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Sample records for alpine tectonic evolution

  1. Alpine tectonics and rotation pole evolution of Iberia

    NASA Astrophysics Data System (ADS)

    de Jong, Koen

    1990-12-01

    The geological evolution of the Betic Cordilleras and Pyrenees reflects the Cretaceous and Tertiary rotation pole and kinematic evolution of the Iberian and African plates. New constraints on the Alpine tectonic evolution of the Iberian plate are provided by P- T- t data and regionally consistent stretching lineations from the metamorphic parts of the Betic Cordilleras. High-pressure low-temperature metamorphism in the Betic Cordilleras resulted from continent-continent collision which caused subduction to a maximum depth of 37 km. A preliminary 116 ± 10 Ma radiometric age for this event corresponds to the initiation of seafloor spreading to the west of Iberia which lasted until about 80 Ma. Intracontinental thrusting in the Betics between 99 Ma and 83 Ma took place after subduction ended. E-W to ESE-WNW trending stretching lineations indicate the direction of thrusting, which resulted in extensional strains of 200-600%. The timing of thrusting in the Betics coincides with a 95-80 Ma tectonic phase in northern Africa, during which E-W stretching lineations were formed. The stretching lineations are coincident with the 110-80 Ma motion vector of Africa-Iberia with respect to Eurasia. Thrusting in the Betics and deformation in northern Africa was driven by convergence of Africa-Iberia and Eurasia. Cretaceous deformation is further recorded by terrigeneous sedimentation in the Mauritanian Flysch and by the tectosedimentary evolution of the Malaguide Complex. Crustal thinning, magmatism and metamorphism in the Pyrenees during the 110-85 Ma period is governed by a left-lateral strike-slip of Africa-Iberia with respect to Eurasia around the same rotation pole as thrusting in the Betics. During the 80-54 Ma period the rotation pole was situated west of Gibraltar, near the previous active collision zone. This inhibited large-scale overthrusting and related penetrative deformation in northern Africa and the Betic Cordilleras. Deformation was instead transferred to the

  2. The Alpine tectonic evolution of the Danube Basin and its northern periphery (southwestern Slovakia)

    NASA Astrophysics Data System (ADS)

    Hók, Jozef; Kováč, Michal; Pelech, Ondrej; Pešková, Ivana; Vojtko, Rastislav; Králiková, Silvia

    2016-10-01

    The tectonic evolution of the pre-Cenozoic basement, as well as the Cenozoic structures within the Danube Basin (DB) and its northern periphery are presented. The lowermost portion of the pre-Cenozoic basement is formed by the Tatricum Unit which was tectonically affected by the subduction of the Vahicum / Penninicum distal continental crust during the Turonian. Tectonically disintegrated Tatricum overlaid the post-Turonian to Lower Eocene sediments that are considered a part of the Vahicum wedge-top basin. These sediments are overthrust with the Fatricum and Hronicum cover nappes. The Danube Basin Transversal Fault (DBTF) oriented along a NW-SE course divided the pre-Neogene basement of the DB into two parts. The southwestern part of the DB pre-Neogene basement is eroded to the crystalline complexes while the Palaeogene and Mesozoic sediments are overlaid by the Neogene deposits on the northeastern side of the DBTF. The DBTF was activated as a dextral fault during the Late Oligocene - Earliest Miocene. During the Early Miocene (Karpatian - Early Badenian) it was active as a normal fault. In the Middle - Late Miocene the dominant tectonic regime with NW - SE oriented extension led to the disintegration of the elevated pre-Neogene basement under the simple and pure shear mechanisms into several NE - SW oriented horst and graben structures with successive subsidence generally from west to east. The extensional tectonics with the perpendicular NE - SW orientation of the Shmin persists in the Danube Basin from the ?Middle Pleistocene to the present.

  3. Orogen-parallel brittle extension as a major tectonic imprint in the Neogene evolution of the south-western Alpine arc

    NASA Astrophysics Data System (ADS)

    Beucher, Romain; Sue, Christian; Tricart, Pierre

    2017-04-01

    We present a new analysis of the late Alpine brittle deformation in the southern branch of the western Alpine arc, focusing on the stack of internal metamorphic nappes east of the Argentera external crystalline massif. The regional-scale fault network is dominated by a NW-SE-striking right-lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area. A second fault set strikes N-S and is mainly represented by normal faults which accommodate orogen-parallel extension. Structural analysis and paleostress tensors derived from inversion of fault-slip data reveal a complex pattern of deformation involving extensional and strike-slip deformation events. The orogen-parallel extension previously described in the internal zones at the east of the Pelvoux massif is confirmed further south, and we show that it is combined with right-lateral strike-slip deformation that increases in intensity towards the south-west. The stability of the minimum stress axis (σ3) direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension, parallel to the strike of the belt, and the strike-slip strain field driven by the counterclockwise rotation of the Apulia-Adria plate. The curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external Alpine zones. We propose that the Neogene tectonic history is a result of the unique curved tectonic architecture of the south-western Alps with respect to the rotation of the Apulia-Adria indenting plate. The southern tip of the western Alpine arc represents a transitional zone between extension in the inner chain and strike-slip/compression in the outer parts.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Study of the tectonic evolution of the South-Eastern Alpine and Western Dinaric Foredeep by means of tomographic analysis from multichannel seismic reflection data in the Gulf of Trieste (North Adriatic Sea)

    NASA Astrophysics Data System (ADS)

    Dal Cin, Michela; Böhm, Gualtiero; Busetti, Martina; Zgur, Fabrizio

    2017-04-01

    The Gulf of Trieste (GOT) is located south of the intersection between the External Dinarides and the South-Eastern Alps. It is considered the foredeep of both the orogens and its sedimentary sequence consists of the Mesozoic-Paleogenic Carbonate Platform, the Eocene turbiditic sediments of the Flysch, the Late Oligocene-Miocenic continental to coastal units of Molassa, the Plio-Quaternary continental and marine deposits. The area underwent a multiphase tectonic activity that started in the Mesozoic, when an extensional regime, with NW-SE oriented normal faults, allowed the aggradation of the Carbonate Platform. In the Late Cretaceous-Paleogene, the Dinaric fold-thrust system gradually migrated towards SW, deflecting the Carbonate Platform E-ward. The main frontal ramp of the External Dinarides is the Karst Thrust that extends along the eastern and rocky coastline of the GOT and that separates the hanging-wall, topographically expressed by the Karst highland, from the footwall lying in the gulf. In the Oligocene-Miocene, the convergence that generated the S-ward vergent Southern Alpine orogen, caused a N-ward deepening of the platform and reactivated the inherited Mesozoic and Cenozoic structures with a dextral transcurrent motion. In the last decade, a dense geophysical dataset has been acquired in the GOT: it consists of 632 km of multichannel seismic (MCS) reflection and sub-bottom profiles, that have been processed and interpreted in time domain by OGS. The data evidenced fault systems related to the extensional Mesozoic and compressional Cenozoic phases and their reactivation with transcurrent kinematics, due to the ongoing N-ward motion of the Adria plate. The transcurrent fault systems show evidence of neotectonic activity and are often the preferential way along which fluids migrate from the carbonates to the seafloor. The MCS lines were used in this work to perform a tomographic analysis providing a detailed velocity model that can enhance seismic imaging

  9. 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.

  10. 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.

  11. Galapagos Tectonics and Evolution (Invited)

    NASA Astrophysics Data System (ADS)

    Hey, R. N.

    2010-12-01

    Galapagos is now considered one of the type-examples of hotspot-ridge interaction, although in the early years of plate tectonics it was generally thought that this interpretation was demonstrably wrong, with two influential groups insisting that non-hotspot models were required for this area. The key to understanding Galapagos tectonic evolution was the recognition that small ridge axis jumps toward the hotspot had occurred, producing complicated magnetic anomalies and asymmetric lithospheric accretion. My dissertation work, guided by Jason Morgan, showed that this simple modification to plate tectonic theory could resolve the seemingly compelling geometric arguments against the Cocos and Carnegie aseismic ridges being Galapagos hotspot tracks, and further that if Galapagos were a hotspot near Fernandina, fixed with respect to the Hawaii hotspot, there should be aseismic ridges on the Cocos and Nazca plates with the observed Cocos and Carnegie ridge geometry, both aseismic ridges forming when the hotspot was ridge-centered, but only the Carnegie ridge since the plate boundary migrated north of the hotspot. A great deal of subsequent research has shown that some areas are considerably more complicated than originally thought, but the following basic model still appears to hold. The Farallon plate split apart along the Grijalva scarp, possibly a preexisting Pacific-Farallon FZ that intersected the hotspot at this time (although alternative interpretations exist), probably in response to tensional stress caused by slab pull in different directions at the Mid-America and Peru-Chile trenches. This break-up allowed more orthogonal subduction of independent Cocos and Nazca plates beginning shortly after 25 Ma. The original Cocos-Nazca ridge trended E-NE, but soon reorganized into N-S spreading segments. The subsequent evolution involved substantial northward ridge migration and ridge jumps, mostly toward the Galapagos hotspot. Recent ridge jumps have occurred in

  12. Magmatic-Tectonic Evolution of Tharsis

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Dohm, J. M.

    2000-01-01

    The tectonic history of the western hemisphere region of Mars was dominated by the formation of the Tharsis rise. In this study, we identify local centers of tectonic activity and examine how each of the centers fit into the overall evolution of the Tharsis region.

  13. Magmatic-Tectonic Evolution of Tharsis

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Dohm, J. M.

    2000-01-01

    The tectonic history of the western hemisphere region of Mars was dominated by the formation of the Tharsis rise. In this study, we identify local centers of tectonic activity and examine how each of the centers fit into the overall evolution of the Tharsis region.

  14. 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.

  15. Preliminary analysis of Venusian tectonics and evolution

    NASA Astrophysics Data System (ADS)

    Nikishin, A. M.

    1990-11-01

    Five stages in the evolution of Venus are discussed: accretion, segregation of early crust from magma ocean; volcanic reworking of early crust, development of tectonics of soft plastic plates with formation of tesserae in compression zones and plains in dilatation zones; formation of weakened planetary zones of dilatation saturated by mantel hot-spot structures against a backdrop of dispersed mantel hot-spot tectonics and plateau volcanism. The following subjects are discussed: types of structures and structural regions of Venus; tectonic structure of Venus and its interpretation; thickness and composition of Venusian crust; model of geological evolution of Venus; asymmetry of tectonic structure of Venus; and reasons for the great differences in the tectonics of the Earth and Venus. The tectonics of Venus differ from those of the Earth because Venus was always impoverished in terms of water, a highly important agent of magmatism and the main fluid involved in the fusion fo sialic rocks. Venusian volcanism therefore was less intense and a sialic crust is largely absent. The greenhouse effect on Venus causes increased plasticity of its lithosphere.

  16. Plate tectonics: Crustal recycling evolution

    NASA Astrophysics Data System (ADS)

    Magni, Valentina

    2017-09-01

    The processes that form and recycle continental crust have changed through time. Numerical models reveal an evolution from extensive recycling on early Earth as the lower crust peeled away, to limited recycling via slab break-off today.

  17. Tectonic evolution of the terrestrial planets.

    PubMed

    Head, J W; Solomon, S C

    1981-07-03

    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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Alpine metamorphic evolution of Ligurian Alps (North-West Italy): chemography and petrological constraints inferred from metamorphic climax assemblages

    NASA Astrophysics Data System (ADS)

    Messiga, B.

    1987-03-01

    The up-to-date petrological and microtextural information on the Ligurian Alps indicates that the metamorphic rocks from the oceanic lithosphere and the paleo-European continental margin underwent an alpine-type metamorphic evolution characterized by low dT/dP gradients. In particular, rocks from the Ligurian-Piedmontese oceanic lithosphere underwent an alpine metamorphism typical of alpine-type blueschist rocks. The distribution of the alpine metamorphic facies in paleo-European continental margin is closely related to the structural position of the different tectonic units. The prograde evolution frequently preserves paragenetic and textural relics of the earlier parageneses. If relics of the earlier parageneses are preserved, the rock exhibits continuous prograde reactions confirmed by strong compositional zoning of the metamorphic minerals. Therefore, these reactions lead to chemical and microtextural equilibrium relations, between the minerals, in limited domains of the rocks (microtextural sites). The main compositional aspect of coronitic textures is the mineral zoning, particularly when the minerals of the coronas are the consequence of a wide range of solid solutions. In such cases, the reacting minerals are armored and the kinetics are lowered. The prograde metamorphic evolution, which involved the rocks from the oceanic lithosphere and the paleo-European continental margin, is quite consistent with a subduction-type geodynamic process in different ages during alpine times.

  3. 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.

  4. Lower Oligocene Alpine geodynamic change: tectonic and sedimentary evidences in the western arc

    NASA Astrophysics Data System (ADS)

    Dumont, T.; Rolland, Y.; Simon-Labric, T.

    2009-04-01

    The formation of the western Alpine arc started during the earliest Oligocene, after a drastic kinematic change in the collisional regime. (A) Previously, south-southeast dipping subduction of the European lithosphere (including Briançonnais) underneath Adria resulted in an underfilled flexural basin propagating towards the north-northwest on the European foreland, which had already been moderately deformed due to the Iberian microplate motion. This propagation appears consistent with the Africa-Europe relative motion (Rosenbaum et al., 2002). During this early stage of collision, some oceanic units were obducted over the southern part of European continent (Corsica, Briançonnais). (B) From the early Oligocene on, the western Alps kinematics were dominated by lateral (westward) escape of the Internal Alps indenter, whose displacement with anticlockwise rotation progressively formed the arc. The structures of this mature stage of collision crosscut the buildup issued from (A), and its kinematics were probably more driven by local lithospheric forces of the Mediterranean domain (Jolivet et al., 1999) than by Africa-Europe convergence. The western and southern parts of the western Alpine arc display many evidences for this major syn-collisional change: - Structural interferences are found at various scales. For example, the circular-shape Pelvoux massif resulted in part from crossed shortening stages (SE-NW and E-W; Dumont et al., 2008). It is located in the footwall of two nappes stacks having propagated northwestwards and west- to southwestwards, respectively. The latter crosscuts the former south of Briançon city. - Tectonic transport directions are strongly variable both in the external and in the internal zones, but they consistently display anticlockwise rotation through time. The most important changes are found in the southern part of the western Alps, giving birth to a radial distribution propagating into the external zone. - Instead of beeing gradual, the

  5. 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.

  6. Kinematic evolution of a tectonic wedge above a flat-lying décollement: The Alpine foreland at the interface between the Jura Mountains (Northern Alps) and the Upper Rhine graben

    NASA Astrophysics Data System (ADS)

    Nivière, Bertrand; Giamboni, Marzio; Innocent, Christophe; Winter, Thierry

    2006-06-01

    We estimate strain rates of three parameters that describe the buildup of a tectonic wedge (Jura front, France). The uplift rate on frontal ramps decreases with the slip on the ramps and the coeval increase of vertical loads. The migration rate of the tip of the sole thrust appears to be episodic and faster than the translation rate of the backstop. The long-term tilting rate appears to be constant, whereas the short-term rate is slightly slower. We propose a model of wedge growth that proceeds without underthrusting. In a prefractured medium, the wedge would activate the frontal ramp with a weaker frictional resistance than the forward décollement. An instantaneous forward jump of the deformation front would occur when the resistance on the ramp equals the resistance of the frontal décollement. This model differs from those proposed for accretionary zones, and relates to the backstop of a single tapered orogenic belt.

  7. Punctuated tectonic evolution of the earth

    NASA Astrophysics Data System (ADS)

    Davies, Geoffrey F.

    1995-12-01

    The potential of a phase transformation barrier to cause mantle layering has been incorporated into calculations of the thermal evolution of the earth's mantle based on parameterised convection theory. A range of possible behaviors is demonstrated, depending on parameter values, including episodic layering, long-term layering or no layering. Novel findings are 1-2 Ga phases that might correspond with major tectonic eras, and that early mantle overturns may have caused global magmatic and tectonic convulsions. For the more plausible parameter values, the models are initially layered, but typically the layering becomes unstable and breaks down episodically via mantle overturns. Subsequently the models evolve into whole-mantle convection due to the increasing ability of subducted plates to penetrate the phase barrier as the mantle cools, consistent with geophysical evidence against strong layering of the present mantle. The early layering-overturn cycles may occur on timescales of a few hundred million years. The overturns replace cooler upper mantle material with hotter lower mantle material, and would cause global convulsions that potentially correspond with episodes of crust formation. Such models permit plate tectonics to operate in the Archean between overturns, though the early crust may record mainly the effects of overturns, which could generate, aggregate and/or rework large volumes of mafic crust in a short time. They would help to explain present degrees of depletion of the mantle in incompatible elements as well as strong upper mantle depletion in the early Archean. The early convulsions may have controlled the composition of the atmosphere and frustrated the development of life.

  8. 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.

  9. 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.

  10. Structure and emplacement of the Alpine-type peridotites from Beni Bousera, Rif, Morocco: A polyphase tectonic interpretation

    NASA Astrophysics Data System (ADS)

    Reuber, Ingrid; Michard, André; Chalouan, Ahmed; Juteau, Thierry; Jermoumi, Bahija

    1982-02-01

    The Beni Bousera peridotite antiform, in the southern branch of the Gibraltar orocline exhibits a lherzolitic core, containing thin pyroxenite layers surrounded by harzburgites, then by dunites and garnet-bearing dunite. In the peripheral areas, the amount of pyroxenite greatly increases by the development of garnet-pyroxenite veins. These data indicate a gradient of partial-melting increasing upward. We conclude that a reversed geothermal gradient was temporarily established in the upper part of the peridotite, just under its migmatitic roof (kinzigite aureole, then sillimanite-gneiss). Study of ductile, penetrative structures and discussion of the later "cold" structures show that the foliation of the tectonites was originally flat, with a NW-SE-trending stretching lineation. Orthopyroxene crystals are used as tectonic markers. "Isostrain zones" indicate that simple shear and finite strain increase upward. We conclude that a ductile shear zone acted between peridotite and gneiss. Strain heating along this shear zone probably has been responsible for partial melting of the upper part of the peridotite. In our model, the peridotite emplacement into the mid-continental crust began during crustal extension. Then, as comparison with the Rondà massif suggests, an intracrustal thrusting stage was followed by high-temperature and relatively low-pressure metamorphism and by intrusion of acidic dikes. The uplift of the mantle slab continued by compressive upthrusting and isostatic doming. This complex, polyphase evolution probably extended beyond the Alpine orogeny, as suggested by Kornprobst.

  11. 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.

  12. Morphology and Tectonic Evolution of Endeavor Deep

    NASA Astrophysics Data System (ADS)

    Pockalny, R. A.; Larson, R. L.; Popham, C. T.; Natland, J. H.; Abrams, L. J.; Sonder, L. J.

    2004-12-01

    Endeavor Deep is located on the Nazca/Juan Fernandez plate boundary near the triple junction of the Pacific, Nazca and Antarctic plates. The deep is the tip of the northward propagating East Ridge, which defines the eastern side of the microplate and is presently exposing ~3 Myr old oceanic crust created at the ultra-fast spreading (~150 km/myr) East Pacific Rise. Recently collected high-resolution EM300 bathymetry, deep-tow DSL120 sidescan, surface-towed magnetics, and near-bottom JASON II observations provide important details about the tectonic character and origin of Endeavor Deep. These data define a 70 km-long, 40 km-wide, and 3 km-deep rift which shoals and narrows toward the rift tip to the NW and is deeper and wider away from the rift tip toward the SE. The southern wall of the rift is uplifted and has a characteristic flexural profile. The northern wall is also uplifted, however, the classic flexural profile is complicated by the presence of a large EW-trending massif, which appears to be a rift-truncated compressional ridge emplaced during a phase of NS-oriented compression. Along both rift walls, a series of terraces suggest a series of down-dropped blocks associated with ongoing extension. Along the rift floor, a relatively flat, featureless bottom in the NW evolves into hummocky terrane in the central part of the basin that is characterized by volcanic features reminiscent of 1-2 km diameter pancakes in plan-view. Farther to the SE, tectonic lineations and pillow ridges oriented parallel to the trend of the rift valley dominate the basin floor. Magnetic profiles across this portion of the survey area indicate a well-formed central magnetic anomaly with a width equivalent to a spreading rate of 20 km/Myr, which is predicted by tectonic reconstructions of the plate boundary. Overall, these observations define a four-phase evolution of Endeavor Deep: 1) initial crustal formation at the ultra-fast spreading East Pacific Rise ~3 Ma, 2) regional compression

  13. Hotspot evolution and Venusian tectonic style

    NASA Astrophysics Data System (ADS)

    McGill, George E.

    1994-11-01

    Because hotspots represent an important manifestation of heat loss on Venus, their geological evolution is of fundamental importance for any attempt to understand Venusian tectonics. Eistla Regio is an approximately 7500-km-long, moderately elevated region inferred to overlie one or more large mantle upwellings or hotspots. It also contains many shield volcanoes and coronae believed due to the rise of thermal plumes in the mantle. Central Eistla Regio includes two large volcanoes, Sappho and Anala, and several coronae in close proximity. Detailed mapping in this region results in two conclusions of tectonic significance: (1) Sappho and Anala occur near the intersection of two major extensional deformation zones, and (2) the coronae are older than the large volcanoes. Several of the coronae occur as a chain along Guor Linea, one of the major extensional deformation zones. Stratigraphic relationships indicate that the coronae began forming very soon after the emplacement of the widespread regional plains materials. Thus Central Eistla Regio was the site of a swarm of plumes that first formed coronae and then later formed shield volcanoes. The expected result of such a swarm would be thermal thinning of the elastic lithosphere with time. However, model results, geological observations, and gravity data suggest that the change from coronae to shield volcanoes was accompanied by a thickening of the lithosphere with time. This thickening is interpreted to be the result of global cooling of the lithosphere following the most recent episode of near-global resurfacing. The global cooling must have occurred faster than local heating of the lithosphere due to the impingement of thermal plumes.

  14. Hotspot evolution and Venusian tectonic style

    NASA Technical Reports Server (NTRS)

    Mcgill, George E.

    1994-01-01

    Because hotspots represent an important manifestation of heat loss on Venus, their geological evolution is of fundamental importance for any attempt to understand Venusian tectonics. Eistla Regio is an approximately 7500-km-long, moderately elevated region inferred to overlie one or more large mantle upwellings or hotspots. It also contains many shield volcanoes and coronae believed due to the rise of thermal plumes in the mantle. Central Eistla Regio includes two large volcanoes, Sappho and Anala, and several coronae in close proximity. Detailed mapping in this region results in two conclusions of tectonic significance: (1) Sappho and Anala occur near the intersection of two major extensional deformation zones, and (2) the coronae are older than the large volcanoes. Several of the coronae occur as a chain along Guor Linea, one of the major extensional deformation zones. Stratigraphic relationships indicate that the coronae began forming very soon after the emplacement of the widespread regional plains materials. Thus Central Eistla Regio was the site of a swarm of plumes that first formed coronae and then later formed shield volcanoes. The expected result of such a swarm would be thermal thinning of the elastic lithosphere with time. However, model results, geological observations, and gravity data suggest that the change from coronae to shield volcanoes was accompanied by a thickening of the lithosphere with time. This thickening is interpreted to be the result of global cooling of the lithosphere following the most recent episode of near-global resurfacing. The global cooling must have occurred faster than local heating of the lithosphere due to the impingement of thermal plumes.

  15. Tectonic evolution of the northernmost Okinawa Trough

    NASA Astrophysics Data System (ADS)

    Oiwane, H.; Tonai, S.; Nakamura, Y.; Kiyokawa, S.; Tokuyama, H.

    2007-12-01

    Over the last decades, mechanism of backarc opening has been the subject of controversy. Okinawa Trough has been noticed as an incipient continental backarc basin. So far studies on the Okinawa Trough have been conducted mainly in its southern and middle part. Nevertheless, only a few studies have been conducted on the relationship between geologic structures and the tectonic evolution of northernmost Okinawa Trough. Our main object is to consider the tectonic evolution of the Okinawa Trough by means of structural geology, not only in ocean but also land area. We executed seismic reflection survey in northernmost Okinawa trough and investigated fault systems on Koshikijima islands located on northeastern edge of the Okinawa Trough. Then we compared geologic structures on land and sea floor. First of all, we interpreted seismic reflection data acquired by hydraulic department of Japan Coast Guard in northernmost Okinawa Trough in 1975. Furthermore, we executed multi-channel seismic reflection survey in this area (KT06-03, KT07-03 cruise). NNE and ENE trending fault systems were recognized. It is clear that Northernmost Okinawa Trough has been subsided by activation of NNE trending fault system at the east edge of trough basin with several hundred meters of displacement. The ENE trending fault system has displacement in the surface sediment, which means they are active faults. On the other hand, we held on-land field survey in northern part of the Koshikijima Islands. Fault system, which can be related to the Okinawa Trough, is reported in this area (Inoue et al., 1982). So we focused on that NNE trending normal fault system (F2 fault system). On the basis of crosscut relationship and K-Ar dating of fault rocks and dikes, F2 fault system was formed after late Miocene and likely to have been formed in a shallow underground. F2 fault system on Koshikijima islands and NNE trending fault systems in the Okinawa Trough have similar strike, displaced direction and

  16. 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.

  17. 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.

  18. Coupled Tectonic and Climatic Shifts in Planetary Evolution

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Growing evidence suggests that the tectonic mode of the Earth has changed over its geologic lifetime. During a tectonic regime shift, the planet will be very far from any dynamic equilibrium point and, as such, standard thermal history modelling will not be applicable. A regime shift will also be associated with changes that can effect the large scale climate of a planet. Recently it has been shown that significant feedbacks are possible between planetary tectonics and the climate of a planet [e.g., 1, 2, and references therein]. How those feedbacks operate during a tectonic regime shift (e.g., the initiation of plate-tectonics) has, to date, not been fully explored. To explore linked tectonic-climate effects, during transitions between tectonic states, we couple 3D mantle convection and planetary tectonics simulations to climate models. A planet initially in a single plate state can transition to a plate-tectonic like mode as it cools. Initial lithosphere yielding, for systems with moderate convective vigor, results in an increase of pCO2 by a factor of 50 - 100 (from increased melt production), indicating that the onset of global subduction, may be significant driver of the atmospheric, in addition to the tectonic evolution. All else being held equal, the initiation time of yielding as well as the planetary position within the Solar System allow for results ranging from a climatic shutdown of an incipient mode of plate-tectonics, to a buffered atmosphere and long lived plate-tectonics, to a final 'dead snowball state'. These results illustrate the need to think of tectonics and habitably within a temporal framework in which tectonic regime shifts can be a first order control on the long term habitability potential of a planet. [1] Foley et al., (2012) EPSL; [2] Weller et al., (2015) EPSL

  19. 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.

  20. Tectonic stress and fault rock fabrics in the vicinity of the Alpine Fault inferred from DFDP-2 borehole televiewer imagery

    NASA Astrophysics Data System (ADS)

    Shigematsu, N.; Massiot, C.; Townend, J.; Doan, M. L.; Mcnamara, D. D.; Toy, V.; Sutherland, R.

    2015-12-01

    The present-day upper crustal stress regime near the central Alpine Fault represents the superposition of topographic and tectonic stresses late in the fault's typical earthquake cycle. Previous estimates based on focal mechanism analysis of the principal stress orientations at seismogenic depths reveal a regional axis of maximum horizontal compressive stress trending approximately 115°. However seismicity adjacent to the Alpine Fault is sparse and does not constrain the stress field close to the fault or with sufficient spatial resolution to distinguish variations. The analysis of fractures revealed in borehole televiewer (BHTV) logs collected during DFDP-2B drilling provides an opportunity to examine stresses in the hanging-wall of the Alpine Fault. Here we present the results of stress analysis utilizing a dataset consisting of 418 fractures. On average, many of the fractures dip at 50-60° towards the southeast, consistent with the regional attitude of the Alpine Fault. We compute stress parameters using the Hough transform method, which enables us to analyze incomplete fault slip measurements that do not contain slip directions. For this analysis, we assumed that all fractures represent reverse-faulting components in response to a single homogeneous stress tensor, and that fractures with similar geometries to the Alpine Fault involve similar top to the west shear. Our preliminary analysis of the dataset as a whole yields orientations (trends/plunge) for the maximum and minimum compressive stress axes σ1 and σ3 of 129/26 and 27/23 (±30°), respectively and a stress ratio of (σ2-σ3)/(σ1-σ3)=~0.3. These parameters yield an axis of maximum horizontal compressive stress of 136±30°, implying that the trend of σHmax is rotated clockwise from the regional azimuth into a direction more perpendicular to the strike of the Alpine Fault near the fault. The orientations are compatible with previously determined horizontal shortening from analysis of small scale

  1. 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.

  2. 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.

  3. 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

  4. Tectonic Evolution of the Terceira Rift (Azores)

    NASA Astrophysics Data System (ADS)

    Stratmann, Sjard; Huebscher, Christian; Terrinha, Pedro; Ornelas Marques, Fernando; Weiß, Benedik

    2017-04-01

    The Azores Plateau is located in the Central Atlantic at the Eurasian, Nubian and North-American plates (RRT) Azores Triple Junction. The Terceira Rift (TR) connects the Mid-Atlantic Ridge with the Gloria Fault, hence establishing a transtensional-transform present day plate boundary between the Eurasian and the Nubian plates. Three volcanic islands arose along the TR, Graciosa, Terceira and Sao Miguel. In the geological past, the plate boundary in the Azores area between the Eurasian and Nubian plates was located further south at the East Azores Fracture Zone. The timing of the plate boundary jump, which marks the onset of rifting along the TR, is heavily disputed. Published ages vary from 36 to 1 Ma. Based on bathymetric data and high-resolution marine 2D multi-channel seismic data acquired during M113 cruise of R/V Meteor in 2014/2015 we discuss the structural evolution of the TR and address the question whether the divergence between both plates is entirely accommodated by the TR. The central TR between São Miguel and Terceira, also known as Hirondelle Basin, is up to 70 km wide. Rifting created two asymmetric graben sections separated by a rift parallel horst. The north-eastern and south-western graben sections are ca. 4 km and 3 km deep, respectively, and the corresponding graben floors are tilted towards the central horst. Volcanic cones emerged on the central horst and rift shoulders. Bright spots in the basin fill deposits indicate fluid flow out of the volcanic basement. The seafloor is displaced by faults which suggest recent fault displacement. In the Eastern Graciosa Basin between Terceira and Graciosa Islands the rift narrows to ca. 40 km and shallows to ca. 3200 m water depth. The central horst is no longer detectable. Instead, a buried normal fault and a small escarpment are observed. Shallow faults and block rotation are less pronounced compared to the basins to the south-east and north-west. The Western Graciosa Basin is about 30 km wide and ca

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Storetvedt, K. M.

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

  7. Late Alpine to recent thick-skinned tectonics of the central Swiss Molasse Basin, Canton of Bern, Switzerland

    NASA Astrophysics Data System (ADS)

    Mock, Samuel; Allenbach, Robin; Wehrens, Philip; Reynolds, Lance; Kurmann-Matzenauer, Eva; Michael, Salomè; Herwegh, Marco

    2017-04-01

    The Swiss Molasse Basin (SMB) forms part of the North Alpine Foreland Basin. It is a typical peripheral foreland basin, which developed in Paleogene and Neogene times in response to flexural bending of the European lithosphere induced by the orogenic loading of the advancing Alpine thrust wedge. The tectonics of the SMB and the role of Paleozoic and Mesozoic structures are still poorly understood. It is widely accepted that during the main deformation phase of the Jura fold-and-thrust belt, the SMB was riding piggy-back above a major detachment horizon situated within Triassic evaporites. In recent years it has been observed that the Jura fold-and-thrust belt is today deforming in a thick-skinned tectonic style. As for the western and central SMB, most authors still argue in favor of a classical foreland type, thin-skinned style of deformation. Based on the geological 3D modeling of seismic interpretations, we present new insights into the structural configuration of the central SMB. Revised and new interpretations of 2D reflection seismic data from the 1960s to the 1980s reveal a major strike-slip fault zone affecting not only the Mesozoic and Cenozoic cover, but also the crystalline basement beneath. The fault zone reactivated late Paleozoic synsedimentary normal faults bounding a Permo-Carboniferous trough. Basement-involved thrusting observed in the southern part of the SMB seems to be controlled by the presence of slightly inverted Permo-Carboniferous troughs as well. These observations, combined with a compiled structural map and the distribution of recent earthquake hypocenters suggest a late stage, NNW-SSE directed, compressional thick-skinned and strike-slip dominated tectonic activity of the central SMB, post-dating the main deformation phase of the Jura fold-and-thrust belt. This still ongoing deformation might be related to the slab rollback of the European plate and the associated lower crustal delamination as recently suggested by Singer et al. (2014

  8. 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.

  9. Transformation of graphite by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Kirilova, Matina; Toy, Virginia; Timms, Nicholas; Halfpenny, Angela; Menzies, Catriona; Craw, Dave; Rooney, Jeremy; Giorgetti, Carolina

    2017-04-01

    Graphite is a material with one of the lowest frictional strengths, with coefficient of friction of 0.1 and thus in natural fault zones it may act as a natural solid lubricant. Graphitization, or the transformation of organic matter (carbonaceous material, or CM) into crystalline graphite, is induced by compositional and structural changes during diagenesis and metamorphism. The supposed irreversible nature of this process has allowed the degree of graphite crystallinity to be calibrated as an indicator of the peak temperatures reached during progressive metamorphism. We examine processes of graphite emplacement and deformation in the Alpine Fault Zone, New Zealand's active continental tectonic plate boundary. Raman spectrometry indicates that graphite in the distal, amphibolite-facies Alpine Schist, which experienced peak metamorphic temperatures up to 640 ◦C, is highly crystalline and occurs mainly along grain boundaries within quartzo-feldspathic domains. The subsequent mylonitisation in the Alpine Fault Zone resulted in progressive reworking of CM under lower temperature conditions (500◦C-600◦C) in a structurally controlled environment, resulting in spatial clustering in lower-strain protomylonites, and further foliation-alignment in higher-strain mylonites. Subsequent brittle deformation of the mylonitised schists resulted in cataclasites that contain over three-fold increase in the abundance of graphite than mylonites. Furthermore, cataclasites contain graphite with two different habits: highly-crystalline, foliated forms that are inherited mylonitic graphite; and lower-crystallinity, less mature patches of finer-grained graphite. The observed graphite enrichment and the occurrence of poorly-organised graphite in the Alpine Fault cataclasites could result from: i) hydrothermal precipitation from carbon-supersaturated fluids; and/or ii) mechanical degradation by structural disordering of mylonitic graphite combined with strain-induced graphite

  10. 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

    2017-03-01

    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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Tectonic evolution of the Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    Pan, Guitang; Wang, Liquan; Li, Rongshe; Yuan, Sihua; Ji, Wenhua; Yin, Fuguang; Zhang, Wanping; Wang, Baodi

    2012-07-01

    The Qinghai-Tibet Plateau, composed of several continental slivers within the eastern Tethyan domain, is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on Earth. This plateau is generally inferred to be a collage of several continental blocks that rifted from Gondwanaland and subsequently accreted to the Asian continent. However, recent recognition of over twenty ophiolite mélange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision. Based on 177 recently finished 1:250,000 scale geological maps and related studies, we summarize the main tectonic context of the Qinghai-Tibet Plateau and propose a new integrated model to account for the new findings. The complex orogen of the immense Qinghai-Tibet Plateau, consisting of multiple island arc-basin systems that developed at different stages while surrounded by the North China, Yangtze, Tarim, and Indian plates, is emphasized. The entire orogen, surrounded by suture zones that mark the locations of oceanic closure, is investigated by examining (I) the first-order tectonic units and ophiolitic mélanges (including arc-arc/continent collision zones) and (II) their internally enclosed blocks as the second-order tectonic units. Therefore, the Qinghai-Tibet Plateau is divided into three major orogenic systems, namely, from northeast to southwest, the Early Paleozoic Qinling-Qilianshan-Kunlunshan (Qin-Qi-Kun), the Late Paleozoic-Triassic Qiangtang-Sanjiang, and the Late Paleozoic to Cenozoic Gangdese-Himalaya orogenic systems, which are separated by the Kangxiwa-Muzitagh-Maqin-Mianxian and the Bangong-Shuanghu-Changning-Menglian sutures, respectively. We propose that the formation and evolution of the Qinghai-Tibet Plateau to have been intrinsically related to those of the eastern Tethys, recorded by the Longmu Co-Shuanghu ophiolite mélange zone, the Southern Qiangtang Paleozoic accretionary arc

  16. 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.

  17. Tectonism

    NASA Image and Video Library

    2011-10-24

    This image from NASA 2001 Mars Odyssey spacecraft shows evidence of tectonic stresses that deform and fracture rocks and planetary surfaces. Right angles seen here are a good indication that the feature was formed by tectonic stresses.

  18. Multiagent simulation of evolutive plate tectonics applied to the thermal evolution of the Earth

    NASA Astrophysics Data System (ADS)

    Combes, M.; Grigné, C.; Husson, L.; Conrad, C. P.; Le Yaouanq, S.; ParenthoëN, M.; Tisseau, C.; Tisseau, J.

    2012-05-01

    The feedback between plate tectonics and mantle convection controls the Earth's thermal evolution via the seafloor age distribution. We therefore designed the MACMA model to simulate time-dependent plate tectonics in a 2D cylindrical geometry with evolutive plate boundaries, based on multiagent systems that express thermal and mechanical interactions. We compute plate velocities using a local force balance and use explicit parameterizations to treat tectonic processes such as trench migration, subduction initiation, continental breakup and plate suturing. These implementations allow the model to update its geometry and thermal state at all times. Our approach has two goals: (1) to test how empirically- and analytically-determined rules for surface processes affect mantle and plate dynamics, and (2) to investigate how plate tectonics impact the thermal regime. Our predictions for driving forces, plate velocities and heat flux are in agreement with independent observations. Two time scales arise for the evolution of the heat flux: a linear long-term decrease and high-amplitude short-term fluctuations due to surface tectonics. We also obtain a plausible thermal history, with mantle temperature decreasing by less than 200 K over the last 3 Gyr. In addition, we show that on the long term, mantle viscosity is less thermally influential than tectonic processes such as continental breakup or subduction initiation, because Earth's cooling rate depends mainly on its ability to replace old insulating seafloor by young thin oceanic lithosphere. We infer that simple convective considerations alone cannot account for the nature of mantle heat loss and that tectonic processes dictate the thermal evolution of the Earth.

  19. Tectonic and stratigraphic evolution in South Alboran Sea (Morocco)

    NASA Astrophysics Data System (ADS)

    D'Acremont, E.; Gorini, C.; El Abbassi, M.; Farran, M.; Leroy, S.; Mercier De Lepinay, B. F.; Migeon, S.; Poort, J.; Ammar, A.; Smit, J.; Ercilla, G.; Alonso, B.; Scientific Team of the Marlboro project

    2011-12-01

    The Alboran Basin, in western Mediterranean, concentrates on a relatively small surface and densely-populated, a large structural complexity linked to seismic activity with recurrent mass-transport deposits that may trigger tsunamis. It was formed by Oligo-Miocene extension while tectonic inversion occurred since the Late Miocene (Tortonian) due to the African-European collision. This North-South compression produces a conjugated fault system located in the central area from Al Hoceima to Andalusia. Numerous instabilities are linked to the recent and present-day seismic activity and show the link between seismicity and erosion-sedimentation processes. On the Andalusia margin the active structures have been identified and recently mapped in detail by using MBES data (including backscatter), and high-resolution seismic data. Such detailed studies have not yet been carried out on the Moroccan margin. The Marlboro-1 oceanographic cruise (R/V Côtes de la Manche, July 2011) has imaged and constrained active structures and associated sedimentary systems through seismic reflection data (MCS). The Xauen/Tofino banks (growth folds), the Alboran Ridge, and the Al Hoceima basin offshore Morocco have been selected because they constitute key-study areas that record a complete deformation history since the Tortonian. Active features including faults, growth folds, channels, mass transport deposits, contourites and volcanoes has provided first order tectonic and sedimentary markers of the basin's evolution. A high chrono-stratigraphical resolution will constitute the basis for reconstructing the evolution of this tectonically active area marked by strong seismic activity. The Marlboro-1 cruise will allow determining key-study area of the Marlboro-2 cruise scheduled for 2012 (R/V Téthys-II, CNFC Call). These cruises should allow for the acquisition of data necessary to characterize basin morphology, active tectonic and sedimentary structures and also make the link with existing

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Alpine-type tectonics in the Paleoproterozoic Lapland-Kola Orogen

    NASA Astrophysics Data System (ADS)

    Mudruk, S. V.; Balagansky, V. V.; Gorbunov, I. A.; Raevsky, A. B.

    2013-07-01

    The Kola region in the northeastern Baltic Shield is characterized by diverse Paleoproterozoic collision processes. The Keivy Terrane is one of the major tectonic units in the northeastern foreland of the Paleoproterozoic Lapland-Kola Collisional Orogen, which markedly differs in a number of parameters from other tectonic units of the Kola region. The study of the Keivy Terrane allowed us to unravel one more basic difference: the large Paleoproterozoic sheath synform of the Serpovidny (Crescentic) Range localized in this terrane. Its core is occupied by volcanic and sedimentary rocks, which correlate with the fill of the Imandra-Varzuga Rift; the limbs are composed of metamorphosed mature sedimentary rocks known as Keivy paraschists of Neoarchean or Paleoproterozoic age. The lower limb of the Serpovidny Synform is strongly squeezed, whereas the upper limb consists of almost undeformed rocks. The deformed rocks underwent ductile flow under conditions of simple or general shear. In the degree of its asymmetry and main parameters, the Serpovidny Synform is similar to the plunging and recumbent anticlines in the Helvetic nappes of the Alps. It is concluded that the Paleoproterozoic core of the Serpovidny Sheath Synform, or plunging anticline, is a fragment of the almost completely eroded deep Serpovidny Nappe of the Helvetic type. During the collision related to the Lapland-Kola Orogeny (1.9-2.0 Ga), this nappe was pushed out northward from the Paleoproterozoic Imandra-Varzuga Rift, which is situated 50 km south of the Serpovidny structure, and thrust over the Keivy paraschists. The latter, together with underlying the Lebyazhka Gneiss, were folded in the process of thrusting and were involved in the structure of the Serpovidny Synform. The Keivy paraschists make up a para-autochthon or a separate nappe of the Pennine type. The Archean Lebyazhka metafelsic volcanics underlie the Keivy paraschists and overlie granitoids of the Archean basement that remained undeformed

  6. 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.

  7. 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.

  8. The Meliata and Piemont-Ligurian rifted margins: stratigraphic record and tectonic evolution of polyphase rift systems

    NASA Astrophysics Data System (ADS)

    Decarlis, Alessandro; Manatschal, Gianreto; Masini, Emmanuel

    2013-04-01

    The Late Permian to Late Jurassic paleogeographic evolution of the Alpine domain was strongly controlled by the formation of polyphase rift systems. If these rift systems are the result of a single, long lasting rifting event or if they are generated by two distinct rift pulses, is still a matter of debate. Recent studies seem to agree on the second hypothesis, supporting two distinct rift events: one Early-Middle Triassic (Meliata s.l.) and one Early to Middle Jurassic (Piemont-Liguria s.l.). Nevertheless major incertitudes arise on the interpretations of the evolution of the former rifting, which lead to multiple or single, continuous oceanic branches. This uncertainity is mainly due to the successive orogenic overprint related to the formation of the Alpine belt and of the Western Mediterranean domain. The aim of this work is to explore how rifting events are recorded by the stratigraphic and structural evolution using both the vast existing literature and own observations. Selected areas belonging to different paleogeographic domains in the Alpine realm (Southalpine, Brianconnais s.l. and Austroalpine) will be studied in order to define relevant time-marker levels to map and correlate the temporal and spatial evolution of rift events. With this "basinal" approach we point to major tectonic events, filtering smaller-scale tectonics and minor environmental controlling factors on sedimentation. Our final goal is to identify "fingerprints" for major rifting events that may reveal the location and timing of hyper-extended domains. The evaporitic successions, the development of thick carbonate platforms, their demise or drowning, the iron-manganese hardgrounds sedimentation that could represent a response of hydrothermal circulation associated with hyper-extension, may correspond to correlable and mappable residues of large-scale, hyper-extended rift events. This data, together with subsidence analysis, basement and volcanics data provide a major, well constrained

  9. 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.

  10. 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.

  11. 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

  12. Genetic structure and evolution of Alpine polyploid complexes: Ranunculus kuepferi (Ranunculaceae) as a case study.

    PubMed

    Burnier, J; Buerki, S; Arrigo, N; Küpfer, P; Alvarez, N

    2009-09-01

    The alpine white-flowered buttercup, Ranunculus kuepferi Greuter & Burdet, is a polyploid complex with diploids endemic to the southwestern Alps and polyploids - which have been previously described as apomictic - widespread throughout European mountains. Due to the polymorphic status of both its ploidy level and its reproductive mode, R. kuepferi represents a key species for understanding the evolution of polyploid lineages in alpine habitats. To disentangle the phylogeography of this polyploid taxon, we used cpDNA sequences and AFLP (amplified fragment length polymorphism) markers in 33 populations of R. kuepferi representative of its ploidy level and distribution area. Polyploid individuals were shown to be the result of at least two polyploidization events that may have taken place in the southwestern Alps. From this region, one single main migration of tetraploids colonized the entire Alpine range, the Apennines and Corsica. Genetic recombination among tetraploids was also observed, revealing the facultative nature of the apomictic reproductive mode in R. kuepferi polyploids. Our study shows the contrasting role played by diploid lineages mostly restricted to persistent refugia and by tetraploids, whose dispersal abilities have permitted their range extension all over the previously glaciated Alpine area and throughout neighbouring mountain massifs.

  13. Tectonic Evolution of the Reykjanes Ridge During the Past 15

    NASA Astrophysics Data System (ADS)

    Benediktsdóttir, Á.; Hey, R. N.; Martinez, F.; Höskuldsson, Á.

    2012-04-01

    We present a new detailed tectonic model of the Reykjanes Ridge which examines the rift propagation hypothesis for the V-shaped gravity and topography ridges and its asymmetric lithospheric accretion. Forward modeling of the Reykjanes Ridge magnetic anomalies south of Iceland strongly suggest rift propagation both toward and away from Iceland, explaining the observed discontinuous asymmetric lithospheric accretion. Four major southward rift propagations extend through our entire survey area and several additional small scale rift propagations are observed, including northward propagators. If plume pules drive southward propagators, then two mechanically different kinds of propagators must exist. We find that there is a major difference in the crustal accretion asymmetry between the area immediately off the Iceland shelf and farther south, both in rift propagation pattern and free air gravity lineations. The pattern is more complex on the Iceland shelf but simplifies further south on the Reykjanes Ridge, at a greater distance from the anomaly under Iceland. Furthermore, we identify two small shortlived offset features coined ponsu-transforms, from which rift propagation is both initiated and stopped. Also, we have identified northward pointing Vs in the free air gravity and a major flowline-parallel free air gravity low, re-enforcing the conclusion that the V-shaped Ridges are not simple linear continuous features. We attempt to link the rift propagation model to the tectonic evolution of Iceland. By linearly extrapolating the four major southward rift propagations to Iceland we can estimate when they left Iceland. Two of these, that left Iceland at ca. 15 Ma and 6.5 Ma, coincide with the shut down of two well established paleo-spreading centers on Iceland (Vestfirðir and Snæfellsnes-Skagi, respectively). Rift propagation might have been initiated at these shut downs, because a local change in the tectonic geometry limited the supply of magma down the ridge. If

  14. 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.

  15. Tectonic evolution of the southern Levant margin since Mesozoic

    NASA Astrophysics Data System (ADS)

    Hardy, Clément; Homberg, Catherine; Eyal, Yehuda; Barrier, Éric; Müller, Carla

    2010-11-01

    Recognition of syndepositional faults and mechanical analysis of fault-slip data are used to reconstruct a high resolution tectonic evolution of Israel, and to characterize the stress fields associated with the major tectonic deformation events of this area since Mesozoic times. Syndepositional normal faults recognized in Mesozoic and Paleogene rocks indicate three extensive deformation phases that were active at least during Early Jurassic, Campanian, and Eocene times. Inversion of fault-slip data indicate that a NE-SW extension characterizes the two first events, whereas orientation of extension during the Eocene was N-S to NNE-SSW. Several scenarios are proposed to explain these newly documented normal faults. Measured faults also document synchronous strike-slip and reverse regimes. Unambiguous chronological relationships between fault-data and bedding attest that a WNW-ESE to NW-SE compression is associated with the Syrian Arc folding event during the Late Cretaceous times. This compression pursued during the development of the Dead Sea transform plate boundary but its relationship with Neogene structures is unclear. Fault-data suggest that folding during the Neogene was driven by a regional NNW-SSE compression. A minor NE-SW compression was also recognized but no compatible large-scale structures were found to date. We also show that the post-Pliocene normal faults developed under a NE-SW extension.

  16. 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.

  17. 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.

  18. Transpressional tectonics in the Marrakech High Atlas: Insight by the geomorphic evolution of drainage basins

    NASA Astrophysics Data System (ADS)

    Delcaillau, Bernard; Amrhar, Mostafa; Namous, Mustapha; Laville, Edgard; Pedoja, Kevin; Dugué, Olivier

    2011-11-01

    The Ouzzelarh Massif extends across the Marrakech High Atlas (MHA) and forms the highest elevated mountain belt. To better understand the evolution of collision-related topography, we present the results of a geomorphological study in which elevation changes generated by reactivated pre-Alpine (Variscan and Triassic-Jurassic) faults drive a landscape evolution model. We aim to evaluate the relationship between the geometry of the drainage network and the main fault systems in this region. New insight into geomorphological changes in drainage patterns and related landforms is based on geological fieldwork combined with DEM analysis. To quantitatively measure landscape features we used several classical geomorphic indices (spacing ratio, hypsometric curves and integral, stream frequency drainage, stream length-gradient). The Ouzzelarh Massif is bounded to the north by the Tizi N'Test Fault Zone (TTFZ) and to the south by the Sour Fault Zone (SFZ). These faults delimit a pop-up structure. By using the above geomorphic parameters, we ascertained that the Ouzzelarh Massif is affected by a high spatial variability of uplift. The actual landscape of the Ouzzelarh Massif reveals remnants of an uplifted ancient erosional surface and the heterogeneity of exposed rocks in the range explaining the possibility that the topographic asymmetry between north and south flanks is due to differences in lithology-controlled resistance to erosion. Drainage, topography and fault pattern all concur to show uplifted rhomboidal-shaped blocks. It exhibits high stream frequency drainage and uplift in separate tectonically-uplifted blocks such as Jebel Toubkal which is characterized by asymmetric drainage basins.

  19. The evolution of dwarf shrubs in alpine environments: a case study of Alchemilla in Africa

    PubMed Central

    Gehrke, Berit; Kandziora, Martha; Pirie, Michael D.

    2016-01-01

    Background and Aims Alpine and arctic environments worldwide, including high mountains, are dominated by short-stature woody plants (dwarf shrubs). This conspicuous life form asserts considerable influence on local environmental conditions above the treeline, creating its own microhabitat. This study reconstructs the evolution of dwarf shrubs in Alchemilla in the African tropical alpine environment, where they represent one of the largest clades and are among the most common and abundant plants. Methods Different phylogenetic inference methods were used with plastid and nuclear DNA sequence markers, molecular dating (BEAST and RelTime), analyses of diversification rate shifts (MEDUSA and BAMM) and ancestral character and area reconstructions (Mesquite). Key Results It is inferred that African Alchemilla species originated following long-distance dispersal to tropical East Africa, but that the evolution of dwarf shrubs occurred in Ethiopia and in tropical East Africa independently. Establishing a timeframe is challenging given inconsistencies in age estimates, but it seems likely that they originated in the Pleistocene, or at the earliest in the late Miocene. The adaptation to alpine-like environments in the form of dwarf shrubs has apparently not led to enhanced diversification rates. Ancestral reconstructions indicate reversals in Alchemilla from plants with a woody base to entirely herbaceous forms, a transition that is rarely reported in angiosperms. Conclusions Alchemilla is a clear example of in situ tropical alpine speciation. The dwarf shrub life form typical of African Alchemilla has evolved twice independently, further indicating its selective advantage in these harsh environments. However, it has not influenced diversification, which, although recent, was not rapid. PMID:26520565

  20. Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological-geophysical record of spreading and subduction in the Alps

    NASA Astrophysics Data System (ADS)

    Handy, Mark R.; Schmid, Stefan M.; Bousquet, Romain; Kissling, Eduard; Bernoulli, Daniel

    2010-10-01

    A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84 Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131 Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35 Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35 Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this

  1. 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.

  2. Tectonic evolution of the South Fiji Basin: UNCLOS helps tackle regional tectonics

    NASA Astrophysics Data System (ADS)

    Herzer, R.; Roest, W.; Barker, D.; Mortimer, N.; Mauffret, A.; Lafoy, Y.

    2005-12-01

    Marine surveys to study the evolution of remnant arcs and backarc basins north of New Zealand have been complemented by UNCLOS surveys by three countries - France, New Zealand and Australia - with potential extended continental shelf claims in the region. The UNCLOS factor allowed 9 cruises to focus on the region in the past 9 years, collecting approximately 30,000 km of seismic reflection (5,000 deep crustal), 263,700 sq km of swath bathymetry, and 70 dredge samples. Feedback through sharing or publishing data and joint participation allowed efficient planning and deployment of academic and UNCLOS cruises. Two models for South Fiji (SFB) and Norfolk (NB) basin evolution arise from current studies: at the level of the Three Kings Ridge - NB - southern SFB both involve Pacific trench roll-back and southward propagating spreading, but one also uses two subduction systems and arc-continent collision. Linked spreading of the NB and SFB is invoked in both models, but the veracity and geodynamics of the link are not investigated. A growing body of petrological and radiometric evidence and the tectonics of the New Zealand continental margin point to tandem Early Miocene spreading of the SFB and NB despite published magnetic interpretations that would confine SFB spreading to the Oligocene. The Franco-NZ NOUCAPLAC-1 cruise, the last cruise relevant to UNCLOS in this region, included a scientific objective to investigate the SFB-NB link in the critical area bounded by the Loyalty Ridge (LR), the Cook Fracture Zone (CFZ), the Bounty spreading centre (BSC) and the Julia Lineament (JL) with swath mapping, magnetics and seismic reflection. Initial results show a complex bathymetry where a possible link between the BSC and the CFZ involves ridge propagation, overlapping spreading centres, rift blocks and overprinting volcanoes. The link to the JL was not adequately tested due to sparse coverage. Closer to the LR, a thick, faulted sedimentary basin was found.

  3. 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.

  4. 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

  5. Tectonic evolution of the Pacific margin of Antarctica 1. Late Cretaceous tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Larter, Robert D.; Cunningham, Alex P.; Barker, Peter F.; Gohl, Karsten; Nitsche, Frank O.

    2002-12-01

    We present new Late Cretaceous tectonic reconstructions of the Pacific margin of Antarctica based on constraints from marine magnetic data and regional free-air gravity fields. Results from interpretation of new seismic reflection and gravity profiles collected in the Bellingshausen Sea are also incorporated in the reconstructions. The reconstructions show regional constraints on tectonic evolution of the Bellingshausen and Amundsen Seas following the breakup between New Zealand and West Antarctica. The breakup began at c. 90 Ma with the separation of Chatham Rise, probably accompanied by the opening of the Bounty Trough. Campbell Plateau separated from West Antarctica later, during chron 33r (83.0-79.1 Ma). A free-air gravity lineation northeast of Chatham Rise represents the trace of a triple junction that formed as a result of fragmentation of the Phoenix plate a few million years before Chatham Rise separated from West Antarctica. Remnants of the western fragment, the Charcot plate, are preserved in the Bellingshausen Sea. Subduction of the Charcot plate stopped before 83 Ma, and part of it became coupled to the Antarctic Peninsula across the stalled subduction zone. Subsequent convergence at the western margin of this captured ocean floor produced the structures that are the main cause of the Bellingshausen gravity anomaly. Part of a spreading ridge at the western boundary of the Phoenix plate (initially Charcot-Phoenix, evolving into Marie Byrd Land-Phoenix, and eventually Bellingshausen-Phoenix (BEL-PHO)) probably subducted obliquely beneath the southern Antarctic Peninsula during the Late Cretaceous. All of the Phoenix plate ocean floor subducted at the Antarctic Peninsula margin during the Late Cretaceous was probably <14 Myr old when it reached the trench. Several observations suggest that independent Bellingshausen plate motion began near the end of chron 33n (73.6 Ma). Reconstructions in which part of the West Antarctic continental margin, including

  6. Sediment storage quantification and postglacial evolution of an inner-alpine sedimentary basin (Gradenmoos, Schober Mountains, Austria)

    NASA Astrophysics Data System (ADS)

    Götz, J.; Buckel, J.; Otto, J. C.; Schrott, L.

    2012-04-01

    Knickpoints in longitudinal valley profiles of alpine headwater catchments can be frequently assigned to the lithological and tectonical setting, to damming effects through large (rockfall) deposits, or to the impact of Pleistocene glaciations causing overdeepened basins. As a consequence various sedimentary sinks developed, which frequently interrupt sediment flux in alpine drainage basins. Today these locations may represent landscape archives documenting a sedimentary history of great value for the understanding of alpine landscape evolution. The glacially overdeepened Gradenmoos basin at 1920 m a.s.l. (an alpine lake mire with adjacent floodplain deposits and surrounding slope storage landforms; approx. 4.1 km2) is the most pronounced sink in the studied Gradenbach catchment (32.5 km2). The basin is completely filled up with sediments delivered by mainly fluvial processes, debris flows, and rock falls, it is assumed to be deglaciated since Egesen times and it is expected to archive a continuous stratigraphy of postglacial sedimentation. As the analysis of denudation-accumulation-systems is generally based on back-calculation of stored sediment volumes to a specific sediment delivering area, most reliable results will be consequently obtained (1) if sediment output of the system can be neglected for the investigated period of time, (2) if - due to spatial scale - sediment storage can be assessed quantitatively with a high level of accuracy, and (3) if the sediment contributing area can be clearly delimited. All three aspects are considered to be fulfilled to a high degree within the Gradenmoos basin. Sediment storage is quantified using geophysical methods, core drillings and GIS modelling whereas postglacial reconstruction is based on radiocarbon dating and palynological analyses. Subject to variable subsurface conditions, different geophysical methods were applied to detect bedrock depth. Electrical resistivity surveying (2D/3D) was used most extensively as it

  7. Tectonic Evolution of Mozambique Ridge in East African continental margin

    NASA Astrophysics Data System (ADS)

    Tang, Yong

    2017-04-01

    Tectonic Evolution of Mozambique Ridge in East African continental margin Yong Tang He Li ES.Mahanjane Second Institute of Oceanography,SOA,Hangzhou The East Africa passive continental margin is a depression area, with widely distributed sedimentary wedges from southern Mozambique to northern Somali (>6500km in length, and about 6km in thickness). It was resulted from the separation of East Gondwana, and was developed by three stages: (1) rifting in Early-Middle Jurassic; (2) spreading from Late Jurassic to Early Cretaceous; (3) drifting since the Cretaceous period. Tectonic evolution of the Mozambique continental margin is distinguished by two main settings separated by a fossil transform, the Davie Fracture Zone; (i) rifting and transform setting in the northern margin related to opening of the Somali and Rovuma basins, and (ii) rifting and volcanism setting during the opening of the Mozambique basin in the southern margin. 2D reflection seismic investigation of the crustal structure in the Zambezi Delta Depression, provided key piece of evidence for two rifting phases between Africa and Antarctica. The magma-rich Rift I phase evolved from rift-rift-rift style with remarkable emplacement of dyke swarms (between 182 and 170 Ma). Related onshore outcrops are extensively studied, the Karoo volcanics in Mozambique, Zimbabwe and South Africa, all part of the Karoo "triple-junction". These igneous bodies flow and thicken eastwards and are now covered by up to 5 km of Cretaceous and Tertiary sediments and recorded by seismic and oil exploration wells. Geophysical and geological data recorded during oceanographic cruises provide very controversial results regarding the nature of the Mozambique Ridge. Two conflicting opinions remains open, since the early expeditions to the Indian Ocean, postulating that its character is either magmatic (oceanic) or continental origin. We have carried out an China-Mozambique Joint Cruise(CMJC) on southern Mozambique Basin on 1st June to

  8. 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

  9. 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.

  10. 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.

  11. Contrasting effects of winter and summer climate on alpine timberline evolution in monsoon-dominated East Asia

    NASA Astrophysics Data System (ADS)

    Cheng, Ying; Liu, Hongyan; Wang, Hongya; Piao, Shilong; Yin, Yi; Ciais, Philippe; Wu, Xiuchen; Luo, Yao; Zhang, Caina; Song, Yaqiong; Gao, Yishen; Qiu, Anan

    2017-08-01

    Alpine timberline is particularly sensitive to global climate change, with the danger of losing essential ecosystem services in high elevational regions. Its evolution is generally linked to annual average thermal regimes, and is regarded as an indicator of climate warming. However, the effect of uneven seasonal climate change stressed by the Hijioka et al. (2014) on alpine timberline dynamics in terms of both position migration and species composition remains unclear. Here, we documented approximately 6000 years of postglacial alpine timberline evolution on Mt. Tabai in the monsoon-dominated East Asian subtropical-temperate transition. We analyzed three high-resolution lacustrine sediment sequences located below, within, and above the current alpine timberline, an ecotone between the forest line and treeline, respectively. The timberline position appears to have varied coincidently with the temperature effect of cold East Asian Winter Monsoon (EAWM), implying that enhanced EAWM shortened the duration of the growing season and reduced forest survival at the alpine timberline. Unlike position migration, however, timberline species composition depends on summer precipitation. We found that drought-tolerant herb and shrub species were much more sensitive to variations in the water-bearing East Asian Summer Monsoon (EASM) than mesophytic trees at the alpine timberline. Our results suggest that prediction of future timberline dynamics should consider uneven seasonal climate changes.

  12. 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.

  13. Peculiarities of Quaternary tectonic evolution of the Altai Mountains

    NASA Astrophysics Data System (ADS)

    Agatova, Anna; Nepop, Roman

    2010-05-01

    The Altai Mountains form the northern part of the Central Asia orogenic belt and is a transpressional zone formed due to oblique thrusting. Its late Cenozoic reactivation is attributed to India-Eurasia collision, and to ongoing indentation India to Eurasia. Continued strain and stress build-up has been partly partitioned by propagation northward to Eurasia's interior along preexisting fault zones. Deformation along these zones has been responsible for building of the modern mountain belts. Geological and geomorphological data indicate that the impact of India-Eurasia collision on the northern Tien Shan, Altai and northern Kazakhstan regions showed up at 11, 5 and 3 Ma respectively. Along with the morphotectonic analysis, analysis of sediment fillings of intermountain depressions and piedmont plains we study the distribution and extension of the Pleistocene glaciations within the Altai Cenozoic uplift which reveal some peculiarities of tectonic evolution of the Altai Mountains: 1) Rejuvenation of the mountain systems within Altai Mountains in south-eastern direction which is opposite to the stress propagation related to India-Eurasia collision. 2) The simplification of neotectonic structure in south-eastern direction. Fan-like system of mountain ridges and intermountain depressions in Russian Altai is changed in Mongolian Altai by several contiguous, sub parallel mountain chains with the narrow lowerings between. Goby Altai is formed by far distant, separate ridges pierced through piedmont depressions. 3) Steep bench of base level of orogen between North- and South-Eastern parts of Russian Altai which was formed at the edge of the middle- and the late- Pleistocene. Clear-cut distinction of types of the middle Pleistocene glaciations in different parts of Altai Mountains argues for the fact that its orographic structure had been generally formed by the middle Pleistocene. At the same time drastic changes of glaciations type in the late Pleistocene (that occurred in

  14. Tectonic Evolution of the Eastern Hemisphere of Mars

    NASA Technical Reports Server (NTRS)

    Pounders, E.; Anderson, R. C.; Dohm, J. M.; Haldemann, A. F. C.; Golombek, M. P.

    2002-01-01

    The magmatic-tectonic history of Mars is largely dominated by the Tharsis magmatic complex of the western hemisphere and the Elysium rise of the eastern hemisphere. In order to address the history of Mars, the tectonic history of the eastern hemisphere must also be unraveled. Additional information is contained in the original extended abstract.

  15. Tectonic Evolution of the Eastern Hemisphere of Mars

    NASA Technical Reports Server (NTRS)

    Pounders, E.; Anderson, R. C.; Dohm, J. M.; Haldemann, A. F. C.; Golombek, M. P.

    2002-01-01

    The magmatic-tectonic history of Mars is largely dominated by the Tharsis magmatic complex of the western hemisphere and the Elysium rise of the eastern hemisphere. In order to address the history of Mars, the tectonic history of the eastern hemisphere must also be unraveled. Additional information is contained in the original extended abstract.

  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. MEVTV study: Early tectonic evolution of Mars: Crustal dichotomy to Valles Marineris

    NASA Technical Reports Server (NTRS)

    Frey, Herbert V.; Schultz, Richard A.

    1990-01-01

    Several fundamental problems were addressed in the early impact, tectonic, and volcanic evolution of the martian lithosphere: (1) origin and evolution of the fundamental crustal dichotomy, including development of the highland/lowland transition zone; (2) growth and evolution of the Valles Marineris; and (3) nature and role of major resurfacing events in early martian history. The results in these areas are briefly summarized.

  18. 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.

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

    PubMed

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

    2014-03-31

    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.

  20. 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

  1. Tectonic and sedimentary evolution of the Luna field area, Italy

    SciTech Connect

    Roveri, M. )

    1990-05-01

    The Luna gas field is located near Crotone (Calabria region, southern Italy) in a shallow-water/onshore area. It was discovered and put into production during the early 1970s. Up to now it has produced 19 {times} 10{sup 9} sm{sup 3} of gas; its productivity (50 {times} 10{sup 6} sm{sup 3}/y) has remained virtually unaltered since the beginning. The field is located on the axial culmination of a thrust-related anticline of the Apennine postcollisional thrust belt; it can be roughly subdivided into two areas characterized by different stratigraphic contexts. In the northern and central parts of the field is a structural trap. Reservoir rocks are Serravallian to Tortonian deep marine resedimented conglomerates and sandstones. These deposits represent part of the infill of a middle-upper Miocene foredeep. Reservoir rocks are now thrusted, eroded, and unconformably overlain by lower Pliocene shales, which are the most important seal in this part of the field. In the southern part of the field is a combination trap. Reservoir rocks are upper Tortonian shallow-water sandstones. They lap onto a Tortonian unconformity related to a tectonic phase which split the previous foredeep into minor piggyback basins. The upper Tortonian sandstones are overlain and sealed by Messinian shales and evaporites. Tectonosedimentary evolution of the area and, consequently, areal distribution and geometry of sedimentary bodies - both potential reservoirs and seals - have been reconstructed using a sequence stratigraphy approach. The sedimentary record has been informally subdivided into five main depositional sequences bounded by unconformities or their correlative conformities; classic facies analysis and petrophysical, seismic, and biostratigraphic data have been utilized to define the internal characteristics of each sequence.

  2. 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.

  3. 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.

  4. Magmato-tectonic Evolution of Asal Rift, Afar Depression

    NASA Astrophysics Data System (ADS)

    Pinzuti, P.; Manighetti, I.; Humler, E.

    2001-12-01

    We investigate the relationships between magmatic and tectonic activities during rifting, taking the example of Asal, one of the most recent and active rifts of Afar. We sampled and performed combined geochemical (major and trace elements) and paleomagnetic analyses of the successive basaltic lava flows (total: 48) exposed in three of the highest ( ~30-80 m) normal fault escarpments, on either side of the rift inner floor and of the Fieale volcano. Previous dating suggests that lava emplaced in the rift from ~300 ka on, and the piles we analyzed between ~110 and 90 ka. The chemical analyses (48 samples) reveal that all lava was poured out from the same shallow (< a few km) reservoir. Each pile is made of two to four distinct flow sets, each ~10 to 50 m-high and having slightly, hence rapidly evolved through low pressure crystallization. The chemical evolution from one flow set to the next suggests re-feeding of the reservoir (or slight cooling of the mantle). The paleomagnetic analyses (190 samples) reveal that each flow set was erupted very rapidly, as a pulse, in less than a ~thousand years. By contrast, the entire flow piles have properly recorded the secular variation of the magnetic field, including the Blake excursion. It results that, at least between ~110 and 90 ka, the magmatic activity occurred by pulses rapidly pouring out large volumes of lavas every 10+/-5 ka. At the sites analyzed, the lava accumulated during each pulse at a rate of ~1-5 cm/yr, much larger than the fault slip rates. One might conclude that flows continuously covered up and erased tectonic features during rifting. However, the long time-span which separates the initiation of the present rift faults ( ~50+/-20 ka) from the latest lava flows (on rift shoulders, ~90 ka) implies that these faults did not exist before, with the possible exception of those bounding the present inner floor. Rifting therefore occurred through dominant magmatic activity, at least from ~300 to 50 ka, when normal

  5. 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.

  6. Far field effects of Alpine plate tectonism in the Iberian microplate recorded by fault-related denudation in the Spanish Central System

    NASA Astrophysics Data System (ADS)

    de Bruijne, C. H.; Andriessen, P. A. M.

    2002-05-01

    Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events resulted in up to 2.8±0.9 km of denudation in the western Sierra de Gredos and 3.6±1.0 km in the central and eastern Gredos (assuming a paleogeothermal gradient of 28±5 °C and a surface temperature of 10 °C). The greatest amount of denudation (5.0±1.6 km) occurred in the Sierra de Guadarrama. Accompanying rock uplift was 4.7±1.0 and 5.9±1.6 km in the eastern Gredos and Guadarrama, respectively. Most denudation in the Gredos occurred from the Middle Eocene to the Early Miocene and can be related to the N-S stress field, induced by the Pyrenean compression. In the Guadarrama, the greatest denudation was Pliocene to Recent of age and seems related to the ongoing NW-SE Betic compression. The fact that the formation of the E-W trending Gredos coincides with the N-S Pyrenean compression and the creation of the present day morphology of the NE-SW trending Guadarrama with the younger NW-SE Betic compression, indicates that they record the far field effects of Alpine plate tectonics on Iberia. The trend of pre-existing lineaments was of major importance in influencing the style and magnitude of these of far field effects.

  7. The Evolution of Paleostress Fields Adjacent to the Transpressional Alpine Fault in Southwest New Zealand

    NASA Astrophysics Data System (ADS)

    Judge, P.; Klepeis, K.

    2006-05-01

    The Alpine Fault in southwestern New Zealand is part of the transpressional Australia-Pacific plate boundary. Paleostress analyses using fault-slip data from a 400 km2 area of the Darran Mountain, southeast of the Alpine Fault near Milford Sound, reveal both spatial and temporal variations in Tertiary paleostress fields. The northern margin of the Darran Range, within 15 km of the Alpine Fault, records mostly dextral, oblique strike- slip, and thrusts faults. Diorite along this margin also preserves evidence of distributed ductile deformation, recrystallization, and fluid-induced retrogression. The deviatoric stress solution that satisfies the majority of faults from this region has a nearly horizontal west-northwest trending (285° - 295°) axis of maximum compression (σ1). This solution agrees well with published σ1 axes from paleostress data elsewhere along the central (σ1=126° ± 10°) and the northern (σ1=290° - 300°) parts of the Alpine Fault. This σ1 orientation is also congruent with published P-axes determined from earthquakes in southwestern New Zealand. Approximately 25 - 40 km south of the Alpine Fault, normal faults in the central Darran Range record NE-SW directions of subhorizontal extension. These normal faults are consistently cross-cut by widely-spaced (500 - 1000 m) dextral strike-slip and oblique-slip faults. The stress solution that satisfies the majority of the strike-slip faults in this distal region shows a σ1 direction that plunges gently towards the NE (035° - 045°), and a SE-trending (125° - 135°) axis of minimum compression (σ3). We interpret the differences in structure and paleostress states in the Darran Mountains to reflect the superposition of several stress regimes. The stress regime preserved closest to the Alpine Fault is the youngest. Cross-cutting relationships and good agreement between this stress state and P-axes from earthquakes suggest that the west-northwest directions of maximum compression are similar to

  8. 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

  9. Lunar mascon basins - Lava filling, tectonics, and evolution of the lithosphere

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Head, J. W.

    1980-01-01

    The paper extends the study of the relationships among lunar mare filling, mare basin tectonics, and global thermal evolution to the major mascon maria: Imbrium, Crisium, Orientale, Humorum, Nectaris, Smythii, Grimaldi, and Serenitatis. For each of the eight major mascon mare basins on the moon, the paper describes the distribution and history of major mare units, the characteristics and geometry of basin-related tectonic features, the temporal relations between tectonic features and geologic units, the response of the lunar lithosphere to basalt loading as a function of space and time, and the relationship between loading stress and global thermal stress in controlling lunar tectonic history. The principal features of the volcanic, tectonic, and thermal history of the mascon maria are summarized.

  10. Lunar mascon basins - Lava filling, tectonics, and evolution of the lithosphere

    NASA Astrophysics Data System (ADS)

    Solomon, S. C.; Head, J. W.

    1980-02-01

    The paper extends the study of the relationships among lunar mare filling, mare basin tectonics, and global thermal evolution to the major mascon maria: Imbrium, Crisium, Orientale, Humorum, Nectaris, Smythii, Grimaldi, and Serenitatis. For each of the eight major mascon mare basins on the moon, the paper describes the distribution and history of major mare units, the characteristics and geometry of basin-related tectonic features, the temporal relations between tectonic features and geologic units, the response of the lunar lithosphere to basalt loading as a function of space and time, and the relationship between loading stress and global thermal stress in controlling lunar tectonic history. The principal features of the volcanic, tectonic, and thermal history of the mascon maria are summarized.

  11. Lunar mascon basins - Lava filling, tectonics, and evolution of the lithosphere

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Head, J. W.

    1980-01-01

    The paper extends the study of the relationships among lunar mare filling, mare basin tectonics, and global thermal evolution to the major mascon maria: Imbrium, Crisium, Orientale, Humorum, Nectaris, Smythii, Grimaldi, and Serenitatis. For each of the eight major mascon mare basins on the moon, the paper describes the distribution and history of major mare units, the characteristics and geometry of basin-related tectonic features, the temporal relations between tectonic features and geologic units, the response of the lunar lithosphere to basalt loading as a function of space and time, and the relationship between loading stress and global thermal stress in controlling lunar tectonic history. The principal features of the volcanic, tectonic, and thermal history of the mascon maria are summarized.

  12. 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

  13. The tectonic evolution of the Irtysh tectonic belt: New zircon U-Pb ages of arc-related and collisional granitoids in the Kalaxiangar tectonic belt, NW China

    NASA Astrophysics Data System (ADS)

    Hong, Tao; Klemd, Reiner; Gao, Jun; Xiang, Peng; Xu, Xing-Wang; You, Jun; Wang, Xin-Shui; Wu, Chu; Li, Hao; Ke, Qiang

    2017-02-01

    Precise geochronological constraints of the Irtysh tectonic belt situated between the Saur Island Arc and the Altay Terrane are crucial to a better understanding of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Recently, we discovered repeatedly deformed arc-related and collisional granitoids in the Kalaxiangar tectonic belt (KTB), which is located in the eastern part of the Irtysh tectonic belt. In this study, we report new whole-rock geochemical, zircon U-Pb and Hf isotopic data of the arc-related and collisional granitoids. Our data reveal that 1) arc-related granodioritic porphyries formed at ca. 382-374 Ma. Recrystallized zircon grains from a (ultra-)mylonitic granodiorite of the Laoshankou zone in the southern KTB display a U-Pb age of ca. 360 Ma; 2) syn-collisional granodioritic porphyries, which distribute along faults and parallel to the cleavage, were emplaced at ca. 367-356 Ma, with εHf(t) values varying from + 7.8 to + 14.2 and Hf model ages from 873 to 459 Ma; 3) a post-collisional A-type granodioritic porphyry, which crosscuts the NW-NNW trending schistosity of the metasedimentary country rocks at a low angle, has an age of ca. 324-320 Ma, while the εHf(t) values range from + 7.6 to + 14.4 with Hf model ages from 850 to 416 Ma; 4) post-collisional strike-slip A-type granite dykes, exposed along strike-slip faults, gave ages between 287 and 279 Ma, whereas the εHf(t) values range from + 4.9 to + 12.7 and the Hf model ages from 995 to 500 Ma; and 5) A-type biotite granite dykes, which intruded along conjugate tension joints, have ages of 274-271 Ma, and εHf(t) values from + 1.5 to + 13.2 with Hf model ages from 1196 to 454 Ma. Consequently, we propose that the collision between the Saur Island Arc and the Altay Terrane occurred in the Early Carboniferous (ca. 367-356 Ma) and the subsequent post-collisional tectonic process continued to the Late Carboniferous (ca. 324-320 Ma). It is further suggested that the Irtysh tectonic belt

  14. 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.

  15. Tectonic evolution of the Arctic shelf of Siberia from Riphean through Mesozoic time

    SciTech Connect

    Gramberg, I.S.; Kos'ko, M.K.; Pogrebitskiy, Yu.E.

    1986-08-01

    Paleotectonic structures are a most important factor to be considered during geological exploration for oil, gas, and other mineral resources, particularly for studies in the vast, but poorly accessible Arctic shelves. The authors have treated the paleotectonic evolution of the Arctic shelves of Siberia on the basis, of a three-dimensional tectonic model of the region, which consists of an assemblage of tectonic maps for specific stages, each representing a specific surface within the sedimentary-metamorphic envelope. The surfaces mapped in each case correspond to the top of one of the tectonic megacomplexes (Baykalian, Caledonian, and early Hercynian, late Hercynian, and Mesozoic) and reflect levels of the most significant gross changes in the crustal evolution of Siberia. The megacomplexes in their turn consist of tectonic complexes, separable on the basis of structural-material characteristics, which reflect a particular tectonic regime. As a synthesis of modern geological and geophysical data, the assemblage of tectonic maps depicts the principal features of the evolution of the Arctic shelves in Siberia during the Riphean-Mesozoic interval, that is, prior to the development of the oceanic basins and the formation of a specific syn-oceanic complex of Danian-Quaternary sediments on the shelves. 15 references.

  16. 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.

  17. Late Cenozoic Tectonic Evolution of the Northern Himalaya, China

    NASA Astrophysics Data System (ADS)

    Zhang, J.

    2009-12-01

    After the India-Asia collision and the following thickening, the northern Himalaya began experiencing extensional tectonics since Eocene-Oligocene transition. Both the two-mica granite caused by thickening melting in the northern Himalayan gneiss domes and the leucogranite intruding along the STDS give the same U-Pb age of about 35Ma. This indicates a tectonic transition from thickening to extension along the northern Himalaya at this time, and the STDS might begin to be active since then, which is much earlier than the results of current studies. The thrusting and thickening before 35Ma caused the partial melting in middle-lower crust, which formed the weak root of the thickened crust or the so-called “channel flow”. This “channel flow” triggered the collapse of the orogen and the onset of the extensional tectonics of the STDS. The melts intruded along the STDS, forming the leucogranite with the older ages of around 35Ma. The STDS’s extension and the resultant thinning led to the further partial melting of the crust, which caused the larger-scale magmatism related to the emplacement of leucogranite in Miocene. The diapirism of these leucogranites formed the northern Himalayan gneiss domes which exposed the greater Himalayan crystalline complex and the shear zones of the STDS in northern Himalaya. A change in tectonic regime happened in northern Himalaya at about 13Ma, when the N-S extension of the STDS ceased and gave the way to E-W extension of the N-trending rifts. This change possibly represent the start of the eastward channel flowing, or a change of the convergent velocity between India and Asia.

  18. 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

  19. Morphometric analysis of El Salvador Fault Zone. Implications to the tectonic evolution. Central America.

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    It is considered that the study of the recent topography development, and the use of geomorphological indexes are good tools for the quantification of the active tectonics. We have used quantitative geomorphology in order to improve our understanding of the recent activity and tectonic evolution of the El Salvador Fault Zone (ESFZ); an E-W oriented strike-slip fault zone that extends 150 km through El Salvador (Martínez-Díaz et al. 2004). Previous studies propose a transtensive tectonic regime at the Central America Volcanic Arc in El Salvador, which induces relative vertical motions on the faults within El Salvador Fault Zone (i.e. Álvarez-Gómez et al., 2008, Cáceres et al. 2005,). This relative vertical displacement can be quantified with the use of hypsometry as a geomorphological character. The morphometric analysis done contributes to a better understanding of the ESFZ. We have defined km scale tectonic block relative displacements that may be useful to constrain the strain distribution along the ESFZ, length of segments with homogeneous vertical movements and lateral relay of active structures. This study supports the hypothesis of a recent migration in the maximum shortening direction, and the accomodation of the current deformation through the reactivation of pre-existing structures inherited from a previous tectonic frame. A similar tectonic evolution as described Weinberg (1992) in Nicaragua, is interpreted from the results of this study.

  20. Plate motion and the evolution of Alpine Corsica and Northern Apennines

    NASA Astrophysics Data System (ADS)

    Argnani, Andrea

    2012-12-01

    The polarity of subduction in the Corsica-Northern Apennine system is a long-debated issue. Models adopting an original W-dipping subduction and models preferring a flip in the polarity of subduction, from E-dipping to W-dipping present inconsistencies that are mainly due to the 2D approach. A new proposal is presented, using Late Cretaceous to Present-Day kinematic reconstructions of the Central Mediterranean. A wide oceanic embayment is required to the west of the Adriatic Promontory, to account for the Oligocene-Present calcalkaline volcanism and back-arc extension. This implies that the continental collision that originated the Alps s.s. could not continue SW-ward of Adria. The change in subduction polarity, going from the Alps, to the Apennines, is taken as on original feature since the beginning of convergence. Kinematic reconstructions show that the point where subduction polarity changes moved N-ward along the plate boundary, from Late Cretaceous to Eocene. As a result, areas that previously experienced the continental collision of the Adriatic Promontory were subsequently affected by the oceanic subduction of the Tethyan embayment. This sequence of events caused the collapse of Alpine Corsica and led to the opening of the Balearic back-arc basin. A similar kinematic evolution is ongoing in Taiwan, where the N-ward subduction of the Philippine Sea plate is progressively substituting the E-ward subduction of the Eurasian plate, causing the collapse of the orogen in northern Taiwan. The slivers of continental basement rocks that are encased within the uppermost nappe in Corsica have been interpreted as remnants of a microplate that collided with Corsica. Plate kinematics offers an alternative explanation, with these basement rocks being derived from the colliding Adriatic promontory during Paleocene-Eocene; the promontory then passed away laterally, allowing the juxtaposition of the Alpine belt of Corsica with the early Apennines.

  1. Tectonic Evolution of Bell Regio, Venus: Regional Stress, Lithospheric Flexure, and Edifice Stresses

    NASA Astrophysics Data System (ADS)

    Rogers, P. G.; Zuber, M. T.

    1996-03-01

    Analyses of the tectonic features associated with large volcanoes provide important insight into the relationship between volcanic and tectonic processes and the stress state of a planet's crust over time, and provide constraints on the local and regional geologic evolution. This investigation focuses on the tectonism and volcanism of Bell Regio, a major highland uplift n Venus. The stress environments and resulting tectonic features associated with the major volcanic edifices in this region are examined using Magellan ynthetic aperture radar (SAR) images and altimeter measurements of topography. The major volcanoes of Bell Regio, Tepev Mons and the "Eastern Volcanic Center" (EVC), exhibit tectonic characteristics that are unique relative to other volcanic edifices on Venus. The most prominent distinctions are the lack of large rift zones within the overall highland uplift and the presence of radial tectonic and concentric fractures associated with the major edifices. This study examines the regional stress field in Bell Regio through analysis of structural features believed to be a consequence of lithospheric flexure due to volcanic loading and tectonic features that likely resulted from edifice stresses associated with magma chamber inflation.

  2. 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

  3. 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

  4. ERTS-1, earthquakes, and tectonic evolution in Alaska

    NASA Technical Reports Server (NTRS)

    Gedney, L.; Vanwormer, J.

    1974-01-01

    In comparing seismicity patterns in Alaska with ERTS-1 imagery, it is striking to see the frequency with which earthquake epicenters fall on, or near, lineaments visible on the imagery. Often these lineaments prove to be tectonics faults which have been mapped in the field. But equally as often, existing geologic and tectonic maps show no evidence of these features. The remoteness and inaccessibility of most of Alaska is responsible, in large part, for the inadequacy of the mapping. ERTS-1 imagery is filling a vital need in providing much of the missing information, and is pointing out many areas of potential earthquake hazard. Earthquakes in central and south-central Alaska result when the northeastern corner of the north Pacific lithospheric plate underthrusts the continent. North of Mt. McKinley, the seismicity is continental in nature and of shallow origin, with earthquakes occurring on lineaments, and frequently at intersections of lineaments. The shallower events tend to align themselves with lineaments visible on the imagery.

  5. Tectonic evolution of the West Junggar Region, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Feng, Y.; Coleman, R. G.; Tilton, G.; Xiao, X.

    1989-08-01

    The West Junggar region of northwestern China consists of a Hercynian-age fold belt occupying a late Paleozoic zone of convergence between three major Eurasian plates: Siberian, Tarim, and Kazakhstan. The northern part of the West Junggar area includes part of the Irtysh-Zaysan fold belt that extends to the northwest into the USSR, where it marks a broad boundary between the Siberian and Kazakhstan plates. The central part of the West Junggar area includes the southeastern extension of the Chingiz-Tarbgatay early Paleozoic island arc sequence. The southern part of the West Junggar area is truncated by the deep fundamental Junggar-Alakol fault that has brought the Yili microplate into juxtaposiition with the West Junggar region in the vicinity of Ebin Nur Lake. To the east the Junggar area is covered by sediments of the Junggar Basin. Paleogeographic reconstructions and geologic evidence indicates that these plates began converging in the Middle Carboniferous, and by Late Carboniferous alkali granites began invading the imbricated leading edges of the coalescing plates. Paleomagnetic data reveals that the plates continued to move along strike-slip faults, bringing the Tarim plate and Yili microplate into their present positions sometime in the early Mesozoic. Six separate ophiolite occurrences in the West Junggar region are strongly tectonized and dismembered. The Tangbale ophiolite is considered to be Late Cambrian (508 ± 20 Ma.) and represents the earliest known oceanic crust in Western China. Petrologic and chemical data indicate that the Tangbale ophiolite represents a possible back arc or forearc tectonic setting situated close to a developing island arc. The Darbut ophiolite has been tectonized to a melange and is overlain by Late Devonian flysch. Ages of the radiolaria in the cherts associated with the pillow lavas indicate that it formed in the Middle Devonian. Other occurrences of ophiolite melange in the northern part of the West Junggar region may be as

  6. Hot-spot evolution and the global tectonics of Venus

    SciTech Connect

    Phillips, R.J.; Grimm, R.E. ); Malin, M.C. )

    1991-05-03

    The global tectonics of Venus may be dominated by plumes rising from the mantle and impinging of the lithosphere, giving rise to hot spots. Global sea-floor spreading does not take place, but direct convective coupling of mantle flow fields to the lithosphere leads to regional-scale deformation and may allow lithospheric transport on a limited scale. A hot-spot evolutionary sequence comprises (1) a broad domal uplift resulting from a rising mantle plume, (2) massive partial melting in the plume head and generation of a thickened crust or crustal plateau, (3) collapse of dynamic topography, and (4) creep spreading of the crustal plateau. Crust on Venus is produced by gradual vertical differentiation with little recycling rather than by the rapid horizontal creation and consumption characteristic of terrestrial sea-floor spreading.

  7. Distinct phases of eustatic and tectonic forcing for late Quaternary landscape evolution in southwest Crete, Greece

    NASA Astrophysics Data System (ADS)

    Mouslopoulou, Vasiliki; Begg, John; Fülling, Alexander; Moraetis, Daniel; Partsinevelos, Panagiotis; Oncken, Onno

    2017-09-01

    The extent to which climate, eustasy and tectonics interact to shape the late Quaternary landscape is poorly known. Alluvial fans often provide useful indexes that allow the decoding of information recorded on complex coastal landscapes, such as those of the eastern Mediterranean. In this paper we analyse and date (using infrared stimulated luminescence (IRSL) dating) a double alluvial fan system on southwest Crete, an island straddling the forearc of the Hellenic subduction margin, in order to constrain the timing and magnitude of its vertical deformation and discuss the factors contributing to its landscape evolution. The studied alluvial system is exceptional because each of its two juxtaposed fans records individual phases of alluvial and marine incision, thus providing unprecedented resolution in the formation and evolution of its landscape. Specifically, our analysis shows that the fan sequence at Domata developed during Marine Isotope Stage (MIS) 3 due to five distinct stages of marine transgressions and regressions and associated river incision, in response to sea-level fluctuations and tectonic uplift at averaged rates of ˜ 2.2 mm yr-1. Interestingly, comparison of our results with published tectonic uplift rates from western Crete shows that uplift during 20-50 kyr BP was minimal (or even negative). Thus, most of the uplift recorded at Domata must have occurred in the last 20 kyr. This implies that eustasy and tectonism impacted the landscape at Domata over mainly distinct time intervals (e.g. sequentially and not synchronously), with eustasy forming and tectonism preserving the coastal landforms.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. Tectonic evolution and mantle structure of the Caribbean

    NASA Astrophysics Data System (ADS)

    van 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

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Neodymium isotope constraints on the tectonic evolution of East Gondwana

    NASA Astrophysics Data System (ADS)

    Harris, N. B. W.; Bartlett, J. M.; Santosh, M.

    East Gondwana incorporates a collage of polymetamorphic terrains with long-lived tectonic histories from the Early Archaean to the Neoproterozoic. The oldest cratonic areas have been identified in South India (north of the Palghat-Cauvery shear zone) and East Antarctica (the Napier Complex). These terrains are remnants of an East Gondwana craton that underwent initial crustal growth during the Early Archaean and granulite-facies metamorphism at ˜2.5 Ga. Both were virtually unaffected by the Pan-African orogeny (1.1-0.5 Ga). In contrast, Proterozoic terrains were subject to high-grade metamorphism during the Pan-African event. On the basis of published Nd model ages, a direct correlation can be made between southern Madagascar (south of the Ranotsara shear zone), southern India (the Madurai Block and Kerala Khondalite Belt) and the Highland/Southwestern Complex of Sri Lanka, which comprise a Later Archaean-Palaeoproterozoic (3.2-2.0 Ga) mobile belt that may extend eastwards into East Antarctica. The youngest period of crustal growth in East Gondwana has been recognised at 1.5-0.8 Ga from isotopic studies of the Mozambique Belt of East Africa, the Vijayan Complex of Sri Lanka and the Yamato-Belgica Complex/Sør Rondane Mountains of East Antarctica. Small slivers of terrain of intermediate age (1.9-1.2 Ga) have been recognised in South India (Achankovil metasediments) and Sri Lanka (Wanni Complex) that may represent mixed-age contributions to clastic sedimentary basins.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. Tectonic structure and post-Hercynian evolution of the Serre, Calabrian Arc, southern Italy: Geological, petrological and radiometric evidences

    NASA Astrophysics Data System (ADS)

    Moro, Aldo Del; Paglionico, Antonio; Piccarreta, Giuseppe; Rottura, Alessandro

    1986-04-01

    Conflicting opinions exist concerning the structure and the post-Hercynian evolution of the Serre. The present paper deals with these topics on the basis of new geological, petrological and radiometric evidence. The composition of the so-called Stilo and Polia-Copanello units has been redefined. The above domains—former sections of upper and lower Palaeozoic continental crust respectively—came into contact, due to transcurrent movements 130-140 Ma ago. A significant vertical component during the transcurrent movements, probably, exhumed the former section of lower crust. The above domains, juxtaposed, were successively involved as a single kinematic body in the Alpine orogenesis. The results enable us to make inferences for the Calabrian Arc evolution and call attention to similarities between an Austro-Alpine element (Stilo + Polia-Copanello) of the Calabrian chain and a South-Alpine sector of the Alps (Ivrea + Ceneri zones).

  6. 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)

  7. Animation of the Tectonic Evolution of the Southwest Pacific

    NASA Astrophysics Data System (ADS)

    Lawver, L. A.; Gahagan, L. M.

    2002-12-01

    The marginal and back arc basins of the southwestern Pacific cover a region from almost the equator south to 40°S and from 150°E to 175°W. Included in this region is the well-studied Tasman Sea which ranges in age from Late Cretaceous to Early Eocene with its distinct abandoned spreading center clearly showing in the satellite-derived gravity data. The Coral Sea, also with a distinct abandoned seafloor spreading center is dated as Paleocene to Early Eocene. Opening of these two marginal basins set the stage for the development of the Fiji Basins/Lau Basin complex of back-arc basins. 'Eua, a volcanic arc island on the Tonga Arc, is dated from at least Middle Eocene. It rode outward as the southwestern Pacific back-arc and marginal basins opened behind it and indicates that subduction was on-going through most of the Cenozoic. While subduction zones make closure of plate circuits difficult, a reasonable plate tectonic scenerio for the southwestern Pacific will be presented in a global context. The impact of large igneous provinces [LIPs], such as the Ontong Java, as well as possible hotspot tracks on the southwestern Pacific will be considered. Prior to the opening of the Eocene and younger, southwestern Pacific back-arc basins, the west-dipping subduction zone that existed beneath the Lord Howe Rise - Three Kings Rise region was roughly sub-parallel to the magnetic isochrons found in the Central Pacific from anomalies C30 [~66 Ma] to C7 [~25 Ma]. These magnetic lineations between the major Galapagos and Resolution fracture zones disappear after C7 and only conclusively reappear after C4 [~7 Ma] with a different trend that is now roughly subparallel to the present day orientation of the Tonga-Kermadec trench. It is possible that the opening of the southwestern marginal basins and the reorientation of the westward-dipping subduction zone had a profound effect on the spreading direction of the East Pacific Rise.

  8. 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.

  9. 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.

  10. Prograde evolution of the Scottish Caledonides and tectonic implications

    NASA Astrophysics Data System (ADS)

    Ashley, Kyle T.; Thigpen, J. Ryan; Law, Richard D.

    2015-05-01

    Recent thermometric analyses of samples collected in thrust-parallel structural transects across the Scandian (435-415 Ma) orogenic wedge in northwest Scotland provide a comprehensive characterization of the synorogenic retro-wedge thermal architecture. However, the paucity of petrologically-important metamorphic mineral phases (e.g., staurolite, Al-silicates) has limited investigation of pressure-temperature (P-T) histories, which hinders our ability to examine the nature of orogen-scale kinematic and thermal coupling. New data collected along a foreland-to-hinterland transect from the Moine to the Naver thrust sheets provides additional constraints for characterizing the prograde metamorphic evolution. In addition, we characterized Ti diffusion profiles in quartz inclusions in garnet to constrain duration of metamorphic heating. These results are used to develop coupled kinematic-thermal models of Scandian orogenic evolution. Early garnet core growth conditions are constrained by isopleth intersections, with peak P-T estimates determined by conventional exchange and net transfer thermobarometry and thermodynamic calculations. Most samples follow normal prograde heating and burial profiles, with peak conditions of 450 °C and 5.0 kbar in the immediate hanging wall to the Moine thrust, increasing in temperature and pressure to 733 °C and 9.5 kbar in the immediate hanging wall to the Naver thrust. These normal prograde pressure trajectories are interpreted to reflect burial of incipient thrust sheets beneath the overriding wedge at the leading edge of the orogen. Prograde heating coeval with burial is interpreted to result from surface-directed isotherm perturbation due to thrust-related advection in the overriding wedge. One exception to this is a sample from the top of the Moine thrust sheet, where prograde heating occurs during decompression (540 °C and 8.1 kbar to 590 °C and 7.0 kbar). In this case, the short lag times between motion on the Moine and Ben Hope

  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. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. 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.

  18. The Tectonic and Volcanic Evolution of Ganymede and its Implications for the Satellite's Internal Structure and Evolution.

    NASA Astrophysics Data System (ADS)

    Murchie, Scott Lawrence

    Volcanism and tectonic deformation on Ganymede were separated on the basis of relative age into three broad episodes, each of which was characterized in detail. These observations were used to test multiple models of the relationship of surface features to the satellite's internal structure and evolution. This analysis results in the following model for Ganymede's volcanic and tectonic history: Dark terrain was emplaced at least 3.8 Gyr ago, by accumulation of dark volcanic materials to a global average thickness of about 5 km. Two large systems of radial and concentric furrows, one each in the sub-Jovian and anti-Jovian hemisphere, formed throughout this period by endogenic extensional tectonic reactivation of impact-generated fracture zones. Younger and thicker dark volcanic materials accumulated within a geologically "anomalous" region around 25^ circS,122^circW, within which tectonic deformation was also more concentrated. At the end of dark-material volcanism a third furrow system formed, and is characterized by a radius of over 5000 km and an arrangement of troughs radial to the coordinates given above. Ganymede underwent a fundamental change in the style of its tectonics and volcanism at least 3.8 Gyr ago. Initially, large lithospheric blocks underwent significant shear offsets, accompanied by pervasive deformation of reticulate and lineated terrains. Light material then began to be emplaced, in close association with formation of U-shaped tectonic grooves. The oldest or nearly oldest light materials accumulated in the geologically anomalous region as a distinct terrain type. As grooved and light terrain formation became widespread, they occurred in a three-stage sequence that is recognizable across large areas. Groove formation was initiated by reactivation of preexisting structures, including both furrows and an additional global lithospheric "fabric" that may be related to tidal despinning. It is proposed that this sequence of tectonism and volcanism

  19. Aspects of sedimentary basin evolution assessed through tectonic subsidence analysis. Example: northern Gulf of Thailand

    NASA Astrophysics Data System (ADS)

    Pigott, John D.; Sattayarak, Nares

    Tectonic subsidence and subsidence rate analyses were conducted using a forward burial technique for the Cenozoic sediments of the northern Gulf of Thailand, a region presently bounded and intersected by major strike-slip fault systems. Basins represented by the seven wells studied are the Thon Buri, Hua Hin, Chumphon, Kra, and Pattani basins. The total observed subsidence was stratigraphically calibrated using well biostratigraphy and/or regional seismic stratigraphy. Tectonic subsidence was subsequently determined assuming local Airy isostasy by correcting decompacted sediments for sediment loading and variations in paleowater depths. Statistical comparison of the observed tectonic subsidence profile versus the theoretical thermal subsidence profile reveals zero-intercept times of incipient thermal-rifting and furthermore helps differentiate times of thermal subsidence from episodes of fault-controlled mechanical subsidence. Differences in tectonic subsidence, tectonic subsidence rates, and in the zero-intercept times of thermal rifting imply the Paleogene thermal associated rifting of the northern Gulf of Thailand was neither restricted spatially nor universally synchronous among the basins, but instead both spatially and time transgressive. Although coupled thermal-mechanical subsidence played a major role in the evolution for most of these basins, in some basins, e.g. the Thon Buri and northern Kra basins, subsidence was not thermally initiated. Instead, these basins experienced relatively slow-paced sediment loaded subsidence until a sudden fault-associated acceleration commenced in the Pliocene. Additional evidence for temporal and spatial changes in local strain is demonstrated by observed asynchronous episodes of "see-saw" subsidence-uplift of the basin floors. For example, while the northern Hua Hin Basin experienced Miocene-Pliocene alternations of subsidence and uplift, portions of the Pattani Basin to the southeast underwent periods of subsidence and

  20. Tectonic evolution of the offshore Sarawak and Sabah Basins, Northwest Borneo

    SciTech Connect

    Hazebroek, H.; Tan, D.; Swinburn, P. )

    1994-07-01

    The offshore Sarawak and Sabah Basins, northwest Borneo, contain up to 12 km of Oligocene to Holocene sediments. On the basis of marked different structural styles and stratigraphy, these basins can be divided into 13 tectono-stratigraphic provinces. Many of these, e.g., Balingian southwest Luconia, central Luconia, Baram delta, inboard belt, and outboard belt, are proven hydrocarbon provinces. Stratigraphically, these provinces generally become younger toward the northwest and/or northeast, with the older provinces overlying unconformably the Paleogene Rajang Group deep-marine sediments in the south. There is a great variation in structural styles. However, general structural trends can be recognized in that the older provinces in the southeast, e.g., Balingian, updip part of Baram delta, Rajang Group fold and thrust belt, inboard belt, and outboard belt, have been subjected to strong compressional tectonics, whereas the younger provinces in the northwest, e.g., central Luconia, north Luconia, southwest Luconia, and the central part of the Baram delta, have undergone predominantly extensional tectonics. The tectonic evolution of these provinces from late Eocene to Holocene, relative to the postulated subduction zones and major tectonic lineations recognized in the region, are discussed.

  1. 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.

  2. 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.

  3. Tectonic evolution of West Junggar (NW China): implications for accretionary orogens processes in Central Asia

    NASA Astrophysics Data System (ADS)

    Choulet, Flavien; Faure, Michel; Chen, Yan; Cluzel, Dominique; Wang, Bo; Lin, Wei

    2014-05-01

    Understanding the development and evolution of accretionary orogens is crucial for characterizing continental crust growth in time and space. In the Altaids tectonic collage of Central Asia, conflicting geodynamic models have been proposed about the Paleozoic evolution, during which juvenile continental crust has been extensively formed. This study focuses on West Junggar (NW China), a key region that has not been extensively studied yet. A multidisciplinary approach, including detrital zircon provenance study, geochemistry, field structural analysis and paleomagnetism provides new constraints on the Paleozoic evolution of West Junggar. Oceanic subduction predominates in Early Paleozoic time, as indicated by ophiolitic mélanges, fore-arc volcaniclastic turbidites and magmatic arc suites. However, the development of an olistostrome supplied by a sub-contemporaneous carbonate platform, the occurrence of continental molasse, and the chronology and geochemistry of magmatic events reveal interruptions of subduction. Discrete collisions of volcanic arcs and micro-continent are inferred from the tectonic structure of the belt, which displays allochthonous units rooted in the suture zone. Early Paleozoic magmatic and sedimentary rocks of West Junggar bear some resemblance to contemporaneous analogues in Eastern Kazakhstan, and suggest a lateral connection. During Late Paleozoic, tectonic features that develop in response to plate convergence are strongly controlled by geometry of two new subduction zones. A Carboniferous accretionary complex composed of fore-arc sedimentary rocks and ophiolitic mélanges has been identified. The occurrence of quasi-synchronous upright folds and folds with vertical axes suggests that transpression plays a significant role in the Late Paleozoic tectonic evolution of the West Junggar. Latest Carboniferous (ca. 300 Ma) alkaline plutons postdate this early phase of folding, which was synchronous with accretion of the Carboniferous complex. The

  4. 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.

  5. 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.

  6. The tectonic evolution of the southeastern Terceira Rift/São Miguel region (Azores)

    NASA Astrophysics Data System (ADS)

    Weiß, B. J.; Hübscher, C.; Lüdmann, T.

    2015-07-01

    The eastern Azores Archipelago with São Miguel being the dominant subaerial structure is located at the intersection of an oceanic rift (Terceira Rift) with a major transform fault (Gloria Fault) representing the westernmost part of the Nubian-Eurasian plate boundary. The evolution of islands, bathymetric highs and basin margins involves strong volcanism, but the controlling geodynamic and tectonic processes are currently under debate. In order to study this evolution, multibeam bathymetry and marine seismic reflection data were collected to image faults and stratigraphy. The basins of the southeastern Terceira Rift are rift valleys whose southwestern and northeastern margins are defined by few major normal faults and several minor normal faults, respectively. Since São Miguel in between the rift valleys shows an unusual W-E orientation, it is supposed to be located on a leaky transform. South of the island and separated by a N120° trending graben system, the Monacco Bank represents a N160° oriented flat topped volcanic ridge dominated by tilted fault blocks. Up to six seismic units are interpreted for each basin. Although volcanic ridges hamper a direct linking of depositional strata between the rift and adjacent basins, the individual seismic stratigraphic units have distinct characteristics. Using these units to provide a consistent relative chrono-stratigraphic scheme for the entire study area, we suggest that the evolution of the southeastern Terceira Rift occurred in two stages. Considering age constrains from previous studies, we conclude that N140° structures developed orthogonal to the SW-NE direction of plate-tectonic extension before ~ 10 Ma. The N160° trending volcanic ridges and faults developed later as the plate tectonic spreading direction changed to WSW-ENE. Hence, the evolution of the southeastern Terceira Rift domain is predominantly controlled by plate kinematics and lithospheric stress forming a kind of a re-organized rift system.

  7. 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

  8. Can Mantle Potential Temperatures be Used to Infer the Tectonic Evolution of Terrestrial Planets?

    NASA Astrophysics Data System (ADS)

    Weller, M. B.; Duncan, M. S.

    2015-12-01

    A survey of geologic activity within the Solar System finds most planetary bodies to be currently operating within a stagnant-lid regime. However, Earth is an outlier and is the only body in the solar system for which we have direct observations of tectonic state. Venus, "Earth's twin" has the potential to be another such outlier, with its broad similarity in size and bulk composition to the Earth, its current and past tectonic states are hotly debated [1-3]. However, Earth is currently the only body for which significant information about internal planetary processes is accessible, and for which direct estimates of internal temperatures of the mantle (mantle potential temperatures - TP) can be estimated. While TP estimates for other bodies have been made remotely [4,5], they tend to have high error, low sample size, and lack internal context. Recently it has been shown that the internal temperatures of 3D numerical simulations follow well prescribed scaling laws [6], and that specific lid states have specific predictions for temperatures [6], i.e., stagnant-lids have measurably greater temperatures than mobile-lids for the same parameter values. These results allow for TP to be considered in a new context. Here we calculate TP for Venus, Mars, Mercury, and the Earth using available geochemical data with well-established relationships between olivine composition and TP, and use these constraints to infer the thermal-tectonic evolution of planets using the scaling laws derived from numerical simulations [4]. We show the remotely determined TPto be viable indicators of lid-state, and offer the first quantitative and data driven determination of tectonic states through the inner Solar System. Implications for the evolution of Mercury, Mars, Venus, and Earth will be discussed. [1] Schubert et al. (1997) Univ. Arizona Press; [2] Turcotte (1993) JGR; [3] Kiefer (2013) LPSC; [4] Lee et al. (2009) EPSL; [5] Filliberto and Dasgupta (2015) JGR; [6] Weller et al. (2014) AGU

  9. Impact of tectonic and volcanism on the Neogene evolution of isolated carbonate platforms (SW Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Courgeon, S.; Jorry, S. J.; Jouet, G.; Camoin, G.; BouDagher-Fadel, M. K.; Bachèlery, P.; Caline, B.; Boichard, R.; Révillon, S.; Thomas, Y.; Thereau, E.; Guérin, C.

    2017-06-01

    Understanding the impact of tectonic activity and volcanism on long-term (i.e. millions years) evolution of shallow-water carbonate platforms represents a major issue for both industrial and academic perspectives. The southern central Mozambique Channel is characterized by a 100 km-long volcanic ridge hosting two guyots (the Hall and Jaguar banks) and a modern atoll (Bassas da India) fringed by a large terrace. Dredge sampling, geophysical acquisitions and submarines videos carried out during recent oceanographic cruises revealed that submarine flat-top seamounts correspond to karstified and drowned shallow-water carbonate platforms largely covered by volcanic material and structured by a dense network of normal faults. Microfacies and well-constrained stratigraphic data indicate that these carbonate platforms developed in shallow-water tropical environments during Miocene times and were characterized by biological assemblages dominated by corals, larger benthic foraminifera, red and green algae. The drowning of these isolated carbonate platforms is revealed by the deposition of outer shelf sediments during the Early Pliocene and seems closely linked to (1) volcanic activity typified by the establishment of wide lava flow complexes, and (2) to extensional tectonic deformation associated with high-offset normal faults dividing the flat-top seamounts into distinctive structural blocks. Explosive volcanic activity also affected platform carbonates and was responsible for the formation of crater(s) and the deposition of tuff layers including carbonate fragments. Shallow-water carbonate sedimentation resumed during Late Neogene time with the colonization of topographic highs inherited from tectonic deformation and volcanic accretion. Latest carbonate developments ultimately led to the formation of the Bassas da India modern atoll. The geological history of isolated carbonate platforms from the southern Mozambique Channel represents a new case illustrating the major

  10. Evolution of the structural fault permeability in argillaceous rocks in a polyphased tectonic context

    NASA Astrophysics Data System (ADS)

    Constantin, J.; Peyaud, J. B.; Vergély, P.; Pagel, M.; Cabrera, J.

    Deep argillaceous formations have petrophysical and hydrodynamic properties favourable to long-term radioactive waste confinement (very low intrinsic permeability, high sorption capacity,…). However, these properties may be modified by the development of discontinuities in the host-rock. The tectonic activity is responsible on the one hand for creating the fractures and on the other hand for reactivating them. Today, the calcite crystallisations in faults give evidence of paleofluid flows during the tectonic deformation. The microstructural study shows that faults were alternately and temporarily impermeable, permeable or “semi-permeable” during the tectonic activity. These “hydraulic states” were controlled by the nature and the architecture of the microstructures and by variations in the petrophysical properties of the rock in the core zone (CZ) and damage zone (DZ) of the faults. Within DZ, the structural fault permeability evolution is associated with (1) microcracking and (2) a probable ductile behaviour of the shales. Within CZ, the structural fault permeability is associated with the development of cavities generated by (1) dilation, (2) shearing and openings in extensional stepover and (3) microcracking in pre-existing calcite fillings. During the tectonic evolution, the development of a new structural porosity both in CZ and DZ gave up the faults permeable. The crystallisation sealing of the total structural porosity gave up the faults impermeable. But, when only the CZ was sealed, the fault was “semi-permeable”. Finally, we show that (1) the fluid transfers occurred principally from the DZ to the CZ, (2) the DZ constituted a “storage zone” in fluids for the CZ, (3) the DZ then remained longer permeable than the CZ and became permeable with weaker stress intensity and (4) the sealed discontinuities constituted zones of weakness (fracture reactivation with or without shearing) in the argillaceous material.

  11. 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

  12. Sill genesis in the Paleoproterozoic tectonic evolution of the Onega Trough, Baltic shield

    NASA Astrophysics Data System (ADS)

    Poleshchuk, A. V.

    2011-07-01

    This study considers the role of sill genesis in the tectonic evolution of the Onega Trough during the Middle to Late Paleoproterozoic (Jatulian-Vepsian). The evolution of the Onega Trough is divided into three stages: pre-sill, or preparatory, subsynchronous, and post-sill. Sill magmatism manifested itself most completely at the subsynchronous stage of the evolution of the Onega Trough within the initial, principal, and final phases of sill genesis. Sill formation followed the stage of regional downwarping of the area reaching its maximum during the Early Ludicovian. Paragenesis of sills and high carbon shungite rocks was accompanied by the formation of peperites, while sills influenced the structure of the host rocks. A model reflecting the regular patterns of manifestations of sill genesis identified in the Onega Trough has been proposed.

  13. 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

  14. 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

    2017-07-01

    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

  15. Late Cretaceous to recent tectonic evolution of the North German Basin and the transition zone to the Baltic Shield/southwest Baltic Sea

    NASA Astrophysics Data System (ADS)

    Al Hseinat, M.; Hübscher, C.

    2017-06-01

    In this study we investigate the Late Cretaceous to recent tectonic evolution of the southwestern Baltic Sea based on a dense grid of seismic reflection profiles. This area covers the Baltic Sea sector of the salt influenced North German Basin and its transition to the salt free Baltic Shield across the Tornquist Zone. The Upper Cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high-resolution time-structure maps of the main horizons, i.e., the Upper Cretaceous, Tertiary and Pleistocene. The Upper Cretaceous and Tertiary layers reveal numerous significant faults throughout the study area. Several of these faults propagate upwards across the unconsolidated Pleistocene sediments and occasionally penetrate the surface. The salt influenced North German Basin reveals three major fault trends: NW-SE, N-S and NNE-SSW. Several of these faults are located directly above basement (sub-salt) faults and salt pillows. The majority of these faults are trending N-S to NNE-SSW and parallel the direction of the Glückstadt Graben faults. In the salt free Tornquist Zone, we identify two major shallow fault trends, which are NW-SE and NE-SW. The majority of these faults are located above basement faults, following the direction of the Tornquist Zone. We conclude that generally basement tectonics controls activation and trends of shallow faults. If salt is present, the ductile salt layer causes a lateral shift between the sub- and supra-salt faults. Major plate reorganisation related to the Africa-Iberia-Europe convergence and the subsequent Alpine Orogeny caused reactivation of pre-existing faults and vertical salt movement in the Late Cretaceous. The change of stress orientation from NE-SW to a NW-SE during Neogene caused another phase of fault and salt tectonic reactivation. We explain that the ice-sheet loading and/or present-day stress field may have acted in combination, causing the recent tectonics and upward extension of

  16. Tectonic evolution of the north depression of the south Yellow Sea basin since late Cretaceous

    NASA Astrophysics Data System (ADS)

    Li, Nan; Li, Weiran; Long, Haiyan

    2016-12-01

    On the basis of subsidence history analysis and balanced cross-section analysis, the vertical uplift/subsidence history and horizontal extension/compression history of the north depression of the south Yellow Sea basin are quantitatively studied. The results show that the tectonic evolution of the north depression of the south Yellow Sea basin since late Cretaceous can be divided into a rifting phase (late Cretaceous to Paleogene) and a post-rifting phase (Neogene to Quaternary). The rifting phase can be further subdivided into an initial rifting stage (late Cretaceous), an intensive rifting stage (Paleocene), a rifting termination stage (Eocene), and an inversion-uplifting stage (Oligocene). Together, this division shows the characteristics of an episodic-evolved intracontinental rift-depression basin. The deformation of the north depression of the south Yellow Sea basin since late Cretaceous was mainly fault-related. The horizontal extension and tectonic subsidence were controlled by the activity of faults. The differential evolution of faults also caused variations in local uplift/subsidence movements and the regional heterogeneity in extension. The late Cretaceous initial rifting of the north depression of the south Yellow Sea basin is related to the Pacific-Eurasia convergence. From the Paleocene intensive rifting stage to present, the Pacific-Eurasia convergence and India-Eurasia convergence have played important roles in the evolution of this region.

  17. 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

  18. Landscapes of human evolution: models and methods of tectonic geomorphology and the reconstruction of hominin landscapes.

    PubMed

    Bailey, Geoffrey N; Reynolds, Sally C; King, Geoffrey C P

    2011-03-01

    This paper examines the relationship between complex and tectonically active landscapes and patterns of human evolution. We show how active tectonics can produce dynamic landscapes with geomorphological and topographic features that may be critical to long-term patterns of hominin land use, but which are not typically addressed in landscape reconstructions based on existing geological and paleoenvironmental principles. We describe methods of representing topography at a range of scales using measures of roughness based on digital elevation data, and combine the resulting maps with satellite imagery and ground observations to reconstruct features of the wider landscape as they existed at the time of hominin occupation and activity. We apply these methods to sites in South Africa, where relatively stable topography facilitates reconstruction. We demonstrate the presence of previously unrecognized tectonic effects and their implications for the interpretation of hominin habitats and land use. In parts of the East African Rift, reconstruction is more difficult because of dramatic changes since the time of hominin occupation, while fossils are often found in places where activity has now almost ceased. However, we show that original, dynamic landscape features can be assessed by analogy with parts of the Rift that are currently active and indicate how this approach can complement other sources of information to add new insights and pose new questions for future investigation of hominin land use and habitats. Copyright © 2010 Elsevier Ltd. All rights reserved.

  19. Tectonic evolution of the Pacific Phoenix Farallon triple junction in the South Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Viso, Richard F.; Larson, Roger L.; Pockalny, Robert A.

    2005-04-01

    Analysis of multibeam and gravity data reveals the tectonic history of the mid-Cretaceous (119-107 Ma) Penrhyn basin in the equatorial south Pacific Ocean. The basin formed during a period of heightened geodynamic activity and cessation of magnetic reversals. Similarities in the geometry of the Tongareva triple junction and the Rodriguez triple junction in the Indian Ocean make this study an interesting comparison between modern and ancient tectonics. Changes in abyssal hill trends during the formation of the basin suggest either a change in the location of the Euler pole describing the relative motion between the Pacific and Farallon plates, or a significant period of oblique spreading. Interaction between the local stress field associated with the break-up of the Manihiki plateau and the regional stress field controlling major plate motions complicated the tectonic evolution of the Penrhyn basin. Construction of velocity triangles from abyssal hill trends and measurements of the triple junction trace suggests that the triple junction oscillated between ridge-ridge-ridge and ridge-ridge-fault configurations. At least two reorganizations in the geometry of the triple junction occurred within 10 Ma of the initial rifting of the Manihiki plateau. Both changes in triple junction geometry coincide with discontinuities in the triple junction trace and result in right-lateral displacements of the triple junction trace. Changes in the bathymetric expression of the triple junction trace suggest a period of triple junction propagation controlled by rift propagation shortly after the change in Euler pole location.

  20. Tectonic evolution of Ovda Regio: An example of highly deformed continental crust on Venus?

    NASA Astrophysics Data System (ADS)

    Romeo, I.; Capote, R.

    2011-10-01

    A detailed structural analysis of several selected areas of Ovda Regio provides evidence of a complex tectonic evolution. We have reported thrusting in the marginal fold belts indicating together with the presence of short-wavelength folds a significant amount of shortening. Extensional tectonics postdate at least in some locations contraction, while the contrary was not observed. Both contraction and extension occur on a complex layered crust yielding contemporary structures of different wavelengths. The thrust and fold belts of the plateau margins are characterized by concentric contraction followed by concentric contraction with perpendicular extension and finally radial extension. Deformation in the thrust and fold belts of Ovda margins is gradually transmitted to the external plains. A complex tectonic history has been revealed in the internal area of Ovda, basically characterized by contraction in different directions generating basin and dome interference at different wavelengths. Small amounts of a non-coaxial component of deformation have been observed both in the margins and in the central area of the plateau. All the reported observations can be explained if Ovda Regio is a continent that survived a global subduction event.

  1. Usbnd Pb detrital zircon ages from some Neoproterozoic successions of Uruguay: Provenance, stratigraphy and tectonic evolution

    NASA Astrophysics Data System (ADS)

    Pecoits, Ernesto; Aubet, Natalie R.; Heaman, Larry M.; Philippot, Pascal; Rosière, Carlos A.; Veroslavsky, Gerardo; Konhauser, Kurt O.

    2016-11-01

    The Neoproterozoic volcano-sedimentary successions of Uruguay have been the subject of several sedimentologic, chrono-stratigraphic and tectonic interpretation studies. Recent studies have shown, however, that the stratigraphy, age and tectonic evolution of these units remain uncertain. Here we use new Usbnd Pb detrital zircon ages, combined with previously published geochronologic and stratigraphic data in order to provide more precise temporal constraints on their depositional age and to establish a more solid framework for the stratigraphic and tectonic evolution of these units. The sequence of events begins with a period of tectonic quiescence and deposition of extensive mixed siliciclastic-carbonate sedimentary successions. This is followed by the development of small fault-bounded siliciclastic and volcaniclastic basins and the emplacement of voluminous granites associated with episodic terrane accretion. According to our model, the Arroyo del Soldado Group and the Piedras de Afilar Formation were deposited sometime between ∼1000 and 650 Ma, and represent passive continental margin deposits of the Nico Pérez and Piedra Alta terranes, respectively. In contrast, the Ediacaran San Carlos (<552 ± 3 Ma) and Barriga Negra (<581 ± 6 Ma) formations, and the Maldonado Group (<580-566 Ma) were deposited in tectonically active basins developed on the Nico Pérez and Cuchilla Dionisio terranes, and the herein defined Edén Terrane. The Edén and the Nico Pérez terranes likely accreted at ∼650-620 Ma (Edén Accretionary Event), followed by their accretion to the Piedra Alta Terrane at ∼620-600 Ma (Piedra Alta Accretionary Event), and culminating with the accretion of the Cuchilla Dionisio Terrane at ∼600-560 Ma (Cuchilla Dionisio Accretionary Event). Although existing models consider all the Ediacaran granites as a result of a single orogenic event, recently published age constraints point to the existence of at least two distinct stages of granite generation

  2. 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

  3. Interaction of two successive Alpine deformation fronts: constraints from low-temperature thermochronology and structural mapping (NW Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Martín-González, F.; Barbero, L.; Capote, R.; Heredia, N.; Gallastegui, G.

    2012-07-01

    The lateral termination of the Alpine-Pyrenean Orogen relief onshore is located in the NW Iberian Peninsula. It overlies a Variscan basement (Iberian Massif), where the sedimentary record of the Alpine tectonic is very scarce. Thus, the characterisation of the tectonic evolution of the lateral termination is difficult and timing and geometries of the main tectonic structures remain unclear. Combining the tectonothermal histories obtained by modelling of the apatite fission-track data (AFT) with structural mapping allows for a comparative study of the different tectonic scenarios and deformation transfer in the lateral termination of an orogen. AFT ages for the studied area vary from 53.5 ± 12.9 and 222 ± 12 Ma (from Late Triassic to Early Eocene). The beginning of the Cenozoic cooling episodes is in agreement with the infilling of the Tertiary basins (Late Eocene or Oligocene). Calculated uplift for the Alpine Orogeny is around 2,400 m. The Cantabrian Mountains were uplifted and emplaced southwards and the main period of exhumation began in the Palaeogene at rates of ~0.02 mm/a and continued during the Neogene at rates of ~0.06 mm/a. However, the Galaico-Leoneses Mountains, located to the south of the studied area, were uplifted and emplaced northwards during the Neogene, showing more rapid uplift rates of ~0.08 mm/a, suggesting that the western termination of the Alpine-Pyrenean Orogen relief is the result of the successive interaction of two Alpine deformation fronts.

  4. P-T Alpine metamorphic evolution of the Monte Rosa nappe along the Piedmont Zone boundary (Gressoney Valley, NW Italy)

    NASA Astrophysics Data System (ADS)

    Gasco, Ivano; Borghi, Alessandro; Gattiglio, Marco

    2011-11-01

    The pseudosection modelling of two chemical systems (both metabasic and metapelitic) allowed to reconstruct the exhumation P-T path followed by the southern slope of the Monte Rosa nappe (Upper Gressoney Valley) during the Alpine orogenesis. The metamorphic evolution of the polymetamorphic basement complex from the Monte Rosa nappe is marked by texturally distinct mineral assemblages, defining four Alpine metamorphic stages (M1 to M4) reflecting a sequence of different P-T conditions. Well preserved eclogitic boudins (M1 and M2 assemblages) were investigated to reconstruct the HP history related to the subduction phase, while re-equilibrated metapelites allowed to infer the P-T conditions attained during the development of the regional foliation (M3 and M4 assemblages). The HP stage (M1) occurred at 550-570 °C and 24-27 kbar and is characterised by the assemblage Omp + Grt + Lws + Phe + Qtz + Gln ± Tlc in the eclogites. The M2 metamorphic stage consists of the assemblage Omp + Grt + Barr + Zo + Phe + Pg + Qtz and developed at 590-630 °C and 14.5-16.5 kbar suggesting a T increasing during decompression. After a further decompressional stage associated with a T decrease, the M3 tectono-metamorphic stage developed syn-kinematically with the main regional foliation S1. It is marked by the assemblage Phe + Pg + Grt + Chl + Ab/Olig + Hbl + Qtz + Rt/Ilm ± Bt in metapelites and by Cam (blue-green) + Chl + Ab + Bt + Qtz + Rt in the re-equilibrated metabasite boudins. S1 developed during increasing T (from 550 to ca. 600 °C) and sligthly increasing P (from 7 to 9 kbar). Finally, the M4 assemblage grew as rims over the M3 minerals or overgrew the S1 regional foliation (albite porphyroblasts overgrowing the S1 foliation already defined by albite) and therefore can be considered as the final stage of the M3 stage. The P-T path proposed for the Monte Rosa nappe differs from previous works. In particular, we propose post-eclogitic decompression trajectory up to 7 kbar

  5. Evolution characteristics of shallow-water carbonates and their respond to tectonic evolution in the Liyue Basin, South China Sea

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Ren, J.; Yao, Y.; TONG, D.

    2016-12-01

    The Liyue Basin is located around the Liyue Bank (Reed Bank) in the southeast part of the South China Sea (SCS), adjoining the Palawan Island. It is a complex structural transition zone of the south collision convergent edge and the east subduction convergent margin of the SCS. However, the geological history of the Liyue Basin is not well understood due to the poor quality geophysical data. In this study, we combine the reprocessing 2D seismic data and limited well logging data to investigate the shallow-water carbonates evolution and their respond to tectonic evolution in the Liyue Basin. A set of prominent reflectors in seismic profile is associated with widespread Late Oligocene to Early Miocene (28-15Ma) shallow-water carbonate platforms. The carbonate platforms were featured with high-amplitude continuous reflections at the top and low-amplitude subparallel reflections within which is similar to the proven carbonates in the offshore Palawan. Carbonates remained abundant but mainly as isolated reefs that grew on top of tilted fault blocks, basement highs to the Middle Miocene, and even to present in the Liyue Bank. These reflectors and the underlying carbonates can be used to constrain the timing of the unconformities and the rifting history of the Liyue Basin. We identify the carbonate platforms and reefs which grew on region unconformities (T4). It is a post-rift unconformity responds to the breakup of the South China Sea and represents the transformation from half-graben basin to down-warped basin. Many reefs stopped growth beneath another region unconformity (Red Unconformity, 19-16Ma), which responds to the ceasing of the NW Sub-basin expanding. Synthetically the tectonic evolution mainly controls the development of carbonate platforms and reefs in the Liyue Basin. The Liyue Basin was in a relatively tectonic stable condition during the drifting stage of SCS. An everlasting shallow marine environment and low sediments input contributed to the development

  6. 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

  7. Thermal Evolution of Terrestrial Planets: Earth, Mars, Size, Temperature, Tectonics, and Deep Volatile Cycling

    NASA Astrophysics Data System (ADS)

    Lenardic, A.; Hero, J.; McGovern, P. J., Jr.

    2014-12-01

    Recent efforts to constrain the thermal evolution of the Martian lithosphere suggest that the ratio of mantle heat production to heat loss, termed the Urey ratio, on Mars may be greater than unity at present (or in Mars' recent past). For comparison, the present day Earth value is 0.33. These estimates fly in the face of conventional wisdom that a smaller planet like Mars should have cooled faster than the Earth - and certainly should not be heating up at present. We perform a sensitivity analysis, using a thermal history modeling approach, to asses the relative effects of changing planetary size, mode of tectonics, and nature of deep volatile cycling (focussing on water). Our results indicate that differences in the nature of volatile cycling (degassing vs regassing over time) can outweigh the effects of size and tectonic mode in determining the thermal state of a planet. Mars models in which degassing dominates can give Urey ratios that exceed unity. Earth models in which regassing dominates over degassing in the later geologic stages of evolution lead to lower Urey ratio values.

  8. Neogene tectonic evolution of the Gibraltar Arc: New paleomagnetic constrains from the Betic chain

    NASA Astrophysics Data System (ADS)

    Mattei, M.; Cifelli, F.; Rojas, I. Martín; Crespo Blanc, A.; Comas, M.; Faccenna, C.; Porreca, M.

    2006-10-01

    New paleomagnetic results from Neogene sedimentary sequences from the Betic chain (Spain) are here presented. Sedimentary basins located in different areas were selected in order to obtain paleomagnetic data from structural domains that experienced different tectonic evolution during the Neogene. Whereas no rotations have been evidenced in the Late Tortonian sediments in the Guadalquivir foreland basin, clockwise vertical axis rotations have been measured in sedimentary basins located in the central part of the Betics: the Aquitanian to Messinian sediments in the Alcalà la Real basin and the Tortonian and Messinian sediments in the Granada basin. Moreover, counterclockwise vertical axis rotations, associated to left lateral strike-slip faults have been locally measured from sedimetary basins in the eastern Betics: the Middle Miocene to Lower Pliocene sites from the Lorca and Vera basins and, locally, the Tortonian units of the Huercal-Overa basin. Our results show that, conversely from what was believed up to now, paleomagnetic rotations continued in the Betics after Late Miocene, enhancing the role of vertical axis rotations in the recent tectonic evolution of the Gibraltar Arc.

  9. 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

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

    NASA Astrophysics Data System (ADS)

    Dong, Yunpeng

    2017-04-01

    The East Kunlun Orogen, located at the northern Tibet Plateau, represents the western segment of the Central China Orogenic Belt which was formed by amalgamation of the North China blocks and South China blocks. It is a key to understanding the formation of Eastern Asian continent as well as the evolution of the Pangea supercontinent. Based on detailed geological mapping, geochemical and geochronological investigations, the orogen is divided into three main tectonic belts, from north to south, including the Northern Qimantagh, Central Kunlun and Southern Kunlun Belts by the Qimantagh suture, Central Kunlun suture and South Kunlun fault. The Qimantagh suture is marked by the Early Paleozoic ophiolites outcropped in the Yangziquan, Wutumeiren, and Tatuo areas, which consist mainly of peridotites, gabbros, diabases and basalts. Besides, the ophiolite in the Wutumeiren is characterized by occurring anorthosite while the ophiolite in the Tatuo occurring chert. The basalts and diabases from both Yaziquan and Tatuo areas display depletion of Nb, Ta, P and Ti, and enrichment of LILE, suggesting a subduction related tectonic setting. LA-ICP-MS zircon U-Pb age of 421 Ma for the diabase represents the formation age of the Yaziquan ophiolite, while the U-Pb ages of 490 Ma and 505 Ma for gabbro and anorthosite, respectively, constrain the formation age of the Tatuo ophiolite. The basaltic rocks in the Wutumeiren area display flat distribution of HFSEs (such as Nb, Ta, K, La, Ce, Pr, Nd, Zr, Sm, Eu, Ti, Dy, Y, Yb and Lu) and slightly enrichment in LREEs, while the peridotites showing depletion in MREEs. The LA-ICP-MS zircon U-Pb age of 431 Ma for the gabbro represents the formation age of the Wutumeiren ophiolite. Together with regional geology, we suggest herewith a back-arc basin tectonic setting during ca. 505-421 Ma at least for the Qimantagh suture. The Central Kunlun suture is represented by the ophiolite in the Wutuo area, which is characterized by depletion of Nb, Ta, P

  11. 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.

  12. 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

  13. Geomorphology, active tectonics, and landscape evolution in the Mid-Atlantic region: Chapter

    USGS Publications Warehouse

    Pazzaglia, Frank J.; Carter, Mark W.; Berti, Claudio; Counts, Ronald C.; Hancock, Gregory S.; Harbor, David; Harrison, Richard W.; Heller, Matthew J.; Mahan, Shannon; Malenda, Helen; McKeon, Ryan; Nelson, Michelle S.; Prince, Phillip; Rittenour, Tammy M.; Spotilla, James; Whittecar, G. Richard

    2015-01-01

    In 2014, the geomorphology community marked the 125th birthday of one of its most influential papers, “The Rivers and Valleys of Pennsylvania” by William Morris Davis. Inspired by Davis’s work, the Appalachian landscape rapidly became fertile ground for the development and testing of several grand landscape evolution paradigms, culminating with John Hack’s dynamic equilibrium in 1960. As part of the 2015 GSA Annual Meeting, the Geomorphology, Active Tectonics, and Landscape Evolution field trip offers an excellent venue for exploring Appalachian geomorphology through the lens of the Appalachian landscape, leveraging exciting research by a new generation of process-oriented geomorphologists and geologic field mapping. Important geomorphologic scholarship has recently used the Appalachian landscape as the testing ground for ideas on long- and short-term erosion, dynamic topography, glacial-isostatic adjustments, active tectonics in an intraplate setting, river incision, periglacial processes, and soil-saprolite formation. This field trip explores a geologic and geomorphic transect of the mid-Atlantic margin, starting in the Blue Ridge of Virginia and proceeding to the east across the Piedmont to the Coastal Plain. The emphasis here will not only be on the geomorphology, but also the underlying geology that establishes the template and foundation upon which surface processes have etched out the familiar Appalachian landscape. The first day focuses on new and published work that highlights Cenozoic sedimentary deposits, soils, paleosols, and geomorphic markers (terraces and knickpoints) that are being used to reconstruct a late Cenozoic history of erosion, deposition, climate change, and active tectonics. The second day is similarly devoted to new and published work documenting the fluvial geomorphic response to active tectonics in the Central Virginia seismic zone (CVSZ), site of the 2011 M 5.8 Mineral earthquake and the integrated record of Appalachian

  14. Palaeogeographic, climatic and tectonic change in southeastern Australia: the Late Neogene evolution of the Murray Basin

    NASA Astrophysics Data System (ADS)

    McLaren, Sandra; Wallace, Malcolm W.; Gallagher, Stephen J.; Miranda, John A.; Holdgate, Guy R.; Gow, Laura J.; Snowball, Ian; Sandgren, Per

    2011-05-01

    The Murray Basin is a low-lying but extensive intracratonic depocentre in southeastern Australia, preserving an extraordinary record of Late Neogene sedimentation. New stratigraphic and sedimentologic data allow the long-term evolution of the basin to be re-evaluated and suggest a significant role for: (1) tectonism in controlling basin evolution, and (2) progressive and step-wise climatic change beginning in the early Pleistocene. Tectonic change is associated with regional uplift, occurring at approximately the same rate from the early Pliocene until the present day, and possibly associated with changing mantle circulation patterns or plate boundary processes. This uplift led to the defeat and re-routing of the Murray River, Australia's major continental drainage system. Key to our interpretation is recognition of timing relationships between four prominent palaeogeographic features - the Loxton-Parilla Sands strandplain, the Gambier coastal plain, palaeo megalake Bungunnia and the Kanawinka Escarpment. Geomorphic and stratigraphic evidence suggest that during the Early Pliocene the ancestral Murray River was located in western Victoria, flowing south along the Douglas Depression. Relatively small amounts of regional uplift (<200 m) defeated this drainage system, dramatically changing the palaeogeography of southeastern Australia and forming Plio-Pleistocene megalake Bungunnia. At its maximum extent Lake Bungunnia covered more than 50,000 km 2, making it one of the largest known palaeo- or modern-lakes in an intracontinental setting. Magnetostratigraphic constraints suggest lake formation c. 2.4 Ma. The formation of Lake Bungunnia influenced the Pliocene coastal dynamics, depriving the coastline of a sediment source and changing the coastal system from a prograding strandline system to an erosional one. Erosion during this period formed the Kanawinka Escarpment, a palaeo sea-cliff and one of the most prominent and laterally extensive geomorphic features in

  15. 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

  16. High resolution evolution of post-rift terrigenous sediment yields in the Provence Basin (Western Mediterranean): relation with climate and tectonics

    NASA Astrophysics Data System (ADS)

    Leroux, Estelle; Rabineau, Marina; Aslanian, Daniel; Gorini, Christian; Molliex, Stéphane; Bache, François; Robin, Cécile; Droz, Laurence; Moulin, Maryline; Poort, Jeffrey; Rubino, Jean-Loup; Suc, Jean-Pierre

    2017-04-01

    The correlation of stratigraphic markers between the shelf, the slope and the deep basin have enabled us to provide a complete and quantitative view of sediments fluxes for the last 6 Ma on the entire Gulf of Lions margin. Messinian units and Pliocene and Pleistocene chronostratigraphic markers have been correlated from the shelf to the deep basin and the total sediment thickness from the basement (20 Ma) to the present-day seafloor has also been mapped. After Time/Depth conversion and decompaction of each stratigraphic interval, sedimentary volumes were calculated. Sediment flux evolution shows that a dramatic terrigenous peak occurred during the Messinian Salinity Crisis. The Pliocene-Pleistocene average flux appears to have been three times higher than that of the Miocene, which seems in agreement with published measurements from the World's ocean. This study also highlights the Mid-Pleistocene Revolution around 0.9 Ma, which resulted in an almost doubling of sedimentary detrital fluxes in the Provencal Basin. These results are discussed in relation with world-wide climate and alpine tectonics.

  17. Fault zone evolution in a Cenozoic inversion tectonic setting, SE Korea

    NASA Astrophysics Data System (ADS)

    Kim, Young-Seog; Lee, Minjoo; Han, Seung-Rok

    2010-05-01

    The Korean peninsula has been considered as a tectonically safe region from earthquakes, because it is located in a stable margin of the Eurasian plate. However, more than 30 Quaternary faults have recently been reported from the southeastern part of the Korean peninsula. The studied fault zone is an N-S trending fault located in the northern extent of the Quaternary Eupcheon Fault, which composed of several fault gouges indicating multiple deformations. The fault zone (fault core) is exposed over 1 km long and the thickness is up to 2m. The fault gouge zone is composed of several different colored gouge bands. Well-exposed vertical and horizontal sections are analyzed so as to understand the characteristics of the fault and fault zone evolution. The analyzed kinematic indicators such as cleavages, lineations and slickenlines suggest that the fault underwent early normal slip under SE extension and was later reactivated under NNW compression resulting in inversion tectonics. Major fault zones do not cross-cut each other; instead, the fault gouges within the fault zone split and merge into other fault zones. Fault rocks developed in this fault zone show asymmetrical features including lens-shaped breccias blocks in gouge zones, and asymmetric distributions of grain size and fracture density, indicating mature fault system and asymmetric fault zone evolution. The hanging wall block of the fault shows relatively highly damaged fracture patterns indicating that the hanging wall is weaker than footwall. Therefore, detailed analysis of fault and fracture patterns, and characteristics of fault zones must be very useful in evaluation of fault zone evolution and characteristics of foundation.

  18. 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.

  19. Temporal stability of pollinator preference in an alpine plant community and its implications for the evolution of floral traits.

    PubMed

    Gong, Yan-Bing; Huang, Shuang-Quan

    2011-07-01

    A traditional view of diverse floral traits is that they reflect differences in foraging preferences of pollinators. The role of pollinators in the evolution of floral traits has been questioned recently by broad community surveys, especially studies concerning variation in pollinator assemblages and visitation frequency, which suggest a diminished role of pollinators in floral evolution. Here, we investigate the relationships between six categories of floral traits of 29 species and 10 pollinator functional groups in an alpine meadow in the Hengduan Mountains of China, over three consecutive years. Simpson's diversity index was used to estimate the level of pollinator generalization of each plant species by considering both pollinator groups and their relative visitation frequencies. Multivariate analyses indicated that eight of the ten pollinator groups showed constant preferences for at least two floral traits, leading to a relatively stable level of ecological generalization for most floral traits (two out of three categories), despite the fact that the level of generalization of the entire community varied across years. Shape preferences of butterflies, honeybees and beeflies varied such that open flowers exhibited a lower level of ecological generalization in 2007 than closed flowers, in contrast with the other 2 years. These results suggest that temporally stabilized preferences of diverse pollinators may contribute to the evolution of specialized versus generalized floral traits; however, their role may be moderated by variation in community structure, including both the composition and abundance of plants and pollinators.

  20. Evolution of tectonic compaction in the Barbados accretionary prism: Estimates from logging-while-drilling

    NASA Astrophysics Data System (ADS)

    Saito, Saneatsu; Goldberg, David

    1997-05-01

    Resistivity and bulk-density logs acquired while drilling are used to document the evolution of porosity, volumetric loss, and effective stress in the upper 300 m of the Barbados accretionary prism. The computed profiles across a thrust fault enable the separation of pre-, syn-, and post-accretion components; total volume loss is divided into normal consolidation (pre-accretion), tectonic volume loss (syn-accretion), and thrust fault loading (post-accretion) in the footwall. Quantitatively, the tectonic volume loss in the Barbados accretionary prism, estimated from the normal consolidation in a reference section, is as large as the pre-accretion volume loss. The compaction history of the accretionary prism is essentially controlled by the vertical displacement of the thrust and the predicted maximum volume loss throughout the prism may be extrapolated from the volume loss trend in the hanging wall. The porosity and effective stress profile at the present time is consistently larger than its corresponding syn-accretion trend and less than the extrapolated maximum from the hanging wall. The present profile is approximately equal to the average of the two curves. The remaining difference in the accretionary prism above the inferred syn-accretion trend is due to post-accretion compaction. The post-accretion volume loss is a physical feedback process due to the superposition of thrust sheets in an accretionary prism. In the case of multiple thrusts developing in a prism, the porosity and effective stress profiles are saw-toothed and approach the maximum tectonic volume loss gradient with depth. The cumulative post-accretion compaction increases with depth and becomes increasingly greater than the pre- and syn-accretion compaction with thickening of the accretionary prism. Post-accretionary loading is the dominant mechanism of volume loss and dewatering in an accretionary prism during its early stages of growth.

  1. 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.

  2. 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.

  3. Alpine ecosystems

    Treesearch

    P.W. Rundel; C.I. Millar

    2016-01-01

    Alpine ecosystems are typically defined as those areas occurring above treeline, while recognizing that alpine ecosystems at a local scale may be found below this boundary for reasons including geology, geomorphology, and microclimate. The lower limit of the alpine ecosystems, the climatic treeline, varies with latitude across California, ranging from about 3500 m in...

  4. 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

  5. Transient Fluvial Response to Alpine Deglaciation, Mount Rainier, WA: Geomorphic Process Domains and Proglacial Flux Controls on Channel Evolution.

    NASA Astrophysics Data System (ADS)

    Beyeler, J. D.; Montgomery, D.; Kennard, P. M.

    2016-12-01

    Downwasting of all glaciers on the flanks of Mount Rainier, WA, in recent decades has debuttressed Little Ice Age glaciogenic sediments driving proglacial responses to regionally warming climate. Rivers draining the deglaciating edifice are responding to paraglacial sedimentation processes through transient storage of retreat-liberated sediments in aggrading (e.g., >5m) fluvial networks with widening channel corridors (i.e., 50-150%) post-LIA (ca., 1880-1910 locally). We hypothesize that the downstream transmission of proglacial fluxes (i.e., sediment and water) through deglaciating alpine terrain is a two-step geomorphic process. The ice-proximal portion of the proglacial system is dominated by the delivery of high sediment-to-water ratio flows (i.e., hyperconcentrated and debris slurries) and sediment retention by in-channel accumulation (e.g., confined debris fans within channel margins of valley segments) exacerbated by recruitment and accumulation of large wood (e.g., late seral stage conifers), whereas ice-distal fluvial reworking of transient sediment accumulations generates downstream aggradation. Historical Carbon River observations show restricted ice-proximal proglacial aggradation until a mainstem avulsion in 2009 initiated incision into sediment accumulations formed in recent decades, which is translating into aggradation farther down the network. Surficial morphology mapped with GPS, exposed subsurface sedimentology, and preliminary dating of buried trees suggest a transitional geomorphic process zone has persisted along the proglacial Carbon River through recent centuries and prior to the ultimate LIA glaciation. Structure-from-motion DEM differencing through the 2016 water year shows discrete zones of proglacial evolution through channel-spanning bed aggradation forced by interactions between large wood and sediment-rich flows that transition to fluvial process dominance as sediment is transported downstream. Long-term DEM differencing suggests

  6. Palinspastic reconstruction of the Alpine thrust belt at the Alpine-Carpathian transition - A geological Sudoku

    NASA Astrophysics Data System (ADS)

    Beidinger, A.; Decker, K.; Zamolyi, A.; Hölzel, M.; Hoprich, M.; Strauss, P.

    2009-04-01

    The palinspastic reconstruction of the Austroalpine thrust belt is part of the project Karpatian Tectonics, which is funded by OMV Austria. The objective is to reconstruct the evolution of the thrust belt through the Early to Middle Miocene in order to obtain information on the palaeogeographic position of the Northern Calcareous Alps (NCA) in the region of the present Vienna Basin. A particular goal of the study is to constrain the position of reservoir rocks within the Rhenodanubic Flysch units and the NCA with respect to the autochthonous Malmian source rocks overlying the European basement below the Alpine-Carpathian thrust wedge, and to constrain the burial history of these source rocks. Reconstruction uses regional 2D seismic lines crossing from the European foreland into the fold-thrust belt, 3D seismic data covering the external thrust sheets, and lithostratigraphic data from a total of 51 selected wells, which were drilled and provided by OMV Austria. The main criterion, whether a well was suitable for palinspastic reconstruction or not, was its penetration of Alpine thrust sheets down to the Autochthonous Molasse of the foreland. Additional wells, which do not penetrate the entire Alpine thrust complex but include the Allochthonous Molasse or the external Alpine-Carpathian nappes (Waschberg and Roseldorf thrust unit, Rhenodanubic Flysch nappes) in their well path, were also taken into account. The well data in particular comprise stratigraphic information on the youngest overthrust sediments of the different thrust units and the underlying Autochthonous foreland Molasse. These data allow constraining the timing of thrust events in the allochthonous thrust units and overthrusting of the Autochthonous Molasse. In the particular case of overthrust Autochthonous Molasse, additionally to the timing of overthrusting, which can be derived from the youngest overthrust sediments, the palaeogeographic position of the Alpine Carpathian thrust front could directly be

  7. 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

  8. Multi-phase structural and tectonic evolution of the Andaman Sea Region

    NASA Astrophysics Data System (ADS)

    Masterton, Sheona; Hill, Catherine; Sagi, David Adam; Webb, Peter; Sevastjanova, Inga

    2017-04-01

    opening of the South China Sea to the east. Consequently, the obliquity of plate convergence along this margin increased, ultimately resulting in a change from minor strain partitioning to hyper oblique convergence and full strain partitioning by the mid-Miocene. Investigation into the effects of slab-steepening and dynamic subsidence in the Indochina region could be used as further tests of our proposed tectonic evolution of the Andaman Sea.

  9. 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.

  10. 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.

  11. 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.

  12. Relationships between fluvial evolution and karstification related to climatic, tectonic and eustatic forcing in temperate regions

    NASA Astrophysics Data System (ADS)

    Harmand, Dominique; Adamson, Kathryn; Rixhon, Gilles; Jaillet, Stéphane; Losson, Benoît; Devos, Alain; Hez, Gabriel; Calvet, Marc; Audra, Philippe

    2017-06-01

    This paper reviews the diversity of relationships between river evolution and karstogenesis. It also underlines the fundamental role of numerical dating methods (e.g. cosmogenic nuclides) applied to sedimentary sequences in tiered cave passages as they have provided new insights into these complex interactions. Although karst terrain is widespread worldwide, we focus on European karst catchments, where the sedimentary records are especially well preserved. We review the recent dating of fluvial sediments and speleothems, to examine the timing of karstification, incision and deposition in cave levels. The most complete alluvial records occur in tectonically uplifted high mountains where some of the oldest sediment fills date to the Miocene. Evidence indicates that not only uplift, but also climatic conditions and fluvial dynamics (e.g. knickpoint retreat, increased channel flow and/or sediment load, and stream piracies) can play a major role in speleogenesis and geomorphological evolution. In evaporite rocks, speleogenesis is characterized by rapid dissolution and subsidence. In European catchments, gypsum cave development largely occurred during cold climate periods, while limestone caves formed during warm interglacial or interstadial phases. Our synthesis is used to propose four models of fluvial and karst evolution, and highlight perspectives for further research.

  13. 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.

  14. 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.

  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. 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.

  18. The P-T-t History of the Alpine Schist, New Zealand: Constraining Tectonic Processes During the Late Stages of Gondwana Breakup

    NASA Astrophysics Data System (ADS)

    Briggs, S. I.; Smit, M. A.; Cottle, J. M.; Hagen-Peter, G.

    2015-12-01

    Separation of the microcontinent Zealandia from the Marie Byrd Land sector of Antarctica in the Late Cretaceous marked the final stage in the breakup of Gondwana. Two contrasting ideas for the Late Cretaceous rifting of Zealandia from Gondwana have been proposed. One is that subduction at the paleo-Pacific - Gondwana convergent margin ceased after the last pulse of batholith emplacement at ~100 Ma, followed by a rapid transition to extension and seafloor spreading at 82 Ma. The other hypothesis is that convergence continued along Zealandia simultaneously with back-arc extension until ~85 M. This hypothesis is based on recently reported Late Cretaceous ages from the Alpine Schist, a metamorphosed accretionary wedge assemblage. Without accompanying pressure-temperature (P-T) information, the significance of Late Cretaceous ages from the Alpine Schist in terms of the orogenic processes that occurred during cessation of subduction at the paleo-Pacific - Gondwana margin remains unclear. In this study, Lu-Hf geochronology of Alpine Schist garnet is paired with phase equilibria modelling to elucidate the P-T-t history of the orogen and clarify the mechanisms behind Zealandia-Gondwana rifting. Garnet Lu-Hf dates have been obtained from 9 samples ranging in bulk composition from quartzo-feldspathic schists to mafic amphibolites. Garnet yields Early Cretaceous ages from the southern Alpine Schist, whereas northern Alpine Schist garnet yields Late Cretaceous ages. Garnet textures and major and trace element compositional zoning suggest that an additional, later period of garnet growth or recrystallization may be recorded in the northern samples. P-T-t data from each dated sample is supplemented with thermobarometric analysis from an adjacent sample of different lithology, with the advantage of providing more complete local P-T-t paths. The P-T-t paths define whether garnet grew during increasing P-T (prograde early), decreasing P and increasing T (prograde late), and

  19. 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

  20. 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

  1. 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.

  2. Tectonic Evolution of Naxos (cyclades): A Record of The Thermal-mechanical Evolution of An Orogenic Wedge

    NASA Astrophysics Data System (ADS)

    Vanderhaeghe, O.; Duchêne, S.; Hibsch, C.; Malartre, F.; Aissa, R.; Martin, L.; Fotiades, .; de St Blanquat, M.; Habert, G.

    A synthesis of published work and preliminary results from a multidisciplinary study of the various crustal levels exposed in the island of Naxos in the Cyclades allows to propose a model for the evolution of the orogenic accretionary wedge in this region. Naxos is characterized by the juxtaposition of metamorphic rocks and Late Oligocene- Early Miocene to Upper Pliocene sedimentary basins along a low-angle detachment. Migmatites, dated at ca. 15 Ma (Keay et al., 2001), appear in the core of a structural dome and are surrounded by a sequence of metasedimentary rocks. From the edge of the island to the core of the dome, the metasedimentary sequence is affected by a metamorphism grading from blue schists to amphibolite facies (Jansen and Schuil- ing, 1976). Ar-Ar ages decrease from ca. 45 in the blue schists to ca. 10 Ma in the migmatites (Andriessen et al., 1979, Wijbrans and McDougall, 1986). The sedimen- tary basins are filled mainly by coarse silicoclastic deposits. Sedimentological and geomorphological features suggest a transition from a shallow marine to a continental environment during Miocene time. Data from the metamorphic rocks indicate that the dynamic evolution of the wedge is marked by a first stage of burial and subsequent exhumation of the metasedimen- tary rocks controlled by the interplay between deformation related to convergence and denudation (erosion and tectonic). The formation of the dome cored by migmatites is interpreted as the result of the development of a gravitational instability associated to the genesis of a partially molten layer at depth in the thickened orogenic wedge. This event is synchronous to the activity of the low-angle detachment and the per- vasive top-to-the-North non-coaxial deformation which affects all rock units above the migmatites. The nature of the link between diapiric upwelling of the dome and the transition from thickening to thinning of the orogenic wedge remains to be estab- lished. Progressive exhumation and

  3. 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.

  4. Formation and evolution of yardangs activated by Late Pleistocene tectonic movement in Dunhuang, Gansu Province of China

    NASA Astrophysics Data System (ADS)

    Wang, Yanjie; Wu, Fadong; Zhang, Xujiao; Zeng, Peng; Ma, Pengfei; Song, Yuping; Chu, Hao

    2016-12-01

    Developed in the Anxi-Dunhuang basin, the yardangs of Dunhuang (western China) are clearly affected by tectonic movement. Based on fieldwork, this study ascertained three levels of river terrace in the area for the first time. Through the analysis of river terraces formation and regional tectonic movement, the study ascertained that the river terraces were formed mainly by Late Pleistocene tectonic uplift, which had activated the evolution of yardangs in the study area. By electron spin resonance (ESR) dating and optically stimulated luminescence (OSL) dating, the starting time and periodicity of the evolution of the yardangs were determined. The river terraces designated T3, T2 and T1 began to evolve at 109.0 ˜98.5, 72.9 ˜66.84 and 53.2 ˜38.0 kaBP, respectively, which is the evidence of regional neotectonic movement. And, the formation of the yardangs was dominated by tectonic uplift during the prenatal stage and mainly by wind erosion in the following evolution, with relatively short stationary phases. This research focused on the determination of endogenic processes of yardangs formation, which would contribute to further understanding of yardangs formation from a geological perspective and promote further study of yardang landform.

  5. 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.

  6. Low-temperature constraints on the Alpine thermal evolution of the Western Carpathian basement rock complexes

    NASA Astrophysics Data System (ADS)

    Králiková, Silvia; Vojtko, Rastislav; Hók, Jozef; Fügenschuh, Bernhard; Kováč, Michal

    2016-10-01

    The Cretaceous to Palaeogene Alpine exhumation of previously buried Variscan basements is recorded in the southern portion of the Western Carpathians in the Gemeric and Veporic units. The Meso-Cenozoic collisional processes resulted in basement exhumation of the Tatric Unit from Palaeogene to Neogene times. According to zircon and apatite fission track data, the Gemeric Unit, an uppermost thick-skinned thrust sheet, cooled from depth levels of ∼10 up to 2.5 km (temperature interval of ∼250-60 °C) about 88-64 Ma ago, after the collapse of overlying Meliata-Turňa-Silica Mesozoic accretionary prism. The middle and lower thick-skinned thrust sheets, Veporic and Tatric units, cooled from the depths of ∼10 up to 2.5 km ∼110-40 Ma ago. The process was controlled by unroofing of footwall from beneath the Gemeric Unit. About 50-20 Ma ago, the internal zone of Tatric Unit gradually exhumed to depth of <2 km and some parts of the unit appeared at the surface level. However, the external zone of Tatric Unit was buried beneath the Eocene to Lower Miocene sedimentary successions and exhumed to the subsurface level at ∼21-8 Ma ago, as a result of oblique collision of the Western Carpathians with the European Platform.

  7. 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

  8. 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.

  9. Polyploid evolution and Pleistocene glacial cycles: A case study from the alpine primrose Primula marginata (Primulaceae)

    PubMed Central

    2012-01-01

    Background Recent studies highlighted the role of Pleistocene climatic cycles in polyploid speciation and of southern Alpine refugia as reservoirs of diversity during glacial maxima. The polyploid Primula marginata, endemic to the southwestern Alps, includes both hexaploid and dodecaploid cytotypes that show no ecological or morphological differences. We used flow cytometry to determine variation and geographic distribution of cytotypes within and between populations and analyses of chloroplast (cp) and nuclear ribosomal (nr) DNA sequences from the Internal Transcribed Spacer (ITS) region to infer the evolutionary history of the two cytotypes and the auto- vs. allopolyploid origin of dodecaploid populations. Results We did not detect any intermediate cytotypes or variation of ploidy levels within populations. Hexaploids occur in the western and dodecaploids in the eastern part of the distributional range, respectively. The cpDNA and nrDNA topologies are in conflict, for the former supports shared ancestry between P. marginata and P. latifolia, while the latter implies common origins between at least some ITS clones of P. marginata and P. allionii. Conclusions Our results suggest an initial episode of chloroplast capture involving ancestral lineages of P. latifolia and P. marginata, followed by polyploidization between P. marginata-like and P. allionii-like lineages in a southern refugium of the Maritime Alps. The higher proportion of ITS polymorphisms in dodecaploid than in hexaploid accessions of P. marginata and higher total nucleotide diversity of ITS clones in dodecaploid vs. hexaploid individuals sequences are congruent with the allopolyploid hypothesis of dodecaploid origin. PMID:22530870

  10. 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

  11. Tectonic evolution of the Western Eger rift: a tale of two faults

    NASA Astrophysics Data System (ADS)

    Tomasek, Jan; Kley, Jonas; Fischer, Tomáš; Štěpančíková, Petra

    2017-04-01

    The Eger Rift and Cheb basin in northwestern Bohemia are part of the European Cenozoic Rift System. They are associated with earthquake swarms, voluminous CO2 outgassing and Quaternary mantle-derived volcanism. The Eger Graben, of which the Cheb basin is traditionally considered a subbasin, contains a Cenozoic volcano-sedimentary record no thicker than 500 m. The structure of the extensional system is dominated by two large faults: (1) the ENE-striking Krušné Hory Fault (KHF), which delimits the northwestern shoulder of the Eger rift and has accommodated tilting and uplift of the Erzgebirge, creating a present day elevation difference of 700 m; (2) the NNW-striking Mariánské Lázně Fault (MLF), which is the master fault of the Cheb basin. First-order structural relationships indicate that the MLF has cross-cut the Eger rift at right angle and offset it with dominantly normal sense of motion. These relationships suggest that activity on the MLF was accentuated late in the history of the rift, around early Pliocene time, reflecting a fundamental change of the governing stress field. We aim to constrain, in conjunction with a Czech companion project focussing on tectonic geomorphology and seismology, the tectonic evolution of the two basins, and in particular the kinematics and timing of the Krušné Hory (Erzgebirge) and Mariánské Lázně bounding faults over Late Cenozoic time. This will be done by modelling the subsidence of the basins from stratigraphic and structural data. Rift shoulder uplift, exhumation and fault offsets will be constrained by low-T thermochronology, especially (U-Th)/He on apatite (AHe). 2D cross-sections and restorable structural 3D models will delimit the range of possible fault geometries and constrain the magnitude of fault displacements, their gradients and the deep architecture of the large faults. The Cheb basin forms an approximate semi-ellipse in map view, suggesting it is a half-graben bounded by a listric, WSW-dipping MLF

  12. Towards a Holistic Model for the Tectonic Evolution of the North China Craton

    NASA Astrophysics Data System (ADS)

    Kusky, T. M.; Polat, A.; Windley, B. F.; Wang, J.; Deng, H.

    2016-12-01

    The North China Craton (NCC) consists of distinctly different tectonic elements assembled during the late Archean - early Proterozoic. We propose a new tectonic evolution of the NCC. The Eastern Block (EB) consists of small microblocks that resemble a collage of accreted arc-rocks from a sutured archipelago similar to the SW Pacific, accreted between 2.6 and 2.7 Ga. An Atlantic-type margin developed on the western side of the EB by 2.5 Ga, and a >1,300 km long arc/accretionary prism collided with this passive margin at 2.5 Ga, obducting ophiolites and ophiolitic mélanges, and forming a foreland basin. This was followed by arc-polarity reversal, and injection of mantle wedge-derived melts. By 2.43 Ga, the ocean behind the accreted arc closed through the collision of an oceanic plateau. Rifting of the amalgamated craton followed at 2.4-2.35 Ga, with a failed rift arm preserved in the center of the craton, and two that successfully made an ocean along the northern margin. By 2.3 Ga an arc built on older cratonic material collided with this passive margin which soon converted to an Andean-type margin. Andean margin tectonics affected much of the craton from 2.3-1.9 Ga, forming a broad E-W swath of continental margin magmas, and retro-arc sedimentary basins including a superimposed basin over the passive margin on the northern margin. From 1.88-1.79 Ga the craton experienced a craton-wide granulite facies metamorphism and basement reactivation event with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the craton. Early Proterozoic granulites and anatectic melts were generated by high-grade metamorphism and partial melting at mid-crustal levels beneath a collisionally-thickened plateau. This collision of the NCC on its northern margin was with the Columbia (Nuna) Continent. The NCC broke out in the period 1753-1673 Ma, as indicated by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites

  13. 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

  14. Constraints on the evolution of the Naga Hills: from disparate origins to tectonic amalgamation

    NASA Astrophysics Data System (ADS)

    Aitchison, J. C.; Clarke, G. L.; Ireland, T. R.; Ao, A.; Bhowmik, S. K.; Kapesa, L.; Roeder, T.; Stojanovic, D.; Kachovich, S.

    2016-12-01

    structural architecture differ markedly from that seen in classic Himalayan transects. New detrital zircon U/Pb studies reveal a fascinating history that suggests derivation of some units from Sibumasu rather than the Lhasa or Qiangtang terranes. Detailed study of this area sheds important light on the tectonic evolution of the SE Asia region.

  15. Pre-Mid-Mesozoic tectonic evolution of the Yukon-Tanana Terrane, Yukon and Alaska

    NASA Astrophysics Data System (ADS)

    Mortensen, J. K.

    1992-08-01

    Yukon-Tanana Terrane (YTT) underlies much of central and western Yukon and east central Alaska. Its history and tectonic evolution, particularly prior to mid-Mesozoic time, has been largely obscured by younger magmatism and tectonism. The application of geochronological and isotopic techniques over the past decade, together with detailed field studies in certain critical areas of the terrane, has shed new light on the early history of YTT. Much of YTT is a product of episodic continental arc magmatism, with three main pulses in Late Devonian-Early Mississippian, mid-Permian, and Late Triassic-Early Jurassic time. From Late Devonian to mid-Mississippian time, subduction was north or northeast dipping, but arc polarity was apparently reversed by mid-Permian time. The main, subhorizontal structural fabric characterizing much of YTT was produced between mid-Permian time and the onset of renewed magmatism in Late Triassic time and probably reflects a major continent-continent collision. Although the Triassic-Jurassic magmatism is also considered to be arc related, it occurred over a very broad area of not only YTT, but also Quesnellia, and the Stikine, Nisling, Cache Creek, and Slide Mountain terranes. This magmatism appears to have coincided with final amalgamation of the Intermontane Superterrane, and the arc polarity and the position and orientation of the associated subduction zone is still controversial. Available evidence suggests that Nisling Terrane is closely related to YTT and mainly consists of older strata that underlie the Devonian and younger units generally considered to be more typical of YTT. There are close similarities between YTT and a number of other "pericratonic" terranes in the central and eastern parts of the Cordillera, and it is likely that these terranes originally formed a single arc and arc basement assemblage which has now been fragmented and dispersed by transcurrent faulting.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Coastal evolution of the Sultanate Oman (Arabian Peninsula) - tectonic versus sea-level forcing

    NASA Astrophysics Data System (ADS)

    Hoffmann, Goesta; Gruetzner, Christoph; Reicherter, Klaus

    2010-05-01

    Along the coastline of the Sultanate of Oman (SE Arabian Peninsula) we find geological evidences for tsunamis, neotectonic movements and differential crustal uplift. These evidences are used to describe the Quaternary evolution of the coastline and to construct future scenarios. Coastal areas are dynamic and fast changing natural environments. Several factors, acting on different time scales control their evolution. Furthermore, coastal areas are densely populated, especially in the Sultanate of Oman where more than half of the population is living at the coast. Due to economic improvements Oman experiences substantial changes in land utilization, particularly in Al Batinah and Muscat regions. With the given natural boundary conditions different interests of various user groups are in conflict. Ongoing global climate change will result in further intensification of the situation. Coastal evolution is a function of several forcing factors e.g.: differential land movement which in turn is an effect of local variations in the tectonic stress field; climate and sediment availability. The various forcing factors are quantified by analysing Quaternary coastal sediments and geomorphologic features (e.g. terraces, notches) as archives and indicators. Long-term changes are described by the reconstruction and comparison of the relative sea-level development along the coastline. Short-term coastal changes are often related to natural hazards. Hurricanes as well as tsunamis are known to have affected Oman's coastline in the past. By analysing geological archives information regarding recurrence intervals and potential damages are revealed which allows assessing the risk and estimating the vulnerability. This is done for different areas along the coast which have been identified as key-locations. Sediment cores and ground-penetrating radar (GPR) surveys are used to analyse Quaternary coastal sediments.

  3. Late Quaternary loess landscape evolution on an active tectonic margin, Charwell Basin, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Hughes, Matthew W.; Almond, Peter C.; Roering, Joshua J.; Tonkin, Philip J.

    2010-10-01

    Loess deposits constitute an important archive of aeolian deposition reflecting wider patterns of glacial atmospheric circulation, and more localised interactions between riverine source areas, loess trapping efficiency and geomorphic controls on erosion rate. Conceptual models have been formulated to explain the coeval evolution of loess mantles and associated landscapes (loess landscape models) but none apply to areas of tectonically induced base-level lowering. This study uses an age sequence of alluvial fill terraces in the Charwell Basin, north-eastern South Island New Zealand, which straddles the transpressive Hope Fault, to investigate geomorphic controls on loess landscape evolution in an active tectonic region. We hypothesize that the more evolved drainage networks on older terraces will more effectively propagate base-level lowering by way of a greater areal proportion of steep and convex hillslopes and a smaller proportion of non-eroding interfluves. Eventually, as the proportion of interfluves diminishes and hillslope convexity increases, terraces shift from being net loess accumulators to areas of net loess erosion. We investigate the nature of erosion and the geomorphic thresholds associated with this transition. Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. The number of loess sheets and the thickness of loess increased across the three youngest terraces. The next oldest (ca. 150 ka) terrace remnant had the greatest maximum number of loess sheets (3) and loess thickness (8 m) but the loess mantle was highly variable. A detailed loess stratigraphic analysis and the morphometric analysis place this terrace in a transition between dominantly planar, uniformly loess-mantled landforms and loess-free ridge and valley terrain

  4. 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

  5. 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. Published by Oxford University Press on behalf of the Annals of Botany Company.

  6. 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.

  7. 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

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

    PubMed

    Bentley, Joanne; Verboom, G Anthony; Bergh, Nicola G

    2014-02-13

    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. 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. 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 sympatric species of Macowania indicates

  9. 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

  10. Multi-parameter monitoring of the construction and evolution of a snow bridge over a crevasse on an Alpine glacier

    NASA Astrophysics Data System (ADS)

    Ravanel, Ludovic; Malet, Emmanuel; Batoux, Philippe

    2017-04-01

    Snow bridges that form over the crevasses of the Alpine glaciers allow mountaineers and skiers to cross them easily but constitute an important danger in case of rupture. Between 2008 and 2014, 37 injured persons and 13 deaths related to falls into crevasse were recorded (i.e. an average of two deaths per year) on the glaciers of the French side of the Mont Blanc massif - out of the famous Vallée Blanche ski route, which however embodies an important part of the aid related to falls into crevasses. To understand the construction and evolution of these fragile structures, instrumentation was set up on the Glacier du Géant, at 3450 m a.s.l., near the Aiguille du Midi (3842 m a.s.l.), on the French side of the Mont Blanc massif, close to a crevasse whose bridge had recently collapsed over a length of 37 m. The maximum width of the crevasse in this area is 6 m. At the top of a 7-m-high pole - to prevent future snowfalls -, sensors have been installed in September 2016 to measure different snow and weather parameters: air temperature, wind speed and direction, snow height. An automatic camera surveys the crevasse and the snow bridge geometry. Several other sensors monitor the temperature of snow and air in the crevasse. In addition, an extensometer was installed into the crevasse to measure the evolution of its width. The results of the first 6 months of survey are presented, including the formation of the bridge in mid-November, during a period of snowfall associated with a strong wind. Although the instrumentation is well suited to the high mountain conditions, its maintenance is delicate due to the strong instability of the environment (glacier movements and extreme weather conditions, primarily) but the results of this work will bring new glaciological knowledges which should participate in a better safety on glaciers.

  11. Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Zhao, Yan; Sun, Yong; Diwu, Chunrong; Zhu, Tao; Ao, Wenhao; Zhang, Hong; Yan, Jianghao

    2017-05-01

    The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic. Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430-410 Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet + amphibole + rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370-360 Ma) and middle Carboniferous stage (ca. 335-315 Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of

  12. Precambrian tectonic evolution of the Tarim Block, NW China: New geochronological insights from the Quruqtagh domain

    NASA Astrophysics Data System (ADS)

    Shu, L. S.; Deng, X. L.; Zhu, W. B.; Ma, D. S.; Xiao, W. J.

    2011-10-01

    The Tarim Block is an important tectonic unit to understand the Proterozoic tectonic framework of the Central Asian Orogenic Belt and the supercontinent Rodinia. The granitic, dioritic, gabbroic intrusive rocks and volcanic-volcanoclastic rocks are widely distributed in the Quruqtagh domain of NE-Tarim. The precise ages of these rocks and their tectonic implications in this part of the world are not well understood. This paper reports geochronological data of gabbro, diorite and granitic rocks from Quruqtagh. LA ICPMS U-Pb zircon ages suggest that numerous of gabbroic and granitic rocks were mainly crystallized at ca. 800 Ma. New geochronological data from the magmatic zircons of gabbro, granite and paragneiss can be preliminarily divided into four groups, which are (1) 2469 ± 12 Ma or 2470 ± 24 Ma, (2) 933 ± 11 Ma to 1048 ± 19 Ma, (3) 806 ± 8 Ma, 798 ± 7 Ma, 799 ± 24 Ma, 698 ± 51 Ma (lower intercept age of the paragneiss), and (4) 1930 Ma (upper intercept age of the paragneiss), respectively. These age data are consistent with four tectono-thermal events that took ever place in the Tarim Block. The 93 U-Pb age data (seven for average Concordia age from seven igneous plutons, 86 for xenocrystic and metamorphic ones) from eight samples can be divided into four evolutionary stages: 2360-2550 Ma (peak of 2510 Ma), 1800-2020 Ma (peak of 1870 Ma), 860-1140 Ma (peak of 920 Ma) and 680-840 Ma (peak of 800 Ma), respectively. The age peak of 2500 Ma, consistent with characteristic period of a global building-continent event, indicates that the late Neoarchean-early Paleoproterozoic magmatism had been ever taken place in Tarim. Two peaks at 1870 Ma and 920 Ma, being two assembly periods of the middle Paleoproterozoic Columbia and the Neoproterozoic Rodinia supercontinents, suggest that Tarim had connections with both Columbia and Rodinia, whereas structural evidence of these two events is absent in Tarim. Notable peak of 800 Ma is interpreted as a response to the

  13. 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.

  14. Detailed tectonic evolution of the Reykjanes Ridge during the past 15 Ma

    NASA Astrophysics Data System (ADS)

    Benediktsdóttir, Á.; Hey, R.; Martinez, F.; HöSkuldsson, Á.

    2012-02-01

    We present a new detailed tectonic model of the Reykjanes Ridge which examines the rift propagation hypothesis for the V-shaped ridges and its asymmetric lithospheric accretion. Four major southward rift propagations extend through our entire survey area and several additional small scale rift propagations are observed, including northward propagators. If plume pulses only drive southward propagators, then two different driving mechanisms for propagators must exist. There is a major difference in the crustal accretion asymmetry between the area immediately off the Iceland shelf and that farther south, both in rift propagation pattern and free air gravity lineations. Furthermore, we identify two small offset features coined ponsu-transforms, from which rift propagation is both initiated and stopped. The pattern of the V-shaped ridges on the Reykjanes Ridge is not symmetric about the Reykjanes Ridge and the V-shaped ridges are not linear continuous features. Our rift propagation model produces excellent fits to magnetic data and provides a self-consistent model for the evolution of the Reykjanes Ridge during the past 15 Ma.

  15. 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.

  16. 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.

  17. Longitudinal to transverse drainage network evolution in the High Atlas (Morocco): The role of tectonics

    NASA Astrophysics Data System (ADS)

    Babault, Julien; van den Driessche, Jean; Teixell, Antonio

    2012-08-01

    The High Atlas of Morocco is a still-active, linear intracontinental mountain chain in the NW African plate, which results from weak crustal thickening associated with rift inversion during the Cenozoic and from uplift related to mantle thermal doming. A striking morphological feature of the High Atlas is the occurrence of both transverse and longitudinal (i.e., strike-parallel) drainage characterized by deep fluvial incision of more than 1000 m in low-relief topography of the axial zone of the chain. Most of the transverse component of the drainage appears to postdate the longitudinal component as indicated by recent or incipient captures and wind gaps. The longitudinal drainage is inherited from an early stage of fluvial organization controlled by the tectonic structures developed during upper crustal folding and thrusting in the post-Paleozoic cover. Amplification of N-S regional slope in the western High Atlas by continued crustal shortening and thickening triggered: (i) higher erosion rates in transverse than in longitudinal catchments and (ii) captures of longitudinal streams by transverse ones, creating a new organization of the drainage system toward the regional slope. Such evolution from a longitudinal to a transverse-dominated drainage may represent a common mechanism of fluvial network development in mountain belts where the amplification of the regional slope results from long-lived lithospheric convergence.

  18. 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

  19. Polyphase ductile/brittle deformation along a major tectonic boundary in an ophiolitic nappe, Alpine Corsica: Insights on subduction zone intermediate-depth asperities

    NASA Astrophysics Data System (ADS)

    Magott, Rémi; Fabbri, Olivier; Fournier, Marc

    2017-01-01

    In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-metagabbro interfaces, rare or absent at serpentinite-metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-metagabbro contacts could correspond to asperities whereas low-friction serpentinite-metagabbro contacts could correspond to creeping zones.

  20. Role of tectonic stress in seepage evolution along the gas hydrate-charged Vestnesa Ridge, Fram Strait

    NASA Astrophysics Data System (ADS)

    Plaza-Faverola, A.; Bünz, S.; Johnson, J. E.; Chand, S.; Knies, J.; Mienert, J.; Franek, P.

    2015-02-01

    Methane expulsion from the world ocean floor is a broadly observed phenomenon known to be episodic. Yet the processes that modulate seepage remain elusive. In the Arctic offshore west Svalbard, for instance, seepage at 200-400 m water depth may be explained by ocean temperature-controlled gas hydrate instabilities at the shelf break, but additional processes are required to explain seepage in permanently cold waters at depths >1000 m. We discuss the influence of tectonic stress on seepage evolution along the ~100 km long hydrate-bearing Vestnesa Ridge in Fram Strait. High-resolution P-Cable 3-D seismic data revealed fine-scale (>10 m width) near-vertical faults and fractures controlling seepage distribution. Gas chimneys record multiple seepage events coinciding with glacial intensification and active faulting. The faults document the influence of nearby tectonic stress fields in seepage evolution along this deepwater gas hydrate system for at least the last ~2.7 Ma.

  1. 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.

  2. The role of tectonics and climate in the late Quaternary evolution of a northern Amazonian River

    NASA Astrophysics Data System (ADS)

    Cremon, Édipo Henrique; Rossetti, Dilce de Fátima; Sawakuchi, André de Oliveira; Cohen, Marcelo Cancela Lisboa

    2016-10-01

    The Amazon basin has most of the largest rivers of the world. However, works focusing the geological evolution of the trunk river or its tributaries have been only partly approached. The Branco River constitutes one of the main northern Amazonian tributaries. A previous work proposed that, before flowing southward into the Negro-Amazon Rivers, the Branco River had a southwest to northeast course into the Caribbean Sea. The present work aimed to establish if the proposed change in the course of this river is supported by morphological and sedimentological data. Other goals were to discuss the factors influencing river development and establish its evolution over time within the chronological framework provided by radiocarbon and optically stimulated luminescence dating. The work considered the entire course of the Branco River downstream of the Precambrian Guiana Shield, where the river presumably did not exist in ancient times. The river valley is incised into fluvial sedimentary units displaying ages between 100 and 250 ky old, which record active and abandoned channels, crevasse splay/levees, and point bars. The sedimentary deposits in the valley include two alluvial plain units as old as 18.7 ky and which intersects a Late Pleistocene residual megafan. These characteristics suggest that a long segment of the Branco River was established only a few thousand years ago. Together with several structural anomalies, these data are consistent with a mega-capture at the middle reach of this river due to tectonic reactivation in the Late Pleistocene. This integrated approach can be applied to other Amazonian tributaries to unravel how and when the Amazonian drainage basin became established.

  3. Constraints on the tectonic and landscape evolution of the Bhutan Himalaya from thermochronometry

    NASA Astrophysics Data System (ADS)

    Adams, B. A.; Hodges, K. V.; Whipple, K. X.; Ehlers, T. A.; Soest, M. C.; Wartho, J.

    2015-06-01

    The observed geomorphology and calculated thermal histories of the Bhutan Himalaya provide an excellent platform to test ideas regarding the influence of tectonics and climate on the evolution of a convergent mountain range. However, little consensus has been reached regarding the late Cenozoic history of the Bhutan Himalaya. Some researchers have argued that observed geologic relationships show slowing deformation rates, such that the range is decaying from a geomorphic perspective, while others see the range as growing and steepening. We suggest that a better understanding is possible through the integrated interpretation of geomorphic and thermochronometric data from the comparison of predictions from models of landscape evolution and thermal-kinematic models of orogenic systems. New thermochronometric data throughout Bhutan are most consistent with a significant decrease in erosion rates, from 2 to 3 km/Ma down to 0.1-0.3 km/Ma, around 6-4 Ma. We interpret this pattern as a decrease in rock uplift rates due to the activation of contractional structures of the Shillong Plateau, an uplifted region approximately 100 km south of Bhutan. However, low-relief, fluvial landscapes throughout the Bhutanese hinterland record a late pulse of surface uplift likely due to a recent increase in rock uplift rates. Constraints from our youngest thermochronometers suggest that this increase in rock uplift and surface uplift occurred within the last 1.75 Ma. These results imply that the dynamics of the Bhutan Himalaya and Shillong Plateau have been linked during the late Cenozoic, with structural elements of both regions active in variable ways and times over that interval.

  4. The Cenozoic Tectonic Evolution of the West Qinling: Constraints on the Uplift and Deformation of the Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    GUO, Jinjing; HAN, Wenfeng; LI, Xuefeng

    The Cenozoic tectonic and geomorphologic processes of the West Qinling as a part of Qinghai-Tibet plateau could provide some constraints on the uplift and deformation model of the Qinghai-Tibet plateau. On the basis of the analysis for the Cenozoic sedimentary basin and its deformation features, regional fault frameworks and its kinematics, and geomorphologic records, the following preliminary conclusions could be drawn as follows: (1) Late Mesozoic-Cenozoic red bed sedimentary strata in the West Qinling, based upon their rock composition, spatial distribution, and tectonic deformation characteristics, can be divided into three tectonic lithostratigraphic units, that are Late Jurassic-Early Cretaceous, Late Cretaceous-Paleogene, and Neogene, which are corresponded to three tectonic evolution stages; (2) The fault-thrusting and fold-shortening of K 2-E in the West Qinling occurred at the end of Paleocene, synchronous with the crust shortening and thrusting in the entire Qinghai-Tibet plateau, which may indicate that the compressive tectonic stress from the collision convergence between the Indian plate and Eurasian plate had been transmitted to the West Qinling; (3) The West Qinling had entered a, relatively, stable tectonic period since the beginning of Neogene in which extensive erosion and planation occurred, and main planation surface and associated Neogene sedimentary strata consisting of red conglomerate and red clay finally formed before 3.6 Ma. This planation surface at present-day decreased gradually from 3200 m in the west to 1200 m in the east, which can be interpreted as continuous uplift of the West Qinling in the eastward expansion of the Qinghai-Tibet Plateau; (4) The structural deformation transition from thrusting-shortening to extension-strike slipping at 13-14 Ma or 8 Ma in the Southern Tibet have not appeared wide in the West Qinling, whereas fault thrusting predominated the total Cenozoic tectonic history and left-lateral strike-slip only

  5. Structural variety and tectonic evolution of strike-slip basins related to the Philippine Fault System, northern Luzon, Philippines

    NASA Astrophysics Data System (ADS)

    Ringenbach, Jean Claude; Pinet, Nicolas; StéPhan, Jean FrançOis; Delteil, Jean

    1993-02-01

    The northern part of the Philippine fault zone, in Luzon, corresponds to a complex braided system of left-lateral strike-slip faults. The NW oriented main active branch, which emerges from the Philippine Sea, splits into an array of north striking splays responsible for the tectonic evolution of the Central Cordillera. This complex fault pattern has favored local stress field variations. Strike-slip basins have evolved in this framework along or in the vicinity of the main splays of the Philippine fault. Apart from the classical pull-apart tectonics on a releasing fault termination, overlap, or bend, we describe other mechanisms such as the strike-slip tilting or the warping of a strip limited by two strike-slip faults. The strike-slip basins are good recorders of the evolution of the Philippine fault system. Those located along the north striking cordilleran faults individualized in late early Pliocene to Pleistocene time when the present-day Philippine fault initiated, but their main control is the fault shape acquired in upper middle Miocene time. The recent tectonic evolution of the fault system is best recorded in central Luzon, where the active basins trace an asymmetrical V shape, with the longest branch trending NE parallel to the East Luzon Trough, and the shortest one trending NW related to the Philippine fault. Both the fault pattern and the basin distribution demonstrate the influence of the Benham Rise in the tectonic evolution of Luzon. The structural setting is interpreted as the result of an early Miocene collision event between the Benham Rise and the eastern margin of Luzon, and subsequent inception of the NW striking strand of the Philippine fault. The present locations of the basins result from the interaction between the structural heritage and the present-day regional plate motion.

  6. Insights into the evolution of tectonically-active glaciated mountain ranges from digital elevation model analyses

    NASA Astrophysics Data System (ADS)

    Brocklehurst, S. H.; Whipple, K. X.

    2003-12-01

    Glaciers have played an important role in the development of most active mountain ranges around the world during the Quaternary, but the interaction between glacial erosion (as modulated by climate change) and tectonic processes is poorly understood. The so-called glacial buzzsaw hypothesis (Brozovic et al., 1997) proposes that glaciers can incise as rapidly as the most rapid rock uplift rates, such that glaciated landscapes experiencing different rock uplift rates but the same snowline elevation will look essentially the same, with mean elevations close to the snowline. Digital elevation model-based analyses of the glaciated landscapes of the Nanga Parbat region, Pakistan, and the Southern Alps, New Zealand, lend some support to this hypothesis, but also reveal considerably more variety to the landscapes of glaciated, tectonically-active mountain ranges. Larger glaciers in the Nanga Parbat region maintain a low downvalley gradient and valley floor elevations close to the snowline, even in the face of extremely rapid rock uplift. However, smaller glaciers steepen in response to rapid uplift, similar to the response of rivers. A strong correlation between the height of hillslopes rising from the cirque floors and rock uplift rates implies that erosion processes on hillslopes cannot initially keep up with more rapid glacial incision rates. It is these staggering hillslopes that permit mountain peaks to rise above 8000m. The glacial buzzsaw hypothesis does not describe the evolution of the Southern Alps as well, because here mean elevations rise in areas of more rapid rock uplift. The buzzsaw hypothesis may work well in the Nanga Parbat region because the zone of rapid rock uplift is structurally confined to a narrow region. Alternatively, the Southern Alps may not have been rising sufficiently rapidly or sufficiently long for the glacial buzzsaw to be imposed outside the most rapidly uplifting region, around Mount Cook. The challenge now is to understand in detail

  7. Thermochronological Evolution of the Sierra Maestra, Cuba: Significance for Caribbean Tectonics

    NASA Astrophysics Data System (ADS)

    Rojas-Agramonte, Y.; Neubauer, F.; Handler, R.; Hejl, E.; Bojar, A.; Garcia-Delgado, D. E.

    2002-12-01

    The Sierra Maestra in southeastern Cuba comprises Paleogene intraoceanic volcanic arc sequences which have been accreted to the North American continental margin during the late Middle Eocene, during the final stages of collision with the Caribbean plate. Geochronological analysis and geobarometric investigations on samples from Eocene granitoids constrain the cooling history and tectonic evolution of the region. Granitoids intruded at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of approx. 4.5-8 km. 40Ar/39Ar dating of biotite yielded ages of 50+/-2 to 54+/-4 Ma (2-sigma errors), indicating cooling through ca. 300 oC. Zircon and apatite fission track ages range from 32+/-3 to 46+/-4 Ma and 31+/-10 to 44+/-13 Ma, respectively, and date cooling through 250+/-50 oC and 110+/-20 oC. These data suggest fast cooling and exhumation of the granitoids during collisional processes in the Eocene. Apatite track length measurements show a bimodal frequency distribution suggesting initial very fast cooling between 45 and 40 Ma, down to 120 oC, followed by a period of 30 Ma where almost no variation occurred in the temperature. Final cooling occurred since 12 Ma and is probably related to transform faulting along the southern margin of the Sierra Maestra. We propose that slab breakoff of the subducting North American plate occurred during the final stages of collision between the North American and Caribbean plates, and we argue, therefore, that the granitoids cooled and were exhumed as a consequence of this process and eastward migration of the slab-tear. Several lines of evidence support this model: (1) Published cooling and exhumation ages of the granitoids are younging from west to east, with old ages (ca. 56 Ma) in the west and young ones in the east (ca. 49 Ma). (2) Subsequent rapid cooling through 300 to 110 °C occurred also partly in the Middle to early Late Eocene, suggesting rapid uplift and cooling of the entire crust as granitoids intruded at a

  8. Provenance Constraints on the Mesozoic-Cenozoic Tectonic Evolution of the Queen Charlotte Islands Region

    NASA Astrophysics Data System (ADS)

    Mahoney, J.; Haggart, J. W.; Kimbrough, D.; Grove, M.

    2007-05-01

    The medial Cretaceous magmatic arc system of western North America was flanked by a series of forearc basins extending from Mexico to Alaska. Cretaceous strata in the Queen Charlotte Islands of northwest British Columbia are unique in this series of basins, as these strata have been displaced from the arc system by formation of the extensional Queen Charlotte basin in Cenozoic time. This displacement complicates reconstruction of the forearc basin, and makes it difficult to evaluate the controls on basin evolution. Sedimentologic, paleontologic, and detrital zircon analyses of forearc strata represented by the Valanginian- Campanian Queen Charlotte Group (QCG) constrain basin evolution and provide a framework for an interpretation of the Mesozoic-Cenozoic tectonic evolution of the Queen Charlotte Islands region. Basin subsidence initiated in Valanginian time with a marine transgression over irregular topography consisting of extensional fault blocks of pre-Cretaceous strata. Locally derived conglomerates at the base of the Longarm Formation are overlain by shallow marine shelf deposits that represent a westward-deepening, fining-upward transgressive succession with an eastern depositional edge that migrated eastward during Valanginian to Aptian time. West-directed paleocurrents and a unimodal detrital zircon population of 120-175 Ma grains provide the first linkage between the Cretaceous QCG and unroofed Jura-Cretaceous plutons of the Coast Plutonic Complex to the east. This initial transgressive sequence is superseded by a second pulse of clastic detritus in early Albian time, characterized by an easterly-derived, fossiliferous shallow-shelf sandstone (Haida Formation), fine-grained, outer shelf to upper slope strata (Bearskin Bay Formation), and mass-sediment gravity flows (Skidegate Formation). The unimodal zircon population (ca 140-175 Ma) in the lower Haida Formation is interpreted to reflect renewed uplift of Jura-Cretaceous arc plutons by contractional

  9. Tectono-metamorphic evolution of the upper plate of the Eo-Alpine nappe-stack: constraints from the Oberhof Window (Carinthia, Austria)

    NASA Astrophysics Data System (ADS)

    Hollinetz, Marianne Sophie; Huet, Benjamin; Iglseder, Christoph; Rantitsch, Gerd; Grasemann, Berhard

    2017-04-01

    The Upper Austro-Alpine Unit in the Eastern Alps corresponds to a nappe-stack that formed during the Eo-Alpine Cretaceous event. It is dominated by crystalline rocks that show Variscan, Permo-Triassic, Eo-Alpine and Neo-Alpine metamorphic imprints. Understanding the tectono-metamorphic evolution of the Eo-Alpine nappe-stack is therefore hampered by a complex polyphase history. Most published studies focused on the subducted lower plate that contains the eclogite-bearing nappes (Koralpe-Wölz nappe system) but the upper plate (Ötztal-Bundschuh nappe system and Drauzug-Gurktal nappe system) is less understood. Our contribution focuses on the tectono-metamorphic evolution of the Bundschuh nappe (Oberhof Window, Carinthia, Austria). This nappe contains metasediments intruded by granites of Ordovician age. Characteristically, these rocks underwent Variscan amphibolite-facies. They were later covered by Carboniferous to Mesozoic sediments and, all together, overprinted by greenschist to amphibolite-facies metamorphism in the upper plate of the Eo-Alpine wedge. During this event, the Bundschuh nappe was overthrusted by the nappes of the Drauzug-Gurktal nappe system. The core of the window is occupied by the middle-grained "Oberhof orthogneiss". LA-ICP-MS U/Pb zircon dating yielded a late Ordovician age for its protolith. The orthogneiss is overlain by the transgressive Carboniferous metasediments comprising meta-conglomerate, graphite schist and quartzite. The Bundschuh nappe is overthrusted by garnet-micaschist, amphibolite, hornblende-garbenschist, calc-micaschist, quarzite and graphitic schist interpreted as parts of the basal Drauzug-Gurktal nappe system. Deformation is characterized by isoclinal folds with an E-W/SE-NW trending fold-axes and top-to-the-East/South-East shearing. This kinematics is related to normal faulting in the upper part of the Eo-Alpine orogenic wedge. The graphite schist contains an assemblage of isolated round garnet and abundant chloritoid in

  10. The tectonic evolution of the Songpan-Garzê (North Tibet) and adjacent areas from Proterozoic to Present: A synthesis

    NASA Astrophysics Data System (ADS)

    Roger, Françoise; Jolivet, Marc; Malavieille, Jacques

    2010-09-01

    The Triassic orogeny in North Tibet results from interactions between the South China, North China and Qiangtang (North Tibet) blocks during the closure of the Paleotethys ocean. It is mainly composed, from west to east, by the Bayan Har, Songpan-Garzê, and Yidun (or Litang-Batang) terranes. We focus here on the Triassic Songpan-Garzê fold belt and the actual eastern margin of the Tibetan Plateau which is one of the key areas for understanding the tectonic evolution of the Asian continent and the Tibetan Plateau. At least three major deformation phases are recognized in eastern Tibet and south-east of the South China block: a Neoproterozoic phase (1-0.75 Ga) correlated to the assembly and break-up of the Rodinia Continent, a Late Triassic compression event and finally a Tertiary deformation related to the India-Asia collision. The tectonic and geodynamic history of this part of Asia is very complex and often vigorously debated. For example the Triassic compression event in Tibet is usually associated to the Indosinian Orogeny originally defined in Vietnam but this is probably an oversimplification. Our purpose is to review the various models proposed in the literature and to synthesize the tectonic and geodynamic history of this area. We show that the Songpan-Garzê fold belt is not a typical collisional belt: the triangular shape of the closing oceanic basin as well as the huge volume of accreted sediments did not allow a complete continent-continent collision. Finally, the tectonic inheritance plays a major role in the evolution of the eastern margin of Tibet as most of the major Tertiary tectonic structures in the Longmen Shan are reactivated Paleozoic and Mesozoic faults.

  11. 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

  12. Quantitative reconstruction of late Holocene surface evolution on an alpine debris-flow fan

    NASA Astrophysics Data System (ADS)

    Schürch, Peter; Densmore, Alexander L.; Ivy-Ochs, Susan; Rosser, Nick J.; Kober, Florian; Schlunegger, Fritz; McArdell, Brian; Alfimov, Vasili

    2016-12-01

    Debris-flow fans form a ubiquitous record of past debris-flow activity in mountainous areas, and may be useful for inferring past flow characteristics and consequent future hazard. Extracting information on past debris flows from fan records, however, requires an understanding of debris-flow deposition and fan surface evolution; field-scale studies of these processes have been very limited. In this paper, we document the patterns and timing of debris-flow deposition on the surface of the large and exceptionally active Illgraben fan in southwestern Switzerland. We use terrain analysis, radiocarbon dating of sediment fill in the Illgraben catchment, and cosmogenic 10Be and 36Cl exposure dating of debris-flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years. We show that the fan surface preserves a set of debris-flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago. This rock avalanche shifted the apex of the fan and impounded sediment within the Illgraben catchment. Subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe, revealed by the cosmogenic radionuclide dates and by cross-cutting geometrical relationships on the fan surface. This pattern of frequent avulsion and fan surface occupation provides field-scale evidence of the type of large-scale compensatory behavior observed in experimental sediment routing systems.

  13. Tectonic evolution of northwestern Imbrium of the Moon that lasted in the Copernican Period

    NASA Astrophysics Data System (ADS)

    Daket, Yuko; Yamaji, Atsushi; Sato, Katsushi; Haruyama, Junichi; Morota, Tomokatsu; Ohtake, Makiko; Matsunaga, Tsuneo

    2016-09-01

    The formation ages of tectonic structures and their spatial distributions were studied in the northwestern Imbrium and Sinus Iridum regions using images obtained by Terrain Camera and Multiband Imager on board the SELENE spacecraft and the images obtained by Narrow Angle Camera on board LRO. The formation ages of mare ridges are constrained by the depositional ages of mare basalts, which are either deformed or dammed by the ridges. For this purpose, we defined stratigraphic units and determined their depositional ages by crater counting. The degradation levels of craters dislocated by tectonic structures were also used to determine the youngest limits of the ages of the tectonic activities. As a result, it was found that the contractions to form mare ridges lasted long after the deposition of the majority of the mare basalts. There are mare ridges that were tectonically active even in the Copernican Period. Those young structures are inconsistent with the mascon tectonics hypothesis, which attributes tectonic deformations to the subsidence of voluminous basaltic fills. The global cooling or the cooling of the Procellarum KREEP Terrane region seems to be responsible for them. In addition, we found a graben that was active after the Eratosthenian Period. It suggests that the global or regional cooling has a stress level low enough to allow the local extensional tectonics.[Figure not available: see fulltext.

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

    NASA Astrophysics Data System (ADS)

    Goren, Liran; Petit, Carole

    2017-04-01

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

  15. 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

  16. Lithospheric structure of the Gorringe Bank: Insights into its origin and tectonic evolution

    NASA Astrophysics Data System (ADS)

    JiméNez-Munt, I.; Fernã Ndez, M.; VergéS, J.; Afonso, J. C.; Garcia-Castellanos, D.; Fullea, J.

    2010-10-01

    The Gorringe Bank is a 5000 m high seamount near the Atlantic coast of Iberia characterized by a 9 m high geoid anomaly and a ˜120 mGal Bouguer anomaly relative to the surrounding abyssal plains. It has been linked to a NW directed thrust carrying exhumed upper mantle rocks and transitional crust on top of flexed-down Eurasian oceanic crust along the Tagus Abyssal Plain. However, estimations of crustal shortening have yielded dissimilar results, and the deep structure of the ridge remains highly unknown. We present a restored cross section and a new model of the lithospheric structure based on gravity, geoid, elevation, and the presence of serpentinized peridotites. At least 20 km of shortening took place along a flat-ramp-flat thrust fault, and the density structure of the lithosphere is consistent with mantle serpentinization varying from 70% at the surface to 20% at 14 km depth and 0% at 40 km. The topographic relief and gravity anomalies are explained by assuming a flexural isostatic model with an elastic thickness Te of ˜30 km. The evolution of the Gorringe Bank since the Late Jurassic is interpreted in relation to Eurasia-Africa-North America plate motion in four stages: (1) transtension between Newfoundland-Iberia and Africa, which generated small oceanic basins and mantle exhumation; (2) opening of the North Atlantic and seafloor spreading at the NW side of the exhumed Gorringe, which produced gabbro intrusions and serpentinization; (3) a quiescent tectonic period dominated by subsidence and sediment accumulation; and (4) a transpressional plate boundary between Eurasia and Africa with NW directed subcrustal thrusting and generation of the present Gorringe relief.

  17. Quaternary tectonic evolution of the Northern Gulf of Elat/Aqaba along the Dead Sea Transform

    NASA Astrophysics Data System (ADS)

    Hartman, Gal; Niemi, Tina M.; Tibor, Gideon; Ben-Avraham, Zvi; Al-Zoubi, Abdallah; Makovsky, Yizhaq; Akawwi, Emad; Abueladas, Abdel-Rahman; Al-Ruzouq, Rami

    2014-12-01

    The northern Gulf of Elat/Aqaba is located in the transition between the deep marine basins of the gulf and the shallow onland basins of the Arava Valley. Interpretation of 500 km of high-resolution seismic reflection data collected across the northern shelf reveals the tectonic structure and evolution of this transition. Six NNE-trending faults and one E-W trending transverse fault are mapped. Slip rates are calculated based on measured offsets and age determination based on a radiocarbon-calibrated sedimentation rate and a Quaternary age model. The most active fault is the Evrona Fault that absorbs most of the left lateral slip within the basin with an average sinistral slip rate of 0.7 ± 0.3 mm/yr through the Late Pleistocene and 2.3-3.4 mm/yr during the Holocene. Two intrabasin faults east of the Evrona Fault that have been inactive for the last several tens of thousands of years were mapped, and motion from these faults has likely transferred to the Evrona Fault. The basin is flanked on the west by the Elat Fault and on the east by the Aqaba Fault. Both faults are marked by large bathymetric escarpments. Based on displaced seismic reflectors, we calculate a Holocene vertical slip rate of 1.0 ± 0.2 and 0.4 ± 0.1 mm/yr for the Elat and Aqaba Faults, respectively. The geometry, slip rates, and slip history of the northern Gulf of Elat/Aqaba faults show that during the Late Pleistocene several intrabasin faults became dominant across the basin but that during the Holocene the Evrona Fault accommodates most of the strike slip.

  18. 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.

  19. South China sea tectonic evolution and hydrocarbon potential: new geological and geophysical constraints

    SciTech Connect

    Ru, K.; Pigott, J.D.

    1985-02-01

    The South China Sea has yet to receive a DSDP investigation; consequently, numerous untested models have been proposed for its post-Cretaceous evolution. From a compilation of regional oceanographic heat-flow measurements with offshore and onshore bore-hole temperatures, the authors thermally model and constrain possible interpretations of its tectonic evolutionary path. The heat-flow data, together with magnetic profiles, depth to basement determinations, and regional sediment isopachs, characterize two principal subbasin extensional elements - one trending east-west (northern area between Hainan and Luzon) and the other trending northeast-southwest (central area between Palawan and Vietnam. The thermal models of simple lithosphere cooling suggest the central area began spreading 55-58 m.y.B.P. and the northern region 34-35 m.y.B.P. These dates of incipient extension correspond to two principal unconformities in Paleocene and Oligocene strata of both offshore China and Palawan, and together they indicate regional uplift of the South China Sea owing to thermal expansion prior to the spreading events. The thermal models also suggest that in the northern region, spreading ceased approximately 19 m.y.B.P., which compares favorably with published magnetic estimates of 17.7 m.y. B.P.A. late Cenozoic heating event is evidenced by a thermal anomaly in the southern portion of the central region (southern Vietnam margin) that may be related to incipient spreading along a zone of crustal weakness inherited from the Jurassic-Cretaceous Sunda-Tethys suture. Overall, these data tend to support the hypothesis of spreading occurring first in the central region and then in the northern region.

  20. Formation and tectonic evolution of the Pattani Basin, Gulf of Thailand

    SciTech Connect

    Bustin, R.M.; Chonchawalit, A.

    1995-10-01

    The stratigraphic and structural evolution of the Pattani Basin, the most prolific petroleum basin in Thailand, reflects the extensional tectonic regime of continental Southeast Asia. E-W extension resulting from the northward collision of India with Eurasia since the Early Tertiary resulted in the formation of a series of N-S-trending sedimentary basins, which include the Pattani Basin. The sedimentary succession in the Pattani Basin is divisible into synrift and postrift sequences. Deposition of the synrift sequence accompanied rifting and extension, with episodic block faulting and rapid subsidence. The synrift sequence comprises three stratigraphic units: (1) Upper Eocene to Lower Olikgocene alluvial-fan, braided-river, and floodplain deposits; (2) Upper oligocene to Lowe Miocene floodplain and channel deposits; and (3) a Lower Miocene regressive package consisting of marine to nonmarine sediments. Post-rift succession comprises: (1) a Lower to Middle Miocene regressive package of shallow marine sediments through floodplain and channel deposits; (2) an upper Lower Miocene transgressive sequence; and (3) and Upper Miocene to Pleistocene transgressive succession. The post-rift phase is characterized by slower subsidence and decreased sediment influx. The present-day shallow-marine condition in the Gulf of Thailand is the continuation of this latest transgressive phase. The subsidence and thermal history of the Pattani Basin is consistent with a nonuniform lithospheric-stretching model. The amount of extension as well as surface heat flow generally increases from the margin to the basin center. The crustal stretching factor ({beta}) varies form 1.3 at the basin margin to 2.8 in the center. The subcrustal stretching factor ({delta}) ranges from 1.3 at the basin margin to more than 3.0 in the basin center. 31 refs., 13 figs., 4 tabs.

  1. 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.

  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. 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.

  4. 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

  5. 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

  6. 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.

  7. The Central Anatolian Volcanic Province: Geochronological Constraints on the Spatiotemporal Evolution of Volcanism and Links to Tectonic Processes

    NASA Astrophysics Data System (ADS)

    Schleiffarth, W. K.; Reid, M. R.; Darin, M. H.; Cosca, M. A.

    2016-12-01

    Volcanism associated with the Miocene to Holocene Central Anatolian Volcanic Province (CAVP) occurred during a complex tectonic transition from collision to tectonic escape. The temporal and spatial evolution of volcanism, as well as its relationship to regional tectonic events, remain poorly constrained in Central Anatolia. New 40Ar/39Ar geochronology along with a comprehensive compilation of published age data provide new insights into the evolution of the volcanic province. These new data also suggest that the CAVP should be expanded to include similar age volcanic centers farther east, namely Yamadağ, Kepezdağ, and Sivas. We identify three major phases of Miocene and younger volcanism and present a new tectono-magmatic framework for Central Anatolia. Phase 1 (20-12 Ma) is characterized by voluminous, mafic-intermediate volcanic centers concentrated near fault zones >100 km north of the Bitlis-Zagros suture zone, primarily in eastern Central Anatolia. Phase 2 (11-5 Ma) is characterized by an ignimbrite flare-up and eruptions at small, intermediate, polygenetic volcanic centers; both are concentrated in western Central Anatolia, west of the Ecemiş fault zone. Phase 3 (4-0 Ma) is characterized by large stratovolcanoes and monogenetic volcanoes primarily concentrated at Erciyesdağ and Hasandağ along the Ecemiş and Tuz Gölü fault zones, respectively. These new constraints on the evolution of the CAVP suggest a close link to large-scale tectonic processes in the region, and here we propose a new tectono-magmatic model for Central Anatolia. From late Eocene to early Miocene time ( 40­-20 Ma), north-directed flat-slab subduction beneath Central Anatolia resulted in widespread contraction and volcanic quiescence. Major contraction associated with "hard" Arabia-Eurasia collision at 20 Ma coincided with the initiation of volcanism in the CAVP (Phase 1), the latter caused by initial slab foundering and rollback. Slab rollback volcanism continued into the late

  8. 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

  9. Deciphering thermal - tectonic evolution of early Earth : High-P rocks in Paleoproterozoic orogens

    NASA Astrophysics Data System (ADS)

    Ganne, Jérôme; de Andrade, Vincent; Weinberg, Roberto; Dubacq, Benoît.; Vidal, Olivier; Baratoux, Lenka; Chardon, Dominique; Dioh, Edmond; Kagambèga, Nicolas; Naba, Séta

    2010-05-01

    Significant progress in metamorphic modelling has opened new opportunities to decode the P-T records of low-temperature metamorphic rocks (Yamato et al, 2007 and refs. therein) that comprise large tracts of exposed Archean and Paleoproterozoic terrains. We have seized these opportunities and report on the first discovery of blueschist metamorphic conditions (14 kb, 450°C) preserved within greenstone belts from a large Paleoproterozoic magmatic province in the West Africa Craton. Results obtained with two different thermodynamic approaches (multi-equilibrium vs pseudosection calculations) using updated and independent thermodynamic databases ("Tweeq" vs " Perple-X") are complementary. They yield a coherent metamorphic evolution (from M1 to M2), which reflect a temporal change in the thermal evolution during tectonic activity in the Birimian province. M1 is a relic metamorphic event. It is characterized by early parageneses with T between 300-450°C and low geothermal gradient (10-15°C/km) throughout. High-P (14kb), low-T (450°C) chlorite-phengite assemblages have been clearly identified along low-T granitoids-greenstones contacts in the Fada N'Gourma area (sample Fa-33, Fa-34). Similar HP-LT conditions are also expected in the core of greenstones belts (work in process). They display tight P-T paths and clockwise isothermal decompressions. M1 assemblages are linked to a remnant fabric termed S1, probably developed during a short-lived event (D1) and predating the major pulse of granitoids intrusions at 2.15 Ga. M2a is a contact metamorphism with dominant parageneses indicative of T ranging between 250-650°C and moderate geothermal gradients (20-30°/km). M2a assemblages are linked to a regional NNE-SSW to NE-SW trending steeply-dipping planar fabric termed S2 and associated with magma intrusion. S2 is likely to occur during a long-lived D2 shortening event, probably starting after 2.15 Ga, and that will shape the greenstones basins into narrow belts (pure

  10. Source and Magma Evolution of the tuff of Elevenmile Canyon, Stillwater Range/ Clan Alpine and northern Desatoya Mountains, western Nevada.

    NASA Astrophysics Data System (ADS)

    Stepner, D.; O'Neil, J.; Cousens, B.; Landon-Browne, A.

    2016-12-01

    The mid-Tertiary Ignimbrite Flare-up, related to the subduction and subsequent rollback of the Farallon plate beneath western North America, was one of the most voluminous episodes of felsic pyroclastic volcanism in the world. In order to better understand the implication of felsic volcanism in the evolution of the Great Basin, this study presents new geochemical and isotopic measurements from the tuff of Elevenmile Canyon (TEC) within the Western Nevada Volcanic Field. The 25.1 Ma TEC is the largest volume tuff ( 2500 km3) related to 6 Oligocene overlapping calderas and related plutons in the southern Stillwater Range and Clan Alpine and Desatoya Mountains. The TEC is a crystal-rich tuff containing plagioclase > quartz @ K-feldspar > biotite ± hornblende and clinopyroxene. The TEC exhibits evolved compositions ranging from trachyandesite to rhyolite (SiO2 = 61-76%) . Modeled major and trace element variations are consistent with fractional crystallization from a mafic parental magma. However, none of the observed mafic lava compositions in the region match the required parental composition. Isotopic compositions of pumice fragments and whole rock samples show a strong enriched mantle affinity (initial 87Sr/86Sr = 0.70495 - 0.70535, initial eNd= -1.13 - -0.39) similar to that of coeval but unrelated Cenozoic basalts. Initial 87Sr/86Sr in plagioclase phenocrysts are less than whole-rock values, indicated plagioclase crystallized from a less evolved (deeper?) magma and was mixed with more evolved magma. Pb isotopes (initial 206Pb/204Pb = 19.042 - 19.168, 207Pb/204Pb = 15.557 - 15.664), which are more sensitive to crustal assimilation, suggest only a minor contamination from an unexposed, radiogenic basement unit. Chemical and isotopic modeling show only a minor role for assimilation of upper crustal units found as xenoliths within the TEC. These observations suggest that, in the context of the mid-Tertiary flare-up, upper crustal anatexis played only a minor role in

  11. Origin and tectonic evolution of the accretionary complex in Central Mongolia

    NASA Astrophysics Data System (ADS)

    Ueda, T.; Otoh, S.; Fujimoto, T.; Yoshikazu, K.; Yamamoto, K.

    2016-12-01

    Introduction Mongolia occupies a part of the Central Asian Orogenic Belt and consists of a complicated collage of terranes. However, the origin and formation processes of these terranes have been obscure. We study the origin and tectonic evolution of accretionary complexes (AC's) in Central Mongolia (CM) from detrital zircon geochronology. Geologic setting CM consists of (1) the Haraa terrane composed of an Early Paleozoic AC cut by Late Ordovician plutons (Orolmaa and Erdenesajhan) and (2) the underlying Khentei terrane composed of a Middle to Late Paleozoic AC and shallow-marine cover (Kurihara et al., 2009). The AC's strike NE and dip to NW. The sandstone of the AC's is mostly lithic arenite with volcanic rock fragments. Method The U-Pb age of detrital zircons from sandstone samples (7 samples from the Haraa AC and 8 from the Khentei AC) was determined with the LA-ICPMS installed in the Graduate School of Environmental Studies, Nagoya University. Results The upper 3 Haraa samples showed multimodal age distributions with small peaks at 420-650 Ma, 700-1000 Ma, 1600-2200 Ma, and 2300-2700 Ma. The lower 12 showed unimodal age distributions with the youngest peaks (YP) between the Devonian and the Early Permian. Discussion The volcaniclastic nature of the measured sandstone indicates that the YP indicates the depositional age (DA) of each sample. The range of DA of the multimodal sandstone was 526-426 Ma, whereas the ranges of DA of the unimodal sandstone were 409-374 Ma (Early Devonian), 358-332 Ma (Early Carboniferous), and 304-259 Ma (Early Permian). The DA clearly showed a downward-younging age polarity and roughly coincides with the age of Paleozoic igneous activity in the Tuva-Mongol Massif, indicating that the AC's intermittently grew downwards in front of it. The multimodal age distribution with Pan-African (550-750 Ma) zircons is close to that of the Early Paleozoic sandstone of the Kufra Basin in the Saharan Metacraton, which occupied a northern margin of

  12. Formation and tectonic evolution of Southeastern China and Taiwan: Isotopic and geochemical constraints

    NASA Astrophysics Data System (ADS)

    John, B. M.; Zhou, X. H.; Li, J. L.

    1990-11-01

    The southern part of China consists of the Proterozoic Yangtze Craton and the Phanerozoic South China foldbelts (including the Himalayan foldbelt of Taiwan). Models for continental growth have been many and controversial. Isotopic and geochemical data from Mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of Southeastern China and to evaluate whether the young Phanerozoic foldbelts are representative of old rejuvenated landmass, whether they characterize crustal accretion through successive subduction processes, hence suggesting a net growth of continental mass, or whether they represent some intermediate situation. Available Sm-Nd isotopic data for Phanerozoic granitoids and metasediments from the South China foldbelts and Taiwan invariably show Proterozoic model ages ( TDM) ranging from 1 to 2.5 Ga, with a mean of 1.54 ± 0.30 (1σ) Ga. All rocks have negative ɛNd(T) values (-2 to -15), suggesting variable but important contributions of old continental materials to the sources of the Phanerozoic rocks. Obviously they do not represent wholesale growth of continental mass. The granitoids of the South China foldbelts have multiple origins as viewed from their chemical and isotopic characteristics. Secular geochemical variation has been established for inland granitoids of Proterozoic to Mesozoic age. Their high ISr values (0.710-0.737) suggest that most granitoids are essentially anatectic products of ancient continental crust. This is compatible with remelting via microcontinental collision or terrane accretion. Repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization. Mesozoic granitoids (excluding A-type alkaline granites) in the coastal region and Taiwan show relatively low ISr(0.705-0.710) and high ɛNd values, implying that greater amounts of mantle components have been added to ancient continental material in the generation of these

  13. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys

    NASA Astrophysics Data System (ADS)

    Metcalfe, I.

    2013-04-01

    Present-day Asia comprises a heterogeneous collage of continental blocks, derived from the Indian-west Australian margin of eastern Gondwana, and subduction related volcanic arcs assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones containing ophiolites, accretionary complexes and remnants of ocean island arcs. The Phanerozoic evolution of the region is the result of more than 400 million years of continental dispersion from Gondwana and plate tectonic convergence, collision and accretion. This involved successive dispersion of continental blocks, the northwards translation of these, and their amalgamation and accretion to form present-day Asia. Separation and northwards migration of the various continental terranes/blocks from Gondwana occurred in three phases linked with the successive opening and closure of three intervening Tethyan oceans, the Palaeo-Tethys (Devonian-Triassic), Meso-Tethys (late Early Permian-Late Cretaceous) and Ceno-Tethys (Late Triassic-Late Cretaceous). The first group of continental blocks dispersed from Gondwana in the Devonian, opening the Palaeo-Tethys behind them, and included the North China, Tarim, South China and Indochina blocks (including West Sumatra and West Burma). Remnants of the main Palaeo-Tethys ocean are now preserved within the Longmu Co-Shuanghu, Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub Suture Zones. During northwards subduction of the Palaeo-Tethys, the Sukhothai Arc was constructed on the margin of South China-Indochina and separated from those terranes by a short-lived back-arc basin now represented by the Jinghong, Nan-Uttaradit and Sra Kaeo Sutures. Concurrently, a second continental sliver or collage of blocks (Cimmerian continent) rifted and separated from northern Gondwana and the Meso-Tethys opened in the late Early Permian between these separating blocks and Gondwana. The eastern Cimmerian continent, including the South Qiangtang block and

  14. 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.

  15. Deformed Neogene basins, active faulting and topography in Westland: Distributed crustal mobility west of the Alpine Fault transpressive plate boundary (South Island, New Zealand)

    NASA Astrophysics Data System (ADS)

    Ghisetti, Francesca; Sibson, Richard H.; Hamling, Ian

    2016-12-01

    Tectonic activity in the South Island of New Zealand is dominated by the Alpine Fault component of the Australia-Pacific plate boundary. West of the Alpine Fault deformation is recorded by Paleogene-Neogene basins coeval with the evolution of the right-lateral/transpressive plate margin. Initial tectonic setting was controlled by N-S normal faults developed during Late Cretaceous and Eocene-early Miocene rifting. Following inception of the Alpine Fault (c. 25 Ma) reverse reactivation of the normal faults controlled tectonic segmentation that became apparent in the cover sequences at c. 22 Ma. Based on restored transects tied to stratigraphic sections, seismic lines and wells, we reconstruct the vertical mobility of the Top Basement Unconformity west of Alpine Fault. From c. 37-35 Ma to 22 Ma subsidence was controlled by extensional faulting. After 22 Ma the region was affected by differential subsidence, resulting from eastward crustal flexure towards the Alpine Fault boundary and/or components of transtension. Transition from subsidence to uplift started at c. 17 Ma within a belt of basement pop-ups, separated by subsiding basins localised in the common footwall of oppositely-dipping reverse faults. From 17 to 7-3 Ma reverse fault reactivation and uplift migrated to the WSW. Persistent reverse reactivation of the inherited faults in the present stress field is reflected by the close match between tectonic block segmentation and topography filtered at a wavelength of 25 km, i.e. at a scale comparable to crustal thickness in the region. However, topography filtered at wavelength of 75 km shows marked contrasts between the elevated Tasman Ranges region relative to regions to the south. Variations in thickness and rigidity of the Australian lithosphere possibly control N-S longitudinal changes, consistent with our estimates of increase in linear shortening from the Tasman Ranges to the regions located west of the Alpine Fault bend.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  19. Evolution of geological processes; International Geological Congress, Session, 28th, Washington, DC, July 9-19, 1989, Reports

    NASA Astrophysics Data System (ADS)

    Ianshin, A. L.

    Topics discussed include the initial stages in the evolution of lithosphere, the tectonic evolution of the lithosphere in the Precambrian and the Phanerozoic, the evolution of sedimentation and lithogenesis in the Precambrian and the Phanerozoic, the evolution of the paleoenvironment of the ocean, and the evolution of ore formation. Papers are presented on the evolution of granite-greenstone terrains according to Sm-Nd geochronometry; volcanic belts as indicators of the tectonic evolution of the eastern continental margin of Eurasia; and the role of the earth tides in the tectonic evolution of the earth. Attention is also given to the evolution of Alpine-type molasses, the phenomena of irreversibility and recurrence in ore-formation in the course of the earth's geological history, the main features in the evolution of volcanogenic ferroaccumulation in the Early Precambrian, and the evolution of hydrocarbon and ore formation in the sedimentary strata of platform regions.

  20. Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

    PubMed Central

    Loyd, S. J.; Becker, T. W.; Conrad, C. P.; Lithgow-Bertelloni, C.; Corsetti, F. A.

    2007-01-01

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ∼0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past. PMID:17720806

  1. 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.

  2. Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

    PubMed

    Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

    2007-09-04

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

  3. Two year evolution of radon emission and tectonic movements in Tuzla Fault, Seferihisar-İzmir.

    PubMed

    Içhedef, M; Saç, M M; Harmanşah, C; Taskopru, C

    2014-04-01

    Previous studies showed that tectonic movement and meteorological events are accompanied with radon release. In this study soil gas radon and tectonic movements were investigated with meteorological factors taking into account. Soil gas radon measurements were collected over a-two year period (2008-2010) at the Tuzla Fault in Turkey. The relationship between radon anomalies and seismic activities was evaluated using Dobrovolsky's form. It is shown that not only magnitude of earthquake but also distance from the measurement site should be used for identifying radon anomalies. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. 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.

  5. Combined use of relative and absolute dating techniques for detecting signals of Alpine landscape evolution during the late Pleistocene and early Holocene

    NASA Astrophysics Data System (ADS)

    Favilli, Filippo; Egli, Markus; Brandova, Dagmar; Ivy-Ochs, Susan; Kubik, Peter; Cherubini, Paolo; Mirabella, Aldo; Sartori, Giacomo; Giaccai, Daniele; Haeberli, Wilfried

    2009-11-01

    A combination of three relative and two absolute (numerical) dating techniques, applied on nine soil profiles in an Alpine environment located in Val di Rabbi (Trentino, Northern Italy), was used to improve the investigation methodology of Alpine sites in response to climate change and to reconstruct the chronology of late Pleistocene and early Holocene landscape evolution. The degree of podzolisation, clay mineral evolution and the element mass balances of each site were investigated. Furthermore, the stable fraction of the soil organic matter (SOM) was extracted with 10% H 2O 2 and 14C-dated. The age of the organic residues was compared with the age of charcoal fragments found in one of the studied soils and with the age of rock boulders obtained by surface exposure dating (SED) with cosmogenic 10Be. Numerical dating and weathering characteristics of the soils showed a fairly good agreement and enabled a relative and absolute differentiation of landscape elements. The combination of 14C-dating of SOM and SED indicated that deglaciation processes in Val di Rabbi were already far advanced by around 14 000 cal BP and that glacier oscillations affected the highest part of the region until about 9000 cal BP. The development of clay minerals is time-dependent and reflects weathering intensity. We found a close link between secondary clay minerals like smectite or vermiculite and soil age as obtained by the dating of the organic residues after the H 2O 2 treatment. Calculated element mass balances strongly correlated with the ages derived from 14C measurements. Old soils have lost a major part of base cations (up to 75% compared to the parent material), Fe and Al, which indicates a continuous high weathering intensity. Results of the chemical and mineralogical analyses were in good agreement with numerical dating techniques, showing the dynamics of an Alpine landscape within a relatively small area. The combination of relative and absolute dating techniques is a

  6. 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.

  7. Detrital Thermochronology of the Indus-Yarlung suture zone and implications for the tectonic and surface evolution of southern Tibet

    NASA Astrophysics Data System (ADS)

    Carrapa, B.; Hassim, F.; Kapp, P. A.

    2015-12-01

    Detrital thermochronology has the unique potential to resolve the timing of source cooling associated with magmatic, tectonic and surface processes. Correct interpretation of the detrital signature requires a multi-dating approach involving chronometers sensitive to different temperatures and processes. A multi-dating study of modern river sands from southern Tibet reveals distinct cooling signals that provide significant information about tectonic and erosional evolution of the Indus-Yarlung suture (IYS) after the India-Asia collision with implications for the Cenozoic topographic evolution of the Tibetan Plateau. Modern sands from tributaries of the Yarlung River provide an opportunity to broadly sample source rocks exposed within the suture zone, including the Gangdese batholith, Xigaze forearc, Cenozoic basins, and Tethyan Himalayan rocks, and to investigate their regional geochemical signatures. Samples from rivers along the IYS in southern Tibet, between Xigaze and Mt. Kailas, were analyzed for detrital geochronology and low-temperature thermochronology. Comparison between ages recorded in the source and the detrital signature indicates that both the ages and their proportions directly reflect the ages and relative areas of source rocks in the catchment basins. Apatite fission track ages show two main cooling signals at 22-18 Ma and 12 Ma, which are consistent with accelerated exhumation of the Gangdese batholith and Oligo-Miocene Kailas basin and indicate significant regional exhumation of the IYS during the Miocene. Regional exhumation recorded throughout the IYS is likely the combined product of active Miocene tectonics and erosion of a paleo-Yarlung River. Efficient incision and evacuation of material from the IYS zone by a paleo-Yarlung River during the Miocene suggests a significantly different paleoenvironment than that which exists today. Miocene capture of the Yarlung River by the Brahmaputra River may have enhanced erosion in the IYS zone.

  8. Lithospheric stresses due to radiogenic heating of an ice-silicate planetary body - Implications for Ganymede's tectonic evolution

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.; Parmentier, E. M.

    1984-01-01

    Thermal evolution models of differentiated and undifferentiated ice-silicate bodies containing long-lived radiogenic heat sources are examined. Lithospheric sresses arise due to volume change of the interior and temperature change in the lithosphere. For an undifferentiated body, the surface stress peaks early in the evolution, while in the differentiated case, stresses peak later and continue to accumulate for longer periods of time. The variation of near-surface stress with depth shows that stresses for the undifferentiated body initially penetrate to great depths, but rapidly concentrate within a few kilometers of the surface. For the differentiated body, elastic stresses never accumulate at a depth greater than a few kilometers. These models are applied to consider long-term rdioactive heating as a possible mechanism of tectonic activity and bright terrain formation on Ganymede.

  9. 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.

  10. Tectonic Evolution of the Bristol Bay basin, southeast Bering Sea: Constraints from seismic reflection and potential field data

    NASA Astrophysics Data System (ADS)

    Walker, Kristoffer T.; McGeary, Susan E.; Klemperer, Simon L.

    2003-10-01

    We interpret the tectonic evolution of the Bristol Bay basin, also known as the North Aleutian basin, on the basis of a deep seismic reflection profile, lithologic data from a well, unreversed seismic refraction profiles, a bathymetry profile, a magnetics profile, forward modeling of a gravity profile, and flexural modeling of a basin-wide paleosurface. We present evidence that (1) an early or middle Eocene through late Miocene phase of extension led to fault-controlled subsidence; (2) a late Eocene through early Miocene phase of volcanic-arc loading led to flexural subsidence, which was amplified by additional factors possibly including lithospheric cooling, tectonic compression, reverse or thrust faulting, or small-scale intrusions of dense magma; and (3) a late Miocene through Holocene resurgence of arc volcanism and a northward prograding delta continued (or possibly increased) flexural subsidence in the back arc region. Our interpretations imply that the fault-controlled subsidence in the Bristol Bay basin is genetically linked to that found in the other outer Bering Shelf basins, but the subsequent flexural subsidence of these basins is not related. More fundamentally, our observations suggest that the basin's evolution is unusual and has components typically found in both back arc (extension) and retroarc foreland (flexure) basins.

  11. Tectonic Setting and Structural Evolution of the Late Cenozoic Gobi Altai Orogen, Mongolia

    NASA Astrophysics Data System (ADS)

    Cunningham, W. D.

    2009-12-01

    structural and basinal elements similar to continental transform systems undergoing transpressional deformation, such as the San Andreas system, it differs in several important aspects. The Gobi Altai is a reactivated mechanically weak belt between more rigid basement blocks in a continental interior. The Gobi Altai does not transfer plate motions, but terminally accommodates intraplate strain by oblique deformation. The Gobi Altai is a diffuse belt of deformation, but no singular strike-slip fault is dominant as is the case with the San Andreas Fault or Dead Sea Transform. Because the Gobi Altai is an actively developing youthful mountain range in an arid region with low erosion rates, it provides an excellent opportunity to study the way a continental interior reactivates due to a distant continental collision. Preserved peneplain surfaces, fresh alluvial fans, and sharply defined fault scarps and active mountain fronts express a very strong tectonic signal, without the obscuring effects of a humid/high erosion rate climate signal. Finally, the Gobi Altai is a useful analog for how other more advanced intracontinental transpressional orogens such as the eastern Tien Shan and Altai developed during earlier stages of their evolution.

  12. Triple junction orogeny: tectonic evolution of the Pan-African Northern Damara Belt, Namibia

    NASA Astrophysics Data System (ADS)

    Lehmann, Jérémie; Saalmann, Kerstin; Naydenov, Kalin V.; Milani, Lorenzo; Charlesworth, Eugene G.; Kinnaird, Judith A.; Frei, Dirk; Kramers, Jan D.; Zwingmann, Horst

    2014-05-01

    Trench-trench-trench triple junctions are generally geometrically and kinematically unstable and therefore can result at the latest stages in complicated collisional orogenic belts. In such geodynamic sites, mechanism and timescale of deformations that accommodate convergence and final assembly of the three colliding continental plates are poorly studied. In western Namibia, Pan-African convergence of three cratonic blocks led to pene-contemporaneous closure of two highly oblique oceanic domains and formation of the triple junction Damara Orogen where the NE-striking Damara Belt abuts to the west against the NNW-striking Kaoko-Gariep Belt. Detailed description of structures and microstructures associated with remote sensing analysis, and dating of individual deformation events by means of K-Ar, Ar-Ar (micas) and U-Pb (zircon) isotopic studies from the Northern Damara Belt provide robust constraints on the tectonic evolution of this palaeo-triple junction orogeny. There, passive margin sequences of the Neoproterozoic ocean were polydeformed and polymetamorphosed to the biotite zone of the greenschist facies to up to granulite facies and anatexis towards the southern migmatitic core of the Central Damara Belt. Subtle relict structures and fold pattern analyses reveal the existence of an early D1 N-S shortening event, tentatively dated between ~635 Ma and ~580 Ma using published data. D1 structures were almost obliterated by pervasive and major D2 E-W coaxial shortening, related to the closure of the Kaoko-Gariep oceanic domain and subsequent formation of the NNW-striking Kaoko-Gariep Belt to the west of the study area. Early, km-scale D1 E-W trending steep folds were refolded during this D2 event, producing either Type I or Type II fold interference patterns visible from space. The D2 E-W convergence could have lasted until ~533 Ma based on published and new U-Pb ages. The final D3 NW-SE convergence in the northernmost Damara Belt produced a NE-striking deformation

  13. The Sinai subplate and tectonic evolution of the northern Red Sea region

    NASA Astrophysics Data System (ADS)

    Badawy, Ahmed; Horváth, Ferenc

    1999-03-01

    Although the precise boundaries and kinematics of the Sinai subplate are still doubtful, it has a significant role in the tectonic evolution of the northern Red Sea region. On the basis of earthquake distribution, the Sinai region can be considered as a subplate partially separated from the African plate by the Suez rift. The relative motion between Africa, Sinai and Arabia is the main source generating the present-day earthquake activity in the Gulf of Suez and the Gulf of Aqaba regions. According to geological observations, the southern segment of the Dead Sea fault system can be characterized by a left-lateral displacement of about 107km since the Middle Miocene, in contrast to the northern segment where only 25 to 35km offset can be inferred. We think that along the southern segment the total displacement was 72km until the late Miocene (10Ma). The earthquake activity is strongly reduced along the northern segment of the Dead Sea fault segment. Therefore, we suggest that the northern part (Yammouneh fault) evolves through initial cracking of the crust due to build-up of stress since the Pliocene time (5Ma) and propagates northward into Lebanon and Syria. This last 5 million years is the period when the southern and northern segments became linked and formed a single fault system with a new displacement of 35km. According to the proposed model the predicted opening pole of the Red Sea is near 34.0̊N, 22.0̊E with an angle of total rotation of 3.4̊ since the early miocene, providing a 0.82cm/a opening rate in the northern Red Sea. We suggest that the Dead Sea strike-slip fault was active since Middle Miocene time (15Ma) with a slip rate of 0.72cm/a to provide a total displacement of about 107km. This strike slip motion occured about an Euler pole near 33.0̊N, 21.0̊E with a rotation angle of about 3.0̊. It can be inferred from the proximity of the pole and angle of rotations for the Red Sea and Dead Sea fault that more than 85% of the motion has been

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. Sm-Nd geochronology of the Erro-Tobbio gabbros (Ligurian Alps, Italy): Insights into the evolution of the Alpine Tethys

    NASA Astrophysics Data System (ADS)

    Rampone, Elisabetta; Borghini, Giulio; Romairone, Anna; Abouchami, Wafa; Class, Cornelia; Goldstein, Steven L.

    2014-09-01

    The Alpine-Apennine ophiolites are considered analogs of the oceanic lithosphere formed at ocean-continent transition zones and very slow oceanic spreading centers. They are lithospheric remnants of the Jurassic Piedmont-Ligurian ocean, a branch of the Mesozoic Tethys separating the European and Adriatic continental margins. Previous geochronological studies on gabbroic rocks of the Alpine Tethys indicated a rather large time span of crust formation. In this paper, we present Sm-Nd geochronological data on well-preserved olivine gabbros intruded in mantle peridotites from the Erro-Tobbio ophiolitic unit (Ligurian Alps, Italy). Borghini et al. (2007) documented that these gabbros crystallized at low-P conditions (< 5 kb) from primitive N-MORB melts, similar to many gabbroic rocks from Alpine-Apennine ophiolites. Here four plagioclase-clinopyroxene internal Sm-Nd isochrons are presented, yielding equivalent ages and initial εNd values. The ages are 177 ± 7 Ma, 179 ± 7 Ma, 178 ± 21 Ma and 182 ± 19 Ma, reflecting a weighted mean age of 178 ± 5 Ma with initial εNd of 9.2 ± 0.4 (2SD). Similar ages are only recorded in gabbroic rocks from the External Liguride Units (Northern Apennines) and represent the oldest ages available for the gabbroic crust of the Alpine Tethys. These Mg-rich gabbros can therefore be considered as representative of early (syn-rift) melt intrusions in thinned lithospheric mantle exhumed at ocean-continent transition domains, likely close to Adria's continental margin, similar to the hyper-extended Western Iberian Margin. Our new results together with previous ages of the Tethys oceanic crust allow for the reconstruction of the spatial distribution of oceanic gabbros over time, and evaluation of the spreading and propagation rates of this paleo-ocean. The northward propagation rifting velocity, estimated at ~ 5 cm/year, is presumably higher than the lateral spreading rate of ~ 2 cm/year. Our rate estimates suggest that the Red Sea is a

  19. The polyphased tectonic evolution of the Anegada Passage in the northern Lesser Antilles subduction zone

    NASA Astrophysics Data System (ADS)

    Laurencin, M.; Marcaillou, B.; Graindorge, D.; Klingelhoefer, F.; Lallemand, S.; Laigle, M.; Lebrun, J.-F.

    2017-05-01

    The influence of the highly oblique plate convergence at the northern Lesser Antilles onto the margin strain partitioning and deformation pattern, although frequently invoked, has never been clearly imaged. The Anegada Passage is a set of basins and deep valleys, regularly related to the southern boundary of the Puerto Rico-Virgin Islands (PRVI) microplate. Despite the publications of various tectonic models mostly based on bathymetric data, the tectonic origin and deformation of this Passage remains unconstrained in the absence of deep structure imaging. During cruises Antithesis 1 and 3 (2013-2016), we recorded the first deep multichannel seismic images and new multibeam data in the northern Lesser Antilles margin segment in order to shed a new light on the structure and tectonic pattern of the Anegada Passage. We image the northeastern extent of the Anegada Passage, from the Sombrero Basin to the Lesser Antilles margin front. Our results reveal that this northeastern segment is an EW trending left-stepping en échelon strike-slip system that consists of the Sombrero and Malliwana pull-apart basins, the Malliwana and Anguilla left-lateral faults, and the NE-SW compressional restraining bend at the Malliwana Hill. Reviewing the structure of the Anegada Passage, from the south of Puerto Rico to the Lesser Antilles margin front, reveals a polyphased tectonic history. The Anegada Passage is formed by a NW-SE extension, possibly related to the rotation or escape of PRVI block due to collision of the Bahamas Bank. Currently, it is deformed by an active WNW-ESE strike-slip deformation associated to the shear component of the strain partitioning resulting from the subduction obliquity.

  20. 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

  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. Subcontinental mantle evidence for the onset of plate tectonics at 3 Ga in relation to Earth's thermal evolution

    NASA Astrophysics Data System (ADS)

    Richardson, S. H.; Shirey, S. B.

    2011-12-01

    Recent insights regarding the temporal distribution of components in the subcontinental lithospheric mantle (SCLM), coupled with tectonic aspects of the crust, provide a window into the thermal evolution of the Earth. Mantle evolution, crustal growth, and geochemical cycles of heat-producing elements may be linked to profound geodynamic changes. Substantial differences exist globally between >3.2 Ga versus <3.0 Ga old crust and SCLM. This age has been proposed as a boundary between different geodynamic regimes, marking the onset of plate tectonics and decline of pre-plate tectonic styles [1,2]. Geochemical studies of silicate and sulfide inclusions in cratonic macrodiamonds have been used to characterize the SCLM through time. Diamonds formed at >3.2 Ga contain exclusively peridotitic (harzburgitic) silicate and sulfide inclusions whereas diamonds formed at <3.0 Ga contain inclusions that are predominantly eclogitic and to a lesser extent lherzolitic. Similarly, >3.0 Ga old kimberlite-borne eclogite xenoliths are largely absent in the SCLM rock record, whereas they are common thereafter [1]. The lack of early eclogite implies an absence of steep slab subduction. Archean crust also records major differences across the 3.0-3.2 Ga interval. Prior to 3.2 Ga, crust grew by vertical accretion over upwelling mantle in long-lived plateaux floored by extremely depleted residual harzburgitic SCLM or via slab melting and crustal imbrication over shallow subduction zones, whereas lateral accretion, allochthonous greenstone belt growth and calcalkaline magmatic products of mantle wedge melting emerge only after 3.2 Ga [2]. A step-wise shift in tectonic style is evident from rapid mantle convection, small plates, shallow subduction, and localized recycling at >3.2 Ga, followed by large plates, steep subduction, and full upper mantle recycling at <3.0 Ga. These changes occur around the time (3 Ga) when the convecting mantle temperature reaches a maximum as heat-producing elements

  3. 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.

  4. Tectonic and sequence stratigraphic evolution of asymmetric extensional back-arc basins: seismic interpretations in the Pannonian Basin

    NASA Astrophysics Data System (ADS)

    Balázs, Attila; Matenco, Liviu; Magyar, Imre; Horváth, Ferenc; Cloetingh, Sierd

    2015-04-01

    The evolution of the Pannonian Basin is generally thought to be driven by subduction roll-back associated with mantle flow dynamics. The Miocene back-arc extension resulted in the formation of dominantly half-grabens in the hanging wall of low-angle detachments and listric normal faults, associated with coeval large-scale exhumation of their footwalls. To quantify the evolution of these asymmetric extensional structures, a novel kinematic and seismic sequence stratigraphic interpretation was performed. Based on reflection terminations and characteristic seismic facies we separated systems tracts of the half-graben deposits that formed as a result of interplay between subsidence, sedimentation and water-level variations. Lower order systems tracts were defined by separating rift initiation, rift climax, immediate post-rift and late post-rift systems tracts, while a higher order transgressive-regressive cyclicity and associated unconformities were locally identified in the syn-tectonic basin fill. Connecting these observations demonstrates that extension migrated in time and space across the basin. Extension started during Early Miocene in the oldest sub-basins, while Middle Miocene rift climax is quite common in the entire study area. The youngest syn-tectonic strata were deposited during Late Miocene times in the eastern parts of the Pannonian Basin, for instance, in the Derecske, Makó and Szeged Troughs. The syn-rift/post-rift boundary cannot be interpreted as a discrete event in the entire basin system, because it is a progressive, process-related expression. The obtained results significantly improve the classic ideas of syn-rift/post-rift evolution of the Pannonian Basin.

  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. Late Neogene stratigraphy and tectonic control on facies evolution in the Laguna Salada Basin, northern Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Martín-Barajas, A.; Vázquez-Hernández, S.; Carreño, A. L.; Helenes, J.; Suárez-Vidal, F.; Alvarez-Rosales, J.

    2001-10-01

    The Laguna Salada Basin (LSB) in northeastern Baja California records late-Neogene marine incursions in the Salton Trough and progradation of the Colorado River delta. Early subsidence and subsequent tectonic erosion are related to evolution of the Sierra El Mayor detachment fault during late Miocene time (<12 Ma). The stratigraphy of uplifted blocks on the east-central margin of the Laguna Salada Basin and from three exploratory wells allows reconstruction of the main sedimentary and tectonic events. Marine mudstone and sandstone, and subordinate conglomerate of the Imperial Formation tectonically overlie metamorphic and granitic basement. Microfossils, lithology, and sedimentary structures in the Imperial Formation define Upper Miocene (<6 Ma) outer-shelf facies that grade up-section into inner-shelf and tide-dominated delta plain deposits of the ancient Colorado River. Lower Pliocene (˜4-2 Ma) reddish, sub-arkosic fluvial sandstone and siltstone of the Palm Spring Formation defines progradation of non-marine fluvio-deltaic deposits over the marine Imperial Formation. Continuous outcrops of the Palm Spring are less than 170-m thick, but correlative deposits are more than 570 m thick in the lower part of a 2400-m deep geothermal exploratory well on the eastern margin of LSB. Interfingering fluvial-sandstone deposits and prograding alluvial fanglomerates with coarse debris-flow and rock-avalanche deposits crudely mark the onset of vertical slip along the Laguna Salada fault and rapid uplift of Sierra Cucapa and Sierra El Mayor. Up to 2 km of Quaternary alluvial-fan and lacustrine deposits accumulated along the eastern margin of LSB, whereas lower subsidence rates produced a thinner sedimentary wedge over a ramp-like crystalline basement along the western margin. In early Pleistocene time (˜2-1 Ma), the Laguna Salada became progressively isolated from the Colorado River delta complex, and the Salton Trough by activity on the Elsinore and Laguna Salada fault zones.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  8. Three-dimensional coupling of landscape evolution and rheologically layered thermomechanical models - towards a tectonic perspective on drainage patterns

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Willett, S.; Gerya, T.

    2012-12-01

    Surface topography and drainage topology contain, amongst others, diverse information about tectonic deformation. Differentiation of the tectonic contribution from climate factors is however controversial, and poses limitations on the potential reconstruction of deformation histories from a first-grade data set. In studying the interplay between tectonics and surface processes, various types of numerical models provide valuable yet partial insights. Landscape evolution models (LEM) capture the operation of an excerpt, according to scale and climate, of fluvial, glacial and hillslope processes. They can be applied to specific problems with simple, feedback-free kinematics to study the response of landscape to tectonics. In contrast, large-scale thermomechanical models incorporate simplified continuous surface functions that do not respect the scale-dependency of surface processes, and that do not reproduce landscape characteristics other than gross elevation. Aiming at combining each side's capabilities, the coupled models that have been brought forward so far have been subjected to limitations like two-dimensionality, lack of rheological layering, and computationally limited resolution, exacerbating the inaccuracy of discretized divide location. They have explored the sensitivity of topography and strain partitioning, on the efficiency of surface processes, but have not advanced to addressing the evolution of drainage patterns. Such research objectives are becoming more feasible as recent developments move towards coupling LEMs to three-dimensional, rheologically layered thermomechanical models at increasing resolution. In this contribution, we present results from coupling a scale-robust LEM with a full thermomechanical model. The new LEM code DAC combines numerical-analytical modelling of fluvial and hillslope processes, and is capable of treating large model domains at feasible numerical resolution without loss of accuracy. First, location and migration of

  9. Tectonic evolution at an early proterozoic continental margin: The Svecokarelides of eastern Finland

    NASA Astrophysics Data System (ADS)

    Park, A. F.; Bowes, D. R.; Halden, N. M.; Koistinen, T. J.

    1984-12-01

    The early Proterozoic history of the Baltic Shield in Fennoscandia provides evidence of fragmentation of a late Archaean craton, continental sedimentation and then back-arc spreading, interpreted as being associated with the uprise of a mantle diapir. Basin subsidence and infilling with flysch debris is explained on the basis of thermal decay, locking of a subduction zone and erosion of an uplifted arc. Compressive tectonism in the Karelian part of the Svecokarelian orogen resulted in obduction of the contents of the back-arc basin on to the continental foreland. Further compression caused further thickening of the supracrustal pile and interdigitation of tectonic slices of basement and cover due to thrusting. Subsequently movement was resolved along major NW-trending wrench-faults that generally follow the margin of teh craton and which represent zones of reactivation of planar features developed in late Archaean times. As the crustal pile was warped and uplifted in subsequent deformational phases, the deep levels of the wrench-faults acted as sites of granitoid emplacement. The tectonic activity in the Karelian part of the Svecokarelides is interpreted as the response to the northward movement of oceanic lithosphere in the Svecofennian part of the orogen where successively-formed early Proterozoic island arcs moved northwards and were intensely deformed, associated with the development and emplacement of large masses of igneous material. The resultant orogen, consisting of a stable craton, obducted nappes, exotic terrane, transcurrent faults and island arcs that moved obliquely to the margin of the craton, shows many similarities in development to that of the western Cordillera of North America.

  10. Tectonic evolution of the Mid-Polish Trough: modelling implications and significance for central European geology

    NASA Astrophysics Data System (ADS)

    Dadlez, R.; Narkiewicz, M.; Stephenson, R. A.; Visser, M. T. M.; van Wees, J.-D.

    1995-12-01

    The Polish Basin forms the easternmost part of the Permian-Mesozoic northwest European basin. The depocentral axis of the Polish Basin, the Mid-Polish Trough (MPT), is superimposed on the boundary between the west European Phanerozoic and east European Proterozoic crustal domains, within the Trans-European Suture Zone. The presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the MPT, concentrating stresses during post-Variscan wrench and extensional tectonics in central Europe. Tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the Polish Basin indicates the occurrence of an initial Late Permian-Early Triassic (255-241 Ma) 'rifting' phase that was followed by subsequent episodes of increased tectonic subsidence during the Oxfordian-Kimmeridgian (˜ 157-152 Ma) and beginning in the Cenomanian (˜97 Ma). The Oxfordian-Kimmeridgian episode is interpreted as corresponding to a second extensional event, which correlated with intersified rifting and wrench activity within the Arctic-North Atlantic rift system and along the northern Tethyan margin, while the Cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest Cretaceous and Paleocene. Forward modelling results, in view of existing geophysical interpretations which show the presence of a deep Moho and a very velocity lower crustal layer beneath theMPT, suggest that Permo-Mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning.

  11. A structural transect in the Lower Dolpo: Insights on the tectonic evolution of Western Nepal

    NASA Astrophysics Data System (ADS)

    Carosi, R.; Montomoli, C.; Visonà, D.

    2007-02-01

    We present the results of a structural transect in Lower Dolpo, cross-cutting the upper part of the Lesser Himalaya (LH), the Higher Himalayan Crystallines (HHC) and the lower part of the Tibetan Sedimentary Sequence (TSS). The MCT zone affects the upper part of the LH as well as the lower part of the HHC and shows a later brittle reactivation. Mean vorticity in the MCT points to non-coaxial deformation. These data, together with available kinematic data along the belt, on the South Tibetan Detachment System (STDS) and in the core of the HHC, point to increasing simple shear toward the tectonic boundaries. A top-to-the-SW high-temperature shear zone (Toijem Shear Zone) is recognized in the middle part of the HHC at the boundary between Units 1 and 2. It developed during the earlier stages of exhumation of the HHC, enhancing the decompression of the hanging wall and the emplacement of leucogranite dykes and sills. Its development could be explained by a change in the velocity profile during the extrusion of the HHC, triggered by first order changes in rock types of the tectonic unit. The STDS is marked by a wide zone of high strain and by a metamorphic jump from amphibolite facies in the carbonate rocks of the upper part of the HHC to greenschist facies marbles in the lower part of the TSS. The development of a pervasive foliation towards the bottom of the TSS indicates increasing strain, related to top down-to-the-NE tectonic transport. A Low P metamorphic event, marked by the growth of post-D1 biotite porphyroblasts at the base of the TSS, is related to the conductive heating from the underlying HHC.

  12. Structural and diagenetic evolution of deformation bands in contractional and extensional tectonic regimes

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.; O'Brien, C. M.; Elliott, S. J.

    2016-12-01

    Mechanisms of brittle deformation of sediments and sedimentary rock change with burial because of increasing confining stress, change in pore fluid chemical and temperature conditions, and diagenetic state. In the field, these changes are observed in a transition from early non-cataclastic to later cataclastic deformation bands and to joint-based structures. Jurassic eolian sandstones in the San Rafael monocline and adjacent San Rafael Desert region, Utah, allow comparison of deformation band structures and their diagenetic attributes in contractional and extensional tectonic settings in close proximity. In the Entrada and Navajo Sandstones, we observe up to six generations of deformation bands, with earliest non-cataclastic bands having diffuse boundaries to host rock, and short and irregular traces. Later bands are cataclastic, more sharply defined, with long and straight traces. Cataclastic bands in the San Rafael monocline are interpreted to form as reverse faults during progressive rotation of the steeply dipping fold limb, resulting in an array of bands of varying dip. Bands in the San Rafael Desert form as normal faults with a narrower dip range. Although structural characteristics of bands differ in extensional and contractional tectonic regimes, cataclastic bands in either regime have comparable amount of porosity loss and quartz cementation indicating that tectonic regime does not influence band diagenesis. Abundance of quartz cement in bands, determined by point counting of SEM images, increases from earlier to later generations of bands and, within a single generation, with increasing slip along the band, reaching up to 24% of band volume. This trend is attributed to an increase in cataclasis with increasing host rock cementation and confining stress during burial, and, within the same generation, with increasing slip. Porosity loss by cementation tends to dominate over porosity loss by mechanical compaction. These findings demonstrate that quartz

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  14. Mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution.

    PubMed

    Gastaldo, R A; Guthrie, G M; Steltenpohl, M G; Gastaldo, R A; Steltenpohl, M G

    1993-10-29

    Fossils of Periastron reticulatum Unger emended. Beck recovered from the Erin Slate of the Talladega slate belt of Alabama establish that these rocks have a Mississippian (Kinderhookian-Tournaisian) age. The Talladega slate belt, the southwestern extension of the western Blue Ridge belt, was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the Acadian orogeny. This fossil find indicates that metamorphism and deformation of the Talladega belt occurred after the Early Carboniferous (Alleghanian), requiring a reevaluation of tectonic interpretations of the southernmost Appalachians.

  15. Basic tectonic features of the Knipovich Ridge (North Atlantic) and its neotectonic evolution

    NASA Astrophysics Data System (ADS)

    Peive, A. A.; Chamov, N. P.

    2008-01-01

    The geological and geophysical data primarily on the structure of the upper sedimentary sequence of the northern Knipovich Ridge (Norwegian-Greenland Basin) that were obtained during Cruise 24 of the R/V Akademik Nikolai Strakhov are considered. These data indicate that the recent kinematics of the northern Knipovich Ridge is determined by dextral strike-slip displacements along the Molloy Fracture Zone (315° NW). This stress field is superimposed by a system related to rifting and latitudinal opening of rifts belonging to the ridge proper. Thus, the structural elements formed under the effect of two stress fields are combined in this district. Several stages of tectonic movements are definable. The first stage (prior to 500 ka ago) is marked by the dominant normal faults, which are overlain by the lower and upper sedimentary sequences. The second stage (prior to 120-100 ka ago) is characterized by development of normal and reverse faults, which displace the lower sequence and are overlain by the upper sequence. Both younger and older structural features reveal peaks of tectonic activity separated by intermediate quiet periods 50-60 ka long. The stress field of the regional strike-slip faulting is realized in numerous oblique NE-trending normal and normal-strike-slip faults that divide the rift valley and its walls into the segments of different sizes. Their strike (20°-30° NE) is consistent with a system of secondary antithetic sinistral strike-slip faults. The system of depressions located 40 km west of the rift valley axis may be considered a paleorift zone that is conjugated at 78°07' N and 5°20' W with the NW-trending fault marked by the main dextral offset. The stress field that existed at this stage was identical to the recent one. The rift valley axis migrated eastward to its present-day position approximately 2 Ma ago (if the spreading rate of ˜0.7 cm/yr is accepted). The obtained data substantially refine the understanding of the initial breakup of

  16. 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

  17. 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

  18. The pressure-temperature-time evolution of the Antarctic Peninsula - magmatic arc and/or terrane tectonics?

    NASA Astrophysics Data System (ADS)

    Wendt, A. S.; Vidal, O.; Vaughan, A.

    2003-04-01

    The tectonic mobility in orogenic systems requires that the geologic history of each rock unit must be evaluated on the merits of the information gleaned more from individual outcrops than from regional generalisation. Continental margins affected by tectonic processes commonly have a region where the stratigraphic elements should be considered suspect in regard to palaeogeographic linkages both among the elements and between each element and the adjoining continent. Such occurrences might be considered as a natural consequence of the mobility and transient state of oceanic crust so that exotic far-travelled crustal fragments can be expected. The collision of those fragments and their distribution patterns reflect in general a combination of several tectonic phases such as overthrusting, stitching of plutons along the contact and welding metamorphism. The Antarctic Peninsula is an example "par excellence" for testing those tectonic processes occurring along continental margins. Prior to Mid-Jurassic times, the peninsula in its entity is thought to have formed a part of the palaeo-Pacific margin. East-directed subduction along the margin occurred during Mesozoic-Tertiary times producing a magmatic arc complex, in which volcanic and plutonic rocks are distributed widely along the length of the peninsula. However, recent discoveries suggest also that the Antarctic Peninsula is composed of at least two terranes in transpressional contact with para-autochthonous continental Gondwana margin. The reconstruction of the geological history becomes a challenging task in the hostile environment of the Antarctic where individual outcrops are scattered over large geographical distances, and structural relationships are obscured by thick layers of ice. In this work, we are attempting to correlate for the first time the pressure-temperature-time evolution of metamorphic rocks parallel to the spine of the peninsula and their structural relationship to the volcanic and plutonic

  19. Tracking the evolution of mantle sources with incompatible element ratios in stagnant-lid and plate-tectonic planets

    NASA Astrophysics Data System (ADS)

    Condie, Kent C.; Shearer, Charles K.

    2017-09-01

    The distribution of high field strength incompatible element ratios Zr/Nb, Nb/Th, Th/Yb and Nb/Yb in terrestrial oceanic basalts prior to 2.7 Ga suggests the absence or near-absence of an enriched mantle reservoir. Instead, most oceanic basalts reflect a variably depleted mantle source similar in composition to primitive mantle. In contrast, basalts from hydrated mantle sources (like those associated with subduction) exist from 4 Ga onwards. The gradual appearance of enriched mantle between 2 and 3 Ga may reflect the onset and propagation of plate tectonics around the globe. Prior to 3 Ga, Earth may have been in a stagnant-lid regime with most basaltic magmas coming from a rather uniform, variably depleted mantle source or from a non-subduction hydrated mantle source. It was not until the extraction of continental crust and accompanying propagation of plate tectonics that ;modern type; enriched and depleted mantle reservoirs developed. Consistent with the absence of plate tectonics on the Moon is the near absence of basalts derived from depleted (DM) and enriched (EM) mantle reservoirs as defined by the four incompatible element ratios of this study. An exception are Apollo 17 basalts, which may come from a mixed source with a composition similar to primitive mantle as one end member and a high-Nb component as the other end member. With exception of Th, which requires selective enrichment in at least parts of the martian mantle, most martian meteorites can be derived from sources similar to terrestrial primitive mantle or by mixing of enriched and depleted mantle end members produced during magma ocean crystallization. Earth, Mars and the Moon exhibit three very different planetary evolution paths. The mantle source regions for Mars and the Moon are ancient and have HFS element signatures of magma ocean crystallization well-preserved, and differences in these signatures reflect magma ocean crystallization under two distinct pressure regimes. In contrast, plate

  20. 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

  1. Chronology of Miocene Pliocene deposits at Split Mountain Gorge, Southern California: A record of regional tectonics and Colorado River evolution

    NASA Astrophysics Data System (ADS)

    Dorsey, Rebecca J.; Fluette, Amy; McDougall, Kristin; Housen, Bernard A.; Janecke, Susanne U.; Axen, Gary J.; Shirvell, Catherine R.

    2007-01-01

    Late Miocene to early Pliocene deposits 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.

  2. 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.

  3. 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.

  4. Linked fluid and tectonic evolution in the High Himalaya mountains (Nepal)

    NASA Astrophysics Data System (ADS)

    Boullier, Anne-Marie; France-Lanord, Christian; Dubessy, Jean; Adamy, Jérôme; Champenois, Michel

    1991-05-01

    Fluid inclusions were studied in a quartz lens from the structurally highest unit of the Himalaya mountains in Nepal from a textural, geometrical, chemical and isotopic point of view. Six types of fluid inclusions were distinguished. One of these types consists of annular inclusions; this shape is attributed to a confining pressure increase in a non-isotropic stress field. Two successive stress fields were deduced from the orientation of the inclusion planes relative to the schistosity. The bulk composition of the fluid was dominated by CO2 (>84 mol%) and H2O. The composition remained constant during the whole history of the sample indicating that it was buffered by the carbonaceous host rock and/or that one single fluid was reworked in situ by decrepitation. Stable isotope of fluids and minerals indicate (1) that fluids were buffered by surrounding rocks for O and C and (2) that at least two types of water (metamorphic and meteoric) were involved. Finally, a P-T-t-ɛ-σ path is proposed for the sample, taking into account the southward thrusting along the Main Central Thrust, the northward tectonic denudation of the Himalaya mountains inducing tectonic burying below the Annapurna Range, and lastly, rapid uplift.

  5. Tectonic evolution and hydrocarbon accumulation in the Yabulai Basin, western China

    NASA Astrophysics Data System (ADS)

    Zheng, Min; Wu, Xiaozhi

    2014-05-01

    The Yabulai petroliferous basin is located at the north of Hexi Corridor, western China, striking NEE and covering an area of 1.5×104 km2. It is bounded on the south by Beidashan Mountain to the Chaoshui Basin, on the east by Bayanwulashan Mountain to the Bayanhaote Basin, and on the northwest by Yabulai Mountain to the Yingen-Ejinaqi Basin. It is a Meso-cenozoic compressive depression residual basin. In view of regional geotectonics, the Yabulai basin sits in the middle-southern transition belt of Arershan massif in North China Craton. Driven by Indosinian movement at the late Triassic, two near EW normal faults were developed under the regional extensional stress along the northern fringe of Beidashan Mountain and the southern fringe of Yabulai Mountain front in the Arershan massif, forming the embryonic form of the Yabulai rift lake basin. Since Yanshan period, the Yabulai basin evolved in two major stages: Jurassic rift lake basin and Cretaceous rift lake basin. During early Yanshan period, EW striking Yabulai tensional rift was formed. Its major controlling fault was Beidashan normal fault, and the depocenter was at the south of this basin. During middle Yanshan period, collision orogenesis led to sharp uplift at the north of this basin where the middle-lower Jurassic formations were intensely eroded. During late Yanshan period, the Alashan massif and its northern area covered in an extensional tectonic environment, and EW striking normal faults were generated at the Yabulai Mountain front. Such faults moved violently and subsided quickly to form a new EW striking extensional rift basin with the depocenter at the south of Yabulai Mountain. During Himalayan period, the Alashan massif remained at a SN horizontal compressional tectonic environment; under the compressional and strike slip actions, a NW striking and south dipping thrusting nappe structure was formed in the south of the Yabulai basin, which broke the Beidashan normal fault to provide the echelon

  6. 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.

  7. 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.

  8. Post-Pan-African tectonic evolution of South Malawi in relation to the Karroo and recent East African rift systems

    NASA Astrophysics Data System (ADS)

    Castaing, C.

    1991-05-01

    Structural studies conducted in the Lengwe and Mwabvi Karroo basins and in the basement in South Malawi, using regional maps and published data extended to cover Southeast Africa, serve to propose a series of geodynamic reconstructions which reveal the persistence of an extensional tectonic regime, the minimum stress σ3 of which has varied through time. The period of Karroo rifting and the tholeiitic and alkaline magmatism which terminated it, were controlled by NW-SE extension, which resulted in the creation of roughly NE-SW troughs articulated by the Tanganyika-Malawi and Zambesi pre-transform systems. These were NW-SE sinistral-slip systems with directions of movement dipping slightly to the Southeast, which enabled the Mwanza fault to play an important role in the evolution of the Karroo basins of the Shire Valley. The Cretaceous was a transition period between the Karroo rifting and the formation of the Recent East African Rift System. Extension was NE-SW, with some evidence for a local compressional episode in the Lengwe basin. Beginning in the Cenozoic, the extension once more became NW-SE and controlled the evolution in transtension of the Recent East African Rift System. This history highlights the major role of transverse faults systems dominated by strike-slip motion in the evolution and perpetuation of the continental rift systems. These faults are of a greater geological persistence than the normal faults bounding the grabens, especially when they are located on major basement anisotropies.

  9. Tectonic evolution and depositional environment change of the Jeju and Socotra basins in the northern East China Sea

    NASA Astrophysics Data System (ADS)

    Koh, C.; Yoon, S. H.

    2016-12-01

    This study focuses on the tectonic evolution and depositional environment change of the Jeju and Socotra basins which were formed by the early Tertiary continental rifting in the northern East China Sea region. Multi-channel seismic reflection profiles (by Korea Institute of Ocean Science and Technology) are analyzed in terms of seismic stratigraphy, geologic structures, and seismic facies. The Jeju and Socotra basins commonly occur as the local basement lows surrounded by large-scale basement highs. The basin-filling sedimentary sequences are subdivided into 4 megasequences (MS1-MS4) by regional unconformities and their correlated conformities. The chronostratigraphy of megasequences from Eocene to Plio-Pleistocene is established based on biostratigraphic data from the existing hydrocarbon exploration wells. Geologic structures in Socotra Basin are characterized by rift-stage normal faults involved with basement rotation and subsequent folds and local normal faults in Oligocene sequence interval, while the Jeju Basin shows predominant occurrence of reverse faults and folds within Eocene to Miocene sequences. Based on the acoustic characters and reflection configurations, 6 types of seismic facies are classified and interpreted as geologic basement (B1), volcanic-sedimentary complex (B2), inner-shelf deposit (S1), fluvio-lacustrine deposit (S2), coastal deposit (S3), and volcanic sill or volcanic edifice (S4). The integration of these results suggests 4-stage reconstruction of tectonic evolution and depositional environment change in the study area, which is associated with initial rifting in Eocene, and following post-rift subsidence punctuated by 3 events (early Oligocene, early Miocene, and late Miocene) of regional uplift and compressional deformation.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. Tectonic evolution of Kishtwar Window with respect to the Main Central Thrust, northwest Himalaya, India

    NASA Astrophysics Data System (ADS)

    Singh, Keser

    2010-08-01

    The crystalline rocks of the Himalaya (High Himalayan Crystallines, Central Crystallines, etc.) are bounded to the north by the South Tibetan Detachment/Zanskar Shear Zone/Trans Himadri Fault System at the top and to the south by the Main Central Thrust (MCT) at the base. To the south and tectonically below the MCT lies the Lesser Himalaya comprising low grade meta-sedimentary thrust sheets and the crystallines klippen. North and tectonically above the Zanskar Shear Zone lies the sedimentary succession of the Tethys Himalaya. However, there is a different geological set-up to the northwest of Beas valley, which defies this normal set-up, i.e., the Tethyan rocks either lie in contact with the Lesser Himalayan thrust sheets or they, to a large extent, surround the High Himalayan Crystallines (HHC). This unique set-up is documented around areas comprising Chamba, Kishtwar and Zanskar regions in the northwest Himalaya. The Lesser Himalayan imbricated sequence, extending progressively into deeper structural level beneath and crops-out as Kishtwar Window within the HHC. This tectonic contact along the window was described as the MCT. However, the present study of the window indicates that its western side is bounded by a high angle NE dipping reverse fault (Kishtwar Thrust). The structural analyses reveal that this fault is younger than the MCT and is interpreted here as Breach Thrust. Present observations suggest that the rocks of the window and the northeasterly lying HHC have been folded and exhumed together as an antiform along the Kishtwar Thrust. The HHC occurring south of the Kishtwar Window have actually been thrust over the Lesser Himalayan thrust sheet. This contact is observed and marked for the first time and is accordingly described as the Main Central Thrust as per convention along the length of the Himalayan belt. Northeast and in the hangingwall of the MCT, the repetition of the contact of the Lesser Himalayan rocks and the HHC is interpreted here as the

  15. Tectonics, orbital forcing, global climate change, and human evolution in Africa: introduction to the African paleoclimate special volume.

    PubMed

    Maslin, Mark A; Christensen, Beth

    2007-11-01

    The late Cenozoic climate of Africa is a critical component for understanding human evolution. African climate is controlled by major tectonic changes, global climate transitions, and local variations in orbital forcing. We introduce the special African Paleoclimate Issue of the Journal of Human Evolution by providing a background for and synthesis of the latest work relating to the environmental context for human evolution. Records presented in this special issue suggest that the regional tectonics, appearance of C(4) plants in East Africa, and late Cenozoic global cooling combined to produce a long-term drying trend in East Africa. Of particular importance is the uplift associated with the East African Rift Valley formation, which altered wind flow patterns from a more zonal to more meridinal direction. Results in this volume suggest a marked difference in the climate history of southern and eastern Africa, though both are clearly influenced by the major global climate thresholds crossed in the last 3 million years. Papers in this volume present lake, speleothem, and marine paleoclimate records showing that the East African long-term drying trend is punctuated by episodes of short, alternating periods of extreme wetness and aridity. These periods of extreme climate variability are characterized by the precession-forced appearance and disappearance of large, deep lakes in the East African Rift Valley and paralleled by low and high wind-driven dust loads reaching the adjacent ocean basins. Dating of these records show that over the last 3 million years such periods only occur at the times of major global climatic transitions, such as the intensification of Northern Hemisphere Glaciation (2.7-2.5 Ma), intensification of the Walker Circulation (1.9-1.7 Ma), and the Mid-Pleistocene Revolution (1-0.7 Ma). Authors in this volume suggest this onset occurs as high latitude forcing in both Hemispheres compresses the Intertropical Convergence Zone so that East Africa

  16. U-Pb zircon geochronology of amphibolites: new insight on the tectonic evolution of the southwestern Ossa Morena Zone, Portugal

    NASA Astrophysics Data System (ADS)

    Akker, Vénice; Burg, Jean-Pierre; Tajčmanová, Lucie; Marques, Fernando

    2017-04-01

    The tectonic evolution of the Évora - Beja domain, in the southwestern Ossa Morena Zone, is disputed because of the scarcity of integrated structural, petrological and geochronological data. Therefore, no strong correlation exists between terranes of the Ossa Morena Zone. We combine geochronological data and geochemistry with the structural and metamorphic evolutions in order to constrain the geological history of the Évora - Beja domain, between the ophiolitic units of the Pulo du Lobo and the Beja - Acebuches complexes, to the south, and the Central Portuguese Zone, to the north. The rocks in the Évora - Beja domain include marbles, micaschists and quartzites, a volcano- sedimentary sequence and phyllites, with local occurrences of amphibolites. New U-Pb age dating on zircons of amphibolites yield upper Proterozoic protolith ages of 789.3±4.5 Ma. Accordingly, most of the marbles, the micaschists and quartzites in the Évora - Beja domain can be ascribed to the Série Negra formation. The geochemical characterization of the amphibolites, which shows a basaltic protolith with subalkaline affinity, suggest a back-arc setting related to the oldest part of the tectonic evolution in the late Neoproterozoic. Phase equilibria modelling of amphibolites shows a metamorphic path consisting of three parts: (1) high pressure/low temperature event of ca 480±20°C and 1.04±0.06 GPa, (2) medium pressure/high temperature event of ca 550±20°C and 0.72±0.06 Gpa, and (3) retrogression into the greenschist facies, at less than 425°C and 0.7 GPa. The second stage is closely related to the magmatic emplacement of the Beja Igneous Complex and related deformation in the late Paleozoic. The geodynamic evolution of the Ossa Morena Zone is reportedly affected by two orogenic cycles, the Cadomian and Variscan orogenies, recording a geological history which goes back to Proterozoic times. The geology of the Évora - Beja domain contributes to this history.

  17. 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

  18. Evolution of the Sibişel Shear Zone (South Carpathians): A study of its type locality near Răşinari (Romania) and tectonic implications

    NASA Astrophysics Data System (ADS)

    Ducea, Mihai N.; Negulescu, Elena; Profeta, Lucia; Sǎbǎu, Gavril; Jianu, Denisa; Petrescu, Lucian; Hoffman, Derek

    2016-09-01

    The Sibişel Shear Zone is a 1-3 km wide, ductile shear zone located in the South Carpathian Mountains, Romania. In the Rășinari area, the ductile shear zone juxtaposes amphibolite facies rocks of the Lotru Metamorphic Suite against greenschist facies rocks of the Râuşorul Cisnădioarei Formation. The first represents the eroded remnants of Peri-Gondwanan arcs formed between the Neoproterozoic-Silurian (650-430 Ma), regionally metamorphosed to amphibolite facies during the Variscan orogeny (350-320 Ma). The second is composed of metasedimentary and metavolcanic Neoproterozoic-Ordovician (700-497 Ma) assemblages of mafic to intermediate bulk composition also resembling an island arc metamorphosed during the Ordovician (prior to 463 Ma). Between these lie the epidote amphibolite facies mylonitic and ultramylonitic rocks of the Sibișel Formation, a tectonic mélange dominated by mafic actinolite schists attenuated into a high strain ductile shear zone. Mineral Rb-Sr isochrons document the time of juxtaposition of the three domains during the Permian to Early Triassic ( 290-240 Ma). Ductile shear sense indicators suggest a right lateral transpressive mechanism of juxtaposition; the Sibişel shear zone is a remnant Permo-Triassic suture between two Early Paleozoic Gondwanan terranes. A zircon and apatite U-Th/He age transect across the shear zone yields Alpine ages (54-90 Ma apatite and 98-122 Ma zircon); these data demonstrate that the exposed rocks were not subjected to Alpine ductile deformation. Our results have significant implications for the assembly of Gondwanan terranes and their docking to Baltica during Pangea's formation. Arc terranes free of Variscan metamorphism existed until the Early Triassic, emphasizing the complex tectonics of terrane amalgamation during the closure of Paleotethys.

  19. 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

  20. Sedimentologic and tectonic evolution of the Upper Cretaceous-Lower Tertiary succession at Wadi Qena, Egypt

    NASA Astrophysics Data System (ADS)

    Soliman, Mohamed A.; Habib, Mohamed E.; Ahmed, Ezzat A.

    1986-01-01

    The Upper Cretaceous-Lower Tertiary rocks around Wadi Qena, Egypt, represent a mixed siliciclastic-carbonate-phosphorite succession including (from base to top) the Nubia Sandstone, Quseir Shale, Duwi Formation, Dakhla Shale, Tarawan Chalk, Esna Shale and Thebes Formation. Facies and microfacies investigations were carried out. The Nubia Sandstone was deposited by a fluviatile system, whereas the Quseir Shale was laid down by deltaic sedimentation. The Dakhla Shale, Esna Shale and Tarawan Chalk were formed in open marine (pelagic) realms. The Thebes Formation is a shallowing carbonate facies. Phosphorites were accumulated as lag deposits by reworking and winnowing of pre-existing phosphatic materials. The sedimentation of the Upper Cretaceous-Lower Tertiary rocks were affected by regional and local tectonics (i.e., faulting). The latter played a substantial role in the distribution of the different facies particularly the siliciclastic-carbonate facies.

  1. Paleomagnetic Investigations on the Tectonic Evolution of the Southeastern Anatolian Ophiolites in Late Cretaceous

    NASA Astrophysics Data System (ADS)

    Cengiz Cinku, M.; Karabulut, S.; Parlak, O.; Cabuk, B. S.; Ustaömer, T.; Hisarli, M. Z.

    2016-12-01

    Two E-W trending ophiolite belts crop out in SE Turkey, The southerly located ophiolites (Hatay, Koçali) were emplaced onto the Arabian Platform in Late Cretaceous whereas the northerly located ophiolites (Göksun, İspendere, Kömürhan, Guleman) were underthrust the S Tauride margin (i.e. Malatya-Keban Platform) in Late Cretaceous. Here we report our first paleomagnetic results from 155 different sites which was was focused on to the sheeted dyke complex, cumulate gabbros and extrusive sequences of each ophiolite from the N and S belts, while the cover units where sampled to distinguish emplacement related tectonic rotations from post-emplacement tectonic rotations. Rock magnetic experiments showed evidence of magnetite/titanomagnetite as the main magnetic carriers at the majority of sites. Progressive thermal and alternating demagnetization revealed that the characteristic remanent component is removed between 500 and 580 °C or 30-100 mT, respectively. Our new paleomagnetic results from the ophiolitic rocks emplaced in Arabian platform and the SE Anatolia show important implications to the spreading centre of the former ocean (s). Large counterclockwise rotations up to 100° are obtained from the sheeded dykes of the Hatay ophiolite in the Arabian plate with a paleolatitude of 16°, in contrast to the sheeded dykes of the Göksun ophiolite emplaced in the SE Anatolian with clockwise rotation of 90° and a paleolatitude of 22°. The relative movement of the ophiolitic series show their emplacement in the different zones. This study was financially supported by the project of the Scientific and Technical Research Council of Turkey (TUBITAK) with Project number 114R024.

  2. Tectonic evolution of the Malay Peninsula inferred from Jurassic to Cretaceous paleomagnetic results

    NASA Astrophysics Data System (ADS)

    Otofuji, Yo-ichiro; Moriyama, Yuji T.; Arita, Maiko P.; Miyazaki, Masanari; Tsumura, Kosuke; Yoshimura, Yutaka; Shuib, Mustaffa Kamal; Sone, Masatoshi; Miki, Masako; Uno, Koji; Wada, Yutaka; Zaman, Haider

    2017-02-01

    A primary remanent magnetization is identified in the Jurassic-Cretaceous red bed sandstones of the Tembeling Group in Peninsular Malaysia. This high-temperature magnetic component is unblocked at 680-690 °C, revealing a clockwise deflected direction of Ds = 56.8°, Is = 31.6° (where ks = 8.5, α95 = 11.3° and N = 22) in stratigraphic coordinates. The primary origin of this component is ascertained by a positive fold test and a geomagnetic polarity reversal in the Kuala Wau section. Secondary remanent magnetizations are identified in the rocks of the Tembeling and Bertangga basins, which indicate a counter-clockwise deflection in the geographic coordinates (Dg = 349.1°, Ig = 15.3° where kg = 11.8, α95 = 5.1°, N = 72). The comparison with the expected paleomagnetic directions from the 130 Ma and 40 Ma Eurasian poles indicates two-stages of tectonic movement in the southern Malay Peninsula: (1) a clockwise rotation of 61.1° ± 11.9° accompanied by a 13.3° ± 8.1° southward displacement after the Cretaceous; and (2) a subsequent counter-clockwise rotation of 18.5° ± 5.0° to the present day position. The first stage of rotation is ascribed to tectonic deformation caused by the indentation of India into Asia after 55 Ma, while the second stage is attributed to the collision of the Australian Plate with SE Asia after 30-20 Ma. The present paleomagnetic results from the Jurassic-Cretaceous Tembeling Group thus reveal impacts of both of these collisions on SE Asia in general and on Peninsular Malaysia in particular.

  3. Asymmetric exhumation across the Pyrenean orogen: implications for the tectonic evolution of a collisional orogen

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.; Muñoz, J. A.; Coney, P. J.; Baldwin, S. L.

    1999-11-01

    The Pyrenees are a collisional mountain belt formed by convergence between the Afro-Iberian and European plates. Apatite fission track thermochronology from three vertical profiles along the ECORS seismic line constrain the exhumation history of the Pyrenean orogen and hence tectonic models for its formation. In the Eocene there is relatively uniform exhumation across the Pyrenees, but significantly more exhumation occurs on the southern flank of the axial zone in the Oligocene. The variation in exhumation patterns is controlled by a change in how convergence is accommodated within the Pyrenean double-wedge. Accommodation of thrusting on relict extensional features that leads to inversion dominated thrust stacking resulted in relatively slow exhumation in the Eocene. However, subsequent crustal wedging and internal deformation in the upper crust under the stacked duplex of antiformal nappes resulted in extremely rapid exhumation on the southern flank in the Oligocene. The Maladeta profile in the southern axial zone records extremely rapid Early Oligocene exhumation followed by dramatic slowing or cessation of exhumation in the middle Oligocene and the formation of an apatite partial annealing zone (PAZ). This PAZ has subsequently been exhumed 2-3 km since the Middle Miocene, supporting the observations of Coney et al. [J. Geol. Soc. London 153 (1996) 9-16] that the southern flank of the range was buried by ≤2-3 km of syntectonic conglomerates in the Oligocene and subsequently re-excavated from Late Miocene to Recent. The present-day topographic form of the Pyrenees is largely a relict of topography that formed in the Eocene and the Oligocene. Comparison with paleoclimatic records indicates that the Eocene-Oligocene exhumation patterns are controlled by tectonic forces rather than resulting from an orographic effect due to uplift of the Pyrenees.

  4. 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

  5. Tectonic-depositional environment and proto-type basins evolution of the Late Ordovician in the Tarim Basin

    NASA Astrophysics Data System (ADS)

    Gao, Huahua; He, Dengfa; Tong, Xiaoguang; Wen, Zhixin; Wang, Zhaoming

    2017-04-01

    south. In the Lianglitage Formation-Sangtamu Formation stages, the subsidence and deposition fill occurred overall the basin, the depression died out making the depocenter reversed. In the Tierekeawati Formation stage, the northern and southern part of basin uplifted severely and became land, only the middle part of the basin was covered by water, marking the formation of the uplift-depression pattern differentiated from north to south. Under the background that the coupling between basins and orogenic belts increasingly strengthened, the injection of large terrigenous clastics and the up and down of topography made tectonic-depositional environment change rapidly. At the end of the Ordovician, with the sea level descended drastically and the emergence of provenance basin within the basin, the Tarim Basin terminated the history that carbonate sediment grew extensively, signing that basin evolution entered into a new stage. Key words: tectonic-depositional environment; proto-type basin; Late Ordovician; Tarim basin

  6. Evolution of Tidal Influence During the ETS Seismic Cycle Reveals Competition Between Tectonic Loading and Fault Healing

    NASA Astrophysics Data System (ADS)

    Houston, H.

    2015-12-01

    Following the discovery of the evolution of tremor response to tidal stress over the duration of ETS slip at a spot (Houston 2015; Royer et al 2015;Yabe et al 2015), we investigate whether and how it may evolve between major large ETSs, which occur quasi-periodically in several subduction zones. Preliminary results show that tidal response does evolve over the average interETS period in northern Cascadia - decaying over the first quarter of the cycle to lowest values then climbing back up in the second half of the cycle part of the way toward the strong response seen late during major ETSs. Thus far, we have ignored the possible role of transient stresses during interETS tremor because tremor bursts are mostly small. We explore a strength-threshold model where tidal influence is stronger when stress is close to strength and weaker when they are farther apart. Shortly after a major ETS, both stress and strength are presumed to have fallen over the large region where slow slip occurred. Then, however, stress rebuilds quasi-linearly by plate tectonic loading, whereas strength rebuilds as the logarithm of time (e.g., Vidale et al 1994). Thus, model stress and strength diverge the most midway through the interETS cycle, the period of weakest tidal sensitivity. Tidal stresses become more effective in triggering tremor later in the cycle as the linearly-growing stress approaches the logarithmically-growing strength. This model broadly fits our observed evolution of tidal response. However, the tendency of ETSs to initiate downdip may require an additional process that varies along dip. This approach illuminates the competition between healing on the plate interface and reloading with tectonic stress, and can help constrain and perhaps even monitor physical conditions on the deep subduction interface. The figure shows the evolution of two measures of tidal influence on tremor, consistency and sensitivity (right), and the data on which they are based - probability

  7. 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).

  8. 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.

  9. SHRIMP U-Pb in zircon geochronology of granitoids from Myanmar: temporal constraints on the tectonic evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Barley, M. E.; Zaw, Khin

    2009-04-01

    The Mesozoic to Tertiary tectonic evolution of Southeast Asia is the result of the convergence and collision of fragments of Gondwanaland with Eurasia culminating in the collision of India. A rapidly growing geochronological database is placing tight constraints on the timing and duration of magmatic episodes, metallogenic and tectonic events in the Himalayas, Tibet and eastern Indochina. However, there is little comparable geochronology for Myanmar. This SHRIMP U-Pb in zircon geochronology focuses on granitoids from the Mogok Metamorphic Belt (MMB, a belt of high grade metamorphic rocks at the edge of the Shan-Thai Terrane), the Myeik Archipelago (Shan-Thai Terrane) and the west Myanmar Terrane. Strongly deformed granitic orthogneisses in the MMB near Mandalay contain Jurassic (~170 Ma) zircons that have partly recrystallised during ~43 Ma high-grade metamorphism. A hornblende syenite from Mandalay also contains Jurassic zircons with evidence of Eocene metamorphism rimmed by thin zones of 30.9 ±0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma). I-type granitoids in the MMB, Myeik Archipelago and west Myanmar confirm that prior to the collision of India, an up to 200km wide magmatic belt extended along the Eurasian margin. The primitive I-type Khanza Chaung granodiorite in the Wuntho batholith in the west Myanmar terrane hosts porphyry-style mineralisation and has a magmatic age of 94  1 Ma. Triassic (~240 Ma), Jurassic (~170 Ma) and Early Cretaceous xenocryst zircons in this granitoid correspond with peaks of granitoid magmatism in the Shan-Thai terrane and establish that west Myanmar was part of the margin of Eurasia during the Mesozoic. A suite of highly fractionated metaluminous to peraluminous I-type granitoids with associated Sn-W-Ta mineralisation emplaced in the Myeik Archipelago of

  10. Plio-pleistocene volcano-tectonic evolution of la Reforma Caldera, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Demant, Alain; Ortlieb, Luc

    1981-01-01

    La Reforma volcanic complex, in east-central Baja California, shows a characteristic caldera structure, 10 km in diameter. The first eruptive stage, during the Pliocene, was manifested by ash and pumice falls and by subaqueous pumitic flows. In a second stage basic flows were deposited in a near-shore environment (subaerial and pillow lavas). During the early Pleistocene a large ignimbritic eruption, producing mainly pantelleritic tuffs, immediately predated the formation of the caldera itself. Afterwards, along marginal fractures of the caldera, some rhyolitic domes and flows partially covered the thick ignimbritic sheet. A block of Miocene substratum, in the center of the caldera, has been uplifted, nearly 1 km, by "resurgent doming". Small outcrops of diorite might constitute the top of coarse-grained crystallized magmatic bodies, and thus support the "resurgent doming" interpretation. A few basaltic cones were finally built on the flanks of the caldera complex; the latter are not related to the caldera history but to the extension tectonics of the Gulf of California which are also responsible for the Tortuga Island and the Holocene Tres Virgenes tholeiitic cones. South of la Reforma are found the highest (+300 m) Pleistocene marine deposits of the Gulf coast of Baja California. The uplift of this area is due in part to the positive epeirogenic movements of the whole peninsular crustal block, and also to the late doming of the caldera. On the coastal (eastern) flank of La Reforma complex up to seven stepped wave-cut terraces have been preserved, the highest reaching more than +150 m and the lowest ones +25 m. Lateral correlations of the marine terraces along the whole Gulf of California suggest that this volcano-tectonic uplift, that is still active, is of the order of 240 mm/10 3 y. The set of terraces is interpreted to be Middle (700-125 × 10 3y) to Upper (125-80 × 10 3y) Pleistocene, and is tentatively correlated with the paleoclimatic chronology of deep

  11. 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.

  12. 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

  13. Structural Evolution of the Alasehir (Gediz) and Buyuk Menderes Grabens: Implications for Cenozoic Extensional Tectonics in Western Turkey

    NASA Astrophysics Data System (ADS)

    Çemen, Ibrahim; Merey, Osman; Granath, James; Sert, Seren; Mahatsente, Rezene

    2017-04-01

    In western Turkey, the Cenozoic extensional tectonics was initiated in late Oligocene and produced the Menderes Metamorphic Core Complex (MMCC) and associated extensional structures. The Alaşehir and Büyük Menderes Grabens are two major E-W trending grabens that border the central part of the MMCC to the north and south, respectively. These two grabens were previously considered by many researchers as symmetrical grabens developed under the control of two oppositely dipping detachment surfaces; the north-dipping Alaşehir detachment to the north and the south-dipping Büyük Menderes detachment to the south. These researchers proposed that the detachments were formed in early Miocene as high angle normal faults and rotated to low angle detachment faults. Detailed field mapping and structural interpretation of seismic reflection profiles by many previous studies in the Alaşehir Graben suggest the presence of a well-developed roll over structure associated with the listric geometry of the north-dipping Alaşehir detachment surface. Recently, we have interpreted several N-S and E-W trending seismic reflection profiles in the Büyük Menderes Graben. The seismic lines reveal that the south dipping normal fault along the northern flank of the Büyük Menderes Graben is not listric and does not contain a roll over structure on its hanging wall. Kinematic modeling using backstripped cross sections and tectonic subsidence rates suggests that the evolution of the Büyük Menderes Graben was controlled by two active planar boundary faults, one on each margin with numerous internal planar subsidiary faults. Therefore, we suggest that the kinematic development of the Büyük Menderes Graben fundamentally differs from that of the Alaşehir Graben. The Büyük Menderes Graben seems to have been initiated by slip on the boundary faults during the early Miocene. The development of the graben was largely controlled by slip on the south-dipping (master) boundary fault that

  14. 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

  15. Tectonic evolution of high-grade metamorphic terranes in central Vietnam: Constraints from large-scale monazite geochronology

    NASA Astrophysics Data System (ADS)

    Nakano, Nobuhiko; Osanai, Yasuhito; Owada, Masaaki; Nam, Tran Ngoc; Charusiri, Punya; Khamphavong, Keo

    2013-09-01

    on the pressure-temperature-time-protolith evolutions, metamorphic rocks from central Vietnam provide a continuous record of subduction-accretion-collision tectonics between the South China and Indochina blocks: in the Ordovician-Silurian, the region was characterized by active continental margin tectonics, followed by continental collision during the Late Permian to Early Triassic and subsequent exhumation during the Late Triassic. The results also suggest that the timing of metamorphism and protolith formation as well as the geochemical features in other Southeast Asian terranes should be verified to achieve a better understanding of the Precambrian to Early Mesozoic tectonic history in Asia.

  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. 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.

  18. 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.

  19. 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.

  20. Analysis of the stress regime and tectonic evolution of the Azerbaijan Plateau, Northwestern Iran

    NASA Astrophysics Data System (ADS)

    Alizadeh, A.; Hoseynalizadeh, Z.

    2017-05-01

    The increasing number of earthquakes in recent decades in Northwestern Iran and the determination of the epicenters of these events makes possible to estimate accurately the changing tectonic regime using the Win-Tensor inversion focal mechanism program. For this purpose focal mechanism data were collected from various sources, including the Centroid Moment Tensor catalog (CMT). The focal mechanism and fault slip data were analyzed to determine change in the stress field up to the present day. The results showed that two stages of brittle deformation occurred in the region. The first stage was related to Eocene compression in NE-SW direction, which created compressional structures with NW-SE strike, including the North and South Bozgush, south Ahar and Gushedagh thrust belts. The second brittle stage began in the Miocene with NW-SE compression and caused developing thrusts with N-S trends that were active presently. These stress regimes were created by the counter-clockwise rotation of the Azerbaijan plateau caused by movement on strike slip faults and continuous compression between the Arabian plate, the south Caspian basin and the Caucasus region. Pliocene-Quaternary activity of the Sabalan and Sahand volcanoes as well as recent earthquakes occurred as a result of this displacement and rotational movement. The abundance of hot springs in the Ardebil, Hero Abad and Bostanabad areas also bore witness to this activity.

  1. A review of the pressure temperature time evolution of the Limpopo Belt: Constraints for a tectonic model

    NASA Astrophysics Data System (ADS)

    Rigby, M.; Mouri, H.; Brandl, G.

    2008-02-01

    clockwise evolution. Granitoid magmatism is broadly contemporaneous in all three zones at ca. 2.7-2.5 suggesting a possible causal geodynamic link. P- T contrasts between and within the respective zones prevent, at present, the construction of a coherent and inter-related tectonic model that can account for all of the available evidence. Detailed and fully-integrated petrological and geochronological studies are required to produce reliable P- T- t paths that may resolve some of these pertinent issues.

  2. From the valley floor to the peaks: Stratigraphy and landscape evolution of the Alpine Lateglacial in the Kitzbühel Alps (Tyrol, Austria)

    NASA Astrophysics Data System (ADS)

    Dippenaar, Elijah; Reitner, Jürgen

    2017-04-01

    Our understanding of Alpine landscape evolution and more specifically, chronology of glacier activity during the Alpine Lateglacial (ALG; c. 19 - 11.7 ka) i.e. the timespan between the Würmian Pleniglacial (= Alpine Last Glacial Maximum; AlpLGM) and the beginning of the Holocene, is based on the evidence of only few areas in the Alps. In order to get a better understanding of glaciation and palaeoclimate during this phase, N-S and E-W transects are needed. The Kitzbühel Alps, which are currently not glaciated, span an area of 1700km2 and have peaks that reach c. 2400m a.s.l. They lie at the center of the Eastern Alps on the northern rim, which is more humid than the relatively dry central parts. A modern geological investigation of the ALG record is missing in the Kitzbühel Alps. In order to overcome this gap of knowledge and to gain a more complete understanding of the ALG landscape development, a pioneering study has been performed in the area of Langer Grund Valley, a tributary valley of the Kelchsau Valley. This was done through detailed field mapping, thereby describing the shape and sediment composition of Quaternary morphological features, such as moraines, landslides and rock glacier deposits. Sedimentary evidence of one short glacial advance and two glacial stadials were identified. In chronological order they were named the: Frommbach advance, the Arnbach (glacier) halt and the Küharn halt. Where possible, palaeoglaciers were constructed using ArcGIS. With the palaeoglaciers, equlibrium line altitudes (ELA) were calculated and compared to ELA values of known glacial stadials in an attempt to correlate the relative local stratigraphy to the Lateglacial stratigraphy. Four methods to calculate ELAs were used; Maximum Elevation of Lateral Moraines (MELM), Toe to Headwall Altitude Ratio (THAR), Area x Altitude (AA) and Accumulation Area Ratio (AAR). Furthermore, the glacial sedimentary sequence of the study area was compared to that of the Gschnitz Valley

  3. 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.

  4. 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

  5. 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

  6. Rhaetian extensional tectonics in the Slovenian Basin (Southern Alps): Preliminary results of an outcrop study

    NASA Astrophysics Data System (ADS)

    Oprčkal, P.; Gale, L.; Kolar-Jurkovšek, T.; Rožič, B.

    2012-04-01

    A Late Triassic palaeogeographic position of the Slovenian Basin on the passive continental margin of the Neotethys Ocean to the East and later the Alpine Tethys to the West, implements that its evolution intimately depended on the events in these two areas of extension. Recent research of the "Bača dolomite", the typical Norian-Rhaetian lithologic unit of the Slovenian Basin, resulted in recognition of four extensional tectonic events (Gale et al., this volume). The Lower and Middle Norian tectonic pulses can be recognized throughout the basin. A weakened tectonic activity was recognized in the Rhaetian, followed by more pronounced, but spatially restricted tectonics at the Triassic-Jurassic boundary. Extensional tectonics was attributed to the diminishing rifting in the Neotethys area and to the incipient opening of the Alpine Tethys (Gale et al., this volume). The ongoing fieldwork in the vicinity of Škofja Loka (central Slovenia) resulted in the discovery of palaeofaults in the small-sized quarry that directly evidences the Late Triassic extensional tectonics. Based on superposition, the observed section of the "Bača dolomite" is of the Rhaetian age. The discovery is particularly important because it represents the first direct documentation of the Late Triassic down-faulting in the region. The lowest strata exposed consist of highly bituminous bedded dolostones with scour structures and several meters of mud-supported dolo-breccias. Breccias were downthrown along a normal fault and the created accommodation space filled with bedded dolostone. After complete leveling of topography, another differentiation took place, during which a new normal fault originated, whereas the pre-existing fault was reactivated in an antithetic sense. Thin-bedded dolostones were deposited during slowly abiding movements. The final cessation of tectonics is marked by a uniform deposition of massive dolostone, entirely overlying the fault-dissected sediments.

  7. Stratigraphic and Tectonic Evolution of the Jurassic Hazelton Trough-Bowser Basin, Northwest British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Gagnon, Jean-Francois

    The Hazelton trough--Bowser basin is a large sedimentary basin that developed on volcanic arc rocks of the Stikine terrane in northern British Columbia, Canada. Its fill mostly consists of the Lower to Middle Jurassic Hazelton Group and the Middle Jurassic to Lower Cretaceous Bowser Lake Group. Regional correlations indicate that the Hazelton Group can be divided in two distinct lithostratigraphic intervals separated in most places by an unconformity. The lower Hazelton Group (LHG) is dominated by arc-related volcanic rocks, whereas the upper Hazelton Group (UHG) contains mainly fine-grained clastic rocks and lesser bimodal rift-related volcanic rocks. Lowermost coarse-grained strata of the UHG, including the bioturbated and fossiliferous units of the Smithers Formation and the Spatisizi River Formation, record a transgressive trend consistent with thermal subsidence and relative sea-level rise. Transgression of the Stikine arc culminated with the establishment of deep-water conditions in the Late Toarcian-Early Aalenian, and deposition of the Quock Formation. Interbedded siliceous mudstone and rusty-weathered tuff of the Quock Formation are correlated throughout most of the basin, except in the Iskut River area on the northwestern margin of the basin, where contemporaneous strata of the Iskut River Formation are dominated by rift-related volcanic rocks and conglomerates. Inception of rifting in the Iskut River area constitutes an independent extensional event on Stikinia, and could be related to reorganization of tectonic plates during a protracted period of terrane accretion in the Middle Jurassic. Obduction of the Cache Creek terrane over Stikinia in early Middle Jurassic provided a new source of sediment, which led to accumulation of the Bowser Lake Group. The second pulse of subsidence observed at Todagin Mountain can be explained by sediment loading of the accommodation previously generated during extension of the Hazelton trough in Early Jurassic time.

  8. 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.

  9. 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.

  10. Miocene carbonate reservoirs related to tectonic and thermal evolution of southeast Asian marginal basins

    SciTech Connect

    Fulthorpe, C.S.; Brodholt, J.P.; Jurdy, D.M.; Schlanger, S.O.

    1986-05-01

    The early Miocene global sea level rise and oceanic warming period allowed the tropical reef growth belt to expand and fostered the development of major carbonate buildups throughout southeast Asia. A regional paleogeographic reconstruction for 18 m.y. places reefal, shelf, and basinal facies in a tectonic setting of island arcs, subduction zones, and marginal basins. For typical basins, such as the Sulu, Celebes, and South China Sea basins, basin formation and sedimentation models have been developed based on ages inferred from identified marine magnetic anomalies and heat flow data. These basins have many of the attributes needed for hydrocarbon development and maturation. They accumulated sediment from pelagic sources and surrounding island arcs and landmasses fringed by reefs. During the early Miocene, limited water circulation in restricted basins, such as the Sulu and Celebes basins, may have induced dysaerobic conditions that enhanced organic carbon preservation. Models of marginal basin formation provide the basis for studying the time-dependent thermal histories of their sediment sequences. The authors models show that, for example, lower Miocene sediments deposited at a rate of 100 m/m.y. on 20-m.y.-old crust in a typical basin have just entered the oil-generation window. Lower sedimentation rates require deposition on younger crust in order for the sediments to reach an equivalent maturation stage. Estimates of the hydrocarbon potential of such marginal basins should be based on a sequential time-slice analysis of each basin in terms of sediment type, sedimentation rate, sea floor age and thermal regime, and the presence of reservoirs.

  11. 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

  12. Evolution of the Median Tectonic Line fault zone, SW Japan, during exhumation

    NASA Astrophysics Data System (ADS)

    Shigematsu, Norio; Kametaka, Masao; Inada, Noriyuki; Miyawaki, Masahiro; Miyakawa, Ayumu; Kameda, Jun; Togo, Tetsuhiro; Fujimoto, Koichiro

    2017-01-01

    Like many crustal-scale fault zones, the Median Tectonic Line (MTL) fault zone in Japan preserves fault rocks that formed across a broad range of physical conditions. We examined the architecture of the MTL at a large new outcrop in order to understand fault behaviours under different crustal levels. The MTL here strikes almost E-W, dips to the north, and juxtaposes the Sanbagawa metamorphic rocks to the south against the Izumi Group sediments to the north. The fault core consists mainly of Sanbagawa-derived fault gouges. The fault zone can be divided into several structural units, including two slip zones (upper and lower slip zones), where the lower slip zone is more conspicuous. Crosscutting relationships among structures and kinematics indicate that the fault zone records four stages of deformation. Microstructures and powder X-ray diffraction (XRD) analyses indicate that the four stages of deformation occurred under different temperature conditions. The oldest deformation (stage 1) was widely distributed, and had a top-to-the-east (dextral) sense of slip at deep levels of the seismogenic zone. Deformation with the same sense of slip, then became localised in the lower slip zone (stage 2). Subsequently, the slip direction in the lower slip zone changed to top-to-the-west (sinistral-normal) (stage 3). The final stage of deformation (stage 4) involved top-to-the-north normal faulting along the two slip zones within the shallow crust (near the surface). The widely distributed stage 1 damage zone characterises the deeper part of the seismogenic zone, while the sets of localised principal slip zones and branching faults of stage 4 characterise shallow depths. The fault zone architecture described in this paper leads us to suggest that fault zones display different behaviours at different crustal levels.

  13. 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.

  14. 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.

  15. Thermochronology of the PoSen complex, northern Vietnam: Implications for tectonic evolution in SE Asia

    NASA Astrophysics Data System (ADS)

    Wang, Pei-Ling; Lo, Ching-Hua; Lan, Ching-Ying; Chung, Sun-Lin; Lee, Tung-Yi; Nam, Tran Ngoc; Sano, Yuji

    2011-03-01

    The PoSen complex, located closely adjacent to the southwestern margin of the Red River shear zone represents the uplifted basement of north Vietnam and may record the motion of the shear zone. However, its thermochronological history has not been fully examined yet. Here we applied U-Pb and 40Ar/ 39Ar dating methods to reveal its thermochronological history. U-Pb analysis of composite zircon grains by TIMS yielded an average age of 760 ± 25 Ma, clustering on the concordia line. Twelve SHRIMP U-Pb analyses also yielded a consistent result of 751 ± 7 Ma. Along with the geochemical features, the U-Pb dating results suggest the PoSen complex was a late Proterozoic magmatic complex, which could correspond to the Chengjiang orogeny, a widespread thermal event in southwest China. Results of 40Ar/ 39Ar dating of micas and K-feldspars were in the range of 36-30 Ma, revealing a rapid cooling and exhumation history of the PoSen complex during the late Paleogene. The time span of cooling and exhumation of the PoSen complex is slightly older than the main cooling phases of the Ailao Shan-Red River (ASRR) metamorphic massifs (28-17 Ma), but is synchronous with the early igneous activity stage in the eastern Indo-Asian collision zone of southeast China and north Vietnam. Owing to the ongoing debate about the initiation and offset of the ASRR shear zone, the tectonic force for the late Paleogene cooling of the PoSen complex is still inconclusive. The rapid exhumation of the PoSen complex could be in response to either the detachment of the Neo-Tethyan slab or a transpressional phase of continental subduction along the ASRR shear system in the eastern Indo-Asian collision zone.

  16. 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.

  17. 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.

  18. Space-time evolution of soil moisture, evapotranspiration and snow cover patterns in a dry alpine catchment: an interdisciplinary numerical and experimental approach

    NASA Astrophysics Data System (ADS)

    Bertoldi, Giacomo; Della Chiesa, Stefano; Niedrist, Georg; Rist, Armin; Tasser, Erich; Tappeiner, Ulrike

    2010-05-01

    The project Climate Change in South Tyrol aims to study the effects of climate change (CC) on the water balance and the consequences for the vegetation in a dry Alpine region, using an innovative multidisciplinary approach that combines modelling and experimentation. Regional climate scenarios predict a temperature increase and a summer precipitation decrease for the European Alps. This will likely lead to drier conditions, especially during the vegetation growth period. As this evolution will be more problematic in already dry regions, the inner Alpine continental Mazia Valley (South Tyrol, Italy) was chosen as study area in 2009 for long-term ecological research. As a preliminary case study, the extreme 2002-2003 water year was selected to simulate a retrospective water balance at catchment scale, using the hydrological model GEOtop. The model proved to simulate realistic values for the spatial and temporal dynamics of soil moisture, evapotranspiration, snow cover and runoff production, depending on soil properties, land cover, land use intensity and catchment morphology. In the study area of Mazia Valley 13 monitoring stations were installed in fall 2009 to continuously measure soil moisture, biomass production, as well as standard micrometeorological variables. The stations were distributed over the whole catchment to encompass its variability in elevation, slope aspect, soil properties, and land cover. Furthermore, snow depth and snow water equivalent were recorded at representative points throughout the catchment. In addition, the spatial distribution of the snow cover was determined by means of remote sensing and the discharge of the catchment was measured as integrating hydrological variable. The use of different types of data permits a multi-scale validation of the model, in order to close the water balance and accurately estimate the space-time evolution of soil moisture, evapotranspiration and snow cover both at the plot and at the catchment scale. A

  19. 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

  20. Climatic, tectonic, and biological factors affecting the oxidation state of the atmosphere and oceans: Implications for Phanerozoic O2 evolution

    NASA Astrophysics Data System (ADS)

    Ozaki, K.; Tajika, E.

    2015-12-01

    The Earth's atmosphere and oceans have seen fundamental changes in its oxidation state in response to the climatic, tectonic and geochemical variations. Over the past decade, several geochemical proxies have led to significant progress in understanding the paleredox states of ancient oceans. However, a quantitative interpretation of these data for atmospheric O2 levels remain unclear because the relationship between atmospheric O2 levels (pO2) and oceanic redox state depends on several environmental factors, such as terrestrial weathering rate, sea-level stands, and sinking rate of particulate organic matter (POM) in the water column and so on. It is widely thought that the redox-dependent P cycling also plays a crucial role in regulating pO2 because it acts as a negative feedback on a geological timescale. It is important that strength of this feedback for a given pO2 is also modulated by environmental factors, affecting not only O2 levels at steady state but also its susceptibility to environmental changes. In this study, a quantitative role of environmental factors in the oxidation state of Earth's surface environment is evaluated with an oceanic biogeochemical cycle model (CANOPS) coupled with global C cycle model, which enables us to understand the ancient CO2 and O2 evolution. Our results demonstrate that atmospheric O2 level at steady state is affected by CO2 input flux from Earth's interior via changes in biogeochemical cycles, but its response is modulated by several internal factors such as shelf area and POM sinking rate. We also found that early Paleozoic atmospheric O2 levels before the advent of land plant would be determined so that oceans may locate at the "edge of anoxia (EoA)" where the redox-dependency of marine P cycle plays a crucial role in regulating O2 cycle, and that POM sinking rate has a great impact on the EoA. Our findings provide insights into the O2 cycle over the Phanerozoic in response to the climatic and tectonic variations and

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  2. Systematics and evolution of Arctic-Alpine Arabis alpina (Brassicaceae) and its closest relatives in the eastern Mediterranean.

    PubMed

    Karl, Robert; Kiefer, Christiane; Ansell, Stephan W; Koch, Marcus A

    2012-04-01

    The high mountains in southern Anatolia and the eastern Mediterranean are assumed to play a major role as a primary center of genetic diversity and species richness in Eurasia. We tested this hypothesis by focusing on the widespread perennial arctic-alpine Arabis alpina and its sympatrically distributed closest relatives in the eastern Mediterranean. Plastid (trnL intron, trnL-F intergenic spacer) and nuclear (ITS) DNA sequence analysis was used for phylogenetic reconstruction. Broad-scale plastid haplotype analyses were conducted to infer ancestral biogeographic patterns. Five Arabis species, identified from the eastern Mediterranean (Turkey mainland and Cyprus), evolved directly and independently from A. alpina, leaving Arabis alpina as a paraphyletic taxon. These species are not affected by hybridization or introgression, and species divergence took place at the diploid level during the Pleistocene. Pleistocene climate fluctuations produced local altitudinal range-shifts among mountain glacial survival areas, resulting not only in the accumulation of intraspecific genotype diversity but also in the formation of five local species. We also show that the closest sister group of Arabis alpina consists exclusively of annuals/winter annuals and diverged prior to Pleistocene climatic fluctuations during the colonization of the lowland Mediterranean landscape. These findings highlight that Anatolia is not only a center of species richness but also a center for life-history diversification.

  3. Tectonic evolution of the Transbaikal region (Siberia) from Late Jurassic to Present. Implications for the Mongol-Okhotsk orogeny.

    NASA Astrophysics Data System (ADS)

    Jolivet, M.; Arzhannikova, A.; Arzhannikov, S.; Chauvet, A.; Vassallo, R.; Kulagina, N.; Akulova, V.

    2012-04-01

    The Transbaikal region extends over several hundreds of kilometres east of the Baikal Rift System. It is characterized by a number of sub-parallel Mesozoic grabens or half grabens generally filled with late Jurassic to Early Cretaceous clastic sediments interbedded with coal layers (1). Similar basins occur on an even larger area spanning from the Transbaikal region down to Korea implying a large-scale extensional process affecting most of the Amuria plate during the Mesozoic. In the Transbaikal region, the normal faults controlling the edges of the Mesozoic basins are generally superimposed to Palaeozoic ductile shear zones implying a strong localisation of the extensional deformation on inherited structures. Recent studies, associated to our own fieldwork demonstrated that some of the faults were again activated (2), still as extensional faults, during the Tertiary or Quaternary, and that some of them are presently active. The closure of the Mongol-Okhotsk ocean separating the Siberian plate from the Amurian block during the Mesozoic corresponds to a major event in the growth process of the East Asian continent. The oceanic suture zone is situated on the southern edge of the Transbaikal region and its roughly SW-NE direction is parallel to the basins (3). The timing of the closure of the Mongol-Okhotsk ocean is still highly debated: while sedimentological and tectonic data suggest that the oceanic closure and the following collision occurred in early Middle Jurassic (4), paleomagnetic studies advocate for a Early Cretaceous collision (5). Furthermore, several other questions remain on the localization, the size and the fate of the relief that most probably formed during the collision between the Amuria block and the Siberian craton. In order to answer those questions we used low temperature thermochronology data associated to tectonic, sedimentology and palinology to investigate the evolution of the Transbaikal grabens from Mesozoic to Present. Tectonic and

  4. 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

  5. Tectonic evolution of the Neoproterozoic São Gabriel block, southern Brazil: Constraints on Brasiliano orogenic evolution of the Rio de la Plata cratonic margin

    NASA Astrophysics Data System (ADS)

    Saalmann, K.; Remus, M. V. D.; Hartmann, L. A.

    2006-07-01

    Precambrian rocks of southernmost Brazil display a complex tectonometamorphic evolution since the Archean. Neoproterozoic juvenile rocks in the São Gabriel block offer a unique opportunity to study unequivocal Brasiliano fabric and tectonics. The stratigraphic succession comprises the Palma Group, which consists of metasedimentary rocks and juxtaposed (ultra-)mafic to intermediate volcanic and volcanoclastic rocks formed mainly in a subduction zone environment, as well as the juvenile metadiorites, -tonalites and -trondhjemites of the Cambaí Complex, which represent relics of magmatic arcs. Four deformational events, the first three characterized by ductile deformation, can be distinguished in the São Gabriel block. The first deformation, D1, led to the formation of a first foliation and metamorphic layering, possibly related to a first folding event. The D2 event reached amphibolite facies metamorphic peak conditions and corresponds to southeast-directed thrusting. D1 and D2 can be observed only in the lower Palma Group rocks. D3 led to the tectonic juxtaposition of different lithologic units along major SW-NE-striking shear zones, which defines the final overall geometry of the area represented by a dextral transpressive, southeast-vergent ductile thrust stack. Ductile SW-NE-oriented strike-slip shearing occurred predominantly in syntectonic (syn-D3) plutonic rocks of the Cambaí Complex due to the lower viscosity and strength of the magmatic rocks, whereas deformation in the wall rocks (Palma Group) was accommodated mainly by southeast-vergent folding. The main part of the D3 deformation took place under upper greenschist to lower amphibolite facies metamorphic conditions. The last deformation, D4, is characterized by semi-brittle, southeast-directed thrusting. A plate tectonic model for the São Gabriel block comprises (1) eastward subduction of oceanic crust and approximately 880 Ma accretion of the intraoceanic Passinho arc to the eastern border of the Rio

  6. Geochronology, geochemistry and tectonic evolution of the Western and Central cordilleras of Colombia

    NASA Astrophysics Data System (ADS)

    Villagómez, Diego; Spikings, Richard; Magna, Tomas; Kammer, Andreas; Winkler, Wilfried; Beltrán, Alejandro

    2011-08-01

    Autochthonous rocks of the pre-Cretaceous continental margin of NW South America (the Tahami Terrane) are juxtaposed against a series of para-autochthonous rock units that assembled during the Early Cretaceous. Allochthonous, oceanic crust of the Caribbean Large Igneous Province collided with and accreted onto the margin during the Late Cretaceous. We present the first regional-scale dataset of zircon U-Pb LA-ICP-MS ages for intrusive and metamorphic rocks of the autochthonous Tahami Terrane, Early Cretaceous igneous para-autochthonous rocks and accreted oceanic crust. The U-Pb zircon data are complemented by multiphase 40Ar/ 39Ar crystallization and cooling ages. The geochronological data are combined with whole rock major oxide, trace element and REE data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the Western Cordillera, Cauca-Patía Valley and the Central Cordillera of Colombia. The Tahami Terrane includes lower Paleozoic orthogneisses (~ 440 Ma) that may have erupted during the active margin stage of the Rheic Ocean. Basement gneisses were intruded by Permian, continental arc granites during the final assembly of Pangea. Triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high-T metamorphism associated with rifting of western Pangea during 240-220 Ma. Continental arc magmatism during 180-145 Ma is preserved along the whole length of the Central Cordillera and was followed by an Early Cretaceous out-board step of the arc axis and the inception of the Quebradagrande Arc that fringed the continental margin. Back-stepping of the arc axis may have been caused by the collision of buoyant seamounts, which were coeval with plateau rocks exposed in the Nicoya Peninsular of Costa Rica. Rapid westward drift of South America closed the Quebradagrande basin in the late Aptian and caused medium-high P-T metamorphic rocks of the Arquía Complex to exhume and obduct onto

  7. 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.

  8. 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

  9. 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

  10. Peralkaline granitoid magmatism in the Mongolian-Transbaikalian Belt: Evolution, petrogenesis and tectonic significance

    NASA Astrophysics Data System (ADS)

    Jahn, B. M.; Litvinovsky, B. A.; Zanvilevich, A. N.; Reichow, M.

    2009-12-01

    The Central Asian Orogenic Belt (CAOB) is well-known for its massive generation of juvenile crust in the Phanerozoic. In eastern CAOB, voluminous peralkaline and alkaline (alkali-feldspar) granitoids and genetically related bimodal volcanics were emplaced in three stages from Early Permian to late Mesozoic: 295-270 Ma, 230-190 Ma and 150-120 Ma. They occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area. Among them the 2500 km-long Mongolian-Transbaikalian Belt (MTB) is the most spectacular and it comprises more than 350 granite-syenite plutons and stocks, with numerous co-genetic volcanic fields. The three stages of granitoids have similar chemical compositions but show temporal variation in Nd isotopic composition. Initial ɛNd( T) values range from - 1 to - 5 for the Early Permian, 0 to + 4 for the early Mesozoic, and - 2 to - 3.5 for the late Mesozoic granitoids. The negative ɛNd( T) values observed in the MTB are not typical of the CAOB granitoids, which are generally characterized by positive values. However, several pieces of evidence suggest that the MTB peralkaline and alkali feldspar granitoids were produced from enriched mantle-derived sources. The evidence includes: (1) Felsic and mafic rocks formed in the same stage have similar initial Nd-Sr isotopic ratios and Sm-Nd model ages ( TDM). (2) The granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces, but no correlation is found in chemical compositions between the granitoids and country rocks. (3) The abundant syenites are considered to be cogenetic or, in some cases, parental to the granites. Experimental and isotope data argue for the derivation of syenites from an enriched mantle source, thus the granites (and comendites) are regarded as mantle-derived. (4) A study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000-1100 °C for the magma

  11. 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

  12. 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 faul