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Sample records for alpine tectonic evolution

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  5. 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.

  6. Alpine extensional detachment tectonics in the Grande Kabylie metamorphic core complex of the Maghrebides (northern Algeria)

    NASA Astrophysics Data System (ADS)

    Saadallah, A.; Caby, R.

    1996-12-01

    The Maghrebides are part of the peri-Mediterranean Alpine orogen. They expose in their inner zone inliers of high-grade crystalline rocks surrounded by Oligo-Miocene and younger Miocene cover. Detailed mapping coupled with structural and petrological investigations in the Grande Kabylie massif, and the reinterpretation of the available geochronological data, allow us to refute the traditional concept of rigid behaviour of this massif during Alpine events. We show that the dome geometry, the kinematic and metamorphic evolutions and the age pattern are typical of metamorphic core complexes exhumed by extension. A major low-angle detachment fault defined by mylonites and by younger cataclasites has been traced in the massif. The upper unit encompasses pre-Permian phyllites with Variscan {40Ar }/{39Ar } cooling ages, capped by unconformable Mesozoic to Tertiary cover of the Calcareous Range, both mainly affected by extensive Tertiary brittle deformation and normal faulting. The lower unit exposes in two half-domes a continuous tectonic pile, 6-8 km thick, of amphibolite facies rocks and orthogneisses affected by syndashmetamorphic ductile deformation, devoid of retrogression. The regular increase of paleotemperature downward and the {40Ar }/{39Ar } plateau ages around 80 Ma suggest that the high-temperature foliation and associated WNW-directed shear under a high geothermal gradient relate to extensional tectonics developed during Mesozoic lithospheric thinning of the Variscan south European margin. To the north, the Sidi Alli Bou Nab massif exposes another crustal section affected throughout by WNW-directed extensional shear during {HP }/{HT } syndashmetamorphic thinning and with overall {40Ar }/{39Ar } plateau ages of 25 Ma. The Eocene oblique collisional event responsible for crustal thickening was totally overprinted by this new extensional regime, synchronous with the beginning of the opening of the Western Mediterranean oceanic basin. This was also coeval with

  7. Tectonic evolution of the Caribbean

    NASA Technical Reports Server (NTRS)

    Burke, Kevin

    1988-01-01

    The development of the Caribbean is discussed in terms of modern tectonic theory. The nature of the site on which the Caribbean formed is examined, and the development of the rifted margins of the Caribbean is described. Constraints on Caribbean evolution from the relative motions of North and South America are briefly examined, and the Caribbean Oceanic Plateau is discussed. The great island-arc system of the Caribbean is addressed in detail, emphasizing the way the Great Arc of the Caribbean was segmented. The role of Central America in Caribbean history is briefly considered.

  8. 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.

  9. 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.

  10. 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

  11. Caribbean paleomagnetism and tectonic evolution

    SciTech Connect

    MacDonald, W.D.

    1985-01-01

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

  12. Tectonic evolution of the terrestrial planets.

    PubMed

    Head, J W; Solomon, S C

    1981-07-01

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

  13. Tectonic evolution of the terrestrial planets.

    PubMed

    Head, J W; Solomon, S C

    1981-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  15. 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.

  16. 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.

  17. 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.

  18. Lu-Hf dating, petrography, and tectonic implications of the youngest Alpine eclogites (Tauern Window, Austria)

    NASA Astrophysics Data System (ADS)

    Nagel, T. J.; Herwartz, D.; Rexroth, S.; Münker, C.; Froitzheim, N.; Kurz, W.

    2013-06-01

    Isotopic dating of metamorphic minerals places fundamental constraints on the rates and mechanisms of burial and exhumation in collisional orogens. The Eclogite Zone in the Tauern Window has been the focus of many studies on subduction-related high-pressure metamorphism. However, the age and duration of the high-pressure stage remains the subject of ongoing debate. 32 Ma Sr-Rb ages interpreted to date eclogite-facies metamorphism (Glodny et al., 2005) appear too young in traditional tectonic reconstructions of plate collision in the Alps. These ages have either been interpreted to indicate extremely rapid exhumation from more than 60 kilometre depth to mid-crustal levels within 1 Ma years or to date retrogression subsequent to high-pressure metamorphism. We present element distribution maps and lutetium-hafnium (Lu-Hf) garnet ages of three samples from the Eclogite Zone. All samples display almost unaltered eclogite-facies assemblages and garnets preserve growth zoning. Lu-Hf ages are thus considered as formation ages recording metamorphism towards peak-pressure conditions. In the sample with the smallest grain size, garnet shows regular bell-shaped element distributions with respect to manganese and the iron-magnesium ratio. A six-point isochron of this sample yields 32.8 ± 0.5 Ma (MSWD = 1.06), interpreted as the age of Alpine eclogite-facies metamorphism. In one of the other two, coarser-grained samples' garnet chemistry is identical. The third sample, however, shows complex zoning in large garnet crystals. Cores with a very low iron-magnesium ratio are surrounded by a second garnet generation which is very similar to the Alpine generation in the other two samples. The two coarser-grained samples yield scattered ages between 26.9 ± 9.8 Ma and 62.7 ± 1.8 Ma for individual garnet-whole-rock pairs as the analysed garnet fractions display very different 176Hf/177Hf vs. 176Lu/177Hf ratios. This scatter reflects varying degrees of mixing between Alpine and pre-Alpine

  19. The Tectonics and Evolution of Venus

    NASA Technical Reports Server (NTRS)

    Kaula, William M.

    1997-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1996-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  2. Late Cenozoic tectonic evolution of southwestern California

    NASA Technical Reports Server (NTRS)

    Sedlock, Richard L.; Hamilton, Douglas H.

    1991-01-01

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

  3. 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.

  4. Geodynamical Evolution and Tectonic Framework of China

    NASA Astrophysics Data System (ADS)

    LIU, Guangding

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

  5. 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.

  6. Unravelling the interaction between tectonic and sedimentary processes during lithospheric thinning in the Alpine Tethys margins

    NASA Astrophysics Data System (ADS)

    Mohn, Geoffroy; Manatschal, Gianreto; Müntener, Othmar; Beltrando, Marco; Masini, Emmanuel

    2010-10-01

    The discovery of exhumed continental mantle and hyper-extended crust in present-day magma-poor rifted margins is at the origin of a paradigm shift within the research field of deep-water rifted margins. It opened new questions about the strain history of rifted margins and the nature and composition of sedimentary, crustal and mantle rocks in rifted margins. Thanks to the benefit of more than one century of work in the Alps and access to world-class outcrops preserving the primary relationships between sediments and crustal and mantle rocks from the fossil Alpine Tethys margins, it is possible to link the subsidence history and syn-rift sedimentary evolution with the strain distribution observed in the crust and mantle rocks exposed in the distal rifted margins. In this paper, we will focus on the transition from early to late rifting that is associated with considerable crustal thinning and a reorganization of the rift system. Crustal thinning is at the origin of a major change in the style of deformation from high-angle to low-angle normal faulting which controls basin-architecture, sedimentary sources and processes and the nature of basement rocks exhumed along the detachment faults in the distal margin. Stratigraphic and isotopic ages indicate that this major change occurred in late Sinemurian time, involving a shift of the syn-rift sedimentation toward the distal domain associated with a major reorganization of the crustal structure with exhumation of lower and middle crust. These changes may be triggered by mantle processes, as indicated by the infiltration of MOR-type magmas in the lithospheric mantle, and the uplift of the Briançonnais domain. Thinning and exhumation of the crust and lithosphere also resulted in the creation of new paleogeographic domains, the Proto Valais and Liguria-Piemonte domains. These basins show a complex, 3D temporal and spatial evolution that might have evolved, at least in the case of the Liguria-Piemonte basin, in the formation

  7. 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.

  8. 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.

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

    SciTech Connect

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

    1988-08-01

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

  10. 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.

  11. 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.

  12. 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

  13. History and Evolution of Precambrian plate tectonics

    NASA Astrophysics Data System (ADS)

    Fischer, Ria; Gerya, Taras

    2014-05-01

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

  14. 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.

  15. Tectonic evolution of northern Wadi Araba, Jordan

    NASA Astrophysics Data System (ADS)

    Atallah, Mohammad

    1992-03-01

    In the area east of northern Wadi Araba several phases of tectonic fracturing can be distinguished. The oldest is of Precambrian age and is represented by a system of dikes. A second, pre-Cretaceous, tectonic phase is represented by a distinct joint system, which is restricted to the Cambrian sediments and has not cut the Cretaceous sediments. The major tectonic movements which lead to the formation of the Dead Sea rift produced faults and joint systems which cut all rock sequences. The major deformation of the area started in the early Tertiary, when the accumulation of the SE-NW directed compressive stresses produced fold structures which are older than the rift movements. As a result of this stress a conjugate system of fractures was produced; ESE-trending right-lateral (antithetic) faults and SSE-trending left-lateral (synthetic) faults. A major group of tensional faults and fractures, trending 130°, was produced due to this compression. The major displacement along the rift followed the formation of the above mentioned faults. These fault systems dissected the area into different blocks. As the compression continued, the faults and the blocks between them were rotated relative to each other. Two phases of rotational movements were recorded, contemporaneous with the two phases of the rift formation. During its northward movement, the Arabian plate came into collision with the Sinai-Palestine plate in the Dahal area in northern Wadi Araba. Various indications prove that the Wadi Araba fault is still active and the northward displacement of the Arabian plate along this fault continues in recent time.

  16. Plate Tectonics and Planetary Evolution: Implications for Understanding Exoplanets

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L. T.

    2015-12-01

    A primary purpose in our study of exoplanets is the search for life. In hypothesizing how we might detect life, we start by examining life on Earth; it is our only example. How do we understand the meaning of habitability when there is only one example? All clues seem significant: the common need for the existence of water, the range of temperatures over which life on Earth is found, and the chemical cycles that maintain the surface and near-surface of the Earth within that range. A common assertion is that plate tectonics is necessary for the carbon cycle that keeps the Earth at habitable temperatures by sequestering carbon in limetone in oceans, and parceling it back into the atmosphere through volcanoes. This is an unproven hypothesis. There are other tectonic processes that cycle carbon into a planetary interior and back to the atmosphere; one possibility is small-scale convection that returns lithospheric material to the mantle and produces small-scale volcanism. Whether this process is sufficient to stabilize climate on one-plate planets or planets with sluggish convection remains to be demonstrated. Before we can discuss the criticality of plate tectonics on other planets we need to understand its criticality on Earth, and its apparent lack on Venus. And before we can predict whether plate tectonics should exist on a given exoplanet, we need to understand why it exists on Earth, and apparently not on Venus, and we need to know more about that exoplanet than can currently be detected. In this talk I will compare the predictions for exoplanetary conditions conducive to plate tectonics, walk through possible pathways in planetary evolution that lead to plate tectonics, and discuss whether any aspect of plate tectonics on an exoplanet is detectable from Earth. Predicting and hoping to detect plate tectonics on exoplanets is walking out a shaky limb; making cautious incremental advances in understanding terrestrial plate tectonics is critical before extending

  17. Plate tectonics, surface mineralogy, and the early evolution of life

    NASA Astrophysics Data System (ADS)

    Parnell, J.

    2004-04-01

    In addition to the accepted roles of plate tectonics in regulating planetary habitability through the composition of the atmosphere and temperature, and creating continents to enhance land-based evolution and biodiversity, it has a hitherto unexplored role in influencing surface mineralogy with possible implications for early evolution. Plate tectonics creates continents through the accretion of buoyant granitic crust. Erosion of the granites yields specific minerals including quartz, radioactive (uranium-, thorium-bearing) phases and phosphates, which could play a role in early evolution. Radioactive grains could help to concentrate carbon and increase its complexity through irradiation-induced polymerization at the prebiotic stage, and possibly influence mutation rates once life was established. Weathering of phosphate minerals was an important source of phosphorus for the biochemistry that is essential to life. Quartz-rich sands provide a translucent refuge for early photosynthesizers below the harmful effects of ultra-violet irradiation at the surface. Uranium is also important to the development of nuclear power in an advanced civilization. The mineralogy that engenders these processes is distinct from that to be expected on a planet without plate tectonics, where volcanogenic sediments would predominate, and further emphasizes the importance of plate tectonics to the evolution of life.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Lee, Eun Young; Wagreich, Michael

    2016-04-01

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

  20. Tectonic Evolution of the Terrestrial Planets

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  1. 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.

  2. Role of fluids in the tectonic evolution of Titan

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    SciTech Connect

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

    1991-08-01

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

  4. 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.

  5. Tectonic evolution of the Qinling orogen, China: Review and synthesis

    NASA Astrophysics Data System (ADS)

    Dong, Yunpeng; Zhang, Guowei; Neubauer, Franz; Liu, Xiaoming; Genser, Johann; Hauzenberger, Christoph

    2011-05-01

    This contribution reviews the tectonic structure and evolution of the Qinling orogenic belt, which extends east-west nearly 2500 km across Central China and is a giant orogenic belt formed by the convergence and collision between North China and South China Blocks. The principal tectonic elements including metamorphic basement and its Neoproterozoic to Triassic cover, ophiolitic sutures, nature and ages of granitoid belts, provenance studies and tectonometamorphic studies of metamorphic belts allow tracing the polarity of two stages of plate convergence and collision and the further tectonic history. In this review, we present new distribution maps of the Early Paleozoic ophiolites and associated volcanics in the Shangdan suture zone and the Middle Devonian-Middle Triassic ophiolitic melange in the Mianlue suture zone, as well as the maps of granitoid and metamorphic belts displaying various ages (Silurian-Devonian, Triassic, Late Jurassic-Early Cretaceous). These maps allow better constrain the polarity of subduction and collision. We also discuss the significance of the Early Cretaceous Yanshanian events, which represent a linkage between tectonic events in the Tethyan and East China/Pacific realms. Two ophiolitic sutures, the Shangdan suture zone in the north and the Mianlue suture in the south, have been intensively studied during the past two decades. The Qinling Orogen is divided into the North Qinling and the South Qinling Belts by the Shangdan suture zone, and this suture zone is thought to represent the major suture separating the North China and South China Blocks. However, the timing and processes of convergence between these two blocks have been disputed for many years, and Silurian-Devonian or Late Triassic collision has been proposed as well. Based on the recent results, a detailed convergent evolutionary history between the North China and South China Blocks along the Shangdan suture is here proposed. The Mianlue suture zone is well documented and

  6. Fluid-rock interaction and thermal evolution during thrusting of an Alpine metamorphic complex (Tinos island, Greece)

    NASA Astrophysics Data System (ADS)

    Matthews, A.; Lieberman, J.; Avigad, D.; Garfunkel, Z.

    This study examines the fluid-rock interaction and thermal evolution along a thrust that juxtaposes calcite-rich marbles of high P-T metamorphic unit of the Attic-Cycladic Massif (Greece) on top of a lower-grade dolomite marble unit. The Tertiary thrust represents a major phase of tectonic movement related to the decompression of the Alpine orogen in the Hellenides. The stable isotope signatures of the thrust plane and adjacent sections of the footwall and hanging wall rocks are characterized by significant carbon and oxygen isotope depletions. The depletion is most pronounced in calcite, but is almost entirely missing in coexisting dolomite. The isotopic patterns in the thrust zone can be explained by the infiltration of an externally derived water-rich H2O-CO2-CH4 fluid [XC (=XCO2+XCH4)<0.05] at water-rock ratios on the order of 0.1 to 0.5 by weight. The fluid-induced calcite recrystallization is viewed as an important rheological control during thrusting. The temperature evolution of the footwall, hanging wall and mylonitic tectonic contact was determined by calcite-dolomite solvus thermometry. Histograms of calcite-dolomite temperatures are interpreted as indicating a heating of the footwall dolomite marble during the thrusting of the hotter upper plate. Conversely, the hanging wall marble unit was cooled during the thrusting. The calcite-dolomite thermometry of the thrust plane gives temperatures intermediate between the initial temperatures of the lower and upper marble units, and this leads to the conclusion that conductive heat transfer rather than fluid infiltration controlled the thermal evolution during thrusting.

  7. 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

  8. Phanerozoic tectonic evolution of the Circum-North Pacific

    USGS Publications Warehouse

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

    2000-01-01

    The Phanerozoic tectonic evolution of the Circum-North Pacific is recorded mainly in the orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern part of the North Asian Craton and the western part of the North American Craton. These collages consist of tectonostratigraphic terranes that are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons; they are overlapped by continental-margin-arc and sedimentary-basin assemblages. The geologic history of the terranes and overlap assemblages is highly complex because of postaccretionary dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins.We analyze the complex tectonics of this region by the following steps. (1) We assign tectonic environments for the orogenic collages from regional compilation and synthesis of stratigraphic and faunal data. The types of tectonic environments include cratonal, passive continental margin, metamorphosed continental margin, continental-margin arc, island arc, oceanic crust, seamount, ophiolite, accretionary wedge, subduction zone, turbidite basin, and metamorphic. (2) We make correlations between terranes. (3) We group coeval terranes into a single tectonic origin, for example, a single island arc or subduction zone. (4) We group igneous-arc and subduction- zone terranes, which are interpreted as being tectonically linked, into coeval, curvilinear arc/subduction-zone complexes. (5) We interpret the original positions of terranes, using geologic, faunal, and paleomagnetic data. (6) We construct the paths of tectonic migration. Six processes overlapping in time were responsible for most of the complexities of the collage of terranes and overlap assemblages around the Circum-North Pacific, as follows. (1) During the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along

  9. Tectonic evolution of Brazilian equatorial continental margin basins

    SciTech Connect

    Azevedo, R.P. )

    1993-02-01

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

  10. Tectonic evolution of the Brooks Range ophiolite, Alaska

    SciTech Connect

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

    1993-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2013-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  13. 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.

  14. 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.

  15. 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.

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

    PubMed

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

    2000-07-01

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

  17. 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.

  18. 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

  19. Basement units in the southernmost Austroalpine domain (Nötsch, Eastern Alps): Significance for Alpine-Carpathian tectonics and paleogeography

    NASA Astrophysics Data System (ADS)

    Neubauer, Franz; Genser, Johann; Heberer, Bianca; Liu, Xiaoming; Friedl, Gertrude; Bernroider, Manfred; Dong, Yunpeng

    2015-04-01

    result from an advanced stage of Alpine rifting. White mica from orthogneiss boulders of the Pölland Fm. from the Nötsch Group show plateau ages ranging from 343 ± 4 Ma to 380 ± 2 Ma and are affected by a post-depositional very low-grade metamorphic overprint. The new data demonstrate, beside its significance for the Variscan history, that the tectonic succession of the Nötsch area at the southernmost part of the Austroalpine unit has a strong similarity to the nappe stack (including the NVO unit) of the northern Austroalpine sectors (Greywacke zone and Ochtina area). We consider, therefore, these three units of the Nötsch area as a remnant of the root zone of the basement and cover nappes in the footwall of the Meliata suture. The structural relationships demonstrate >150-200 km large-scale nappe transport of the Meliata suture remnants in the Eastern Alps and the involvement of large, hitherto undetected Cenozoic strike-slip faults in the Austroalpine structure.

  20. Tectonic and sedimentary evolution of Bransfield Basin, Antarctica

    SciTech Connect

    Jeffers, J.D.; Thomas, M.A.; Anderson, J.B.

    1988-01-01

    The Bransfield basin is the youngest and best developed of a series of extensional marginal basins on the Pacific margin of the Antarctic Peninsular. Marine geophysical data collected over five seasons show that the back arc is segmented laterally into three subbasins separated by transform zones. These subbasins differ in width, depth, structural style, and seisimicity and are correlated with three different age segments of subducted sea floor. The distribution of principal sedimentary environments, identified from high-resolution seismic reflection data, and their associated lithofacies, seen in piston cores and surface sediment samples, is controlled largely by the tectonic segmentation of the basins. Terrigenous sediments prograde into the basin from the continent side, whereas sediment gravity-flow processes deliver volcaniclastic material from the arc to slope-base aprons and to fan lobes at the outlets of fiords. Organic-rich muds fill the deep basin; their proximity to submarine volcanic centers produces thermogenic hydrocarbons. Understanding the recent tectonic and sedimentary evolution of the Bransfield basin may help refine interpretations of the older deformed marginal basin sequences of southern South America, the Scotia Arc, and the Antarctic Peninsula.

  1. 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.

  2. Tectonic evolution of Kashmir basin in northwest Himalayas

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    PubMed

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Meyerhoff, Arthur A.

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

  5. 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.

  6. Disentangling reticulate evolution in an arctic-alpine polyploid complex.

    PubMed

    Guggisberg, Alessia; Mansion, Guilhem; Conti, Elena

    2009-02-01

    Although polyploidy plays a fundamental role in plant evolution, the elucidation of polyploid origins is fraught with methodological challenges. For example, allopolyploid species may confound phylogenetic reconstruction because commonly used methods are designed to trace divergent, rather than reticulate patterns. Recently developed techniques of phylogenetic network estimation allow for a more effective identification of incongruence among trees. However, incongruence can also be caused by incomplete lineage sorting, paralogy, concerted evolution, and recombination. Thus, initial hypotheses of hybridization need to be examined via additional sources of evidence, including the partitioning of infraspecific genetic polymorphisms, morphological characteristics, chromosome numbers, crossing experiments, and distributional patterns. Primula sect. Aleuritia subsect. Aleuritia (Aleuritia) represents an ideal case study to examine reticulation because specific hypotheses have been derived from morphology, karyology, interfertility, and distribution to explain the observed variation of ploidy levels, ranging from diploidy to 14-ploidy. Sequences from 5 chloroplast and 1 nuclear ribosomal DNA (nrDNA) markers were analyzed to generate the respective phylogenies and consensus networks. Furthermore, extensive cloning of the nrDNA marker allowed for the identification of shared nucleotides at polymorphic sites, investigation of infraspecific genetic polymorphisms via principal coordinate analyses PCoAs, and detection of recombination between putative progenitor sequences. The results suggest that most surveyed polyploids originated via hybridization and that 2 taxonomic species formed recurrently from different progenitors, findings that are congruent with the expectations of speciation via secondary contact. Overall, the study highlights the importance of using multiple experimental and analytical approaches to disentangle complex patterns of reticulation.

  7. 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.

  8. 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

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

    NASA Astrophysics Data System (ADS)

    Miller, E. L.

    2011-12-01

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

  10. Paleogene Alpine tectonics and Icelandic plume-related magmatism and deformation in Ireland: Evidence from the regional, high resolution Tellus geophysical survey

    NASA Astrophysics Data System (ADS)

    Cooper, Mark; Walsh, John; van Dam, Chris; Young, Michael; Earls, Garth; Anderson, Hugh; Adrian, Walker

    2010-05-01

    The Cenozoic tectonic history of NW Europe is generally attributed to some combination of three principal controlling factors: North Atlantic opening, Alpine collision and formation of the Icelandic mantle plume. Here we present the results of an interpretation of high resolution aeromagnetic imagery from the Tellus survey of Northern Ireland. This dataset distinguishes four distinct dyke swarms, which together with the known extrusive history of the Antrim Lava Group and intrusive history of the central igneous complexes, supports the concept that Paleocene plume activity was pulsed. Differential displacement of the dyke swarms and central igneous complexes by both sinistral and dextral strike-slip faults indicates, for the first time, that N-S Alpine compression, of Paleocene through to Oligocene age, temporally overlapped with plume-related intrusions. Whilst this evidence shows, for the first time, that N-S Alpine compression was periodically overwhelmed by the dynamic stresses and uplift associated with pulsed mantle plume-related deformation, related strike-slip faulting may have controlled the locus of volcanic activity and central igneous complexes, and the location of sedimentary depocentres.

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

    NASA Astrophysics Data System (ADS)

    Meyerhoff, Arthur A.

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

  12. A planetary perspective on Earth evolution: Lid Tectonics before Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Piper, John D. A.

    2013-03-01

    Plate Tectonics requires a specific range of thermal, fluid and compositional conditions before it will operate to mobilise planetary lithospheres. The response to interior heat dispersion ranges from mobile lids in constant motion able to generate zones of subduction and spreading (Plate Tectonics), through styles of Lid Tectonics expressed by stagnant lids punctured by volcanism, to lids alternating between static and mobile. The palaeomagnetic record through Earth history provides a test for tectonic style because a mobile Earth of multiple continents is recorded by diverse apparent polar wander paths, whilst Lid Tectonics is recorded by conformity to a single position. The former is difficult to isolate without extreme selection whereas the latter is a demanding requirement and easily recognised. In the event, the Precambrian palaeomagnetic database closely conforms to this latter property over very long periods of time (~ 2.7-2.2 Ga, 1.5-1.3 Ga and 0.75-0.6 Ga); intervening intervals are characterised by focussed loops compatible with episodes of true polar wander stimulated by disturbances to the planetary figure. Because of this singular property, the Precambrian palaeomagnetic record is highly effective in showing that a dominant Lid Tectonics operated throughout most of Earth history. A continental lid comprising at least 60% of the present continental area and volume had achieved quasi-integrity by 2.7 Ga. Reconfiguration of mantle and continental lid at ~ 2.2 Ga correlates with isotopic signatures and the Great Oxygenation Event and is the closest analogy in Earth history to the resurfacing of Venus. Change from Lid Tectonics to Plate Tectonics is transitional and the geological record identifies incipient development of Plate Tectonics on an orogenic scale especially after 1.1 Ga, but only following break-up of the continental lid (Palaeopangaea) in Ediacaran times beginning at ~ 0.6 Ga has it become comprehensive in the style evident during the

  13. 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.

  14. The tectonic evolution of the New Siberian Islands

    NASA Astrophysics Data System (ADS)

    Piepjohn, K.; Brandes, C.; Gaedicke, C.; Franke, D.; Mrugalla, S.; Sobolev, N.; Tolmacheva, T.

    2012-04-01

    The New Siberian Islands are located on the wide arctic shelf between the Laptev Sea in the west and the East-Siberian Sea in the east and represent the westernmost part of the Chuchotka-Alaska Terrane. Geologically, they are bounded by the Laptev Sea Rift in the west, the passive continental margin towards the Arctic Ocean in the north and the South Anyui Suture Zone in the south. Two scenarios are discussed: (1) the New Siberian Islands were situated at the North American margin before the start of the break-up of Laurasia in Jurassic times, and (2) the New Siberian Islands are part of the Siberian platform since at least Palaeozoic times. Compared with the structural evolution of Severnaya Semlya, Franz Joseph Land and Svalbard, the sedimentary succession of the New Siberian Islands is only very little affected by tectonicdeformation. There is no evidence for the Caledonian and Ellesmerian orogeny on the New Siberian Islands. Although there are some Late Ordovician volcanics exposed on the DeLong Islands, the stratigraphic succession continues without important breaks from Cambrian to Middle Carboniferous, a time span which includes both orogenies. Furthermore, the Paleozoic evolution of the sedimentary basin on the New Siberian Islands has more affinities to the Siberian platform than to Severnaya Semlya, Franz Joseph Land and Svalbard. The only observed deformation on the New Siberian Islands is related to the plate tectonic re-organisation of the recent Arctic during the break-up of the Arctic Ocean in probably Early Tertiary times. The deformation on the Anyui Islands is characterized by mostly gentle, open synclines and anticlines with NW-SE trending axis. The deformation increases westwards towards the Laptev Sea, and is dominated by tight folding, thrusting and partly cleavage-development at the west coast of Koteĺny Island and on Beĺkovski Island. The fold-vergencies and the cross-cutting relationships of bedding and cleavage indicate NE

  15. 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

  16. 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.

  17. 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.

  18. Initiation and Evolution of Plate Tectonics on Earth: Theories and Observations

    NASA Astrophysics Data System (ADS)

    Korenaga, Jun

    2013-05-01

    The inception of plate tectonics on Earth and its subsequent evolution are discussed on the basis of theoretical considerations and observational constraints. The likelihood of plate tectonics in the past depends on what mechanism is responsible for the relatively constant surface heat flux that is indicated by the likely thermal history of Earth. The continuous operation of plate tectonics throughout Earth's history is possible if, for example, the strength of convective stress in the mantle is affected by the gradual subduction of surface water. Various geological indicators for the emergence of plate tectonics are evaluated from a geodynamical perspective, and they invariably involve certain implicit assumptions about mantle dynamics, which are either demonstrably wrong or yet to be explored. The history of plate tectonics is suggested to be intrinsically connected to the secular evolution of the atmosphere, through sea-level changes caused by ocean-mantle interaction.

  19. 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

  20. 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.

  1. Magmatic-tectonic evolution of a volcanic rifted margin

    SciTech Connect

    Eldholm, O. )

    1990-05-01

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

  2. 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.

  3. 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.

  4. Tectonic evolution and oil and gas of Tarim basin

    NASA Astrophysics Data System (ADS)

    Yuzhu, Kang; Zhihong, Kang

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

  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. Igneous and tectonic evolution of Venusian and terrestrial coronae

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.; Komatsu, G.

    1992-12-01

    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.

  7. 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

  8. 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.

  9. 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

  10. Orogeny and large-scale strike-slip faulting on Venus - Tectonic evolution of Maxwell Montes

    NASA Astrophysics Data System (ADS)

    Vorder Bruegge, R. W.; Head, J. W.; Campbell, D. B.

    1990-06-01

    Complementary data sets from the Arecibo and Venera 15/16 imaging radar systems are used here to produce geologic and structural maps of the Maxwell Montes, a region of large-scale strike-slip faulting on Venus. The maps are compared with the characteristics of other linear mountain belts. The tectonic deformation occurring in Maxwell Montes is assessed, identifying the structural elements, their tectonic origin, and their sequence. A geologic and tectonic chronology is developed and a model for the origin and evolution of Maxwell Montes is proposed.

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

    NASA Technical Reports Server (NTRS)

    1986-01-01

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

  12. Holocene Tectonic and Sedimentary Evolution of Coastal San Diego

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  13. 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

  14. 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.

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. Tectonic evolution of the East Junggar terrane, CAOB

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  19. 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.

  20. The relationship between crustal tectonics and internal evolution in the moon and Mercury

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.

    1977-01-01

    The relationship between crustal tectonics and thermal evolution is discussed in terms of the moon and Mercury. Finite strain theory and depth and temperature-dependent thermal expansion are used to evaluate previous conclusions about early lunar history. Factors bringing about core differentiation in the first 0.6 b.y. of Mercurian evolution are described. The influence of concentrating radioactive heat sources located in Mercury's crust on the predicted contraction is outlined. The predicted planetary volume change is explored with regard to quantitative limits on the extent of Mercurian core solidification. Lunar and Mercurian thermal stresses involved in thermal evolution are reviewed, noting the history of surface volcanism. It is concluded that surface faulting and volcanism are closely associated with the thermal evolution of the whole planetary volume. As the planet cools or is heated, several types of tectonic and volcanic effects may be produced by thermal stress occurring in the lithosphere.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1991-05-01

    The global tectonics of Venus may be dominated by plumes rising from the mantle and impinging on 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.

  3. New constraints on the tectonic evolution of the Salton Trough

    NASA Astrophysics Data System (ADS)

    Brothers, D.; Driscoll, N.; Kent, G.

    2008-12-01

    The Salton Trough is a critical structure where two very different styles of deformation meet; spreading-center dominated deformation to the south in the Gulf of California and dextral strike-slip deformation along the San Andreas fault system(SAF) to the north. Seismic CHIRP data acquired in the Salton Sea provide new constraints on the interaction between the San Andreas, San Jacinto and Imperial fault systems and reveal distinct changes in deformational style from north to south. Based on the stratal geometry observed in CHIRP profiles, we propose three distinct phases of tectonic deformation: (1) Late- Pleistocene transpression north of the Extra Fault Zone (EFZ) replaced by (2) late-Holocene differential subsidence south of the EFZ and (3) recent formation of the Brawley Seismic Zone (BSZ), a through-going crustal shear zone. An angular unconformity is observed to separate the folded and faulted (late?) Pleistocene strata of the Brawley Formation from the overlying Holocene Cahuilla Formation (CF). North of the EFZ reflectors in the CF suggest little to no active deformation. Conversely, south of the EFZ reflectors exhibit marked divergence with their dip systematically increasing with depth. Such a pattern of divergence indicates that the rate of sedimentation has kept pace with the rate of tectonically-induced accommodation. As such, it appears that the EFZ is a tectonic hinge zone delineating the northern limit of active subsidence, high heat flow, and volcanism. Furthermore, given the observed subsidence pattern, we predict the existence of a NE trending basin-bounding normal fault, or series of normal faults, near the southern shoreline of the Salton Sea. In our conceptual model, the early distributed faulting and transrotation between the San Andreas and San Jacinto faults accounts for the compressional folding observed in the Brawley Formation, but later gave way to extension-dominated deformation as significant slip became focused along the Imperial

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

    PubMed Central

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

    2013-01-01

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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Marinangeli, L.

    1996-09-01

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

  8. A window of opportunity for plate tectonics in evolution of Earth-like planets?

    NASA Astrophysics Data System (ADS)

    O'Neill, C.

    2011-12-01

    A rocky planet may exhibit stagnant lid behaviour under hot internal conditions due to a decrease in internal viscosity, associated with high internal temperatures, which results in lower induced lithospheric stress. These conditions may be relevant to a planet's early evolution. At the other extreme, cold, sluggish planets, approaching the end of their evolutionary cycle, may also exhibit stagnant behaviour, due to low mantle velocities, and the development of a thick, strong lithospheric lid. This leads to the possibility of a 'window' for plate tectonic behaviour in the evolution of rocky planets; where initial hot planets may exhibit stagnant lid behaviour, evolving into tectonically active planets, before, eventually, entering into a slow decline of tectonism and eventually entering a cold, senescent stagnant mode more typical of Mars today. Here we explore models of viscoplastic mantle convection, with varying internal heating and bottom temperature conditions, and demonstrate a stress maximum exists for middle-aged planets. We present an implementation of evolving internal heat production and basal temperatures through time, and show the viability of a 'window' for plate tectonic behaviour in the evolution of Earth-like planets.

  9. 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

  10. Tectonic evolution and mantle structure of the Caribbean

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  11. Tectonic evolution and mantle structure of the Caribbean

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  12. 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.

  13. 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.

  14. Subsidence history and tectonic evolution of Campos basin, offshore Brazil

    SciTech Connect

    Mohriak, W.U.; Karner, G.D.; Dewey, J.F.

    1987-05-01

    The tectonic component of subsidence in the Campos basin reflects different stages of crustal reequilibration subsequent to the stretching that preceded the breakup of Pangea. Concomitant with rifting in the South Atlantic, Neocomian lacustrine rocks, with associated widespread mafic volcanism, were deposited on a vary rapidly subsiding crust. The proto-oceanic stage (Aptian) is marked by a sequence of evaporitic rocks whose originally greater sedimentary thickness is indicated by residual evaporitic layers with abundant salt flow features. An open marine environment begins with thick Albian/Cenomanian limestones that grade upward and basinward into shales. This section, with halokinetic features and listric detached faulting sloping out on salt, is characterized by an increased sedimentation rate. The marine Upper Cretaceous to Recent clastic section, associated with the more quiescent phase of thermal subsidence, is characterized by drastic changes in sedimentation rate. Stratigraphic modeling of the sedimentary facies suggests a flexurally controlled loading mechanism (regional compensation) with a temporally and spatially variable rigidity. Locally, the subsidence in the rift-phase fault-bounded blocks shows no correspondence with the overall thermal subsidence, implying that the crust was not effectively thinned by simple, vertically balanced stretching. Deep reflection seismic sections show a general correspondence between sedimentary isopachs and Moho topography, which broadly compensates for the observed subsidence. However, even the Moho is locally affected by crustal-scale master faults that apparently are also controlling the movement mechanisms during the rift-phase faulting.

  15. 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

  16. 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.

  17. Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa

    NASA Astrophysics Data System (ADS)

    Bergner, A. G. N.; Strecker, M. R.; Trauth, M. H.; Deino, A.; Gasse, F.; Blisniuk, P.; Dühnforth, M.

    2009-12-01

    The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modern climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen 14C and 40Ar/ 39Ar dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.

  18. 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

  19. 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.

  20. Tectonic evolution of the Notre Dame magmatic arc, Newfoundland Appalachians

    NASA Astrophysics Data System (ADS)

    van Staal, C.

    2003-12-01

    Notre Dame continental arc magmatism in Newfoundland had an overall lifespan of c. 60 Ma (489-429 Ma). Extensive age dating suggests that arc construction took place in 3 distinct stages, separated by gaps of magmatic quiescence (arc shut-off). The first phase of quiescence (c. 480-468 Ma) corresponds to the start of Taconic collision between the initially west-facing Notre Dame arc and Laurentia. The second phase of magmatic quiescence (455-445 Ma) corresponds to collision between the now east-facing Notre Dame arc and the west-facing, peri-Gondwanan Victoria arc built on a piece of Ganderian crust. Resurgence of arc magmatism followed stepping- back of the west-dipping subduction zone into the oceanic marginal basin that separated the Victoria arc from the Gander margin. A gradual transition (431-429 Ma) from arc-like to mainly juvenile, bimodal within plate-like magmatism coincides with suturing of the Notre Dame arc with the Gander margin along the Dog Bay line and probably reflects break off of the west-dipping Ganderian slab. Preservation of an unconformable and unmetamorphosed Silurian cover, consisting of red beds and bimodal volcanic rocks, over large tracts of the Notre Dame arc indicates that the arc was extinct and stabilized by the Late Silurian (c. 425 Ma) and did not experience any significant overprint during the Early Devonian Acadian orogeny, the effects of which were mainly localized further to the east due to accretion of Avalonia to Laurentia. The second, Mid-Ordovician phase of arc magmatism (c. 469-456 Ma) appears most voluminous and was mainly characterized by K-poor, calc-alkaline quartz diorite to tonalite and, to a lesser extent granodiorite, plutons. These calc-alkaline plutons intruded during deformation and significant thickening of the Notre Dame arc, presumably as a result of ongoing shortening following initial collision with Laurentia and an arc-polarity reversal. Such a tectonic scenario is consistent with the high metamorphic

  1. 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)

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

    SciTech Connect

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

    1994-11-01

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

  3. 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.

  4. 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.

  5. 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.

  6. 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

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

    NASA Astrophysics Data System (ADS)

    Kovács, Gábor; Telbisz, Tamás; Székely, Balázs

    2014-05-01

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

  8. 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

  9. 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.

  10. Thermo-tectonic evolution of the Upper Rhine Graben rift shoulders

    NASA Astrophysics Data System (ADS)

    Link, K.; Rahn, M.; Keller, J.

    2003-04-01

    The Upper Rhine Graben (URG) is the central segment of the European Cenozoic rift system, extending from the Mediterranean to the North Sea (Ziegler, 1992). The URG extends over a distance of 300 km from Basel (Switzerland) to Frankfurt (Germany) with an average width of 30--40 km. An initial rifting phase is recognised by Middle Eocene (Lutetian) lake deposits. The main rifting phase started at the end of the Eocene (Priabonian) and was followed by prominent uplift in the southern URG area in the Miocene (Schumacher, 2002). Apatite fission track (FT) dating is used to constrain the thermo-tectonic evolution of the rift shoulders. By FT data modelling varying cooling histories are derived for different tectonic blocks of the rift shoulders. In some areas tectonic uplift started in the Upper Cretaceous, a long time before the initial rifting of the URG. In the modelled data no increase in cooling, which might represent rift shoulder uplift and denudation related to the main rifting phase, can be observed. In contrast, in the southern part, the cooling rate increased in Miocene times due to greater uplift and denudation, although the climate changed to cooler and dryer conditions. Contemporaneous with this phase is enormous sediment erosion in the southern graben segment. As a consequence, the driving forces leading to the observed thermo-tectonic evolution of the rift shoulders cannot be explained by URG formation and/or climate changes alone, but must be seen in the context of a European intraplate stress regime. References: Schumacher, M.E. (2002): Tectonics, 21: 1--17. Ziegler, P.A. (1992): Tectonophysics, 208: 91--111.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. Relationship between tectonic evolution of North China craton and Pacific plate subduction slab evolution since ~47 Ma

    NASA Astrophysics Data System (ADS)

    An, M.

    2011-12-01

    The Pacific plate movement happened some obviously changes at ~47 Ma. If we only consider the Pacific plate subduction just since this time, we can find that the subduction slab can reach eastern North China after ~20My (at ~27 Ma), and the slab may be destructed completely when it reach this position (An et al., 2009, G-cubed, doi:10.1029/2009GC002562). In the 20-My-movement processes, the evolution of the cold slab can be divided into several stages with the slab is heated and destructed. In different evolution stages, the slab also can result in different effects on the overlying asthenosphere and lithosphere. The slab evolution showed some temporal consistence with the tectonic activities in the eastern North China, and also with the Japan Sea opening; Furthermore, the possible effects acted on the overlying lithosphere by the slab in different stages can interpret the tectonic events happened in eastern North China since the early Paleogene (An et al., 2011, Earth Science Frontiers, 18(3)(in Chinese with English abstract), http://www.earthsciencefrontiers.net.cn/CN/abstract/abstract4277.shtml). For example, regional lithosphere seems to be thickening, Tangshan-Xingtai faults became active but the activities of the Taihangshan Piedmont faults decreased.

  20. 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

  1. 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

  2. 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.

  3. 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

  4. The lachlan belt of eastern Australia and Circum-Pacific tectonic evolution

    NASA Astrophysics Data System (ADS)

    Coney, Peter J.

    1992-11-01

    There is considerable evidence that the Pacific Ocean basin has had a remarkable permanency at least throughout the Phanerozoic. The orogenic systems that have evolved around its margins are accretionary continental margin orogens and show little or no evidence of continental collisions in their evolutionary history. This is in dramatic contrast to the Circum-Atlantic and Tethyan realms which have experienced repeated openings and closures of, or successive transfer of continental fragments across, ocean areas that were relatively never large. In other words, the Wilson Cycle has dominated tectonic evolution of Atlantic and Tethyan realms, but has not been important in the Circum-Pacific. The northeastern margin of the Pacific Ocean is the North American Cordillera which is a "classic" continental margin-accretionary system dominated by a well-developed complex miogeoclinal terrace, significant fringing or "exotic" arc-trench systems and other "oceanic" accretions progressively consolidated into North America from mid-Paleozoic times, but mainly from mid-Meso-zoic times to the present. The northwestern margin of the Pacific Ocean is the collage of Asia which was produced by Tethyan tectonics, not Pacific tectonics — i.e., the progressive transfer of Gondwanaland fragments across Tethys to Baltica-Siberia. Only since the early Mesozoic have minor Pacific accretions, such as Japan, produced the present margin. The southeastern, southern, and southwestern margins of the Pacific Ocean are South America, Antarctica, and Australia, respectively. Through Paleozoic-early Mesozoic times they were joined and a very enigmatic Pacific margin orogenic system extended for 20,000 km from northwestern South America to northeastern Australia. The Lachlan Fold Belt in particular, and the Tasman belt in general, are important windows into that enigma. Lack of a well-developed through-going miogeocline is notable, and late Precambrian but mostly extensive lower Paleozoic, fairly

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. Timing and modes of granite magmatism in the core of the Alboran Domain, Rif chain, northern Morocco: Implications for the Alpine evolution of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Rossetti, Federico; Theye, Thomas; Lucci, Federico; Bouybaouene, Mohamed L.; Dini, Andrea; Gerdes, Axel; Phillips, David; Cozzupoli, Domenico

    2010-04-01

    The Betic-Rif orogen forms the western termination of the Alpine orogenic system in the Mediterranean region. The precise timing, structural evolution, and distribution of high-grade metamorphic units (Alpine versus pre-Alpine) in the inner zones of the orogen (Alboran Domain) remain controversial issues. In this paper we report occurrence of distinct generations of peraluminous granitic bodies intruded within Beni Bousera peridotites and their amphibolite-to-granulite facies envelope, in the core of the Alboran Domain of the Rif chain (northern Morocco). These granitic bodies are central to the reconstruction of the high-grade evolution of the Alboran Domain because they provide first-order structural markers to assess the P-T-t deformation history of the high-grade terranes. Here we document the petrography and structural relationships with the host rocks and constrain the timing of granite emplacement using laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon and/or monazite dating, complemented by 40Ar/39Ar dating. The results indicate that granite emplacement occurred in two major episodes of anatectic magmatism, during the Hercynian (circa 300 Ma) and Alpine (circa 22 Ma) periods, respectively. These data (1) provide conclusive evidence for an important phase of Hercynian magmatism and high-grade metamorphism in the Alboran Domain and (2) permit a revaluation of the significance of the high-grade early Miocene event documented in the Alboran Domain in terms of a late stage, thermal pulse that reworked a polymetamorphic (Hercynian and Alpine) nappe pile. These results provide new constraints for construction of a feasible tectonometamorphic model for the Alpine evolution of the western Mediterranean.

  7. Paleozoic and Mesozoic Tectonic Evolution of Central Asia: From Continental Assembly to Intracontinental Deformation

    NASA Astrophysics Data System (ADS)

    Burke, Kevin

    Thirty years ago, the interior of Asia was inaccessible to most Earth scientists, as was much of the relevant literature. Students of continental evolution were frustrated. We knew that Asia, nearly alone among the Earth's continents, had been assembled in relatively recent geological times, but we could only speculate about the processes that led to its assembly. In the past 27 years, Asian and international researchers have improved our understanding. Ideas about continental evolution as diverse as modeling the deforming lithosphere as a thin, viscous sheet; tectonic escape; Altaid style assembly; crustal doubling; orogenic collapse; delamination; the role of ultra-high pressure metamorphism; the role of localized erosion and active deformation on local and continental scales are all being tested in Asia. There is no consensus yet, but the Asian natural laboratory is being used well. We may soon come to know which ideas we should abandon.

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  10. 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.

  11. 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

  12. 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

  13. 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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Charvet, Jacques

    2013-08-01

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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Evolution of the Southern San Joaquin Basin and mid-Tertiary "transitional" tectonics, central California

    NASA Astrophysics Data System (ADS)

    Goodman, Emery D.; Malin, Peter E.

    1992-06-01

    A Cenozoic tectonic and sedimentary history is proposed for the Southern San Joaquin Basin (SSJB) and Tehachapi Mountains that evolved adjacent to the plate margin off central California. Seismic reflection, borehole, field, biostratigraphic, and paleomagnetic data are integrated into geologic and fault structure maps, cross sections, and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence, timing, and distribution of complex, tectonically linked events. The largely buried structures and strata in the SSJB preserve an unusually complete record of the mid-Tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the Pliocene. Significant structural relief, existing across both extensional and contractile features, is preserved in the subsurface and an active fold-thrust belt propagates basinward along the margin of the U-shaped Tejon embayment The Cenozoic evolution of the SSJB reflects the regional deformation of central California as different tectonic events followed each other along the adjacent North American plate margin. Five Oligocene-Miocene basin phases are identified in the SSJB: (1) late Oligocene/early Miocene extensional subsidence, with high- and low-angle normal faulting, accompanied by volcanism and deposition of coarse syntectonic conglomerates; (2) middle Miocene uplift; (3) later mid-Miocene transtensional subsidence to lower bathyal depths; (4) alternating subsidence and uplift until the late Miocene; and (5) flexural subsidence due to Pliocene to Recent contraction. Reconstructions of mid-Tertiary California place the southern San Joaquin/Tehachapi extensional terrane as a paleotectonic block located between the Western Mojave terrane (then to the east) and the Western California terrane (then to the south and west). Regional extension occurred during a long transition period between convergent and transform boundaries along

  3. 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.

  4. Tectonic evolution and continental crust growth of Northern Xinjiang in northwestern China: Remnant ocean model

    NASA Astrophysics Data System (ADS)

    Xu, Qin-Qin; Ji, Jian-Qing; Zhao, Lei; Gong, Jun-Feng; Zhou, Jing; He, Guo-Qi; Zhong, Da-Lai; Wang, Jin-Duo; Griffiths, Lee

    2013-11-01

    The Northern Xinjiang region is located in the southwestern part of the Central Asian Orogenic Belt (CAOB, also known as the Altaid Tectonic Collage). Despite extensive research aimed at understanding the crustal growth of the CAOB and the evolution of the Paleo-Asian Ocean, the tectonic evolution mechanism of continental crust growth in Northern Xinjiang remains controversial. The geology of Northern Xinjiang is characterized by widespread ophiolites, granitoids, intermediate-basic dikes. Most of the ophiolites were generated in the early Paleozoic. The ophiolites are widely spread around the Junggar Basin, but their distribution does not indicate a well-defined band. Their outcrops are generally related to various faults. The basic rocks widespread in Northern Xinjiang are grouped into two categories: (i) gabbros, diabases basalts of the ophiolites and (ii) basic dikes that intrude into the Paleozoic strata granite plutons. The basic rocks associated with the early Paleozoic ophiolites were reworked by later geothermal events with a peak 40Ar/39Ar age of 310-290 Ma. The basic dikes intruded into Paleozoic strata and granite plutons during the Carboniferous-Jurassic, displaying three peaks of emplacement at 260-250 Ma, 220 Ma, and 200-190 Ma. These two types of basic rocks and the documented Variscan magmatic rocks were derived from the same source. Their isotope geochemical characteristics and widespread distribution suggest that since the Paleozoic, a large geochemical province has existed in Northern Xinjiang with an affinity to mid-ocean ridge basalts (MORB) and ocean island basalts (OIB), which is related to a long-lived remnant ocean and the underlying early Paleozoic oceanic crust. The existence of remnant oceanic crust in Northern Xinjiang was confirmed by seismic, gravity and aeromagnetic data. Therefore, we propose the following remnant ocean model for the Paleozoic tectonic evolution of Northern Xinjiang. It consists of three stages: 1) oceanic crust

  5. 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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  8. Seismic stratigraphy, subsidence history, and tectonic evolution of the Alboran Sea, western Mediterranean

    SciTech Connect

    Watts, A.B. ); Doherty, J.I.C.; Banda, E. ); Platt, J. )

    1991-08-01

    Seismic reflection profile, gravity and geoid data, and well data have been used to examine the tectonic evolution of the Alboran Sea, a small basin in the western Mediterranean. Previous seismic refraction data suggest that the basin is underlain by stretched continental crust which thins from about 40 km beneath Iberia and Morocco to as much as 15 km in the basin center. According to commercial well data, the earliest sediments are lower Burdigalian, suggesting that extension was initiated during the early Miocene. The thinning is part of a sidespread extensional event that appears have modified the crustal structure in the Balearic, Algerian, and Valencia Trough basins to the east. In the case of the Alboran Sea basin, however, the extent to which extensional processes account for the crustal structure is obscured by the competing effects of compression due, for example, to thrust/fold loading in the flanking Betic and Rif cordillera. Backstripping of commercial wells in the Iberian margin reveals an exponentially decreasing subsidence that is similar in form to that of many rift-type basins. However, DSDP Site 121, located on a basement high in the basin center, shows an accelerating subsidence that is more typical of foreland-type basins. Recent studies in the Valencia Trough, show that the relative of extensional and compressional processes can be estimated through an integrated approach of flexural backstripping, crustal restoration, and gravity and geoid modeling along selected transects of a basin. The authors paper presents the results of such an approach to the Alboran Sea and evaluates its implications for current models for the tectonic evolution of the basin.

  9. 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.

  10. 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

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

    NASA Astrophysics Data System (ADS)

    Seeley, John Martin

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  13. Climate variability and Alpine glaciers evolution in Northwestern Italy from the Little Ice Age to the 2010s

    NASA Astrophysics Data System (ADS)

    Nigrelli, Guido; Lucchesi, Stefania; Bertotto, Stefania; Fioraso, Gianfranco; Chiarle, Marta

    2015-11-01

    In this work, we analyze climate variability and glacier evolution for a study area in the Northwestern Italian Alps from the Little Ice Age (LIA) to the 2010s. In this area, glacier retreat has been almost continuous since the end of the LIA, and many glaciers are now extinct. We compared glaciological and climatic data in order to evaluate the sensitivity of glaciers to temperature and precipitation trends. We found that temperatures show significant warming trends, while precipitation shows no clear signal. After the 1980s, the total number of positive trends in temperature increased, particularly minimum temperature. The latter does not seem to be the only cause of glacier shrinkage but rather on acceleration of an ongoing trend documented since the end of the LIA. In some rare cases, the effects of warming trends on glacier dynamics have been accentuated by a concomitant decrease in precipitation. We hope that this study will contribute to increase the knowledge of the relationships between climate variation and glacier evolution in the Greater Alpine Region.

  14. 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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. In-situ measurement of the temporal evolution of the thermal conductivity of alpine snow layers

    NASA Astrophysics Data System (ADS)

    Morin, S.; Domine, F.; Arnaud, L.; Picard, G.; Jacobi, H.; Willemet, J.

    2009-12-01

    We report on a 3-months long time series of in-situ measurements of the thermal conductivity (kT) of snow in 6 different layers in an alpine snowpack in the Mont-Blanc moutain range, France, at an altitude of 2400 m. Automatic measurements were carried out every two days using the heated-needle probe technique. Results show consistent patterns of thermal conductivity increase throughout the measurements campaign. The temporal rate of change of kTvaries up to 0.01 W m-1 K-1 dy-1, with maximum values just after snowfall. Temporal rates of kTincrease are compared with results from laboratory experiments under controlled conditions and with published theoretical assessments. A case where kT decreased over time in a given snow layer was documented both in the field and in the laboratory. Possible reasons for such a behaviour are discussed. A cursory comparison of the field measured kTvalues with the prediction of the snowpack model CROCUS shows that at first order the model performs satisfactorily. However, a quantitative understanding and modeling of the variations of kT over time would require an in-depth assessment of physical processes occurring during snow metamorphism.

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

    PubMed

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

    2015-10-01

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

  3. 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.

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

    PubMed

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

    2015-01-01

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

  5. 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

  6. 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.

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

    SciTech Connect

    Emery, M. ); Georgiev, G. )

    1993-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Robertson, Alastair; Shallo, Minella

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  11. Tectonic evolution of the gulf of Aqaba-Dead Sea transform fault system

    NASA Astrophysics Data System (ADS)

    Barjous, M.; Mikbel, Sh

    1990-08-01

    Neogene tectonic phases related to stresses which created the Gulf of Aqaba-Dead Sea transform fault system were recorded from evidence in the central part of the Wadi Araba. The chronological sequence of deformation stages is as follows: (1) Epeirogeny (latest late Eocene-Oligocene). (2) Faulting and warping (?Oligocene-Middle Miocene). (3) Folding striking between north-northeast and northeast, E-W trending and N-S shear faulting, and NW-SE normal faulting (Miocene). (4) Uplift and faulting (Pliocene-Pleistocene). (5) Faulting with volcanic activity (Pleistocene). (6) Sinistral movement along the major shear fault in the Wadi Araba. Indications are that this phase is still active (Pleistocene-Recent). The re-strain phases recognised are clues for the investigated area and the entire region to the understanding of the tectonic evolution of the Gulf of Aqaba-Dead Sea transform. Structural features contributing to evidence of strike-slip movement are: drag folds, reverse and normal flower structures, alternation of the downthrown side along the fault trace, gently waved vertical fault planes, horizontal slickensides, transpressive and transtensional pressure ridges and rhombs, linear fault traces without marked vertical throw, and fault plane ridges. A sinistral offset of 40 km along the N-S Al Quweira Fault was deduced from the displacement of distinctive andesitic rocks found on both sides of the fault. For the E-W Salawan Fault, a dextral movement of at least 7 km was determined from the offset of formation boundaries. North-northeast-striking deformed belts containing monoclinal to recumbent en-echelon folds can be seen in the Gulf of Aqaba-Dead Sea transform fault zone. The axial planes of the folds dip southeast and face northwest. These structural elements indicate local SE-NW compressional stress.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  16. 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.

  17. 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

  18. 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.

  19. The influence of mechanical properties on the link between tectonic and topographic evolution

    NASA Astrophysics Data System (ADS)

    Koons, Peter O.; Upton, Phaedra; Barker, Adam D.

    2012-01-01

    In actively deforming orogens, the material strength at the Earth's surface is controlled in part by strain localization determined by the local stress fields which in turn are driven by contributions from local topography and far field plate velocities. Material weakening associated with strain localization imparts partially predictable, and entirely inescapable heterogeneity to the material fabric of an orogen. The characteristic damage structure of individual fault zones that undergo strain weakening, as imaged in dam site excavations, deep drill holes and geological observations, results in geomorphically relevant strength variations normal to the fault of many orders of magnitude. The sensitivity of hillslope and fluvial erosion to the strength parameters coupled with the large and oriented strain-related strength variations, cause the topographic evolution to be dominated by tectonically driven rheological behavior at multiple wavelengths. Using three-dimensional, lithospheric scale modeling of two oblique orogens, Southern Alps, New Zealand and the Eastern Himalayan Syntaxis, we examine the generation of model surface strength fields that occur as a consequence of a simple strain softening upper crustal rheological model. Mapping of topographic anisotropy of the Southern Alps and the Eastern Himalaya Syntaxis indicates azimuthal control on correlation distances that are spatially related to the different strain regimes of the two orogens. By defining landscape evolution in terms of mechanical failure in the conventional motion—stress mechanical framework, the behavior of Earth's surface can be brought into the same theoretical framework as the behavior of the sub-surface and many of the observational—theoretical inconsistencies arising from application of dominantly potential field theory can be obviated. Heterogeneity and anisotropy of material strength are fundamental aspects of active orogens and description of the strength field in terms of

  20. 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.

  1. 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.

  2. On the Dynamics of Plate Tectonics: Multiple Solutions, the Influence of Water, and Thermal Evolution

    NASA Astrophysics Data System (ADS)

    Crowley, John W.

    An analytic boundary layer model for thermal convection with a finite-strength plate and depth-dependent viscosity is developed. The model includes a specific energy balance for the lithosphere and accounts for coupling between the plate and underlying mantle. Multiple solutions are possible with three solution branches representing three distinct modes of thermal convection. One branch corresponds to the classic boundary layer solution for active lid plate tectonics while two new branches represent solutions for sluggish lid convection. The model is compared to numerical simulations with highly temperature dependent viscosity and is able to predict both the type of convection (active, sluggish, or stagnant lid) as well as the presence of single and multiple solution regimes. The existence of multiple solutions suggests that the mode of planetary convection may be history dependent. The dependence of mantle viscosity on temperature and water concentration is found to introduce a strong dynamic feedback with plate tectonics. A dimensionless parameter is defined to quantitatively evaluate the relative strength of this feedback and demonstrates that water and heat transport may be equally important in controlling present-day plate-mantle dynamics for the Earth. A simple parameterized evolution model illustrates the feedback and agrees well with our analytic results. This suggests that a simple relationship may exist between the rate of change of water concentration and the rate of change of temperature in the mantle. This study concludes by investigating the possibility of a magnetic field dynamo in early solar system planetesimals. The thermal evolution of planetesimals is modeled by considering melting, core formation, and the onset of mantle convection and then employing thermal boundary layer theory for stagnant lid convection (if possible) to determine the cooling rate of the body. We assess the presence, strength and duration of a dynamo for a range of

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  4. 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

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  7. 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.

  8. 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.

  9. 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.

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

    PubMed

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

    2015-06-01

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

  11. 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.

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

    SciTech Connect

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

    1996-08-01

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

  13. Neogene sedimentary evolution of Baja California in relation to regional tectonics

    NASA Astrophysics Data System (ADS)

    Helenes, J.; Carreño, A. L.

    1999-11-01

    During the Neogene, the tectonic and sedimentary evolution of the Baja California Peninsula followed four stages: (1) during the early Miocene (22 Ma), the initiation of transform motion between Pacific and North American plates, caused a rapid subsidence in the Continental Borderland Province and in some adjacent areas.This subsidence coincided in time with with a global rise in sea level. At this time, the eastern and southern parts of the peninsula did not show any evidence of subsidence. (2) During the middle Miocene (12 Ma), normal and strike slip faulting migrated eastward, causing subsidence in the northern part of the Gulf of California, where the oldest Tertiary marine sedimentary rocks were deposited. The areas in central Baja California Sur and the central part of the Gulf itself received abundant volcanic deposits related to continental extension. (3) During the late Miocene (8 Ma), the western margin of the Peninsula changed to a slightly compressive regime, while the northern part of the Gulf contained a marine basin with upper bathyal environments. The central area of the Gulf continued receiving abundant volcanic deposits, while the Los Cabos block received marine sedimentation, correlatable with sedimentary units reported from the continental margins in Nayarit, Jalisco and Michoacán. (4) Beginning in the early Pliocene (5 Ma), the present configuration of the Gulf of California developed through right-lateral strike slip and extension in the Gulf itself. Since Pliocene times, the Gulf presents widespread marine sedimentation with deep basins reaching lower bathyal depths.

  14. 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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  17. 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.

  18. Brittle tectonic history document the late- to post-orogenic evolution in the Lufilian Arc, RDCongo

    NASA Astrophysics Data System (ADS)

    Kipata, Louis; Delvaux, Damien; Ntabwoba Sebagenzi, Mwene; Cailteux, Jean-Jacques; Sintubin, Manuel

    2013-04-01

    Pan-African orogenic processes in Centra Africa involve intracontinental collision but also late-orogenic and intraplate processes that occurred in dominantly brittle conditions and can be documented by fault kinematic analysis and paleostress reconstructions. The Congo and Tanzania cratons in Central Africa are surrounded by Pan-African belts orogenic belts which all entered almost synchronously in collision stage in the early Paleozoic. While their tectonic history up to the collision stage is increasingly better documented by ductile deformation and metamorphic studies, their late evolution remain poorly known as soon as they enter in the brittle deformation regime. This results in an incomplete understanding of the orogenic processes, especially when the transition from ductile to the brittle regime occurred at the end of the orogenic compression. In this case, the last compressional stages and the entire late orogenic extension and extensional collapse stages remain undocumented. This is the case for the Lufilian orogeny which developed along the southern margin of the Congo Craton in Central Africa during the pan-African and was marked by a collisional event with crustal thickening and white schist formation at 550-530 Ma. The Lufilian Arc which forms the external part of the Lufilian orogeny developed as an arcuate fold-and-thrust belt. Its foreland is formed by the Kundelungu plateau, between the Bangweulu block and the Kibaran belt. This entire region is also tectonically active, as part of the incipient SW branch of the East African rift system. The long period between the paroxysm of the Lufilian orogeny and the late Neogene to Quaternary rifting has been investigated by fault-kinematic analysis and paleostress reconstruction in open mines spread over the entire arc and foreland. Paleostress tensors were computed from 23 sites totaling 1900 fault-slip data by interactive stress tensor inversion and data subset separation, and a succession of 8 brittle

  19. 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

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

    NASA Astrophysics Data System (ADS)

    Kadioglu, Yusuf K.; Dilek, Yildirim

    2010-05-01

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

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

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

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.

    1992-01-01

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

  7. 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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Harris, R. A.

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Yinglu, Pan; Bingsong, Yu

    2015-04-01

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

  12. 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.

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Rogers, Patricia G.; Zuber, Maria T.

    1998-07-01

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

  16. 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

    2007-09-01

    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 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.

  17. 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.

  18. 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.

  19. 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.

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

    SciTech Connect

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

    1996-08-01

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

  1. Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey

    NASA Astrophysics Data System (ADS)

    Sarp, Gulcan

    2015-02-01

    The Erzincan pull-apart basin is located in the eastern section of the North Anatolian Fault System (NAFS). The tectonic evolution of this basin is mostly controlled by strike slip master faults of the NAFS. This study examines the topography-structure relationships in an effort to evaluate the tectonic signatures in the landscape, paying special attention to recent tectonic activity. In the study, the main focus is on the tectonic controls of the NAFS on the geomorphic evolution of alluvial fans and fan catchments in the Erzincan pull-apart basin. The observations of the amount of tilting of the alluvial fans (β) and its relation with morphometric (Asymmetry Factor (AF), Hypsometric Integral (HI), Fractal analysis of drainage networks (D)) properties of the fan catchments provide valuable information about the tectonic evolution of the basin area. The results of the analyses showed that the alluvial fan and fan catchment morphology in the pull-apart basin are mainly controlled by the ongoing tectonic activity of the NAFS. The fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin, and aggradation processes by causing channel migration, channel incision and tilting the alluvial fans.

  2. 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.

  3. Late Quaternary stratigraphic and tectonic evolution of the northeastern Aegean Sea

    NASA Astrophysics Data System (ADS)

    Isler, Ekrem Bursin

    The late Quaternary--Recent stratigraphic and tectonic evolution of the NE Aegean Sea, between the Islands of Bozcaada and Lesbos and the Biga Peninsula, is examined using ˜1600 km of seismic reflection and side scan profiles and six cores collected during cruises in 1998, 2000, 2002, and 2003. Detailed examination of the seismic reflection profiles showed that several vertically stacked depositional sequences developed within three NE-SW trending basins. These depositional sequences exhibit oblique- to complex oblique-sigmoid internal seismic reflection configuration and are separated from one another by shelf-crossing unconformities. The chronology of the depositional sequences is constrained by seven radiocarbon and two U/Th dates on in situ shell samples extracted from five cores. Sedimentation rates calculated by using these dates range between 19 cm/kyr and 30 cm/kyr. The ages and the stacked architecture of the depositional sequences, together with the correlations with the oxygen isotopic stages and global sea-level curve reveal that these seaward-prograded delta sequences were developed in a sufficiently rapidly subsiding shelf environment during successive global eustatic sea-level falls associated with late Quaternary glaciations. The progradation of the depositional sequences decelerated and eventually halted shortly after the subsequent major transgressions during which the shelf-crossing unconformities were generated. The terrigenous materials transported throughout the development of the depositional sequences originated from the Tuzla, Karamenderes, and Dumbek rivers draining the Biga Peninsula. Seismic reflection profiles showed no evidence for a major E--W-trending fault system, suggesting that the western continuation of the central strand of the North Anatolian Transform Fault does not exit into the Aegean Sea at Ezine. Detailed mapping of the seismic data showed that two major faults, A1 and beta8, constitute the main fault system in the study

  4. Cenozoic Fault Evolution During Three Successive Tectonic Episodes in the Outer Continental Borderland off Southern California

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Langenheim, V. E.; Sliter, R. W.; Wong, F. L.

    2006-12-01

    Multichannel seismic reflection (MCS) sections as well as aeromagnetic and oil-well data reveal that a complex geographic distribution of normal, reverse and strike-slip faults developed during the Cenozoic in the outer part of the California Continental Borderland. A close spatial association between magnetic basement rocks and inverted Miocene graben points to the importance of structural inheritance in shaping the outer Borderland. For instance, we focus on a northwest-trending series of bathymetric knolls and ridges that closely follows the east flank of rocks that cause strong magnetic anomalies. These rocks are probably pre-Cenozoic basement. Sedimentary rocks forming these knolls and ridges originally were deposited within Miocene graben, but since the Miocene, these graben have been inverted tectonically and deformed by reverse and strike-slip faults. The sequence of graben formation and inversion shows that the study area first underwent regional extension and then contraction. This interpreted tectonic sequence accords with findings from other studies of the Borderland (e.g. Crouch and Suppe, 1993; Bohannan and Geist, 1998). The earliest of three tectonic episodes started from during the Mesozoic and persisted into the early Miocene and involved eastward subduction of the Farallon plate beneath the continental margin. Except for a forearc basin that is partly filled with a southwest-thinning wedge of Paleogene sedimentary rocks, few structures stemming from this tectonic episode can be recognized. The second tectonic episode began during the Miocene and involved crustal extension intense enough to expose the Mesozoic Catalina Schist in one or more metamorphic-core complexes. MCS data reveal two extensional episodes. The earlier caused low-angle detachments to form, and the later produced high-angle faults that crosscut the detachments. In the southeastern part of the study area, east-dipping reflections from within basement may reveal an extensional

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

    NASA Astrophysics Data System (ADS)

    Williams, Nathan Robert

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

  6. The Tectonic Evolution of Kinematic Blocks Along Major Plate Boundaries: the Case History of the Hyblean Region (Central Mediterranean)

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    The Hyblean Region (SE Sicily) in the Central Mediterranean represents a crustal block, which is entrapped at the junction between two major plate boundaries. The former consists of the E-W oriented Nubia-Eurasia boundary and the latter is represented by an incipient, roughly N-S trending, divergent margin, which has propagated from the Italian Peninsula through the African continental domains of Sicily. Usually interpreted as part of the stable African platform, the Hyblean region, during the Quaternary, has actually played the role of an independent crustal block, if framed in the larger scale plate motion. Since about 1.5 Ma, the Hyblean Block, in fact, was isolated from the rest of the Africa margin, as consequence of the propagation of the divergent margin through the SE Sicily. Since the Middle Pleistocene (≤0.8Ma), the Hyblean Block was accreted to the Nubia-Eurasia boundary, as the result of a sudden east-ward jumping of the divergent margin, to its present location. The Quaternary evolution of the Hyblean Block has emphasized some peculiar tectonic, kinematic and dynamic features that, being potentially diagnostic also for the identification of microplates, can be summarised as follow: 1. Occurrence of main regional Quaternary (<1.5 Ma) tectonics that are incongruent with the stress-in-situ measurements, focal mechanisms and geodetic data; 2. Evidence of very recent positive tectonic inversion of the Early Quaternary structures, coupled with sudden change in the displacement rate, not accompanied by variation in the larger scale plate motion; 3. Distribution of high- magnitude seismicity (6≤M≤7) along the tectonic boundaries of the crustal block; 4. Distribution of low- magnitude seismicity within the block, mostly independent from the geometry of the major Quaternary tectonics. The recognition of the Hyblean Block represents a key constraint in modelling the large scale deformation of the Central Mediterranean region. The correction of the GPS

  7. 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.

  8. 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.

  9. 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

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

    USGS Publications Warehouse

    Hamilton, W.

    1987-01-01

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

  11. Changes in the manner of tectonic movements under the Earth's evolution

    NASA Astrophysics Data System (ADS)

    Kuzmin, M. I.; Yarmolyuk, V. V.

    2016-08-01

    Variations in the O, Sr, Nd, and Hf isotopic compositions in rocks of various ages, minerals, and mantle temperature in the geological history are considered. Two periods in the Earth's history are studied: the beginning of the formation of the planet until the turn of (3.4) 2.7-2.5 Ga and the tectonic movement period in the last 2 Ga, and also the transitional period within 2.7-2.0 Ga.

  12. 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.

  13. 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

  14. 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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  17. Grenville tectonic events and evolution of the Yenisei Ridge at the western margin of the Siberian Craton

    NASA Astrophysics Data System (ADS)

    Likhanov, I. I.; Nozhkin, A. D.; Reverdatto, V. V.; Kozlov, P. S.

    2014-09-01

    Geological, petrologic, geochemical, and isotopic geochronological evidence for Grenville events at the western margin of the Siberian Craton are considered. These events were related to assembly of the Rodinia supercontinent. Multiple manifestations of riftogenic and within-plate magmatism at the final stage of orogenic evolution gave rise to breakdown of Rodinia and the formation of the Paleoasian ocean. The results allowed us to develop a new concept on the Precambrian geological evolution of the Yenisei Ridge and the processes that created its tectonic structure. The chronological sequence of events in the history of the Transangarian Yenisei Ridge is based on geological evidence and isotopic dating of Precambrian complexes variable in geodynamic nature. Four tectonic stages dated at 1.4-1.1, 1.1-0.9, 0.90-0.85, and 0.8-0.6 Ga were controlled by collision and extension recognized from large regional linear crustal structural elements. The evolution of the Transangarian Yenisei Ridge, which lasted for ˜650 Ma, corresponds in duration to supercontinental cycles that begin from rifting and breakdown of the predated supercontinent and was completed by orogeny and the formation of a new supercontinent. The regional geodynamic history correlates with the synchronous sequence and similar style of tectonothermal events at the periphery of the large Precambrian Laurentia and Baltica cratons. This is evidenced by paleocontinental reconstructions, which confirm close spatiotemporal links of Siberia with cratons in the northern Atlantic 1400-600 Ma ago and indicate incorporation of the Siberian Craton into the ancient Nuna and Rodinia supercontinents.

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

    NASA Astrophysics Data System (ADS)

    Porreca, M.; Mattei, M.

    2012-04-01

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

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. Magmatic evolution of the Andean Eastern Cordillera of Colombia during the Cretaceous: Influence of previous tectonic processes

    NASA Astrophysics Data System (ADS)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.; Sudo, Masafumi; Moreno-Murillo, Juan Manuel

    2010-03-01

    The Eastern Cordillera of the Colombian Andes represents an inverted Cretaceous basin where Cretaceous magmatism is characterized by rare mafic dykes and sills. We use 40Ar/ 39Ar, Sr-Nd-Pb isotopes, as well as major and trace elements analyses of Cretaceous intrusions from both flanks of the Eastern Cordillera in combination with structural data to document the complex evolution of the basin. Magmatism, which is diachronous and geochemically diverse, seems to be related to mantle melting beneath the most subsiding segments of each sub-basin during enhanced extensional tectonics. The mafic intrusions display two different compositional series: an alkaline one with OIB-like pattern and a tholeiitic one with MORB-like features. This indicates at least two diverse mantle sources. Trace-element patterns suggest that the intrusions were emplaced in an extensional setting. 40Ar/ 39Ar dating on primary plagioclase and hornblende provides plateau ages between ˜136 and ˜74 Ma. The geochemical and temporal diversities show that the emplacement of the magmas was tectonically controlled, each sub-basin reflecting an individual subsidence event.

  5. 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

  6. 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.

  7. 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.

  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. 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.

  10. GPS-Constrained Microplate Kinematics and Plio-Pleistocene Tectonic Evolution of the North Anatolian Fault and North Aegean Sea

    NASA Astrophysics Data System (ADS)

    Thatcher, W.

    2004-12-01

    Emerging evidence from Global Position System (GPS) survey measurements in the Aegean and elsewhere suggests that present-day active continental deformation occurs largely due to the relative motions of a small number of rigid blocks or microplates. However, it is not universally agreed whether the continental microplate description of the GPS data is superior to other proposed models, nor is it clear whether present-day movement patterns can be usefully extrapolated into the geologic past. Here I examine the known deformation history of the North Aegean over the past ~10 Ma and compare it with predictions based on the present-day microplate model. Agreement provides independent support for the GPS-based model and demonstrates its value in bettering our understanding of Aegean tectonics. If we knew nothing about late Cenozoic North Aegean tectonics and provisionally assumed the correctness of the Aegean microplate model of Nyst & Thatcher [2004 JGR], we would predict several features of the tectonic evolution that accord with geologic evidence. First, the North Aegean Sea would be created by extension due to SSW motion of the South Aegean and concomitant CW rotation of central Greece during the past 10 Ma. The same kinematic process would cause extension to be succeeded by strike-slip motion as the `ridge-transform-ridge' triple junction migrates WSW 24 km/Ma and the North Anatolian fault propagates into the region. The Plio-Pleistocene history of the North Aegean shows these same general features. Drilling and seismic imaging document the existence of young (< 10 Ma) and thick (up to 6 km) sedimentary sequences attributed to crustal extension by a factor of 3-4. Seismic profiling and bathymetric mapping show a mesh of roughly orthogonal faults with dip-slip offsets. Structural studies of sub-aerial exposures of these faults suggest an earlier episode of extension was followed by predominantly strike-slip motions. The plate kinematic reconstruction of late Cenozoic

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

    NASA Astrophysics Data System (ADS)

    Backé, G.

    2006-12-01

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

  13. Global tectonics since the breakup of Pangea 180 million years ago: evolution maps and lithospheric budget

    NASA Astrophysics Data System (ADS)

    Weijermars, Ruud

    Pangea, the Earth's youngest single supercontinent, broke up 180 million years ago. Tectonic plates were subsequently formed by dispersal of the continental fragments and accretion of new oceanic lithosphere. The configurations of all the major lithospheric plates at 0, 20, 65, 95, 140, 180 Ma BP are reconstructed on six globes of the Earth, each with a radius of 10 cm. It appears that plate boundaries maintain a remarkably close fit on model globes of constant radii if the reconstructions include the recovery of subducted spreading patterns. This is illustrated with maps in equatorial orthographic, oblique orthographic and transverse Hammer-Aitoff projections. The snug fit of the tectonic plates at every tested time since the breakup of Pangea 180 Ma BP is consistent with the theory of plate tectonics on a non-expanding Earth and contradicts rapidly expanding Earth models. The areas of oceanic lithosphere produced and consumed during the past 180 Ma BP are estimated from surface measurements of the globes reconstructed on the basis of particular assumptions. These measurements suggest a consistent increase in the production rate of oceanic lithosphere during the past 140 Ma. It was decided to revise the assumptions and see if alternative reconstructions of the ancient spreading patterns on the floors of the Tethys and Eo-Pacific oceans could avoid implying an increase of lithospheric production rates with time. This appeared to be possible. The revised maps suggest that ophiolites older than 180 Ma BP may have been obducted in Cenozoic collision zones of the Himalayas, Andes, Rockies, and the western part of the Banda Arc (Timor, New Guinea). Estimates of the ocean floor production and consumption budget appear to be quite similar for both map series, and only the possible ranges are summarized here, time averaged for the past 180 Ma. World-wide production and consumption of oceanic lithosphere appears to have varied between 2.6 and 3.5 km 2 a -1 at most. The mean

  14. 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

  15. 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

  16. 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

  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. Northwest margin of California continental borderland: marine geology and tectonic evolution.

    USGS Publications Warehouse

    Crouch, J.K.

    1981-01-01

    The NW margin of the California continental border land consists of 2 NW-trending pre-Neogene lithologic belts blanketed by Miocene and younger strata. These represent facies corresponding to the subduction complex and forearc-basin deposits of a late Mesozoic and Paleogene continental-margin arc-trench system. The outer belt, which forms the acoustic basement is characterized by: 1) moderately high compressional velocities; 2) discordant and discontinuous seismic reflectors; and 3) nonfossiliferous and diverse rock types. Landward, the inner Great Valley sequence belt is characterized by: 1) intermediate compressional velocities; 2) concordant and relatively continuous reflectors, and 3) a thick turbidite sequence. Well-developed wrench-fault structures in overlying Miocene strata record a transition from Paleogene subduction to Neogene transform faulting. The timing of volcanism and uplift, and of the younger wrenching event, closely matches the plate-tectonic model of Atwater and Molnar.-from Author

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

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

    1994-09-01

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

  2. The Supra-Detachment Sedimentary Evolution of hyper-extended Rifted Margins: the Example of the Alpine Tethys Fossil Analogue Exposed in the Alps (SE Switzerland)

    NASA Astrophysics Data System (ADS)

    Masini, Emmanuel; Mohn, Geoffroy; Manatschal, Gianreto; Ghienne, Jean-François; Lafont, François

    2010-05-01

    Rifting processes leading to the formation of deep-water hyper-extended, magma-starved rifted margins are poorly constrained due to the lack of data from present-day rifted margins. In many present-day examples the classical models remain unable to predict the observed tectonic, sedimentary and subsidence history. Therefore, finding good field analogues, which preserve primary relationships between structures and syn-tectonic sediments is a key to understand the timing and evolution of these margins. Our study focuses on the Jurassic Adriatic rifted margin, which is preserved in the Central Alps in SE Switzerland. The margin architecture can be restored and rift structures with their associated syn- to post- tectonic sedimentary sequences can be mapped through three main paleogeographic domains. A "proximal domain" with classical fault bounded basins, a "necking zone" dominated by thinning structures, and a "distal domain" with exhumed crustal rocks overlain by extensional allochthons that pass oceanwards into an exhumed subcontinental mantle domain. The low syn-rift sedimentation rate of the whole Adriatic margin gives an opportunity to study the exhumation history and its related tectono-sedimentary record. In our poster we constrain the tectono-sedimentary evolution of a supra-detachment rift basin, which is preserved between the necking zone and the exhumed subcontinental mantle in the so-called ocean continent transition. The syn-tectonic record can be divided into four main stratigraphic units on top of an evolving detachment system: (1) the Bardella Fm records the delamination of the hanging-wall blocks (pre-rift platform) on top of an active detachment system, leading to the formation of local debris-flows in fault bounded basins. (2) the Saluver A Fm records the first exhumation of the detachment and its footwall (the basement) which becomes an efficient new source feeding the debris-flows. (3) the Saluver B Fm consists of the onset of axial sand

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  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. Crustal source of the Late Cretaceous Satansarı monzonite stock (central Anatolia - Turkey) and its significance for the Alpine geodynamic evolution

    NASA Astrophysics Data System (ADS)

    Köksal, Serhat; Toksoy-Köksal, Fatma; Göncüoğlu, M. Cemal; Möller, Andreas; Gerdes, Axel; Frei, Dirk

    2013-04-01

    The Late Cretaceous granitic rocks within central Anatolia (Turkey) not only date and show the magmatic aspects of the Alpine realm, but also give clues about its geodynamic character. Among them, the Satansarı monzonite stock (SMS), part of the Terlemez pluton (Aksaray), characterizing the inception of an extensional tectonic regime in central Anatolia, has a subalkaline, metaluminous and magnesian geochemical nature with depletion in Ba, Nb, P and Ti, and with enrichment of Th, U, K and Pb relative to primitive mantle. The SMS has LREE enriched patterns ([La/Yb]N = 18.45-21.21) with moderately negative Eu-anomalies ([Eu/Eu*]N = 0.65-0.73). The geochemical data infer a crustal source with an inherited subduction-related component, and fractionation of plagioclase and amphibole. A crustal signature for the SMS is also inferred from high 87Sr/86Sr(t) ratios (0.70826-0.70917), and low ɛNd(t) values (-6.9 to -7.6). Zircon crystals from the SMS typically have magmatic rims overgrowing inherited cores that are reworked, resorbed and overgrown. Completely new zircon crystals grown in a single magmatic episode have also been identified. Laser ablation ICP-MS U-Pb zircon analyses yield a mean 206Pb/238U age of 74.4 ± 0.6 Ma (2σ) for the intrusion of the SMS. Rare discordant analyses range from the Devonian to the Proterozoic (i.e., 207Pb/206Pb ages between 364 Ma and 1263 Ma). In situ zircon Hf isotope analyses reveal low 176Lu/177Hf ratios and negative ɛHf(t) values, which is consistent with a predominantly crustal source of the SMS. We suggest that the water-rich magmas were generated in a hot zone within the crust produced by residual melts from basalt crystallization and partial melts of pre-existing metamorphic and igneous rocks within the lower crust of central Anatolia. The SMS likely formed by episodic injections of these hybrid monzonite melts by adiabatic ascent to shallow crust where they crystallized. This interpretation may be useful in interpreting the

  6. 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).

  7. 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

  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. Determination of the tectonic evolution of the Edremit Gulf based on seismic reflection studies

    NASA Astrophysics Data System (ADS)

    Kurtuluş, C.; Doğan, B.; Sertçelik, F.; Canbay, M.; Küçük, H. M.

    2009-06-01

    The Edremit Gulf, which developed during the Neogene-Quaternary, is a seismically active graben in NW Anatolia (Turkey) surrounded by the Sakarya continent. The sedimentary deposits in the gulf overlie the bedrock unconformably and can be separated into two parts as upper and lower deposits based on similarity of their seismic characteristics, and because the contact between them is clear. The lower deposits are characterized in the seismic profiles by the absence of well defined, continuous reflectors and are strongly disturbed by faults. A tectonic map and structural model of the Edremit Gulf was derived from interpreting 21 deep seismic profiles trending NE-SW and NW-SE within the gulf. Two fault systems were distinguished on the basis of this compilation. The NNW-SSE trending parallel faults are low-angle normal faults formed after compression. They controlled and deformed the lower basin deposits. A syncline and anticline with a broad fold-curvature length resulted in folds that developed parallel to basin boundaries in the lower basin deposits. The ENE-WSW trending high-angle faults have controlled and deformed the northern basin of the Edremit Gulf. The folds developed within the northern lower deposits originated from the listric geometry of the faults. These faults are normal faults associated with regional N-S extension in western Anatolia. The Edremit Gulf began to open under the control of low-angle NNW-SSE trending faults that developed after the compression of western Anatolia in an E-W direction in the early Neogene. Subsequently, regional N-S extensional stress and high-angle normal faults cut the previous structures, opened the northern basin, and controlled and deformed the lower basin deposits in the gulf. As a result, the Edremit Gulf has not been controlled by any strike-slip faults or the Northern Anatolian Fault. The basin developed in the two different tectonic regimes of western Anatolia as an Aegean type cross-graben from the Neogene to

  10. 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

  11. 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

  12. A synopsis of recent conceptual models on supercontinent tectonics in relation to mantle dynamics, life evolution and surface environment

    NASA Astrophysics Data System (ADS)

    Santosh, M.

    2010-09-01

    and energy through mantle downwelling and upwelling associated with supercontinent assembly and breakup is thought to affect the Earth's dynamo which would lead to catastrophic environmental changes, sometimes even triggering mass extinction. When a rising plume impinges the base of a supercontinent, the resultant continental rifting, formation of large igneous provinces and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to understand the history of life, and to trace the major surface environmental changes of our planet.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Grenholm, Mikael; Scherstén, Anders

    2015-11-01

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

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

    PubMed

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

    2011-04-01

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

  16. 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.

  17. 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.

  18. Tectonic evolution of Hanna Basin, Wyoming: Laramide block rotation in the Rocky Mountain foreland

    SciTech Connect

    LeFebre, G.B.

    1988-01-01

    From late Early Cretaceous through late Early Eocene time the Hanna Basin area of south-central Wyoming developed in response to regional and local tectonic forces. Subsidence history, flexural modeling, depositional setting and history, coal moisture content of Tertiary coal and fission-track thermochronology document the evolutionary history of this small ({approx}2600 km{sup 2}), deep ({approx}16 km offset on the Precambrian basement) intermontane basin. The present geologic configuration of Hanna Basin is the result of five evolutionary phases: (1) initial regional subsidence ({approx}119 Ma) as part of the expanding foredeep in front of the Sevier Orogenic belt, (2) breakup of this foredeep into discrete depocenters and nascent uplifts began between 88.5 Ma and 97.5 Ma (locally, uplift of the Sweetwater Arch and downwarp of the Hanna trough are most important), (3) breakup of the Hanna trough and development of the Hanna Basin by basement block rotation facilitated by sediment loading (began at 68-70 Ma and continued through {approx}52 Ma), (4) late Early Eocene - early Middle Eocene uplift of Shirley Mountains area and final destruction of the old Hanna trough (final movement on the Shirley Thrust) and (5) post Early Eocene sedimentary fill of about 2.4 km and its subsequent erosion prior to {approx}29 Ma.

  19. 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.

  20. 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.

  1. 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.

  2. Compressional deformation and tectonic evolution of the Tharsis region of Mars

    NASA Astrophysics Data System (ADS)

    Watters, T. R.

    The Tharsis region of Mars is dominated by volcanic and tectonic features. The major structural features observed throughout the region are ridges and faults. The Tharsis ridges are morphologically similar to ridges observed on the Moon, Mercury and the Columbia Plateau on Earth. The interpretation of the Columbia Plateau ridges as anticlinal folds forms a strong basis for the interpretation of the Tharsis ridges as compressional folds. The Tharsis ridge system is, to a first approximation, circumferentially oriented around the regional topographic high of northern Syria Planum. Ridge-fault crosscutting relations on the ridged plains indicate that the major ridge forming events in the Tharsis region were coincident with, and in many cases, prior to the extensional events that generated the faulting of the Tempe, Coprates and Memnonia regions and the rifting of Valles Marineris. Based on superposition relations, the compressional events that generated the ridges occurred after the emplacement of the ridged plains volcanic units and did not extend beyond the emplacement of the Syria Planum Formation or Tharsis Formation volcanic units.

  3. Cenozoic Landscape evolution of the South-African Plateau around the Orange Valley: tectonic and climate coupling

    NASA Astrophysics Data System (ADS)

    Dauteuil, Olivier; Bessin, Paul; Guillocheau, François

    2014-05-01

    The plateaus form the key geomorphic element of the African relief with the occurrence of the South African (or Kalahari) Plateau, extending from South Africa to southern Congo (Fig. 1). The origin and evolution of this large relief with a mean elevation ranging 1 to 2 kilometres were largely debated. This work discussed the landscape growth of the South African plateau on both sides of the Orange valley in term of planation process, incision, deformation and climate change. This work is mainly based on a geomorphic analysis done from DEM and field data. First, we proposed a new typology of planation surfaces based on their genetic process (weathering versus erosion), and not depending the elevation, as previously. Five types of planation surfaces were retained: etchplain, peneplain, pediplain, top-weathering surface and wav-cut platform. Using this approach to determine the evolution of Orange valley, we recognised three planation surfaces of which origin is not controlled by the lithology: a top weathering surface recorded the end of Eocene weathering period, a first etchplain-to-pediplain formed during the Oligocene and finally a pediplain initiated after a deformation event during the Miocene. This event reorganised completely the drainage network and the catchment of the Orange River that became similar to the current one. It corresponds to a regional tilting of the southern part of the plateau with a elevation of 200 m at least. Afterwards, global eustatic variations driven the landscape evolution because the Orange River gained the current stream connected to the sea level. Thus the landscape growth of the South African plateau results in a change in planation processes driven by a first climate change occurring during a slow uplift, then a regional tilting and at least by eustasy. Thus, an accurate and detail geomorphic analysis allows discriminating the tectonic to climatic processes causing the current landscape.

  4. 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.

  5. 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

  6. 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

  7. Tectonic and lithological constraints on the evolution of the Karoo graben of northern Malawi (East Africa)

    NASA Astrophysics Data System (ADS)

    Ring, U.

    1995-09-01

    The results of a lithostratigraphic, tectonic and kinematic study of the Karoo deposits of northern Malawi are reported. The objective of the lithostratigraphic study is to correlate the deposits of the Karoo basins of northern Malawi with the well-known deposits of southern Tanzania, thus establishing a stratigraphic framework through which the timing of faulting can be constrained. The kinematic analysis of faulting constrains the opening direction for the Karoo graben in this area and provides basic data to discuss the Karoo graben development within the regional tectonic framework of south-eastern Africa. The studied adults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15 m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions. In this study, small faults (offset < 10 m) and meso-scale faults (offset > 10 m, but generally not exceeding 30 40 m) have been distinguished. Methods used to analyse the kinematic data include the ‘pressure tension’ (PT) method, which estimates the principal axes for the bulk brittle strain, and the internal rotation axis (IRA) method, which estimates the axis of bulk internal rotation and the overall sense of slip at the faults. A mass balance calculation reveals a volume increase of up to 16% during cataclastic deformation in the fault zones. The PT method shows an approximately east trending extension direction for faults that occur only in the latest Carboniferous (?) and Early Permian strata, whereas the fault kinematics from faults that cut middle Permian to Early Triassic rocks is characterized by a ESE to SE trending extension direction. The small faults yield essentially the same kinematic results as the meso-scale faults. In a transport-parallel cross-sectional view, the principal extension axes are at an acute angle of approximately 60° to the major fault planes. Given the moderate fault density, the relatively high angle

  8. Tectonic and lithological constraints on the evolution of the Karoo graben of northern Malawi (East Africa)

    NASA Astrophysics Data System (ADS)

    Ring, U.

    The results of a lithostratigraphic, tectonic and kinematic study of the Karoo deposits of northern Malawi are reported. The objective of the lithostratigraphic study is to correlate the deposits of the Karoo basins of northern Malawi with the well-known deposits of southern Tanzania, thus establishing a stratigraphic framework through which the timing of faulting can be constrained. The kinematic analysis of faulting constrains the opening direction for the Karoo graben in this area and provides basic data to discuss the Karoo graben development within the regional tectonic framework of south-eastern Africa. The studied faults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions. In this study, small faults (offset <10m) and meso-scale faults (offset >10m, but generally not exceeding 30-40m) have been distinguished. Methods used to analyse the kinematic data include the 'pressure tension' (PT) method, which estimates the principal axes for the bulk brittle strain, and the internal rotation axis (IRA) method, which estimates the axis of bulk internal rotation and the overall sense of slip at the faults. A mass balance calculation reveals a volume increase of up to 16% during cataclastic deformation in the fault zones. The PT method shows an approximately east trending extension direction for faults that occur only in the latest Carboniferous (?) and Early Permian strata, whereas the fault kinematics from faults that cut middle Permian to Early Triassic rocks is characterized by a ESE to SE trending extension direction. The small faults yield essentially the same kinematic results as the meso-scale faults. In a transport-parallel cross-sectional view, the principal extension axes are at an acute angle of approximately 60° to the major fault planes. Given the moderate fault density, the relatively high angle between the

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. 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.

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

    SciTech Connect

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

    1996-02-01

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

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Raz, U.; Honegger, K.

    1989-04-01

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

  16. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  18. 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

  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. 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.

  1. 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

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Amantov, Aleksey; Fjeldskaar, Willy

    2015-04-01

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

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  11. 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

  12. 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

  13. Paleostress field pattern and tectonic evolution of the New Siberian Islands and De Long Islands, NE Russia

    NASA Astrophysics Data System (ADS)

    Brandes, C.; Piepjohn, K.; Franke, D.; Gaedicke, C.

    2012-12-01

    The New Siberian Islands and De Long Islands are located in a key position between the Laptev and the East Siberian Sea. On these islands, the rocks of the east Russian Arctic shelf are exposed and allow a detailed assessment of the structural evolution of the region. We present initial results of a comprehensive onshore analysis carried out during the CASE 13 expedition in 2011, covering large parts of the New Siberian Islands and De Long Islands. Special focus was the reconstruction of the regional paleostress field. Paleostress directions were derived based on the orientation of faults, slickensides, intersection lineations and conjugate joint sets. On the New Siberian Islands and De Long Islands, sedimentary rocks of Cambrian to Tertiary age are exposed. To a lesser amount, igneous rocks are present. Ordovician rocks are represented by shallow water carbonates in the northern part of Kotelny Island and by deepwater clastics on Bennett and Henrietta Island. Belkovsky Island and the southwestern part of Kotelny Island are dominated by Devonian shales. The Cretaceous rocks vary from deepwater clastics (Great Lyakhovsky Island) to soft coals (Novaya Sibir). The deformation in the study area is unevenly distributed. Whereas the successions on Belkovsky Island are strongly folded, the rocks on Stolbovoy Island, are only slightly deformed into open synclines and anticlines. Deformation is high in the west (Belkovsky Island) and in the south (Great Lyakhovsky Island). The eastern (Novaya Sibir) and northeastern (Henrietta Island) parts of the study area in contrast, are less deformed. Initial results point to at least three different tectonic phases in the area: two compressional phases and an extensional one. The first tectonic phase was probably a WNW-ESE directed horizontal contraction that can be observed in outcrops on Bennett and Kotelny Island. The second phase is best exposed on Great Lyakhovsky Island, where the fabrics indicate a horizontal compressional

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

    NASA Technical Reports Server (NTRS)

    Norman, Marc D.; Leeman, William P.

    1989-01-01

    The relationships between Cretaceous to Neogene magmatism and the tectonic setting of southwestern and central Idaho are evaluated. An overview of the tectonics and geology of the northwestern U.S. is presented. Major element, trace element, and Sr, Pb, and Nd isotopic data for the region are used to place constraints on magma source characteristics, the manner in which the magmatic sources evolved through time, and the nature of interactions among mantle and crustal domains in response to changing tectonic environment.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  16. Structural evolution of the Rieserferner Pluton: insight into the localization of deformation and regional tectonics implications

    NASA Astrophysics Data System (ADS)

    Ceccato, Alberto; Pennacchioni, Giorgio

    2016-04-01

    deformation structures within the RFP is controlled by the development and later reactivation in shear of two main sets of joints during cooling and progressive exhumation of the pluton. These joints were either exploited as faults or localized ductile shear zones. In the RFP, the kinematics of shear reactivation is complex, with the same joint set recording different senses of shear and transport directions. Preliminary kinematic analysis and qualitative paleostress reconstruction show that there has been a clockwise rotation of the main regional shortening direction from WNW-ESE, during the first ductile event, to N-S during later brittle deformation. These two different shortening directions fit with those inferred, respectively, for Austroalpine nappe stacking by Ratschbacher (1989) and for the Alpine convergence during late Oligocene-Miocene within the Tauern window (Pennacchioni & Mancktelow, 2007). References Cesare, B. (1994). Hercynite as the product of staurolite decomposition in the contact aureole of Vedrette di Ries, eastern Alps, Italy. Contributions to Mineralogy and Petrology, 116(3), 239-246. Pennacchioni, G., Di Toro, G., Brack, P., Menegon, L., & Villa, I. M. (2006). Brittle-ductile-brittle deformation during cooling of tonalite (Adamello, Southern Italian Alps). Tectonophysics, 427(1), 171-197. Pennacchioni, G., & Mancktelow, N. S. (2007). Nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions. Journal of Structural Geology, 29(11), 1757-1780. Ratschbacher, L., Frisch, W., Neubauer, F., Schmid, S. M., & Neugebauer, J. (1989). Extension in compressional orogenic belts: the eastern Alps. Geology, 17(5), 404-407. Romer, R. L., & Siegesmund, S. (2003). Why allanite may swindle about its true age. Contributions to Mineralogy and Petrology, 146(3), 297-307. Steenken, A., Siegesmund, S., & Heinrichs, T. (2000). The emplacement of the Rieserferner Pluton (Eastern

  17. Metasomatic Evolution in Tectonically Mixed Zones (Mélange) and Significance for Geochemical Evolution of the Slab-Mantle Interface

    NASA Astrophysics Data System (ADS)

    Bebout, G. E.; King, R. L.

    2012-12-01

    Fluid flow focused in highly deformed zones (shear zones), and the physical juxtaposition of chemically disparate rocks (via mechanical mixing) in such zones, can lead to extensive metasomatism, including volume strain, and result in rocks with hybridized compositions little resembling the compositions of the incorporated rock types [1-5]. In the Catalina Schist (California), lawsonite-albite, lawsonite-blueschist, and amphibolite-facies units contain shear zones at scales of meters to kilometers, each containing "blocks" (with more spherical or more tabular dimensions) co-facial in grade with the "matrix" surrounding these blocks [1-3]. Oxygen isotope data for these "mélange" units, and adjacent more "coherent" expanses, indicate enhanced fluid flow in the more strongly deforming mélange zones while fluid flow in coherent domains was dominantly fracture-controlled and episodic. The amphibolite-facies mélange unit shows evidence for km-scale equilibration of varying mineral assemblages with H2O-rich fluids with uniform O and H isotope compositions consistent with a lower-grade metasedimentary source. This unit is believed to have formed largely by mechanical mixing of mafic and ultramafic compositions, partly because of the scarcity of sedimentary blocks. However, the mélange matrix in this unit preserves a number of sedimentary chemical/isotopic characteristics (e.g., Pb isotope compositions [3]) that could reflect the incorporation of sedimentary rocks, with or without fluid-related fractionation, and possibly fluid-mediated additions. Tectonically mixed zones such as these, if volumetrically significant at the slab-mantle interface, could exert disproportionate control on the compositions of hydrous fluids or silicate melts emanating from subducting slabs and entering the forearc to backarc mantle wedge, including those contributing to arc magmatism [1-5]. Geochemical studies of arc lavas should consider the possibility that the "fluids" contributed from

  18. Jurassic extension and Cenozoic inversion tectonics in the Asturian Basin, NW Iberian Peninsula: 3D structural model and kinematic evolution

    NASA Astrophysics Data System (ADS)

    Uzkeda, Hodei; Bulnes, Mayte; Poblet, Josep; García-Ramos, José Carlos; Piñuela, Laura

    2016-09-01

    We constructed a geological map, a 3D model and cross-sections, carried out a structural analysis, determined the stress fields and tectonic transport vectors, restored a cross section and performed a subsidence analysis to unravel the kinematic evolution of the NE emerged portion of the Asturian Basin (NW Iberian Peninsula), where Jurassic rocks crop out. The major folds run NW-SE, normal faults exhibit three dominant orientations: NW-SE, NE-SW and E-W, and thrusts display E-W strikes. After Upper Triassic-Lower Jurassic thermal subsidence, Middle Jurassic doming occurred, accompanied by normal faulting, high heat flow and basin uplift, followed by Upper Jurassic high-rate basin subsidence. Another extensional event, possibly during Late Jurassic-Early Cretaceous, caused an increment in the normal faults displacement. A contractional event, probably of Cenozoic age, led to selective and irregularly distributed buttressing and fault reactivation as reverse or strike-slip faults, and folding and/or offset of some previous faults by new generation folds and thrusts. The Middle Jurassic event could be a precursor of the Bay of Biscay and North Atlantic opening that occurred from Late Jurassic to Early Cretaceous, whereas the Cenozoic event would be responsible for the Pyrenean and Cantabrian ranges and the partial closure of the Bay of Biscay.

  19. Post-glacial landform evolution in the middle Satluj River valley, India: Implications towards understanding the climate tectonic interactions

    NASA Astrophysics Data System (ADS)

    Sharma, Shubhra; Bartarya, S. K.; Marh, B. S.

    2016-04-01

    Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ˜13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ˜5 and 0.4 ka (mid- to late-Holocene), was during the declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (˜6.5-7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene declining ISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions.

  20. Variscan tectonics in Dodecanese, Kalymnos island, Greece

    NASA Astrophysics Data System (ADS)

    Chatziioannou, Eleftheria; Grasemann, Bernhard; Schneider, David; Hubmann, Bernhard; Soukis, Konstantinos

    2015-04-01

    Kalymnos island is located in the Dodecanese, southeastern Aegean Sea, and geologically appears to be part of the external Hellenides. Pre-Alpidic basement rocks on the Dodecanese islands have been suggested to record compelling similarities with the basement rocks in Eastern Crete with respect to their lithologies and pre-Alpidic metamorphic evolution. The lithotectonic units experienced greenschist to amphibolite facies conditions during the Variscan orogeny. Whereas the rocks in Eastern Crete reveal Alpine high-pressure overprint, the Variscan basement units in the Dodecanese record no or low-grade Alpine metamorphism. A field study of basement rocks below Mesozoic limestones and dolomites in the NW part of Kalymnos near Emporios uncovered a complex history of metamorphism, folding and faulting. Three different tectonic units can be discriminated from top to bottom: a) a quartz-mica schist, b) a white-grey, fossiliferous coarse grained marble and c) a fine-grained fossiliferous blue-grey marble. In the marbles macrofossils such as brachiopods, ammonoid cephalopods (Goniatids?) and crinoids suggest a Middle-Upper Devonian deposition age (Givetian- Frasnian). Structural mapping the area resolved a dominant W-E shortening event, resulting in an overall inverted metamorphic gradient. The lowermost blue-grey marble unit is folded into large-scale upright folds, which are truncated by top-to-east overthrusting of the white-grey marble unit. Whereas deformation mechanisms in the blue-grey marble unit are dominated by dissolution-precipitation creep, the white-grey marble suffered intense crystal plastic deformation with localized high-strain mylonitic shear zones. The uppermost quartz-mica schist unit is separated from the lower units by a cataclastic phyllonitic shear zone. 40Ar/39Ar geochronological dating on white micas from the quartz-mica schists yielded cooling ages between 240 and 334 Ma indicative of Variscan cooling. Our data suggest that this part of the

  1. Structure and Evolution of Northwest Corner of South China Sea: implications for Cenozoic tectonics in Southeast Asia

    NASA Astrophysics Data System (ADS)

    Lei, C.; Ren, J.; Willett, S.; Clift, P. D.

    2012-12-01

    The Yinggehai-Song Hong Basin (YGHB) and Qiongdongnan Basin (QDNB) are in the northwest corner of the South China Sea, which positioned at a juncture between a strike-slipping zone and an extensional zone. The basins lie at the southern termination of the largest Tibetan strike-slip zones, the Red River Fault, and are the principal repository of materials eroded from the Red River drainage. The basins are flanked to the East by an oceanic ridge and border the Nansha area to the South, which is being subducted underneath the Borneo Block. Hainan Island, located between the YGHB and QGNB, is composed primarily of granites and basalts. A combination of regional, high-quality reflection seismic and well data was used to unravel the basin history in greater detail than previously possible, which will enrich our knowledge about structure and evolution in Southeast Asia. After ca. 55 Ma the basins started to subside and grabens bounded by small-scale and NE-SW trending faults developed across wide areas. However, the evolution of YGHB and QDNB was shown different after 32 Ma. Strike-slip deformation of the YGHB took place after 32 Ma in response to the left-lateral movement of the Red River Fault. After the Middle Miocene the YGHB was inverted and generated prominent folds in the Lingao Uplift and Hanoi Basin. Inversion ceased at different times in different parts of the basin, indicating that the transition from compression to extension moved northward during the period 15.5-5.5 Ma. In contrast, to the west of YGHB, the QDNB displays a very different basin structure and evolution since 32 Ma. Larger-scale, partly fault-controlled depressions are superimposed clearly over underlying, faulted-bounding grabens on seismic profiles. The evolution of QDNB was controlled by extension, which is strongly influenced by the initiation of ridge spreading in the South China Sea. We also reconstructed the sedimentary flux from the Red River drainage constrained by higher resolution

  2. Late Paleozoic to Jurassic tectonic evolution of the Bogda area (northwest China): Evidence from detrital zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Tang, Wenhao; Zhang, Zhicheng; Li, Jianfeng; Li, Ke; Chen, Yan; Guo, Zhaojie

    2014-06-01

    Since the Cenozoic, the Tian Shan is rejuvenated by crustal shortening related to the ongoing India-Asia collision. However, the tectonic process prior to the Cenozoic remains ambiguous, especially in the Bogda area of the eastern Tian Shan. The continuous Late Paleozoic-Mesozoic sequences in the Bogda area record abundant information about the basin-mountain interaction. U-Pb (LA-ICP-MS) dating of detrital zircons from seven sandstone samples from Permian to Jurassic was used to investigate the changes of provenance and basin-mountain interaction in the Bogda area. During the Permian, proximal and synchronous pyroclastic materials were the major source. The Late Paleozoic magmatic belt in the North Tian Shan (NTS) had gradually become one of the main sources by the Late Permian, which implies the uplift and exhumation in the NTS area. This is interpreted in terms of near-source sedimentation in basin developing in a post-orogenic extension setting. The large range of U-Pb ages of detrital zircons observed in the Early-Middle Jurassic sediments encompasses most of the available sources implying a wide drainage pattern developing on a rather flat topography. Re-emergence of the Early Permian peak in the spectrum implies that the Bogda Mountains has existed as a gentle positive relief and began to provide materials to the submountain regions. The southern Junggar Basin extended towards to the south and evolved as a passively subsiding basin from the Middle Triassic to the Middle Jurassic. However, the synchronous pyroclastic (tuff) and the exhumed late Paleozoic detrital materials from the uplifted Bogda Mountains were the major component of the Upper Jurassic sediments. Associated to the conglomerate in the Kalaza Formation, the basin-range evolution entered a compression uplift stage. The basin pattern evolution of the Bogda area is consistent with that of the southern Junggar Basin.

  3. Cretaceous-Cenozoic Geological Evolution of Tibet: Tectonic Interpretations and Outstanding Questions (Invited)

    NASA Astrophysics Data System (ADS)

    Kapp, P. A.; Decelles, P. G.; Ding, L.; van Hinsbergen, D. J.

    2010-12-01

    explain how ~2000 km of India-Asia convergence was accommodated south of the IYS since ~50 Ma (with the remaining ~1000 km accommodated by shortening of Asian lithosphere). Outstanding questions include: (1) What are the explanations for major, coeval geological changes in the Lhasa terrane, Gangdese forearc, IYS, and TH at 65-63 Ma, which have led some workers to argue for initiation of India-Asia collision at this time? (2) What was the nature of the subducted TH lithosphere and its former paleogeographic and tectonic relationships to Indian cratonic lithosphere? (3) Why has only <50% of the estimated 2000 km of post-50 Ma convergence south of the Indus-Yarlung suture been documented as shortening within the Tethyan-Himalayan thrust belts? (4) Why did Asian lithosphere in Pamir and Tibet behave so differently in response to collisional orogenesis?

  4. Tectonic and petrologic evolution of the Western Mediterranean: the double polarity subduction model

    NASA Astrophysics Data System (ADS)

    Melchiorre, Massimiliano; Vergés, Jaume; Fernàndez, Manel; Torné, Montserrat; Casciello, Emilio

    2016-04-01

    The geochemical composition of the mantle beneath the Mediterranean area is extremely heterogeneous. This feature results in volcanic products whose geochemical features in some cases do not correspond to the geodynamic environment in which they are sampled and that is observed at present day. The subduction-related models that have been developed during the last decades to explain the evolution of the Western Mediterranean are mainly based on geologic and seismologic evidences, as well as petrography and age of exhumation of the metamorphic units that compose the inner parts of the different arcs. Except few cases, most of these models are poorly constrained from a petrologic point of view. Usually the volcanic activity that affected the Mediterranean area since Oligocene has been only used as a corollary, and not as a key constrain. This choice is strictly related to the great geochemical variability of the volcanic products erupted in the Western Mediterranean, due to events of long-term recycling affecting the mantle beneath the Mediterranean since the Variscan Orogeny, together with depletion episodes due to partial melting. We consider an evolutionary scenario for the Western Mediterranean based on a double polarity subduction model according to which two opposite slabs separated by a transform fault of the original Jurassic rift operated beneath the Western and Central Mediterranean. Our aim has been to reconstruct the evolution of the Western Mediterranean since the Oligocene considering the volcanic activity that affected this area since ~30 Ma and supporting the double polarity subduction model with the petrology of the erupted rocks.

  5. Geology of the Blue Mountains region of Oregon, Idaho, and Washington; petrology and tectonic evolution of pre-Tertiary rocks of the Blue Mountains region

    USGS Publications Warehouse

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

    1995-01-01

    This Professional Paper contains 14 chapters on the Blue Mountains region of Oregon, Idaho, and Washington. The authors discuss petrology and tectonic evolution of an island arc that formed in the ancestral Pacific Ocean during the Permian to Cretaceous interval. The island arc was accreted to cratonal North America in the Early Cretaceous and thereby became one of the several exotic terranes in western North America.

  6. Reconnaissance geochronology of tuffs in the Miocene Barstow Formation: implications for basin evolution and tectonics in the central Mojave Desert

    USGS Publications Warehouse

    Miller, D.M.; Leslie, S.R.; Hillhouse, J.W.; Wooden, J.L.; Vazquez, J.A.; Reynolds, R.E.

    2010-01-01

    Early to middle Miocene lacustrine strata of the Barstow Formation are well dated in just a few places, limiting our ability to infer basin evolution and regional tectonics. At the type section in the Mud Hills, previous studies have shown that the lacustrine interval of the Barstow Formation is between ~16.3 Ma and ~13.4 Ma. Elsewhere, lake beds of the Barstow Formation have yielded vertebrate fossils showing the Hemingfordian/Bartovian transition at ~16 Ma but are otherwise poorly dated. In an attempt to clarify the age and depositional environments of the lake deposits, we are mapping the Barstow Formation and dating zircons from interbedded tuffs, as well as testing ash-flow tuffs for the distinctive remanent magnetization direction of the widespread Peach Spring Tuff. Thus far, our new U-Pb zircon ages inficate that the Barstow lake beds contain tuff beds as old as 19.1 Ma and as young as 15.3 Ma. At Harvard Hill, Barstow lake beds contain a thick tuff dated at 18.7 Ma. On the basis of zircon ages, mineralogy, zircon chemistry, and paleomagnetic results, we consider the thick tuff to be a lacustrine facies of the Peach Spring Tuff. We have identified the Peach Spring Tuff by similar methods at eight localities over a broad area, providing a timeline for several fluvial and lacustrine sections. The new dates indicate that long-lived lacustrine systems originated before 19 Ma and persisted to at least 15 Ma. The onset of lacustrine conditions predates the Peach Spring Tuff in most Barstow Formation sections and may be older than 19.5 Ma in some places. The new data indicate that the central Mojave Desert contained narrow to broad lake basins during and after extension, and that Barstow lacustrine deposits did not exclusively postdate extensional tectonics. At present, it is unclear whether several separate, small lake basins coexisted during the early to middle Miocene, or if instead several small early Miocene basins gradually coalesced over about 6 millions

  7. Reconnaissance geochronology of tuffs in the Miocene Barstow Formation: implications for basin evolution and tectonics in the central Mojave Desert

    USGS Publications Warehouse

    Miller, David M.; Leslie, Shannon R.; Hillhouse, John W.; Wooden, Joseph L.; Vazquez, Jorge A.; Reynolds, R.E.

    2010-01-01

    Early to middle Miocene lacustrine strata of the Barstow Formation are well dated in just a few places, limiting our ability to infer basin evolution and regional tectonics. At the type section in the Mud Hills, previous studies have shown that the lacustrine interval of the Barstow Formation is between ~16.3 Ma and ~13.4 Ma. Elsewhere, lake beds of the Barstow Formation have yielded vertebrate fossils showing the Hemingfordian/Barstovian transition at ~16 Ma but are otherwise poorly dated. In an attempt to clarify the age and depositional environments of the lake deposits, we are mapping the Barstow Formation and dating zircons from interbedded tuffs, as well as testing ash-flow tuffs for the distinctive remanent magnetization direction of the widespread Peach Spring Tuff. Thus far, our new U-Pb zircon ages indicate that the Barstow lake beds contain tuff beds as old as 19.1 Ma and as young as 15.3 Ma. At Harvard Hill, Barstow lake beds contain a thick tuff dated at 18.7 Ma. On the basis of zircon ages, mineralogy, zircon chemistry, and paleomagnetic results, we consider the thick tuff to be a lacustrine facies of the Peach Spring Tuff. We have identified the Peach Spring Tuff by similar methods at eight localities over a broad area, providing a timeline for several fluvial and lacustrine sections. The new dates indicate that long-lived lacustrine systems originated before 19 Ma and persisted to at least 15 Ma. The onset of lacustrine conditions predates the Peach Spring Tuff in most Barstow Formation sections and may be older than 19.5 Ma in some places. The new data indicate that the central Mojave Desert contained narrow to broad lake basins during and after extension, and that Barstow lacustrine deposits did not exclusively postdate extensional tectonics. At present, it is unclear whether several separate, small lake basins coexisted during the early to middle Miocene, or if instead several small early Miocene basins gradually coalesced over about 6 million

  8. Structure of Palaeogene sediments in east Ellesmere Island: Constraints on Eurekan tectonic evolution and implications for the Nares Strait problem

    NASA Astrophysics Data System (ADS)

    Saalmann, K.; Tessensohn, F.; Piepjohn, K.; von Gosen, W.; Mayr, U.

    2005-08-01

    The "Nares Strait problem" represents a debate about the existence and magnitude of left-lateral movements along the proposed Wegener Fault within this seaway. Study of Palaeogene Eurekan tectonics at its shorelines could shed light on the kinematics of this fault. Palaeogene (Late Paleocene to Early Eocene) sediments are exposed at the northeastern coast of Ellesmere Island in the Judge Daly Promontory. They are preserved as elongate SW-NE striking fault-bounded basins cutting folded Early Paleozoic strata. The structures of the Palaeogene exposures are characterized by broad open synclines cut and displaced by steeply dipping strike-slip faults. Their fold axes strike NE-SW at an acute angle to the border faults indicating left-lateral transpression. Weak deformation in the interior of the outliers contrasts with intense shearing and fracturing adjacent to border faults. The degree of deformation of the Palaeogene strata varies markedly between the northwestern and southeastern border faults with the first being more intense. Structural geometry, orientation of subordinate folds and faults, the kinematics of faults, and fault-slip data suggest a multiple stage structural evolution during the Palaeogene Eurekan deformation: (1) The fault pattern on Judge Daly Promontory is result of left-lateral strike-slip faulting starting in Mid to Late Paleocene times. The Palaeogene Judge Daly basin formed in transtensional segments by pull-apart mechanism. Transpression during progressive strike-slip shearing gave rise to open folding of the Palaeogene deposits. (2) The faults were reactivated during SE-directed thrust tectonics in Mid Eocene times (chron 21). A strike-slip component during thrusting on the reactivated faults depends on the steepness of the fault segments and on their obliquity to the regional stress axes. Strike-slip displacement was partitioned to a number of sub-parallel faults on-shore and off-shore. Hence, large-scale lateral movements in the sum of 80

  9. Gravity modeling constraints on the Gatun-Chagres Basin and tectonic evolution of north-central Panama

    NASA Astrophysics Data System (ADS)

    Mynhier, Kelci

    The Oligocene-Miocene collision between Panama and South America significantly influenced ocean currents, global climate, and species diversification. Intraplate deformation of the Panama Block also played an important role in the evolution of this tectonic system, but is not well understood. A high-resolution gravity survey, coupled with geologic observations, was conducted in north-central Panama to better constrain the processes responsible for the Isthmus' modern configuration. Approximately 110 gravity stations were collected from Colon to Nombre de Dios, Panama and merged with existing data. Subsequently, four 2.5-D gravity models were produced to constrain the geometry of the Gatun-Chagres Basin using different sedimentary densities (1.8, 2.0, and 2.2 g/cm 3) to produce a realistic range of basin thicknesses. Overall, models with an average basin density of 2.0 g/cm3 are most consistent with offshore seismic profiles and field evidence, suggesting basin thickness is ~3.0--3.5 km. Previous seismic reflection data and geochemical analyses of Miocene arc volcanic rocks delineate a zone of extension in the Panama Canal Region, and gravity analysis from this study supports this hypothesis. Field evidence of multiple NW-facing normal faults suggests that they separate the basin from uplifted arc basement rocks east of the Canal, resulting in a 60 mGal gravity gradient. Beneath the basin, gravity models indicate ~5--10 km of crustal thinning. 3-D reconstruction of the 2.5-D models show a northward thickening basin and two depocenters that correspond to the Rio Indio and Toro facies of the Chagres Formation. This analysis suggests two directional extension of the Gatun-Chagres Basin; an east-west direction corresponding to the initial formation of the basin, and a modern northwest-southeast direction. To the northeast, gravity modeling indicates that there is a ~150 m-thick, Cretaceous-Holocene sedimentary basin present from Portobelo to Nombre de Dios. Sedimentary

  10. Morphological Analysis of Apo Volcanic Complex in Southern Mindanao, Philippines: implications on volcano-tectonic evolution of different volcanic units

    NASA Astrophysics Data System (ADS)

    Herrero, T. M. L.; van Wyk de Vries, B.; Lagmay, A. M. A.; Eco, R. C.

    2015-12-01

    The Apo Volcanic Complex (AVC) is one of the largest volcanic centers in the Philippines, located in the southern island of Mindanao. It is composed of four edifices and several smaller cones. The youngest volcanic unit, the Apo Dome, is the highest elevation in the Philippines. This unit is classified as potentially active, whereas other units, Talomo, Sibulan and Kitubod, are inactive. The study gives insight to the construction and deformation history of the volcanic units and imparts foresight to subsequent events that can affect populated areas. A morphological analysis integrating high-resolution digital terrain models and public domain satellite data and images was done to recognize and discriminate volcanic units and characterize volcano-tectonic features and processes. Morphological domains were defined based on surface textures, slope variation, degrees and controls of erosion, and lineament density and direction. This establishes the relative ages and extent of volcanic units as well as the volcano-tectonic evolution of the complex. Six edifice building events were recognized, two of which form the elevated base of Apo dome. The geodynamic setting of the region is imprinted in the volcanic units as five morphostructural lineaments. They reveal the changes in maximum regional stress through time such as the N-S extension found across the whole volcanic complex displaying the current stress regime. This has implications on the locality and propagation of geothermal activity, magma ascent, and edifice collapses. One main result of the compounded effects of inherited structures and current stress regime is the Sandawa Collapse Zone. This is a large valley formed by several collapses where NE-SW fractures propagate and the increasing lateral spreading by debuttressing continue to eat away the highest peak. The AVC is surrounded by the major metropolitan area of Davao City to the east and the cities of Kidapawan and Digos to the west and south, respectively

  11. Analysis of the influence of tectonics on the evolution valley network based on the SRTM DEM and the relationship of automatically extracted lineaments and the tectonic faults, Jemma River basin, Ethiopia

    NASA Astrophysics Data System (ADS)

    Kusák, Michal

    2016-04-01

    The Ethiopian Highland is good example of high plateau landscape formed by combination of tectonic uplift and episodic volcanism (Kazmin, 1975; Pik et al., 2003; Gani et al., 2009). Deeply incised gorges indicate active fluvial erosion which leads to instabilities of over-steepened slopes. In this study we focus on Jemma River basin which is a left tributary of Abay - Blue Nile to assess the influence of neotectonics on the evolution of its river and valley network. Tectonic lineaments, shape of valley networks, direction of river courses and intensity of fluvial erosion were compared in six subregions which were delineate beforehand by means of morphometric analysis. The influence of tectonics on the valley network is low in the older deep and wide canyons and in the and on the high plateau covered with Tertiary lava flows while younger upper part of the canyons it is high. Furthermore, the coincidence of the valley network with the tectonic lineaments differs in the subregions. The fluvial erosion along the main tectonic zones (NE-SW) direction made the way for backward erosion possible to reach far distant areas in E for the fluvial erosion. This tectonic zone also separates older areas in the W from the youngest landscape evolution subregions in the E, next to the Rift Valley. We studied the functions that can automatically extract lineaments in programs ArcGIS 10.1 and PCI Geomatica. The values of input parameters and their influence of the final shape and number of lineaments. A map of automated extracted lineaments was created and compared with 1) the tectonic faults by Geology Survey of Ethiopia (1996); and 2) the lineaments based on visual interpretation of by the author. The comparation of lineaments by automated visualization in GIS and visual interpretation of lineaments by the author proves that both sets of lineaments are in the same azimuth (NE-SW) - the same direction as the orientation of the rift. But it the mapping of lineaments by automated

  12. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.

    2015-11-01

    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  13. Evolution of the Gulf of Cadiz and west Portugal contourite depositional system: tectonic, sedimentary and paleoceanographic implications from IODP Expedition 339

    NASA Astrophysics Data System (ADS)

    Hernández Molina, F. J.; Sierro, F. J.; Llave, E.; Roque, C.; Stow, D. A. V.; Williams, T.; Lofi, J.; Van der Schee, M.; Arnaíz, A.; Ledesma, S.; Rosales, C.; Rodriguez-Tovar, F. J.; Pardo-Igúzquiza, E.; Brackenridge, R.

    2015-12-01

    The contourite depositional systems (CDS) along the southwestern Iberian Margin (SIM) bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution. We identify significant changes in sedimentary style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM. Following the 4.5 Ma cessation of a previous phase of tectonic activity related to the Miocene-Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8 Ma duration with a pronounced overprint of ~2 -2.5 Ma cycles. Two major compressional events affecting to the Neogene basins at 3.2-3 Ma and 2-2.3 Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33-3.2 Ma) with a weak MOW, 2) a transitional-drift stage (3.2-2 Ma) and 3) a growth-drift stage (2 Ma-present time) with enhanced MOW circulation and attendant contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7-0.9 Ma and 0.3-0.6 Ma record the effects of renewed tectonic activity on basin evolution. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over

  14. The Monte Orfano Conglomerate revisited: stratigraphic constraints on Cenozoic tectonic uplift of the Southern Alps (Lombardy, northern Italy)

    NASA Astrophysics Data System (ADS)

    Sciunnach, Dario; Scardia, Giancarlo; Tremolada, Fabrizio; Premoli Silva, Isabella

    2010-09-01

    The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (“ molassa”). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.

  15. Formation and tectonic evolution of the Cretaceous Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites

    NASA Astrophysics Data System (ADS)

    Khan, Mehrab; Kerr, Andrew C.; Mahmood, Khalid

    2007-10-01

    The Muslim Bagh ophiolitic complex Balochistan, Pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the Indian and Eurasian plates. These ophiolites were obducted onto the Indian continental margin around the Late Cretaceous, prior to the main collision between the Indian and Eurasian plates. The upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes. Each pluton has a transitional dunite-rich zone at its base, and new geochemical data suggest a similar mantle source region for both the plutons and dykes. In contrast, the lower nappe consists of pillow basalts, deep-marine sediments and a mélange of ophiolitic rocks. The rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid-ocean ridge. The basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the Indian plate. The two nappes of the Muslim Bagh ophiolitic complex are thus distinctively different in terms of their age, lithology and tectonic setting. The recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved.

  16. Diachronous evolution of the alpine continental subduction wedge: Evidence from P-T estimates in the Briançonnais Zone houillère (France - Western Alps)

    NASA Astrophysics Data System (ADS)

    Lanari, Pierre; Guillot, Stéphane; Schwartz, Stéphane; Vidal, Olivier; Tricart, Pierre; Riel, Nicolas; Beyssac, Olivier

    2012-05-01

    diachronous evolution of the Briançonnais zone involved in alpine continental subduction at different times. The geothermal gradient in the Briançonnais zone changes from 8 °C/km during early continental subduction, to 40 °C/km during the collisional event at about 35-30 Ma. The intermediate gradient of 15 °C/km estimated in the Briançonnais Zone houillère suggests that this unit was buried later, than the more internal Briançonnais units, after 40 Ma.

  17. Tectonic evolution of the Salton Sea inferred from seismic reflection data

    USGS Publications Warehouse

    Brothers, D.S.; Driscoll, N.W.; Kent, G.M.; Harding, A.J.; Babcock, J.M.; Baskin, R.L.

    2009-01-01

    Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The formation of these basins has generally been studied using laboratory experiments or numerical models. Here we combine seismic reflection data and geological observations from the Salton Sea to understand the evolution of this nascent pull-apart basin. Our data reveal the presence of a northeast-trending hinge zone that separates the sea into northern and southern sub-basins. Differential subsidence (10 mm yr 1) in the southern sub-basin suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline, which may control the spatial distribution of young volcanism. Rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull-apart basin began after 0.5 million years ago. We suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the Salton Sea. In contrast to previous models based on historical seismicity patterns, the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull-apart basins. ?? 2009 Macmillan Publishers Limited.

  18. Cenozoic tectonic evolution leading to the Choco-South America collision (Panama-Colombia), from seismic profiles interpretations

    NASA Astrophysics Data System (ADS)

    Barat, F.; Maurin, T.; Auxietre, J.; Mercier de Lépinay, B.; Salmon, P.; Sosson, M. M.

    2012-12-01

    The Choco Block is located in eastern Panama and western Colombia, at the western boundary of the Caribbean Plate (CP), and is mainly characterized by a Late Cretaceous-Paleogene volcanic arc overlying the Caribbean Large Igneous Province (CLIP). This block was accreted to South American plate (SAP) during Middle to Late Miocene. Geological, chronological and structural data are scarce in the Choco Block. Our study aims at reconstructing the evolution at a local scale, to provide new constraints to the regional scale tectonic processes that have occurred since the Paleogene. In that perspective, we have interpreted offshore seismic reflection profiles. This interpretation was supported by biostratigraphic data from two wells. We focused our studies in the Uraba Gulf area, a triple junction between the Choco Block, the SAP and the Caribbean oceanic plateau. This poorly understood zone offers rare observation of two accretionary wedges, the North Panama Deformed Belt (NPDB), and the Sinu Belt, located at the margins of the Choco Block and the SAP, respectively. They are the results of two opposite convergent zones, and collide along the active Uramita strike-slip Fault Zone (UFZ), a suture zone between the Choco Block and the SAP. This area may provide information on the ages of both accretionary wedges, on the tectonic processes responsible for the disappearance of the CP, and on the late formation of the Choco Block. Our results evidence a northward propagating deformation along the Choco Block, miocene or older in the South of the Uraba Gulf, pliocene in the North of the Uraba Gulf, and active along the northern margin of Panama. This deformation is the result of the progressive accretion of Choco Block along the SAP. At the Uraba triple junction, a thick sedimentary sequence was deposited since late Miocene. North verging progradations suggest that sediments came from the drainage of the western cordillera of Colombia by a Paleo-Sinu river and actual Atrato river

  19. Unravelling the influence of orogenic inheritance on the architecture and tectonic evolution of hyper-extended rift systems

    NASA Astrophysics Data System (ADS)

    Chenin, Pauline; Manatschal, Gianreto; Lavier, Luc

    2014-05-01

    The aim of this starting PhD thesis is to determine under what conditions inheritance produced by former orogens influences subsequent rifting, and to unravel the influence of inherited structures and heterogeneities on the architecture and tectonic evolution of hyper-extended rift systems. To complete this task, we map along the Central and North Atlantic margin 1) rift domains; 2) age of the major rift events; and 3) key structure and heterogeneities inherited from the Caledonian and Variscan orogens. We will then study these data in the light of minimal numerical modelling experiments and use them as a basis for designing more comprehensive numerical models for the North Atlantic rifting. In order to map the Atlantic margins, we use gravity, magnetic data, seismic reflection and refraction to identify the necking zone and the continentward limit of the oceanic domain. This allows us to define the proximal domain where continental crust is not or barely thinned on one side, the unequivocal oceanic domain on the other side, and the hyper-extended domain between them. Within the hyper-extended domain, we rely on seismic data (refraction and reflection) to distinguish the area where the crust and the mantle are decoupled from the area where they are coupled, and to identify potential zones with mantle exhumation and/or magmatic additions. Previous studies mapped these domains along Iberia-Newfoundland and Bay of Biscay. The objective of this PhD is to extend this mapping further to the North, along the Irish, UK and Norwegian margins, into domains with polyphase rifting and magmatic additions. One of the goals of this work is to highlight potential correlations between first-order changes in the architecture and/or magmatic evolution of the Atlantic margin and first-order structures and heterogeneities inherited from the Caledonian and/or Variscan orogens. We also aim to assess the importance of inheritance in structuring and controlling the evolution of hyper

  20. Tectonic evolution of a Laramide transverse structural zone: Sweetwater Arch, south central Wyoming

    NASA Astrophysics Data System (ADS)

    Weil, Arlo Brandon; Yonkee, Adolph; Schultz, Mary

    2016-05-01

    Structural, anisotropy of magnetic susceptibility (AMS), and paleomagnetic data record patterns of layer-parallel shortening (LPS), vertical-axis rotation, and regional fault-fold evolution across the Sweetwater Arch, a major west to WNW trending, basement-cored Laramide uplift in Wyoming. The southern arch flank is bounded by a WNW striking reverse fault zone that imbricated basement and cover rocks, the northern flank is bounded by a west striking fault zone with a component of strike-slip and NW trending en echelon folds, and the eastern plunge transitions into an area of multiple-trending faults and folds. Synorogenic strata record major arch uplift from Maastrichtian to Early Eocene time, followed by arch collapse. LPS, with development of systematic minor fault sets and AMS lineations, preceded large-scale folding. LPS directions, estimated from both minor fault and AMS data, were oriented WSW along the northern flank, subparallel to Laramide regional shortening, but were refracted to the SSW along the southern flank, and to the west along the eastern arch plunge. Additional minor faults developed along steep fold limbs during continued shortening, with directions remaining SSW along the southern flank but becoming more variable along the eastern plunge where an increasingly heterogeneous stress field developed as additional faults were activated along basement heterogeneities. Vertical-axis rotation was limited along the arch flanks, whereas the eastern plunge underwent counterclockwise rotation. Deflections in shortening directions were partly related to basement heterogeneities, including weak supracrustal belts on the arch flanks, a strong granitic core, and local reactivation of Precambrian shear zones.

  1. Stable Isotope Paleoaltimetry: Linking Tectonics to the Evolution of Landscapes and Life

    NASA Astrophysics Data System (ADS)

    Mulch, A.; Chamberlain, C. P.

    2015-12-01

    Stable isotope paleoaltimetry exploits systematic changes in the oxygen or hydrogen isotopic composition of precipitation that occur when lifting of moist air masses over topography induces orographic precipitation. Stable isotope-based reconstructions of topography, therefore, have greatly expanded what used to be very sparse global paleoaltimetric information. The topography of mountain ranges and plateaus, however, not only reflects the geodynamic processes that shape the Earth's surface; it also represents a key control for continental moisture transport, atmospheric circulation and the distribution of biomes and biodiversity. The challenge now lies in disentangling the surface uplift component from the impact of long-term climate change on paleoaltimetry records. The robustness of stable isotope paleoaltimetry reconstructions can be greatly enhanced when high-elevation isotope proxy data are referenced against low-elevation records that track climate-modulated oxygen and hydrogen isotopes in precipitation through time. In addition, evaluating the record of precipitation upstream of the orogen reduces commonly encountered complexities such as topographic threshold conditions to atmospheric circulation, variable moisture recharge to the atmosphere through evapotranspiration over the continents or the impact of hemispheric-scale atmospheric teleconnections; all of which may conspire in setting the isotopic composition of precipitation.Here, we highlight some of these challenges a) by using stable isotope paleoaltimetry data from the central Andes to show how differences in oxygen isotopes in precipitation between high and low elevation sites may enhance the robustness of Andean stable isotope paleoaltimetry, and b) by linking a large set of spatially distributed isotope and biological proxy data to evaluate the impact of Palaeogene surface uplift on mammalian evolution in western North America prior and during the Eocene-Oligocene transition.

  2. Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models

    NASA Astrophysics Data System (ADS)

    Armann, Marina; Tackley, Paul J.

    2012-12-01

    Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid and recent resurfacing history. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick crust, inconsistent with observations. Partitioning of heat-producing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature ˜constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. The basalt density inversion below the olivine-perovskite transition causes compositional stratification around 730 km breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature ˜rheological temperature scale lower than TCMB is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start. Core heat flow decreases with time, possibly shutting off the dynamo, particularly in episodic cases.

  3. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Abdelsalam, M.; Ali, K. A.; Bingen, B.; Collins, A. S.; Fowler, A. R.; Ghebreab, W.; Hauzenberger, C. A.; Johnson, P. R.; Kusky, T. M.; Macey, P.; Muhongo, S.; Stern, R. J.; Viola, G.

    2013-10-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of

  4. Influence of intrusive magmatism on Venus' tectonics and long-term thermo-chemical mantle evolution

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Lourenco, D.; Golabek, G.

    2014-04-01

    Here the models of [1] are extended. Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid, recent resurfacing history and surface deformation. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In [1] it was assumed that all magmatism is extrusive, i.e. melt generated in the lithosphere is immediately placed at the surface at the surface temperature, which constitutes the well-known "heatpipe" mode. This leads to a cold, strong crust/lithosphere. It was found that in stagnant lid convection the dominant mode of heat loss is this magmatic heat pipe, which requires massive magmatism and produces very thick, cold crust, inconsistent with observations. Partitioning of heatproducing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values.The basalt density inversion below the olivineperovskite transition causes compositional stratification around 730 km; breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature approximately a rheological temperature scale lower than T_CMB is not reached

  5. Garnet shapes within Kimberlite xenoliths record the tectonic evolution of a cratonic root

    NASA Astrophysics Data System (ADS)

    Michibayashi, K.; Kino, M.; Okamoto, A.; Katayama, I.; Komiya, T.

    2013-12-01

    are then fitted to theoretical curves in the L-R space under conditions of 1000 degree C and for a period of 1 billion years with various differential stresses of less than 0.005 MPa. Okamoto, A. and Michibayashi, K., 2005. Progressive shape evolution of a mineral inclusion under differential stress at high temperature: example of garnet inclusions within a granulite facies from the Lutow-Holm complex, East Antarctica. Journal of Geophysical Research, 110, B11203, doi:10.1029/2004JB003526.

  6. Tectonic evolution of the West Florida Basin, Eastern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Gregg, Andrea Christine

    Basement geometry of the Eastern Gulf of Mexico developed following the breakup of Pangea and the opening of the Gulf of Mexico in Late Triassic time. Nine 2-D pre-stack depth migrated seismic profiles and a structural restoration provide insight into the evolution and development of the southern West Florida Basin, located west of the Florida Escarpment in the Eastern Gulf of Mexico. Seismic reflection profiles reveal basement structures probably developed following a combination of Late Triassic extension and extension and subsequent oceanic crust emplacement in Middle Jurassic time. During Late Triassic rifting, the West Florida Basin developed as a rift graben; however, the graben was later dissected during the Middle Jurassic drift episode. Absence of faulting, syn-rift deposition and sagging in the Lower Cretaceous seismic section indicates that extension and rotation of the Yucatan block must have stopped prior to Cretaceous time. After extension terminated and the Gulf of Mexico reached its modern day configuration, subsidence from lithospheric cooling and sediment loading dominated throughout Cretaceous time. A structural restoration confirms that following Late Triassic rifting, basement topography remains relatively elevated to the south in the West Florida Basin. Subsequent extension and subsidence further dissected the basement allowing for the deposition of Middle and Late Jurassic syn-rift and Cretaceous post-rift sediments. Because of the lack of well control in the West Florida Basin, seismic packages are correlated northward to the northern margin of the West Florida Basin and slope, the Tampa Embayment, and the Apalachicola Basin and southward to the Straits of Florida and Yucatan. Seismic interpretations reveal two syn-rift packages, Triassic-Jurassic (TJ) and Jurassic-Cretaceous (JK), and one post rift package, Early Cretaceous (EK), were deposited prior to the Mid-Cretaceous Sequence Boundary, a basin-wide unconformity that marks the

  7. Tectono-sedimentary events and geodynamic evolution of the Mesozoic and Cenozoic basins of the Alpine Margin, Gulf of Tunis, north-eastern Tunisia offshore

    NASA Astrophysics Data System (ADS)

    Melki, Fetheddine; Zouaghi, Taher; Chelbi, Mohamed Ben; Bédir, Mourad; Zargouni, Fouad

    2010-09-01

    The structural pattern, tectono-sedimentary framework and geodynamic evolution for Mesozoic and Cenozoic deep structures of the Gulf of Tunis (north-eastern Tunisia) are proposed using petroleum well data and a 2-D seismic interpretation. The structural system of the study area is marked by two sets of faults that control the Mesozoic subsidence and inversions during the Paleogene and Neogene times: (i) a NE-SW striking set associated with folds and faults, which have a reverse component; and (ii) a NW-SE striking set active during the Tertiary extension episodes and delineating grabens and subsiding synclines. In order to better characterize the tectono-sedimentary evolution of the Gulf of Tunis structures, seismic data interpretations are compared to stratigraphic and structural data from wells and neighbouring outcrops. The Atlas and external Tell belonged to the southernmost Tethyan margin record a geodynamic evolution including: (i) rifting periods of subsidence and Tethyan oceanic accretions from Triassic until Early Cretaceous: we recognized high subsiding zones (Raja and Carthage domains), less subsiding zones (Gamart domain) and a completely emerged area (Raouad domain); (ii) compressive events during the Cenozoic with relaxation periods of the Oligocene-Aquitanian and Messinian-Early Pliocene. The NW-SE Late Eocene and Tortonian compressive events caused local inversions with sealed and eroded folded structures. During Middle to Late Miocene and Early Pliocene, we have identified depocentre structures corresponding to half-grabens and synclines in the Carthage and Karkouane domains. The north-south contractional events at the end of Early Pliocene and Late Pliocene periods are associated with significant inversion of subsidence and synsedimentary folded structures. Structuring and major tectonic events, recognized in the Gulf of Tunis, are linked to the common geodynamic evolution of the north African and western Mediterranean basins.

  8. The early Paleozoic sedimentary-tectonic evolution of the circum-Mangar areas, Tarim block, NW China: Constraints from integrated detrital records

    NASA Astrophysics Data System (ADS)

    Dong, Shunli; Li, Zhong; Jiang, Lei

    2016-07-01

    The Mangar depression, located in the eastern part of the Tarim basin, had deposited extremely-thick lower Paleozoic sediments, which yields great scientific value and hydrocarbon resource potential. Due to the lack of enough outcrop and core studies, many issues, e.g., early Paleozoic geographical evolution, basin nature and tectonic affinity, are still poorly understood. In this study, we selected circum-Mangar areas (i.e., the South Quruqtagh, Tabei and Tazhong areas), and carried out comprehensive detrital provenance analysis including detrital modal analysis, heavy mineral and trace element analysis, and detrital zircon U-Pb dating on the Middle-Upper Ordovician and Silurian sandstones. The results show that Upper Ordovician-Lower Silurian detrital provenances of the South Quruqtagh and Tabei areas were primarily derived from the intracontinental uplifts in Tarim. Meanwhile, Upper Silurian detrital provenances of the above two areas were mainly derived from the mix of intracontinental uplifts and continental-margin arcs. Dramatic Late Silurian provenance-change suggests the evident tectonic transition of the northern Tarim margin, which is the opening of the South Tianshan back-arc oceanic basin. Combining the previous studies, an integral redefinition model for the Mangar depression has been made. The evolution process of the Mangar depression could be divided into four stages: graben stage (late Neoproterozoic), transitional stage (Cambrian to Middle Ordovician), downwarp stage (Late Ordovician to Early Silurian) and extinction stage (Late Silurian). Hence, the Mangar depression evolved as an aulacogen. Significantly, the evolutional scenario of the Mangar aulacogen was consistent with that of the North Altyn Tagh and the North Qilian, suggesting that the Mangar aulacogen was involved mainly in the Proto-Tethys tectonic realm south to the Tarim block. However, the Late Silurian tectonic activity in the northern Tarim margin did produce massive detrital

  9. The tectonic evolution of the Mid-Atlantic Ridge between 55°55'N and the Bight Transform Fault during the past 6 Ma

    NASA Astrophysics Data System (ADS)

    Benediktsdottir, A.; Hey, R. N.; Martinez, F.; Hoskuldsson, A.

    2014-12-01

    We present a new propagating rift model of the Mid-Atlantic Ridge between 55°55'N and the Bight Transform Fault (BTF) explaining the tectonic history of the area during the past 6 Ma, using marine magnetic anomalies collected in the fall of 2013. The data consist of thirteen flowline parallel lines across the ridge and they show that the accretion across the ridge has not been symmetric. Using Magellan, a new tool to model magnetic anomalies, we obtain a tectonic evolution of the area for the past 6 Ma. The area just south of the BTF (at 0-20 km distance) is characterized by a very large asymmetry in the magnetic data. This asymmetry is most clearly seen within the Brunhes anomaly, which has a big divide in it. Our model suggests that the ridge has shifted twice some 8-12 km to the east within the past 2 Ma resulting from two very rapid rift propagations. We could not determine whether the propagations were to the south or north because of very rapid propagation rates. The tectonic evolution of the area 20-90 km south of the BTF is simpler and the model is more readily understood. The model suggests that a few short lived propagators cause asymmetry in the area. They all, but one, propagate north toward the BTF and all, but one, transfer lithosphere from the Eurasian plate to the North-American plate. Unlike the prominent far reaching (> 100km) propagators just south of Iceland these propagators are short. They play an important role in the tectonic evolution of the ridge and our results suggest that the Mid-Atlantic Ridge in this area is very dynamic.

  10. Geology of the Santa Elena Peninsula, Costa Rica and its implications for the tectonic evolution of the Central America-Caribbean region

    SciTech Connect

    Lew, L.R.

    1985-01-01

    The Santa Elena Peninsula of Costa Rice represents an Aptian to Middle Eocene intraoceanic volcanic arc formed on a basement of serpentinized periodotite. This peridotite was probably part of the oceanic lithosphere formed at a spreading ridge which began to separate South America from North America in pre-Jurassic time. The arc resulted from northward subduction of oceanic crust along one ENE-trending trench about 70 km south of Santa Elena. The first phase of tectonism, arc volcanism, and sedimentation occurred in the area from Aptian to Campanian time. Carbonate bank limestone were deposited on the peridotite, which had been tilted and uplifted along E-W-trending high angle faults. A second volcanic arc developed above the limestone and was active until the Middle Eocene. From the Campanian to the Middle Eocene a forearc basin evolved south of the arc and a backarc basin north of it. A major Middle Eocene tectonic episode was associated with termination of activity of the Santa Elena subduction zone. This involved both thin-skinned deformation and reactivation of the steep basement faults to juxtapose peridotite and Campanian to Middle Eocene sediments. Existing models of the early plate tectonic evolution of the region, postulating initiation of spreading in the Jurassic, and development of a major transform in the Santa Elena area in the Cretaceous, are incompatible with the geology of the Santa Elena area. New models have been formulated genetically relating the structures in the Santa Elena tectonic province to northward subduction.

  11. New insights and questions about the Meso-Cenozoic Tectonic evolution of Eastern Black Sea and Caucasus.

    NASA Astrophysics Data System (ADS)

    Sosson, Marc; Rolland, Yann; Hässig, Marc; Meijers, Maud; Smith, Brigitte; Muller, Carla; Adamia, Shota; Melkonian, Rafael; Kangarli, Talat; Sahakyan, Lilit; Sadradze, Nino; Avagyan, Ara; Galoyan, Ghazar; Alania, Victor; Enukidze, Onice; Sheremet-Korniyenko, Yevgeniya; Yegorova, Tamara

    2014-05-01

    Since last decade a lot of new field researches (supported by MEBE and DARIUS programmes) were carried out in order to clarify the tectonic evolution of the South Caucasus and Eastern Black Sea regions. A summary of these improvements are as following: 1. Evidence of only one suture zone in the Lesser Caucasus: the Sevan-Akera suture zone as the eastward continuity of the Izmir-Ankara-Erzincan one. 2. Timing and modalities of the Upper Cretaceous obduction process of the Sevan-Akera back-arc basin. 3. Paleolatitude reconstruction of the Taurides-Anatolides-South Armenia microplate (TASAM) since the Late Cretaceous 4. Paleocene to Miocene tectonic evolution of the collision zone between Eurasia and the TASAM. 5. Structures and propagation of the Lesser Caucasus and Greater Causasus foreland basins from Paleocene to Miocene. 6. Structures of the inverted Paleocene-Eocene Adjara-Trialeti basin of the Eurasian margin and timing of deformations from Lesser Caucasus to Greater Caucasus. 7. New stratigraphic data from the Crimea Mountain which argues for a Lower Cretaceous rifting of the Eastern Black Sea. According to aforementioned results and previous studies, this widespread zone (from the Eastern Black Sea to the Lesser Caucasus) appears act as a large puzzle of heterogeneous lithospheres (continental, oceanic, arc, back-arc basins) since the Early Cretaceous. This is probably why this area has differently reacted in time and space to the northward collision of the TASAM with Eurasia since the Late Cretaceous and then of Arabian plate since the Oligo-Miocene. It seems that some lithospheres which have cold mantellic behavior (especially the Black Sea) react as rigid blocks, while others with a continental origin, reheated by magmatism, (as the Taurides-Anatolides) were extruded to the west or bended as an orocline (as the Lesser Caucasus, the Pontides). This is why some main questions remain, are not solved and are still debated. 1. The continuity of main structures

  12. Detrital zircon age populations from the Moine Supergroup, Scotland, and their implications for tectonic evolution

    NASA Astrophysics Data System (ADS)

    Kindgren, Kelly; Steltenpohl, Mark; Strachan, Rob; Law, Rick; Cawood, Peter; Schwartz, Joshua

    2016-04-01

    absence of detrital grains younger than ~1050 Ma in the lower unit suggests evolution in the nature of rock units exposed in the source and/or a stratigraphic break between the upper and lower units of the succession. Furthermore, the age profile of the lower unit is consistent with, but not limited to, the interpretation that it correlates with the Torridon Group of the foreland, which has been argued to represent a foreland basin to the end Mesoproterozoic Grenville orogenic belt.

  13. Rheological control on the tectonic evolution of a continental suture zone: the Variscan example from NW Iberia (Spain)

    NASA Astrophysics Data System (ADS)

    Díez Fernández, Rubén; Foster, David A.; Gómez Barreiro, Juan; Alonso-García, Montserrat

    2013-07-01

    The Variscan continental suture zone exposed in NW Iberia is examined to uncover the long-lived rheological control exerted by the strata deposited over the external parts of Gondwana on its geodynamic evolution. The suture occurs within a set of allochthonous terranes whose limits were taken as domain boundaries to interpret the Variscan stacking of Paleozoic continental domains and retrodeform the resulting nappe pile. The suture zone formed due to closure of ocean basins located between Gondwana and Laurussia during the Late Paleozoic and consists of relics of oceanic and transitional crust. The suture zone exhibits a tabular to lens shape due to repeated tectonic events dominated by non-coaxial deformation (thrusts and low-angle normal faults). Thrusting and normal faulting also involved the margins of the continents bounding the suture. The structure of the continental blocks, however, is dominated by folds, particularly large nappe folds with pronounced superimposed flattening. The upper part of the basal allochthonous units comprises a rheologically incompetent domain below the suture zone. This domain is typified by the carbonaceous-rich strata, which are probably Ordovician-Silurian sediments based on U-Pb detrital zircon populations. The rheology of this layer determined the location of the first accretionary thrust that initiated the Late Devonian subduction of the Gondwana margin below the suture zone. By favoring fault development, the upper sequence of the basal allochthonous units as a whole influenced the exhumation of deep-seated continental crust, the transference of the suture zone over Gondwana, and the re-equilibration of the resulting overthickened crust.

  14. Depositional Record of the Bagua Basin, Northern Peru: Implications for Climate and Tectonic Evolution of Tropical South America

    NASA Astrophysics Data System (ADS)

    Moreno, F.; George, S. W. M.; Williams, L. A.; Horton, B. K.; Garzione, C. N.

    2015-12-01

    The Andes Mountains exert critical controls on the climate, hydrology, and biodiversity of South America. The Bagua Basin, a low elevation (400-600 m) intermontane basin in northern Peru, offers a unique opportunity to study the ecological, climatic, and structural evolution of the western topographic boundary of the Amazonian foreland. Situated between the Marañon fold-thrust belt of the Western Cordillera and basement block uplifts of the Eastern Cordillera, the Bagua region contains a protracted, semi-continuous record of Triassic through Pleistocene sedimentation. Whereas Triassic-Cretaceous marine deposits were potentially related to extension and regional thermal subsidence, a Paleocene-Eocene shift to shallow marine and fluvial systems marks the onset of foreland basin conditions. Oligocene-Miocene sedimentation corresponds to a braided-meandering fluvial system with exceptional development of paleosols. In this study, we use new detrital zircon U-Pb geochronologic and oxygen stable isotopic datasets to establish a chronology of pre-Andean and Andean processes within the Bagua Basin. Detrital zircon geochronology provides constraints on when the Western and Eastern cordilleras shed sediments into the basin. Syndepositional zircons within Eocene, Oligocene and Miocene strata provide key age control for a previously poorly constrained depositional chronology. Preliminary results suggest a dramatic provenance shift in which Paleocene deposits contain almost exclusively cratonic populations (500-1600 Ma) whereas Eocene deposits show a mix of syndepositional zircons from the magmatic arc, recycled Mesozoic zircons, and cratonic zircon populations. Oxygen stable isotopes (δ18O) of carbonate nodules from Neogene paleosols will help elucidate when the Eastern Cordillera became an orographic barrier intercepting moisture from the Amazon basin to the east. Together, these records will help uncover the history of tectonics and climate interaction in tropical South

  15. Evolution of terrace risers along the upper Rhine graben inferred from morphologic dating methods: evidence of climatic and tectonic forcing

    NASA Astrophysics Data System (ADS)

    Nivière, B.; Marquis, Guy

    2000-06-01

    We show that morphologic dating techniques that have been applied successfully in arid and semi-arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments. We have attempted two morphologic approaches, based on diffusion, to relate the present-day shape of an abandoned terrace riser to its age. The first assumes a model of scarp degradation based on a diffusive process (the D method). The second evaluates the state of scarp degradation using the slope distribution (the SD method) along a topographic profile. By using a manmade scarp of known age, we have obtained a mass diffusivity close to 1.4m2ka-1 when the area experiences a temperate climate characterized by a continuous vegetation cover. However, this value decreases during glacial episodes, probably on account of the permafrost. Even though the SD method requires an age correction that can be easily computed, only this method reveals that at several profiles a later scarp reactivation event has occurred. Indeed, along several profiles, the slope distribution was best fitted by two offset Gaussian curves, suggesting that some scarps have undergone a complex evolution that cannot be modelled with a single diffusive process. This scarp reactivation may correspond to a new incisive episode and allows one to estimate the vertical incision rate along the terrace riser. Applied to a Wurmian terrace riser of the upper Rhine valley (NE France), this approach reveals that the vertical incision rate ranges from 0.2 to 0.85mmyr-1 between 35 and 15ka and that the terrace bevelling occurred during two episodes related to climatic forcing. Moreover, we can identify a component of tectonic forcing evidenced by an increase to the north of vertical incision rate and Rhine stream-power. Another major result is showing that this terrace riser is not isochronous along its strike and that younger portions result from lateral incision of a 30ka pre-existing scarp.

  16. Longitudinal evolution of the tectonic style along the Cyprus Arc, northern margin of the Levant and Herodotus Basins

    NASA Astrophysics Data System (ADS)

    Symeou, Vasilis; Homberg, Catherine; Nader, Fadi; Darnault, Romain; Lecomte, Jean-Claude

    2016-04-01

    The Levant Basin is bounded to the north by the Cyprus Arc zone which was created by the northward movement of the African plate with respect to the Eurasian plate since Late Cretaceous time. The westward movement of the Anatolian micro-plate since Late Miocene created an additional strike-slip component along the plate boundary. The main objective of this contribution is to portray the structural architecture and features offshore Cyprus by analyzing available 2D seismic data in order to investigate the transition in tectonic style from compression to strike slip along the Cyprus Arc zone. We identified three different crustal domains offshore Cyprus that are from east to west: the eastern domain which belongs to the Levant Basin, the South-central domain which includes the Eratosthenes Seamount, and the South-West domain of Cyprus which corresponds to the Herodotus Basin. In the Levant Basin, the sequences identified are from Base Pliocene extending until the Senonian unconformity. The same sequences in the Cyprus Basin are offset and less thick due to the movement of the Latakia Ridge, which is identified as a steeply dipping sub-vertical fault on our data. In the central domain, the horizons identified on the Eratosthenes Seamount indicate that the Seamount is a Mesozoic carbonate platform covered by thin Miocene/Plio-Pleistocene sediments. A subdivision of the sedimentary sequence in the Herodotus Basin is proposed down to the Paleocene-Eocene basis. A major change in the structural style of the deformation is observed form west to east. Whereas the Levant Basin is almost undeformed south of the Latakia Ridge, several structures were mapped in the central domain, like flexural basin, pop-up structures and back-thrusts. South-verging thrusts were also, identified in the Cyprus Basin. All these structures show a Pliocene activity. Our data suggest that the heterogeneity of the crustal structure played a major role in the longitudinal evolution of the plate

  17. Late Cretaceous ARC to MORB compositional switch in the Quebradagrande Complex, Colombian Andes: understanding the long term tectonic evolution of a magmatic arc.

    NASA Astrophysics Data System (ADS)

    Jaramillo, J. S.; Cardona, A.; Zapata, S.; Valencia, V.

    2014-12-01

    The spatial and compositional characters of arc rocks are sensible markers of the tectonic changes experienced by convergent margins and therefore provide a fundamental view to the continuous tectonic evolution of active margins. The Early to Late Cretaceous tectonic evolution of the Northern Andes have been related to the growth and accretion of different continental and oceanic arc systems that were juxtaposed at the beginning of the Andean Orogeny in the Late Cretaceous. The Quebradagrande Complex is a tectonostratigraphic unit made of mafic to intermediate plutonic rocks, basic to intermediate volcanic flows and associated marine sedimentary rocks that have been related to a single Albian arc or back-arc environment that discontinuously outcrops along the western margin of the Central Cordillera of Colombia. New field, geochronological and geochemical data from the plutonic and volcanic rocks of the Quebradagrande complex shows that the pre-90-80 Ma volcanic arc rocks are intruded by ca. 90 Ma pyroxene gabbroic and hornblende dioritic plutons with medium to pegmatitic grain size characterized by a contrasting MORB-type signature. We related the compositional change to a transient modification of the convergent margin system, where and extensional roll-back related configuration or the subduction of an oceanic ridge allows the flux of the astenospheric mantle. This continental magmatic arc was subsequently deformed due to the collision and accretion of an allocthonous oceanic arc that migrate from the southeast Pacific at the beginning of the Andean orogeny.

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

    SciTech Connect

    Elmi, S.

    1988-08-01

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

  19. The Evolution of Deformation-Induced Grain-Boundary Porosity and Dynamic Permeability in Crustal Fault Zones: Insights From the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Sauer, K. M.; Toy, V.

    2015-12-01

    Fluids and minor phases have an important influence on the bulk rheology of a deforming rock mass, but they are not uniformly distributed at any scale within fault zones. Additionally, exhumed ductile shear zones show little interconnected porosity or static permeability, requiring a dynamic process at depth to allow fluids to access the deforming rock mass. It was recently recognized that reactive fluids interact with high-strain sites to generate cavities on quartz grain boundaries, increasing the grain-scale porosity and dynamic permeability of the rock and allowing for additional fluids to infiltrate the shear zone along interlinking cavities, stimulating further reaction and cavitation. Grain-boundary cavities and fine-grained secondary phases impede grain-boundary mobility and cause a transition in deformation mechanisms from grain-size insensitive dislocation creep to grain-size sensitive creep, which is recognized as a weakening mechanism that promotes strain localisation. At present, it is unclear how the distribution of grain-boundary pores within fault rocks reflects the bulk mineralogy and phase arrangement, which is a function of shear strain. We have used micro-computed x-ray tomography (μ-CT), SEM imaging, and EDS analyses to examine how the distribution of grain-boundary pores varies in relation to the arrangement of secondary phases in exhumed protomylonites, mylonites, and ultramylonites within the actively-deforming Alpine Fault zone, and in samples acquired from the Deep Fault Drilling Project (DFDP). Additionally, EBSD is coupled with µ-CT and EDS analyses to characterise the evolution of microstructures in three dimensions across a finite strain gradient. Here we examine the relationship and competition between grain-boundary cavitation and microstructural processes during deformation in a high-strain shear zone, and discuss the implications of these grain-scale deformation processes on strain localisation and continental fault zone dynamics.

  20. Seismic signature of the Alpine indentation, evidence from the Eastern Alps

    PubMed Central

    Bianchi, I.; Bokelmann, G.

    2014-01-01

    The type of collision between the European and the Adriatic plates in the easternmost Alps is one of the most interesting questions regarding the Alpine evolution. Tectonic processes such as compression, escape and uplift are interconnected and shape this area. We can understand these ongoing processes better, if we look for signs of the deformation within the Earth's deep crust of the region. By collecting records from permanent and temporary seismic networks, we assemble a receiver function dataset, and analyze it with the aim of giving new insights on the structure of the lower crust and of the shallow portion of the upper mantle, which are inaccessible to direct observation. Imaging is accomplished by performing common conversion depth stacks along three profiles that crosscut the Eastern Alpine orogen, and allow isolating features consistently persistent in the area. The study shows a moderately flat Moho underlying a seismically anisotropic middle-lower crust from the Southern Alps to the Austroalpine nappes. The spatial progression of anisotropic axes reflects the orientation of the relative motion and of the stress field detected at the surface. These observations suggest that distributed deformation is due to the effect of the Alpine indentation. In the shallow upper mantle right below the Moho interface, a further anisotropic layer is recognized, extended from the Bohemian Massif to the Northern Calcareous Alps. PMID:26525181

  1. The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea.

    PubMed

    Matenco, Liviu; Munteanu, Ioan; ter Borgh, Marten; Stanica, Adrian; Tilita, Marius; Lericolais, Gilles; Dinu, Corneliu; Oaie, Gheorghe

    2016-02-01

    Understanding the natural evolution of a river-delta-sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River-western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during

  2. Alpine geodynamic evolution of passive and active continental margin sequences in the Tauern Window (eastern Alps, Austria, Italy): a review

    NASA Astrophysics Data System (ADS)

    Kurz, W.; Neubauer, F.; Genser, J.; Dachs, E.

    The Penninic oceanic sequence of the Glockner nappe and the foot-wall Penninic continental margin sequences exposed within the Tauern Window (eastern Alps) have been investigated in detail. Field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units. Volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the Variscan orogeny, to its disintegration associated with subsidence and rifting in the Triassic and Jurassic, the formation of the Glockner oceanic basin and its consumption during the Upper Cretaceous and the Paleogene. These units are incorporated into a nappe stack that was formed during the collision between a Penninic Zentralgneis block in the north and a southern Austroalpine block. The Venediger nappe and the Storz nappe are characterized by metamorphic Jurassic shelf deposits (Hochstegen group) and Cretaceous flysch sediments (Kaserer and Murtörl groups), the Eclogite Zone and the Rote Wand-Modereck nappe comprise Permian to Triassic clastic sequences (Wustkogel quartzite) and remnants of platform carbonates (Seidlwinkl group) as well as Jurassic volcanoclastic material and rift sediments (Brennkogel facies), covered by Cretaceous flyschoid sequences. Nappe stacking was contemporaneous to and postdated subduction-related (high-pressure) eclogite and blueschist facies metamorphism. Emplacement of the eclogite-bearing units of the Eclogite zone and the Glockner nappe onto Penninic continental units (Zentralgneis block) occurred subsequent to eclogite facies metamorphism. The Eclogite zone, a former extended continental margin, was subsequently overridden by a pile of basement-cover nappes (Rote Wand-Modereck nappe) along a ductile out-of-sequence thrust. Low-angle normal faults that have developed during the Jurassic extensional phase might have been inverted during nappe emplacement.

  3. Tectonic evolution and crustal structure of the central Indonesian region from geology, gravity and other geophysical data

    NASA Astrophysics Data System (ADS)

    Guntoro, Agus

    Bone Bay, the Makassar Strait, the Central Java Sea, the East Java Sea and the Flores Sea provinces. Each province is examined and their stratigraphy, structural and tectonic styles correlated in order to have a complete understanding of their evolution. Variations in gravity values and models demonstrate that the continental crust in the CIR was attenuated by subduction roll-back and then subjected to rifting by extensional forces. The extension in the Makassar Strait, Central Java Sea and East Java Sea took place in the Eocene, forming marginal basins. Bone Bay opened due to collision between the Banggai- Sula microcontinent and Sulawesi in the Middle Miocene and was followed by clockwise rotation of Java, Sumbawa and Flores which cause the opening of the Flores Sea. The present configuration of the CIR is influenced by the collision between the Indo-Australian Plate and the Banda-Sunda arcs.

  4. Neoproterozoic tectonic evolution of the Jebel Saghro and Bou Azzer - El Graara inliers, eastern and central Anti-Atlas, Morocco

    USGS Publications Warehouse

    Walsh, Gregory J.; Aleinikoff, John N.; Harrison, Richard W.; Burton, William C.; Quick, James E.; Benziane, Foudad; Yazidi, Abdelaziz; Saadane, Abderrahim

    2012-01-01

    New mapping, geochemistry, and 17 U–Pb SHRIMP zircon ages from rocks of the Sirwa, Bou Azzer–El Graara, and Jebel Saghro inliers constrain the Neoproterozoic evolution of the eastern Anti-Atlas during Pan-African orogenesis. In the Sirwa inlier, Tonian quartzite from the pre Pan-African passive margin deposits of the Mimount Formation contains detrital zircon derived entirely from the West African Craton (WAC), with most grains yielding Eburnean Paleoproterozoic ages of about 2050 Ma. Cryogenian Pan-African orogenic activity (PA1) from about 760 to 660 Ma included northward-dipping subduction to produce a volcanic arc, followed by ophiolite obduction onto the WAC. In the Bou Azzer–El Graara inlier, calc-alkaline granodiorite and quartz diorite, dated at 650–646 Ma, are syn- to post-tectonic with respect to the second period of Pan-African orogenesis (PA2), arc-continent accretion, and related greenschist facies metamorphism. Slab break-off and lithospheric delimination may have provided the source for the supra-subduction calc-alkaline plutons. At about 646 Ma, quartz diorite intruded the Tiddiline formation placing an upper limit on molassic deposition. Widespread Ediacaran high-K calc-alkaline to shoshonitic plutonism and volcanism during the final stage of Pan-African orogenesis (PA3) occurred in a setting related to either modification of the margin of the WAC or formation of a continental volcanic arc above a short-lived southward-dipping subduction zone. In the Saghro inlier, eight plutonic rocks yield ages ranging from about 588 to 556 Ma. Sampled plutonic rocks previously considered to be Cryogenian yielded Ediacaran ages. Peraluminous rhyolitic volcanic rocks in the lower part of the Ouarzazate Supergroup, including ash-flow tuffs of the Oued Dar’a caldera, yield ages between about 574 and 571 Ma. The Oued Dar’a caldera developed in a pull-apart graben produced by a left-step in a northeast-trending, left-lateral strike-slip fault zone, and

  5. Kinematic Evolution of fold-and-thrust Belts in the Yubei Area: Implications for the Tectonic Events of Ordovician at the Southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    As a response to tecto-orogenic processes of the South Altun and the West Kunlun (Monlar P, 1975; He Bizhu, 2011), early Paleozoic tectonic evolution of the southern Tarim craton was distinctively one of the extensions and was followed by compression (Morris W.Leighton, 1990; Gao Zhiqian, 2015). From the late Ordovician, the Yubei area developed distinctively NE-SW trending fold-and-thrust belts in rows which were eroded and deformed through multiphase tectonic movement (Dengfa He, 2007), with similarities and dissimilarities between each other rows in many aspects, at the Southern Tarim inner basin (Fig. 1). The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation (Brown LF, 1979). In this contribution, based on geophysical log, core and 2D/3D seismic data, we constructed its tectonic geometry morphology, controlled by detailed chronostratigraphic framework. According to the fault-related fold theory, rows of asymmetric fault-propagation folds grew in the Yubei area during the late Caledonian period, with the evidence of interpreted growth strata from the high resolution 3D seismic data (Suppe J et al., 1990). That intercontinental tecto-orogenic events from southern Tarim basin, leading to the transformation of its margins, affected inner basin at that time, modified the basin into the Tarim metacraton (Jean-Paul Liégeois, 2013; Zieglar P.A., 1998). Correlating the four tectonic groups of the identified with the axis variation of strata and fold amplitude distribution showed that fault evolution progressed in several superimposed stages: Precambrian, late Ordovician to early Carboniferous (Zhao Zongju, 2009), Carboniferous to Permian, Cenozoic. Analyzing the sedimentary development and structure evolution the tectonic paleo-geographic setting is reconstructed, providing

  6. Tectonic and deformation history of the Gyeonggi Massif in and around the Hongcheon area, and its implications in the tectonic evolution of the North China Craton

    NASA Astrophysics Data System (ADS)

    Yengkhom, Kesorjit S.; Lee, Byung Choon; Oh, Chang Whan; Yi, Kee Wook; Kang, Ji Hoon

    2015-04-01

    The Gyeonggi Massif (GM) in South Korea is considered to be a part of the North China Craton. The Precambrian rocks of the GM in and around the Hongcheon area, South Korea, consist of the Yongduri Gneiss Complex (YGC), Euiam Group (EG) and Euiam Gneiss Complex (EGC). The YGC and EG composed mainly of partially migmatised metasedimentary rocks and the EGC is Paleoproterozoic intrusive rock that intruded the EG. At least three major folding (F1, F2 & F3), two-stage ductile shearing and three-stages of metamorphic events (M1, M2 & M3) occurred in the study area. The F1 folds are extremely drawn out, isoclinal, intrafolial folds and have Class 2 to Class 1C geometry. The F1 folds and regional S1 foliation in the YGC and EG are results of the E-W compression during the D1 deformation. Ductile shearing in the southern part of the EG is marked by the Palbongsan Shear Zone that indicates top-to-the SW sheared movement during syn to post-F1 folding. The F2 folds are open to tight, SW plunging and inclined folds, and have Class 1A to 1C geometry. The F2 folding and subsequent NNE thrusting along multiple ductile shear zones parallel to S2 planar fabrics are results of the D2 deformation due to N-S progressive shortening. The D3 deformation was coaxial with the D1 deformation, leading to the development of the F3 kink bands in the mylonite zones. The SHRIMP U-Pb detrital zircon ages from quartzite and banded gneisses in the EG indicate that the sedimentation in the Chunseong basins began after ca. 2094 Ma. The banded gneisses yield M1 metamorphic age of 1917-1925 Ma. However ca.1867-1883 Ma, M2 metamorphism previously reported from the YGC is absent or weakly preserved in the EG representing that the M2 metamorphism was not strong enough to form new zircon in the EG. The igneous zircons form augen gneisses in the EGC yield intrusion age of ca. 1867-1881 Ma and the geochemistries of the EGC gneisses show post-collision tectonic origin. The D1deformation observed in the YGC and

  7. Flower evolution of alpine forbs in the open top chambers (OTCs) from the Qinghai-Tibet Plateau.

    PubMed

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

    2015-01-01

    Effects of global changes on biodiversity have been paid more and more attention world widely, and the open top chambers (OTCs) are the most common tools to study the effects of climatic warming on plant diversity. However, it remains unclear how flowers evolve under environmental changes, which could help us to understand the changes of plant diversity in the OTCs. We compared the insect diversity and pollen:ovule (P/O) ratio of eight outcrossing species with different life histories inside and outside the OTCs on the Qinghai-Tibet Plateau, to examine the effects induced by OTCs on the evolution of floral traits. In the OTCs, P/O ratio decreased in annuals, but increased in perennials, indicating an overall trend toward selfing in annuals. We found that the insect diversity differed significantly inside and outside the OTCS, with decreases of dipteran insects and bees. We concluded that changes of P/O ratio in the studied plant species might result from pollination failure, which might be the results of mismatch between flowering time and pollinator activities. We also suggested annuals might be in a more extinction risk than perennials in OTCs, if strong inbreeding depression occurs in these annual outcrossing plants.

  8. Internal structure and current evolution of very small debris-covered glacier systems located in alpine permafrost environments

    NASA Astrophysics Data System (ADS)

    Bosson, Jean-Baptiste; Lambiel, Christophe

    2016-04-01

    This contribution explores the internal structure of very small debris-covered glacier systems located in permafrost environments and their current dynamical responses to short-term climatic variations. Three systems were investigated with electrical resistivity tomography and dGPS monitoring over a 3-year period. Five distinct sectors are highlighted in each system: firn and bare-ice glacier, debris-covered glacier, heavily debris-covered glacier of low activity, rock glacier and ice-free debris. Decimetric to metric movements, related to ice ablation, internal deformation and basal sliding affect the glacial zones, which are mainly active in summer. Conversely, surface lowering is close to zero (-0.04 m yr-1) in the rock glaciers. Here, a constant and slow internal deformation was observed (c. 0.2 m yr-1). Thus, these systems are affected by both direct and high magnitude responses and delayed and attenuated responses to climatic variations. This differential evolution appears mainly controlled by (1) the proportion of ice, debris and the presence of water in the ground, and (2) the thickness of the superficial debris layer.

  9. Structural Framework of the Sub-Himalaya and its tectonic evolution along Kameng river section: Arunachal Pradesh, India

    NASA Astrophysics Data System (ADS)

    Goswami, T.; Bezbaruah, D.; Sarmah, R. K.

    2012-04-01

    The structural style or architecture of the Neogene-Quaternary foreland basin is studied in the Kameng River section of Arunachal Pradesh. The Kimi, Dafla-Subansiri, and Kimin formations correspond to Lower, Middle and Upper Siwaliks. The outcrop scale structures from the Main Boundary Thrust (MBT) towards S shows an overall ramp and flat geometry. The intervening strata between two parallel thrust faults (roof thrust and floor thrust) are sub-parallel. The individual subsidiary faults in imbricate fashion (horses) occur as planar units with straight sides. These duplex structures are significant manifestation of the processes involved in the internal domain of the Siwalik rocks and they represent the mechanism of the slip transfer processes from one glide horizon at depth to another at shallower depth. This process of slip transfer and formation of horses are responsible for the formation of structural thickening, duplex growth and mass addition to the moving thrust complex. In the present area the Siwalik strata showing duplex structures have undergone structural thickness in their internal domain mainly in Dafla formation. The lithology in the foreland basin dominantly composed of the sandstones (Greywacke and lithic -arenite), siltstone, claystone, carbonaceous shale, boulder beds in the upper part. In the microscopic scale, the lithological response in the structural development is well documented as pressure solution seams, elongated quartz and feldspar grains, bent micas, kinked biotites, strained quartz grains, healed grains, and micro-fractures. The basement asperities play a significant role as the moving thrust front produced a major lateral ramp. The differential movement of the mountain front on both sides of the ramp is visible in the field as the mountain front of the western part of the Kameng River move more southeastward compared to the eastern part. The tectonic evolution of the area initiated with the development of the MBT, which resulted in

  10. Tectonic vs. gravitational morphostructures in the central Eastern Alps (Italy): Constraints on the recent evolution of the mountain range

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

    Deep-seated gravitational slope deformations (DSGSDs) influence landscape development in tectonically active mountain ranges. Nevertheless, the relationships among tectonics, DSGSDs, and topography are poorly known. In this paper, the distribution of DSGSDs and their relationships with tectonic structures and active processes, surface processes, and topography were investigated at different scales. Over 100 DSGSDs were mapped in a 5000 km 2 sector of the central Eastern Alps between the Valtellina, Engadine and Venosta valleys. Detailed lineament mapping was carried out by photo-interpretation in a smaller area (about 750 km 2) including the upper Valtellina and Val Venosta. Fault populations were also analysed in the field and their mechanisms unravelled, allowing to identify different structural stages, the youngest being consistent with the regional pattern of the ongoing crustal deformation. Finally, four DSGSD examples have been investigated in detail by geological and 2D geomechanical modelling. DSGSDs affect more than 10% of the study area, and mainly cluster in areas where anisotropic fractured rock mass and high local relief occur. Their onset and development is subjected to a strong passive control by mesoscopic and major tectonic features, including regional nappe boundaries as well as NW-SE, N-S and NE-SW trending recent brittle structures. The kinematic consistency between these structures and the pattern of seismicity suggests that active tectonics may force DSGSDs, although field evidence and numerical models indicate slope debuttressing related to deglaciation as a primary triggering mechanism.

  11. A kinematic model for Afar Depression lithospheric thinning and its implications for hominid evolution: an exercise in plate-tectonic paleoanthropology

    NASA Astrophysics Data System (ADS)

    Redfield, T.; Often, M.; Wheeler, W. H.

    2002-12-01

    We present a detailed Nubia-Arabia-Somalia (NU-AR-SOM) kinematic reconstruction based on magnetic sea floor isochrons in the Gulf of Aden and Red Sea and piercing points along the Red Sea margins. The reconstruction is combined with digital topographic and depth-to-Moho data to constrain in 4D the Late Oligocene to present-day evolution of the Afar supra-Moho crust. Opposite end-member models for crustal evolution are described. We conclude that less than 20% of the present-day Afar supra-Moho crust was constructed by magmatic processes such as diking and underplating. The reconstructions indicate that the greater percentage of crustal thinning (extension) occurred before 6.2 Ma. We model the thinning of the effective elastic lithosphere that accompanied extension, and show that the regional-scale topographic development of the Afar depression was virtually complete by Mid Pliocene time. The plate-tectonic model has paleoanthropological implications. Prior to 6.2 Ma the proximal positions of NU-SOM, AR, and the Danakil block suggest subaerial conditions prevailed between Yemen and Ethiopia. Uninhibited Africa-Eurasia faunal exchange through Afar and Arabia (corroborated by isotopic and paleontologic data) was tectonically permissible until the time of the earliest hominids. Continued stretching caused the Afar land bridge(s) to disappear during Early to Mid Pliocene time. Primitive hominid populations living within the Afar Depression became isolated from AR sometime before ~3.2 Ma. With the plateau becoming less habitable due to long-term Late Neogene cooling, hominids that remained in the Afar Depression were required to adapt to a smaller range that was effectively bounded by the already well-developed NU-SOM escarpments and the newly opened Straits of Bab el Mandeb. The combination of high quality habitat,topographic confinement, and a gradual (tectonic) reduction in range, exacerbated by potentially severe fluctuations in local climate (well documented by land

  12. Early Paleozoic magmatic history of central Inner Mongolia, China: implications for the tectonic evolution of the Southeast Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Wu, Chen; Liu, Changfeng; Zhu, Yan; Zhou, Zhiguang; Jiang, Tian; Liu, Wencan; Li, Hongying; Wu, Chu; Ye, Baoying

    2016-07-01

    To provide insights into the Early Paleozoic tectonic evolution of the southern portion of the long-lived Central Asian Orogenic Belt, we have conducted major and trace element analyses and zircon U-Pb dating of granitoid samples from central Inner Mongolia. Our study area covers three pre-Mesozoic tectonic units from north to south: the Wenduermiao subduction-accretionary complex, the Bainaimiao magmatic belt, and the northern margin of the North China craton. Our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units. Accordingly, we suggest that the Wenduermiao subduction-accretionary complex developed in the Middle Cambrian-Late Silurian (509-421 Ma), comprising of coeval oceanic crust, arc magmatism, and forearc deposits. The Bainaimiao continental arc was developed during the Late Cambrian to Early Silurian (501-437 Ma), which superposed on the basement with the affinity of the North China craton. The back-arc basin opened prior to Early Silurian and lasted to the Late Silurian, which is slightly younger than Bainaimiao island arc. The Wenduermiao Ocean, between the Wenduermiao subduction-accretionary complex and the Bainaimiao continental arc, existed in Early Paleozoic.

  13. Implications for the tectonic transition zone of active orogeny in Hoping drainage basin, by landscape evolution at the multi-temporal timescale

    NASA Astrophysics Data System (ADS)

    Chang, Q.; Chen, R. F.; Lin, W.; Hsieh, P. S.

    2015-12-01

    In an actively orogeny the landscape are transient state of disequilibrium in response to climatic and tectonic inputs. At the catchment scale, sensitivity of river systems plays an important role in landscape evolution. Hoping drainage basin is located at the tectonic transition zone in the north-eastern Taiwan, where the behavior of Philippine Sea plate switches from overriding above the east-dipping Eurasian Continental plate to northward subducting under the Ryukyu arc. However, extensive deep-seated landslides, debris flow, and numerous large alluvial terraces can be observed, suggesting strong surface processes in this watershed. This effect on regional climate fundamentally changed the landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. In this study we review the morphological evidence from multi-temporal timescale, including in-situ cosmogenic nuclides denudation rate and suspension load data, coupled with the analysis of the longitudinal profiles. The main goal of this study is to compare Holocene erosion rates with thermochronology and radiometric dating of river terraces to investigate the erosion history of Hoping area. The result shows that short-term erosion rate is around twice as large as the long-term denudation rate, which might due to the climate-driven erosion events such as typhoon-induced landslide. We've also mapped detail morphological features by using the high-resolution LiDAR image, which help us to identify not only the landslide but also tectonic features such as lineation, fault scarps, and fracture zones. The tectonic surface features and field investigation results show that the drainage basin is highly fractured, suggesting that even though the vertical tectonic activity rate is small, the horizontal shortening influenced by both southward opening of the back-arc Okinawa trough and the north-western collision in this area is significant. This might cause the reducing in rock strength

  14. The transition from Alboran to Algerian basins (Western Mediterranean Sea): Chronostratigraphy, deep crustal structure and tectonic evolution at the rear of a narrow slab rollback system

    NASA Astrophysics Data System (ADS)

    Medaouri, Mourad; Déverchère, Jacques; Graindorge, David; Bracene, Rabah; Badji, Rabie; Ouabadi, Aziouz; Yelles-Chaouche, Karim; Bendiab, Fethi

    2014-07-01

    The eastern Alboran basin and its transition to the Algerian basin is a key area in the Mediterranean realm where controversial kinematic and geodynamical models are proposed. Models imply striking differences regarding the nature of the crust, the prevalence of brittle faulting and ductile shear, the origin of magmatism, the style of Miocene deformation and the driving mechanisms of the Alboran plate kinematics. Combining a new chronostratigraphic chart of the Alboran and Algerian basins based on the Habibas (HBB-1) core drill, deep seismic sections striking WSW-ENE and SSE-NNW, and potential field data, we re-assess the tectonic evolution that controlled the sedimentation and basement deformation of the westernmost limit of the Algerian basin and its transition with the Alboran domain. A WSW-directed extensional tectonic phase has shaped a stretched continental crust with typical tilted blocks along ∼100 km from Burdigalian to Tortonian times, which is assumed to result from the WSW-directed migration of the Alboran block driven by a narrow slab rollback. In the Algerian basin, this event was followed by the emplacement of an oceanic-type crust. Potential field signatures of the deep basin as well as geometrical correlations with onland outcrops of inner zones suggest a minimum WSW-directed displacement of the Alboran terrane of ∼200 km. At the southern foot of the Algerian basin, the continent-ocean transition is sharp and may result from the westward propagation of a slab tear at depth, forming two segments of STEP (Subduction-Transform Edge Propagator) margins. Our results support models of intense shear tractions at the base of an overriding plate governed by slab rollback-induced mantle flow. Finally, Messinian salt tectonics affected overlying deposits until today. A late Tortonian to Quaternary dominantly transpressive tectonic episode linked to the Africa-Iberia convergence post-dates previous events, deforming the whole margin.

  15. Regional models of the upper mantle structure in the greater Alpine area

    NASA Astrophysics Data System (ADS)

    Plomerova, J.; Babuska, V.; Vecsey, L.; Munzarova, H.; Karousova, H.

    2012-04-01

    the Alpine area requires to install sufficiently dense and uniformly spaced network of broad-band stations, which will record teleseismic earthquakes whose rays will as evenly as possible illuminate the upper mantle. We support the general consensus on combing the national efforts in imaging the Alpine crust and upper mantle, and plan to contribute to the AlpArray studies by retrieving 3D anisotropic models of the upper mantle aiming at better understanding tectonics and evolution of the region.

  16. Pressure-temperature-deformation-time of the ductile Alpine shearing in Corsica: From orogenic construction to collapse

    NASA Astrophysics Data System (ADS)

    Rossetti, Federico; Glodny, Johannes; Theye, Thomas; Maggi, Matteo

    2015-03-01

    Definition of the Tertiary tectono-metamorphic history of Alpine Corsica is a key task to decipher the space-time linkage between the Alpine and Apennine subduction systems in the Mediterranean region. Alpine Corsica exposes a nappe stack of oceanic- and continental-derived units, structurally juxtaposed onto the former European continental margin (Hercynian Corsica). Still uncertain is the timing of involvement of the continental-derived units in orogenic construction and shift to regional extension. This paper focuses on reconstruction of the pressure-temperature-deformation-time evolution of selected ductile shear zones activated during transition from the tectonic underplating to the extensional reworking stages. New Rb-Sr mineral age data, integrated with structural and thermobarometric investigations constrain the waning stages of the high-pressure (from blueschist to greenschist facies metamorphic conditions) top-to-the-W thrusting of the HP, oceanic-derived realm (Schistes Lustrés Complex) onto the Hercynian Corsica along the East Tenda Shear Zone in the early Oligocene (from ~ 32 to ~ 27 Ma). This early compressional evolution is overprinted by a major phase of retrogressive, syn-greenschist top-to-the-E extensional shearing in the Schistes Lustrés Complex with the last episode of deformation-related ductile recrystallization recorded during the early Miocene at ~ 20-21 Ma, in a continuum transition from ductile to brittle shearing. The same early Miocene Rb-Sr deformation ages are recovered from the ductile-to-brittle top-to-the-E reactivation domains within the East Tenda Shear Zone, documenting that transition from compression to extension in Alpine Corsica occurred during the late Oligocene-early Miocene time lapse. Implications of these data are discussed in the broader context of the Tertiary geodynamic evolution of the Central Mediterranean region.

  17. Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada

    USGS Publications Warehouse

    du Bray, Edward A.; John, David A.; Cousens, Brian L.

    2013-01-01

    Although rocks in the two arc segments have similar metal abundances, they are metallogenically distinct. Small porphyry copper deposits are characteristic of the northern segment whereas significant epithermal precious metal deposits are most commonly associated with the southern segment. These metallogenic differences are also fundamentally linked to the tectonic settings and crustal regimes within which these two arc segments evolved.

  18. Seismic site characterization for the Deep-Fault-Drilling-Project Alpine Fault

    NASA Astrophysics Data System (ADS)

    Glomb, Vera; Buske, Stefan; Kovacs, Adrienn; Gorman, Andrew

    2013-04-01

    The Alpine Fault in New Zealand (South Island) is one of the largest active plate-bounding continental fault zones on earth with earthquakes of magnitude 7.9 occuring every 200-400 years. Due to the surface exposure and the shallow depth of mechanical and chemical transitions it is a globally significant natural laboratory. Within the ICDP Deep-Fault-Drilling-Project Alpine Fault (DFDP-AF; https://wiki.gns.cri.nz/DFDP) a drill hole shall give insight into the geological structure of the fault zone and its evolution to understand the related deformation and earthquake processes. With the help of advanced seismic imaging techniques the shallow structure of the Alpine Fault is imaged to find the most suitable drill site location. A new seismic reflection profile has been acquired in 2011 by the WhataDUSIE project team consisting of partners from the University of Otago (New Zealand), TU Bergakademie Freiberg (Germany) and the University of Alberta (Canada). The reflection profile, located in the Whataroa river valley, has a total length of about 5 km. Up to 643 geophones with spacings between 4-8 m recorded the approximately 100 shot points along the profile line. Single shot gathers as well as preliminary imaging results will be presented. The high-quality data show various indicators of the Alpine Fault such as strong reflections and distorted first-arrival wavefields which are clearly visible already in single shot gathers. With the help of high resolution seismic images we can study the shallow structures of the subsurface thus gaining information about the location and dip of reflectors. Further detailed processing and intensive interpretative work will enable a seismic site characterization providing important information for the selection of the borehole location. Additionally the high resolution seismic images themselves allow a better understanding of the tectonic and geodynamic settings.

  19. The Structural Architecture and Tectonic Inheritance of the Vlora-Elbasan Transfer Zone in Albanides-Albania

    NASA Astrophysics Data System (ADS)

    Abus, E. D.; Dilek, Y.

    2014-12-01

    The Albanides in the Balkan Peninsula are part of the Alpine orogenic belt and host one of the most significant oil fields in SE Europe. The late Mesozoic-Cenozoic evolution of the Albanides has been strongly controlled by the relative movements of Adria or Apulia, a microcontinent with a West Gondwana affinity with respect to Eurasia. In northeastern Albania, the Internal Albanides consist of Paleozoic - Jurassic basement rocks, which involved subduction zone tectonics of the Pindos-Mirdita ocean basin. The External Albanides, on the other hand, represent a fold-and-thrust belt with deformation in a broad zone of oblique convergence. This tectonic domain is divided, from east to west, into five major structural zones: the Krasta-Cukali Zone, the Kruja Zone, the Peri-Adriatic Depression, the Ionian Zone, and the Sazani Zone, which is represented by the Apulian platform carbonates. The zone is characterized by NW-SE-running and SW-verging thrust fault systems that involve a thick series of Mesozoic - Tertiary passive margin carbonates, unconformably overlain by Oligocene clastic units. These two tectonic zones are dissected by the NE-SW-striking Vlora-Elbasan Transfer Zone, which extends eastwards into the Internal Albanides, affecting the structural architecture and the tectonic evolution of the entire mountain belt. This fault zone that has been tectonically active from the Triassic to recent have display diapiric structures along it.

  20. The Plio-Pleistocene evolution of the Crotone Basin (southern Italy): Interplay between sedimentation, tectonics and eustasy in the frame of Calabrian Arc migration

    NASA Astrophysics Data System (ADS)

    Zecchin, Massimo; Caffau, Mauro; Civile, Dario; Critelli, Salvatore; Di Stefano, Agata; Maniscalco, Rosanna; Muto, Francesco; Sturiale, Giovanni; Roda, Cesare

    2012-12-01

    The Crotone Basin is the exposed part of a larger Neogene forearc basin developed in the Ionian Sea in the frame of the SE-ward migration of the Calabrian Arc, which led to the subduction of the Ionian lithosphere and the spreading of the Tyrrhenian back-arc Basin (central Mediterranean). Taking into account the geologic context that accompanied its accumulation, the Plio-Pleistocene part of the Crotone Basin succession is exceptionally well preserved, and consists of a suite of continental, paralic, shallow-marine and deep-marine deposits organized to form unconformity bounded stratal units that in turn compose two main tectono-stratigraphic cycles. The unconformities separating these units are well recognizable along the basin margin and tend to vanish basinwards, and they record phases of basin reorganization linked to large-scale tectonics. In particular, the basin evolution was characterized by a cyclic pattern consisting of an alternation between longer subsidence phases, that favored the accumulation of stratal units, and uplift phases that led to base-level falls and the generation of unconformities. These phases were strictly related to an alternation between active subduction of the Ionian lithosphere below the Calabrian Arc, accompanied by the spreading of the Tyrrhenian back-arc Basin and by extension and subsidence in the forearc basin, and regional-scale compressional and transpressional events, during which the Arc migration temporarily stopped. The younger uplift of the basin, started during middle Pleistocene and still active, was characterized by extensional tectonics, and its interplay with glacio-eustasy controlled the formation of marine terraces. Since the Plio-Pleistocene tectonic episodes affecting the Calabrian Arc during its SE-ward migration seem to be all recorded in the Crotone Basin, the recognition of their effects on the basin fill and their time constraint become both critical, representing a reference to develop a clearer picture

  1. Structure and tectonic evolution of the NE segment of the Polish-Ukrainian Carpathians during the Late Cenozoic: subsurface cross-sections and palinspastic models

    NASA Astrophysics Data System (ADS)

    Kuśmierek, Jan; Baran, Urszula

    2016-08-01

    The discrepant arrangement of the Carpathian nappes and syntectonic deposits of the Carpathian Foredeep reveals the oroclinal migration of the subduction direction of the platform margin during the Late Cenozoic. Formation of the nappes was induced by their detachment from disintegrated segments of the European Platform; the segments were shortened as a result of their vertical rotation in zones of compressional sutures. It finds expression in local occurrence of the backward vergence of folding against the generally forward vergence toward the Carpathian Foredeep. The precompressional configuration of sedimentation areas of particular nappes was reconstructed with application of the palinspastic method, on the basis of the hitherto undervalued model which emphasizes the influence of the subduction and differentiated morphology of the platform basement on the tectonic evolution of the fold and thrust belt. Superposition of the palaeogeographic representations and the present geometry of the orogen allows understanding of the impact of the magnitudes of tectonic displacements on the differentiation of the geological structure in the NE segment of the Carpathians. The differentiation has inspired different views of Polish and Ukrainian geologists on structural classification and evolution of the frontal thrusts.

  2. Tectonic evolution of the Lachlan Fold Belt, southeastern Australia: constraints from coupled numerical models of crustal deformation and surface erosion driven by subduction of the underlying mantle

    NASA Astrophysics Data System (ADS)

    Braun, Jean; Pauselli, Cristina

    2004-04-01

    We have used a coupled thermo-mechanical finite-element (FE) model of crustal deformation driven by mantle/oceanic subduction to demonstrate that the tectonic evolution of the Lachlan Fold Belt (LFB) during the Mid-Palaeozoic (Late Ordovician to Early Carboniferous) can be linked to continuous subduction along a single subduction zone. This contrasts with most models proposed to date which assume that separate subduction zones were active beneath the western, central and eastern sections of the Lachlan Orogen. We demonstrate how the existing data on the structural, volcanic and erosional evolution of the Lachlan Fold Belt can be accounted for by our model. We focus particularly on the timing of fault movement in the various sectors of the orogen. We demonstrate that the presence of the weak basal decollement on which most of the Lachlan Fold Belt is constructed effectively decouples crustal structures from those in the underlying mantle. The patterns of faulting in the upper crust appears therefore to be controlled by lateral strength contrasts inherited from previous orogenic events rather than the location of one or several subduction zones. The model also predicts that the uplift and deep exhumation of the Wagga-Omeo Metamorphic Belt (WOMB) is associated with the advection of this terrane above the subduction point and is the only tectonic event that gives us direct constraints on the location of the subduction zone. We also discuss the implications of our model for the nature of the basement underlying the present-day orogen.

  3. The Pennsylvanian-early permian bird spring carbonate shelf, Southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications

    USGS Publications Warehouse

    Stevens, C.H.; Stone, P.

    2007-01-01

    The Bird Spring Shelf in southeastern California, along with coeval turbidite basins to the west, records a complex history of late Paleozoic sedimentation, sea-level changes, and deformation along the western North American continental margin. We herein establish detailed correlations between deposits of the shelf and the flanking basins, which we then use to reconstruct the depositional history, paleogeography, and deformational history, including Early Permian emplacement of the regionally significant Last Chance allochthon. These correlations are based on fusulinid faunas, which are numerous both on the shelf and in the adjoining basins. Study of 69 fusulinid species representing all major fusulinid-bearing Pennsylvanian and Lower Permian limestone outcrops of the Bird Spring Shelf in southeastern California, including ten new species of the genera Triticites, Leptotriticites, Stewartina, Pseudochusenella, and Cuniculinella, forms the basis for our correlations. We group these species into six fusulinid zones that we correlate with fusulinid-bearing strata in east-central and southern Nevada, Kansas, and West Texas, and we propose some regional correlations not previously suggested. In addition, we utilize recent conodont data from these areas to correlate our Early Permian fusulinid zones with the standard Global Permian Stages, strengthening their chronostratigraphic value. Our detailed correlations between the fusulinid-bearing rocks of the Bird Spring Shelf and deep-water deposits to the northwest reveal relationships between the history of shelf sedimentation and evolution of basins closer to the continental margin. In Virgilian to early Asselian (early Wolfcampian) time (Fusulinid Zones 1 and 2), the Bird Spring Shelf was flanked on the west by the deep-water Keeler Basin in which calcareous turbidites derived from the shelf were deposited. In early Sakmarian (early middle Wolfcampian) time (Fusulinid Zone 3), the Keeler Basin deposits were uplifted and

  4. Holocene to Pliocene tectonic evolution of the region offshore of the Los Angeles urban corridor, southern California

    USGS Publications Warehouse

    Bohannon, R.G.; Gardner, J.V.; Sliter, R.W.

    2004-01-01

    Quaternary tectonism in the coastal belt of the Los Angeles urban corridor is diverse. In this paper we report the results of studies of multibeam bathymetry and a network of seismic reflection profiles that have been aimed at deciphering the diverse tectonism and at evaluating the relevance of published explanations of the region's tectonic history. Rapid uplift, subsidence in basins, folds and thrusts, extensional faulting, and strike-slip faulting have all been active at one place or another throughout the Quaternary Period. The tectonic strain is reflected in the modern physiography at all scales. Los Angeles (LA) Basin has filled from a deep submarine basin to its present condition with sediment impounded behind a large sill formed behind uplifts near the present shoreline. Newport trough to the south-southeast of LA Basin also accumulated a large volume of sediment, but remained at midbathyal depths throughout the Period. There is little or no evidence of Quaternary extensional tectonism in either basin although as much as 6 km of subsidence, which mainly occurred by sagging, has been recorded in places since the middle Miocene. The uplifts include folded and thrust faulted terranes in the Palos Verdes Hills and the shelves of Santa Monica and San Pedro Bays. The uplifted areas have been shortened in a southwest-northeast direction by 10% or slightly more, and some folds are reflected in the bathymetry. Two large adjacent midbathyal basins, Santa Monica and San Pedro, show strong evidence of subsidence and slight west-northwest extension (10%) during the same time folding was taking place in the uplifts. The tectonic boundaries between uplifts and basins are folded, normal faulted, reverse-faulted, and strike-slip faulted depending on location. The rapid Quaternary uplift and subsidence, along with the filling of LA Basin, have produced a reversal in the regional physiography. In the early Pliocene, LA Basin was a submarine deep, Palos Verdes and the shelves

  5. Old stories and lost pieces of the Eastern Mediterranean puzzle: a new approach to the tectonic evolution of the Western Anatolia and the Aegean Sea

    NASA Astrophysics Data System (ADS)

    Yaltırak, Cenk; Engin Aksu, Ali; Hall, Jeremy; Elitez, İrem

    2015-04-01

    During the last 20 or so years, the tectonic evolution of Aegean Sea and Western Anatolia has been dominantly explained by back-arc extension and escape tectonics along the North Anatolian Fault. Various datasets have been considered in the construction of general tectonic models, including the geometry of fault patterns, paleomagnetic data, extensional directions of the core complexes, characteristic changes in magmatism and volcanism, the different sense of Miocene rotation between the opposite sides of the Aegean Sea, and the stratigraphy and position of the Miocene and Pliocene-Quaternary basins. In these models, the roles of the Burdur-Fethiye Shear Zone, the Trakya-Eskişehir Fault Zone, the Anaximander Mountains and Isparta Angle have almost never been taken into consideration. The holistic evaluation of numerous land and marine researches in the Aegean Sea and western Anatolia suggest the following evolutionary stages: 1. during the early Miocene, Greece and western Anatolia were deformed under the NE-SW extensional tectonics associated with the back-arc extension, when core complexes and supra-detachment basins developed, 2. following the collision of the Anaximander Mountains and western Anatolia in early Miocene , the Isparta Angle locked this side of the western arc by generating a triangle-shaped compressional structure, 3. while the Isparta Angle penetrated into the Anatolia, the NE-striking Burdur-Fethiye Shear Zone in the west and NW-striking Trakya-Eskişehir Fault Zone in the north developed along the paleo-tectonic zones , 4. the formation of these two tectonic structures allowed the counterclockwise rotation of the western Anatolia in the middle Miocene and this rotation removed the effect of the back-arc extension on the western Anatolian Block, 5. the counterclockwise rotation developed with the early westward escape of the Western Anatolian reached up to 35-40o and Trakya-Eskişehir Fault Zone created a total dextral displacement of about 200

  6. U-Th-Pb and 230Th/ 238U disequilibrium isotope systematics: Precise accessory mineral chronology and melt evolution tracing in the Alpine Bergell intrusion

    NASA Astrophysics Data System (ADS)

    Oberli, Felix; Meier, Martin; Berger, Alfons; Rosenberg, Claudio L.; GierÉ, Reto

    2004-06-01

    equilibrium with sequential allanite zoning. Comparison of calculated (Th/U) magma with measured total-rock Th/U = 0.79 requires fractional crystallization of allanite at an early stage. This process of removal of allanite, and thus Th, from the melt was operative at least until ˜31.5 Ma, providing an upper limit for the time of emplacement of the studied magma batch. The fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep-seated plutons with intrusion ages. The persistence of magmatic conditions over a period of ˜5 Ma, concentrated in a narrow collision zone between the European and the African plate, has been a major controlling factor for the Oligocene evolution of the adjacent Insubric fault, the main tectonic lineament of the Alps being active from late Cretaceous to Miocene times.

  7. Plants in alpine environments

    USGS Publications Warehouse

    Germino, Matthew J.

    2014-01-01

    Alpine and subalpine plant species are of special interest in ecology and ecophysiology because they represent life at the climate limit and changes in their relative abundances can be a bellwether for climate-change impacts. Perennial life forms dominate alpine plant communities, and their form and function reflect various avoidance, tolerance, or resistance strategies to interactions of cold temperature, radiation, wind, and desiccation stresses that prevail in the short growing seasons common (but not ubiquitous) in alpine areas. Plant microclimate is typically uncoupled from the harsh climate of the alpine, often leading to substantially warmer plant temperatures than air temperatures recorded by weather stations. Low atmospheric pressure is the most pervasive, fundamental, and unifying factor for alpine environments, but the resulting decrease in partial pressure of CO2 does not significantly limit carbon gain by alpine plants. Factors such as tree islands and topographic features create strong heterogeneous mosaics of microclimate and snow cover that are reflected in plant community composition. Factors affecting tree establishment and growth and formation of treeline are key to understanding alpine ecology. Carbohydrate and other carbon storage, rapid development in a short growing season, and physiological function at low temperature are prevailing attributes of alpine plants. A major contemporary research theme asks whether chilling at alpine-treeline affects the ability of trees to assimilate the growth resources and particularly carbon needed for growth or whether the growth itself is limited by the alpine environment. Alpine areas tend to be among the best conserved, globally, yet they are increasingly showing response to a range of anthropogenic impacts, such as atmospheric deposition.

  8. Morphological expression of active tectonics in the Southern Alps

    NASA Astrophysics Data System (ADS)

    Robl, Jörg; Heberer, Bianca; Neubauer, Franz; Hergarten, Stefan

    2015-04-01

    Evolving drainage pattern and corresponding metrics of the channels (e.g. normalized steepness index) are sensitive indicators for tectonic or climatic events punctuating the evolution of mountain belts and their associated foreland basins. The analysis of drainage systems and their characteristic properties represents a well-established approach to constrain the impact of tectonic and climatic drivers on mountainous landscapes in the recent past. The Southern Alps (SA) are one of the seismically most active zones in the periphery of northern Adria. Recent deformation is caused by the ongoing convergence of the Adriatic and European plate and is recorded by numerous earthquakes in the domain of the SA. Deformation in the SA is characterized by back-thrusting causing crustal thickening and should therefore result in uplift and topography formation. The vertical velocity field determined by GPS-data clearly indicates a belt of significant uplift in the south South alpine indenter between Lake Garda in the west and the Triglav in the east and strong subsidence of the foreland basin surrounding the Mediterranean Sea near Venice, although subsidence is often related to ongoing subduction of the Adriatic microplate underneath Appennines. Despite of these short term time series, timing, rates and drivers of alpine landscape evolution are not well constrained and the linkage between crustal deformation and topographic evolution of this highly active alpine segment remains unclear for the following reasons: (1) The eastern Southern Alps were heavily overprinted by the Pleistocene glaciations and tectonic signals in the alpine landscape are blurred. Only the transition zone to the southern foreland basin remained unaffected and allows an analysis of a glacially undisturbed topography. (2) The major part of this domain is covered by lithology (carbonatic rocks) which is unsuitable for low temperature geochronology and cosmogenic isotope dating so that exhumation and erosion

  9. The Lower Engadine Window: sediment deposition and accretion in relation to the plate-tectonic evolution of the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Waibel, A. F.; Frisch, W.

    1989-05-01

    The Lower Engadine Window comprises a weakly metamorphosed, heterogeneous mixture of continental fragments and oceanic ophiolites embedded in a disrupted mass of deep-sea sediments ranging from the mid-Jurassic to the Early Eocene, mostly turbidites. Its geological features are reviewed in the light of recent research and its relationships with other Penninic outcrops in the Eastern Alps discussed. In the Falknis, Sulzfluh and Tasna zones it is thought that the entire spectrum of post-Liassic sediments was deposited to the north of the Austro-Alpine continental margin. This is based on downcurrent variations of sedimentary structures to the north or northwest in the same direction as the trend of paleocurrent indicators, and on the close petrographic resemblance of coarse parent rock materials to Austro-Alpine units. Of particular significance are granitic rocks exposed by vertical movements along fault scarps associated with the first formation of oceanic crust. These granitic rocks, together with their Permo-Mesozoic sedimentary cover, were to be eroded and slumped down from the continental margin until the Senonian. Throughout the Jurassic, the clastic sediments were shed laterally onto the abyssal plain and base of the continental slope. Pelagic sedimentation during parts of the Late Jurassic and earliest Cretaceous, including Aptychus limestones deposited close to the calcite compensation depth, suggests that maximum subsidence of the initially passive continental margin had been attained by this time period. With the onset of continental convergence in the earliest Cretaceous, underthrusting of oceanic crust gave rise to an accretionary trench system. The Cretaceous sediments were deposited in a deep-sea fan environment affected by chaotic mass movements from the inner trench wall. It is believed that the close proximity to the source area of the vast majority of Jurassic and Cretaceous deposits reflects the relative motion between the plates, which must have

  10. The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Menzies, Catriona D.; Teagle, Damon A. H.; Niedermann, Samuel; Cox, Simon C.; Craw, Dave; Zimmer, Martin; Cooper, Matthew J.; Erzinger, Jörg

    2016-07-01

    Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid-rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island, New Zealand and appears to fail in regular (329 ± 68 yrs) large earthquakes (Mw ∼ 8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87Sr/86Sr > 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15-0.81 RA) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at ∼6 km. Geochemical tracer transport modelling suggests only ∼0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this

  11. Active tectonic influence on the evolution of drainage and landscape: Geomorphic signatures from frontal and hinterland areas along the Northwestern Himalaya, India

    NASA Astrophysics Data System (ADS)

    Malik, Javed N.; Mohanty, C.

    2007-03-01

    The Kangra Re-entrant in the NW Himalaya is one of the most seismically active regions, falling into Seismic Zone V along the Himalaya. In 1905 the area experienced one of the great Himalayan earthquakes with magnitude 7.8. The frontal fault system - the Himalayan Frontal Thrust (HFT) associated with the foreland fold - Janauri Anticline, along with other major as well as secondary hinterland thrust faults, provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region. The present study suggests that the flat-uplifted surface in the central portion of the Janauri Anticline represents the paleo-exit of the Sutlej River. It is suggested that initially when the tectonic activity propagated southward along the HFT the Janauri Anticline grew along two separate fault segments (north and south faults), the gap between these two fault and the related folds allowed the Sutlej River to flow across this area. Later, the radial propagation of the faults towards each other resulted in an interaction of the fault tips, which caused the rapid uplift of the area. Rapid uplift resulted in the disruption and longitudinal deflection of the Sutlej river channel. Fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past. Geomorphic signatures, like the sharp mountain fronts along the HFT in some places, as well as along various hinterland subordinate faults like the Nalagarh Thrust (NaT), the Barsar Thrust (BaT) and the Jawalamukhi Thrust (JMT); the change in the channel pattern, marked by a tight incised meander of the Beas channel upstream of the JMT indicate active tectonic movements in the area. The prominent V-shaped valleys of the Beas and Sutlej rivers, flowing across the thrust fronts, with Vf values ranging from <1.0-1.5 are also suggestive of ongoing tectonic activity along major and hinterland faults. This suggests that not only is the HFT

  12. Unraveling the geodynamic evolution and tectonic history of the Guatemala Suture Zone: a world-class natural laboratory

    NASA Astrophysics Data System (ADS)

    Flores, K. E.; Brocard, G. Y.; Harlow, G. E.

    2013-12-01

    The Guatemala Suture Zone (GSZ) is the fault-bound region in central Guatemala that contains the present North American-Caribbean plate boundary. It is bounded by the Maya Block to the north and by the Chortís Block to the south. This major composite geotectonic unit contains a variety of ophiolites, serpentinite mélanges, and metavolcano-sedimentary sequences along with high-grade schist, gneisses, low-grade metasediments and metagranites thrusted north and south of the active Motagua fault system (MFS). This modern plate boundary has accommodated at least ~1100 km of left-lateral strike-slip motion over the Cenozoic and brings into contact the geological provinces described above. Classically, the GSZ has been interpreted as the result of a single progressive collision of a Chortís Block-related island arc with the passive margin of the Maya Block. This model was based on geochemical signatures of basaltic rocks in oceanic crust sequences both north and south of the MFS. However, results from our research challenge this single collision hypothesis. Oceanic and continental high-pressure-low-temperature (HP-LT) rocks astride the MFS have recorded multiple tectonic events revealed by their multiple metamorphic ages (Sm-Nd, U-Pb and Ar-Ar) and distinct PT paths. These tectonic events differ in age north and south of the MFS. Moreover, the continental and oceanic sequences across the MFS are geochemically and stratigraphically distinct, suggesting different tectonic origins. The southern margin of the Maya Block and the northern section of the GSZ can be clearly interpreted as a Cretaceous-Paleocene flexural passive margin tectonically overridden by ultramafic rocks and a Cretaceous island arc sequence. In contrast, the southern section of the GSZ is composed of a Carboniferous-Jurassic active margin tectonically imbricated with ultramafic rocks and a circum-Pacific Jurassic MORB and IAT metavolcano-sedimentary sequence. Thus, based on these results, we identify at

  13. Architecture and evolution of an Early Permian carbonate complex on a tectonically active island in east-central California

    USGS Publications Warehouse

    Stevens, Calvin H.; Magginetti, Robert T.; Stone, Paul

    2015-01-01

    The newly named Upland Valley Limestone represents a carbonate complex that developed on and adjacent to a tectonically active island in east-central California during a brief interval of Early Permian (late Artinskian) time. This lithologically unique, relatively thin limestone unit lies within a thick sequence of predominantly siliciclastic rocks and is characterized by its high concentration of crinoidal debris, pronounced lateral changes in thickness and lithofacies, and a largely endemic fusulinid fauna. Most outcrops represent a carbonate platform and debris derived from it and shed downslope, but another group of outcrops represents one or possibly more isolated carbonate buildups that developed offshore from the platform. Tectonic activity in the area occurred before, probably during, and after deposition of this short-lived carbonate complex.

  14. Investigating Tectonic Drivers of Miocene - Pliocene Polar Climate Evolution using the HadCM3 Climate Model.

    NASA Astrophysics Data System (ADS)

    Hunter, S. J.; Knies, J.; Haywood, A. M.; Dolan, A. M.; Pound, M. J.

    2015-12-01

    We model the climate of the Miocene (Tortonian and the Messinian) and the Pliocene (Piacenzian) using the HadCM3 Atmosphere-Ocean GCM. We use baseline Miocene and Pliocene geographies that have different reconstruction lineages so we describe methods to create a set of self-consistent paleogeographies that represent the main features of the three stages. We present large-scale features of the evolving climate and examine model fidelity by comparing modelled climatology against palaeoenvironmental proxy data. We focus on the climate of the Arctic region and investigate tectonic drivers of sea ice expansion by comparing and interpreting model predictions against borehole data from the North Atlantic and Arctic Ocean. In particular how Late Miocene/ early Pliocene tectonic uplift in the Svalbard/Barents Sea and Greenland region, the opening of the Bering Strait, and the onset of deep water Atlantic-Arctic exchange influenced the development of modern sea ice cover.

  15. Integrated Analysis of Airborne Geophysical Data to Understand the Extent, Kinematics and Tectonic Evolution of the Precambrian Aswa Shear Zone in East Africa.

    NASA Astrophysics Data System (ADS)

    Katumwehe, A. B.; Atekwana, E. A.; Abdelsalam, M. G.; Laó-Dávila, D. A.

    2014-12-01

    The Aswa Shear zone (ASZ) is a Precambrian lithospheric structure which forms the western margin of the East African Orogeny (EAO) that influenced the evolution of many tectonic events in Eastern Africa including the East African Rift System. It separates the cratonic entities of Saharan Metacraton in the northeast from the Congo craton and the Tanzanian craton and the Kibaran orogenic belt to the southwest. However little is known about its kinematics and the extent and tectonic origin are not fully understood. We developed a new technique based on the tilt method to extract kinematic information from high-resolution airborne magnetic data. We also used radiometric data over Uganda integrated with Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) in South Sudan to understand the extent, kinematics and define the tectonic origin of ASZ. (1) Our results suggest that the ASZ extends in a NW-SE for ~550 km in Uganda and South Sudan. (2) The airborne magnetic and radiometric data revealed a much wider (~50 km) deformation belt than the mapped 5-10 km of exposed surface expression of the ASZ. The deformation belt associated with the shear is defined by three NW-trending sinistral strike-slip shear zones bounding structural domains with magnetic fabrics showing splays of secondary shear zones and shear-related folds. These folds are tighter close to the discrete shear zones with their axial traces becoming sub-parallel to the shear zones. Similar fold patterns are observed from South Sudan in the SRTM DEM. We interpret these folds as due to ENE-WSW shortening associated with the sinistral strike-slip movement. (3) To the northeast of the shear zone, the magnetic patterns suggest a series of W-verging nappes indicative of strong E-W oriented shortening. Based on the above observations, we relate the evolution of the ASZ to Neoproterozoic E-W collision between East and West Gondwana. This collision produced E-W contraction resulting in W-verging thrusts

  16. Integration of natural data within a numerical model of ablative subduction: A possible interpretation for the Alpine dynamics of the Austroalpine crust.

    NASA Astrophysics Data System (ADS)

    Roda, M.; Spalla, M. I.; Marotta, A. M.

    2012-04-01

    A numerical modelling approach is used to validate the physical and geological reliability of the ablative subduction mechanism during Alpine convergence in order to interpret the tectonic and metamorphic evolution of an inner portion of the Alpine belt: the Austroalpine Domain. The model predictions and the natural data for the Austroalpine of the Western Alps agree very well in terms of P-T peak conditions, relative chronology of peak and exhumation events, P-T-t paths, thermal gradients and the tectonic evolution of the continental rocks. These findings suggest that a pre-collisional evolution of this domain, with the burial of the continental rocks (induced by ablative subduction of the overriding Adria plate) and their exhumation (driven by an upwelling flow generated in a hydrated mantle wedge) could be a valid mechanism that reproduces the actual tectono-metamorphic configuration of this part of the Alps. There is less agreement between the model predictions and the natural data for the Austroalpine of the Central-Eastern Alps. Based on the natural data available in the literature, a critical discussion of the other proposed mechanisms is presented, and additional geological factors that should be considered within the numerical model are suggested to improve the fitting to the numerical results; these factors include variations in the continental and/or oceanic thickness, variation of the subduction rate and/or slab dip, the initial thermal state of the passive margin, the occurrence of continental collision and an oblique convergence.

  17. Tectonic map of Uruguay

    NASA Astrophysics Data System (ADS)

    Sanchez Bettucci, L.; Oyhantcabal, P.

    2008-05-01

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

  18. Tectonic Geomorphology.

    ERIC Educational Resources Information Center

    Bull, William B.

    1984-01-01

    Summarizes representative quantitative tectonic-geomorphology studies made during the last century, focusing on fault-bounded mountain-front escarpments, marine terraces, and alluvial geomorphic surfaces (considering stream terraces, piedmont fault scarps, and soils chronosequences). Also suggests where tectonic-geomorphology courses may best fit…

  19. Triassic to recent tectonic evolution of a crestal collapse graben above a salt-cored anticline in the Glückstadt Graben/North German Basin

    NASA Astrophysics Data System (ADS)

    Al Hseinat, M.; Hübscher, C.; Lang, J.; Lüdmann, T.; Ott, I.; Polom, U.

    2016-06-01

    In this study we investigate faulting above a salt wall in the Glückstadt Graben/North German Basin. Two supra-salt faults are mapped from coast to coast over a distance of 6-9 km based on offshore and onshore seismic data. These faults form a ca. 2 km wide crestal collapse graben and pierce the seafloor. Salt wall evolution started in the early Late Triassic to Early Jurassic due to regional extension and resulting sub-salt faulting. The salt wall was eroded following exposure to costal and sub-aerial erosion by the regional Mid-Late Jurassic to Early Cretaceous uplift. Late Cretaceous to Early Paleogene compressional tectonics reactivated the vertical salt movement and shortened the salt wall, creating a salt-cored anticline with the crestal collapse graben above. The supra-salt faults were reactivated between the Late Eocene and Middle Miocene when the principal horizontal stress orientation changed from a NE-SW to a NW-SE, the present-day orientation. Stratigraphic data indicate that these faults moved mainly in the Cenozoic. Several observations strongly suggest that the faults continued developing during the Pleistocene until today: (i) the Pleistocene Unconformity is concave upwards and cut by faults; (ii) growth strata within the marine Holocene deposits above the graben imply recent tectonic movements; (iii) onshore high-resolution P-wave vibroseis data of the south-eastern Eckernförde Bay suggest about 10 m of faulted Holocene strata; and (iv) marine seismic data show the faults piercing the seafloor. We suggest that the recent salt tectonics and upward propagation of supra-salt faults resulted from differential ice-sheet loading. That effect on the salt wall stopped once ice grew over the whole structure, at which time the wall subsided because of ice loading. The salt wall and faults were reactivated again once the ice front retreated so that the ice loaded only one side of the structure.

  20. Volcano-Tectonic Evolution of the Central Death Valley Volcanic Field - Insights Derived from the Geologic Map of the Death Valley Junction 30' x 60' Quadrangle

    NASA Astrophysics Data System (ADS)

    Thompson, R. A.; Fridrich, C.; Chan, C. F.; Zellman, K. L.; Workman, J. B.

    2014-12-01

    The geologic map of the Death Valley Junction 30' x 60' quadrangle encompasses many geologic features recording the Cenozoic volcano-tectonic evolution of central Death Valley. Most notable is the central Death Valley rhombochasm. The rhombochasm is a 65x80-km rhombic pull-apart basin complex that occupies the releasing step-over between the northern Death Valley—Furnace Creek and southern Death Valley faults. Stewart (1983) documented this feature by palinspastically restoring offset thrust fault segments and isopachs, thereby closing the rhombochasm. The central Death Valley volcanic field records the coincident and related magmatism that occurred during the extension and strike-slip strain that formed the rhombochasm. In the multi-stage evolution of this tectonomagmatic feature, changes in volcanic and structural styles, rates, and loci were synchronized, both spatially and temporally. The volcanic field covers an area of 3600 km2, and consists of >700 km3 of lava flows, domes, and pyroclastic deposits. Cenozoic map units reflect four major eruptive stages: Stage 1 (11-9 Ma: rhyolite and andesite), Stage 2 (9-7.5 Ma: dacite>basalt>andesite), Stage 3 (7-5 Ma: dacite>basalt), and Stage 4 (4.5-0.7 Ma: basalt). The predominant loci of eruptive centers migrated northwestward during this volcanic evolution, coeval with northwestward migration of adjacent depocenters. Stage 1 and 2 volcanism is broadly correlative to the supradetachment stage of rhombochasm development. Related intrusions include exposed upper-plate hypabyssal and lower-plate plutonic bodies. Stage 3 and 4 volcanism occurred during two tectonic stages in which higher-angle faults cut across the detachment fault, forming basins that are nested within the original detachment-floored area of the rhombochasm. Time-transgressive changes from dominantly silicic and intermediate magmas in Stages 1 and 2 to dominantly mafic and lesser intermediate magmas in Stages 3 and 4 coincided with decreases in eruptive

  1. Geochronology and geochemistry of Early Jurassic volcanic rocks in the Erguna Massif, northeast China: Petrogenesis and implications for the tectonic evolution of the Mongol-Okhotsk suture belt

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Tang, Jie; Xu, Wen-Liang; Wang, Feng

    2015-03-01

    The Mongol-Okhotsk suture belt played an important role in the tectonic evolution of northeast Asia during the Mesozoic. However, few studies have examined the influence of this tectonic belt on the geological evolution of northeast China. In this paper, we present zircon U-Pb geochronology, major and trace element geochemistry, and zircon Hf-O isotopic data for Early Jurassic volcanic rocks in the Erguna Massif of northeast China, with the aim of constraining the evolution of the Mongol-Okhotsk suture belt and its influence on the tectonic history of China during the Early Jurassic. Zircon U-Pb dating indicates that the trachybasalt and basaltic andesite in the study area were erupted between 193 ± 5 Ma and 181 ± 9 Ma (i.e., in the Early Jurassic). These Early Jurassic volcanic rocks belong to the high-K calc-alkaline series and are enriched in large ion lithophile elements and light rare earth elements, as well as being depleted in heavy rare earth elements and high field strength elements such as Nb and Ta. The rocks show a small negative Eu anomaly. The zircon εHf (182 Ma) values of the volcanic rocks range from - 1.9 to + 5.1, corresponding to TDM1 values of 640-901 Ma and TDM2 values of 901-1345 Ma. Zircons from two volcanic rocks yield δ18O values of 7.2‰ ± 1.5‰ (n = 19) and 6.6‰ ± 0.7‰ (n = 35). Geochemically, these Early Jurassic volcanic rocks are similar to those from active continental margin settings, and their primary magmas could have been derived from the partial melting of a lithospheric mantle wedge modified by fluid from a subducted slab. The discovery of Early Jurassic calc-alkaline volcanic rocks in the Erguna Massif, together with the coeval porphyry Cu-Mo deposits, indicates that an active continental margin existed in the Erguna area during the Early Jurassic. Taken together, we conclude that southward subduction of the Mongol-Okhotsk oceanic plate took place beneath the Erguna Massif during the Early Jurassic.

  2. Analysis of the geological structure and tectonic evolution of Xingning-Jinghai sag in deep water area, northern South China Sea

    NASA Astrophysics Data System (ADS)

    Han, Xiaoying; Ren, Jianye; Lin, Zi; Yang, Linlong

    2015-04-01

    Recent years, oil and gas exploration of the Pearl River Mouth Basin in the northern margin of South China Sea continuously achieved historic breakthroughs. The Xingning-Jinghai sag, which is located in southeast of the Pearl River Mouth Basin, is a deep-water sag with a great exploration potential. Its tectonic evolution is extremely complex. It experienced Mesozoic subduction to Cenozoic intra-continental rifting background, and finally evolved into a deep-water sag of the northern continental margin of South China Sea. The geological characteristics and the tectonic evolution of Xingning-Jinghai sag was closely related to the process of formation and evolution of the passive continental margin of the northern South China Sea. It is confirmed by many geophysical data that compared with adjacent Chaoshan depression, the crustal thickness of Xingning-Jinghai sag was rapidly thinning, and it developed detachment faults with later magmatic intrusion. The development of detachment faults have dynamic significance for the spreading of the South China Sea. Based on the seismic geological interpretation of 2D seismic data in the study area, the characteristics of detachment fault and supra-detachment basin have been proposed in this study. The characteristics of the detachment fault are low angle and high ratio between heave and throw. The geometry of the detachment fault is a typical lisric shape, with the dip of fault decreasing generally from the seismic profile. The detachment basin where sediments are not deposited over a tilting hanging-wall block but onto a tectonically exhumed footwall which is different from the typical half graben basin. Seismic profiles indicate two different structural styles in the east and west part of Xingning-Jinghai sag. In the west of the sag, there developed two large detachment faults, which control their detachment basin systems and the typical H block, and the two detachment faults are dipping landward and seaward, respectively. In

  3. Greenstone belt tectonics: Thermal constraints

    NASA Technical Reports Server (NTRS)

    Bickle, M. J.; Nisbet, E. G.

    1986-01-01

    Archaean rocks provide a record of the early stages of planetary evolution. The interpretation is frustrated by the probable unrepresentative nature of the preserved crust and by the well known ambiguities of tectonic geological synthesis. Broad constraints can be placed on the tectonic processes in the early Earth from global scale modeling of thermal and chemical evolution of the Earth and its hydrosphere and atmosphere. The Archean record is the main test of such models. Available general model constraints are outlined based on the global tectonic setting within which Archaean crust evolved and on the direct evidence the Archaean record provides, particularly the thermal state of the early Earth.

  4. Reconstruction of the Ogcheon Rift Basin and Pre-Cenozoic Tectonic Evolution of the Central Ogcheon Belt, Korea

    NASA Astrophysics Data System (ADS)

    Kang, J. H.

    2015-12-01

    The pre-Cenozoic tectonic structures of the Central Ogcheon Belt, Korea, were formed at least through five times of tectonic phases [D* Gyemyeongsan phase of Neoproterozoic˜Middle Permian, D1 Ogcheon-Cheongsan phase (Songnim orogeny) of Late Permian˜Middle Triassic, D2 Honam phase (Daebo orogeny) of Early˜Late Jurassic, D3 Cheongmari phase of Early Cretaceous, D4 Geumgang phase before Late Cretaceous] and three times of metamorphism [M1 medium-pressure type metamorphism of Late Permian, M2 contact metamorphism of Middle Jurassic, M3 retrograde metamorphism of Early Cretaceous]. The D* tectonic phase is marked by the rifting of the original Gyeonggi Massif into North Gyeonggi Massif (NGM: present Gyeonggi Massif) and South Gyeonggi Massif (SGM: Bakdallyeong and Busan gneiss complexes). Its associated bimodal type volcano-plutonism occurred at least four times, two times at Neoproterozoic, a Early Paleozoic, a Late Paleozoic ages. The lower (quartzose psammitic, pelitic, calcareous and basic rocks) and upper (conglomerate and pelitic rocks and acidic rocks) units of Ogcheon Supergroup (OSG) were deposited in the Ogcheon rift basin (ORB) during Early and Late Paleozoic times, respectively. The D1 phase is characterized by the coupling of NGM and SGM with closing of ORB and the M1 metamorphism of OSG at its earlier phase, and by the coupling of South China block (Gyeonggi Massif and Ogcheon Zone) and North China block (Yeongnam Massif and Taebaksan Zone) and Cheongsan dextral strike-slip shearing and formation of Middle Triassic Dadong basin in its later phase. The D2 is marked by Honam dextral strike-slip shearing and the M2 metamorphism of OSG by the intrusion of Daebo granitoids at the inter-tectonic phase. The D3 is by NNE-trending sinistral strike-slip shearing and the M3 retrograde metamorphism of OSG. The D4 occurred along Geumgang fault, and formed a giant-scale Geumgang drag fold intruded by Late Cretaceous acidic dykes.

  5. The Comparison of Periods of the Change in the Earth's Magnetic and Tectonic Processes and Periods of Evolution Change of the new Biological Kinds

    NASA Astrophysics Data System (ADS)

    Kharitonov, Andrey

    The Comparison of Periods of the Change in the Earth's Magnetic and Tectonic Processes and Periods of Evolution Change of the new Biological Kinds Kharitonov Andrey L., Kharitonova Galina P. Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of a Rus-sian Academy of Sciences, 142190, Troitsk, Moscow region, Russia, E-mail: ahariton@izmiran.ru The carrying-out theoretical analysis of the paleomagnetic, geochronological and paleobiological data allows to say, that at certain space parameters of motion of the Earth along space orbit, together with all Solar Planetary system (SPS), there are sharp enough changes of composition of atmosphere, changes of the climate (arid or freezing), change of the level of waters of the World Ocean (the transgression or the regression of the eustatic sea level), the blossom or the dead of biological kinds, and also activation or damping of tectonic processes in the Earth's interior (activity of earthquakes and many other geophysical and geotectonic processes). The change of the space factors during the motion of the Solar Planetary system, calls change geotectonic and accordingly climatic, biological processes in the Earth. The activity is executed at support of Russian Foundation of Basic Research, grant 10-05-00343-a.

  6. Geochronology of the Baie Verte Peninsula, Newfoundland: implications for the tectonic evolution of the Humber and Dunnage Zones of the Appalachian Orogen

    SciTech Connect

    Dallmeyer, R.D.; Hibbard, J.

    1984-09-01

    U-Pb analyses of zircon from the Burlington Granodiorite suggest intrusion at c. 460-465 Ma. Hornblende and biotite from central portions of the pluton record markedly younger /sup 40/Ar//sup 39/Ar plateau dates (410-420 Ma) which are interpreted to date contact metamorphic effects associated with the widespread emplacement of Silurian-Devonian igneous suites. Northern portions of the Burlington Granodiorite are polydeformed and regionally metamorphosed. Hornblende and biotite from this terrane yield /sup 40/Ar//sup 39/Ar plateau ages of 345-350 Ma. U-Pb analyses of zircon from the Dunamagon Granite indicate emplacement at c. 440-460 Ma, thereby providing an upper limit for tectonic juxtapositioning of the Humber and Dunnage Zones along the Baie Verte Line. Similar ages are also recorded by hornblende and biotite throughout northerly portions of the Mings Bight (Humber Zone) and Pacquet Harbour (Dunnage Zone) Groups. These results indicate that the tectonic evolution of the Baie Verte Line as polygenetic, and involved: (1) regionally significant tectonothermal activity prior to the Middle Ordovician and (2) Middle to Late Paleozoic tectonothermal activity centered along easterly segments of the Baie Verte Line. The regional metamorphism associated with this orogenic activity altered primary U-Pb and Rb-Sr isotopic systems within various igneous suites exposed in northeastern portions of the Burlington Peninsula, which may explain some inconsistent geochronological results previously obtained. 54 references, 6 figures, 5 tables.

  7. Morphotectonic evolution of triangular facets and wine-glass valleys in the Noakoh anticline, Zagros, Iran: Implications for active tectonics

    NASA Astrophysics Data System (ADS)

    Bahrami, Shahram

    2012-07-01

    The Noakoh anticline is located in Kermanshah province and is part of the Simply Folded Belt of Zagros. Boundaries of 97 triangular facets and 67 wine-glass (W-G) valleys, which formed on anticline limbs, were delineated using Quickbird satellite imagery. The strata dip (D), area (A), base length (BL), topographic slope (S) of facets, the maximum width (M), outlet width (O) and ratio of maximum width to outlet width (W index) of W-G valleys were analysed in detail. Noakoh anticline was subdivided into 9 tectonic zones on the basis of dip, topographic slopes and width of limbs. Results show that there are strong positive correlations between means of D-BL and S-BL pairs. Poor positive correlations exist between means of D-A and S-A pairs. Among W-G valley metrics, the W index has strong relations with D and S parameters. Based on the results, steep facets with long bases and well developed W-G valleys with narrow outlets and wide upper parts are associated with more rotated limbs having steep slopes. Facets on the northeastern slope have more forest cover, micro-organism activity, karstic features and soil cover, whereas facets on relatively drier southwestern slope are characterized by physical weathering processes and minor karstic landforms. This study demonstrates that, apart from tectonic activity as a major control on the morphometry of facets and valleys, climate and slope aspect have also acted as secondary factors on the development of the studied landforms.

  8. Nappes, tectonics of oblique plate convergence, and metamorphic evolution related to 140 million years of continuous subduction, Franciscan Complex, California

    SciTech Connect

    Wakabayashi, J. )

    1992-01-01

    This paper presents a new synthesis of Franciscan Complex tectonics, with the emphasis on the pre-San Andreas fault history of these rocks. Field relations suggest that the Franciscan is characterized by nappe structures that formed during sequential accretion at the trench. The presence of these structures along with other field relations, including the lack of evidence for large offset of conglomerate suites, indicates that strike-slip fault systems of large displacement ({gt}500 km) did not cut the Franciscan Complex during subduction. Regional geology and comparisons to modern arc-trench systems suggest that strike-slip faulting associated with oblique subduction took place inboard (east) of the Franciscan in the vicinity of the magmatic arc. The Franciscan varies along strike, because individual accreted elements (packets of trench sediment, seamounts, etc.) did not extend the full length of the trench. Different depths of underplating, distribution of post-metamorphic faulting, and level of erosion produced the present-day surface distribution of high P/T metamorphism. Franciscan Complex tectonic history is presented in this paper.

  9. Tectonic evolution of 200 km of Mid-Atlantic Ridge over 10 million years: Interplay of volcanism and faulting

    NASA Astrophysics Data System (ADS)

    Cann, Johnson R.; Smith, Deborah K.; Escartin, Javier; Schouten, Hans

    2015-07-01

    We reconstruct the history of the mode of accretion of an area of the Mid-Atlantic Ridge south of the Kane fracture zone using bathymetric morphology. The area includes 200 km of the spreading axis and reaches to 10 Ma on either side. We distinguish three tectonic styles: (1) volcanic construction with eruption and intrusion of magma coupled with minor faulting, (2) extended terrain with abundant large-offset faults, (3) detachment faulting marked by extension on single long-lived faults. Over 40% of the seafloor is made of extended terrain and detachment faults. The area includes products of seven spreading segments. The spreading axis has had detachment faulting or extended terrain on one or both sides for 70% of the last 10 Ma. In some parts of the area, regions of detachment faulting and extended terrain lie close to segment boundaries. Regions of detachment faulting initiated at 10 Ma close to the adjacent fracture zones to the north and south, and then expanded away from them. We discuss the complex evidence from gravity, seismic surveys, and bathymetry for the role of magma supply in generating tectonic style. Overall, we conclude that input of magma at the spreading axis has a general control on the development of detachment faulting, but the relationship is not strong. Other factors may include a positive feedback that stabilizes detachment faulting at the expense of volcanic extension, perhaps through the lubrication of active detachment faults by the formation of low friction materials (talc, serpentine) on detachment fault surfaces.

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

    USGS Publications Warehouse

    Dorsey, R.J.; Fluette, A.; McDougall, K.; Housen, B.A.; Janecke, S.U.; Axen, G.J.; Shirvell, C.R.

    2007-01-01

    Late Miocene to early Pliocene deposit at Split Mountain Gorge, California, preserve a record of basinal response to changes in regional tectonics, paleogeogra