realm already during the Pliocene, indicating two different river systems—the proto-Rhine and the Aare-Doubs—draining the Alpine realm toward the North Sea and Mediterranean Sea. The investigated sediments contain detritus from two central Alpine sources, one showing a regional exhumational equilibrium and the other characterized by increasing exhumation rates. Discharge of the latter source ceased after ~2 Ma, reflecting a northward shift of the main Alpine drainage divide. Between ~2.0 and 1.2 Ma, the drainage system was affected by a major change, which we explain as resulting from a change in the Alpine stress field leading to tectonic exhumation and topography reduction in the area of the southern Aar massif. Generally, it seems that between ~4 and 1.2 Ma, the drainage system was mainly controlled by tectonic processes, despite first glaciations that already affected the north-Alpine foreland by ~2 Ma. The drainage system only seems to have reacted to the late Cenozoic climate changes after ~1.2 Ma, i.e., at the time of the most intense Alpine glaciation. At that time, the course of the Rhine River shifted toward the area of the Hegau volcanics, and the size of the Rhine River catchment became strongly reduced.

  10. Tectonics of the Northern Bresse region (France) during the Alpine cycle

    NASA Astrophysics Data System (ADS)

    Rocher, Muriel; Chevalier, Francis; Petit, Christophe; Guiraud, Michel

    2003-11-01

    Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE-SW, E-W and NW-SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N-S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE-SW in the graben. After a transitional minor E-W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE-SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE-SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.

  11. Caribbean paleomagnetism and tectonic evolution

    SciTech Connect

    MacDonald, W.D.

    1985-01-01

    Approximately fifty papers treating diverse aspects of Caribbean paleomagnetism have appeared since Creer's pioneering work in the early 1960s. Apparently anomalous early results were initially attributed to anomalous geomagnetic field behavior, to unusual mineralogic effects in rock magnetism and to complex remagnetizations. Eventually the importance of structural and tectonic influences were recognized in paleomagnetic data of the Caribbean area, as elsewhere. Large tectonic rotation is evident from the unusual paleomagnetic declination found at many Caribbean localities. Latitudinal transport, with its plate motion implications, is more subtly expressed in the paleomagnetic inclination parameter, with its typically large relative variance. A review of Caribbean paleomagnetic data is given to form a basis for composing realistic tectonic models.

  12. Structural evolution of Alpine salt deposits, Austria and Bavaria

    NASA Astrophysics Data System (ADS)

    Leitner, Ch.; Neubauer, F.; Genser, H.; Borojevic Sostaric, S.

    2009-04-01

    Structural evolution of Alpine salt deposits, Austria and Bavaria Alpine salt deposits consist of a tectonic melange of rocksalt and shale called haselgebirge representing the Haselgebirge Formation of Permian to Early Triassic age and mainly exposed within the central and eastern Northern Calcareous Alps. The initial evaporitic sediments were transformed into a breccia (protocataclasite, mylonite) during Alpine orogeny. Residual rocks of shale, anhydrite, polyhalite, sandstone and limestone float as isolated bodies in the haselgebirge matrix. Field investigations of foliation, halite mineral lineation, fold axis, veins and the overall present slickensides in shale revealed an individual history for all investigated mines (Dürrnberg, Berchtesgaden, Altaussee, in part Hallstatt). Ar-Ar dating of various micostructural types of polyhalite yield several preliminary age groups: 235 Ma, 180 Ma, and 110 Ma. Fluid inclusion measurements on anhydrite together with vitrinite reflectance data showed that temperatures of 140-180 °C were reached in Berchtesgaden and around 250° C in Altaussee. Microstructural analysis of anhydrite reveals strong stretching structures with lobate grain boundaries and the fomation of large anhydrite crystals in polyhalite (locally called muriazite). Rock salt and Haselgebirge samples were gamma-irradiated to intensify contrasts in thin section analysis. No primary structures like fluid inclusion bands or chevrons were found. The oldest visible parts are innner cores of large residual grains. All other types of grains suffered grain size reduction during the subsequent deformation. Using subgrain piezometry, high differential stresses of around 5 MPa formed the present microstructure. The Alpine rock salt deposits suffered a complex deformation history. A first peak was the formation of polyhalite veins, 235 Ma ago. The overburden was around 800 m (Rantitsch & Russegger, 2005) and first differentiation of the sea floor occurred (Mandl, 1984

  13. Basement lithostratigraphy of the Adula nappe: implications for Palaeozoic evolution and Alpine kinematics

    NASA Astrophysics Data System (ADS)

    Cavargna-Sani, Mattia; Epard, Jean-Luc; Bussy, François; Ulianov, Alex

    2014-01-01

    The Adula nappe belongs to the Lower Penninic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U-Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Garenstock Augengneiss); Ordovician metamorphic volcanic-sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Variscan + Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre-Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, mélange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity.

  14. Tectonic evolution of the terrestrial planets.

    PubMed

    Head, J W; Solomon, S C

    1981-07-01

    The style and evolution of tectonics on the terrestrial planets differ substantially. The style is related to the thickness of the lithosphere and to whether the lithosphere is divided into distinct, mobile plates that can be recycled into the mantle, as on Earth, or is a single spherical shell, as on the moon, Mars, and Mercury. The evolution of a planetary lithosphere and the development of plate tectonics appear to be influenced by several factors, including planetary size, chemistry, and external and internal heat sources. Vertical tectonic movement due to lithospheric loading or uplift is similar on all of the terrestrial planets and is controlled by the local thickness and rheology of the lithosphere. The surface of Venus, although known only at low resolution, displays features both similar to those on Earth (mountain belts, high plateaus) and similar to those on the smaller planets (possible impact basins). Improved understanding of the tectonic evolution of Venus will permit an evaluation of the relative roles of planetary size and chemistry in determining evolutionary style. PMID:17741171

  15. A review of Alpine tectonics in Portugal: Foreland detachment in basement and cover rocks

    NASA Astrophysics Data System (ADS)

    Ribeiro, A.; Kullberg, M. C.; Kullberg, J. C.; Manuppella, G.; Phipps, S.

    1990-12-01

    The Alpine foreland in Portugal was deformed by compressional tectonism during the Miocene. In the NNE-SSW oriented Lusitanian Basin, most folds and thrusts in the Meso-Cenozoic cover are oriented ENE-WSW, parallel to the Alpine front in the Betic Cordillera, and verge towards the north-northwest and south-southeast. The thrusts are connected by lateral ramps: most of these are oriented NNE-SSW to N-S and show sinistral movement, and some are transpressional. The lateral ramps result from reactivation of older extensional faults related to crustal thinning of the continental margin. In the E-W oriented Algarve Basin a simpler basin inversion occurred, with older E-W normal faults reactivated as essentially pure thrusts. In both basins Alpine structures formed above décollements in the Hettangian evaporite-clastic complex. Variscan basement was also deformed by ENE-WSW reverse faults during Miocene time. The similarity in orientation and style of the basement structures to those in the cover suggests that they also occurred by detachment, but their larger scale indicates that the detachment is deep and involves much of the crust. Thus, we interpret the Central Cordillera, in which basement rocks are thrust over Miocene sediments on both sides, as a "pop-up" of crustal scale, elevated above downward-flattening faults that dip towards each other and merge into a single deep detachment. Alpine structures in the Iberian foreland are therefore similar in structural style to those of the Appalachian and Laramide forelands of North America and the Alpine foreland of northwest Europe.

  16. Tectonic evolution of northwest Siberia

    SciTech Connect

    Natapov, L.P. )

    1993-09-01

    The ancient Siberian continent was split from early Pangen in early Riphean. The newly formed continent drifted from the southern to the northern hemisphere, reaching high altitudes only in the Late Paleozoic. Up to the Early Carboniferous, a typical passive margin of the Atlantic type, prograding to the ocean, developed along the present northern and eastern boundaries of this continent. In Upper Paleozoic, Triassic, and Jurassic, the carbonate sedimentation was replaced by the accumulation of thick terrigenous complexes along the northern and southern margins. Large submarine plains were formed by the merging of fans, while eustatic lowering of the ocean level enlarged the source area of detrital material. Distal facies, with time, were moving into the ocean. Rifting, penetrating inside the continent, conditioned for formation of large sedimentary basins. The development of the Sukhanskaya syneclise is associated with Riphean rifting, and Vilyuiskaya with Upper Devonian rifting. In the Upper Mesozoic, the covergent boundaries of lithospheric plates existed along the northern and eastern boundaries of the Siberian continent. As a result of the final collision of the continental margin with blocks of different nature (microcontinents, island arcs, etc.) transported by the Kula plate, and with chukchi and north Taimyr arctic blocks, Verkhoyansk and Taimyr fold belts appeared in the Upper Cretaceous. They were over-thrusted on clastic wedges, putting into shape the present-day structure of foredeeps. In the paper, principal attention is devoted to peculiarities of structure and development of sedimentary basins, formation of oil-producing complexes, and structures favorable for accumulation of hydrocarbons. All these features are analyzed at the background of this plate tectonic scenario.

  17. Phanerozoic tectonic evolution of Tarim Basin

    SciTech Connect

    Sun Zhaocai; Zhang Yigang

    1995-08-01

    The tectonic evolution of Tarim Basin can be divided into two stages. In the first stage, there developed three Palaeozoic sequences (Pt3-01, O2-3-D and C1-P2), the deposition of which were controlled by Palaeoasian Tectonic Domain. In the second stage, there appeared five Meso-Cenozoic sequences (T1-2, T3, J, K2-E and N1-Q), controlled by Tethys Sea Tectonic Domain. Both of the first sequence of each stage (Pt3-01 and T1-2) are of typical rift-drift facies, overlain by flexural facies. The Palaeozoic tectonic style is characterized by basement-involved, back-thrusted uplifts and the pop-up held inbetween them. The main tectonic style since Late Triassic time has been thin-skin decoupling anticlines developed near the deep troughs in the foreland basins. Corresponding to the two above-mentioned stages, two major petroleum systems were formed. However, the early petroleum system was partly destroyed due to the marked overturn of the basin during Late Palaeozoic time.

  18. Tectonic Evolution of the Jurassic Pacific Plate

    NASA Astrophysics Data System (ADS)

    Nakanishi, M.; Ishihara, T.

    2015-12-01

    We present the tectonic evolution of the Jurassic Pacific plate based on magnetic anomly lineations and abyssal hills. The Pacific plate is the largest oceanic plate on Earth. It was born as a microplate aroud the Izanagi-Farallon-Phoenix triple junction about 192 Ma, Early Jurassic [Nakanishi et al., 1992]. The size of the Pacific plate at 190 Ma was nearly half that of the present Easter or Juan Fernandez microplates in the East Pacific Rise [Martinez et at, 1991; Larson et al., 1992]. The plate boundary surrounding the Pacific plate from Early Jurassic to Early Cretaceous involved the four triple junctions among Pacific, Izanagi, Farallon, and Phoenix plates. The major tectonic events as the formation of oceanic plateaus and microplates during the period occurred in the vicinity of the triple junctions [e.g., Nakanishi and Winterer, 1998; Nakanishi et al., 1999], implying that the study of the triple junctions is indispensable for understanding the tectonic evolution of the Pacific plate. Previous studies indicate instability of the configuration of the triple junctions from Late Jurassic to Early Cretaceous (155-125 Ma). On the other hand, the age of the birth of the Pacific plate was determined assuming that all triple junctions had kept their configurations for about 30 m.y. [Nakanishi et al., 1992] because of insufficient information of the tectonic history of the Pacific plate before Late Jurassic.Increase in the bathymetric and geomagnetic data over the past two decades enables us to reveal the tectonic evolution of the Pacific-Izanagi-Farallon triple junction before Late Jurassic. Our detailed identication of magnetic anomaly lineations exposes magnetic bights before anomaly M25. We found the curved abyssal hills originated near the triple junction, which trend is parallel to magnetic anomaly lineations. These results imply that the configuration of the Pacific-Izanagi-Farallon triple junction had been RRR before Late Jurassic.

  19. The Tectonics and Evolution of Venus

    NASA Technical Reports Server (NTRS)

    Kaula, William M.

    1997-01-01

    This shift corresponded to a focusing of research on Venus. Some work included comparison with other planets. Venus research is being continued. The research can be summarized under five headings: (1) Planet formation; (2) Thermal and Compositional Evolution; (3) Tectonic structures and processes; (4) Determination and interpretation of gravity; and (5) Analyses of Ishtar Terra. Thirty-four publications were produced. References to publications supporting the summary are by year and letter: e.g., (1990 c,d) for the emphasis on the terminal phases in formation studies.

  20. Mechanical model for subduction-collision tectonics of Alpine-type compressional orogens

    NASA Astrophysics Data System (ADS)

    Beaumont, Christopher; Ellis, Susan; Hamilton, Juliet; Fullsack, Philippe

    1996-08-01

    Alpine-type orogens are characterized by three distinct convergent tectonic phases: subduction with deformation that has primarily single vergence, a transition from subduction to collision, and continental collision with double vergence. Although the Cenozoic history of the European Alps has additional complexities, a mechanical explanation for these three phases would provide the necessary crustal-scale framework in which to develop an understanding of the smaller-scale processes. We present results from a simple numerical model, which explain the mechanics of these three phases as a consequence of the changing buoyancy of the lithosphere subducted beneath the orogen. The development and exhumation of a subduction complex, suture zone, and basement nappe stack (Piemont suture, Penninic Nappes); the presence of a crustal-scale back fold and thrust (Insubric Line); and uplift of basement on the pro- (European) side of the orogen (external basement massifs) may be explained as a simple consequence of changing dynamics during the transition from subduction to collision.

  1. Alpine tectonic wedging and crustal delamination in the Cantabrian Mountains (NW Spain)

    NASA Astrophysics Data System (ADS)

    Gallastegui, Jorge; Pulgar, Javier A.; Gallart, Josep

    2016-07-01

    The Cantabrian Mountains have been interpreted as a Paleozoic basement block uplifted during an Alpine deformation event that led to the partial closure of the Bay of Biscay and the building of the Pyrenean range in the Cenozoic. A detailed interpretation of deep seismic reflection profile ESCIN-2 and the two-dimensional seismic modelling of the data allowed us to construct a N-S geological cross section along the southern border of the Cantabrian Mountains and the transition to the Duero Cenozoic foreland basin, highlighting the Alpine structure. The proposed geological cross section has been constrained by all geophysical data available, including a 2-D gravity model constructed for this study as well as refraction and magnetotelluric models from previous studies. A set of south-vergent thrusts dipping 30 to 36° to the north, cut the upper crust with a ramp geometry and sole in the boundary with the middle crust. These thrusts are responsible for the uplift and the main Alpine deformation in the Cantabrian Mountains. A conspicuous reflective Moho shows that the crust thickens northwards from the Duero basin, where subhorizontal Moho is 32 km deep, to 47 km in the northernmost end of ESCIN-2, where Moho dips to the north beneath the Cantabrian Mountains. Further north, out of the profile, Moho reaches a maximum depth of 55 km, according to wide-angle/refraction data. ESCIN-2 indicates the presence of a tectonic wedge of the crust of the Cantabrian margin beneath the Cantabrian Mountains, which is indented from north to south into the delaminated Iberian crust, forcing its northward subduction.

  2. Late Cenozoic tectonic evolution of southwestern California

    NASA Technical Reports Server (NTRS)

    Sedlock, Richard L.; Hamilton, Douglas H.

    1991-01-01

    Geologic and geophysical data from southern California and adjoining areas are used to reconstruct the tectonic evolution of the southern Coast Ranges, western Transverse Ranges, and borderland regions since 30 Myr ago. Premises include specified relative plate motions for times prior to 10.5 Myr ago and after 3 Myr ago, a mid-Tertiary bight in the continental margin, midcrustal detachment faults, rotation of the western Transverse Ranges about an eastern pivot, and specified fault displacement histories. Prior to 18 Myr ago, about 90 percent of the tangential component of Pacific-North America relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope. From 18 to 5.5 Myr ago, dextral slip was accommodated predominantly on the offshore system but also on a second, inboard system that included the San Andreas fault.

  3. Sediment connectivity evolution on an alpine catchment undergoing glacier retreat

    NASA Astrophysics Data System (ADS)

    Goldin, Beatrice; Rudaz, Benjamin; Bardou, Eric

    2014-05-01

    Climate changes can result in a wide range of variations of natural environment including retreating glaciers. Melting from glaciers will have a significant impact on the sediment transport characteristics of glacierized alpine catchments that can affect downstream channel network. Sediment connectivity assessment, i.e. the degree of connections that controls sediment fluxes between different segments of a landscape, can be useful in order to address management activity on sediment fluxes changes of alpine streams. Through the spatial characterization of the connectivity patterns of a catchment and its potential evolution it is possible to both define sediment transport pathways and estimate different contributions of the sub-catchment as sediment sources. In this study, a topography based index (Cavalli et al., 2013) has been applied to assess spatial sediment connectivity in the Navisence catchment (35 km2), an alpine basin located in the southern Walliser Alps (Switzerland) characterized by a complex glacier system with well-developed lateral moraines on glacier margins already crossed by several lateral channels. Glacier retreat of the main glacial edifice will provide a new connectivity pattern. At present the glacier disconnects lateral slopes from the main talweg: it is expected that its retreat will experience an increased connectivity. In order to study this evolution, two high resolution (2 m) digital terrain models (DTMs) describing respectively the terrain before and after glacier retreat have been analyzed. The current DTM was obtained from high resolution photogrammetry (2 m resolution). The future DTM was derived from application of the sloping local base level (SLBL) routine (Jaboyedoff et al., 2004) on the current glacier system, allowing to remove the ice body by reconstituting a U-shaped polynomial bedrock surface. From this new surface a coherent river network was drawn and slight random noise was added. Finally the river network was burned into

  4. Relief Evolution in Tectonically Active Mountain Ranges

    NASA Technical Reports Server (NTRS)

    Whipple, Kelin X.

    2004-01-01

    The overall aims of this 3-yr project, as originally proposed were to: (1) investigate quantitatively the roles of fluvial and glacial erosion in the evolution of relief in mountainous regions, and (2) test rigorously the quality and accuracy of SRTM topographic data in areas of rugged relief - both the most challenging and of greatest interest to geomorphic, neotectonic, and hazards applications. Natural laboratories in both the western US and the Southern Alps of New Zealand were identified as most promising. The project has been both successful and productive, despite the fact that no SRTM data for our primary field sites in New Zealand were released on the time frame of the work effort. Given the delayed release of SRTM data, we pursued the scientific questions of the roles of fluvial and, especially, glacial erosion in the evolution of relief in mountainous regions using available digital elevation models (DEMs) for the Southern Alps of New Zealand (available at both 25m and 50m pixel sizes), and USGS 10m and 30m DEMs within the Western US. As emphasized in the original proposal, we chose the emphasis on the role of glacial modification of topographic relief because there has been little quantitative investigation of glacial erosion processes at landscape scale. This is particularly surprising considering the dramatic sculpting of most mid- and high-latitude mountain ranges, the prodigious quantities of glacially-derived sediment in terrestrial and marine basins, and the current cross-disciplinary interest in the role of denudational processes in orogenesis and the evolution of topography in general. Moreover, the evolution of glaciated landscapes is not only a fundamental problem in geomorphology in its own right, but also is at the heart of the debate over Late Cenozoic linkages between climate and tectonics.

  5. Geodynamical Evolution and Tectonic Framework of China

    NASA Astrophysics Data System (ADS)

    LIU, Guangding

    In this paper, we show that the tectonic framework of mainland China consists of "three latitudinal strips", namely, Tianshan-Yinshan-Yanshan, Qinling-Dabie, and Nanling; "two longitudinal strips" namely, Daxing'anling Taihangshan Wulingshan, Helanshan-Longmenshan; and "two triangles", Songpan-Ganzi, and Chaidamu. The geodynamic evolution of China can be considered in five-stages, which can be summarised as a kind of "teeterboard-like" process. The evolutionary process is that in the Palaeozoic era, the China mainland had lower elevation in the west and higher in the east, with OrdosSichuan as an axis. After the Mesozoic era, because the blocks of Qiangtang, Gangdese, and India collided and sutured with the Tarim block. During this time closure of the Tethys ocean occurred, and the Qinghai-Tibet Plateau formed. In the Cenozoic subduction of the Pacific plate northwestwards under the Philippine Sea began, and the Philippine Sea block converged towards the Eurasian plate. This was associated with extension and thinning of the crust in East China, which resulted in the uplift of the land in the west and subsidence in the east of China. Finally, we point out that research on the geodynamic evolution of the terranes is of practical significance in prospecting for mineral deposits and hydrocarbon resources.

  6. MEVTV Workshop on Early Tectonic and Volcanic Evolution of Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. (Editor)

    1988-01-01

    Although not ignored, the problems of the early tectonic and volcanic evolution of Mars have generally received less attention than those later in the evolution of the planet. Specifically, much attention was devoted to the evolution of the Tharsis region of Mars and to the planet itself at the time following the establishment of this major tectonic and volcanic province. By contrast, little attention was directed at fundamental questions, such as the conditions that led to the development of Tharsis and the cause of the basic fundamental dichotomy of the Martian crust. It was to address these and related questions of the earliest evolution of Mars that a workshop was organized under the auspices of the Mars: Evolution of Volcanism, Tectonism, and Volatiles (MEVTV) Program. Four sessions were held: crustal dichotomy; crustal differentiation/volcanism; Tharsis, Elysium, and Valles Marineris; and ridges and fault tectonics.

  7. Correlation between tectonic events in the most recent period of earth evolution

    NASA Astrophysics Data System (ADS)

    Kukina, N. V.; Makarov, V. I.; Trifonov, V. G.; Volchkova, G. I.

    Methods used in correlating various neotectonic events are described, together with a general discussion of short-lived changes in tectonic activity. Neotectonic events in the Carpathian-Caucasus-Kopetdag segment and in ancient folded areas (including Tien Shan and segments of Rhodope mountains) of the Alpine-Asian orogenic belt are analyzed. Correlation of neotectonic events of the earth's mobile belts revealed the presence in the earth crust of segments which are characterized by the synchronism of the most important events in tectonic activity. Common activating phases disclosed in these areas indicate the presence of global rhythmicity in tectogenesis. In addition, the studies have uncovered some specificities in the neotectonic stage of the Mesozoic-Cenozoic period of the earth evolution.

  8. Workshop on the Tectonic Evolution of Greenstone Belts

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The Workshop on the Tectonic Evolution of Greenstone Belts, which is part of the Universities Space Research Association, Lunar and Planetary Institute, of Houston, Texas, met there on Jan. 16-18, 1986. A number of plate tectonic hypotheses have been proposed to explain the origin of Archean and Phanerozoic greenstone/ophiolite terranes. These hypotheses are explored in the abstracts.

  9. Alpine tectonics of granites in basement of Ysyk-Köl Basin, northern Tien Shan

    NASA Astrophysics Data System (ADS)

    Leonov, M. G.; Przhiyalgovsky, E. S.; Lavrushina, E. V.; Poleshchuk, A. V.; Rybin, A. K.

    2016-07-01

    The Ysyk-Köl Basin filled with Lower Jurassic-Quaternary sedimentary rocks is the largest intermontane negative structural unit of the northern Tien Shan. The basement of this basin is composed of Precambrian-Paleozoic rocks, largely of Ordovician and Silurian granitoids exposed in mountain ranges of the basin framework and as separate anticlinal domes situated in areas occupied by the Mesozoic-Cenozoic sedimentary cover. The postmagmatic tectonic internalstructure of the Chonkurchak (Chunkurchak), Kyzyl-Choku, Kyzyl-Bulak, and Prishib massifs emplaced in the basement, as well as their relationships to the sedimentary cover, are described in the paper. The study was carried out using the morphostructural method, detailed geological mapping, structural kinematic analysis, and petrographic examination of rocks. The internalstructure of Paleozoic granites in the basement and indications of their 3D tectonic flow are characterized. It is shown that granites underwent 3D deformation after their emplacement in the consolidated crust, and this process had a substantial influence on tectonic processes at the plate and orogenic stages of regional evolution.

  10. Tectonic evolution of Abu Gharadig basin

    SciTech Connect

    Meshref, W.M.; Beleity, A.E.H.; Hammouda, H.; Kamel, M.

    1988-08-01

    The Abu Gharadig basin, northwestern desert of Egypt, is considered the most petroliferous basin in the Western Desert as far as hydrocarbon production and potential. The basin is believed to be growing and developing throughout geologic time. Aeromagnteic data and subsurface information, derived from a set of isopach maps from wells including complete sections only, revealed that the Abu Gharadig basin was subjected to different tectonic events that resulted in different tectonic trends. These trends include (1) north-south to north-northwest-south-southeast of Precambrian age, (2) east-west (Y-trends) of Paleozoic to Jurassic age, (3) west-northwest (R-trends) of Late Jurassic to Early Cretaceous, and (4) east-northeast (P-trends) of Late Cretaceous to Eocene age. The previously mentioned tectonic trends can be explained by a convergent wrench model that affected northern Egypt.

  11. Late Tertiary paleogeographic and tectonic evolution of the Mediterranean area

    SciTech Connect

    Arnott, R.J.; Haan, E.A.

    1988-08-01

    The present geography of the Mediterranean Sea is the result of late Tertiary tectonic processes and hardly reflects its Mesozoic and early Tertiary evolution. This paper outlines a plate tectonics model for the Mediterranean area from the Oligocene to the Pliocene. Seismic and well data have been integrated into the regional structural framework to produce a set of paleogeographic maps, which includes the Oligocene, early and middle Miocene, late Miocene, and Pliocene. These maps highlight the changes in sedimentation patterns in response to the tectonic development of the Mediterranean area. Special attention will be given to the Messinian desiccation event.

  12. Rapid biological speciation driven by tectonic evolution in New Zealand

    NASA Astrophysics Data System (ADS)

    Craw, Dave; Upton, Phaedra; Burridge, Christopher P.; Wallis, Graham P.; Waters, Jonathan M.

    2016-02-01

    Collisions between tectonic plates lead to the rise of new mountain ranges that can separate biological populations and ultimately result in new species. However, the identification of links between tectonic mountain-building and biological speciation is confounded by environmental and ecological factors. Thus, there are surprisingly few well-documented examples of direct tectonic controls on terrestrial biological speciation. Here we present examples from New Zealand, where the rapid evolution of 18 species of freshwater fishes has resulted from parallel tectonic landscape evolution. We use numerical models to reconstruct changes in the deep crustal structure and surface drainage catchments of the southern island of New Zealand over the past 25 million years. We show that the island and mountain topography evolved in six principal tectonic zones, which have distinct drainage catchments that separated fish populations. We use new and existing phylogenetic analyses of freshwater fish populations, based on over 1,000 specimens from more than 400 localities, to show that fish genomes can retain evidence of this tectonic landscape development, with a clear correlation between geologic age and extent of DNA sequence divergence. We conclude that landscape evolution has controlled on-going biological diversification over the past 25 million years.

  13. A window for plate tectonics in terrestrial planet evolution?

    NASA Astrophysics Data System (ADS)

    O'Neill, Craig; Lenardic, Adrian; Weller, Matthew; Moresi, Louis; Quenette, Steve; Zhang, Siqi

    2016-06-01

    The tectonic regime of a planet depends critically on the contributions of basal and internal heating to the planetary mantle, and how these evolve through time. We use viscoplastic mantle convection simulations, with evolving core-mantle boundary temperatures, and radiogenic heat decay, to explore how these factors affect tectonic regime over the lifetime of a planet. The simulations demonstrate (i) hot, mantle conditions, coming out of a magma ocean phase of evolution, can produce a "hot" stagnant-lid regime, whilst a cooler post magma ocean mantle may begin in a plate tectonic regime; (ii) planets may evolve from an initial hot stagnant-lid condition, through an episodic regime lasting 1-3 Gyr, into a plate-tectonic regime, and finally into a cold, senescent stagnant lid regime after ∼10 Gyr of evolution, as heat production and basal temperatures wane; and (iii) the thermal state of the post magma ocean mantle, which effectively sets the initial conditions for the sub-solidus mantle convection phase of planetary evolution, is one of the most sensitive parameters affecting planetary evolution - systems with exactly the same physical parameters may exhibit completely different tectonics depending on the initial state employed. Estimates of the early Earth's temperatures suggest Earth may have begun in a hot stagnant lid mode, evolving into an episodic regime throughout most of the Archaean, before finally passing into a plate tectonic regime. The implication of these results is that, for many cases, plate tectonics may be a phase in planetary evolution between hot and cold stagnant states, rather than an end-member.

  14. The Caspian megabasin: tectonics and evolution

    NASA Astrophysics Data System (ADS)

    Khain, V. E.; Bogdanov, N. A.

    2003-04-01

    The Caspian Sea occupies at longitudinally elongated depression, superimposed in the latest Miocene on different structural units, oriented in WNW-ESE direction and belonging to the southern edge of the East European Craton and to the Mediterranean mobile belt. The Caspian megabasin comprises three basins - Northern, Middle and Southern with different age of basement and sedimentary fill, structural style and recent tectonics. The evolution of the whole region could be followed from Neoproterozoic onwards. At that epoch, an oceanic basin-Prototethys appeared after the breakup of Rodinia between Baltica and Gondwana. Its volcano-sedimentary sequence outcrops in the Greater Caucasus and Dzirula massif in Transcaucasia. After the Baikalian (=Cadomian/Panafrican) orogeny the central and southern part of the region was cratonised and formed the northern rim of Gondwana, presumably separated from Baltica by a relic of Prototethys. In Ordovician two branches of the Paleotethys crossed the region - the northern passed through the Greater Caucasus, the southern through Talesh; they were separated by the Transcaucasian microcontinent. At the southern edge of Baltica the Donets-Karpinsky Ridge rift system was formed in mid-Devonian. The northern branch of the Paleotethys was severely deformed, intruded by granites and metamorphosed by the Hercynian orogeny; only a remnant marine basin persisted to the south of the orogen. It was deformed in its tour, along with the southern-Paleotethys branch by the Eocimmerian orogeny which also caused the final inversion of the Donets-Karpinsky rift system. After these events the Fore-Caucasus region became the young Scythian platform - part of the Eurasian continent. In the Early Jurassic rifting opened the Greater Caucasus basin, marginal in respect to the Neotethys, one of the main branch of which passed through the Lesser Caucasus and probably along the southern border of the Alborz Range, separating it from the Iranian microcontinent

  15. Strong coupling between tectonic fractures, postglacial erosion and sediment flux in alpine environment, Alaska

    NASA Astrophysics Data System (ADS)

    Champagnac, Jean-Daniel

    2014-05-01

    to an even larger extent between the deeper canyons and the preserved surfaces) imply that the erosion is highly not homogeneously distributed over the entire area. Field (and airplane) observations show that fracturing is dense, pervasive, associated with thick fault gouges, kakirite and cataclase to the Northeast, whereas rock is very compact, with only a few widely space fracture to the West. Remote sensing detection of more than 1000 fracture also exhibit a striking difference of the fracture density, very penetrative to the North East, and widely spaced to the south and SW. These fractures are preferably oriented ENE-WSW, and to a minor amount E-W and NW-SW. The two main river draining this range have similar drainage basin (~400km2) toward the North, but the one draining the densely fractured / incised landscape shows an impressive fan delta prograding onto the Chitina River floodplain. This study highlight the strong coupling between tectonic fracturing of rock, erosion and sediment transfer in alpine environments.

  16. History and Evolution of Precambrian plate tectonics

    NASA Astrophysics Data System (ADS)

    Fischer, Ria; Gerya, Taras

    2014-05-01

    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental

  17. Variscan tectonics in the Holy Cross Mountains (Poland) and the role of structural inheritance during Alpine tectonics

    NASA Astrophysics Data System (ADS)

    Lamarche, J.; Mansy, J. L.; Bergerat, F.; Averbuch, O.; Hakenberg, M.; Lewandowski, M.; Stupnicka, E.; Swidrowska, J.; Wajsprych, B.; Wieczorek, J.

    1999-11-01

    The present study was carried out in the Holy Cross Mountains (HCM) of south-central Poland and includes computation of palaeostresses following Angelier's method and field structural analysis. The Palaeozoic basement of the HCM comprises two tectonic units separated by the major WNW-ESE-striking Holy Cross Fault (HCF). Fold analysis indicates a N-S to NNE-SSW direction of Variscan shortening. Micro-structures and fold analysis from Upper Devonian rocks further reveal: (1) a brittle tectonic event due to a NW-SE compression preceding folding that could be related to pre-Late Carboniferous tectonics, due to block transport within the Tornquist-Teisseyre Zone (TTZ), and (2) polyphase Variscan folding comprising (a) an early stage of N-S shortening marked by north-verging ramps, (b) a main folding event and axial cleavage formation involving N-S to NNE-SSW shortening, and (c) a late stage of shortening deforming older folds and cleavage. A mainly extensional tectonic regime dominated from the Permian until the Cretaceous, during which time the HCF was reactivated as a normal fault. Large NW-SE faults bordering the Mid-Polish Trough (MPT) developed. Subsequent tectonic inversion of the MPT resulted in basin uplift (`Mid-Polish Swell', MPS). Palaeostress computations from Mesozoic strata suggest a NE-SW direction for the main Maastrichtian-Paleocene shortening phase, in addition to two minor brittle events resulting from N-S and E-W compression. Analysis of local folds in the Mesozoic cover indicates a causal relationship with the Maastrichtian-Paleocene reactivation of older faults. In particular, en-échelon folds in the Radomsko Elevation suggest a sinistral reactivation of the Palaeozoic HCF. Folds in the southwestern part of the HCM argue for reactivation in the reverse mode of a NW-SE-trending fault bordering the MPS that originated in the Mesozoic. In Palaeozoic strata, post-Variscan brittle deformation and micro-fault reactivation are attributed to the tectonic

  18. Geochronological evidence for the Alpine tectono-thermal evolution of the Veporic Unit (Western Carpathians, Slovakia)

    NASA Astrophysics Data System (ADS)

    Vojtko, Rastislav; Králiková, Silvia; Jeřábek, Petr; Schuster, Ralf; Danišík, Martin; Fügenschuh, Bernhard; Minár, Jozef; Madarás, Ján

    2016-01-01

    Tectono-thermal evolution of the Veporic Unit was revealed by multiple geochronological methods, including 87Rb/86Sr on muscovite and biotite, zircon and apatite fission-track, and apatite (U-Th)/He analysis. Based on the new data, the following Alpine tectono-thermal stages can be distinguished: The Eo-Alpine Cretaceous nappe stacking (~ 135-95 Ma) resulted in burial of the Veporic Unit beneath the northward overthrusting Gemeric Unit and overlying Jurassic Meliata accretionary wedge. During this process the Veporic Unit reached metamorphic peak of greenschist- to amphibolite facies accompanied by orogen-parallel flow in its lower and middle crust. The subsequent evolution of this crust is associated with two distinct exhumation mechanisms related to collision with the northerly Tatric-Fatric basement. The first mechanism (~ 90-80 Ma) is associated with internal subhorizontal shortening of the Veporic Unit reflected by large-scale upright folding and heterogeneous exhumation of the Veporic lower crust in the cores of crustal-scale antiforms. This led to juxtaposition of the higher and lower grade parts of basement, all cooled down to ~ 350 °C by ~ 80 Ma. The second mechanism is associated with the overthrusting of the Veporic Unit over the attenuated Fatric crust. This led to a passive en-block exhumation of the Veporic crust from ~ 350 °C to 60 °C between ~ 80 and 55 Ma followed by erosion (~ 55-35 Ma). The erosion processes resulted in formation of planation surface before the Late Eocene transgression. After erosion and planation, a new sedimentary cycle of the Central Carpathian Palaeogene Basin was deposited with the sedimentary strata thickness of ~ 1.5-2.0 km (~ 21-17 Ma). The early to middle Miocene is characterised by destruction tectonic disintegration and erosion of this basin (~ 20-13 Ma) and formation of the Neogene Vepor Stratovolcano (~ 13 Ma). The final shaping of the area has been linked to erosional processes of the volcanic structure since

  19. Structural-tectonic controls and geomorphology of the karst corridors in alpine limestone ridges: Southern Carpathians, Romania

    NASA Astrophysics Data System (ADS)

    Tîrlă, Laura; Vijulie, Iuliana

    2013-09-01

    The relationship between surface karst development and the geological frame is widely acknowledged in the study of karst landforms. It is of considerable interest especially in alpine environments (e.g. Alpine-Dinaric-Carpathian orogenic system). Karst corridors are generally known as kluftkarren or bogaz and form by solution of limestone along a lithoclase network. The Vânturariţa-Buila Massif (Carpathians, Romania) is a typical alpine karst ridge and a former carbonate platform of Upper Jurassic age in which geologically-controlled karst features have been developing over a geologic timescale. Field research and mapping were useful in extracting geologic features. Joint- and structure-controlled karst corridors are common in the upper section of the mountain, between 1600 and 1850 m. First, a complex system of lithoclases (fissures, joints and faults) occurred; then, surface runoff or meltwater solutionally enlarged them. Tension fractures strike in a northeast-southwest direction, parallel to homoclinal limestone layers. The exposed fault walls often preserve draperies and speleothem remnants. Further, statistical analysis of joint, fault and bogaz orientations has shown the close relation between the three datasets, and morphometric analysis centered only on the karst corridor system. Results derived from the statistical analysis of orientation data show that there is a strong preferred orientation of the bogaz or bogaz-like forms along the directional faults and that they commonly develop in extensional (tectonically active) environments. Additional features typical to fluviokarst are also present — subterranean connections between the karst corridors and the headwalls of the pocket valleys, generating headward recession both by continuous sapping of karst springs at the headwall base followed by collapses. An extremely poor surface drainage network developed in the upper pavement facing southeast, compared to that on the middle and lower sides.

  20. Tectonic Evolution of the Terrestrial Planets

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Senski, David G. (Technical Monitor)

    2002-01-01

    The NASA Planetary Geology and Geophysics Program supported a wide range of work on the geophysical evolution of the terrestrial planets during the period 1 April 1997 - 30 September 2001. We here provide highlights of the research carried out under this grant over the final year of the award, and we include a full listing of publications and scientific meeting presentations supported by this project. Throughout the grant period, our group consisted of the Principal Investigator and several Postdoctoral Associates, all at the Department of Terrestrial Magnetism (DTM) of the Carnegie Institution of Washington.

  1. Polyphase tectonic subsidence evolution of the Vienna Basin inferred from quantitative subsidence analysis of the northern and central parts

    NASA Astrophysics Data System (ADS)

    Lee, Eun Young; Wagreich, Michael

    2016-04-01

    The Vienna Basin is a tectonically complex Neogene basin situated at the Alpine-Carpathian transition. This study analyzes a detailed quantification of subsidence in the northern and central parts of the Vienna Basin to understand its tectonic subsidence evolution. About 200 wells were used to arrange stratigraphic setting, and wells reaching the pre-Neogene basement were analyzed for subsidence. To enhance the understanding of the regional subsidences, the wells were sorted into ten groups based on their position on major fault blocks. In the Early Miocene, subsidence was slow and along E-W to NE-SW trending axis, indicating the development of thrust-controlled piggyback basins. During the late Early Miocene data show abruptly increasing subsidence, making the initiation of the Vienna pull-apart basin system. From the Middle Miocene, the tectonic subsidence curves show regionally different patterns. The tectonic subsidence during the Middle Miocene varies laterally across the Vienna Basin, and the differential subsidence can be related to the changing tensional regime of weakening transtension and strengthening extension toward the late Middle Miocene. From the late Middle Miocene to the Late Miocene, the tectonic subsidence occurred dominantly along the regional active faults, and corresponds to the axis of E-W trending extension of the western parts of the Pannonian Basin system. In the Quaternary the Vienna Basin has been reactivated, and resulted in subsidence along the NE-SW trending Vienna Basin transfer fault system.

  2. Tectonic evolution of Bransfield Strait, West Antarctica

    NASA Astrophysics Data System (ADS)

    Barker, Daniel Hugh Njal

    Bransfield Strait is a young (<4 Ma?), actively extending marginal basin located between the NW Antarctic Peninsula and the South Shetland Islands, in the backarc region of the South Shetland Trench. Its structural evolution is probably influenced by both subduction-related processes at the trench and the Antarctic-Scotia strike-slip plate boundary to the NE. Previous studies suggest that Bransfield Strait is floored by thinned continental crust formed by rifting of the South Shetland Islands away from the Antarctic Peninsula, with axial neovolcanism interpreted as evidence of sea-floor spreading. New deep-penetration multichannel seismic (MCS) data reveal more complexity. The basin is in a transitional stage of rifting. Basin-opening occurs by propagation of rifting from NE to SW, evidenced by changes in the neovolcanic expression along the basin axial deep and by changes in structural style along the Antarctic Peninsula margin. A phase of magmatically-induced uplift is interpreted in the earlier stage of rifting (SW), followed by subsidence and extension on low-angle, NW-dipping detachment faults (NE). Local magmatism and footwall uplift is associated with the detachments. The structural asymmetry of Bransfield Strait and identification of detachment faults suggests that the basin is opening by simple-shear lithospheric extension. Comparison with the East African Rift system, Lau Basin-Havre Trough backarc, Woodlark basin and Mesozoic-age Rocas Verdes basin supports the contention that Bransfield Strait rifting is in a transitional stage between continental/arc rifting and organized sea-floor spreading, and that it is a useful modern analog for the Rocas Verdes basin. Furthermore, it suggests that detachment faulting may be a common feature of backarc basins. Recognition of low-angle detachment faulting and simple-shear extension is essential for estimating basin extension, and the amount of crustal shortening and thickening that may occur during inversion of a

  3. Comparative effects of tectonism on Silurian carbonate platform evolution

    SciTech Connect

    Soja, C.M. . Geology Dept.)

    1992-01-01

    Detailed comparisons of Silurian carbonates that formed under similar subtropical-tropical conditions in an island arc (Alexander terrane, Alaska), an orogenic belt (Oslo region, Norway), and on a stale craton (Gotland, Sweden) are used to evaluate tectonic controls on carbonate platform sedimentation. Silurian carbonates from Alaska record the evolution of a submarine platform in an island arc affected by late Silurian orogenesis. Silurian limestones that formed on the Baltoscandinavian epicontinental platform experienced Caledonian orogenesis in the Oslo region but accumulated on Gotland several 100 km east of the Caledonide front under quiescent tectonic conditions. This study shows that previous models for carbonate platform development do not predict the disproportionately thick carbonate sequences and characteristics of rocks preserved in the Alaskan island arc. High rates of subsidence and accumulation, steep submarine slopes, tectonic instability, and biogeographic isolation resulted in extraordinarily thick platform and periplatform carbonates, sequential evolution of fringing and barrier reefs, and patterns of faunal turnover that differentiate Silurian arc deposits from coeval carbonates that formed on the craton and in the orogenic belt. On the craton and in the orogenic belt, marine organisms were relatively unaffected by tectonic disturbances, but in the island arc marine biotas experienced regional extinction and faunal turnover. Similarities in the stages in carbonate platform development in the Oslo region and Alaska reflect comparable events involving compression, foreland basin evolution, and subsequent rejuvenation of carbonate depositional sites. Widespread destruction of carbonate environments correlated with orogenic activity and global marine regression eventually produced similar subaerial conditions in the Alexander terrane and across Baltoscandinavia by the late Silurian.

  4. Tectonic evolution of the Tobago Trough forearc basin

    NASA Technical Reports Server (NTRS)

    Speed, R.; Torrini, R., Jr.; Smith, P. L.

    1989-01-01

    The histories of configurational changes and sedimentation in the Tobago Trough, which is a modern bathymetric forearc basin of the Lesser Antilles island arc, were investigated using marine seismic data from the Tobago Trough. Special attention is given to two tectonic problems. The first is the evolution of the southeastern corner of the Caribbean as related to the finding that the early forearc basins had substantially different configurations from that of the modern forearc basin. The second is the interaction between the forearc basin and the accretionary prism within the Lesser Antilles system. It is pointed out that Miocene and younger features of the Tobago Trough might reflect a superposition of tectonism associated with the development of the Neogene Lesser Antilles arc on an older arc system.

  5. Role of fluids in the tectonic evolution of Titan

    NASA Astrophysics Data System (ADS)

    Liu, Zac Yung-Chun; Radebaugh, Jani; Harris, Ron A.; Christiansen, Eric H.; Rupper, Summer

    2016-05-01

    Detailed analyses of slopes and arcuate planform morphologies of Titan's equatorial mountain ridge belts are consistent with formation by contractional tectonism. However, contractional structures in ice require large stresses (4-10 MPa), the sources of which are not likely to exist on Titan. Cassini spacecraft imagery reveals a methane-based hydrological cycle on Titan that likely includes movement of fluids through the subsurface. These crustal liquids may enable contractional tectonic features to form as groundwater has for thrust belts on Earth. In this study, we show that liquid hydrocarbons in Titan's near subsurface can lead to fluid overpressures that facilitate contractional deformation at smaller stresses (<1 MPa) by significantly reducing the shear strength of materials. Titan's crustal conditions with enhanced pore fluid pressures favor the formation of thrust faults and related folds in a contractional stress field. Thus, surface and near-surface hydrocarbon fluids made stable by a thick atmosphere may play a key role in the tectonic evolution of Titan.

  6. Plate tectonic evolution of circum-Antarctic passive margins

    SciTech Connect

    Scotese, C.R.; Lawver, L.A.; Sclater, J.G.; Mayes, C.L.; Norton, I.; Royer, J.

    1987-05-01

    Passive margins that formed during the Late Jurassic and Cretaceous account for approximately 80% of the 15,000-km circumference of Antarctica. There are no passive margins younger than Late Cretaceous. Approximately 28% of these margins are Late Jurassic in age, 24% are Early Cretaceous in age, and the remaining 48% formed during the Late Cretaceous. The tectonic style of the rifting events that formed these margins varies considerably along the perimeter of Antarctica. In several areas the initiation of sea-floor spreading was preceded by a long period of extension and predrift stretching (Wilkes Land). Along other portions of the margin, rifting proceeded rapidly with little evidence for a lengthy phase of pre-drift extension (Queen Maud Land). Though extension is the dominant tectonic style, there is evidence for large-scale strike-slip movement associated with the early phases of continental breakup along the coasts of Crown Princess Martha Land and Victoria Land. Except for a short segment of the margin between the West Antarctic peninsula and Marie Byrdland, the Antarctic passive margins have not been affected by subsequent subduction-related compressive deformation. This presentation will review the plate tectonic evolution of the Circum-Antarctic passive margins during five time intervals: Early Jurassic, Late Jurassic, Early Cretaceous, mid-Cretaceous, and latest Cretaceous. A map illustrating the relative amounts of extension along the margin of Antarctica will be presented, and a computer animation illustrating the breakup of Gondwana from an Antarctic perspective will be shown.

  7. The tectonic evolution of Red Sea and Gulf of Aden

    SciTech Connect

    Allen, R.B. ); Sikander, A.H. ); Abouzakhm, A.G.

    1991-08-01

    The Red Sea and Gulf of Aden, formed by rifting of the Arabian plate away from Africa, have been the subjects of numerous studies since the 1960s. Geophysical and geological data gathered during hydrocarbon exploration by several companies are being synthesized as part of the World Bank-executed Red Sea/Gulf of Aden Regional Hydrocarbon Study Project. This synthesis provides an opportunity to study the regional variation in tectonic history and structural style within the two basins, particularly toward the basin margins, where data coverage is most complete and a thinner sedimentary cover allows more reliable interpretation of deeper horizons. Based on this data, most of the Red Sea shows a similar tectonic history to that of the Gulf of Suez. Widespread normal faulting developed contemporaneous with deposition of a dominantly clastic sequence of Oligocene( ) to middle Miocene age. The faulting often dies out within or below thick middle to upper Miocene evaporite deposits with only few faults affecting the younger units. The Gulf of Aden, on the other hand, shows a strong contrast between largely west-northwest-east-southeast oriented extensional structures on land, and generally more east-west oriented extensional structures on the continental shelves and slopes. The onshore extensional structures oriented oblique to the coast, and approximately perpendicular to transform fault trends in the oceanic crust of the central Gulf of Aden. This contrast is extensional structure orientations has important implications for the tectonic evolution of the Gulf of Aden.

  8. 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

  9. Tectonic evolution of Brazilian equatorial continental margin basins

    SciTech Connect

    Azevedo, R.P. )

    1993-02-01

    The structural style and stratigraphic relationships of sedimentary basins along the Brazilian Equatorial Atlantic Continental Margin were used to construct an empirical tectonic model for the development of ancient transform margins. The model is constrained by detailed structural and subsidence analyses of several basins along the margin. The structural framework of the basins was defined at shallow and deep levels by the integration of many geophysical and geological data sets. The Barreirinhas and Para-Maranhao Basins were divided in three tectonic domains: the Tutoia, Caete, and Tromai subbasins. The Caete area is characterized by northwest-southeast striking and northeast-dipping normal faults. A pure shear mechanism of basin formation is suggested for its development. The structure of the Tutoia and Tromai subbasins are more complex and indicative of a major strike-slip component with dextral sense of displacement, during early stages of basin evolution. These two later subbasins were developed on a lithosphere characterized by an abrupt transition (<50 km wide) from an unstretched continent to an oceanic lithosphere. The subsidence history of these basins do not comply with the classical models developed for passive margins or continental rifting. The thermo-mechanical model proposed for the Brazilian equatorial margin includes heterogeneous stretching combined with shearing at the plate margin. The tectonic history comprises: (1) Triassic-Jurassic limited extension associated with the Central Atlantic evolution; (2) Neocomian intraplate deformation consisting of strike-slip reactivation of preexisting shear zones; (3) Aptian-Cenomanian two-phase period of dextral shearing; and (4) Late Cretaceous-Cenozoic sea-floor spreading.

  10. Tectonic evolution of the Brooks Range ophiolite, Alaska

    SciTech Connect

    Harris, R.A. . Dept. of Geology)

    1993-04-01

    Detailed studies of the composition, internal structure, and age of the Brooks Range ophiolite (BRO) and its metamorphic sole reveal new constraints for its tectonic evolution. The BRO consists of six separate thrust masses of consanguineous composition, internal organization, structure and age. Subophiolite metamorphic rocks are locally preserved along its structural base, which is well exposed in several places. The metamorphic sole is locally transitional with mafic volcanic sequences, chert, tuffs, and minor clastic sedimentary material of the Copter Peak Complex, which is correlative with the Angayucham terrane. This terrane is much older than, and chemically distinct from the BRO. The internal structure of the BRO is characterized by NE-SW trending igneous layers that expose the transition zone from crust to mantle. Residual mantle material consists of tectonized peridotite in abrupt contact with dunite pods up to 4 km thick. Ductile and brittle structures of the BRO preserve various phases of its dynamic evolution from a magma body to a fragmented thrust sheet. The earliest deformational effects are recorded by ductile lattice and shape fabrics in dunites and the layered series of the BRO. Magmatic flow planes generally parallel the petrologic moho, and dip 40[degree]--70[degree] to the NW and SE. Flow lineations consistently plunge ESE-ENE from 39[degree]--54[degree]. Igneous laminations and compositional layers represent patterns of magmatic flow in, and plastic deformation of, a cumulate sequence -- not the deposition pattern of cumulate layers. In the upper layered series, amphiboles with a shape-preferred orientation yield Ar/Ar plateau ages of 163--169 Ma. These ages overlap with plateau ages of the same kind from amphibolite of the metamorphic sole. This concordance in age indicates that cooling of the BRO coincided with its tectonic emplacement.

  11. Tectonic, Climatic, and Cryospheric Evolution of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2013-06-01

    For millennia, Antarctica has been a frozen continent, a land of ice and snow where complex life persists rather than thrives. But Antarctica has not always been this way. Millions of years ago the southern continent was teeming with life. Changing oceans and a plummeting atmospheric carbon dioxide concentration drove a dramatic evolution of the Antarctic continent. To provide a record of these ancient climatic shifts, the 2005-2006 SHALDRIL drilling program collected sediment cores from the bed of the iceberg-filled seas off the Antarctic Peninsula. In the AGU book Tectonic, Climatic, and Cryospheric Evolution of the Antarctic Peninsula, editors John B. Anderson and Julia S. Wellner draw on the findings garnered from SHALDRIL to explore the changing Antarctic Peninsula. In this interview, Eos talks to John B. Anderson.

  12. Structural and metamorphic evolution of serpentinites and rodingites recycled in the Alpine subduction wedge

    NASA Astrophysics Data System (ADS)

    Zanoni, D.; Rebay, G.; Spalla, M. I.

    2015-12-01

    Hydration-dehydration of mantle rocks affects the viscosity of the mantle wedge and plays a prominent role in subduction zone tectonics, facilitating marble cake-type instead of large-slice dynamics. An accurate structural and petrologic investigation of serpentinites from orogenic belts, supported by their long-lived structural memory, can help to recognize pressure-sensitive mineral assemblages for deciphering their P-prograde and -retrograde tectonic trajectories. The European Alps preserve large volumes of the hydrated upper part of the oceanic lithosphere that represents the main water carrier into the Alpine subduction zone. Therefore, it is important to understand what happens during subduction when these rocks reach P-T conditions proximal to those that trigger the break-down of serpentine, formed during oceanic metamorphism, to produce olivine and clinopyroxene. Rodingites associated with serpentinites are usually derived from metasomatic ocean floor processes but rodingitization can also happen in subduction environments. Multiscale structural and petrologic analyses of serpentinites and enclosed rodingites have been combined to define the HP mineral assemblages in the Zermatt-Saas ophiolites. They record 3 syn-metamorphic stages of ductile deformation during the Alpine cycle, following the ocean floor history that is testified by structural and metamorphic relics in both rock types. D1 and D2 developed under HP to UHP conditions and D3 under lower P conditions. Syn-D2 assemblages in serpentinites and rodingites indicate conditions of 2.5 ± 0.3 GPa and 600 ± 20°C. This interdisciplinary approach shows that the dominant structural and metamorphic imprint of the Zermatt-Saas eclogitized serpentinites and rodingites developed during the Alpine subduction and that subduction-related serpentinite de-hydration occurred exclusively at Pmax conditions, during D2 deformation. In contrast, in the favourable rodingite bulk composition (Ca-rich), hydrated minerals

  13. 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.

  14. Tectonic subsidence history and thermal evolution of the Orange Basin

    NASA Astrophysics Data System (ADS)

    Hirsch, K. K.; Scheck-Wenderoth, M.; van Wees, J.; Paton, D. A.; Kuhlmann, G.

    2008-12-01

    The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension. We present results of a combined approach using subsidence analysis and basin history inversion models. Our results show that a classical uniform stretching model does not account for the observed tectonic subsidence. Moreover we find that that the thermal and subsidence implications of underplating need to be considered. Another departure from the uniform stretching model is re-newed sub-crustal stretching and linked to that uplift in the Cenozoic which is necessary to reproduce the observed phases of erosion and the present day depth of the basin. The dimension of these events has been examined and quantified in terms of tectonic uplift and sub-crustal stretching. Based on these forward models we predict the heat flow evolution not only for the available real wells but also for virtual wells over the entire study area. Finally the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks.

  15. A Lost Realm in the Internal Domains of the Betic-Rif Orogen (Spain and Morocco): Evidence from Conglomerates and Consequences for Alpine Geodynamic Evolution.

    PubMed

    Martín-Algarra; Messina; Perrone; Russo; Maate; Martín-Martín

    2000-07-01

    The Malaguide-Ghomaride Complex is capped by Upper Oligocene-Aquitanian clastic deposits postdating early Alpine orogenesis but predating the main tectonic-metamorphic evolution, end of nappe emplacement, unroofing, and exhumation of the metamorphic units of the Betic-Rif Orogen. Two conglomerate intervals within these deposits are characterized by clasts of sedimentary, epimetamorphic, and mafic volcanic rocks derived from Malaguide-Ghomaride units and by clasts of acidic magmatic and orthogneissic rocks of unknown provenance, here studied. Magmatic rocks originated from late-Variscan two-mica cordierite-bearing granitoids and, subordinately, from aplitic dikes. Orthogneisses derive from similar plutonic rocks but are affected by an Alpine metamorphic overprint evolving from greenschist (T=510&j0;-530 degrees C and P=5-6 kbar) to low-temperature amphibolite facies (T>550&j0;C and P<3 kbar). Such a plutonic rock suite is unknown in any Betic-Rif unit or in the basement of the Alboran Sea, and the metamorphic evolution in the orthogneisses is different from (and older than) that of Alpujarride-Sebtide rocks to which they were formerly ascribed. Magmatic and metamorphic rocks very similar to those studied characterize the basements of some Kabylia and Calabria-Peloritani units. Therefore, the source area is a currently lost continental-crust realm of Calabria-Peloritani-Kabylia type, located to the ESE of the Malaguide-Ghomaride Domain and affected by a pre-latest Oligocene Alpine metamorphism. Increasingly active tectonics transformed this realm into rising areas from which erosion fed small subsiding synorogenic basins formed on the Malaguide-Ghomaride Complex. This provenance analysis demonstrates that all these domains constituted a single continental-crust block until Aquitanian-Burdigalian times, before its dispersal around nascent western Mediterranean basins. PMID:10856014

  16. Geomorpho-tectonic evolution of the Jamaican restraining bend

    NASA Astrophysics Data System (ADS)

    Domínguez-González, Leomaris; Andreani, Louis; Stanek, Klaus P.; Gloaguen, Richard

    2015-01-01

    This work applies recent advances in tectonic geomorphology in order to understand the geomorphic evolution of the Jamaican restraining bend located along the Caribbean-Gonâve-North American plate boundary. We propose a classification of landscapes according to their erosional stages. The approach is mainly based on the combination of two DEM-based geomorphic indices: the hypsometric integral which highlights elevated surfaces, and the surface roughness which increases when the relief is incised by the drainage network. River longitudinal profiles were also analyzed as the drainage network responds quickly to base-level change triggered by external forcing such as tectonics. Anomalies in river profiles (knickpoints and convex segments) were mapped using stream length-gradient (SL) and normalized steepness (ksn) indices. The results provide new insights for understanding the complex evolution of the Jamaican restraining bend. Three main morphotectonic regions were identified in Jamaica: (1) the Blue Mountain-Wagwater unit located at the eastern tip of the island, (2) the Jamaican highlands plateau which covers most of the northern and central areas and (3) the tilted block province located along the southern part of Jamaica. Each region has a specific morphological signature which marks a different stage in the Late Miocene to present evolution of the Jamaican restraining bend. The evolution of the bend is mainly associated with the western propagation of major E-trending strike-slip faults and NW-trending thrusts. In the western and central parts of Jamaica the present-day motion between the Caribbean plate and the Gonâve microplate is broadly distributed along several structures, while in the easternmost part of the island this motion seems to be almost completely accommodated along the Blue Mountain range and the Plantain-Garden Fault.

  17. Role of structural heritage and global tectonics events in evolution of Algerian Triassic basin: Tectonic inversion and reservoir distribution

    SciTech Connect

    Boudjema, A.; Tremolieres, P.

    1988-01-01

    Fieldwork and subsurface studies (350 bore holes and more than 100 seismic profiles) show the structural evolution of the Triassic Saharian basin. This evolution is controlled by the successive motions of ancient faults of the Paleozoic basement during the different compressional and distensional tectonic phases. These movements led to some tectonic inversions. Depending on the strike of the faults, the present results correspond to normal throw or reverse throw at the level of hydrocarbon reservoirs. These tectonic phases clearly result from relative motions between African, American, and European lithospheric plates. The Triassic basin, a mobile zone between two rigid shields, constitutes a very good indication of the successive motions. The distribution and the nature of hydrocarbon fields are clearly related to the proximity of the faults, the post-tectonic erosion of a part of the source rocks, the burial and maturation of the organic matter, and the age of structural traps.

  18. The tectonic and volcanic evolution of Venus: Catastrophic or gradual?

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1993-01-01

    different degree of layering, then the planet may in the last 500 My have attained lesser mantle temperatures, lower mantle heat flux, and a significantly lesser rate of magma production than Earth yet still display evidence for ongoing convection and active tectonics. Such a 'cold Venus' scenario would be broadly consistent with observations yet be characterized by a gradual volcanic and tectonic evolution.

  19. Tectonic evolution of Honey Lake basin, northeastern California

    SciTech Connect

    Wagner, D.L. ); Saucedo, G.J. ); Grose, T.L.T. . Dept. of Geology and Geological Engineering)

    1993-04-01

    New geologic mapping in northeastern California provides additional data on the age and tectonic evolution of the Honey Lake Basin. Rhylitic ash flow tuffs of latest Oligocene to early Miocene age (30 to 22 Ma) occur in the Fort Sage Mountains and in the Sierra Nevada but are not apparent in wells drilled in the Honey Lake basin. Though other interpretations can be made, the authors take this as evidence that the basin did not exist at that time. Volcanic rocks as old as 12 Ma do occur in the basin indicating initiation in mid-Miocene time probably as a graben due to block faulting. Syntectonic andesitic and basaltic volcanism occurred along faults bounding the Sierra Nevada block at 9 to 10 Ma. Lava issuing from these fractures flowed westward along Tertiary drainages indicating that the Sierran block had been uplifted and tilted westward. Andesites erupted during this time north and east of the basin are lithologically distinct from Sierran andesites. Strike-slip faulting began to dominate the tectonic setting of the region during late Pliocene and Quaternary time with the development of the Honey Lake Fault Zone. Holocene strike-slip displacement is indicated by offsets of the 12,000 year old Lake Lahontan shoreline and deposits containing a 7,000 year old ash.

  20. Tectonic evolution of Kashmir basin in northwest Himalayas

    NASA Astrophysics Data System (ADS)

    Alam, Akhtar; Ahmad, Shabir; Bhat, M. Sultan; Ahmad, Bashir

    2015-06-01

    Geomorphology has long been recognised as a key to evaluate the interplay between tectonics and landscape geometry in the regions of active deformation. We use geomorphic signatures at varied spatial scales interpreted from SRTM-DEM/Landsat-ETM data, supplemented with field observations to review the tectonic evolution of Kashmir basin in northwest Himalayas. Geomorphic evidence is persuasive of a credible NNW-SSE trending dextral strike-slip structure (central Kashmir Fault - CKF), with the strike length of ~ 165 km, stretched centrally over the NNW-SSE length of the Kashmir basin. As a result of the strike-slip motion and subsequent erosion, significant deformation has taken place along the CKF. In addition, broad geomorphic architecture of the basin reveals typical pull-apart characteristics. Hence, we deduce that the Kashmir basin has evolved as a pull-apart Quaternary sediment depression owing to the deformation along the central Kashmir Fault. The spatial distribution pattern of seismic events (NEIC-catalogue, 1973-2013) and GPS measurements (published), collectively substantiate our geomorphic interpretations.

  1. A model for plate tectonic evolution of mantle layers.

    PubMed

    Dickinson, W R; Luth, W C

    1971-10-22

    In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years. PMID:17796091

  2. Tectonic evolution of the Archaean high-grade terrain of South India

    NASA Technical Reports Server (NTRS)

    Ramakrishnan, M.

    1988-01-01

    The southern Indian shield consists of three major tectonic provinces viz., (1) Dharwar Craton, (2) Eastern Ghat Mobile Belt, and (3) Pandyan Mobile Belt. An understanding of their mutual relations is crucial for formulating crustal evolution models. The tectonic evolution of these provinces is summarized.

  3. Evidence of adaptive evolution of alpine pheasants to high-altitude environment from mitogenomic perspective.

    PubMed

    Gu, Peng; Liu, Wei; Yao, Yong-fang; Ni, Qing-yong; Zhang, Ming-wang; Li, Di-yan; Xu, Huai-liang

    2016-01-01

    Adaptive evolutions to high-altitude adaptation have been intensively studied in mammals. However, considering the additional vertebrate groups, new perception regarding selection challenged by high-altitude stress on mitochondrial genome can be gained. To test this hypothesis, we compiled and analyzed the mitochondrial genomes of 5 alpine pheasants and 12 low-altitude species in Phasianidae. The results that evolutionary rates of ATP6 and ND6 showing significant fluctuation among branches when involved with five alpine pheasants revealed both genes might have implications with adapting to highland environment. The radical physico-chemical property changes identified by the modified MM01 model, including composition (C) and equilibrium constant (ionization of COOH) (Pk') in ATP6 and beta-structure tendencies (Pβ), Pk', and long-range non-bonded energy (El) in ND6, suggested that minor overall adjustments in size, protein conformation and relative orientation of reaction interfaces have been optimized to provide the ideal environments for electron transfer, proton translocation and generation of adenosine triphosphate (ATP). Additionally, three unique substitution sites were identified under selection in ND6, which could be potentially important adaptive changes contributing to cellular energy production. Our findings suggested that adaptive evolution may occur in alpine pheasants, which are an important complement to the knowledge of genetic mechanisms against the high-altitude environment in non-mammal animals. PMID:24708132

  4. The evolution of Tharsis: Implications of gravity, topography, and tectonics

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.; Golombek, M. P.

    1990-01-01

    Dominating the Western Hemisphere of Mars, the Tharsis rise is an elongate area centered on Syria Planum that ascends as much as 8 to 10 km above the datum. It is intensely fractured by long, narrow grabens that extend radially hundreds of kilometers beyond the rise and is ringed by mostly concentric wrinkle ridges that formed over 2,000 km from the center of the rise. Its size, involving a full hemisphere of Mars, gives it a central role in the thermo-tectonic evolution of the planet and has stimulated a number of studies attempting to determine the sequence of events responsible for this feature. The constraints that gravity and topography data place on the current structure of Tharsis, along with insights into its development derived from comparisons of detailed regional mapping of faulting with theoretical deformation models are reviewed. Finally, a self-consistent model for the structure of Tharsis is proposed.

  5. Garnet Porphyroblasts and the Tectonic Evolution of Iberia

    NASA Astrophysics Data System (ADS)

    Aerden, D. G.

    2013-12-01

    Porphyroblast inclusion trails constitute an exceptionally detailed record of deformation histories undergone by metamorphic rocks. Their orientations have been shown to be remarkably consistent in mountain belts and to relate to large-scale orogenic processes. For example, vertical and horizontal preferred orientations are almost universally developed and resulted from multiple gravitational collapse stages that periodically interrupted plate-driven (horizontal) crustal shortening. Over the past 20 years, a large body of orientation data has become available for Foliation Intersection Axes (FIA) defined by inclusion trails in orogenic belts around the world. This data reveals that FIAs in metamorphic regions generally can be grouped into a discrete number of age sets with distinctive geographic trends. Such FIA sequences apparently track shifts in the direction of crustal shortening with time. Garnet is a particularly useful porphyroblastic mineral where it comes to linking deformation and metamorphic paths, due to a unique combination of properties: (1) lengthy growth histories along extended P-T paths and in rocks with variable bulk compositions, (2) sub-spherical crystal shapes and rigid behavior favoring the nucleation of tectonic foliations against garnet edges and their preservation in continued garnet-growth stage, (3) chemical compositions sensitive to changes in metamorphic conditions that can be modeled thermodynamically, (4) abundance of datable micro-inclusions, such as monazite, and (5) the possibility of dating garnet itself via the Sm-Nd or Lu-Hf methods. In Iberia, integrated microstructural and petrological analysis of garnet porphyroblasts in the Betic Cordillera (European Alpine belt) has recently established a sequence of 4 FIA sets. The successive geographic trends of these FIA (NE-SW, NW-SE, ENE-WSW, and NNW-SSE) remarkably correlate with known changes in relative Iberia-Africa plate motion from ca. 50-10Ma. In Hercynian Iberia (Iberian

  6. Surge-tectonic evolution of southeastern Asia: a geohydrodynamics approach

    NASA Astrophysics Data System (ADS)

    Meyerhoff, Arthur A.

    The repeated need for ad hoc modifications in plate-tectonic models to explain the evolution of southeastern Asia reveals their inability to fully explain the complex features and dynamics of this region. As one example, the hypothesis does not provide a mechanism to explain the 180° turns and twists along the strike of several foldbelts and island arcs in the region (e.g. Banda arc). Convection-cell configuration renders such 180° contortions and Rayleigh-Bénard-type convection impossible. However, during the last 10 years, new data bearing on the convection-cell problem have become available in the form of seismotomographic images of the earth's interior. These images show that (i) mantle diapirs as proposed by traditional plate-tectonic models do not exist; (ii) there is no discernible pattern of upper or lower mantle convection, and thus no longer an adequate mechanism to move plates; and (iii) the lithosphere above a depth of about 80 km is permeated by an interconnected network of low-velocity channels. Seismic-reflection studies of the low-velocity channels discovered on the seismotomographic images reveal that these channels have walls with a 7.1-7.8 km s -1 P-wave velocity. Commonly, the interiors of the channels are acoustically transparent, with much slower P-wave velocities, in places as low as 5.4 km s -1. The author and co-workers have interpreted the low velocities as evidence for the presence of partial melt in the channels, and they postulated that this melt moves preferentially eastward as a result of the earth's rotation. They named these channels "surge channels" and their new hypothesis for earth dynamics "surge tectonics". Surge channels underlie every type of tectonic belt, which includes mid-ocean ridges, aseismic ridges, continental rifts, strike-slip fracture zones, and foldbelts. In southeastern Asia, surge channels—mainly foldbelts—lie between all platform and cratonic massifs. These massifs, platforms, and tectonics belts

  7. Scientific results of the NASA-sponsored study project on Mars: Evolution of volcanism, tectonics, and volatiles

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C. (Editor); Sharpton, Virgil L. (Editor); Zimbelman, James R. (Editor)

    1990-01-01

    The objectives of the Mars: Evolution of Volcanism, Tectonics, and Volatiles (MEVTV) project are to outline the volcanic and tectonic history of Mars; to determine the influence of volatiles on Martian volcanic and tectonic processes; and to attempt to determine the compositional, thermal, and volatile history of Mars from its volcanic and tectonic evolution. Available data sets were used to test general models of the volcanic and tectonic history of Mars.

  8. The Cretaceous and Cenozoic tectonic evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Zahirovic, S.; Seton, M.; Müller, R. D.

    2014-04-01

    Tectonic reconstructions of Southeast Asia have given rise to numerous controversies that include the accretionary history of Sundaland and the enigmatic tectonic origin of the proto-South China Sea. We assimilate a diversity of geological and geophysical observations into a new regional plate model, coupled to a global model, to address these debates. Our approach takes into account terrane suturing and accretion histories, the location of subducted slabs imaged in mantle tomography in order to constrain the evolution of regional subduction zones, as well as plausible absolute and relative plate velocities and tectonic driving mechanisms. We propose a scenario of rifting from northern Gondwana in the latest Jurassic, driven by northward slab pull from north-dipping subduction of Tethyan crust beneath Eurasia, to detach East Java, Mangkalihat, southeast Borneo and West Sulawesi blocks that collided with a Tethyan intra-oceanic subduction zone in the mid-Cretaceous and subsequently accreted to the Sunda margin (i.e., southwest Borneo core) in the Late Cretaceous. In accounting for the evolution of plate boundaries, we propose that the Philippine Sea plate originated on the periphery of Tethyan crust forming this northward conveyor. We implement a revised model for the Tethyan intra-oceanic subduction zones to reconcile convergence rates, changes in volcanism and the obduction of ophiolites. In our model the northward margin of Greater India collides with the Kohistan-Ladakh intra-oceanic arc at ∼53 Ma, followed by continent-continent collision closing the Shyok and Indus-Tsangpo suture zones between ∼42 and 34 Ma. We also account for the back-arc opening of the proto-South China Sea from ∼65 Ma, consistent with extension along east Asia and the formation of supra-subduction zone ophiolites presently found on the island of Mindoro. The related rifting likely detached the Semitau continental fragment from South China, which accreted to northern Borneo in

  9. The efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles

    NASA Astrophysics Data System (ADS)

    Moore, W. B.; Lenardic, A.

    2015-11-01

    Consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes (rigid-lid convection, plate tectonics, and heat pipe volcanism) reveals that if the efficiency of plate tectonic heat transport decreases at higher mantle temperature, then it cannot govern quasi-equilibrium dynamical evolution, and the system is always evolving away from the plate tectonic regime. A planet on which plate tectonics is less efficient at higher temperature stays in heat pipe mode longer, spends less time undergoing plate tectonics, and has a low and ever-decreasing Urey number during this phase. These conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior. Commonly used quasi-equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature.

  10. Into thin air: Physiology and evolution of alpine insects.

    PubMed

    Dillon, Michael E; Frazier, Melanie R; Dudley, Robert

    2006-02-01

    Numerous physical parameters that influence insect physiology vary substantially with altitude, including temperature, air density, and oxygen partial pressure. Here, we review existing literature and present new empirical data to better characterize the high-altitude environment, and then consider how this environment affects the physiology and evolution of insects. Using weather balloon data from fifty-three sites across the globe, we estimate a mean altitudinal temperature lapse rate of 6.0 °C/km. We also present empirically determined lapse rates for P(o(2)) and air density. The temperature decline with elevation may substantially compromise insect thermoregulation at high altitude. However, heat-transfer models predict that lower air density at elevation reduces convective heat loss of insects by to a surprisingly large degree. This effect combined with behavioral thermoregulation and the availability of buffered microhabitats make the net thermal consequences of high-altitude residence strongly context-specific. The decline in P(o(2)) with elevation may compromise insect development and physiology, but its effects are difficult to predict without simultaneously considering temperature and air density. Flying insects compensate for low air densities with both short-term responses, such as increased stroke amplitude (but not wingbeat frequency), and with long-term developmental and/or evolutionary increases in wing size relative to body size. Finally, in contrast to predictions based on Bergmann's Rule, a literature survey of thirty-six insect species suggests that those living in colder, higher altitudes do not tend to have larger body sizes. PMID:21672722

  11. Mesozoic Plate Tectonic Evolution of the Northern Margin of Pangea

    NASA Astrophysics Data System (ADS)

    Miller, E. L.

    2011-12-01

    Asia joined Laurentia and Baltica during the formation of the Urals in the Early Permian. Subsequently, the northern margin of Pangea shared a paleo-Pacific facing margin. Analysis of events along this (mostly active) margin provides insight into the plate tectonic setting and evolution of the Arctic basins and their temporal links to Pacific margin events. A 3-phase tectonic evolution characterizes the northern margin of Pangea during the Mesozoic: 1. Permo-Triassic rifting (Siberian Trap magmatism)was linked to rifting in a series of back-arc basins developed along the northern margin of Pangea. Triassic-Jurasic deep-water sedimentary seqences deposited in these basins were subsequently deformed during phase 2 events. 2. Lithospheric shortening/convergence across this margin deformed these basinal sediments and shed syn-orogenic deposits cratonward in the Jura-Cretaceous. Syn-orogenic basinal successions are widespread from the Verkoyansk margin of Siberia to the Brooks Range fold and thrust belt. Their sources are well-characterized by U-Pb ages of detrital zircon suites and include Pennsylvanian-Permian, Triassic and Jurassic magmatic belts, implying convergence and emplacement of a long-lived arc system onto the continental margin. 3. Structures related to phase 2 are cut and overprinted by voluminous, syn-extensional, slab-related magmatism that developed during southward or Pacific-ward migration of a N-dipping subducting slab. It is inferred that the earliest part of the Amerasia Basin likely opened during part of this magmatic event, 135 to 90 Ma. The final culmination of this magmatic event is the Ohotsk-Chukotsk volcanic belt, ~90-75 Ma;after this, magmatism continues to migrate Pacific-ward in a series of steps. Utilizing plate models of the Arctic by Lawver et al.(2002) it can be shown that some of the differences in the timing and style of Mesozoic orogenesis along the northern paleo-Pacific margin of Pangea (and especially the differences between the

  12. Surge-tectonic evolution of southeastern Asia: a geohydrodynamics approach

    NASA Astrophysics Data System (ADS)

    Meyerhoff, Arthur A.

    The repeated need for ad hoc modifications in plate-tectonic models to explain the evolution of southeastern Asia reveals their inability to fully explain the complex features and dynamics of this region. As one example, the hypothesis does not provide a mechanism to explain the 180° turns and twists along the strike of several foldbelts and island arcs in the region (e.g. Banda arc). Convection-cell configuration renders such 180° contortions and Rayleigh-Bénard-type convection impossible. However, during the last 10 years, new data bearing on the convection-cell problem have become available in the form of seismotomographic images of the earth's interior. These images show that (i) mantle diapirs as proposed by traditional plate-tectonic models do not exist; (ii) there is no discernible pattern of upper or lower mantle convection, and thus no longer an adequate mechanism to move plates; and (iii) the lithosphere above a depth of about 80 km is permeated by an interconnected network of low-velocity channels. Seismic-reflection studies of the low-velocity channels discovered on the seismotomographic images reveal that these channels have walls with a 7.1-7.8 km s -1 P-wave velocity. Commonly, the interiors of the channels are acoustically transparent, with much slower P-wave velocities, in places as low as 5.4 km s -1. The author and co-workers have interpreted the low velocities as evidence for the presence of partial melt in the channels, and they postulated that this melt moves preferentially eastward as a result of the earth's rotation. They named these channels "surge channels" and their new hypothesis for earth dynamics "surge tectonics". Surge channels underlie every type of tectonic belt, which includes mid-ocean ridges, aseismic ridges, continental rifts, strike-slip fracture zones, and foldbelts. In southeastern Asia, surge channels—mainly foldbelts—lie between all platform and cratonic massifs. These massifs, platforms, and tectonics belts

  13. The Tectonic Evolution and Mineralization in Altay, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Dong, Y.; Ding, R.; Zhang, C.

    2011-12-01

    China Altai located in the center of Altai belt and experienced a long history of complex tectonic evolution, and the rich mineral resources were formed in the belt. The copper-zinc, lead- zinc and other non-ferrous metals deposits are produced in 230 -380 Ma ago, gold deposits are produced in 260-310 Ma and 135 Ma ago, and the rare metal deposits produced mainly in 148 -198 Ma ago in the Altay, Xinjiang, China. These ore deposits were formed in zoning and can be classified into following ore-forming belts such as Irtysh belt, Ashele belt, Chonghuer-Maizi belt and Keketuohai1belt. As Siberia plate and Kazakhstan plate expansion in sinian Period, the paleo-Asia ocean was formed,and the paleo-Asia ocean subducted to Siberia plate in the same time, shallow sea clastic rock formation was developed in Altay in Early Palaeozoic (Cambrian to early Ordovician) . The Siberian block cracked open along the southwestern edge of Siberian block since early Hercynian (400-380Ma) to cause the bimodal magma eruptive and invasive activities occurred strongly along the rift zone at the floor. The volcanic activity center moved from east to west to form a series of volcanic basin such as Maizi, Kelan, Chonghuer and Ashele volcanic basins in southern Altay, and the iron, lead, zinc, copper and zinc deposit formed in these volcanic basins. Because of the Continental crust relaxation, the Nurt volcanic sedimentary basin was formed between 370-330Ma. Volcanic rock erupted, granite intruded, And the source bed of lead, zinc and epithermal gold deposits were formed. Early Carboniferous (Hercynian middle and late ,320-280Ma) Junggar plate collision to the Siberian plate, the collision zone at roughly the irtysh melange rock zone distribution area, and the deep tensile fracture occurred along this tectonic belt to cause mantle material intrusion along this belt because of pressure depressing and the partial melting of magma to form basic and ultrabasic rock to form copper, nickel, platinum

  14. Style of Alpine tectonic deformation in the Castellane fold-and-thrust belt, (SW Alps, France): Insights from balanced cross-sections

    NASA Astrophysics Data System (ADS)

    Jourdon, Anthony; Rolland, Yann; Petit, Carole; Bellahsen, Nicolas

    2015-04-01

    This study proposes a reappraisal of the role of the basement tectonics in the structuration of the Alpine foreland, across the Castellane fold-and-thrust belt located in southwestern Alps. We construct three 30 km length N-S balanced cross-sections across the entire fold-and-thrust belt, in order to quantify the amount of horizontal shortening due to the Pyrenean and Alpine deformations. We then assess the role of the basement inherited structures during the compressional phases which resulted in the exhumation of the Argentera-Mercantour External crystalline massif and the Barrot Dome. The construction of these balanced cross-sections suggests a dominant thick-skinned deformation style, which includes the reactivation of inherited Permian and Early Cretaceous basement normal faults. We reconstructed three restoration stages: the oldest one highlights the geometry of Permian and Early Cretaceous extensional structures; the intermediate one after the Late Cretaceous evidences a first compressional episode linked to the Pyrenean compression; the latest one in the Oligocene shows the first Alpine folds resulting from the southward thrusting of the internal units over the external ones along of the Penninic Frontal Thrust. Balanced cross-sections suggest very moderate crystalline basement - sedimentary cover decoupling. On the western and central cross-sections, the estimated amount of shortening ranges from 9.5 to 10 km (21%) whereas on the easternmost one shows ~5 km of shortening (9%). These shortening values are consistent with previously published estimates in the surrounding foreland subalpine chains. They highlight a decreasing value of Pyrenean shortening towards the east, while the Alpine shortening dominates and amplifies this first phase in a similar direction. We interpret this dominantly thick-skinned structural style as a possible consequence of the Neogene thermal weakening in the European passive margin above the Ligurian slab rollback.

  15. The Cretaceous and Cenozoic tectonic evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Zahirovic, S.; Seton, M.; Müller, R. D.

    2013-08-01

    Tectonic reconstructions of Southeast Asia have given rise to numerous controversies which include the accretionary history of Sundaland and the enigmatic tectonic origin of the Proto South China Sea. We assimilate a diversity of geological and geophysical observations into a new regional plate model, coupled to a global model, to address these debates. Our approach takes into account terrane suturing and accretion histories, the location of subducted slabs imaged in mantle tomography in order to constrain the opening and closure history of paleo-ocean basins, as well as plausible absolute and relative plate velocities and tectonic driving mechanisms. We propose a scenario of rifting from northern Gondwana in the Late Jurassic, driven by northward slab pull, to detach East Java, Mangkalihat, southeast Borneo and West Sulawesi blocks that collided with a Tethyan intra-oceanic subduction zone in the mid Cretaceous and subsequently accreted to the Sunda margin (i.e. southwest Borneo core) in the Late Cretaceous. In accounting for the evolution of plate boundaries, we propose that the Philippine Sea Plate originated on the periphery of Tethyan crust forming this northward conveyor. We implement a revised model for the Tethyan intra-oceanic subduction zones to reconcile convergence rates, changes in volcanism and the obduction of ophiolites. In our model the northward margin of Greater India collides with the Kohistan-Ladakh intra-oceanic arc at ∼53 Ma, followed by continent-continent collision closing the Shyok and Indus-Tsangpo suture zones between ∼42 and 34 Ma. We also account for the back-arc opening of the Proto South China Sea from ∼65 Ma, consistent with extension along east Asia and the emplacement of supra-subduction zone ophiolites presently found on the island of Mindoro. The related rifting likely detached the Semitau continental fragment from east China, which accreted to northern Borneo in the mid Eocene, to account for the Sarawak Orogeny

  16. Landscape evolution and bedrock incision in the northern Alpine Foreland since the last 2 Ma

    NASA Astrophysics Data System (ADS)

    Claude, Anne; Akçar, Naki; Schlunegger, Fritz; Ivy-Ochs, Susan; Kubik, Peter; Christl, Marcus; Vockenhuber, Christof; Dehnert, Andreas; Kuhlemann, Joachim; Rahn, Meinert; Schlüchter, Christian

    2016-04-01

    The landscape evolution of the Swiss Alpine Foreland since the early Pleistocene is of utmost importance for modelling the long-term safety of deep geological repositories for nuclear waste disposal in the northern Alpine Foreland. The oldest Quaternary sediments in the northern foreland are proximal glaciofluvial sediments lying unconformably on Tertiary Molasse or Mesozoic carbonate bedrock. These deposits form topographically distinct and discontinuous isolated plateaus. Terrace morphostratigraphy has a reversed stratigraphic relationship, i.e. today older sediments are located at higher altitudes and vice versa. In this study, we focus on the landscape evolution and long-term bedrock incision in the Swiss Alpine Foreland. We reconstruct the terrace chronology in the foreland at six key locations at different altitudes ranging from 433 m a.s.l. to 675 m a.s.l. by applying cosmogenic depth-profile and isochron-burial dating techniques. First results from these sites indicate that the gravels at studied sites were accumulated in the foreland between 1 and 2 Ma. Based on this reconstructed chronology, long-term bedrock incision rates between 0.1 and 0.2 mm/a were calculated. Thus, we inferred a landscape at that time that was most likely characterized by smoother hillslopes than at present. During the Mid-Pleistocene Revolution (ca. 0.95 Ma), a re-organization of the drainage systems occurred in the Alpine Foreland with a significant lowering of the base level of stream channels. Existing data suggest slightly increased incision rates after this drainage network re-organisation compared to our results. The reconstruction of the chronology at the remaining sites may allow quantifying a pronounced incision as well as the exact timing of the acceleration in the incision rates. REFERENCES Heuberger, S. & Naef, H. (2014). NAB 12-35: Regionale GIS-Kompilation und -Analyse der Deckenschotter-Vorkommen im nördlichen Alpenvorland. Nagra Arbeitsbericht. Kuhlemann, J. & Rahn

  17. Tectonic evolution of Western Patagonia and hydrocarbon habitats

    SciTech Connect

    Urien, C.M. )

    1993-02-01

    In Devonian times, Western Patagonia was a Pericratonic Foreland basin. The rift-like, faulted platform underwent several marine transgressions-regressions related to tectonic episodes occurring mainly from Hercynian to Andean (Pyrenaic) times that modified the extension and nature of sedimentation in the region, due to the evolution of the Pacific Plate and Margin, and the accretion of successive acidic magmatic arcs. The marine sequences that flooded Patagonia, uneven in extension, shifted from North to South in accordance with differential subsidence in this margin, particularly in the three main sedimentary embayments: Neuquen, San Jorge and Magellan-Malvinas. Transversal ridges, following ancestral transtensional features, rejuvenated during the Atlantic opening separate these embayments. Marine sequences evolved into restricted circulation oxygen poor seas, whose organic matter rich sediments originated hydrocarbon source rocks, identified in the three most important basinal complexes of Patagonia. The beginning of the Andean Orogeny and the emplacement of the Andean Batholith, hindered the Pacific marine presence in western Patagonian basins. Subsequently, an Eastern elongated region-wide subsidence allowed the accumulation of molasse-like sequences over most foredeep sediments in the region, creating several hydrocarbons habitats grouped as follows: Neuquen: Proven: Liassic-Aptian; Potential: Triassic; San Jorge: Proven: U. Jurassic-L. Cretaceous; Unproven: L. Paleozoic-L. Jurassic; Magellan/Malvinas: Proven: L. Cretaceous; Unproven: Jurassic-U. Cretaceous During Laramic time, Atlantic highstand sea levels flooded a great part of Extra Andean Patagonia, while the Andean Chain started rising with an active magmatic arc.

  18. Tectonics

    NASA Astrophysics Data System (ADS)

    John Dewey will complete his term as editor-in-chief of Tectonics at the end of 1984. Clark Burchfiel's term as North American Editor will also end. Tectonics is published jointly with the European Geophysical Society. This newest of AGU's journals has already established itself as an important journal bridging the concerns of geophysics and geology.James A. Van Allen, president of AGU, has appointed a committee to recommend candidates for both editor-in-chief and North American editor for the 1985-1987 term.

  19. Pollen sensitivity to ultraviolet-B (UV-B) suggests floral structure evolution in alpine plants

    PubMed Central

    Zhang, Chan; Yang, Yong-Ping; Duan, Yuan-Wen

    2014-01-01

    Various biotic and abiotic factors are known to exert selection pressures on floral traits, but the influence of ultraviolet-B (UV-B) light on the evolution of flower structure remains relatively unexplored. We have examined the effectiveness of flower structure in blocking radiation and the effects of UV-B on pollen viability in 42 species of alpine plants in the Hengduan Mountains, China. Floral forms were categorized as either protecting or exposing pollen grains to UV-B. The floral materials of plants with exposed and protected pollen grains were able to block UV-B at similar levels. Exposure to UV-B radiation in vitro resulted in a significantly greater loss of viability in pollen from plant species with protective floral structures. The pronounced sensitivity of protected pollen to UV-B radiation was associated with the type of flower structure. These findings demonstrate that UV-B plays an important role in the evolution of protective floral forms in alpine plants. PMID:24682234

  20. 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

  1. New tectonic concept of the Arctic region evolution

    NASA Astrophysics Data System (ADS)

    Petrov, O. V.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Sobolev, N. V.; Petrov, E.

    2012-12-01

    -Early Cretaceous continental rifting and volcanic activity. Reactivation of rifting in the Central Arctic at the beginning of Cenozoic led to the onset of spreading 56 million years ago along the emerging Gakkel Ridge and to the subsequent formation of the Eurasian Basin. Approximately 33 million years ago, the newly formed Eurasian oceanic basin connected with the Norwegian-Greenland Basin of the North Atlantic. Combined interpretation of seismostratigraphic data and drilling results suggests that during the Paleogene shallow-water sedimentation in the Central Arctic occurred, which indicates the high-standing sea level. Only in the Early Miocene (about 20 million years ago) the sea bottom sank sharply reaching its present-day depth and causing transition to deep-water deposition. This essential tectonic event is recorded throughout the Central Arctic elevations by a regional unconformity in seismostratigraphic sections. The Cenozoic expansion of the North Atlantic into the Central Arctic occurred across the structural assemblages whose formation was controlled by the preceding evolution of the Asian paleo-ocean.

  2. Post-Jurassic tectonic evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Zahirovic, Sabin; Seton, Maria; Dietmar Müller, R.; Flament, Nicolas

    2014-05-01

    The accretionary growth of Asia, linked to long-term convergence between Eurasia, Gondwana-derived blocks and the Pacific, resulted in a mosaic of terranes for which conflicting tectonic interpretations exist. Here, we propose solutions to a number of controversies related to the evolution of Sundaland through a synthesis of published geological data and plate reconstructions that reconcile both geological and geophysical constraints with plate driving forces. We propose that West Sulawesi, East Java and easternmost Borneo rifted from northern Gondwana in the latest Jurassic, collided with an intra-oceanic arc at ~115 Ma and subsequently sutured to Sundaland by 80 Ma. Although recent models argue that the Southwest Borneo core accreted to Sundaland at this time, we use volcanic and biogeographic constraints to show that the core of Borneo was on the Asian margin since at least the mid Jurassic. This northward transfer of Gondwana-derived continental fragments required a convergent plate boundary in the easternmost Tethys that we propose gave rise to the Philippine Archipelago based on the formation of latest Jurassic-Early Cretaceous supra-subduction zone ophiolites on Halmahera, Obi Island and Luzon. The Late Cretaceous marks the shift from Andean-style subduction to back-arc opening on the east Asian margin. Arc volcanism along South China ceased by ~60 Ma due to the rollback of the Izanagi slab, leading to the oceanward migration of the volcanic arc and the opening of the Proto South China Sea (PSCS). We use the Apennines-Tyrrhenian system in the Mediterranean as an analogue to model this back-arc. Continued rollback detaches South Palawan, Mindoro and the Semitau continental blocks from the stable east Asian margin and transfers them onto Sundaland in the Eocene to produce the Sarawak Orogeny. The extrusion of Indochina and subduction polarity reversal along northern Borneo opens the South China Sea and transfers the Dangerous Grounds-Reed Bank southward to

  3. Magmatic-tectonic evolution of a volcanic rifted margin

    SciTech Connect

    Eldholm, O. )

    1990-05-01

    Many North Atlantic margins are underlain by huge volcanic edifices near the continent-ocean boundary. A crustal hole drilled at the outer Voering Plateau during ODP (Ocean Drilling Project) Leg 104 has provided important constraints on the breakup history and the subsequent margin evolution by penetrating more than 900 m of igneous rocks and interbedded sediment below a post-early Eocene cover. The recovered basement rocks constitute two different volcanic series. The Upper Series, comprising a seaward-dipping reflector wedge, consists of transitional mid-oceanic tholeiitic lava flows and thin volcaniclastic sediments. Dacitic flows, some dikes and thicker sediments constitute the Lower Series. The margin evolved by Paleocene crustal extension, uplift and pervasive intrusion in the rift zone. Just prior to breakup, magma from shallow crustal melts produced the Lower Series. The Upper Series was constructed during an intense, rapidly waning subaerial surge following breakup in the earliest Eocene. The Upper Series covers both new oceanic crust and large areas of continental crust. The dipping wedge was formed by subsidence due to loading and thermal contraction probably amplified by a tectonic force. When the surge had abated, the injection center subsided and a normal oceanic crust was formed. A direct temporal and compositional relationship exists between the onshore North Atlantic Volcanic Province and the volcanic margins. Whereas the central transverse part of the province, near the Iceland hotspot has been active for 60 m.y., the volcanic margins reflect a 2,000-km-long transient phenomenon lasting only 3 m.y. The breakup volcanism and lack of initial subsidence are related to a regional, about 50C{degree}, increased temperature at the base of the lithosphere (hot carpet) combined with opening in previously extended crust.

  4. Eastern Ishtar Terra: Tectonic evolution derived from recognized features

    NASA Technical Reports Server (NTRS)

    Vorderbruegge, R. W.; Head, James W.

    1989-01-01

    Previous analyses have recognized several styles and orientations of compressional deformation, crustal convergence, and crustal thickening in Eastern Ishtar Terra. An east to west sense of crustal convergence through small scale folding, thrusting, and buckling is reflected in the high topography and ridge-and-valley morphology of Maxwell Montes and the adjacent portion of Fortuna Tessera. This east to west convergence was accompanied by up to 1000 km of lateral motion and large scale strike-slip faulting within two converging shear zones which has resulted in the present morphology of Maxwell Montes. A more northeast to southwest sense of convergence through large scale buckling and imbrication is reflected in large, northwest-trending scarps along the entire northern boundary of Ishtar Terra, with up to 2 km of relief present at many of the scarps. It was previously suggested that both styles of compression have occurred at the expense of pre-existing tessera regions which have then been overprinted by the latest convergence event. The difference in style is attributed mostly to differences in the properties of the crust converging with the tessera blocks. If one, presumably thick, tessera block converges with another tessera region, then the widespread, distributed style of deformation occurs, as observed in western Fortuna Tessera. However, if relatively thin crust (such as suggested for the North Polar Plains converges with thicker tessera regions, then localized deformation occurs, as reflected in the scarps along Northern Ishtar Terra. The purpose is to identify the types of features observed in Eastern Ishtar Terra. Their potential temporal and spatial relationships, is described, possible origins for them is suggested, and how the interpretation of some of these features has led to the multiple-style tectonic evolution model described is shown.

  5. Tectonic structure and evolution of the Atlantic continental margin

    SciTech Connect

    Klitgord, K.D.; Schouten, H.; Hutchinson, D.R.

    1985-01-01

    The Atlantic continental margin developed across the boundary between continental and oceanic crust as rifting and then sea-floor spreading broke apart and separated the North American and African plates, forming the Atlantic Ocean Basin. Continental rifting began in Late Triassic with reactivation of Paleozoic thrust faults as normal faults and with extension across a broad zone of subparallel rift basins. Extension became localized in Early to Middle Jurassic along the zone that now underlies the large marginal basins, and other rift zones, such as the Newark, Hartford, and Fundy basins, were abandoned. Rifting and crustal stretching between the two continents gave way to sea-floor spreading Middle Jurassic and the formation of oceanic crust. This tectonic evolution resulted in formation of distinctive structural features. The marginal basins are underlain by a thinner crust and contain a variety of fault-controlled structures, including half-grabens, seaward- and landward-tilted blocks, faults that die out within the crust, and faults that penetrate the entire crust. This variable structure probably resulted from the late Triassic-Early Jurassic pattern of normal, listric, and antithetic faults that evolved from the Paleozoic thrust fault geometry. The boundary between marginal basins and oceanic crust is marked approximately by the East Coast Magnetic Anomaly (ECMA). A major basement fault is located in the Baltimore Canyon trough at the landward edge of the ECMA and a zone of seaward dipping reflectors is found just seaward of the ECMA off Georges Bank. The fracture zone pattern in Mesozoic oceanic crust can be traced landward to the ECMA.

  6. Tectonic evolution and oil and gas of Tarim basin

    NASA Astrophysics Data System (ADS)

    Yuzhu, Kang; Zhihong, Kang

    According to the new results achieved in the past ten years and more, using mobilism and the theory of polycycle by Huang Jiqing (1977, 1984), the formation of the basement of the Tarim basin and its characteristics are summarized. The prototype basins formed since Sinian times are classified into rift basin, continental marginal basin, cratonic basin, foreland basin and others. The Tarim basin is regarded as a huge oil- and gas-bearing basin superposed by prototype basins of different ages. The tectonic characteristics of these basins including tectonic movements, tectonic migrations, faults and trap types are summarized. In addition, structural control over oil and gas and oil-forming features are analysed.

  7. Tectonic and climatic control on geomorphological and sedimentary evolution of the Mercure basin, southern Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Robustelli, Gaetano; Ermolli, Elda Russo; Petrosino, Paola; Jicha, Brian; Sardella, Raffaele; Donato, Paola

    2014-06-01

    The morpho-tectonic and sedimentary evolution of the Mercure intramontane basin (Calabria-Lucania boundary, southern Apennines) has been assessed through facies analysis, morphostratigraphy and geomorphological correlation with adjacent areas. The Mercure basin, one of the most active seismogenic zones of the southern Apennines, is a favorable area for reconstructing the main stages of landscape evolution of the axial zone because of its capability to record changes in base level during the Quaternary. In addition, the presence of both erosional and depositional Palaeosurfaces is a useful marker for reconstructing tectonic and morphogenetic events, and hence to detect the role played by tectonics and climate in its genesis, evolution and extinction. The present study identifies the key role of tectonics and denudation, combined with high-frequency floods, as mechanisms controlling alluvial sedimentation in the study area. During endorheic conditions, denudational processes driven by pulses of extensional deformation of the basin margin caused strong alluvial inputs that resulted in the development of alluvial fans. Alluvial facies are mainly characterized by turbulent, subaerial, hyperconcentrated flood flows deposited during the glacial, semi-arid conditions of MIS 14. The retrogradational stacking pattern of the alluvial system indicates decreasing rates of tectonic activity along with declining river gradients. The Mercure coalescing alluvial fans were inundated by lake transgression during MIS 13 in response to (i) abrupt tectonic subsidence at the basin margins and (ii) large decrease of coarse sediment supply due to the interplay among climate, tectonics and catchment size changes. In this regard, it is suggested that tectonic control on the drainage network along with climate and long-term slope evolution may have caused marked pulses in sediment supply, thus influencing the arrangement of facies associations in the sedimentary succession. In addition, the

  8. Igneous and tectonic evolution of Venusian and terrestrial coronae

    NASA Technical Reports Server (NTRS)

    Kargel, J. S.; Komatsu, G.

    1992-01-01

    A great variety of tectonic and volcanic features have been documented on Venus. It is widely appreciated that there are close spatial associations among certain types of tectonic structures and some classes of volcanic flows and constructs. Coronae are endowed with a particularly rich variety of volcanism. It is thought that coupled tectonic and volcanic aspects of coronae are cogenetic manifestations of mantle plumes. An outstanding feature of most venusian coronae is their circular or elliptical shape defined by peripheral zones of fracturing and/or folding. Some coronae are composite, consisting of two or more small coronae within a larger enclosing corona, suggesting complex histories of structured diapirism analogous in some ways to salt dome tectonics. Coronae range widely in size, from smaller than 100 km to over 1000 km in diameter. Volcanic features associated with venusian coronae include lunar-like sinuous rilles, thin lava flows, cinder cone-like constructs, shield volcanos, and pancake domes. Several types of volcanic features are often situated within or near a single corona, in many instances including land-forms indicating effusions of both low- and high-viscosity lavas. In some cases stratigraphic evidence brackets emplacement of pancake domes during the period of tectonic development of the corona, thus supporting a close link between the igneous and tectonic histories of coronae. These associations suggest emplacement of huge diapirs and massive magmatic intrusions, thus producing the tectonic deformations defining these structures. Igneous differentiation of the intrusion could yield a range of lava compositions. Head and Wilson suggested a mechanism that would cause development of neutral buoyancy zones in the shallow subsurface of Venus, thereby tending to promote development of massive igneous intrusions.

  9. Geodynamic controls on a salt giant formation. The Messinian salinity crisis and the tectonic evolution of the westernmost Mediterranean

    NASA Astrophysics Data System (ADS)

    Garcia-Castellanos, Daniel

    2016-04-01

    The landlocked location of the Mediterranean is presumed to be the result of the southward retreat of subducted Tethyan lithospheric slabs after the collision between Europe and Africa. The western end of the Alpine orogeny (the Gibraltar Arc) shaped the last marine connection to the ocean during the upper Miocene, but in this complex tectonic region, the dominant polarity of subduction (Tethys underneath Iberia/Europe/Anatolia) might not be accomplished, based on plate reconstructions, mantle tomography, and the present position of the Kabylies and the Alboran nappes. This tectonic evolution determined the vertical motions purportedly responsible for the restriction of the Mediterranean and the widespread salt accumulation during the Messinian Salinity Crisis. Following the concept of isostasy, the enormous and rapid mass redistribution implied by the crisis should have induced in turn remarkable vertical motions of the Mediterranean margins. While the predicted isostatic motions during the crisis range in the order of hundreds of meters, little evidence has been documented so far. The mechanical response of the Iberian margins can be inferred by using crustal and lithospheric cross sections derived from potential fields (gravity and geoid anomalies), heatflow, and topography modeling. The preliminary results are consistent with a low rigidity of the lithosphere, in agreement with their young thermomechanical age. These rigidity values are then used for a first-order estimation of the vertical motions associated to the accumulation of salt and the possible partial evaporation of the water column during the crisis. Recent seismic stratigraphic data show that the Balearic promontory hosts a unique set of intermediate-depth basins where halite deposited in smaller amounts than in the deeper basins. If future drillings provide more precise constraints on the paleobathymetry of the sedimentary units before and after the crisis, the various proposed models for its

  10. The Tectonic and Climatic Evolution of High Plateaux

    NASA Astrophysics Data System (ADS)

    Bershaw, John

    High topography significantly affects climate and atmospheric circulation, often separating areas of intense precipitation from relatively arid rainshadows inland. Temporal variations in climate on high plateaux have been inferred from both rocks and ice and may be related to changes in global climate, local atmospheric circulation, and/or changes in surface elevation. Constraints on how and when surface topography was generated not only provide insight into the relationship between high plateaux and climate, but help us distinguish between different geodynamic mechanisms responsible for their formation. The following research employs multiple techniques across the Andean Plateau, the Pamir, and Tibetan Plateau, to better understand both the tectonic evolution of high plateaux and how they affect climate and atmospheric circulation, particularly in continental settings. The Andean Plateau in South America is the second highest and most extensive topographic feature on Earth. Paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern Andean plateau, on the order of 2.5 +/- 1 km, occurred between ˜10.3 and 6.4 million years ago (Ma). South American teeth from modem and extinct mammal taxa spanning from the Oligocene (˜29 Ma) to present were collected as they preserve a record of surface water isotopes and the type of plants that animals ingested. Previous studies have shown that the isotopic composition of oxygen (delta18O) in modern precipitation and surface waters decreases systematically with increasing elevations across the central Andes. Results from high elevation sites show substantially more positive delta18O values for late Oligocene tooth samples compared to <10 Ma tooth delta18O values. Late Oligocene teeth collected from low elevation sites in southeast Brazil show delta18O values within 2 per mil (‰) of contemporaneous teeth collected at high elevation

  11. Workshop on the Tectonic Evolution of Greenstone Belts (supplement containing abstracts of invited talks and late abstracts)

    NASA Technical Reports Server (NTRS)

    1986-01-01

    Topics addressed include: greenstone belt tectonics, thermal constaints, geological structure, rock components, crustal accretion model, geological evolution, synsedimentary deformation, Archean structures and geological faults.

  12. Holocene Tectonic and Sedimentary Evolution of Coastal San Diego

    NASA Astrophysics Data System (ADS)

    Maloney, J. M.; Driscoll, N. W.; Brothers, D. S.; Babcock, J. M.; Kent, G.

    2010-12-01

    The shelf and nearshore region of San Diego, California, between La Jolla cove in the north and the U.S.- Mexico border in the south, is an important ecological and economic resource. It contains two of the largest kelp forests in southern California and lies offshore miles of popular beaches. Understanding the interplay between tectonic and sedimentary processes in this area is critical because it will allow us to assess how other forcing functions such as the rapid sea level rise (2 - 3 mm/yr) and predicted climate change associated with global warming are impacting the kelp and nearshore environments. The fault architecture and sedimentary deposits offshore San Diego have been mapped using high-resolution seismic CHIRP profiling. The mapped area lies within the inner California Continental Borderland (CCB), which is characterized by a system of basins and ridges and extensive strike-slip faulting. The CHIRP data clearly images several splays of the Coronado Bank Fault Zone (CBFZ), a major fault in the area, which show recent activity in the upper 30 m of sediment with the most recent deformation at ~4 m below seafloor. Several sediment packages as deep as 50 m below the seafloor are imaged and place important constraints on tectonic deformation and sediment dispersal in the region as well as the earthquake recurrence interval on the CBFZ. Exposed and buried wavecut terraces identified on numerous CHIRP profiles, which can be correlated to terraces mapped regionally, provide insight into tectonic uplift rates and sea-level fluctuations. Finally, the extensive kelp forests offshore Mount Soledad and Point Loma occur where hardgrounds are exposed at the seafloor as a consequence of tectonic uplift. High resolution mapping offshore San Diego is providing new insight into the complex interplay between tectonics, sedimentation, and biology in this ecologically diverse region.

  13. Sequence stratigraphy and paleogene tectonic evolution of the Transylvanian Basin (Romania, eastern Europe)

    NASA Astrophysics Data System (ADS)

    Proust, Jean-Noël; Hosu, Alexandru

    1996-09-01

    The Transylvanian Basin of Romania belongs to the 800 × 400 km wide Pannonian domain of the European Alpine megasuture bordered to the east and the north by the Carpathians. It represents a digitation of the epicontinental Tethyan seaways locally connected during the Palaeogene to the peripheral foredeep troughs. During that time, it was filled up by a 500-m-thick sediment pile organized into three shallow marine and non-marine facies alternations. Each evolved from alluvial fans to restricted marine and outer marine environments. They are dated from Lutetian to Chattian times. The study is focused on the lowermost alternation onlapping the basal, post-Maastrichtian unconformity. This alternation consists of the superimpossition of a thick retrogradational and a thin progradational depositional system. The retrogradational depositional system grades upwards from stacked, fault-controlled deposits of alluvial fan, ephemeral stream, salina and sabkha, and restricted marine bioclastic shales. The progradational depositional system is composed of outer marine to estuarine sandstones and shales. The two depositional systems are bounded at their tops by two baselevel change unconformities underlain by highly mobile, low relief sandstone bodies that were deposited in shoal belts. These two unconformities mark significant changes in the regime of the subsidence. These are, respectively, a baselevel rise or 'drowning' unconformity where the shoal deposits were associated with oolitic ironstones and glauconitic shales that typify basin starvation during a period of maximum basin drowning, and a baselevel fall or 'uplifting' unconformity where the bioclastic shoal deposits were buried by alluvial flood plain deposits that characterize periods of relief rejuvenation tentatively attributed to compressive events. This bimodal succession is interpreted in terms of underfilled-overfilled stages related to intraplate tectonic deformation. The underfilled stage corresponds to the

  14. Cenozoic tectonic evolution of Asia: A preliminary synthesis

    NASA Astrophysics Data System (ADS)

    Yin, An

    2010-06-01

    of east Asia was developed in two stages: initially in a widely distributed zone that has an east-west width of 500-800 km during 65-35 Ma, which was followed by localized extension and opening of back-arc basins associated with the development of spreading centers at 32-17 Ma (e.g., Japan Sea or East Korea Sea, Bohai Bay, and South China Sea). Opening of the back-arc basins could be induced by (1) rapid eastward migration of the western Pacific trench system or (2) oblique subduction of Pacific plate beneath Asia that had produced a series of en echelon right-slip primary shear zones linking with back-arc spreading centers oriented obliquely to the strike of the nearby trench. Since ~ 15 Ma, the eastern margin of Asia became contractional in the east-west direction, as indicated by the collapse of back-arc basins in the western Pacific and the development of fold-thrust belts along the eastern continental margin. Coeval with the contraction is widespread east-west extension in Siberia, North China, and the Tibetan plateau. The above observations can be explained by a change in boundary condition along the eastern margin of Asia that allowed the thickened Asian continent to spread eastward, causing east-west extension in its trailing edge and east-west compression in its leading edge. In west Asia, continental-margin extension started at about 25-20 Ma in the Aegean and Cretan regions, which was associated with a rapid southward retreat of the Hellenic arc. The complex evolution of Cenozoic deformation in Asia may be explained by a combined effect of temporal changes in plate boundary conditions, thermal evolution of the upper mantle perturbed by collisional tectonics, and the built-up of gravitational energy through crustal thickening and thermal heating. Although the past research in Asia has treated the India-Asia and Arabia-Asia convergence as separate collisional processes, their interaction may have controlled the far-field Cenozoic deformation in Asia. The

  15. Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability

    NASA Astrophysics Data System (ADS)

    De Pascale, Gregory P.; Chandler-Yates, Nicholas; Dela Pena, Federico; Wilson, Pam; May, Elijah; Twiss, Amber; Cheng, Che

    2016-04-01

    The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (<20 km away) and has 3500 m of dip-slip displacement, but it has been unknown if the fault is active. Here the first evidence for SWFZ thrust faulting in the "stable" Australian Plate is shown with cumulative dip-slip displacements up to 5.9 m (with 3 m throw) on Pleistocene and Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post-12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth.

  16. The influence of tectonic grain to the Neogene evolution of the Mesopotamian basin: 3D tectonic-surface processes modeling

    NASA Astrophysics Data System (ADS)

    Fillon, Charlotte; Garcia-Castellanos, Daniel; Vergés, Jaume

    2015-04-01

    The Mesopotamian basin is a plate-scale foreland basin commonly linked to the tectonic load of the Zagros mountain belt. Its current drainage pattern shows the two main river systems (Tigris and Euphrates) draining the basin longitudinally from NW to SE, likely to be influenced by other large-scale geodynamic events, such as the uplift of the Anatolian Plateau (Middle Miocene) to the NW and/or the Arabian plate flank tilting to the W (from early Miocene). By using an integrated modeling of surface processes, lithospheric flexure and kinematic fault deformation, we test the influences of each main tectonic units on the basin evolution. The numerical model is particularly designed to study the 3D foreland basin evolution and to identify large-scale relationships between tectonic movements and sediment transport and deposition. We specifically aim at reproducing the drainage conditions in the basin, the flexural profile and the sediment thicknesses and geometry of deposition, by investigating the basin history at the scale of the Arabian plate (3000 km x 1200 km), over a long period of time (i.e. since 35 Ma to present day), and with integrating realistic climatic conditions. The main results reveal 1) the need for an external load in addition to the Zagros to reproduce the flexural profile of the basin and 2) the important contributions of both Arabian plate flank tilting and Anatolian plateau uplift to the drainage system, all of them suggesting a significant contribution from deep geodynamic events occurring in early to middle Miocene times in shaping the present day Mesopotamian basin.

  17. Tectonic evolution of the East Junggar terrane, CAOB

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang

    2016-04-01

    The East Junggar terrane is one of the important tectonic units of the Central Asian Orogenic Belt (CAOB; Zonenshain et al., 1990). Debate surrounds the tectonics of the East Junggar area, including tectonic setting, age, basement nature, subduction polarity and collisional time between the East Junggar terrane and Junggar block (e.g., Xiao et al., 2008, 2011; Long et al., 2012; Huang et al., 2012). Among the two popular models, one suggests that the Junggar is a continental block (e.g. Zhang et al., 1984, 1993; Watson et al., 1987; Xiao et al., 1992; He et al., 1994; Li et al., 2000; Charvet et al., 2001, 2007; Xu et al., 2003; Zhao et al., 2003; Buslov et al., 2004; Xu and Ma, 2004; Dong et al., 2009; Bazhenov et al., 2012; Choulet et al., 2012; Zhang et al., 2012). The other model proposes that the Junggar has a basement of Paleozoic oceanic crust (e.g., Carroll et al., 1990; Zheng et al., 2007) or oceanic island arc complexes (e.g., Coleman, 1989; Chen and Jahn, 2004; Windley et al., 2007) of the Altaid Paleozoic rocks (e.g., Sengör et al., 1993; Sengör and Natal'in, 1996; Allen and Vincent, 1997; Filippova et al., 2001; Xiao et al., 2004a, 2004b, 2008, 2009, 2010a, 2010b, 2012). The tectonics in the Eastern Junggar area are interpreted to be related to late Paleozoic intra-oceanic accretion induced by northward subduction of the Junggar oceanic lithosphere (e.g. Xiao et al., 2008, 2009; Biske and Seltmann, 2010; Wan et al., 2011; Yang et al., 2011) or by the southward subduction of the Paleo-Asian oceanic lithosphere (Zhang et al., 2004; Wong et al., 2010; Su et al., 2012). Recently, we did detailed field survey and petrological, geochemical and chronological analysis of the metamorphosed volcanic rocks and magmatic rocks, and new discovered gneiss and magnetite quartzite enclaves from the Taheir tectonic window in the East Junggar region which is situated between the Zaisan-Erqis-the Main Mongolian Lineament-suture and the Kelameili suture. The new results

  18. Understanding the Interior Evolution of Mercury from Its Tectonic History

    NASA Astrophysics Data System (ADS)

    Byrne, P. K.; Klimczak, C.; Sengor, A. M. C.; Hauck, S. A., II; Solomon, S. C.

    2015-12-01

    The surface of Mercury provides compelling insight into the planet's interior. Excluding impact craters and basins, the most prominent landforms on Mercury are tectonic; these features are distributed globally and crosscut all major surface units. More than seven years of flyby and orbital observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show that tectonism on Mercury is overwhelmingly shortening in nature; extensional structures occur only within volcanically flooded impact craters and basins, in part the result of thermal contraction of thick plains units. Shortening structures show no coherent, planet-wide pattern, although many have an approximately north-south orientation, and some form fold-and-thrust belts thousands of kilometers long. Even so, their widespread distribution points to a global source of stress, primarily from global contraction in response to secular interior cooling. Some of the largest such landforms are 2-3 km in relief and hundreds of kilometers long, their underlying thrust faults penetrating 30-40 km into the lithosphere. Shortening landforms as small as hundreds of meters in length have been identified during MESSENGER's low-altitude campaign; the crisp morphology of these features indicates that thrust faulting, and thus global contraction, continued until the geologically recent. Displacement-length scaling analysis shows that Mercury's shortening landforms have accommodated a reduction in planetary radius of up to 7 km since the end of the late heavy bombardment. Such a magnitude of contraction is more consistent with models of global contraction from interior cooling and partial core crystallization than pre-MESSENGER estimates of tectonic shortening. Notably, the emplacement of major volcanic plains deposits on Mercury ended globally by 3.6 Ga, consistent with the onset of a state of net horizontal lithospheric compression that served to inhibit the vertical ascent and

  19. Evolution of ancient Lake Ohrid: a tectonic perspective

    NASA Astrophysics Data System (ADS)

    Hoffmann, N.; Reicherter, K.; Fernández-Steeger, T.; Grützner, C.

    2010-06-01

    Lake Ohrid Basin is a graben structure situated in the Dinarides at the border of the Former Yugoslavian Republic of Macedonia (FYROM) and Albania. It hosts one of the oldest lakes in Europe and is characterized by a basin and range-like geological setting together with the half-graben basins of Korca, Erseka and Debar. The basin is surrounded by Palaeozoic metamorphics in the northeast and north and Mesozoic ultramafic, carbonatic and magmatic rocks in the east, northwest, west and south. Palaeocene to Pliocene units are present in the southwest. With the basin development, Neogene sediments from Pliocene to recent deposited in the lows. Three major deformation phases lead to the basin formation: A) NW-SE shortening from Late Cretaceous to Miocene; B) uplift and diminishing compression during Messinian - Pliocene; C) vertical uplift and (N)E-(S)W extension from Pliocene to recent. Neotectonic activity of the study area concentrates on N-S trending normal faults that flank the Ohrid Basin on the east and west. Seismic activity with moderate to strong events is documented during the last 2000 y; the seismic hazard level is among the highest of the Balkan Peninsula. Activity of the youngest faults is evidenced by earthquake data and field observations. Morphotectonic features like a wind-gap, fault scarps, a stepped series of active normal faults, deformed palaeosols, and fault-related hydrothermal activity are preserved around Lake Ohrid and allow delineating the tectonic history. It is shown that the Lake Ohrid Basin can be characterized as a seismogenic landscape. This paper presents a tectonic history of the Lake Ohrid Basin and describes tectonic features that are preserved in the recent landscape. The analysis of morphotectonic features is used to derive the deformation history. The stratigraphy of the area is summarized and concentrates on the main units.

  20. Evolution of ancient Lake Ohrid: a tectonic perspective

    NASA Astrophysics Data System (ADS)

    Hoffmann, N.; Reicherter, K.; Fernández-Steeger, T.; Grützner, C.

    2010-10-01

    Lake Ohrid Basin is a graben structure situated in the Dinarides at the border of the Former Yugoslavian Republic of Macedonia (FYROM) and Albania. It hosts one of the oldest lakes in Europe and is characterized by a basin and range-like geological setting together with the halfgraben basins of Korca, Erseka and Debar. The basin is surrounded by Paleozoic metamorphics in the northeast and north and Mesozoic ultramafic, carbonatic and magmatic rocks in the east, northwest, west and south. Paleocene to Pliocene units are present in the southwest. With the basin development, Neogene sediments from Pliocene to recent deposited in the lows. There are three major deformation phases: (A) NW-SE shortening from Late Cretaceous to Miocene; (B) uplift and diminishing compression during Messinian - Pliocene; (C) vertical uplift and (N)E-(S)W extension from Pliocene to recent led to the basin formation. Neotectonic activity of the study area concentrates on N-S trending normal faults that bound the Ohrid Basin eastwards and westwards. Seismic activity with moderate to strong events is documented during the last 2000 yrs; the seismic hazard level is among the highest in Albania and Macedonia. Activity of the youngest faults is evidenced by earthquake data and field observations. Morphotectonic features like fault scarps, a stepped series of active normal faults, deformed paleosols, a wind gap and fault-related hydrothermal activity are preserved around Lake Ohrid and allow delineating the tectonic history. It is shown that the Lake Ohrid Basin can be characterized as a seismogenic landscape. This paper presents a tectonic history of the Lake Ohrid Basin and describes tectonic features that are preserved in the recent landscape. The analysis of morphotectonic features is used to derive the deformation history. The stratigraphy of the area is summarized and concentrates on the main units.

  1. Tectonic evolution of the East Junggar terrane, CAOB

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang

    2016-04-01

    The East Junggar terrane is one of the important tectonic units of the Central Asian Orogenic Belt (CAOB; Zonenshain et al., 1990). Debate surrounds the tectonics of the East Junggar area, including tectonic setting, age, basement nature, subduction polarity and collisional time between the East Junggar terrane and Junggar block (e.g., Xiao et al., 2008, 2011; Long et al., 2012; Huang et al., 2012). Among the two popular models, one suggests that the Junggar is a continental block (e.g. Zhang et al., 1984, 1993; Watson et al., 1987; Xiao et al., 1992; He et al., 1994; Li et al., 2000; Charvet et al., 2001, 2007; Xu et al., 2003; Zhao et al., 2003; Buslov et al., 2004; Xu and Ma, 2004; Dong et al., 2009; Bazhenov et al., 2012; Choulet et al., 2012; Zhang et al., 2012). The other model proposes that the Junggar has a basement of Paleozoic oceanic crust (e.g., Carroll et al., 1990; Zheng et al., 2007) or oceanic island arc complexes (e.g., Coleman, 1989; Chen and Jahn, 2004; Windley et al., 2007) of the Altaid Paleozoic rocks (e.g., Sengör et al., 1993; Sengör and Natal'in, 1996; Allen and Vincent, 1997; Filippova et al., 2001; Xiao et al., 2004a, 2004b, 2008, 2009, 2010a, 2010b, 2012). The tectonics in the Eastern Junggar area are interpreted to be related to late Paleozoic intra-oceanic accretion induced by northward subduction of the Junggar oceanic lithosphere (e.g. Xiao et al., 2008, 2009; Biske and Seltmann, 2010; Wan et al., 2011; Yang et al., 2011) or by the southward subduction of the Paleo-Asian oceanic lithosphere (Zhang et al., 2004; Wong et al., 2010; Su et al., 2012). Recently, we did detailed field survey and petrological, geochemical and chronological analysis of the metamorphosed volcanic rocks and magmatic rocks, and new discovered gneiss and magnetite quartzite enclaves from the Taheir tectonic window in the East Junggar region which is situated between the Zaisan-Erqis-the Main Mongolian Lineament-suture and the Kelameili suture. The new results

  2. Cenozoic tectonic evolution of the Bohai Bay Basin and its coupling relationship with Pacific Plate subduction

    NASA Astrophysics Data System (ADS)

    Liang, Jintong; Wang, Hongliang; Bai, Ying; Ji, Xinyuan; Duo, Xuemei

    2016-09-01

    The Bohai Bay Basin is a Mesozoic-Cenozoic rift basin in eastern China. Based mainly on a balanced-section analysis, this study compares the spatio-temporal differences of tectonic evolution in relation to strike-slip faults among different depressions within the basin. In combination with the analysis of subsidence characteristics, the study also attempts to clarify the Cenozoic tectonic evolution of the basin and its coupling relationship with the subduction of the Pacific Plate. It was found that: (1) the strike-slip faults were activated generally from south to north and from west to east during the Cenozoic; (2) there is a negative correlation between the intensity of tectonic activity in the Bohai Bay Basin and subduction rate of the Pacific Plate; and (3) the migration direction of the basin depocenters is consistent with the direction of Pacific Plate subduction.

  3. Natural selection and neutral evolution jointly drive population divergence between alpine and lowland ecotypes of the allopolyploid plant Anemone multifida (Ranunculaceae).

    PubMed

    McEwen, Jamie R; Vamosi, Jana C; Rogers, Sean M

    2013-01-01

    Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst  = 0.074-0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST  = 0.041-0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence. PMID:23874801

  4. Natural Selection and Neutral Evolution Jointly Drive Population Divergence between Alpine and Lowland Ecotypes of the Allopolyploid Plant Anemone multifida (Ranunculaceae)

    PubMed Central

    McEwen, Jamie R.; Vamosi, Jana C.; Rogers, Sean M.

    2013-01-01

    Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst  = 0.074–0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST  = 0.041–0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence. PMID:23874801

  5. The geology and tectonic evolution of Waigeo Island, NE Indonesia

    NASA Astrophysics Data System (ADS)

    Charlton, T. R.; Hall, R.; Partoyo, E.

    Waigeo occupies a critical position between the Halmahera-Philippine arcs to the northwest and Australia-New Guinea to the southeast. The island consists of a deformed ophiolitic basement of supra-subduction zone type overlain by probable Paleogene forearc sedimentary rocks. The forerarc basement is cut by mylonite shear zones and the basement and sedimentary cover rocks were deformed by southward-directed thrusts and associated folds during the Oligocene. The deformed sequences are intruded by basic dykes, thought to be coeval with basalts and andesites of Late Oligocene age. The entire Paleogene sequence is overlain unconformably by a thick (up to 2000 m) sequence of Miocene limestones which accumulated during a tectonically quiet period. A final phase of deformation occurred during the Pliocene which caused the development of two very large anticlines and an intervening syncline, associated with left-lateral wrench faults. Waigeo is interpreted to have been situated in a forearc position in an intra-oceanic island arc during the early Paleogene, forming part of the East Halmahera-Waigeo forearc terrane. The Waigeo arc terrane collided with a continental block in about the Middle Oligocene, contemporaneous with similar arc-continent collision in northern New Guinea. A period of tectonic quiescence during the Miocene was followed by Pliocene deformation in Waigeo related to a left-lateral wrench faulting on splays of the Sorong Fault in northern New Guinea. The Pliocene deformation is interpreted as resulting from compression on a right-stepping restraining bend in this wrench fault system.

  6. The tectonic evolution of a critical segment of the Dinarides-Alps connection: Kinematic and geochronological inferences from the Medvednica Mountains, NE Croatia

    NASA Astrophysics Data System (ADS)

    Gelder, I. E.; Matenco, L.; Willingshofer, E.; Tomljenović, B.; Andriessen, P. A. M.; Ducea, M. N.; Beniest, A.; Gruić, A.

    2015-09-01

    The transition zone between the Alps and Dinarides is a key area to investigate kinematic interactions of neighboring orogens with different subduction polarities. A study combining field kinematic and sedimentary data, microstructural observations, thermochronological data (Rb-Sr and fission track), and regional structures in the area of Medvednica Mountains has revealed a complex polyphase tectonic evolution. We document two novel stages of extensional exhumation. The first stage of extension took place along a Late Cretaceous detachment following the late Early Cretaceous nappe stacking, burial, and greenschist facies metamorphism. Two other shortening events that occurred during the latest Cretaceous-Oligocene were followed by a second event of extensional exhumation, characterized by asymmetric top-NE extension during the Miocene. Top-NW thrusting took place subsequently during the Pliocene inversion of the Pannonian Basin. The Cretaceous nappe burial, Late Cretaceous extension, and the Oligocene(-Earliest Miocene) contraction are events driven by the Alps evolution. In contrast, the latest Cretaceous-Eocene deformation reflects phases of Dinaridic contraction. Furthermore, the Miocene extension and subsequent inversion display kinematics similar with observations elsewhere in the Dinarides and Eastern Alps. All these processes demonstrate that the Medvednica Mountains were affected by Alpine phases of deformations to a much higher degree than previously thought. Similarly with what has been observed in other areas of contractional polarity changes, such as the Mediterranean, Black Sea, or New Guinea systems, the respective tectonic events are triggered by rheological weak zones which are critical for localizing the deformation created by both orogens.

  7. Tectonic Evolution of Western Ishtar Terra (Akna Montes-Atropos Tessera), Venus

    NASA Astrophysics Data System (ADS)

    Marinangeli, L.

    1996-09-01

    The Akna Montes-Atropos Tessera region appears to have undergone three phases of tectonic evolution. The first one consists of compressional deformations, folds and thrust faults trending NE, that formed the Akna Montes and most of the compressional features in western Atropos Tessera. A second phase, likely contemporaneous with the first one, is dominated by shear stress deformations which involved most of the Atropos Tessera and probably developed along NW planes. The tectonic pattern is expressed as sinuous, tightly closed ridges arranged in an "en-echelon"; similar tectonic pattern has been previously recognised in Itzpapalotl Tessera (1). The third phase consists of extension probably related to the gravitational spreading of the Akna Montes that strongly involved the western portion of the Akna belt and the part of Atropos close to the mountain. A major consequence of the spreading is the splitting of the Akna Montes in two portions separated by a lava flooded valley which parallel the compressional deformation of the Akna belt. Also, many grabens trending NW developed in the western Akna during this phase (2). Minor evidences of extension have been found in the western Atropos Tessera and interpreted as related to the pro-gradation to the West of the relaxation of the mountain belt (3). This scenario is quite similar to the tectonic of terrestrial high plateaus associated with mountain belts (Tibet, Altiplano, Basin and Range) where compression, shear and extension represent the tectonic evolution of the plateau over time (4). This tectonic evolution is explained by the variations of the values of principal average stresses due to the gradual thickening of the crust. References: (1) Kaula et al. (1992), Jour. Geophys. Res., 97:16,085-16,120 (2) Smerekar & Solomon (1992), Jour. Geophys. Res., 97:16,121-16,148 (3) Ori & Marinangeli (1996), LPSC XXVI:985-986 (4) Froidevaux & Ricard (1987), Tectonophysics:227-238

  8. Multiphase salt tectonic evolution in NW Germany: seismic interpretation and retro-deformation

    NASA Astrophysics Data System (ADS)

    Mohr, M.; Kukla, P. A.; Urai, J. L.; Bresser, G.

    2005-12-01

    The Central European Basin is a classic area of salt tectonics, characterized by heterogeneous structural evolution and complex salt movement history. We studied an area on its SW margin, based on prestack depth-migrated 2D and 3D seismic data. We use seismic interpretation and retro-deformation to obtain a better understanding of salt tectonics, structural control, and sedimentary response in this region. The first phase of salt tectonic evolution started with two main events of NW-SE extension and rafting in the Triassic before the Upper Bunter and before the Upper Muschelkalk. Rafting was accompanied by first salt diapirism and an increased sedimentary thickness adjacent to the salt structure. After salt supply ceased updip to the salt structure, a mini-basin grew in the intra-raft area. This sedimentary differential loading caused salt movement and growth of a pillow structure basinward. The second phase of salt movement was initiated by the formation of a NNW-SSE striking basement graben in the Middle Keuper that triggered reactive diapirism, the breakthrough of the pillow’s roof and salt extrusion. The following downbuilding process was characterized by sedimentary wedges with basal unconformities, onlap structures and salt extrusions that ceased in the Jurassic. The third and latest phase of salt tectonic evolution was activated in the Late Cretaceous to Lower Tertiary by compressional tectonics indicated by salt rise and a small horizontal shortening of the diapir. The interpreted salt tectonic processes and the resulting geometries can now be better tied in with the regional heterogeneous framework of the basin.

  9. Forearc tectonic evolution of the South Shetland Margin, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Maldonado, A.; Larter, R. D.; Aldaya, F.

    1994-12-01

    The main provinces of the South Shetland margin, Antarctic Peninsula characterized on the basis of multichannel seismic, long-range side scan sonar and swath bathymetry data, include from northwest to southeast (1) the oceanic crust of the former Phoenix Plate, flexed down toward the margin and affected by normal faulting in the upper crust; (2) a narrow trench, with a horizontally layered sediment fill which onlaps the thin sedimentary cover on the oceanic crust and shows incipient deformation near its landward edge; (3) an accretionary prism with a complex internal structure, the toe of which is overthrust above the youngest trench deposits; (4) a midslope forearc basin, with an asymmetric synformal structure; and (5) the continental shelf, which includes two distinct tectonic provinces. Calculations of the late Cenozoic convergence history at the trench indicate a rapid decrease in convergence rate after 6.7 Ma from about 60 mm/yr, resulting from the slowing and eventual cessation of spreading on the Antarctic-Phoenix ridge. Once spreading had completely ceased (3.5-2.4 Ma), the convergence rate at the trench equalled the rate of extension in Bransfield Strait, which was probably less than 10 mm/yr at first but may have increased since 1.3 Ma, and this, in turn, would imply a corresponding increase in convergence rate. Above the basal detachment the toe of the accretionary prism is composed of a stack of thrust fault bounded wedges, laterally and vertically segmented by normal faults. Most of the trench fill sediments are overthrust by the toe of the accretionary prism and subducted beneath it for as far as they can be traced on the seismic profiles. This suggests that there may be tectonic erosion of the forearc since a large part of the trench sediment appears to be derived from erosion on the forearc slope. The forearc basin records a long history of subsidence, during which the depocenter migrated landward, paralleling retrogradational erosion of the distal

  10. Tectonic evolution and mantle structure of the Caribbean

    NASA Astrophysics Data System (ADS)

    van Benthem, Steven; Govers, Rob; Spakman, Wim; Wortel, Rinus

    2013-04-01

    In the broad context of investigating the relationship between deep structure & processes and surface expressions, we study the Caribbean plate and underlying mantle. We investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P-wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Rico. These anomalies are interpreted as remnants of Atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the Lesser Antilles island arc during the past ~45 Myr. The imaged Lesser-Antilles slab consists of a northern and southern anomaly, separated by a low velocity anomaly across most of the upper mantle, which we interpret as the subducted North-South America plate boundary. The southern edge of the imaged Lesser Antilles slab agrees with vertical tearing of South America lithosphere. The northern Lesser Antilles slab is continuous with the Puerto Rico slab along the northeastern plate boundary. This results in an amphitheater-shaped slab and it is interpreted as westward subducting North America lithosphere that remained attached to the surface along the northern boundary. At the Muertos Trough, however, material is imaged until a depth of only 100 km, suggesting a small amount of subduction. The location and length of the imaged South Caribbean slab agrees with proposed subduction of Caribbean lithosphere under the northern South America plate. An anomaly related to proposed Oligocene subduction at the Nicaragua rise is absent in the tomographic model. Beneath Panama, a subduction window exists across the upper mantle, which is related to the cessation of subduction of the Nazca plate under Panama since 9.5 Ma and possibly the preceding subduction of the extinct Cocos-Nazca spreading center. In the lower mantle two large anomaly patterns are

  11. Tectonic evolution and mantle structure of the Caribbean

    NASA Astrophysics Data System (ADS)

    Benthem, Steven; Govers, Rob; Spakman, Wim; Wortel, Rinus

    2013-06-01

    investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Rico. These anomalies are interpreted as remnants of Atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the Lesser Antilles island arc during the past ~45 Myr. The imaged Lesser Antilles slab consists of a northern and southern anomaly, separated by a low-velocity anomaly across most of the upper mantle, which we interpret as the subducted North America-South America plate boundary. The southern edge of the imaged Lesser Antilles slab agrees with vertical tearing of South America lithosphere. The northern Lesser Antilles slab is continuous with the Puerto Rico slab along the northeastern plate boundary. This results in an amphitheater-shaped slab, and it is interpreted as westward subducting North America lithosphere that remained attached to the surface along the northeastern boundary of the Caribbean plate. At the Muertos Trough, however, material is imaged until a depth of only 100 km, suggesting a small amount of subduction. The location and length of the imaged South Caribbean slab agrees with proposed subduction of Caribbean lithosphere under the northern South America plate. An anomaly related to proposed Oligocene subduction at the Nicaragua rise is absent in the tomographic model. Beneath Panama, a subduction window exists across the upper mantle, which is related to the cessation of subduction of the Nazca plate under Panama since 9.5 Ma and possibly the preceding subduction of the extinct Cocos-Nazca spreading center. In the lower mantle, two large anomaly patterns are imaged. The westernmost anomaly agrees with the subduction of Farallon lithosphere. The second lower mantle anomaly is found east of

  12. Tectonic evolution of the frontal Longmen San thrust belt

    NASA Astrophysics Data System (ADS)

    Chang, C.-P.; Xu, X.-W.; Yuan, R.-M.; Li, K.; Sun, X.-Z.; Chen, W.-S.

    2012-04-01

    The Longmen Shan thrust belt in the eastern margin of the Tibetan Plateau underwent deformation associated with the eastward growth of the Tibetan Plateau. Many geological features indicate that this range is not a typical active convergent mountain belt. Some of the features that indicated that this range is atypical are the fact that it is a young, high mountain, has a thickened crust with a very low GPS shortening rate, and has no corresponding foreland subsidence. Many geologists believe that the crustal thickening that occurred in this area is caused by ductile deformation rather than by thrust faulting or crustal shortening. This hypothesis successfully explains why the upper crust is largely uplifted although the horizontal shortening at the surface is still very small. However, some recent studies based on quantitative structural analysis and a balanced cross-section indicates that a large increase in shortening occurs near the range front, and the structural relief produced by folds and faults is also closely related to the topography of this front. These imply that upper-crustal deformation is the primary mechanism for generating uplift and topography in the foothills of Longmen Shan Range. This idea obviates the need for lower-crustal flow and inflation to produce and maintain the Longmen Shan Range. Scientists have created many different conceptions for the mode of tectonic deformation across the eastern margin of the Tibetan Plateau. However, almost all scientists agree that the eastern Tibetan Plateau has an exceptionally low mechanical strength, inherited from Mesozoic tectonics of the region. On the 12th of May 2008, Mw 7.9 Wenchuan earthquake occurred in this area provides a direct manifestation of the active crustal shortening and documents the importance of active crustal shortening in developing and supporting the Longmen Shan Range. The co-seismic surface rupture pattern of Wenchuan earthquake, involving multiple structures, is one of the most

  13. Phanerozoic tectonic and paleogeologic evolution of southern South America

    SciTech Connect

    Urien, C.M. ); Zambrano, J.J. )

    1991-03-01

    Before pre-Variscan time, southern South America had a quasicratonic nature. New structural alignments were overimposed due to Gondwana breakup and South Atlantic opening. Phanerozoic tectonic history is divided as follows: (1) 'Caledonian Geosyncline.' Situated west of Brazilian shield and massives, consists of Cambrian to mid-Devonian clastics, carbonates, and intrusives. (2) Variscan Intracratonic Rifting and Foreland Basins. Alluvial and glaciolacustrine sediments accumulated in grabens and marine clastics accumulated in marginal basins along the western continental edge. This period ends in Late Jurassic time (Gondwana breakup) with basaltic extrusions along rifting zones. (3) Inter Malm Taphogenesis. Basement fracturing and Proto-Atlantic opening took place and marine flooding advanced from the south. Along the western margin, a magmatic arc existed since Early Jurassic. The back-arc basins were filled by marine clastics and evaporites, alternating with acidic volcanics and making up the 'Andine Geosyncline.' (4) Subhercynian Drifting. Sedimentary prisms were formed on the Atlantic margin. On the western margin, continental clastics were laid during the Middle and Late Cretaceous. Acidic extrusions and Andean batholith intrusion began during this time. (5) Laramic Flooding. An Atlantic transgression covered a great part of the extra-Andean region and Andean chains were formed. (6) Cenozoic Mountain Building. A new transgression expanded again over Argentine plains and Patagonia. New Andean uplifting phases, sub-Andean belt folding, and basement fracturing originated intermontane basins. Thick, alluvial, and piedmont sediments accumulated here.

  14. Renewal: Continential lithosphere evolution as a function of tectonic environment

    SciTech Connect

    McMillan, N.J.; Baldridge, W.S.

    1995-06-01

    The Cenozoic tectonic environment and stress regime of the southwestern United States have changed dramatically from compression during shallow-angle subduction during the Laramide orogeny in the early Cenozoic to the current mode of Basin and Range extension. Questions remain unresolved concerning the causes of this transition, including the timing of the initiation of extension (estimates range from 36 to 25 Ma), and is the Basin and Range simply an mega-example of back-arc extension, or is extension related to the subduction of an oceanic spreading center about 30 Ma? We have examined the patterns of magmagenesis and geochemical composition through Cenozoic time in southern New Mexico. We have defined four magma sources that have contributed to Cenozoic magmas. Immediately following the Laramide, magmas contain substantial contributions from the lower crust. Mid-Tertiary extension is related to the eruption of rhyolitic ash-flow tuffs and basalts. The basalts were generated by melting of the lithospheric mantle; intercalated rhyolites have a strong upper crustal signature. Eruption of basalts and andesites with sources in the lithospheric mantle and lower crust continued for several million years after rhyolitic volcanism ceased. The region was nearly void of volcanic activity for 16 million years despite continued extension, but at 10 Ma, basalts derived from the asthenosphere began to erupt.

  15. Renewal: Continental lithosphere evolution as a function of tectonic environment

    NASA Astrophysics Data System (ADS)

    McMillan, N. J.; Baldridge, W. S.

    1995-04-01

    The Cenozoic tectonic environment and stress regime of the southwestern United States have changed dramatically from compression during shallow-angle subduction during the Laramide orogeny in the early Cenozoic to the current mode of Basin and Range extension. Questions remain unresolved concerning the causes of this transition, including the timing of the initiation of extension (estimates range from 36 to 25 Ma), and is the Basin and Range simply an mega-example of back-arc extension, or is extension related to the subduction of an oceanic spreading center about 30 Ma? We have examined the patterns of magmagenesis and geochemical composition through Cenozoic time in southern New Mexico. We have defined four magma sources that have contributed to Cenozoic magmas. Immediately following the Laramide, magmas contain substantial contributions from the lower crust. Mid-Tertiary extension is related to the eruption of rhyolitic ash-flow tuffs and basalts. The basalts were generated by melting of the lithospheric mantle; intercalated rhyolites have a strong upper crustal signature. Eruption of basalts and andesites with sources in the lithospheric mantle and lower crust continued for several million years after rhyolitic volcanism ceased. The region was nearly void of volcanic activity for 16 million years despite continued extension, but at 10 Ma, basalts derived from the asthenosphere began to erupt.

  16. Tectonic evolution of the southeastern Caribbean in Cenozoic time

    SciTech Connect

    Speed, R.C.

    1985-01-01

    Oblique collision between the southern Lesser Antilles arc and continental South America controlled tectonics from end Eocene to present in the S.E. Caribbean. There, terranes are from N to S: 1. magmatic arc platform (Margarita to Grenadines); 2. forearc basin; 3. ophiolite belt that may be basement to the forearc basin; 4. accretionary prism whose structurally shallow rocks near Barbados may be equivalent to formerly deep-seated metasediments exposed in Tobago, Trinidad, Paria, and Araya; 5. foreland thrust belt in the slope and shelf cover of S. America; 6. E. Venezuelan-Trinidad foreland basin; and 7. S. American shield. The boundary between terranes 4 and 5 is probably a N-dipping thrust. Early in the Eocene, the southern L.A. arc was probably intra-Atlantic, NE-trending, and positioned offshore of the N-facing passive margin of northern S. America. The arc moved SE relative to S. America, first consuming Mesozoic oceanic lithosphere and accreting sediment of S. American provenance to its forearc, then riding obliquely over the slope and outer shelf of the continental passive margin. Major effects of the collision are uplift of deep-seated arc rocks, imbrication of arc elements, generation of the El Pilar tear fault, and foreland contraction and basining. The southern Lesser Antilles arc was not attached to a far traveled Caribbean plate of Pacific provenance. This implies the existence of boundaries within the Caribbean between an exotic Caribbean plate and the southern Antillean arc.

  17. Escape tectonics and foreland basin evolution: The Austrian-German Molasse basin

    NASA Astrophysics Data System (ADS)

    Ortner, Hugo

    2016-04-01

    The Alpine peripheral foreland basin formed during Eocene collision of the lower, European plate and the upper, Adriatic plate. Two marine to continental megasequences fill the basin. The transition form deep marine to continental deposits of the first megasequence at the Early - Late Oligocene boundary has been related to a change from predominant horizontal to vertical movements in the core of the orogenic wedge. The second megasequence is, however, poorly understood, and different models have been put forward. I present an alternative explanation for the development of this second megacycle, based on an analysis of the Subalpine Molasse thrust belt east of the Rhine river (Ortner et al., 2015). The main characteristics of the Subalpine Molasse thrust belt are: 1) A frontal anticline/thrust started to develop during deposition of the older, marine portion of the second megasequence. Structures continued to grow throughout deposition of the younger, continental part of the megasequence. Structural growth is documented by growth strata. 2) The thrusts in the Subalpine Molasse evolved in a break-back sequence. 3) The amount of shortening during depositon of the second megasequence reduces from 40-50 km near the Rhine valley to zero in the east in the Salzburg area. The onset of the second megasequence in the foreland north of the Subalpine Molasse thrust belt is characterized by an angular unconformity documenting a tilt of the foreland toward the orogen, and therefore ongoing flexure of the lower plate. East of the eastern end of the Subalpine Molasse thrust belt, the deposits of the second megasequence are in a horizontal position, lower plate flexure had stopped. In the internal part of the Alpine orogenic wedge, shortening, exhumation and E-directed stretching of the Tauern Window as a consequence of escape tectonics was active. Most probably shortening was transferred from the Alpine front into the zone of lateral escape, causing the break-back thrust sequence

  18. The Effects of Gravitational Instability on the Tectonic Evolution of Continental Orogens

    NASA Astrophysics Data System (ADS)

    Gemmer, L.; Houseman, G. A.

    2005-05-01

    Convergent continental orogens have been the research focus of numerous geological and geophysical surveys and dynamical modeling studies, but the mechanisms controlling the evolution of these systems are still under debate. The temporal and spatial distribution of tectonic processes in orogenic regions is complex, and the interplay between buoyancy forces and regional tectonics in some of these systems is still not well understood. In several cases the extensional collapse of mountain belts is associated with dramatic thinning of the mantle part of the lithosphere, more so than the crust. A key region for investigating these processes is the Carpathian-Pannonian system of eastern Europe, where rapid extension took place in the Pannonian Basin simultaneously with contractional deformation in the surrounding orogens. Previous studies show that gravitational instabilities may play a fundamental role in the tectonics of mountain ranges. In general, the lithosphere is colder and thereby denser than the underlying asthenosphere. Under some circumstances this may cause the lithosphere to sink into the underlying asthenosphere. We use dynamic numerical models to investigate how such gravitational instabilities may affect the evolution of continental orogens. We show how a crust initially thickened by localized convergence may promote lithospheric gravitational instabilities that cause the collapse of high topography and focused, depth-variable lithospheric thinning developing simultaneously with contractional deformation and lithospheric downwelling in the adjacent areas. We investigate the relative importance of buoyancy and regional tectonics in convergent continental orogens and show how density and viscosity (Newtonian or non-Newtonian) affect the evolution of a model system. We investigate the distribution and amplitude of lithospheric downwelling and examine how the instability develops adjacent to the corner of an initially rectangular region of thickened crust in

  19. Tectonic evolution of the west Spitsbergen fold belt

    NASA Astrophysics Data System (ADS)

    Craddock, C.; Hauser, E. C.; Maher, H. D.; Sun, A. Y.; Guo-Qiang, Zhu

    1985-04-01

    The west Spitsbergen fold belt has a complex tectonic history which is recorded in a thick, nearly complete upper Proterozoic-Phanerozoic layered sequence. Work since 1977 near Bellsund allows recognition of the main deformational events in that segment of the fold belt. The strata are grouped informally into the metamorphosed Hecla Hoek (HH) sequence (Proterozoic) and the Van Keulenfjorden (VK) sequence (Carboniferous-Cretaceous), separated by a pronounced unconformity. The HH is divided into the Antoniabreen succession, the Chamberlindalen succession, and the Kapp Lyell tillite; the first two consist of diverse clastic and carbonate rocks, along with some volcanic rocks. The VK is a platform sequence of shallow marine and terrestrial sedimentary rocks. These layered rocks are intruded by a few Mesozoic dolerite sills and dikes. Subhorizontal Paleogene sedimentary rocks are preserved in a small graben. Both layered sequences have undergone strong deformation. Structures (mainly Caledonian age) in the HH can be grouped as phase 1 (small isoclinal folds, subhorizontal axial planar foliation, ridge-groove lineation in the foliation, and large recumbent folds), phase 2 (tight to isoclinal folds, axial planar foliation), and younger (weak folds and foliations, kink bands, crinkles). Structures (mainly Tertiary age) in the VK include faults (thrust, reverse, down-to-the-east bedding-plane normal, other normal); folds (symmetric, asymmetric, overturned, recumbent, isoclinal); and foliation (in some tightly folded Triassic shales). Six deformational events can be identified here, each described below in terms of age, intensity, and kinematic pattern: D 1 - Vendian or early Paleozoic; very strong; NNW-SSE shortening?, NNW transport? D 2 - Early Paleozoic (pre-Carboniferous); strong; NE-SW shortening, NE vergence. D 3 - Middle (?) Carboniferous; moderate; unclear (limited exposure). D 4 - Early Cretaceous (?); weak; extension, direction unclear. D 5 - Early (?) Tertiary

  20. The tectonic evolution of the greater South China Sea

    SciTech Connect

    Hayes, D.E. )

    1990-06-01

    The South China Sea (SCS) basin is composed of two major subbasins. The eastern subbasin was formed by seafloor spreading in the middle Tertiary and is associated with roughly E-W-trending magnetic lineations. The southwestern subbasin of the South China Sea is characterized by NE-SW tectonic and magnetic trends and is considerably narrower than the eastern subbasin. There is no obvious structural discontinuity between the two subbasins; hence the initial opening of the eastern subbasin was likely accommodated to the west by a prolonged period of extension of the continental crust that was not accompanied by the formation of normal oceanic crust. The southwest subbasin was eventually also formed by seafloor spreading processes. Although the sequence of magnetic lineations recorded there is relatively short, these data coupled with heatflow and crustal depth data strongly suggest that the southwestern subbasin was not formed until the early-middle Miocene, coincident with the last phase of spreading in the adjacent eastern subbasin. It is still unclear whether or not a significant change in spreading direction occurred within the SCS basin during the early Miocene. The geometry of the deep SCS basin as defined by the seaward limit of the continent-ocean boundary zone provides important constraints on the east-to-west variations in the total crustal extension manifested in the rifted margins of the South China Sea. The amount of new oceanic crust created by seafloor spreading plus the amount of crustal extension accommodated within the continental crust must be nearly the same for all points along the rifted margins. Because the amount of oceanic crust present is quite variable, it follows that the amount of crustal extension must be similarly variable and in a predictable way.

  1. High-resolution seismic analysis of the coastal Mecklenburg Bay (North German Basin): the pre-Alpine evolution

    NASA Astrophysics Data System (ADS)

    Zöllner, H.; Reicherter, K.; Schikowsky, P.

    2008-09-01

    The pre-Alpine structural and geological evolution in the northern part of the North German Basin have been revealed on the basis of a very dense reflection seismic profile grid. The study area is situated in the coastal Mecklenburg Bay (Germany), part of the southwestern Baltic Sea. From the central part of the North German Basin to the northern basin margin in the Grimmen High area a series of high-resolution maps show the evolution from the base Zechstein to the Lower Jurassic. We present a map of basement faults affecting the pre-Zechstein. The pre-Alpine structural evolution of the region has been determined from digital mapping of post-Permian key horizons traced on the processed seismic time sections. The geological evolution of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk. Salt pillows, which were previously unmapped in the study area, are responsible for the creation of smaller subsidence centers and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous.

  2. A review of the tectonic evolution of the Northern Pacific and adjacent Cordilleran Orogen

    NASA Astrophysics Data System (ADS)

    Jakob, Johannes; Gaina, Carmen; Johnston, Stephen T.

    2014-05-01

    Numerous plate kinematic models for the North Pacific realm have been developed since the advent of plate tectonics in the early seventies (e.g Atwater (1970), Mammerickx and Sharman (1988)). Although published kinematic models are consistent with the broad scale features of the North Pacific, the link between plate motions and the evolution of the North American Cordillera remains poorly understood. Part of the problem lies in conflicting interpretations of geological versus paleomagnetic data sets, with the result being a lack of consensus regarding: the paleolocation of key geological units; the paleogeography of terrane formation and amalgamation; the motion, boundaries and even existence of oceanic plates; and the character (e.g. trend of subduction) and position of plate boundaries within the northern Pacific basin. Remnants of the Farallon and Kula plates, and some short-lived microplates, demonstrate the complicated tectonic evolution of the oceanic realm west of the North American margin (e.g. Rea and Dixon (1983); McCrory and Wilson (2013); Shephard et al. (2013)). The creation and destruction of major tectonic plates and microplates has presumably left a record in the Cordilleran orogen of western North America. However, working backward from the geological relationships to plate reconstructions remains difficult. Here we investigate the relationship between the plate motions of the Pacific Ocean and the terrane movements in the North American Cordillera by revising the marine magnetic and gravity anomalies of the northern Pacific. In particular, we reevaluate plate boundaries at times of major changes in plate geometry of the Pacific, Kula, Chinook and Farallon plates from C34n onward. Our focus is also on the plate geometries of the Resurrection, Eshamy and Siletz-Crescent plates during the time between anomaly C26 and C12, and the links between plate interactions and on-shore tectonic events recorded in the geological record of Vancouver Island

  3. Tectonic Evolution of the Çayirhan Neogene Basin (Ankara), Central Turkey

    NASA Astrophysics Data System (ADS)

    Behzad, Bezhan; Koral, Hayrettin; İşb&idot; l, Duygu; Karaaǧa; ç, Serdal

    2016-04-01

    Çayırhan (Ankara) is located at crossroads of the Western Anatolian extensional region, analogous to the Basin and Range Province, and suture zone of the Neotethys-Ocean, which is locus of the North Anatolian Transform since the Late Miocene. To the north of Çayırhan (Ankara), a Neogene sedimentary basin comprises Lower-Middle Miocene and Upper Miocene age formations, characterized by swamp, fluvial and lacustrine settings respectively. This sequence is folded and transected by neotectonic faults. The Sekli thrust fault is older than the Lower-Middle Miocene age formations. The Davutoǧlan fault is younger than the Lower-Middle Miocene formations and is contemporaneous to the Upper Miocene formation. The Çatalkaya fault is younger than the Upper Miocene formation. The sedimentary and tectonic features provide information on mode, timing and evolution of this Neogene age sedimentary basin in Central Turkey. It is concluded that the region underwent a period of uplift and erosion under the influence of contractional tectonics prior to the Early-Middle Miocene, before becoming a semi-closed basin under influence of transtensional tectonics during the Early-Middle Miocene and under influence of predominantly extensional tectonics during the post-Late Miocene times. Keywords: Tectonics, Extension, Transtension, Stratigraphy, Neotectonic features.

  4. Tectonics, fluvial transport, and long-term episodicity in landscape evolution. (Invited)

    NASA Astrophysics Data System (ADS)

    Garcia-Castellanos, D.

    2010-12-01

    Modelling studies of the long-term evolution (>1 Myr) of tectonic sedimentary basins are generally based on the assumption that both tectonics and surface transport act as gradual mechanisms, if not at constant rates or conditions. Even under this premise, recent models predict geologically rapid changes in landscape evolution related to changes in basin connectivity that result from non-linear interplay between climate, tectonics, and transport. These results underline the importance of the development of internal drainage (endorheism) in controlling abrupt, non-tectonic changes in sedimentary basins such as the Ebro Basin (Pyrenees, Spain), the Sichuan Basin (Tibetan Plateau, China), or the Pannonian-Dacic system (Carpathian Mountains). These basins underwent long, lacustrine, endorheic periods followed by fast basin erosion, suggesting that, also in the large spatial and temporal scales, pulses in sedimentary infill, usually interpreted as the result of accelerated tectonic activity, may often be linked to hydrological reorganization. However, these long-term landscape evolution models are based on the assumption of steady flow, while abrupt changes in connectivity (e.g., overtopping of lacustrine basins) take place under very non-steady conditions. Accordingly, existing mathematical models cannot estimate the rapidity of the transition from lacustrine to erosional stages after basin overflow. Pleistocene scenarios such as the overspill of Lake Bonneville show that at least the largest basins are likely to trigger large floods when overspilling, leaving a significant imprint on landscape in a very short period of time. Numerical modelling can reveal whether the complexity observed in landscape can be explained as the result of the interaction between simple processes. Results so far suggest a need for implementing episodicity and non-steady flow in surface processes models, and to consider the statistical distribution of discrete meteorological events to better

  5. Geology and Tectonic Evolution of the Kazdaǧ Massif (NW Anatolia)

    NASA Astrophysics Data System (ADS)

    Erdoğan, B.; Akay, E.; Hasözbek, A.; Satır, M.; Siebel, W.

    2009-04-01

    and paleogeographic evolution of the southern part of the northwestern Anatolia. Geologica Romana 27, 13-80 Bingöl, E. (1971) Classification of age determination methods and application of Rb/Sr and K/Ar methods in Kazdağ. Bulletin of the Mineral Research and Exploration Institute of Turkey 14, 1-16 (in Turkish) Duru, M., Pehlivan, Ş., Şentürk, Y., Yavaş, F. ve Kar, H. (2004) New results on the lithostratigraphy of the Kazdağ Massif in northwest Turkey. Turkish Journal of Earth Sciences 13, 177-186 Okay, A.I and Monie, P. (1997) Early Mesozoic subduction in the eastern Mediterranean: Evidence from Triassic eclogite in northwest Turkey. Geology 25, 595-598 Okay, A.I and Satır, M. (2000) Coeval plutonism and metamorphism in a latest Oligocene metamorphic core complex in northwestern Turkey. Geological Magazine 137, 495-516 Okay, A.I, Siyako, M and Burkan, K.A. (1991) Geology and tectonic evolution of the Biga Peninsula, northwestern Turkey. Bulletin of the Technical University of İstanbul 44, 191-256 Okay, A.I, Monod, O and Monie, P. (2002) Triaasic blueschists and eclogites from northwestern Turkey: vestiges of the Paleo-Tethyan subduction. Lithos 64, 155-178 Okay, A.I, Satır, M., Maluski, H., Sıyako, M., Monie, P., Metzger, R., Akyüz, S., (1996) Paleo- and Neo-Tethyan events in northwestern Turkey: Geologic and geochronologic constrains. The Tectonic Evolution of Asia, 420-441 Topuz, G, Altıner, D, Satır, M, and Schwartz, W.H. (2004) Low-grade metamorphic rocks from the Pulur Complex, NE Turkey: implications for the pre-Liassic evolution of the Eastern Pontides. International Journal of Earth Science, 93, 72-91 Yaltırak C. and Okay A.İ (1994) Geology of the Paleo-Tethyan units in the north of Edremit Bay. Bulletin of the Technical University of İstanbul , 3/1, 67-79 (in Turkish)

  6. Traces of Late Miocene and Pleistocene tectonics on recent surface morphology in the Western Pannonian Alpine Foothills - a case study of geomorphometry

    NASA Astrophysics Data System (ADS)

    Kovács, Gábor; Telbisz, Tamás; Székely, Balázs

    2014-05-01

    effective method on apparently totally flat area in showing location of tectonic forces. We compared the revealed features with the basement morphology using previously composed basement maps and industrial seismic sections. Latter proved that morphological similarities are not only observable between the basement and the surface, but the geometry of basin-fill lacustrine sediment horizons strengthen the correspondence and in some cases explain the root causes. Our results provide additional information to the geodynamic sketch of the Alpine-Pannonian transition zone and emphasize the applicability of geomorphometry in tectonic studies. The study was supported by Hungarian Scientific Research Fund (OTKA NK83400) and was realized in the frames of TÁMOP 4.2.4.A/2-11-1-2012-0001 high priority "National Excellence Program - Elaborating and Operating an Inland Student and Researcher Personal Support System convergence program" project's scholarship support.

  7. 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. PMID:19198771

  8. Paleozoic plate-tectonic evolution of the Tarim and western Tianshan regions, western China

    SciTech Connect

    Yangshen, S.; Huafu, L.; Dong, J.

    1994-11-01

    The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the creation of a magmatic belt. 21 refs., 7 figs., 1 tab.

  9. Pele III, plate tectonics, atmospheric and biotic evolution

    SciTech Connect

    Sloan, R.E. . Dept. of Geology and Geophysics)

    1994-04-01

    This paper is an elaboration of Pele I and II, Landis et al GSA Abstr. V. 25 No.6, and Hengst et al GSA Abstr. V. 25 No.6. The Pele hypothesis is that CO[sub 2] concentration in the atmosphere is directly related to the rate of seafloor spreading and the existence of superplumes. Excess CO[sub 2] favors expansion of plants and is converted to O[sub 2] by photosynthesis and deposition of buried carbon and carbonate. O[sub 2] is removed from the atmosphere by weathering. Resulting major variations in atmospheric CO[sub 2] and O[sub 2] have significant impact on the evolution and extinction of organisms.

  10. Tectonic evolution of the Gulf of Mexico and Caribbean

    SciTech Connect

    Pindell, J.L.; Barrett, S.F.; Dewey, J.F.

    1985-01-01

    The authors propose a three-phase geologic-kinematic model for the evolution of the Gulf of Mexico/Caribbean region starting with a detailed Late Paleozoic (Alleghenian) plate reconstruction and using a revised relative-motion history for North America (NOAM) and South American (SOAM). The completely closed initial reconstruction incorporates the effects of Jurassic syn-rift crustal extension, an improved Equatorial Atlantic fit, and the post-rift accretion and deformation in northwestern South America. The Yucatan block and western Bahamas continental basement occupied the area of the present Gulf of Mexico. The three phases of evolution are: MIDDLE JURASSIC-CHAMPANIAN; SOAM migrated east-southeast from NOAM, and the Yucatan block rotated 43/sup 0/CCW about a pole in northern Florida reaching its present position by the Berriasian. Carbonate shelves formed along the rifted margins of the Gulf of Mexico and proto-Caribbean. Early Cretaceous crust of the Caribbean Plate (CARIB) formed in the Pacific Basin and was intruded by medial Cretaceous basalts (B'') somewhere to the west of South America. CARIB partially collided with southern Yucatan and northwest SOAM in the Late Cretaceous, and with the Bahamas in the late Paleocene-Middle Eocene. POST-MIDDLE EOCENE: Minor west-northwest NOAM-SOAM convergence occurred along preexisting Atlantic fracture zones. CARIB has migrated eastward by 1200 km, subducting proto-Caribbean crust and forming the Lesser Antilles arc. The original Greater Antilles-Aves Ridge arc has been dissected by anastomosing transforms connecting the Middle American and Lesser Antilles trenches.

  11. Simulation of Evolutive Plate Tectonics: the Size of Plates Depends on Mantle Temperature

    NASA Astrophysics Data System (ADS)

    Grigne, C.; Combes, M.

    2013-12-01

    We use a dynamic model of plate tectonics based on a multiagent approach, in a 2D cylindrical geometry (Combes et al., 2012), to study how evolutive plate tectonics affect the long term thermal state of the mantle, and in return, to analyze the relationship between the mantle mean temperature and the geometry of plate tectonics. Our model accounts for first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. We show that when processes for plate boundary creation (subduction initiation and ridge creation) are relying on a brittle criterion, namely when a fixed yield strength has to be reached, the average size of plates adapts to the mantle thermal state: longer plates are obtained for a hotter mantle, which implies a maximum seafloor age that remains fairly high throughout Earth's thermal history and limits mantle heat loss. This is consistent with petrological and geochemical constraints on Earth's cooling history. Important fluctuations in the mantle heat flux and velocities of plates are obtained on a timescale of a few hundred Myr, but on the long term, the relationship between the average wavelength of plate tectonics and mantle temperature can be explained by a simple scaling law. Recent compilations of geological records infer that passive margins had longer lifespans in the past (e.g. Bradley 2008; 2011), which has been linked to 'sluggish' plate tectonics and slow plates in the Precambrian (Korenaga, 2006). Our simulations outputs include lifespans of tectonic entities such as passive margins, as well as statistical data about events of plates reorganizations. We obtain faster plates in the past than at present day, but counterintuitively we also observe a low episodicity of tectonic

  12. Tectonic activity and the evolution of submarine canyons: The Cook Strait Canyon system, New Zealand

    NASA Astrophysics Data System (ADS)

    Micallef, Aaron; Mountjoy, Joshu; Barnes, Philip; Canals, Miquel; Lastras, Galderic

    2016-04-01

    Submarine canyons are Earth's most dramatic erosional features, comprising steep-walled valleys that originate in the continental shelf and slope. They play a key role in the evolution of continental margins by transferring sediments into deep water settings and are considered important biodiversity hotspots, pathways for nutrients and pollutants, and analogues of hydrocarbon reservoirs. Although comprising only one third of continental margins worldwide, active margins host more than half of global submarine canyons. We still lack of thorough understanding of the coupling between active tectonics and submarine canyon processes, which is necessary to improve the modelling of canyon evolution in active margins and derive tectonic information from canyon morphology. The objectives of this study are to: (i) understand how tectonic activity influences submarine canyon morphology, processes, and evolution in an active margin, and (2) formulate a generalised model of canyon development in response to tectonic forcing based on morphometric parameters. We fulfil these objectives by analysing high resolution geophysical data and imagery from Cook Strait Canyon system, offshore New Zealand. Using these data, we demonstrate that tectonic activity, in the form of major faults and structurally-generated tectonic ridges, leaves a clear topographic signature on submarine canyon location and morphology, in particular their dendritic and sinuous planform shapes, steep and linear longitudinal profiles, and cross-sectional asymmetry and width. We also report breaks/changes in canyon longitudinal slope gradient, relief and slope-area regression models at the intersection with faults. Tectonic activity gives rise to two types of knickpoints in the Cook Strait Canyon. The first type consists of low slope gradient, rounded and diffusive knickpoints forming as a result of short wavelength folds or fault break outs and being restored to an equilibrium profile by upstream erosion and

  13. Towards an Integrated Model of Earth's Thermo-Chemical Evolution and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Xie, S.

    2001-05-01

    It has long been a challenge for geodynamicists, who have typically modeled homogeneous mantles, to explain the geochemical evidence for the existence of several distinct chemical reservoirs, in terms of a dynamically and chemically self-consistent model. While the mixing behavior of generalized tracers has received much attention in the modeling community, a recent trend has been towards mantle convection models that track the evolution of specific chemical species, both major and minor, and can thus be related to geochemical observations. However, obtaining realistic chemical evolution in such models is dependent on their having a reasonable representation of plate tectonic behavior since the recycling of oceanic crust and complementary depleted residuum is a key process in Earth that other terrestrial planets may lack. In general, this has required inserting plate motions by hand in models. In recent years, however, we have learned how to perform numerical simulations of mantle convection in which plate tectonic behavior is introduced self-consistently through plastic yielding of the lithosphere. In this presentation, models of mantle convection that combine a treatment of geochemical evolution with self-consistently generated plate tectonics, will be presented. Preliminary results indicate that the system can self-consistently evolve regions which have a HIMU-like signature as well as regions with a high He3/He4 ratio.

  14. 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.

  15. Basaltic Magmatism: The Dominant Factor in the Petrologic and Tectonic Evolution of the Earth

    NASA Technical Reports Server (NTRS)

    Lowman, Paul D., Jr.

    2003-01-01

    Silicate bodies such as the Moon, Mars, probably Mercury, and possibly Venus, appear to have evolved in three main stages: a first (felsic) differentiation, a late heavy bombardment, and a second (basaltic) differentiation. It has been proposed that the Earth underwent a similar sequence. This paper argues that the second differentiation, basaltic magmatism, has dominated the petrologic and tectonic evolution of the Earth for four billion years. A global andesitic crust, formed during and after accretion of the planet, was disrupted by major impacts that triggered mantle upwelling and sea-floor spreading about 4 billion years ago. The oceanic crust collectively has since been formed by basaltic volcanism, from spreading centers and mantle plumes. However, the continental crust has also been greatly affected. Basaltic underplating has promoted anatexis and diapiric intrusion of granitoids in granite-greenstone terrains, as well as providing heat for regional metamorphism. Basaltic intrusions, such as the Nipissing diabase of the Sudbury area, have added to the thickness of continental crust. Satellite magnetic surveys suggest that there are more such basaltic intrusions than previously realized; examples include the Bangui anomaly of central Africa and the Kentucky anomaly. Basaltic overplating from mafic dike swarms has repeatedly flooded continents; had it not been for erosion, they would be covered with basalt as Venus is today. The tectonic effects of basaltic volcanism on continents have only recently been realized. The World Stress Map project has discovered that continents are under horizontal compressive stress, caused by push from mid-ocean ridges, i.e., by basaltic volcanism. The stress fields are generally uniform over large intraplate areas, and could contribute to intraplate tectonism. Seafloor spreading has demonstrably been effective for at least 200 million years, and ridge push thus a contributor to tectonic activity for that long. Collectively, the

  16. A unit of instruction on the plate tectonic evolution of New England

    SciTech Connect

    Reusch, D. )

    1993-03-01

    A unit of instruction has been developed which enables high school students to decipher the plate tectonic evolution of a typical mountain belt, the New England segment of the Appalachian Orogen. It integrates a wide variety of geological topics including: geological time, the fossil record, global tectonics, geological environments, rocks, minerals, and representative sedimentary, igneous, and metamorphic processes. Students are provided with a simplified tectonic map of the New England area and data cards on each of 12 units. They use fossils and radiometric dates to sort the units chronologically and the map to sort them geographically. Next, they compare the fossil and geological data for each unit with modern tectonic settings and interpret each unit as either oceanic crust [+-] mantle, volcanic arc, arc margin, continental crust, passive margin (rift, shelf, or slope), granite system, or collision margin. Finally, they reconstruct the paleogeography for each time period which reveals the cycle of Iapetus Ocean growth and destruction and the initiation of the Atlantic Ocean cycle.

  17. Differentiating tectonic from climatic factors in the evolution of alluvial fans

    SciTech Connect

    Wilson, D.S.; West, R.B. . Dept. of Geology)

    1993-04-01

    Alluvial fans are integral parts of landscapes of arid and semi-arid regions and are most commonly found along the flanks of tectonically active mountain ranges. Alluvial fans are sensitive indicators of tectonic and climatic activity through time. Three dimensional fan modelling has the potential to discriminate between these two forces and provide quantitative estimates of deformation of fan surfaces due to tilting, faulting, or folding. The model has tremendous potential for seismic hazard evaluation at both the reconnaissance and detailed level of investigation. The ability to recognize deformation of alluvial fans alleviates the need for postulation of complex interactions between climate and internal variables in the depositional system leading to present fan morphology. The greatest problems associated with fan modelling come from failure to identify individual segments. Inclusion of more than one segment can lead to poor model performance or, more likely, inaccurate results. The long term tectonic influence on a fan's evolution can be assessed from the differences in deformation of different segments. Reliable correlations of segments from different fans along the same mountain front can provide a means to asses regional deformation. Once tectonic effects are taken into account, then climatic effects can be evaluated. Previous fan models have failed to recognize areal limitations, failed to account for deformation, or assumed deformation geometry.

  18. How do Early Impacts Modulate the Tectonic, Magnetic and Climatic Evolutions of Terrestrial Planets?

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The landmark discovery showing that the 142Nd/144Nd ratio of the accessible modern terrestrial mantle is greater than ordinary-chondrites has remarkable implications for the formation, as well as the geodynamic, magnetic and climatic histories of Earth. If Earth is derived from ordinary chondrite precursors, mass balance requires that a missing reservoir with 142Nd/144Nd lower than ordinary chondrites was isolated from the accessible mantle within 20-30 Myr following accretion. Critically for Earth evolution, this reservoir hosts the equivalent of the modern continents' budget of radioactive heat-producing elements (U, Th and K). If this reservoir was lost to space through mechanical erosion by early impactors, the planet's radiogenic heat generation is 18-45% lower than chondrite-based compositional estimates. Recent geodynamic calculations suggest that this reduced heat production will favor the emergence of Earth-like plate tectonics. However, parameterized thermal history calculations favor a relatively recent transition from mostly Atlantic-sized plates to the current plate tectonic mode characterized predominantly by the subduction of Pacific-sized plates. Such a transition in the style of Earth's plate tectonics is also consistent with a delayed dynamo and an evolving rate of volcanic outgassing that ultimately favors Earth's long-term clement climate. By contrast, relatively enhanced radiogenic heat production related to a less early impact erosion reduces the likelihood of present day plate tectonics: A chondritic Earth has a stronger likelihood to evolve as a Venus-like planet characterized by potentially wild swings in tectonic and climatic regime. Indeed, differences in internal heat production related to varying extents of impact erosion may exert strong control over Earth's climate and explain aspects of the differences among the current climatic regimes of Earth, Venus and Mars.

  19. The evolution of volcanism, tectonics, and volatiles on Mars - An overview of recent progress

    NASA Technical Reports Server (NTRS)

    Zimbelman, James R.; Solomon, Sean C.; Sharpton, Virgil L.

    1991-01-01

    Significant results of the 'Mars: Evolution of Volcanism, Tectonics, and Volatiles' (MEVTV) project are presented. The data for the project are based on geological mapping from the Viking images, petrologic and chemical analyses of SNC meteorites, and both mapping and temporal grouping of major fault systems. The origin of the planet's crustal dichotomy is examined in detail, the kinematics and formation of wrinkle ridges are discussed, and some new theories are set forth. Because the SNC meteorites vary petrologically and isotopically, the sources of the parental Martian magma are heterogeneous. Transcurrent faulting coupled with the extensional strains that form Valles Marineris suggest early horizontal movement of lithospheric blocks. A theory which connects the formation of the crustal dichotomy to the Tharsis region associates the horizontal motions with plate tectonics that generated a new lithosphere.

  20. Plio-Quaternary canyons evolution on South Colombian convergent margin : Tectonic causes and implications

    NASA Astrophysics Data System (ADS)

    Ratzov, Gueorgui; Sosson, Marc; Collot, Jean-Yves; Migeon, Sebastien

    2010-05-01

    Investigations of seafloor morphology and sediment deposits associated with the incision of the South Colombia active margin by a major submarine canyon system are used to reveal out-of-sequence fault activity at least since the Middle Pleistocene. The South Colombian convergent margin is located along Northwestern South America, where the Nazca plate underthrusts eastward the South America plate with a 58 mm.yr-1 convergence rate. The morphology and deep multichannel seismic reflection lines obtained across the margin reflect a frontal accretionnary wedge, as well as antiform and faulted internal structural highs that locally extend up to near the continental shelf, suggesting wide-spread Plio-Quaternary tectonic activity. The Amadeus cruise conduced in 2005 brought new seismic and sedimentary data together with 150m and 60m-resolution EM12D multibeam bathymetry. The newly mapped Mira and Patia canyons system incises the South Colombian margin slope over a distance of ~90 and ~150 km respectively, forming an unequivocal Z-shape in map view, breaching the deformation front and feeding a 30-km wide trench fan system. The morphology of the canyon exhibits meanders, steep over-incised walls (~25-30 degrees), alternation between concave-up and convex-up downstream profiles, slope failures scars, and buried channels. These features reflect interactions between tectonics, sedimentation and the canyon evolution. A synthesis of all the data reveals that: A) Uplifting structural highs control canyons path and incision stages. B) Canyons developed asynchronously across the upper, mid and lower margin slopes according to three main stages: a) upper slope incision by downward cutting during Pleistocene, and possibly by retrogressive headward erosion, b) infill of a mid-slope basin bounded by uplifting structural highs, and c) overspill of the slope basin, and breaching its seaward bounding ridge, and the accretionary prism ~150 kyr ago. These processes led to the construction

  1. Evidence of Variscan and Alpine tectonics in the structural and thermochronological record of the central Serbo-Macedonian Massif (south-eastern Serbia)

    NASA Astrophysics Data System (ADS)

    Antić, Milorad D.; Kounov, Alexandre; Trivić, Branislav; Spikings, Richard; Wetzel, Andreas

    2016-07-01

    The Serbo-Macedonian Massif (SMM) represents a composite crystalline belt within the Eastern European Alpine orogen, outcropping from the Pannonian basin in the north to the Aegean Sea in the south. The central parts of this massif (south-eastern Serbia) consist of the medium- to high-grade Lower Complex and the low-grade Vlasina Unit. Outcrop- and micro-scale ductile structures in this area document three major stages of ductile deformation. The earliest stage D1 is related to isoclinal folding, commonly preserved as up to decimetre-scale quartz-feldspar rootless fold hinges. D2 is associated with general south-eastward tectonic transport and refolding of earlier structures into recumbent metre- to kilometre-scale tight to isoclinal folds. Stages D1 and D2 could not be temporally separated and probably took place in close sequence. The age of these two ductile deformation stages was constrained to the Variscan orogeny based on indirect geological evidence (i.e. ca. 408-ca. 328). During this period, the SMM was involved in a transpressional amalgamation of the western and eastern parts of the Galatian super-terrane and subsequent collision with Laurussia. Outcrop-scale evidence of the final stage D3 is limited to spaced and crenulation cleavage, which are probably related to formation of large-scale open upright folds as reported previously. 40Ar/39Ar thermochronology was applied on hornblende, muscovite, and biotite samples in order to constrain the age of tectonothermal events and activity along major shear zones. These 40Ar/39Ar data reveal three major cooling episodes affecting the central SMM. Cooling below greenschist facies conditions in the western part of the Vlasina Unit took place in a post-orogenic setting (extensional or transtensional) in the early Permian (284 ± 1 Ma). The age of activity along the top-to-the-west shear zone formed within the orthogneiss in the Božica area of the Vlasina Unit was constrained to Middle Triassic (246 ± 1 Ma). This

  2. Andean subduction orogeny: feedbacks between tectonics, relief evolution and global climate

    NASA Astrophysics Data System (ADS)

    Lacassin, Robin; Armijo, Rolando; Coudurier-Curveur, Aurélie; Carrizo, Daniel

    2016-04-01

    The Andean subduction margin, largest tectonic relief on the Earth (13 km vertically from the trench to the Altiplano) has a stepped morphology, which results of the evolution over the past 50 Myr of two parallel flat-ramp thrust systems, at the - previously unidentified - West Andean Thrust (WAT), and at the subduction interface. The evolution of those thrusts appears concomitant with increasing aridity in the Atacama Desert, which keeps a large-scale record of interplaying tectonics and Cenozoic climate change. The coastal morphology is dominated by the Atacama Bench, a giant uplifted terrace at 1-2km asl. Geomorphic and climatic data, numerical experiments of drainage formation are consistent with the development of a flat Atacama morphology close to sea level, interrupted at ≤10 Ma by tectonic uplift prevailing to the present. This suggests recent trench-ward relief growth by incorporation of the coastal Atacama Bench to the Andes reliefs. Thrust splay structures and other complexities above the subduction interface may explain this relief growth, as well as the distribution of asperities under the oceanward forearc, and the down-dip segmentation of coupling and seismicity on the megathrust. Combining those results with geological knowledge at the scale of the whole Central Andes, we show that the Andean orogeny results from protracted processes of bivergent crustal shortening in a wide region squeezed between the rigid Marginal Block and the S America Plate. The overall growth curve of Andean orogeny over the past 50 Myr appears synchronous with the onset of the "ramp-shaped" temperature decrease since the Early Eocene climatic optimum. Andean growth and global cooling may have operated under the same forcing mechanism at plate-scale, involving viscous flow in the mantle. But Andean growth appears modulated by climatic feedbacks causative of stepwise reductions of erosive power over the Andean margin. The first of such events is coeval with Late Eocene

  3. Integrating Geochemical and Geodynamic Numerical Models of Mantle Evolution and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Xie, S.

    2001-12-01

    The thermal and chemical evolution of Earth's mantle and plates are inextricably coupled by the plate tectonic - mantle convective system. Convection causes chemical differentiation, recycling and mixing, while chemical variations affect the convection through physical properties such as density and viscosity which depend on composition. It is now possible to construct numerical mantle convection models that track the thermo-chemical evolution of major and minor elements, and which can be used to test prospective models and hypotheses regarding Earth's chemical and thermal evolution. Model thermal and chemical structures can be compared to results from seismic tomography, while geochemical signatures (e.g., trace element ratios) can be compared to geochemical observations. The presented, two-dimensional model combines a simplified 2-component major element model with tracking of the most important trace elements, using a tracer method. Melting is self-consistently treated using a solidus, with melt placed on the surface as crust. Partitioning of trace elements occurs between melt and residue. Decaying heat-producing elements and secular cooling of the mantle and core provide the driving heat sources. Pseudo-plastic yielding of the lithosphere gives a first-order approximation of plate tectonics, and also allows planets with a rigid lid or intermittent plate tectonics to be modeled simply by increasing the yield strength. Preliminary models with an initially homogeneous mantle show that regions with a HIMU-like signature can be generated by crustal recycling, and regions with high 3He/4He ratios can be generated by residuum recycling. Outgassing of Argon is within the observed range. Models with initially layered mantles will also be investigated. In future it will be important to include a more realistic bulk compositional model that allows continental crust as well as oceanic crust to form, and to extend the model to three dimensions since toroidal flow may alter

  4. Unraveling the Interaction Between Mantle Processes and the Tectono-Sedimentary Evolution During Final Rifting Based on the Study of Remnants of the Alpine Tethys Rifted Margins Exposed in the Alps

    NASA Astrophysics Data System (ADS)

    Mohn, G.; Masini, E.; Manatschal, G.; Muntener, O.; Kusznir, N.

    2007-12-01

    The tectonic, sedimentary and isostatic evolution of distal rifted margins are poorly constrained and the available data from present-day magma-poor rifted margins, such as the Iberia-Newfoundland or the Southern Atlantic margins suggest that its evolution is complex and very different from that of proximal margins. In contrast to present-day rifted margins, where rift structures are covered by sediments and are at abyssal depth, remnants of ancient margins preserved in collisional orogens bear, if not overprinted by later deformation, important information on the stratigraphic, tectonic and mantle evolution during rifting. This is particularly true for the Adriatic and parts of the European margins exposed in the Alps in Central Europe. From these margins remnants of the first oceanic crust, the subcontinental mantle, from lower crustal rocks, detachment systems, remnants of the distal and proximal margins and the stratigraphic record of rifting, including pre-, syn- and post-rift sediments are preserved. A paleogeographic reconstruction of all these structures including the associated stratigraphy and the underlying basement represents a unique opportunity to study the relations between shallow crustal and mantle processes during rifting. Previous studies suggested that the margins in the Alps resulted from a complex poly-phase evolution that initiated with distributed stretching (220 to 190 Ma), continued with localized thinning (around 180 Ma) and terminated with exhumation of mantle rocks and first MOR-type magmatism (at 160 Ma). Thus, rifting leading to breakup and opening of the Alpine Tethys was shown to be the result of strain localization and to include a transition from decoupled to coupled deformation in which detachment faulting played an important role. How crustal thinning is linked in detail with strain localization, uplift of distal domains and melt infiltration in the rising mantle during crustal thinning is, however, not yet understood. We will

  5. Geomorphological evolution of the Tilcara alluvial fan (Jujuy Province, NW Argentina): Tectonic implications and palaeoenvironmental considerations

    NASA Astrophysics Data System (ADS)

    Sancho, Carlos; Peña, José Luis; Rivelli, Felipe; Rhodes, Ed; Muñoz, Arsenio

    2008-07-01

    The development and evolution of the Tilcara alluvial fan, in the Quebrada de Humahuaca (Andean Eastern Cordillera, NW Argentina), has been analysed by using geomorphological mapping techniques, sedimentological characterisation of the deposits and OSL chronological methods. It is a complex segmented alluvial fan made up of five evolutionary stages (units Qf1, Qf2, Qf3, Qf4 and Qf5) developed under arid climatic environments as well as compressive tectonic conditions. Segmentation processes, including aggradation/entrenchment cycles and changes in the location of the depositional lobe, are mainly controlled by climatic and/or tectonic changes as well as channel piracy processes in the drainage system. Alluvial fan deposits include debris flows, sheet flows and braided channel facies associated with high water discharge events in an arid environment. The best mean OSL age estimated for stage Qf2 is 84.5 ± 7 ka BP. In addition, a thrust fault affecting these deposits has been recognized and, as a consequence, the compressive tectonics must date from the Upper Pleistocene in this area of the Andean Eastern Cordillera.

  6. Miocene to recent tectonic and sedimentary evolution of the Anaximander Seamounts; eastern Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Cranshaw, Jennifer

    This thesis is focused on the Messinian to Recent tectonic and sedimentary evolution of the Anaximander Mountains and surrounding environs in the eastern Mediterranean Sea. It is based on processing of high-resolution seismic reflection data and the interpretation and mapping of seismic reflection profiles collected from this area during the 2001 and 2007 research cruises. The data show that the greater Anaximander Mountains region experienced a short interval of tectonic quiescence during the Messinian when a thin evaporite unit was deposited across a major erosional surface. This phase of limited tectonic activity ended in the latest Miocene and was replaced by an erosional phase. Major unconformities in the area are interpreted to develop during the desiccation of the eastern Mediterranean associated with the so-called Messinian salinity crisis. During the early Pliocene, the region experienced an increase in tectonic activity, dominated by transpression. Small amounts of growth observed in Pliocene-Quaternary sediments suggested that the tectonic activity remained low during the early Pliocene-Quaternary. However, the extensive growth strata wedges developed in older sediments indicate a period of accelerated tectonic activity during the mid-late Pliocene-Quaternary. This study suggests that the Anaximander Mountain (sensu stricto ) and the Anaximenes Mountain developed during the Pliocene-Quaternary as the result of a crustal-scale thick-skinned linked imbricate thrust fan. The development of back thrusts in both mountains heightened the seafloor morphology of these submarine mountains and brought Eocene-Oligocene sediments into the core of these mountains. The Sim Erinc Plateau represents a 30-40 km wide transpressional fault zone developed during the Pliocene-Quaternary. In this region the corrugated seafloor morphology observed in the multibeam bathymetry map is the reflection of high-angle faults. It is speculated that this transpressional fault zone

  7. New constraints on the tectonic and thermal evolution of the Central-Western Carpathians

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The Central-Western Carpathians have been studied for long time but they are a still matter of discussion. In addition, they are one of the principal East European targets for oil and gas exploration. Understanding the tectonic evolution and the spatial and temporal variation of the thermal regime is crucial for this purpose. This orogene formed after the collision between the European Platform and the ALCAPA and Tisza-Dacia microplates from the Upper Jurassic to the Neogene. The widely accepted interpretation suggests the occurrence of the oceanic lithosphere subducting under the two microplates and the development of the oceanic suture in the Pieniny Klippen Belt area during the Paleocene. The subduction ends when the accretionary wedge reaches its present-day position on top of the southern border of the European Platform. The Carpathian arc can be subdivided into three tectonic domains: • Outer Carpathians made up of Upper Jurassic to Lower Miocene siliciclastic deposits intercalated with shales and sandstones; • Pieniny Klippen Belt formed by Mesozoic olistoliths and olistostromes in a sandy-clay Cretaceous sheared matrix; • Inner Carpathians consisting in Variscan allochthonous crystalline basement with its Mesozoic cover involved in the late Cretaceous folding and thrusting These deposits are unconformably overlain by the undeformed Central Carpathian Paleogene Basin successions. Cross-section balancing and sequential restoration integrated with low-temperature thermochronometry (apatite fission track and apatite (U-Th-Sm)/He analysis) can better constrain the tectonic evolution of this area and, in particular, its exhumation history. Seven balanced sections have been constructed across the Polish and Ukrainian Carpathians. The sequential restoration shows a thick-skinned tectonics during the Upper Cretaceous, involving the Inner Carpathian basin. The erosion of the Mesozoic basement cover and the sedimentation of these deposits in the foreland basin

  8. Tectonic evolution of the western boundary of the Attico-Cycladic complex (Lavrio, Greece)

    NASA Astrophysics Data System (ADS)

    Scheffer, Christophe; Vanderhaeghe, Olivier; Tarantola, Alexandre; Lanari, Pierre; Ponthus, Leandre; France, Lyderic; Photiades, Adonis

    2015-04-01

    The Lavrio peninsula, South East of Athens, is located along the western boundary of the Attic-Cycladic Metamorphic Complex in the internal zone of the Hellenic orogenic belt, at the intersection between thrusts and detachments. It is thus a perfect target to decipher the tectonic evolution of an orogenic wedge from tectonic accretion to gravitational collapse. The nappe stack is overlain by a non-metamorphic limestone and is made, from top to bottom by (i) an ophiolitic melange, (ii) the Lavrio tectonic unit dominated by schists and displaying mineral paragenesis typical of blueschist facies, (iii) the Kamariza tectonic unit dominated by marbles and affected by pervasive greenschist facies metamorphism. The Lavrio and Kamariza tectonic units are juxtaposed by a low-angle mylonitic to cataclastic detachement. A more detailed investigation of the relationships between mineral paragenesis and microstructures indicates that the transition from the Lavrio to the Kamariza tectonic units, across the low-angle detachment, is marked by progressive transposition of the blueschist facies fabric coeval with retrogression under greenschist facies conditions. Indeed, the Kamariza unit is characterized by a relatively steep foliation associated with isoclinal folds of weakly organized axial orientation that is partially to totally transposed into a shallow dipping foliation bearing a N-S trending lineation. The degree of transposition increases from top to bottom and is particularly marked at the transition from the Lavrio to the Kamariza unit across the low-angle detachement. The blueschist facies foliation of the Lavrio schists is underlined by glaucophane and HP phengite intergrown with chlorite crystals. The Kamariza tectonic unit is dominated by LP phengite intergrown with chlorite but contains relics of the blueschist mineral paragenesis. Detailed microprobe mapping of the composition of the phengite and chlorite crystals reveal distinct variations of the PT conditions

  9. Main Stages of Geodynamic Evolution of the Caucasian Segment of the Alpine-Mediterranean Belt

    NASA Astrophysics Data System (ADS)

    Gamkrelidze, Irakli; Shengelia, David; Maisadze, Ferando; Tsutsunava, Tamara; Chichinadze, Giorgi

    2013-04-01

    Within the oceanic area of Tethys, with a typical oceanic crust, in geological past relatively small continental or subcontinental plates (terranes) were situated. The Greater Caucasian, Black Sea - Central Transcaucasian, Baiburt - Sevanian and Iran - Afghanian accretionary terranes, which in geological past represented island arcs or microcontinents, are identified in the Caucasian segment of the Alpine-Mediterranean belt. They are separated by ophiolite sutures (relics of small or large oceanic basins) of different age. During the Late Precambrian, Paleozoic and Early Mesozoic these terranes underwent horizontal displacement in different directions and ultimately they joined the Eurasian continent. New LA-ICP-MS U-Pb zircon dating along with available geologic, petrologic and geochemical investigations, allow to trace with confidence the main stages of regional metamorphism, granite formation and, consequently, pre-Alpine continental crust making within the Caucasus. At the pre-Grenville stage (1200 Ma and more) between the Baltica and Gondvana ancient continents, on the oceanic crust of Prototethys accumulation mainly of terrigenous sediments and of basic volcanites took place. At the Grenville stage (1000-800 Ma) subcontinental or primitive continental crust (gneiss-migmatite complex and synmetamorphic grenitoids of sodium series) were formed in suprasubduction conditions by both sides of Proto-Paleotethys and along the northern peripheries of comparatively small oceanic basins of the Arkhiz and Southern Slope of the Greater Caucasus. At the Baikalian stage (650-550 Ma) plagiogneissic complex has been cut by Precambrian gabbroids and intruded by large bodies of quartz-diorites. The next, Late Baikalian stage (540-500 Ma) is determined by the intrusion of Cambrian basites and Late Baikalian granitoids and by manifestation of intensive suprasubduction regional metamorphism. Late Baikalian tectogenesis is accompanied by contraction of the small oceanic basin of

  10. Hinterland tectonics and drainage evolution recorded by foreland basin archives: the Neogene Siwaliks of the Himalaya

    NASA Astrophysics Data System (ADS)

    Huyghe, Pascale; van der Beek, Peter; Matthias, Bernet; Catherine, Chauvel; Jean-Louis, Mugnier; Laurent, Husson; François, Chirouze

    2014-05-01

    Provenance analysis and detrital thermochronology of detrital synorogenic sediments, derived from erosion of mountain belts and deposited in surrounding sedimentary basins, are well-established methods to examine the exhumation history of convergent zones, tectonic activity and the associated evolution of the drainage network. We have conducted multidisciplinary studies on magnetostratigraphically dated sections throughout the Neogene Siwalik foreland basin of the Himalayan belt since more than 10 years. Sr, Nd and Hf isotopes are used as provenance indicators, providing information on the nature and size of catchment basins and their evolution through time in response to tectonics. Detrital zircon and apatite thermochronology provides constraints on exhumation rates in the hinterland of the Himalaya and the deformation of the Sub-Himalayan foreland basin. Throughout the Himalaya, detrital zircons from the Siwaliks generally show three age peaks: two static peaks (i.e., displaying constant peak ages through time), and a moving peak. The latter shows a constant lag time of ~4 m.y. corresponding to source-area exhumation rates on the order of 1.8 km/my, while the two static peaks respectively reveal a major 15-20 Ma exhumation event in the belt, the significance of which is still debated, and inheritance of pre-Himalayan ages that indicate recycling of Tethyan sediments. Therefore, our ZFT results suggest that the exhumation dynamics are broadly similar throughout the Himalaya since at least 13 m.y, as also shown by the Bengal Fan detrital sediment record. We relate this switch in tectonic regime to the destabilization of the Himalayan wedge that is rendered overcritical as a response to the transience of dynamic topography caused by the deforming underlying Indian slab. Nonetheless, in detail, the timing of thrusting in the Siwalik domain is delayed by about 1 my eastward as demonstrated by both structural and apatite fission-track data, suggesting overall eastward

  11. The role of salt tectonics in the evolution of the northeastern Pyrenees

    NASA Astrophysics Data System (ADS)

    Ford, Mary; Christophoul, Frédéric; Menzer, Lionel; Simonis, Jules; Saura, Eduard; Vergés, Jaume

    2016-04-01

    Evaporites can play a major role in controlling the architecture of external orogenic belts, both during extensional and subsequent compressional phases. However, salt can also 'hide' deformation due to its ability to flow and dissolve. The challenge is to recognise the imprint of its past presence and influence. In the NE Pyrenees multiple deformation phases have been identified based on locally anomalous stratigraphic and structural relationships. This has resulted in complex, sometimes incoherent and often conflictual models of orogenic history. For example, a pre-Cenomanian deformation phase has been interpreted as either extensional or compressional. As part of the ANR-PYRAMID project, we have re-examined key localities around the eastern Mouthoumet massif, in the Corbières foreland and along the Corbières thrust front to reconstruct a coherent deformation history involving salt tectonics. Keuper (Carnian - Rhetian) evaporitic deposits gave rise to diapirs and detachments that were particularly active during Early to Late Cretaceous extension and later during Late Cretaceous to Eocene compression. Growth unconformities and rapid thickness changes in the Aptian Quillan basin indicate that it developed as a salt controlled minibasin. Olistoliths, gypsum breccias and presence of bipyramidal quartz in Albian strata preserved as footwall imbricates along the North Pyrenean thrust front (e.g. around Cucugnan) attest to the proximity of a large diapiric body. Below the Cenomanian unconformity, rotated fault blocks of Liassic to Albian strata lie above a Keuper detachment. These extensional fault blocks have already been recognised at the Serre de Bouchard. They are also preserved north of Cucugnan, in the Montagne de Tauch and in the Fontfroide massif with little or no alpine inversion. In the Corbières foreland area salt-influenced extensional and compressional deformation generated growth folds, with completely overturned limbs (flaps), welds, growth

  12. Geohistory analysis of the Santa Maria basin, California, and its relationship to tectonic evolution of the continental margin

    SciTech Connect

    McCrory, P.A.; Arends, R.G. ); Ingle, J.C. Jr. ); Isaacs, C.M.; Stanley, R.G. ); Thornton, M.L.C. )

    1991-02-01

    The Santa Maria basin of central California is a geologically complex area located along the tectonically active California continental margin. The record of Cenozoic tectonism preserved in Santa Maria strata provides an opportunity to compare the evolution of the region with plate tectonic models for Cenozoic interactions along the margin. Geohistory analysis of Neogene Santa Maria basin strata provides important constraints for hypotheses of the tectonic evolution of the central California margin during its transition from a convergent to a transform plate boundary. Preliminary analyses suggest that the tectonic evolution of the Santa Maria area was dominated by coupling between adjacent oceanic plates and the continental margin. This coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin subsidence and uplift which occurred during periods of tectonic plate adjustment. Stratigraphic evidence indicates that the Santa Maria basin originated on the continental shelf in early Miocene time. A component of margin subsidence is postulated to have been caused by cessation of spreading on adjacent offshore microplates approximately 19-18 ma. A sharp reduction in rate of tectonic subsidence in middle Miocene time, observed in the Santa Maria basin both onshore and offshore, was coeval with rotation of crustal blocks as major shearing shifts shoreward. Tectonic uplift of two eastern sites, offshore Point Arguello and near Point Sal, in the late Miocene may have been related to a change to transpressional motion between the Pacific and North American plates, as well as to rotation of the western Transverse Ranges in a restraining geometry.

  13. The Neogene tectonic evolution and climatic change of the Tianshui Basin, NE Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Peng, T.; Li, J.; Song, C.; Zhao, Z.; Zhang, J.; Wang, X.; Hui, Z.

    2013-12-01

    The Tianshui Basin, located at the conjunction of NE Tibetan Plateau and Chinese Loess Plateau, has received intensive attention recently. Fine-grained Miocene sediment was identified as loess in its north part and this pushes the onset of Asian aridification into 22 Ma. However, our sedimentological, biomarker, pollen, diatom and mammalian fossils evidence propose that these sediments were suggested to be mudflat/distal fan and floodplain deposit instead of eolian deposit. So detailed tectonic background and climate reconstruction may illustrate the controversy and shed light on the tectonic, climate and ecology interactions. Here we report our integrated studies on the tectonic evolution, climate change and paleoecology reconstruction in the Tianshui basin. Based on the magnetostratigraphy and fossil mammal ages, sedimentological and detrital fission-track thermochronologic (DFT) analysis reveals four episodic tectonic uplift events occurred at ~20 Ma, ~14 Ma, ~9.2-7.4 Ma and ~3.6 Ma along the basin and its adjacent mountains. The timing of these activities at Western Qinling have been documented at many segments of the Tibetan Plateau, so most likely they were the remote response to the ongoing India-Asia collision. Pollen, mammalian fossils and biomarker data permit us to illustrate the paleoenvironment in the Tianshui Basin. During the period of ~17-10 Ma, the climate was generally warm-humid revealed by the broad-leaved forest and low Average Chain Length (ACL) values, when the Paltybelodon and Gomphotherium were roaming near an extensive aquatic setting. In addition, the observed Middle Miocene Climatic Optimum and Middle Miocene Climatic Transition events may be a terrestrial response to global climate changes. During the interval of ~10-6 Ma, the climate was relatively arid characterized by the rapid development of steppe and appearance of the Hipparion fauna, consistent with the biomarker proxy. Although the NE Tibetan Plateau experienced a phase of

  14. The relationship between tectonic evolution and oil-cracking gas accumulation in late stage for marine superimposed basins

    NASA Astrophysics Data System (ADS)

    Zheng, Min; Wu, Xiaozhi

    2015-04-01

    The marine superimposed basins are rich in oil-cracking gas resources. Their hydrocarbon accumulation processes of late stage have experienced early paleo-oil reservoir accumulation period and late oil-cracking gas period, which are apparently controlled by tectonic evolution. Studying the relationship between tectonic evolution and oil-cracking gas accumulation of late stage has great significance to guide the exploration of oil-cracking gas reservoirs. Taking the relationship between tectonic evolution and oil-cracking gas accumulation of late stage for the Shunan area in the Sichuan Basin as example, through the analysis on the respons of structural evolution to deposition, the relationship between hydrocarbon generation process of ancient source rocks, initial hydrocarbon accumulation, oil cracking and gas accumulation of late stage was studied. The source rocks of the Cambrian Qiongzhusi Fm in the Shunan area experienced three periods of hydrocarbon generation and two periods of hydrocarbon generation lag. During the large-scale tectonic uplift and thick erosion event in the periods of the Caledonian and the Hercynian, the source rocks of the Qiongzhusi Fm had experienced two times of hydrocarbon generation and two times of hydrocarbon generation lag. The overlying super-thick strata deposited during the Indosinian and Yanshan periods made the source rocks of the Qiongzhusi Fm continuously generate oil and gas. The crude oil in the paleo-reservoir of the Longwangmiao Fm had experienced one time of oil-cracking gas process. After the Indo-Chinese epoch, the burial depth of the Triassic strata was deep enough to promote the crude oil in the paleo-reservoir of the Longwangmiao Fm to be cracked gas. This process continued to the late Yanshan period, providing sufficient gas source. The following five conclusions are obtained: The tectonic and depositional evolution of the marine superimposed basins controlled the development of the basic hydrocarbon geology

  15. Structure and tectonic evolution of the Fuegian Andes (southernmost South America) in the framework of the Scotia Arc development

    NASA Astrophysics Data System (ADS)

    Torres Carbonell, Pablo J.; Dimieri, Luis V.; Olivero, Eduardo B.; Bohoyo, Fernando; Galindo-Zaldívar, Jesús

    2014-12-01

    The major structural and tectonic features of the Fuegian Andes provide an outstanding onshore geological framework that aids in the understanding of the tectonic evolution of the Scotia Arc, mainly known from offshore studies. The orogenic history of the Fuegian Andes (Late Cretaceous-Miocene) is thus compared and integrated with the tectonic history of the Scotia Sea. Late Cretaceous-Paleocene structures in the Fuegian Andes suggest a N-directed contraction consistent with an oroclinal bending of the southernmost South America-Antarctic Peninsula continental bridge. This N-directed contraction in the Fuegian Andes continued during the spreading of the West Scotia Ridge, between 40-50 and 10 Ma ago. The onset of major strike-slip faulting in Tierra del Fuego is considered here to be not older than the late Miocene, consistent with the recent history of the North Scotia Ridge; thus forming part of a tectonic regime superposed to the prior contraction in the Fuegian Andes.

  16. Dating tectonic structures on Mercury: new clues to understand the planet's thermal evolution

    NASA Astrophysics Data System (ADS)

    Giacomini, Lorenza; Massironi, Matteo; Marchi, Simone; Fassett, Caleb I.; Di Achille, Gaetano; Cremonese, Gabriele

    2014-05-01

    The global tectonic scenario of Mercury is dominated by contractional features mainly represented by lobate scarps and related to planetary cooling (Watters et al., 1998, Geology, 26, 991-994). Topography of lobate scarps on Mercury: New constraints on the planet's contraction. These structures are the expression of surface-breaking thrust faults and are linear or arcuate features widely distributed on Mercury. Since they display a broad distribution of orientations, lobate scarps are thought to be related to a global contractional strain. The MESSENGER MDIS camera (with a wide-angle and a narrow-angle channels), acquired images of new regions of the Mercury surface that allowed us to detect several new lobate scarps especially where the illumination geometry is more favorable for structural analysis. Among them a 2000-km long thrust system, located between 80° and 100°E of longitude, has been detected. This system consists of several lobate scarps all exhibiting a N-S orientation and a westward vergence. Due to its considerable extension, this feature can give clues to the stress field affecting the surface in a wide sector of the planet. Dating these features and comparing the results with independent age determinations, and structural and stratigraphic evidences might concur to further constrain the age of tectonic deformation on Mercury and possibly increase our knowledge on the thermal evolution of the planet. The dating of the system was performed with different methods. Indeed, traditional stratigraphic study was accompanied by crater counts of geological units overlapping the thrust and the buffered crater counting technique, allowing us to determine an absolute model age determination for the tectonic feature. The employment of these different methods gave consistent results suggesting that thrust activity ended between 3.7-3.8 Ga, with Neukum Production Function (NPF), and 3.5-3.7 Ga, with Model Production Function (MPF), respectively.

  17. Ionian marine terraces of southern Italy: Insights into the Quaternary tectonic evolution of the area

    NASA Astrophysics Data System (ADS)

    Caputo, R.; Bianca, M.; D'Onofrio, R.

    2010-08-01

    New detailed morphotectonic analyses of a well exposed flight of marine terraces along the Ionian coast of southern Italy has been carried out. The area represents a key transect for investigating the middle-late Quaternary evolution of the Southern Apennines chain-foredeep-foreland geodynamic system. A major result of the research is the reconstruction of a virtually complete 3D geometry of the marine surfaces along a coastal sector of ca. 70 km, which (1) documents the occurrence of 18 paleo-shorelines and (2) provides evidence for a strong regional uplift affecting the investigated area. Following a systematic critical review of literature relating to geochronological data, integrated with a morphogenetic model based on the interaction between tectonic uplift and eustatic sea level changes, the different terraces are correlated to as many highstand sea level peaks, dating the highest/oldest terrace to ca. 600 ka (MIS 15). The vertical and horizontal distribution of the terraces show a general convergence of the paleo-shorelines toward NNE, which indicates a decreasing trend in differential uplift in that direction ranging from almost 2 mm/a in the southwestern sector to about 0.2 mm/a in the northeastern sector. Detailed mapping and 3D reconstruction also emphasize the partitioning of the area into three distinct sectors characterized by different tilting rates. This behavior is likely caused by the combined role and activity of three major tectonic structures working at different scales and rates including (1) the reactivation of an out-of-sequence thrust, (2) sliding along the basal detachment of the external Apennines wedge and (3) a lithospheric-scale duplexing (crustal or deeper). As a major conclusion, within the external sector of the Southern Apennines chain and its foredeep, regional shortening and a contractional tectonic regime persisted throughout the whole Quaternary and it is probably still active.

  18. Structural characteristics of Pavonis Mons, Mars, and implications for its volcano-tectonic evolution

    NASA Astrophysics Data System (ADS)

    Gwinner, Klaus; Head, James W.; Wilson, Lionel

    2010-05-01

    Pavonis Mons is the smallest of the three large Tharsis Montes volcanic edifices on Mars. While Viking-based studies have already revealed main structural features of these shields and have provided a framework on their evolution, detailed information on major aspects of their volcano-tectonic structure and evolution is still incomplete. In particular this is the case for the nature of asymmetries that develop along a NE direction, roughly coincident with the crest line of the Tharsis rise, as well as the evolution of the magma reservoir as the shields were built above the ground, and the related consequences for caldera formation and edifice stability. In addition, different morpho-structural features of the Martian shields have been discussed controversially, such as flank "terraces", rillelike channels, and evidence of flank instabilities. We have analyzed recently available high-resolution data, in particular DTMs with up to 50 m grid spacing derived from HRSC data, as well as high-resolution imagery (HRSC, CTX, HIRISE) and regional-scale MOLA DTMs for obtaining new constraints on the volcano-tectonic structure and evolution of Pavonis. We mapped tectonic elements (faults and fractures, wrinkle ridges, collapse pits), main volcanic elements (vent locations, limits of shield, apron and caldera floor units), and elements of flank morphology. Analysis of edifice morphometry is based on slope maps and slope statistics. We were able to identify several major fault systems affecting flanks and base of the edifice. Widespread occurrence of normal faulting from 2-3 km below the summit plateau to the base shows that the middle and lower flanks are characterized by extension. While the summit plateau and uppermost flanks show evidence for compressional deformation, including wrinkle ridges and downslope-convex flank facets interpreted as surface expression of flank thrusts, the system of intersecting flank facets that have been denoted as compressional "terraces" instead

  19. Tectonic evolution of the Anadyr Basin, northeastern Eurasia, and its petroleum resource potential

    NASA Astrophysics Data System (ADS)

    Antipov, M. P.; Bondarenko, G. E.; Bordovskaya, T. O.; Shipilov, E. V.

    2009-09-01

    The published data on the sedimentation conditions, structure, and tectonic evolution of the Anadyr Basin in the Mesozoic and Cenozoic are reviewed. These data are re-examined in the context of modern tectonic concepts concerning the evolution of the northwestern Circum-Pacific Belt. The re-examination allows us not only to specify the regional geology and tectonic history, but also to forecast of the petroleum resource potential of the sedimentary cover based on a new concept. The sedimentary cover formation in the Anadyr Basin is inseparably linked with the regional tectonic evolution. The considered portion of the Chukchi Peninsula developed in the Late Mesozoic at the junction of the ocean-type South Anyui Basin, the Asian continental margin, and convergent zones of various ages extending along the Asia-Pacific interface. Strike-slip faulting and pulses of extension dominated in the Cenozoic largely in connection with oroclinal bending of structural elements pertaining to northeastern Eurasia and northwestern North America against the background of accretion of terranes along the zone of convergence with the Pacific oceanic plates. Three main stages are recognized in the formation of the sedimentary cover in the Anadyr Basin. (1) The lower portion of the cover was formed in the Late Cretaceous-Early Eocene under conditions of alternating settings of passive and active continental margins. The Cenomanian-lower Eocene transitional sedimentary complex is located largely in the southern Anadyr Basin (Main River and Lagoonal troughs). (2) In the middle Eocene and Oligocene, sedimentation proceeded against the background of extension and rifting in the northern part of the paleobasin and compression in its southern part. The compression was caused by northward migration of the foredeep in front of the accretionary Koryak Orogen. The maximum thickness of the Eocene-Oligocene sedimentary complex is noted mainly in the southern part of the basin and in the Central and

  20. Late Paleozoic-Mesozoic tectonic evolution of SW Japan: A review - Reappraisal of the accretionary orogeny and revalidation of the collisional model

    NASA Astrophysics Data System (ADS)

    Charvet, Jacques

    2013-08-01

    This paper makes a review of the interpretations of the tectonic evolution of SW Japan during the last three decades. In the late 1970s, the dominant model was the so-called "Pacific-type orogeny", emphasizing the purported absence of nappes and the contrast with the alpine chains, and interpreting the evolution as due to a steady oceanic subduction since the Paleozoic time. In the 80s, the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models, involving the intermittent underthrusting of buoyant blocks like micro-continents. At the same time, the use of high-resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges, with a reconstructed ocean plate stratigraphy of individual accreted units, especially in the Tanba and Shimanto zones. Also, precise radiometric dating permitted the distinction of metamorphosed units, especially in Sanbagawa and Shimanto belts. As a result of these new data, since the 1990s, the plate tectonic interpretation of the history of the Japanese Islands was revised by Japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction, with an episodic ridge subduction: the so-called "Miyashiro-type orogeny". The review of different data leads to the following conclusions. The structure of SW Japan is made of a pile of sub-horizontal nappes, polydeformed, with a geometry similar to the one encountered in collisional orogens. The geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept (Miyashiro-type orogeny) are inappropriate. A permanent oceanic subduction with the intermittent "collision" (actually subduction) of an active ridge or seamount chain is unable to build such structures, as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate; the underthrusting of a micro-continent or mature arc is likely needed. The

  1. Tectonic and stratigraphic evolution of the Western Alboran Sea Basin in the last 25 Myrs

    NASA Astrophysics Data System (ADS)

    Do Couto, Damien; Gorini, Christian; Jolivet, Laurent; Lebret, Noëmie; Augier, Romain; Gumiaux, Charles; d'Acremont, Elia; Ammar, Abdellah; Jabour, Haddou; Auxietre, Jean-Luc

    2016-05-01

    The Western Alboran Basin (WAB) formation has always been the subject of debate and considered either as a back-arc or a forearc basin. Stratigraphic analyses of high-resolution 2D seismic profiles mostly located offshore Morocco, enabled us to clarify the tectonic and stratigraphic history of the WAB. The thick pre-rift sequence located beneath the Miocene basin is interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP-LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution from the Serravallian to the late Tortonian. Tectonic reconstructions in map view and in cross section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere hence explaining the considerable thickness (10 km) of the mostly undeformed sedimentary infill.

  2. Tectonic and stratigraphic evolution of the Western Alboran Sea basin since the last 25 Myrs

    NASA Astrophysics Data System (ADS)

    Do Couto, Damien; Gorini, Christian; Jolivet, Laurent; Lebret, Noëmie; Augier, Romain; Gumiaux, Charles; D'Acremont, Elia; Ammar, Abdellah; Auxietre, Jean-Luc

    2016-04-01

    The Western Alboran Basin (WAB) formation has always been a matter of debate and was either considered as a backarc or a forearc basin. Based on stratigraphic analysis of high-resolution 2D seismic profiles mostly located offshore Morocco, the tectonic and stratigraphic history of the WAB is clarified. A thick pre-rift sequence is observed beneath the Miocene basin and interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP-LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution, from the Serravallian to the Late Tortonian. Tectonic reconstructions in map view and cross-section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that has migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere explaining the large thickness (10 km) of the mostly undeformed sedimentary infill.

  3. Tectonic evolution of the El Salvador Fault Zone. Insights from analogue experiments.

    NASA Astrophysics Data System (ADS)

    Alonso-Henar, Jorge; Schreurs, Guido; Jesús Martínez-Díaz, José; Álvarez-Gómez, José Antonio

    2014-05-01

    The El Salvador Fault Zone (ESFZ) is an active, c. 150 km long and 20 km wide segmented, dextral strike-slip fault zone within the El Salvador Volcanic Arc striking N90°-100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Our analysis of structural field data, remote sensing images and morphometric indices reveals a trenchward migration of the volcanic arc and furthermore suggests that not all structures within the ESFZ can be explained within the current tectonic context, but require a phase of extension or an extensional component of deformation at some stage in the evolution of the ESFZ. Such an extension and trenchward migration of the volcanic arc could be related to subduction roll-back of the Cocos Plate beneath the Chortis Block in Mio-Pliocene times. Such a possible evolution leads to open questions that we address in our research: Is the ESFZ a neo-formed fault zone, i.e. did it form during one phase of strike-slip or transtensional deformation, or do the structures in the ESFZ reflect a two-phase evolution, i.e. an early phase of extension overprinted by a later phase of strike-slip or transtension? Did subduction roll-back occur beneath El Salvador? We carried out analogue model experiments to test whether or not an early phase of extension is required to form the present-day fault pattern in the ESFZ. Analogue modeling is an effective tool in testing various hypotheses, as it allows the experimenter to control specific parameters and to test their influence on the resulting structures. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures of the ESFZ and can explain the shallow geometry of the fault zone. This extensional phase is followed by a strike-slip dominated regime, which results in inter

  4. Ice-load induced tectonics controlled tunnel valley evolution - instances from the southwestern Baltic Sea

    NASA Astrophysics Data System (ADS)

    Al Hseinat, M.; Hübscher, C.

    2014-08-01

    Advancing ice sheets have a strong impact on the earth's topography. For example, they leave behind an erosional unconformity, bulldozer the underlying strata and form tunnel valleys, primarily by subglacial melt-water erosion and secondarily by direct glacial erosion. The conceptual models of the reactivation of faults within the upper crust, due to the ice sheets' load, are also established. However, this phenomenon is also rather under-explored. Here, we propose a causal link between ice-load induced tectonics, the generation of near-vertical faults in the upper crust above an inherited deep-rooted fault and the evolution of tunnel valleys. The Kossau tunnel valley in the southeastern Bay of Kiel has been surveyed by means of high-resolution multi-channel seismic and echosounder data. It strikes almost south to north and can be mapped over a distance of ca 50 km. It is 1200-8000 m wide with a valley of up to 200 m deep. Quaternary deposits fill the valley and cover the adjacent glaciogenic unconformity. A near-vertical fault system with an apparent dip angle of >80°, which reaches from the top Zechstein upwards into the Quaternary, underlies the valley. The fault partially pierces the seafloor and growth is observed within the uppermost Quaternary strata only. Consequently, the fault evolved in the Late Quaternary. The fault is associated with an anticline that is between 700 and 3000 m wide and about 20-40 m high. The fault-anticline assemblage neither resembles any typical extensional, compressional or strike-slip deformation pattern, nor is it related to salt tectonics. Based on the observed position and deformation pattern of the fault-anticline assemblage, we suggest that these structures formed as a consequence of the differential ice-load induced tectonics above an inherited deep-rooted sub-salt fault related to the Glückstadt Graben. Lateral variations in the ice-load during the ice sheet's advance caused differential subsidence, thus rejuvenating the

  5. Early Paleozoic sedimentary record of the Chinese Altai: Implications for its tectonic evolution

    NASA Astrophysics Data System (ADS)

    Long, Xiaoping; Sun, Min; Yuan, Chao; Xiao, Wenjiao; Cai, Keda

    The Chinese Altai is a typical part of the Central Asian Orogenic Belt (CAOB), but its tectonic evolution is not well understood. Geochemical study of Early Paleozoic metasedimentary rocks was conducted to better constrain their provenance and tectonic environment. These rocks have relatively low CIA values (49 to 79), with ICV values (0.73-1.36) higher than that of post-Archean Australian average shale (PAAS), suggesting that they experienced relatively weak chemical weathering and were mainly derived from an immature source. Compared to PAAS and upper crust, the samples mostly have relatively lower high field strength elements (HFSE) (e.g. Zr, Hf, Nb, Ta) and large ion lithophile element (LILE) contents (e.g. Rb, Sr, Ba, Th, U, Pb). However, their relatively high Rb concentrations (> 40 ppm), low Rb/Sr (0.04-3.24) and Th/U (Th/U = 3-8) ratios are indicative of an acidic-intermediate igneous source that had undergone weak chemical weathering. All of the samples are moderately enriched in LREE (light REE) and show relatively flat Chondrite-normalized HREE (heavy REE) patterns (La N/Yb N = 3.2-12.6) with various negative Eu anomalies (Eu/Eu* = 0.4-0.9). Meta-arenaceous samples have moderate SiO 2 (average 72.9 wt.%), Al 2O 3 (average 11.5 wt.%), Fe 2O 3T + MgO (average 7.16 wt.%) contents and moderate Al 2O 3/SiO 2 (average 0.16), K 2O/Na 2O (average 0.93) ratios, similar to those of graywackes from continental island arcs or active continental margins. However, meta-argillaceous samples have high SiO 2 (average 60.8 wt.%), Al 2O 3 (average 17.2 wt.%), Fe 2O 3T + MgO (average 12.2 wt.%) contents and high K 2O/Na 2O (average 3.45), Al 2O 3/SiO 2 (average 0.28) ratios similar to mudstones from continental arc basins. This kind of tectonic environment is also manifested in tectonic discrimination diagrams including Th-Sc-Zr/10 and La-Th-Sc. These geochemical characteristics suggest that the metasedimentary rocks were deposited in an active continental margin or

  6. Tectonic evolution of Kazakhstan and Tien Shan in Neoproterozoic and Early-Middle Paleozoic

    NASA Astrophysics Data System (ADS)

    Samygin, S. G.; Kheraskova, T. N.; Kurchavov, A. M.

    2015-05-01

    Geological information on Kazakhstan and the Tien Shan obtained up to the present time has been considered and integrated in order to demonstrate the main features of continental massifs, basins with oceanic crust, island arcs, marginal volcanic-plutonic belts, and transform fault zones differing in type and age. We ascertained the character and probable causes of their evolution and transformations resulting in the origination and development of mosaic structural assembly at margin of the Paleoasian ocean that existed from Neoproterozoic. The main stages of the geodynamic history of Paleozoides in Kazakhstan and Tien Shan are characterized, and a model of the probable course of regional tectonic events has been proposed. This model is illustrated by published paleomagnetic data and a series of paleotectonic reconstructions for time intervals 950-900, 850-800, 750-700, 650-630, 570-550, 530-515, 500-470, 460-440, and 390-380 Ma.

  7. Cenozoic tectonic evolution and petroleum exploration in Perl River Mouth basin, South China Sea

    SciTech Connect

    Chi Yukun; Xu Shice )

    1990-06-01

    The Pearl River Mouth basin is a large Cenozoic continental margin basin that is rich in hydrocarbon potential. Fluvial-lake sequences were deposited before Oligocene, but all were covered by Miocene marine clastic and carbonate rocks. Both paleo-Pearl River delta system and reef/bank carbonate system were widely developed. At the early stage of the evolution, two subsidence belts and one uplift between them distributed in NE regional direction; grabens occurred in the north belt and depressions in the south belt. Tectonic movement was stronger in the east than the west. The main production zones have been drilled both in Miocene sandstone and carbonate rocks. As the exploration activities are developing, the basin will be one of the most significant China offshore oil production areas.

  8. Neogene marine isotopic evolution and the erosion of Lesser Himalayan strata: Implications for Cenozoic tectonic history

    NASA Astrophysics Data System (ADS)

    Myrow, Paul M.; Hughes, Nigel C.; Derry, Louis A.; Ryan McKenzie, N.; Jiang, Ganqing; Webb, A. Alexander G.; Banerjee, Dhiraj M.; Paulsen, Timothy S.; Singh, Birendra P.

    2015-05-01

    An extensive, northward deepening blanket of Neoproterozoic and Cambrian sedimentary rocks once extended from the Himalayan margin far onto the Indian craton. Cambrian deposits of this "upper Lesser Himalayan" succession, which include deposits of the "outer" Lesser Himalaya tectonic unit, are enriched in radiogenic 187Os. They make up part of a proximal marine facies belt that extends onto the craton and along strike from India to Pakistan. By contrast, age-equivalent facies in the Tethyan Himalaya are more distal in nature. Neoproterozoic to Cambrian strata of the upper Lesser Himalayan succession are now missing in much of the Lesser Himalaya, with their erosion exposing older Precambrian Lesser Himalayan strata. We suggest that exhumation and weathering of the upper Lesser Himalaya and related strata caused dramatic changes in the 187Os/188Os and 87Sr/86Sr Neogene record of seawater starting at ∼ 16 Ma. First-order estimates for the volume of upper Himalayan strata, as well as the volume of all LH rock eroded since this time, and geochemical box modeling, support this idea. Exhumation at 16 Ma is a fundamental event in the evolution of the Himalayan orogeny and the geochemical evolution of the oceans, and will be a critical part of the construction of future models of Himalayan thrust belt evolution.

  9. Origin and Evolution of Limestone Caves of Chhattisgarh and Orissa, India: Role of Geomorphic, Tectonic and Hydrological Processes

    NASA Astrophysics Data System (ADS)

    Gautam, P. K.; Allu, N. C.; Ramesh, R.; Yadava, M. G.; Panigrahi, C. P.

    2014-12-01

    Carbonate rocks undergo karstic process and karst morphology is a key to understand the nature and genesis of caves. The primary energy source for the formation of karst landforms is hydrological cycle. Geomorphic features along with hydrological characteristics provide important information not only on karst formation but also climate and environmental conditions. In this paper, we present the tectonic and geomorphic features that played a role in evolution of caves located in Chhattisgarh and Orissa States of India. The geomorphic and tectonic aspects of Kotumsar, Kailash, and Gupteshwar caves are discussed in relation to the origin and evolution of these caves. Caves are located near the water falls. The area is folded and faulted along the Eastern Ghat Mobile Belt (EGMB) due to tectonic reactivation. Shaly-limestone beds exhibit vertical dipping near Gupteshwar cave, and steeply inclined near Kotumsar and Kailash caves. Indrāvati and Sabari/Kolab tributaries of the Godavari River drain the area. The landscape evolution and the origin of caves in the region is a multistage process, where the lithology, orogeny, fluvial action, and monsoon are the main agents, which is similar to the four state model (Ford and Ewers, 1978). The river basin evolution and regional tectonism also caused the initiation of karstification in the region. The evolution of caves is believed to have taken place in Pre-Pliocene under more humid conditions that coincided with the initiation of monsoon in India. Further, during the Quaternary wet-dry/cold-warm phases altered physical and chemical weathering of limestone rocks. Contrasting relief features of Bastar plateau have also helped the extensive cave formation in the region. The dissolution along weak planes initiated the openings of caves, further enlarged by geomorphic agents. Both monsoon and tectonics have caused fluctuations in water levels along river courses, which acted as active agents in evolution of caves.

  10. Southern African perspectives on the long-term morpho-tectonic evolution of cratonic interiors

    NASA Astrophysics Data System (ADS)

    Kounov, Alexandre; Viola, Giulio; Dunkl, István; Frimmel, Hartwig E.

    2013-08-01

    We propose a refined conceptual model for the Paleo- and Mesozoic morpho-tectonic evolution of the southern African cratonic interior. Constraints are derived from new zircon and apatite fission-track and (U-Th-[Sm])/He dates (ZFT, AFT, ZHe and AHe) of rocks from the Augrabies Falls and Fish River Canyon regions in South Africa and southern Namibia, respectively. The combined ZFT and ZHe thermochronological results suggest a smooth and simple tectonic evolution, wherein the study area cooled monotonically as one coherent block from the Early Silurian to the Mid Triassic in response to very low denudation rates of less than 5 m/myr. Some of the new zircon ages may indicate a discrete and short-lived period of enhanced cooling interrupting this monotonic cooling during the Mid Devonian-Early Carboniferous. We tentatively correlate this episode to the events that caused the regional hiatus that separates the Cape Supergroup from the overlying Karoo Supergroup. Apatite fission-track and (U-Th-[Sm])/He data joint modeling reveals a period of accelerated regional cooling through 120 to 40 °C between 100 and 65 Ma ago. We interpret the latter as most probably due to regional uplift in combination with high river gradients and enhanced erosion rates in the Orange and Fish River basins, which, during the Cretaceous, were probably part of the greater Kalahari River catchment area. Based on the apatite results, a denudation rate of ca. 25 m/myr was calculated for the Late Cretaceous. At that time the area was probably characterized by an elevated average altitude and low relief, as indicated by the AFT and AHe age patterns.

  11. Tectonic, magmatic, and metallogenic evolution of the Late Cretaceous arc in the Carpathian-Balkan orogen

    NASA Astrophysics Data System (ADS)

    Gallhofer, Daniela; Quadt, Albrecht von; Peytcheva, Irena; Schmid, Stefan M.; Heinrich, Christoph A.

    2015-09-01

    The Apuseni-Banat-Timok-Srednogorie Late Cretaceous magmatic arc in the Carpathian-Balkan orogen formed on the European margin during closure of the Neotethys Ocean. It was subsequently deformed into a complex orocline by continental collisions. The Cu-Au mineralized arc consists of geologically distinct segments: the Apuseni, Banat, Timok, Panagyurishte, and Eastern Srednogorie segments. New U-Pb zircon ages and geochemical whole rock data for the Banat and Apuseni segments are combined with previously published data to reconstruct the original arc geometry and better constrain its tectonic evolution. Trace element and isotopic signatures of the arc magmas indicate a subduction-enriched source in all segments and variable contamination by continental crust. The magmatic arc was active for 25 Myr (~92-67 Ma). Across-arc age trends of progressively younger ages toward the inferred paleo-trench indicate gradual steepening of the subducting slab away from the upper plate European margin. This leads to asthenospheric corner flow in the overriding plate, which is recorded by decreasing 87Sr/86Sr (0.70577 to 0.70373) and increasing 143Nd/144Nd (0.51234 to 0.51264) ratios over time in some segments. The close spatial relationship between arc magmatism, large-scale shear zones, and related strike-slip sedimentary basins in the Timok and Pangyurishte segments indicates mild transtension in these central segments of the restored arc. In contrast, the Eastern Srednogorie segment underwent strong orthogonal intraarc extension. Segmental distribution of tectonic stress may account for the concentration of rich porphyry Cu deposits in the transtensional segments, where lower crustal magma storage and fractionation favored the evolution of volatile-rich magmas.

  12. Hydrological modelling of alpine headwaters using centurial glacier evolution, snow and long-term discharge dynamics

    NASA Astrophysics Data System (ADS)

    Kohn, Irene; Vis, Marc; Freudiger, Daphné; Seibert, Jan; Weiler, Markus; Stahl, Kerstin

    2016-04-01

    The response of alpine streamflows to long-term climate variations is highly relevant for the supply of water to adjacent lowlands. A key challenge in modelling high-elevation catchments is the complexity and spatial variability of processes, whereas data availability is rather often poor, restricting options for model calibration and validation. Glaciers represent a long-term storage component that changes over long time-scales and thus introduces additional calibration parameters into the modelling challenge. The presented study aimed to model daily streamflow as well as the contributions of ice and snow melt for all 49 of the River Rhine's glaciated headwater catchments over the long time-period from 1901 to 2006. To constrain the models we used multiple data sources and developed an adapted modelling framework based on an extended version of the HBV model that also includes a time-variable glacier change model and a conceptual representation of snow redistribution. In this study constraints were applied in several ways. A water balance approach was applied to correct precipitation input in order to avoid calibration of precipitation; glacier area change from maps and satellite products and information on snow depth and snow covered area were used for the calibration of each catchment model; and finally, specific seasonal and dynamic aspects of discharge were used for calibration. Additional data like glacier mass balances were used to evaluate the model in selected catchments. The modelling experiment showed that the long-term development of the coupled glacier and streamflow change was particularly important to constrain the model through an objective function incorporating three benchmarks of glacier retreat during the 20th Century. Modelling using only streamflow as calibration criteria had resulted in disproportionate under and over estimation of glacier retreat, even though the simulated and observed streamflow agreed well. Also, even short discharge time

  13. Plio-Quaternary tectonic evolution of the western Catanzaro Trough (Calabria, South Italy)

    NASA Astrophysics Data System (ADS)

    Brutto, Fabrizio; Muto, Francesco; Loreto, Maria Filomena; Tripodi, Vincenzo; Critelli, Salvatore

    2015-04-01

    controlled the post-Tortonian evolution of Calabrian Arc. In the frame of the basin evolution, the right-lateral faults, which are subordinate on respect to left- lateral faults, show a N-S and NW-SE oriented fault systems. The WNW-ESE oriented faults can be considered responsible for opening of a NW-SE palaeo-strait that connected the Tyrrhenian area to the Ionian Sea during multiphase tectonics until Early Pleistocene. While the NE-SW and N-S fault systems confine and control the western portion of Catanzaro Basin, also named Catanzaro Trough Sub-basin, arranged as a Graben System with conjugate fault located in the offshore of S. Eufemia Gulf. Keywords: fault planes, slickensides, rotaxes, Calabria arc

  14. Studies of the proterozoic tectonic evolution of the southwestern United States

    NASA Astrophysics Data System (ADS)

    Seeley, John Martin

    proximal portions, while storm processes dominated on distal portions. Chapter 5 of this manuscript presents a hypothesis for the Proterozoic tectonic evolution of southwestern Laurentia during the Mesoproterozoic and Neoproterozoic. Recent tectonic models of Grenville-age rocks along this margin document arc-continent and continent-continent collision ca. 1150--1120 Ma. Current interpretations, however, do not take into account the prior, and coeval tectonic history of Proterozoic rocks of southwestern regions of Laurentia that currently comprise the southwestern United States.

  15. Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

    NASA Astrophysics Data System (ADS)

    Becker, T. W.; Conrad, C. P.; Buffett, B.; Muller, D.; Loyd, S.; Lithgow-Bertelloni, C.; Corsetti, F.

    2008-12-01

    Variations in the rates of seafloor generation and recycling have potentially far-reaching consequences for sea level, ocean chemistry and climate. A parameterized framework to describe such variations could guide the study of non-uniformitarian plate tectonic activity, but there is little agreement on the appropriate mechanical description of the surface boundary layer. A strong constraint on the statistics of oceanic convection systems comes from the preserved seafloor age distribution, and additional inferences are possible when paleo-seafloor is modeled based on plate motion reconstructions. Based on previously reconstructed seafloor ages, we recently inferred that oceanic heat flow was larger by ~15% at 60~Ma than today. This signal is mainly caused by the smaller plates that existed previously in the Pacific basin with relatively larger ridge-proximal area of young seafloor. The associated decrease in heat flow is larger than any plausible decrease due to cooling, and therefore hint at cyclic behavior in plate tectonics. We also consider area-per-age statistics for the present-day and back to 140~Ma from new paleo-age reconstructions. Using a simplified seafloor age evolution model we explore which physical parameterizations for the average behavior of the oceanic lithosphere are compatible with broad trends in the data. In particular, we show that a subduction probability based on lithospheric buoyancy ("sqrt(age)") leads to results that are comparable to, or better than, that of the probability distribution that is required to obtain the "triangular" age distribution with age-independent destruction of ocean floor. The current, near triangular distribution of ages and the relative lull in heat flow are likely only snapshots of a transient state during the Wilson cycle. Current seafloor ages still contain hints of a ≤sssim 60~Myr period, cyclic variation of seafloor production, and using paleo-ages for 140~Ma, we find a ~ 400~Myr best-fitting variation

  16. Metamorphic and tectonic evolution of Ceuta peninsula (Internal Rif): new interpretation in the framework of arc and back arc evolution

    NASA Astrophysics Data System (ADS)

    Homonnay, Emmanuelle; Lardeaux, Jean-Marc; Corsini, Michel; Cenki-Tok, Bénédicte; Bosch, Delphine; Munch, Philippe; Romagny, Adrien; Ouazzani-Touhami, Mohamed

    2016-04-01

    In the last twenty years, various geophysical investigations have established that the Western Mediterranean opened in a subduction context as a back arc domain. In the Alboran basin the dip of the subduction plane is eastwards or southeastwards depending of considered models. If the geological records of back-arc opening are well-known, the arc-related tectonic and petrologic evolutions are still poorly documented. In order to decipher these markers, we focalised structural, petrological and thermo-chronological studies on the Ceuta peninsula located in the Rif belt, on the western part of the Gibraltar arc to the North of Morocco. The present-day tectonic pile is constituted by: (1) the upper Ceuta unit, composed of High Pressure and High Temperature metapelites retromorphosed under Amphibolite-facies condition, with Ultra-High Pressure relicts, and pyrigarnite and spinel bearing peridotites boudins at its base, (2) the lower Monte Hacho unit, with orthogneisses metamorphosed under Amphibolite-facies conditions. Structural analysis indicates a polyphase tectonic evolution: (1) an earlier deformation phase only observed in the UHP metapelites and characterized by a steep S1 foliation plane, (2) a main deformation phase associated to a pervasive gently dipping S2 foliation plane bearing a L2 stretching lineation and synschistose folds whose axes are parallel to L2 and (3) a late deformation phase which developed S3 foliation plane and L3 stretching lineation coeval with development of narrow normal ductile shear zones. A zone of increasing deformation, several dozen meters wide, is identified as a major ductile shear zone involving the peridotitic lenses at the base of the metapelites of the Ceuta unit and overlaying this upper unit on top of the orthogneisses of the Monte Hacho lower unit. The attitude of mylonitic foliation and stretching and mineral lineations as well as the numerous shear sense indicators observed in the shear zone are consistent with a

  17. Alpine endemic spiders shed light on the origin and evolution of subterranean species.

    PubMed

    Mammola, Stefano; Isaia, Marco; Arnedo, Miquel A

    2015-01-01

    We designed a comparative study to unravel the phylogeography of two Alpine endemic spiders characterized by a different degree of adaptation to subterranean life: Troglohyphantes vignai (Araneae, Linyphiidae) and Pimoa rupicola (Araneae, Pimoidae), the latter showing minor adaptation to hypogean life. We sampled populations of the model species in caves and other subterranean habitats across their known geographical range in the Western Alps. By combining phylogeographic inferences and Ecological Niche Modeling techniques, we inferred the biogeographic scenario that led to the present day population structure of the two species. According to our divergent time estimates and relative uncertainties, the isolation of T. vignai and P. rupicola from their northern sister groups was tracked back to Middle-Late Miocene. Furthermore, the fingerprint left by Pleistocene glaciations on the population structure revealed by the genetic data, led to the hypothesis that a progressive adaptation to subterranean habitats occurred in T. vignai, followed by strong population isolation. On the other hand, P. rupicola underwent a remarkable genetic bottleneck during the Pleistocene glaciations, that shaped its present population structure. It seems likely that such shallow population structure is both the result of the minor degree of specialization to hypogean life and the higher dispersal ability characterizing this species. The simultaneous study of overlapping spider species showing different levels of adaptation to hypogean life, disclosed a new way to clarify patterns of biological diversification and to understand the effects of past climatic shift on the subterranean biodiversity. PMID:26734503

  18. Diagenetic Evolution and Reservoir Quality of Sandstones in the North Alpine Foreland Basin: A Microscale Approach.

    PubMed

    Gross, Doris; Grundtner, Marie-Louise; Misch, David; Riedl, Martin; Sachsenhofer, Reinhard F; Scheucher, Lorenz

    2015-10-01

    Siliciclastic reservoir rocks of the North Alpine Foreland Basin were studied focusing on investigations of pore fillings. Conventional oil and gas production requires certain thresholds of porosity and permeability. These parameters are controlled by the size and shape of grains and diagenetic processes like compaction, dissolution, and precipitation of mineral phases. In an attempt to estimate the impact of these factors, conventional microscopy, high resolution scanning electron microscopy, and wavelength dispersive element mapping were applied. Rock types were established accordingly, considering Poro/Perm data. Reservoir properties in shallow marine Cenomanian sandstones are mainly controlled by the degree of diagenetic calcite precipitation, Turonian rocks are characterized by reduced permeability, even for weakly cemented layers, due to higher matrix content as a result of lower depositional energy. Eocene subarkoses tend to be coarse-grained with minor matrix content as a result of their fluvio-deltaic and coastal deposition. Reservoir quality is therefore controlled by diagenetic clay and minor calcite cementation.Although Eocene rocks are often matrix free, occasionally a clay mineral matrix may be present and influence cementation of pores during early diagenesis. Oligo-/Miocene deep marine rocks exhibit excellent quality in cases when early cement is dissolved and not replaced by secondary calcite, mainly bound to the gas-water contact within hydrocarbon reservoirs. PMID:26365327

  19. Alpine endemic spiders shed light on the origin and evolution of subterranean species

    PubMed Central

    Mammola, Stefano; Arnedo, Miquel A.

    2015-01-01

    We designed a comparative study to unravel the phylogeography of two Alpine endemic spiders characterized by a different degree of adaptation to subterranean life: Troglohyphantes vignai (Araneae, Linyphiidae) and Pimoa rupicola (Araneae, Pimoidae), the latter showing minor adaptation to hypogean life. We sampled populations of the model species in caves and other subterranean habitats across their known geographical range in the Western Alps. By combining phylogeographic inferences and Ecological Niche Modeling techniques, we inferred the biogeographic scenario that led to the present day population structure of the two species. According to our divergent time estimates and relative uncertainties, the isolation of T. vignai and P. rupicola from their northern sister groups was tracked back to Middle–Late Miocene. Furthermore, the fingerprint left by Pleistocene glaciations on the population structure revealed by the genetic data, led to the hypothesis that a progressive adaptation to subterranean habitats occurred in T. vignai, followed by strong population isolation. On the other hand, P. rupicola underwent a remarkable genetic bottleneck during the Pleistocene glaciations, that shaped its present population structure. It seems likely that such shallow population structure is both the result of the minor degree of specialization to hypogean life and the higher dispersal ability characterizing this species. The simultaneous study of overlapping spider species showing different levels of adaptation to hypogean life, disclosed a new way to clarify patterns of biological diversification and to understand the effects of past climatic shift on the subterranean biodiversity. PMID:26734503

  20. Tectonic Evolution of the Cretaceous Sava-Klepa Massif, Former Yugoslav Republic of Macedonia, based on field observations and microstructural analysis - Towards a new geodynamic Model

    NASA Astrophysics Data System (ADS)

    Altmeyer, Tobias; Peternell, Mark; Prelević, Dejan; Köpping, Jonas

    2016-04-01

    the deformation history, i.e. the switch from compressive to extensional, rift forming, regime. REFERENCES Ferrill, D.A. et al. (2004). Calcite twin morphology: a low-temperature deformation geothermometer. Journal of Structural Geology 26: 1521-1529. Peternell, M. et al. (2010). Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques. Journal of Structural Geology 32: 803-817. Robertson, A.H.F. & Karamata, S. (1994). The role of subduction-accretion processes in the tectonic evolution of the Mesozoic Tethys in Serbia. Tectonophysics, 234:73-94. Schmid, S.M. et al. (2008). The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units. Swiss Journal of Geoscience, 101:139-183.

  1. 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.

  2. Interactions between recent tectonic activity and the evolution of mountain relief of the Inner Cottians Alps (Western Alps): preliminary morphotectonic map.

    NASA Astrophysics Data System (ADS)

    Bacenetti, Marco; Morelli, Michele; Cadoppi, Paola; Giardino, Marco; Perotti, Luigi; Perrone, Gianluigi

    2014-05-01

    Possible interactions between recent tectonic activity and the evolution of mountain relief have been investigated at the regional (1:50,000) and local (1:5,000) scale in the Germanasca Valley (Cottian Alps, NW-Italy) through an integrated, multidisciplinary approach combining Structural analysis, Quaternary Geology, Geomorphology and Geomatics. The inner edge of the Cottians Alps and the adjacent Po Plain are among the most densely populated portions of the Piemonte Region (NW-Italy). This area corresponds to the junction between the Alpine and Apennine chains and it is affected by a diffuse low- to moderate- seismicity (Ml<5) and hypocenters at a shallow crustal level (< 20 Km). Available apatite fission track data indicate that this sector reached shallow crustal levels, where brittle deformation mechanisms prevail since Late Oligocene times. Historical earthquakes (e.g. Prarostino's earthquakes, 1808 Ml=5.5; Cumiana's earthquakes, 1980 Ml=4.8) caused both material and social damage in the area. Since faults activity is often associated with characteristic geomorphological features, linear valleys, ridgelines, slope-breaks, steep slopes of uniform aspect, regional anisotropy and tilt of terrain, have been detected in the area. Analysis of digital elevation models, by means of numerical geomorphology, provides a tool to recognize linear features and characterizing the tectonics of an area in a quantitative way. Geomorphology and morphotectonic analyses have been performed using digital orthophotos (AGEA Orthophoto 2009), aerial stereo couples and DEMs (LiDAR5x5 meters, Regione Piemonte 2009). The morphotectonic lineament analysis was conducted using TerraExplorer® Software Systems, Inc. For the field mapping activities, it was used an application called "SRG2" (Support to Geological / Geomorphological Surveys), an extension for ArcPad (ESRI mobile GIS). Into ArcPad, the SRG2 application adds a toolbar made up of several functions for a useful mapping and

  3. Tectonic evolution of the eastern margin of the Thaumasia Plateau (Mars) as inferred from detailed structural mapping and analysis

    NASA Astrophysics Data System (ADS)

    Borraccini, F.; Di Achille, G.; Ori, G. G.; Wezel, F. C.

    2007-05-01

    The eastern margin of the Thaumasia Plateau (EMTP) is characterized by a diversity of tectonic features, which recorded its complex, and still controversial, tectonic history. A detailed structural survey and analyses have been carried out in order to assess the kinematics and relative age of the main deformational events. Combining results from statistics of lineament orientations and density of fault length for each geologic unit and taking into account crosscutting relationships among tectonic structures, three main deformational events have been recognized. The early stage of the tectonic evolution of EMTP is recorded by Noachian units at the southern edge of Melas Dorsa and is represented by N-S oriented grabens sutured by Early Hesperian formations. Starting from Late Noachian, the extensional stress field became NE-SW oriented and resulted in the formation of NW-SE striking sets of grabens. At the boundary between Noachian and Hesperian, the most important change in tectonic regime occurred. The Hesperian tectonics are characterized by an E-W shortening possibly related to an eastward motion of the Thaumasia Plateau. This tectonic phase likely produced a N-S-oriented wrinkle ridges as well as regional folds and thrust faults. E-W-oriented preexisting tectonic lineaments could have been reactivated forming regional transfer zones. In this scenario, Coprates Rise, Melas Dorsa, and Thaumasia Ridge could be interpreted as mountain belts resulting from buckling and thrust faulting of the eastern and southern margins of the Thaumasia plateau. The proto-Valles Marineris could have experienced a left-lateral component of displacement and played a role of a transfer shear zone.

  4. Deep Structure and Evolution of the Cyprus Arc, With Implications for the Tectonic Evolution of Anatolia

    NASA Astrophysics Data System (ADS)

    Wortel, M. J.; Spakman, W.; Govers, R.; Ben-Avraham, Z.

    2006-12-01

    Eratosthenes Seamoumt may explain the moderate development of the Cyprus (back-)arc relative to the Hellenic arc. The deep mantle anomalies below Anatolia are very similar to those below the Aegean region, pointing to a largely common earlier (pre-Oligo-Miocene) convergence history. Implications of the lateral and temporal variations in plate boundary configuration for the tectonics of Anatolia are addressed.

  5. Drainage response to active tectonics and evolution of tectonic geomorphology across the Himalayan Frontal Thrust, Kumaun Himalaya

    NASA Astrophysics Data System (ADS)

    Luirei, Khayingshing; Bhakuni, Surendra S.; Kothyari, Girish Ch.

    2015-06-01

    We present the results of integrated studies of geomorphic indices of drainage networks and landforms developed across the mountain front along the Himalayan Frontal Thrust (HFT) between the Dabka and Baur rivers, Kumaun Himalaya. The HFT is a morphogenic structure in nature, creating a 100-m-high E-W trending escarpment that extends ~ 21 km. Geomorphological evidence indicates ~ 10.5 km westward migration of the Dabka River and ~ 5.2 km eastward migration of the Baur River. These migrations are a result of uplift of the hanging wall along the HFT. The HFT is offset by a transverse fault, which suggests that the latter postdates the reactivation of the HFT between 500 and 100 ka. Presence of different levels of strath terraces along the mountain front suggests the active nature of the HFT. To assess the relative tectonic activity, morphometric indices such as stream-gradient (SL) index, mountain front sinuosity (Smf) index, and ratio of valley floor width to valley height (Vf) have been analyzed. Results of the former two are consistent with the tectonic landforms developed in thrust zones. Paleochannels of the Dabka and Baur rivers are characterized by high Vf values while other valleys show low Vf values. Quaternary alluvial sediments have been deformed along the Pawalgarth Thrust, a splay of the HFT. Deformation has resulted in the formation of the Pawalgarh Anticline, a thrust-related asymmetric fold.

  6. Genome evolution in alpine oat-like grasses through homoploid hybridization and polyploidy

    PubMed Central

    Winterfeld, Grit; Wölk, Alexandra; Röser, Martin

    2016-01-01

    Hybridization and polyploidization can radically impact genome organization from sequence level to chromosome structure. As a result, often in response to environmental change and species isolation, the development of novel traits can arise and will tend to result in the formation of homoploid or polyploid hybrid species. In this study we focus on evidence of hybridization and polyploidization by ascertaining the species parentage of the endemic alpine Helictotrichon parlatorei group. This group comprises five taxa; the diploids H. parlatorei, Helictotrichon setaceum subsp. setaceum and subsp. petzense, their putative hybrid Helictotrichon ×krischae and the hexaploid Helictotrichon sempervirens. For molecular analyses, cloned nuclear Topoisomerase VI genes of H. sempervirens and H. ×krischae were sequenced and compared with sequences of the diploids to estimate the evolutionary history in this group. In addition, detailed chromosome studies were carried out including fluorescence in situ hybridization (FISH) with 5S and 45S ribosomal and satellite DNA probes, and fluorochrome staining with chromomycin and DAPI. Two distinct types of Topoisomerase VI sequences were identified. One of them (SET) occurs in both subspecies of H. setaceum, the other (PAR) in H. parlatorei. Both types were found in H. ×krischae and H. sempervirens. Karyotypes of H. parlatorei and H. setaceum could be distinguished by chromosomes with a clearly differentiated banding pattern of ribosomal DNAs. Both patterns occurred in the hybrid H. ×krischae. Hexaploid H. sempervirens shares karyotype features with diploid H. parlatorei, but lacks the expected chromosome characteristics of H. setaceum, possibly an example of beginning diploidization after polyploidization. The geographic origin of the putative parental species and their hybrids and the possible biogeographical spread through the Alps are discussed. PMID:27255513

  7. Genome evolution in alpine oat-like grasses through homoploid hybridization and polyploidy.

    PubMed

    Winterfeld, Grit; Wölk, Alexandra; Röser, Martin

    2016-01-01

    Hybridization and polyploidization can radically impact genome organization from sequence level to chromosome structure. As a result, often in response to environmental change and species isolation, the development of novel traits can arise and will tend to result in the formation of homoploid or polyploid hybrid species. In this study we focus on evidence of hybridization and polyploidization by ascertaining the species parentage of the endemic alpine Helictotrichon parlatorei group. This group comprises five taxa; the diploids H. parlatorei, Helictotrichon setaceum subsp. setaceum and subsp. petzense, their putative hybrid Helictotrichon ×krischae and the hexaploid Helictotrichon sempervirens. For molecular analyses, cloned nuclear Topoisomerase VI genes of H. sempervirens and H. ×krischae were sequenced and compared with sequences of the diploids to estimate the evolutionary history in this group. In addition, detailed chromosome studies were carried out including fluorescence in situ hybridization (FISH) with 5S and 45S ribosomal and satellite DNA probes, and fluorochrome staining with chromomycin and DAPI. Two distinct types of Topoisomerase VI sequences were identified. One of them (SET) occurs in both subspecies of H. setaceum, the other (PAR) in H. parlatorei. Both types were found in H. ×krischae and H. sempervirens Karyotypes of H. parlatorei and H. setaceum could be distinguished by chromosomes with a clearly differentiated banding pattern of ribosomal DNAs. Both patterns occurred in the hybrid H. ×krischae Hexaploid H. sempervirens shares karyotype features with diploid H. parlatorei, but lacks the expected chromosome characteristics of H. setaceum, possibly an example of beginning diploidization after polyploidization. The geographic origin of the putative parental species and their hybrids and the possible biogeographical spread through the Alps are discussed. PMID:27255513

  8. Tectonic evolution and hydrocarbon potential of the southern Moesian platform and Balkan-Forebalken regions of northern Bulgaria

    SciTech Connect

    Emery, M. ); Georgiev, G. )

    1993-09-01

    The major tectonic elements of northern Bulgaria are the east-west-trending Balkan-Forebalkan fold belt and the Moesian platform. Moderate hydrocarbon exploration potential exists in trapping geometries generated during the tectonic evolution of the region coupled with reservoir/seal pairs and source rocks within Mesozoic strata. The tectonic evolution of the region includes Early Triassic to Early Jurassic intracratonic rifting followed by multiphase compression that contracted the rift basin and produced a north vergent fold and thrust belt along the southern margin of the stable Moesian platform. Compression began during the Early Cretaceous, continued during the Paleocene, and concluded during the middle Eocene. Trap types generated during the tectonic evolution include normal fault-bounded rotated blocks in the autochthonous section and elongate, asymmetric anticlines in the allochthonous section. Triassic to Upper Jurassic Marine facies were deposited in an east-west-trending rift. Sediments deposited in a shallow foredeep, which evolved during Lower cretaceous compression, overlay the rift sequence. The Early Mesozoic rift sequence provides the depositional settings for Middle Triassic and lower Middle Jurassic source rock shales and sandstone/carbonate reservoirs ranging from Middle Triassic to Lower Cretaceous. Carbonate reservoirs generally are porous dolomites with intercrystalline, moldic, and vugular pore types interbedded with nonporous limestones. Clastic reservoirs are quartz-rich sandstones with pore types that are reduced intergranular, dissolution, and microporosity. These heterogeneous reservoir targets exhibit poor to good reservoir characteristics and are overlain with sealing lithologies of variable thicknesses.

  9. Mesozoic Tertiary tectonic evolution of Albania in its regional Eastern Mediterranean context

    NASA Astrophysics Data System (ADS)

    Robertson, Alastair; Shallo, Minella

    2000-01-01

    Research carried out since the opening of Albania to the 'western' geological community in the 1990s allows the geology and tectonics of this small Balkan country to be integrated into an overall interpretation of Neotethys in the Eastern Mediterranean region, specifically Greece and the former Yugoslavia region. Albanian geology is most famous for the occurrence of contrasting ophiolites of Jurassic age. The country is sub-divided into three main geotectonic units. Those in the west (i.e. Sazani, Ionian, Kruja, Krasta-Cukali and the Albanian Alps) relate to the western margin of Apulia, effectively part of North Africa from Early Mesozoic time onwards. In the east is the Korabi zone, interpreted as a microcontinent located further northeast within Neotethys. Between the two is the Mirdita zone, dominated by two contrasting Jurassic ophiolites: the 'Western-type' ophiolite and the 'Eastern-type' ophiolite. Taking account of evidence from Greece and former Yugoslavia, the following tectonic evolution is proposed. From Early Mesozoic time onwards, Neotethys in Albania existed as a northward continuation of the Pindos oceanic basin in Greece (Pindos-Mirdita ocean). A Korabi microcontinent was rifted off Apulia in the Early-Mid Triassic, followed by passive margin subsidence until late Middle Jurassic time. A rifted, slow-spreading, MOR-type ophiolite formed within the western Pindos-Mirdita oceanic basin in Late Triassic?-early Late Jurassic time (using present co-ordinates). The Shkoder-Peje (Scutari-Peć) lineament in the north of Albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire Mesozoic-Early Tertiary rift/drift/emplacement history of the Pindos-Mirdita ocean. Taking account of evidence from the Greek and former Yugoslavia ophiolites, the easterly Albanian ophiolites formed within the Pindos-Mirdita ocean above a westward-dipping intra-oceanic subduction zone in the early Late Jurassic

  10. Origin, mobility, and temporal evolution of arsenic from a low-contamination catchment in Alpine crystalline rocks.

    PubMed

    Pili, Eric; Tisserand, Delphine; Bureau, Sarah

    2013-11-15

    The reduction to 10 μg/l of the limit for arsenic in drinking water led many resource managers to deal with expensive treatments. In the very common case of arsenic levels close to the recommended maximum concentration, knowing the origin and temporal evolution of As has become of great importance. Here we present a case study from an alpine basin. Arsenic speciation, isotopic compositions of pyrite, sulfate and water, and concentrations of major and trace elements demonstrate a geogenic source for arsenic linked to the dissolution of pyrite. We provide new tools to further study As at low concentrations where many processes may be masked. The observed negative correlation between δ(34)SSO4 and [As] is interpreted as a Rayleigh-type sulfur-isotope fractionation during increasing pyrite dissolution. The observed positive correlation between δ(18)OSO4 and As(V)/As(III) could help to retrieve initial redox conditions. A 3-year long monitoring at high-resolution demonstrated that drought conditions enhance pyrite dissolution whose degradation products are scavenged by recharge water. An increase in As in groundwater may result from droughts due to enhanced oxygen entry in the unsaturated zone. The 2003 European heatwave had a major effect. PMID:22819960

  11. Melting and Tectonics from Coupled Orbital and Thermal Evolution of the Pluto-Charon System

    NASA Astrophysics Data System (ADS)

    Collins, G. C.; Barr, A. C.

    2015-12-01

    As New Horizons data is returned, we should consider the possibility that Pluto and Charon went through an intense period of activity following the Charon-forming impact. Our prior work (Barr and Collins 2015) shows that if the deep layer of Pluto's ice shell is initially warmer than ~200 K after the impact, energy dissipation within Pluto can lead to melting and rapid thinning of the ice shell and tidal stresses can drive tectonics on both bodies. Here, we build upon our prior work to simulate the coupled thermal and orbital evolution of the Pluto/Charon system after the Charon-forming impact, taking into account the growth/freezing of an ocean, the onset/cessation of solid-state ice shell convection, and how the changing interior state of Pluto changes the magnitude of tidal deformation and dissipation. We track the heat flow in Pluto as a function of time for a variety of starting conditions after Charon is formed. We find that if Pluto has even a small ocean after Charon forms, the system can readily evolve to its present dual synchronous state. A feedback mechanism exists in which tidal dissipation in the basal ice above the ocean increases its temperature, which in turn leads to faster tidal dissipation. This feedback leads to a heat pulse within Pluto and rapid buildup of tectonic stresses on Pluto and Charon. If Pluto never had any liquid at the base of its ice shell, the tidal dissipation is too small to keep Pluto's interior warm. Without a starting ocean, it is difficult to start the thermal-orbital feedback process, and difficult for Charon to evolve to its presently observed orbital state within the timespan of solar system history.

  12. Tectonic evolution of the Perth Abyssal Plain's Quiet Zone, Southeast Indian Ocean

    NASA Astrophysics Data System (ADS)

    Ehrlich, Zohar Louis; Granot, Roi; Williams, Simon E.

    2013-04-01

    During the Late Jurassic period, the Greater-Indian plate was torn away from Australia, dissociating East Gondwanaland. The Perth Abyssal Plain (PAP) is the southernmost rift segment along the western Australian margin, and has an onset age of ~136 Ma. New marine magnetic and swath bathymetry data, crossing the entire PAP, were acquired recently on geophysical cruise ss2011v06 aboard the R/V Southern Surveyor. These have lead to the outline of conjugate Indian and Australian M-series isochrons in the east and west PAP, respectively [1]. Yet, most of the PAP was created during the Cretaceous Normal Superchron (CNS, 121-83 Ma), a period of no geomagnetic field reversals, hence no comprehensive tectonic model for the PAP exists . Here we present preliminary findings of an analytic bathymetric and magnetic investigation aimed at elucidating the PAP's quiet zone. Recent discoveries regarding the evolution of the geomagnetic field during the CNS [2] provide new time markers that can be utilized to date the oceanic crust. The magnetic anomaly data exhibit the Q2 anomaly marker (~108 Ma), further constraining the spreading history of the PAP. Together with the ridgelet transform method [3] for automated abyssal hill delineation, we present new constraints on the development of crustal construction processes (spreading location, direction and rates) that took place along the PAP spreading center. References: [1] S.E. Williams, J.M. Whittaker, R. Granot, R.D. Muller (in preparation), New constraints on the seafloor spreading history in the Perth Abyssal Plain. [2] Granot, R., J. Dyment, and Y. Gallet (2012), Geomagnetic field variability during the Cretaceous Normal Superchron, Nature Geoscience, 5(3), 220-223. [3] Downey, N. J. and R. W. Clayton (2007), A ridgelet transform method for constraining tectonic models via abyssal-hill morphology, Geochemistry Geophysics Geosystems, 8, Q03004, doi: 10.1029/2006GC001440.

  13. The late Mesozoic-Cenozoic tectonic evolution of the South China Sea: A petrologic perspective

    NASA Astrophysics Data System (ADS)

    Yan, Quanshu; Shi, Xuefa; Castillo, Paterno R.

    2014-05-01

    This paper presents a review of available petrological, geochonological and geochemical data for late Mesozoic to Recent igneous rocks in the South China Sea (SCS) and adjacent regions and a discussion of their petrogeneses and tectonic implications. The integration of these data with available geophysical and other geologic information led to the following tectono-magmatic model for the evolution of the SCS region. The geochemical characteristics of late Mesozoic granitic rocks in the Pearl River Mouth Basin (PRMB), micro-blocks in the SCS, the offshore continental shelf and Dalat zone in southern Vietnam, and the Schwaner Mountains in West Kalimantan, Borneo indicate that these are mainly I-type granites plus a small amount of S-type granites in the PRMB. These granitoids were formed in a continental arc tectonic setting, consistent with the ideas proposed by Holloway (1982) and Taylor and Hayes (1980, 1983), that there existed an Andean-type volcanic arc during later Mesozoic era in the SCS region. The geochonological and geochemical characteristics of the volcanics indicate an early period of bimodal volcanism (60-43 Ma or 32 Ma) at the northern margin of the SCS, followed by a period of relatively passive style volcanism during Cenozoic seafloor spreading (37 or 30-16 Ma) within the SCS, and post-spreading volcanism (tholeiitic series at 17-8 Ma, followed by alkali series from 8 Ma to present) in the entire SCS region. The geodynamic setting of the earlier volcanics was an extensional regime, which resulted from the collision between India and Eurasian plates since the earliest Cenozoic, and that of the post-spreading volcanics may be related to mantle plume magmatism in Hainan Island. In addition, the nascent Hainan plume may have played a significant role in the extension along the northern margin and seafloor spreading in the SCS.

  14. Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone

    USGS Publications Warehouse

    van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego

    2010-01-01

    Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ≤1 km. Late Miocene–recent transpression caused inversion and ≤1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.

  15. Tectonic evolution of the Gaoua region, Burkina Faso: Implications for mineralization

    NASA Astrophysics Data System (ADS)

    Baratoux, L.; Metelka, V.; Naba, S.; Ouiya, P.; Siebenaller, L.; Jessell, M. W.; Naré, A.; Salvi, S.; Béziat, D.; Franceschi, G.

    2015-12-01

    The interpretation of high-resolution airborne geophysical data integrated with field structural and lithological observations were employed in the creation of a litho-structural framework for the Gaoua region, Burkina Faso. The granite-greenstone domain of Paleoproterozoic age was affected by multiple deformation and mineralization events. The early tectonic phase is characterized by the emplacement of voluminous tholeiitic and calc-alkaline lavas, probably in a volcanic arc setting. The copper mineralization in Gongondy, Dienemera and Mt Biri is concentrated in a diorite/andesite breccia, and is interpreted as porphyry-copper style formed at an early stage of the evolution of the area. Evidence for the first deformation event D1Ga corresponding to N-S shortening was only found in the E-W trending mafic unit bordering the Gaoua batholith to the south. A second deformation phase D2Ga occurred under greenschist facies conditions and lead to a development of more or less penetrative metamorphic foliation and its subsequent folding under overall E-W compression. At later stages, the D2Ga switched to a transcurrent regime characterized by intense N-S to NW-trending steeply dipping shear zones. The first significant gold mineralization event is related to this transcurrent tectonic phase. During subsequent D3Ga, intense network of brittle to brittle-ductile NW and NE faults developed. Economic gold concentrations are attributed to the D3Ga event and are associated with the remobilization of early disseminated low grade gold concentrations. Significant deposits in the area are Nassara, Gomblora, Batié West and Kampti. The last deformation event D4Ga resulted in E-W trending thrust faults and crenulation cleavage planes, under overall N-S compression. No mineralization events related to this stage have been seen.

  16. The climatic, biotic and tectonic evolution of the Paleogene Renova formation of southwestern Montana

    NASA Astrophysics Data System (ADS)

    Lielke, Kevin John

    The Renova Formation of southwestern Montana contains an important record of Paleogene floral, faunal, climate and tectonic change in the northern Rocky Mountains. The period between the end of the early Eocene and the early Oligocene (˜49--32 Ma) was a time of rapid and far-reaching climate change. This period saw the end of global greenhouse climate and the establishment of icehouse conditions across the Earth. These changes led to profound alterations in both marine and terrestrial ecosystems. This study examines the late Eocene/early Oligocene history of the northern Rocky Mountains by means of an integrated study of the sedimentology, tectonics and fossil content of the Renova Formation. The first part of this study examines plant fossils found in the Renova Formation in order to examine changes in the composition of the vegetation across the late Eocene/ early Oligocene (E/O) boundary. Plant remains are an effective proxy for climate and are used to estimate multiple climatic parameters across the E/O boundary. The second part of this study examines the paleotopography and paleodrainage patterns of the basins which accumulated the Renova sediments. This is accomplished by a combination of sedimentary facies and detrital zircon analysis. The third part of this study examines the tectonic underpinnings of Paleogene southwestern Montana through a combination of geologic field work and geodynamic modeling. The results of this study indicate that a seasonal summer dry climate became established in the northern Rocky Mountains by early Oligocene time. This is indicated by the elimination of subtropical plant species, the establishment of dry-adapted species and by paleoclimate parameters calculated from leaf physiognomy. Geodynamic calculations and field data indicate that the Renova Formation was deposited in a series of sub-basins separated by relict paleotopography and inverted topography formed by contemporary lava flows. Normal faulting was not active until

  17. Integrating seismological and tectonic studies to constrain lithospheric evolution at complex plate boundaries

    NASA Astrophysics Data System (ADS)

    Hayes, Gavin Peter

    The relative motion of tectonic plates across their boundaries generates deformation in the surrounding lithosphere. How this deformation is expressed reflects both present-day plate configurations and how plate boundaries evolve. To understand the behavior of plate boundaries, we must study how they have developed. The advances made in seismology over the past fifty years---both in observation and application---provide tools ideal for such analysis. Here, I use these tools to investigate the tectonic evolution of complex plate boundaries. I focus on two areas that have experienced geologically recent plate tectonic variations---the Mendocino triple junction in northern California, and the Australia:Pacific plate boundary south of New Zealand. In northern California, the northward migration of the Mendocino triple junction over the past ˜10Ma has driven a synchronous pattern of thickening and thinning of North American crust. In studying this deformation I find major thinning is localized to a narrow region of crust in the Redwood Valley area. This thinning is accompanied by a steeply dipping Moho (>15°), and by high Poisson's Ratio's in the lower crust, characteristic of layers of melt. These melts may link to shallow (˜10km) dike injections that drive a migrating sequence of seismicity in the shallow crust near Lake Pillsbury. The limited data sets available led me to develop new tools in receiver function and crustal velocity ratio analyses that significantly improve our ability to resolve spatial changes in crustal properties. The application of these techniques forms a second major aspect of this thesis. Finally, I analyze the deformation of Australian lithosphere adjacent to the plate boundary south of New Zealand. I perform earthquake relocations on the distribution of intra- and inter-plate seismicity, and combined with plate reconstructions since the late Oligocene show that deformation occurs over a ˜150km wide area west of the current plate boundary

  18. Granitoid generation and laxfordian tectonic evolution in the northern part of the lewisian complex

    NASA Astrophysics Data System (ADS)

    Castro, A.; Lopez, S.; Fernandez, C.

    2003-04-01

    transpression episode, with the southern block (Assynt terrane) overthrusting the northern block (Rhiconich terrane). The described process of in-situ granitization was favoured by tectonic deformation in the footwall to this transpressional zone, where large volumes of basic magma were emplaced. Therefore, the generation of granitoids seems to be intimately linked to the tectonic evolution of the Early Proterozoic orogenic belts.

  19. Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

    NASA Astrophysics Data System (ADS)

    Becker, Thorsten W.; Conrad, Clinton P.; Buffett, Bruce; Müller, R. Dietmar

    2009-02-01

    Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean chemistry, and climate. However, there is little agreement on the correct parameterization for the time-dependent evolution of plate motions. A strong constraint is given by seafloor age distributions, which are affected by variations in average spreading rate, ridge length, and the age distribution of seafloor being removed by subduction. Using a simplified evolution model, we explore which physical parameterizations of these quantities are compatible with broad trends in the area per seafloor age statistics for the present-day and back to 140 Ma from paleo-age reconstructions. We show that a probability of subduction based on plate buoyancy (slab-pull, or "sqrt(age)") and a time-varying spreading rate fits the observed age distributions as well as, or better than, a subduction probability consistent with an unvarying "triangular" age distribution and age-independent destruction of ocean floor. Instead, we interpret the present near-triangular distribution of ages as a snapshot of a transient state of the evolving oceanic plate system. Current seafloor ages still contain hints of a ˜ 60 Myr periodicity in seafloor production, and using paleoages, we find that a ˜ 250 Myr period variation is consistent with geologically-based reconstructions of production rate variations. These long-period variations also imply a decrease of oceanic heat flow by ˜ - 0.25%/Ma during the last 140 Ma, caused by a 25-50% decrease in the rate of seafloor production. Our study offers an improved understanding of the non-uniformitarian evolution of plate tectonics and the interplay between continental cycles and the self-organization of the oceanic plates.

  20. Evolution of an Alpine fluvioglacial system at the LGM decay: The Cormor megafan (NE Italy)

    NASA Astrophysics Data System (ADS)

    Fontana, Alessandro; Monegato, Giovanni; Zavagno, Enrico; Devoto, Stefano; Burla, Ivonne; Cucchi, Franco

    2014-01-01

    within the glacial amphitheatre. After this depositional phase, the Cormor megafan was deactivated because of water and sediment discharge concentration of the Tagliamento catchment in the Tagliamento River. This study demonstrates the possibility to reconstruct the timing of the decline of the Tagliamento moraine amphitheatre by studying the distal portion of the related outwash plain. Moreover, new geochronological dating allows chronological comparison of the glacial withdrawal in the eastern sector of the Southern Alps with the global chronology. The results suggest that we can apply this approach also in the distal part of the other alluvial megafans formed by Alpine glacial outwashes in the central part of the Po plain where radiocarbon chronology is almost lacking.

  1. Erosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus

    PubMed Central

    2014-01-01

    Background The role of tectonic uplift in stimulating speciation in South Africa’s only alpine zone, the Drakensberg, has not been explicitly examined. Tectonic processes may influence speciation both through the creation of novel habitats and by physically isolating plant populations. We use the Afrotemperate endemic daisy genus Macowania to explore the timing and mode (geographic versus adaptive) of speciation in this region. Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry. A dated molecular phylogenetic hypothesis for Macowania elucidates species’ relationships and is used to address the potential impact of uplift on diversification. Morphological divergence of a small sample of reproductive and vegetative characters, used as a proxy for adaptive divergence, is measured against species’ range distributions to estimate mode of speciation across two subclades in the genus. Results The Macowania crown age is consistent with the hypothesis of post-uplift diversification, and we find evidence for both vicariant and adaptive speciation between the two subclades within Macowania. Both subclades exhibit strong signals of range allopatry, suggesting that geographic isolation was important in speciation. One subclade, associated with dry, rocky environments at high altitudes, shows very little morphological and ecological differentiation but high range allopatry. The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges. Conclusions Species in Macowania are likely to have diversified in response to tectonic uplift, and we invoke uplift and uplift-mediated erosion as the main drivers of speciation. The greater relative morphological divergence in

  2. Tectonic versus climate influence on landscape evolution: A case study from the upper Spiti valley, NW Himalaya

    NASA Astrophysics Data System (ADS)

    Anoop, A.; Prasad, S.; Basavaiah, N.; Brauer, A.; Shahzad, F.; Deenadayalan, K.

    2012-04-01

    We have undertaken structural, geomorphological, and morphometric analyses to investigate the role of tectonism and climate in the landscape evolution in the upper Spiti valley, NW Himalayas. Geomorphometric analyses coupled with field investigations reveal active tectonic deformation in the Spiti region. The calculated geomorphic indices (steepness, concavity and Hack) demonstrate uplift/subsidence along the Kaurik-Chango fault, whereas transverse topographic index (T-index) reveals basin tilting associated with active faulting near Hansa and Lingti valley. Investigation of well-dated Mane palaeolake sediments also provides evidence of regional tectonic instability. Four episodes (ca. 7.8, 7.4, 6.5 and 6.1 cal ka) of neotectonic activity have been identified during the period of the lake's existence. We have also compiled data on the regional climate variability and compared it with the age of the Mane palaeo-landslide. Our results indicate that the landslide occurred towards the end of the early Holocene intensified monsoon phase and is located near an active fault. Our data on regional tectonic instability and the coincidences of modern and palaeo-landslides with zones of active deformation suggest that tectonism is an important factor governing landscape stability in the Spiti region.

  3. New aerogeophysical survey targets crustal architecture and tectonic evolution of East Antarctica in the Recovery frontier

    NASA Astrophysics Data System (ADS)

    Ferraccioli, F.; Forsberg, R.; Jordan, T. A.; Matsuoka, K.; Olesen, A. V.; Ghidella, M. E.

    2013-12-01

    East Antarctica is the size of the conterminous US; it represents the least known continent on Earth despite being regarded as a keystone in Gondwana, Rodinia and possibly even earlier Columbia/Nuna supercontinents. Significant progress has however been made in recent years in the exploration of East Antarctica using airborne geophysical techniques. Spurred by the International Polar Year major collaborative international aerogeophysical campaigns have been performed over the Wilkes Subglacial Basin, the Aurora Subglacial Basin and the Gamburtsev Mountains in recent years, and these are continuing to provide fundamental new glimpses into the crustal architecture in interior East Antarctica, as well as several new interpretations regarding its linkages with tectonic and geodynamic evolution from Precambrian to Mesozoic/Cenozoic times. Here we present the first results of a major reconnaissance aerogeophysical survey over the largely unexplored Recovery ice stream catchment in East Antarctica completed during the IceGRAV 2012-13 field campaign, as part of an international Danish, Norwegian, UK and Argentine collaboration. Over 29,000 line km of new radio-echo sounding, laser altimetry, gravity and magnetic data were acquired using a British Antarctic Survey Twin Otter that surveyed the region. We focus primarily on the new potential field datasets for the area. Specifically, we present the first aeromagnetic anomaly maps, free air and Bouguer and isostatic residual maps obtained for the region. These images provide new geophysical perspectives that are required in order to address a cascade of open questions over this region. Where are the major tectonic boundaries between the Coats Land Block, the Shackleton Range, and the collage of different provinces recently proposed from aeromagnetic studies in Dronning Maud Land (Mieth and Jokat, 2013, GR)? Is the Coats Land crustal block a tectonic tracer for Laurentia (Loewy et al., 2011, Geology), and how and when was this

  4. Volcano-tectonic evolution of the polygenetic Kolumbo submarine volcano/Santorini (Aegean Sea)

    NASA Astrophysics Data System (ADS)

    Hübscher, Christian; Ruhnau, M.; Nomikou, P.

    2015-01-01

    Here we show for the first time the 3D-structural evolution of an explosive submarine volcano by means of reflection seismic interpretation. Four to five vertically stacked circular and cone-shaped units consisting mainly of volcaniclastics build the Kolumbo underwater volcano which experienced its first eruption > 70 ka ago and its last explosive eruption 1650 AD, 7 km NE of Santorini volcano (southern Aegean Sea). The summed volume of volcaniclastics is estimated to range between 13-22 km3. The entire Kolumbo volcanic complex has a height of ≥ 1 km and a diameter of ≥ 11 km. All volcaniclastic units reveal the same transparent reflection pattern strongly suggesting that explosive underwater volcanism was the prevalent process. Growth faults terminate upwards at the base of volcaniclastic units, thus representing a predictor to an eruption phase. Similarities in seismic reflection pattern between Kolumbo and near-by volcanic cones imply that the smaller cones evolved through explosive eruptions as well. Hence, the central Aegean Sea experienced several more explosive eruptions (≥ 23) than previously assumed, thus justifying further risk assessment. However, the eruption columns from the smaller volcanic cones did not reach the air and- consequently - no sub-aerial pyroclastic surge was created. The Anydros basin that hosts Kolumbo volcanic field opened incrementally NW to SE and parallel to the Pliny and Strabo trends during four major tectonic pulses prior to the onset of underwater volcanism.

  5. Structural synthesis and tectonic evolution of the Maracaibo and Barinas-Apure basins, Western Venezuela

    SciTech Connect

    De Toni, B.; Loureiro, D.; Colletta, B.; Rourke, F.

    1996-08-01

    Seismic profiles have imaged the complex and multiphase geometry of major structures in the Maracaibo and Barinas-Apure basins and foothills of the adjacent orogens. Pre-Mesozoic structuring can be documented in subsurface as a peneplaned south-southeast vergent fold-thrust-belt of Hercynian or Caledonian age. In Jurassic times, rifting developed in connection with the opening of western Tethys and thick continental red beds were deposited in the rift grabens. In Late Cretaceous times, postrift thermal subsidence was subsequently recorded. From Maastrichtian through Eocene times, the obduction of the Tethyan ophiolites and the coeval tectonic accretion of the Caribbean allocthon loaded the South American foreland lithosphere, inducing the development of a flexural basin in the northeastern part of the Maracaibo basin. In Late Eocene and Oligocene times, a major extensional event took place in the East Zulia and Falcon area soon after the Caribbean compressional deformation ceased. Since the Neogene, structuring was related to the Andean orogeny, and the deformation was partially superimposed onto older Paleogene and Jurassic structures. These results, integrated with geochemical and chronostratigraphic models, have been used to understand the evolution of the petroleum system and to improve the play fairway risk assessment for exploration.

  6. Periodic Vesicle Formation in Tectonic Fault Zones--an Ideal Scenario for Molecular Evolution.

    PubMed

    Mayer, Christian; Schreiber, Ulrich; Dávila, María J

    2015-06-01

    Tectonic fault systems in the continental crust offer huge networks of interconnected channels and cavities. Filled mainly with water and carbon dioxide (CO2), containing a wide variety of hydrothermal chemistry and numerous catalytic surfaces, they may offer ideal reaction conditions for prebiotic chemistry. In these systems, an accumulation zone for organic compounds will develop at a depth of approximately 1 km where CO2 turns sub-critical and dissolved components precipitate. At this point, periodic pressure changes caused for example by tidal influences or geyser activity may generate a cyclic process involving repeated phase transitions of carbon dioxide. In the presence of amphiphilic compounds, this will necessarily lead to the transient formation of coated water droplets in the gas phase and corresponding vesicular structures in the aqueous environment. During this process, the concentration of organic components inside the droplets and vesicles would be drastically increased, allowing for favorable reaction conditions and, in case of the vesicles generated, large trans-membrane concentration gradients. Altogether, the process of periodic formation and destruction of vesicles could offer a perfect environment for molecular evolution in small compartments and for the generation of protocells. The basic process of vesicle formation is reproduced experimentally with a lipid in a water/CO2 system. PMID:25716918

  7. Periodic Vesicle Formation in Tectonic Fault Zones—an Ideal Scenario for Molecular Evolution

    NASA Astrophysics Data System (ADS)

    Mayer, Christian; Schreiber, Ulrich; Dávila, María J.

    2015-06-01

    Tectonic fault systems in the continental crust offer huge networks of interconnected channels and cavities. Filled mainly with water and carbon dioxide (CO2), containing a wide variety of hydrothermal chemistry and numerous catalytic surfaces, they may offer ideal reaction conditions for prebiotic chemistry. In these systems, an accumulation zone for organic compounds will develop at a depth of approximately 1 km where CO2 turns sub-critical and dissolved components precipitate. At this point, periodic pressure changes caused for example by tidal influences or geyser activity may generate a cyclic process involving repeated phase transitions of carbon dioxide. In the presence of amphiphilic compounds, this will necessarily lead to the transient formation of coated water droplets in the gas phase and corresponding vesicular structures in the aqueous environment. During this process, the concentration of organic components inside the droplets and vesicles would be drastically increased, allowing for favorable reaction conditions and, in case of the vesicles generated, large trans-membrane concentration gradients. Altogether, the process of periodic formation and destruction of vesicles could offer a perfect environment for molecular evolution in small compartments and for the generation of protocells. The basic process of vesicle formation is reproduced experimentally with a lipid in a water/CO2 system.

  8. Tracing long term tectonic evolution of accretionary orogens by U-Pb zircon geochronology: Proterozoic to Jurassic tectonics of the Santander Massif, northern Colombia

    NASA Astrophysics Data System (ADS)

    Valencia, V. A.; Cardona, A.; Gehrels, G. E.; Ruiz, J.; Ibañez, M.

    2009-12-01

    Accurate orogenic models are nedded to reconstruct complex tectonic histories of long lived convergent margins. Integrated zircon U-Pb geochronology on igneous, sedimentary and metasedimentry rocks within single crustal domains is a powerful tool, as it can be used to trace the timing of rock forming events, magmatic style and episodity, and identify crustal recycling. U-Pb detrital zircon and magmatic geochronology was carried on multiple litostratigraphic units of the Santander Massif in the northeastern Andes, in order to reconstruct its long term Late Proterozoic to Early Mesozoic tectonic evolution. Major zircon forming events includ well defined Grenvillian, Late Neoproterozoic to Ordovician, Silurian, Early Permian and Jurassic events. Major peaks of activity at ca. 197 Ma, 440-410 Ma and 470-490 Ma and 950-1052 Ma, support the existence of continental scale tectonic cycles. Older Mesoproterozoic (1.3-1.5 Ga) crustal input in metasediments and magmatic rocks link these units to crustal recycling on the margins of the Amazon Craton, whereas the older 950-1052 Ma peak indicates the link of this crustal segment with other Andean Grenvillian remnant. Previous interpretations of the Paleozoic Silgara Formation seem incorrect, as acquired dates from this study includ different metamorphic units, deposited and formed after the Silurian and Permian during final stages of Pangea's assemblage, probably as Laurentia migrated to its final Alleghanian position. Finally the presence of the NW South America Jurassic arc is also present in the region by granitoid ages. The limited input of this arc signature within the contemporaneous and overlapping Early Cretaceous sedimentary rocks suggest that this arc was developed in a back arc setting.

  9. Tectonics and sedimentary evolution of the Sandino forearc basin off Nicaragua, Central America

    NASA Astrophysics Data System (ADS)

    Costa Pisani, P.; Silver, E.; McIntosh, K.; Ahmed, I.; Ranero, C. R.; Taylor, B.

    2003-04-01

    The Sandino basin is the Nicaragua sector of the Central American forearc, where the Cocos plate subducts beneath the Middle America trench. Recently, Ranero et al. have interpreted a seismic section across the margin and proposed a history of formation of the forearc which is constrained by industry drilling in the basin. They suggested a late Cretaceous to Paleocene accretion event, followed by later subduction erosion processes. The margin wedge consists of the ophiolitic Nicoya complex. The seismic units, unconformities and tectonic features record a rich history of both local and regional vertical movements occurring since the Middle Eocene, which are linked to the evolution of the Pacific convergent margin. During June, 2000, 2800 kms of multichannel seismic reflection data were collected on the R/V Ewing off Nicaragua. Analysis of the 240 channels dataset indicates rapid changes along strike in the Sandino basin. The basin is relatively thin in the southern part, thinning quite rapidly southward against the Nicoya complex of the Santa Elena peninsula of Costa Rica. The forearc sediments thickness approaches and locally exceeds 10 kms in the central and northern parts of the Sandino basin. The oldest units (Upper Cretaceous-Middle Eocene) are very thick off northern Nicaragua, with relatively thin middle to late Cenozoic deposits. However, off central Nicaragua the latter units (Middle-Upper Miocene) attain great thicknesses and the older units appear to thin. This pattern suggests a history of successive deepening of the basin from north to south, after the convergent system evolved from accretion to subduction erosion processes. Present efforts are devoted to quantifying this change in development and using it to understand the dynamics of forearc basin evolution offshore of Central America.

  10. The tectonic evolution of western Central Iran seen through detrital white mica

    NASA Astrophysics Data System (ADS)

    Kargaranbafghi, Fariba; Neubauer, Franz; Genser, Johann

    2015-05-01

    A first order survey of 40Ar/39Ar dating of detrital white mica from Jurassic to Pliocene sandstones has been carried out in order to reveal the tectonic evolution of blocks in Central Iran. The Central Iran block was believed to represent a stable Precambrian block. Our results indicate that: (1) Only a very small proportion of Precambrian but abundant Paleozoic and Mesozoic detrital white mica indicate the Phanerozoic, mostly Mesozoic age of metamorphic crust exposed in Central Iran. The oldest but scarce detrital white mica grains have ages ranging from 524 to 826 Ma heralding a Late Precambrian and Cambrian crystalline basement or cannibalism from older clastic successions. (2) Jurassic and Cretaceous sandstones from the west and east of the Chapedony fault yield different age spectra, with a dominance of Variscan ages (ca. 308-385 Ma) in the Biabanak unit west of the Chapedony fault compared to coeval sandstones from the block east of the Chapedony fault, where Variscan ages are subordinate and Cimmerian ages predominate. The micas from the Biabanak unit are most likely derived from the Variscan accretionary complex exposed in the Anarak-Jandaq areas further northwest. This result underlines the importance of a major block boundary identified as the Chapedony fault, which is in extension of a fault previously proposed. (3) Two stages of Cimmerian events are visible in our data set from Cretaceous and Paleogene sandstones, a cluster around 170 Ma and at ca. 205 Ma. These clusters suggest a two-stage Cimmerian evolution of the largely amphibolite-grade metamorphic Posht-e-Badam and Boneh Shurow complexes. (4) The youngest micas in Paleogene conglomerates have an age of ca. 100 Ma and are most likely derived from the base of the Posht-e-Badam complex. No record of the uplifted Eocene Chapedony metamorphic core complex has been found in Eocene and Pliocene clastic rocks.

  11. Tectonic evolution of the Brusque Group, Dom Feliciano belt, Santa Catarina, Southern Brazil

    NASA Astrophysics Data System (ADS)

    Basei, M. A. S.; Campos Neto, M. C.; Castro, N. A.; Nutman, A. P.; Wemmer, K.; Yamamoto, M. T.; Hueck, M.; Osako, L.; Siga, O.; Passarelli, C. R.

    2011-12-01

    The Dom Feliciano Belt constitutes the main geotectonic unit of the southeastern portion of Brazil and Uruguay. It was formed by the end of the Neoproterozoic as a result of the interaction among the Rio de La Plata, Paranapanema, Congo and Kalahari cratons during the formation of Western Gondwana. The Brusque Group represents the supracrustal units of the Dom Feliciano Belt that occur in its northernmost part, which ends in the Brazilian coast and probable continuity in the Kaoko Belt in southwestern Africa. It is possible to constrain the evolution of the Brusque Group paleobasin to the Neoproterozoic, with the rift phase starting in the Tonian (940-840 Ma) and the main sedimentation occurring until 640 Ma, as indicated by the ages of the acid volcanic rocks intercalated with the metasedimentary sequence. The supracrustal rocks can be grouped in three main units lithostratigraphically organized from the oldest to the youngest: Rio Oliveira Formation (rift phase, predominating metavolcanic units), Botuverá Formation (metasedimentary) and Rio da Areia Formation (metavolcano-carbonatic). Between 640 and 600 Ma several metamorphism and deformation phases affected the Brusque Group. Around 600 ± 10 Ma the three granitic suites (São João Batista, Valsungana and Nova Trento) were emplaced within regional metamorphites, producing post-foliation S2 metamorphic aureoles. S2 represents the main foliation observed in the metavolcanosedimentary rocks that constitute the Brusque Group. The tectonic model for the evolution of Brusque Group can be better achieved only when the geochemical, isotopic and geochronologic information available for the Dom Feliciano Belt in Santa Catarina, is considered as a whole. Therefore it is here suggested that the Brusque Group initially evolved in an independent peri-cratonic basin setting separated from the Florianópolis - Pelotas-Aiguá magmatic arc by the Adamastor ocean, having been juxtaposed to it only around 600 Ma, when Brusque

  12. The deformation and tectonic evolution of the Huahui Basin, northeast China, during the Cretaceous-Early Cenozoic

    NASA Astrophysics Data System (ADS)

    Huang, Shiqi; Dong, Shuwen; Zhang, Yueqiao; Zhang, Fuqin; Huang, Dezhi; Wei, Shi; Li, Zhenhong; Miao, Laicheng; Zhu, Mingshuai

    2015-12-01

    The Cretaceous Huahui basin lies along the Dunhua-Mishan fault (Dun-Mi fault), which is one of the northern branches of Tan-Lu fault in northeastern China. The study of the formation and the tectonic movements that took place in the basin can provide very important information for deciphering the tectonic evolution of northeastern China during Cretaceous-Early Cenozoic. The field analysis of fault-slip data collected from different units in the basin, demonstrates changes in the paleo-stress state that reveals a three-stage tectonic movement during the Cretaceous-Early Cenozoic. The earliest tectonic movement was NW-SE extension, which was responsible for the formation of the basin and sedimentary infilling during the Early Cretaceous. Dating of the andesite in the fill indicates it began during about 119.17 ± 0.80 Ma. The extensional structures formed in the Latest Early Cretaceous imply that this tectonic movement lasted until the beginning of the Late Cretaceous. The second stage began during the Late Cretaceous when the tectonic stress state changed and was dominated by NW-SE compression and NE-SW extension, which caused the inversion of the extensional basin. This compression folded the Early Cretaceous deposits and reactivated pre-existing faults and uplifted pre-existing granite in the basin. The strata and the unconformity in the basin shows that this compressive phase probably took place during the Late Cretaceous and ended in the Early Paleogene by a compressional regime with NE-SW compression and NW-SE extension that constitutes the third stage. The tectonic stress fields documented in the Huahui basin provide insight into the influences of plate tectonics on the crustal evolution of northeastern China during the Cretaceous to Early Cenozoic. These results show that the development of Huahui basin was controlled by the northwestward subduction of the paleo-Pacific plate during the Cretaceous, and later by the far-field effects of India-Asia collision in

  13. Composition and tectonic evolution of the Chinese continental crust constrained by Poisson's ratio

    NASA Astrophysics Data System (ADS)

    Ji, Shaocheng; Wang, Qian; Salisbury, Matthew H.

    2009-01-01

    We have measured both P- and S-wave velocities ( Vp and Vs) and Poisson's ratios ( υ) of 60 typical ultrahigh pressure (UHP) metamorphic rock samples from the Chinese Continental Scientific Drilling (CCSD) main and pre-pilot holes and surface outcrops in the Sulu-Dabie orogenic belt at hydrostatic confining pressures up to 850 MPa. The experimental results, together with those compiled in Handbook of Seismic Properties of Minerals, Rocks and Ores [ Ji, S.C., Wang, Q., Xia, B., 2002. Handbook of Seismic Properties of Minerals, Rocks and Ores. Polytechnic International Press, Montreal, 630 pp.], reveal that except for monomineralic rocks such as quartzite, serpentinite, anorthosite, limestone, and marble the rest of the rock types have Poisson's ratios falling along an upward convex curve determined from the correlations between elastic moduli and density. Poisson's ratios increase with density as the lithology changes from granite, felsic gneiss and schist, through diorite-syenite, intermediate gneiss and metasediment, to gabbro-diabase, amphibolite, and mafic gneiss, and then decrease as the rocks become ultramafic in composition. Eclogite has a higher density but a lower Poisson's ratio than peridotite. The results were applied to constrain the crustal composition and tectonic evolution of the Chinese continental crust based on crustal thickness ( H) and Poisson's ratio ( υ) from 248 broadband seismic stations, measured using teleseismic receiver function techniques. The North China, Yangtze, South China and Northeast China blocks and Songpan-Ganzi Terrane are dominated by low ( υ < 0.26) and moderate (0.26 ≤ υ < 0.28) υ values (> 70%), suggesting the dominance of felsic composition in the crust. The Lhasa terrane, Qiangtang terrane, and Indochina block are characterized by high proportions (33-42%) of measurements with very high υ values (≥ 0.30 and H is found for the South China block, Northeast block, Lhasa block, Qiangtang terrane and Indochina block

  14. Tectonic Evolution of Chingshui Geothermal Field Inferred from Evidence of Quartz and Calcite Veins

    NASA Astrophysics Data System (ADS)

    Lu, Y. C.; Song, S. R.; Wang, P. L.; Liu, C. M.; Yeh, E. C.

    2014-12-01

    The Chingshui geothermal field is located in the valley of Chingshui stream, where is about 27 km SW of Ilan, northeastern Taiwan. It is a tectonically complex area occurred by the Philippine Plate subducting beneath the Eurasian plate in the south with Okinawa Trough opening in the Ilan Plain. Owing to complicated geological structure, the heat source of Chingshui geothermal field is still controversial. For understanding hot fluid sources and tectonic evolution, this study focuses on field survey of veins and scaling in the Chingshui geothermal field, and the results inferred from the data of SEM, XRD, carbon and oxygen isotope, and Uranium-thorium dating. The Chingshui hot fluid contains both high concentrations of SiO­2 and HCO3-, therefore, temperature and pressure both drop when the hot fluids inject into shallower fractures, and calcite and quartz both could be precipitated with competition or simultaneously. In Chilukeng River, many euhedral quartz crystals occurred in large damage zone of Xioananao fault that indicated the temperature drop played the dominated role when the hot fluids injected into the shallow. It inferred that the quartz crystal precipitated under compression stress, evidenced by the Xioananao thrust fault with no surface rupture. Whiles, there are gouges in normal fault with abundant calcite or calcite with quartz veins cropped out in the confluence of Chingshui River and Chilukeng River. The results indicate that those veins occurred in more recent period by U-Th dating data, because of degassing CO2 occurred in open fractures by normal faulting or the stress changing from compression to extension. The standard oxygen isotopes range from 1.29 to 20.73 permil of SMOW and the clumped isotope of Δ47 outcrop is 0.385 in calcite veins, suggest that the highest temperature of thermal fulids with calcite precipitations is 222℃±9℃ by calibrated equation of Passey and Henkes 2012. Meanwhile, it also indicates that the oxygen isotope of

  15. Teaching about the Early Earth: Evolution of Tectonics, Life, and the Early Atmosphere

    NASA Astrophysics Data System (ADS)

    Mogk, D. W.; Manduca, C. A.; Kirk, K.; Williams, M. L.

    2007-12-01

    The early history of the Earth is the subject of some of the most exciting and innovative research in the geosciences, drawing evidence from virtually all fields of geoscience and using a variety of approaches that include field, analytical, experimental, and modeling studies. At the same time, the early Earth presents unique opportunities and challenges in geoscience education: how can we best teach "uncertain science" where the evidence is either incomplete or ambiguous? Teaching about early Earth provides a great opportunity to help students understand the nature of scientific evidence, testing, and understanding. To explore the intersection of research and teaching about this enigmatic period of Earth history, a national workshop was convened for experts in early Earth research and undergraduate geoscience education. The workshop was held in April, 2007 at the University of Massachusetts at Amherst as part of the On the Cutting Edge faculty professional development program. The workshop was organized around three scientific themes: evolution of global tectonics, life, and the early atmosphere. The "big scientific questions" at the forefront of current research about the early Earth were explored by keynote speakers and follow-up discussion groups: How did plate tectonics as we know it today evolve? Were there plates in the Hadean Eon? Was the early Earth molten? How rapidly did it cool? When and how did the atmosphere and hydrosphere evolve? How did life originate and evolve? How did all these components interact at the beginning of Earth's history and evolve toward the Earth system we know today? Similar "big questions" in geoscience education were addressed: how to best teach about "deep time;" how to help students make appropriate inferences when geologic evidence is incomplete; how to engage systems thinking and integrate multiple lines of evidence, across many scales of observation (temporal and spatial), and among many disciplines. Workshop participants

  16. Cenozoic Tectonics and Magmatic Evolution of Central Anatolia (Turkey): From Collision to Slab Breakoff to Delamination

    NASA Astrophysics Data System (ADS)

    Kadioglu, Yusuf K.; Dilek, Yildirim

    2010-05-01

    The latest Mesozoic-Cenozoic tectonic evolution of Central Anatolia was controlled largely by the behavior of the subducting lithosphere of the Inner-Tauride Ocean and the mantle response to it. Following the demise of the Inner-Tauride oceanic lithosphere at a NE-dipping subduction zone and the emplacement of the late Cretaceous, incipient arc-forearc ophiolites onto the northern edge of the Tauride ribbon continent, subduction was arrested by the underplating of the buoyant Tauride continental crust. The leading edge of the subducted Tethyan slab broke off from the rest of the Tauride continental lithosphere, resulting in the development of an asthenospheric window. The juxtaposition of this asthenospheric heat source against the overlying continental lithosphere caused melting of the metasomatized mantle layers, producing the high-K shoshonitic magmas of the latest Cretaceous monzonitic plutons and then the more-enriched alkaline magmas of the syenitic plutons in the Central Anatolian Crystalline Complex (CACC). Continued convergence between the Tauride and CACC blocks resulted in a continental collision in the Paleocene that led to deformation, crustal thickening, and metamorphism in the hinterland, and to southward transport of the already-emplaced Tauride ophiolites and mélanges and flysch formation together with fold and thrust belt development in the foreland. Significant crustal thickening and development of a dense mafic lower crust beneath the young orogenic belt resulted in foundering of the orogenic root and eventually in partial delamination of the thickened lithosphere. Asthenospheric upwelling around and above the delaminated root provided excess heat and enhanced geothermal gradient that triggered partial melting of the hydrated lithospheric mantle and mafic lower crustal rocks. This melting event produced the high-Al adakitic magmas of the Horoz granitoid (55 Ma) and other similar plutons along the northern edge of the Tauride micro

  17. Distribution and erosion of the Paleozoic tectonic unconformities in the Tarim Basin, Northwest China: Significance for the evolution of paleo-uplifts and tectonic geography during deformation

    NASA Astrophysics Data System (ADS)

    Lin, Changsong; Yang, Haijun; Liu, Jingyan; Rui, Zhifeng; Cai, Zhenzhong; Zhu, Yongfeng

    2012-03-01

    The distribution and erosional features of the Paleozoic major tectonic unconformities in the Tarim Basin, and their genetic relation to the development of paleo-uplifts as well as the evolution of geodynamic settings, are documented in this paper based on the integral analysis of seismic, drilling, and outcrop data. During the Paleozoic, the Tarim Basin underwent three major tectonic deformation stages, which resulted in three angular unconformities and in significant changes in basin geomorphology and paleogeography. The tectonic deformation at the end of the Middle Ordovician was characterized by development of the southern central paleo-uplift, the northern depression, and the southeastern Tangguzibasi depression in the basin. The thickest denudation belts of the unconformity (Tg5-2) are distributed mainly along the thrust structural highs. A stronger deformation event took place at the end of the Late Ordovician and formed a huge uplift along the southwestern and southeastern basin margins and the western part of the Tabei uplift along the northern basin margin, producing an extensive angular unconformity (Tg5) with maximum erosion thickness of 1500-2000 m. This tectonic event resulted in an abrupt change in overall geography of the basin, from a deepwater marine environment at the late stages of the Late Ordovician to a littoral and neritic basin in the Early Silurian. The deformation that occurred at the end of the Middle Devonian was the strongest in the Paleozoic. It generated the most widespread angular unconformity (Tg3) within the basin and led to extensive erosion, with maximum denudation thickness of 3000-5000 m in the northern and northeastern parts of the basin. The topography of the basin during the late Devonian was characterized by a high in the northeast and a low in the southwest, forming an embayment basin opening to the southwest during the Early Devonian to Carboniferous. The transgression in general from southwest to northeast deposited

  18. Determination of the tectonic evolution from fractures, faults, and calcite twins on the southwestern margin of the Indochina Block

    NASA Astrophysics Data System (ADS)

    Arboit, Francesco; Amrouch, Khalid; Collins, Alan S.; King, Rosalind; Morley, Christopher

    2015-08-01

    In polyphase tectonic zones, integrating a study of fault and fracture with calcite twin analysis can determine the evolving paleostress magnitudes and principle stress directions that affected the area. This paper presents the results of the analyses of fractures, striated faults, and calcite twins collected within the Khao Khwang Fold-Thrust Belt in central Thailand (SE Asia). Here we attempt to reconstruct the orientation of the principal stresses that developed during the tectonic evolution of this highly deformed, polyphase orogen. Tectonic data were collected in the Permian carbonates of the Khao Khad Formation of the Saraburi Group, and five successive tectonic stages are determined that are interpreted to have developed before, during, and after, the Triassic Indosinian Orogeny. The first three stages predate the main deformation event: the first stage is interpreted as a pre-Indosinian N-S extensional stage, the second stage described a N-S strike-slip and compressional regime, largely perpendicular to the fold axes of the main structures, while the third stage is associated with an E-W compressional strike-slip phase. A further two stages took place after, or during, the main folding event and correspond to N-S compression and to an E-W composite strike-slip/contractional stage, the latter which is interpreted to represent Cenozoic deformation related to the India-Asia collision.

  19. Structural style and tectonic evolution of the easternmost Gulf of Aden conjugate margins (Socotra - Southern Oman)

    NASA Astrophysics Data System (ADS)

    Nonn, Chloe; Leroy, Sylvie; Castilla, Raymi; de Clarens, Philippe; Lescanne, Marc

    2016-04-01

    Observations from distal rifted margins in present day magma-poor rifted margins led to the discovery of hyperextended crust and exhumed sub-continental mantle. This finding allowed to better figure out how thinning process are accommodate by tectonic structures, forming various crustal domains, as the deformation localized towards the future area of breakup. However, some of the current challenges are about clarifying how factors as oblique kinematic, pre-existing structures and volcanism can control the 3D geometry and crustal architecture of the passive margins? A key to better understand the rifting evolution in its entirety is to study conjugate margins. The gulf of Aden is a young oceanic basin (with a global trend about N75°E) oblique to the divergence (about 30°N), separating Arabia from Somalia of less than 800 km. Thanks to its immerged margins and its thin post-rift sediment cover, the gulf of Aden basin is a natural laboratory to investigate conjugate margins and strain localisation throughout the rift history. In this contribution, we focus our interest on offshore Socotra Island (Yemen) and its conjugate in Southeastern Oman. This area extends from Socotra-Hadbeen (SHFZ) and the eastern Gulf of Aden fault zones (EGAFZ). In the easternmost part of the gulf of Aden, we provide new insights into crustal deformation and emplacement of the new oceanic crust thanks to bathymetric, magnetic, gravimetric data and single-, multi-channel, high speed seismic reflection data collected during Encens-Sheba (2000), Encens (2006) and the more recent Marges-Aden (2012) cruises respectively. The results obtained after compilation of these data, previous geological (field works) and geophysical (receiver functions, Pn-tomography, magnetic anomalies, heat flow) studies on the focused area, allowed us to provide new structural mapping and stratigraphic correlation between onshore and offshore parts of Socotra and Oman margins. We precisely defined and map crustal

  20. Geomorphic evolution of Dehra Dun, NW Himalaya: Tectonics and climatic coupling

    NASA Astrophysics Data System (ADS)

    Sinha, Swati; Sinha, Rajiv

    2016-08-01

    The Dehra Dun is a good example of a piggyback basin formed from the growth of the Siwalik hills. Two large rivers, the Ganga and the Yamuna, and their tributaries deposit a significant part of their sediment load in the Dun before they enter the Gangetic plains. This work documents the geomorphic complexities and landform evolution of the Dehra Dun through geomorphic mapping and chronostratigraphic investigation of the incised fan sections. Lesser Himalayan hills, inner and outer dissected hills, isolated hills, proximal fan, distal fan, dip slope unit, floodplains, and terraces are the major geomorphic units identified in the area. Isolated hills of fan material (IHF), proximal fan (PF), and distal fan (DF) are identified as fan surfaces from north to south of the valley. The OSL based chronology of the fan sediments suggests that the IHF is the oldest fan consisting of debris flow deposits with a maximum age of ~ 43 ka coinciding with the precipitation minima. The proximal fan consisting of sheet flow deposits represents the second phase of aggradation between 34 and 21 ka caused by shifting of deposition locus downstream triggered by high sediment supply that exceeded the transport capacity. The distal fan was formed by braided river deposits during 20-11 ka coinciding with the deglacial period. The IHF, PF and DF surfaces were abandoned by distinct incision phases during ~ 40-35, ~ 20-17, and ~ 11-4 ka respectively. A minor phase of terrace deposition in Dehra Dun was documented during 3-2 ka. Our results thus show that the evolutionary history of the alluvial fans in Dehra Dun was primarily controlled by climatic forcing with tectonics playing a minimum role in terms of providing accommodation space and sediment production.

  1. Exploring the Influence of Ice Temperature in Alpine Glaciers on the Evolution of Longitudinal Valley Profiles

    NASA Astrophysics Data System (ADS)

    Duhnforth, M.; Anderson, R. S.; Colgan, W.

    2012-12-01

    The erosional signature of a glacier is often characterized by a longitudinal valley profile that exhibits a stepped morphology, decreased valley floor slope, and overdeepened basin. Numerical modeling experiments have demonstrated that the evolution of such profiles is highly dependent on ice discharge, and hence subglacial water pressure-dependent sliding speed, as well as the material properties of the underlying bedrock. While there are abundant examples of landscapes that demonstrate the valley profile characteristic of efficient glacial erosion, some highly glaciated mountain ranges such as the Himalayas maintain exceptionally tall peaks. These exceptionally tall peaks may be interpreted as evidence for the absence of efficient glacial erosion. One possible explanation for the absence of efficient glacial erosion is the presence of cold-based glacial conditions. Alternatively, the presence of erosionally resistant bedrock with wide fracture spacing may limit erosion. In temperate glaciers, in which basal ice temperatures are warm, or at the pressure melting point (PMP), sliding and erosion occur whenever and wherever high subglacial water pressures exist. In polythermal glaciers, by contrast, erosion efficiency is strongly modulated by basal ice temperature. Sliding, and hence erosion, is prevented when and where basal ice temperatures are cold, or below the PMP. To date, the influence of spatial and temporal variations in basal ice temperature on the efficiency of glacial erosion over long timescales (>1 Ma) remains largely unexplored. We present numerical model results in which we explore the influence of glacier ice temperature on the longitudinal valley profile that emerges during long-term glacial erosion. We focus on identifying conditions that maintain polythermal glaciers in which the basal ice at high elevations is cold, while the basal ice at lower elevations is at the PMP. These unique conditions limit sliding and erosion to low elevations. In

  2. Simulating the Thermochemical Magmatic and Tectonic Evolution of Venus's Mantle and Lithosphere: Intrusive vs. Extrusive Magmatism

    NASA Astrophysics Data System (ADS)

    Tackley, Paul; Armann, Marina

    2013-04-01

    the purely extrusive magmatism assumed in [1]. Intrusive magmatism warms and weakens the crust, resulting in substantial surface deformation and a thinner crust. This is further enhanced by using a basaltic rheology for the crust instead of assuming the same rheological parameters as for the mantle. Here we quantitatively analyse the resulting surface deformation and other signatures, and compare to observations in order to constrain the likely ratio of intrusive to extrusive magmatism. [1] Armann, M., and P. J. Tackley (2012), Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models, J. Geophys. Res., 117, E12003, doi:10.1029/2012JE004231.

  3. Late Pliocene-Quaternary evolution of outermost hinterland basins of the Northern Apennines (Italy), and their relevance to active tectonics

    NASA Astrophysics Data System (ADS)

    Sani, Federico; Bonini, Marco; Piccardi, Luigi; Vannucci, Gianfranco; Delle Donne, Dario; Benvenuti, Marco; Moratti, Giovanna; Corti, Giacomo; Montanari, Domenico; Sedda, Lorenzo; Tanini, Chiara

    2009-10-01

    We examine the tectonic evolution and structural characteristics of the Quaternary intermontane Mugello, Casentino, and Sansepolcro basins, in the Northern Apennines fold-and-thrust belt. These basins have been classically interpreted to have developed under an extensional regime, and to mark the extension-compression transition. The results of our study have instead allowed framing the formation of these basins into a compressive setting tied to the activity of backthrust faults at their northeastern margin. Syndepositional activity of these structures is manifested by consistent architecture of sediments and outcrop-scale deformation. After this phase, the Mugello and Sansepolcro basins experienced a phase of normal faulting extending from the middle Pleistocene until Present. Basin evolution can be thus basically framed into a two-phase history, with extensional tectonics superposed onto compressional structures. Analysis of morphologic features has revealed the occurrence of fresh fault scarps and interaction of faulting with drainage systems, which have been interpreted as evidence for potential ongoing activity of normal faults. Extensional tectonics is also manifested by recent seismicity, and likely caused the strong historical earthquakes affecting the Mugello and Sansepolcro basins. Qualitative comparison of surface information with depth-converted seismic data suggests the basins to represent discrete subsiding areas within the seismic belt extending along the axial zone of the Apennines. The inferred chronology of deformation and the timing of activity of normal faults have an obvious impact on the elaboration of seismic hazard models.

  4. The Alegre Lineament and its role over the tectonic evolution of the Campos Basin and adjacent continental margin, Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Calegari, Salomão Silva; Neves, Mirna Aparecida; Guadagnin, Felipe; França, George Sand; Vincentelli, Maria Gabriela Castillo

    2016-08-01

    The structural framework and tectonic evolution of the sedimentary basins along the eastern margin of the South American continent are closely associated with the tectonic framework and crustal heterogeneities inherited from the Precambrian basement. However, the role of NW-SE and NNW-SSE structures observed at the outcropping basement in Southeastern Brazil and its impact over the development of those basins have not been closely investigated. In the continental region adjacent to the Campos Basin, we described a geological feature with NNW-SSE orientation, named in this paper as the Alegre Fracture Zone (AFZ), which is observed in the onshore basement and can be projected to the offshore basin. The main goal of this work was to study this structural lineament and its influence on the tectonic evolution of the central portion of the Campos Basin and adjacent mainland. The onshore area was investigated through remote sensing data joint with field observations, and the offshore area was studied through the interpretation of 2-D seismic data calibrated by geophysical well logs. We concluded that the AFZ occurs in both onshore and offshore as a brittle deformation zone formed by multiple sets of fractures that originated in the Cambrian and were reactivated mainly as normal faults during the rift phase and in the Cenozoic. In the Campos Basin, the AFZ delimitates the western side of the Corvina-Parati Low, composing a complex fault system with the NE-SW faults and the NW-SE transfer faults.

  5. Structural setting and tectonic evolution of the Apennine Units of northern Calabria

    NASA Astrophysics Data System (ADS)

    Iannace, Alessandro; Bonardi, Glauco; D'Errico, Marco; Mazzoli, Stefano; Perrone, Vincenzo; Vitale, Stefano

    2005-12-01

    A new structural-stratigraphic synthesis of the Apennine units of northern Calabria is presented. The Meso-Cenozoic successions are grouped into two tectonic units, named Pollino-Ciagola Unit (PCU) and Lungro-Verbicaro Unit (LVU), comprising terrains formerly attributed to five different tectonic units. Fe sbnd Mg carpholite and blue amphibole record HP-LT metamorphism in the LVU, followed by progressive decompression leading to final greenschist facies re-equilibration during dominantly extensional deformation. Final tectonic emplacement of the LVU over the PCU post-dated the metamorphism of the LVU and was accompanied by intense ductile deformation along zones of strain localisation in footwall rocks. All of the units were later affected by folding and minor thrusting during subsequent Apennine tectonics. To cite this article: A. Iannace et al., C. R. Geoscience 337 (2005).

  6. Apollo 17: One giant step toward understanding the tectonic evolution of the Moon

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.

    1992-01-01

    Our present understanding of the tectonic history of the Moon has been shaped in large measure by the Apollo Program, and particularly the Apollo 17 Mission. I attempt to summarize some of the interpretations that have emerged since Apollo 17, focusing on some of the problems and uncertainties that remain to stimulate future exploration of the Moon. The topics covered include: (1) Taurus-Littrow Valley; (2) origin of mare ridges; and (3) nature and timing of tectonic rille formation.

  7. Influence of substrate tectonic heritage on the evolution of composite volcanoes: Predicting sites of flank eruption, lateral collapse, and erosion

    NASA Astrophysics Data System (ADS)

    Tibaldi, Alessandro; Corazzato, Claudia; Kozhurin, Andrey; Lagmay, Alfredo F. M.; Pasquarè, Federico A.; Ponomareva, Vera V.; Rust, Derek; Tormey, Daniel; Vezzoli, Luigina

    2008-04-01

    This paper aims to aid understanding of the complicated interplay between construction and destruction of volcanoes, with an emphasis on the role of substrate tectonic heritage in controlling magma conduit geometry, lateral collapse, landslides, and preferential erosion pathways. The influence of basement structure on the development of six composite volcanoes located in different geodynamic/geological environments is described: Stromboli (Italy), in an island arc extensional tectonic setting, Ollagüe (Bolivia-Chile) in a cordilleran extensional setting, Kizimen (Russia) in a transtensional setting, Pinatubo (Philippines) in a transcurrent setting, Planchon (Chile) in a compressional cordilleran setting, and Mt. Etna (Italy) in a complex tectonic boundary setting. Analogue and numerical modelling results are used to enhance understanding of processes exemplified by these volcanic centres. We provide a comprehensive overview of this topic by considering a great deal of relevant, recently published studies and combine these with the presentation of new results, in order to contribute to the discussion on substrate tectonics and its control on volcano evolution. The results show that magma conduits in volcanic rift zones can be geometrically controlled by the regional tectonic stress field. Rift zones produce a lateral magma push that controls the direction of lateral collapse and can also trigger collapse. Once lateral collapse occurs, the resulting debuttressing produces a reorganization of the shallow-level magma migration pathways towards the collapse depression. Subsequent landslides and erosion tend to localize along rift zones. If a zone of weakness underlies a volcano, long-term creep can occur, deforming a large sector of the cone. This deformation can trigger landslides that propagate along the destabilized flank axis. In the absence of a rift zone, normal and transcurrent faults propagating from the substrate through the volcano can induce flank

  8. 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.

  9. The role of the Anaxagoras Mountain in the Miocene to Recent tectonic evolution of the eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Colbourne, Mark; Hall, Jeremy; Aksu, Ali; Çifçi, Günay

    2014-05-01

    The Anaximander Mountains are one of the many enigmatic structures situated along the morphologically and structurally complicated junction between the Hellenic and Cyprus Arcs, in the eastern Mediterranean. Interpretation of ~750 km of marine multi-channel seismic reflection data show that the present day Anaximander Mountains underwent several distinct phases of tectonic activity since Miocene. During the mid-late Miocene, a protracted, contractional tectonic regime produced the east-west trending, south-verging fold-thrust belt observed in the area. The Messinian was a period of relatively low tectonic activity, and is marked by the deposition of an evaporite layer. This phase lasted until the latest Miocene - earliest Pliocene, when a major erosional event associated with the Messinian salinity crisis occurred. Beginning in the early-mid Pliocene-Quaternary a transpressional and rotational tectonic regime prevailed over the area. The Anaximander Mountain (sensu stricto) and Anaximenes Mountain developed in the Pliocene-Quaternary associated with the reactivation, uplift and rotation of a linked, thick skinned pre-Messinian imbricate thrust fan. Back thrusting in the region accentuated the morphology of these mountains. The Anaxagoras Mountain differs both lithologically and morphologically from the Anaximander Mountain (sensu stricto) and the Anaximenes Mountain. It is probably developed associated with the emplacement of the ophiolitic Antalya Nappe Complex. Faulting in the Anaxagoras region is characterized by southwest striking thrust and/or oblique thrust faults. Due to the similarities in morphology between the Isparta Angle of southwestern Turkey and the Anaximander Mountains (sensu lato), it is hypothesized that the tectonic evolution of the two regions are similar in nature. The Anaximander Mountains (sensu lato) can thus be considered the offshore replication of the Isparta Angle, produced by similar mechanisms, but being of a younger age.

  10. The influence of surface and tectonic processes on landscape evolution of the Iberian Chain (Spain): Quantitative geomorphological analysis and geochronology

    NASA Astrophysics Data System (ADS)

    Scotti, V. N.; Molin, P.; Faccenna, C.; Soligo, M.; Casas-Sainz, A.

    2014-02-01

    In tectonically active areas, the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes. We investigated the recent landscape evolution of the Iberian Chain (NE Spain), an intraplate thrust-belt formed in Cenozoic times and characterized by a dome-shaped topography. In its central sector the landscape is dominated by low relief surfaces, Late Neogene (?) in age, presently standing at an average altitude of 1300 m. A recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape. In this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters, focusing on topography (map of local relief, swath profiles) and hydrography (basin hypsometric curve and integral, basin asymmetry factor, river longitudinal profiles and relative indices), and using SRTM DEM. The results of morphometric analysis have been coupled with radiometric uranium-series dating of calcareous tufas lying on fluvial strath terraces. The obtained ages allow the estimation of incision rate along the High Tajo and Martín rivers. Our results indicate that uplift and rock-type erodibility are the main factors influencing landscape evolution of the study area. The incision rates are very similar throughout the central sector of the range, indicating that, despite subtle local variation, the rivers are responding to a main tectonic input: the regional uplift. In conclusion, the Iberian Chain landscape is in a transient state in response to a recent dome-like uplift. Indeed, the fluvial processes that weakly incised this landscape at a rate of ~ 0.6 mm/yr are approaching a radial pattern. On the basis of geological and geomorphic constraints, we hypothesize that the uplift started around or after 3 Ma.

  11. Metamorphic and tectonic evolution of the Greater Himalayan Crystalline Complex in Nyalam region, south Tibet

    NASA Astrophysics Data System (ADS)

    Wang, Jia-Min; Zhang, Jin-Jiang; Rubatto, Daniela

    2016-04-01

    Recent studies evoke dispute whether the Himalayan metamorphic core - Greater Himalayan Crystalline Complex (GHC) - was exhumed as a lateral crustal flow or a critical taper wedge during the India-Asia collision. This contribution investigated the evolution of the GHC in the Nyalam region, south Tibet, with comprehensive studies on structural kinematics, metamorphic petrology and geochronology. The GHC in the Nyalam region can be divided into the lower and upper GHC. Phase equilibria modelling and conventional thermobarometric results show that peak temperature conditions are lower in the lower GHC (~660-700°C) and higher in the upper GHC (~740-780°C), whereas corresponding pressure conditions at peak-T decrease from ~9-13 kbar to ~4 kbar northward. Monazite, zircon and rutile U-Pb dating results reveal two distinct blocks within the GHC of the Nyalam region. The upper GHC underwent higher degree of partial melting (15-25%, via muscovite dehydration melting) that initiated at ~32 Ma, peaked at ~29 Ma to 25 Ma, possibly ended at ~20 Ma. The lower GHC underwent lower degree of melting (0-10%) that lasted from 19 to 16 Ma, which was produced mainly via H2O-saturated melting. At different times, both the upper and lower blocks underwent initial slow cooling (35 ± 8 and 10 ± 5°C/Myr, respectively) and subsequent rapid cooling (120 ± 40°C/Myr). The established timescale of metamorphism suggests that high-temperature metamorphism within the GHC lasted a long duration (~15 Myr), whereas duration of partial melting lasted for ~3 Myr in the lower GHC and lasted for 7-12 Myr in the upper GHC. The documented diachronous metamorphism and discontinuity of peak P-T conditions implies the presence of the Nyalam Thrust in the study area. This thrust is probably connected to the other thrusts in Nepal and Sikkim Himalaya, which extends over ~800 km and is named the "High Himalayan Thrust". Timing of activity along this thrust is at ~25-16 Ma, which is coeval with active

  12. Rift architecture and evolution: The Sirt Basin, Libya: The influence of basement fabrics and oblique tectonics

    NASA Astrophysics Data System (ADS)

    Abdunaser, K. M.; McCaffrey, K. J. W.

    2014-12-01

    zones and adjoining highs. Late Eocene rocks exposed in the western part of the basin exhibit a complex network of branching segmented normal and strike-slip faults, generally with a NNW-SSE structural orientations. Many surface structural features have been interpreted from satellite images which confirm sinistral strike-slip kinematics. Relay ramp structures, numerous elongate asymmetric synclines associated with shallow west limbs and steeper dipping east limbs are developed in the hangingwalls adjacent to west downthrowing normal faults. These structural patterns reflect Cretaceous/Tertiary extensional tectonics with additional control by underlying pre-existing Pan-African basement fabrics and ENE-WSW trending Hercynian structures. We relate the Sirt Basin rift development as exemplified in our study area to the break-up of Gondwana represented by the structural evolution of the West-Central African rift system, and the South and Central Atlantic, the Tethys and the Indian Oceans.

  13. A decade of aerogeophysical exploration provides new perspectives on crustal architecture and tectonic evolution in Antarctica

    NASA Astrophysics Data System (ADS)

    Ferraccioli, Fausto

    2013-04-01

    Antarctica stands out as the least understood continent on Earth, despite being a keystone within the Gondwana and Rodinia supercontinents. Here I review several major results from a decade of intense aerogeophysical exploration that significantly advance our knowledge of Antarctica by unveiling crustal architecture and tectonic evolution, in particular in the interior of the continent. In western Dronning Maud, high-resolution aerogeophysical data have enabled analyses of the subglacial Jutulstraumen rift that heralded Gondwana break up, and also identified remnants of a Grenvillian-age (ca 1.1. Ga) igneous province and magmatic arc along its flanks. Further in the interior of East Antarctica, a mosaic of largely unknown Precambrian provinces has recently been recognised from aeromagnetic and satellite magnetic patterns, coupled with new models of crustal thickness and lithospheric strength (Ferraccioli et al., 2011, Nature). A major suture is marked by a 20 km step in Moho depth and a major change in crustal density and effective elastic thickness and separates the Archean Ruker Province from an inferred Meso-Paleoproterozoic Gamburtsev Province. Geophysical interpretations favour the hypothesis for Grenville-age accretion and collision of these provinces linked to Rodinia assembly and/or older Paleoproteroic events related to Nuna/Columbia assembly. Rather that new lithosphere formation in late Pan-African times, this interpretation favours the hypothesis for reactivation of the proposed suture in a more intraplate setting. Independently of the hotly debated timing of the assembly of interior East Antarctica, 3D models of effective elastic thickness indicate that the inherited mosaic of Precambrian provinces clearly influenced the location of the newly identified East Antarctic Rift System, which extends for 3,500 km from India to the Recovery Highlands. Continental rifting has been modelled as a key tectonic trigger for uplift of the Gamburtsev Subglacial

  14. Quantifying Tectonic Controls on Regional Cenozoic Surface Evolution in the Eastern Lhasa Block

    NASA Astrophysics Data System (ADS)

    Schmidt, J. L.; Zeitler, P. K.; Shuster, D. L.; Tremblay, M. M.; Harrison, M.

    2013-12-01

    and their frequent coincidence with major N-S trending rifts suggests a coupling of plateau-scale tectonics and local-scale erosional patterns. We propose that a change in river base level drove Jiacha knickpoint formation and subsequent upstream migration and that its present-day spatial correlation with the Nari Yun Chu Rift indicates that additional headward cutting is accommodated by motion on the rift, thereby pinning the knickpoint and preventing further incision of the Tsangpo and dissection of the Tibetan plateau. Preliminary geomorphic analysis of the Tsangpo and Nyang rivers and their tributaries including SL-indices and slope-area plots indicates that a set of ~3500 m elevation knickpoints remnant of the migration of the Jiacha knickpoint exists through the drainage network. Additional 4He/3He apatite analyses are in progress to determine the time-temperature evolution of bedrock samples downstream of the knickpoint to constrain the timing of gorge incision along the Yarlung Tsangpo, testing the hypothesis that if the knickpoint evolved by upstream migration samples downstream of the knickpoint, the onset of rapid cooling should be positively correlated with distance from the knickpoint.

  15. Quaternary landscape evolution of tectonically active intermontane basins: the case of the Middle Aterno River Valley (Abruzzo, Central Italy)

    NASA Astrophysics Data System (ADS)

    Falcucci, Emanuela; Gori, Stefano; Della Seta, Marta; Fubelli, Giandomenico; Fredi, Paola

    2014-05-01

    The Middle Aterno River Valley is characterised by different Quaternary tectonic depressions localised along the present course of the Aterno River (Central Apennine) .This valley includes the L'Aquila and Paganica-Castelnuovo-San Demetrio tectonic basins, to the North, the Middle Aterno Valley and the Subequana tectonic basin, to the South. The aim of this contribution is to improve the knowledge about the Quaternary geomorphological and tectonic evolution of this portion of the Apennine chain. A synchronous lacustrine depositional phase is recognized in all these basins and attributed to the Early Pleistocene by Falcucci et al. (2012). At that time, this sector of the chain showed four distinct closed basins, hydrologically separated from each other and from the Sulmona depression. This depression, actually a tectonic basin too, was localized South of the Middle Aterno River Valley and it was drained by an endorheic hydrographic network. The formation of these basins was due to the activity of different fault systems, namely the Upper Aterno River Valley-Paganica system and San Pio delle Camere fault, to the North, and the Middle Aterno River Valley-Subequana Valley fault system to the South. These tectonic structures were responsible for the origin of local depocentres inside the depressions which hosted the lacustrine basins. Ongoing surveys in the uppermost sectors of the Middle Aterno River Valley revealed the presence of sub-horizontal erosional surfaces that are carved onto the carbonate bedrock and suspended several hundreds of metres over the present thalweg. Gently dipping slope breccias referred to the Early Pleistocene rest on these surfaces, thus suggesting the presence of an ancient low-gradient landscape adjusting to the local base level.. Subsequently, this ancient low relief landscape underwent a strong erosional phase during the Middle Pleistocene. This erosional phase is testified by the occurrence of valley entrenchment and of coeval fluvial

  16. The Qartaba Anticline (central Mount Lebanon): Implications for the tectonic evolution of onshore Lebanon

    NASA Astrophysics Data System (ADS)

    Asmar, Chloe; Grasemann, Bernhard; Nader, Fadi; Tari, Gabor

    2013-04-01

    . In this study, contours were digitized from available maps as well as stratigraphic and structural cross sections. Dip/strike measurements taken in the field combined with measurements derived from high-resolution satellite images were also utilized in the digitized maps. The new three dimensional structural model of the Qartaba Anticline contains important information about the subsurface geology and features susbtantial implications for the tectonic evolution of the broader area in Lebanon (part of eastern margin of the Levant Basin).

  17. Tectonic Evolution of the Banda Arc-Continent Collision in the Timor Region

    NASA Astrophysics Data System (ADS)

    Harris, R. A.

    2011-12-01

    Recent detailed studies of the active Banda arc-continent collision reveal many new features about its tectonic evolution, such as (1) when collision initiated, (2) conditions and age of metamorphism, (3) timing of island emergence and exhumation, (4) how the arc is affected by collision, (5) differences between rock and surface uplift rates, (6) the temporal distribution of strain and (7) natural hazards. (1) The youngest Australian continental margin material incorporated into the Banda orogen is 7-8 Ma in East Timor and 6 Ma in West Timor. (2) Collision-related metamorphic rocks in East Timor yield max. temperatures of 850 °C and pressures of 12 kb. The age of the metamorphism is constrained by zircon U/Pb ages of 6.7 Ma. (3) Island emergence and erosional exhumation is constrained by foraminifera depth vs. age estimates of the transition from deep marine chalk to distal turbidite deposition at 4.2 Ma in East Timor and younger to the east and west. Exhumation of metamorphic rocks is constrained by amphibole with Ar/Ar cooling ages of ~6 Ma (~525°C), zircons with U/He ages of 4.5 Ma (215°C), and apatite with U/He ages of 3.5 Ma (90°C). Younger exhumation ages are found to the south. (4) Contamination of the volcanic arc by subducted continental material is first detected in eroded arc islands near East Timor at 5 Ma. The age of contamination youngs both east and west in less eroded, active arc islands. The main arc edifice north of East Timor is abandoned at 1-3 Ma and is shifted 30 km to the north by the Wetar backarc thrust. A new volcanic center emerges further north. (5) Coral terraces encrust the rising islands and yield highly variable uplift rates, with some as high as 1.5 mm/a. The highest rates correspond with active thrust faults and diapirs. Rock uplift rates associated with exhumation of the schist belt are as high as 8 mm/a. (6) GPS velocities in the most advanced part of the collision (central Timor) show that 70% of the 70 mm/a convergence

  18. Tectonic Evolution of Tarim Basin in Cambrian-Ordovician and the Implication for Reservoir Development, NW China

    NASA Astrophysics Data System (ADS)

    Yinglu, Pan; Bingsong, Yu

    2015-04-01

    In order to search after the control of regional tectonic evolution of Tarim basin on the inside distribution of sedimentary facies and reservoir development, this paper, based on the research of plate-tectonic evolution of Tarim basin, conducts an in-depth analysis on the basin's inside sedimentary response to the Eopaleozoic regional geodynamic reversion from extension to convergence around Tarim plate, and concludes that the regional geodynamic environment of surrounding areas closely contributes to the formation and evolution of paleo-uplifts, differentiation of sedimentary facies in platform, distribution of high-energy reef and bank facies belts, conversion of sedimentary base level from fall to rise, obvious change of lithology from dolomite to limestone, and formation of several unconformity surfaces in Ordovician System in the basin. A series of sedimentary responses in the basin are controlled by the regional dynamic setting, which not only controls the distribution of reservoirs in reef and bank facies but also restricts the development and distribution of karst reservoirs controlled by the unconformity surfaces. This offers the macro geological evidences for us to further analyze and evaluate the distribution of favorable reservoirs.

  19. Tectonic evolution of Tarim basin in Cambrian-Ordovician and its implication for reservoir development, NW China

    NASA Astrophysics Data System (ADS)

    Bingsong, Yu; Zhuang, Ruan; Cong, Zhang; Yinglu, Pan; Changsong, Lin; Lidong, Wang

    2016-03-01

    In order to find the impact of regional tectonic evolution of Tarim basin on the inside distribution of sedimentary facies and reservoir development, this paper, based on the research of plate-tectonic evolution of Tarim basin, conducts an in-depth analysis on the basin's inside sedimentary response to the Eopaleozoic regional geodynamic reversion from extension to convergence around Tarim plate, and concludes that the regional geodynamic environment of surrounding areas closely contributes to the formation and evolution of paleo-uplifts, differentiation of sedimentary facies in platform, distribution of high-energy reef and bank facies belts, conversion of sedimentary base level from fall to rise, obvious change of lithology from dolomite to limestone, and formation of several unconformity surfaces in Ordovician system in the basin. A series of sedimentary responses in the basin are controlled by regional dynamic setting, which not only controls the distribution of reservoirs in reef and bank facies but also restricts the development and distribution of karst reservoirs controlled by the unconformity surfaces. This offers the macro geological evidences for us to further analyze and evaluate the distribution of favorable reservoirs.

  20. Tectonic-sedimentary evolution of the eastern Brazilian marginal basins: Implications in their petroleum systems

    SciTech Connect

    Francisco, N.F.; Azambuja, N.C.; Mello, M.R. )

    1993-02-01

    A geological survey of eastern Brazilian marginal basins using sedimentological, tectonic and geochemical data has been carried out. The almost 4000 km long set of basins can be classified as component of a typical divergent, mature Atlantic-continental margin. Based on their tectonic-sedimentary sequence, they can be linked to a single evolutionary history, which can be divided in three main stages: pre-rift, rift, and drift. The integration of all data allowed the characterization of two major petroleum systems that represent about 90% of the known Brazilian hydrocarbons reserves: (1) the rift (Early Cretaceous) and the drift (Late Cretaceous-Paleogene). With respect to the oil-in-place volume and production, the most significant one is the drift system associated with the siliciclastic deep water turbidites reservoirs deposited in bathyal environments. Such reservoirs are clearly controlled by a favorable relationship of stratigraphic and tectonic settings.

  1. Topography, surface properties, and tectonic evolution. [of Venus and comparison with earth

    NASA Technical Reports Server (NTRS)

    Mcgill, G. E.; Warner, J. L.; Malin, M. C.; Arvidson, R. E.; Eliason, E.; Nozette, S.; Reasenberg, R. D.

    1983-01-01

    Differences in atmospheric composition, atmospheric and lithospheric temperature, and perhaps mantle composition, suggest that the rock cycle on Venus is not similar to the earth's. While radar data are not consistent with a thick, widespread and porous regolith like that of the moon, wind-transported regolith could be cemented into sedimentary rock that would be indistinguishable from other rocks in radar returns. The elevation spectrum of Venus is strongly unimodal, in contrast to the earth. Most topographic features of Venus remain enigmatic. Two types of tectonic model are proposed: a lithosphere too thick or buoyant to participate in convective flow, and a lithosphere which, in participating in convective flow, implies the existence of plate tectonics. Features consistent with earth-like plate tectonics have not been recognized.

  2. Geophysical and seismo-tectonic evolution in Dahshure area, SW Cairo-Egypt

    NASA Astrophysics Data System (ADS)

    Mekkawi, Mahmoud; Abdel Aziz, Khiry; Mohamed, Abuela; Elbuieb, Mustafa

    2016-04-01

    The study of seismic hazard assessment around greater Cairo-Egypt is very important due to condense population (more than 20 million) in that area. Although, Egypt is characterized by low seismic activity. The seismotectonic zones and high activity are occurred along the Gulf of Aqaba-Dead Sea transform, the Northern Red Sea triple junction point, Aswan, Dahshur, and Cairo-Suez District . In this study, earthquake catalogue (up to 2015) of all seismo-tectonic zones in Egypt and its surroundings are used. Beside the seismicity analysis, gravity and magnetic maps of Dahshur area are analyses for tracing active subsurface faults that are responsible of earthquakes activity. The surface geology and subsurface faults are used to evaluate the tectonic framework in the area under study. Also, The seismicity maps, focal depths and seismic hazards values are calculated. Keyword: Seismo-tectonic, seismic hazards assessment, potential fields, Greater Cairo-Egypt

  3. Tectonic Geomorphology in the Laboratory: Evolution of landscape along an active thrust, normal and strike-slip fault

    NASA Astrophysics Data System (ADS)

    Graveleau, Fabien; Strak, Vincent; Dominguez, Stéphane; Malavieille, Jacques; Chatton, Marina; Manighetti, Isabelle; Petit, Carole

    2015-04-01

    Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. We present here results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension and strike-slip. Experimental results outline first that experimental morphologies evolve significantly at a short timescale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike-slip setting, the complex morphology of the wrench zone, composed of

  4. Tectonic evolution of Bell Regio, Venus: Regional stress, lithospheric flexure, and edifice stresses

    NASA Astrophysics Data System (ADS)

    Rogers, Patricia G.; Zuber, Maria T.

    1998-07-01

    In order to understand the relationship between volcanic and tectonic processes and the stress state in the lithosphere of Venus, we analyzed the stress environments and resulting tectonic features associated with the major volcanic edifices in Bell Regio, using Magellan synthetic aperture radar (SAR) images and altimeter measurements of topography. The major volcanoes of Bell Regio, Tepev Mons and Nyx Mons, exhibit tectonic characteristics that are unique relative to other volcanic edifices on Venus. The most prominent distinction is the lack of large rift zones within the overall highland uplift, which characterize many other highland rises on Venus. Also, previous studies have determined that many large Venus volcanoes exhibit radial tectonic structures on their flanks but generally lack the circumferential graben which surround volcanoes on Earth and Mars. Tepev and Nyx Montes exhibit both the radial tectonic features associated with other Venusian edifices and numerous concentric graben. Nyx Mons implies a more distributed magmatic system by its broad shape, radial chains of pit craters, and expansive flow fields, whereas Tepev Mons is a more centralized volcanic system, with limited associated long flows. We investigate the regional stresses associated with Bell Regio and structural features believed to be a consequence of lithospheric flexure due to volcanic loading, modeling both Nyx Mons and Tepev Mons as axisymmetric loads with Gaussian mass distributions on an elastic plate. The relationship between the tectonic features surrounding Tepev Mons and stresses associated with magma chamber inflation are also examined through finite element analysis. Using topography data to model the shape of the volcano, we determine that a horizontally ellipsoidal or tabular reservoir at a range of depths from approximately 20 to 40 km can satisfy the locations of graben formation observed in Magellan images. These results imply a shift in volcanic style within Bell Regio

  5. Plate Tectonics: Geodynamic models of evolution of oil and gas bearing basins of Kazakhstan

    SciTech Connect

    Zholtayev, G. )

    1994-07-01

    Five types of sedimentary basins in Kazakhstan have been recognized by using plate tectonics to reinterpret geological and geophysical data: (1) intracontinental, central pre-Caspian, above rift, south pre-Caspian; (2) passive margin, east pre-Caspian; (3) back-arc, Turgan and Sir-Daria; (4) intra-arc, north Kisil-Koum, interior, Tengis and Chu-Sarisiu; and (5) marginal, north Usturt. Paleozoic history of these basins was connected with the spreading and collision of two lithospheric plates: east European and Kazakhstanian, which were separated by the paleo-Ural Ocean. Different tectonic positions of sedimentary basins were the reason for their different oil and gas potential.

  6. Thermal and tectonic evolution of the central and southern Appalachians: evidence from distribution, age, and origin of granitic rocks

    SciTech Connect

    Sinha, A.K.; Guy, R.; Hund, E.; Tamburro, E.

    1985-01-01

    The distribution and resolution of thermal events and associated igneous activity can discriminate between tectonic processes that form orogenic terrains, i.e., accretion of terranes, overthrusting of terranes versus thrust stacking within terranes. Reinterpretation of regional tectonics (Higgins et al., 1984) coupled with the authors interpretation of the age, origin, and distribution of granitic rocks suggest a very different mechanism for the evolution of the central and southern Appalachian orogenic belt. The Cambro-Ordovician magmatic arc (weakly bimodal) separated from the North American Margin by a Back arc basin, was thrust over the North American plate margin during the middle Ordovician. The Avalon terrane (Little River allochthon of Higgins et al., 1984) arrived during the late Silurian - but unlike earlier models that require subduction zone related with its arrival, the authors postulate strike-slip tectonics. The gabbro-diorite-syenite association in the Charlotte belt (Macon melange of Higgins) is probably related to grabens associated with the strike-slip accretion. Rocks of similar age (Siluro-Devonian) in the present day Blue Ridge and Inner Piedmont blocks are related to decompressional melting after the Ordovician thrusting. The high pressure metamorphism and associated melting show a range in ages indicating variations in uplift rates or thickness of the crust caused by the initial overthrusting, and do not require a discrete subduction or orogenic event. The Permo-Carboniferous igneous activity, and associated uplift and thrusting with a strike-slip component are related to oblique subduction and post-subduction collision processes.

  7. Cenozoic paleoaltimetry of the SE margin of the Tibetan Plateau: Constraints on the tectonic evolution of the region

    NASA Astrophysics Data System (ADS)

    Li, Shanying; Currie, Brian S.; Rowley, David B.; Ingalls, Miquela

    2015-12-01

    An improved understanding of the elevation history of the Tibetan Plateau is crucial in discriminating among the various tectonic models for the evolution of the India-Asia continental collision. We reconstruct the paleoelevation history for three Cenozoic sedimentary basins from SE Tibet and Yunnan, China, to provide more constraints on the tectonic processes for raising the SE margin of the Tibetan Plateau. The results presented here, together with those of previous studies, indicate that (1) the plateau margin of NW Yunnan was near its elevation (˜ 2.6 km) by the latest middle Eocene (˜ 40 Ma); (2) the plateau margin of SE Yunnan reached its current elevation (˜ 1.6 km) by the middle Miocene (˜ 13 Ma). Interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well-documented surface geology. We conclude that high landscape (˜ 2.6 km elevation) in NW Yunnan may represent the remnants of the Eocene Tibetan plateau that originally formed in the northeastern Qiangtang Block by crustal thickening associated with the India-Asia continental collision. The near-modern elevation of SE Yunnan since ˜ 13 Ma probably reflects the initiation of lower crustal flow in this area by at least that time. Collectively, our paleoaltimetric interpretations disagree with previously proposed models of middle Miocene to Pliocene crustal flow acting as a sole tectonic process for raising the SE margin of the plateau, but support a protracted history of surface uplift that most likely involved crustal thickening during the Eocene, southeastward extrusion of a portion of Eocene Tibetan plateau during the Oligocene to early Miocene, and lower crustal flow beneath this region since at least the early Miocene.

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

    SciTech Connect

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

    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 Gulf 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.

  9. The inverted Lamar sub-basin, Lake Maracaibo, Venezuela: Tectonic evolution and hydrocarbon habitat

    SciTech Connect

    Arminio, J.F.; Growcott, A.M.

    1996-08-01

    In the central part of the Maracaibo basin, integration of recently acquired 3-D seismic and existing geological data has led to the definition of the Lamar sub-basin as an array of partially inverted half grabens which formed during Late Cretaceous and Early to Middle Eocene times as a result of transtensional episodes along older rift structures. This integration exercise has also led to the addition of new reserves in a mature oil province. Six major tectonic phases can be distinguished: (a.) Extension of the existing Paleozoic substrate during Jurassic rifting; (b.) Passive margin tectonic quiescence from Middle to Late Cretaceous; (c.) Paleocene uplift and erosion; (d.) Eocene transtension along reactivated Jurassic lineaments; (e.) Late Eocene to Mid Miocene inversion; (f.) Late Miocene to Recent post inversion and regional tilt. Distinctive tectonically induced unconformities within the Eocene sedimentary fill imply tectonic overprint rather than eustatic controls. The Eocene extensional structures were inverted in a selective manner depending upon their orientation relative to the dominant compressional vector. This in turn resulted in significant hydrocarbon re-migration and a rather complex fluid distribution throughout the area.

  10. Early Diagenesis of Lower Pliensbachian Sediments from the Algarve Basin (Portugal): Characterisation and Relation with Tectonic Evolution

    NASA Astrophysics Data System (ADS)

    Ribeiro, Carlos; Terrinha, Pedro; Rosario Azevedo, M.; Ouajhain, Brahim

    2010-05-01

    The Lower Jurassic (Lower Pliensbachian) sedimentary record of the western end of the Algarve Basin (Portugal) is made of decimetric thick layers of limestone and dolomitized limestone with chert nodules and inter-layered chert beds. Most of the observable lithologies are the product of an early diagenetic evolution and the original lithological content of the formation included limestones, marls and calciclastic limestones. In this area the sedimentation was controlled by the tectonic stretching responsible for the evolution of the Algarve Basin, as well as by short-lived events of tectonic inversion. These episodes of tectonic inversion were responsible for the some uplift with the development of unconformities, sometimes with erosional surfaces separating the different sedimentary packages. The early diagenesis affecting the Lower Pliensbachian sediments is characterized by: (i) a mechanical event controlled by the syn-sedimentary stretching, responsible for the development of calciclastic dikes and nodules alignements; (ii) the substitution of the carbonates from the most permeable calciclastic limestone layers by silica, leading to the development of the observed cherts; (iii) the dolomitization of the preserved limestones; and (iv) the infilling of joints and normal fault planes by silica-rich fluids leading to the development of quartz veins. This set of diagenetic transformations took place before the Upper Pliensbachian which lacks the evidences of their occurrence. The whole-rock geochemical data of the carbonate and siliceous sediments of the Lower Pliensbachian revealed some affinities between both lithological types namely the lack of Ce anomalies and the presence of La anomalies in the REE patterns of all samples. The similarities between the carbonate lithologies which diagenetic evolution is marked by the replacement of calcite by dolomite and the siliceous sediments derived from the replacement of calcite by quartz establish a chemical connection

  11. Complex basin evolution in the Gökova Gulf region: implications on the Late Cenozoic tectonics of southwest Turkey

    NASA Astrophysics Data System (ADS)

    Gürer, Ömer Feyzi; Sanğu, Ercan; Özburan, Muzaffer; Gürbüz, Alper; Sarica-Filoreau, Nuran

    2013-11-01

    Southwestern Turkey experienced a transition from crustal shortening to extension during Late Cenozoic, and evidence of this was recorded in four distinct basin types in the Muğla-Gökova Gulf region. During the Oligocene-Early Miocene, the upper slices of the southerly moving Lycian Nappes turned into north-dipping normal faults due to the acceleration of gravity. The Kale-Tavas Basin developed as a piggyback basin along the fault plane on hanging wall blocks of these normal faults. During Middle Miocene, a shift had occurred from local extension to N-S compression/transpression, during which sediments in the Eskihisar-Tınaz Basins were deposited in pull-apart regions of the Menderes Massif cover units, where nappe slices were already eroded. During the Late Miocene-Pliocene, a hiatus occurred from previous compressional/transpressional tectonism along intermountain basins and Yatağan Basin fills were deposited on Menderes Massif, Lycian Nappes, and on top of Oligo-Miocene sediments. Plio-Quaternary marked the activation of N-S extension and the development of the E-W-trending Muğla-Gökova Grabens, co-genetic equivalents of which are common throughout western Anatolia. Thus, the tectonic evolution of the western Anotolia during late Cenozoic was shifting from compressional to extensional with a relaxation period, suggesting a non-uniform evolution.

  12. Tectonic and stratigraphic evolution of the Tjornes Fracture Zone, northern Iceland

    NASA Astrophysics Data System (ADS)

    Fenwick, Rebecca Ann

    Rifted margins and plate boundary tectonics dominate the surface morphology of the ocean basins, in particular the processes that occur in rifted margins and transform fault zones remain poorly understood. Northern Iceland is an ideal area to investigate distributed extensional deformation and the evolution of transform fault zones because of the repeated rift jumps eastward back to the Iceland plume. Studying this continually evolving system allows us the opportunity to understand better the complicated nature of evolving transform faults. Using CHIRP subbottom, MCS, multibeam bathymetry, side-scan sonar, and towcam images we imaged the three basins that comprise the Tjornes Fracture Zone: Eyjafjordur, Skjalfandi, and Oxarfjordur bays. In the Tjornes Fracture Zone, there appears to have been an initial stage of distributed extension accommodation: graben faulting with normal faults accommodating the extension between the newly formed North Volcanic Zone and the southern extent of the Kolbeinsey Ridge. This appears to have been followed and overprinted by more traditional oceanic transform faulting, with the development of the Husavik-Flatey Fault and then the Grimsey Lineament that was subsequently formed with the northward propagation of the North Volcanic Zone. Pockmarks are increasingly being commonly identified along margins, and our data allowed us to investigate controls over their occurrence, morphology and location in Skjalfandi Bay. In this area they have been observed in a band 15-22 km offshore, and in along the Husavik-Flatey fault scarp near shore. Pockmarks along the fault scarp are easily attributed to fluid migration along the fault plan from depth, and we observed an increasing biota density and abundance within these pockmarks. This is likely due to either an increased nutrient flux from depth or increased detrital deposition within the pockmarks. Offshore pockmarks occur in a well-defined band determined by the interplay of the distribution of

  13. Gravity sliding in basinal setting, a surficial record of tectonic and geodynamic evolution; examples from the southern W. Alps and their foreland

    NASA Astrophysics Data System (ADS)

    Dumont, T.; Franzi, V.; Matthews, S. J.

    2012-04-01

    The occurrence of large-scale submarine landslides, although commonly observed in the present basins, is only exceptionally mentioned in the Alpine orogen and foreland. The southern part of the Western Alpine arc and the SE basin of France provide examples of such features which could be related with particular geodynamic events, in relation with the motion of the Iberian and Adriatic microplates : - A >50km2 slump scar formed in Aptian times at the northwestern edge of the SE France (so-called Vocontian) basin, giving a low-angle detachment surface which was onlapped by Albian hemipelagic marls (Ferry & Flandrin, 1979). The latter mark the maximum deepening stage of the basin, and the head of the scar is located over a deep-seated fault bounding the platform, which strongly suggest that sliding was caused by differential subsidence due to Middle Cretaceous extension, as a consequence of Iberia-Europe divergence. - Later on, a deep-marine erosion surface developed further down the basin over a >100km2 area (Dévoluy massif; Michard et al., 2010), which had been previously affected by Mid-Cretaceous extension. Typical inversion structures are found beneath the surface, which indicate that NS shortening overprinted the extensional pattern. The removal of up to 400m of Mesozoic sediments was controlled by gravity processes, probably triggered by the deformation of the basin floor following tectonic inversion. The overlying pelagic carbonates indicate that shortening occurred before the Campanian, which is closely comparable with the earliest stages of tectonic inversion in the Pyrenees. - The transition slope between the Paleogene Alpine flexural basin and the NW-ward propagating accretionary prism provides examples of basin floor degradation and of gravity-driven emplacement of large-scale blocks, generally regarded as thrust-sheets in the Alps. These features allow to reconstruct the early stages of the Adria-Europe collision, which strongly differ from the Oligo

  14. Tectonics and evolution of the Juan Fernandez microplate at the Pacific-Nazca-Antarctic triple junction

    NASA Technical Reports Server (NTRS)

    Anderson-Fontana, S.; Larson, R. L.; Engein, J. F.; Lundgren, P.; Stein, S.

    1986-01-01

    Magnetic and bathymetric profiles derived from the R/V Endeavor survey and focal mechanism studies for earthquakes on two of the Juan Fernandez microplate boundaries are analyzed. It is observed that the Nazca-Juan Fernandez pole is in the northern end of the microplate since the magnetic lineation along the East Ridge of the microplate fans to the south. The calculation of the relative motion of the Juan Fernandez-Pacific-Nazca-Antarctic four-plate system using the algorithm of Minster et al. (1974) is described. The development of tectonic and evolutionary models of the region is examined. The tectonic model reveals that the northern boundary of the Juan Fernandez microplate is a zone of compression and that the West Ridge and southwestern boundary are spreading obliquely; the evolutionary model relates the formation of the Juan Fernandez microplate to differential spreading rates at the triple junction.

  15. The structural evolution of the western Irish Variscides: an example of obstacle tectonics?

    NASA Astrophysics Data System (ADS)

    Meere, Patrick A.

    1995-06-01

    Detailed mesostructural and strain analysis investigations across the Killarney Mallow Fault, i.e. the traditional Variscan "Front" in southwest Ireland, reveal that this structural line separates two distinct tectonic regimes. North of the Killarney Mallow Fault bulk shortening orthogonal to orogenic strike is estimated to be 12%, all of which is accounted for by late stage buckling. Microscopic strain analysis reveals that there is only local development of a tectonic fabric. South of the front, bulk shortening is ≈ 40% due to combined layer parallel shortening (LPS), buckling and faulting. Variscan deformation is presented as being essentially coaxial. The regional finite strain pattern outlined above is thought to be primarily controlled by the combined effect of a buried basement obstacle in eastern Iveragh and increased sedimentary pile thickness at the western end of the orogen.

  16. Stratigraphy, sedimentology and tectonic evolution of the Upper Cretaceous/Paleogene succession in north Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    El Ayyat, Abdalla M.; Obaidalla, Nageh A.

    2013-05-01

    , fine-grained limestones and fine siliciclastic shales (Sudr, Dakhla, Tarawan and Esna formations). The northeastern parts are marked by little contents of planktonic foraminifera and dolomitized, slumped carbonates, intercalated with basinal facies. Tectonically, four remarkable syn-depositional tectonic events (SdTEs) controlled the evolution of the studied succession. These events took place strongly within the Campanian-Ypresian time interval and were still active till Late Eocene. These events took place at: the Santonian/Campanian (S/C) boundary; the Campanian/Maastrichtian (C/M) boundary; the Cretaceous/Paleogene (K/P) boundary; and the Middle Paleocene-Early Eocene interval. These tectonic events are four pronounced phases in the tectonic history of the Syrian Arc System (SAS), the collision of the Afro-Arabian and Eurasian plates as well as the closure of the Tethys Sea.

  17. Breaking Ground on the Moon and Mars: Reconstructing Lunar Tectonic Evolution and Martian Central Pit Crater Formation

    NASA Astrophysics Data System (ADS)

    Williams, Nathan Robert

    Understanding the structural evolution of planetary surfaces provides key insights to their physical properties and processes. On the Moon, large-scale tectonism was thought to have ended over a billion years ago. However, new Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) high resolution images show the Moon's surface in unprecedented detail and show many previously unidentified tectonic landforms, forcing a re-assessment of our views of lunar tectonism. I mapped lobate scarps, wrinkle ridges, and graben across Mare Frigoris -- selected as a type area due to its excellent imaging conditions, abundance of tectonic landforms, and range of inferred structural controls. The distribution, morphology, and crosscutting relationships of these newly identified populations of tectonic landforms imply a more complex and longer-lasting history of deformation that continues to today. I also performed additional numerical modeling of lobate scarp structures that indicates the upper kilometer of the lunar surface has experienced 3.5-18.6 MPa of differential stress in the recent past, likely due to global compression from radial thermal contraction. Central pit craters on Mars are another instance of intriguing structures that probe subsurface physical properties. These kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They are inferred to form in the presence of a water-ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. I assessed radial trends in grain size around central pits using thermal inertias calculated from Thermal Emission Imaging System (THEMIS) thermal infrared images. Average grain size decreases with radial distance from pit rims -- consistent with pit-derived ejecta but not

  18. Plate-tectonic evolution of the western U.S.A.

    USGS Publications Warehouse

    Hamilton, W.

    1987-01-01

    Changing interactions of lithospheric plates provide the framework for this review of the 3100 m.y. geological history of some 3 million km2 of mountains, deserts, plateaux and plains. The Precambrian to Neogene development of the western U.S.A. is outlined in terms of plate collisions, subduction events and deformation of lithospheric slabs, with some interpretations based on SE Asia and other regions of complex tectonics.-R.A.H.

  19. High precision U-PB geochronology and implications for the tectonic evolution of the Superior Province

    NASA Technical Reports Server (NTRS)

    Davis, D. W.; Corfu, F.; Krogh, T. E.

    1986-01-01

    The underlying mechanisms of Archean tectonics and the degree to which modern plate tectonic models are applicable early in Earth's history continue to be a subject of considerable debate. A precise knowledge of the timing of geological events is of the utmost importance in studying this problem. The high precision U-Pb method has been applied in recent years to rock units in many areas of the Superior Province. Most of these data have precisions of about + or - 2-3 Ma. The resulting detailed chronologies of local igneous development and the regional age relationships furnish tight constraints on any Archean tectonic model. Superior province terrains can be classified into 3 types: (1) low grade areas dominated by meta-volcanic rocks (greenstone belts); (2) high grade, largely metaplutonic areas with abundant orthogneiss and foliated to massive I-type granitoid bodies; and (3) high grade areas with abundant metasediments, paragneiss and S-type plutons. Most of the U-Pb age determinations have been done on type 1 terrains with very few having been done in type 3 terrains. A compilation of over 120 ages indicates that the major part of igneous activity took place in the period 2760-2670 Ma, known as the Kenoran event. This event was ubiquitous throughout the Superior Province.

  20. Polyphase tectonic evolution of the Aksu Basin, Isparta Angle (Southern Turkey)

    NASA Astrophysics Data System (ADS)

    Üner, Serkan; Özsayin, Erman; Kutluay, Alkor; Dirik, Kadir

    2015-04-01

    The Aksu Basin, within the Isparta Angle, is located to the north of the intersection of the Aegean and Cyprus arcs and has been evolving since the Middle Miocene. Correlation of: (1) kinematic analysis of fault planes that cut the basin fill, (2) the reactivation/inversion of fault planes and (3) sedimentological data indicate that the Aksu Basin has evolved by four alternating compressional and extensional tectonic phases since its formation. The first phase was NW-SE oriented compression caused by the emplacement of the Lycian Nappe units which ended in Langhian. This compressional phase that induced the formation and the initial deformation of the basin was followed by a NW-SE extensional phase. This tectonic phase prevailed between the Langhian and Messinian and was terminated by a NE-SW compressional regime known as the Aksu Phase. The neotectonic period is characterized by NE-SW extension and began in the Late Pliocene. Correlation with the existing tectonic literature shows that the order of deformational phases proposed in this study might also be valid for the entire Isparta Angle area.

  1. 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

  2. The tectonic evolution of the Arctic since Pangea breakup: Integrating constraints from surface geology and geophysics with mantle structure

    NASA Astrophysics Data System (ADS)

    Shephard, Grace E.; Müller, R. Dietmar; Seton, Maria

    2013-09-01

    The tectonic evolution of the circum-Arctic, including the northern Pacific, Siberian and North American margins, since the Jurassic has been punctuated by the opening and closing of ocean basins, the accretion of autochthonous and allochthonous terranes and associated deformation. This complexity is expressed in the uncertainty of plate tectonic models of the region, with the time-dependent configurations and kinematic history remaining poorly understood. The age, location, geometry and convergence rates of the subduction zones associated with these ancient ocean basins have implications for mantle structure, which can be used as an additional constraint for refining and evaluating plate boundary models. Here we integrate surface geology and geophysics with mantle tomography models to generate a digital set of tectonic blocks and plates as well as topologically closed plate boundaries with time-dependent rotational histories for the circum-Arctic. We find that subducted slabs inferred from seismic velocity anomalies from global P and S wave tomography models can be linked to various episodes of Arctic subduction since the Jurassic, in particular to the destruction of the South Anuyi Ocean. We present a refined model for the opening of the Amerasia Basin incorporating seafloor spreading between at least 142.5 and 120 Ma, a "windshield" rotation for the Canada Basin, and opening orthogonal to the Lomonosov Ridge for the northern Makarov and Podvodnikov basins. We also present a refined pre-accretionary model for the Wrangellia Superterrane, imposing a subduction polarity reversal in the early Jurassic before accretion to North America at 140 Ma. Our model accounts for the late Palaeozoic to early Mesozoic opening and closure of the Cache Creek Ocean, reconstructed between the Wrangellia Superterrane and Yukon-Tanana Terrane. We suggest that a triple junction may also explain the Mid-Palaeozoic opening of the Slide Mountain, Oimyakon and South Anuyi oceans. Our

  3. Petrogenesis and Tectonic Evolution of Granitic Rocks in The Northern Margin of North China Plate

    NASA Astrophysics Data System (ADS)

    Xu, X.; Zhao, Q.; Zheng, C.; Liu, W.; Xu, B.

    2010-12-01

    The late Paleozoic-early Mesozoic granites in Daqingshan district of the northern margin of north China plate is classified into six types as follows.Aguigou intrusion is consists of gabbro, diorite, quartz diorite, and granodiorite.Its feature is rich in mafic compositions.The formation age is 284.5±2.9Ma or 283.7±3.7Ma for the quartz diorite, and 281.1±3.4Ma for granodiorite. The genesis of the intrusion belongs to I-type granite. Laoyinhada intrusion comprises fine biotite monzonitic granite and porphyritic biotite monzonitic granite. The age is 272±4Ma for the fine biotite monzonitic granite. The genesis of the body is I-type granite.Halaheshao intrusion is a group of medium-coarse biotite-bearing monzonitic granites and large porphyritic-bearing monzonitic granite. The age is 260±0.5Ma for the biotite-bearing monzonitic granite.The tectonic environment belongs to post-orogenic granites.Taolegai intrusion consists of medium-fine granite, medium-coarse granite, porphyritic-bearing granite, and fine granite. The age is 224±3Ma for medium-coarse granite.Its genesis is light color granite co-occurred with muscovite peraluminous granites. The tectonic environment belongs to post-orogenic granites.Gechoushan intrusion is medium-fine monzonitic granite, a kind of typical muscovite granites. Its formation era is late Triassic. The tectonic environment belongs to post-orogenic granite.Shadegai intrusion is mainly composed of biotite granites. The age is 211.2±0.7Ma for medium-coarse biotite granite. The tectonic setting belongs to post-orogenic granites. The different types granites in the area basically reveal all the magmatic events from late Palaeozoic orogeny, to post-orogeny, and to intracontinental orogeny in the north edge of the north China plate. Early Permian Aguigou intrusion is a magmatic arc granite, formed in the continental edge in the early period of the middle Asia ocean plate subduction. Mid-Permian Laoyinhada intrusion is a magmatic arc granite

  4. The asymmetric evolution of the Colombian Eastern Cordillera. Tectonic inheritance or climatic forcing? New evidence from thermochronology and sedimentology

    NASA Astrophysics Data System (ADS)

    Ramirez-Arias, Juan Carlos; Mora, Andrés; Rubiano, Jorge; Duddy, Ian; Parra, Mauricio; Moreno, Nestor; Stockli, Daniel; Casallas, Wilson

    2012-11-01

    New thermochronological data, facies, paleocurrents and provenance allow us to refine the chronology of deformation in the central segment of the Colombian Eastern Cordillera. Based on a new extensive AFT dataset, we document the spatial evolution of active deformation, from the axial zone of the Eastern Cordillera at about 50 Ma in to active growth of the frontal thin skinned structures in Late Miocene time. Paleocurrents allow us to push backwards into the Middle to Early Late-Miocene the emergence of the easternmost frontal thrust; whereas careful assessment of exposure gates tied to AFT data enable to refine the unroofing history for Eocene to Miocene times. Based on that, we produced a kinematically restored cross section with higher resolution than previous assessments. Using these datasets, we compare the evolution of the central segment of the Eastern Cordillera in this region with the evolution of adjacent areas in the context of climatic forcing of orogenic evolution. We find that in this region and, in the Eastern Cordillera in general, tectonic inheritance and transpression exert an initial dominant control on the initial orogen asymmetry, which is later enhanced due to an orographically-focused erosion. We therefore suggest that it is not climate alone the factor controlling orogenic asymmetry in the Eastern Cordillera of Colombia.

  5. Tectonic and environmental evolution of Quaternary intramontane basins in Southern Apennines (Italy): insights from palaeomagnetic and rock magnetic investigations

    NASA Astrophysics Data System (ADS)

    Porreca, M.; Mattei, M.

    2010-08-01

    Southern Apennines is characterized by active extensional tectonics with NE-SW stretching direction. The seismicity of the region is very well understood and continuously monitored. In contrast, the onset of extensional tectonics is chronologically poorly constrained. The aim of this study is that to give important constraints on the development of extensional regime and the onset of the continental deposition during Quaternary in Southern Apennines. We report the results of palaeomagnetic and rock magnetic analyses from four Quaternary small intramontane basins in the Picentini Mountains (Southern Apennines). The sedimentary sequences are located at different altitudes, from 600 to 1200 m a.s.l., and were deposited in fluvial-lacustrine environments. We sampled 29 sites in clays and lacustrine limestones from Tizzano, Piano del Gaudo and Acerno basins and in red palaeosoils and matrix-supported conglomerates from the Iumaiano basins. In the clay and limestones samples magnetite, titano-magnetite, hematite and iron-sulphide have been recognized as the main magnetic carriers, whereas magnetite and hematite characterize the Iumaiano conglomerates and red soils. Palaeomagnetic results have been integrated with published radiometric data in order to constrain the age of each sedimentary basins. Sites from the Iumaiano basin, which represents the substrate of the Tizzano and Piano del Gaudo basins, show a reverse polarity and therefore have been attributed to the lower Matuyama chron. In contrast, palaeomagnetic data from Tizzano basin show a transition from reversed to normal polarity along the exposed section, which has been interpreted as the Matuyama/Brunhes transition. Sites from Acerno and Piano del Gaudo basins show a normal polarity, which, according to radiometric and pollen data, have been correlated to the Brunhes epoch. On the base of such results we discuss the tectono-stratigraphic evolution of the basins and the role of extensional tectonics in this

  6. AMS fabric and tectonic evolution of Quaternary intramontane extensional basins in the Picentini Mountains (southern Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Porreca, M.; Mattei, M.

    2012-04-01

    In this work, we report the results of combined geological, structural, and anisotropy of magnetic susceptibility (AMS) studies carried out on Quaternary deposits in the Picentini Mountains, southern Apennines (Italy). The study concerns four small continental basins, Acerno, Tizzano, Iumaiano, and Piano del Gaudo, related to fluvial-lacustrine depositional environments, ranging in altitude from 600 to 1,200 m a.s.l. and strongly incised during recent time. Stratigraphic and structural analyses, integrated by low- and high-field anisotropy of magnetic susceptibility (AMS), show that the formation of these basins has been controlled by extensional and transtensional tectonics. Most of the AMS sites exhibit a well-defined magnetic foliation parallel to the bedding planes. A well-defined magnetic lineation has also been measured within the foliation planes. In the Iumaiano, Tizzano, and Piano del Gaudo basins, magnetic lineations cluster around NNE-SSW trend and are parallel to the stretching directions inferred by structural analysis of faults and fractures. On the basis of structural, sedimentological, and high-field AMS data, we suggest a tectonic origin for the magnetic lineation, analogously to what has been observed in other weakly deformed sediments from Neogene and Quaternary extensional basins of the Mediterranean region. Our results demonstrate that onset and the evolution of the investigated basins have been mainly controlled since lower Pleistocene by NW-SE normal and transtensional faults. This deformation pattern is consistent with a prevalent NE-SW extensional tectonic regime, still active in southern Apennines, as revealed by seismological and geodetic data.

  7. Magmatic responses to Late Cretaceous through Oligocene tectonic evolution of the western Alaska Range

    NASA Astrophysics Data System (ADS)

    Todd, E.; Jones, J. V., III; Karl, S.; Ayuso, R. A.; Bradley, D. C.; Box, S. E.; Haeussler, P. J.

    2014-12-01

    New geochemistry, U/Pb geochronology, and radiogenic isotopes, together with existing datasets, contribute to a refined model of the petrogenetic history of magmatism in the western Alaska Range. Plutons within the study area were emplaced into Kahiltna basin Mesozoic turbiditic strata. The Kahiltna sequence overlies Mesozoic Peninsular oceanic terrane rocks in the SE half of the basin and Proterozoic to Paleozoic Farewell continental terrane rocks to the NW. This study focuses on successive intrusion suites, most of which are thought to intrude Kahiltna or underlying Farewell terrane rocks, but include older, perhaps more deeply exhumed rocks emplaced in Peninsular terrane basement to the SE. The chemically diverse sequence records magmatism associated with major tectonic reorganization events on the southern Alaska circum-Pacific subduction margin. The oldest pluton suite (~100-80 Ma) is mostly intermediate to evolved calcalkaline granite and coincides with final closure of the Kahiltna basin and a regional transition to transpression-dominated tectonics. The post-closure magmatic pulse (~75-67 Ma) is compositionally varied, including primitive subalkaline melts, peraluminous high-K granites, and a subset of sodic, adakite-like granites. A Paleocene (~63-57 Ma) magmatic flare-up follows, dominated by extremely fractionated subalkaline melts. Rare, more primitive melts of this suite are metaluminous, from gabbro to syenite. This stage may represent relaxed melt productivity or shallowing of the slab dip, yielding more laterally diffuse melting. An early Eocene magmatic hiatus precedes middle Eocene circum-Pacific tectonic reorganization, regionally resulting in initiation of proto-Aleutian/Meshik arc magmatism, and locally in the 44-37 Ma emplacement of subalkaline intermediate to felsic plutons associated with andesite to rhyolite volcanic deposits. An Oligocene (~31-25 Ma) magmatic pulse involved emplacement of a compositionally variable suite ranging from

  8. Active tectonics and Quaternary landscape evolution across the western Panama block, Costa Rica, Central America

    NASA Astrophysics Data System (ADS)

    Marshall, Jeffrey Scott

    Three aspects of active tectonism are examined across central Costa Rica: (1) fault kinematics; (2) volcanic arc retreat; and (3) spatially variable coastal uplift. Diffuse faulting along the Central Costa Rica Deformed Belt (CCRDB) defines the western margin of the Panama block and aligns with the rough-smooth boundary (RSB) on the subducting Cocos plate. Sub-horizontal subduction of rough, hotspot thickened crust (Cocos Ridge and seamounts) shifts active shortening into the volcanic arc along the CCRDB. Mesoscale faults express variable kinematics across three domains: transtension in the forearc, transcurrent motion across the volcanic arc, and transpression in the back arc. Fault kinematics agree with seismicity and GPS data, and isotopic ages confirm that faulting postdates the late Neogene onset of shallow subduction. Stratigraphic correlation augmented by 40Ar/39Ar dating constrain the timing of Quaternary arc migration from the Neogene Aguacate range to the modern Cordillera Central. The Valle Central basin, between the cordilleras, filled with thick sequences of lavas, pyroclastic flows, and lahars. Middle Pleistocene drainage capture across the Aguacate arc linked the Valle Central with the Pacific slope and ash flows descended onto the coastal Orotina debris fan. Arc retreat reflects slab shallowing and enhanced tectonic erosion as rough crust entered the subduction zone. Differing subduction parameters across the RSB (crustal age, slab dip, roughness) produce marked contrasts in coastal tectonism. Varying uplift rates across coastal faults reflect sub-horizontal subduction of seamount roughness. Three groups (I--III) of fluvial terraces are correlated along the coast by isotopic ages and geomorphic characteristics. Base level fluctuations and terrace genesis reflect interaction between eustatic sea level and spatially variable rock uplift. Low uplift rates (north of RSB), yield one surface per terrace group, whereas moderate rates (south of RSB

  9. Cretaceous sequence stratigraphy of the Northern South American Passive Margin: Implications for tectonic evolution

    SciTech Connect

    Kauffman, E.G.; Villamil, T.; Johnson, C.C. )

    1993-02-01

    The passive margin of northern South America, from Colombia to northeastern Venezuela, was relatively stable through the Cretaceous and only broadly affected by the entry of the Caribbean Plate into the Protocaribbean Basin. This region offers a unique opportunity to test the relative effects of global sealevel change, autocyclic sedimentologic processed, and regional tectonics in shaping the stratigraphic record of Cretaceous passive margins. High-resolution stratigraphic studies of Colombia and Venezuela have established a precise system of regional chronology and correlation with resolution <1 Ma (50-500 ka for the middle Cretaceous). This allows precise separation of allocyclic and autocyclic controls on facies development. This new chronology integrates assemblage zone biostratigraphy with event/cycle chronostratigraphy. Newly measured Cretaceous sections in Venezuela and throughout Colombia are calibrated to this new chronology, and sequence stratigraphic units independently defined to the third-order of resolution. Graphic correlation of all sections is used to identify sequences with regional stratigraphic expression, and those which correlate to sequence stratigraphic standards of North America, Europe and the global cycles of Hag et al. (1988). 50-60 percent of the stratigraphic sequences across the South American passive margin correlate to other continents and to the global sequence stratigraphic standard, reflecting strong eustatic influence on Cretaceous sedimentation across northern South America. The remaining sequences in this region reflect tectonic modification of the passive margin and autocyclic sedimentary processes.

  10. Laurentian origin for the North Slope of Alaska: Implications for the tectonic evolution of the Arctic

    USGS Publications Warehouse

    Strauss, J. V.; Macdonald, F. A.; Taylor, J. F.; Repetski, John E.; McClelland, W. C.

    2013-01-01

    The composite Arctic Alaska–Chukotka terrane plays a central role in tectonic reconstructions of the Arctic. An exotic, non-Laurentian origin of Arctic Alaska–Chukotka has been proposed based on paleobiogeographic faunal affinities and various geochronological constraints from the southwestern portions of the terrane. Here, we report early Paleozoic trilobite and conodont taxa that support a Laurentian origin for the North Slope subterrane of Arctic Alaska, as well as new Neoproterozoic–Cambrian detrital zircon geochronological data, which are both consistent with a Laurentian origin and profoundly different from those derived from similar-aged strata in the southwestern subterranes of Arctic Alaska–Chukotka. The North Slope subterrane is accordingly interpreted as allochthonous with respect to northwestern Laurentia, but it most likely originated farther east along the Canadian Arctic or Atlantic margins. These data demonstrate that construction of the composite Arctic Alaska–Chukotka terrane resulted from juxtaposition of the exotic southwestern fragments of the terrane against the northern margin of Laurentia during protracted Devonian(?)–Carboniferous tectonism.

  11. 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

  12. Stratigraphic assessment of the Arcelia Teloloapan area, southern Mexico: implications for southern Mexico's post-Neocomian tectonic evolution

    NASA Astrophysics Data System (ADS)

    Cabral-Cano, E.; Lang, H. R.; Harrison, C. G. A.

    2000-10-01

    Stratigraphic assessment of the "Tierra Caliente Metamorphic Complex" (TCMC) between Arcelia and Teloloapan in southern Mexico, based on photo interpretation of Landsat Thematic Mapper images and field mapping at the 1:100,000 scale, tests different tectonic evolution scenarios that bear directly on the evolution of the southern North American plate margin. The regional geology, emphasizing the stratigraphy of a portion of the TCMC within the area between Arcelia and Teloloapan is presented. Stratigraphic relationships with units in adjacent areas are also described. The base of the stratigraphic section is a chlorite grade metamorphic sequence that includes the Taxco Schist, the Roca Verde Taxco Viejo Formation, and the Almoloya Phyllite Formation. These metamorphic units, as thick as 2.7 km, are covered disconformably by a sedimentary sequence, 2.9 km thick, composed of the Cretaceous marine Pochote, Morelos, and Mexcala Formations, as well as undifferentiated Tertiary continental red beds and volcanic rocks. The geology may be explained as the evolution of Mesozoic volcanic and sedimentary environments developed upon attenuated continental crust. Our results do not support accretion of the Guerrero terrane during Laramide (Late Cretaceous-Paleogene) time.

  13. Aerogeophysical survey over Sør Rondane Mountains and its implications for revealing the tectonic evolution of East Antarctica

    NASA Astrophysics Data System (ADS)

    Mieth, Matthias; Steinhage, Daniel; Ruppel, Antonia; Damaske, Detlef; Jokat, Wilfried

    2013-04-01

    We are presenting new magnetic and gravity data of a high-resolution aerogephysical survey over the area of the Sør Rondane Mountains in the eastern Dronning Maud Land (DML). The aircraft survey is part of the joint geological and geophysical GEA campaign (Geodynamic Evolution of East Antarctica) of the Federal Agency for Geosciences and Natural Resources (BGR) and Alfred-Wegener-Institute for Polar and Marine Research (AWI), in cooperation with the Universities of Ghent, Bremen and Bergen. It was completed during the Antarctic summer season 2012/13, covering an area of more than 100000 square kilometer with a line spacing of 5 km. The data will be correlated with geological structures exposed in the mountain range as well as matched and merged with the data sets of the eastern and southern DML (acquired by AWI during the last decade) for comparison and discussion in the greater context of the tectonic evolution of East Antarctica. Preliminary results show that the magnetic anomaly pattern over the Sør Rondane Mountains differs from the pattern found over the central DML mountains as well as from the low amplitude pattern in between both regions, indicating a significant difference in the evolution of this region, which is in accordance with latest geological findings in this region.

  14. Impact of Cenozoic strike-slip tectonics on the evolution of the northern Levant Basin (offshore Lebanon)

    NASA Astrophysics Data System (ADS)

    Ghalayini, Ramadan; Daniel, Jean-Marc; Homberg, Catherine; Nader, Fadi H.; Comstock, John E.

    2014-11-01

    Sedimentary basins adjacent to plate boundaries contain key tectonic and stratigraphic elements to understand how stress is transmitted through plates. The Levant Basin is a place of choice to study such elements because it flanks the Levant Fracture System and the Africa/Anatolia boundary. This paper uses new high-quality 3-D seismic reflection data to unravel the tectonic evolution of the margin of this basin during the Cenozoic, the period corresponding to the formation of the Levant Fracture System, part of the Africa/Arabia plate boundary. Four major groups of structures are identified in the interpreted Cenozoic units: NW-SE striking normal faults, NNE-SSW striking thrust-faults, ENE-WSW striking dextral strike-slip faults, and NNE trending anticlines. We demonstrate that all structures, apart of the NW-SE striking normal faults, are inherited from Mesozoic faults. Their reactivation and associated folding started during the late Miocene prior to the Messinian salinity crisis due to a NW-SE compressional stress field. No clear evidence of shortening at present-day offshore Lebanon and no large NNE-SSW strike-slip faults parallel to the restraining bend are found indicating that the Levant Fracture System is mainly contained onshore at present day. The intermittent activity of the interpreted structures correlates with the two stages of Levant Fracture System movement during late Miocene and Pliocene. This paper provides a good example of the impact of the evolution of plate boundaries on adjacent basins and indicates that any changes in the stress field, as controlled by the plate boundary, will affect immediately the preexisting structures in adjacent basins.

  15. New insights into the tectonic evolution of the Boconó Fault, Mérida Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Backé, G.

    2006-12-01

    The Boconó fault is a major right-lateral strike-slip fault that cuts along strike the Mérida Andes in Venezuela. The uplift of this mountain range started in the Miocene as a consequence of the relative oblique convergence between two lithospheric units named the Maracaibo block to the northwest and the Guyana shield to the southeast. Deformation in the Mérida Andes is partitioned between a strike-slip component along the Boconó fault and shortening perpendicular to the belt. Distinctive features define the Boconó fault: it is shifted southward relative to the chain axis and it does not have a continuous and linear trace but is composed of several fault segments of different orientations striking N35°E to N65°E. Quaternary fault strike-slip motion has been evidenced by various independent studies. However, onset of the strike-slip motion, fault offset and geometry at depth remains a matter of debate. Our work, based on morphostructural analyses of satellite and digital elevation model imagery, provides new data on both the geometry and the tectonic evolution of this major structure. We argue that the Boconó fault affects only the upper crust and connects at depth to a décollement. Consequently, it can not be considered as a plate boundary. The Boconó fault does however form the boundary between two different tectonic areas in the central part of the Mérida Andes as revealed by the earthquake focal mechanisms. South of the Boconó fault, the focal mechanisms are mainly compressional and reverse oblique-slip in agreement with NW SE shortening in the foothills. North of the Boconó fault, extensional and strike-slip deformation dominates. Microtectonic measurements collected in the central part of the Boconó fault are characterized by polyphased tectonics. The dextral shearing along the fault is superimposed to reverse oblique-slip to reverse motion, showing that initiation of transcurrent movement is more likely to have occurred after a certain amount of

  16. Geology of the Blue Mountains region of Oregon, Idaho, and Washington: Petrology and tectonic evolution of pre-tertiary rocks of the Blue Mountains region. Professional paper

    SciTech Connect

    Vallier, T.L.; Brooks, H.C.

    1995-12-31

    U.S. Geological Survey Professional Paper 1438 is one volume of a five-volume series on the geology, paleontology, and mineral resources of the Blue Mountains region eastern Oregon, western Idaho, and southeastern Washington. This professional paper deals specifically with petrology and tectonic evolution.

  17. The Geomorphological Evolution of a Landscape in a Tectonically Active Region: the Sennwald Landslide

    NASA Astrophysics Data System (ADS)

    Aksay, Selçuk; Ivy-Ochs, Susan; Hippe, Kristina; Graemiger, Lorenz; Vockenhuber, Christof

    2016-04-01

    The Säntis nappe is a fold-and-thrust structure in eastern Switzerland consisting of numerous tectonic discontinuities that make rocks vulnerable to rock failure. The Sennwald landslide is one of those events that occurred due to the failure of Lower Cretaceous Helvetic limestones. This study reveals the surface exposure age of the event in relation to geological and tectonic setting, earthquake frequency of the Central Alps, and regional scale climate/weather influence. Our study comprises detailed mapping of landform features, thin section analysis of landslide boulder lithologies, landslide volume estimation, numerical DAN-3D run-out modelling, and the spatial and temporal relationship of the event. In the Sennwald landslide, 92 million m3 of limestones detached from the south-eastern wall of the Säntis nappe and slid with a maximum travel distance of ~4'500 m and a "fahrboeschung" angle of 15° along the SE-dipping sliding plane almost parallel to the orientation of the bedding plane. Numerical run-out modelling results match the extent and the thickness of landslide deposits as observed in the field. The original bedrock stratigraphy was preserved as geologically the top layer in the bedrock package travelled the farthest and the bottom layer came to rest closest to the release bedrock wall during the landslide. Velocities of maximum 90 m/s were obtained from the numerical run-out modelling. Total Cl and 36Cl were determined at ETH AMS facility with isotope dilution methods defined in the literature (Ivy-Ochs et al., 2004). Surface exposure ages of landslide deposits in the accumulation area are revealed from twelve boulders. The distribution of limestone boulders in the accumulation area, the exposure ages, and the numerical run-out modelling support the hypothesis that the Sennwald landslide was a single catastrophic event. The event is likely to have been triggered by at least light to moderate earthquakes (Mw=4.0-6.0). The historical and the last 40-year

  18. Implications Of Fault Damaged Bedrock To Tectonic and Landscape Evolution In Coastal Alaska

    NASA Astrophysics Data System (ADS)

    Boucher, A.; Koons, P. O.; Roy, S. G.; Birkel, S. D.; Kaluzienski, L. M.; Campbell, S. W.

    2015-12-01

    Bedrock material strength properties heavily impact erosion rates in temperate glacial environments. We focus on the influence of localized tectonic crustal weakening in southeast Alaska on modern glacial erosion rates, thereby quantifying a primary feedback in tectonic/climatic coupling. Southeast Alaska, with its coincident high strain rates, vigorous glacial erosion and rapid sedimentation rates, provides an excellent setting in which to evaluate this interaction. To characterize the relationship between fault damage and glacial incision, we collected data in transects across the strike-slip Fairweather Fault in Yakutat and Disenchantment Bays, in deglaciated valleys below the Mendenhall, Herbert, Ptarmigan, and Lemon Creek Glaciers on the perimeter of the Juneau Icefield, and on deglaciated nunataks on the Echo and Vaughan Lewis Glaciers in the interior of the Juneau Icefield. The mechanical properties of the bedrock are characterized by estimates of fault spacing and material cohesion. In structurally-controlled bedrock valleys exploited by glaciers, fracture spacing may vary by several orders of magnitude across fault damage zones, from more than 10 m to less than 0.1 m. Analysis of active and quiescent fault zones indicate that this variation approximates a power law relationship and correlates with a gradient in cohesive strength varying from greater than 50 MPa to less than 50 kPa between intact bedrock and the core of fault damage zones. The width and orientation of the damage zones is highly variable and we have chosen our field sites to sample zones of very large total displacement, up to kilometers along the Fairweather Fault, and substantially smaller displacements, down to centimeters for the Juneau Icefield locales. Using a Cordilleran Ice sheet model to extend our modern observations into last glacial maximum conditions, we predict both erosion rates and sediment provenance for a material strength pattern influenced by tectonically induced fault

  19. Consequences of Chixculub Impact for the Tectonic and Geodynamic Evolution of the Gulf of Mexico North Carribean Region

    NASA Astrophysics Data System (ADS)

    Rangin, C.; Crespy, A.; Martinez-Reyes, J.

    2013-05-01

    The debate for Pacific exotic origin versus in situ inter American plate Atlantic origin of the Caribbean plate is active in the scientific community since decades. Independently of the origin of this plate, its fast motion towards the east at a present rate of 2cm/yr is accepted to have been initiated during the early-most Cenozoic. The Paleocene is a key period in the global evolution of Central America mainly marked also by the Chicxulub multiring meteor impact in Yucatan. We question here the genetic relationship between this impact event and the incipient tectonic escape of the Caribbean plate. The mostly recent published models suggest this impact has affected the whole crust down to the Moho, the upper mantle being rapidly and considerably uplifted. The crust was then fragmented 600km at least from the point of impact, and large circular depressions were rapidly filled by clastic sediments from Cantarell to Western Cuba via Chiapas and Belize. North of the impact, the whole Gulf of Mexico was affected by mass gravity sliding, initiated also during the Paleocene in Texas, remaining active in this basin up to present time. South of the impact, in the Caribbean plate, the Yucatan basin was rapidly opened, indicating a fast escape of the crustal material towards the unique free boundary, the paleo-Antilles subduction zone. Shear waves velocity data below the Caribbean plate suggest this crustal tectonic escape was enhanced by the fast eastward flowing mantle supporting a fragmented and stretched crust. The proposed model suggests Chicxulub impact (but also the hypothetic Beata impact) have fragmented brittle crust, then easily drifted towards the east. This could explain the Paleogene evolution of the Caribbean plate largely stretched during its early evolution. Geologically, this evolution could explain the absence of evident Paleogene oblique subduction along the Caribbean plate northern and southern margins, marked only by Mid Cretaceous dragged volcanic

  20. Interaction of tectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin

    USGS Publications Warehouse

    Maldonado, A.; Nelson, C.H.

    1999-01-01

    This study provides an integrated view of the growth patterns and factors that controlled the evolution of the Gulf of Cadiz continental margin based on studies of the tectonic, sedimentologic and oceanographic history of the area. Seven sedimentary regimes are identified, but there are more extensive descriptions of the late Cenozoic regimes because of the larger data base. The regimes of the Mesozoic passive margin include carbonate platforms, which become mixed calcareous-terrigenous deposits during the Late Cretaceous-early Tertiary. The Oligocene and Early Miocene terrigenous regimes developed, in contrast, over the active and transcurrent margins near the African-Iberian plate boundary. The top of the Gulf of Cadiz olistostrome, emplaced in the Late Miocene, is used as a key horizon to define the 'post-orogenic' depositional regimes. The Late Miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the Miocene Atlantic-Mediterranean gateways. The terrigenous drift depositional regime of the Early Pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the Mediterranean outflow currents that developed after the opening of the Strait of Gibraltar. The Late Pliocene and Quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels. Deposition of shelf-margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence. During the highstand regimes of the Holocene, inner shelf prograding deltas and deep-water sediment drifts were developed under the influence of the Atlantic inflow and Mediterranean outflow currents, respectively. A modern human cultural regime began 2000 years ago with the Roman occupation of Iberia; human cultural effects on sedimentary regimes may have equalled natural factors such as climate change. Interplay of tectonic and

  1. Structure and tectonic evolution of the Southern Eurasia Basin, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Sekretov, Sergey B.

    2002-07-01

    Multichannel seismic reflection data acquired by Marine Arctic Geological Expedition (MAGE) of Murmansk, Russia in 1990 provide the first view of the geological structure of the Arctic region between 77-80°N and 115-133°E, where the Eurasia Basin of the Arctic Ocean adjoins the passive-transform continental margin of the Laptev Sea. South of 80°N, the oceanic basement of the Eurasia Basin and continental basement of the Laptev Sea outer margin are covered by 1.5 to 8 km of sediments. Two structural sequences are distinguished in the sedimentary cover within the Laptev Sea outer margin and at the continent/ocean crust transition: the lower rift sequence, including mostly Upper Cretaceous to Lower Paleocene deposits, and the upper post-rift sequence, consisting of Cenozoic sediments. In the adjoining Eurasia Basin of the Arctic Ocean, the Cenozoic post-rift sequence consists of a few sedimentary successions deposited by several submarine fans. Based on the multichannel seismic reflection data, the structural pattern was determined and an isopach map of the sedimentary cover and tectonic zoning map were constructed. A location of the continent/ocean crust transition is tentatively defined. A buried continuation of the mid-ocean Gakkel Ridge is also detected. This study suggests that south of 78.5°N there was the cessation in the tectonic activity of the Gakkel Ridge Rift from 33-30 until 3-1 Ma and there was no sea-floor spreading in the southernmost part of the Eurasia Basin during the last 30-33 m.y. South of 78.5°N all oceanic crust of the Eurasia Basin near the continental margin of the Laptev Sea was formed from 56 to 33-30 Ma.

  2. Tectonic evolution, structural styles, and oil habitat in the Sonda de Campeche, Mexico

    SciTech Connect

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

    1994-09-01

    The Sonda de Campeche is located in the southern part of the Gulf of Mexico and hosts one half of the oil reserves of Mexico. The stratigraphic section is 7500 m thick, ranging from Middle Jurassic to Holocene. The Mesozoic sequence includes Callovian salt deposits, Upper Jurassic sandstones, anhydrites, limestones, and shales; and Cretaceous limestones, dolomites, and carbonate breccias. In some places, this sequence displays condensed sections related to an early movement of salt. The Cenozoic sequence is formed mostly of benthonitic shales and minor sandstones, and shows two unconformities: the older one between the lower Miocene and the Oligocene, and the younger one between the middle Miocene and the upper Miocene. In the Sonda de Campeche, three main tectonic regimes are recorded: extensional, compressional, and extensional. The first one extended from Middle Jurassic to Late Jurassic and is related to the opening of the Gulf of Mexico. During this regime, tilted block faults trending northwest-southeast were dominant. The subsequent compressional regime took place at the end of the early Miocene and was related to northeast tangential stresses that added to the flow of Callovian salt, gave rise to huge anticlines, faulted, and often overturned. The last extensional regime extended throughout the middle and late Miocene and is related to salt tectonics and growth faults that have as a detachment surface a middle Miocene shaly horizon. The main source rocks are Tithonian shales and shaly limestones. Oolite bars, slope and shelfal 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.

  3. A numerical model of continental topographic evolution integrating thin sheet tectonics, river transport, and climate

    NASA Astrophysics Data System (ADS)

    Garcia-Castellanos, D.; Jimenez-Munt, I.

    2013-12-01

    How much does the erosion and sedimentation at the crust's surface influence on the patterns and distribution of tectonic deformation? This question has been mostly addressed from a numerical modelling perspective, at scales ranging from local to orogenic. Here we present a model that aims at constraining this phenomenon at the continental scale. With this purpose, we couple a thin-sheet viscous model of continental deformation with a stream-power surface transport model. The model also incorporates flexural isostatic compensation that permits the formation of large sedimentary foreland basins and a precipitation model that reproduces basic climatic effects such as continentality and orographic rainfall and rain shadow. We quantify the feedbacks between these 4 processes in a synthetic scenario inspired by the India-Asia collision. The model reproduces first-order characteristics of the growth of the Tibetan Plateau as a result of the Indian indentation. A large intramountain basin (comparable to the Tarim Basin) develops when predefining a hard inherited area in the undeformed foreland (Asia). The amount of sediment trapped in it is very sensitive to climatic parameters, particularly to evaporation, because it crucially determines its endorheic/exorheic drainage. We identify some degree of feedback between the deep and the surface processes occurs, leading locally to a <20% increase in deformation rates if orographic precipitation is account for (relative to a reference model with evenly-distributed precipitation). These enhanced thickening of the crust takes place particularly in areas of concentrated precipitation and steep slope, i.e., at the upwind flank of the growing plateau. This effect is particularly enhanced at the corners of the indenter (syntaxes). We hypothesize that this may provide clues for better understanding the mechanisms underlying the intriguing tectonic aneurisms documented in the syntaxes of the Himalayas.

  4. Thermochronometry reveals headward propagation of erosion in an alpine landscape.

    PubMed

    Shuster, David L; Cuffey, Kurt M; Sanders, Johnny W; Balco, Greg

    2011-04-01

    Glacial erosion of mountain ranges produces spectacular alpine landscapes and, by linking climate with tectonics, influences a broad array of geophysical phenomena. Although the resultant landforms are easily identified, the timing and spatial pattern of topographic adjustment to Pleistocene glaciations remain poorly known. We investigated topographic evolution in the archetypal glacial landscape of Fiordland, New Zealand, using (U-Th)/He thermochronometry. We find that erosion during the past 2 million years removed the entire pre-Pleistocene landscape and fundamentally reshaped the topography. Erosion focused on steep valley segments and propagated from trunk valleys toward the heads of drainage basins, a behavior expected if subglacial erosion rate depends on ice sliding velocity. The Fiordland landscape illustrates complex effects of climate on Earth's surface morphology. PMID:21454785

  5. Tectono-stratigraphic evolution of the Canete Basin, Lima, Peru, a plate tectonic model for the Mesozoic evolution of the Central Andes

    SciTech Connect

    Aleman, A.M. )

    1993-02-01

    An arc-trench system has been active in the Central Andes since at least since Late Triassic. This Mesozoic margin was characterized by subduction-erosion processes, PreMesozoic metamorphic outer basement high, pervasive extension, tectonic inversion, sporadic igneous activity and segmentation of the arc. Episodic variations in the tectonic evolution of the associated basins were controlled by the variable angle of subduction, age of the subducted plate, rate and angle of convergence, and the relative motion of the Farallon and South America Plates. The Canete Basin is an elongate frontal arc basin, subparallel to the arc, which documents the early evolution of the Andean Orogeny. In the Canete Basin, the oldest arc volcanism is documented by the interbedded tuffs, lava flows and tuffaceous marine shales of the Late Jurassic Puente Piedra Group which was deposited along a series of isolated and elongated troughs that formed adjacent to the arc. During Late Berriasian the arc subsided and the lithofacies changed from arc to continental derived lithologies. The shallow marine, quartz rich Morro Solar Group was derived from the uplifted metamorphic basement high in the west, as the result of ensialic extension. Locally, volcanic quiescence was interrupted by deposition of the volcaniclastic rich Pucusana Formation. The Late Hauterivian to Aptian Lima Group consists of lime mudstones, shales and subordinated gypsum and bioclastic limestones with volcaniclastic and lava flow facies of the Chilca Group. Stratigraphic relationship rapid changes in thickness and facies of this unit document the development of an incipient arc and the persistence of ensialic extension prior to the maximum paroxysm of volcanic activity of the overlying Albian to Cenomanian Chillon Group. Interbedded volcaniclastic sandstones, lava flows, hyaloclastic breccias and the tuffaceous shales of the Chillon Group were coeval with the early phases of emplacement of the Coastal Batholith (CB).

  6. A quantitative geomorphological approach to constraining the volcanic and tectonic evolution of the active Dabbahu rift segment, Afar, Ethiopia.

    NASA Astrophysics Data System (ADS)

    Medynski, Sarah; Pik, Raphaël; Burnard, Peter; Vye-Brown, Charlotte; Blard, Pierre-Henri; France, Lydéric; Dumont, Stéphanie; Grandin, Raphaël; Schimmelpfennig, Irene; Benedetti, Lucilla; Ayalew, Dereje; Yirgu, Gezahegn

    2013-04-01

    In the Afar depression (Ethiopia), extension is organised along rift segments that morphologically resemble oceanic rifts. Segmentation results from interactions between dyke injection and volcanism, as observed during the well-documented 2005 rifting event on the Dabbahu rift segment. This tectono-volcanic crisis was observed in detail via remote sensing techniques, providing invaluable information on the present-day tectonic - magmatic interplay during a sequence of dyke intrusions. However, lack of data remains on timescales of 1 to 100 kyr, the period over which the main morphology of the 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. We use cosmogenic nuclides (3He and 36Cl) to determine the ages of young (<100 kyr) lava flows and to date the initiation and movement of fault scarps, which cut the lavas. Where possible, we analysed vertical profiles along fault scarps, in an attempt to distinguish individual tectonic events that offset the scarp, estimate their amplitudes and date the recurrence intervals. These geochronological constraints, combined with major & trace element compositions, field mapping and digital mapping (Landsat, ASTER and SPOT imagery), provide valuable insights on the magmatic and tectonic history of the segment. The results show that over the last 100 ka, the northern part of the Dabbahu segment was supplied by at least two different magma reservoirs, which can be identified from their distinctive chemistries. The main reservoir is located beneath Dabbahu volcano at the northern tip of the rift segment, and has been supplied with magma for at least 72 ka. The second reservoir is located further south on the rift axis and corresponds to the current mid-segment magma chamber, which was responsible for the 2005 rifting episode. Two magmatic cycles linked to the Dabbahu magma chamber were recorded, lasting 20-30 kyr

  7. Late Paleozoic tectonic evolution and concentrated mineralization in Balkhash and West Junggar, western part of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Dong, Shuwen; Chen, Xuanhua; Chen, Zhengle

    2016-04-01

    course thermo-history of the minearl deposits from their formation in the deep to the exhumation in the surface. It reveals the arc-related granitic magmatism and the metallogeneses of skarn Cu, porphyry Cu-Mo, quartz-vein/greisen W-Mo, and orogenic Au in Late Paleozoic, the medium-temperature regional cooling in Late Paleozoic and Early Mesozoic, and the low-temperature exhumation of the deposits in Mesozoic. The timing, combined with geochemistry of granitoids, suggests a transition of tectonic environment from syn-collision and volcanic arc in Late Carboniferous to post-collision extension in Early Permian, and the concentrated mineralization of Cu, Mo, rare metals, and Au during this tectonic transition. The complete metallogenic series for the concentrated mineralization are from skarn and porphyry Cu-Mo deposits to rare metal and gold deposits. Key words: Late Paleozoic; Tectonic evolution; Concentrated mineralization; Balkhash-Junggar tectono-metallogenic belt; Central Asian Orogenic Belt

  8. Paleogeographic and tectonic controls on the evolution of Cenozoic basins in the Altiplano and Western Cordillera of southern Peru

    NASA Astrophysics Data System (ADS)

    Carlotto, Víctor

    2013-03-01

    Integrated studies of stratigraphy, sedimentology, paleogeography and tectonic controls on Cenozoic basins provide the basis for a series of time-slice reconstructions of basin evolution in the Andes of southern Peru. The Altiplano and adjacent margin of the Western Cordillera are characterized by several Paleocene-Miocene synorogenic continental basins with thicknesses locally exceeding 10 km. The evolution of these basins has been controlled by NW-trending tectonic features that mark the Altiplano-Western Cordillera and Altiplano-Eastern Cordillera boundaries and the Condoroma structural high. Sedimentary deposits of Paleocene age preserved in the Altiplano are the result of nonmarine sedimentation in a distal foreland basin. During the early Eocene, predominantly dextral strike-slip movements in the Altiplano between the Cusco-Lagunillas and Urcos-Ayaviri fault systems created the transpressional Kayra basin. The Soncco and Anta basins (middle Eocene-early Oligocene) are related to NE shortening (43-30 Ma) and represent proximal, wedge-top and foredeep basin environments preserved on the Altiplano. At ~ 29-28 Ma, a change to predominantly E-W shortening produced sinistral strike-slip motion along NW-striking faults, resulting in intermontane, transpressional basins. In the Altiplano, the Tinajani and Punacancha (29-5 Ma), and Paruro (12-6 Ma) basins were controlled by the Cusco-Lagunillas and the Urcos-Ayaviri fault systems. The Maure, Tincopalca-Huacochullo and Condoroma basins (22-5 Ma) of the Western Cordillera developed between the Condoroma high and the Cusco-Lagunillas fault system. Oligocene-Miocene sedimentation commonly evolved from proximal (alluvial) facies along the borders to distal (lacustrine) facies. These basins were linked to sinistral strike-slip faults that evolved into reverse-sinistral structures. Plate kinematics may play a role in Andean basin evolution, with deformation influenced by major preexisting faults that dictated paleogeographic

  9. Extensional salt tectonics in the partially inverted Cotiella post-rift basin (south-central Pyrenees): structure and evolution

    NASA Astrophysics Data System (ADS)

    López-Mir, Berta; Muñoz, Josep Anton; García-Senz, Jesús

    2015-03-01

    The Cotiella Massif in the south-central Pyrenees hosts upper Cretaceous gravity-driven extensional faults which were developed in the Bay of Biscay-Pyrenean paleorift margin of the Atlantic Ocean. They accommodate up to 6 km of post-rift carbonates above relict upper Triassic salt. Subsequent Pyrenean contractional deformation preserved the main extensional features, but most of the upper Triassic salt was expulsed and then dissolved, leaving little indications of the original salt volume. Nonetheless, several distinctive salt-related features are still recognizable both at outcrop and at basin scale, providing an exposed analogue for salt-floored extensional basins developed on passive margins. Based on field research, we re-interpret the tectonic evolution of the area and suggest that passive diapirs were coeval with gravity-driven extension during the development of the Cotiella basin. The given interpretations are supported with detailed geological maps, original structural data, cross sections and outcrop photographs. The discovery of previously unknown post-rift salt structures in the Cotiella Massif is an extra element to consider in the paleogeographic reconstructions of the upper Cretaceous passive margin of the Bay of Biscay-Pyrenean realm and consequently helps in our understanding of the evolution of current Atlantic-type margins.

  10. Tectonic evolution of the Songpan Garzê and adjacent areas (NE Tibet) from Triassic to Present : a synthesis.

    NASA Astrophysics Data System (ADS)

    Roger, F.; Jolivet, M.; Malavieille, J.

    2009-04-01

    The 12th May 2008 Wenchuan earthquake in the Longmen Shan occurred on a large thrust fault largely inherited from an Indosinian structure itself probably controlled by an older structural heritage of the South China block continental margin. Within the whole northeast Tibet region, such a structural inheritance has had a major impact on the Tertiary deformation. It appears of primary importance to assess the pre-Tertiary tectonic evolution of the main blocks involved to understand the actual deformation in the eastern edge of Tibet. Over the past decades, the Proterozoic to Cenozoic tectonic, metamorphic and geochronologic history of the Longmen Shan and Songpan Garzê area have been largely studied. We present a synthesis of the tectonic evolution of the Songpan Garzê fold and thrust belt from Triassic to present. The Songpan-Garzê belt was formed during closure of a wide oceanic basin filled with a thick (5 to 15 km) sequence of Triassic flyschoid sediments [10]. Closure of the basin due to Triassic subduction involved strong shortening, intense folding and faulting of the Triassic series. A large-scale décollement, that presently outcrops along the eastern boundary of the belt (Danba area), allowed the growth of a wide and thick accretionary wedge [9]. It develops in the Paleozoic and Triassic series and separates the accretionary prism from an autochthonous crystalline basement [5, 12, 6] which shares many similarities with the basement of the Yangtze Craton (0.7-0.9 Ga). To the north and northwest, below the thickened Triassic series of the belt, the composition (oceanic or continental) of the basement remains unknown. During the Indosinian orogeny the emplacement of orogenic granites (220 - 150 Ma) was associated to crustal thickening [12, 13, 17, 15]. The isotopic composition of granitoids shows that their magma source were predominantly derived from melting of the proterozoic basement with varying degrees of sedimentary material and negligible mantle

  11. A hypothesis for Proterozoic-Phanerozoic supercontinent cyclicity, with implications for mantle convection, plate tectonics and Earth system evolution

    NASA Astrophysics Data System (ADS)

    Grenholm, Mikael; Scherstén, Anders

    2015-11-01

    We present a conceptual model for supercontinent cycles in the Proterozoic-Phanerozoic Eons. It is based on the repetitive behavior of C and Sr isotopes in marine carbonates and U-Pb ages and εHf of detrital zircons seen during the Neoproterozoic-Paleozoic and Paleoproterozoic Eras, respectively. These records are considered to reflect secular changes in global tectonics, and it is hypothesized that the repetitive pattern is caused by the same type of changes in global tectonics. The fundamental premise of this paper is that such repetitive changes should also be recorded in orogenic belts worldwide. This carries the implication that Neoproterozoic-Paleozoic orogenic belts should have Paleoproterozoic equivalents. It is proposed that this is the case for the East African, Uralides and Ouachita-Alleghanian orogens, which have Paleoproterozoic analogs in the West African-Amazon, Laurentian and East European cratons, respectively. The Neoproterozoic-Paleozoic orogenic belts are not isolated features but occur in a specific global context, which correspond to the relatively well-constrained Neoproterozoic break-up of Rodinia, and the subsequent Late Paleozoic assembly of Pangea. The existence of Paleoproterozoic equivalents to Neoproterozoic-Paleozoic orogens requires that the same cycle defined the Paleoproterozoic. We therefore hypothesize that there were Paleoproterozoic supercontinents equivalent to Rodinia and Pangea, and that Proterozoic-Phanerozoic supercontinents are comprised of two basic types of configurations, equivalent to Rodinia (R-type) and Pangea (P-type). The Paleoproterozoic equivalent of Rodinia is likely the first supercontinent to have formed, and Proterozoic-Phanerozoic supercontinent cycles are therefore defined by R- to R-type cycles, each lasting approximately 1.5 Gyr. We use this cyclic pattern as a framework to develop a conceptual model that predicts the configuration and cycles of Proterozoic-Phanerozoic supercontinents, and their

  12. U-Pb Detrital Zircon Ages from Sarawak: Changes in Provenance Reflecting the Tectonic Evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Breitfeld, H. T.; Galin, T.; Hall, R.

    2014-12-01

    Sarawak is located on the northern edge of Sundaland in NW Borneo. Five sedimentary basins are distinguished with ages from Triassic to Cenozoic. New light mineral, heavy mineral and U-Pb detrital zircon ages show differences in provenance reflecting the tectonic evolution of the region. The oldest clastic sediments are Triassic of the Sadong-Kuching Basin and were sourced by a Carnian to Norian volcanic arc and erosion of Cathaysian rocks containing zircons of Paleoproterozoic age. Sandstones of the Upper Jurassic to Cretaceous Bau-Pedawan Basin have distinctive zircon populations indicating a major change of tectonic setting, including initiation of subduction below present-day West Sarawak in the Late Jurassic. A wide range of inherited zircon ages indicates various Cathaysian fragments as major source areas and the arrival of the SW Borneo Block following subduction beneath the Schwaner Mountains in the early Late Cretaceous. After collision of the SW Borneo Block and the microcontinental fragments with Sundaland in the early Late Cretaceous, deep marine sedimentation (Pedawan Formation) ceased, and there was uplift forming the regional Pedawan-Kayan unconformity. Two episodes of extension were responsible for basin development on land from the latest Cretaceous onwards, probably in a strike-slip setting. The first episode formed the Kayan Basin in the Latest Cretaceous (Maastrichtian) to Early Paleocene, and the second formed the Ketungau Basin and the Penrissen Sandstone in the Middle to Late Eocene. Zircons indicate nearby volcanic activity throughout the Early Cenozoic in NW Borneo. Inherited zircon ages indicate an alternation between Borneo and Tin Belt source rocks. A large deep marine basin, the Rajang Basin, formed north of the Lupar Line fault. Zircons from sediments of the Rajang Basin indicate they are of similar age and provenance as the contemporaneous terrestrial sediments to the south suggesting a narrow steep continental Sundaland margin at the

  13. Tectonic control on Pleistocene basin-filling processes and landscape evolution: the intermontane Kangra Basin, NW Sub-Himalaya, India

    NASA Astrophysics Data System (ADS)

    Dey, Saptarshi; Thiede, Rasmus; Schildgen, Taylor; Strecker, Manfred

    2015-04-01

    The growth of a collisional mountain belt like the Himalaya is dynamically coupled both to tectonics and climate and can result in strong temporal variations in the delivery of sediment to intermontane basins and the foreland. Orogenic critical taper models have been helpful to explain the processes controlling the evolution of mountain fronts in such settings. Rapid and voluminous sediment accumulations might destabilize the orogenic wedge and force architectural re-organization by outward propagation of the deformation front, while basin evacuation can induce out-of-sequence-thrusting to return the wedge to a critical taper. Structural reentrants along the Himalayan front are promising locations to study sediment delivery, storage, and sediment-evacuation mechanisms, as those areas commonly expose extensive transiently stored foreland-basin sediments. The Kangra re-entrant in the NW Sub-Himalaya hosts intermontane valley fills of Pleistocene age, eroded from the Dhauladhar Range. The sediments were unconformably deposited on top of Neogene foreland-basin sediments (i.e. the Siwaliks) in the hanging wall of the NW-SE striking Jwalamukhi Thrust. This major sediment accumulation phase appears to have preceded a phase of sediment evacuation in the course of episodic re-incision into the fill unit, which carved a series of fill-terrace levels. Angular unconformities, differential fluvial incision, tilted fluvial terraces, drainage re-organization, and steepened river segments in the hanging wall of the Jwalamukhi Thrust indicate post-depositional shortening and uplift in the Kangra re-entrant. From this evidence, we infer a primary importance of the Jwalamukhi Thrust in controlling the Quaternary sediment deposition in the Kangra re-entrant - however, we cannot exclude the influence of climate as the main trigger for sediment aggradation and subsequent excavation. However, knickpoints and steep river-channel gradients crossing other tectonic structures within the

  14. Paleoproterozoic structural evolution of the Man-Leo Shield (West Africa). Key structures for vertical to transcurrent tectonics

    NASA Astrophysics Data System (ADS)

    Lompo, Martin

    2010-08-01

    In the Man-Leo Shield, Paleoproterozoic (Birimian) belts crop out in nine countries of West Africa. Dominant domains include: (i) greenstone belts composed of plutono-volcanic, volcano-clastic and sedimentary rocks, deformed and weakly metamorphosed under regional greenschist facies conditions; (ii) widespread granitoid batholiths. The domains display a basin and dome-like architecture, and are overprinted by partitioned structures from successively shallower crustal depth. Analyses of key ductile and brittle structures has shown that the structural evolution of Man-Leo Shield is characterized by early vertical magmato-tectonics and subsequently, horizontal transcurrent tectonics with progression from ductile to brittle behavior. Basin and dome-like architectures, and the formation of an ubiquitous vertical foliation (MF) formed during emplacement of early amphibole-bearing (PAG) granite plutons at ca. 2.2 Ga by diapirism during NW-SE crustal shortening. Subsequent to a late stage of predominantly NW-SE shortening that created steeply-dipping mylonite zones (Mz1), transcurrent faults became predominant. The formation of transcurrent faults began transpressively, with development of N-S trending regional-scale mylonite zones (Mz1), and a steeply-plunging stretching lineation that probably formed during emplacement of PAG-type granitoids ca. 2.15 Ga. NNE-SSW transpressive sinistral horsetail faults and many NW-SE trending tension veins are interpreted to have formed at this stage. After cooling of the upper crust ca. 2.1 Ga, transcurrent faults became strike-slip in character with formation of dominantly NE-SW dextral faults (Mz2) and the passive emplacement of biotite (PBG) granitoids. Clockwise rotation of the extensional stress axis ( σ3) from NNE-SSW trending to ENE-SSW trending assisted the propagation of dextral NE-SW and sinistral NW-SE extensional en echelon horsetail faults. WNW-ESE trending extension jogs (Egz) are interpreted to have been initiated under

  15. Tectonic evolution of west Antarctica and its relation to east Antarctica

    SciTech Connect

    Dalziel, I.W.D.

    1987-05-01

    West Antarctica consists of five major blocks of continental crust separated by deep sub-ice basins. Marie Byrd Land appears to have been rifted off the adjacent margin of the East Antarctic craton along the line of the Transantarctic Mountains during the Mesozoic. Ellsworth-Whitmore mountains and Haag Nunataks blocks were also rifted from the margin of the craton. They appear to have moved together with the Antarctic Peninsula and Thurston Island blocks, segments of a Pacific margin Mesozoic-Cenozoic magmatic arc, during the Mesozoic opening of the Weddell Sea basin. Paleomagnetic data suggest that all four of these blocks remained attached to western Gondwanaland (South America-Africa) until approximately 125 m.y. ago, and that the present geographic configuration of the Antarctic continent was essentially complete by the mid-Cretaceous, although important Cenozoic rifting has also occurred. Fragmentation of the Gondwanaland supercontinent was preceded in the Middle to Late Jurassic by an important and widespread thermal event of uncertain origin that resulted in the emplacement of an extensive bimodal igneous suite in South America, Africa, Antarctica, and Australia. This was associated with the development of the composite back-arc basin along the western margin of South America. Inversion of this basin in the mid-Cretaceous initiated Andean orogenesis. The presentation will include new data from the joint US-UK West Antarctic Tectonics Project.

  16. Age and tectonic evolution of the northwest corner of the West Philippine Basin

    NASA Astrophysics Data System (ADS)

    Doo, Wen-Bin; Hsu, Shu-Kun; Yeh, Yi-Ching; Tsai, Ching-Hui; Chang, Ching-Ming

    2015-09-01

    To understand the tectonic characteristics and age of the northwestern part of the West Philippine Basin (WPB), multi-beam bathymetry and geomagnetic data have been collected and analyzed. The seafloor morphology obviously shows NW-SE trending seafloor fabrics and NE-SW trending fracture zones, indicating a NE-SW seafloor spreading direction. An overlapping spreading center near 22°20'N and 125°E is identified. Besides, numerous seamounts indicate an excess supply of magma during or after the oceanic crust formation. A V-shaped seamount chain near 21°52'N and 124°26'E indicates a southeastward magma propagation and also indicates the location of the seafloor spreading ridge. On the basis of the newly collected geomagnetic data, the magnetic anomaly shows NW-SE trending magnetic lineations. Both bathymetry and geomagnetic data reveal NE-SW seafloor spreading features between the Gagua Ridge and the Luzon Okinawa fracture zone (LOFZ). Our magnetic age modeling indicates that the age of the northwestern corner of the WPB west of the LOFZ is between 47.5 to 54 Ma (without including overlapping spreading center), which is linked to the first spreading phase of the WPB to the east of the LOFZ. In addition, the age of the Huatung Basin is identified to be between 33 to 42 Ma, which is similar to the second spreading phase of the WPB.

  17. Cenozoic thermal, mechanical and tectonic evolution of the Rio Grande rift

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Seager, W. R.; Golombek, M. P.

    1986-01-01

    Two areas of New Mexico which exhibit complex but similar Cenozoic histories of extensional tectonism are analyzed. The first study area is the Basin and Range province and southern Rio Gande rift in southern New Mexico; the second study area is the central Rio Grande rift in central and northern New Mexico, the southern San Luis basin, the Espanola basin, and the Albuquerque basin. Two phases of extension were identified: the first phase which began in mid-Oligocene was characterized by local high-strain extension events, low-angle faulting, and the development of broad, shallow basins, all indicating an approximately NE-SW + or - 25 deg extension direction; the later phase which occurred primarily in the late Miocene, was characterized by synchronous, high-angle faulting, resulting in large vertical strains which produced the modern Rio Grande rift morphology. Extension direction was approximately E-W. Geotherms were estimated and lithospheric strength curves were calculated for these two phases of extension. A high geotherm was deduced for the early phase resulting in a shallow crustal brittle transition, and insignificant mantle strength. The lithosphere subsequently cooled, resulting in a significant zone of mantle strength beneath the Moho. It is concluded that the interrelationship among regional and local prerifting, synrifting, and postrifting events in the Rio Grande rift attests to the fact that the rifting (in the region studied) should be considered in the context of other geologic events.

  18. Gravitational spreading, bookshelf faulting, and tectonic evolution of the South Polar Terrain of Saturn's moon Enceladus

    NASA Astrophysics Data System (ADS)

    Yin, An; Pappalardo, Robert T.

    2015-11-01

    Despite a decade of intense research the mechanical origin of the tiger-stripe fractures (TSF) and their geologic relationship to the hosting South Polar Terrain (SPT) of Enceladus remain poorly understood. Here we show via systematic photo-geological mapping that the semi-squared SPT is bounded by right-slip, left-slip, extensional, and contractional zones on its four edges. Discrete deformation along the edges in turn accommodates translation of the SPT as a single sheet with its transport direction parallel to the regional topographic gradient. This parallel relationship implies that the gradient of gravitational potential energy drove the SPT motion. In map view, internal deformation of the SPT is expressed by distributed right-slip shear parallel to the SPT transport direction. The broad right-slip shear across the whole SPT was facilitated by left-slip bookshelf faulting along the parallel TSF. We suggest that the flow-like tectonics, to the first approximation across the SPT on Enceladus, is best explained by the occurrence of a transient thermal event, which allowed the release of gravitational potential energy via lateral viscous flow within the thermally weakened ice shell.

  19. Tectonic and volcanic evolution of dark terrain and its implications for the internal structure and evolution of Ganymede

    NASA Technical Reports Server (NTRS)

    Murchie, Scott L.; Head, James W.; Plescia, Jeffrey B.

    1990-01-01

    The origins of the ancient dark terrain on Ganymede and its three furrow systems are investigated using detailed geologic mapping of the furrows and dark-terrain units, observations and crater density measurements, and calculations of relative crater ages of material units. The results of the analysis are used to develop a hypothesis of the early evolution of Ganymede. Multiple testable models of furrow origin are presented.

  20. Mantle convection, tectonics and the evolution of the Tethyan subduction zone

    NASA Astrophysics Data System (ADS)

    Jolivet, Laurent; Sternai, Pietro; Menant, Armel; Faccenna, Claudio; Becker, Thorsten; Burov, Evguenii

    2014-05-01

    Mantle convection drives plate tectonics and the size, number and thermotectonic age of plates codetermines the convection pattern. However, the degree of coupling of surface deformation and mantle flow is unclear. Most numerical models of lithospheric deformation are designed such that strain is a consequence of kinematic boundary conditions, and rarely account for basal stresses due to mantle flow. On the other hand, convection models often treat the lithosphere as a single-layer stagnant lid with vertically undeformable surface. There is thus a gap between convection models and lithospheric-scale geodynamic models. The transmission of stresses from the flowing mantle to the crust is a complex process. The presence of a ductile lower crust inhibits the upward transmission of stresses but a highly extended crust in a hot environment such as a backarc domain, with no lithospheric mantle and a ductile lower crust in direct contact with asthenosphere, will be more prone to follow the mantle flow than a thick and stratified lithosphere. We review geological observations and present reconstructions of the Aegean and Middle East and discuss the possible role played by basal drag in governing lithospheric deformation. In Mediterranean backarc regions, lithosphere-mantle coupling is effective on geological time scale as shown by the consistency of SKS fast orientations in the mantle with stretching directions in the crust. The long-term geological history of the Tethyan convergent zone suggests that asthenospheric flow has been an important player. The case of Himalaya and Tibet strongly supports a major contribution of a northward asthenospheric push, with no persistent slab that could drive India after collision, large thrust planes being then decoupling zones between deep convection and surface tectonics. The African plate repeatedly fragmented during its northward migration with the separation of Apulia and Arabia. Indeed, extension has been active on the northern

  1. Petrologic, tectonic, and metallogenic evolution of the Ancestral Cascades magmatic arc, Washington, Oregon, and northern California

    USGS Publications Warehouse

    du Bray, Edward A.; John, David A.

    2011-01-01

    reflects extensional tectonics that dominated during these periods of arc magmatism. Mineral deposits associated with ancestral Cascades arc rocks are uncommon; most are small and low grade relative to those found in other continental magmatic arcs. The small size, low grade, and dearth of deposits, especially in the southern two-thirds of the ancestral arc, probably reflect many factors, the most important of which may be the prevalence of extensional tectonics within this arc domain during this magmatic episode. Progressive clockwise rotation of the forearc block west of the evolving Oregon part of the ancestral Cascades magmatism produced an extensional regime that did not foster significant mineral deposit formation. In contrast, the Washington arc domain developed in a transpressional to mildly compressive regime that was more conducive to magmatic processes and hydrothermal fluid channeling critical to deposit formation. Small, low-grade porphyry copper deposits in the northern third of the ancestral Cascades arc segment also may be a consequence of more mature continental crust, including a Mesozoic component, beneath Washington north of Mount St. Helens.

  2. Tectonomagmatic evolution of the Earth: from the primordial crust to plate tectonics

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.; Bogatikov, O. A.

    2009-12-01

    There are two dominating hypotheses about composition of the primordial Earth’s crust now: basic or sialic. Both models require a global melting of primary chondritic material, and final result would depend on degree of melt differentiation during hardening of global magmatic ocean. Such a solidification, due to difference in adiabatic and melting point gradients proceeded in bottom-top direction and resulted in accumulation of low-temperature derivates in outer shell of the planet. Geological data, namely granite-dominated Archean crust, composed mainly by tonalite-trondhjemite-granodiorite (TTG) rocks, and Hadean detrital zircons from Australia with U-Pb age 4.4-4.2 Ga supports the primordial-sialic crust hypothesis. Formation of the sialic crust was responsible for the depletion of the upper mantle matter. The early Precambrian (Archean, Early Paleoproterozoic) tectonomagmatic activity was rather different from the Phanerozoic: the major structures were granite-greenstone terranes and their separating granulite belts; high-Mg melts (komatiite-basaltic and boninite-like), derived from a depleted source of the first generation mantle superplumes, predominated. Situation can be described in terms of plume-tectonics. Cardinal change of tectonomagmatic processes occurred in the period of 2.3 to 2.0 Ga, which was characterized by voluminous eruption of Fe-Ti picrites and basalts similar to the Phanerozoic within-plate magmas, derived from geochemical-enriched mantle source. Simultaneously, important compositional changes occurred in the atmosphere, hydrosphere and biosphere (Melezhik et al., 2005). The first Phanerozoic-type orogens (Svecofennian of the Baltic Shield, Trans-Hudson and others of the Canadian Shield, etc.) appeared ca. 2 Ga. Since then, subduction of the ancient sialic continental crust (together with newly-formed oceanic crust) is a permanent process and the crustal material has stored in the “slab graveyard”, estimated in the mantle by seismic

  3. Geophysical Evidence for the Tectonic Evolution of the Inverted Belt-Purcell Basin, Northwestern Montana

    NASA Astrophysics Data System (ADS)

    Rutherford, B. S.; Speece, M. A.; Constenius, K. N.

    2015-12-01

    The geometry of the Precambrian Belt-Purcell basin and subsequent allochthon, that dominates the geology of northwestern Montana, played a critical role in the development of compressional structures during orogenesis and their ensuing reactivation during the later phase of extensional collapse. Five reprocessed seismic reflection profiles provide images in the Swan Range and adjacent valleys that we have correlated to published seismic data north into Canada. Reflections from syndepositional sills encased within Lower Belt rocks offer clues to the configuration of the basin prior to its tectonic inversion. Thick basinal facies of the Lewis salient are contrasted by thin shelfal facies found in hanging wall rocks of frontal Belt carrying thrusts south of the salient. The along strike change in hanging wall rocks reflects the original configuration of the Belt basin margin. Rocks of the Lewis salient were deposited in an embayment on the northeastern margin of the Belt basin. Shelfal accumlations of the embayment comprise an autochthonous wedge that has remained in the footwall of the Lewis thrust system. South of the embayment and related salient, nearly the entire Belt basin was detached from pre-Belt crystalline rocks and inverted at the latitude of the Sawtooth Range. Deeply exhumed Phanerozoic rocks of the Sawtooth Range are a direct consequence of the thin wedge geometry of the detached basin south of the Lewis salient that required growth of a substantial orogenic wedge to obtain critical taper values. We offer an alternate interpretation of a >10 km high, west facing décollement ramp that coincides with the Belt-Purcell basin margin. Previous interpretations in Montana have inferred the location of the basin margin ramp to approximate the trace of the Purcell Anticlinorium. Seismic data and cross-section balancing suggest the Rocky Mountain Trench as a more accurate location. Based on our proposed position of the basin margin the Belt-Purcell allocthon

  4. Paleozoic archipelagic tectonic evolution of Western Junggar, NW China: implications for continental growth of southern Altaids

    NASA Astrophysics Data System (ADS)

    Zhang, Jien; Xiao, Wenjiao; Han, Chunming; Ma, Chong; Song, Dongfang

    2013-04-01

    The Western Junggar, NW China, a dominant site for continental growth in Southern Altaids, bridges the Circum-Balkhash and Junggar belts and exposes ophiolite, igneous rocks and strata from Cambrian to Carboniferous. Recent updated data on structure, geochronology, geochemisty and paleomagnetism, integrated with previous data, present a newly Paleozoic spatial and temporal framework of Western Junggar. In Cambrian, the Western Junggar begins to birth at the Tangbale area to south, where occurs Ordovician blueschist and top-to-south vergence structures, indicating north-dipping subduction. This event triggers intra-arc extension to generate Ordovician island arc in the Hongguleleng-Xiemisitai area to north and seamount in the Mayile area, middle of Western Junggar. Until Silurian, a southeastward subduction begins in the extended back-arc basin to west of Mayile, occurring blueschist at the Barleik trench and the Nalunsuo magmatic arc, at the rear of which generates Devonian back-arc basin around the Durbut area. Meanwhile, a Silurian Xiemisitai magmatic arc has been developed at the northern part of Western Junggar, along which a northward subduction has emplaced the Tarbahatai ophiolite and generates the Carboniferous Sawur magmatic arc. At the middle part of Western Junggar, the coeval adakite and sanukitic dykes, charnockite, multiple properties of ophiolite and plutons, SSZ-like andesite, dacite and rhyolite and regional structures suggest that there develop double-subduction systems with ridge-trench interaction in Carboniferous. These features suggest that the Western Junggar experiences rollback, intra-oceanic extension and subduction polarity reversal/flip in back-arc basin settings. Furthermore, positive ɛNd(t) values and no huge movements of blocks suggest that the Western Junggar is amalgamated by juvenile elements with different orientations. Therefore, we conclude that the Western Junggar enlarges from an island arc to Paleozoic tectonic regime with

  5. Volcano-tectonic evolution of the Castle Mountains: 22 to 14 MA

    SciTech Connect

    Capps, R.C. . Dept. of Geology)

    1993-04-01

    The alkali-calcic Castle Mountains Volcanic rocks (CMV) are host to major gold mineralization. They are located about 100 km south of Las Vegas, Nevada and are on the boundary between the Basin and Range Province and Colorado River extensional corridor (35[degree]18 minutes 45 seconds N, 115[degree]05 minutes 10 seconds W). New data show the following chronology. 22 Ma. A regional rhyolite ash-flow tuff, the Castle Mountain Tuff member, was deposited on a Proterozoic-Paleozoic basement of low relief. <22 Ma - > 17 Ma. Normal faulting (N30--60[degree]W, 60--65[degree]NE) formed half-grabens. Latite and basalt flows, minor ash-flow tuffs, lahars and sediments (Jacks Well member - JW) were deposited unconformably. JW magmas are enriched in light REE compared to the younger CMV. <17 Ma to 15.5 Ma. Oxidizing upper portions (796 C) of a shallowly emplaced silicic melt erupted to form the high-silica rhyolite dome complexes and intrusives (Linder Peak member - LP) of the NNE-striking Castle Mountains. NW-striking transverse structures caused discontinuities in strike direction of the subvolcanic intrusive and domes and helped form a synvolcanic depression. During a hiatus in volcanism, early Hart Peak member (HP) sediments were deposited marginal to the Castle Mountains. Major gold mineralization and widespread hydrothermal alteration occurred at about 15.5 Ma. 16 Ma to 14 Ma. Early HP volcaniclastic sediments, rhyolite pyroclastic-surge tuff, and basaltic flows, were deposited during late hydrothermal alteration and then fractured and displaced by NNE-striking normal faults, especially in the eastern and northeastern CMV. < 14 Ma. Tectonically significant flat-lying boulder conglomerate and unconformably overlying, largely andesitic flows fill depressions in the Castle Mountains and the Piute Range to the east.

  6. Geohistory analysis of Neogene Point Arena Basin, California: implications for its tectonic evolution

    SciTech Connect

    Loomis, K.B.; Ingle, J.C. Jr.

    1988-03-01

    The Neogene Point Arena basin of northwestern California is located west of the San Andreas fault system and south of the Mendocino triple junction. Key units of the Point Arena sequence are exposed from Iversen Landing north to Point Arena, California, including the Oligocene-Miocene Iversen Basalt (23.8 Ma), the lower Miocene Skooner Gulch and Gallaway Formations, and the lower to mid-Miocene Point Arena Formation. Lithologic and thickness data, together with evidence of age and paleobathymetry from both onshore and offshore sequences in the Point Arena basin, were used in a geohistory analysis of basin development. The resulting geohistory diagram tracks depths of specific stratigraphic zones, variations in paleobathymetry, and patterns of subsidence and uplift during late Paleogene through Neogene time. Geohistory analysis indicates that the late Paleogene margin was uplifted during approach of the Pacific-Farallon spreading ridge. Subsequently, a pulse of volcanism during latest Oligocene-Miocene signaled initial Neogene subsidence of the margin as marked by the Iversen Basalt. Subsidence likely involved both initial thermal subsidence as well as later transtensional deformation during the passage of the Mendocino triple junction and initiation of the San Andreas fault system. Rapid initial subsidence was accompanied by deposition of turbidites (Skooner Gulch and Gallaway Formation). The highly organic shales and petroliferous sands of the overlying Point Arena Formation indicate an abrupt cessation of turbidite deposition and a slower rate of basin subsidence during the middle Miocene. Episodes of warping from mid-Miocene through Holocene can be attributed to crustal flexing associated with wrench tectonism, with a major event bringing the Point Arena sequence above sea level during the late Pliocene-Pleistocene.

  7. Tectonic Structure, Classification, and Evolution of Arachnoids on Venus: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Krassilnikov, A. S.

    2002-09-01

    An analysis has been done of the topography and geologic structure of arachnoids-specific radial/concentric volcannic-tectonic structures on the surface of Venus. A representative sample (53 arachnoids) from 265 structures of this type, which are listed in the catalog of volcanic structures of the surface of Venus (Crumpler and Aubele, 2000), has been studied. The overwhelming majority of arachnoids are shown to be depressions that are commonly outlined by concentric extensional structures. Following Head et al. (1992) and Aittola and Kostama (2001), the assumption is confirmed and substantiated that arachnoids are formed by gravitational relaxation of small magmatic diapirs. Several types of arachnoids are identified on the basis of an analysis of structural patterns characteristic of such structures. It is also shown that the formation of different types of arachnoids depends on the depth of the magmatic diapir under the surface, on the thickness and reologic properties of the structures superposed on the evolving magmatic diapir, and on the character of regional stress fields that arise in the process of formation of such structures. The conclusion is drawn that most of the arachnoids were formed due to the gravitational relaxation of magmatic diapirs within the brittle part of the lithosphere, and some of them appeared as a result of the gravitational relaxation of radially fractured centers-novae. It is also shown that arachnoids are long-lived and multistep structures. At least some of them began to evolve before the formation of regional plains with wrinkle ridges, and their development ended after this event.

  8. Tectonic/physiographic evolution of the southern margin of the Colorado Plateau, central Arizona

    SciTech Connect

    Nations, J.D.; Potochnik, A.R. . Dept. of Geology)

    1993-04-01

    Six tectonostratigraphic assemblages along the southern boundary of the Colorado Plateau document progressively greater extensional partitioning of the Transition Zone during the Tertiary. (1) In the Eocene, the Mogollon Rim assemblage (>37.6 Ma) was deposited by laterally extensive, northeastward-flowing streams in the Transition Zone and on the Colorado Plateau on an erosion surface cut on Proterozoic through early Permian rocks. Deposition occurred prior to structural lowering in the Transition Zone, predating formation of the Plateau's southern escarpment in this area. (2) The Late Oligocene-Early Miocene (>21.5 Ma) Beavertail fluvial assemblage was deposited on a similar erosion surface extending at least 48 km south of the Plateau. Sedimentologic analyses indicate northeastward transport toward the Plateau, then diversion along a strike valley toward the southeast at the base of an ancestral escarpment. (3) The unconformably overlying Early to Middle Miocene (17.9--10 Ma) Hickey assemblage are basalts and fluvial volcaniclastics also deposited within the Transition Zone and south of the ancestral escarpment. Abundant basalt suggests onset of Basin and Range tectonism in the area but distribution beyond the bounds of the Verde Basin indicates deposition prior to subsidence of the Verde basin. Unconformably overlying the Hickey assemblage are basalts and fluvial lacustrine deposits which represent deposition in discrete basins within the Transition Zone. External drainage of these three basins was initiated during Blancan time (2--4 Ma), probably due to headward erosion by Colorado River tributaries following opening of the Gulf of California beginning about 5.5 Ma.

  9. Magmatic and tectonic evolution of the Ladakh Block from field studies

    NASA Astrophysics Data System (ADS)

    Raz, U.; Honegger, K.

    1989-04-01

    The Ladakh Block is in an intermediate position between the Indian plate in the south and the Karakorum-Tibetan plate in the north. To the west it is separated from the Kohistan Arc by the Nanga Parbat Syntaxis, to the east it is cut off from the Lhasa Block by the Gartok-Nubra Fault. Present data, together with previously published results, show, that the Ladakh Block consists of an island arc in the south and a calc-alkaline batholith in the north with remnants of a continental crust. Migmatitic gneisses and metasedimentary sequences, such as quartzites and metapelites, interbedded with basaltic volcanics and overlain by thick platform carbonates were found as evidence of a continental crust. Remnants of megafossils ( Megalodon and Lithiotis) within the high-grade metamorphic marbles indicate a probable age of Late Triassic to Early Jurassic. These sediments were intruded by a faintly layered hornblende-gabbro, which preceded the calc-alkaline magmatic episode. Gabbro and gabbronorites are found as roof pendants and large inclusions within diorites and granodiorites. The major part of the batholith consists of granodiorite and biotite-granite plutons, ranging from Late Cretaceous to Tertiary. Associated with the intrusives are volcanic rocks with trachyandesite to alkalibasalt and basalt-andesite to rhyolite compositions. Garnet-bearing leucogranites succeeded the emplacement of the major plutons. The magmatic stage ended, finally, by intense fracturing and injections of NE-SW striking andesitic dykes. The southernmost unit of the Ladakh Block is formed by oceanic crust with serpentinized peridotite and hornblende-gabbro and is covered by volcanics of an island-arc type (Dras volcanics). These units are intruded by gabbronorite, as well as Middle and Upper Cretaceous granodiorite and coarse-grained biotite-granite. In a plate tectonic view the Ladakh Block represents a transitional sector between the pure island arc of Kohistan in the west and the Andean type

  10. The Tectonic Evolution of SE Canada: Seismic Evidence from the QM-III Experiment

    NASA Astrophysics Data System (ADS)

    Bastow, I. D.; Boyce, A.; Darbyshire, F. A.; Levin, V. L.; Menke, W. H.; Ellwood, A.

    2014-12-01

    Much of the geological record can be interpreted in the context of processes operating today at plate boundaries. This works well to explain processes and products during the Phanerozoic era; during Precambrian times when the oldest rocks were forming, however, conditions on the younger, hotter, more ductile Earth were likely very different, making analogies with modern day tectonics less certain. Gathering evidence preserved deep within the plates in the shields is thus essential to improve our understanding of the early Earth. Shields are usually underlain by thick, seismically fast roots that are absent beneath younger portions of Earth's surface. The thermochemically distinct nature of cratonic roots is often associated with Archean processes such as the extraction of komatiitic magmas. However, the cratonic core of North America does not fit easily into this Archean formation paradigm: part of the Canadian shield extends beneath the Archean Superior craton, but much of it persists beneath younger Proterozoic crust as well. We present here a relative arrival-time tomographic study of mantle seismic structure using data from a new seismograph network operating in SE Canada. Our stations extend from the Archean Superior craton around the southern tip of Hudson Bay, through Proterozoic Grenville terranes, and into Paleozoic coastal Maine and Nova Scotia. Tomographic images display three broad zones of mantle wavespeed: slow in the Appalachian terranes; fast in the Grenville Province; very fast within the Superior craton. Archean lithosphere has been modified by the Great Meteor hotspot, but we find no evidence for major plate-scale underthrusting during the Grenville orogeny. The abrupt wavespeed transition from Archean to Proterozoic mantle is thus consistent with the emerging consensus that keels form in two stages: a chemically depleted layer in Archean times followed by the thermal development of a less-depleted lithosphere during Proterozoic times.

  11. Structural and tectonic evolution of the eastern Cayman Trough (Caribbean Sea) from seismic reflection data

    SciTech Connect

    Leroy, S.; Mauffret, A.; Pubellier, M.

    1996-02-01

    The eastern Cayman Trough preserves a record of the Late Cretaceous to Paleogene Caribbean history that is largely affected by Neogene strike-slip tectonics of the current plate boundary. We conducted an analysis of seismic data within the eastern Cayman Trough, based upon single and multi-channel seismic reflection profiles collected during the Seacarib II cruise in 1987 and the Casis cruise in 1992. These data show that the basement of the eastern Cayman Trough can be divided into four domains from east to west, with distinct morphologic and sedimentary character and inferred older to younger ages: (1) a province of rifted Mesozoic continental crust exhibiting seven parallel horst blocks striking northeast-southwest; (2) a continent-ocean transition between provinces 1 and 3 that exhibits seamounts, small hills, and sedimentary basins; (3) an Eocene oceanic crust with rough basement but smoother relief than the rifted crust; basement trends are roughly north-south and oblique to the northwest trend in domain 1, and (4) the northern Jamaica slope, which forms an east-west-trending slope, with northward-dipping strata that flank the three deeper water domains of the Cayman Trough. The domains are interpreted to be the product of the Eocene east-west opening of the Cayman Trough as a pull-apart basin in a left-lateral strike-slip setting. Closure of the 1100 km of Eocene and younger oceanic crust of the Cayman Trough places the fault-block province adjacent to the Belize margin of Central America. A Neogene phase of transpression has reactivated structures in the four domains, along with on-land structures described by previous authors in Jamaica. The proximity of the eastern margin of the Cayman Trough to petroliferous, continental rocks in Central America suggests an improved possibility of hydrocarbon potential. Unfortunately, sediment thicknesses of less than 1 km probably are not conducive to hydrocarbon formation.

  12. Tectonic Evolution of the Patagonian Orocline: New Insights from a Paleomagnetic Study in Southernmost America

    NASA Astrophysics Data System (ADS)

    Roperch, P. J.; Poblete, F.; Arriagada, C.; Herve, F.; Ramirez de Arellano, C.

    2015-12-01

    One of the most noteworthy features of the Southern Andes is its bend, where the orogenic trend and main tectonic provinces change from Andean N-S oriented structures to W-E orientations in Tierra del Fuego. Few paleomagnetic studies have been carried out, and whether the bending is a primary curvature or a true orocline is still matter of controversy; also the mechanism of its formation. We have conducted a paleomagnetic study between 50°S to ~56°S, where 146 sites were drilled. Paleomagnetic data were obtained in 44 sites. Results in Early Cretaceous sediments and volcanics rocks confirm a remagnetization event during the mid-Cretaceous and record ~90° of counterclockwise rotation. Paleomagnetic results in mid-Cretaceous intrusives rocks record large counterclockwise rotation (>90°) while Late Cretaceous-Early Eocene intrusive rocks only record ~45° to ~30°. The paleomagnetic results reveal a systematic pattern of rotation—the Fueguian rotation pattern—suggesting that the curvature of Patagonia would have occurred in two stages: the first stage during the collapse and obduction of the Rocas Verdes basin in the mid-Cretaceous and a second stage between the Late Cretaceous and the Paleocene, concomitant with exhumation of Cordillera Darwin and propagation of the fold and thrust belt into the Magallanes foreland. Integrating this result in plate reconstructions shows the Antarctic Peninsula as a prolongation of Patagonia and would have acted as a non-rotational rigid block, facilitating the development of the Patagonia Bend. This land bridge could be a dispersal mechanism for fauna between Australia and South America and would have restricted deep ocean water circulation.

  13. 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.

  14. Crustal structure and tectonic evolution of the Hecataeus Rise near the Cyprus-Eratosthenes Seamount collision zone

    NASA Astrophysics Data System (ADS)

    Reiche, Sönke; Welford, Kim; Hübscher, Christian; Hall, Jeremy

    2015-04-01

    The Hecataeus Rise represents a plateau-like structure, adjacent to the southern Cyprus margin and directly next to the Cyprus - Eratosthenes Seamount convergence zone, where incipient continent- continent-collision is believed to occur. Newly acquired wide-angle seismic profiles together with a dense grid of seismic reflection and multibeam bathymetric data provide insight into the crustal structure and Miocene-Quaternary structural evolution of this yet underexplored sector along the African-Anatolian plate boundary. Refraction seismic modeling suggests that the Hecataeus Rise is composed of a thick sedimentary cover underlain by an intermediate crust of presumably continental origin. Velocity models show significant lateral velocity variations along the African-Anatolian plate boundary, directly south of the Hecataeus Rise. High-velocity basement blocks coincide with highs in the magnetic field and appear to extend parallel to the margin of the Hecataeus Rise. We relate these high-velocity blocks to the presence of remnant Tethyan oceanic crust along a transform margin. Seismic reflection interpretation suggests that a Miocene period of tectonic compression has significantly deformed the western and southern part of the plateau area. Onshore Cyprus, structural lineaments were presumably active at the same time (Robertson, 1998) and can be traced offshore across the Hecataeus Rise. Post-Messinian convergence was accommodated along the southeastern flank of the Hecataeus Rise, where NE-SW trending anticlinal structures experienced reactivation and significant growth. A prominent intra-Pliocene-Quaternary unconformity in the northwestern part of the plateau area may correlate with the Plio-Pleistocene transition and indicates the near synchronous occurrence of several tectonostratigraphic events. We suggest that these events represent a chain of structural and depositional changes initiated by incipient collision of Eratosthenes Seamount with Cyprus and the

  15. Tectonic evolution of early Paleozoic HP metamorphic rocks in the North Qilian Mountains, NW China: New perspectives

    NASA Astrophysics Data System (ADS)

    Song, Shuguang; Niu, Yaoling; Zhang, Lifei; Wei, Chunjing; Liou, June G.; Su, Li

    2009-07-01

    The North Qilian Mountain range is one of the three oldest orogenic belts preceded with a cold oceanic subduction-zone so far recognized on Earth with a subduction history from 490 Ma to 440 Ma in rock record. This orogenic belt has received much attention over the past decades. A significantly improved understanding of the tectonic evolution of the orogenic belt is now emerging thanks to detailed mineralogical, petrologic, geochemical and geochronological studies as well as field observations carried out over the past few years. In this paper, we offer new perspectives on the tectonic evolution of the North Qilian orogenesis in terms of subduction-zone metamorphism by integrating existing observations and our new data. We provide fairly comprehensive documentation of various observations to support our interpretations, which will also serve as a convenient guide for the field excursion of the 8th International eclogite conference. In the North Qilian subduction-zone complex (suture zone), two sub-belts of high-pressure (HP) metamorphism have been distinguished in terms of mineral assemblages, i.e., the low-grade blueschist belt and high-grade blueschist-eclogite belt. The low-grade blueschist belt consists of lawsonite-pumpellyite-glaucophane schist, lawsonite-glaucophanite and minor lawsonite-bearing felsic blueschist with a typical mineral assemblage of Lws + Pmp + Gln + Ab + Chl ± Arg. This assemblage constrains the metamorphic conditions of T = ˜250-350 °C and P = 0.6-1.1 GPa. Protoliths of the lawsonite-bearing mafic blueschist are similar to present-day N-type MORB. The high-grade blueschist belt occurs as three slices within the island-arc volcanic complex and consists of blueschist- to eclogite-facies metamorphosed greywacke, basite, serpentinite, meta-pelite, chert and marble. Lawsonite and Mg-carpholite occur in eclogites and meta-pelites, respectively. P- T estimation yields peak metamorphic conditions of P = 2.2-2.6 GPa and T = 460-540 °C for

  16. Stress fields recorded on large-scale strike-slip fault systems: Effects on the tectonic evolution of crustal slivers during oblique subduction

    NASA Astrophysics Data System (ADS)

    Veloso, Eugenio E.; Gomila, Rodrigo; Cembrano, José; González, Rodrigo; Jensen, Erik; Arancibia, Gloria

    2015-11-01

    In continental margins, large-scale, strike-slip fault-systems resulted from oblique subduction commonly exhibit a complex pattern of faulting where major faults define the inland boundary of tectonic slivers that can be detached from the margin. In turn, subsidiary faults bound and define internal tectonic blocks within the sliver which are expected to rotate, translate and/or internally disrupt in order to accommodate the internal deformation. The geometrical and spatial arrangement of faults and tectonic blocks thus determines the evolution of the sliver given a particular stress field regime. The Paposo segment of the Atacama Fault System in northern Chile displays a series of brittle faults whose orientations are hierarchically arranged: low-order faults splay off higher-order faults forming Riedel-type and strike-slip duplexes geometries at several scales. The master (1st- and highest-order) Paposo Fault defines the inland boundary of a tectonic sliver whereas subsidiary faults bound and disrupt internal tectonic blocks. By using newly collected brittle fault-slip data we estimated the orientations and regimes of the stress fields that acted upon the entire sliver, the different fault-orders and the tectonic blocks. Results indicate that an overall transtensional - with NW-compressional and NE-tensional principal axes - strike-slip regime affected the sliver and triggered the development of left-lateral strike-slip structures. An incomplete split of the stress field imposed by the subduction process resulted in the generation of a nested pattern of R-type faults as well as in a combined strike-slip/normal faulting disruption of the tectonic blocks within the sliver.

  17. Analysis of topography and relief as a function of the tectonic - geomorphologic evolution of the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Bungies, Nadin; Rosenberg, Claudio

    2014-05-01

    Alpine topography and relief vary regionally (Frisch et al., 1997), even on the scale of tens of kilometers. The causes of these differences are the aim of this work that is based on a geomorphological study of the eastern Alps. Earlier investigations on the topography of the Central Alps (Rosenberg & Garcia, 2013) show, by using 50 km, 75 km, and 100 km swath profiles, that the relief northward of the Insubric Line increases westward, whereas the relief southwards of the Insubric Line decreases eastward. This trend reflects collisional shortening trends recently observed in the Central Alps (Rosenberg & Kissling, 2013). In this work, we analyse the topography of the eastern Alps from the Brenner Area in the west to the Steiermark Area in the east, based on satellite images and digital terrain models, that cover an area of 36 000 km2 in the Austrian and Italian Alps. Based on these data, new GIS-aided datasets containing selected relief factors have been derived. These data are set in relationship to the eastward decrease in collisional shortening to test whether the latter trend has a geomorphic expression. In order to assess such a relationship north-south striking profiles, subparallel to the shortening direction and in addition to an E-W profile are investigated. It can be shown that the total relief of 3100 m (500-3600 m asl.) in the west of the working area is more pronounced than the total relief of 2300 m (700-3000 m asl) in the east of the working area. Furthermore slopes have higher amplitudes in the west when compared to the east. In the west approximately 65% of the slope profile show slopes larger than 50° while in the east approximately 40% of slopes are larger than 50° (based on 30 m topographic data). The evaluation of potential influencing factors will be achieved by conducting spatial and statistical data analysis and interpretation and is complemented by local studies investigating the evolution of relief for selected geologic units. Here

  18. Miocene to Holocene Tectonic Evolution of the Dushanzi Anticline (northern Tianshan): a Structural and Geomorphologic Perspective

    NASA Astrophysics Data System (ADS)

    Saint-Carlier, D.; Charreau, J.; Lavé, J.; Blard, P.; Dominguez, S.; Avouac, J.; Malatesta, L. C.; Wang, S.

    2013-12-01

    The Tianshan is one of the largest and highest mountain belts in central Asia and accommodates an important part of the total India/Eurasia convergence. It is therefore critical to better quantify the deformation across this range especially across its piedmonts which focus most of the tectonics. The northern Tianshan piedmont deformation is partitioned across several thrusts and folds including the Dushanzi anticline identified as a fault-bend-fold. Across this fold we document the shortening rate from the Mio-Pliocene to the Holocene using different approaches. First, the Mio-Pliocene history of folding and shortening is constrained by subsurface seismic profile, magnetostratigraphic dating, and surface structural measurements, and using a kinematic fold model. The Dushanzi anticline was active at least since 9Ma and we identify two periods of fold growth. The first period lasts from 9 to 2Ma and corresponds to a relatively gentle growth at a shortening rate of ~0.45 mm/yr. Then, from 2 to at least 1.4Ma the deformation was probably enhanced and the shortening rate increases to ~1.5 mm/yr. The initiation of fold growth since at least 9Ma and the acceleration around 2Ma were also confirmed by an independent approach based on a geomorphic analysis of a deformed 10-Kyr-old alluvial terrace that is continuously preserved across the fold. In absence of growth strata, during fault-bend-folding, a simple trigonometric rule links shortening to terrace uplift and bedding dip measurements at surface: the initiation of growth strata is therefore easily identified on the fold back-limb by a marked departure of the local apparent value of shortening when using this relation. In addition, for the pre-growth strata domain, terrace uplift and fault-bend-fold model indicates a mean shortening rate of ~ 5 mm/yr since the terrace abandonment. Such rate is coherent, despite being slightly higher, than a rate of ~4 mm/yr obtained when using a decollement level at 7km and an excess

  19. Tectonics, structure, and metamorphic evolution of the Himalayan fold-thrust belt, western Bhutan

    NASA Astrophysics Data System (ADS)

    Tobgay, Tobgay

    Field mapping in western Bhutan in combination with U-Pb ages, geochemical data, stratigraphic columns, mineral assemblages and reaction textures, micro- and macro-scale structural observations, and balanced cross sections have allowed us to: (1) evaluate the use of detrital zircon and geochemical signatures for tectonic interpretation, (2) define tectonostratigraphy of litho-units in western Bhutan, particularly the Paro Formation, (3) produce pressure-temperature paths of deformed rocks, and (4) evaluate the magnitudes and rates of shortening through this portion of the Himalayan orogen. We divide the Lesser Himalayan (LH) section into four map units that range from Paleoproterozoic to Ordovician in age. The Paro Formation is interpreted as the distal equivalent of the Jaishidanda Formation based on a similar structural position immediately below the Main Central thrust (MCT) as well as similarity in detrital zircon signatures. Th-Pb ages of metamorphic monazite from Greater Himalayan (GH) rocks and a single age from the upper LH rocks bracket the minimum age of the MCT displacement between 20.4 +/- 1.0 and 15.1 +/- 0.4 Ma. Young monazite ages indicate that GH rocks continued to cool even until ˜10 Ma. A total displacement of ˜230 km achieved over 5 Myr yields a long-term horizontal shortening rate of 4.3 +/- 1.2 cm/yr. In western Bhutan, patterns of metamorphic isograds show an inversion of metamorphic field gradient extending from the upper LH section to the higher structural levels of GH right below the lower-South Tibetan Detachment. In the GH section, deformation postdates peak metamorphic conditions that prevailed at ˜20 Ma. In the Paro Formation, the presence of deformed kyanite at the base of the section and presence of undeformed sillimanite at the upper part of the section suggests burial to the kyanite stability field and syn- to post-deformational growth of sillimanite. A balanced cross-section across western Bhutan illustrates three endmember

  20. Volcanic field elongation, vent distribution and tectonic evolution of continental rift: The Main Ethiopian Rift example

    NASA Astrophysics Data System (ADS)

    Mazzarini, Francesco; Le Corvec, Nicolas; Isola, Ilaria; Favalli, Massimiliano

    2015-04-01

    Magmatism and faulting operate in continental rifts and interact at a variety of scales, however their relationship is complex. The African rift, being the best example for both active continental rifting and magmatism, provides the ideal location to study the interplay between the two mechanisms. The Main Ethiopian Rift (MER), which connects the Afar depression in the north with the Turkana depression and Kenya Rift to the south, consists of two distinct systems of normal faults and its floor is scattered with volcanic fields formed by tens to several hundreds monogenetic, generally basaltic, small volcanoes and composite volcanoes and small calderas. The distribution of vents defines the overall shape of the volcanic field. Previous work has shown that the distribution of volcanic vents and the shape of a field are linked to its tectonic environment and its magmatic system. In order to distinguish the impact of each mechanism, we analyzed four volcanic fields located at the boundary between the central and northern MER, three of them (Debre Zeyit, Wonji and Kone) grew in the rift valley and one (Akaki) on the western rift shoulder. The elongation and shape of the fields were analyzed based on their vent distribution using the Principal Component Analysis (PCA), the Vent-to-Vent Distance (VVD), and the two dimensional symmetric Gaussian kernel density estimate methods. We extracted from these methods several parameters characterizing the spatial distribution of points (e.g., eccentricity (e), eigenvector index (evi), angular dispersion (Da)). These parameters allow to define at least three types of shape for volcanic fields: strong elongate (line and ellipse), bimodal/medium elongate (ellipse) and dispersed (circle) shapes. Applied to the natural example, these methods well differentiate each volcanic field. For example, the elongation of the field increases from shoulder to rift axis inversely to the angular dispersion. In addition, the results show that none of

  1. Geochronologic, Thermochronologic, and Thermobarometric Constraints on the Tectonic Evolution of the Northeastern Pamir

    NASA Astrophysics Data System (ADS)

    Robinson, A. C.; Yin, A.; Manning, C. E.; Harrison, T. M.; Hei, W.; Xiong, M. Y.; Feng, W. X.

    2001-12-01

    exhumation of the Kongur Shan (and Muztaghata) massifs along the Kongur normal fault. High grade metamorphism in the Kongur Shan massif due to tectonic burial is constrained to be ~ 9 Ma from in-situ SIMS monazite geochronology. A 10 Ma biotite 40Ar/39Ar age from two km west of the ductile shear zone is interpreted to roughly indicate the timing of initiation of normal faulting.

  2. The Morphology of the Tasmantid Seamounts: Interactions between Tectonic Inheritance and Magmatic Evolution

    NASA Astrophysics Data System (ADS)

    Richards, Fred; Kalnins, Lara; Watts, Anthony; Cohen, Benjamin; Beaman, Robin

    2015-04-01

    The Tasmantid seamounts extend for over 2000 km off the east coast of Australia and constitute one of three contemporaneous, sub-parallel Cenozoic hotspot tracks that traverse the region (the Tasmantid, Lord Howe, and East Australian volcanic chains), locally separated by as little as 500 km. Where dated, the three chains young from north to south, spanning ca. 34-6 Ma. At multiple locations, the Tasmantid chain intersects the extinct Tasman Sea spreading centre, which was active from 84 Ma to 53 Ma. Detailed morphological analysis reveals a strong correlation between tectonic setting, seamount orientation, and volcanic structure. Seamounts at inside corners of the spreading segment-transform intersections are more rugged and constructed via numerous intersecting fissure-fed volcanic ridges, whereas off-axis seamounts tend to be conical with summit craters and isolated dyke-fed flank cones. In addition, the orientation of the Bouguer gravity anomaly highs, interpreted as magmatic conduits, and the long axes of the seamounts align closely with the principal stress directions expected for a ridge system in which strong mechanical coupling occurs across transform faults. Such a strong connection between the long-lived mantle upwelling, ridge structure, and subsequent dyke emplacement ' despite the ≥ 20 Ma offset between spreading cessation and initial seamount emplacement ' suggests deep faulting of the Tasman Sea oceanic lithosphere in order to channel melts along pre-existing structural trends. Despite the large size of the edifices, up to ~ 4000 m high, slope gradient and backscatter analysis along the chain point to sluggish mass wasting rates with few or no large sector collapse structures. In addition, most seamounts are associated with Bouguer gravity highs. Together, these features suggest that the seamounts have dense, coherent cores with high intrusive to extrusive volume ratios. This indicates low rates of melt generation and intra-lithospheric transport

  3. Elastic thickness of the lithosphere and tectonic evolution: implications for GIA models

    NASA Astrophysics Data System (ADS)

    Amantov, Aleksey; Fjeldskaar, Willy

    2015-04-01

    Rheological properties used in GIA models require independent verifications and possible modifications. To estimate the flexural rigidity of the lithosphere in simple platform areas we use peneplain distortion, which enable us to compute isostatic response from sediment load and compare the results with observed changes in geometry. This was done for several different platform regions: - Baltic (Fennoscandian) Shield, including structural elements of the Russian Platform - Barents Sea platform areas - Kara and Western Siberian domain - Eastern Siberian Platform In the East European and East Siberian old cratons we modeled isostatic distortion of Neoproterozoic Ediacaran peneplain and some other relevant surfaces. For the Arctic we used Mid-Late Jurassic surface (JP) as a distinct unconformity and well-traced (by seismic and well data) surface in the Arctic region. The isostatic distortion of peneplains under sediment load / erosion for the old Archean - Proterozoic cratons in general confirms earlier rheology model with the flexural rigidity of the lithosphere around 5x10**23 Nm (effective elastic thickness of 30-40 km), but could be slightly lower in the Barents basins. Deviations are generally relatively small and could be explained by e.g. by averaging over fault-zones, tectonic events, compaction structures and density variations. However, the situation for the Kara-Western Siberian domain is very different, with large deviations between observations and calculations. With a slight reduction of the effective elastic thickness in the Kara Sea to 10-20 km the fit is much better. Based on the results we suggest two different major types of lithosphere rigidity in the area. This seems reasonable because they typify domains with different crustal age. Western Siberian platform, with Kara continuation has much younger basement, in addition to significant magmatic activity and Early Mesosoic extension. The lithosphere rigidity is a function of age and temperature; as

  4. Stable isotope paleoaltimetry: Tectonics and the evolution of landscapes and life

    NASA Astrophysics Data System (ADS)

    Mulch, Andreas

    2015-04-01

    Stable isotope paleoaltimetry exploits systematic changes in the oxygen (δ18O) or hydrogen (δD) isotopic composition of precipitation when lifting of moist air masses over topography induces orographic precipitation. The past 10 years have witnessed rapidly expanding research activities in stable isotope paleoaltimetry that resulted in a broad array of fascinating tectonic studies many of which concentrated on the elevation histories of continental plateau regions. Stable isotope based reconstructions of topography, therefore, have greatly expanded what used to be very sparse global paleoaltimetric information. The topography of mountain ranges and plateaus, however, not only reflects the geodynamic processes that shape the Earth's surface; it also represents a key element in controlling continental moisture transport, atmospheric circulation and the distribution of biomes and biodiversity. The challenge now lies in disentangling the surface uplift component from the inevitable impact of climate change on long-term records of δ18O and δD in precipitation that accompanies surface uplift. The robustness of stable isotope paleoaltimetry reconstructions can be greatly enhanced when high-elevation δ18O or δD proxy data are referenced against low-elevation records that track climate-modulated δ18O or δD of precipitation through time. In addition, evaluating δ18O or δD of precipitation upstream of the orogen/continental plateau region reduces commonly encountered complexities such as topographic threshold conditions to atmospheric circulation, variable moisture recharge to the atmosphere through evapotranspiration over the continents or the impact of hemispheric-scale atmospheric teleconnections; all of which may conspire in setting δ18O or δD of precipitation. Here, I present examples where stable isotope paleoaltimetry data successfully track topographic thresholds to changes in atmospheric circulation and precipitation with a particular focus on the effect

  5. Plio-Quaternary tectonic evolution off Al Hoceima, Moroccan Margin of the Alboran Basin.

    NASA Astrophysics Data System (ADS)

    Lafosse, Manfred; d'Acremont, Elia; Rabaute, Alain; Mercier de Lépinay, Bernard; Gorini, Christian; Ammar, Abdellah; Tahayt, Abdelilah

    2015-04-01

    We use data from a compilation of industrial and academic 2D surveys and recent data from MARLBORO-1 (2011), MARLBORO-2 (2012), and SARAS (2012) surveys, which provide high resolution bathymetry and 2D seismic reflexion data. We focus on the key area located south of the Alboran Ridge and the Tofiño Bank, and encompassing the Nekor and Boudinar onshore-offshore basins on the Moroccan side of the Alboran Sea. The Nekor basin is a present pull-apart basin in relay between inherited N050° sinistral strike-slip faults. We consider that these faults define the Principal Displacement Zones (PDZ). The northern PDZ marks the position of the crustal Bokkoya fault, which is connected to the Al-Idrisi Fault Zone en relais with the Adra and Carboneras Fault Zones. On the seabed, right-stepping non-coalescent faults characterize the sinistral kinematics of the northern PDZ and give a general N050° azimuth for the crustal discontinuity. The southern PDZ corresponds to the Nekor fault Zone, a Miocene sinistral strike-slip fault acting as the structural limit of the External Rif. On its eastern edge, the Nekor basin is bounded by the N-S onshore-offshore Trougout fault, connecting the northern and the southern PDZ. The western boundary of the Nekor basin is marked by the Rouadi and El-Hammam Quaternary active N-S normal faults. In the offshore Nekor basin, recent N155° conjugated normal faults affect the seabed. Further east, the Boudinar basin is a Plio-Quaternary uplifted Neogene basin. The northeastern segment of the Nekor fault bounds this basin to the south but is inactive in the Quaternary. Normal east-dipping N150° faults are visible offshore in the continuity of the Boudinar fault. From our perspective, the orientation of major tectonic structures (Bokkoya, Nekor and Carboneras faults and the Alboran ridge) under the present compressive regime due to the Europe/Africa convergence is not compatible with a strike-slip motion. The orientation of the most recent Plio

  6. Cenozoic tectonic evolution of the basin and range province in northwestern Nevada

    USGS Publications Warehouse

    Colgan, J.P.; Dumitru, T.A.; Reiners, P.W.; Wooden, J.L.; Miller, E.L.

    2006-01-01

    A regional synthesis of new and existing geologic and thermochronologic data document late Cretaceous - early Cenozoic regional erosion, Oligocene - Miocene volcanism, and subsequent late Miocene extension of the Basin and Range Province in northwestern Nevada and northeastern California. Across an ???220-km-wide region between the Santa Rosa and Warner Ranges, conformable sequences of 35 to 15 Ma volcanic rocks are cut by only a single generation of high-angle normal faults that accommodated ???23 km of total east-west extension (???12%). Fission-track, (U-Th)/He, geologic, and structural data from the Pine Forest Range show that faulting there began at 11 to 12 Ma, progressed at a relatively constant rate until at least 3 Ma, and has continued until near the present time. Extension in the Santa Rosa Range to the east took place during the same interval, although the post-6 Ma part of this history is less well constrained. Less complete constraints from adjacent ranges permit a similar timing for faulting, and we infer that extensional faulting in northwestern Nevada began everywhere at 12 Ma and has continued up to the present. Faulting in the Warner Range in northeastern California can only be constrained to have begun between 14 and 3 Ma, but may represent westward migration of Basin and Range extension during the Pliocene. Compared to the many parts of the Basin and Range in central and southern Nevada, extension in northwestern Nevada began more recently, is of lesser total magnitude, and was accommodated entirely by high-angle normal faults. Fission-track data document Late Cretaceous unroofing of Cretaceous (115 - 100 Ma) granitic basement rocks in northwestern Nevada, followed by a long period of relative tectonic quiescence that persisted through Oligocene and Miocene volcanism until the onset of Basin and Range extension at ???12 Ma. The low magnitude of extension (12%) and early Tertiary stability suggest that the modern ???31 km thick crust in

  7. The structure and stratigraphy of deepwater Sarawak, Malaysia: Implications for tectonic evolution

    NASA Astrophysics Data System (ADS)

    Madon, Mazlan; Kim, Cheng Ly; Wong, Robert

    2013-10-01

    The structural-stratigraphic history of the North Luconia Province, Sarawak deepwater area, is related to the tectonic history of the South China Sea. The Sarawak Basin initiated as a foreland basin as a result of the collision of the Luconia continental block with Sarawak (Sarawak Orogeny). The foreland basin was later overridden by and buried under the prograding Oligocene-Recent shelf-slope system. The basin had evolved through a deep foreland basin ('flysch') phase during late Eocene-Oligocene times, followed by post-Oligocene ('molasse') phase of shallow marine shelf progradation to present day. Seismic interpretation reveals a regional Early Miocene Unconformity (EMU) separating pre-Oligocene to Miocene rifted basement from overlying undeformed Upper Miocene-Pliocene bathyal sediments. Seismic, well data and subsidence analysis indicate that the EMU was caused by relative uplift and predominantly submarine erosion between ˜19 and 17 Ma ago. The subsidence history suggests a rift-like subsidence pattern, probably with a foreland basin overprint during the last 10 Ma. Modelling results indicate that the EMU represents a major hiatus in the sedimentation history, with an estimated 500-2600 m of missing section, equivalent to a time gap of 8-10 Ma. The EMU is known to extend over the entire NW Borneo margin and is probably related to the Sabah Orogeny which marks the cessation of sea-floor spreading in the South China Sea and collision of Dangerous Grounds block with Sabah. Gravity modelling indicates a thinned continental crust underneath the Sarawak shelf and slope and supports the seismic and well data interpretation. There is a probable presence of an overthrust wedge beneath the Sarawak shelf, which could be interpreted as a sliver of the Rajang Group accretionary prism. Alternatively, magmatic underplating beneath the Sarawak shelf could equally explain the free-air gravity anomaly. The Sarawak basin was part of a remnant ocean basin that was closed by

  8. Geochronology and geochemistry of tuff beds from the Shicaohe Formation of Shennongjia Group and tectonic evolution in the northern Yangtze Block, South China

    NASA Astrophysics Data System (ADS)

    Du, Qiuding; Wang, Zhengjiang; Wang, Jian; Deng, Qi; Yang, Fei

    2016-03-01

    Meso- to Neoproterozoic magmatic events are widespread in the Yangtze Block. The geochronology and tectonic significance of the Shennongjia Group in the Yangtze Block are still highly controversial. An integrated geochronology and geochemistry approach provides new insights into the geochronological framework, tectonic setting, magmatic events, and basin evolution of the northern Yangtze Block. Our new precise sensitive high-resolution ion microprobe U-Pb data indicate a deposition age of 1180 ± 15 Ma for the Shicaohe Formation subalkaline basaltic tuff that is geochemically similar to modern intracontinental rift volcanic rocks. The integration of available geochemical data together with our new U-Pb ages indicates the Shicaohe Formation subalkaline basaltic tuff formed ca. 1180 in a continental rift-related setting on a passive continental margin. The Shennongjia Group is topped by the Zhengjiaya Formation volcanic sequence, indicating arc-related igneous events at 1103 Ma. The transition of the late Mesoproterozoic tectonic regime from intracontinental extension to convergence occurred between ca. 1180 and 1103 Ma in the northern Yangtze Block. Tectonic evolution in the Neoproterozoic led to accretion along the northern margin of the Yangtze Block. These results provide geochronological evidence, which is of utmost importance for reconfiguration of the chronostratigraphic framework and for promoting research on Mesoproterozoic strata in China, thereby increasing understanding of magmatic events and basin evolutionary history in the northern Yangtze Block.

  9. Geophysical Evidence for the Tectonic Evolution of the Inverted Belt-Purcell Basin, Northwestern Montana

    NASA Astrophysics Data System (ADS)

    Rutherford, B. S.; Speece, M. A.; Constenius, K. N.

    2015-12-01

    The geometry of the Precambrian Belt-Purcell basin and subsequent allochthon, that dominates the geology of northwestern Montana, played a critical role in the development of compressional structures during orogenesis and their ensuing reactivation during the later phase of extensional collapse. Five reprocessed seismic reflection profiles provide images in the Swan Range and adjacent valleys that we have correlated to published seismic data north into Canada. Reflections from syndepositional sills encased within Lower Belt rocks offer clues to the configuration of the basin prior to its tectonic inversion. Thick basinal facies of the Lewis salient are contrasted by thin shelfal facies found in hanging wall rocks of frontal Belt carrying thrusts south of the salient. The along strike change in hanging wall rocks reflects the original configuration of the Belt basin margin. Rocks of the Lewis salient were deposited in an embayment on the northeastern margin of the Belt basin. Shelfal accumlations of the embayment comprise an autochthonous wedge that has remained in the footwall of the Lewis thrust system. South of the embayment and related salient, nearly the entire Belt basin was detached from pre-Belt crystalline rocks and inverted at the latitude of the Sawtooth Range. Deeply exhumed Phanerozoic rocks of the Sawtooth Range are a direct consequence of the thin wedge geometry of the detached basin south of the Lewis salient that required growth of a substantial orogenic wedge to obtain critical taper values. We offer an alternate interpretation of a >10 km high, west facing décollement ramp that coincides with the Belt-Purcell basin margin. Previous interpretations in Montana have inferred the location of the basin margin ramp to approximate the trace of the Purcell Anticlinorium. Seismic data and cross-section balancing suggest the Rocky Mountain Trench as a more accurate location. Based on our proposed position of the basin margin the Belt-Purcell allocthon

  10. Geochemical evolution of Cenozoic-Cretaceous magmatism and its relation to tectonic setting, southwestern Idaho, U.S.A

    NASA Technical Reports Server (NTRS)

    Norman, Marc D.; Leeman, William P.

    1989-01-01

    The relationships between Cretaceous to Neogene magmatism and the tectonic setting of southwestern and central Idaho are evaluated. An overview of the tectonics and geology of the northwestern U.S. is presented. Major element, trace element, and Sr, Pb, and Nd isotopic data for the region are used to place constraints on magma source characteristics, the manner in which the magmatic sources evolved through time, and the nature of interactions among mantle and crustal domains in response to changing tectonic environment.

  11. Structural evolution of the Rieserferner Pluton: insight into the localization of deformation and regional tectonics implications

    NASA Astrophysics Data System (ADS)

    Ceccato, Alberto; Pennacchioni, Giorgio

    2016-04-01

    deformation structures within the RFP is controlled by the development and later reactivation in shear of two main sets of joints during cooling and progressive exhumation of the pluton. These joints were either exploited as faults or localized ductile shear zones. In the RFP, the kinematics of shear reactivation is complex, with the same joint set recording different senses of shear and transport directions. Preliminary kinematic analysis and qualitative paleostress reconstruction show that there has been a clockwise rotation of the main regional shortening direction from WNW-ESE, during the first ductile event, to N-S during later brittle deformation. These two different shortening directions fit with those inferred, respectively, for Austroalpine nappe stacking by Ratschbacher (1989) and for the Alpine convergence during late Oligocene-Miocene within the Tauern window (Pennacchioni & Mancktelow, 2007). References Cesare, B. (1994). Hercynite as the product of staurolite decomposition in the contact aureole of Vedrette di Ries, eastern Alps, Italy. Contributions to Mineralogy and Petrology, 116(3), 239-246. Pennacchioni, G., Di Toro, G., Brack, P., Menegon, L., & Villa, I. M. (2006). Brittle-ductile-brittle deformation during cooling of tonalite (Adamello, Southern Italian Alps). Tectonophysics, 427(1), 171-197. Pennacchioni, G., & Mancktelow, N. S. (2007). Nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions. Journal of Structural Geology, 29(11), 1757-1780. Ratschbacher, L., Frisch, W., Neubauer, F., Schmid, S. M., & Neugebauer, J. (1989). Extension in compressional orogenic belts: the eastern Alps. Geology, 17(5), 404-407. Romer, R. L., & Siegesmund, S. (2003). Why allanite may swindle about its true age. Contributions to Mineralogy and Petrology, 146(3), 297-307. Steenken, A., Siegesmund, S., & Heinrichs, T. (2000). The emplacement of the Rieserferner Pluton (Eastern

  12. Metasomatic Evolution in Tectonically Mixed Zones (Mélange) and Significance for Geochemical Evolution of the Slab-Mantle Interface

    NASA Astrophysics Data System (ADS)

    Bebout, G. E.; King, R. L.

    2012-12-01

    Fluid flow focused in highly deformed zones (shear zones), and the physical juxtaposition of chemically disparate rocks (via mechanical mixing) in such zones, can lead to extensive metasomatism, including volume strain, and result in rocks with hybridized compositions little resembling the compositions of the incorporated rock types [1-5]. In the Catalina Schist (California), lawsonite-albite, lawsonite-blueschist, and amphibolite-facies units contain shear zones at scales of meters to kilometers, each containing "blocks" (with more spherical or more tabular dimensions) co-facial in grade with the "matrix" surrounding these blocks [1-3]. Oxygen isotope data for these "mélange" units, and adjacent more "coherent" expanses, indicate enhanced fluid flow in the more strongly deforming mélange zones while fluid flow in coherent domains was dominantly fracture-controlled and episodic. The amphibolite-facies mélange unit shows evidence for km-scale equilibration of varying mineral assemblages with H2O-rich fluids with uniform O and H isotope compositions consistent with a lower-grade metasedimentary source. This unit is believed to have formed largely by mechanical mixing of mafic and ultramafic compositions, partly because of the scarcity of sedimentary blocks. However, the mélange matrix in this unit preserves a number of sedimentary chemical/isotopic characteristics (e.g., Pb isotope compositions [3]) that could reflect the incorporation of sedimentary rocks, with or without fluid-related fractionation, and possibly fluid-mediated additions. Tectonically mixed zones such as these, if volumetrically significant at the slab-mantle interface, could exert disproportionate control on the compositions of hydrous fluids or silicate melts emanating from subducting slabs and entering the forearc to backarc mantle wedge, including those contributing to arc magmatism [1-5]. Geochemical studies of arc lavas should consider the possibility that the "fluids" contributed from

  13. Variscan tectonics in Dodecanese, Kalymnos island, Greece

    NASA Astrophysics Data System (ADS)

    Chatziioannou, Eleftheria; Grasemann, Bernhard; Schneider, David; Hubmann, Bernhard; Soukis, Konstantinos

    2015-04-01

    Kalymnos island is located in the Dodecanese, southeastern Aegean Sea, and geologically appears to be part of the external Hellenides. Pre-Alpidic basement rocks on the Dodecanese islands have been suggested to record compelling similarities with the basement rocks in Eastern Crete with respect to their lithologies and pre-Alpidic metamorphic evolution. The lithotectonic units experienced greenschist to amphibolite facies conditions during the Variscan orogeny. Whereas the rocks in Eastern Crete reveal Alpine high-pressure overprint, the Variscan basement units in the Dodecanese record no or low-grade Alpine metamorphism. A field study of basement rocks below Mesozoic limestones and dolomites in the NW part of Kalymnos near Emporios uncovered a complex history of metamorphism, folding and faulting. Three different tectonic units can be discriminated from top to bottom: a) a quartz-mica schist, b) a white-grey, fossiliferous coarse grained marble and c) a fine-grained fossiliferous blue-grey marble. In the marbles macrofossils such as brachiopods, ammonoid cephalopods (Goniatids?) and crinoids suggest a Middle-Upper Devonian deposition age (Givetian- Frasnian). Structural mapping the area resolved a dominant W-E shortening event, resulting in an overall inverted metamorphic gradient. The lowermost blue-grey marble unit is folded into large-scale upright folds, which are truncated by top-to-east overthrusting of the white-grey marble unit. Whereas deformation mechanisms in the blue-grey marble unit are dominated by dissolution-precipitation creep, the white-grey marble suffered intense crystal plastic deformation with localized high-strain mylonitic shear zones. The uppermost quartz-mica schist unit is separated from the lower units by a cataclastic phyllonitic shear zone. 40Ar/39Ar geochronological dating on white micas from the quartz-mica schists yielded cooling ages between 240 and 334 Ma indicative of Variscan cooling. Our data suggest that this part of the

  14. Post-glacial landform evolution in the middle Satluj River valley, India: Implications towards understanding the climate tectonic interactions

    NASA Astrophysics Data System (ADS)

    Sharma, Shubhra; Bartarya, S. K.; Marh, B. S.

    2016-04-01

    Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ˜13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ˜5 and 0.4 ka (mid- to late-Holocene), was during the declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (˜6.5-7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene declining ISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions.

  15. Structure and Evolution of Northwest Corner of South China Sea: implications for Cenozoic tectonics in Southeast Asia

    NASA Astrophysics Data System (ADS)

    Lei, C.; Ren, J.; Willett, S.; Clift, P. D.

    2012-12-01

    The Yinggehai-Song Hong Basin (YGHB) and Qiongdongnan Basin (QDNB) are in the northwest corner of the South China Sea, which positioned at a juncture between a strike-slipping zone and an extensional zone. The basins lie at the southern termination of the largest Tibetan strike-slip zones, the Red River Fault, and are the principal repository of materials eroded from the Red River drainage. The basins are flanked to the East by an oceanic ridge and border the Nansha area to the South, which is being subducted underneath the Borneo Block. Hainan Island, located between the YGHB and QGNB, is composed primarily of granites and basalts. A combination of regional, high-quality reflection seismic and well data was used to unravel the basin history in greater detail than previously possible, which will enrich our knowledge about structure and evolution in Southeast Asia. After ca. 55 Ma the basins started to subside and grabens bounded by small-scale and NE-SW trending faults developed across wide areas. However, the evolution of YGHB and QDNB was shown different after 32 Ma. Strike-slip deformation of the YGHB took place after 32 Ma in response to the left-lateral movement of the Red River Fault. After the Middle Miocene the YGHB was inverted and generated prominent folds in the Lingao Uplift and Hanoi Basin. Inversion ceased at different times in different parts of the basin, indicating that the transition from compression to extension moved northward during the period 15.5-5.5 Ma. In contrast, to the west of YGHB, the QDNB displays a very different basin structure and evolution since 32 Ma. Larger-scale, partly fault-controlled depressions are superimposed clearly over underlying, faulted-bounding grabens on seismic profiles. The evolution of QDNB was controlled by extension, which is strongly influenced by the initiation of ridge spreading in the South China Sea. We also reconstructed the sedimentary flux from the Red River drainage constrained by higher resolution

  16. Late Paleozoic to Jurassic tectonic evolution of the Bogda area (northwest China): Evidence from detrital zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Tang, Wenhao; Zhang, Zhicheng; Li, Jianfeng; Li, Ke; Chen, Yan; Guo, Zhaojie

    2014-06-01

    Since the Cenozoic, the Tian Shan is rejuvenated by crustal shortening related to the ongoing India-Asia collision. However, the tectonic process prior to the Cenozoic remains ambiguous, especially in the Bogda area of the eastern Tian Shan. The continuous Late Paleozoic-Mesozoic sequences in the Bogda area record abundant information about the basin-mountain interaction. U-Pb (LA-ICP-MS) dating of detrital zircons from seven sandstone samples from Permian to Jurassic was used to investigate the changes of provenance and basin-mountain interaction in the Bogda area. During the Permian, proximal and synchronous pyroclastic materials were the major source. The Late Paleozoic magmatic belt in the North Tian Shan (NTS) had gradually become one of the main sources by the Late Permian, which implies the uplift and exhumation in the NTS area. This is interpreted in terms of near-source sedimentation in basin developing in a post-orogenic extension setting. The large range of U-Pb ages of detrital zircons observed in the Early-Middle Jurassic sediments encompasses most of the available sources implying a wide drainage pattern developing on a rather flat topography. Re-emergence of the Early Permian peak in the spectrum implies that the Bogda Mountains has existed as a gentle positive relief and began to provide materials to the submountain regions. The southern Junggar Basin extended towards to the south and evolved as a passively subsiding basin from the Middle Triassic to the Middle Jurassic. However, the synchronous pyroclastic (tuff) and the exhumed late Paleozoic detrital materials from the uplifted Bogda Mountains were the major component of the Upper Jurassic sediments. Associated to the conglomerate in the Kalaza Formation, the basin-range evolution entered a compression uplift stage. The basin pattern evolution of the Bogda area is consistent with that of the southern Junggar Basin.

  17. Evolution of Intrusions in Lunar Floor-Fractured Craters: Degassing, Solidification and Relationship to Tectonic and Volcanic Features

    NASA Astrophysics Data System (ADS)

    Jozwiak, L.; Head, J. W., III

    2014-12-01

    Lunar floor-fractured craters are a class of 170 craters characterized by their anomalously shallow, heavily fractured floors; associated floor morphologies include deposits of mare material, pyroclastic deposits, and vents. Floor-fractured craters are located in close proximity to surface mare deposits, and are also closely associated with both the interiors and edges of lunar basins. The interior volcanic features, in conjunction with the morphologic and morphometric characteristics of the craters, suggest a formation consistent with subcrater magmatic intrusion and sill formation. Morphometric data suggests that the areal extent of the intrusion mirrors the dimensions of the crater floor, and that the intrusion does not extend past the crater wall region. The intrusion thickness can be calculated by comparing the observed depth of the craters with the predicted depth of a crater of similar diameter, and the averaged intrusion thickness is ~ 1 km. Thus these intrusions represent large subsurface magmatic provinces. We investigate the evolution of these large magmatic intrusions with emphasis on how the degassing of the intrusion leads to pyroclastic eruptions in certain craters, and whether these eruptions utilize fractures created by the tectonic deformation of the crater floor, or if they instead form from subsidiary diking off of the intrusion. We also investigate the amount of volatiles necessary to produce the pyroclastic eruptions, considering both inherent volatiles in the magma, and volatiles generated by reactions during the shallow subsurface evolution of the magma. The craters Alphonsus and Humboldt serve as ideal study cases to compare and contrast floor morphology, fracture location, and observed volcanic deposits. The results of this analysis have importance for why pyroclastic eruptions occurred in certain locations, and it also has implications for the volatile budget of lunar magmas.

  18. Geologic Evolution of the eastern Panama Isthmus from biostratigraphic, tectonic and geophysical data

    NASA Astrophysics Data System (ADS)

    Barat, F.; Mercier de Lépinay, B.; Sosson, M.; Müller, C.

    2012-04-01

    identified a magmatic episode during the Lower Miocene in Mahé and Sapo Massifs. We present a new structural map of eastern Panama and five geological transects across the isthmus, summarizing the complex history. Our study documents: (1) a southwestward compression phase (in its present-day position) between Late Campanian and Middle Eocene, along the Pacific coast, in agreement with the subduction activity; (2) a Middle Eocene extension phase (Chucunaque-Tuira forearc basin formation); (3) a Middle Miocene compression phase, inverting some of the inherited normal faults and reactivating geological structures; (4) and a Plio-quaternary transpressive tectonic regime, evidenced by several left-lateral strike-slip faults with en echelon folds in the areas of Mahé Massif, Sanson Hills, Pirre Massif and Sapo Massif. These deformations are the result of the collision of Panama Choco block with the South America Plate.

  19. Permian to late Cenozoic evolution of northern Patagonia: Main tectonic events, magmatic activity, and depositional trends

    NASA Astrophysics Data System (ADS)

    Uliana, M. A.; Biddle, K. T.

    The late Paleozoic to late Cenozoic evolution of northern Patagonia was influenced significantly by events that occurred while the area was part of the South American sector of Gondwanaland. Late Paleozoic to Middle Triassic subduction along the edge of the supercontinent formed a broad convergent-margin system that is the underpinning of northern Patagonia. Deformation (Gondwanidian orogeny) associated with the subduction is recognized in both the forearc and the convergent backarc areas. Regional extension, accompanied by bimodal volcanism, began in the Late Triassic and led to the formation of a number of north-northwest trending rift basins in Patagonia, which generally followed the Gondwanidian basement grain. Continued extension in the Jurassic and Early Cretaceous led to the opening of the Rocas Verdes marginal basin in southern Chile and, ultimately, to the opening of the South Atlantic Ocean. Once oceanic crust began to form, faulting and volcanism declined in Patagonia. During the late Early Cretaceous to the Late Cretaceous, sags over the rift basins coalesced to form a broad backarc basin behind the volcanic arc to the west. These sags are suggestive of thermally driven subsidence. Subsidence of the evolving Atlantic margin allowed extensive marine transgressions to take place from the east. The stratigraphic record of northern Patagonia reflects these events. The upper Paleozoic to upper Mesozoic sedimentary sequences were deposited in basins directly associated with convergent activity along the margin of Gondwanaland or in rift basins created during its breakup. Even though the Tertiary evolution of Patagonia was dominated by events along the western margin of South America, the patterns of sediment transport, thickness, and general shoreline position were still influenced by the locations of the Mesozoic rifts formed during the breakup of Gondwanaland.

  20. Tectonic and petrologic evolution of the Western Mediterranean: the double polarity subduction model

    NASA Astrophysics Data System (ADS)

    Melchiorre, Massimiliano; Vergés, Jaume; Fernàndez, Manel; Torné, Montserrat; Casciello, Emilio

    2016-04-01

    The geochemical composition of the mantle beneath the Mediterranean area is extremely heterogeneous. This feature results in volcanic products whose geochemical features in some cases do not correspond to the geodynamic environment in which they are sampled and that is observed at present day. The subduction-related models that have been developed during the last decades to explain the evolution of the Western Mediterranean are mainly based on geologic and seismologic evidences, as well as petrography and age of exhumation of the metamorphic units that compose the inner parts of the different arcs. Except few cases, most of these models are poorly constrained from a petrologic point of view. Usually the volcanic activity that affected the Mediterranean area since Oligocene has been only used as a corollary, and not as a key constrain. This choice is strictly related to the great geochemical variability of the volcanic products erupted in the Western Mediterranean, due to events of long-term recycling affecting the mantle beneath the Mediterranean since the Variscan Orogeny, together with depletion episodes due to partial melting. We consider an evolutionary scenario for the Western Mediterranean based on a double polarity subduction model according to which two opposite slabs separated by a transform fault of the original Jurassic rift operated beneath the Western and Central Mediterranean. Our aim has been to reconstruct the evolution of the Western Mediterranean since the Oligocene considering the volcanic activity that affected this area since ~30 Ma and supporting the double polarity subduction model with the petrology of the erupted rocks.

  1. Geology of the Blue Mountains region of Oregon, Idaho, and Washington; petrology and tectonic evolution of pre-Tertiary rocks of the Blue Mountains region

    USGS Publications Warehouse

    Vallier, T. L., (Edited By); Brooks, H.C.

    1995-01-01

    This Professional Paper contains 14 chapters on the Blue Mountains region of Oregon, Idaho, and Washington. The authors discuss petrology and tectonic evolution of an island arc that formed in the ancestral Pacific Ocean during the Permian to Cretaceous interval. The island arc was accreted to cratonal North America in the Early Cretaceous and thereby became one of the several exotic terranes in western North America.

  2. Morphological Analysis of Apo Volcanic Complex in Southern Mindanao, Philippines: implications on volcano-tectonic evolution of different volcanic units

    NASA Astrophysics Data System (ADS)

    Herrero, T. M. L.; van Wyk de Vries, B.; Lagmay, A. M. A.; Eco, R. C.

    2015-12-01

    The Apo Volcanic Complex (AVC) is one of the largest volcanic centers in the Philippines, located in the southern island of Mindanao. It is composed of four edifices and several smaller cones. The youngest volcanic unit, the Apo Dome, is the highest elevation in the Philippines. This unit is classified as potentially active, whereas other units, Talomo, Sibulan and Kitubod, are inactive. The study gives insight to the construction and deformation history of the volcanic units and imparts foresight to subsequent events that can affect populated areas. A morphological analysis integrating high-resolution digital terrain models and public domain satellite data and images was done to recognize and discriminate volcanic units and characterize volcano-tectonic features and processes. Morphological domains were defined based on surface textures, slope variation, degrees and controls of erosion, and lineament density and direction. This establishes the relative ages and extent of volcanic units as well as the volcano-tectonic evolution of the complex. Six edifice building events were recognized, two of which form the elevated base of Apo dome. The geodynamic setting of the region is imprinted in the volcanic units as five morphostructural lineaments. They reveal the changes in maximum regional stress through time such as the N-S extension found across the whole volcanic complex displaying the current stress regime. This has implications on the locality and propagation of geothermal activity, magma ascent, and edifice collapses. One main result of the compounded effects of inherited structures and current stress regime is the Sandawa Collapse Zone. This is a large valley formed by several collapses where NE-SW fractures propagate and the increasing lateral spreading by debuttressing continue to eat away the highest peak. The AVC is surrounded by the major metropolitan area of Davao City to the east and the cities of Kidapawan and Digos to the west and south, respectively

  3. Fast cooling following a Late Triassic metamorphic and magmatic pulse: implications for the tectonic evolution of the Korean collision belt

    NASA Astrophysics Data System (ADS)

    de Jong, Koen; Han, Seokyoung; Ruffet, Gilles

    2015-11-01

    We discuss the evolution of Korea in the context of a relatively short-lived, tectonically induced, magmatic and metamorphic pulse that affected large portions of the crust of the peninsula's southern part during the Late Triassic. Recent 40Ar/39Ar single grain laser step-heating dates imply a prolonged metamorphic recrystallization between 243 and 220 Ma, which occurred in distinct phases that were not coeval throughout the peninsula. We obtained identical plateau ages between 231.4 ± 0.8 and 228.9 ± 0.8 Ma (1σ; 85-95% 39Ar release) on single grains of detrital muscovite from Jurassic sandstones (Gimpo Group). A literature review shows that the ages of detrital muscovites are identical to: (1) concordant 40Ar/39Ar ages of biotite (228 Ma) and amphibole (230 Ma) in amphibolites of the Deokjeongri Gneiss Formation and the Weolhyeonri Complex, pointing to very rapid cooling of 100-150 °C/Ma, and (2) 231-229 Ma muscovite from the low-grade metamorphic mid-Paleozoic turbidites of the Taean Formation. The efficiency of cooling is further underlined by the near-coincidence of these 40Ar/39Ar ages with 243-229 Ma (average: 234.6 Ma) zircon U-Pb ages in the Gyeonggi Massif and the Hongseong belt, in the literature. It is argued that the Late Triassic magmatic and metamorphic pulse is superimposed on an earlier tectono-metamorphic event, possibly related to collision, indicated by: (1) ~ 243-237 Ma muscovite ages, or age components in age spectra, and (2) two generations of folds and associated tectonic foliations truncated by ~ 229.5-Ma-old syenites and earlier mafic dykes. The Late Triassic thermal pulse could have been the result of post-collisional delamination of the lower crust and uppermost mantle, and/or oceanic slab break-off, which is also suggested by almost coeval, widespread mantle-sourced Mg-rich potassic magmatism. Continuing ductile deformation is shown by mylonitization of Late Triassic magmatic rocks; an ~ 220 Ma muscovite age may be related to this.

  4. Structure of northeastern New Mexico from deep seismic reflection profiles: Implications for the Proterozoic tectonic evolution of southwestern North America

    NASA Astrophysics Data System (ADS)

    Eshete, Tefera Gashu

    2001-09-01

    Previous geologic, geochronologic, structural, isotope, and xenolith studies have shown that the Precambrian rocks of northern New Mexico belong to the Yavapai and Mazatzal provinces. The boundary between the provinces is a wide zone defined on its northern edge by the northern extent of 1.65 Ga deformation and southern edge by the southern most extent of Yavapai crust (pre-1.7 Ga). However, the nature of the Precambrian province boundary at depth, its evolution through time, and the tectonic processes that affected the interior of these provinces, are not well understood. In order to obtain new information concerning these problems, processing and interpretation of reflection seismic data was conducted on data collected during the 1999 Continental Dynamics-Rocky Mountain (CD-ROM) project and data obtained from industry. In this study I present new information on the crustal structure of northern New Mexico provided by processing and interpretation of three seismic reflection profiles (NM-1, TB-1 and TB-2).The seismic data present evidence for Precambrian crustal growth and amalgamation, followed by subsequent reactivation of Precambrian structures. A seismic profile and gravity modeling across the NM-1 show a strongly reflective high-density (2850 kg-m-3) dome-shaped body in the middle to lower crust. On the basis of the absence of a hanging-wall antiform, the occurrence of normal sense of deflection of reflectors in the footwall, possibly Moho pullup, and geological information such as an exposed Proterozoic extensional shear zone in the Sandia Mountains, this feature is interpreted to represent a 1.4 Ga? extensional shear zone which resulted in rotation of ˜1.65 Ga imbricate thrust zones. Layered reflectivity directly below the top of Precambrian basement on profiles TB-1 and the eastern part of TB-2, based on geophysical and geological information from nearby areas is interpreted as a sequence of ˜1.4 Ga volcanic and sedimentary rocks within the Proterozoic

  5. Gravity modeling constraints on the Gatun-Chagres Basin and tectonic evolution of north-central Panama

    NASA Astrophysics Data System (ADS)

    Mynhier, Kelci

    The Oligocene-Miocene collision between Panama and South America significantly influenced ocean currents, global climate, and species diversification. Intraplate deformation of the Panama Block also played an important role in the evolution of this tectonic system, but is not well understood. A high-resolution gravity survey, coupled with geologic observations, was conducted in north-central Panama to better constrain the processes responsible for the Isthmus' modern configuration. Approximately 110 gravity stations were collected from Colon to Nombre de Dios, Panama and merged with existing data. Subsequently, four 2.5-D gravity models were produced to constrain the geometry of the Gatun-Chagres Basin using different sedimentary densities (1.8, 2.0, and 2.2 g/cm 3) to produce a realistic range of basin thicknesses. Overall, models with an average basin density of 2.0 g/cm3 are most consistent with offshore seismic profiles and field evidence, suggesting basin thickness is ~3.0--3.5 km. Previous seismic reflection data and geochemical analyses of Miocene arc volcanic rocks delineate a zone of extension in the Panama Canal Region, and gravity analysis from this study supports this hypothesis. Field evidence of multiple NW-facing normal faults suggests that they separate the basin from uplifted arc basement rocks east of the Canal, resulting in a 60 mGal gravity gradient. Beneath the basin, gravity models indicate ~5--10 km of crustal thinning. 3-D reconstruction of the 2.5-D models show a northward thickening basin and two depocenters that correspond to the Rio Indio and Toro facies of the Chagres Formation. This analysis suggests two directional extension of the Gatun-Chagres Basin; an east-west direction corresponding to the initial formation of the basin, and a modern northwest-southeast direction. To the northeast, gravity modeling indicates that there is a ~150 m-thick, Cretaceous-Holocene sedimentary basin present from Portobelo to Nombre de Dios. Sedimentary

  6. Density variability - fundamental basis of structure formation and tectonic-geodynamic evolution of the Earth

    NASA Astrophysics Data System (ADS)

    Guliyev, Hatam; Guliyev, Ibrahim; Yetirmishli, Gurban

    2014-05-01

    It was shown that there are some common geomechanical basis of process of consolidation, deconsolidation, phase transitions, formation of zones of small shear stiffness (waveguides), realization of material and energetic mass flow in the internal structures of the Earth based on fundamental properties of basic systems of equations of nonlinear mechanics of the deformed bodies, data and results of Green, Ringwood, Liu's known experimental studies. Its instability for different geological media was shown studying the distribution of medium density depending on deformation changes. Distinguishing various forms of instability it was shown that there is general deformation mechanism of consolidation process of compressible medium according to which transfer to deconsolidation occurs at certain stages due to specific change of equilibrium states. Instability of deformation process contributes to emergence of geometric structures in composition of geological medium which are favorable to form deconsolidation zones and zones of small shear stiffness. Destruction by delamination at various depth of the Earth's interior can lead to formation of voids of various scale. Various forms of instability can be realized in the process of further evolution in the vicinity of these free surfaces, and voids can be filled by the loosened mass, i.e. deconsolidation process occurs under compression conditions. More hard bodies of local scale in the form of rod, strips, plates, cylindrical bodies, voids etc. can exist at different depth of mantle. These bodies can lose the stability under compression conditions. Therefore, part of their material and environment are loosened and deconsolidation process occurs again. The above described cases significantly depends on the realized form of deformation. Unevenness of deformation has a great value. Partial melting and magma formation can occur in these deconsolidated zones depending on mineral associations, petrochemical properties, thermobaric

  7. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.

    2015-11-01

    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  8. Analysis of the influence of tectonics on the evolution valley network based on the SRTM DEM and the relationship of automatically extracted lineaments and the tectonic faults, Jemma River basin, Ethiopia

    NASA Astrophysics Data System (ADS)

    Kusák, Michal

    2016-04-01

    The Ethiopian Highland is good example of high plateau landscape formed by combination of tectonic uplift and episodic volcanism (Kazmin, 1975; Pik et al., 2003; Gani et al., 2009). Deeply incised gorges indicate active fluvial erosion which leads to instabilities of over-steepened slopes. In this study we focus on Jemma River basin which is a left tributary of Abay - Blue Nile to assess the influence of neotectonics on the evolution of its river and valley network. Tectonic lineaments, shape of valley networks, direction of river courses and intensity of fluvial erosion were compared in six subregions which were delineate beforehand by means of morphometric analysis. The influence of tectonics on the valley network is low in the older deep and wide canyons and in the and on the high plateau covered with Tertiary lava flows while younger upper part of the canyons it is high. Furthermore, the coincidence of the valley network with the tectonic lineaments differs in the subregions. The fluvial erosion along the main tectonic zones (NE-SW) direction made the way for backward erosion possible to reach far distant areas in E for the fluvial erosion. This tectonic zone also separates older areas in the W from the youngest landscape evolution subregions in the E, next to the Rift Valley. We studied the functions that can automatically extract lineaments in programs ArcGIS 10.1 and PCI Geomatica. The values of input parameters and their influence of the final shape and number of lineaments. A map of automated extracted lineaments was created and compared with 1) the tectonic faults by Geology Survey of Ethiopia (1996); and 2) the lineaments based on visual interpretation of by the author. The comparation of lineaments by automated visualization in GIS and visual interpretation of lineaments by the author proves that both sets of lineaments are in the same azimuth (NE-SW) - the same direction as the orientation of the rift. But it the mapping of lineaments by automated

  9. 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.

  10. Evolution of the Gulf of Cadiz and west Portugal contourite depositional system: tectonic, sedimentary and paleoceanographic implications from IODP Expedition 339

    NASA Astrophysics Data System (ADS)

    Hernández Molina, F. J.; Sierro, F. J.; Llave, E.; Roque, C.; Stow, D. A. V.; Williams, T.; Lofi, J.; Van der Schee, M.; Arnaíz, A.; Ledesma, S.; Rosales, C.; Rodriguez-Tovar, F. J.; Pardo-Igúzquiza, E.; Brackenridge, R.

    2015-12-01

    The contourite depositional systems (CDS) along the southwestern Iberian Margin (SIM) bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution. We identify significant changes in sedimentary style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM. Following the 4.5 Ma cessation of a previous phase of tectonic activity related to the Miocene-Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8 Ma duration with a pronounced overprint of ~2 -2.5 Ma cycles. Two major compressional events affecting to the Neogene basins at 3.2-3 Ma and 2-2.3 Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33-3.2 Ma) with a weak MOW, 2) a transitional-drift stage (3.2-2 Ma) and 3) a growth-drift stage (2 Ma-present time) with enhanced MOW circulation and attendant contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7-0.9 Ma and 0.3-0.6 Ma record the effects of renewed tectonic activity on basin evolution. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over

  11. Tectono-sedimentary events and geodynamic evolution of the Mesozoic and Cenozoic basins of the Alpine Margin, Gulf of Tunis, north-eastern Tunisia offshore

    NASA Astrophysics Data System (ADS)

    Melki, Fetheddine; Zouaghi, Taher; Chelbi, Mohamed Ben; Bédir, Mourad; Zargouni, Fouad

    2010-09-01

    The structural pattern, tectono-sedimentary framework and geodynamic evolution for Mesozoic and Cenozoic deep structures of the Gulf of Tunis (north-eastern Tunisia) are proposed using petroleum well data and a 2-D seismic interpretation. The structural system of the study area is marked by two sets of faults that control the Mesozoic subsidence and inversions during the Paleogene and Neogene times: (i) a NE-SW striking set associated with folds and faults, which have a reverse component; and (ii) a NW-SE striking set active during the Tertiary extension episodes and delineating grabens and subsiding synclines. In order to better characterize the tectono-sedimentary evolution of the Gulf of Tunis structures, seismic data interpretations are compared to stratigraphic and structural data from wells and neighbouring outcrops. The Atlas and external Tell belonged to the southernmost Tethyan margin record a geodynamic evolution including: (i) rifting periods of subsidence and Tethyan oceanic accretions from Triassic until Early Cretaceous: we recognized high subsiding zones (Raja and Carthage domains), less subsiding zones (Gamart domain) and a completely emerged area (Raouad domain); (ii) compressive events during the Cenozoic with relaxation periods of the Oligocene-Aquitanian and Messinian-Early Pliocene. The NW-SE Late Eocene and Tortonian compressive events caused local inversions with sealed and eroded folded structures. During Middle to Late Miocene and Early Pliocene, we have identified depocentre structures corresponding to half-grabens and synclines in the Carthage and Karkouane domains. The north-south contractional events at the end of Early Pliocene and Late Pliocene periods are associated with significant inversion of subsidence and synsedimentary folded structures. Structuring and major tectonic events, recognized in the Gulf of Tunis, are linked to the common geodynamic evolution of the north African and western Mediterranean basins.

  12. Cenozoic tectonic evolution leading to the Choco-South America collision (Panama-Colombia), from seismic profiles interpretations

    NASA Astrophysics Data System (ADS)

    Barat, F.; Maurin, T.; Auxietre, J.; Mercier de Lépinay, B.; Salmon, P.; Sosson, M. M.

    2012-12-01

    The Choco Block is located in eastern Panama and western Colombia, at the western boundary of the Caribbean Plate (CP), and is mainly characterized by a Late Cretaceous-Paleogene volcanic arc overlying the Caribbean Large Igneous Province (CLIP). This block was accreted to South American plate (SAP) during Middle to Late Miocene. Geological, chronological and structural data are scarce in the Choco Block. Our study aims at reconstructing the evolution at a local scale, to provide new constraints to the regional scale tectonic processes that have occurred since the Paleogene. In that perspective, we have interpreted offshore seismic reflection profiles. This interpretation was supported by biostratigraphic data from two wells. We focused our studies in the Uraba Gulf area, a triple junction between the Choco Block, the SAP and the Caribbean oceanic plateau. This poorly understood zone offers rare observation of two accretionary wedges, the North Panama Deformed Belt (NPDB), and the Sinu Belt, located at the margins of the Choco Block and the SAP, respectively. They are the results of two opposite convergent zones, and collide along the active Uramita strike-slip Fault Zone (UFZ), a suture zone between the Choco Block and the SAP. This area may provide information on the ages of both accretionary wedges, on the tectonic processes responsible for the disappearance of the CP, and on the late formation of the Choco Block. Our results evidence a northward propagating deformation along the Choco Block, miocene or older in the South of the Uraba Gulf, pliocene in the North of the Uraba Gulf, and active along the northern margin of Panama. This deformation is the result of the progressive accretion of Choco Block along the SAP. At the Uraba triple junction, a thick sedimentary sequence was deposited since late Miocene. North verging progradations suggest that sediments came from the drainage of the western cordillera of Colombia by a Paleo-Sinu river and actual Atrato river

  13. Stable Isotope Paleoaltimetry: Linking Tectonics to the Evolution of Landscapes and Life

    NASA Astrophysics Data System (ADS)

    Mulch, A.; Chamberlain, C. P.

    2015-12-01

    Stable isotope paleoaltimetry exploits systematic changes in the oxygen or hydrogen isotopic composition of precipitation that occur when lifting of moist air masses over topography induces orographic precipitation. Stable isotope-based reconstructions of topography, therefore, have greatly expanded what used to be very sparse global paleoaltimetric information. The topography of mountain ranges and plateaus, however, not only reflects the geodynamic processes that shape the Earth's surface; it also represents a key control for continental moisture transport, atmospheric circulation and the distribution of biomes and biodiversity. The challenge now lies in disentangling the surface uplift component from the impact of long-term climate change on paleoaltimetry records. The robustness of stable isotope paleoaltimetry reconstructions can be greatly enhanced when high-elevation isotope proxy data are referenced against low-elevation records that track climate-modulated oxygen and hydrogen isotopes in precipitation through time. In addition, evaluating the record of precipitation upstream of the orogen reduces commonly encountered complexities such as topographic threshold conditions to atmospheric circulation, variable moisture recharge to the atmosphere through evapotranspiration over the continents or the impact of hemispheric-scale atmospheric teleconnections; all of which may conspire in setting the isotopic composition of precipitation.Here, we highlight some of these challenges a) by using stable isotope paleoaltimetry data from the central Andes to show how differences in oxygen isotopes in precipitation between high and low elevation sites may enhance the robustness of Andean stable isotope paleoaltimetry, and b) by linking a large set of spatially distributed isotope and biological proxy data to evaluate the impact of Palaeogene surface uplift on mammalian evolution in western North America prior and during the Eocene-Oligocene transition.

  14. Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models

    NASA Astrophysics Data System (ADS)

    Armann, Marina; Tackley, Paul J.

    2012-12-01

    Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid and recent resurfacing history. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick crust, inconsistent with observations. Partitioning of heat-producing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature ˜constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. The basalt density inversion below the olivine-perovskite transition causes compositional stratification around 730 km breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature ˜rheological temperature scale lower than TCMB is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start. Core heat flow decreases with time, possibly shutting off the dynamo, particularly in episodic cases.

  15. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Abdelsalam, M.; Ali, K. A.; Bingen, B.; Collins, A. S.; Fowler, A. R.; Ghebreab, W.; Hauzenberger, C. A.; Johnson, P. R.; Kusky, T. M.; Macey, P.; Muhongo, S.; Stern, R. J.; Viola, G.

    2013-10-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of

  16. Garnet shapes within Kimberlite xenoliths record the tectonic evolution of a cratonic root

    NASA Astrophysics Data System (ADS)

    Michibayashi, K.; Kino, M.; Okamoto, A.; Katayama, I.; Komiya, T.

    2013-12-01

    are then fitted to theoretical curves in the L-R space under conditions of 1000 degree C and for a period of 1 billion years with various differential stresses of less than 0.005 MPa. Okamoto, A. and Michibayashi, K., 2005. Progressive shape evolution of a mineral inclusion under differential stress at high temperature: example of garnet inclusions within a granulite facies from the Lutow-Holm complex, East Antarctica. Journal of Geophysical Research, 110, B11203, doi:10.1029/2004JB003526.

  17. Influence of intrusive magmatism on Venus' tectonics and long-term thermo-chemical mantle evolution

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Lourenco, D.; Golabek, G.

    2014-04-01

    Here the models of [1] are extended. Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid, recent resurfacing history and surface deformation. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In [1] it was assumed that all magmatism is extrusive, i.e. melt generated in the lithosphere is immediately placed at the surface at the surface temperature, which constitutes the well-known "heatpipe" mode. This leads to a cold, strong crust/lithosphere. It was found that in stagnant lid convection the dominant mode of heat loss is this magmatic heat pipe, which requires massive magmatism and produces very thick, cold crust, inconsistent with observations. Partitioning of heatproducing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values.The basalt density inversion below the olivineperovskite transition causes compositional stratification around 730 km; breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature approximately a rheological temperature scale lower than T_CMB is not reached

  18. Tectonic evolution of the West Florida Basin, Eastern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Gregg, Andrea Christine

    Basement geometry of the Eastern Gulf of Mexico developed following the breakup of Pangea and the opening of the Gulf of Mexico in Late Triassic time. Nine 2-D pre-stack depth migrated seismic profiles and a structural restoration provide insight into the evolution and development of the southern West Florida Basin, located west of the Florida Escarpment in the Eastern Gulf of Mexico. Seismic reflection profiles reveal basement structures probably developed following a combination of Late Triassic extension and extension and subsequent oceanic crust emplacement in Middle Jurassic time. During Late Triassic rifting, the West Florida Basin developed as a rift graben; however, the graben was later dissected during the Middle Jurassic drift episode. Absence of faulting, syn-rift deposition and sagging in the Lower Cretaceous seismic section indicates that extension and rotation of the Yucatan block must have stopped prior to Cretaceous time. After extension terminated and the Gulf of Mexico reached its modern day configuration, subsidence from lithospheric cooling and sediment loading dominated throughout Cretaceous time. A structural restoration confirms that following Late Triassic rifting, basement topography remains relatively elevated to the south in the West Florida Basin. Subsequent extension and subsidence further dissected the basement allowing for the deposition of Middle and Late Jurassic syn-rift and Cretaceous post-rift sediments. Because of the lack of well control in the West Florida Basin, seismic packages are correlated northward to the northern margin of the West Florida Basin and slope, the Tampa Embayment, and the Apalachicola Basin and southward to the Straits of Florida and Yucatan. Seismic interpretations reveal two syn-rift packages, Triassic-Jurassic (TJ) and Jurassic-Cretaceous (JK), and one post rift package, Early Cretaceous (EK), were deposited prior to the Mid-Cretaceous Sequence Boundary, a basin-wide unconformity that marks the

  19. The early Paleozoic sedimentary-tectonic evolution of the circum-Mangar areas, Tarim block, NW China: Constraints from integrated detrital records

    NASA Astrophysics Data System (ADS)

    Dong, Shunli; Li, Zhong; Jiang, Lei

    2016-07-01

    The Mangar depression, located in the eastern part of the Tarim basin, had deposited extremely-thick lower Paleozoic sediments, which yields great scientific value and hydrocarbon resource potential. Due to the lack of enough outcrop and core studies, many issues, e.g., early Paleozoic geographical evolution, basin nature and tectonic affinity, are still poorly understood. In this study, we selected circum-Mangar areas (i.e., the South Quruqtagh, Tabei and Tazhong areas), and carried out comprehensive detrital provenance analysis including detrital modal analysis, heavy mineral and trace element analysis, and detrital zircon U-Pb dating on the Middle-Upper Ordovician and Silurian sandstones. The results show that Upper Ordovician-Lower Silurian detrital provenances of the South Quruqtagh and Tabei areas were primarily derived from the intracontinental uplifts in Tarim. Meanwhile, Upper Silurian detrital provenances of the above two areas were mainly derived from the mix of intracontinental uplifts and continental-margin arcs. Dramatic Late Silurian provenance-change suggests the evident tectonic transition of the northern Tarim margin, which is the opening of the South Tianshan back-arc oceanic basin. Combining the previous studies, an integral redefinition model for the Mangar depression has been made. The evolution process of the Mangar depression could be divided into four stages: graben stage (late Neoproterozoic), transitional stage (Cambrian to Middle Ordovician), downwarp stage (Late Ordovician to Early Silurian) and extinction stage (Late Silurian). Hence, the Mangar depression evolved as an aulacogen. Significantly, the evolutional scenario of the Mangar aulacogen was consistent with that of the North Altyn Tagh and the North Qilian, suggesting that the Mangar aulacogen was involved mainly in the Proto-Tethys tectonic realm south to the Tarim block. However, the Late Silurian tectonic activity in the northern Tarim margin did produce massive detrital

  20. Geology of the Santa Elena Peninsula, Costa Rica and its implications for the tectonic evolution of the Central America-Caribbean region

    SciTech Connect

    Lew, L.R.

    1985-01-01

    The Santa Elena Peninsula of Costa Rice represents an Aptian to Middle Eocene intraoceanic volcanic arc formed on a basement of serpentinized periodotite. This peridotite was probably part of the oceanic lithosphere formed at a spreading ridge which began to separate South America from North America in pre-Jurassic time. The arc resulted from northward subduction of oceanic crust along one ENE-trending trench about 70 km south of Santa Elena. The first phase of tectonism, arc volcanism, and sedimentation occurred in the area from Aptian to Campanian time. Carbonate bank limestone were deposited on the peridotite, which had been tilted and uplifted along E-W-trending high angle faults. A second volcanic arc developed above the limestone and was active until the Middle Eocene. From the Campanian to the Middle Eocene a forearc basin evolved south of the arc and a backarc basin north of it. A major Middle Eocene tectonic episode was associated with termination of activity of the Santa Elena subduction zone. This involved both thin-skinned deformation and reactivation of the steep basement faults to juxtapose peridotite and Campanian to Middle Eocene sediments. Existing models of the early plate tectonic evolution of the region, postulating initiation of spreading in the Jurassic, and development of a major transform in the Santa Elena area in the Cretaceous, are incompatible with the geology of the Santa Elena area. New models have been formulated genetically relating the structures in the Santa Elena tectonic province to northward subduction.

  1. Eocene-Oligocene granitoids in southern Tibet: Constraints on crustal anatexis and tectonic evolution of the Himalayan orogen

    NASA Astrophysics Data System (ADS)

    Hou, Zeng-Qian; Zheng, Yuan-Chuan; Zeng, Ling-Sen; Gao, Li-E.; Huang, Ke-Xian; Li, Wei; Li, Qiu-Yun; Fu, Qiang; Liang, Wei; Sun, Qing-Zhong

    2012-10-01

    Tectonic models for the evolution of the Himalayan orogen interpret the Greater Himalayan crystalline complex (GHC) to be the result of either thick-skinned thrusting involved Indian basement, thin-skinned thrusting involving exotic terranes, middle-crustal ductile flow, or wedge extrusion of the Indian crust during India-Asia collision. Two key pieces of information needed to test the validity of these models is the temporal-spatial distribution of, and the identification of the dynamic mechanisms involved in, regional melting under southern Tibet. Here, we document an Eocene-Oligocene melting event in southern Tibet, which forms a 150-km-long, NW-SE-trending granitoid belt along the Zedong-Lhunze traverse between the Indus-Yarlung suture (IYS) and the south Tibetan detachment (STD). U-Pb dating of magmatic zircons indicates that this granitoid belt youngs northward from ˜46 Ma (in Lhunze) to ˜30 Ma (in Zedong). 40Ar/39Ar dating of deformed biotite within 42-46 Ma granitoids constrains the timing of shearing to ˜39-41 Ma. The granitoid belt of southern Tibet is dominated by Eocene two-mica granites in the Tethyan Himalaya, with minor ˜30 Ma granodiorites along the IYS and ˜35 Ma granites in the Yelaxiangbo dome, where Indian mid-crustal rocks are exposed. The ˜35 Ma granites are characterized by variable Na2O/K2O ratios (1.03-4.44), relatively high Sr concentrations, and high Sr/Y (14.0-126.3) and La/Yb (11.1-42.8) ratios, which distinguish these granitoids from Miocene leucogranites in the Himalaya. Comparison of the Sr-Nd isotopic compositions of these granites with mid-crustal amphibolites exposed in the Yelaxiangbo dome suggests that the granites were derived from melting of the amphibolites at ˜880 °C and ˜10 kbar. The ˜30 Ma granodiorites and ˜42-46 Ma two-mica granites are Na-rich and peraluminous, and are adakitic. They contain inherited Proterozoic zircons, and have a much wider range in ɛNd(t) of -14.9 to -2.5 and (87Sr/86Sr)i of 0

  2. The Thermo-Tectonic Evolution of Hoodoo Dome, Ellef Ringnes Island: Implications for Petroleum Exploration in the Sverdrup Basin

    NASA Astrophysics Data System (ADS)

    Springer, A. C.; Guest, B.

    2011-12-01

    Over one hundred evaporite diapirs, cored by Carboniferous Otto Fiord Fm., reside along the Sverdrup Basin's axis in the Canadian High Arctic. However, due to the remoteness of this region their tectonic evolution and hydrocarbon potential remain poorly understood. This study focuses on one of the better known diapirs, Hoodoo Dome, located on Ellef Ringnes Island. We use ground-based geological mapping as well as (U-Th)/He thermochronology to better understand the thermal evolution of the rocks around the dome and tectonic influences on salt migration. Our goal is to improve the understanding of thermal histories and hydrocarbon potential of the salt structures in the Sverdrup Basin. The Sverdrup Basin is a steep sided pericratonic trough estimated to contain approximately thirteen kilometers of Carboniferous to Tertiary strata. At Hoodoo Dome, sandstone samples from the Early Cretaceous Isachsen Fm. and Late Cretaceous Hassle Fm. were collected at Hoodoo Dome for apatite and zircon (U-Th)/He thermochronology, a fairly new low temperature thermochronometric technique that yields cooling ages marking a sample's passage through the ~ 70°C and ~175-193°C isothermal surfaces. Samples were collected along 2 transects (north-south and east-west) across Hoodoo Dome, where seven samples yielded sufficient apatite grains and ten samples yielded sufficient zircon grains. The apatite sample suite exhibits a large distribution of apatite helium (AHe) ages, both reset and non-rest. Only 2 samples, BG 14-35-2 and BG 14-34-4 are interpreted as completely reset. Sample BG 14-35-2, the stratigraphically oldest sample, yielded a mean AHe age of 59.2 ±3.9 Ma, whereas sample BG 14-34-4, approx. 150m up section from BG 14-35-2 yielded a mean AHe age of 69.4 ±4.2 Ma. These reset ages suggest that dome uplifting was active by ≈70 Ma at the latest and continued until at least ≈60 Ma, consistent with the timing the Eurekan Orogeny. The remaining AHe ages from samples collected

  3. New insights and questions about the Meso-Cenozoic Tectonic evolution of Eastern Black Sea and Caucasus.

    NASA Astrophysics Data System (ADS)

    Sosson, Marc; Rolland, Yann; Hässig, Marc; Meijers, Maud; Smith, Brigitte; Muller, Carla; Adamia, Shota; Melkonian, Rafael; Kangarli, Talat; Sahakyan, Lilit; Sadradze, Nino; Avagyan, Ara; Galoyan, Ghazar; Alania, Victor; Enukidze, Onice; Sheremet-Korniyenko, Yevgeniya; Yegorova, Tamara

    2014-05-01

    Since last decade a lot of new field researches (supported by MEBE and DARIUS programmes) were carried out in order to clarify the tectonic evolution of the South Caucasus and Eastern Black Sea regions. A summary of these improvements are as following: 1. Evidence of only one suture zone in the Lesser Caucasus: the Sevan-Akera suture zone as the eastward continuity of the Izmir-Ankara-Erzincan one. 2. Timing and modalities of the Upper Cretaceous obduction process of the Sevan-Akera back-arc basin. 3. Paleolatitude reconstruction of the Taurides-Anatolides-South Armenia microplate (TASAM) since the Late Cretaceous 4. Paleocene to Miocene tectonic evolution of the collision zone between Eurasia and the TASAM. 5. Structures and propagation of the Lesser Caucasus and Greater Causasus foreland basins from Paleocene to Miocene. 6. Structures of the inverted Paleocene-Eocene Adjara-Trialeti basin of the Eurasian margin and timing of deformations from Lesser Caucasus to Greater Caucasus. 7. New stratigraphic data from the Crimea Mountain which argues for a Lower Cretaceous rifting of the Eastern Black Sea. According to aforementioned results and previous studies, this widespread zone (from the Eastern Black Sea to the Lesser Caucasus) appears act as a large puzzle of heterogeneous lithospheres (continental, oceanic, arc, back-arc basins) since the Early Cretaceous. This is probably why this area has differently reacted in time and space to the northward collision of the TASAM with Eurasia since the Late Cretaceous and then of Arabian plate since the Oligo-Miocene. It seems that some lithospheres which have cold mantellic behavior (especially the Black Sea) react as rigid blocks, while others with a continental origin, reheated by magmatism, (as the Taurides-Anatolides) were extruded to the west or bended as an orocline (as the Lesser Caucasus, the Pontides). This is why some main questions remain, are not solved and are still debated. 1. The continuity of main structures

  4. Detrital zircon age populations from the Moine Supergroup, Scotland, and their implications for tectonic evolution

    NASA Astrophysics Data System (ADS)

    Kindgren, Kelly; Steltenpohl, Mark; Strachan, Rob; Law, Rick; Cawood, Peter; Schwartz, Joshua

    2016-04-01

    absence of detrital grains younger than ~1050 Ma in the lower unit suggests evolution in the nature of rock units exposed in the source and/or a stratigraphic break between the upper and lower units of the succession. Furthermore, the age profile of the lower unit is consistent with, but not limited to, the interpretation that it correlates with the Torridon Group of the foreland, which has been argued to represent a foreland basin to the end Mesoproterozoic Grenville orogenic belt.

  5. Evolution of terrace risers along the upper Rhine graben inferred from morphologic dating methods: evidence of climatic and tectonic forcing

    NASA Astrophysics Data System (ADS)

    Nivière, B.; Marquis, Guy

    2000-06-01

    We show that morphologic dating techniques that have been applied successfully in arid and semi-arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments. We have attempted two morphologic approaches, based on diffusion, to relate the present-day shape of an abandoned terrace riser to its age. The first assumes a model of scarp degradation based on a diffusive process (the D method). The second evaluates the state of scarp degradation using the slope distribution (the SD method) along a topographic profile. By using a manmade scarp of known age, we have obtained a mass diffusivity close to 1.4m2ka-1 when the area experiences a temperate climate characterized by a continuous vegetation cover. However, this value decreases during glacial episodes, probably on account of the permafrost. Even though the SD method requires an age correction that can be easily computed, only this method reveals that at several profiles a later scarp reactivation event has occurred. Indeed, along several profiles, the slope distribution was best fitted by two offset Gaussian curves, suggesting that some scarps have undergone a complex evolution that cannot be modelled with a single diffusive process. This scarp reactivation may correspond to a new incisive episode and allows one to estimate the vertical incision rate along the terrace riser. Applied to a Wurmian terrace riser of the upper Rhine valley (NE France), this approach reveals that the vertical incision rate ranges from 0.2 to 0.85mmyr-1 between 35 and 15ka and that the terrace bevelling occurred during two episodes related to climatic forcing. Moreover, we can identify a component of tectonic forcing evidenced by an increase to the north of vertical incision rate and Rhine stream-power. Another major result is showing that this terrace riser is not isochronous along its strike and that younger portions result from lateral incision of a 30ka pre-existing scarp.

  6. Rheological control on the tectonic evolution of a continental suture zone: the Variscan example from NW Iberia (Spain)

    NASA Astrophysics Data System (ADS)

    Díez Fernández, Rubén; Foster, David A.; Gómez Barreiro, Juan; Alonso-García, Montserrat

    2013-07-01

    The Variscan continental suture zone exposed in NW Iberia is examined to uncover the long-lived rheological control exerted by the strata deposited over the external parts of Gondwana on its geodynamic evolution. The suture occurs within a set of allochthonous terranes whose limits were taken as domain boundaries to interpret the Variscan stacking of Paleozoic continental domains and retrodeform the resulting nappe pile. The suture zone formed due to closure of ocean basins located between Gondwana and Laurussia during the Late Paleozoic and consists of relics of oceanic and transitional crust. The suture zone exhibits a tabular to lens shape due to repeated tectonic events dominated by non-coaxial deformation (thrusts and low-angle normal faults). Thrusting and normal faulting also involved the margins of the continents bounding the suture. The structure of the continental blocks, however, is dominated by folds, particularly large nappe folds with pronounced superimposed flattening. The upper part of the basal allochthonous units comprises a rheologically incompetent domain below the suture zone. This domain is typified by the carbonaceous-rich strata, which are probably Ordovician-Silurian sediments based on U-Pb detrital zircon populations. The rheology of this layer determined the location of the first accretionary thrust that initiated the Late Devonian subduction of the Gondwana margin below the suture zone. By favoring fault development, the upper sequence of the basal allochthonous units as a whole influenced the exhumation of deep-seated continental crust, the transference of the suture zone over Gondwana, and the re-equilibration of the resulting overthickened crust.

  7. Longitudinal evolution of the tectonic style along the Cyprus Arc, northern margin of the Levant and Herodotus Basins

    NASA Astrophysics Data System (ADS)

    Symeou, Vasilis; Homberg, Catherine; Nader, Fadi; Darnault, Romain; Lecomte, Jean-Claude

    2016-04-01

    The Levant Basin is bounded to the north by the Cyprus Arc zone which was created by the northward movement of the African plate with respect to the Eurasian plate since Late Cretaceous time. The westward movement of the Anatolian micro-plate since Late Miocene created an additional strike-slip component along the plate boundary. The main objective of this contribution is to portray the structural architecture and features offshore Cyprus by analyzing available 2D seismic data in order to investigate the transition in tectonic style from compression to strike slip along the Cyprus Arc zone. We identified three different crustal domains offshore Cyprus that are from east to west: the eastern domain which belongs to the Levant Basin, the South-central domain which includes the Eratosthenes Seamount, and the South-West domain of Cyprus which corresponds to the Herodotus Basin. In the Levant Basin, the sequences identified are from Base Pliocene extending until the Senonian unconformity. The same sequences in the Cyprus Basin are offset and less thick due to the movement of the Latakia Ridge, which is identified as a steeply dipping sub-vertical fault on our data. In the central domain, the horizons identified on the Eratosthenes Seamount indicate that the Seamount is a Mesozoic carbonate platform covered by thin Miocene/Plio-Pleistocene sediments. A subdivision of the sedimentary sequence in the Herodotus Basin is proposed down to the Paleocene-Eocene basis. A major change in the structural style of the deformation is observed form west to east. Whereas the Levant Basin is almost undeformed south of the Latakia Ridge, several structures were mapped in the central domain, like flexural basin, pop-up structures and back-thrusts. South-verging thrusts were also, identified in the Cyprus Basin. All these structures show a Pliocene activity. Our data suggest that the heterogeneity of the crustal structure played a major role in the longitudinal evolution of the plate

  8. Depositional Record of the Bagua Basin, Northern Peru: Implications for Climate and Tectonic Evolution of Tropical South America

    NASA Astrophysics Data System (ADS)

    Moreno, F.; George, S. W. M.; Williams, L. A.; Horton, B. K.; Garzione, C. N.

    2015-12-01

    The Andes Mountains exert critical controls on the climate, hydrology, and biodiversity of South America. The Bagua Basin, a low elevation (400-600 m) intermontane basin in northern Peru, offers a unique opportunity to study the ecological, climatic, and structural evolution of the western topographic boundary of the Amazonian foreland. Situated between the Marañon fold-thrust belt of the Western Cordillera and basement block uplifts of the Eastern Cordillera, the Bagua region contains a protracted, semi-continuous record of Triassic through Pleistocene sedimentation. Whereas Triassic-Cretaceous marine deposits were potentially related to extension and regional thermal subsidence, a Paleocene-Eocene shift to shallow marine and fluvial systems marks the onset of foreland basin conditions. Oligocene-Miocene sedimentation corresponds to a braided-meandering fluvial system with exceptional development of paleosols. In this study, we use new detrital zircon U-Pb geochronologic and oxygen stable isotopic datasets to establish a chronology of pre-Andean and Andean processes within the Bagua Basin. Detrital zircon geochronology provides constraints on when the Western and Eastern cordilleras shed sediments into the basin. Syndepositional zircons within Eocene, Oligocene and Miocene strata provide key age control for a previously poorly constrained depositional chronology. Preliminary results suggest a dramatic provenance shift in which Paleocene deposits contain almost exclusively cratonic populations (500-1600 Ma) whereas Eocene deposits show a mix of syndepositional zircons from the magmatic arc, recycled Mesozoic zircons, and cratonic zircon populations. Oxygen stable isotopes (δ18O) of carbonate nodules from Neogene paleosols will help elucidate when the Eastern Cordillera became an orographic barrier intercepting moisture from the Amazon basin to the east. Together, these records will help uncover the history of tectonics and climate interaction in tropical South

  9. Seismic signature of the Alpine indentation, evidence from the Eastern Alps

    PubMed Central

    Bianchi, I.; Bokelmann, G.

    2014-01-01

    The type of collision between the European and the Adriatic plates in the easternmost Alps is one of the most interesting questions regarding the Alpine evolution. Tectonic processes such as compression, escape and uplift are interconnected and shape this area. We can understand these ongoing processes better, if we look for signs of the deformation within the Earth's deep crust of the region. By collecting records from permanent and temporary seismic networks, we assemble a receiver function dataset, and analyze it with the aim of giving new insights on the structure of the lower crust and of the shallow portion of the upper mantle, which are inaccessible to direct observation. Imaging is accomplished by performing common conversion depth stacks along three profiles that crosscut the Eastern Alpine orogen, and allow isolating features consistently persistent in the area. The study shows a moderately flat Moho underlying a seismically anisotropic middle-lower crust from the Southern Alps to the Austroalpine nappes. The spatial progression of anisotropic axes reflects the orientation of the relative motion and of the stress field detected at the surface. These observations suggest that distributed deformation is due to the effect of the Alpine indentation. In the shallow upper mantle right below the Moho interface, a further anisotropic layer is recognized, extended from the Bohemian Massif to the Northern Calcareous Alps. PMID:26525181

  10. Late Cretaceous ARC to MORB compositional switch in the Quebradagrande Complex, Colombian Andes: understanding the long term tectonic evolution of a magmatic arc.

    NASA Astrophysics Data System (ADS)

    Jaramillo, J. S.; Cardona, A.; Zapata, S.; Valencia, V.

    2014-12-01

    The spatial and compositional characters of arc rocks are sensible markers of the tectonic changes experienced by convergent margins and therefore provide a fundamental view to the continuous tectonic evolution of active margins. The Early to Late Cretaceous tectonic evolution of the Northern Andes have been related to the growth and accretion of different continental and oceanic arc systems that were juxtaposed at the beginning of the Andean Orogeny in the Late Cretaceous. The Quebradagrande Complex is a tectonostratigraphic unit made of mafic to intermediate plutonic rocks, basic to intermediate volcanic flows and associated marine sedimentary rocks that have been related to a single Albian arc or back-arc environment that discontinuously outcrops along the western margin of the Central Cordillera of Colombia. New field, geochronological and geochemical data from the plutonic and volcanic rocks of the Quebradagrande complex shows that the pre-90-80 Ma volcanic arc rocks are intruded by ca. 90 Ma pyroxene gabbroic and hornblende dioritic plutons with medium to pegmatitic grain size characterized by a contrasting MORB-type signature. We related the compositional change to a transient modification of the convergent margin system, where and extensional roll-back related configuration or the subduction of an oceanic ridge allows the flux of the astenospheric mantle. This continental magmatic arc was subsequently deformed due to the collision and accretion of an allocthonous oceanic arc that migrate from the southeast Pacific at the beginning of the Andean orogeny.

  11. The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea.

    PubMed

    Matenco, Liviu; Munteanu, Ioan; ter Borgh, Marten; Stanica, Adrian; Tilita, Marius; Lericolais, Gilles; Dinu, Corneliu; Oaie, Gheorghe

    2016-02-01

    Understanding the natural evolution of a river-delta-sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River-western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during

  12. Internal structure and current evolution of very small debris-covered glacier systems located in alpine permafrost environments

    NASA Astrophysics Data System (ADS)

    Bosson, Jean-Baptiste; Lambiel, Christophe

    2016-04-01

    This contribution explores the internal structure of very small debris-covered glacier systems located in permafrost environments and their current dynamical responses to short-term climatic variations. Three systems were investigated with electrical resistivity tomography and dGPS monitoring over a 3-year period. Five distinct sectors are highlighted in each system: firn and bare-ice glacier, debris-covered glacier, heavily debris-covered glacier of low activity, rock glacier and ice-free debris. Decimetric to metric movements, related to ice ablation, internal deformation and basal sliding affect the glacial zones, which are mainly active in summer. Conversely, surface lowering is close to zero (-0.04 m yr-1) in the rock glaciers. Here, a constant and slow internal deformation was observed (c. 0.2 m yr-1). Thus, these systems are affected by both direct and high magnitude responses and delayed and attenuated responses to climatic variations. This differential evolution appears mainly controlled by (1) the proportion of ice, debris and the presence of water in the ground, and (2) the thickness of the superficial debris layer.

  13. Flower evolution of alpine forbs in the open top chambers (OTCs) from the Qinghai-Tibet Plateau.

    PubMed

    Zhang, Chan; Wang, Lin-Lin; Yang, Yong-Ping; Duan, Yuan-Wen

    2015-01-01

    Effects of global changes on biodiversity have been paid more and more attention world widely, and the open top chambers (OTCs) are the most common tools to study the effects of climatic warming on plant diversity. However, it remains unclear how flowers evolve under environmental changes, which could help us to understand the changes of plant diversity in the OTCs. We compared the insect diversity and pollen:ovule (P/O) ratio of eight outcrossing species with different life histories inside and outside the OTCs on the Qinghai-Tibet Plateau, to examine the effects induced by OTCs on the evolution of floral traits. In the OTCs, P/O ratio decreased in annuals, but increased in perennials, indicating an overall trend toward selfing in annuals. We found that the insect diversity differed significantly inside and outside the OTCS, with decreases of dipteran insects and bees. We concluded that changes of P/O ratio in the studied plant species might result from pollination failure, which might be the results of mismatch between flowering time and pollinator activities. We also suggested annuals might be in a more extinction risk than perennials in OTCs, if strong inbreeding depression occurs in these annual outcrossing plants. PMID:25998558

  14. Flower evolution of alpine forbs in the open top chambers (OTCs) from the Qinghai-Tibet Plateau

    PubMed Central

    Zhang, Chan; Wang, Lin-Lin; Yang, Yong-Ping; Duan, Yuan-Wen

    2015-01-01

    Effects of global changes on biodiversity have been paid more and more attention world widely, and the open top chambers (OTCs) are the most common tools to study the effects of climatic warming on plant diversity. However, it remains unclear how flowers evolve under environmental changes, which could help us to understand the changes of plant diversity in the OTCs. We compared the insect diversity and pollen:ovule (P/O) ratio of eight outcrossing species with different life histories inside and outside the OTCs on the Qinghai-Tibet Plateau, to examine the effects induced by OTCs on the evolution of floral traits. In the OTCs, P/O ratio decreased in annuals, but increased in perennials, indicating an overall trend toward selfing in annuals. We found that the insect diversity differed significantly inside and outside the OTCS, with decreases of dipteran insects and bees. We concluded that changes of P/O ratio in the studied plant species might result from pollination failure, which might be the results of mismatch between flowering time and pollinator activities. We also suggested annuals might be in a more extinction risk than perennials in OTCs, if strong inbreeding depression occurs in these annual outcrossing plants. PMID:25998558

  15. The Ingul block of the Ukrainian Shield (the East European Craton): multiple stress changes during the Palaeoproteozoic tectonic evolution

    NASA Astrophysics Data System (ADS)

    Gintov, O. B.; Mychak, S. V.

    2012-04-01

    The Palaeoproterozoic Ingul block occupies the central part of the Ukrainian Shield in the Sarmatian crustal segment of the East European Craton. It is situated between two groups of Archaean blocks, the Middle Dniepr and Azov blocks in the east, and the Podolian and Bug blocks, in the southwest. In the Archaean and the earliest Palaeoproterozoic these western and eastern Archaean blocks had different structural evolutions and thus most probably were separated by an ocean. The Ingul block appears to have been formed during the closure of that ocean. Structurally, the Ingul block is a part of an up to 200 km wide zone of NS-trending dextral strike-slip faults. It extends far to the south and to the north and is also marked by the Kherson-Smolensk transregional fault zone. Archaean and Palaeoproterozoic rock complexes occur at the margins of the Ingul block whereas its middle part is completely Palaeoproterozoic. Its formation began during the 2.1-2.05 Ga collisional closing of the assumed ocean and the docking of the Archaean eastern and western continental blocks with each other. It was accompanied by dextral strike-slip faulting and strong compression. As a result, the Golovanevsk and Ingulets-Krivoi Rog suture zones were formed along the edges of the Eastern and Western Sarmatian microplates. Between 2.05 and 1.75 Ga, intense tectonothermal reworking and strike-slip faulting took place in the Ingul block. Several phases of deformation have been recognized. These are: • At 2.05-2.0 Ga - the Kherson phase of extension (azimuth/dip angle of the tension axis σ3 278/10, the compression axis σ1 8/00, dextral strike-slip faulting) accompanied by the intrusion of the Novo-Ukrainka monzogranitoids and some anatectic granitoids, and the formation of the Kherson-Smolensk fault zone, • At 2.0-1.8 Ga - two subsequent phases of compression: (1) the Kirovograd phase (σ1 49/00, σ3 319/00) and the development of a system of dextral strike-slip faults in the central part

  16. Neoproterozoic tectonic evolution of the Jebel Saghro and Bou Azzer - El Graara inliers, eastern and central Anti-Atlas, Morocco

    USGS Publications Warehouse

    Walsh, Gregory J.; Aleinikoff, John N.; Harrison, Richard W.; Burton, William C.; Quick, James E.; Benziane, Foudad; Yazidi, Abdelaziz; Saadane, Abderrahim

    2012-01-01

    New mapping, geochemistry, and 17 U–Pb SHRIMP zircon ages from rocks of the Sirwa, Bou Azzer–El Graara, and Jebel Saghro inliers constrain the Neoproterozoic evolution of the eastern Anti-Atlas during Pan-African orogenesis. In the Sirwa inlier, Tonian quartzite from the pre Pan-African passive margin deposits of the Mimount Formation contains detrital zircon derived entirely from the West African Craton (WAC), with most grains yielding Eburnean Paleoproterozoic ages of about 2050 Ma. Cryogenian Pan-African orogenic activity (PA1) from about 760 to 660 Ma included northward-dipping subduction to produce a volcanic arc, followed by ophiolite obduction onto the WAC. In the Bou Azzer–El Graara inlier, calc-alkaline granodiorite and quartz diorite, dated at 650–646 Ma, are syn- to post-tectonic with respect to the second period of Pan-African orogenesis (PA2), arc-continent accretion, and related greenschist facies metamorphism. Slab break-off and lithospheric delimination may have provided the source for the supra-subduction calc-alkaline plutons. At about 646 Ma, quartz diorite intruded the Tiddiline formation placing an upper limit on molassic deposition. Widespread Ediacaran high-K calc-alkaline to shoshonitic plutonism and volcanism during the final stage of Pan-African orogenesis (PA3) occurred in a setting related to either modification of the margin of the WAC or formation of a continental volcanic arc above a short-lived southward-dipping subduction zone. In the Saghro inlier, eight plutonic rocks yield ages ranging from about 588 to 556 Ma. Sampled plutonic rocks previously considered to be Cryogenian yielded Ediacaran ages. Peraluminous rhyolitic volcanic rocks in the lower part of the Ouarzazate Supergroup, including ash-flow tuffs of the Oued Dar’a caldera, yield ages between about 574 and 571 Ma. The Oued Dar’a caldera developed in a pull-apart graben produced by a left-step in a northeast-trending, left-lateral strike-slip fault zone, and

  17. Tectonic and magmatic evolution of a fossil (Ultra-)Slow Spreading Ocean: the study case of the Jurassic Ligurian Tethys.

    NASA Astrophysics Data System (ADS)

    Piccardo, G. B.

    2008-12-01

    The Jurassic Ligurian Tethys oceanic basin has been recognized as the fossil analogue of modern (Ultra- )Slow Spreading Ridges. Stratigraphic and structural studies on the Western Alpine - Northern Apennine (AA) ophiolites, that are remnants of the lithosphere of the ancient basin, evidence that the basin was characterized by the sea-floor exposure on mantle peridotites, discontinuously covered by MORB volcanites and pelagic sediments (i.e. radiolarion cherts). The related passive margins were typically not-volcanic. Palaeogeographic restorations indicate that exhumed sub-continental mantle was exposed at the ocean- continent transition (OCT) zones, frequently associated to continental crust material and pelagic sediments. These exhumed sub-continental lithospheric peridotites were equilibrated under spinel-facies conditions, preserving diffuse structural relicts of precursor garnet, and show widespread spinel(-garnet)-pyroxenites bands. Sm-Nd isotope data on Cpx from these peridotites indicate DMM affinity and Proterozoic model ages, that have been interpreted as early accretion to, and long residence in, the sub-continental lithosphere. OCT peridotites frequently show strong localized deformation along km-scale shear zones that were formed during lithosphere extension leading to the oceanic opening. Isotope data indicate that mantle exhumation during lithosphere extension was already active during Triassic times and was most probably accomodated by a network of lithosphere-scale shear zones. Lithospheric thinning caused asthenosphere adiabatic upwelling and decompression melting along the axial zone of the extensional system. The asthenospheric MORB melts infiltrated by porous flow and percolated through the overlying extending lithospheric mantle causing significant melt-peridotite interaction. The pristine lithospheric mantle was tranformed to strongly pyroxene-depleted (i.e. reactive and replacive peridotites) or plagioclase-enriched (i.e. impregnated and

  18. Kinematic Evolution of fold-and-thrust Belts in the Yubei Area: Implications for the Tectonic Events of Ordovician at the Southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    As a response to tecto-orogenic processes of the South Altun and the West Kunlun (Monlar P, 1975; He Bizhu, 2011), early Paleozoic tectonic evolution of the southern Tarim craton was distinctively one of the extensions and was followed by compression (Morris W.Leighton, 1990; Gao Zhiqian, 2015). From the late Ordovician, the Yubei area developed distinctively NE-SW trending fold-and-thrust belts in rows which were eroded and deformed through multiphase tectonic movement (Dengfa He, 2007), with similarities and dissimilarities between each other rows in many aspects, at the Southern Tarim inner basin (Fig. 1). The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation (Brown LF, 1979). In this contribution, based on geophysical log, core and 2D/3D seismic data, we constructed its tectonic geometry morphology, controlled by detailed chronostratigraphic framework. According to the fault-related fold theory, rows of asymmetric fault-propagation folds grew in the Yubei area during the late Caledonian period, with the evidence of interpreted growth strata from the high resolution 3D seismic data (Suppe J et al., 1990). That intercontinental tecto-orogenic events from southern Tarim basin, leading to the transformation of its margins, affected inner basin at that time, modified the basin into the Tarim metacraton (Jean-Paul Liégeois, 2013; Zieglar P.A., 1998). Correlating the four tectonic groups of the identified with the axis variation of strata and fold amplitude distribution showed that fault evolution progressed in several superimposed stages: Precambrian, late Ordovician to early Carboniferous (Zhao Zongju, 2009), Carboniferous to Permian, Cenozoic. Analyzing the sedimentary development and structure evolution the tectonic paleo-geographic setting is reconstructed, providing

  19. Tectonic and deformation history of the Gyeonggi Massif in and around the Hongcheon area, and its implications in the tectonic evolution of the North China Craton

    NASA Astrophysics Data System (ADS)

    Yengkhom, Kesorjit S.; Lee, Byung Choon; Oh, Chang Whan; Yi, Kee Wook; Kang, Ji Hoon

    2015-04-01

    The Gyeonggi Massif (GM) in South Korea is considered to be a part of the North China Craton. The Precambrian rocks of the GM in and around the Hongcheon area, South Korea, consist of the Yongduri Gneiss Complex (YGC), Euiam Group (EG) and Euiam Gneiss Complex (EGC). The YGC and EG composed mainly of partially migmatised metasedimentary rocks and the EGC is Paleoproterozoic intrusive rock that intruded the EG. At least three major folding (F1, F2 & F3), two-stage ductile shearing and three-stages of metamorphic events (M1, M2 & M3) occurred in the study area. The F1 folds are extremely drawn out, isoclinal, intrafolial folds and have Class 2 to Class 1C geometry. The F1 folds and regional S1 foliation in the YGC and EG are results of the E-W compression during the D1 deformation. Ductile shearing in the southern part of the EG is marked by the Palbongsan Shear Zone that indicates top-to-the SW sheared movement during syn to post-F1 folding. The F2 folds are open to tight, SW plunging and inclined folds, and have Class 1A to 1C geometry. The F2 folding and subsequent NNE thrusting along multiple ductile shear zones parallel to S2 planar fabrics are results of the D2 deformation due to N-S progressive shortening. The D3 deformation was coaxial with the D1 deformation, leading to the development of the F3 kink bands in the mylonite zones. The SHRIMP U-Pb detrital zircon ages from quartzite and banded gneisses in the EG indicate that the sedimentation in the Chunseong basins began after ca. 2094 Ma. The banded gneisses yield M1 metamorphic age of 1917-1925 Ma. However ca.1867-1883 Ma, M2 metamorphism previously reported from the YGC is absent or weakly preserved in the EG representing that the M2 metamorphism was not strong enough to form new zircon in the EG. The igneous zircons form augen gneisses in the EGC yield intrusion age of ca. 1867-1881 Ma and the geochemistries of the EGC gneisses show post-collision tectonic origin. The D1deformation observed in the YGC and

  20. Geometry and kinematics of extension in Alpine Corsica

    NASA Astrophysics Data System (ADS)

    Jolivet, Laurent; Daniel, Jean-Marc; Fournier, Marc

    1991-06-01

    The geometry of the most recent deformation in Alpine Corsica is discussed in terms of reactivation of thrusts as normal faults and crustal extension, following crustal thickening in late Cretaceous and Eocene time. A cross section interpreted in terms of obduction in previous works is shown here to be a result of ductile and brittle extension in late Oligocene and Early Miocene time. This new interpretation is based on field observations of the brittle and ductile structures and their relations to the metamorphic history in the Tenda-col de Teghime and Centuri regions, as well as additional observations in other parts of Alpine Corsica. The following geological features are observed: (1) The recent deformation was partly achieved during a top-to-the-east ductile shear close to the brittle-ductile transition and was later superimposed by brittle shear indicating a transition in time from ductile to brittle regime. (2) Extensional brittle structures in the Early Miocene Saint Florent limestone and sense of tilt are compatible with the eastward sense of shear observed in the ductile rocks. (3) The movement along major "thrust" contacts is associated with retrograde metamorphism which overprinted the early high- P-low- T paragenesis at less severe P-T conditions. They also bring tectonic units with contrasted metamorphic evolutions into close contacts. (4) There is a regional correlation between retromorphosis and recent deformation since the high- P-low- T paragenesis are better preserved in southern of Alpine Corsica where the recent deformation is less pervasive. (5) Highly non-coaxial deformation is localized along east-dipping shear zones close to brittle normal faults which bounds tilted Miocene basins; in between the geometry is more symmetric and the finite strain therefore more coaxial. (6) Late extensional brittle structures are observed at many sites in the metamorphic rocks. In the present paper we discussed these first-order observations and describe the

  1. Tectonic and sedimentary evolution of a Cretaceous continental arc-backarc system in the Korean peninsula: New view

    NASA Astrophysics Data System (ADS)

    Chough, S. K.; Sohn, Y. K.

    2010-08-01

    This paper focuses on the tectonic and sedimentary evolution of the Cretaceous volcanic rocks and nonmarine successions in the southeastern part of the Korean peninsula, which constitute an ancient continental arc system. The arc system (Gyeongsang Arc System), comprising an arc platform (Gyeongsang Volcanic Arc) and a backarc basin (Gyeongsang Backarc Basin), was a southwestward extension of the Japanese Arc formed by oblique northward subduction of the proto-Pacific (Izanagi) plate under the Asian continent. The backarc basin was initiated in the southeastern part of the Korean peninsula in the Early Cretaceous as a narrow NS-trending trough. The basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated. Sediments were deposited in streamflow-dominated alluvial fans adjacent to the fault-bounded basin margin in the north and low-gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers. Sediments were also derived from the western highland margin, draining Precambrian to Jurassic basement rocks. The initially narrow trough progressively expanded toward the east, resulting in eastward migration of depocenters that eventually generated a broad fluvio-lacustrine plain fringing the volcanic arc platform. The arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network. Pyroclastic density currents and landslides, which originated from the arc platform, also entered the basin. In addition, extrusion of basaltic volcanic rocks was continual within the basin during basin expansion. The resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin. In the Late Cretaceous, andesitic to rhyolitic volcanism became climactic in the arc platform, producing

  2. Structural Framework of the Sub-Himalaya and its tectonic evolution along Kameng river section: Arunachal Pradesh, India

    NASA Astrophysics Data System (ADS)

    Goswami, T.; Bezbaruah, D.; Sarmah, R. K.

    2012-04-01

    The structural style or architecture of the Neogene-Quaternary foreland basin is studied in the Kameng River section of Arunachal Pradesh. The Kimi, Dafla-Subansiri, and Kimin formations correspond to Lower, Middle and Upper Siwaliks. The outcrop scale structures from the Main Boundary Thrust (MBT) towards S shows an overall ramp and flat geometry. The intervening strata between two parallel thrust faults (roof thrust and floor thrust) are sub-parallel. The individual subsidiary faults in imbricate fashion (horses) occur as planar units with straight sides. These duplex structures are significant manifestation of the processes involved in the internal domain of the Siwalik rocks and they represent the mechanism of the slip transfer processes from one glide horizon at depth to another at shallower depth. This process of slip transfer and formation of horses are responsible for the formation of structural thickening, duplex growth and mass addition to the moving thrust complex. In the present area the Siwalik strata showing duplex structures have undergone structural thickness in their internal domain mainly in Dafla formation. The lithology in the foreland basin dominantly composed of the sandstones (Greywacke and lithic -arenite), siltstone, claystone, carbonaceous shale, boulder beds in the upper part. In the microscopic scale, the lithological response in the structural development is well documented as pressure solution seams, elongated quartz and feldspar grains, bent micas, kinked biotites, strained quartz grains, healed grains, and micro-fractures. The basement asperities play a significant role as the moving thrust front produced a major lateral ramp. The differential movement of the mountain front on both sides of the ramp is visible in the field as the mountain front of the western part of the Kameng River move more southeastward compared to the eastern part. The tectonic evolution of the area initiated with the development of the MBT, which resulted in

  3. Structural and metamorphic evolution of an ocean-continent transition (OCT) zone mélange deformed under HP conditions during Alpine subduction (Western Italian Alps)

    NASA Astrophysics Data System (ADS)

    Gosso, G.; Benciolini, L.; Dilek, Y.; Festa, A.; Spalla, M.; Tartarotti, P.

    2011-12-01

    We report on the structural architecture and metamorphic evolution of a mélange, developed originally in an ocean-continent transition (OCT) zone along the boundary between the continental crust of the Sesia-Lanzo (SLZ) and the oceanic Piemonte Zones (PZ) in the axial part of the Western Alps. All these units were deformed together under high-pressure conditions. The mélange consists of thin layers of calcschist, fine-grained gneiss, quartzite, minor metabasic rocks and serpentinite, and occurs all along the western margin of southern SLZ, extending from Santanel klippe to Lanzo Massif, over a distance of 50 km (Spalla et al., 1983; Battiston et al., 1984). Calcschist rocks range from phyllites to carbonatic schists and marbles; fine-grained gneisses of continental origin (very similar to those of SLZ) include phengitic white mica, chlorite, ± garnet ± albite and relict allanite. Thinly layered quartzites are white mica- and garnet-bearing. Metabasic rocks consist of metagabbros and metabasalts with minor mylonitic serpentinites. All these lithologies of the mélange unit and the rocks of SLZ and PZ together underwent four episodes of deformation, giving rise to a complex regional tectonostratigraphy. The earliest deformational structures are represented by up to ten meter-scale isoclinal rootless folds. The metamorphic mineral assemblages marking successive foliations indicate that all rock units in the mélange, SLZ and PZ (Spalla et al., 1983; Benciolini et al., 1984) experienced an early eclogite facies imprint, followed by re-equilibration under blueschist facies conditions, and that they were finally widely retrogressed under greenschist facies conditions during the last two deformational episodes (D3 and D4 structures). The strong synmetamorphic deformation of this mélange prevents an unequivocal interpretation of its origin; hence, we envisage two possible scenarios: i) the present day configuration of these thin, intermingled layers, including

  4. A kinematic model for Afar Depression lithospheric thinning and its implications for hominid evolution: an exercise in plate-tectonic paleoanthropology

    NASA Astrophysics Data System (ADS)

    Redfield, T.; Often, M.; Wheeler, W. H.

    2002-12-01

    We present a detailed Nubia-Arabia-Somalia (NU-AR-SOM) kinematic reconstruction based on magnetic sea floor isochrons in the Gulf of Aden and Red Sea and piercing points along the Red Sea margins. The reconstruction is combined with digital topographic and depth-to-Moho data to constrain in 4D the Late Oligocene to present-day evolution of the Afar supra-Moho crust. Opposite end-member models for crustal evolution are described. We conclude that less than 20% of the present-day Afar supra-Moho crust was constructed by magmatic processes such as diking and underplating. The reconstructions indicate that the greater percentage of crustal thinning (extension) occurred before 6.2 Ma. We model the thinning of the effective elastic lithosphere that accompanied extension, and show that the regional-scale topographic development of the Afar depression was virtually complete by Mid Pliocene time. The plate-tectonic model has paleoanthropological implications. Prior to 6.2 Ma the proximal positions of NU-SOM, AR, and the Danakil block suggest subaerial conditions prevailed between Yemen and Ethiopia. Uninhibited Africa-Eurasia faunal exchange through Afar and Arabia (corroborated by isotopic and paleontologic data) was tectonically permissible until the time of the earliest hominids. Continued stretching caused the Afar land bridge(s) to disappear during Early to Mid Pliocene time. Primitive hominid populations living within the Afar Depression became isolated from AR sometime before ~3.2 Ma. With the plateau becoming less habitable due to long-term Late Neogene cooling, hominids that remained in the Afar Depression were required to adapt to a smaller range that was effectively bounded by the already well-developed NU-SOM escarpments and the newly opened Straits of Bab el Mandeb. The combination of high quality habitat,topographic confinement, and a gradual (tectonic) reduction in range, exacerbated by potentially severe fluctuations in local climate (well documented by land

  5. Pressure-temperature-deformation-time of the ductile Alpine shearing in Corsica: From orogenic construction to collapse

    NASA Astrophysics Data System (ADS)

    Rossetti, Federico; Glodny, Johannes; Theye, Thomas; Maggi, Matteo

    2015-03-01

    Definition of the Tertiary tectono-metamorphic history of Alpine Corsica is a key task to decipher the space-time linkage between the Alpine and Apennine subduction systems in the Mediterranean region. Alpine Corsica exposes a nappe stack of oceanic- and continental-derived units, structurally juxtaposed onto the former European continental margin (Hercynian Corsica). Still uncertain is the timing of involvement of the continental-derived units in orogenic construction and shift to regional extension. This paper focuses on reconstruction of the pressure-temperature-deformation-time evolution of selected ductile shear zones activated during transition from the tectonic underplating to the extensional reworking stages. New Rb-Sr mineral age data, integrated with structural and thermobarometric investigations constrain the waning stages of the high-pressure (from blueschist to greenschist facies metamorphic conditions) top-to-the-W thrusting of the HP, oceanic-derived realm (Schistes Lustrés Complex) onto the Hercynian Corsica along the East Tenda Shear Zone in the early Oligocene (from ~ 32 to ~ 27 Ma). This early compressional evolution is overprinted by a major phase of retrogressive, syn-greenschist top-to-the-E extensional shearing in the Schistes Lustrés Complex with the last episode of deformation-related ductile recrystallization recorded during the early Miocene at ~ 20-21 Ma, in a continuum transition from ductile to brittle shearing. The same early Miocene Rb-Sr deformation ages are recovered from the ductile-to-brittle top-to-the-E reactivation domains within the East Tenda Shear Zone, documenting that transition from compression to extension in Alpine Corsica occurred during the late Oligocene-early Miocene time lapse. Implications of these data are discussed in the broader context of the Tertiary geodynamic evolution of the Central Mediterranean region.

  6. Early Paleozoic magmatic history of central Inner Mongolia, China: implications for the tectonic evolution of the Southeast Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Wu, Chen; Liu, Changfeng; Zhu, Yan; Zhou, Zhiguang; Jiang, Tian; Liu, Wencan; Li, Hongying; Wu, Chu; Ye, Baoying

    2016-07-01

    To provide insights into the Early Paleozoic tectonic evolution of the southern portion of the long-lived Central Asian Orogenic Belt, we have conducted major and trace element analyses and zircon U-Pb dating of granitoid samples from central Inner Mongolia. Our study area covers three pre-Mesozoic tectonic units from north to south: the Wenduermiao subduction-accretionary complex, the Bainaimiao magmatic belt, and the northern margin of the North China craton. Our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units. Accordingly, we suggest that the Wenduermiao subduction-accretionary complex developed in the Middle Cambrian-Late Silurian (509-421 Ma), comprising of coeval oceanic crust, arc magmatism, and forearc deposits. The Bainaimiao continental arc was developed during the Late Cambrian to Early Silurian (501-437 Ma), which superposed on the basement with the affinity of the North China craton. The back-arc basin opened prior to Early Silurian and lasted to the Late Silurian, which is slightly younger than Bainaimiao island arc. The Wenduermiao Ocean, between the Wenduermiao subduction-accretionary complex and the Bainaimiao continental arc, existed in Early Paleozoic.

  7. 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

  8. Seismic site characterization for the Deep-Fault-Drilling-Project Alpine Fault

    NASA Astrophysics Data System (ADS)

    Glomb, Vera; Buske, Stefan; Kovacs, Adrienn; Gorman, Andrew

    2013-04-01

    The Alpine Fault in New Zealand (South Island) is one of the largest active plate-bounding continental fault zones on earth with earthquakes of magnitude 7.9 occuring every 200-400 years. Due to the surface exposure and the shallow depth of mechanical and chemical transitions it is a globally significant natural laboratory. Within the ICDP Deep-Fault-Drilling-Project Alpine Fault (DFDP-AF; https://wiki.gns.cri.nz/DFDP) a drill hole shall give insight into the geological structure of the fault zone and its evolution to understand the related deformation and earthquake processes. With the help of advanced seismic imaging techniques the shallow structure of the Alpine Fault is imaged to find the most suitable drill site location. A new seismic reflection profile has been acquired in 2011 by the WhataDUSIE project team consisting of partners from the University of Otago (New Zealand), TU Bergakademie Freiberg (Germany) and the University of Alberta (Canada). The reflection profile, located in the Whataroa river valley, has a total length of about 5 km. Up to 643 geophones with spacings between 4-8 m recorded the approximately 100 shot points along the profile line. Single shot gathers as well as preliminary imaging results will be presented. The high-quality data show various indicators of the Alpine Fault such as strong reflections and distorted first-arrival wavefields which are clearly visible already in single shot gathers. With the help of high resolution seismic images we can study the shallow structures of the subsurface thus gaining information about the location and dip of reflectors. Further detailed processing and intensive interpretative work will enable a seismic site characterization providing important information for the selection of the borehole location. Additionally the high resolution seismic images themselves allow a better understanding of the tectonic and geodynamic settings.

  9. Sub-crustal forcing on the tectonic and topographic evolution of collision-subduction transition zones: possible application to the eastern Tibetan margin

    NASA Astrophysics Data System (ADS)

    Sternai, Pietro; Avouac, Jean-Philippe; Jolivet, Laurent; Faccenna, Claudio; Gerya, Taras; Becker, Thorsten W.; Menant, Armel

    2016-04-01

    The tectonic and topographic evolution of the eastern Tibetan margin is controlled by the India-Eurasia collision, gravitational collapse of the uplifted reaches and the dynamics of the Sunda and other western Pacific subduction zones, but their relative contributions remain elusive. Because crustal tectonics is the most serious contributor to the vertical ground motion and surface structures, previous models mostly focused on the partitioning between clock-wise rigid rotation or viscous eastward evacuation of the Eurasian crust in response to these driving mechanisms. Some authors further argued that large-scale mantle convection provides support to the topography of the Southeast Asia through vertical stresses and contribute to the overall India-Eurasia convergence. Minor attention, however, has been given to the potential forcing from the asthenospheric return flow owing to differential along-strike slab kinematics related to rollback and tearing of the Indian, Sunda and western Pacific slabs. Here, we analyze 3D numerical geodynamic modeling results involving a collision-subduction system and show that vigorous asthenospheric flow due to differential along-strike slab kinematics may contribute to the surface strain and topography at the collision-subduction transition zone. We argue that protracted northward migration of the Indian slab and indentation front during south to south-westward rollback (late-Eocene to middle-Miocene) or stable (middle-Miocene to present) subduction along the Sunda and western Pacific margins may have produced a similar asthenospheric flow. This flow could have contributed to the Southeast Asia extrusion tectonics and uplift of the terrains around the eastern Himalayan syntaxis and protruding from southeast Tibet. Therefore, we suggest that the tectonics and topographic growth east and southeast of Tibet are controlled not only by crustal and lithospheric deformation but also by the asthenospheric dynamics.

  10. Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada

    USGS Publications Warehouse

    du Bray, Edward A.; John, David A.; Cousens, Brian L.

    2013-01-01

    Although rocks in the two arc segments have similar metal abundances, they are metallogenically distinct. Small porphyry copper deposits are characteristic of the northern segment whereas significant epithermal precious metal deposits are most commonly associated with the southern segment. These metallogenic differences are also fundamentally linked to the tectonic settings and crustal regimes within which these two arc segments evolved.

  11. The Structural Architecture and Tectonic Inheritance of the Vlora-Elbasan Transfer Zone in Albanides-Albania

    NASA Astrophysics Data System (ADS)

    Abus, E. D.; Dilek, Y.

    2014-12-01

    The Albanides in the Balkan Peninsula are part of the Alpine orogenic belt and host one of the most significant oil fields in SE Europe. The late Mesozoic-Cenozoic evolution of the Albanides has been strongly controlled by the relative movements of Adria or Apulia, a microcontinent with a West Gondwana affinity with respect to Eurasia. In northeastern Albania, the Internal Albanides consist of Paleozoic - Jurassic basement rocks, which involved subduction zone tectonics of the Pindos-Mirdita ocean basin. The External Albanides, on the other hand, represent a fold-and-thrust belt with deformation in a broad zone of oblique convergence. This tectonic domain is divided, from east to west, into five major structural zones: the Krasta-Cukali Zone, the Kruja Zone, the Peri-Adriatic Depression, the Ionian Zone, and the Sazani Zone, which is represented by the Apulian platform carbonates. The zone is characterized by NW-SE-running and SW-verging thrust fault systems that involve a thick series of Mesozoic - Tertiary passive margin carbonates, unconformably overlain by Oligocene clastic units. These two tectonic zones are dissected by the NE-SW-striking Vlora-Elbasan Transfer Zone, which extends eastwards into the Internal Albanides, affecting the structural architecture and the tectonic evolution of the entire mountain belt. This fault zone that has been tectonically active from the Triassic to recent have display diapiric structures along it.

  12. U-Th-Pb and 230Th/ 238U disequilibrium isotope systematics: Precise accessory mineral chronology and melt evolution tracing in the Alpine Bergell intrusion

    NASA Astrophysics Data System (ADS)

    Oberli, Felix; Meier, Martin; Berger, Alfons; Rosenberg, Claudio L.; GierÉ, Reto

    2004-06-01

    equilibrium with sequential allanite zoning. Comparison of calculated (Th/U) magma with measured total-rock Th/U = 0.79 requires fractional crystallization of allanite at an early stage. This process of removal of allanite, and thus Th, from the melt was operative at least until ˜31.5 Ma, providing an upper limit for the time of emplacement of the studied magma batch. The fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep-seated plutons with intrusion ages. The persistence of magmatic conditions over a period of ˜5 Ma, concentrated in a narrow collision zone between the European and the African plate, has been a major controlling factor for the Oligocene evolution of the adjacent Insubric fault, the main tectonic lineament of the Alps being active from late Cretaceous to Miocene times.

  13. Mesozoic Cenozoic tectonic evolution of the Zhuanghai area, Bohai-Bay Basin, east China: the application of balanced cross-sections

    NASA Astrophysics Data System (ADS)

    Wu, Shiguo; Yu, Zhaohua; Zhang, Rongqiang; Han, Wengong; Zou, Dongbo

    2005-06-01

    The technique of balancing cross-sections, an important method for studying the tectonic history of sedimentary basins, has many applications. It enables one to compile charts for petroleum exploration and development, and growth sections of ancient structures can be restored so that the structural growth history can be studied. In order to study tectonic evolution in the Zhuanghai area of the Bohai-Bay basin, we selected two seismic profiles and compiled two structural growth sections. Based on the two balanced cross-sections, the evolution can be divided into four phases: the Triassic-Middle Jurassic phase, Late Jurassic-Cretaceous phase, Palaeogene extension phase, and Late Palaeogene-to-present phase. The whole area was uplifted during the Triassic-Middle Jurassic phase because of intense extrusion stress related to the Indo-China movement. During the Late Jurassic and Early Cretaceous, intense extension occurred in east China, and the whole area rifted, leading to the deposition of a thick sedimentary sequence. In the Late Cretaceous, the area suffered uplift and compression associated with the sinistral strike slip of the Tanlu fault. In the Palaeogene, a rifting basin developed in the area. Finally, it became stable and was placed in its present position by dextral strike-slip motion. In addition, some problems associated with compiling balanced cross-sections are discussed.

  14. Tectonic control of the Guadiana Basin drainage development (Iberian Peninsula, Spain)

    NASA Astrophysics Data System (ADS)

    Tejero, Rosa; Gerzón Heydt, Guillermina; Babín Vich, Rosa Blanca; Fernández García, Paloma; Tsige, Meaza

    2010-05-01

    Far from plate margins, where tectonic activity is of low intensity over long time periods, relief evolves over million years and is the outcome of long-term interplay between building and erosion processes. Forms created by individual tectonic structures are difficult to recognise due to extensive reworking or their disappearance altogether yet, on the regional scale, the decisive role of tectonics in relief building is evident. This is the case of the Atlantic divide of the Iberian Peninsula in which we examined the drainage basin of the Guadiana River. It is the southern one of a series of E-W to NE-SW trending sedimentary basins infilled with continental materials and separated by parallel mountain chains. Such tectonic units arose from the convergence of European and African plates during the Alpine orogeny. Alpine tectonics reshaped the ancient post-Variscan landscape to create elevated and depressed zones that were to control river patterning. To examine the relationship between Alpine crust deformation drainage, we undertook a spectral analysis of the topography and we constructed subenvelop maps of the drainage network. We consider that the harmonic surfaces that better describe the main topographic and tectonic features of the area should represent, on the one hand, relationships among the main drainage basins and tectonic units (mountain chains and sedimentary basins) on a regional (peninsular) scale, and on the other hand, show the Alpine structures controlling the current landscape within the large morphotectonic units. On a regional scale the wavelengths of 200 km suits the Guadiana basin and its divides. The basin is described as a gentle depression which an amplitude of 500 m. The subenvelop map shows spaced curves with smooth contours characteristics of plateau zones. The eastern part of the Guadiana Basin shows the characteristics of a perched plain where subenvelops barely indicate the presence of incision, adopting open slightly concave contours

  15. The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Menzies, Catriona D.; Teagle, Damon A. H.; Niedermann, Samuel; Cox, Simon C.; Craw, Dave; Zimmer, Martin; Cooper, Matthew J.; Erzinger, Jörg

    2016-07-01

    Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid-rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island, New Zealand and appears to fail in regular (329 ± 68 yrs) large earthquakes (Mw ∼ 8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87Sr/86Sr > 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15-0.81 RA) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at ∼6 km. Geochemical tracer transport modelling suggests only ∼0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this

  16. Tracing trends in erosion and exhumation during the Middle-Late Paleozoic tectonic evolution of the Farewell terrane, SW Alaska

    NASA Astrophysics Data System (ADS)

    Hampton, B. A.; Malkowski, M. A.; Bradley, D. C.; Fujita, K.; O'Sullivan, P. B.

    2010-12-01

    The Farewell terrane of southwest and west-central Alaska is located at the northernmost endpoint of the North American Cordillera and is just beyond the present-day margin of the Amerasia Basin. The initial geologic framework of this region has been constrained, yet the origin, Paleozoic tectonic development, and paleogeography of the Farewell terrane prior to opening of the Arctic Ocean remain unknown. In southwestern Alaska, the Farewell is defined by a three-part succession that consist of (1) Neoproterozoic-Devonian carbonate rocks and subordinate clastic strata of the Nixon Fork subterrane, (2) Cambrian-Devonian clastic and carbonate units of the Dillinger subterrane, and (3) Devonian-Permian(?) siliciclastic strata of the Mystic subterrane. Although previous studies have suggested a Siberian origin for the oldest parts of the Farewell based on faunal data, it has yet to be determined if the Dillinger and Mystic subterranes share links with regions to the north (e.g. Siberia, Baltica, Greenland) or with the northern and western regions of Laurentia. Here we present U-Pb detrital zircon data as well as modal composition trends from Paleozoic strata of the Dillinger and Mystic subterranes that reflect an upsection transition in detrital contribution from middle to top of the Farewell terrane. U-Pb detrital zircon age spectra from Silurian-Devonian strata of the Dillinger subterrane reveal a range of Precambrian and Paleozoic ages with primary occurrences between 400-440 and 1000-2000 Ma. Isolated age peaks occur at 430, 500, 890, 1100, and1400 Ma. The oldest strata from the overlying Mystic subterrane contain primary peaks at 380, 420, 925 Ma with an elevated occurrence of Proterozoic ages between 500-2000 Ma. Younger Devonian-Permian age strata of the Mystic subterrane yield primary age peaks between 300-350 and 420-450 Ma with smaller peaks between 1800-2000 Ma. Modal composition trends from the Dillinger and Mystic subterranes reveal pervasive occurrences of

  17. Old stories and lost pieces of the Eastern Mediterranean puzzle: a new approach to the tectonic evolution of the Western Anatolia and the Aegean Sea

    NASA Astrophysics Data System (ADS)

    Yaltırak, Cenk; Engin Aksu, Ali; Hall, Jeremy; Elitez, İrem

    2015-04-01

    During the last 20 or so years, the tectonic evolution of Aegean Sea and Western Anatolia has been dominantly explained by back-arc extension and escape tectonics along the North Anatolian Fault. Various datasets have been considered in the construction of general tectonic models, including the geometry of fault patterns, paleomagnetic data, extensional directions of the core complexes, characteristic changes in magmatism and volcanism, the different sense of Miocene rotation between the opposite sides of the Aegean Sea, and the stratigraphy and position of the Miocene and Pliocene-Quaternary basins. In these models, the roles of the Burdur-Fethiye Shear Zone, the Trakya-Eskişehir Fault Zone, the Anaximander Mountains and Isparta Angle have almost never been taken into consideration. The holistic evaluation of numerous land and marine researches in the Aegean Sea and western Anatolia suggest the following evolutionary stages: 1. during the early Miocene, Greece and western Anatolia were deformed under the NE-SW extensional tectonics associated with the back-arc extension, when core complexes and supra-detachment basins developed, 2. following the collision of the Anaximander Mountains and western Anatolia in early Miocene , the Isparta Angle locked this side of the western arc by generating a triangle-shaped compressional structure, 3. while the Isparta Angle penetrated into the Anatolia, the NE-striking Burdur-Fethiye Shear Zone in the west and NW-striking Trakya-Eskişehir Fault Zone in the north developed along the paleo-tectonic zones , 4. the formation of these two tectonic structures allowed the counterclockwise rotation of the western Anatolia in the middle Miocene and this rotation removed the effect of the back-arc extension on the western Anatolian Block, 5. the counterclockwise rotation developed with the early westward escape of the Western Anatolian reached up to 35-40o and Trakya-Eskişehir Fault Zone created a total dextral displacement of about 200

  18. Unraveling the geodynamic evolution and tectonic history of the Guatemala Suture Zone: a world-class natural laboratory

    NASA Astrophysics Data System (ADS)

    Flores, K. E.; Brocard, G. Y.; Harlow, G. E.

    2013-12-01

    The Guatemala Suture Zone (GSZ) is the fault-bound region in central Guatemala that contains the present North American-Caribbean plate boundary. It is bounded by the Maya Block to the north and by the Chortís Block to the south. This major composite geotectonic unit contains a variety of ophiolites, serpentinite mélanges, and metavolcano-sedimentary sequences along with high-grade schist, gneisses, low-grade metasediments and metagranites thrusted north and south of the active Motagua fault system (MFS). This modern plate boundary has accommodated at least ~1100 km of left-lateral strike-slip motion over the Cenozoic and brings into contact the geological provinces described above. Classically, the GSZ has been interpreted as the result of a single progressive collision of a Chortís Block-related island arc with the passive margin of the Maya Block. This model was based on geochemical signatures of basaltic rocks in oceanic crust sequences both north and south of the MFS. However, results from our research challenge this single collision hypothesis. Oceanic and continental high-pressure-low-temperature (HP-LT) rocks astride the MFS have recorded multiple tectonic events revealed by their multiple metamorphic ages (Sm-Nd, U-Pb and Ar-Ar) and distinct PT paths. These tectonic events differ in age north and south of the MFS. Moreover, the continental and oceanic sequences across the MFS are geochemically and stratigraphically distinct, suggesting different tectonic origins. The southern margin of the Maya Block and the northern section of the GSZ can be clearly interpreted as a Cretaceous-Paleocene flexural passive margin tectonically overridden by ultramafic rocks and a Cretaceous island arc sequence. In contrast, the southern section of the GSZ is composed of a Carboniferous-Jurassic active margin tectonically imbricated with ultramafic rocks and a circum-Pacific Jurassic MORB and IAT metavolcano-sedimentary sequence. Thus, based on these results, we identify at

  19. Architecture and evolution of an Early Permian carbonate complex on a tectonically active island in east-central California

    USGS Publications Warehouse

    Stevens, Calvin H.; Magginetti, Robert T.; Stone, Paul

    2015-01-01

    The newly named Upland Valley Limestone represents a carbonate complex that developed on and adjacent to a tectonically active island in east-central California during a brief interval of Early Permian (late Artinskian) time. This lithologically unique, relatively thin limestone unit lies within a thick sequence of predominantly siliciclastic rocks and is characterized by its high concentration of crinoidal debris, pronounced lateral changes in thickness and lithofacies, and a largely endemic fusulinid fauna. Most outcrops represent a carbonate platform and debris derived from it and shed downslope, but another group of outcrops represents one or possibly more isolated carbonate buildups that developed offshore from the platform. Tectonic activity in the area occurred before, probably during, and after deposition of this short-lived carbonate complex.

  20. Investigating Tectonic Drivers of Miocene - Pliocene Polar Climate Evolution using the HadCM3 Climate Model.

    NASA Astrophysics Data System (ADS)

    Hunter, S. J.; Knies, J.; Haywood, A. M.; Dolan, A. M.; Pound, M. J.

    2015-12-01

    We model the climate of the Miocene (Tortonian and the Messinian) and the Pliocene (Piacenzian) using the HadCM3 Atmosphere-Ocean GCM. We use baseline Miocene and Pliocene geographies that have different reconstruction lineages so we describe methods to create a set of self-consistent paleogeographies that represent the main features of the three stages. We present large-scale features of the evolving climate and examine model fidelity by comparing modelled climatology against palaeoenvironmental proxy data. We focus on the climate of the Arctic region and investigate tectonic drivers of sea ice expansion by comparing and interpreting model predictions against borehole data from the North Atlantic and Arctic Ocean. In particular how Late Miocene/ early Pliocene tectonic uplift in the Svalbard/Barents Sea and Greenland region, the opening of the Bering Strait, and the onset of deep water Atlantic-Arctic exchange influenced the development of modern sea ice cover.

  1. The link between tectonic and sedimentation in an asymmetric extensional basin: the late Miocene evolution of the Sarajevo-Zenica basin, Bosnia and Hercegovina

    NASA Astrophysics Data System (ADS)

    Andric, Nevena; Sant, Karin; Matenco, Liviu; Tomljenovic, Bruno; Pavelic, Davor; Mandic, Oleg; Hrvatovic, Hazim; Demir, Vedad

    2015-04-01

    Extensional back-arc basins develop in overriding tectonic plates during the slab retreat, as often observed for instance in the Panonian, Aegean or Western Mediterranean domains. In this type of basins, pre-existing major thrusts or nappe contacts inherited from the earlier orogenic evolution provide contrasts in rheology and localize the extensional deformation along large-scale asymmetric detachments. Their footwall exhumation is associated with the formation of asymmetric extensional basins in the hanging-wall controlled by normal faults forming half-graben geometries. In such tectonically active basins, the architecture of the sedimentary infill is controlled dominantly by the balance between pulses of tectonic subsidence along normal faults driving accommodation space and coeval moments of tectonic exhumation controlling the variations in sediment supply. In such systems, deformation migrates in space and time in the direction of the extensional transport affecting the spatial architecture of the basin infill. One optimal place to study the interplay between tectonic and sedimentation in asymmetric extensional basins is the Dinarides orogenic area, where the back-arc extension was responsible for the creation of a large number of small-scale basins that are part of the Oligo-Miocene Dinaride lake system. The Sarajevo-Zenica basin is the largest basin in this intra-mountain system and is located near the transition between the External and Internal Dinarides. The basin formed in the hanging-wall of a large-scale top-NNE detachment associated with the exhumation of the Mid-Bosnian Schists Mountains in its footwall. The basin was filled with Upper Oligocene - Pliocene alluvial-fluvial and lacustrine sediments characterized by an endemic fossil fauna. The study of basin normal faults and associated syn-kinematic sedimentation has demonstrated that the deformation migrates SW-wards in time. This is indicated by the NE-tapering syn-kinematic wedges, the migration

  2. 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.

  3. Integrated Analysis of Airborne Geophysical Data to Understand the Extent, Kinematics and Tectonic Evolution of the Precambrian Aswa Shear Zone in East Africa.

    NASA Astrophysics Data System (ADS)

    Katumwehe, A. B.; Atekwana, E. A.; Abdelsalam, M. G.; Laó-Dávila, D. A.

    2014-12-01

    The Aswa Shear zone (ASZ) is a Precambrian lithospheric structure which forms the western margin of the East African Orogeny (EAO) that influenced the evolution of many tectonic events in Eastern Africa including the East African Rift System. It separates the cratonic entities of Saharan Metacraton in the northeast from the Congo craton and the Tanzanian craton and the Kibaran orogenic belt to the southwest. However little is known about its kinematics and the extent and tectonic origin are not fully understood. We developed a new technique based on the tilt method to extract kinematic information from high-resolution airborne magnetic data. We also used radiometric data over Uganda integrated with Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) in South Sudan to understand the extent, kinematics and define the tectonic origin of ASZ. (1) Our results suggest that the ASZ extends in a NW-SE for ~550 km in Uganda and South Sudan. (2) The airborne magnetic and radiometric data revealed a much wider (~50 km) deformation belt than the mapped 5-10 km of exposed surface expression of the ASZ. The deformation belt associated with the shear is defined by three NW-trending sinistral strike-slip shear zones bounding structural domains with magnetic fabrics showing splays of secondary shear zones and shear-related folds. These folds are tighter close to the discrete shear zones with their axial traces becoming sub-parallel to the shear zones. Similar fold patterns are observed from South Sudan in the SRTM DEM. We interpret these folds as due to ENE-WSW shortening associated with the sinistral strike-slip movement. (3) To the northeast of the shear zone, the magnetic patterns suggest a series of W-verging nappes indicative of strong E-W oriented shortening. Based on the above observations, we relate the evolution of the ASZ to Neoproterozoic E-W collision between East and West Gondwana. This collision produced E-W contraction resulting in W-verging thrusts

  4. Late Cenozoic tectonic evolution of the Ailao Shan-Red River fault (SE Tibet): implications for kinematic change during Plateau growth

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zhang, Bo; Schoenbohm, Lindsay; Zhang, Jinjiang; Zhou, Renjie; Hou, Jianjun

    2016-04-01

    The India-Eurasia continental collision has created the Tibetan Plateau, a spectacular example of continental plateaus. Along its southeastern margin, surface uplift, river incision, shear-zone exhumation and displacement along active faults have all interacted to shape the landscape. The Ailao Shan-Red River fault, a continental-scale strike-slip fault striking over 1000 km from the Tibetan Plateau to South China Sea, is an excellent recorder for those processes, providing important insights into the evolution of the southeastern plateau margin. However, its late Cenozoic tectonic evolution still remains elusive. This work presents new structural and stratigraphic data from the Miocene basin in the bend area and apatite (U-Th)/He thermochronological data from the shear zone to put constraints on the timing and nature of structural and geomorphic evolution of the Ailao Shan-Red River fault region. Our observations indicate that the major bend in the fault was a releasing bend in the early Miocene, but became a restraining bend after the late Miocene reversal of displacement. The strata preserved in bend area record the nature and timing of exhumation of the shear zone. Apatite (U-Th)/He data show two phases of rapid exhumation in the Miocene. The first rapid exhumation occurred before 16 Ma, the timing of which is supported by the early Miocene sedimentary record and previous geochronologic results. It may have ended before the formation of a low-relief erosion surface. The second episode of rapid exhumation began at ~14-13 Ma, lasting 2-3Myr. During this interval, the Ailao Shan range may have uplift to the modern elevation and the high relief may have developed along the range due to river incision. Metamorphic clasts from the shear zone were deposited in the Red River valley. Regional compilation reveals a coincidence of tectonic events in the Tibetan Plateau and its surroundings in the middle-late Miocene, indicating dramatic kinematic change during the course

  5. Tectonic Geomorphology.

    ERIC Educational Resources Information Center

    Bull, William B.

    1984-01-01

    Summarizes representative quantitative tectonic-geomorphology studies made during the last century, focusing on fault-bounded mountain-front escarpments, marine terraces, and alluvial geomorphic surfaces (considering stream terraces, piedmont fault scarps, and soils chronosequences). Also suggests where tectonic-geomorphology courses may best fit…

  6. Triassic to recent tectonic evolution of a crestal collapse graben above a salt-cored anticline in the Glückstadt Graben/North German Basin

    NASA Astrophysics Data System (ADS)

    Al Hseinat, M.; Hübscher, C.; Lang, J.; Lüdmann, T.; Ott, I.; Polom, U.

    2016-06-01

    In this study we investigate faulting above a salt wall in the Glückstadt Graben/North German Basin. Two supra-salt faults are mapped from coast to coast over a distance of 6-9 km based on offshore and onshore seismic data. These faults form a ca. 2 km wide crestal collapse graben and pierce the seafloor. Salt wall evolution started in the early Late Triassic to Early Jurassic due to regional extension and resulting sub-salt faulting. The salt wall was eroded following exposure to costal and sub-aerial erosion by the regional Mid-Late Jurassic to Early Cretaceous uplift. Late Cretaceous to Early Paleogene compressional tectonics reactivated the vertical salt movement and shortened the salt wall, creating a salt-cored anticline with the crestal collapse graben above. The supra-salt faults were reactivated between the Late Eocene and Middle Miocene when the principal horizontal stress orientation changed from a NE-SW to a NW-SE, the present-day orientation. Stratigraphic data indicate that these faults moved mainly in the Cenozoic. Several observations strongly suggest that the faults continued developing during the Pleistocene until today: (i) the Pleistocene Unconformity is concave upwards and cut by faults; (ii) growth strata within the marine Holocene deposits above the graben imply recent tectonic movements; (iii) onshore high-resolution P-wave vibroseis data of the south-eastern Eckernförde Bay suggest about 10 m of faulted Holocene strata; and (iv) marine seismic data show the faults piercing the seafloor. We suggest that the recent salt tectonics and upward propagation of supra-salt faults resulted from differential ice-sheet loading. That effect on the salt wall stopped once ice grew over the whole structure, at which time the wall subsided because of ice loading. The salt wall and faults were reactivated again once the ice front retreated so that the ice loaded only one side of the structure.

  7. Volcano-Tectonic Evolution of the Central Death Valley Volcanic Field - Insights Derived from the Geologic Map of the Death Valley Junction 30' x 60' Quadrangle

    NASA Astrophysics Data System (ADS)

    Thompson, R. A.; Fridrich, C.; Chan, C. F.; Zellman, K. L.; Workman, J. B.

    2014-12-01

    The geologic map of the Death Valley Junction 30' x 60' quadrangle encompasses many geologic features recording the Cenozoic volcano-tectonic evolution of central Death Valley. Most notable is the central Death Valley rhombochasm. The rhombochasm is a 65x80-km rhombic pull-apart basin complex that occupies the releasing step-over between the northern Death Valley—Furnace Creek and southern Death Valley faults. Stewart (1983) documented this feature by palinspastically restoring offset thrust fault segments and isopachs, thereby closing the rhombochasm. The central Death Valley volcanic field records the coincident and related magmatism that occurred during the extension and strike-slip strain that formed the rhombochasm. In the multi-stage evolution of this tectonomagmatic feature, changes in volcanic and structural styles, rates, and loci were synchronized, both spatially and temporally. The volcanic field covers an area of 3600 km2, and consists of >700 km3 of lava flows, domes, and pyroclastic deposits. Cenozoic map units reflect four major eruptive stages: Stage 1 (11-9 Ma: rhyolite and andesite), Stage 2 (9-7.5 Ma: dacite>basalt>andesite), Stage 3 (7-5 Ma: dacite>basalt), and Stage 4 (4.5-0.7 Ma: basalt). The predominant loci of eruptive centers migrated northwestward during this volcanic evolution, coeval with northwestward migration of adjacent depocenters. Stage 1 and 2 volcanism is broadly correlative to the supradetachment stage of rhombochasm development. Related intrusions include exposed upper-plate hypabyssal and lower-plate plutonic bodies. Stage 3 and 4 volcanism occurred during two tectonic stages in which higher-angle faults cut across the detachment fault, forming basins that are nested within the original detachment-floored area of the rhombochasm. Time-transgressive changes from dominantly silicic and intermediate magmas in Stages 1 and 2 to dominantly mafic and lesser intermediate magmas in Stages 3 and 4 coincided with decreases in eruptive

  8. Analysis of the geological structure and tectonic evolution of Xingning-Jinghai sag in deep water area, northern South China Sea

    NASA Astrophysics Data System (ADS)

    Han, Xiaoying; Ren, Jianye; Lin, Zi; Yang, Linlong

    2015-04-01

    Recent years, oil and gas exploration of the Pearl River Mouth Basin in the northern margin of South China Sea continuously achieved historic breakthroughs. The Xingning-Jinghai sag, which is located in southeast of the Pearl River Mouth Basin, is a deep-water sag with a great exploration potential. Its tectonic evolution is extremely complex. It experienced Mesozoic subduction to Cenozoic intra-continental rifting background, and finally evolved into a deep-water sag of the northern continental margin of South China Sea. The geological characteristics and the tectonic evolution of Xingning-Jinghai sag was closely related to the process of formation and evolution of the passive continental margin of the northern South China Sea. It is confirmed by many geophysical data that compared with adjacent Chaoshan depression, the crustal thickness of Xingning-Jinghai sag was rapidly thinning, and it developed detachment faults with later magmatic intrusion. The development of detachment faults have dynamic significance for the spreading of the South China Sea. Based on the seismic geological interpretation of 2D seismic data in the study area, the characteristics of detachment fault and supra-detachment basin have been proposed in this study. The characteristics of the detachment fault are low angle and high ratio between heave and throw. The geometry of the detachment fault is a typical lisric shape, with the dip of fault decreasing generally from the seismic profile. The detachment basin where sediments are not deposited over a tilting hanging-wall block but onto a tectonically exhumed footwall which is different from the typical half graben basin. Seismic profiles indicate two different structural styles in the east and west part of Xingning-Jinghai sag. In the west of the sag, there developed two large detachment faults, which control their detachment basin systems and the typical H block, and the two detachment faults are dipping landward and seaward, respectively. In

  9. Geochronology of the Baie Verte Peninsula, Newfoundland: implications for the tectonic evolution of the Humber and Dunnage Zones of the Appalachian Orogen

    SciTech Connect

    Dallmeyer, R.D.; Hibbard, J.

    1984-09-01

    U-Pb analyses of zircon from the Burlington Granodiorite suggest intrusion at c. 460-465 Ma. Hornblende and biotite from central portions of the pluton record markedly younger /sup 40/Ar//sup 39/Ar plateau dates (410-420 Ma) which are interpreted to date contact metamorphic effects associated with the widespread emplacement of Silurian-Devonian igneous suites. Northern portions of the Burlington Granodiorite are polydeformed and regionally metamorphosed. Hornblende and biotite from this terrane yield /sup 40/Ar//sup 39/Ar plateau ages of 345-350 Ma. U-Pb analyses of zircon from the Dunamagon Granite indicate emplacement at c. 440-460 Ma, thereby providing an upper limit for tectonic juxtapositioning of the Humber and Dunnage Zones along the Baie Verte Line. Similar ages are also recorded by hornblende and biotite throughout northerly portions of the Mings Bight (Humber Zone) and Pacquet Harbour (Dunnage Zone) Groups. These results indicate that the tectonic evolution of the Baie Verte Line as polygenetic, and involved: (1) regionally significant tectonothermal activity prior to the Middle Ordovician and (2) Middle to Late Paleozoic tectonothermal activity centered along easterly segments of the Baie Verte Line. The regional metamorphism associated with this orogenic activity altered primary U-Pb and Rb-Sr isotopic systems within various igneous suites exposed in northeastern portions of the Burlington Peninsula, which may explain some inconsistent geochronological results previously obtained. 54 references, 6 figures, 5 tables.

  10. Neoarchean and Paleoproterozoic granitoids marginal to the Jeceaba-Bom Sucesso lineament (SE border of the southern São Francisco craton): Genesis and tectonic evolution

    NASA Astrophysics Data System (ADS)

    Campos, José Carlos Sales; Carneiro, Maurício Antônio

    2008-12-01

    The sialic crust of the southern São Francisco craton along the Jeceaba-Bom Sucesso lineament, central-southern part of Minas Gerais (Brazil), encompasses, among other rock types, Neoarchean and Paleoproterozoic granitoids. These granitoids, according to their petrographic, lithogeochemical and geochronologic characteristics, were grouped into two Neoarchean suites (Samambaia-Bom Sucesso and Salto Paraopeba-Babilônia) and three Paleoproterozoic suites (Cassiterita-Tabuões, Ritápolis and São Tiago). Varied processes and tectonic environments were involved in the genesis of these suites. In particular, the lithogeochemistry of the (Archean and Paleoproterozoic) TTG-type granitoids indicates an origin by partial melting of hydrated basaltic crust in a subduction environment. In the Neoarchean, between 2780 and 2703 Ma, a dominant TTG granitoid genesis related to an active continental margin was followed by another granite genesis related to crustal anatexis processes at 2612-2550 Ma. In the Paleoproterozoic, the generation of TTG and granites s.s. occurred at three distinct times: 2162, 2127 and 1887 Ma. This fact, plus the rock-type diversity produced by this granite genesis, indicates that the continental margin of the southern portion of the São Francisco craton was affected by more than one consumption episode of oceanic crust, involving different island arc segments, and the late Neoarchean consolidate continent. A Paleoproterozoic tectonic evolution in three stages is proposed in this work.

  11. Age and petrogenesis of late Paleozoic granites from the northernmost Alxa region, northwest China, and implications for the tectonic evolution of the region

    NASA Astrophysics Data System (ADS)

    Zhang, Wen; Pease, Victoria; Meng, Qingpeng; Zheng, Rongguo; Wu, Tairan; Chen, Yan; Gan, Lisheng

    2016-01-01

    The Wudenghan, Huhetaoergai and Zhuxiaobuguhe plutons, northern Alxa region, in the southern Central Asia Orogenic Belt are dated by U-Pb zircon to 383 ± 3, 356 ± 3 and 286 ± 2 Ma, respectively. The late Devonian Wudenghan monzogranite, a highly fractionated I-type granite with ɛ Nd(t) (-0.2 to -0.1) and very low (87Sr/86Sr) t (0.704719-0.706113), is from mantle-derived magmas and shows volcanic arc characteristics. The early Carboniferous Huhetaoergai granodiorite with medium-K calc-alkaline peraluminous characteristics represents a volcanic arc granite generated from partial melting of lower continental crust combined with mantle-derived input. The early Permian Zhuxiaobuguhe pluton, an unfractionated calc-alkaline granodiorite with moderately low ɛ Nd(t) (-2.0 to -1.1) and low (87Sr/86Sr) t (0.708370-0.708462), was likely derived from partial melting of the mafic lower crust of a paleo-volcanic arc and represents a post-collisional granite. Our revised tectonic evolution of the region includes (1) northward subduction of the oceanic crust represented by the Engger Us Ophiolitic Belt and formation of the late Devonian Wudenghan monzogranite, (2) northward subduction of the ocean between the Huhetaoergai and Zhusileng tectonic zones and the formation of the Huhetaoergai volcanic arc granite during the early Carboniferous and (3) the emplacement of the Zhuxiaobuguhe pluton in the early Permian during post-collisional extension.

  12. Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, Enlou; Wang, Yongbo; Sun, Weiwei; Shen, Ji

    2016-02-01

    We present the results of pollen analyses from a 1105 cm long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed humid period in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño-Southern Oscillation strength in the tropical Pacific.

  13. Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, E.; Wang, Y.; Sun, W.; Shen, J.

    2015-10-01

    We present the results of pollen analyses from a 1105-cm-long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed strengthening of the ISM in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño Southern Oscillation strength in the tropical Pacific.

  14. Nappes, tectonics of oblique plate convergence, and metamorphic evolution related to 140 million years of continuous subduction, Franciscan Complex, California

    SciTech Connect

    Wakabayashi, J. )

    1992-01-01

    This paper presents a new synthesis of Franciscan Complex tectonics, with the emphasis on the pre-San Andreas fault history of these rocks. Field relations suggest that the Franciscan is characterized by nappe structures that formed during sequential accretion at the trench. The presence of these structures along with other field relations, including the lack of evidence for large offset of conglomerate suites, indicates that strike-slip fault systems of large displacement ({gt}500 km) did not cut the Franciscan Complex during subduction. Regional geology and comparisons to modern arc-trench systems suggest that strike-slip faulting associated with oblique subduction took place inboard (east) of the Franciscan in the vicinity of the magmatic arc. The Franciscan varies along strike, because individual accreted elements (packets of trench sediment, seamounts, etc.) did not extend the full length of the trench. Different depths of underplating, distribution of post-metamorphic faulting, and level of erosion produced the present-day surface distribution of high P/T metamorphism. Franciscan Complex tectonic history is presented in this paper.

  15. Morphotectonic evolution of triangular facets and wine-glass valleys in the Noakoh anticline, Zagros, Iran: Implications for active tectonics

    NASA Astrophysics Data System (ADS)

    Bahrami, Shahram

    2012-07-01

    The Noakoh anticline is located in Kermanshah province and is part of the Simply Folded Belt of Zagros. Boundaries of 97 triangular facets and 67 wine-glass (W-G) valleys, which formed on anticline limbs, were delineated using Quickbird satellite imagery. The strata dip (D), area (A), base length (BL), topographic slope (S) of facets, the maximum width (M), outlet width (O) and ratio of maximum width to outlet width (W index) of W-G valleys were analysed in detail. Noakoh anticline was subdivided into 9 tectonic zones on the basis of dip, topographic slopes and width of limbs. Results show that there are strong positive correlations between means of D-BL and S-BL pairs. Poor positive correlations exist between means of D-A and S-A pairs. Among W-G valley metrics, the W index has strong relations with D and S parameters. Based on the results, steep facets with long bases and well developed W-G valleys with narrow outlets and wide upper parts are associated with more rotated limbs having steep slopes. Facets on the northeastern slope have more forest cover, micro-organism activity, karstic features and soil cover, whereas facets on relatively drier southwestern slope are characterized by physical weathering processes and minor karstic landforms. This study demonstrates that, apart from tectonic activity as a major control on the morphometry of facets and valleys, climate and slope aspect have also acted as secondary factors on the development of the studied landforms.

  16. Tectonic evolution of 200 km of Mid-Atlantic Ridge over 10 million years: Interplay of volcanism and faulting

    NASA Astrophysics Data System (ADS)

    Cann, Johnson R.; Smith, Deborah K.; Escartin, Javier; Schouten, Hans

    2015-07-01

    We reconstruct the history of the mode of accretion of an area of the Mid-Atlantic Ridge south of the Kane fracture zone using bathymetric morphology. The area includes 200 km of the spreading axis and reaches to 10 Ma on either side. We distinguish three tectonic styles: (1) volcanic construction with eruption and intrusion of magma coupled with minor faulting, (2) extended terrain with abundant large-offset faults, (3) detachment faulting marked by extension on single long-lived faults. Over 40% of the seafloor is made of extended terrain and detachment faults. The area includes products of seven spreading segments. The spreading axis has had detachment faulting or extended terrain on one or both sides for 70% of the last 10 Ma. In some parts of the area, regions of detachment faulting and extended terrain lie close to segment boundaries. Regions of detachment faulting initiated at 10 Ma close to the adjacent fracture zones to the north and south, and then expanded away from them. We discuss the complex evidence from gravity, seismic surveys, and bathymetry for the role of magma supply in generating tectonic style. Overall, we conclude that input of magma at the spreading axis has a general control on the development of detachment faulting, but the relationship is not strong. Other factors may include a positive feedback that stabilizes detachment faulting at the expense of volcanic extension, perhaps through the lubrication of active detachment faults by the formation of low friction materials (talc, serpentine) on detachment fault surfaces.

  17. Constraints on the tectonic evolution of the westernmost Mediterranean and northwestern Africa from shear wave splitting analysis

    NASA Astrophysics Data System (ADS)

    Miller, Meghan S.; Allam, Amir A.; Becker, Thorsten W.; Di Leo, Jeanette F.; Wookey, James

    2013-08-01

    The westernmost Mediterranean mantle and lithosphere have evolved into their current configuration due to complex interactions between the African and Eurasian plates. To help unravel the regional tectonics, we use new broadband seismic data across the Gibraltar arc and into southern Morocco to infer azimuthal seismic anisotropy and flow patterns for the upper mantle based on shear wave splitting analysis. A deep (>600 km) earthquake in April 2010 was recorded by the array and allowed us to compare 31 direct S measurements with 235 teleseismic SK(K)S events from 3 years of deployment. The patterns of apparent fast polarization orientations and delay times suggest three major tectonic domains when interpreted jointly with recent tomographic images of the subducted slab: (1) a subducted slab related toroidal flow domain centered upon the Alboran Sea and southern Spain, leading to complex splits, (2), a region where the west African craton deflects mantle flow in the Anti-Atlas and High Plateaux, and, (3), an intermediate domain across the central High Atlas. Across the axis of the mountain belt a coherent, regional maximum of delay times is observed for both S and SKS splitting measurements, with polarizations predominantly parallel to the strike. We interpret this as possible SW-NE channeling of mantle flow beneath the region with a thinned lithosphere and slow seismic velocities beneath the central High Atlas Mountains.

  18. Chronology of Miocene-Pliocene deposits at Split Mountain Gorge, Southern California: A record of regional tectonics and Colorado River evolution

    USGS Publications Warehouse

    Dorsey, R.J.; Fluette, A.; McDougall, K.; Housen, B.A.; Janecke, S.U.; Axen, G.J.; Shirvell, C.R.

    2007-01-01

    Late Miocene to early Pliocene deposit at Split Mountain Gorge, California, preserve a record of basinal response to changes in regional tectonics, paleogeography, and evolution of the Colorado River. The base of the Elephant Trees Formation, magnetostratigraphically dated as 8.1 ?? 0.4 Ma, provides the earliest well-dated record of extension in the southwestern Salton Trough. The oldest marine sediments are ca. 6.3 Ma. The nearly synchronous timing of marine incursion in the Salton Trough and northern Gulf of California region supports a model for localization of Pacific-North America plate motion in the Gulf ca. 6 Ma. The first appearance of Colorado River sand at the Miocene-Pliocene boundary (5.33 Ma) suggests rapid propagation of the river to the Salton Trough, and supports a lake-spillover hypothesis for initiation of the lower Colorado River. ?? 2007 Geological Society of America.

  19. Rubidium-strontium geochronology and plate-tectonic evolution of the southern part of the Arabian Shield

    USGS Publications Warehouse

    Fleck, Robert J.; Greenwood, W.R.; Hadley, D.G.; Anderson, R.E.; Schmidt, D.L.

    1980-01-01

    Rubidium-strontium studies of Precambrian volcanic and plutonic rocks of the Arabian Shield document an early development of the Arabian craton between 900 and 680 m.y. (million years) ago. Geologic studies indicate an island-arc environment characterized by andesitic (dioritic) magmas, volcaniclastic sedimentation, rapid deposition, and contemporaneous deformation along north or northwest-trending axes. Magmatic trends show consistent variation in both composition and geographic location as a function of age. The oldest units belong to an assemblage of basaltic strata exposed in western Saudi Arabia that yield an age of 1165:!:110 m.y. The oldest andesitic strata studied yield an age of 912:!:76 m.y. The earliest plutonic units are diorite to trondhjemite batholiths that range from 800 to 9,00 m.y. in age and ,occur along the western and southern parts of Saudi Arabia. Younger plutonic units, 680 to 750 m.y. in age, range from quartz diorite to granodiodte and become more abundant in the central and northeastern parts of the Arabian Shield. Initial 'Sr/ 86 Sr ratios for both dioritic groups range from 0.7023 to 0.7030 and average 0.7027. The absence of sialic detritus in sedimentary units and the evidence for an island-arc environment suggest the early development of the Arabian craton at a convergent plate margin between plates of oceanic lithosphere. Active subduction apparently extended from at least 900 m.y. to about 680 m.y. Subsequent to this subduction-related magmatism and tectonism, called the Hijaz tectonic cycle, the Arabian craton was sutured to the late Precambrian African plate in a collisional event. This period of orogeny, represented in Arabia and eastern Africa by the Mozambiquian or Pan-African event, extended from some time before 650 m.y. to at least 540 m.y. and perhaps 520 m.y. B.P. Although the tectonic processes of subduction and continental collision during the 900+ to 500-m.y. period require similar directions of plate convergence, the

  20. The impact of salt tectonics on supra-salt (Lago Mare?) deposits and on the structural evolution of the Cyprus-Eratosthenes collision zone

    NASA Astrophysics Data System (ADS)

    Reiche, Sönke; Hübscher, Christian; Ehrhardt, Axel

    2015-04-01

    Averagely 1.5 km thick Messinian evaporites laterally continue from the Levant Basin, easternmost Mediterranean Sea, into the collision zone between Cyprus and Eratosthenes Seamount where incipient continent-continent-collision is believed to occur. In this study, the impact of Messinian evaporites on the structural evolution of the collision zone is investigated for the first time based on a comprehensive set of seismic reflection profiles. Results show that the collision zone may be subdivided into an eastern and a western domain. In the eastern part, bordered by Eratosthenes Seamount and the Hecataeus Rise, compressionally thickened autochthonous salt is observed. Sub- and supra-salt deposits within this area appear to be in the stage of active accretion. Further west, between Cyprus and Eratosthenes Seamount strongly deformed allochthonous salt has evidently started to advance across sediments of post-Messinian age. In this domain, previously active sediment accretion at the Cyprus margin has now become inactive and shortening is largely accommodated at the leading edge of the allochthonous salt sheet. Such observations bear important implications for the structural interrelation between salt tectonics and the evolution of a young collision zone. On top of highly deformed mobile Messinian evaporites, up to 700 m thick late Messinian supra-salt deposits are mapped within the western part of the Cyprus - Eratosthenes collision zone. Their uppermost 200 m were drilled in the course of ODP Leg 160 (Site 968) and interpreted as Lago Mare sediments, deposited during the final stage of the Messinian Salinity Crisis (Robertson, 1998). These sediments occupy small sub-basins flanked by salt diapirs, indicating a salt-tectonic control on late Messinian sediment deposition. Distribution of these sediments may have further been controlled by sea-level, inferred from rapid eastward thinning and pinchout of Messinian supra-salt deposits towards the Levant Basin

  1. Tectonic and paleoenvironmental evolution of Mesozoic sedimentary basins along the Andean foothills of Argentina (32°-54°S)

    NASA Astrophysics Data System (ADS)

    Franzese, Juan; Spalletti, Luis; Pérez, Irene Gómez; Macdonald, David

    2003-05-01

    Chronoenvironmental and tectonic charts are presented for Mesozoic basins located along the Andean foothills of the South American plate. On the basis of the main tectonic events, pre-Andean basins, break-up-related basins, extensional back-arc basins, and Andean foreland basins are recognized. The pre-Andean basins were formed by continental extension and strike-slip movement before the development of the Mesozoic-Cenozoic Andean magmatic arc. Upper Permian to Middle Triassic extension along Palaeozoic terrane sutures resulted in rifting, bimodal magmatism (Choiyoi group), and continental deposition (Cuyo basin). From the Late Triassic to the Early Jurassic, continental extension related to the collapse of the Gondwana orogen initiated a series of long, narrow half-grabens that filled with continental volcaniclastic deposits. These depocenters were later integrated into the Neuquén basin. Coeval development of the shallow marine Pampa de Agnia basin (42-44°S) is related to short-lived extension, probably driven by dextral displacement along major strike-slip faults (e.g. the Gastre fault system). Widespread extension related to the Gondwana breakup (180-165 Ma) and the opening of the Weddell Sea reached the western margin of the South American plate. As a result, wide areas of Patagonia were affected by intraplate volcanism (Chon Aike province), and early rifting occurred in the Magallanes basin. The Andean magmatic arc was almost fully developed by Late Jurassic times. A transgressive stage with starvation and anoxia characterized the Neuquén basin. In western Patagonia, back-arc and intra-arc extension produced the opening of several grabens associated with explosive volcanism and lava flows (e.g. Rı´o Mayo, El Quemado). To the south, a deep marginal basin floored by oceanic crust (Rocas Verdes) developed along the back-arc axis. In mid-to late Cretaceous times, Andean compressional tectonics related to South Atlantic spreading caused the inversion of