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Sample records for exhumation

  1. Westernmost Tian Shan (Uzbekistan): Magmatism and Exhumation

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    Abdulhameed, Sanaa; Ratchbacher, Lothar; Gagala, Lukasz; Jonkheere, Raymond

    2014-05-01

    The westernmost segment of the Tian Shan comprises the Ghissar-Alai Range of Tajikistan and Uzbekistan; its southwestern promontory contains the Baysunta crystalline massif. This orocline extends northwest of the Pamir and southeast of the Turan platform and forms the (north) western margin of the intra-orogenic Afghan-Tajik basin that was inverted during the India-Asia collision, mainly as a result of the gravitational collapse of the Pamir Plateau. The area contains Paleozoic slope and shelf clastics mantling crystalline basement rocks, altogether intruded by massif granitoids; it hides the cryptic Late Paleozoic South Ghissar suture. In Uzbekistan, the crystalline basement rocks of the westernmost Tien Shan are involved in the folding and thrusting of the Jurassic to Neogene sediments of the Afghan-Tajik basin, spectacularly proving thick-skinned deformation and demonstrating basement involvement below the Jurassic evaporate décollement underneath the Afghan-Tajik basin. We sampled the crystalline basement rocks of the Tian Shan of Uzbekistan to constrain the formation of the enigmatic Baysunta block and date the crystallization and high-grade metamorphism of the granitoids and associated metamorphic rocks of the Ghissar range; we employed U-Pb zircon geochronology. To time the deformation and exhumation of the fold-and thrust belt of the westernmost Afghan-Tajik basin, we used apatite fission-track thermochronology. Concordant U-Pb crystallization ages of zircons in the orthogneiss and paragneiss comprise 620 to 300 Ma; the Neoproterozoic ages imply a correlation of the Baysunta block with the Garm crystalline massif of the central Ghissar-Alai range of northeastern Tajikistan. The youngest zircon crystallization ages from granitoids are ~220 Ma, revealing enigmatically young magmatism, post-dating the last known collision event by >50 Ma. Together with 270-240 Ma meta-basaltic dykes and stocks in Tajikistan, they may trace a regional post

  2. Inferring earthquake mechanics from exhumed faults (Invited)

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    di Toro, G.; Griffith, A.; Nielsen, S. B.; Smith, S. A.; Niemeijer, A. R.; Bistacchi, A.; Mittempergher, S.

    2009-12-01

    Destructive earthquakes nucleate at 7-15 km depth; therefore monitoring active faults at the Earth's surface or interpretation of seismic waves yields limited information regarding earthquake mechanics. A complementary approach involves the integration of field studies of fossil seismic sources now exhumed at the Earth's surface with laboratory friction experiments that reproduce deformation conditions typical of seismic slip. Microstructural and geochemical comparison of the natural and experimental fault rock materials can be used to constrain boundary conditions for theoretical earthquake models. Here we will discuss the preliminary results of a project that takes such an integrated approach. In particular, rock friction experiments, including experiments in a cutting-edge high-velocity-rock-friction apparatus recently installed in Italy, suggest coseismic fault lubrication at seismogenic depths for a variety of host lithologies and tectonic settings. This result is consistent with estimates from field observations and theoretical analysis of rock friction at seismic slip rates. Moreover, experimental and natural fault products have strikingly similar microstructural and geochemical features, suggesting that experiments reproduce natural deformation processes. High velocity friction experiments were performed on smooth surfaces and under low normal stress, so direct extrapolation to seismogenic depths should be performed with caution. For instance, the presence of bumps along natural faults might impede the smooth sliding observed in the experiments. To resolve this scaling issue we measured the fault surface roughness of natural seismogenic faults exposed in large glacially polished outcrops over a range of scales (from 102 to 10-5 m) using (1) terrestrial laser-scanning (LIDAR), (2) orthorectified mosaics of high-resolution digital photographs and, (3) scans of thin sections from cores of the slipping zones. LIDAR scans and photomosaics were georeferenced in 3

  3. Exhumation of (ultra-high-pressure terranes: concepts and mechanisms

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    C. J. Warren

    2013-02-01

    Full Text Available The formation and exhumation of high and ultra-high-pressure, (UHP, rocks of crustal origin appears to be ubiquitous during Phanerozoic plate subduction and continental collision events. Exhumation of (UHP material has been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. Subduction zone style and internal force balance change in both time and space, responding to changes in width, steepness, composition of subducting material and velocity of subduction. In order for continental crust, which is relatively buoyant compared to the mantle even when metamorphosed to (UHP assemblages, to be subducted to (UHP conditions, it must remain attached to a stronger and denser substrate. Buoyancy and external tectonic forces drive exhumation, although the changing spatial and temporal dominance of different driving forces still remains unclear. Exhumation may involve whole-scale detachment of the terrane from the subducting slab followed by exhumation within a subduction channel (perhaps during continued subduction or a reversal in motion of the entire plate (eduction following the removal of a lower part of the subducting slab. Weakening mechanisms that may be responsible for the detachment of deeply subducted crust from its stronger, denser substrate include strain weakening, hydration, melting, grain size reduction and the development of foliation. These may act locally to form narrow high-strain shear zones separating stronger, less-strained crust or may act on the bulk of the subducted material, allowing whole-scale flow. Metamorphic reactions, metastability and the composition of the subducted crust

  4. Toxicological Analysis of Exhumed Specimens: A Challenge for Toxicologists

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    Muhammad Taimoor Chaudhary

    2016-06-01

    Full Text Available The objective of this work is to describe the type of biological samples submitted for toxicological analysis after exhumation. Forensic toxicologists receive a variety of biological samples, but exhumed biological specimens with varying degrees of putrefaction pose a greater challenge for analysis. Usually, immunoassay and colorimetric screening are the first line approach for toxicological analysis. Suitable samples can be selected for direct analysis using chromatographic techniques with a mass spectrometer, providing reliable results. The authors report two case studies where exhumed specimens were submitted for the determination of possible intoxication. The deceased were severely injured and remained hospitalized for more than 24 hours before death. Their corpses were exhumed for chemical analysis. For the toxicological analysis, selected samples were analyzed by immunoassay and a gas chromatograph mass spectrometer (GC/MS with electron impact ionization. Although the samples were negative for drugs of abuse (benzodiazepines and opiates, by immunoassay, midazolam (benzodiazepine was detected in putrefied material using GC/MS, thus indicating the hospitalization before death.

  5. Southwest USA Exhumation History Recorded Below the Great Unconformity

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    Heizler, M. T.; Karlstrom, K. E.

    2002-05-01

    The Southwestern USA Precambrian terranes preserve a long and variable exhumation history that can be tracked using thermochronological methods. This exhumation history is controlled on two interrelated scales. At first order, it is recognized that 1.7 to 1.4 Ga mid-crustal (10 km, 2-4 kbar) rocks were ultimately exhumed and reside below unconformities of variable age. In Arizona, Mesoproterozoic Apache Group and Neoproterozoic Supergroup sedimentary rocks lie directly on basement and thus indicate exhumation of some regions relatively soon following the 1.4 Ga events. In the Rocky Mountains of Colorado and the Rio Grande rift uplifts of New Mexico, basement is generally overlain by Cambrian to Mississippian strata. The unconformities are useful markers of net exhumation; however do not reveal a time-integrated path. Using published, and hundreds of new 40Ar/39Ar analyses of hornblende, muscovite, biotite and K-feldspar, and a growing U/Pb accessory mineral thermochronology database, we are extracting exhumation information with great detail. The thermochronological data continue to support the claim that relatively low net exhumation occurred following 1.7 to 1.6 Ga accretion of volcanic arc terranes to the southern margin of Laurentia. Mid-crustal (2-4 kbar) rocks stabilized soon after accretion, whereas in some regions like the Upper Granite Gorge, Grand Canyon deeper (6 kbar) metamorphic terranes decompressed to 3 kbar before stabilization. The cooling history of these mid-crustal rocks post 1.65 Ga remains somewhat unknown. Overall slow-cooling models (550 \\deg C to 300 \\deg C from 1.7 to 1.4 Ga) require high geothermal gradients in order to maintain 10 km deep rocks at high temperatures for 100's of Ma. Alternatively, isobaric cooling models to more normal geothermal gradients (i.e. 25 \\deg C/km) at ca. 1.65 Ga require later (1.4 Ga) thermal pulses and/or Mesoproterozoic vertical displacements to explain highly discordant thermochronological data. Either

  6. Exhumation history of the Serra do Mar, southeast Brazil

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    Carina Siqueira-Ribeiro, Marli; Hackspacher, Peter; Stuart, Finlay M.

    2016-04-01

    The Serra do Mar (SM) mountain range located along the southeast Brazilian continental margin is characterized by a low-lying coastal plateau separated from the elevated inland plateau by a steep escarpment. This morphology is a result of reactivation of Precambrian shear zones since the break-up of the Western Gondwana and opening of the South Atlantic Ocean in Early Cretaceous (1). Previous Thermochronological data from southeast Brazilian highlands (2,3), indicates that the landscape evolution is associated with several distinct exhumation events. In order to clarify the intensity and duration of the post-break up tectonic processes that shaped the SM we have undertaken a low temperature thermochronology study of crystalline basement, from the plateaus and escarpments situated between south of Rio de Janeiro and São Paulo state. Apatite fission track (AFT) and (U-Th/He) and (AHe) dating has been combined with geologic information to generate precise thermal histories and make initial attempts to quantify the amount of exhumation. AFT ages range from 145 to 53 Ma whereas preliminary AHe ages range from 75 to 37 Ma. Forward modeling using QTQt confirms Late Cretaceous-Paleogene cooling identified earlier (4,5) and identifies a distinct cooling phase in Neogene, between 30 and 10 Ma. Neogene cooling rapid caused exhumation of rocks 1 km through of the crust mainly in south portion of the SM in Rio de Janeiro state. (1) Almeida, 1976. An. Academia Bras de Cien 48 (suppl.), 15-(2) (2) Hackspacher et al. 2004. Gondwana Research,vol.2, 91-101. (3) Hiruma et al. 2010. Gondwana Research,18,674-687. (4) Siqueira-Ribeiro et al. 2011. Revista Bras. de Geomorfologia, 13, 3-14 (5) Cogné et al. 2012. Journal Geophysical Research, vol.117,1-16.

  7. An exhumed Late Paleozoic canyon in the rocky mountains

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    Soreghan, G.S.; Sweet, D.E.; Marra, K.R.; Eble, C.F.; Soreghan, M.J.; Elmore, R.D.; Kaplan, S.A.; Blum, M.D.

    2007-01-01

    Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator. ?? 2007 by The University of Chicago. All rights reserved.

  8. Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan

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    McQuarrie, Nadine; Tobgay, Tobgay; Long, Sean P.; Reiners, Peter W.; Cosca, Michael A.

    2014-01-01

    We link exhumational variability in space and time to the evolving geometry of the Himalayan fold–thrust belt in western Bhutan. By combining new and published geochronologic and thermochronologic data we document the burial age, peak temperatures and complete cooling history from 20 Ma to the present over an across-strike distance of ∼125 km. These integrated cooling curves highlight windows of fast exhumation that vary spatially and temporally. We propose that pulses of fast exhumation are a result of structures that facilitate the vertical motion of material, illustrated in sequentially-restored cross sections. Due to a range of permissible geometries at depth, we explore and evaluate the impact of geometry on kinematics and rates of deformation. The linked cooling history and cross sections provide estimates of both magnitude and timing of thrust sheet displacement and highlight temporal variability in potential shortening rates. Structural and chronologic data illustrate a general north to south progression of Himalayan deformation, with emplacement of the Main Central thrust (MCT), Paro thrust and Shumar thrust by 12 to no later than 9 Ma. Two different geometries and kinematic scenarios for the Lesser Himalayan duplex are proposed. A north to south propagating duplex system requires that the southern portion of that system, south of the MCT, deformed and cooled by 9 Ma, leaving only the southernmost thrust sheets, including the Main Boundary and Main Frontal thrusts, to deform between 9 and 0 Ma. This limited post 9 Ma shortening would necessitate a marked slowdown in convergence accommodated on the Main Himalayan thrust. A two-tiered duplex system, which allows for the Paro window duplex and the southern Baxa duplex to form simultaneously, permits duplex formation and accompanying exhumation until 6 Ma. Limited cooling from ∼200 °C to the surface post 6 Ma suggests either a decrease in shortening rates from 6 to 0 Ma or that duplex formation and

  9. Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan

    Science.gov (United States)

    McQuarrie, Nadine; Tobgay, Tobgay; Long, Sean P.; Reiners, Peter W.; Cosca, Michael A.

    2014-01-01

    We link exhumational variability in space and time to the evolving geometry of the Himalayan fold-thrust belt in western Bhutan. By combining new and published geochronologic and thermochronologic data we document the burial age, peak temperatures and complete cooling history from 20 Ma to the present over an across-strike distance of ∼125 km. These integrated cooling curves highlight windows of fast exhumation that vary spatially and temporally. We propose that pulses of fast exhumation are a result of structures that facilitate the vertical motion of material, illustrated in sequentially-restored cross sections. Due to a range of permissible geometries at depth, we explore and evaluate the impact of geometry on kinematics and rates of deformation. The linked cooling history and cross sections provide estimates of both magnitude and timing of thrust sheet displacement and highlight temporal variability in potential shortening rates. Structural and chronologic data illustrate a general north to south progression of Himalayan deformation, with emplacement of the Main Central thrust (MCT), Paro thrust and Shumar thrust by 12 to no later than 9 Ma. Two different geometries and kinematic scenarios for the Lesser Himalayan duplex are proposed. A north to south propagating duplex system requires that the southern portion of that system, south of the MCT, deformed and cooled by 9 Ma, leaving only the southernmost thrust sheets, including the Main Boundary and Main Frontal thrusts, to deform between 9 and 0 Ma. This limited post 9 Ma shortening would necessitate a marked slowdown in convergence accommodated on the Main Himalayan thrust. A two-tiered duplex system, which allows for the Paro window duplex and the southern Baxa duplex to form simultaneously, permits duplex formation and accompanying exhumation until 6 Ma. Limited cooling from ∼200 °C to the surface post 6 Ma suggests either a decrease in shortening rates from 6 to 0 Ma or that duplex formation and

  10. Direct observation of strain localization along the differentially exhumed SEMP fault system, Austria

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    Frost, E.; Dolan, J. F.; Hacker, B. R.; Ratschbacher, L.; Sammis, C. G.; Seward, G.; Cole, J.

    2009-12-01

    Structural analysis of key outcrops from ~5 to ~25 km exhumation depth along the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault-zone in Austria reveal highly localized deformation in the seismogenic crust down through the brittle-ductile transition (BDT), widening into a 2-km-wide mylonite at mid-crustal levels. Specifically, grain-size distribution analysis of brittley-deformed dolomite exhumed from the seismogenic crust reveals that strain progressively localized into a 10-m-wide fault core. Microstructural analysis of marbles and greywackes exhumed from the BDT shows off-fault ductile deformation only accommodated a minor portion of the displacement along the SEMP, with most of the strain localized along the contact between these two units. Similar analysis of gneisses and amphibolite-facies metasediments exhumed from just below the BDT shows that at this depth, the majority of displacement is focused into a 100-m-wide ductile shear zone, with further evidence for strain localization along grain boundaries, creating throughgoing shear zones at the grain-scale. At deeper exhumation levels (Rosenberg and Schneider, 2008), the SEMP is a 1-2-km-wide mylonite zone that extends to depths of at least 25 km. Collectively, these data indicate that slip along the SEMP was highly localized from throughout the seismogenic crust downward into at least the mid-crust.

  11. Exhumation History Of Brasilian Highlands After Late Cretaceous Alcaline Magmatism

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    Doranti Tiritan, Carolina; Hackspacher, Peter Christian; Carina Siqueira Ribeiro, Marli; Glasmacher, Ulrich Anton; Françoso de Godoy, Daniel

    2017-04-01

    The southeast Brazilian margin recorded a long history of tectonic and magmatic events after the Gondwana continent break up. The drifting of the South American Platform over a thermal anomaly generated a series of alkaline intrusions that are distributed from the interior to the coast from west to east. Several exhumation events are recorded on the region and we are providing insights on the landscape evolution of the region since Late Cretaceous, comparing low temperature thermochronology results from two alkaline intrusions regions. Poços de Caldas Alkaline Massif (PCAM), is lied in the interior, 300km from the coastline, covering over 800km2 intruding the Precambrian basement around 83Ma, nepheline syenites, phonolites and tinguaites intruded in a continuous and rapid sequence lasting between 1 to 2 Ma. São Sebastião Island (SSI) on the other hand is located at the coast, 200 km southeast of São Paulo. It is characterized by an intrusion in Precambrian/Brazilian orogen and intruded by Early Cretaceous sub-alkaline basic and acid dykes, as well as by Late Cretaceous alkaline stocks (syenites) and dykes (basanite to phonolite). Will be presenting the apatite fission track (AFT) and (U-Th)/He results that shows the main difference between the areas is that PCAM region register older history then the coastal area of SSI, where thermal history starts register cooling event after the South Atlantic rifting process, while in the PCAM area register a previous history, since Carboniferous. The results are giving support to studies that indicate the development of the relief in Brazil being strongly influenced by the local and regional tectonic movements and the lithological and structural settings. The landscape at the Late Cretaceous was witness of heating process between 90 and 60Ma due the intense uplift of South American Platform. The elevation of the isotherms is associated with the mantellic plumes and the crustal thickness that caused thermal anomalies due

  12. Mycoflora in Exhumed Seeds of Opuntia tomentosa and Its Possible Role in Seed Germination

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    María Esther Sánchez-Coronado

    2011-01-01

    Full Text Available The funicular cover of the Opuntia tomentosa seed limits imbibition; germination occurs only when the funicle is weakened or the funicular valve is removed. We investigated the role of fungi in funicular weakening and seed germination. Seeds that had been either buried in one of two sites or stored in the laboratory were germinated with and without a valve. Disinfected or nondisinfected seeds and their naked embryos were cultivated on agar or PDA. None of the 11 identified fungal genera grew on the disinfected control seeds or the embryos. The mycoflora present on disinfected and nondisinfected exhumed seeds suggest that the fungal colonization occurred in the soil and differed between the burial sites. Exhumed seeds with and without a valve germinated in high percentages, whereas only the control seeds without a valve germinated. Scanning electron micrographs showed that the hyphae penetrated, cracked, and eroded the funicular envelope of exhumed seeds.

  13. Softening trigerred by eclogitization, the first step toward exhumation during continental subduction

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    Jolivet, Laurent; Raimbourg, Hugues; Labrousse, Loïc; Avigad, Dov; Leroy, Yves; Austrheim, Håkon; Andersen, Torgeir B.

    2005-09-01

    Direct observation of peak pressure deformation in exhumed subduction channels is difficult because little evidence of this deformation survives later syn-exhumation deformation. Most ultrahigh-pressure parageneses are found in continental derived metamorphic rocks making continental subduction the best context to observe peak pressure deformation. Whereas many studies have enlightened the main driving parameters of exhumation such as buoyancy forces, low viscosity in the subduction channel, overburden removal by erosion and normal faulting, a basic question is seldom considered: why is a tectonic unit disconnected from the descending lithosphere and why does it start its way towards the surface? This event, seminal to exhumation processes, must involve some deformation and decoupling of the exhumed slice from the descending slab at peak pressure conditions or close to it. Our field observations in the Bergen arc show that Caledonian eclogitization and later amphibolitization of a granulitic terrane was achieved with a consistent component of simple shear compatible with the sense of the Caledonian subduction. Thus, the sequence of deformation preserved in the Bergen Arc documents the decoupling of subducted crustal material from the descending slab at the onset of exhumation. This observation suggests that deformation in the subduction channel is largely controlled by kinematic boundary conditions, i.e. underthrusting of the subducting slab. In this context of simple shear, metamorphic reactions assisted by fracturating, fluid infiltration and ductile deformation lower the resistance of rocks and allow the localisation of shear zones and the decoupling of buoyant tectonic units from the subducting slab. These tectonic units can then be incorporated into the channel circulation and start their upward travel.

  14. Geodynamic models for the post-orogenic exhumation of the lower crust

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    Bodur, O. F.; Gogus, O.; Karabulut, H.; Pysklywec, R. N.; Okay, A. I.

    2015-12-01

    Recent geodynamic modeling studies suggest that the exhumation of the high pressure and the very/ultra high-pressure crustal rocks may occur due to the slab detachment (break-off), slab roll-back (retreat) and the buoyancy-flow controlled subduction channel. We use convective removal (Rayleigh-Taylor, 'dripping' instability) mechanism to quantitatively investigate the burial and the exhumation pattern of the lower/middle crustal rocks from ocean subduction to post-collisional geodynamic configuration. In order to address the model evolution and track crustal particles for deciphering P-T-t variation, we conduct a series of thermo-mechanical numerical experiments with arbitrary Eularian-Lagrangian finite element code (SOPALE). We show how additional model parameters (e.g moho temperature, upper-middle crustal activation energy, density contrast between the lithosphere and the underlying mantle) can effectively influence the burial and exhumation depths, rate and the styles (e.g clockwise or counterclockwise). First series of experiments are designed to investigate the exhumation of crustal rocks at 32 km depth for only post-collisional tectonic setting -where pre-existing ocean subduction has not been implemented-. Model predictions show that a max. 8 km lower crustal burial occurs concurrent with the lower crustal convergence as a response to the mantle lithosphere dripping instability. The subsequent exhumation of these rocks up to -25 km- is predicted at an exhumation rate of 1.24 cm/year controlled by the removal of the underlying mantle lithosphere instability with crustal extension. At the second series of experiments, we tracked the burial and exhumation history of crustal particles at 22 and 31 km depths while pre-existing ocean subduction has been included before the continental collision. Model results show that burial depths down to 62 km occurs and nearly the 32 km of exhumation is predicted again by the removal of the mantle lithosphere after the

  15. Partial melting during exhumation of Paleozoic retrograde eclogite in North Qaidam, western China

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    Cao, Yu-ting; Liu, Liang; Chen, Dan-ling; Wang, Chao; Yang, Wen-qiang; Kang, Lei; Zhu, Xiao-hui

    2017-10-01

    Ultrahigh pressure (UHP) rocks are often overprinted by high pressure (HP) granulite-facies metamorphism during exhumation. Here we investigate retrograde eclogite from the Lvliangshan area in North Qaidam which is associated with abundant felsic veins. The eclogite adjacent to the vein shows conversion to garnet amphibolite. Petrographic, mineralogical, geochemical, geochronological data suggest that the eclogite has been experienced peak eclogite facies metamorphism at c. 440 Ma, followed by granulite facies retrogression at c. 420 Ma, and amphibolite facies overprinting at sodic amphibolite dehydration-melting together account for the formation of felsic veins during exhumation from the eclogite-facies to granulite-facies stages.

  16. Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste: Constraints on deformation processes in young orogens

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    Tate, Garrett W.; McQuarrie, Nadine; van Hinsbergen, Douwe J. J.; Bakker, Richard R.; Harris, Ron; Willett, Sean; Reiners, Peter W.; Fellin, Maria Giuditta; Ganerød, Morgan; Zachariasse, Willem Jan

    2014-06-01

    Although exhumation and surface uplift are important parameters in understanding orogenesis, the opportunity to measure both in close proximity is rare. In Timor-Leste (East Timor), deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart, permitting direct relation of uplift and exhumation by comparing micropaleontology to thermochronology interpreted through one-dimensional thermal modeling. Foraminifera in two deepwater synorogenic basins suggest basin uplift from depths of 1-2 km to depths of 350-1000 m between 3.35 and 1.88 Ma. Thermochronologic sampling was conducted in the central mountain belt between these basins. Of four muscovite 40Ar/39Ar samples, one provides a reset age of 7.13 ± 0.25 Ma in the Aileu high-grade belt that suggests 9-16 km of exhumation since that time. Eighteen zircon (U-Th)/He samples contain a group of reset ages in the Aileu Complex ranging from 4.4 to 1.5 Ma, which suggest exhumation rates of 1.0-3.1 mm/yr with 2.7-7.8 km of exhumation since these ages. Thirteen apatite (U-Th)/He ages in the Gondwana Sequence range from 5.5 to 1.4 Ma, suggesting 1-2 km of exhumation and defining a pattern of exhumation rates (ranging from 0.2 to 1.3 mm/yr) that positively correlates with average annual rainfall. Seven apatite fission track samples display varying degrees of partial resetting, with greatest resetting where apatite (U-Th)/He ages are youngest. Together, these data demonstrate extreme variability in surface uplift and exhumation over small spatial scales. We propose ongoing subsurface duplexing driven by subduction and underplating of Australian continental crust as the predominant driver for surface uplift and uplift-induced exhumation.

  17. Mechanisms of continental subduction and exhumation of HP and UHP rocks

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    Burov, Evgene; Francois, Thomas; Yamato, Philippe; Wolf, Sylvie

    We discuss possible scenarios of continental collision, and their relation to mechanisms of exhumation of HP and UHP rocks, inferred from thermo-mechanical numerical models accounting for thermo-rheological complexity of the continental lithosphere. Due to this complexity, mechanisms of continental

  18. Post-breakup burial and exhumation of passive continental margins: nine propositions to inform geodynamic models

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    Green, Paul F.; Duddy, Ian; Japsen, Peter; Chalmers, James; Bonow, Johan

    2017-04-01

    Despite many years of study, the processes involved in the post-breakup development of passive margins remain poorly understood. Integration of apatite fission track analysis (AFTA) and stratigraphic landscape analysis (SLA) at a number of margins has provided new insights into the development of elevated passive continental margins (EPCMs). In particular, these studies have highlighted the importance of integrating evidence from the preserved rock record with information on the deposition and erosional removal of rock units which are no longer present ("missing section"). From these studies we have formulated nine propositions regarding the formation of EPCMs and the nature of the controlling processes, viz: 1: EPCMs are not the inevitable consequence of rifting and breakup 2: Elevated topography at present-day EPCMs developed long after breakup 3: Similar EPCM landscapes at different margins suggest similar controlling processes 4: EPCMs undergo episodic burial and exhumation rather than slow monotonic denudation, both before rifting and after breakup 5: Post-breakup exhumation at continental margins is not restricted to elevated onshore regions 6: Post-breakup burial and exhumation have affected low lying margins as well as EPCMs 7: Episodic km-scale exhumation and re-burial also affects cratonic regions 8: Exhumation events show a broad level of synchroneity across continents and oceans and correlate with plate boundary events and changes in plate motions. 9: EPCMs are located where there is an abrupt, lateral change in crustal or lithospheric thickness These propositions imply that positive and negative vertical motions at passive margins are controlled by plate-scale processes. Many of these key aspects are absent from current geodynamic models of passive margin development. Understanding the processes that control vertical movements at passive continental margins requires development of realistic geodynamic models that honour these propositions.

  19. Rock uplift and exhumation of continental margins by the collision, accretion, and subduction of buoyant and topographically prominent oceanic crust

    National Research Council Canada - National Science Library

    Spikings, Richard; Simpson, Guy

    2014-01-01

    .... Here we combine previous thermochronological data with field observations to determine the amount of exhumation, rock, and surface uplift that occurs in the upper plate of Central and South American...

  20. Exhumation--Providing justice to victims of homicide: The Nigerian experience.

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    Faduyile, Francis Adedayo; Taiwo, Olufemi Joshua; Soyemi, Sunday Sokuunle; Akinde, Olakanmi Raphael

    2015-01-01

    Forensic investigations have been embraced in many developed countries to help investigate homicidal cases in their legal system amongst others. It is however still in infancy state in many developing countries, including Nigeria, making the use of this very vital tool very limited to prosecute cases. Some of the reasons include the low knowledge base of the investigating officers, to the dearth of Forensic personnel and the inability to use the findings to prosecute the offenders. The few cases where proper investigation is done, anatomic pathologists and sometimes medical officers are usually called to provide the forensic evidence. Often this involves exhumation of corpse. Exhumation of corpses for death investigation is not a common occurrence in Nigeria and we present the findings seen in these cases.

  1. Fission track ages and Exhumation mechanisms of the Tauern Window, Eastern Alps

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    Bertrand, Audrey; Rosenberg, Claudio; Garcia, Sebastian

    2010-05-01

    The Tauern Window (TW) is a thermal and structural dome which exposes Penninic basement, its cover units as well as parts of the overlying Austroalpine basement in the central part of the Eastern Alps. The peak of metamorphism was attained approximately at 30Ma (Selverstone et .al, 1992), followed by cooling and exhumation throughout Miocene time. Most of the tertiary exhumation of the Eastern Alps was localized in the TW, from Early Oligocene to late Miocene time. A current debate centers on the exhumation mechanisms of Penninic rocks in the core of the TW, namely to assess whether orogen-parallel extension (e.g., Selverstone, 1988) or a combination of folding and erosion (eg., Rosenberg et al., 2004) with subordinate extension were the controlling processes. E-W extension is well documented at the western (Brenner Fault) and eastern (Katschberg Fault) margins of the window (e.g., Behrmann, 1988; Selverstone, 1988; Genser and Neubauer, 1989). In contrast, upright folding dominates the internal structure of the dome, and in particular along its western part, where fold amplitudes, mostly eroded during folding, attained up to 10 km. This study attempts to assess the relative importance of folding and erosion and of orogen-parallel extension during exhumation by analyzing the spatial and temporal cooling patterns of apatite and zircon fission track ages. The compilation of published apatite and zircon fission track ages indicates a concentric younging of both the apatite and zircon ages toward the core of the TW. The concentric isochrones follow the map trace of the axial planes of the upright folds of the western and eastern TW. This cooling pattern is in contrast to the one expected by a process of extensional unroofing, which in map view would results in isochrons parallel to the extensional faults and progressively younging towards them (e.g., Foster et al., 2001). We therefore propose that folding and erosion were primarily responsible for exhuming the Penninic

  2. On microstructures, fluid pathways and sealing of fractures in exhumed carbonate reservoir outcrop analogues in the Oman Mountains

    OpenAIRE

    Arndt, Max

    2016-01-01

    This thesis focusses on the sealing of fractures in exhumed limestone reservoir outcrop analogues in the Oman Mountains. The work is largely based on observations at micro-scale of veins and cemented faults, which are well constrained to a regional model of successive brittle fracturing and faulting events - termed tectonic phases. Although our observations of (exhumed) deformation structures are static, we have made attempts to identify processes that create and destruct fracture permeabilit...

  3. Exhumation of the North Alpine Foreland Basin- Quantitative insights from structural analysis, thermochronology and a new thermal history model

    Science.gov (United States)

    Luijendijk, Elco; von Hagke, Christoph; Hindle, David

    2016-04-01

    Due to a wealth of geological and thermochronology data the northern foreland basin of the European Alps is an ideal natural laboratory for understanding the dynamics of foreland basins and their interaction with surface and geodynamic processes. We present an unprecedented compilation of thermochronological data from the basin and quantify cooling and exhumation rates in the basin by combining published and new vitrinite reflectance, apatite fission track and U-Th/He data with a new inverse burial and thermal history model. No correlation is obvious between inferred cooling and exhumation rates and elevation, relief or tectonics. We compare derived temperature histories to exhumation estimates based on the retro-deformation of Molasse basin and the Jura mountains, and to exhumation caused by drainage reorganization and incision. Drainage reorganization can explain at most 25% of the observed cooling rates in the basin. Tectonic transport of the basin's sediments over the inclined basement of the alpine foreland as the Jura mountains shortened can explain part of the cooling signal in the western part of the basin. However, overall a substantial amount of cooling and exhumation remains unexplained by known tectonic and surface processes. Our results document basin wide exhumation that may be related to slab roll-back or other lithospheric processes. Uncertainty analysis shows that thermochronometers can be explained by cooling and exhumation starting as early as the Miocene or as late as the Pleistocene. New (U-Th)/He data from key areas close to the Alpine front may provide better constraints on the timing of exhumation.

  4. State of stress in exhumed basins and implications for fluid flow: insights from the Illizi Basin, Algeria

    KAUST Repository

    English, Joseph M.

    2017-05-31

    The petroleum prospectivity of an exhumed basin is largely dependent on the ability of pre-existing traps to retain oil and gas volumes during and after the exhumation event. Although faults may act as lateral seals in petroleum traps, they may start to become hydraulically conductive again and enable fluid flow and hydrocarbon leakage during fault reactivation. We constrain the present day in situ stresses of the exhumed Illizi Basin in Algeria and demonstrate that the primary north–south and NW–SE (vertical strike-slip) fault systems in the study area are close to critical stress (i.e. an incipient state of shear failure). By contrast, the overpressured and unexhumed Berkine Basin and Hassi Messaoud areas to the north do not appear to be characterized by critical stress conditions. We present conceptual models of stress evolution and demonstrate that a sedimentary basin with benign in situ stresses at maximum burial may change to being characterized by critical stress conditions on existing fault systems during exhumation. These models are supportive of the idea that the breaching of a closed, overpressured system during exhumation of the Illizi Basin may have been a driving mechanism for the regional updip flow of high-salinity formation water within the Ordovician reservoirs during Eocene–Miocene time. This work also has implications for petroleum exploration in exhumed basins. Fault-bounded traps with faults oriented at a high angle to the maximum principal horizontal stress direction in strike-slip or normal faulting stress regimes are more likely to have retained hydrocarbons in exhumed basins than fault-bounded traps with faults that are more optimally oriented for shear failure and therefore have a greater propensity to become critically stressed during exhumation.

  5. Cenozoic exhumation history of South China: A case study from the Xuefeng Mt. Range

    Science.gov (United States)

    Wang, Yannan; Zhang, Jin; Zhang, Beihang; Zhao, Heng

    2018-01-01

    New apatite fission track (AFT) dating was applied to the Xuefeng Mt. Range and Yuanma Basin to constrain the Cenozoic exhumation process of the southeastern Yangtze Block, South China. The analyzed samples in this study have AFT ages ranging from 27.9 ± 2.5 to 61.5 ± 5.9 Ma, which are younger than the deposition or crystallization ages of the host rocks. The AFT analysis and thermal history modeling indicate that both the Xuefeng Mt. Range and the Yuanma Basin underwent significant exhumation during the early Cenozoic (ca. 60-40 Ma). These samples were rapidly exhumed to near the surface during this period. Our results suggest that an important tectonic event occurred along or near regional fault zones (e.g., the Qinhang Fault) in South China during the early Cenozoic (ca. 60-40 Ma). However, it is difficult to relate this event to the Eastern Sichuan fold belt, which is much older and is characterized by large-scale folding and thrusting. Combined with fieldwork in the Yuanma, Xupu, and Xinning basins, we refute the Cretaceous "Pan-Yangtze Basin" that was proposed to have been separated by the uplifted Xuefeng Mt. Range after the Late Cretaceous. The exhumation stage from ca. 60 Ma to 40 Ma was an important period during which plate movements across the eastern Asian and Pacific regions were reorganized. The early Cenozoic tectonothermal event in South China can be attributed to a change in the direction and speed of the subduction of the Pacific Plate beneath the Eurasian Plate. An Oligocene-Miocene cooling event was also recorded in the eastern Xuefeng Mt. Range, which we tentatively attribute to the activity of dextral faults in this area as a far-field effect of the collision between the Indian and Eurasian plates.

  6. Late Cretaceous extension and exhumation of the Stong Complex and Taku Schist, NE Peninsular Malaysia

    Science.gov (United States)

    François, Thomas; Afiq Md, Muhammad; Matenco, Liviu; Willingshofer, Ernst; Fatt Ng, Tham; Iskandar Taib, N.; Kamal Shuib, Mustaffa

    2017-04-01

    Dismembering large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts as exemplified by the Stong Complex and Taku Schist of northern Peninsular Malaysia. For this particular case we have employed a field and microstructural kinematic study combined with low temperature thermo-chronology to analyse the tectonic and exhumation history. The results show that the late Palaeozoic - Triassic Indosinian orogeny created successive phases of burial related metamorphism, shearing and contractional deformation. This orogenic structure was then dismembered during a Cretaceous thermal event that culminated in the formation of a large scale late Santonian - early Maastrichtian extensional detachment, genetically associated with crustal melting, the emplacement of syn-kinematic plutons and widespread migmatisation. The emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range, represented by amphibolite-facies mylonites and more brittle structures, such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment. The formation of this detachment and a first phase of Late Cretaceous cooling was followed by renewed Eocene - Oligocene exhumation evidenced from our apatite fission track ages. We infer that an initial Cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and normal fault rotation. These Cretaceous processes played a critical role in the establishment of the presently observed crustal structure of Peninsular Malaysia.

  7. Cooling, exhumation, and kinematics of the Kanchenjunga Himal, far east Nepal

    Science.gov (United States)

    Larson, Kyle P.; Camacho, Alfredo; Cottle, John M.; Coutand, Isabelle; Buckingham, Heather M.; Ambrose, Tyler K.; Rai, Santa Man

    2017-06-01

    New single crystal 40Ar/39Ar and apatite fission track ages from the Kanchenjunga region of far east Nepal yield insight into the timing of assembly of the Himalayan midcrust and the mechanisms that controlled its exhumation. The 40Ar/39Ar data are compared with new U(Th)/Pb zircon and monazite intrusive crystallization ages and existing metamorphic monazite ages from across the study area to test for internal consistency and potential excess Ar contributions. This new data set, which significantly enhances the density and spatial coverage available from the region, shows that inferred thrust-sense discontinuities within the now-exhumed former midcrustal rocks exposed therein must have ceased motion by 12 Ma. Furthermore, the spatial distribution of ages across the Kanchenjunga region, older ages ( 12-16 Ma) to the south and north and younger ages ( 8 Ma) in the middle portion of the transect, is compatible with simulations of tectonic-enhanced exhumation above a developing duplex system in nearby Bhutan.

  8. Exhumation of the Greater Himalayan Sequence Along the Zanskar Shear Zone, NW India

    Science.gov (United States)

    Basta, S.; Beck, E.; Burlick, T.

    2013-12-01

    The Zanskar Shear Zone (ZSZ), the western extent of the South Tibetan Detachment System, exposes high-grade metamorphic rocks of the Greater Himalayan Sequence (GHS) in its footwall. Granites and metapelites collected along the the ZSZ in the Suru River valley provide how and when the GHS rocks exhumed and were deformed. There are two suits of Paleozoic granites deformed within the ZSZ: Pan-African Cambrian-Ordovician granites at the cores of gneiss domes and Mississippian-Permian granites related to Panjal Traps magmatism. Age of Himalayan granites indicates 28-16 Ma which is concurrent with anatectic leucogranite crystallization. The metamorphic mineral assemblage indicates increasing metamorhic grade from NE to SW and comprises Qtz × Kfs + Pl + Bt × Ms × Sil × Ky × Grt × St × Chl × Tur × Rt. In addition to macroscopic evidence, strongly deformed quartz grains, deformation twins, pressure shadows, and kink bands have been observed to demonstrate micro-tectonics evidence. There are two different method to explain exhumation and deformation of the GHS metapelites: Electron backscatter diffraction (EBSD) crystallographic mapping and pseudosection modeling. While EBSD indicates the potential temperature of deformation, pseudosection modeling with Perple_X specifically presents the exhumation path of the GHS rocks. Pseudosection modeling with Perple_X , based on whole-rock geochemical analysis, is set pressure and temperature to 0.4-1.2 GPa and 300-900°C, and uses specific solution models, Bio(TCC), Chl(HP), St(HP), feldspar, Mica(CHA), Gt(HP), and hCrd, namely. These two methods are used by combining with geo/thermochronology data from U-Pb, 40Ar/39Ar, and (U-Th)/He, constraining the age of metamorphism, the cooling and exhumation time of the GHS rocks, and the end of shearing of deformation, respectively. 40Ar/39Ar dating on muscovite and biotite constrains cooling and exhumation ages of the GHS as ~20-19 Ma and 15 Ma, respectively. A metamorphic pressure

  9. Styles and Causes of Deformation and Exhumation Related to Flat-slab Subduction of the Yakutat Microplate: A Low-temperature Thermochronometer Perspective

    Science.gov (United States)

    Armstrong, P. A.; Haeussler, P. J.; Arkle, J. C.

    2011-12-01

    Flat-slab subduction of the Yakutat microplate has caused deformation and exhumation across a NW-SE trending swath (>600-km long by ~250 km wide) across southern Alaska. However, the styles and causes of deformation and exhumation vary markedly along the swath. In SE Alaska and adjacent Canada at the SE end of the swath, apatite (U-Th)/He [AHe] ages of ~0.5 Ma and detrital zircon fission-track peak ages of ~3 Ma record very rapid exhumation. This exhumation is related to focusing of deformation around transpressional bends at the outboard Yakutat collision front. At the NW end of the swath, 1 to 6 Ma AHe and apatite fission-track ages [AFT] in the Alaska Range record a complicated history of rapid exhumation. Several factors may contribute to the deformation history of this inboard region including localized transpressional deformation along the dextral Denali fault, changes in Yakutat microplate thickness, impingement of thicker upper plate crust across the Denali fault system, and changes in plate motion. The Talkeetna Mountains (TM), western Chugach Mountains (CM), and Prince William Sound (PWS) contain regions of focused and rapid exhumation separated by regions of slow exhumation and are key locations, between the inboard Alaska Range and outboard St. Elias areas, in understanding the array of deformation processes related to flat-slab subduction in southern Alaska. TM AHe ages generally are >20 Ma, suggesting relatively slow average long-term exhumation rates, but exhumation may have accelerated recently. Farther south, AHe ages are ~15 Ma in most of the PWS, but decrease northward to 3-4 Ma in the core of the western CM. AFT ages similarly decrease from 30 Ma in the PWS to 6 Ma in the CM core. Collectively, these ages record a bull's eye pattern of exhumation that is concentrated at a syntaxial bend in the regional topographic and structural grain in the western CM. The young exhumation here was probably caused by Yakutat underplating, which was focused into

  10. Mesozoic burial, Mesozoic and Cenozoic exhumation of the Funeral Mountains core complex, Death Valley, Southeastern California

    Science.gov (United States)

    Beyene, Mengesha Assefa

    2011-12-01

    The Funeral Mountains of Death Valley National Park, CA, provide an opportunity to date metamorphism resulting from crustal shortening and subsequent episodic extensional events in the Sevier hinterland. It was not clear whether crustal shortening and thus peak temperature metamorphism in the hinterland of the Sevier-Laramide orogenic wedge have occurred whether in Late Jurassic, Early Cretaceous, Late Cretaceous or somewhere between. Particularly ambiguous is the timing of crustal shortening in the deep levels of the hinterland of the Sevier belt, now manifest in the metamorphic core complexes, and how and when these middle-to-lower crustal rocks were exhumed. A 6-point garnet and a whole rock Savillax isochron from middle greenschist facies pelitic schist of the southeastern Funeral Mountains core complex yields an age of 162.1 +/- 5.8 Ma (2sigma). Composite PT paths determined from growth-zoned garnets from the same samples show a nearly isothermal pressure increase of ˜2 kbar at ˜490°C, suggesting thrust burial at 162.1 +/- 5.8 Ma. A second sample of Johnnie Formation from the comparatively higher metamorphic grade area to the northwest (East of Chloride Cliff) yielded an age of 172.9 +/- 4.9 Ma (2sigma) suggesting an increase of thrust burial age towards the higher grade rocks (northwest part of the core complex), consistent with paleo-depth interpretation and metamorphic grade. 40Ar/ 39Ar muscovite ages along footwall of the Boundary Canyon detachment fault and intra-core Chloride Cliff shear zone exhibit significant 40Ar/39Ar muscovite age differences. For samples from the immediate footwall of BCD, the pattern of ages decreasing toward the northwest is consistent with differences in depth of metamorphism, and for Late Cretaceous, top-to-northwest exhumation by motion along the precursor BCD; consistent with mesoscopic and microscopic kinematic studies. Samples from the footwall of the structurally-lower Chloride Cliff shear zone yield Tertiary 40Ar/39Ar

  11. Deformation Processes of Subduction and Exhumation in Alpine Eclogites with Focus on the Tauern Window

    Science.gov (United States)

    Stipp, M.; Keppler, R.; Behrmann, J. H.; Heidelbach, F.

    2015-12-01

    Deformation processes inside subduction channels or during subduction and exhumation of HP and UHP nappes in collisional orogens are a matter of debate. Dehydration embrittlement, localized faulting and dissolution-precipitation creep have been suggested as major deformation processes. These processes, however, do not correspond to the field-based deformation record of penetrative foliations and stretching lineations in most HP and UHP nappes of the Central Alps, indicative of dislocation and diffusion creep processes including metamorphic reaction transfer. The Eclogite Zone of the Tauern Window (Eastern Alps) consists of fresh and retrogressed eclogites in a matrix of metasediments. Peak metamorphism was at 600°C and 2.0-2.5 GPa in the Oligocene followed by fast exhumation within a few million years. Eclogites and blueschists display a pronounced foliation and lineation fabric. Fresh and retrogressed samples have been investigated by neutron diffraction texture, electron backscatter diffraction and microprobe analysis. All investigated eclogites exhibit a pronounced crystallographic preferred orientation (CPO) of omphacite. In retrogressed eclogites the glaucophane CPO is strong as well and matches topologically always that of omphacite. Omphacite microstructures are characteristic of subgrain rotation recrystallization, identifying high-stress dislocation creep as main deformation mechanism. Diffusion and reaction transfer can be derived from the variable jadeite contents in omphacite porphyroclasts and recrystallized grains. The corresponding CPO of omphacite and glaucophane indicates that progressive CPO development spanned the whole high-pressure part of metamorphism and lasted until retograde blueschist grade. We propose that deformation in the Eclogite Zone was mostly distributed and continuous during subduction and exhumation and that dislocation and diffusion creep processes accommodated most of the strain below the frictional-viscous transition.

  12. Relating orogen width to shortening, erosion, and exhumation during Alpine collision

    OpenAIRE

    Rosenberg, Claudio L.; Berger, A.; Bellahsen, Nicolas; Bousquet, R.

    2015-01-01

    International audience; We investigate along-strike width changes of the thickened, accreted lower plate (TALP) in the Central and in the Eastern Alps. We set the width of the TALP in relation to the inferred amount of collisional shortening and exhumation along six orogen-scale cross sections. Taking the present-day, along-strike gradients in the amount of collisional shortening to represent the temporal evolution of the collisional wedge, it may be concluded that the cross-sectional area of...

  13. Petrofabrics of High-Pressure Rocks Exhumed at the Slab-Mantle Interface from the 'Point of No Return'

    Science.gov (United States)

    Whitney, D. L.; Teyssier, C. P.; Seaton, N. C.; Fornash, K.

    2014-12-01

    The highest pressure typically recorded by metamorphic rocks exhumed from oceanic subduction zones is ~2.5±1 GPa, corresponding to the maximum decoupling depth (MDD) (80±10 km) identified in active subduction zones; beyond the MDD (the 'point of no return') exhumation is unlikely. One of the few places where rocks returned from the MDD largely unaltered is Sivrihisar, Turkey: a structurally coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from ~80 to 45 km. Crystallographic fabrics and other structural features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, heterogeneous microstructures and crystallographic fabrics record deformation and dynamic recrystallization from ~2.6 GPa to ~1.5 GPa, as expressed by transition from prism c-axis patterns through progressive overprinting and activation of rhomb and basal slip. Omphacite, glaucophane, phengite, and lawsonite in quartzite remained stable during deformation. In marble, CaCO3 deformed in dislocation creep as aragonite, producing strong crystallographic fabrics. This fabric persisted through formation of calcite and destruction of the shape-preferred orientation, indicating the strength of aragonite marble. Omphacite in metabasalt and quartzite displays an L-type crystallographic fabric. Lawsonite kinematic vorticity data and other fabrics in metabasalt are consistent with exhumation involving increasing amounts of pure shear relative to simple shear and indicate strain localization and simple shear near the fault contact between the high-pressure unit and a serpentinite body. This large coaxial component multiplied the exhuming power of the subduction channel and forced rocks to return from the MDD.

  14. Tales from the grave: Opposing autopsy reports from a body exhumed.

    Science.gov (United States)

    Gunasekera, R S; Brown, A B; Costas, E H

    2012-07-01

    We report an autopsy case of a 42-year-old woman who, when discovered, had been dead in her apartment for approximately 1 week under circumstances involving treachery, assault and possible drug overdose. This case is unique as it involved two autopsies of the deceased by two different medical examiners who reached opposing conclusions. The first autopsy was performed about 10 days after death. The second autopsy was performed after an exhumation approximately 2 years after burial. Evidence collected at the crime scene included blood samples from which DNA was extracted and analysed, fingerprints and clothing containing dried body fluids. The conclusion of the first autopsy was accidental death due to cocaine toxicity; the conclusion of the second autopsy was death due to homicide given the totality of evidence. Suspects 1 and 2 were linked to the death of the victim by physical evidence and suspect 3 was linked by testimony. Suspect 1 received life in prison, and suspects 2 and 3 received 45 and 20 years in prison, respectively. This case indicates that cocaine toxicity is difficult to determine in putrefied tissue and that exhumations can be important in collecting forensic information. It further reveals that the combined findings of medical examiners, even though contradictory, are useful in determining the circumstances leading to death in criminal justice. Thus, this report demonstrates that such criminal circumstances require comparative forensic review and, in such cases, scientific conclusions can be difficult. Published by Elsevier Ltd.

  15. Toxicological Analysis of Opiates from Alternative Matrices Collected from an Exhumed Body.

    Science.gov (United States)

    Cippitelli, Marta; Mirtella, Dora; Ottaviani, Giovanni; Tassoni, Giovanna; Froldi, Rino; Cingolani, Mariano

    2017-05-18

    In this case study, the body of a 45-year-old man was exhumed after 1 year at the request of the public prosecutor to assess whether the death was caused by drug consumption. Toxicological analyses were performed on several matrices, including liver, kidney, and the alternative matrices hair and teeth. The systematic toxicological analysis (STA), which consisted of basic and acid liquid/liquid extraction and gas chromatography-mass spectrometry (GC-MS) analysis, showed the presence of opiates in each of the matrices analyzed. Subsequently, to confirm and quantify the presence of opioids, samples of each of the matrices were subjected to solid-phase extraction and specific GC-MS analysis. The case presented demonstrates the possibility of drug detection in an exhumed body that has been buried for 1 year, despite the problems of quantitative interpretation of the data, and that toxicological results could be useful along with other forensic evidence. © 2017 American Academy of Forensic Sciences.

  16. Exhumation of the Meliata high-pressure rocks (Western Carpathians: Petrological and structural records in blueschists

    Directory of Open Access Journals (Sweden)

    Faryad Shah Wali

    1999-06-01

    Full Text Available The Meliata unit, situated in the SE part of the Western Carpathians, represents an accretionary complex assembled during the closure of the Triassic-Jurassic Meliata oceanic basin. Blueschists, ophiolites and very low-grade metamorphosed sedimentary rocks are imbricated in a tectonic zone between the Gemericum and the Silica nappe. Petrological and microstructural analyses indicate a single progressive deformation coincident with prograde metamorphism at blueschist facies conditions. The foliation is defined by preferred orientation of mica, blue amphibole and rarely also by Na-pyroxene. The exhumation path is documented by ductite deformation, formed at blueschist-greenschist facies boundary and at greenschist facies conditions. The E-W directed thrust faults which are parallel to the foliation seem to be responsible for exhumation of the blueschists. Later stages of deformation in phyllites are documented by shear bands that crosscut the blueschist facies foliation. Low-temperature Cretaceous nappe tectonics resulted in brittle deformation and used mostly the older tectonic systems that formed at blueschist-greenschist facies conditions

  17. Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

    Science.gov (United States)

    Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

    2017-04-01

    The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

  18. Kinematics of post-orogenic extension and exhumation of the Taku Schist, NE Peninsular Malaysia

    Science.gov (United States)

    Md Ali, M. A.; Willingshofer, E.; Matenco, L.; Francois, T.; Daanen, T. P.; Ng, T. F.; Taib, N. I.; Shuib, M. K.

    2016-09-01

    Recent studies imply that the formation and evolution of many SE Asian basins was driven by extensional detachments or systems of low-angle normal faults that created significant crustal exhumation in their footwalls. In this context, the architecture of the Triassic Indosinian orogen presently exposed in Peninsular Malaysia is compatible with significant extension post-dating the orogenic event. In this study we performed a kinematic analysis based on fieldwork and microstructural observations in the Taku Schist, Kemahang granite and the surrounding Gua Musang sediments of northern Peninsular Malaysia in order to shed light on processes related to the build-up and subsequent demise of the Indosinian orogen. The first three phases of deformation were related to an overall period of E-W oriented contraction and burial metamorphism. These phases of deformation are characterized by isoclinal folding with flat lying axial plane cleavages (D1), asymmetrical folding, top-to-the-W-SW shearing (D2) and upright folding (D3). All are in general agreement with observations of the previously inferred Permo-Triassic Indosinian orogeny. During these times, the Taku Schist, a sequence of Paleozoic clastic sediments with mafic intercalations was metamorphosed to amphibolite facies. These rocks are most likely equivalent to the ones exposed in the Bentong-Raub suture zone. Structural relations suggest that the Triassic Kemahang pluton is syn-kinematic, which provides important constraints for the timing of these contractional events. We demonstrate that the overall shortening was followed by a hitherto undescribed extension in NW-SE direction resulting in the formation of a large-scale detachment, the Taku detachment, in northern Peninsular Malaysia. Extension probably reactivated the former subduction plane as a detachment and exhumed previously buried and metamorphosed rocks of similar lithological composition to the neighboring Bentong-Raub suture zone. Such a mechanism is

  19. Cretaceous–Cenozoic burial and exhumation history of the Chukchi shelf, offshore Arctic Alaska

    Science.gov (United States)

    Craddock, William H.; Houseknecht, David W.

    2016-01-01

    Apatite fission track (AFT) and vitrinite reflectance data from five exploration wells and three seafloor cores illuminate the thermal history of the underexplored United States Chukchi shelf. On the northeastern shelf, Triassic strata in the Chevron 1 Diamond well record apatite annealing followed by cooling, possibly during the Triassic to Middle Jurassic, which is a thermal history likely related to Canada Basin rifting. Jurassic strata exhumed in the hanging wall of the frontal Herald Arch thrust fault record a history of probable Late Jurassic to Early Cretaceous structural burial in the Chukotka fold and thrust belt, followed by rapid exhumation to near-surface temperatures at 104 ± 30 Ma. This history of contractional tectonism is in good agreement with inherited fission track ages in low-thermal-maturity, Cretaceous–Cenozoic strata in the Chukchi foreland, providing complementary evidence for the timing of exhumation and suggesting a source-to-sink relationship. In the central Chukchi foreland, inverse modeling of reset AFT samples from the Shell 1 Klondike and Shell 1 Crackerjack wells reveals several tens of degrees of cooling from maximum paleo-temperatures, with maximum heating permissible at any time from about 100 to 50 Ma, and cooling persisting to as recent as 30 Ma. Similar histories are compatible with partially reset AFT samples from other Chukchi wells (Shell 1 Popcorn, Shell 1 Burger, and Chevron 1 Diamond) and are probable in light of regional geologic evidence. Given geologic context provided by regional seismic reflection data, we interpret these inverse models to reveal a Late Cretaceous episode of cyclical burial and erosion across the central Chukchi shelf, possibly partially overprinted by Cenozoic cooling related to decreasing surface temperatures. Regionally, we interpret this kinematic history to be reflective of moderate, transpressional deformation of the Chukchi shelf during the final phases of contractional tectonism in the

  20. The preservation of high-pressure rocks during exhumation: metagranites and metapelites

    Science.gov (United States)

    Proyer, Alexander

    2003-10-01

    Metagranites in the NKFMASH system require external hydration during prograde high-pressure metamorphism in order to equilibrate to ambient HP conditions by producing more siliceous muscovite. Any lack of external fluid or the disappearance of biotite stops re-equilibration and thus prevents recording of high-pressure conditions. The same hydration reactions cause dehydration during exhumation. Orthogneiss from shear zones or adjacent to metapelites and metabasites will take up external fluid during subduction and record the highest P- T conditions, but will also be the first to dehydrate upon exhumation, now hydrating other lithologies and probably refuelling shearzones. The (de)hydration behavior of Ca-bearing metagranitoids is similar to that in the Ca-free system. However, the anorthite component of plagioclase decomposes with increasing pressure to form either (clino)zoisite or a grossular-rich garnet. Both reactions are fluid-consuming. If H 2O is supplied from an external source, the garnet-bearing assemblage can record P- T conditions up to very high pressures, but dehydrates again during heating and/or decompression to form a more Fe-rich garnet and Al-rich mica(s). The garnet compositions observed in natural HP-metagranites are mostly too Fe-rich to be formed in the presence of an H 2O-rich fluid. N(C)KFMASH metapelites generally have a more complex mineralogy and succession of mineral assemblages along a P- T path. The H 2O contained in hydrous silicates like chlorite and chloritoid is only partly released, but partly transferred to other minerals like paragonite, glaucophane or phengite during subduction and further dehydration during exhumation is common. The mineral assemblage preserved by the rock may then record P- T conditions way below those of the actual pressure and temperature peak of the path. Contouring of the P- T pseudosection of a specific metapelite composition with mode isopleths for H 2O shows which P- T conditions along a given path

  1. Late Cretaceous to Cenozoic deformation and exhumation of the Chilean Frontal Cordillera (28°-29°S), Central Andes

    Science.gov (United States)

    Martínez, Fernando; Parra, Mauricio; Arriagada, César; Mora, Andrés; Bascuñan, Sebastián; Peña, Matías

    2017-11-01

    The Frontal Cordillera in northern Chile is located over the flat-slab subduction segment of the Central Andes. This tectonic province is characterized by a thick-skinned structural style showing evidence of tectonic inversion and basement-involved compressive structures. Field data, U-Pb geochronological and apatite fission track data were used to unravel partially the tectonic history of the area. Previous U-Pb ages of synorogenic deposits exposed on the flanks of basement-core anticlines indicate that Andean deformation started probably during Late Cretaceous with the tectonic inversion of Triassic and Jurassic half-grabens. New U-Pb ages of the synorogenic Quebrada Seca Formation suggest that this deformation continued during Paleocene (66-60 Ma) with the reverse faulting of pre-rift basement blocks. The analysis of new apatite fission-track data shows that a rapid and coeval cooling related to exhumation of the pre-rift basement blocks occurred during Eocene times. This exhumation event is interpreted for first time in the Chilean Frontal Cordillera and it could have occurred simultaneously with the propagation of basement-involved structures. The age of this exhumation event coincides with the Incaic orogenic phase, which is interpreted as the most important to the Central Andes in terms of shortening, uplift and exhumation.

  2. The Alps 2: Controls on crustal subduction and (ultra)high‐pressure rock exhumation in Alpine‐type orogens

    National Research Council Canada - National Science Library

    Butler, Jared P; Beaumont, Christopher; Jamieson, Rebecca A

    2014-01-01

    ...‐type orogens and the Alps per se, focusing on (ultra)high‐pressure ((U)HP) metamorphic rocks. The models show that UHP rocks form and exhume by burial and subsequent buoyant ascent of continental crust in the subduction conduit...

  3. Long-term exhumation of a Palaeoproterozoic orogen and the role of pre-existing heterogeneous thermal crustal properties

    DEFF Research Database (Denmark)

    McGregor, E.D.; Nielsen, S.B.; Stephenson, R.A.

    2013-01-01

    Ma. Modelling the 3D exhumation of a heterogeneous crust with flat topography demonstrates that some of the variability in observed fission-track ages could be attributed to heterogeneity in crustal heat production and thermal conductivity. The remaining variability in the observed dataset...

  4. Early Tertiary exhumation of the flank of a forearc basin, southwest Talkeetna Mountains, Alaska

    Science.gov (United States)

    Bleick, Heather A.; Till, Alison B.; Bradley, Dwight C.; O’Sullivan, Paul; Wooden, Joe L.; Bradley, Dan B.; Taylor, Theresa A.; Friedman, Sam B.; Hults, Chad P.

    2012-01-01

    New geochronologic and thermochronologic data from rocks near Hatcher Pass, southwest Talkeetna Mountains, Alaska, record earliest Paleocene erosional and structural exhumation on the flank of the active Cook Inlet forearc basin. Cretaceous plutons shed sediments to the south, forming the Paleocene Arkose Ridge Formation. A Paleocene(?)-Eocene detachment fault juxtaposed ~60 Ma metamorphic rocks with the base of the Arkose Ridge Formation. U-Pb (analyzed by Sensitive High Resolution Ion Micro Probe Reverse Geometry (SHRIMP-RG)) zircon ages of the Cretaceous plutons, more diverse than previously documented, are 90.3±0.3 (previously considered a Jurassic unit), 79.1±1.0, 76.1±0.9, 75.8±0.7, 72.5±0.4, 71.9±0.3, 70.5±0.2, and 67.3±0.2 Ma. The cooling of these plutons occurred between 72 and 66 Ma (zircon fission track (FT) closure ~225°C). 40Ar/39Ar analyses of hornblende, white mica, and biotite fall into this range (Harlan and others, 2003). New apatite FT data collected on a west-to-east transect reveal sequential exhumation of fault blocks at 62.8±2.9, 54±2.5, 52.6±2.8, and 44.4±2.2 Ma. Plutonic clasts accumulated in the Paleocene Arkose Ridge Formation to the south. Detrital zircon (DZ) ages from the formation reflect this provenance: a new sample yielded one grain at 61 Ma, a dominant peak at 76 Ma, and minor peaks at 70, 80, 88, and 92 Ma. The oldest zircon is 181 Ma. Our apatite FT ages range from 35.1 to 50.9 Ma. Greenschist facies rocks now sit structurally between the plutonic rocks and the Arkose Ridge Formation. They are separated from plutonic rocks by the vertical Hatcher Pass fault and from the sedimentary rocks by a detachment fault. Ar cooling ages (Harlan and others, 2003) and new zircon FT ages for these rocks are concordant at 61-57 Ma, synchronous with deposition of the Arkose Ridge Formation. A cooling age of ~46 Ma came from one apatite FT sample. The metamorphic protolith (previously considered Jurassic) was deposited at or after

  5. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars.

    Science.gov (United States)

    Grotzinger, J P; Gupta, S; Malin, M C; Rubin, D M; Schieber, J; Siebach, K; Sumner, D Y; Stack, K M; Vasavada, A R; Arvidson, R E; Calef, F; Edgar, L; Fischer, W F; Grant, J A; Griffes, J; Kah, L C; Lamb, M P; Lewis, K W; Mangold, N; Minitti, M E; Palucis, M; Rice, M; Williams, R M E; Yingst, R A; Blake, D; Blaney, D; Conrad, P; Crisp, J; Dietrich, W E; Dromart, G; Edgett, K S; Ewing, R C; Gellert, R; Hurowitz, J A; Kocurek, G; Mahaffy, P; McBride, M J; McLennan, S M; Mischna, M; Ming, D; Milliken, R; Newsom, H; Oehler, D; Parker, T J; Vaniman, D; Wiens, R C; Wilson, S A

    2015-10-09

    The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp). Copyright © 2015, American Association for the Advancement of Science.

  6. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

    Science.gov (United States)

    Grotzinger, J.P.; Gupta, S.; Malin, M.C.; Rubin, D.M.; Schieber, J.; Siebach, K.; Sumner, D.Y.; Stack, K.M.; Vasavada, A.R.; Arvidson, R.E.; Calef, F.; Edgar, Lauren; Fischer, W.F.; Grant, J.A.; Griffes, J.L.; Kah, L.C.; Lamb, M.P.; Lewis, K.W.; Mangold, N.; Minitti, M.E.; Palucis, M.C.; Rice, M.; Williams, R.M.E.; Yingst, R.A.; Blake, D.; Blaney, D.; Conrad, P.; Crisp, J.A.; Dietrich, W.E.; Dromart, G.; Edgett, K.S.; Ewing, R.C.; Gellert, R.; Hurowitz, J.A.; Kocurek, G.; Mahaffy, P.G.; McBride, M.J.; McLennan, S.M.; Mischna, M.A.; Ming, D.; Milliken, R.E.; Newsom, H.; Oehler, D.; Parker, T.J.; Vaniman, D.; Wiens, R.C.; Wilson, S.A.

    2015-01-01

    The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

  7. Spatial variations in focused exhumation along a continental-scale strike-slip fault: The Denali fault of the eastern Alaska Range

    Science.gov (United States)

    Benowitz, J.A.; Layer, P.W.; Armstrong, P.; Perry, S.E.; Haeussler, P.J.; Fitzgerald, P.G.; VanLaningham, S.

    2011-01-01

    40Ar/39Ar, apatite fission-track, and apatite (U-Th)/He thermochronological techniques were used to determine the Neogene exhumation history of the topographically asymmetric eastern Alaska Range. Exhumation cooling ages range from ~33 Ma to ~18 Ma for 40Ar/39Ar biotite, ~18 Ma to ~6 Ma for K-feldspar minimum closure ages, and ~15 Ma to ~1 Ma for apatite fission-track ages, and apatite (U-Th)/He cooling ages range from ~4 Ma to ~1 Ma. There has been at least ~11 km of exhumation adjacent to the north side of Denali fault during the Neogene inferred from biotite 40Ar/39Ar thermochronology. Variations in exhumation history along and across the strike of the fault are influenced by both far-field effects and local structural irregularities. We infer deformation and rapid exhumation have been occurring in the eastern Alaska Range since at least ~22 Ma most likely related to the continued collision of the Yakutat microplate with the North American plate. The Nenana Mountain region is the late Pleistocene to Holocene (~past 1 Ma) primary locus of tectonically driven exhumation in the eastern Alaska Range, possibly related to variations in fault geometry. During the Pliocene, a marked increase in climatic instability and related global cooling is temporally correlated with an increase in exhumation rates in the eastern Alaska Range north of the Denali fault system.

  8. Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): Constraints from petrology and thermobarometry

    Science.gov (United States)

    Airaghi, Laura; de Sigoyer, Julia; Lanari, Pierre; Guillot, Stéphane; Vidal, Olivier; Monié, Patrick; Sautter, Benjamin; Tan, Xibin

    2017-06-01

    The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280 ± 30 °C and 7 ± 1 kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20 km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation 40Ar/39Ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135-140 Ma. The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the

  9. Rheo-speedometer: constraining the exhumation rate using inclusion-host system with visco-elastic rheology

    Science.gov (United States)

    Zhong, Xin; Moulas, Evangelos; Tajcmanová, Lucie

    2017-04-01

    Constraining the time scale of rock exhumation is of great interest in geology. Geochronology and diffusion chronometry have been applied to obtain the exhumation duration by using the radioactive isotope decay and the diffusion kinetics of the major/minor elements, respectively. Here, we present an approach based on visco-elastic mechanical solutions applied to inclusion-host systems, e.g. quartz-in-garnet. During cooling and decompression, the difference in the thermal-elastic moduli between the inclusion and host forms a "pressure-vessel" that can generate a gigapascal level pressure jump at the inclusion-host interface as confirmed with the laser Raman spectroscopy (Enami et al., 2007; Sobolev et al., 2000). In order to main the mechanical equilibrium, a differential stress in the host is applied that results in viscous creep and pressure relaxation. The relaxed inclusion pressure can be quantitatively linked to the exhumation rate using the experimentally calibrated viscous flow law of the host mineral. The newly developed, so called, "rheo-speedometer" thus allows to constrain the exhumation rate by measuring the residual pressure with Raman spectroscopy. The rheo-speedometer is applied to four geological case studies of the Stak eclogite (Pakistan), Kokchetav mica schist (Kazakhstan), Udachnaya Kimberlite (Russia), and Sifnos blueschist (Greece). We demonstrate that: 1) the exhumation rate can be quantitatively constrained with certain confidence interval; 2) rocks undergoing either rapid magmatic ascent or slower metamorphic exhumation can be qualitatively distinguished; 3) the elastic limit can be reached for a quartz-in-garnet system below 550°C. References Enami, M., Nishiyama, T., Mouri, T., 2007. Laser Raman microspectrometry of metamorphic quartz: A simple method for comparison of metamorphic pressures. Am. Mineral. 92, 1303-1315. doi:10.2138/am.2007.2438 Sobolev, N.V., Fursenko, B.A., Goryainov, S.V., Shu, J., Hemley, R.J., Mao, H.K., Boyd, F

  10. Thermal evolution and exhumation of deep-level batholithic exposures, southernmost Sierra Nevada, California

    Science.gov (United States)

    Saleeby, J.; Farley, K.A.; Kistler, R.W.; Fleck, R.J.

    2007-01-01

    The Tehachapi complex lies at the southern end of the Sierra Nevada batholith adjacent to the Neogene-Quaternary Garlock fault. The complex is composed principally of high-pressure (8-10 kbar) Cretaceous batholithic rocks, and it represents the deepest exposed levels of a continuous oblique crustal section through the southern Sierra Nevada batholith. Over the southern ???100 km of this section, structural/petrologic continuity and geochronological data indicate that ???35 km of felsic to intermediate-composition crust was generated by copious arc magmatism primarily between 105 and 99 Ma. In the Tehachapi complex, these batholithic rocks intrude and are bounded to the west by similar-composition gneissic-textured high-pressure batholithic rocks emplaced at ca. 115-110 Ma. This lower crustal complex is bounded below by a regional thrust system, which in Late Cretaceous time tectonically eroded the underlying mantle lithosphere, and in series displaced and underplated the Rand Schist subduction assemblage by low-angle slip from the outboard Franciscan trench. Geophysical and mantle xenolith studies indicate that the remnants of this shallow subduction thrust descend northward through the crust and into the mantle, leaving the mantle lithosphere intact beneath the greater Sierra Nevada batholith. This north-dipping regional structure records an inflection in the Farallon plate, which was segmented into a shallow subduc-tion trajectory to the south and a normal steeper trajectory to the north. We combine new and published data from a broad spectrum of thermochronom-eters that together form a coherent data array constraining the thermal evolution of the complex. Integration of these data with published thermobarometric and petro-genetic data also constrains the tectonically driven decompression and exhumation history of the complex. The timing of arc magmatic construction of the complex, as denoted above, is resolved by a large body of U/Pb zircon ages. High

  11. Exhumation of the Western Cordillera of the Peruvian Andes (5-12°S)

    Science.gov (United States)

    Michalak, M.; Hall, S. R.; Farber, D.; Hourigan, J. K.

    2012-12-01

    The topography of mountain belts is the first-order morphological expression of the dynamical forces that drive plate tectonics. Despite recent advances in techniques that quantify tectonic and geomorphologic processes, characterizing the near and far-field forces that form mountainous topography at a continental scale remains challenging. The South American Andes are an example of a long-lived orogen that is morphologically and tectonically segmented. For example, the Northern Peruvian Andes are a region characterized by flat-slab subduction, no active volcanism and a relatively narrow section of high topography, in contrast to the central Andes, which contain the broad Altiplano-Puna plateau, active volcanism and normal-angle subduction. Current models of Andean orogenesis based on paleoelevation estimates, thermochronology data, and structural analysis suggest that most of the high topography evolved sometime in the last 20Ma, possibly characterized by a period of punctuated uplift from 10-6Ma. However, as many of these data are from the central Andes, they may not be directly applicable to the entire Andean chain. Therefore, it is critical to investigate areas outside of the central Andean region using similar techniques to test the applicability of these models elsewhere in the Andes. For this study, we use (U-Th)/He low-temperature thermochronology to characterize the shallow crustal cooling history from three sites in the Western Cordillera of the Peruvian Andes, across seven degrees of latitude (5°S to 12°S). Near-vertical sample transects were taken in three river valleys that expose the Jurassic through Eocene granitoids of the 1,600km long Coastal Batholith of Peru. By using both apatite and zircon (U-Th)/He thermochronometers we are able to quantify crustal exhumation rates as well as detect temporal and spatial accelerations and decelerations of exhumation. This new dataset, combined with existing crystallization ages of the plutonic sequence of the

  12. Geochronological Constraints on the Exhumation and Emplacement of Subcontinental Lithospheric Mantle Peridotites in the Westernmost Mediterranean

    Science.gov (United States)

    Garrido, Carlos J.; Hidas, Károly; Marchesi, Claudio; Varas-Reus, María Isabel; Booth-Rea, Guillermo

    2017-04-01

    Exhumation of subcontinental mantle peridotite in the Western Mediterranean has been attributed to different tectonic processes including pure extension, transpression, or alternating contractive and extensional processes related with continental subduction followed by extension, before final their contractive intracrustal emplacement. Any model trying to explain the exhumation and emplacement of subcontinental lithospheric mantle peridotites in the westernmost Mediterranean should take into account the available geochronological constraints, as well as the petrological and geochemical processes that lead to internal tectono-magmatic zoning so characteristic of the Betic and Rif orogenic peridotites. Different studies have suggested a Hercynian, Cenozoic-Mesozoic or an Alpine age for the late tectono-magmatic evolution and intra-crustal emplacement of Betic-Rif peridotites. The pervasive presence of Mesozoic U-Pb zircon ages in Ronda UHP and HP garnet pyroxenites does not support a Hercynian age for the intracrustal emplacement of the peridotite. A hyper-extended margin setting for is in good agreement with the Jurassic extensional event that pervasively affected ALKAPECA terrains (i.e. the Alboran, Kabylides, Peloritani, and Calabria domains) in the western Mediterranean due to the opening of the Piemonte-Ligurian Ocean. However, a Jurassic age and a passive margin tectonic setting do not account, among other observations, for the late Miocene thermochronological ages recorded in zircons rims (U-Pb) and garnets (Lu-Hf) in garnet pyroxenites from the Betic-Rif peridotites, the pervasive Miocene resetting of U-Pb zircon and monazite ages in the overlying Jubrique crustal section, the supra-subduction radiogenic signature of late pyroxenite intrusive dikes in the Ronda peridotite, and the arc tholeiitic affinity of late mantle-derived, gabbroic dykes intruding in the Ronda and Ojen plagioclase lherzolites. These data are more consistent with a supra

  13. Exhumation of the Source Area of the Cameros Basin revealed by detrital zircon fission track analysis

    Science.gov (United States)

    Del Rio, Pedro; Barbero, Luis; Casas-Sainz, Antonio

    2010-05-01

    The Cameros Basin (NW of the Iberian Range, NE of the Iberian Peninsula) was an intracontinental basin during Mesozoic times, which was inverted during Alpine compression. Its formation was due to a main rifting stage during Thithonian-Albian times related with an extensional period due to the opening of the Bay of Biscay. This extensional period is characterized by high subsidence and the filling of the basin with up to 8 km of continental sediments. A very low-grade metamorphic event is recorded during Albian times reaching maximum temperatures of ~350°C. Although the Cameros Basin has been studied for several decades from different geological points of view, the source area for the Cameros Basin still remains unknown. Previous studies have given some information about the possible location and nature of the source area: (1) Paleocurrent data indicate that the main source area was located SW of the basin (Salas et al., 2001); (2) Calculated chemical alteration indices show no intense chemical weathering of the source area and no significant variations along the stratigraphic section (Mata et al., 2000); (3) mineralogical studies trace elements ratios indicate that the material source should be acid igneous rock or any rock derived from them (Mata et al., 2000). In this work we present new detrital zircon fission track (ZFT) data from samples collected in different stratigraphic units of the Cameros Basin. Five samples were not reset for ZFT during burial and the metamorphic episode that occurred during Albian times. Those samples have a thermal signal previous to their deposition in the Cameros Basin and reveal the cooling history of the source area. Youngest peak ages for ZFT are in a range of 149 to 214 Ma. Lag-time values for those samples show a break-in-slope at ~130 Ma. Older samples show a decrease in lag-time values (from 55 myr to 20 myr) which implies an increase in exhumation rate between 145 and 135 Ma coinciding with the beginning of the rifting

  14. Multiple low‐temperature thermochronology constraints on exhumation of the Tatra Mountains: New implication for the complex evolution of the Western Carpathians in the Cenozoic

    National Research Council Canada - National Science Library

    Anczkiewicz, Aneta Agnieszka; Danišík, Martin; Środoń, Jan

    2015-01-01

    ...—the Tatra Mountains— is investigated by zircon and apatite fission track and zircon (U‐Th)/He (ZHe) dating methods in order to unravel the disputed exhumation and geodynamic processes in the Western Carpathians...

  15. Subduction / exhumation dynamics: Petrochronology in the Glacier-Rafray slice (Western Alps, Italy)

    Science.gov (United States)

    Burn, Marco; Lanari, Pierre; Engi, Martin

    2014-05-01

    allochthons; one would expect these to have entered the subduction zone together with the Piemonte oceanic units. Yet all high-P ages reported for the Piemonte oceanic units are around 40 Ma. We propose that the Glacier-Rafray slice experienced subduction together with Sesia units and may have been juxtaposed on the Piemont-Ligurian-Ocean units during Eocene exhumation. Strain associated with this juxtaposition may have triggered growth of the second allanite. Joint exhumation of the oceanic units and the Glacier-Rafray klippe followed at retrograde T.

  16. Mesozoic and Cenozoic exhumation history of the SW Iberian Variscides inferred from low-temperature thermochronology

    Science.gov (United States)

    Vázquez-Vílchez, Mercedes; Jabaloy-Sánchez, Antonio; Azor, Antonio; Stuart, Finlay; Persano, Cristina; Alonso-Chaves, Francisco M.; Martín-Parra, Luis Miguel; Matas, Jerónimo; García-Navarro, Encarnación

    2015-11-01

    The post-Paleozoic tectonothermal evolution of the SW Iberian Variscides is poorly known mainly due to the scarce low-temperature geochronological data available. We have obtained new apatite fission-tracks and apatite (U-Th)/He ages to constrain the Mesozoic and Cenozoic tectonic evolution of this portion of the Iberian Massif located just north of the Betic-Rif Alpine orogen. We have obtained nine apatite fission-track ages on samples from Variscan and pre-Variscan granitoids. These ages range from 174.4 (± 10.8) to 54.1 (± 4.9) Ma, with mean track lengths between 10.3 and 13.9 μm. We have also performed 5 (U-Th)/He datings on some of the same samples, obtaining ages between 74.6 (± 1.6) and 18.5 (± 1.4) Ma. Time-temperature path modeling of these low-temperature geochronological data leads us to envisage four post-Paleozoic tectonically controlled exhumation episodes in the SW Iberian Variscides. Three of these episodes occurred in Mesozoic times (Middle Triassic to Early Jurassic, Early Cretaceous, and Late Cretaceous) at rates of ≈ 1.1 to 2.5 °C Ma- 1, separated by periods with almost no cooling. We relate these Mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern Atlantic realm. The fourth exhumation episode occurred in Cenozoic times at rates of ≈ 3.2 to 3.6 °C Ma- 1, being only recorded in samples next to faults with topographic escarpments. These samples cooled below 80 °C at ≈ 20 Ma at rates of 3-13 °C Ma- 1 due to roughly N-S oriented compressional stresses affecting the whole Iberian plate, which, in the particular case of SW Iberia, reactivated some of the previous Late Paleozoic thrusts.

  17. ExHuME 1.3: A Monte Carlo event generator for exclusive diffraction

    Science.gov (United States)

    Monk, J.; Pilkington, A.

    2006-08-01

    We have written the Exclusive Hadronic Monte Carlo Event (ExHuME) generator. ExHuME is based around the perturbative QCD calculation of Khoze, Martin and Ryskin of the process pp→p+X+p, where X is a centrally produced colour singlet system. Program summaryTitle of program:ExHuME Catalogue identifier:ADYA_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADYA_v1_0 Program obtainable from:CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:None Programming language used:C++, some FORTRAN Computer:Any computer with UNIX capability. Users should refer to the README file distributed with the source code for further details Operating system:Linux, Mac OS X No. of lines in distributed program, including test data, etc.:111 145 No. of bytes in distributed program, including test data, etc.: 791 085 Distribution format:tar.gz RAM:60 MB External routines/libraries:LHAPDF [ http://durpdg.dur.ac.uk/lhapdf/], CLHEP v1.8 or v1.9 [L. Lönnblad, Comput. Phys. Comm. 84 (1994) 307; http://wwwinfo.cern.ch/asd/lhc++/clhep/] Subprograms used:Pythia [T. Sjostrand et al., Comput. Phys. Comm. 135 (2001) 238], HDECAY [A. Djouadi, J. Kalinowski, M. Spira, HDECAY: A program for Higgs boson decays in the standard model and its supersymmetric extension, Comput. Phys. Comm. 108 (1998) 56, hep-ph/9704448]. Both are distributed with the source code Nature of problem:Central exclusive production offers the opportunity to study particle production in a uniquely clean environment for a hadron collider. This program implements the KMR model [V.A. Khoze, A.D. Martin, M.G. Ryskin, Prospects for New Physics observations in diffractive processes at the LHC and Tevatron, Eur. Phys. J. C 23 (2002) 311, hep-ph/0111078], which is the only fully perturbative model of exclusive production. Solution method:Monte Carlo techniques are used to produce the central exclusive parton level system. Pythia routines are then used to develop a realistic hadronic system

  18. A Comparative Study on Exhumed Seismogenic Faults and Modern Nankai Seismogenic Megathrust

    Science.gov (United States)

    Kimura, G.; Kitamura, Y.; Sakaguchi, A.; Ujiie, K.; Sato, K.

    2003-12-01

    One of the critical questions to understanding the seismogenic subduction zone is what controls the updip limit of the zone. The question is quite significant to address why the rupture zone stops in some case or propagates to shallow portion and results in the tsunamigenesis in another case. The Nankai trough is a single most unique subduction zone in the world, where historical repetition of large earthquakes and tsumani more than 700 years are well recorded and the updip limit is located enough shallow to drill by riser vessel. That is one of the reasons why drilling into the seismogenic plate boundary has been proposed in the Nankai Trough. Before drilling, we are conducting a comparative research on exhumed seismogenic fault in ancient accretionary complex on land, which was once located in the sesimogenic depth, and the modern Nankai Trough of targeted site for drilling. Several new findings from the exhumed rocks stimulate the understanding of the sesimogenic zone and sharpen the targets by drilling. 1. Break and involvement of oceanic basement into the accretionary complex as blocks of melange is suggested to be a seismic process because of ubiquitous brittle (cataclastic to ultracataclastic) breakage of the oceanic fragment in contrast to ductile deformation of underthrusted sediments. 2. A boundary fault such as sandstone dominated coherent unit (might be offscraped) and mudstone dominated chaotic one (might be underthrusted) is a clear seismogenic fault and a candidate for a major seismogenic plate boundary. A discovery of pseudotachyllyte from the fault strongly suggests a melting lubrication for rupture propagation around the updip limit of the sesimogenic zone. 3. Detailed analysis of the melange and the boundary fault suggests a repeated activity of pressure solution creep (interseismic) alternated with cataclastic or melting slip (coseismic) in a thick plate boundary zone. 4. Crack seal mineral veins are also developed in and around the fault. P

  19. Constraining Early Cenozoic exhumation of the British Isles with vertical profile modelling

    Science.gov (United States)

    Doepke, Daniel; Cogné, Nathan; Chew, David

    2016-04-01

    Despite decades of research is the Early Cenozoic exhumation history of Ireland and Britain still poorly understood and subject to contentious debate (e.g., Davis et al., 2012 and subsequent comments). One reason for this debate is the difficultly of constraining the evolution of onshore parts of the British Isles in both time and space. The paucity of Mesozoic and Cenozoic onshore outcrops makes direct analysis of this time span difficult. Furthermore, Ireland and Britain are situated at a passive margin, where the amount of post-rift exhumation is generally very low. Classical thermochronological tools are therefore near the edge of their resolution and make precise dating of post-rift cooling events challenging. In this study we used the established apatite fission track and (U-Th-Sm)/He techniques, but took advantage of the vertical profile approach of Gallagher et al. (2005) implemented in the QTQt modelling package (Gallagher, 2012), to better constrain the thermal histories. This method allowed us to define the geographical extent of a Late Cretaceous - Early Tertiary cooling event and to show that it was centered around the Irish Sea. Thus, we argue that this cooling event is linked to the underplating of hot material below the crust centered on the Irish Sea (Jones et al., 2002; Al-Kindi et al., 2003), and demonstrate that such conclusion would have been harder, if not impossible, to draw by modelling the samples individually without the use of the vertical profile approach. References Al-Kindi, S., White, N., Sinha, M., England, R., and Tiley, R., 2003, Crustal trace of a hot convective sheet: Geology, v. 31, no. 3, p. 207-210. Davis, M.W., White, N.J., Priestley, K.F., Baptie, B.J., and Tilmann, F.J., 2012, Crustal structure of the British Isles and its epeirogenic consequences: Geophysical Journal International, v. 190, no. 2, p. 705-725. Jones, S.M., White, N., Clarke, B.J., Rowley, E., and Gallagher, K., 2002, Present and past influence of the Iceland

  20. Late Paleozoic deformation and exhumation in the Sierras Pampeanas (Argentina): 40Ar/39Ar-feldspar dating constraints

    Science.gov (United States)

    Löbens, Stefan; Oriolo, Sebastián; Benowitz, Jeff; Wemmer, Klaus; Layer, Paul; Siegesmund, Siegfried

    2017-09-01

    Systematic 40Ar/39Ar feldspar data obtained from the Sierras Pampeanas are presented, filling the gap between available high- (> 300 °C) and low-temperature (< 150 °C) thermochronological data. Results show Silurian-Devonian exhumation related to the late stages of the Famatinian/Ocloyic Orogeny for the Sierra de Pocho and the Sierra de Pie de Palo regions, whereas the Sierras de San Luis and the Sierra de Comechingones regions record exhumation during the Carboniferous. Comparison between new and available data points to a Carboniferous tectonic event in the Sierras Pampeanas, which represents a key period to constrain the early evolution of the proto-Andean margin of Gondwana. This event was probably transtensional and played a major role during the evolution of the Paganzo Basin as well as during the emplacement of alkaline magmatism in the retroarc.

  1. A new detrital mica 40Ar/39Ar dating approach for provenance and exhumation of the Eastern Alps

    Science.gov (United States)

    Gemignani, L.; Sun, Xilin; Braun, J.; van Gerve, T. D.; Wijbrans, J. R.

    2017-08-01

    Detrital thermochronology can be used as a tool to quantitatively constrain exhumation rates and its spatial variability from active mountain belts. Commonly used methods for this purpose assume a steady state relationship between tectonic uplift and erosion. However, this assumption does not account for the transitory response of a dynamic orogenic system to changes in the boundary conditions. We propose a different approach that uses the observed detrital age distributions as "markers" of the past exhumation and of the present-day erosion and mixing occurring in a river system. In this paper, we present new 40Ar/39Ar biotite and white mica age distributions for 19 modern river sands from the Eastern Alps north of the Periadriatic line. The results present three main clusters of ages at 0.5-50, 60-120, and 250-350 Ma that record the main orogenic phases in this sector of the Alps. We have applied two numerical methods to the cooling ages to (a) linearly compute the spatial variability of the relative present-day erosion of a set of four detrital mineral samples from drainage basins along the Inn River and (b) quantify the rates of the cooling and erosion in the Tauern Window during Paleocene-Miocene time of the Alpine orogeny. Our results suggest a 0.34-0.84 mm/yr range of exhumation rates for the Tauern Window since the Miocene. Our estimates of exhumation rates of the western Tauern Window are higher than those for the eastern Tauern Window, which is consistent with the previous studies.

  2. Exhuming the Meso–Cenozoic Kyrgyz Tianshan and Siberian Altai-Sayan: A review based on low-temperature thermochronology

    Directory of Open Access Journals (Sweden)

    Stijn Glorie

    2016-03-01

    Full Text Available Thermochronological datasets for the Kyrgyz Tianshan and Siberian Altai-Sayan within Central Asia reveal a punctuated exhumation history during the Meso–Cenozoic. In this paper, the datasets for both regions are collectively reviewed in order to speculate on the links between the Meso–Cenozoic exhumation of the continental Eurasian interior and the prevailing tectonic processes at the plate margins. Whereas most of the thermochronological data across both regions document late Jurassic–Cretaceous regional basement cooling, older landscape relics and dissecting fault zones throughout both regions preserve Triassic and Cenozoic events of rapid cooling, respectively. Triassic cooling is thought to reflect the Qiangtang–Eurasia collision and/or rifting/subsidence in the West Siberian basin. Alternatively, this cooling signal could be related with the terminal terrane-amalgamation of the Central Asian Orogenic Belt. For the Kygyz Tianshan, late Jurassic–Cretaceous regional exhumation and Cenozoic fault reactivations can be linked with specific tectonic events during the closure of the Palaeo-Tethys and Neo-Tethys Oceans, respectively. The effect of the progressive consumption of these oceans and the associated collisions of Cimmeria and India with Eurasia probably only had a minor effect on the exhumation of the Siberian Altai-Sayan. More likely, tectonic forces from the east (present-day coordinates as a result of the building and collapse of the Mongol-Okhotsk orogen and rifting in the Baikal region shaped the current Siberian Altai-Sayan topography. Although many of these hypothesised links need to be tested further, they allow a first-order insight into the dynamic response and the stress propagation pathways from the Eurasian margin into the continental interior.

  3. Lisa K. Perdigao. From Modernist Entombment to Postmodernist Exhumation Dead Bodies in Twentieth-Century American Fiction.

    Directory of Open Access Journals (Sweden)

    Ben Robbins

    2012-04-01

    Full Text Available Lisa K. Perdigao’s monograph titled From Modernist Entombment to Postmodernist Exhumation, seeks to offer a comprehensive study of the corpse as represented in American fiction of the twentieth century. Perdigao explores how novelists from a range of time periods and traditions use dead bodies as a device that is revealing of the wider formal ambitions of narrative. In her introduction, Perdigao sets out the theoretical framework on which her study is based. She draws on poststructuralist the...

  4. Two successive crustal melting events resulting from extensional exhumation and then thrusting of the Ronda Peridotites (South Spain)

    Science.gov (United States)

    Frasca, Gianluca; Gueydan, Frédéric; Poujol, Marc; Brun, Jean-Pierre; Parat, Fleurice; Monié, Patrick; Pichat, Alexandre; Maziers, Sophie

    2017-04-01

    The Alboran Domain, situated at the western end of the Mediterranean subduction system, is characterized by the Ronda Peridotites, one of the world largest exposures of sub-continental mantle. Using U-Pb (LA-ICP-MS) and Ar-Ar dating, we precisely dated two tectonic events associated with the Tertiary exhumation of the Ronda Peridotites. First, shearing along the Crust-Mantle Extensional Shear Zone caused, at ca. 22.5 Ma, mantle exhumation, local partial melting in the deep crust and coeval cooling in the upper crust. Second, the Ronda Peridotites Thrust triggered the final crustal emplacement of the peridotites onto the continental crust at ca. 21 Ma, as testified by granitic intrusions in the thrust hanging-wall. The tectonic evolution of the western Alboran Domain is therefore characterized by a fast switch from a continental lithosphere extension in a backarc setting, with sub-continental mantle exhumation, to a rift inversion by thrusting driven by shortening of the subduction upper plate.

  5. Thermal and exhumation history of Sakhalin Island (Russia) constrained by apatite U-Pb and fission track thermochronology

    Science.gov (United States)

    Glorie, Stijn; Alexandrov, Igor; Nixon, Angus; Jepson, Gilby; Gillespie, Jack; Jahn, Bor-Ming

    2017-08-01

    Sakhalin Island represents a key locality to study the tectonic evolution of the western Pacific. The island is located at the Amur-Okhotsk plate margin and records a complex thermotectonic history. Apatite double dating (U-Pb and fission track) and thermal history modelling were applied to three late Eocene granitoid massifs within central and southern Sakhalin: the Aniva, Okhotsk and Langeri complexes. Apatite U-Pb results yield consistent late Eocene (∼40-37 Ma) ages, suggesting rapid post-magmatic cooling. Apatite fission track results reveal bimodal age distributions with late Eocene - early Oligocene (∼38-33 Ma) and early Miocene (∼20-17 Ma) age populations that can be correlated with variations in Uranium and Chlorine concentrations. Thermal history modelling translates the AFT age bimodality into two-phase cooling histories. The timing of the early cooling phase (∼38-33 Ma) corresponds with the apatite U-Pb ages, indicating rapid cooling to at least ∼100 °C during the late Oligocene. The second cooling phase at ∼20-17 Ma cooled the samples to near-surface temperatures. Both cooling phases correspond with regional unconformities and subsequent accelerations in sedimentation rate, suggesting that cooling was a response to rapid exhumation. In addition, our data suggests that the studied terranes record differential exhumation with respect to the structural architecture. The Miocene exhumation pulse is coeval with the timing of transpressional fault displacement and the subsequent opening of the Kuril Basin.

  6. Miocene burial and exhumation of the India-Asia collision zone in southern Tibet: response to slab dynamics and erosion

    Science.gov (United States)

    Carrapa, Barbara; Orme, D.A.; DeCelles, Peter G.; Kapp, Paul; Cosca, Michael A.; Waldrip, R.

    2014-01-01

    The India-Asia collision zone in southern Tibet preserves a record of geodynamic and erosional processes following intercontinental collision. Apatite fission-track and zircon and apatite (U-Th)/He data from the Oligocene–Miocene Kailas Formation, within the India-Asia collision zone, show a synchronous cooling signal at 17 ± 1 Ma, which is younger than the ca. 26–21 Ma depositional age of the Kailas Formation, constrained by U-Pb and 40Ar/39Ar geochronology, and requires heating (burial) after ca. 21 Ma and subsequent rapid exhumation. Data from the Gangdese batholith underlying the Kailas Formation also indicate Miocene exhumation. The thermal history of the Kailas Formation is consistent with rapid subsidence during a short-lived phase of early Miocene extension followed by uplift and exhumation driven by rollback and northward underthrusting of the Indian plate, respectively. Significant removal of material from the India-Asia collision zone was likely facilitated by efficient incision of the paleo–Indus River and paleo–Yarlung River in response to drainage reorganization and/or intensification of the Asian monsoon.

  7. Late Cretaceous extension and exhumation of the Stong and Taku magmatic and metamorphic complexes, NE Peninsular Malaysia

    Science.gov (United States)

    François, T.; Md Ali, M. A.; Matenco, L.; Willingshofer, E.; Ng, T. F.; Taib, N. I.; Shuib, M. K.

    2017-08-01

    Fragmentation of large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts, as exemplified by the Stong and Taku magmatic and metamorphic complexes of northern Peninsular Malaysia. For this case, we have employed a field and microstructural kinematic study combined with low temperature thermo-chronology to analyse the tectonic and exhumation history. The results show that the Late Palaeozoic - Triassic Indosinian orogeny created successive phases of burial related metamorphism, shearing and contractional deformation. This orogenic structure was subsequently dismembered during a Cretaceous thermal event that culminated in the formation of a large scale Late Santonian - Early Maastrichtian extensional detachment, genetically associated with crustal melting, the emplacement of syn-kinematic plutons and widespread migmatisation. The emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range, represented by amphibolite- and greenschist- facies mylonites and as well as brittle structures, such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment. The formation of this detachment and a first phase of Late Cretaceous cooling was followed by renewed Eocene - Oligocene exhumation, as evidenced from our fission track ages. We infer that an initial Cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults. These Cretaceous processes played a critical role in the establishment of the presently observed crustal structure of Peninsular Malaysia.

  8. Exhumation and topographic evolution of the Namche Barwa Syntaxis, eastern Himalaya

    Science.gov (United States)

    Yang, Rong; Herman, Frédéric; Fellin, Maria Giuditta; Maden, Colin

    2018-01-01

    The Namche Barwa Syntaxis, as one of the most tectonically active regions, remains an appropriate place to explore the relationship between tectonics, surface processes, and landscape evolution. Two leading models have been proposed for the formation and evolution of this syntaxis, including the tectonic aneurysm model and the syntaxis expansion model. Here we use a multi-disciplinary approach based on low-temperature thermochronometry, numerical modeling, river profile and topographic analyses to investigate the interactions between tectonics, erosion, and landscape evolution and to test these models. Our results emphasize the presence of young cooling ages (i.e., < 1 Ma) along the Parlung River, to the north of the syntaxis. Using numerical modeling we argue that a recent increase in exhumation rate is required to expose these young ages. Our river analysis reveals spatial variations in channel steepness, which we interpret to reflect the rock uplift pattern. By establishing the relationship between erosion rates and topographic features, we find that erosion rates are poorly to weakly correlated with topographic features, suggesting that the landscape is still evolving. Altogether, these results seem better explained by a mechanism that involves a northward expansion of the syntaxis, which causes high rock uplift rates to the north of the syntaxis and a transient state of topography adjusting to an evolving tectonic setting.

  9. In search of the Boston Strangler: genetic evidence from the exhumation of Mary Sullivan.

    Science.gov (United States)

    Foran, David R; Starrs, James E

    2004-01-01

    The Boston Strangler was one of the United States' most notorious serial killers, raping and strangling with decorative ligatures thirteen woman in Boston during the early 1960s. Albert DeSalvo, never a suspect in the slayings, confessed in prison (where he was later murdered) to being the Boston Strangler, and the investigation largely ended. Mary Sullivan was the last victim of the Boston Strangler, found sexually assaulted and strangled in her Boston apartment in 1964. Recently, a team of forensic scientists undertook the exhumation and subsequent scientific analysis of Mary Sullivan's remains, in hope of finding consistencies or inconsistencies between DeSalvo's confessed description of the murder and any evidence left behind. Included in these analyses was extensive DNA testing of all UV fluorescent material associated with the body. The large majority of results were negative, however, fluorescent material located on the underwear and entwined in her pubic hair generated two human mitochondrial DNA sequences. Neither of these matched the victim nor members of the forensic team who worked on the evidence. Most importantly, neither DNA sequence could have originated from Albert DeSalvo.

  10. Gunshot wounds (resulting from execution) of exhumed victims of the communist regime in Poland.

    Science.gov (United States)

    Szleszkowski, Łukasz; Thannhäuser, Agata; Szwagrzyk, Krzysztof; Kawecki, Jerzy; Jurek, Tomasz

    2014-07-01

    This study presents the results of the analysis of the remains of 23 executed male individuals aged between 21 and 63 years, recovered from Osobowicki Cemetery in Wroclaw (Poland), field 83B, in 2012. In 1948 and 1949, prisoners sentenced to death by firing squad--most of them associated with the post-war anti-communist underground independence movement in Poland--were buried there. The aim of the study was to analyse fatal wounds and the method of execution, and to compare the results to data from archival documents. The results were also compared with studies concerning executions during a later period, i.e. 1949-1954. The research on the method of execution during this period of history carried out during the exhumations in Osobowicki Cemetery was the first conducted on such a scale in Poland. Forensic analysis revealed a wide variety of gunshot wounds inflicted during executions, revealing both gunshots to the head, especially single shots to the back of the head, and cases corresponding to the use of a firing squad, probably equipped with machine guns. The results of the research indicate that capital punishment by shooting was carried out in ways both similar to those the specified in the regulations and completely different. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  11. Rheological weakening of high-grade mylonites during low-temperature retrogression: The exhumed continental Ailao Shan-Red River fault zone, SE Asia

    Science.gov (United States)

    Cao, Shuyun; Neubauer, Franz; Liu, Junlai; Bernroider, Manfred; Cheng, Xuemei; Li, Junyu; Yu, Zunpu; Genser, Johann

    2017-05-01

    We present a detailed case study of an exhumed continental strike-slip fault zone, the Ailao Shan-Red River (ASRR) strike-slip fault zone, to investigate how deformation promotes strain localization, and how the weak second phases and fluids trigger rheological weakening during retrogression near the ductile to brittle transition during exhumation. Along the ASRR strike-slip fault zone, in the Diancang Shan (DCS) metamorphic massif, high-temperature ductile deformation (D1) pervasively occurred during shearing and exhumation since late Oligocene. The high-temperature microstructures and textures are in part or entirely altered by subsequent low-temperature shearing (D2) since late Miocene, which is under the conditions of frictional-viscous transition of K-feldspar (ca. 450 °C) during further exhumation to the upper crustal levels. The formation of D2 microstructures and shear bands overprinted high-temperature intracrystalline plasticity phases (D1) in mylonitic rocks. Depending on the main rock-forming minerals, the results also demonstrate that the brittle-ductile transition involves a combination of different deformation mechanisms and possible rheological paths. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to exhumation. As a result, grain-size reduction associated with fluids circulating within the ASRR strike-slip fault zone at brittle-ductile transition leads to reaction and texture weakening. Rheological weakening is the consequence of the syntectonic deformation, fluid flow, reaction softening, reaction creep and textural softening. The hydrous fluids resulted in hydration of silicates. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the exhumation through the ductile to ductile-brittle transition involves a combination of different

  12. Stepwise exhumation of the Triassic Lanling high-pressure metamorphic belt in Central Qiangtang, Tibet: Insights from a coupled study of metamorphism, deformation, and geochronology

    Science.gov (United States)

    Liang, Xiao; Wang, Genhou; Yang, Bo; Ran, Hao; Zheng, Yilong; Du, Jinxue; Li, Lingui

    2017-04-01

    The E-W trending Central Qiangtang metamorphic belt (CQMB) is correlated to the Triassic orogeny of the Paleo-Tethys Ocean prior to Cenozoic growth of the Tibetan Plateau. The well-exposed Lanling high-pressure, low-temperature (HP-LT) metamorphic complex was chosen to decipher the process by which it was exhumed, which thereby provides insights into the origin of the CQMB and Qiangtang terrane. After a detailed petrological and structural mapping, three distinct N-S-trending metamorphic domains were distinguished. Microscopic observations show that core domain garnet (Grt)-bearing blueschist was exhumed in a heating plus depressurization trajectory after peak eclogitic conditions, which is more evident in syntectonic vein form porphyroblastic garnets with zoning typical of a prograde path. Grt-free blueschist of the mantle domain probably underwent an exhumation path of temperature increasing and dehydration, as evidenced by pervasive epidote veins. The compilation of radiometric results of high-pressure mineral separates in Lanling and Central Qiantang, and reassessments on the published phengite data sets of Lanling using Arrhenius plots allow a two-step exhumation model to be formulated. It is suggested that core domain eclogitic rocks were brought onto mantle domain blueschist facies level starting at 244-230 Ma, with exhumation continuing to 227-223.4 Ma, and subsequently were exhumed together starting at 223-220 Ma, reaching lower greenschist facies conditions generally after 222-217 Ma. These new observations indicate that the CQMB formed as a Triassic autochthonous accretionary complex resulting from the northward subdcution of the Paleo-Tethys Ocean and that HP-LT rocks therein were very probably exhumed in an extensional regime.

  13. The clumped-isotope geochemistry of exhumed marbles from Naxos, Greece

    Science.gov (United States)

    Ryb, U.; Lloyd, M. K.; Stolper, D. A.; Eiler, J. M.

    2017-07-01

    Exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation, mineral-mineral reactions, water-rock reactions, and diffusion-controlled intra- and inter-mineral atomic mobility. Here, we demonstrate that these processes are recorded in the clumped- and single-isotope (δ13 C and δ18 O) compositions of marbles, which can be used to constrain retrograde metamorphic histories. We collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core-complex of Naxos (Greece), and analyzed their carbonate single- and clumped-isotope compositions. The majority of Δ47 values of whole-rock samples are consistent with exhumation- controlled cooling of the metamorphic complex. However, the data also reveal that water-rock interaction, deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of Δ47 values. We analyzed specific carbonate fabrics influenced by deformation and fluid-rock reaction to study how these processes register in the carbonate clumped-isotope system. Δ47 values of domains drilled from a calcite marble show a bimodal distribution. Low Δ47 values correspond to an apparent temperature of 260 °C and are common in static fabrics; high Δ47 values correspond to an apparent temperature of 200 °C and are common in dynamically recrystallized fabrics. We suggest that the low Δ47 values reflect diffusion-controlled isotopic reordering during cooling, whereas high Δ47 values reflect isotopic reordering driven by dynamic recrystallization. We further studied the mechanism by which dynamic recrystallization may alter Δ47 values by controlled heating experiments. Results show no significant difference between laboratory reactions rates in the static and dynamic fabrics, consistent with a mineral-extrinsic mechanism, in which slip along crystal planes was associated

  14. Eclogite inclusions in migmatite domes as recorders of deep-crust exhumation mechanism, magnitude, and rate

    Science.gov (United States)

    Whitney, Donna; Teyssier, Christian

    2017-04-01

    Fragments of refractory material such as mafic rocks occur in quartzofeldspathic gneiss and migmatite in domal structures that form when the upper crust extends, driving rapid upward flow of the ductile lower crust. The Montagne Noire, French Massif Central, is an example of an eclogite-bearing migmatite 'double dome' characterized by a vertical high-strain zone (HSZ) and flanking subdomes. Two eclogite localities preserve garnet and omphacite: one in the HSZ and one at the SW margin of the dome. Zircon U-Pb and trace-element data for the HSZ eclogite show that high-pressure metamorphism occurred during the same orogenic event as migmatite dome formation, so the P-T-t-deformation records of eclogites in different structural sites can be used to understand deep crust exhumation in the context of dome dynamics. Numerical models predict that material in the HSZ ascends directly from the deep crust. Material in the subdomes may come from the deep crust or from more intermediate crustal levels; in some cases, dome-margin rocks follow a transport path with an earlier vertical component to the top of the dome, followed by flow into the footwall of an extensional shear zone below the shallow crust. In the Montagne Noire dome, eclogite in the HSZ contains garnet with rutile inclusion-bearing, pyrope-rich rims (up to 50 mol%) and omphacite with up to 36 mol% jadeite. Retrogression is characterized by amphibolite + plagioclase symplectite that has preferentially consumed cpx; texturally late biotite also occurs. The lower-pyrope cores of garnet contain abundant quartz inclusions and record prograde amphibolite facies metamorphism. Peak P-T conditions were 1.4 GPa at 725°C, and eclogite metamorphism was closely related to host migmatite at 315 Ma. Exhumation was rapid, from the deep crust (>40 km) to shallow emplacement of the dome at <10 km depth. Dome-margin eclogite occurs along the tectonized contact between migmatite/gneiss and the schist carapace of the dome. Garnets

  15. Deformation and exhumation of the Bhutan Himalaya derived from the inversion of thermochronologic and thermometric data

    Science.gov (United States)

    Coutand, I.; Grujic, D.; Whipp, D. M., Jr.; Bernet, M.; Fellin, M. G.; Landry, K.; McQuarrie, N.

    2012-04-01

    The kinematics of late Tertiary crustal deformation across the Himalaya has seen passionate debate over the past decade. Data acquisition and modelling studies have focused primarily on the western and central Himalaya, where findings about crustal deformation and exhumation, and the resulting thermal structure, have been extrapolated to elsewhere in the orogen. Although the major lithotectonic units and their bounding structures are remarkably continuous along strike, significant differences in other features limit the applicability of individual study conclusions to the greater orogen. In particular, the Eastern Himalaya of Bhutan are difficult to link to existing kinematic models, due to unique documented features including: (1) Preservation of Tethyan metasediments atop the Greater Himalayan Sequence (GHS) indicating a lower exhumation magnitude, (2) apatite fission-track (FT) ages markedly older than further west (3) a steep, convex topographic front spatially restricting modern orographic precipitation to foothill elevations of <2000 m, (4) preservation of low-relief landscape remnants at 2000-3000 m elevation and (5) uplift of a foreland plateau producing tectono-climatic perturbations along the range front since the Late Miocene. We quantify the kinematic history of the Bhutanese Himalaya using low-temperature thermochronology, thermometric data and thermokinematic numerical modelling. We complement published data with 75 apatite FT, 27 zircon FT, 60 apatite (U-Th-Sm)/He (AHe) and 40 zircon (U-Th-Sm)/He (ZHe) ages from bedrock samples along two North-South and one East-West transect across Bhutan. Thermochronometric analysis for up to five systems in selected GHS bedrock samples indicates dissimilar cooling patterns from temperatures of ~375 °C to the near surface (i.e., muscovite 39Ar/40Ar to AHe). Specifically, all the samples from the landscape remnants in central and eastern Bhutan show a marked decrease in cooling rate from 50-100 °C/Ma between 5

  16. Subduction and exhumation structures preserved in Cerro del Almirez HP metaserpentinites (Betic Cordillera, SE Spain)

    Science.gov (United States)

    Jabaloy-Sánchez, Antonio; López Sánchez-Vizcaíno, Vicente; Gómez-Pugnaire, María Teresa; Padrón-Navarta, José Alberto; Garrido, Carlos J.

    2014-05-01

    The Cerro del Almirez massif (Nevado-Filábride Complex, Betic Cordillera, SE Spain) is composed of antigorite serpentinite and chlorite harzburgite separated by a thin reaction front in a paleo-subduction setting. Structural analysis of ultramafic lithologies and metasedimentary host rocks provides information on the tectonic evolution of this massif during prograde metamorphism in a subduction zone and during subsequent exhumation. Here we report for the first time HP structures related to a subduction event underwent by ultramafic rocks of the Nevado-Filábride Complex. The oldest subduction-related structures are preserved in Atg-serpentinites: a penetrative S1 foliation and associated L1 stretching lineation were formed in a non-coaxial regime with a top-to-the-W sense of shearing. This planar linear fabric is crosscut by olivine ± Ti-clinohumite veins formed during the prograde breakdown of brucite and pre-metamorphic clinopyroxene at temperatures ranging from 465 to 500 ºC [1]. Veins occur as a system of decimetric long joints, some of them hybrid open and sheared veins with associated drag folds. They recorded embrittlement processes due to the release of 6% vol. H2O of the rock. S1 foliation can, however, be simultaneous with or be overgrown by olivine and/or tremolite porphyroblasts, product of the prograde reaction Di + Atg → Fo + Tr + H2O, which occurred at T > 600 ºC and P = 1.7-1.9 GPa [1]. Generation of S1/L1 fabric was followed by static annealing at ca. 680 ºC and 1.6-1.9 GPa [2]. The S1/L1 fabric in Atg-serpentinite is crosscut by the Atg-out isograd and overgrown by the Atg-serpentinite dehydration products that gave place to Chl-harzburgite. Peak metamorphic conditions of the Chl-harzburgite assemblage reached 680-710 ºC and 1.6-1.9 GPa [3]. Prograde Chl-harzburgite is crosscut by sets of conjugate zones associated to grain-size reduction of olivine grains [3]. These grain size reduction zones are interpreted as brittle structures

  17. Strain localization in shear zones during exhumation: a graphical approach to facies interpretation

    Science.gov (United States)

    Cardello, Giovanni Luca; Augier, Romain; Laurent, Valentin; Roche, Vincent; Jolivet, Laurent

    2015-04-01

    Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shear zones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailed characterization and processes comprehension are far to be fully addressed. In this work, a graphic approach to tectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), which is mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite. Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, from syn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphic reactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frame of smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5 tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved within large boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetric boudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed by chlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture is progressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequence of stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage. In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formed glaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tension gashes that gradually evolve to blueschist shear bands. This process determinates the

  18. Cenozoic deformation and exhumation of the Kampot Fold Belt and implications for south Indochina tectonics

    Science.gov (United States)

    Fyhn, Michael B. W.; Green, Paul F.; Bergman, Steven C.; Van Itterbeeck, Jimmy; Tri, Tran V.; Dien, Phan T.; Abatzis, Ioannis; Thomsen, Tonny B.; Chea, Socheat; Pedersen, Stig A. S.; Mai, Le C.; Tuan, Hoang A.; Nielsen, Lars H.

    2016-07-01

    Latest Mesozoic to earliest Cenozoic deformation affected SE Asia's Sundaland core. The deformation event bridges the Mesozoic SE Asian fusion with the Cenozoic era of rifting, translation, basin formation, and the creation of modern SE Asian oceans. Southern Cambodia and Vietnam are central to this shift, but geological investigations of the region are in their infancy. Based on apatite and zircon fission track analyses (AFTA and ZFTA), stratigraphic and structural observations, seismic data, thermal maturity, and igneous rock dating, the geological evolution of southern Cambodia and Vietnam is investigated. Diverse depositional styles, igneous activity, structural deformation and subsurface unconformities testify to a highly variable Phanerozoic tectonic setting. Major latest Cretaceous to Paleocene thrusting and uplift affected the Kampot Fold Belt and surrounding regions and the associated up to 11 km exhumation probably exceeds earlier denudation events since at least Permian time. The present relief of the Bokor Mountains rising high above the Kampot Fold Belt represents an artifact after differential erosion and only 2.5-4.5 km of erosion affected this area. The latest Cretaceous to Paleocene orogenesis affected much of greater Indochina probably owing to plate collision along eastern Sundaland or a combination of collisions along both east and west Sundaland. AFTA and ZFTA data document protracted cooling of Cretaceous granites and locally elevated thermal gradients persisting a few tens of million years after their emplacement. The thermal gradient had stabilized by early Miocene time, and Miocene cooling probably reflects a renewed denudation pulse driven by either regional tectonism or climate-enhanced erosion.

  19. Exhumation and reburials of some anticommunist partisans in county of Cluj, Romania, 2009-2010

    Directory of Open Access Journals (Sweden)

    Gherasim Florin

    2013-01-01

    Full Text Available After the Second World War, Romania entered under the USSR political and military sphere of influence, which led to the installation of the communist government. In years that followed many Romanian citizens who didn’t agree with the new regime or its ideology were subjected to terror and repression. Any person suspected of being an enemy of the people would end up in political jails or put to death through collective executions. But there were also people who stood up against the regime. Groups of partisans emerged, groups that endured in forests and mountains for many years, standing up to the Securitatea, the repressive instrument of the state. After the fall of the communist regime, the former “enemies of the people”, victims of repression, benefited from reconsideration and rehabilitation that transformed them into anticommunist heroes. A series of commemorative actions that initiated a new post-communist tradition constitute part of a process called the politics of memory. The processes of unearthing and identification of the victims’ served to map out the magnitude of the crimes, and inventory evidence against the perpetrators. The factual data gathered will be used as incriminating evidence which will help with convicting the executioners. At the same time, the commemorative actions of a large number of victims may, through the representative voices of the survivors’ descendants, symbolically reopen the wounds, cultivate trauma, demonize the Other, identify the Scapegoat. My research aims to show how these theories and mechanisms remain valid and apply to the case of people who were victims of communist repression through isolated and almost anonymous executions. The murder was committed in silence and the murdered is condemned to being forgotten. The exhumation and reburial also remain events with local reverberations.

  20. Tracing the exhumation history of the Rwenzori Mountains, Albertine Rift, Uganda, using low-temperature thermochronology

    Science.gov (United States)

    Bauer, Friederike U.; Glasmacher, Ulrich A.; Ring, Uwe; Karl, Markus; Schumann, Andreas; Nagudi, Betty

    2013-06-01

    The Rwenzori Mtns form a striking feature within the Albertine Rift of the East African Rift System. They are made up of a dissected Precambrian metamorphic basement block reaching heights of more than 5 km. Applying low-temperature thermochronology a complex exhumation history becomes evident, where rock and surface uplift can be traced from Palaeozoic to Neogene times. Fission-track and (U-Th-Sm)/He cooling ages and derived cooling histories allow distinguishing different blocks in the Rwenzori Mtns. In the central part a northern and a southern block are separated by a putative NW-SE trending fault; with the northern block showing distinctly younger apatite fission-track ages (~ 130 Ma) than the southern block (~ 300 Ma). Cooling ages in both blocks do not vary significantly with elevation, despite considerable differences in elevation. Thermal history modelling reflects protracted cooling histories. Modelled t-T paths show decoupled blocks that were relocated separately along distinct fault planes, which reactivated pre-existing structures, inherited from Palaeozoic folding and thrusting. Initial cooling affected the Rwenzori area in Silurian to Devonian times, followed by Mesozoic and Cainozoic cooling events. Pre-Neogene evolution seems to be triggered by tectonic processes like the opening of the Indian Ocean and the south Atlantic. From thermochronological data the formation of a Mesozoic "Albertine high" is conceivable. In Cainozoic times the area was affected by rifting, resulting in differentiated surface uplift. Along the western flank of the Rwenzori Mtns, surface uplift was more pronounced. This is also reflected in their recent topography, formed by accelerated rock uplift in the near past (Pliocene to Pleistocene). Erosion could not compensate for this most recent uplift, resulting in apatite He ages of Oligocene to Miocene age or even older.

  1. Evidence for Mantle Exhumation along the Arabian Margin in the Kermanshah Area (Zagros, Iran)

    Science.gov (United States)

    Wrobel-Daveau, Jean-Chrstophe; Ringenbach, Jean-Claude; Tavakoly, Saied; Frizon de Lamotte, Dominique

    2010-05-01

    The Kermanshah Suture Zone (Zagros, Iran) provides an interesting opportunity to study the Neo-Tethys rifting and obduction processes, for which the local models haven't been revisited since the 80's. The stack of nappes coming from the Neo-tethyan domain and obducted over the Arabian plate during late Cretaceous exposes from SW to NE, radiolarian cherts, the Harsin peridotitic domain, the Bisitoun Lst block and the Saneh peridotites. A new interpretation of the outcrops of Harsin area allows characterizing detachment faults between serpentinites and gabbros and overlying deep marine sediments (i.e.: cherts or pelagic Lst.) and pre-rift Lst (extensional allochtons). The setting can be interpreted as an extremely stretched amagmatic mantle-floored basin filled by radiolarites. Extensional allochtons are preserved pre-rift sediments and are made up of upper Triassic Lst. The radiolarites unconformably overlying the detachment have recently been dated as early Pliensbachian to early Turonian. This allows encompassing the onset of mantle exhumation stage between late Triassic and early Pliensbachian. Apart from its rather small extention, the structural position and the vertical movement deduced from existing stratigraphic descriptions, allow interpreting the Bisitoun platform as the sedimentary cover of a Hanging Wall Block "H Block", remnant of the stretching phase of the continental crust. However, the margin itself and the continental crust have not been mapped. They have likely been subducted and only the cap of the Bisitoun Block was preserved. These preliminary results lead us to re-interpret the geodynamic and structural evolution of this domain using recent models developed for magma poor passive margin.

  2. The eastern Central Pamir Gneiss Domes: temporal and spatial geometry of burial and exhumation

    Science.gov (United States)

    Rutte, Daniel; Stearns, Michael; Ratschbacher, Lothar

    2013-04-01

    We present a structural and thermochronologic study of the Gneiss Domes and their cover in the Central Pamir. Emphasis is laid on presentation and discussion of new 40Ar-39Ar dates embedded in two structural profiles through the central Muskol and western Shatput domes. The structure of the Central Pamir is dominated by Cenozoic deformation related to the India-Asia collision. Only few structures of the Phanerozoic amalgamation of the Pamir were not reactivated. The Cenozoic structural development of the Central Pamir can be simplified into three phases: 1) Between initial collision of India and Asia to 28-20 Ma (peak metamorphism, U-Pb monazite) the emplacement of large thrust sheets led to strong north-south shortening;" in the eastern Central Pamir the major thrust sheet has a minimum displacement of 35 km. The stratigraphic thickness of this nappe is ~7 km but its internal structure and thus its true thickness is weakly constrained by the available data. Klippen of Early Paleozoic strata of this thrust sheet south of the Central Pamir Muskol and Shatput domes cover Carboniferous to Triassic strata of the footwall; they can be linked to the Akbaital nappe previously mapped by Russian geologists north of the domes. In the Sasaksu valley of the Muskol dome, the thrust sheet is intruded by a ~36 Ma granodiorite (new U-Pb zircon dates). (2) This crustal imbricate stack is cut by east-trending normal faults and shear zones that define the Central Pamir Gneiss Domes. Normal shear is concentrated along the northern margin of the domes and was the main process associated with exhumation of the domes from ~30 km depth at 20-15 Ma (U-Th/Pb titanite and monazite, Ar-Ar, fission-track geo-thermochronology). One granite at ~35 Ma (U-Pb zircon) pre-dates exhumation while three leucocratic dykes (18-20 Ma U-Pb monazite and zircon) are dated to be coeval with the initial stages of exhumation. Detrital U-Pb zircon ages of the high-grade metasediments indicate that the protoliths

  3. Constraining the timing of exhumation of the Eastern Himalayan syntaxis, from a study of the palaeo-Brahmaputra deposits, Siwalik Group, Arunachal Pradesh, India

    Science.gov (United States)

    Govin, Gwladys; Najman, Yani; van der Beek, Peter; Millar, Ian; Bernet, Matthias; Dupont-Nivet, Guillaume; Wijbrans, Jan; Gemignani, Lorenzo; Vögeli, Natalie; Huyghe, Pascale

    2015-04-01

    The evolution of Himalayan syntaxes is debated: they have been subjected to anomalously young (controlling influences, from lithospheric channel flow, to tectonic-surface process interactions. Ductile extrusion of weak lower crust from beneath Tibet by "channel flow" 5 is a process that has been proposed to account for the outward growth of the plateau to the east 6, exhumation of the Higher Himalaya in the Miocene when coupled with high erosion rates, and could be responsible for rapid exhumation of the syntaxis 7. Ehlers and Bendick 8 propose that initiation of rapid and localised exhumation at subduction arc terminations may result from the 3D geometry imposed by subducting curved shells at such locations. Clark and Bilham 9 evoke a change in regional stress along the India-Asia-Burma plate boundary, perhaps due to the introduction of denser (oceanic and transitional crust) material into the eastern part of the boundary late in the orogen's history. Zeitler et al 10 consider that exhumation of the syntaxis is driven by surface processes. In order to understand how and why the syntaxis formed, this project aims to better constrain the onset of exhumation of the Namche Barwa using the proximal detrital record of material eroded from the syntaxis by the paleo-Brahmaputra. We analyse the sedimentary record to have access to earlier erosion products than preserved in the bedrock itself, in a proximal location. The Remi River section, in the Siwalik Group, is located directly downstream of the syntaxis and therefore is the most likely location to contain these sediments. Sediment provenance is characterized by U-Pb dating on detrital zircons, which allows specifically documenting an Indus-Yarlung suture-zone (and therefore paleo-Brahmaputra) provenance. Detrital U-Pb rutile, zircon fission track and Ar/Ar mica dating is used to document rapid exhumation. When ages of the youngest population for all analysis types are essentially the same (stacked thermochronological

  4. Exhumation history of the West Kunlun Mountains, northwestern Tibet: Evidence for a long-lived, rejuvenated orogen

    Science.gov (United States)

    Cao, Kai; Wang, Guo-Can; Bernet, Matthias; van der Beek, Peter; Zhang, Ke-Xin

    2015-12-01

    How and when the northwestern Tibetan Plateau originated and developed upon pre-existing crustal and topographic features is not well understood. To address this question, we present an integrated analysis of detrital zircon U-Pb and fission-track double dating of Cenozoic synorogenic sediments from the Kekeya and Sanju sections in the southwestern Tarim Basin. These data help establishing a new chronostratigraphic framework for the Sanju section and confirm a recent revision of the chronostratigraphy at Kekeya. Detrital zircon fission-track ages present prominent Triassic-Early Jurassic (∼250-170 Ma) and Early Cretaceous (∼130-100 Ma) static age peaks, and Paleocene-Early Miocene (∼60-21 Ma) to Eocene-Late Miocene (∼39-7 Ma) moving age peaks, representing source exhumation. Triassic-Early Jurassic static peak ages document unroofing of the Kunlun terrane, probably related to the subduction of Paleotethys oceanic lithosphere. In combination with the occurrence of synorogenic sediments on both flanks of the Kunlun terrane, these data suggest that an ancient West Kunlun range had emerged above sea level by Triassic-Early Jurassic times. Early Cretaceous fission-track peak ages are interpreted to document exhumation related to thrusting along the Tam Karaul fault, kinematically correlated to the Main Pamir thrust further west. Widespread Middle-Late Mesozoic crustal shortening and thickening likely enhanced the Early Mesozoic topography. Paleocene-Early Eocene fission-track peak ages are presumably partially reset. Limited regional exhumation indicates that the Early Cenozoic topographic and crustal pattern of the West Kunlun may be largely preserved from the Middle-Late Mesozoic. The Main Pamir-Tam Karaul thrust belt could be a first-order tectonic feature bounding the northwestern margin of the Middle-Late Mesozoic to Early Cenozoic Tibetan Plateau. Toward the Tarim basin, Late Oligocene-Early Miocene steady exhumation at a rate of ∼0.9 km/Myr is likely

  5. India-Asia convergence: Insights from burial and exhumation of the Xigaze fore-arc basin, south Tibet

    Science.gov (United States)

    Li, Guangwei; Kohn, Barry; Sandiford, Mike; Xu, Zhiqin

    2017-05-01

    The composite fore-arc/syncollisional Xigaze basin in south Tibet preserves a key record of India-Asia collision. New apatite fission track and zircon (U-Th)/He data from an N-S transect across the preserved fore-arc basin sequence near Xigaze show a consistent northward Late Cretaceous to middle Miocene younging trend, while coexisting apatite (U-Th-Sm)/He ages are all Miocene. Corresponding detrital zircon U-Pb data are also reported for constraining the Cretaceous depositional ages of the Xigaze basin sequence in the region. Thermal history modeling indicates that the basin experienced northward propagating episodic exhumation, along with a northward migration of the depocenter and a pre-existing Cenozoic syncollisional basin sequence which had been removed. In the southern part, fore-arc exhumation commenced in the Late Cretaceous ( 89 ± 2 Ma). Following transition to a syncollisional basin in the Paleocene, sedimentation in the central and northern Xigaze basin continued until the latest Eocene ( 34 ± 4 Ma). Ongoing folding and thrusting (e.g., Great Counter Thrusts) caused by progressive plate convergence during late Oligocene-early Miocene time resulted in regional uplift and considerable basin denudation, which fed two fluvial basins along its northern and southern flanks and exposed the basement ophiolite. Subsequent incision of the Yarlung River resulted in Miocene cooling in the region. Different episodes in the exhumation history of the Xigaze basin, caused by thrusting of an accretionary wedge and ophiolitic basement, can be linked to changes in India-Asia convergence rates and the changing subduction pattern of the Indian and Neo-Tethyan slabs.

  6. Exhuming retroarc fold-and-thrust belts: a comparison between the southern Patagonian Andes and the Argentine Precordillera

    Science.gov (United States)

    Fosdick, J. C.

    2014-12-01

    Detailed constraints on erosional flux are critical for understanding how exhumational processes control and respond to tectonic events in orogenic belts. This work compares the thermochronologic record and erosional behavior of retroarc thrust belts at two latitudes in the Andes with contrasting Cenozoic climate and deformational records: the glaciated southern Patagonian Andes and the semiarid Argentine Precordillera of the Central Andes. Both regions have undergone crustal shortening during Andean growth and have been affected by thermotectonic processes associated with subduction of oceanic ridges; the Chile Ridge spreading center and Juan Fernández Ridge, respectively. In Patagonia, deep erosion occurred during Miocene retroarc deformation. Zircon He thermochronology documents regional cooling and unroofing of the thrust belt ~22-17 Ma. This behavior likely reflects an upper plate manifestation of incipient subduction of the Chile Ridge spreading center and enhanced unroofing during thermally driven regional uplift. Late Cenozoic expansion of the Patagonian icesheet led to further excavation of the thrust belt, indicating a strong climatic overprinting on thrust belt erosional behavior. In contrast, less overall Cenozoic exhumation is observed in the Argentine Precordillera, despite high strain and crustal thickening. Pre-Jurassic zircon He dates from the Paleozoic strata within thrust sheets suggest Cenozoic Andean deformation was insufficient to exhume rocks from beneath the zircon He closure depth. The apatite He record shows a close correlation between thrust faulting and locus of erosion, and document eastward in-sequence rock cooling from 16 to 2 Ma across the Precordillera tracking with the progressive faulting of the Blanca, San Roque, and Niquivil thrust faults during this time. Pliocene apatite He dates located along the external margins of the Precordillera suggest that the most recent cooling and unroofing is associated with both out

  7. Structural Analysis of the Exhumed SEMP Fault Zone, Austria: Towards an Understanding of the Mechanics of Shear Zone Localization

    Science.gov (United States)

    Frost, E. K.; Dolan, J. F.; Sammis, C. G.; Hacker, B.; Ratschbacher, L.; Decker, K.; Cole, J.

    2007-12-01

    One of the most exciting frontiers in earthquake science is the linkage between the internal structure and mechanical behavior of fault zones. Little is known about how fault-zone structure varies as a function of depth, yet such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria, a major left-lateral strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. In order to establish the structure of this fault zone, we are studying outcrops at a variety of exhumation levels, from <1 km near the eastern end of the fault, downward through the seismogenic crust, across the brittle- ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present new results and discuss the mechanical implications of these new data from two key outcrops at Gstatterboden and Taxenbach, where the SEMP has experienced 40-60 km of displacement. The outcrop at Gstatterboden has been exhumed from 2-3 km depth. Here the SEMP juxtaposes limestone of the Wettersteinkalk on the south with dolomite of the Ramsaudolomit on the north. Faulting has produced extremely asymmetric damage, extensively shattering and shearing the dolomite while leaving the limestone largely intact. We interpret this brittle damage using both mesoscopic calculations of damage intensity and microscopic grain size distribution analysis, which suggests that shear has localized to a zone approximately 10 m wide. These findings are compared to the brittle-ductile outcrop at Taxenbach, which has been exhumed from depths of up to 10 km. Here, the SEMP juxtaposes Greywacke Zone rocks with carbonate mylonites of the Klammkalk. Microstructural observations of grain size and lattice preferred orientation suggest a marked increase in strain within

  8. Tectonics of an exhumation zone in the Erzgebirge, N-Bohemian Massif: constraints from microstructures and EBSD data

    Science.gov (United States)

    Hallas, Peter; Kroner, Uwe

    2017-04-01

    The overthrusting of isothermally exhumed (U)HP units onto medium pressure gneiss complexes is a striking feature of the variscan Erzgebirge (N-Bohemian Massif). Because of a complex deformation history the exhumation mechanism of the deeply subducted rocks is controversially discussed. Here we present first results from detailed studies of the (U)HP / MP shear zone contact in the roof of the Catherine-Reitzenhain gneiss dome including field work, microscopic observation and EBSD texture analysis. Generally, the entire zone is characterized by a flat lying main foliation partly overprinting preexisting steeper inclined fabrics. The complex particle path in the shear zone is indicated by a large scatter of the x axis of the finite strain ellipsoid. In the medium-pressure units an initially NE-SW oriented stretching lineation is obliterated by a second elongation with WNW-ESE azimuth. In contrast, the (ultra)high-pressure units preserve a WSW-ENE oriented stretching lineation. Additionally, different exhumation paths are revealed by microkinematic indicators with top to the NE, (W)SW and (W)NW shearing. EBSD data from mica generally reveal plane to flattening strain with [001] point maxima near z and point maxima of [100] and [010] near x and y respectively as well as a girdle distribution of [100] and [010] in the xy plane of the finite strain ellipsoid. Textures of samples with an apparent constrictional strain geometry additionally contain a second [001] maxima deviating from the first one up to 90°. We explain this feature by stepwise deformation with different plane strain geometries rather than by a single constrictional process. Quartz shows all features of dynamic recrystallization by pervasive grain boundary migration. The texture is characterized by pronounced point [0001] maxima in y. However, in samples with multiple fabrics the finite quartz texture probably reflects incomplete overprinting of preexisting Crystal Preffered Orientations. In conclusion

  9. Using exhumation histories to constrain Main Himalayan Thrust geometry and seismic hazard in the western Nepal Himalaya

    Science.gov (United States)

    Harvey, J. E.; Burbank, D.

    2016-12-01

    The Himalaya of western Nepal present a challenge to conventional understanding of the geometry and behavior of the Main Himalayan Thrust (MHT), a major seismogenic structure which accommodates 2 cm/yr of Indo-Asian convergence. Slip along a steeper ramp in the MHT drives long-term uplift of the Greater Himalaya along >1000 km of the central range front, resulting in a conspicuous physiographic transition known as PT2. This physiographic break is seemingly absent in western Nepal, which suggests a structural geometry and/or kinematic history distinct from areas along strike. This anomaly must be investigated to clarify how seismic hazard may differ from better-understood areas along strike. The importance of this work is heightened by the recent and catastrophic Gorkha earthquake in 2015. We present a suite of 7 relief transects comprising a mix of apatite and zircon U-Th/He and muscovite Ar-Ar cooling ages. These transects were collected across the more gradual mountain front in western Nepal in an effort to clarify where uplift and exhumation have been focused over the past 10 Ma. We invert these cooling ages using the thermo-kinematic model Pecube in order to constrain exhumation histories that best fit the measured cooling ages. Results confirm that MHT geometry and kinematic history in western Nepal are far more complex than in better-studied areas along strike. Exhumation rates in the along-strike projection of PT2 are slow ( 0.1-0.2 km/Myr) compared with rates 50 km toward the hinterland ( 1.0-1.5 km/Myr), suggesting that exhumation has been more rapid in this more northerly position for the past several Ma. Although a range of kinematic scenarios could explain the anomalous cooling histories, it is likely that a recently active midcrustal ramp in the MHT sits beneath this more northerly position. If the 2015 Gorkha earthquake initiated near the up-dip end of the MHT ramp in central Nepal, it is conceivable that similarly hazardous earthquakes could trigger

  10. Enticed by the punschrulle: Preliminary investigation of the Seve Nappe Complex's incorporation into the Scandinavian Caledonides via 'vacuum-cleaner' exhumation.

    Science.gov (United States)

    Barnes, Chris; Majka, Jaroslaw; Schneider, David; Bukala, Michal; Walczak, Katarzyna

    2017-04-01

    Recent discoveries of ultra-high pressure (UHP) metamorphism in the Seve Nappe Complex (SNC) of the Scandinavian Caledonides provide the basis for new investigations into the subduction - exhumation dynamics of the Baltoscandian margin during Caledonian tectonism. Specifically, exhumation of (U)HP complexes during subduction remains enigmatic. The recently proposed 'vacuum-cleaner' model details a method of exhumation for the SNC driven by conditions of underpressure within the subduction channel. This model, however, still requires extensive testing. Metasedimentary rocks hosting eclogite boudins of the SNC in Norrbotten, Sweden, preserve both metre-scale folding and a pervasive foliation which were developed during exhumation, as purposed by previous studies. Thus, the SNC host-rock offers an excellent region to test the vacuum-cleaner exhumation model. Preliminary investigation of the host-rock reveals a regional mineral assemblage of Qz + Ms + Grt + Bt + Ksp + Pl + Czo + Aln + Ttn (+ Tur + St). Garnet inclusions (Qz + Rt + Ms) are interpreted to represent the peak pressure assemblage. Chemical profiles of Grt show homogenization of the cores with thin retrogressive rims. Homogenization of Grt requires temperatures >700°C, interpreted to represent peak temperature conditions. Field observations of exhumation-related folds uncovered an axial-planar alignment of mica within the fold hinges, and an abundance of Aln and Czo requires upper-greenschist to lower-amphibolite facies conditions and presence of fluids. The current host-rock mineral assemblage is representative of retrogressive metamorphism at geo/thermochronological results and will be instrumental for evaluating the vacuum-cleaner model. This work is financially supported by NCN "CALSUB" research project no. 2014/14/E/ST10/00321.

  11. Petrofabrics of high-pressure rocks exhumed at the slab-mantle interface from the "point of no return" in a subduction zone (Sivrihisar, Turkey)

    Science.gov (United States)

    Whitney, Donna L.; Teyssier, Christian; Seaton, Nicholas C. A.; Fornash, Katherine F.

    2014-12-01

    The highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2.5 GPa, corresponding to the maximum decoupling depth (MDD) (80 ± 10 km) identified in active subduction zones; beyond the MDD (the "point of no return") exhumation is unlikely. The Sivrihisar massif (Turkey) is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from 80 to 45 km. Crystallographic fabrics and other features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, microstructures and crystallographic fabrics record deformation in the dislocation creep regime, including dynamic recrystallization during decompression, and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression ( 2.5 to 1.5 GPa). Phengite, lawsonite, and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation, and omphacite developed an L-type crystallographic fabric. In marble, aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite (P > 1.2 GPa). Results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface. This large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return.

  12. Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA

    Science.gov (United States)

    McDermott, Robert G.; Ault, Alexis K.; Evans, James P.; Reiners, Peter W.

    2017-08-01

    Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U-Th)/He data patterns from these surfaces and host rock apatite (U-Th)/He data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time-temperature histories. Temperatures of >∼700-1200 °C, depending on asperity size, are sufficient to induce 85-100% He loss from hematite within 200 μm of the fault surface. Spatially-isolated, high-temperature microtextures imply spatially-variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (Mw ≈ - 3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes.

  13. Geophysical fingerprints of hyper-extended, exhumed and embryonic oceanic domains: the example from the Iberia-Newfoundland rifted margins

    Science.gov (United States)

    Stanton, Natasha; Manatschal, Gianreto; Autin, Julia; Sauter, Daniel; Maia, Marcia; Viana, Adriano

    2016-09-01

    This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia-Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained.

  14. Exhumation history of the Sanshandao Au deposit, Jiaodong: constraints from structural analysis and (U-Th)/He thermochronology.

    Science.gov (United States)

    Liu, Xuan; Fan, Hong-Rui; Evans, Noreen J; Yang, Kui-Feng; Danišík, Martin; McInnes, Brent I A; Qin, Ke-Zhang; Yu, Xue-Feng

    2017-08-10

    The Sanshandao gold deposit contains an estimated Au resource of >1500 tons, however little is known about the history of exhumation, and the magnitude of displacement on the ore-hosting fault. Structural measurement revealed two phases of normal and one phase of sinistral movement on the fault. Despite of intra-sample dispersions, (U-Th)/He ages from two sub-vertical profiles show decreasing trends from the surface down to -3560 m (zircon: 123 Ma to 55 Ma; apatite 103 Ma to 0.3 Ma). Over-dispersion of AHe ages likely reflects the presence of undetected inclusions. According to the age-depth pattern, we infer that the deposit underwent an early phase of rapid cooling in the late Early Cretaceous, which was followed by a short period of thermal stagnation and a revived rapid cooling between 75 Ma and 55 Ma in response to a combined effects of late normal movement and erosion. Since the Eocene, the deposit has experienced a slow monotonic cooling. Exhumation magnitude estimates suggest that the deposit have been denudated > 5.1 km. The two phases of normal displacement along the fault occurred in the late Early Cretaceous and Late Cretaceous to Paleocene, leading to a total offset magnitude of 0.5-2.3 km.

  15. Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes

    Science.gov (United States)

    Wilke, Franziska D. H.; O'Brien, Patrick J.; Altenberger, Uwe; Konrad-Schmolke, Matthias; Khan, M. Ahmed

    2010-01-01

    Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif-ul-Muluk in the south, to coesite-eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace- element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic-calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east.

  16. From Source to Sink: Exhumation of the North America Cordillera Revealed by Multi-dating of Detrital Minerals from Upper Jurassic-Upper Cretaceous Sevier Foreland Basin

    Science.gov (United States)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.; Gehrels, G. E.; Thomson, S. N.

    2013-12-01

    We sampled twenty-two Late Jurassic to Late Cretaceous syn-orogenic conglomerate clasts in proximal units in the Sevier fold-thrust belt and their distal sandstone equivalents up to 300 km east of the thrust front, in Utah, Colorado, Wyoming, and South Dakota. To better constrain depositional ages, these samples were analyzed using detrital zircon U-Pb (DZ U-Pb) geochronology. To identify a thermochronometer that measures source exhumation in the North America Cordillera, both zircon (U-Th)/He and apatite fission track (AFT) thermochronology was utilized, on both the conglomerate cobbles and sandstone (detrital) samples. Eleven samples were analyzed with zircon (U-Th)/He; however, discordant ages in the conglomerate cobble samples suggest that this system was not fully reset and never experienced T> ~180 °C in the source stratigraphy during the Sevier orogeny. Eleven other samples are analyzed using apatite fission track thermochronology (AFT); AFT ages are generally similar or older than depositional ages indicating that the detrital ages record source exhumation signals, and that exhumation depth corresponds to T>~120 °C. In order to test whether or not the youngest cooling AFT age population represents a source exhumation signal or a co-magmatic signal we here performed double dating of the detrital AFT samples using apatite U-Pb thermochronology. Maximum depositional ages using DZ U-Pb match existing age controls on basin stratigraphy. Our study shows that AFT is an effective thermochronometer to detect source exhumation for Cretaceous foreland stratigraphy in the western U.S.A. Lag-times (i.e. the difference between the source exhumation age and depositional age) are ~0 to 5 Myr with relatively steady-state to slightly increasing exhumation rates suggesting orogenic growth at this time. The very short lag times also indicate limited to no storage time between source and sink. The AFT lag time of the Early Cretaceous Kelvin Formation is ~5 Myr and represents

  17. The first direct dating of Main Central Thrust phyllonite demonstrates exhumation of the Greater Himalayan Crystalline had already taken place

    Science.gov (United States)

    Rajabi, Sareh; Forster, Marnie; Ahmad, Talat; Lister, Gordon

    2017-04-01

    Here we report the results of step-heating experiments that allow the first direct dating of the timing of movement on the Himalayan Main Central Thrust (MCT). Timing of MCT operation has, until now, been inferred based on specific tectonic models, or with data not directly attributable to MCT movement, e.g., the debatable assertion that leucogranite formation is invariably related to crustal shortening, and therefore that the MCT must already have been in operation. However the tectonic evolution may have been more complex, e.g., at times involving horizontal extension. In any case, many different thrust systems operated during India-Asia convergence, and the MCT is only one of them. It is time to move away from models and to bring geology back into the equation. Here we apply 40Ar/39Ar geochronology to directly date highly strained, phyllonitized, muscovite in the MCT above the Kullu-Rampur tectonic window (NW Indian Himalaya), showing that the timing of the shear movement lasted from 15-9 Ma. We show that these ages have been preserved because the white mica was sufficiently retentive of argon to be able to inhibit its diffusional loss at the temperatures and pressures in question. Arrhenius data from ultra-high-vacuum diffusion experiments show that deformation occurred below the closure temperature of this muscovite, for moderate cooling rates. Furthermore, we demonstrate that microscopic shear bands associated with MCT operation overprinted an earlier decussate mica growth. This decussate growth had taken place prior to ˜ 18 Ma. The decussate microstructure, together with foam textures in the host deformed quartzite, demonstrate that low deviatoric stress conditions applied during a prior period of static annealing under middle- to upper-greenschist facies conditions. In this region, therefore, the Greater Himalayan Crystalline had therefore already been significantly exhumed prior to the onset of MCT operation. The foam textures in quartzite and the

  18. Structural Analysis of the Exhumed SEMP Fault Zone, Austria: Towards an Understanding of Fault Zone Architecture Throughout the Seismogenic Crust

    Science.gov (United States)

    Frost, E. K.; Dolan, J. F.; Sammis, C.; Hacker, B.; Ratschbacher, L.

    2006-12-01

    One of the most exciting and important frontiers in earthquake science is the linkage between the internal structure and the mechanical behavior of fault zones. In particular, little is known about how fault-zone structure varies as a function of depth, from near-surface conditions down through the seismogenic crust and into the ductile lower crust. Such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This imperative has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria, a major left-lateral strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. This exhumed fault system provides a unique opportunity to systematically examine depth-dependent changes in fault-zone geometry and structure along a single fault. In order to establish the structure of the fault zone in the seismogenic crust, we are studying exposures of this fault at a variety of exhumation levels, from <1 km near the eastern end of the fault, downward through the seismogenic crust, across the brittle-ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present our results from one of these study sites, a spectacular exposure of the fault zone near the town of Gstatterboden in central Austria. The fault, which at this location has been exhumed from a depth of ~ 2-3 km, juxtaposes limestone of the Wettersteinkalk on the south with dolomite of the Ramsaudolomit on the north. We conducted two detailed structural traverses over a fault-perpendicular width of over 200 m. Analysis of the density and orientation of outcrop scale features, such as faults and fractures, reveals a highly asymmetric pattern of fault zone damage. Dolomite to the north of the fault is extensively shattered, while the limestone unit to the south shows only minor evidence of fault damage

  19. Zircon (U-Th)/He evidence for pre-Eocene orogenic exhumation of eastern North Pyrenean massifs, France

    Science.gov (United States)

    Ternois, Sébastien; Vacherat, Arnaud; Pik, Raphaël; Ford, Mary; Tibari, Bouchaïb

    2017-04-01

    Orogens and their associated foreland basins are considered as part of a single dynamic system evolving from an early, non equilibrated, growth stage to a late, mature, steady-state stage. Most of our understanding in foreland basins, in particular early convergence-stage deposition, comes from the subducting plate, so that the classic paradigm for foreland basins is the pro-wedge. Models that clearly depict the relationship between erosion of the orogenic wedge and sedimentation into its associated foreland basin only focus on the late post-orogenic phase. Relatively little is known and understood about the very long phase of initiation of orogenesis. In the doubly wedged Pyrenean orogen, where we know and understand relatively little about how the early retro-wedge developed, the record of the onset of orogenic denudation from massifs is quite limited, not only in time but also in space. As part of the OROGEN project funded by TOTAL and the BRGM, this study presents first single-grain zircon (U-Th)/He data from two Palaeozoic massifs of the external Northern Pyrenean Zone, the Agly and Salvezines massifs. It aims at constraining the exhumation history of eastern Pyrenean massifs and understanding what is their significance for early orogenic wedge growth. The Pyrenean orogeny was generated from end Santonian (84 Ma) to Oligocene-Miocene due to convergence of the Iberian and European plates. Aquitaine foreland basin history (Ariège region) indicates that convergence took place in two phases, Campanian to Maastrichian and Eocene, separated by a quiet Paleocene phase. Yet, only Eocene cooling events are recorded by low-temperature thermochronometers in the central Pyrenean massifs (Arize and Trois-Seigneurs). Nine bedrock samples were collected along a WNW-ESE traverse (Salvezines and Saint-Arnac granites, Belesta-Caramany gneisses) and analysed for ZHe dating. Zircon (U-Th)/He data for the Agly and Salvezines massifs, together with forward modelling of data for

  20. Cenozoic exhumation patterns of the Sierra Nevada de Santa Marta, northern Colombia, through bayesian modeling of detrital thermochronometric data

    Science.gov (United States)

    Parra, Mauricio; Gallagher, Kerry; Echeverri, Sebastián; María Patiño, Ana

    2017-04-01

    Thermochronometry of modern river sands exploits the natural downstream sampling of detritus in a river catchment to infer plausible regional exhumation patterns. When combined with available bedrock thermochronometric information, this form of detrital thermochronometry can provide a better understanding of spatially variable denudation rates and improved inference of the potential controlling mechanisms. We have developed a Bayesian inversion approach to modeling both detrital and bedrock thermochronometric data. Following the approach presented in Gallagher (2012), we use Markov chain Monte Carlo to sample many candidate thermal histories models. We use the present day hypsometric curve in a drainage basin as a starting point to sample age-elevation profiles predicted for each candidate thermal history. From these we can then predict the detrital age distribution for a detrital sample representative of the catchment. We can accept candidate thermal histories by quantitatively comparing the predictions to the bedrock profile data, the detrital sample data or both. In principle, discrepancies between the predictions from these models allow us to refine the sampling of the age-elevation profile and infer a detrital sampling distribution different to that implied from the hypsometric curve. Application of the method of new and existing bedrock apatite fission track data (AFT) and new detrital apatite (U-Th)/He, AFT and zircon fission-track (ZFT) data from small (Sierra Nevada in northern Colombia documents the long-term Cenozoic exhumation rates associated to dextral convergence of the Caribbean plate along the northern South American margin. Located 85 km to the SE of the Caribbean abyssal plain and with elevations up to 5.8 km, the Santa Marta Sierra Nevada is the highest coastal range on Earth, with a topographic relief in excess of 9 km. Our data reveal spatially variable, episodic exhumation with a major peak in middle to late-Miocene (30-15) and decreasing

  1. New fission-track age constraints on the exhumation of the central Santander Massif: Implications for the tectonic evolution of the Northern Andes, Colombia

    Science.gov (United States)

    Amaya, Sergio; Zuluaga, Carlos Augusto; Bernet, Matthias

    2017-06-01

    The Late Cretaceous to late Neogene exhumation history of the central Santander Massif in the Northern Andes of Colombia is controlled by the geodynamic interactions between the Caribbean, South American and Nazca plates, as well as the Neogene collision and accretion of the Panama arc. Slab-breakoff of the Caribbean plate, with the tip of the slab tear presently being located beneath Bucaramanga, and the east-west oriented Caldas tear are the main structures relating seismic activity and Late Miocene to Pleistocene magmatic/hydrothermal activity and associated gold mineralization in the central Santander Massif. Here we present new apatite (AFT) and zircon fission-track (ZFT) data from 18 samples collected along two profiles in the California-Vetas block (including the Rio Charta), to the south of the Rio Charta fault, and from Bucaramanga to Picacho on the western flank of the central Santander Massif. The fission-track data are used for time-temperature history modelling and for estimating long-term average exhumation rates. The California-Vetas block in the central Santander Massif to the north of the Rio Charta fault cooled rapidly at a rate of about 24 °C/Myr between 10 and 5 Ma. Fast cooling was not related to post-magmatic cooling or hydrothermal activity, but rather to exhumation, with rates based on apatite fission-track cooling ages on the order of 0.3-0.4 km/Myr. However, long-term average exhumation rates since the Late Cretaceous, based on zircon fission-track data, were only on the order of 0.1-0.2 km/Myr. Our data indicate that next to the Rio Charta fault also the Surata fault contributed to the exhumation of the California-Vetas block. The western flank of the central Santander Massif, shows a more complete thermal history along the Bucaramanga-Picacho profile, with the exposure of an exhumed zircon fission-track partial annealing zone. Thermal history modelling of zircon fission-track data of this profile shows that after burial and heating from

  2. Amphibole equilibria as monitors of P-T path and process in the exhumation of HP/UHP terranes

    Science.gov (United States)

    Waters, David; Airaghi, Laura; Czertowicz, Thomas

    2014-05-01

    Recent advances in modelling and the development of refined activity-composition relations allow the calculation of phase diagrams involving complex mineral solid solutions, such as calcic, sodic-calcic and sodic amphiboles (e.g. Diener et al., 2007, J metamorphic Geol.). Amphiboles are commonly found in eclogite facies metabasites, and formed at different metamorphic stages. Such rocks commonly show complex reaction microstructures that reveal their history. The focus in this contribution is on two distinct amphibole types: coarse, post-peak matrix amphibole, and amphibole involved in symplectitic microstructures replacing omphacite. These studies serve as a test of the current activity models and calculation approaches, but more importantly as a framework for understanding the processes and P-T path during exhumation of subducted terranes. Examples are taken from the Western Gneiss Complex of Norway and from the Kaghan Valley (Pakistan), but are more generally applicable to crustal blocks that have exhumed through the P-T 'window' in which comparable petrological features develop. The microstructural types of interest here are: broad irregular interstitial amphibole grains, which commonly merge with a coarse spongy intergrowth of amphibole with quartz and/or albite (most likely replacing omphacite); and a fine-grained symplectite of low-Na clinopyroxene with sodic plagioclase and minor hornblende invading omphacite. Many specimens show these varieties as a sequence, inferred to reflect decreasing pressure (and ultimately, temperature). Amphibole compositions cover a wide range: the most sodic occur in large interstitial grains and fall near the junction of the winchite, barroisite and taramite fields of the IMA classification; they trend towards a pargasitic hornblende, still with significant glaucophane component; spongy amphiboles typically lie on a trend towards lower glaucophane component; symplectite amphibole is generally a common hornblende on a typical

  3. Rapid cooling and exhumation as a consequence of extension and crustal thinning: Inferences from the Late Miocene to Pliocene Palu Metamorphic Complex, Sulawesi, Indonesia

    Science.gov (United States)

    Hennig, Juliane; Hall, Robert; Forster, Margaret A.; Kohn, Barry P.; Lister, Gordon S.

    2017-08-01

    Metamorphic complexes forming high mountains of 1.5-2 km in Western Sulawesi were previously considered to be Mesozoic or older basement of Gondwana crust. However, many of the metamorphic rocks are much younger than previously thought. Some have Eocene sedimentary protoliths. New geothermobarometric and geochronological data from metamorphic rocks of the Palu Metamorphic Complex (PMC) and associated granitoids provide information on the timing and mechanisms of Neogene metamorphism and contemporaneous rapid exhumation. The metamorphic rocks are strongly deformed and some were partially melted to form migmatites. Schists contain relict andalusite, cordierite, staurolite and Mn-rich garnet which are wrapped by a pervasive fabric. 40Ar/39Ar dating of biotite, white mica and amphibole from strongly deformed, mylonitic schists and recrystallised amphibolites reveals cooling occurred in the Early Pliocene (c. 5.3-4.8 Ma) in the northern part and during the Late Pliocene (c. 3.1-2.7 Ma) in the southern part of the PMC. U-Pb, 40Ar/39Ar and (U-Th)/He analyses of various minerals from PMC metamorphic and S-type magmatic rocks give very similar mid to Late Pliocene ages, indicating very fast cooling and rapid exhumation, and show the high speed at which tectonic processes, including magmatism, exhumation, and reworking into a sediment, must have occurred. The high rates could be unique to this area but we suggest they record the true speed of metamorphic complex exhumation in a very young orogenic belt. Rates in older orogens appear lower because they are averages measured over longer periods of time. Contemporaneous magmatism and deformation are interpreted as a consequence of decompressional melting due to extension and thinning of the crust, promoted by possible detachment faults and normal faulting at the major NW-trending Palu-Koro and Tambarana Faults. In contrast, I-type magmatic rocks, separated from the PMC by the Palu-Koro Fault, were exhumed from upper crustal

  4. New views on 40Ar/39Ar dating of high pressure rock exhumation: an example from Oman

    Science.gov (United States)

    Warren, C. J.; Sherlock, S.; Kelley, S. P.

    2008-12-01

    40Ar/39Ar dating has long been considered an unreliable method for determining cooling ages of high pressure terranes as a result of the common (though not ubiquitous) presence of excess argon. New advances in analytical techniques now allow 40Ar/39Ar spots and traverses to be measured within different zones of individual mica grains, thereby creating the possibility of measuring intra-grain age changes in order to determine spatial and temporal variations of excess argon in the micas. We will present phengite single grain fusion and intra-grain UV laser 40Ar/39Ar data from a variety of rocks of different composition and metamorphic grade from Saih Hatat, NE Oman. This high pressure terrane, subducted and exhumed during the Late Cretaceous obduction of the Semail Ophiolite Complex, provides ideal material for testing and refining models of subduction-exhumation mechanisms. Single-grain 40Ar/39Ar fusion data from the highest grade phengites fall into two distinct groups. Chemically growth-zoned phengites from the mafic eclogites and surrounding calcareous and quartz schists yield a spread of ages from 80-120 Ma within individual samples, equal to the complete range of previously reported bulk 40Ar/39Ar (mainly step-heating) ages. By comparison, chemically homogeneous phengites from the interlayered eclogite-facies pelitic schists yield a single age population, with mean ages of ca. 80 Ma, similar to the previously reported 79 Ma U-Pb zircon age. The difference between the 40Ar/39Ar cooling age and the U-Pb crystallisation age indicates either remarkably rapid cooling or the presence of some excess argon. However the tight grouping of ages suggests that the excess argon is distributed similarly in each grain. The combination of these data with zircon U-Pb ages and phengite major- element chemistry, allow us to begin quantifying the behaviour of argon in high pressure phengites, and potentially determine better constrained timescales for orogenic cycling.

  5. Basement - Cover decoupling and progressive exhumation of metamorphic sediments at hot rifted margin. Insights from the Northeastern Pyrenean analog

    Science.gov (United States)

    Clerc, Camille; Lagabrielle, Yves; Labaume, Pierre; Ringenbach, Jean-Claude; Vauchez, Alain; Nalpas, Thierry; Bousquet, Romain; Ballard, Jean-François; Lahfid, Abdeltif; Fourcade, Serge

    2016-08-01

    We compile field data collected along the eastern part of the North Pyrenean Zone (NPZ) to point to a tectonic evolution under peculiar thermal conditions applying to the basin sediments in relation with the opening of the Cretaceous Pyrenean rift. Based on this compilation, we show that when thinning of the continental crust increased, isotherms moved closer to the surface with the result that the brittle-ductile transition propagated upward and reached sediments deposited at the early stage of the basin opening. During the continental breakup, the pre-rift Mesozoic cover was efficiently decoupled from the Paleozoic basement along the Triassic evaporite level and underwent drastic ductile thinning and boudinage. We suggest that the upper Albian and upper Cretaceous flysches acted as a blanket allowing temperature increase in the mobile pre-rift cover. Finally, we show that continuous spreading of the basin floor triggered the exhumation of the metamorphic, ductily sheared pre-rift cover, thus contributing to the progressive thinning of the sedimentary pile. In a second step, we investigate the detailed geological records of such a hot regime evolution along a reference-section of the eastern NPZ. We propose a balanced restoration from the Mouthoumet basement massif (north) to the Boucheville Albian basin (south). This section shows a north to south increase in the HT Pyrenean imprint from almost no metamorphic recrystallization to more than 600 °C in the pre- and syn-rift sediments. From this reconstruction, we propose a scenario of tectonic thinning involving the exhumation of the pre-rift cover by the activation of various detachment surfaces at different levels in the sedimentary pile. In a third step, examination of the architecture of current distal passive margin domains provides confident comparison between the Pyrenean case and modern analogs. Finally, we propose a general evolutionary model for the pre-rift sequence of the Northeastern Pyrenean rifted

  6. Exhumation and stress history in the sedimentary cover during Laramide thick-skinned tectonics assessed by stylolite roughness analysis.

    Science.gov (United States)

    Beaudoin, Nicolas; Lacombe, Olivier; David, Marie-Eléonore; Koehn, Daniel; Coltier, Robin

    2017-04-01

    Basement-involvement in shortening in forelands has a strong impact on the overlying sedimentary cover. The basement influences namely the geometry of folds and structures, the stress evolution and the nature and pathways for fluid migrations. However, these influences are poorly documented in context where the basement/cover interface is shallow (Sevier-Laramide deformation at the front of the Rocky Mountains, in the Bighorn Basin (Wyoming, USA). Stylolite populations have been considered as part of an extensive microstructure investigation including also fractures, striated microfaults and calcite twins in key major structures such as the Sheep Mountain Anticline, the Rattlesnake Mountain Anticline, and the Bighorn Mountains Arch. Stylolite recognized in the field are clearly related to successive stages of deformation of the sedimentary cover, including fold development. We further apply a newly developed roughness analysis of pressure-solution stylolites which grant access (1) to the magnitude of the vertical principal stress, hence the maximum burial depth of the strata based on sedimentary stylolites, (2) to the principal stress orientations and regimes based on tectonic stylolites and (3) ultimately to the complete stress tensor when sedimentary and tectonic stylolites can be considered coeval. This approach was then coupled to mechanical properties of main competent formations exposed in the basin. Results of stylolite paleopiezometry, compared and combined to existing paleostress estimates from calcite twins and to exhumation reconstruction from low-temperature thermochronology, unravel the potential of the method to refine the structural history at the structure- and basin-scale. On top of the advances this case study adds to the methodology, the quantified reconstruction of stress-exhumation evolution in such a broken-foreland context offers a unique opportunity to discuss how thick-skinned tectonics impacts stress distribution in the sedimentary cover.

  7. Thermal history, exhumation and long-term landscape evolution of the South Atlantic passive continental margin, Kaoko Belt, NW Namibia

    Science.gov (United States)

    Menges, Daniel; Glasmacher, Ulrich A.; Hackspacher, Peter C.; Schneider, Gabriele; Zentner, Henning; Karl, Markus

    2014-05-01

    After the Damara Orogeny at the end of the Neoproterozoic the Kaoko Belt in northwestern Namibia was affected by deep erosion of the Damara Sequence, followed by the depositon of the Karoo Supergroup from Permo-Carboniferous to Early Cretaceous. The lithostratigraphic units consist of Late Proterozoic to Cambrian metamorphosed rocks and intrusive complexes of the Damara Group, with ages of 534 (7) Ma to 481 (25) Ma (Miller 1983), that are unconformably overlain by terrestrial deposits of the Karoo Supergroup (Stollhofen 1999), comprising two flood basalt events: the Karoo flood basalts, at 183 (1) Ma (Duncan et al. 1997), and the Early Cretaceous Paraná-Etendeka flood basalts, at 132 (1) Ma (Renne et al. 1996). The latter marking the rift stage of the opening of the South Atlantic. The "passive" continental margin along the Kaoko Belt in northern Namibia is a perfect location to quantify exhumation and uplift rates, model the long-term landscape evolution and provide information about the major processes controlling the landscape evolution in this region. The poster/talk will present thermochronological data, t-T-models and exhumation rates for the Kaoko belt, NW Namibia. References Miller, R. M., 1983. Evolution of the Damara Orogen, Vol. 11, Geol. Soc., South Africa Spec. Pub.. Renne, P.R., Glen, J.M., Milner, S.C., Duncan, A.R., 1996. Age of Etendeka flood volcanism and associated intrusions in southwestern Africa, Geology 24 (7): 659- 662. Duncan, R., Hooper, P., Rehacek, J., March, J. and Duncan, A., 1997. The timing and duration of the Karoo igneous event, southern Gondwana, J. Geophys. Res. 102: 18127-18138. Stollhofen, H., 1999. Karoo Synrift-Sedimentation und ihre tektonische Kontrolle am entstehenden Kontinentalrand Namibias, Z.dt.geol.Ges. 149: 519-632.

  8. Reconstruction of methods of execution of the death penalty by shooting in the years 1949-1954 based on exhumation research of "prison fields" in Osobowicki Cemetery in Wroclaw. Part I--Historical outline and results of research conducted prior to exhumations performed in 2011.

    Science.gov (United States)

    Szleszkowski, Łukasz

    2012-01-01

    In the period between October and December 2011, a series of exhumation research of the so-called prison quarters dating back to 1949-1954 was conducted in Osobowicki Cemetery in Wrocław. Among the buried there were political prisoners executed by shooting--genuine or alleged members of post-war independence organizations. It was a unique opportunity to determine the method of execution of the death penalty in that period because, according to historical data and the results of two test exhumations, this method considerably differed from instructions on the use of a firing squad during execution of the death penalty.

  9. Post-emplacement kinematics and exhumation history of the Almora klippe of the Kumaun-Garhwal Himalaya, NW India: revealed by fission track thermochronology

    Science.gov (United States)

    Singh, Paramjeet; Patel, R. C.

    2017-09-01

    Tectonically transported crystalline thrust sheet over the Lesser Himalayan meta-sedimentary zone along the Main Central Thrust (MCT) is represented by Almora, Baijnath, Askot and Chiplakot crystalline klippen. The Almora-Dadeldhura klippe in the Kumaun-Garhwal and western Nepal Himalaya is the witness and largest representative of these crystalline klippen, south of MCT. Here, we investigate the post-emplacement kinematics and exhumation history of the Almora klippe. The newly derived zircon fission track (ZFT) ages combined with published apatite fission track (AFT), 40Ar-39Ar ages from the Almora-Dadeldhura klippe and Ramgarh thrust sheet to quantify the temporal variation in cooling ages and exhumation rates. Using 1-D numerical modelling approach, we calculate the transient exhumation rates with respect to different time intervals. New ZFT cooling ages along 50-km-long orogeny perpendicular transect across the Almora klippe range between 13.4 ± 0.6 and 21.4 ± 0.9 Ma. Published AFT ages and 40Ar-39Ar ages from the Almora-Dadeldhura klippe range 3.7 ± 0.8-13.2 ± 2.7 and 18.20-25.69 Ma, respectively. AFT ages reported from Ramgarh thrust sheet range 6.3 ± 0.8-7.2 ± 1.0 Ma in Kumaun region and 10.3 ± 0.5-14.4 ± 2.2 Ma in western Nepal. The linear age trend along with youngest ZFT age ( 14 Ma) close to the North Almora Thrust (NAT) in its hanging wall suggests rapid uplift close to the NAT due to its reactivation as back thrust. The transient exhumation rates of Almora klippe agree that the erosion rate was rapid (0.58 mma-1) close to the NAT in its hanging wall and relatively slow (0.31 mma-1) close to the SAT in its hanging wall during 15-11 Ma. We interpret that the fission track ages and transient exhumation rate pattern of crystalline klippen show a dynamic coupling between tectonic and erosion processes in the Kumaun-Garhwal Himalaya. However, the tectonic processes play the major role in controlling the exhumation pattern.

  10. Long-term subsidence, cooling, and exhumation history along the South Atlantic passive continental margin in NW-Namibia

    Science.gov (United States)

    Menges, Daniel; Glasmacher, Ulrich Anton; Salomon, Eric; Hackspacher, Peter Christian; Schneider, Gabi

    2017-04-01

    In northwestern Namibia the Kaoko Belt is one of the most important Precambrian crustal segments that have stored the subsidence, cooling, and exhumation history of Namibia since the Neoproterozoic. ZFT-ages, with ages between 292.7 (46.0) and 436.8 (45.9) Ma, are giving new insights on this early evolution. Paleozoic to Mesozoic sedimentary rocks of the Karoo Supergroup and the Lower Cretaceous volcanic rocks of the Etendeka sequence overlay the Proterozoic metamorphic and intrusive rocks (1). New apatite fission-track (AFT) ages range from 390.9 (17.9) Ma to 80.8 (6.0) Ma. Along the coast apatites of Proterozoic rock samples reveal the youngest ages. Further inland the ages increase significantly. In addition, rapid change of AFT-ages occurs on both sides of major thrust and shear zones. Using the oldest thermochronological data the revealed t-T paths indicate a long era of exhumation, starting at the end of the Pan-African Orogeny in the Neoproterozoic and continuing into the Permo-Carboniferous. The subsequent sedimentation of the Karoo Supergroup initiates a new era of subsidence until the end of Triassic (2).The subsequent period of denudation ends abruptly with the rapid deposition of the Etendeka basalts in the Early Cretaceous (3). The maximum thickness of the Etendeka volcanic suite has been estimated, using the apatite fission-track data, to about 3.2 (1.2) km. With the ongoing opening of the South Atlantic and the formation of the continental margin the Kaoko Belt went through a rapid cooling event starting 130 Ma and ending 80 Ma, at a mean rate of 0.034 km/Ma for the western, and 0.018 km/Ma for the northern and eastern Kaoko Belt. This cooling event was accompanied by a reactivation of major fault zones, like the Purros Mylonite Zone (4). Thereafter, stable conditions were established, with denudation rates generally lower than 0.010 km/Ma, until the Neogene, where a second cooling event led to increased exhumation rates around 0.042 km/Ma. The total

  11. Petrological and geochemical records of short-lived, high temperature metamorphism during exhumation of the Sulu UHP metamorphic terrane

    Science.gov (United States)

    Zong, K.; Liu, Y.; Zhang, X.; Ye, Y.; Gao, C.

    2010-12-01

    The Dabie-Sulu terrane of east-central China is the largest and most well known ultrahigh-pressure (UHP) metamorphic terrane in the world, which has become one of the most important places to study continental subduction-related UHP metamorphism. In the past two decades, numerous petrological, geochemical, petrophysical and tectonophysical studies were carried out in the Dabie-Sulu UHP metamorphic terrane. However, almost all of these studies have focused on UHP metamorphic processes, while only a few studies have focused on the thermal evolution. Here we present a detailed petrological and geochemical study on the southern Sulu UHP eclogites in order to constrain the “hot” exhumation of the Sulu UHP metamorphic terrane. Eclogite-hosted garnet-spinel-corundum-quartz-bearing titanohematite veins near the main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) are described for the first time in the Sulu UHP metamorphic terrane. A vein composed of titanohematite + ilmenite + hematite + spinel + garnet + corundum + quartz + K-feldspar + albite was studied in detail. The unusual mineral assemblage of garnet + spinel + corundum + quartz implies that this vein could have experienced high temperatures (>900 oC). Although within garnets showed well-defined Mg and Mn diffusion zoning in the rim as a result of the high temperature event, slight Mg and Mn growth zoning was preserved in the core. Thus, we suggest that the Sulu UHP terrane could have experienced a short-lived, high-temperature stage during exhumation. This is consistent with trace element zoning recorded by garnet, omphacite and apatite and much higher temperatures recorded by rutiles and zircons with ages of ~200 Ma in the CCSD-MH eclogites. We speculate that slab breakoff may have caused asthenospheric upwelling, which could have provided a heat pulse for the short-lived, high-temperature metamorphism in the Sulu UHP terrane. Such high temperature stage could have contributed to the

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

    Science.gov (United States)

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

    2015-12-01

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

  13. From source to sink in central Gondwana: Exhumation of the Precambrian basement rocks of Tanzania and sediment accumulation in the adjacent Congo basin

    OpenAIRE

    Kasanzu, Charles Happe; Linol, Bastien; Maarten J. De Wit; Brown, Roderick; Persano, Cristina; Stuart, Finlay M.

    2016-01-01

    Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000 m above sea level) but low-relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Bas...

  14. Tectonic burial, thrust emplacement, and extensional exhumation of the Cabot nappe in the Appalachian hinterland of Cape Breton Island, Canada

    Science.gov (United States)

    Lynch, Gregory

    1996-02-01

    Silurian imbricate thrusting, Early Devonian high-grade metamorphic nappe emplacement, and Devonian-Carboniferous extensional denudation characterize deformation in the Appalachian hinterland of Cape Breton Island. Compressional deformation following Early Silurian arc volcanism features imbrication of Cambrian-Precambrian basement rocks of Gondwana derivation with Ordovician-Silurian cover sequences across thick zones of mylonite during south directed transport. High grade metamorphism and gneissic rocks of late Silurian age in the region indicate that significant tectonic burial and crustal thickening occurred as a result of the thrusting. Partial denudation of the high grade assemblages occurred during Early Devonian thrust emplacement of the Cabot nappe toward the northwest, along the Highlands Shear Zone. The nappe is characterized by an amphibolitic gneiss and high-grade schist complex defining a large folded klippe above Silurian units. Kyanite is widespread within the nappe, and a distinctive feature of the thrust sheet is the dynamothermal metamorphism of cooler greenschist-grade footwall rocks producing inverted isograds; staurolite is regionally distributed and occurs in pelitic units in the immediate footwall of the Highlands Shear Zone forming a discontinuous halo around the klippe. Greenschist-grade footwall rocks are exposed in structural windows as a result of folding and faulting. Shear sense indicators along the margins of the Cabot nappe have been rotated into their present positions due to superposed folding, providing apparent movement directions for the nappe. Complete exhumation to surface occurred during Late Devonian extension along the low-angle Margaree Shear Zone.

  15. An osteological revisitation of autopsies: comparing anthropological findings on exhumed skeletons to their respective autopsy reports in seven cases.

    Science.gov (United States)

    Cappella, A; Castoldi, E; Sforza, C; Cattaneo, C

    2014-11-01

    Forensic anthropologists and pathologists are more and more requested to answer questions on bone trauma. However limitations still exist concerning the proper interpretation of bone fractures and bone lesions in general. Access to known skeletal populations which derive from cadavers (victims of violent deaths) who underwent autopsy and whose autopsy reports are available are obvious sources of information on what happens to bone trauma when subjected to taphonomic variables, such as burial, decomposition, postmortem chemical and mechanical insults; such skeletal collections are still however quite rare. This study presents the results of the comparative analysis between the autopsy findings on seven cadavers (six of which victims of blunt, sharp or gunshot wounds) and those of the anthropological assessment performed 20 years later on the exhumed dry bones (part of the Milano skeletal collection). The investigation allowed us to verify how perimortem sharp, blunt and gunshot lesions appear after a long inhumation period, whether they are still recognizable, and how many lesions are no longer detectable or were not detectable at all compared to the autopsy report. It also underlines the importance of creating skeletal collections with known information on cause of death and trauma. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  16. Rapid exhumation of Cretaceous arc-rocks along the Blue Mountains restraining bend of the Enriquillo-Plantain Garden fault, Jamaica, using thermochronometry from multiple closure systems

    Science.gov (United States)

    Cochran, William J.; Spotila, James A.; Prince, Philip S.; McAleer, Ryan J.

    2017-01-01

    The effect of rapid erosion on kinematic partitioning along transpressional plate margins is not well understood, particularly in highly erosive climates. The Blue Mountains restraining bend (BMRB) of eastern Jamaica, bound to the south by the left-lateral Enriquillo-Plantain Garden fault (EPGF), offers an opportunity to test the effects of highly erosive climatic conditions on a 30-km-wide restraining bend system. No previous thermochronometric data exists in Jamaica to describe the spatial or temporal pattern of rock uplift and how oblique (> 20°) plate motion is partitioned into vertical strain. To define the exhumation history, we measured apatite (n = 10) and zircon (n = 6) (U-Th)/He ages, 40Ar/39Ar (n = 2; amphibole and K-spar) ages, and U/Pb zircon (n = 2) crystallization ages. Late Cretaceous U/Pb and 40Ar/39Ar ages (74–68 Ma) indicate rapid cooling following shallow emplacement of plutons during north-south subduction along the Great Caribbean Arc. Early to middle Miocene zircon helium ages (19–14 Ma) along a vertical transect suggest exhumation and island emergence at ~ 0.2 mm/yr. Older zircon ages 10–15 km to the north (44–35 Ma) imply less rock uplift. Apatite helium ages are young (6–1 Ma) across the entire orogen, suggesting rapid exhumation of the BMRB since the late Miocene. These constraints are consistent with previous reports of restraining bend formation and early emergence of eastern Jamaica. An age-elevation relationship from a vertical transect implies an exhumation rate of 0.8 mm/yr, while calculated closure depths and thermal modeling suggests exhumation as rapid as 2 mm/yr. The rapid rock uplift rates in Jamaica are comparable to the most intense transpressive zones worldwide, despite the relatively slow (5–7 mm/yr) strike-slip rate. We hypothesize highly erosive conditions in Jamaica enable a higher fraction of plate motion to be accommodated by vertical deformation. Thus, strike-slip restraining bends may evolve differently

  17. Spatial and temporal development of exhumation at the St. Elias syntaxis in the Yakutat-North American subduction-collision zone, SE Alaska

    Science.gov (United States)

    Falkowski, Sarah; Enkelmann, Eva; Pfänder, Jörg; Drost, Kerstin; Stübner, Konstanze; Ehlers, Todd

    2015-04-01

    Since the Mesozoic, the western North American margin has been built by the subduction-collision of several terranes. Currently, the 15-30 km thick, wedge-shaped oceanic plateau of the Yakutat microplate collides obliquely with North America at the bend of the southern Alaskan margin forming the Chugach-St. Elias Mountains. Glaciation of this orogen started 6-5 Ma and efficient glacial erosion has been reported over different timescales. Particularly rapid and deep exhumation occurs at the St. Elias syntaxis, where the plate boundary bends and the tectonic regime transitions from transpression to convergence and flat-slab subduction. This region comprises the highest topography and is almost completely covered by the Seward-Malaspina and Hubbard-Valerie glacial systems. Very young detrital zircon fission-track exhumation ages (track age distributions derived from 46 glacio-fluvial sand samples confine the area of rapid and deep exhumation on the resolution of catchments to an ~4800 km2 area on the North American Plate around the St. Elias syntaxis. To overcome the shortcoming of a decreased resolution of the provenance signal of sand, we present 22 new crystallization ages of cobble-sized detritus from the Seward-Malaspina Glacier. Zircon U-Th/He ages of the cobbles demonstrate that they originate from below the ice and their provenance is analyzed based on their petrographic information and zircon U/Pb data (30.8±0.8 to 277.1±7 Ma, 2σ). Furthermore, we gained 29 new cooling ages of multiple thermochronometers from the cobbles of the Seward-Malaspina and Hubbard-Valerie Glaciers (hornblende and biotite 40Ar/39Ar, zircon and apatite U-Th/He, apatite fission-track) that reveal different cooling histories for the rocks within the syntaxis. For most cobbles, we can determine the provenance within the glacial catchments of the syntaxis area. The results support previous conclusions of a larger part of the syntaxis being affected by rapid, deep exhumation because

  18. Rapid exhumation of Cretaceous arc-rocks along the Blue Mountains restraining bend of the Enriquillo-Plantain Garden fault, Jamaica, using thermochronometry from multiple closure systems

    Science.gov (United States)

    Cochran, William J.; Spotila, James A.; Prince, Philip S.; McAleer, Ryan J.

    2017-11-01

    The effect of rapid erosion on kinematic partitioning along transpressional plate margins is not well understood, particularly in highly erosive climates. The Blue Mountains restraining bend (BMRB) of eastern Jamaica, bound to the south by the left-lateral Enriquillo-Plantain Garden fault (EPGF), offers an opportunity to test the effects of highly erosive climatic conditions on a 30-km-wide restraining bend system. No previous thermochronometric data exists in Jamaica to describe the spatial or temporal pattern of rock uplift and how oblique (> 20°) plate motion is partitioned into vertical strain. To define the exhumation history, we measured apatite (n = 10) and zircon (n = 6) (U-Th)/He ages, 40Ar/39Ar (n = 2; amphibole and K-spar) ages, and U/Pb zircon (n = 2) crystallization ages. Late Cretaceous U/Pb and 40Ar/39Ar ages (74-68 Ma) indicate rapid cooling following shallow emplacement of plutons during north-south subduction along the Great Caribbean Arc. Early to middle Miocene zircon helium ages (19-14 Ma) along a vertical transect suggest exhumation and island emergence at 0.2 mm/yr. Older zircon ages 10-15 km to the north (44-35 Ma) imply less rock uplift. Apatite helium ages are young (6-1 Ma) across the entire orogen, suggesting rapid exhumation of the BMRB since the late Miocene. These constraints are consistent with previous reports of restraining bend formation and early emergence of eastern Jamaica. An age-elevation relationship from a vertical transect implies an exhumation rate of 0.8 mm/yr, while calculated closure depths and thermal modeling suggests exhumation as rapid as 2 mm/yr. The rapid rock uplift rates in Jamaica are comparable to the most intense transpressive zones worldwide, despite the relatively slow (5-7 mm/yr) strike-slip rate. We hypothesize highly erosive conditions in Jamaica enable a higher fraction of plate motion to be accommodated by vertical deformation. Thus, strike-slip restraining bends may evolve differently depending on

  19. Prograde high- to ultrahigh-pressure metamorphism and exhumation of oceanic sediments at Lago di Cignana, Zermatt-Saas Zone, western Alps

    Science.gov (United States)

    Reinecke, T.

    1998-03-01

    Pelagic metasediments and MORB-type metabasalts of the former Tethyan oceanic crust at Cignana, Valtournanche, Italy, experienced UHP metamorphism and subsequent exhumation during the Early to Late Tertiary. Maximum PT conditions attained during UHP metamorphism were 600-630 °C, 2.7-2.9 GPa, which resulted in the formation of coesite-glaucophane-eclogites in the basaltic layer and of garnet-dolomite-aragonite-lawsonite-coesite-phengite-bearing calc-schists and garnet-phengite-coesite-schists with variable amounts of epidote, talc, dolomite, Na-pyroxene and Na-amphibole in the overlying metasediments. During subduction the rocks followed a prograde HP/UHP path which in correspondance with the Jurassic age of the Tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating. Inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle-plastic transition in the quartz-aragonite-dominated rocks, induced convection in the asthenospheric mantle wedge and/or heat consumption by endothermic reactions over a restricted PT segment during subduction. After detachment from the downgoing slab some 50-70 Ma before present, the Cignana crustal slice was first exhumed to ca. 60 km and concomitantly cooled to ca. 550 °C, tracing back the UHP/HP prograde path displaced by 50-80 °C to higher temperatures. Exhumation at this stage is likely to have occurred in the Benioff zone, while the subduction of cool lithosphere was going on. Subsequently, the rocks were near-isothermally exhumed to ca. 30 km, followed by concomitant decompression and cooling to surface conditions (at glaucophane eclogites, the HP/UHP assemblages of the metasediments have been largely obliterated during exhumation. Relics from which the metamorphic evolution of the rocks during prograde HP metamorphism and the UHP stage can be retrieved are restricted to rigid low

  20. Preliminary results constraining the kinematics of subduction and exhumation processes on Skopelos island, Northern Sporades (Aegean Domain)

    Science.gov (United States)

    Porkolab, Kristof; Willingshofer, Ernst; Sokoutis, Dimitrios; Creton, Iverna

    2017-04-01

    Extension in the Aegean region is a process driven by slab rollback since 45 Ma (e.g. Brun and Sokoutis, 2007; Brun et al. 2016). These and other studies dominantly focused on the northern Aegean/Rhodope or the Cycladic tectonic systems, yielding abundant kinematic, structural, petrologic and geochronological data to constrain their geodynamic evolution. This contrasts with the region of the Northern Sporades, which have not yet been thoroughly studied in the light of subduction-exhumation processes. In particular, a detailed kinematic analysis, the focus of this study, is missing that allows for establishing the relation between the deformation structures on the island, and the large-scale tectonic events in the Aegean domain. The Northern Sporades consist of three major (area ≥ 50km2) islands (Skiathos, Skopelos, and Alonnisos) and a number of smaller islands. As the first phase of exploring the structural evolution of the Northern Sporades, this work reports the results of field work performed on the island of Skopelos, and aims to provide a preliminary model for the deformation history of the island. Skopelos consists from bottom to top of three structural units, which are separated by thrust contacts (Jacobshagen and Wallbrecher, 1984; Matarangas, 1992; Jacobshagen and Matarangas, 2004): the Pelagonian, the Eohellenic, and the Palouki unit. The age of the formations constituting these units ranges from Paleozoic to Paleogene, and all formations have been metamorphosed under lower greenschist or possibly also blueschist facies conditions (Mposkos and Liati, 1991) and experienced polyphase deformation. Based on our field kinematic and structural analysis we suggest the following deformation sequence on Skopelos island: D1 is characterized by tight to isoclinal folding (F1) and the formation of a penetrative foliation (S1), which is the axial plane cleavage to the F1 folds. S1 planes carry a NE-SW trending stretching lineation, along which top-SW shear has been

  1. Characterization and simulation of an exhumed fractured petroleum reservoir. Final report, March 18, 1996--September 30, 1998

    Energy Technology Data Exchange (ETDEWEB)

    Forster, C.B.; Nielson, D.L.; Deo, M.

    1998-12-01

    An exhumed fractured reservoir located near Alligator Ridge in central Nevada provides the basis for developing and testing different approaches for simulating fractured petroleum reservoirs. The fractured analog reservoir comprises a 90 m thickness of silty limestone and shaly interbeds within the Devonian Pilot Shale. A period of regional compression followed by ongoing basin and range extension has created faults and fractures that, in tern, have controlled the migration of both oil and gold ore-forming fluids. Open pit gold mines provide access for observing oil seepage, collecting the detailed fracture data needed to map variations in fracture intensity near faults, build discrete fracture network models and create equivalent permeability structures. Fault trace patterns mapped at the ground surface provide a foundation for creating synthetic fault trace maps using a stochastic procedure conditioned by the outcrop data. Conventional simulations of petroleum production from a 900 by 900 m sub-domain within the reservoir analog illustrate the possible influence of faults and fractures on production. The consequences of incorporating the impact of different stress states (e.g., extension, compression or lithostatic) are also explored. Simulating multiphase fluid flow using a discrete fracture, finite element simulator illustrates how faults acting as conduits might be poorly represented by the upscaling procedures used to assign equivalent permeability values within reservoir models. The parallelized reservoir simulators developed during this project provide a vehicle to evaluate when it might be necessary to incorporate very fine scale grid networks in conventional reservoir simulators or to use finely gridded discrete fracture reservoir simulators.

  2. Patterns of deformation, exhumation and uplift across the Island of Timor: insights into the processes that control the early stages of orogenesis (Invited)

    Science.gov (United States)

    McQuarrie, N.; Tate, G. W.; Van Hinsbergen, D. J.; Harris, R. A.

    2013-12-01

    On the island of Timor, arc-continent collision between the Banda volcanic arc and the Australian continent since the late Miocene has uplifted a mountain range containing both deeply exhumed metamorphic rocks and deepwater synorogenic basins. These varied lithologies are separated by a few tens of kilometers, and provide us with an opportunity to examine the spatial patterns of differential uplift and exhumation and its links to the geometry and magnitude of deformation in an orogen that is still in its infancy. New mapping in Timor has provided a detailed view of how the Australian continental slope and shelf rocks are being structurally repeated below overriding Banda Arc material. In East Timor, a window though the Banda terrane shows Permian and Triassic rocks that are repeated by four NNE-striking thrust faults with ~3 km spacing and 50-75 km along-strike extent. The strike of these faults is rotated 50-60 degrees compared to structures to the east and west of this main window. In addition, mapped fold axes are shown to cut across and warp fault traces. These map patterns indicate that the duplex has been both refolded and tilted since its initial formation. In West Timor, Permian through Triassic stratigraphy is faulted and folded into an antiformal stack with 5 exposed thrusts repeating an ~ 3 km thick section. Both south of and adjacent to these structural highs are 10-20 km wide piggyback basins of deepwater, synorogenic marine limestones and clays that coarsen upward into turbidites. Deposition of these units initiated at 5.5 Ma at lower bathyal depths. Synorogenic deposition directly over the Bobonaro mélange, which acts as the décollement between the overthrust Banda Arc rocks and the structurally repeated Australian margin rocks, requires the removal of both Banda arc material and the Cretaceous and younger Kolbano sequence before deposition. These basins record rapid surface uplift to upper bathyal depths from 3.5-3 Ma with continual uplift to

  3. Burial and exhumation of temperate bedrock reefs as elucidated by repetitive high-resolution sea floor sonar surveys: Spatial patterns and impacts to species' richness and diversity

    Science.gov (United States)

    Storlazzi, Curt D.; Fregoso, Theresa A.; Figurski, Jared D.; Freiwald, Jan; Lonhart, Steve I.; Finlayson, David P.

    2013-01-01

    To understand how chronic sediment burial and scour contribute to variation in the structure of algal and invertebrate communities on temperate bedrock reefs, the dynamics of the substrate and communities were monitored at locations that experience sand inundation and adjacent areas that do not. Co-located benthic scuba-transect surveys and high-resolution swath-sonar surveys were completed on bedrock reefs on the inner shelf of northern Monterey Bay, CA, in early winter 2009, spring 2010, and summer 2010. Analysis of the sonar surveys demonstrates that during the 8 months over which the surveys were conducted, 19.6% of the study area was buried by sand while erosion resulted in the exposure of bedrock over 13.8% of the study area; the remainder underwent no change between the surveys. Substrate classifications from the benthic transect surveys correlated with classifications generated from the sonar surveys, demonstrating the capacity of high-resolution sonar surveys to detect burial of bedrock reefs by sediment. On bedrock habitat that underwent burial and exhumation, species' diversity and richness of rock-associated sessile and mobile organisms were 50–66% lower as compared to adjacent stable bedrock habitat. While intermediate levels of disturbance can increase the diversity and richness of communities, these findings demonstrate that burial and exhumation of bedrock habitat are sources of severe disturbance. We suggest that substrate dynamics must be considered when developing predictions of benthic community distributions based on sea floor imagery. These results highlight the need for predictive models of substrate dynamics and for a better understanding of how burial and exhumation shape benthic communities.

  4. Polyphase exhumation in the western Qinling Mountains, China: Rapid Early Cretaceous cooling along a lithospheric-scale tear fault and pulsed Cenozoic uplift.

    Science.gov (United States)

    Heberer, Bianca; Anzenbacher, Thomas; Neubauer, Franz; Genser, Johann; Dong, Yunpeng; Dunkl, István

    2014-03-17

    The western sector of the Qinling-Dabie orogenic belt plays a key role in both Late Jurassic to Early Cretaceous "Yanshanian" intracontinental tectonics and Cenozoic lateral escape triggered by India-Asia collision. The Taibai granite in the northern Qinling Mountains is located at the westernmost tip of a Yanshanian granite belt. It consists of multiple intrusions, constrained by new Late Jurassic and Early Cretaceous U-Pb zircon ages (156 ± 3 Ma and 124 ± 1 Ma). Applying various geochronometers ( 40 Ar/ 39 Ar on hornblende, biotite and K-feldspar, apatite fission-track, apatite [U-Th-Sm]/He) along a vertical profile of the Taibai Mountain refines the cooling and exhumation history. The new age constraints record the prolonged pre-Cenozoic intracontinental deformation as well as the cooling history mostly related to India-Asia collision. We detected rapid cooling for the Taibai granite from ca. 800 to 100 °C during Early Cretaceous (ca. 123 to 100 Ma) followed by a period of slow cooling from ca. 100 Ma to ca. 25 Ma, and pulsed exhumation of the low-relief Cretaceous peneplain during Cenozoic times. We interpret the Early Cretaceous rapid cooling and exhumation as a result from activity along the southern sinistral lithospheric scale tear fault of the recently postulated intracontinental subduction of the Archean/Palaeoproterozoic North China Block beneath the Alashan Block. A Late Oligocene to Early Miocene cooling phase might be triggered either by the lateral motion during India-Asia collision and/or the Pacific subduction zone. Late Miocene intensified cooling is ascribed to uplift of the Tibetan Plateau.

  5. Reconstruction of the Exhumed Mantle Across the North Iberian Margin by Crustal-Scale 3-D Gravity Inversion and Geological Cross Section

    Science.gov (United States)

    Pedrera, A.; García-Senz, J.; Ayala, C.; Ruiz-Constán, A.; Rodríguez-Fernández, L. R.; Robador, A.; González Menéndez, L.

    2017-12-01

    Recent models support the view that the Pyrenees were formed after the inversion of a previously highly extended continental crust that included exhumed upper mantle rocks. Mantle rocks remain near to the surface after compression and mountain building, covered by the latest Cretaceous to Paleogene sequences. 3-D lithospheric-scale gravity inversion demands the presence of a high-density mantle body placed within the crust in order to justify the observed anomalies. Exhumed mantle, having 50 km of maximum width, continuously extends beneath the Basque-Cantabrian Basin and along the northern side of the Pyrenees. The association of this body with rift, postrift, and inversion structural geometries is tested in a balanced cross section across the Basque-Cantabrian Basin that incorporates a major south-dipping ramp-flat-ramp extensional detachment active between Valanginian and early Cenomanian times. Results indicate that horizontal extension progressed 48 km at variable strain rates that increased from 1 to 4 mm/yr in middle Albian times. Low-strength Triassic Keuper evaporites and mudstones above the basement favor the decoupling of the cover with formation of minibasins, expulsion rollovers, and diapirs. The inversion of the extensional system is accommodated by doubly verging basement thrusts due to the reactivation of the former basin bounding faults in Eocene-Oligocene times. Total shortening is estimated in 34 km and produced the partial subduction of the continental lithosphere beneath the two sides of the exhumed mantle. Obtained results help to pinpoint the original architecture of the North Iberian Margin and the evolution of the hyperextended aborted intracontinental basins.

  6. Rates of burial and exhumation of lawsonite blueschist/eclogite in subduction zones from in situ UV laser ablation 40Ar/39Ar phengite geochronology

    Science.gov (United States)

    Fornash, K.; Cosca, M. A.; Whitney, D. L.; Teyssier, C. P.

    2014-12-01

    Lawsonite eclogites and blueschists are accessible records of processes that occur at depth in subducting slabs and can therefore provide information about the chemical and physical evolution of subduction zones. In composite blueschist-eclogite terranes, blueschists may have formed (1) by prograde metamorphism (pre-eclogite), (2) at the same P-T conditions as eclogite-facies metamorphism as a result of differences in bulk composition, H2O content, or oxidation state, or (3) from retrogression of eclogite, e.g. during exhumation. Field and petrologic observations of lawsonite eclogite and blueschist in the Sivrihisar Massif, Turkey, suggest that some blueschist formed from eclogite during exhumation in the subduction channel, whereas results from thermobarometry suggest that some blueschist formed at the same P-T conditions as eclogite. To test the age, petrologic, and tectonic relationship of coexisting eclogite and blueschist, we applied in situ UV laser ablation 40Ar/39Ar phengite geochronology to eclogite- and blueschist-facies rocks representing different structural positions and displaying different phengite textures and coexisting mineral assemblages. Phengite from fresh lawsonite eclogite yield an age of 93 ± 2 Ma and have the narrowest spread in ages (glaucophane-rich margins of eclogite pods also record 92 Ma. Omphacite-bearing lawsonite blueschist and a blueschist-facies quartzite from the same structural position contain age populations at 97 Ma and 110 Ma. These results document a sequence of events from prograde blueschist-facies (> 93 Ma) to peak eclogite-facies metamorphism and vein formation (~93 Ma) to retrograde metamorphism (< 90 Ma). Combined with P-T estimates, these new results distinguish prograde from retrograde blueschist assemblages and allow calculation of burial/exhumation rates over the depth range ~80-45 km in a subduction zone.

  7. Multi-method geo- and thermochronology of glacially transported cobbles reveals the tectonic and exhumation history of the St. Elias Mountains (Alaska/Yukon)

    Science.gov (United States)

    Falkowski, Sarah; Enkelmann, Eva; Drost, Kerstin; Pfänder, Jörg; Stübner, Konstanze; Ehlers, Todd

    2016-04-01

    Multi-method dating is a powerful tool to understand tectonic processes and mountain building. In the case of inaccessible mountain regions, e.g., due to extensive glaciation, the dating of detrital material and bedrock samples from rare outcrops with geo- and thermochronologic methods is often the only applicable approach to study the timing and rates of tectonic processes. The St. Elias Mountains of southeast Alaska and southwest Yukon are an example of a heavily glaciated orogen. With the help of detrital thermochronology of sand-sized material, exhumation patterns could be mapped, though with a low spatial resolution. In contrast, geo- and thermochronology applied to glacially derived cobbles yields provenance information from cobble lithology, zircon U-Pb dating, and the entire cooling history from multiple mineral phases. Multi-grain and multi-aliquot analyses yield high-precision crystallization and cooling ages, while sand-sized detritus requires analysis of single minerals particularly resistant to weathering. We present a reconstruction of the Cenozoic tectonic and exhumation history of the St. Elias Mountains that was obtained from the analysis of 27 carefully selected and prepared cobble samples taken from two of the largest glacial catchments of the St. Elias Mountains. A total of 21 zircon U-Pb data sets as well as eight amphibole and seven biotite 40Ar/39Ar ages constrain the (maximum) formation and cooling ages, respectively, of the rocks in the source area. In addition, four zircon and six apatite (U-Th)/He ages as well as four apatite fission-track ages reveal the exhumation history of these source rocks. Integration of the cobble results with an additional three bedrock biotite 40Ar/39Ar ages and published geo- and thermochronologic data from along the St. Elias Mountains reveals details on the timing and rates of the Cenozoic tectonic evolution of the North American margin in southeast Alaska. Documented are the earliest Eocene spreading

  8. Exhumation history of the Northern Andes from the Cenozoic syn-tectonic sedimentary fill of the Middle Magdalena Valley Basin, Colombia

    Science.gov (United States)

    Moreno, C. J.; Caballero, V. M.; Horton, B. K.; Mora, A.

    2009-12-01

    The Central Cordillera and the Eastern Cordillera of the northern Andes form the western and eastern flanks of the Colombian Middle Magdalena Valley Basin, respectively. Previous estimates of the timing of onset of exhumation of the two cordilleras vary, and although some recent studies have been in agreement, more work is needed to develop a clear picture. The spatial and chronological distribution of deformation has direct implications for the shortening history of the greater South American Andean margin, as well as for improving predictions of the rapid, lateral facies changes associated with the varying nearby sediment sources. Field-based analyses of the basin fill using paleocurrent measurements of trough-cross-beds, clast imbrication and flute casts, not only provide new insights into the tectonic history, but directly complement recent detrital zircon U-Pb work completed in the MMVB. Between the lower and upper Paleocene strata, the paleocurrent direction shifts from northward to eastward, indicating that uplift of the Central Cordillera was underway by the mid-Paleocene and consistent with the shift from a cratonic to Central Cordilleran sediment source observed in the detrital zircon record. This paleocurrent shift occurs coevally with a shift from delta to fluvial facies. An eastward paleoflow in upper Eocene through lowest Oligocene strata indicate a continuing influence of the Central Cordillera. Paleocurrent directions in the lower Oligocene deposits are highly variable, and, beginning in the middle Oligocene strata, show a switch to a dominantly westward orientation that continues through the Neogene. As the orientation changes, deposits show an increase in energy from muddy, meandering river deposits, to coarser, braided channel facies. We attribute this switch, from eastward to westward paleocurrent orientations, to the onset of exhumation of the Eastern Cordillera. The results of a current, detailed sandstone petrographic study combined with

  9. Syn-exhumation partial melting and melt segregation in the Sulu UHP terrane: Evidences from leucosome and pegmatitic vein of migmatite

    Science.gov (United States)

    Song, Yanru; Xu, Haijin; Zhang, Junfeng; Wang, Deyuan; Liu, Endong

    2014-08-01

    In order to investigate partial melting and melt evolution during exhumation of deeply subducted continental crust, we carried out a combined study on layered leucosomes and pegmatitic veins from the Weihai-Rongcheng migmatites in the Sulu ultra-high pressure (UHP) metamorphic terrane, eastern China. The leucosomes are millimetric to centimetric in thickness and mainly consists of K-feldspar + quartz + plagioclase. The pegmatitic veins emplace along the compositional layers or crosscut them and are mainly composed of K-feldspar + quartz. CL images show that most zircon grains of the leucosomes have a core-rim zoning structure, whereas zircons of the pegmatitic veins are mostly new growth grains with rarely preserved relict domains. The inherited zircon domains (ca. 750 Ma) are of a magmatic origin with zircon εHf(t) values between - 5.7 and 5.3 (mean = - 0.8 ± 1.5), suggesting that the protolith rock is a Mid-Neoproterozoic juvenile crust. The zircon overgrowth rims (223 ± 3 Ma) of the leucosomes and the new zircon grains (217 ± 2 Ma) of the pegmatitic veins formed in equilibrium with melt and are similar to magmatic zircons in terms of their CL images and trace element compositions, e.g., heavy-enriched REE patterns (i.e., very low (Gd/Lu)N ratios) with positive Ce and variably negative Eu anomalies, high Y contents and low Hf/Y ratios. Compared with the inherited protolith zircon domains, the Triassic zircon domains of the leucosomes and the pegmatitic veins have obviously high U but low Th contents, resulting in very low Th/U ratios (temperature for the zircon overgrowth rims in the leucosomes ranges from 648 to 845 °C with spot ages from 235 ± 3 to 210 ± 3 Ma. The growth temperature for the zircon grains from the pegmatitic veins ranges from 809 to 651 °C with spot ages from 230 ± 3 to 207 ± 3 Ma. The features suggest a process of cooling and segregation of melt. Melt segregation results in dramatic increases of zircon 176Yb/177Hf and 176Lu/177Hf

  10. Petrology of HP/LT metapelitic rocks of an accretionary wedge, the Central Pontides, Turkey: evidence for tectonic stacking and syn-subduction exhumation

    Science.gov (United States)

    Aygül, Mesut; Okay, Aral; Oberhänsli, Roland

    2015-04-01

    Cretaceous HP/LT chloritoid-bearing metapelitic rocks crop out widely in the central part of the Pontides, northern Turkey. They are associated with eclogite to blueschist-facies metabasites and represent deep levels of an underplated subduction-accretion complex, which is tectonically overlain by low-grade HP phyllite/metasandstone intercalation along an extensional shear zone. Close to the shear zone, the footwall micaschists consist of quartz, phengite, paragonite, chlorite, rutile with syn-kinematic albite porphyroblast formed by pervasive shearing during exhumation. This type of micaschists is tourmaline-bearing and their retrograde nature suggests high-fluid flux along shear zones. Peak metamorphic assemblages are partly preserved in the chloritoid-micaschist farther away from the shear zone. Three peak metamorphic assemblages are identified and their PT conditions are constrained by pseudosections produced by Theriak-Domino and by Raman spectra of carbonaceous material: 1) garnet-chloritoid-glaucophane with lawsonite pseudomorphs (P: 17.5 ± 1 Kbar, T: 390-450 °C) 2) chloritoid with glaucophane pseudomorphs (P: 16-18 Kbar, T: 475 ± 40 °C) and 3) relatively high-Mg chloritoid (17%) with jadeite pseudomorphs (22-25 Kbar; T: 440 ± 30 °C) in addition to phengite, paragonite, quartz, chlorite, rutile. The last mineral assemblage is interpreted as transformation of the chloritoid + glaucophane assemblage to chloritoid + jadeite paragenesis with increasing pressure. Absence of tourmaline suggests that the chloritoid-micaschist did not interact with B-rich fluids during zero strain exhumation. Peak metamorphic assemblages and PT estimates suggest tectonic stacking within wedge with different depths of burial. 40Ar/39Ar phengite age of a pervasively sheared footwall micaschist is constrained to 100.6 ± 1.3 Ma and that of a chloritoid-micaschist is constrained to 91.8 ± 1.8 Ma suggesting exhumation during on-going subduction. Coupling and exhumation of the

  11. Links between crustal melting, plate boundary forces, and syn-convergent exhumation in the Sierras Pampeanas, Argentina

    Science.gov (United States)

    Mulcahy, S. R.; Roeske, S.; McClelland, W.; Jourdan, F.; Renne, P. R.; Vervoort, J. D.; Vujovich, G. I.

    2011-12-01

    facies metamorphism, throughout a time period marked by regional oblique convergence; and 3) the onset of syn-convergent extension occurred after regional migmatites cooled beneath their solidus, and was synchronous with the establishment of a new plate margin to the west of the Precordillera terrane at ~436 Ma. The presence of large volumes of melt throughout the middle and lower crust was insufficient to drive extension during regional convergence and terrane accretion. Exhumation was likely the result of a change in the plate bounding forces.

  12. Marks of autopsy and identification of victims of human rights violations exhumed from cemeteries: the case of the Spanish Civil War (1936-1939).

    Science.gov (United States)

    Ríos, Luis; Martínez, Berta; García-Rubio, Almudena; Herrasti, Lourdes; Etxeberria, Francisco

    2014-09-01

    The presence of autopsy marks in human skeletal remains indicates a medicolegal procedure related to ascertaining the cause and manner of death. We present here four cases where signs of autopsy were observed in the remains recovered from mass graves and cemeteries of prisoners from the Spanish Civil War (1936-1939), victims of extrajudicial executions, and of death in prison, respectively. With respect to the former, historical evidence indicate that during the first weeks after the coup, official removal of cadavers and autopsy procedures were carried out to the first victims of extrajudicial killings, whose corpses were found abandoned in the road. Once the civil war was established and systematic extrajudicial killings were systematic, official military orders were issued to stop standard forensic proceedings. Therefore, autopsy marks observed in the remains exhumed from mass graves located in cemeteries may be indicative of an earlier chronology of the killings, and this information proved to be relevant for the identification process in one of the cases presented. In a cemetery of political prisoners, autopsy signs were also observed in two skeletal remains and in the official records of two prisoners, a corroboration of information also relevant for the identification process. These findings indicate that autopsy marks can be found in the remains of victims of human rights violations exhumed from cemeteries. Skeletal and archival information could be useful for the identification process in other cases of large-scale violence, where the first victims of extrajudicial executions were buried unidentified in cemeteries after autopsy procedures.

  13. Controls on Cenozoic exhumation of the Tethyan Himalaya from fission-track thermochronology and detrital zircon U-Pb geochronology in the Gyirong basin area, southern Tibet

    Science.gov (United States)

    Shen, Tianyi; Wang, Guocan; Leloup, Philippe Hervé; van der Beek, Peter; Bernet, Matthias; Cao, Kai; Wang, An; Liu, Chao; Zhang, Kexin

    2016-07-01

    The Gyirong basin, southern Tibet, contains the record of Miocene-Pliocene exhumation, drainage development, and sedimentation along the northern flank of the Himalaya. The tectonic controls on basin formation and their potential link to the South Tibetan Detachment System (STDS) are not well understood. We use detrital zircon (ZFT) and apatite (AFT) fission-track analysis, together with detrital zircon U-Pb dating to decipher the provenance of Gyirong basin sediments and the exhumation history of the source areas. Results are presented for nine detrital samples of Gyirong basin sediments (AFT, ZFT, and U-Pb), two modern river-sediment samples (ZFT and AFT), and six bedrock samples (ZFT) from transect across the Gyirong fault bounding the basin to the east. The combination of detrital zircon U-Pb and fission-track data demonstrates that the Gyirong basin sediments were sourced locally from the Tethyan Sedimentary Sequence. This provenance pattern indicates that deposition was controlled by the Gyirong fault, active since 10 Ma, whose vertical throw was probably slab during the middle Miocene, inducing dynamic uplift of the Indian plate overriding its own slab.

  14. Knickzone propagation in the Black Hills and northern High Plains: A different perspective on the late Cenozoic exhumation of the Laramide Rocky Mountains

    Science.gov (United States)

    Zaprowski, Brent J.; Evenson, Edward B.; Pazzaglia, Frank J.; Epstein, Jack B.

    2001-06-01

    Geomorphic research in the Black Hills and northern High Plains poses an intriguing hypothesis for the Cenozoic evolution of this salient of the Laramide Rockies. Most recently, geologists have appealed to late Cenozoic epeirogenic uplift or climate change to explain the post-Laramide unroofing of the Rockies. On the basis of field mapping and the interpretation of long-valley profiles, we conclude that the propagation of knickzones is the primary mechanism for exhumation in the Black Hills. Long profiles of major drainages show discrete breaks in the slope of the channel gradient that are not coincident with changes in rock type. We use the term knickzones to describe these features because their profiles are broadly convex over tens of kilometers. At and below the knickzone, the channel is incising into bedrock, abandoning a flood plain, and forming a terrace. Above the knickzone, the channel is much less incised, resulting in a broad valley bottom. Numerous examples of stream piracy are documented, and in each case, the capture is recorded in the same terrace level. These observations are consistent with migrating knickzones that have swept through Black Hills streams, rearranging drainages in their wake. We demonstrate there are two knickzone fronts associated with mapped terraces. Preliminary field evidence of soil development shows that these terraces are time transgressive in nature. Our data strongly suggest that knickzone propagation must be considered a viable mechanism driving late Cenozoic fluvial incision and exhumation of the northern High Plains and adjacent northern Rocky Mountains.

  15. Knickzone propagation in the Black Hills and northern High Plains: a different perspective on the late Cenozoic exhumation of the Laramide Rocky Mountains

    Science.gov (United States)

    Zaprowski, Brent J.; Evenson, Edward B.; Pazzaglia, Frank J.; Epstein, Jack B.

    2001-01-01

    Geomorphic research in the Black Hills and northern High Plains poses an intriguing hypothesis for the Cenozoic evolution of this salient of the Laramide Rockies. Most recently, geologists have appealed to late Cenozoic epeirogenic uplift or climate change to explain the post-Laramide unroofing of the Rockies. On the basis of field mapping and the interpretation of long-valley profiles, we conclude that the propagation of knickzones is the primary mechanism for exhumation in the Black Hills. Long profiles of major drainages show discrete breaks in the slope of the channel gradient that are not coincident with changes in rock type. We use the term knickzones to describe these features because their profiles are broadly convex over tens of kilometers. At and below the knickzone, the channel is incising into bedrock, abandoning a flood plain, and forming a terrace. Above the knickzone, the channel is much less incised, resulting in a broad valley bottom. Numerous examples of stream piracy are documented, and in each case, the capture is recorded in the same terrace level. These observations are consistent with migrating knickzones that have swept through Black Hills streams, rearranging drainages in their wake. We demonstrate there are two knickzone fronts associated with mapped terraces. Preliminary field evidence of soil development shows that these terraces are time transgressive in nature. Our data strongly suggest that knickzone propagation must be considered a viable mechanism driving late Cenozoic fluvial incision and exhumation of the northern High Plains and adjacent northern Rocky Mountains.

  16. An Early Cretaceous garnet pressure-temperature path recording synconvergent burial and exhumation from the hinterland of the Sevier orogenic belt, Albion Mountains, Idaho

    Science.gov (United States)

    Kelly, Eric D.; Hoisch, Thomas D.; Wells, Michael L.; Vervoort, Jeffrey D.; Beyene, Mengesha A.

    2015-08-01

    Rocks may undergo complex pressure-temperature ( P- T) histories during orogenesis in response to alternating episodes of synconvergent burial and exhumation. In this study, chemical zoning in garnets combined with textural and chemical evidence from the schist of Willow Creek in the Albion Mountains of south-central Idaho (USA), reveals a complex P- T path during the early stages of Sevier orogenesis. The distribution of quartz inclusions combined with internal resorption features establishes a hiatus in garnet growth. Chemical zoning was simulated using a G-minimization approach to yield a P- T path consisting of three distinct pressure changes during increasing temperature, defining an "N" shape. Lu-Hf isochron ages from multiple garnet fractions and whole-rock analyses in two samples are 132.1 ± 2.4 and 138.7 ± 3.5 Ma. The samples were collected from the hanging wall of the Basin-Elba thrust fault and yielded results similar to those previously obtained from the footwall. This leads to several conclusions: (1) Both the hanging wall and footwall experienced the same metamorphic event, (2) the paths document a previously unrecognized crustal thickening and synorogenic extension cycle that fills an important time gap in the shortening history of the Sevier retroarc, suggesting progressive eastward growth of the orogen rather than a two-stage history, and (3) episodes of extensional exhumation during protracted convergent orogenesis are increasingly well recognized and highlight the dynamic behavior of orogenic belts.

  17. The deformation pattern of high-pressure exhumation in the Adula Nappe (Switzerland) - Preliminary results from crystallographic preferred orientations of quartz

    Science.gov (United States)

    Keppler, Ruth; Stipp, Michael; Froitzheim, Niko

    2017-04-01

    The Adula Nappe in the central Alps forms the easternmost part of the Lepontine dome, which mainly consists of basement nappes and their Mesozoic cover. The Adula Nappe was originally part of the distal European continent and entered a south-dipping subduction zone experiencing high- to ultrahigh pressure peak conditions at about 38 Ma. The unit underwent several deformation phases after peak conditions including the Zapport phase, which accomplished the largest part of the exhumational deformation. Despite extensive research in the Adula Nappe, the internal deformation during exhumation is not completely understood. Especially the large pressure-temperature gradient from 12-17 kbar/500-600 C° in the north to 30 kbar/800-850 C° in the south is a topic of recent discussion. This phenomenon either originates from internal, heterogeneous deformation of the Adula Nappe during its exhumation, or it was caused by tectonic overpressure, which would indicate that the Adula Nappe was not as deeply subducted as previously assumed. In this study, we sampled quartzites, micaschists, para- and orthogneisses in a close-meshed net throughout the entire Adula Nappe. Only samples showing Zapport deformation without significant younger overprint were collected. Crystallographic preferred orientations (CPOs) of all mineral phases in the samples were measured with time-of-flight neutron diffraction using the SKAT diffractometer at JINR, Dubna, Russia. Quartz CPOs show great variability. Most of the c-axis patterns yield an asymmetry charateristic of a top-to-the-north sense of shear, although there are few top-to-the-south samples. Most c-axes exhibit peripheral maxima at an angle to the foliation normal pointing to dominant basal slip, especially in the northern Adula Nappe. The samples from the central Adula Nappe show also maxima between Z and Y of the c-axis pole figure indicative of rhomb-, π- and prism slip. These maxima are usually combined with asymmetric crossed or single

  18. Late Miocene to present-day exhumation and uplift of the Internal Zone of the Rif chain: Insights from low temperature thermochronometry and basin analysis

    Science.gov (United States)

    Romagny, A.; Ph. Münch; Cornée, J.-J.; Corsini, M.; Azdimousa, A.; Melinte-Dobrinescu, M. C.; Drinia, H.; Bonno, M.; Arnaud, N.; Monié, P.; Quillévéré, F.; Ben Moussa, A.

    2014-07-01

    Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60-100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events

  19. Thrusting and exhumation of the southern Mongolian Plateau: Joint thermochronological constraints from the Langshan Mountains, western Inner Mongolia, China

    Science.gov (United States)

    Feng, Li-Xia; Brown, Roderick W.; Han, Bao-Fu; Wang, Zeng-Zhen; Łuszczak, Katarzyna; Liu, Bo; Zhang, Zhi-Cheng; Ji, Jian-Qing

    2017-08-01

    The Mongolian Plateau has undergone multi-stage denudation since the Late Triassic, and the NE-trending Langshan Mountains in the southern margin of the Mongolian Plateau is crucial to unraveling the Meso-Cenozoic cooling and exhumation history of the Mongolian Plateau. The Langshan Mountains are dominated by Precambrian gneiss and Permian-Middle Triassic granitic plutons crosscut by a set of NE-striking thrust faults. A joint thermochronological study was conducted on 31 granitic and gneissic samples along the HQ and CU transects across the Langshan Mountains and other two samples from the BQ in the north of the Langshan Mountains. Four biotite/muscovite and three K-feldspar 40Ar/39Ar plateau ages range from 205 ± 1 to 161 ± 1 and 167 ± 1 to 131 ± 1 Ma, respectively. Thirty-three apatite fission track (AFT) ages are between 184 ± 11 and 79 ± 4 Ma, with mean track lengths from 11.1 ± 1.8 to 13.1 ± 1.4 μm of mostly unimodal distributions. Thirty-one single-grain raw AHe ages are in a range of 134 ± 8 to 21 ± 1 Ma. The AFT ages decrease monotonously from NW to SE until thrust faults along the two transects, with an age-jump across thrust F35. Joint thermal history modelling shows a three-stage cooling history as a result of denudation, especially with spatial differentiation in the first stage. Relative slow cooling at c. 0.6-1.0 °C/Ma occurred in the BQ and the northern part of the HQ transect during 220-100 Ma and the northern part of the CU transect during 160-100 Ma, respectively, with an amount of c. 2-3 km denudation between 160 and 100 Ma, implying little movement along the thrusts F13 and F33. In the middle and southern parts of the HQ transect and the southern part of the CU transect, rapid cooling at c. 4.0-7.0 °C/Ma, with c. 6-9 km denudation during 170-130 or 160-100 Ma, respectively, is probably influenced by thrusting of F35, F38 and F42 and the resultant tilting. A combination of thrusting, tilting, and denudation led to the youngering

  20. Behaviour of fluid mobile elements during subduction and exhumation of abyssal peridotites: Example of serpentinites from Cuba and Dominican Republic

    Science.gov (United States)

    Deschamps, F.; Guillot, S.; Godard, M.; Chauvel, C.; Andreani, M.

    2009-04-01

    Seawater interaction with abyssal peridotites at the sea floor is an important process for chemical exchange between lithosperic mantle and ocean at slow-spreading ridge. Serpentinites from oceanic lithosphere are known to represent an important sink for fluid mobile element, notably boron. In parallel we know extreme enrichment in fluid mobile element (As, Sb, B, U, Li) in high-pressure serpentine minerals (antigorite) coming from part of mantle wedge hydrated by slab's fluids released (Himalaya, Deschamps et al., in prep.). In order to constrain geochemical behaviour of fluid mobile element hosted by serpentine during subduction processes, we examined abyssal serpentinites coming from the accretionary wedge of Greater Carribean (Cuba and Dominican Republic). They represent subducted Atlantic oceanic lithosphere, which have experienced low to high- metamorphism (greenschist to eclogite facies), before being exhumed. These rocks are an opportunity to understand the chemical mobility of fluid mobile element during prograde metamorphism occurring along subduction surface. Here we present bulk-rock and in-situ composition of serpentinites and their primary and alteration-related phase obtained on (LA-)HR-ICP-MS. Except for a few cumulates, serpentinites have depleted compositions in agreement with a refractory mantle, but also strong enrichment in U, Pb, Th, Sr, and other fluid mobile element (e.g., U up to 10xPM) indicating extensive fluid-rock intercation. In-situ composition allows the distinction of two groups of serpentine. Group 1 is characterized by relatively flat and depleted REE patterns (Yb ≈ 0.5xChondrite) reflecting formation after olivine, while group 2 formed after pyroxene is characterized by slightly higher HREE content (Yb ≈ 1xChondrite) but light LREE depleted patterns and displays higher content in Sc, V, Ti and Co. Both groups are strongly enriched in B (up to 120 ppm), and reach values already observed in serpentinites from mantle wedge

  1. On thrusting, regional unconformities and exhumation of high-grade greenstones in Neoarchean orogens. The case of the Waroonga Shear Zone, Yilgarn Craton

    Science.gov (United States)

    Zibra, I.; Korhonen, F. J.; Peternell, M.; Weinberg, R. F.; Romano, S. S.; Braga, R.; De Paoli, M. C.; Roberts, M.

    2017-08-01

    During the Neoarchean, the dominant tectonic style progressively changed from an episodic-overturn/stagnant-lid regime to modern-style plate tectonics. The Neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts. The case study presented here provides insights into how such transition in tectonic style occurred, a matter that is generally controversial. We present structural and metamorphic data from the c. 2660 Ma Waroonga Shear Zone (WSZ) in the Neoarchean Yilgarn orogen (Western Australia). The WSZ contains a syntectonic pluton and older, high-grade greenstones. The tectonic fabric in the pluton developed during melt-present thrusting, followed by syn-cooling wrench-dominated transpression. Mafic greenstones preserve three metamorphic assemblages. The M1 assemblage (Grt-Cpx-Qtz) records peak P-T conditions of 12 ± 1 kbar and 800 ± 50 °C, followed by isothermal decompression to 9 kbar (M2). These anhydrous assemblages might predate the WSZ. Greenstones then underwent decompression at c. 2660 Ma (3-4 kbar; 600-650 °C), defined by the amphibole-rich M3 assemblage, synkinematic with the tectonic fabric in the WSZ. We show that shearing along the WSZ exhumed these greenstones by at least 10 km, inducing major uplift and erosion. Archean accretionary orogens developed on weak lithosphere, where deformation suppressed crustal thickening, orogenic relief and synorogenic exhumation of orogenic roots. However, our study indicates a genetic link between (i) strain localization along contractional structures, inducing large-scale uplift; (ii) exhumation of high-grade greenstones; (iii) development of inverse metamorphic gradients; (iv) establishment of a regional unconformity, with clastic sediments fed by the uplifted terrane; (v) incorporation of portions of the newly-formed orogenic basins into the footwall of the WSZ. These features imply that the Yilgarn orogenic lithosphere at c. 2660 Ma was stiff enough to allow

  2. Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

    Science.gov (United States)

    Fornash, Katherine F.; Cosca, Michael A.; Whitney, Donna L.

    2016-01-01

    Geochronologic studies of high-pressure/low-temperature rocks can be used to determine the timing and rates of burial and exhumation in subduction zones by dating different stages of the pressure–temperature history. In this study, we present new in situ UV laser ablation 40Ar/39Ar phengite ages from a suite of lawsonite blueschist- and eclogite-facies rocks representing different protoliths (metabasalt, metasediment), different structural levels (within and outside of a high-strain zone), and different textural positions (eclogite pod core vs. margin) to understand the timing of these events in an exhumed Neo-Tethyan subduction zone (Sivrihisar Massif, Tavşanlı Zone, Turkey). Weighted mean in situ 40Ar/39Ar ages of phengite from the cores of lawsonite eclogite pods (90–93 Ma) are distinctly older than phengite from retrogressed, epidote eclogite (82 ± 2 Ma). These ages are interpreted as the age of peak and retrograde metamorphism, respectively. Eclogite records the narrowest range of ages (10–14 m.y.) of any rock type analyzed. Transitional eclogite- and blueschist-facies assemblages and glaucophane-rimmed lawsonite + garnet + phengite veins from eclogite pod margins record a much wider age range of 40Ar/39Ar ages (~20 m.y.) with weighted mean ages of ~91 Ma. Blueschists and quartzites record more variable 40Ar/39Ar ages that may in part be related to structural position: samples within a high-strain zone at the tectonic contact of the HP rocks with a meta-ultramafic unit have in situ UV laser ablation 40Ar/39Ar ages of 84.0 ± 1.3–103.7 ± 3.1 Ma, whereas samples outside this zone range to older ages (84.6 ± 2.4–116.7 ± 2.7 Ma) and record a greater age range (22–38 m.y.). The phengite ages can be correlated with the preservation of HP mineral assemblages and fabrics as well as the effects of deformation. Collectively, these results show that high-spatial resolution UV laser ablation 40Ar/39Ar phengite data, when considered

  3. Late Cretaceous Localized Crustal Thickening as a Primary Control on the 3-D Architecture and Exhumation Histories of Cordilleran Metamorphic Core Complexes

    Science.gov (United States)

    Gans, P. B.; Wong, M.

    2014-12-01

    The juxtaposition of mylonitic mid-crustal rocks and faulted supracrustal rocks in metamorphic core complexes (MMCs) is usually portrayed in 2 dimensions and attributed to a single event of large-scale slip ± isostatic doming along a low-angle "detachment fault"/ shear zone. This paradigm does not explain dramatic along strike (3-D) variations in slip magnitude, footwall architecture, and burial / exhumation histories of most MMCs. A fundamental question posed by MMCs is how did their earlier thickening and exhumation histories influence the geometric evolution and 3-D slip distribution on the subsequent detachment faults? New geologic mapping and 40Ar/39Ar thermochronology from the Snake Range-Kern Mts-Deep Creek Mts (SKDC) complex in eastern Nevada offer important insights into this question. Crustal shortening and thickening by large-scale non-cylindrical recumbent folds and associated thrust faults during the late Cretaceous (90-80 Ma) resulted in deep burial (650°C, 20-25 km) of the central part of the footwall, but metamorphic grade decreases dramatically to the N and S in concert with decreasing amplitude on the shortening structures. Subsequent Paleogene extensional exhumation by normal faulting and ESE-directed mylonitic shearing is greatest in areas of maximum earlier thickening and brought highest grade rocks back to depths of~10-12 km. After ≥15 Ma of quiescence, rapid E-directed slip initiated along the brittle Miocene Snake Range detachment at 20 Ma and reactivated the Eocene shear zone. The ≥200°C gradient across the footwall at this time implies that the Miocene slip surface originated as a moderately E-dipping normal fault. This Miocene slip surface can be tracked for more than 100 km along strike, but the greatest amount of Miocene slip also coincides with parts of the footwall that were most deeply buried in the Cretaceous. These relations indicate that not only is the SKDC MMC a composite feature, but that the crustal welt created by

  4. Constraining exhumation pathway in an accretionary wedge by (U-Th)/He thermochronology—Case study on Meliatic nappes in the Western Carpathians

    Science.gov (United States)

    Putiš, Marián; Danišík, Martin; Ružička, Peter; Schmiedt, Ivan

    2014-11-01

    This study reconstructs the late stages in the exhumation history of a nappe derived from the Meliatic accretionary wedge in the Western Carpathians by means of zircon and apatite (U-Th)/He dating. The Meliatic accretionary wedge formed due to the closure of the Neotethyan Triassic-Jurassic Meliata-Hallstatt Ocean in the Late Jurassic. The studied fragments of the blueschist-bearing Meliatic Bôrka Nappe were metamorphosed at low-temperature and high- to medium-pressure conditions at ca. 160-150 Ma and included into the accretionary wedge. The time of the accretionary wedge formation constrains the beginning of the Bôrka Nappe northward thrusting over the Gemeric Unit of the evolving Central Western Carpathians (CWC) orogenic wedge. The zircon (U-Th)/He data on four samples recorded three evolutionary stages: (i) cooling through the ∼180 °C isotherm at 130-120 Ma related to starting collapse of the accretionary wedge, following exhumation of the high-pressure slices in the Meliatic accretionary wedge; (ii) postponed exhumation and cooling of some fragments through the ∼180 °C isotherm from 115 to 95 Ma due to ongoing collapse of this wedge; and (iii) cooling from 80 to 65 Ma, postdating the thrusting (∼100-80 Ma) of the Bôrka Nappe slices during the Late Cretaceous compression related to formation of the CWC orogenic wedge. The third stage already documents cooling of the Meliatic Bôrka Nappe slices in the CWC orogenic wedge. The apatite (U-Th)/He data may indicate cooling of a Bôrka Nappe slice to near-surface temperatures at ∼65 Ma. The younger AHe age clusters indicate that at least one, or possibly two, reheating events could have occurred in the longer interval from ∼40 to ∼10 Ma during the Oligocene-Miocene. These were related to sedimentary burial and/or the magmatism as documented in other parts of the CWC.

  5. Sediment dynamics and the burial and exhumation of bedrock reefs along an emergent coastline as elucidated by repetitive sonar surveys: Northern Monterey Bay, CA

    Science.gov (United States)

    Storlazzi, C.D.; Fregoso, T.A.; Golden, N.E.; Finlayson, D.P.

    2011-01-01

    Two high-resolution bathymetric and acoustic backscatter sonar surveys were conducted along the energetic emergent inner shelf of northern Monterey Bay, CA, USA, in the fall of 2005 and the spring of 2006 to determine the impact of winter storm waves, beach erosion, and river floods on biologically-important siliclastic bedrock reef habitats. The surveys extended from water depths of 4 m to 22 m and covered an area of 3.14 km2, 45.8% of which was bedrock, gravel, and coarse-grained sand and 54.2% was fine-grained sand. Our analyses of the bathymetric and acoustic backscatter data demonstrates that during the 6 months between surveys, 11.4% of the study area was buried by fine-grained sand while erosion resulted in the exposure of bedrock or coarse-grained sand over 26.5% of the study area. The probability of burial decreased with increasing water depth and rugosity; the probability of exhumation increased with increasing wave-induced near-bed shear stress, seabed slope and rugosity. Much of the detected change was at the boundary between bedrock and unconsolidated sediment due to sedimentation and erosion burying or exhuming bedrock, respectively. In a number of cases, however, the change in seabed character was apparently due to changes in sediment grain size when scour exposed what appeared to be an underlying coarser-grained lag or the burial of coarser-grained sand and gravel by fine-grained sand. These findings suggest that, in some places, (a) burial and exhumation of nearshore bedrock reefs along rocky, energetic inner shelves occurs over seasonal timescales and appears related to intrinsic factors such as seabed morphology and extrinsic factors such as wave forces, and (b) single acoustic surveys typically employed for geologic characterization and/or habitat mapping may not adequately characterize the geomorphologic and sedimentologic nature of these types of environments that typify most of the Pacific Ocean and up to 50% of the world's coastlines.

  6. Timing of exhumation of the Ereendavaa metamorphic core complex (north-eastern Mongolia) - U-Pb and 40Ar/39Ar constraints

    Science.gov (United States)

    Daoudene, Yannick; Ruffet, Gilles; Cocherie, Alain; Ledru, Patrick; Gapais, Denis

    2013-01-01

    The occurrence of numerous NE-SW trending rift basins that locally bound metamorphic core complexes in Transbaikalia, northern Mongolia and north-eastern China indicates that the eastern domain of the Central Asian Orogenic Belt was affected by a large-scale NW-SE extensional tectonic event during late Jurassic to early Cretaceous times. Available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in Transbaikalia (134-121 Ma) and North China (136-110 Ma) suggesting dome exhumation during the early Cretaceous. In north-eastern Mongolia, the Ereendavaa Range, lined by the Onon Shear Zone, was recently interpreted as one of these metamorphic core complexes, of late Jurassic to early Cretaceous age, on the basis of U-Pb zircons data from two synkinematic pegmatite dykes. However, this wide time range remains to be discussed. The present work constrains the tectono-thermal evolution of the range by providing new MC-ICP-MS U-Pb zircons ages from pegmatite dykes and metamorphic igneous rocks, and mica and amphibole 40Ar/39Ar laser step-heating ages from metamorphic and magmatic rocks that crop out within the range. The results show that (1) the Ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late Jurassic times, (2) cooling of the range began at least at 137.9 ± 0.3 Ma as revealed by a 40Ar/39Ar plateau ages obtained from an hornblende sampled within the range core, and (3) exhumation along the Onon Shear Zone occurred from 130.3 ± 1.9 Ma down to 124.8 ± 0.3 Ma, as shown by ages of most of micas and amphiboles from the Shear zone. These more accurate ages are consistent with metamorphic core complex ages from adjacent areas. Furthermore, they argue for an extensional dynamic paroxysm at the scale of eastern Asia during a narrow time range in the early Cretaceous between ca. 130 Ma and ca. 120 Ma.

  7. Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

    Science.gov (United States)

    Fornash, Katherine F.; Cosca, Michael A.; Whitney, Donna L.

    2016-07-01

    Geochronologic studies of high-pressure/low-temperature rocks can be used to determine the timing and rates of burial and exhumation in subduction zones by dating different stages of the pressure-temperature history. In this study, we present new in situ UV laser ablation 40Ar/39Ar phengite ages from a suite of lawsonite blueschist- and eclogite-facies rocks representing different protoliths (metabasalt, metasediment), different structural levels (within and outside of a high-strain zone), and different textural positions (eclogite pod core vs. margin) to understand the timing of these events in an exhumed Neo-Tethyan subduction zone (Sivrihisar Massif, Tavşanlı Zone, Turkey). Weighted mean in situ 40Ar/39Ar ages of phengite from the cores of lawsonite eclogite pods (90-93 Ma) are distinctly older than phengite from retrogressed, epidote eclogite (82 ± 2 Ma). These ages are interpreted as the age of peak and retrograde metamorphism, respectively. Eclogite records the narrowest range of ages (10-14 m.y.) of any rock type analyzed. Transitional eclogite- and blueschist-facies assemblages and glaucophane-rimmed lawsonite + garnet + phengite veins from eclogite pod margins record a much wider age range of 40Ar/39Ar ages (~20 m.y.) with weighted mean ages of ~91 Ma. Blueschists and quartzites record more variable 40Ar/39Ar ages that may in part be related to structural position: samples within a high-strain zone at the tectonic contact of the HP rocks with a meta-ultramafic unit have in situ UV laser ablation 40Ar/39Ar ages of 84.0 ± 1.3-103.7 ± 3.1 Ma, whereas samples outside this zone range to older ages (84.6 ± 2.4-116.7 ± 2.7 Ma) and record a greater age range (22-38 m.y.). The phengite ages can be correlated with the preservation of HP mineral assemblages and fabrics as well as the effects of deformation. Collectively, these results show that high-spatial resolution UV laser ablation 40Ar/39Ar phengite data, when considered in a petrologic and structural

  8. Contrasting cooling and exhumation histories of tectonic blocks in the eastern part of the Eastern Alps and its possible relationships with lithospheric dynamics

    Science.gov (United States)

    Wölfler, Andreas; Glotzbach, Christoph

    2017-04-01

    enhanced cooling and exhumation in the middle Miocene and again at the late Miocene and Pliocene (Wölfler et al., 2016). Middle Miocene exhumation is interpreted as a result of tectonic escape and convergence that operated simultaneously during lateral extrusion of the Eastern Alps. As the higher late Miocene/Pliocene exhumation rates are restricted to a single tectonic block, namely the Niedere Tauern, we infer a tectonic trigger that is probably related to a change in the external stress field that affected the Alps during this time. References Legrain, N., Stüwe, K., Wölfler, A., 2014. Incised relict landscape in the eastern Alps. Geomorphology 221, 124-138. Handy, M.R., Ustaszewski, K., Kissling, E., 2015. Reconstructing the Alps-Carpathians-Dinarides as a key to understanding switches in subduction polarity, slab gaps and surface motion. International Journal of Earth Sciences 104, 1-26. Wölfler, A., Kurz, W., Fritz, H., Glotzbach, C., Danišik, M., 2016. Late Miocene increasing exhumation rates in the eastern part of the Alps - implications from low temperature thermochronology. Terra Nova 28, 297-305.

  9. The prospect of exhumation and identification of the people who are still listed as missing in armed conflict happened in Kosovo and Metohija 1998/99

    Directory of Open Access Journals (Sweden)

    Matejic S.

    2015-01-01

    Full Text Available During the armed conflict in Kosovo and Metohija, and after it, were killed more than 5 000 people, and according to the International Red Cross Committee in March 2001, 3,338 people were still missing. Until the conclusion of this study, the number of missing persons in Kosovo and Metohia for which the trail is about 1700. This list includes people from all ethnic communities. The primary objective of the forensic investigation is to determine the identity of the missing persons and after that their remains returne to the families, in accordance with Geneva protocols. Experts post-mortem examination after the exhumation determine the cause and manner of death, which indicates a violation of human rights and war crimes. Conclusion. We are facing with reasonable fear that with the passage of time, less interest will be devoted to this issue and the activities on finding and identifying missing persons will completely stop.

  10. From source to sink in central Gondwana: Exhumation of the Precambrian basement rocks of Tanzania and sediment accumulation in the adjacent Congo basin

    Science.gov (United States)

    Kasanzu, Charles Happe; Linol, Bastien; de Wit, Maarten J.; Brown, Roderick; Persano, Cristina; Stuart, Finlay M.

    2016-09-01

    Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000 m above sea level) but low-relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Basement samples were from an exploration borehole located within the craton and up to 2200 m below surface. Surface samples were also analyzed. AFT dates range between 317 ± 33 Ma and 188 ± 44 Ma. Alpha (Ft)-corrected AHe dates are between 433 ± 24 Ma and 154 ± 20 Ma. Modeling of the data reveals two important periods of cooling within the craton: one during the Carboniferous-Triassic (340-220 Ma) and a later, less well constrained episode, during the late Cretaceous. The later exhumation is well detected proximal to the East African Rift (70 Ma). Thermal histories combined with the estimated geothermal gradient of 9°C/km constrained by the AFT and AHe data from the craton and a mean surface temperature of 20°C indicate removal of up to 9 ± 2 km of overburden since the end of Paleozoic. The correlation of erosion of the craton and sedimentation and subsidence within the Congo basin in the Paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far-field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes.

  11. Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production

    Science.gov (United States)

    Weislogel, A.L.; Graham, S.A.; Chang, E.Z.; Wooden, J.L.; Gehrels, G.E.

    2010-01-01

    To test the idea that the voluminous upper Middle to Upper Triassic turbidite strata in the Songpan-Ganzi complex of central China archive a detrital record of Dabie ultrahigh-pressure (UHP) terrane unroofing, we report 2080 single detrital U-Pb zircon ages by sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis from 29 eastern Songpan-Ganzi complex sandstone samples. Low (Paleozoic and bimodally distributed Precambrian zircon populations, which, together with south-to southeast-directed paleocurrent data, indicate derivation from the retro-side of the Qinling-Dabie (Q-D) collisional orogen wedge. In the central depocenter, the dominantly Paleozoic detrital zircon signature and south-to southwest-oriented paleocurrent indicators reflect a profusion of Paleozoic zircon grains. These data are interpreted to reflect an influx of material derived from erosion of Paleozoic supra-UHP rocks of the Dabie terrane in the eastern Qinling-Dabie orogen, which we speculate may have been enhanced by development of a monsoonal climate. This suggests that erosional unroofing played a significant role in the initial phase of UHP exhumation and likely influenced the petrotectonic and structural evolution of the Qinling-Dabie orogen, as evidenced by compressed Triassic isotherms/grads reported in the Huwan shear zone that bounds the Dabie terrane to the north. The central depocenter deposits reflect a later influx of bimodally distributed Precambrian zircon, signifying either a decrease in the influx of Paleozoic zircon grains due to stalled UHP exhumation and/or dilution of the same influx of Paleozoic zircons by spilling of Precambrian zircon from the northeastern depocenter into the central depocenter basin, perhaps due to infilling and bypass of sediment from the northern depocenter or due to initial collapse and constriction of the eastern Songpan-Ganzi complex basin. The

  12. Apatite fission-track thermochronometric constraints on the exhumation and evolution of the southeastern Indian (Tamil Nadu) passive margin and the role of structural inheritance

    Science.gov (United States)

    De Grave, Johan; Glorie, Stijn; Singh, Tejpal; Van Ranst, Gerben; Nachtergaele, Simon

    2017-04-01

    After rifting from Gondwana in the Late Jurassic - Early Cretaceous, and subsequent opening of the Indian Ocean basin, the continental margins of India developed into typical passive margins. Extensional tectonic forces and thermal subsidence gave rise to the formation of both on-shore and off-shore basins along the southeastern passive margin of the Indian continent, along the Tamil Nadu coast. There, basins such as the Cauvery and Krishna-Godavari basin, accumulated Meso- and Cenozoic (Early Cretaceous to recent) detrital sediments coming off the rifted blocks and the Tamil Nadu hinterland. In places, deep rift basins have accumulated up to over 3000 m of sediments. The continental basement of Tamil Nadu is chiefly composed of metamorphic rocks of the Archean to Palaeoproterozoic Eastern Dharwar Craton and the coeval Southern Granulite Terrane (e.g. Peucat et al., 2013). Several crustal scale shear zones crosscut this assemblage and at least some are considered to represent Gondwanan sutures (Santosh et al., 2012). Smaller, younger granitoid plutons intrude the basement at several locations and most of these are of Late Neoproterozoic age (Glorie et al., 2014). In this work metamorphic basements rocks and the younger granitoids were sampled for a apatite fission-track (AFT) thermochronometric study. A North-South profile from Chennai to Thanjavur mainly transects the Salem block of the Southern Granulite Terrane, and crosscuts several crustal scale shear zones, such as the Cauvery, Salem-Attur and Gangavalli shear zones. Apatites from over 30 samples were used in this study. AFT ages all range between about 190 and 120 Ma (Jurassic - Early Cretaceous). These mainly represent the slow, shallow exhumation of the basement during the rift and early drift phase of the Indian plate from Gondwana. AFT mean track lengths vary between 11 and 13 µm and are typical of slowly exhumed basement. Thermal history modelling (using the QTQt software by Gallagher, 2012) confirms

  13. Detrital zircon fission-track thermochronology and magnetic fabric of the Amagá Formation (Colombia): Intracontinental deformation and exhumation events in the northwestern Andes

    Science.gov (United States)

    Piedrahita, V. A.; Bernet, M.; Chadima, M.; Sierra, G. M.; Marín-Cerón, M. I.; Toro, G. E.

    2017-07-01

    New detrital zircon-fission track (ZFT) and magnetic fabric data are presented to constrain the time of deposition, provenance and deformation of the of Lower and Upper members of the Amagá Formation in the Amagá Basin. The Amagá Basin is located in the northern Andes, between the Western and Central Cordilleras of Colombia. The Amagá Formation was deposited in a transpressive geodynamic context and is allegedly synchronous with tectonic events such as the Andean orogeny and the Panama-Choco Block collision with the northwestern South American Plate. Detrital ZFT data confirm an Oligocene age for the Lower Member and a middle-Miocene age for the Upper Member of the Amagá Formation. In addition to constraining the depositional age, the ZFT data presented in this study also reflect Paleocene-Eocene, late to early Oligocene and late to middle Miocene cooling in sediment source areas mainly located in the Central and Western Cordilleras of Colombia. These ages can be associated with regional exhumation events in the central and northern Andes of South America. Collisional stages of the Panama-Choco Block against northwestern South America, subduction of the Farallon-Nazca Plate and strike-slip reactivation periods of the Cauca-Romeral fault system, caused NW-SE compression and NE-SW simple shear in the Amagá Basin. This deformational regime, identified by magnetic fabric data, induces syn- and post-depositional deformation over the Amagá Formation.

  14. A study of the Holzener Asphaltkalk, northern Germany: observations regarding the distribution, composition and origin of organic matter in an exhumed petroleum reservoir

    Energy Technology Data Exchange (ETDEWEB)

    Horsfield, B.; Heckers, J.; Leythaeuser, D.; Littke, R.; Mann, U. (Kernforschungsanlage Juelich GmbH (Germany). Inst. fuer Chemie 5 - Erdoel und Organische Geochemie)

    1991-05-01

    The Holzener Asphalkalk deposit is located on the southwestern flank of the Hils Syncline, northern Germany. It consists of a series of Kimmeridgian-Portlandian bitumen-impregnated limestones (cumulative thickness of nearly 200 m) overlain unconformably by Neocomian claystones and underlain by older Jurassic and Triassic sediments. The most bitumen-rich limestone layers have been extensively mined with the result that there is three-dimensional access to what is probably an exhumed series of stacked petroleum reservoirs. Geochemical, petrological and petrophysical techniques were used to gain some insight into the distribution and the source of the organic matter in two of the 13 layers of the deposit. Most disseminated organic matter was found to be soluble in organic solvents and rich in non-hydrocarbons. Its distribution appears to be controlled by ooid versus carbonate matrix abundances, the occurrence of fractures and degree of impregnation. Small (meso- to micro-) pores have high bitumen saturations whereas large pores (meso- to macro-) have much lower saturations. Mature petroleum is thought to have once filled all pores, but alteration has probably removed as much as 85% of it, mainly from the large pores. Regional geochemical considerations, pyrolysis and stable carbon isotope data indicate that the original petroleum was most probably derived from the underlying Posidonia Shale (Toarcian) source rock. Asphaltene pyrolysis data indicate that an algal lacustrine co-source might have also contributed to the deposit. (author)

  15. Ar-Ar dating of K-feldspar in low grade metamorphic rocks: Example of an exhumed Mesozoic accretionary wedge and forearc, South Island, New Zealand

    Science.gov (United States)

    Mortimer, N.; McLaren, S.; Dunlap, W. J.

    2012-06-01

    New 40Ar/39Ar ages from detrital K-feldspars and metamorphic white micas from the Eastern Province terranes of New Zealand have been used to investigate the thermo-tectonic history of different parts of an exhumed Mesozoic forearc basin and accretionary wedge. K-feldspars from barely metamorphosed sedimentary host rocks mainly record detrital source area ages whereas those from zeolite and prehnite-pumpellyite facies host rocks have textures and argon age spectra that indicate recrystallization during regional low-temperature metamorphism. The results contribute to a model that genetically links thermo-tectonic events across the accretionary wedge and forearc basin elements of the convergent margin, and into the Median Batholith arc probably by the Early Cretaceous and possibly by the Middle Jurassic. Thus, even though multidiffusion domain (MDD) models cannot be used to make inference on cooling histories in such situations, the K-feldspar argon thermochronometer can provide useful information on the timing of geological events in sub-greenschist facies rocks.

  16. Validation of a standard forensic anthropology examination protocol by measurement of applicability and reliability on exhumed and archive samples of known biological attribution.

    Science.gov (United States)

    Francisco, Raffaela Arrabaça; Evison, Martin Paul; Costa Junior, Moacyr Lobo da; Silveira, Teresa Cristina Pantozzi; Secchieri, José Marcelo; Guimarães, Marco Aurelio

    2017-10-01

    Forensic anthropology makes an important contribution to human identification and assessment of the causes and mechanisms of death and body disposal in criminal and civil investigations, including those related to atrocity, disaster and trafficking victim identification. The methods used are comparative, relying on assignment of questioned material to categories observed in standard reference material of known attribution. Reference collections typically originate in Europe and North America, and are not necessarily representative of contemporary global populations. Methods based on them must be validated when applied to novel populations. This study describes the validation of a standardized forensic anthropology examination protocol by application to two contemporary Brazilian skeletal samples of known attribution. One sample (n=90) was collected from exhumations following 7-35 years of burial and the second (n=30) was collected following successful investigations following routine case work. The study presents measurement of (1) the applicability of each of the methods: used and (2) the reliability with which the biographic parameters were assigned in each case. The results are discussed with reference to published assessments of methodological reliability regarding sex, age and-in particular-ancestry estimation. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Grain-scale Sr isotope heterogeneity in amphibolite (retrograded UHP eclogite, Dabie terrane): Implications for the origin and flow behavior of retrograde fluids during slab exhumation

    Science.gov (United States)

    Guo, Shun; Yang, Yueheng; Chen, Yi; Su, Bin; Gao, Yijie; Zhang, Lingmin; Liu, Jingbo; Mao, Qian

    2016-12-01

    To constrain the origin and flow behavior of amphibolite-facies retrograde fluids during slab exhumation, we investigate the textures, trace element contents, and in situ strontium (Sr) isotopic compositions (using LA-MC-ICP-MS) of multiple types of epidote and apatite in the UHP eclogite and amphibolites from the Hualiangting area (Dabie terrane, China). The UHP epidote porphyroblasts in the eclogite (Ep-E), which formed at 28-30 kbar and 660-720 °C, contain high amounts of Sr, Pb, Th, Ba, and light rare earth elements (LREEs) and have a narrow range of initial 87Sr/86Sr ratios (0.70431 ± 0.00012 to 0.70454 ± 0.00010). Two types of amphibolite-facies epidote were recognized in the amphibolites. The first type of epidote (Ep-AI) developed in all the amphibolites and has slightly lower trace element contents than Ep-E. The Ep-AI has a same initial 87Sr/86Sr ratio range as the Ep-E and represents the primary amphibolite-facies retrograde product that is associated with an internally buffered fluid at 8.0-10.3 kbar and 646-674 °C. The other type of epidote (Ep-AII) occurs as irregular fragments, veins/veinlets, or reaction rims on the Ep-AI in certain amphibolites. Elemental X-ray maps reveal the presence of Ep-AI relics in the Ep-AII domains (appearing as a patchy texture), which indicates that Ep-AII most likely formed by the partial replacement of the Ep-AI in the presence of an infiltrating fluid. The distinctly lower trace element contents of Ep-AII are ascribed to element scavenging by a mechanism of dissolution-transport-precipitation during replacement. The Ep-AII in an individual amphibolite exhibits large intra- and inter-grain variations in the initial 87Sr/86Sr ratios (0.70493 ± 0.00030 to 0.70907 ± 0.00022), which are between those of the Ep-AI and granitic gneisses (wall rock of the amphibolites, 0.7097-0.7108). These results verify that the infiltrating fluid was externally derived from granitic gneisses. The matrix apatite in the amphibolites has

  18. Syn- to post-orogenic exhumation of metamorphic nappes: Structure and thermobarometry of the western Attic-Cycladic metamorphic complex (Lavrion, Greece)

    Science.gov (United States)

    Scheffer, Christophe; Vanderhaeghe, Olivier; Lanari, Pierre; Tarantola, Alexandre; Ponthus, Léandre; Photiades, Adonis; France, Lydéric

    2016-05-01

    significant increase in temperature (∼350 °C). These structural, petrologic and thermobarometric data document the tectonic evolution from construction to destruction of the Hellenic orogenic belt. The steep-dipping blueschist facies foliation, preferentially preserved at high structural level in the middle unit, is considered to reflect tectonic accretion marked by successive burial (D1M1) and syn-orogenic exhumation (D2M2) without thermal relaxation. The transposition-retrogression of the blueschist facies mineral assemblage into a shallow-dipping greenschist facies foliation associated with an increase in temperature corresponds to lateral flow of the thermally relaxed nappe stack (D3M3). The development of a low-angle detachment, accommodating post-orogenic exhumation of the orogenic root, is attributed to gravitational collapse of the Hellenic belt.

  19. Onshore-offshore morpho-structural pattern of coastal rocky shore in SW Brittany (France): polyphased generation of rocky, shore and exhumed platforms.

    Science.gov (United States)

    Raimbault, Celine; Duperret, Anne; Le Gall, Bernard; Wyns, Robert; Regard, Vincent; Authemayou, Christine; Molliex, Stephane

    2017-04-01

    A large granitic submarine and shore platform has been mapped in Western Brittany on 580 km2 surfaces with the aid of several high-resolution (LiDAR using Litto3D project (SHOM, IGN, IFREMER) mixed with marine interferometric echosounding sonar (R/V Haliotis) and low depth multibeam echosondeur with high resolution seismic reflection profiles (R/V Thalia). The structural and geomorphological study of this rocky platform allows understanding its formation on time scale between Paleocene to Quaternary. The marine rocky platform is composed of: (1) a tidal part (shore platform) with a very slight seaward mean slope and a maximal width of about 800 m, (2) a > 5 km-wide and weakly dipping subtidal part, labelled the rocky platform, (3) a rocky external part with varying mean slopes, rocky reefs and sedimentary deposits, corresponding to the continental shelf. The coastal continental domain is characterized by a low elevated (erosion. The present-day coastal morphology may be explained by the action of two highstand sea levels since mid-Pleistocene at least, favoring successive eustatic purges of previously weathered granitic rocks. Exposure ages deduced from 10Be content may be considered as minimum age in the aerial part of the platform (marine terrace), with a rocky platform formation near 166 ± 18 kyrs. Whereas the submarine part of the platform may be considered as inherited, recording several exhumations, with a maximum exposure age of 30.5 ± 3.5 kyrs, acquired during the beginning Last Glacial Maximum on a previously cleaned surface.

  20. Late Cenozoic cooling history of the central Menderes Massif: Timing of the Büyük Menderes detachment and the relative contribution of normal faulting and erosion to rock exhumation

    Science.gov (United States)

    Wölfler, Andreas; Glotzbach, Christoph; Heineke, Caroline; Nilius, Nils-Peter; Hetzel, Ralf; Hampel, Andrea; Akal, Cüneyt; Dunkl, István; Christl, Marcus

    2017-10-01

    Based on new thermochronological data and 10Be-derived erosion rates from the southern part of the central Menderes Massif (Aydın block) in western Turkey, we provide new insights into the tectonic evolution and landscape development of an area that undergoes active continental extension. Fission-track and (U-Th)/He data reveal that the footwall of the Büyük Menderes detachment experienced two episodes of enhanced cooling and exhumation. Assuming an elevated geothermal gradient of 50 °C/km, the first phase occurred with an average rate of 0.90 km/Myr in the middle Miocene and the second one in the latest Miocene and Pliocene with a rate of 0.43 km/Myr. The exhumation rates between these two phases were lower and range from 0.14 to 0.24 km/Myr, depending on the distance to the detachment. Cosmogenic nuclide-based erosion rates for catchments in the Aydın block range from 0.1 to 0.4 km/Myr. The similarity of the erosion rates on both sides of the Aydın block (northern and southern flank) indicate that a rather symmetric erosion pattern has prevailed during the Holocene. If these millennial erosion rates are representative on a million-year timescale they indicate that, apart from normal faulting, erosion in the hanging wall of the Büyük Menderes detachment fault did also contribute to the exhumation of the metamorphic rocks.

  1. Timing and processes for exhumation of HP/LT rocks of the southern Brooks Range (AK): Insight from combined geochemistry and 40Ar/39Ar thermochronology of white mica

    Science.gov (United States)

    O'Brien, T.; Miller, E. L.; Grove, M. J.; Hayden, L. A.

    2015-12-01

    The obduction of an island arc onto the Arctic Alaska continental margin in the Jura-Cretaceous led to southward subduction of continental crust and high-pressure/low-temperature (HP/LT) epidote-blueschist facies metamorphism in the southern Brooks Range (BR). A regionally developed greenschist facies normal-sense shear zone system along the southern margin of the BR suggests that extensional faulting had an influential role in the exhumation of the metamorphic core. To better constrain the exhumation history of the metamorphic core of the BR, samples were collected from a N-S transect through the metamorphic core of the orogen. Electron microprobe (EMP) analyses of white micas reveal that they are composed of phengite (Si > 3.0 pfu) or a combination of phengite + paragonite. Si-content of phengites reveal a southward increase in Si from 3.1 to 3.4 pfu (corresponding to an increase in pressure). Si-contents in higher-P phengites are scattered, reflecting subsequent muscovite growth. The Si trend is matched by a southward increase in the 40Ar/39Ar total gas ages of white micas. Phengite from the north are characterized by younger ages (~115 Ma) and flatter 40Ar/39Ar spectra. Farther south, phengites and paragonites yield older 40Ar/39Ar ages. These samples yield convex, staircase 40Ar/39Ar spectra that initiate ~115-120 Ma and flatten-out ~130-138 Ma. Modeling using MacArgon proposes that an initial cooling of HP/LT metamorphism occurred ~130-138 Ma, recorded in the high-Si phengites and paragonites. Following initial cooling, modeling suggests HP/LT rocks stalled in the greenschist facies field before subsequent exhumation, resulting in the staircase 40Ar/39Ar spectra. Flatter 40Ar/39Ar spectra recorded by the northern samples and modeling of 40Ar/39Ar results from the southern samples suggest that these rocks from metamorphic core of the BR were exhumed to temperatures < 300°C by ~115 Ma.

  2. An ignimbrite caldera from the bottom up: Exhumed floor and fill of the resurgent Bonanza caldera, Southern Rocky Mountain volcanic field, Colorado

    Science.gov (United States)

    Lipman, Peter W.; Zimmerer, Matthew J.; McIntosh, William C.

    2015-01-01

    intrusions; (6) brief time span for the entire caldera cycle (33.12 to ca. 33.03 Ma); (7) an exceptionally steep-sided resurgent dome, with dips of 40°–50° on west and 70°–80° on northeast flanks. Some near-original caldera morphology has been erosionally exhumed and remains defined by present-day landforms (western topographic rim, resurgent core, and ring-fault valley), while tilting and deep erosion provide three-dimensional exposures of intracaldera fill, floor, and resurgent structures. The absence of Plinian-fall deposits beneath proximal ignimbrites at Bonanza and other calderas in the region is interpreted as evidence for early initiation of pyroclastic flows, rather than lack of a high eruption column. Although the absence of a Plinian deposit beneath some ignimbrites elsewhere has been interpreted to indicate that abrupt rapid foundering of the magma-body roof initiated the eruption, initial caldera collapse began at Bonanza only after several hundred kilometers of rhyolitic tuff had erupted, as indicated by the minor volume of this composition in the basal intracaldera ignimbrite. Caldera-filling ignimbrite has been largely stripped from the southern and eastern flank of the Bonanza dome, exposing large areas of caldera-floor as a structurally coherent domed plate, bounded by ring faults with locations that are geometrically closely constrained even though largely concealed beneath valley alluvium. The structurally coherent floor at Bonanza contrasts with fault-disrupted floors at some well-exposed multicyclic calderas where successive ignimbrite eruptions caused recurrent subsidence. Floor rocks at Bonanza are intensely brecciated within ∼100 m inboard of ring faults, probably due to compression and crushing of the subsiding floor in proximity to steep inward-dipping faults. Upper levels of the floor are locally penetrated by dike-like crack fills of intracaldera ignimbrite, interpreted as dilatant fracture fills rather than ignimbrite vents. The

  3. Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone

    Science.gov (United States)

    Metcalf, James R.; Fitzgerald, Paul G.; Baldwin, Suzanne L.; Muñoz, Josep-Anton

    2009-10-01

    The Pyrenees Mountains of Spain and France are a collisional orogen cored by a south-vergent antiformal stack of Paleozoic basement thrust sheets (the Axial Zone). Thrusting accommodated shortening due to convergence between Iberia and Europe. Granitic plutons, intruded during the Hercynian orogeny, form an important component of the basement units. Thermochronology of granodioritic samples collected from a vertical [age-elevation] profile from the south-central Maladeta pluton provide new constraints on the timing of thrust faulting and rock exhumation of the Pyrenean orogen. The Maladeta massif lies within the Orri thrust sheet, presently occupying the immediate footwall of the Gavarnie thrust, a major Axial Zone Alpine-age thrust fault. New biotite and K-feldspar 40Ar/ 39Ar and apatite (U-Th)/He (AHe) data combined with previous apatite fission track (AFT) thermochronology and structural studies of the Maladeta pluton constrain the thermal evolution of this massif. Biotite weighted mean plateau and K-feldspar maximum 40Ar/ 39Ar ages from the highest elevations of the Maladeta pluton (2850 m) are ˜ 280 Ma, close to the age of intrusion, and are interpreted to date the timing of rapid cooling in the Hercynian. Subsequently the Maladeta massif remained close to the surface as indicated by the presence of unconformable Triassic continental sediments. K-feldspar 40Ar/ 39Ar multiple diffusion domain thermal models from two samples at lower elevations (1780 m and 1400 m) indicate heating initiated at ˜ 65 Ma, reaching maximum temperatures of 270 to 280 °C. These data are interpreted to record thrust burial of the Maladeta pluton to depths of ˜ 6-10 km in the footwall of the Gavarnie thrust. Burial and heating were followed by a period of relatively rapid cooling beginning at ˜ 50 Ma, recorded in three K-feldspar thermal models from samples at different elevations (2850 m, 1780 m, and 1400 m). AFT thermal models, in conjunction with the AFT and apatite AHe age

  4. Procedimentos em exumações para investigação de vínculo genético em ossos Exhumations procedures for investigating the genetic link in bones

    Directory of Open Access Journals (Sweden)

    João Arnaldo Damião Melki

    2001-08-01

    Full Text Available OBJETIVO: Identificar problemas técnicos nas exumações para pesquisa de DNA em ossos e propor soluções por meio de protocolo. MÉTODOS: Estudo prospectivo e qualitativo das exumações, procedendo cada etapa da perícia conforme proposto na literatura médico-legal. Foram realizadas dez exumações no período de 1995 a 1998, para coleta de restos humanos e extração do DNA, sendo sete de interesse civil e três, criminal. As dificuldades técnicas surgidas na execução desses procedimentos foram resolvidas a partir de alternativas estabelecidas. RESULTADOS: A escassez de informações úteis para a identificação do indivíduo, baseada em seus restos mortais, foi observada em todos os casos. As características morfológicas individuais contribuíram para a identificação em 50% dos casos. O auxílio dos familiares foi importante na revelação dessas características. Em três casos, foi indicado apenas o sexo e, em um, a idade. A falta de infra-estrutura dos cemitérios e de segurança policial dificultou o trabalho pericial. CONCLUSÕES: Para garantir a fidelidade do exame molecular do DNA é necessário identificar de quem são os restos mortais a serem exumados. Para a eficiência da perícia, é fundamental o uso de um protocolo que inclua, entre outras questões, as relativas a identificação, infra-estrutura e segurança pessoal dos peritos no local do exame.OBJECTIVE: To identify technical problems in exhumations performed for DNA detection in bones and to propose solutions through a protocol. METHODS: A prospective and qualitative study of exhumations was carried out according to the methods proposed in the medical legal literature. From 1995 to 1998, were performed 10 exhumations to collect human remains for DNA extraction. Of them, seven cases were of civil interest and three of criminal. Alternatives were sought to overcome technical difficulties found during the execution of these procedures. RESULTS: For all cases

  5. Mineralogical insights for very high temperature conditions during Cretaceous mantle exhumation at the northern Iberian passive margin: the sapphirine-bearing supradetachment deposits of the North Pyrenean Zone in the Lherz area

    Science.gov (United States)

    Uzel, Jessica; Lagabrielle, Yves; Fourcade, Serge; Chopin, Christian; Asti, Riccardo

    2017-04-01

    In order to decipher the mode of exhumation of the Pyrenean peridotites and the mechanisms of extreme thinning of the continental crust, consistent information from the direct geological environment of the mantle bodies has to be collected. Therefore, we focused our field investigations on the metasedimentary formations that occur in direct contact with the Lherz lherzolites in the inverted Aulus Basin of Albian-Cenomanian age, completed by a microscopic observation and microprobe analysis of more than 50 thin sections. This mineralogical approach provides robust constraints on the lithology of the units progressively exhumed during the successive stages of mantle unroofing. We show that various polymictic breccias, microbreccias and sandstones are exposed in the immediate vicinity of the mantle bodies and associated Upper Triassic meta-ophites. Among these detrital sediments, the sapphirine-bearing sandstones (Monchoux, 1970; 1972) are located on the northern edge of the Lherz lherzolite. At this site, we describe a progressive transition from the lherzolite body towards the surrounding massive limestones. This transition consists of breccias and sandstones, whose lithology varies according to the distance to the lherzolite. The mm-sized clasts are mainly composed of Al- and Mg-bearing minerals, such as sapphirine, phlogopite (altered to vermiculite), gedrite, kornerupine, metamorphic Al-spinel and enstatite, in a carbonate cement. Polymineralic clasts have been deposited along with the monomineralic debris, commonly defining a grain-size sorting. In addition, minor isolated clasts originating from the disaggregation of various rock types are observed in the sapphirine-bearing sandstones suite. These clasts include: lherzolite, micaschist, quartzite, alkaline gabbro, meta-ophite, metaevaporite and marble fragments. Sandstones composed of alternating beds of mineral debris deriving from these rock-types are also exposed close to the mantle body. All the sources of

  6. Trans-Amazonian U-Th-Pb monazite ages and P-T-d exhumation paths of garnet-bearing leucogranite and migmatitic country rock of the southeastern Tandilia belt, Rio de la Plata craton in Argentina

    Science.gov (United States)

    Martínez, Juan Cruz; Massonne, Hans-Joachim; Frisicale, María Cristina; Dristas, Jorge A.

    2017-03-01

    A garnet-bearing leucogranite and two country rocks from the Transamazonian Tandilia belt of the Rio de la Plata craton were studied in detail. The leucogranite contains garnet with homogeneous composition of pyr6(gros + andr)2spes5alm87. In a garnet-biotite migmatite, the core and rim compositions of garnet are pyr1.7(gros + andr)5spes5.6alm87.7 and pyr1.2(gros + andr)5.5spes6.7alm86.6, respectively. These compositions in a sillimanite-garnet-muscovite migmatite are pyr4(gros + andr)2.7spes2.7alm90.6 and pyr2.7(gros + andr)4spes3.2alm90.1, respectively. We used this information to decipher the P-T evolution of the rocks applying P-T and T-H2O pseudosections with the PERPLE_X computer software package taking into consideration deformational microstructures. The leucogranite records an isothermal decompression from 5.3 to 3.8 kbar at 665 °C. The garnet-biotite migmatite was exhumed from 5.5 kbar at 630 °C to 4.3 kbar at 615 °C and the sillimanite-garnet-muscovite migmatite from supersolidus conditions of 670 °C and 3.6 kbar to 625 °C at 2.4 kbar. Late andalusite formed in this rock. Seventy four analyses of 28 monazite grains of the country rocks yielded three groups of U-Th-Pb ages which were related to a collisional event (I: ca. 2.13-2.14 Ga.), a postcollisional thermal overprint (II: ca. 2.01 Ga) and slow cooling of the orogen (III: 1.80-1.90 Ga). Inherited ages of 2.28 and 2.25 Ga could refer to an early accretionary stage of the orogen. An age of 2.41 Ga indicates the presence of recycled Siderian continental crust. Synkinematic crystallization of melts and the subsolidus development of an S2-foliation, demonstrated by deformational microstructures, occurred during the exhumation of the studied area from depths of 18 km to 8 km in the time interval 2.01-1.90 Ga.

  7. Cretaceous high-pressure metamorphism and low pressure overprint in the Sistan Suture Zone, eastern Iran: Additional temperature estimates for eclogites, geological significance of U-Pb zircon ages and Rb-Sr constraints on the timing of exhumation

    Science.gov (United States)

    Kurzawa, Timon; Bröcker, Michael; Fotoohi Rad, Gholamreza; Berndt, Jasper; Lisker, Frank

    2017-10-01

    The Sistan Suture Zone, eastern Iran, includes blocks and lenses of eclogite-, blueschist- and/or epidote amphibolite-facies rocks that provide an excellent opportunity to examine the exhumation history of oceanic HP/LT rocks and their retrograde derivatives. Zr-in-rutile thermometry of eclogites corroborates previous interpretations suggesting metamorphic temperatures of ca. 550-600 °C during the HP stage in the Sistan area. Flat HREE distribution patterns and Ti-in-zircon temperatures of ca. 500-600 °C document that zircon in eclogite is of metamorphic origin. REE patterns of zircon from felsic meta-igneous rocks do not allow to distinguish between a magmatic or metamorphic origin, but relatively low temperatures indicated by Ti-in-zircon thermometry (ca. 500-600 °C) and the close similarity of zircon (U-Pb) and white mica (Rb-Sr, Ar-Ar) ages favor a metamorphic zircon origin. Previously published isotopic ages of the felsic rocks cannot unambiguously be linked to the eclogite- and/or blueschist-facies P-T conditions due to the absence of unequivocal mineralogical and petrological evidence. Instead, these rocks may record contemporaneous metamorphic processes that took place at a different depth within the subduction complex, or may indicate active ridge subduction and/or melt formation in the subduction zone at relatively low pressures. Biotite-based internal Rb-Sr isochrons of newly dated epidote amphibolite and biotite-albite gneisses indicate ages of ca. 74-80 Ma, either dating fluid-infiltration-induced formation of biotite during relatively fast uplift, or the time of final passage through the effective biotite closure temperature. Rb-Sr ages of phengite from both an epidote amphibolite and a biotite-albite gneiss yield ages that correspond to the HP/LT stage. This outcome, combined with textural evidence for derivation from eclogitic precursors documents that white mica ages of some strongly overprinted Sistan rocks are compromised by inheritance and do

  8. Reconstruction of methods of execution of the death penalty by shooting in the years 1949-1954 based on exhumation research of "prison fields" in Osobowicki Cemetery in Wroclaw. Part II--analysis of gunshot injuries and an attempt at reconstructing the course of execution.

    Science.gov (United States)

    Szleszkowski, Łukasz; Thannhäuser, Agata; Kawecki, Jerzy; Szwagrzyk, Krzysztof; Swiatek, Barbara

    2012-01-01

    The analysis of gunshot injuries in prisoners who were executed in Wroclaw penitentiary in the years 1949-1954 shows divergences from legal regulations describing the method of execution. This observation leads to the conclusion that the predominant method of execution of the death penalty was a gunshot or gunshots to the back of the head, which is analogous to the results of exhumation works on collective graves of war prisoners executed during World War II in the territory of the former Soviet Union.

  9. Exhuming Trends in Ethnic Conflict and Cooperation in Africa: Some ...

    African Journals Online (AJOL)

    Africa has had more than its fair share of ethnic dissent which has sometimes plummeted states into civil war as was experienced in Nigeria, the Democratic Republic of the Congo (DRC) and reached frightening proportions in Rwanda and now Sudan. Political openings and multiparty elections have led to the formation of ...

  10. A plate tectonics oddity: Caterpillar-walk exhumation of subducted continental crust

    NARCIS (Netherlands)

    Tirel, C.; Brun, J.-P.; Burov, E.; Wortel, M.J.R.; Lebedev, S.

    2013-01-01

    Since plate tectonics began on Earth, grandiose "subduction factories" have continually shaped the continents, accreting continental blocks and new crust at the convergent plate boundaries. An enigmatic product of subduction factories is the high-pressure to ultrahigh-pressure (HP-UHP) metamorphic

  11. Steady-state exhumation pattern in the central Andes SE Peru

    NARCIS (Netherlands)

    Ruiz, G.M.H.; Carlotto, V.; van Heiningen, P.S.; Andriessen, P.A.M.

    2009-01-01

    The Western Cordillera of SE Peru is part of the Central Andes and is situated to the west of the Eastern Andes from which it is separated by the northern termination of the Altiplano - the Inter-Andean Valley. It is a volcanic-volcano-detrital chain that developed in the Palaeogene, and is

  12. Frictional properties of exhumed fault gouges in DFDP-1 cores, Alpine Fault, New Zealand

    Science.gov (United States)

    Boulton, Carolyn; Moore, Diane E.; Lockner, David A.; Toy, Virginia G.; Townend, John; Southerland, Rupert

    2014-01-01

    Principal slip zone gouges recovered during the Deep Fault Drilling Project (DFDP-1), Alpine Fault, New Zealand, were deformed in triaxial friction experiments at temperatures, T, of up to 350°C, effective normal stresses, σn′, of up to 156 MPa, and velocities between 0.01 and 3 µm/s. Chlorite/white mica-bearing DFDP-1A blue gouge, 90.62 m sample depth, is frictionally strong (friction coefficient, μ, 0.61–0.76) across all experimental conditions tested (T = 70–350°C, σn′ = 31.2–156 MPa); it undergoes a transition from positive to negative rate dependence as T increases past 210°C. The friction coefficient of smectite-bearing DFDP-1B brown gouge, 128.42 m sample depth, increases from 0.49 to 0.74 with increasing temperature and pressure (T = 70–210°C, σn′ = 31.2–93.6 MPa); the positive to negative rate dependence transition occurs as T increases past 140°C. These measurements indicate that, in the absence of elevated pore fluid pressures, DFDP-1 gouges are frictionally strong under conditions representative of the seismogenic crust.

  13. Meso-scale kinematic indicators in exhumed mass transport deposits: Definitions and implications

    NARCIS (Netherlands)

    Ogata, Kei; Pini, Gian Andrea; Festa, Andrea; Poga??nik, Z??ljko; Lucente, Claudio Corrado

    2016-01-01

    In this study we combine observations and analytical data from large-scale (10–100s of m-thick and 100 m 2 -extensive), siliciclastic and carbonate MTD/MTCs belonging to the Oligocene – Miocene foredeep and wedge-top suc-cessions of the Northern Apennines and the Paleocene – Eocene Friuli basin of

  14. Tectonic Exhumation and Climate Driven Erosion in Extensional Mountain Blocks: Two Examples from California, USA

    OpenAIRE

    Mason, Cody Curtis

    2017-01-01

    The Pacific-North America plate boundary in central and southern California has a complex tectonic history, and constraints are poor for inception of an extensional fault system linked to the southern San Andreas fault, a major tectonic element of this plate boundary. Furthermore, decades of research has shown relationships between climate, tectonics, and surface processes in most orogens across the globe (e.g. Alps, Himalaya, Andes, Alaska Ranges), however the role climate plays in modulatin...

  15. High-Precision Dating of Migmatites in an Exhumed Continental Arc

    Science.gov (United States)

    Gordon, S. M.; Bowring, S.; Whitney, D. L.; Miller, R. B.; McLean, N.

    2007-12-01

    Migmatites play an important role in the evolution of mountain systems by inducing rheological contrasts and focusing strain. To understand the role of partially molten crust in tectonometamorphic processes, it is important to determine how much of the crust was partially molten for how long, and to link the conditions, timing, and consequences of partial melting to tectonic processes at different crustal levels during construction and collapse of orogens. The Skagit Gneiss, in the high-grade core of the North Cascade range of Washington and BC, contains abundant migmatites generated in a continental magmatic arc. In one outcrop near the E margin of the Skagit Gneiss, leucosomes occur with a variety of textures (e.g., layer-parallel/discordant; fine- grained/pegmatitic). Zircons from different leucosomes were analyzed using the chemical abrasion (CA-TIMS) technique to determine migmatite crystallization ages. Zircon dates range from ca. 53 Ma for a deformed, cross- cutting pegmatitic leucosome that envelops boudins of garnet-bearing metagraywacke, to 47 Ma for a strongly lineated biotite gneiss. A ~ 6 cm thick layer-parallel, coarse-grained leucosome was dated between the pegmatite and biotite gneiss at ca. 51 Ma. Other leucosomes in different textural and structural settings of the Skagit Gneiss yield older zircon crystallization ages (ca. 69-60 Ma), suggesting at least two pulses of migmatite crystallization during the evolution of the magmatic arc. The ca. 50 Ma ages are similar to Ar cooling ages from much of the Skagit Gneiss and to the timing of Eocene extensional basin formation and volcanic activity in the region. Furthermore, the ca. 53-47 Ma dates are at the young end of the age spectrum for the North Cascades and indicate that magmatism, metamorphism, and partial melting were active until the latest stages of orogeny.

  16. Mantle uplift and exhumation caused by long-lived transpression at a major transform fault

    Science.gov (United States)

    Maia, Marcia; Sichel, Susanna; Briais, Anne; Brunelli, Daniele; Ligi, Marco; Campos, Thomas; Mougel, Bérengère; Hémond, Christophe

    2017-04-01

    Large portions of slow-spreading ridges have mantle-derived peridotites emplaced either on, or at shallow levels below the sea floor. Mantle and deep rock exposure in such contexts results from extension through low-angle detachment faults at oceanic core complexes or, along transform faults, to transtension due to small changes in spreading geometry. In the Equatorial Atlantic, a large body of ultramafic rocks at the large-offset St. Paul transform fault forms the archipelago of St. Peter & St. Paul. These islets are emplaced near the axis of the Mid-Atlantic Ridge (MAR), and have intrigued geologists since Darwin's time. They are made of variably serpentinized and mylonitized peridotites, and are presently being uplifted at a rate of 1.5 mm/yr, which suggests tectonic stresses. The existence of an abnormally cold upper mantle or cold lithosphere in the Equatorial Atlantic was, until now, the preferred explanation for the origin of these ultramafics. High-resolution geophysical data and rock samples acquired in 2013 show that the origin of the St. Peter & St. Paul archipelago is linked to compressive stresses along the transform fault. The islets represent the summit of a large push-up ridge formed by deformed mantle rocks, located in the center of a positive flower structure, where large portions of mylonitized mantle are uplifted. The transpressive stress field can be explained by the propagation of the northern MAR segment into the transform domain. The latter induced the overlap of ridge segments, resulting in the migration and segmentation of the transform fault and the creation of a series of restraining step-overs. A counterclockwise change in plate motion at 11 Ma initially generated extensive stresses in the transform domain, forming a flexural transverse ridge. Shortly after the plate reorganization, the MAR segment located on the northern side of the transform fault started to propagate southwards, adjusting to the new spreading direction. Enhanced melt supply at the ridge axis, possibly due to the Sierra Leone thermal anomaly, induced the robust response of this segment.

  17. Resurrection, revenance, and exhumation: the problematics of the dead body in songs and laments

    Directory of Open Access Journals (Sweden)

    Madis Arukask

    2011-01-01

    Full Text Available Different types of folklore texts differ from each other by their function. We can distinguish between genres meant to be believed (like legend and genres recognized in advance as fiction (fairy-tale. At the same time, textual fiction may also have served practical purposes—such as the telling of fairy-tales during the late autumn and early winter for purposes of fertility magic—as used to be the case in the Estonian folk tradition. There are folklore genres that have functioned, among other things, as an accompaniment, comment on, or support to rituals or practices being carried out—for instance, an incantation during a cure, or a lament in death-related procedures, when a person must be separated from his familiar environment. The same textual formulae fulfil different tasks in different genres, which means that they also carry a different meaning. The present paper considers some themes related to the bodily aspect of humanity in various genres of folklore, particularly in songs and laments, as well as in practices related to death and commemoration. As expected, the problems connected with the human body have in these genres undergone transformations of meaning, the understanding and interpretation of which may vary considerably. The mater­ial discussed in the article derives mainly from the Balto-Finnic and north Russian cultural area, partly from the author's own experience during his field trips.

  18. Exhumation history along the eastern Amundsen Sea coast, West Antarctica, revealed by low-temperature thermochronology

    Science.gov (United States)

    Lindow, Julia; Kamp, Peter J. J.; Mukasa, Samuel B.; Kleber, Michel; Lisker, Frank; Gohl, Karsten; Kuhn, Gerhard; Spiegel, Cornelia

    2016-10-01

    West Antarctica experienced a complex tectonic history, which is still poorly documented, in part due to extensive ice cover. Here we reconstruct the Cretaceous to present thermotectonic history of Pine Island Bay area and its adjacent coasts, based on a combination of apatite and zircon fission track and apatite (U-Th-Sm)/He thermochronology. In addition, we report petrographic information for the catchments of Pine Island, Thurston Island, and Thwaites glaciers. Our data suggest that the underlying bedrock of the Pine Island and Thwaites Glacier catchments are very different and vary from granitoids to (Cenozoic?) volcanogenic sequences and low-grade metamorphics. Our thermochronology data show that the upper crustal rocks of Pine Island Bay experienced very rapid cooling during the late Cretaceous. We attribute this rapid cooling of basement rocks and associated reduction in mean elevation to tectonic denudation driven by gravitational collapse of the Cretaceous orogen along the proto-Pacific Gondwana margin. Rapid Cretaceous crustal cooling was followed by very slow cooling during the Cenozoic, with no erosional response—within the limits of thermochronological methods—to the onset of glaciation and subsequent climatic changes. Cenozoic rifting within the West Antarctic Rift appears to have had little effect on erosion processes around Pine Island Bay; instead, our data suggest Cenozoic crustal tilting toward Pine Island Trough, a major geomorphic feature previously suggested to be a branch of the rift system.

  19. Oligocene Laccoliths on the Colorado Plateau: A Key to Understanding Cenozoic Rock Cooling and Exhumation

    Science.gov (United States)

    Murray, K. E.; Reiners, P. W.; Thomson, S. N.

    2014-12-01

    The Colorado Plateau is an exceptional region of high elevation, extensive canyonlands, and minor crustal deformation in the North American Cordillera. Numerous low-temperature thermochronology studies have attempted to constrain the timing and rate(s) at which this enigmatic Cenozoic landscape developed. However, such studies have struggled to robustly interpret the thermal histories of the Plateau's rocks because most contain detrital crystals with diverse time-temperature histories that are partially reset, which confounds efforts to see clear thermochronologic signals of Cenozoic erosion. To overcome this challenge, we targeted sample collection from places on the Plateau where rock thermal histories were reset by Oligocene magmatism: the thermal aureoles of laccolith-cored Henry, La Sal, and Abajo mountains. There, shallow plutons (i.e., laccoliths) heated the late Paleozoic and Mesozoic sedimentary rocks ca. 26 Ma, locally resetting apatite fission track and (U-Th)/He ages so they record subsequent Miocene-Quaternary cooling. Sandstone samples from each mountain range yield single-crystal apatite He ages that vary with effective U concentration (eU). In these key samples, minimum He ages are ~5 Ma with eU 60 ppm. We model and interpret these age-eU patterns together with (1) stratigraphic constraints, (2) the timing of magmatic heating constrained by zircon U/Pb laccolith geochronology, and (3) the extent of resetting temperatures >100 ˚C by apatite fission track analysis. Results require prolonged sample residence in the apatite He partial retention zone (40-60 ˚C) from 25 to 1 km/Myr in parts of the Henry and Abajo mountains. The Plio-Pleistocene was a time of change both regionally and globally, as Colorado River base level dropped with its final integration through the Grand Canyon ca. 5.3 Ma and global climate cooling possibly enhanced erosion rates on the Plateau's high-relief mountain ranges. Ongoing work evaluates the relationship between the erosion of the laccolith-cored ranges and regional denudation.

  20. Rapid crustal exhumation and mantle-melt extraction: Where has the crust gone?

    Science.gov (United States)

    Alvarez-Valero, A. M.; Jagoutz, O.; Manthei, C.

    2012-04-01

    The emplacement of the Beni Bousera and Ronda ultramafic massifs of the Betico-Rifean belt (N Morocco-S Spain) has been discussed for several decades. These massifs are among the largest exposures of mantle rocks on Earth's surface, which obviously confers a special interest for mantle research in Earth Sciences. We present an integrated study of mantle and the surrounding crustal material of Beni Bousera in order to understand the interplay between melt percolation and emplacement of the ultramafic rocks and their relationships to the surrounding crust. Here we focus specifically on detailed petrological studies coupled with phase diagram modeling to elucidate the tectono-metamorphic history of the surrounding granulites. We then compare and relate these results to our understanding of the evolution of the Beni Bousera mantle rocks. The orogenic lherzolite of the ultramafic massif is surrounded by mostly metapelitic high-grade granulites (with local mylonitic layers) that are rimmed in turn by a successive sequence of lower metamorphic grade, from gneisses (with minor migmatites) to schists. The northern part of the massif offers exceptional exposures of a continuous lithospheric section from the ultramafics, via the Moho to the whole granulite packet by showing within the latter the preservation of two pressure events at fairly constant HT of c. 750 °C. A prograde higher-pressure episode (> 12 kbar) is characterized by equilibrium micro-domains with Grt+Bt+Ky+Rt followed by a lower-pressure (c. 5kbar) symplectic assemblage of Crd+Spl. This reveals a dramatic decompression event registered within less than 2 kms of crustal thickness. These results together with structures, numerical modelling and geochronology will extend the knowledge of the mechanisms of mantle emplacement in particular and global tectonics in general.

  1. Reconciling regional continuity with local variability in structure, uplift and exhumation of the Timor orogen

    NARCIS (Netherlands)

    Tate, Garrett W.; McQuarrie, Nadine; Tiranda, Herwin; van Hinsbergen, D.J.J.; Harris, Ron; Zachariasse, Willem Jan; Fellin, Maria Giuditta; Reiners, Peter W.; Willett, Sean D.

    Along-strike variations in orogenic development can be difficult to constrain. Resulting assumptions projecting similarity or variability along strike can lead to erroneous conclusions at the orogen scale. Young orogens provide opportunities to document limits of along-strike projection and test

  2. Utility of forensic detection of rabies virus in decomposed exhumed dog carcasses

    Directory of Open Access Journals (Sweden)

    Wanda Markotter

    2015-03-01

    Full Text Available This report describes four suspected rabies cases in domestic dogs that were involved inhuman exposures. In all these cases, the animals were buried for substantial times beforerabies testing was performed. Animal rabies is endemic in South Africa and domestic dogsare the main vector for transmission to humans. Diagnosis of rabies in humans is complicated,and diagnosis in the animal vector can provide circumstantial evidence to support clinicaldiagnosis of rabies in humans. The gold standard diagnostic method, fluorescent antibodytest (FAT, only delivers reliable results when performed on fresh brain material and thereforedecomposed samples are rarely submitted for diagnostic testing. Severely decomposed brainmaterial was tested for the presence of rabies virus genomic material using a quantitativereal-time reverse transcription polymerase chain reaction (q-real-time RT-PCR assaywhen conventional molecular methods were unsuccessful. This may be a useful tool in theinvestigation of cases where the opportunity to sample the suspected animals post mortem wasforfeited and which would not be possible with conventional testing methodologies becauseof the decomposition of the material.

  3. THE AMBUSH OF AFRICAN PHILOSOPHY: AN EXHUMATION OF CLASSICAL LIBERAL PRINCIPLES IN THE EVOLUTION OF AFRICA SOCIETIES

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    Ibrahim B. Anoba

    2017-05-01

    Full Text Available The persistent resentment towards classical liberal principles especially individualism and free market in contemporary Africa, represents an outcome of decades of ambush against the ideology despite its clear connections with traditional African philosophy and relevance to the prosperity of modern African states. This work attempts to draw comparisons between social and economic organisation in traditional Africa and classical liberal principles. Contrary to literatures that portray the community as the real and only end in traditional African societies, elements like free trade; market economy; consensus; anarchy and limited governance negates this position. While tracing the cause of Africa’s cling to socialism and communism, this paper presents an ideological transition from pre-colonialism to nationalist and post-independent Africa. It concludes by demystifying the arguments of individualism as antithetical to African morality. It also justified the inevitability of classical liberal principles in modern Africa.

  4. Exhumation of the Deylaman fault trend and its effects on the deformation style of the western Alborz belt in Iran

    Science.gov (United States)

    Hakimi Asiabar, Saeid; Bagheriyan, Siyamak

    2017-07-01

    The Alborz range in northern Iran stretches along the southern coast of the Caspian Sea and finally runs northeast and merges into the Pamir mountains in Afghanistan. Alborz mountain belt is a doubly vergent orogen formed along the northern edge of the Iranian plateau in response to the closure of the Neo-Tethys ocean and continental collision between Arabia and Eurasia. The south Caspian depression—the Alborz basin of Mesozoic age (with W-E trend) in northern Iran—inverted in response to the Arabia-Eurasia collision. Pre-existing extensional faults of the south Caspian-Alborz system preferentially reactivated as contractional faults because of tectonic inversion. These contractional structures tend to run parallel to the trends of pre-existing extensional faults and acquire W and WNW-ESE orientations across the previous accommodation zones that were imposed by the reactivation of adjacent extensional faults with different directions. The NNE to N dipping faults show evidences of reactivation. The Deylaman fault is one of the important faults of western Alborz in Iran and is an example of inversion tectonic style of deformation in the western Alborz mountain range. The Deylaman fault, with an E-W trend, contains three discontinuous fault segments in the area under investigation. These fault segments have evidence of oblique right-lateral reverse motion and links eastward to the dextral Kandavan thrust. The importance of this fault is due to its effect on sedimentation of several rock units from the Jurassic to Neogene in western Alborz; the rock facies on each side of this fault are very different and illustrate different parts of tectonic history.

  5. Mesozoic and Eocene ductile deformation of western Central Iran: from Cimmerian collisional orogeny to Eocene extension and exhumation

    Science.gov (United States)

    Kargaranbafghi, Fariba; Neubauer, Franz; Genser, Johann

    2010-05-01

    To advance our understanding of the Mesozoic to Eocene tectonics and kinematics of basement units exposed in the south-western Central Iran plateau, this paper presents new structural and thermochronological data from the Chapedony metamorphic core complex and hangingwall units, particularly from the Posht-e-Badam complex. The overall Paleogene structural characteristics of the area are related to an oblique convergent zone. The Saghand area represent part of a deformation zone between the Arabia and Eurasia plates, and can be interpreted as a product of the Central Iran intracontinental deformation as a weak zone during Mesozoic to Paleogene times. Field and microstructural evidence reveals that the metamorphic and igneous rocks in the study area suffered a ductile shear deformation including mylonitization at the hangingwall boundary of the Eocene Chapedony metamorphic core complex. The shear zone is subhorizontal low-angle normal fault and the shear direction of the hangingwall unit is towards NE, based on the attitude of foliation and lineation of ductility deformed rocks and shear sense indicators. Comparison of deformation features in the described mylonites and other structural features within the footwall unit lead to the conclusion that the mylonites were formed in a subhorizontal shear zone by NE-SW stretching in the extension tectonics during Middle to Late Eocene. The Chapedony metamorphic core complex is characterized by amphibolite-facies metamorphism and development of S and S-L tectonic fabrics. The Posht-e-Badam complex is deformed by two stages during Cimmerian tectonic processes forming the Paleo-Tethyan suture. The Posht-e-Badam complex is overprinted by two stages of metamorphism. White mica ages at 203 and 181 Ma are related to cooling after medium-grade metamorphism respectively ductile shearing. These ages are variably overprinted by low-grade metamorphism also affecting Jurassic metasediments in the Polo area. Consequently, these are younger, and plateau ages at 140 and 90 Ma have been found. The new age data from the Boneh Shurow and Posht-e-Badam complexes argue for a distinct history of these two complexes. Taking the model of Bagheri and Stampfli (2008), the Boneh Shurow comples can be placed together with Variscan accretionary complex. Since the benchmark paper of Şengör (1979), the Cimmerian orogeny is considered to represent the suture of Paleo-Tethys. The Cimmerian orogeny is obviously multiphase, and the Posht-e-Badam complex with its Middle Triassic medium-grade metamorphism and granite intrusions record the main stage of plate collision. The significance of the second, much later event at the Jurassic/Cretaceous boundary remains unclear, but it is compressional as the intercalation of the Raetoliassic phyllites records. REFERENCES: 1. Bagheri, S., Stampfli, G. M., 2008. The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications. Tectonophysics 451, 123-155. 2. Ramezani, J., Tucker, R., 2003. The Saghand region, Central Iran: U-Pb geochronology, petrogenesis and implication for Gondwana tectonics. American Journal of Science 303, 622-665. 3. Sengör, A.M.C., 1979. Mid-Mesozoic closure of Permo-Triassic Tethys and its implications. Nature 279, 590-593. 4. Verdel, C., Wernicke, B. P., Ramezani, J. Hassanzadeh, J., Renne, P. R., Spell, T. L., 2007. Geology and thermochronology of Tertiary Cordilleran-style metamorphic core complexes in the Saghand region of central Iran. Geol. Soc. Am. Bull 119, 961-977.

  6. Thermal history and differential exhumation across the Eastern Musgrave Province, South Australia: Insights from low-temperature thermochronology

    Science.gov (United States)

    Glorie, Stijn; Agostino, Kate; Dutch, Rian; Pawley, Mark; Hall, James; Danišík, Martin; Evans, Noreen J.; Collins, Alan S.

    2017-04-01

    Multi-method geo- and thermochronological data obtained for Palaeo- and Mesoproterozoic granitoids traversing the main structural architecture of the eastern Musgrave Province within South Australia reveal multiphase cooling histories. Apatite U-Pb dating on six samples yield consistent ages of 1075-1025 Ma, suggesting a thermal reset coinciding with mantle-derived magmatism of the greater Warakurna Large Igneous Province ( 1080-1040 Ma). Apatite fission track (AFT) analysis indicate that four discrete thermal events affected the study area, inducing cooling through the AFT partial annealing zone ( 60-120 °C), supported by apatite and zircon (U-Th-Sm)/He data. Late Neoproterozoic cooling from deep crustal levels to temperatures history for the eastern Musgraves and help to elucidate the poorly appreciated tectonic evolution of inland Australia. This study further demonstrates how high-density sample transects across structural architecture can assess the relative crustal level and associated preservation of the thermal history record within fault-reactivated terranes.

  7. Mesozoic and Cenozoic uplift and exhumation of the Bogda Mountain, NW China: Evidence from apatite fission track analysis

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    Wenhao Tang

    2015-07-01

    Full Text Available Apatite fission track (AFT analysis on samples collected from a Paleozoic series is used to constrain the cooling history of the Bogda Mountain, northwest China. AFT ages range from 136.2 to 85.6 Ma and are younger than rock depositional ages and the mean confined track lengths (11.0–13.2 μm mostly showing unimodal distribution are shorten, indicating significant track-annealing. Thermal histories modeling based on the distribution of fission-track lengths combined with the regional geological data show that two rapid cooling phases occurred in the latest Jurassic–early Cretaceous and the Oligocene–Miocene. Those new data together with previous published data show that the AFT ages become younger from the southwest to northeast in the western Bogda Mountain and its adjacent areas. The fission-track ages of the southwest area are relatively older (>100 Ma, recording the earlier rapid uplift phase during the late Jurassic–Cretaceous, while the ages in the north piedmont of the Bogda Mountain (namely the northeast part are younger (<60 Ma, mainly reflecting the later rapid uplift phase in the Oligocene–Miocene. The trend of younger AFT ages towards the northeast might be explained by post-Cretaceous large-scale crustal tilting towards the southwest. In the thrust fault-dominated northern limbs of the Bogda Mountain, AFT ages reveal a discontinuous pattern with age-jumps across the major fault zones, showing a possible strata tilting across each thrust faults due to the thrust ramps during the Cenozoic. The two rapid uplift stages might be related to the accretion and collision in the southern margin of the Asian continent during the late Jurassic and late Cenozoic, respectively.

  8. Thermal and exhumation history of the Costal Cordillera arc of the northern Chile revealed by thermochronological dating

    NARCIS (Netherlands)

    Juez-Larré, J.; Kukowski, N.; Dunai, T.J.; Hartley, A.J.; Andriessen, P.A.M.

    2010-01-01

    The thermal and erosional history of convergent plate boundaries is important for understanding the links between subduction, arc magmatism, genesis of ore deposits, topography and climate of orogenic belts. Unlike the continent-continent collision that formed many of the largest orogenic belts

  9. 3D modelling of a dolomitized syn-sedimentary structure: an exhumed potential analogue of hydrocarbon reservoir.

    Science.gov (United States)

    Martinelli, Mattia; Franceschi, Marco; Massironi, Matteo; Bistacchi, Andrea; Di Cuia, Raffaele; Rizzi, Alessandro

    2016-04-01

    The decrease in discoveries of new hydrocarbon reservoirs has twofold implications: i) the need to improve our knowledge of classic reservoirs, such as traps within extensional syn-sedimentary structures, and ii) enhanced efforts aimed at better understanding complex type of reservoirs. In particular, in the last few years, fault related dolomitized bodies, often associated to extensional faults, received worldwide attention thanks to the capability of dolomitizing fluids to improve the pore network. However, the shape and geometries of the dolomitized bodies within complex fault network as well as the related porosity distribution and evolution is difficult to predict. The study of outcrop analogues can help to solve these issues. In this work, we focused our attention on the Early Jurassic carbonate sediments of the Calcari Grigi Group deposited on the Trento Platform (Italian Southern Alps). The stratigraphic succession encompasses (from bottom to top): the peritidal limestones of the Monte Zugna Formation, the initially highly porous Loppio Oolitic Limestone and the nearly tight marls and marly limestones of the lower Rotzo Formation. During Early Jurassic, after the deposition of the Loppio Oolitic Limestone, the Trento Platform underwent syn-sedimentary extensional tectonics, which caused the formation of numerous tilted blocks. Differential subsidence of these blocks is testified by abrupt thickness changes in Rotzo Formation. This created a structural framework favourable to the formation of syn-sedimentary extensional traps (with the Loppio Oolitic Limestone as reservoir and Rotzo Formation as seal). In the Tertiary, Alpine compressional tectonics caused the reactivation of the Jurassic faults with a strike slip kinematics and was associated with the circulation of dolomitizing fluids. The combination of these events led to the formation of secondary fault-related dolomitized bodies. The enhanced pore network in correspondence of the dolomitized dykes further increase the potential creation of potential hydrocarbon traps. These complex conditions are visible in a syn-sedimentary structure spectacularly exposed on the Monte Testo (Trentino, Italy). In this contribution, we present a 3D geo-model of this structure, obtained with SKUA-gOcad, based on 3D photogrammetric modelling, detailed geological mapping and structural analysis, porosity analysis carried out on representative sections, and geostatistical simulation of porosity on dolomitized bodies. Thanks to the 3D model we obtained: i) a thickness map of the Rotzo Formation that allow us to understand which faults were active during the deposition of the formation and which areas could have been more suitable for hydrocarbon accumulation; ii) a geometric and volumetric model of the structure that permitted us to study the porosity distribution and to define the potential volume of hydrocarbons that could be hosted by a similar structure. These results were eventually extrapolated to the entire platform, providing clues on the hydrocarbon potential of similar buried geologic bodies.

  10. Late Cretaceous extension and exhumation of the Stong and Taku magmatic and metamorphic complexes, NE Peninsular Malaysia

    NARCIS (Netherlands)

    François, T.; Md Ali, M.A.; Matenco, L.; Willingshofer, E.; Ng, T.F.; Taib, N.I.; Shuib, M.K.

    2017-01-01

    Fragmentation of large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts, as exemplified by the Stong and Taku magmatic and metamorphic complexes of northern Peninsular Malaysia. For this

  11. Thermal and exhumation history of the central Rwenzori Mountains, Western Rift of the East African Rift System, Uganda

    Science.gov (United States)

    Bauer, F. U.; Glasmacher, U. A.; Ring, U.; Schumann, A.; Nagudi, B.

    2010-10-01

    The Rwenzori Mountains (Mtns) in west Uganda are the highest rift mountains on Earth and rise to more than 5,000 m. We apply low-temperature thermochronology (apatite fission-track (AFT) and apatite (U-Th-Sm)/He (AHe) analysis) for tracking the cooling history of the Rwenzori Mtns. Samples from the central and northern Rwenzoris reveal AFT ages between 195.0 (±8.4) Ma and 85.3 (±5.3) Ma, and AHe ages between 210.0 (±6.0) Ma to 24.9 (±0.5) Ma. Modelled time-temperature paths reflect a protracted cooling history with accelerated cooling in Permo-Triassic and Jurassic times, followed by a long period of constant and slow cooling, than succeeded by a renewed accelerated cooling in the Neogene. During the last 10 Ma, differentiated erosion and surface uplift affected the Rwenzori Mtns, with more pronounced uplift along the western flank. The final rock uplift of the Rwenzori Mtns that partly led to the formation of the recent topography must have been fast and in the near past (Pliocene to Pleistocene). Erosion could not compensate for the latest rock uplift, resulting in Oligocene to Miocene AHe ages.

  12. Experiments on Graphitization of Diamond in the Presence of Water: Implications for Exhumation of Ultrahigh Pressure Metamorphic Rocks

    Science.gov (United States)

    O'Bannon, E. F.; Xia, G.; Green, H. W.; Wirth, R.; Dobrzhinetskaya, L.

    2012-12-01

    Diamond and graphite occur in the mantle, and crustal ultrahigh pressure metamorphic (UHPM) rocks. The stability fields of carbon are well studied experimentally, but the mechanisms of phase transformation are not well understood. Observations on natural samples from UHPM terranes show that graphitization of diamond is accompanied by the formation of disordered graphite containing nanometric fluid inclusions. Since the structures of diamond and graphite are very dissimilar, it is unlikely that a direct phase transformation would occur during the graphitization process. Such an assumption is also supported by higher enthalpy (1.897) and lower entropy (2.38) of C-diamond with respect of those of C-graphite (enthalpy = 0, entropy=5.74). At least three different mechanisms of diamond-to-graphite transformation have been proposed. To constrain this process we conducted a series of anhydrous and hydrous experiments in a piston-cylinder apparatus and a hydrous experiment in a multianvil apparatus using 20-40 micron size virgin diamonds as the starting material. The piston-cylinder experiments were conducted at P=1 GPa and T=1300oC. In the hydrous experiments 1.15 wt.%. Mg(OH)2 was added to the starting material as the H2O supply according to the breakdown reaction: Mg(OH)2 = MgO + H2O. The multianvil experiment was conducted at P=6GPa and T=1300oC with 1 wt.%. distilled water added to the starting diamonds. Run products were studied with SEM, FIB assisted TEM, and SEM-Raman. The anhydrous experiments show that diamond crystals are "integrated" together producing deformed polycrystallites with complicated textural patterns occurring at the grain boundaries. The hydrous experiments show the formation of metastable nanometric spheroidal carbon particles which were distributed on the surface and between the corners of the diamonds. The metastable phase existed for ~6 months before it decomposed into graphite flakes. The graphite flakes have a disordered structure which was confirmed by TEM electron diffraction analysis. SEM-Raman analysis revealed bands at 1580 cm-1 (1st order graphite peak), and 2700 cm-1(2nd order graphite peak) accompanied by a well-expressed band at 1360 cm-1 which reflects a mixture of sp, sp2 & sp3 hybridyzed C-bonds. Metastable spheroidal carbon particles are identified by the presence of a Raman band at 2100 cm-1. This is hydrocarbon phase (i.e. polyyne CxHy) it is a linear carbon chain, which consists of sp hybrydized C-bonds. These sp hybridizied C-bonds can be transformed to the graphite sp2 structure very easily. Though polyyne is not a typycal geological material, it has been found in meteorites, meteorite craters, and natural rocks. Our experiments showed that graphitization of diamond in conditions corresponding to their uplift from a deep subduction zone to the Earth's surface requires an intermediate metastable phase of a hydrocarbon.

  13. Anthropological Analysis of the Skeletal Series exhumed from the Necropolis of Piatra Neamţ – Dărmăneşti (XIVth – XVth Centuries

    Directory of Open Access Journals (Sweden)

    Vasilica-Monica Groza

    2015-10-01

    Full Text Available This article represents a bioanthropological study of a small osteological series (32 skeletons discovered in 2012 in the necropolis of Piatra Neamţ – Dărmăneşti. According to the authors of diggings (Garvan Daniel, archaeologist, and his collaborators at Piatra Neamţ Museum of History and Archaeology the necropolis is dated between the XIVth and XVth centuries. The general and child mortality rates were analyzed, by gender and age, as well as the average lifespan by calculating the average age at death. We noticed a high mortality rate in childhood stage (0–14 years: 43.75%. If we add to it the teenage mortality rate (14-20 years: 6.25%, we can see that half of the studied population died before reaching adulthood. In the 20-x years interval, the highest mortality rate was recorded for mature people (30–60 years – 25%; the incidence of death among adults (20–30 years and subjects over 60 years is much lower (15.63% and 9.38%, respectively. The average lifespan for the entire population under study (0–x years is 25.63 years, the value recorded by gender, being of 44.17 years in men and 40.36 years in women. Anthropological analysis indicates, on the average, a population of over-middle height in males and middle height in females, with mesocranic skulls in males and brachycranic skulls in females, orthocranic and acrocranic (in the male series, respectively chamecranic and tapeinocranic (in the female series skullcaps. The forehead is eurimetopic (in the male series and metriometopic (in the female series, with averagely wide (in males and wide (in females occipitals. The face is, on the average, leptoprosopic an leptene in males, respectively mesoprosopic and mesene in females, with hypsiconch orbits and leptorrhine nose. Mandible robustness is moderate in both genders.

  14. Rheological and geodynamic controls on the mechanisms of subduction and HP/UHP exhumation of crustal rocks during continental collision : Insights from numerical models

    NARCIS (Netherlands)

    Burov, Evgene; Francois, Thomas; Agard, Philippe; Le Pourhiet, Laetitia; Meyer, Bertrand; Tirel, C.|info:eu-repo/dai/nl/304838209; Lebedev, Sergei; Yamato, Philippe; Brun, Jean Pierre

    2014-01-01

    While subduction of crustal rocks is increasingly accepted as a common scenario inherent to convergent processes involving continental plates and micro-continents, its occurrence in each particular context, as well as its specific mechanisms and conditions is still debated. The presence of

  15. Reconstructing the exhumation history of the Lesser Himalaya, Northern, India, from a multi-technique provenance study of the foreland basin Siwalik Group.

    OpenAIRE

    Najman, Yani; Bickle, Mike; Garzanti, Eduardo; PRINGLE, MALCOLM; Barford, Dan; Brozovic, Nick; Burbank, Doug; Andò, Sergio

    2009-01-01

    This research presents the first multitechnique provenance study of the Siwalik Group in the Himalayan foreland basin in India, using the Jawalamukhi section, magnetostratigraphically dated at 13–5 Ma. Combined with provenance data from a Dharamsala Formation sedimentary section (21–13 Ma) located close by, it forms the longest temporally continuous record of Himalayan erosion in the Indian foreland basin. Sandstone petrography and heavy mineral analysis, conglomerate clast composition, Ar‐Ar...

  16. Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France).

    OpenAIRE

    Carpentier, Cédric; Brigaud, Benjamin; Blaise, Thomas; Vincent, Benoît; Durlet, Christophe; Boulvais, Philippe; PAGEL, Maurice; Hibsch, Christian; Yven, Béatrice; Lach, Philippe; Cathelineau, Michel; Boiron, Marie-Christine; Landrein, Philippe; Buschaert, Stéphane

    2014-01-01

    27 pages; International audience; Several diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ18O, δ13C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky...

  17. La Balouta exhumed karst: a Roman gold-mine-derived landscape within the Las Médulas UNESCO World Heritage Site (Spain

    Directory of Open Access Journals (Sweden)

    José M. Redondo-Vega

    2015-09-01

    Full Text Available The La Balouta Valley, located in the extreme SW region of the Las Médulas Natural Monument and UNESCO World Heritage Site (León, Spain, is one of the largest gold-mining sites developed by the Romans more than 2,000 years ago when excavating a thick series of red Miocene sediments in the area. The main determining feature of the La Balouta Valley, especially if we compare it with the Sil River Valley of which it is a tributary, is its status of a non-functional valley. It is a dry paleo-valley with a flat bottom and is characterized by limited surface water runoff and the presence of small cavities, channels, and residual karst topography. Variscan structures that form the structural framework of the study area underwent long-term erosion and supported deep sediment accumulation in the area during the Miocene, reaching depths of more than 100 m. A portion of these sediments accumulated over a karst, as indicated by karst channels that exhibit total and locally partial filling with red sediments similar to those mined at Las Médulas roughly 2 km further to the east. The presence of gold particles in one of the sediment samples and the identification of several characteristics common of formations mined by the Romans lead us to deem the La Balouta Valley an ancient paleokarst that was initially fossilized by deposition of red Miocene sediments and subsequently excavated via historical mining activities, which formed its current characteristics. In La Balouta, natural and anthropogenic processes have produced a unique cultural landscape that is reflective of systematic gold mining of sediments on the NW Iberian Peninsula by the Romans.

  18. Crystallographic preferred orientations of exhumed subduction channel rocks from the Eclogite Zone of the Tauern Window (Eastern Alps, Austria), and implications on rock elastic anisotropies at great depths

    Czech Academy of Sciences Publication Activity Database

    Keppler, R.; Ullemeyer, K.; Behrmann, J. H.; Stipp, M.; Kurzawski, R. M.; Lokajíček, Tomáš

    647/648, April (2015), s. 89-104 ISSN 0040-1951 Institutional support: RVO:67985831 Keywords : crystallographic preferred orientation * eclogite Zone * elastic properties * P-wave anisotropy * retrogression of eclogites * subduction channel Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.650, year: 2015

  19. Preferential retrogression of high- P metasediments and the preservation of blueschist to eclogite facies metabasite during exhumation, Diahot terrane, NE New Caledonia

    Science.gov (United States)

    Fitzherbert, J. A.; Clarke, G. L.; Powell, R.

    2005-07-01

    High- P metabasites of the Diahot terrane, NE New Caledonia occur as spatially restricted (cm to km-scale) lenses, boudins and layers in psammitic to pelitic metasediments. Although interlayered, the two rock types preserve distinct, tectonically disrupted metamorphic profiles in the transition from lawsonite blueschist in the SW to low- T eclogite in the NE. As the metabasites experienced comparatively low strain, igneous textures, and, more rarely, igneous minerals are preserved. Metamorphic assemblages in the metabasites range from lawsonite-omphacite-glaucophane-bearing assemblages (Zone 1; P=7-10 kbar, T=350-400 °C) in the SW, through clinozoisite-almandine-bearing assemblages (Zone 2; P=14-16 kbar, T=450-550 °C) and finally to clinozoisite-almandine-hornblende-omphacite-bearing assemblages (Zones 3 and 4; P=16-18 kbar, T=550-600 °C) in the NE. Metasedimentary assemblages range from spessartine-lawsonite-albite-chlorite (Zone 1), through almandine-clinozoisite-albite-chlorite (Zone 2) and almandine-epidote-omphacite-albite-bearing (Zone 3) lithologies. Mineral inclusion trails in coarse-grained albite and garnet in Zones 2 and 3 metasediments record prograde mineral assemblages that match the P- T conditions recorded by the metabasites ( P=14-18 kbar, T=450-600 °C). The metasediments were intensely deformed at peak conditions ( P=12-16 kbar, T=550-600 °C) and during retrogression, and developed coarse-grained albite, phengite and chlorite-bearing assemblages. Differences in strain history (competency contrasts), the timing of major dehydration reactions and variation in whole rock composition all played vital roles in developing the distinctive field relationships involving blueschist to eclogite facies metabasites enclosed within strongly retrogressed high- T blueschist to greenschist facies metasedimentary lithologies exposed in NE New Caledonia.

  20. Separation of the Guajira-Bonaire pair in the southern margin of the Caribbean: 65-50 Ma exhumation followed by 300 km right-lateral transtensional deformation

    Science.gov (United States)

    Zapata Henao, S.; Cardona, A.; Montes, C.; Valencia, V.; Vervoort, J. D.; Reiners, P. W.

    2012-12-01

    Middle to upper Eocene fluvial strata in the island of Bonaire contains detrital components that were tracked to the basement massifs of the Guajira Peninsula in northern Colombia. These detrital components confirm previous hypothesis that the Guajira-Bonaire pair constitute a tectonic piercing point along the southern Caribbean plate margin that was right-laterally displaced approximately 300 km after middle Eocene times. Other possible sources, the nearby Curacao and the far away Santa Marta massif, did not pass statistical similarity and overlap tests. U-Pb LA-ICP-MS from the metamorphic boulders of the Soebi Blanco Formation in Bonaire yield Grenvillian ages (1084 Ma, 1130 Ma and 1184 Ma), while the detrital zircons recovered from the sandy matrix of the conglomerates contains populations with peaks of 1000 Ma - 1200 Ma, 750 Ma - 950 Ma, and 200 Ma - 300 Ma. Overlap and Similarity tests run between these populations and published data from Guajira yield values of 0.750 and 0.680, which are significantly higher than the same comparison against the Santa Marta Massif (0.637 and 0.522), and the Curacao island (0.629 and 0.467). Thermochronological results from the metamorphic clasts yield Paleocene-middle Eocene ages (65 - 50 Ma) that confirm not only a regional-scale cooling event in this time period, but also help constrain the maximum depositional age (50 Ma) of the poorly dated Soebi Blanco Formation. Figure 6. U-Pb results from analyzed samples and other Caribbean provinces. (A), Detrital zircons from Soebi Blanco conglomerate matrix; (B), Zircon ages from metamorphic clasts (C), detrital zircons from late Cretaceous Etpana Formation in Guajira Peninsula (Weber et al., 2010); (D), detrital zircons from late Cretaceous Santa Marta San Lorenzo schists (Cardona et al., 2010a); (E), detrital zircons from late Cretaceous Knip Group (Wrigth and Wyld, 2010); (F), overlap and similarity values.

  1. Metamorphic P-T-t-d evolution of (U)HP metabasites from the South Tianshan accretionary complex (NW China) - Implications for rock deformation during exhumation in a subduction channel

    Czech Academy of Sciences Publication Activity Database

    Soldner, J.; Oliot, E.; Schulmann, K.; Štípská, P.; Kusbach, Vladimír; Anczkiewicz, R.

    2017-01-01

    Roč. 47, July (2017), s. 161-187 ISSN 1342-937X Institutional support: RVO:67985530 Keywords : eclogite * Tianshan massif * (U)HP metamorphic belt Subject RIV: DB - Geology ; Mineralogy Impact factor: 6.959, year: 2016

  2. A fluid inclusion study of blueschist-facies lithologies from the Indus suture zone, Ladakh (India): Implications for the exhumation of the subduction related Sapi-Shergol ophiolitic mélange

    Science.gov (United States)

    Sachan, Himanshu Kumar; Kharya, Aditya; Singh, P. Chandra; Rolfo, Franco; Groppo, Chiara; Tiwari, Sameer K.

    2017-09-01

    The best occurrence of blueschist-facies lithologies in Himalaya is that of the Shergol Ophiolitic Mélange along the Indus suture zone in Ladakh region of north-western India. These lithologies are characterized by well preserved lawsonite-glaucophane-garnet-quartz assemblages. This paper presents for the first time the results of a detailed fluid inclusion study on these lithologies, in order to understand the fluid P-T evolution and its tectonic implications. The blueschist rocks from Shergol Ophiolitic Mélange record metamorphic peak conditions at ∼19 kbar, 470 °C. Several types of fluid inclusions are trapped in quartz and garnet, most of them being two-phase at room temperature. Three types of fluid inclusions have been recognised, basing on microtextures and fluid composition: Type-I are primary two-phase carbonic-aqueous fluid inclusions (VCO2 - LH2O); Type-II are two-phase (LH2O - VH2O) aqueous fluid inclusions, either primary (Type-IIa) or secondary (Type-IIb); Type-III are re-equilibrated fluid inclusions. In the Type-I primary carbonic-aqueous inclusions, H2O is strongly predominant with respect to CO2; the homogenization temperature of CO2 range from -7 to -2 °C. The clathrate melting temperature in such inclusions varies in between +7.1 and +8.6 °C. Type-II two-phase aqueous fluid inclusions show a wide range of salinity, from 7.8-14 wt.% NaCleq (Type-IIa) to 1.65-6.37 wt.% NaCleq (Type-IIb) with accuracy ±0.4 wt.% NaCleq. Type-I and Type-IIa primary fluid inclusions are hosted in peak minerals (garnet and quartz included in garnet), therefore they were likely entrapped at, or near to, peak P-T conditions. The dominantly aqueous fluid of both Type-I and Type-IIa inclusions was most likely produced through metamorphic devolatilization reactions occurring in the subducting slab. Despite their primary nature, the isochores of Type-I and Type-IIa inclusions do not intersect the peak metamorphic conditions of the blueschist mineral assemblage, suggesting that these inclusions stretched or re-equilibrated during nearly isothermal decompression from 19 kbar to 3 kbar or less, at T = 290 °C. This conclusion is further supported by their large variability in shapes and sizes which range from irregular inclusions ('C'/arc shaped, hook shape and satellite type). This decompression stage was followed by nearly isobaric cooling, testified by the occurrence of dendritic networks of decrepitated and 'imploded' fluid inclusions.

  3. Unearthing Truth: Forensic Anthropology, Translocal Memory, and "Provention" in Guatemala

    National Research Council Canada - National Science Library

    Colette G Mazzucelli; Dylan Heyden

    2015-01-01

    .... Excavations of mass gravesites and the painstaking exhumation processes carried out by professional forensic anthropology teams continue to allow families to locate lost relatives--reclaiming truth...

  4. Réservoirs fluides et transferts en contexte d'exhumation orogénique : implications sur la position structurale des minéralisations Cu-Pb-Zn-Fe-Ag dans la région Lavrion-Eubée (Grèce)

    OpenAIRE

    Scheffer, Christophe

    2016-01-01

    This thesis is focused on the Attico-Cycladic orogenic wedge formed during the Alpine orogeny. From a multi-method and multi-scale approach using structural geology, petrography, mineral thermobarometry, element and isotope geochemistry, and PVTX data of associated fluid inclusions, this study deciphers the relationships between fluid circulation, fluid-rock interactions and mobilisation-transport-deposits of metals. Marbles and schists from the Evia Island and the Lavrion peninsula testify t...

  5. Late Cretaceous extensional denudation along a marble detachment fault zone in the Kırşehir massif near Kaman, central Turkey

    NARCIS (Netherlands)

    Lefebvre, C.J.C.; Barnhoorn, A.; Hinsbergen, D.J.J. van; Kaymakçi, N.; Vissers, R.L.M.

    2011-01-01

    In the Central Anatolian Crystalline Complex (CACC), 100 km scale metamorphic domains were exhumed in a context of north-south plate convergence during late Cretaceous to Cenozoic times. The timing, kinematics and mechanisms of exhumation have been the focus of previous studies in the southern Ni

  6. Eocene deep crust at Ama Drime, Tibet

    DEFF Research Database (Denmark)

    Kellett, Dawn; Cottle, John; Smit, Matthijs Arjen

    2014-01-01

    burial and exhumation of a cold subducted slab. The rocks instead resulted from crustal thickening during the early stages of continental collision, and resided in the lower-middle crust for >20 m.y. before they were exhumed and reheated. These new data provide solid evidence for the Indian crust having...

  7. Structure and provenance of Late Cretaceous-Miocene sediments located near the NE Dinarides margin: Inferences from kinematics of orogenic building and subsequent extensional collapse

    Science.gov (United States)

    Stojadinovic, Uros; Matenco, Liviu; Andriessen, Paul; Toljić, Marinko; Rundić, Ljupko; Ducea, Mihai N.

    2017-07-01

    The NE part of the Dinarides Mountain chain, located near their junction with the Carpatho-Balkanides, is an area where sedimentary basins associated with the Neotethys subduction and collision are still exposed. We performed a provenance study, based on detrital fission track thermochronology combined with zircon Usbnd Pb magmatic geochronology, and existing studies of kinematics and exhumation. Our study shows rapid sedimentation in the trench and forearc basin overlying the upper European tectonic plate. A number of latest Cretaceous-Early Paleocene igneous provenance ages show a dominant magmatic source area, derived from a Late Cretaceous subduction-related arc. This arc shed short time lag sediments in the forearc and the trench system, possibly associated with focused exhumation in the Serbo-Macedonian margin. This was followed by burial of the trench sediments and a novel stage of Middle-Late Eocene exhumation driven by continued continental collision that had larger effects than previously thought. The collision was followed by Late Oligocene-Miocene exhumation of the former lower Adriatic plate along extensional detachments that reactivated the inherited collisional contact along the entire Dinarides margin. This event re-distributed sediments at short distances in the neighboring Miocene basins. Our study demonstrates that the Dinarides orogenic system is characterized by short lag times between exhumation and re-deposition, whereas the upper tectonic plate is significantly exhumed only during the final stages of collision. Such an exhumation pattern is not directly obvious from observing the overall geometry of the orogen.

  8. Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

    National Research Council Canada - National Science Library

    Angiboust, Samuel; Kirsch, Josephine; Oncken, Onno; Glodny, Johannes; Monié, Patrick; Rybacki, Erik

    2015-01-01

    ... as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30–40 km paleodepth...

  9. Forensic Analysis of a Contact Lens in a Murder Case.

    Science.gov (United States)

    Zwerling, Charles S

    2016-03-01

    Contact lenses have had rare relevance in trials and/or investigations. After 5 years of burial, orbital remnants were retrieved from an exhumed body and subsequently identified as a key piece of material evidence in a murder trial. The exhumed case materials were evaluated under laboratory conditions and were determined to be contact lens remnants. Contact lens fracture and burial simulation studies were performed to provide additional corroboration of the physical findings of the exhumed contact lens remnants. This material evidence was instrumental in providing factual proof refuting the defendant's testimony in the murder trial. A brief history of contact lens composition and use is provided for understanding the methods and observational results. This forensic case study represents the first published documentation of a contact lens from an exhumed body being used in a murder investigation and establishes an operational procedure for future forensic contact lens examinations. © 2016 American Academy of Forensic Sciences.

  10. Thermochronology and Tectonics of the Leeward Antilles: evolution of the Southern Caribbean Plate Boundary Zone and accretion of the Bonaire Block

    Science.gov (United States)

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

    2010-05-01

    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 zircon 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 northwards escape of the Maracaibo Block.

  11. Tectonic and Climatic Control of Landscape Evolution in the Northern Sierras Pampeanas, Argentina

    Science.gov (United States)

    Sobel, E. R.; Strecker, M. R.

    2003-12-01

    Rock uplift, surface uplift and exhumation can be constrained if thermochronologic data can be converted to exhumation and if geological relations provide a datum. In the northern Sierras Pampeanas of Argentina, the Cenozoic Santa María basin, which overlay resistant crystalline basement prior to rapid exhumation, provides an ideal setting to examine the effect of contrasting thermal and erosional regimes. There, tectonically active reverse-fault bounded blocks partly preserve a basement peneplain at elevations >4500 m. Prior to exhumation, the study area was covered by 1 to 1.6 km of ca. 12-6 Ma sediments; this sequence begins with shallow marine deposits immediately overlying the regional erosion surface which are superseded by sandstones and conglomerates. These rapidly deposited sediments have low thermal conductivity and are readily eroded, in contrast to underlying resistant basement. Apatite fission-track data were obtained from two vertical transects in the Calchaquíes and Aconquija ranges bounding the basin. At Cumbres Calchaquíes, erosion leading to the development of the peneplain commenced in the Cretaceous; limited late Neogene cooling is documented by track-length modeling. In contrast, Sierra Aconquija cooled rapidly between 5.5 and 4.5 My. At the onset of this rapid exhumation, sediment was quickly removed, causing fast cooling, but relatively slow rates of surface uplift. Syntectonic conglomerates could only be produced when faulting exposed resistant bedrock; this change in rock erodability lead to enhanced surface uplift rates but decreased exhumation rates. The creation of an orographic barrier after the range had attained sufficient elevation further decreased exhumation rates on the leeward side and increased surface uplift rates. This imbalance cannot be sustained for extended periods of time; either crustal strength or bedrock fluvial incision will ultimately limit the magnitude of relief which can be created before tectonism, and hence

  12. Low-temperature thermochronology applied to ancient settings

    Science.gov (United States)

    Enkelmann, Eva; Garver, John I.

    2016-01-01

    Low-temperature thermochronometric dating techniques are commonly used to reveal and quantify the spatial and temporal pattern of cooling and exhumation in many active mountain belts. These methods illuminate the relationship between rock exhumation, and the processes that bring rock to the surface, including climate-driven surface processes. Thermochronological studies on rocks in ancient settings (Precambrian and Paleozoic) are far more complicated, and in general have largely failed to reveal exhumation processes in orogenic belts, mainly due to imprecision of the technique, complications from radiation damage, and subsequent resetting. However, in a few locations, remnants of the exhumation record of ancient orogens may be studied with low-temperature dating techniques and in these cases we can gather first-order information on tectonics, thermal events, and exhumation processes that have occurred in the deep past. Here we provide an overview of the most common low-temperature thermochronology methods of fission-track and (U-Th)/He dating of apatite and zircon and discuss methodological challenges in their application to old settings. We review several case studies from the Northern Appalachians, central Argentina, the Canadian Shield, central Wyoming, and the European Variscides where thermochronology data have been successful in reconstructing geologic processes in deep-time that have affected the upper crust. With these examples we provide sampling strategies and analytical approaches that partly circumvent issues related to radiation damage in old mineral grains that result in changes in the retention of helium and fission tracks.

  13. Deformation inside a paleosubduction channel - Insights from microstructures and crystallographic preferred orientations of eclogites and metasediments from the Tauern Window, Austria

    Science.gov (United States)

    Keppler, Ruth; Stipp, Michael; Behrmann, Jan H.; Ullemeyer, Klaus; Heidelbach, Florian

    2016-01-01

    The Eclogite Zone, of the Tauern Window is an exhumed subduction channel comprising eclogites with different grades of retrogression in a matrix of high-pressure metasediments. The rocks were exposed to 600 °C and 20-25 kbars, and then retrogressed during their exhumation, first under blueschist facies and later under amphibolite facies metamorphism. To gain insights into the deformation within the subduction channel during subduction and exhumation, both fresh and retrogressed eclogites, as well as the surrounding metasediments were investigated with respect to their deformation microstructures and crystallographic preferred orientations (CPOs). Pristine and retrogressed eclogites show grain boundary migration and subgrain rotation recrystallization microstructures in omphacite. A misorientation axes analysis reveals the activity of complementary deformation mechanisms including grain boundary sliding and dislocation creep. The omphacite CPOs of the eclogites correspond to dominant SL-fabrics characteristic of plane strain deformation, though there are local variations towards flattening or constriction within the paleosubduction channel. The glaucophane CPOs in retrogressed eclogites match those of omphacite, suggesting that a constant strain geometry persisted during exhumation at blueschist facies conditions. Plastic deformation of the host high-pressure metasediments outlasted that of the eclogites, as indicated by white mica fabrics and quartz CPO. The latter is consistently asymmetric, pointing to the operation of non-coaxial deformation. The microstructures and CPO data indicate a continuous plastic deformation cycle with eclogite and blueschist facies metamorphism related to subduction and exhumation of the different rock units.

  14. Structural analysis of three extensional detachment faults with data from the 2000 Space-Shuttle Radar Topography Mission

    Science.gov (United States)

    Spencer, J.E.

    2010-01-01

    The Space-Shuttle Radar Topography Mission provided geologists with a detailed digital elevation model of most of Earth's land surface. This new database is used here for structural analysis of grooved surfaces interpreted to be the exhumed footwalls of three active or recently active extensional detachment faults. Exhumed fault footwalls, each with an areal extent of one hundred to several hundred square kilometers, make up much of Dayman dome in eastern Papua New Guinea, the western Gurla Mandhata massif in the central Himalaya, and the northern Tokorondo Mountains in central Sulawesi, Indonesia. Footwall curvature in profile varies from planar to slightly convex upward at Gurla Mandhata to strongly convex upward at northwestern Dayman dome. Fault curvature decreases away from the trace of the bounding detachment fault in western Dayman dome and in the Tokorondo massif, suggesting footwall flattening (reduction in curvature) following exhumation. Grooves of highly variable wavelength and amplitude reveal extension direction, although structural processes of groove genesis may be diverse.

  15. Miocene to recent extension in NW Sulawesi, Indonesia

    Science.gov (United States)

    Advokaat, Eldert L.; Hall, Robert; White, Lloyd T.; Watkinson, Ian M.; Rudyawan, Alfend; BouDagher-Fadel, Marcelle K.

    2017-10-01

    The Malino Metamorphic Complex (MMC) in the western part of the North Arm of Sulawesi (Indonesia) has previously been suggested to be a metamorphic complex exhumed in the Early - Middle Miocene. This idea was based on limited K-Ar and 40Ar/39Ar age data, but no structural data were presented to provide evidence for the mechanism of exhumation. Here we present new field observations, micro-structural analyses and a revised stratigraphy of NW Sulawesi based on new age data, to provide better constraints on the timing and mechanism of exhumation. The data presented here suggest that the MMC is a metamorphic core complex which underwent lithospheric extension during the Early - Middle Miocene. Although the MMC experienced significant extension, there is no evidence that it was exhumed during this time. There is no contact between the MMC and the Pliocene Ongka Volcanics, contradicting a previously inferred unconformable contact. Pliocene undeformed granitoids intruding the MMC indicate the complex was still at depth during their emplacement. Furthermore, Pliocene and Pleistocene cover sequences do not contain metamorphic detritus. A second phase of extensional uplift was accommodated by brittle faulting from the Late Miocene-Pliocene onwards, during which the MMC was exhumed. This extension is widespread, as indicated by synchronous exhumation of the adjacent Palu Metamorphic Complex in West Sulawesi, and rapid subsidence offshore in Gorontalo Bay. It is linked to northward slab rollback of the southward-subducting Celebes Sea since the Pliocene. GPS data show rapid northward motion of the North Arm of Sulawesi with respect to the Celebes Sea, indicating that this process is ongoing at present day.

  16. Extension above shallow crustal decollements at ultra-distal magma-poor rifted margins: role and nature of the decoupling layer

    Science.gov (United States)

    Gillard, Morgane; Manatschal, Gianreto; Autin, Julia; Sauter, Daniel; Karner, Garry; Johnson, Christopher

    2017-04-01

    Recent studies of ultra-distal, magma-poor rifted margins show that extension associated with mantle exhumation is more complex than previously proposed. The observation of intense tectonic deformation affecting both the sediments and the exhumed basement questions previous models implying one single detachment fault. The new observations suggest that ultra-distal domains result from polyphase out-of-sequence faulting. However, the factors controlling localization, locking and stepping of faults as well as the rooting levels of these faults remain unconstrained. In seismic sections from ultra-distal margins a reflective interface can be observed located approximately 1 sec (TWT) below the top of the exhumed basement. This reflective interface is well observed along the Australia-Antarctica margins and is also present along the distal Newfoundland margin. In these examples, faults can be seen either to detach onto this reflection, or this reflection can be exhumed in the footwall of detachment faults. These observations suggest that this reflection may have acted as a rooting layer of normal faults thus representing a major rheological interface. However, the nature of this interface is uncertain: does it represent a serpentinization front, a level of magmatic underplating or magma-infiltration, or a combination of the three? In our presentation, we discuss how and when this reflection may have been created relative to mantle exhumation and magma emplacement and how it interacts with detachment faults and normal faults. Particular attention will be paid to the interaction with magmatic supply as it appears that this interface could represent a boundary where melt can be trapped. Further, we will compare our observations with those made at ultra-slow spreading ridges and ophiolites. We also propose a model in which this interface may control the mode of extension observed at ultra-distal, exhumed mantle domains.

  17. Constraining thrust-belt thermal histories from partially reset zircon (U-Th)/He datasets: An "inheritance envelope" approach with examples from the Sevier belt of central Utah

    Science.gov (United States)

    Guenthner, W.; Reiners, P. W.; DeCelles, P. G.; Kendall, J. J.

    2015-12-01

    Low-temperature thermochronology has become an established tool for deciphering the time-temperature (t-T) histories of sedimentary units involved in basin burial and thrust-belt exhumation. However, thermochronologic datasets from detrital samples can be complex and difficult to interpret if these samples contain grains with different pre-depositional t-T histories that are only partially reset. Here, we present an approach for interpreting complex detrital zircon (U-TH)/He datasets to constrain the maximum foreland basin burial temperatures and timing of thrust-belt related exhumation in the Sevier belt of central Utah. Using forward modeling of t-T paths, we combine the radiation-damage based kinetic model for He diffusion in zircon with a series of pre-depositional He ages to construct "inheritance envelopes" that encompass a wide range of age variation. A forward model is successful if an inheritance envelope captures or bounds the observed age variation in a given dataset. We highlight this approach with two datasets collected from sedimentary units in the Oquirrh Mountains and Wasatch Range near Provo, UT. For the Oquirrh Mtns. dataset, large observed age variation is modeled using a maximum burial temperature of ~173 °C, and an initial Sevier-belt related exhumation event at 110 Ma. The Wasatch Range samples are more straight-forward, with a lack of partially reset ages but some observed variation caused by radiation damage effects. For these samples, our model results constrain a maximum burial temperature of ~230 °C, with a subsequent exhumation event at 100 Ma. Combined, these results suggest a steady eastward migration of exhumation in the Sevier belt during the Late Cretaceous and demonstrate that our inheritance envelope approach is most sensitive to maximum burial temperatures and the timing of initial exhumation.

  18. Secuencia de exhumación de las unidades cabalgantes de zócalo de los Pirineos centro-occidentales a partirdel análisis de huellas de fisión en apatito

    OpenAIRE

    Labaume, Pierre; MERESSE, Florian; Jolivet, Marc; Teixell, Antonio

    2016-01-01

    International audience; Compilation of new and published apatite fission track data along atransect of the west-central Pyrenees shows that exhumation across thePartial Annealing Zone (~120–60°C) started during the mid Eocene inthe North-Pyrenean Zone and migrated southward to reach the southernedge of the Axial Zone during the early Miocene. An early Miocene stageof exhumation is also detected in the northern part of the Axial Zone,indicating a late pop-up thrust reactivation of the Axial Zo...

  19. The Late Cenozoic Climatic and Tectonic Evolution of the Mount Everest Region, Central Himalaya

    Science.gov (United States)

    Schultz, Mary Hannah

    The collision of India and Eurasia constructed the Himalayan Mountains. Questions remain regarding how subsequent exhumation by climatic and tectonic processes shaped the landscape throughout the Late Cenozoic to create the complex architecture observed today. The Mount Everest region underwent tectonic denudation by extension and bestrides one of the world's most significant rain shadows. Also, glacial and fluvial processes eroded the Everest massif over shorter timescales. In this work, I review new bedrock and detrital thermochronological and geochronological data and both one- and two-dimensional thermal-mechanical modeling that provides insights on the age range and rates of tectonic and erosional processes in this region. A strand of the South Tibetan detachment system (STDS), a series of prominent normal-sense structures that dip to the north and strike along the Himalayan spine, is exposed in the Rongbuk valley near Everest. Using thermochronometric techniques, thermal-kinematic modeling, and published (U-Th)/Pb geochronology, I show exhumation rates were high ( 3-4 mm/a) from at least 20 to 13 Ma because of slip on the STDS. Subsequently, exhumation rates dropped drastically to ≤ 0.5 mm/a and remain low today. However, thermochronometric datasets and thermal-kinematic modeling results from Nepal south of Everest reveal a sharp transition in cooling ages and exhumation rates across a major knickpoint in the river profile, corresponding to the modern-day Himalayan rainfall transition. To the north of this transition, exhumation histories are similar to those in Tibet. Conversely, < 3 km south of the transition, exhumation rates were relatively low until the Pliocene, when they increased to 4 mm/a before slowing at 3 Ma. Such contrasting exhumation histories over a short distance suggest that bedrock exhumation rates correlate with modern precipitation patterns in deep time, however, there are competing interpretations regarding this correlation. My work

  20. LATE TRIASSIC OBLIQUE EXTRUSION OF UHP/HP COMPLEXES IN THE ATBASHI ACCRETIONARY COMPLEX OF SOUTH TIANSHAN, KYRGYZSTAN

    Directory of Open Access Journals (Sweden)

    Wenjiao Xiao

    2017-01-01

    Full Text Available The exhumation and tectonic emplacement of eclogites and blueschists take place in forearc accretionary complexes by either forearc- or backarc-directed extrusion, but few examples have been well analysed in detail. Here we present an example of oblique wedge extrusion of UHP/HP rocks in the Atbashi accretionary complex of the Kyrgyz South Tianshan.

  1. Chaotic thermohaline convection in low-porosity hydrothermal systems

    NARCIS (Netherlands)

    Schoofs, Stan; Spera, Frank J.; Hansen, Ulrich

    1999-01-01

    Fluids circulate through the Earth's crust perhaps down to depths as great as 5^15 km, based on oxygen isotope systematics of exhumed metamorphic terrains, geothermal fields, mesozonal batholithic rocks and analysis of obducted ophiolites. Hydrothermal flows are driven by both thermal and chemical

  2. Post-Variscan evolution of the Anti-Atlas belt of Morocco constrained from low-temperature geochronology

    Science.gov (United States)

    Gouiza, M.; Charton, R.; Bertotti, G.; Andriessen, P.; Storms, J. E. A.

    2017-03-01

    The Anti-Atlas belt of Morocco extends ENE-WSW, over more than 600 km, from the Atlantic margin in the west to the interior of the African plate in the east. It exhibits Precambrian rocks outcropping as basement inliers and surrounded by marine Ediacaran-Cambrian sequences around the axis of the mountain range. The belt, which has for a long time been interpreted as of Variscan age, is now revealed to have experienced major vertical movements through Mesozoic and Cenozoic times. Thereby, the Anti-Atlas domain appears to be affected by two episodes of exhumation separated by an episode of subsidence. The initial episode occurred in the Late Triassic and led to the exhumation of 7.5-10.5 km of crustal rocks by the end of the Middle Jurassic (ca. 160-150 Ma). The following phase resulted in 1-3 km of basement subsidence and occurred during the Late Jurassic and most of the Early Cretaceous. The basement rocks were then slowly brought to the surface after experiencing 2-3.5 km of exhumation throughout the Late Cretaceous and the Cenozoic. The timing of these episodes of exhumation and subsidence coincides with major tectonic and thermal events in relation with the evolution of the Atlantic and Tethys Oceans, indicating that the effects of their rifting and drifting extended beyond their presumed margins.

  3. The significance of Gosau-type basins for the Late Cretaceous tectonic history of the Alpine-Carpathian Belt.

    NARCIS (Netherlands)

    Willingshofer, E.; Neubauer, F.; Cloetingh, S.A.P.L.

    1999-01-01

    A key feature of Late Creataceous tectonics throughout the Alpine-Carpathian-Pannonian (ALCAPA) region is the synchronous formation of sedimentary basins (Gosau basins) and exhumation of metamorphic domes. Initial subsidence, spatially varying in time (Cenomanian-Santonian), within Gosau-type basins

  4. Seawater storage and element transfer associated with mantle serpentinization in magma-poor rifted margins: A quantitative approach

    Science.gov (United States)

    Pinto, Victor Hugo G.; Manatschal, Gianreto; Karpoff, Anne Marie; Ulrich, Marc; Viana, Adriano R.

    2017-02-01

    Continental breakup in magma-poor rifted margins can develop, in some instances, after the formation of a wide exhumed domain that can be several hundreds of km wide. As exhumation of the continental mantle occurs serpentinization, due to seawater circulation, can extend as far down as 5-6 km, as observed in refraction seismic data. The impact caused by the process of serpentinization within the evolving ocean may have the potential to change: (i) seawater chemistry; (ii) sustain the evolution of primitive life; (iii) control depositional environments; and (iv) form weak zones preferentially used during the formation, reactivation and subduction of distal rifted margins. Based on geological observations, and geophysical and geochemical data from present-day and fossil zones of exhumed continental mantle, we present a first-order quantification showing that approximately 0.380 km3 of water per km2 can be stored in the mantle. Using simple methods, it can be shown that serpentinization may account for a significant loss of Si, Mg, Fe, Mn, Ca, Ni and Cr during serpentinization of mantle rocks. In particular during latest stages of rifting, when basins are often restricted and seaways are not yet connected, exhumation and the serpentinization of large areas of continental mantle may result in a major transfer of elements between the main Earth reservoirs, such as the mantle and seawater.

  5. The Anita Peridotite, New Zealand

    DEFF Research Database (Denmark)

    Czertowicz, Tom; Scott, James; Waight, Tod Earle

    2016-01-01

    The orogenic Anita Peridotite in Fiordland, SW New Zealand, provides an opportunity to examine the composition of a large block of upper mantle exhumed from beneath a Cretaceous arc. This Little studied 1km2 km massif is dominated by spinel-facies harzburgite and dunite. Olivine Mg# of 92...

  6. Thermal modeling of the UHP Maksyutov Complex in the south Urals.

    NARCIS (Netherlands)

    drs. Leech, M.; Willingshofer, E.

    2004-01-01

    Two-dimensional thermal modeling of the subduction and exhumation of the ultrahigh-pressure (UHP) Maksyutov Complex in the south Ural Mountains tests factors influencing the low modern heat flow in the Urals and the feeble preservation of UHP index minerals. Best-fit models are obtained with initial

  7. Climatic forcing of asymmetric orogenic evolution in the Eastern Cordillera of Colombia

    NARCIS (Netherlands)

    Mora, A.; Parra, M.; Strecker, M.R.; Sobel, R.A.; Hooghiemstra, H.; Torres, V.; Vallejo Jaramillo, J.

    2008-01-01

    New apatite fission-track data, paleoelevation estimates from paleobotany, and recently acquired geological data from the Eastern Cordillera of Colombia document the onset of increased exhumation rates in the northeastern Andes at ca. 3 Ma. The Eastern Cordillera forms an efficient orographic

  8. The influence of preburial insect access on the decomposition rate.

    Science.gov (United States)

    Bachmann, Jutta; Simmons, Tal

    2010-07-01

    This study compared total body score (TBS) in buried remains (35 cm depth) with and without insect access prior to burial. Sixty rabbit carcasses were exhumed at 50 accumulated degree day (ADD) intervals. Weight loss, TBS, intra-abdominal decomposition, carcass/soil interface temperature, and below-carcass soil pH were recorded and analyzed. Results showed significant differences (p human remains.

  9. Shear zone liquefaction in mass transport deposit emplacement : A multi-scale integration of seismic reflection and outcrop data

    NARCIS (Netherlands)

    Ogata, K.; Mountjoy, J. J.; Pini, Gian Andrea; Festa, A.; Tinterri, R.

    2014-01-01

    We present the integrated outcrop-geophysical study of two mass transport complexes, the exhumed Specchio unit in the Northern Apennines of Italy and the Holocene Poverty unit in the Hikurangi margin of New Zealand. The combination of micro- to meso-scale structural, stratigraphic and sedimentologic

  10. Kinematics of the southern Rhodope Core Complex (North Greece).

    NARCIS (Netherlands)

    Brun, J.P.; Sokoutis, D.

    2007-01-01

    The Southern Rhodope Core Complex is a wide metamorphic dome exhumed in the northern Aegean as a result of large-scale extension from mid-Eocene to mid-Miocene times. Its roughly triangular shape is bordered on the SW by the Jurassic and Cretaceous metamorphic units of the Serbo-Macedonian in the

  11. Antecedence of the Yarlung-Siang-Brahmaputra River, eastern Himalaya

    Science.gov (United States)

    Lang, Karl A.; Huntington, Katharine W.

    2014-07-01

    At the eastern terminus of the Himalayan orogen, distortion and capture of southeast Asian drainage basins reflects regional patterns of crustal strain due to the indentation of the Indian Plate into Eurasia. After flowing eastward >1000 km along the southern margin of Tibet, the Yarlung-Siang-Brahmaputra River turns abruptly southward through the eastern Himalayan syntaxis rapidly exhuming a crustal scale antiform in an impressive >2 km knickpoint. This conspicuous drainage pattern and coincidence of focused fluvial incision and rapid rock exhumation has been explained by the capture of an ancestral, high-elevation Yarlung River by headward erosion of a Himalayan tributary. However, recent observation of Tibetan detritus in Neogene foreland basin units complicates this explanation, requiring a connection from Tibet to the foreland prior to the estimated onset of rapid rock exhumation. We constrain the sedimentary provenance of foreland basin units deposited near the Brahmaputra River confluence in the eastern Himalayan foreland basin using detrital zircon U-Pb geochronology. We interpret the significant presence of Gangdese-age detritus in each foreland basin unit to indicate that connection of the Yarlung-Siang-Brahmaputra River was established during, or prior to foreland deposition in the Early Miocene. Our results indicate that connection of the Yarlung-Siang-Brahmaputra River precedes exhumation of the syntaxis, demonstrating the potential for the progressive coevolution of rock uplift and rapid erosion of the Namche Barwa massif.

  12. [Reconstructive investigations and identification measures in unknown soldiers of the Second World War].

    Science.gov (United States)

    Jopp-van Well, Eilin; Gehl, Axel; Säring, Dennis; Amling, Michael; Hahn, Michael; Sperhake, Jan; Augustin, Christa; Krebs, Oliver; Püschel, Klaus

    2016-01-01

    The article reports on the exhumation and identification of unknown soldiers from the Second World War. With the help of medicolegal investigation and reconstruction methods an American pilot presumably murdered by a shot to the head (lynch law) and an interned Italian soldier could be identified after about 70 years and brought back home.

  13. Current State of Public Cemeteries in Rivers State, Nigeria

    African Journals Online (AJOL)

    DATONYE ALASIA

    In archeology and medical research, places and events have been dated from findings in cemeteries. In forensics and autopsies, cemeteries have been used to solve crimes from the exhumation and pathological examination of dead bodies. They have also been known to be places of meditation and worship. Revenue ...

  14. Limits of windthrow-driven hillslope sediment flux due to varying storm frequency and intensity

    NARCIS (Netherlands)

    Constatine, J.A.; Schelhaas, M.J.; Gabet, E.; Mudd, S.M.

    2012-01-01

    The uprooting and toppling of trees during storms transports soil, exhumes bedrock, and thus influences the evolution of hillslopes. Given predicted increased storminess due to future climate change, we adapt a forest-gap model (ForGEM) to explore windthrow-driven sediment transport in a Douglas fir

  15. Post-rift vertical movements and horizontal deformations in the eastern margin of the Central Atlantic : Middle Jurassic to Early Cretaceous evolution of Morocco

    NARCIS (Netherlands)

    Bertotti, G.; Gouiza, M.

    2012-01-01

    Wide regions of Morocco, from the Meseta to the High Atlas, have experienced km-scale upward vertical movements during Middle Jurassic to Early Cretaceous times following the appearance of oceanic crust in the Central Atlantic. The area experiencing exhumation was flanked to the W by a domain of

  16. The upper Jurassic-lower cretaceous siliciclastic system in the Morocco offshore - Prevenance, transport and deposition

    NARCIS (Netherlands)

    Bertotti, G.; Arantegui, A.; Charton, R.; Luber, T.; Redfern, J.

    2015-01-01

    The Morocco segment of the Central Atlantic passive continental margin experienced km-scale exhumation during the early post-rift (late Jurassic-Early Cretaceous). In the Meseta and the High Atlas this led to the development of a N-S trending ridge sourcing terrigenous sediments which were brought

  17. STRESS CRACKING BEHAVIOR OF HDPE GEOMEMBRANES AND ITS PREVENTION

    Science.gov (United States)

    Geomembranes made from high density polyethylene (HOPE) have a high percent crystallinity and are therefore of concern with regard to stress cracking. A review of the literature plus our field exhuming of various sites-of-opportunity gave rise to twenty-five (25) situations wh...

  18. Fission-track evidence of tectonic evolution in the northwestern ...

    Indian Academy of Sciences (India)

    8

    Tagh fault commenced strike-slip movement (Yue et al., 2001; Yue et al., 2004;. Zhang et al., 2012). .... the deep part of the Altyn Tagh region commenced ductile strike-slip movement (Fig. 4a; Liu et al., ..... 29(2–3), 430-439. Patel, R.C., Singh, P. 2016, Post-Emplacement kinematics and exhumation history of the Almora.

  19. The post-orogenic evolution of the Northeast Greenland Caledonides constrained from apatite fission track analysis and inverse geodynamic modelling

    DEFF Research Database (Denmark)

    Pedersen, Vivi Kathrine; Nielsen, S.B.; Gallagher, Kerry

    2012-01-01

    or deposition, and thermal histories are found by solving the one-dimensional transient conduction–advection heat equation. These thermal histories are used with the observed fission track data to constrain acceptable strain rate histories and exhumation paths. The results suggest that rifting has been focused...

  20. WAft GRAVES REf.ISTERS., MONIJMENTS., HEADSTONES AND f ...

    African Journals Online (AJOL)

    military cemetery. Four days after the burials, the bodies of the British officers were exhumed and taken back to Mount Prospect for reburial. The unit which suffered the highest casualties was the. 60th Rifles, which later erected a fine memorial bearing the names of the fallen. Several years ago this was vandalised and had ...

  1. Tectonic imprints within a granite exposed near Srinagar, Rajasthan ...

    Indian Academy of Sciences (India)

    Partial melting in the middle to lower crustal level produces melts of granitic composition during orogeny. Thrusts play a vital role in their exhumation after consolidation of these granitic melts. In this paper we focus on one such granite along the eastern margin of the Delhi Fold Belt (DFB) rocks near Srinagar, Rajasthan, ...

  2. Dover Port Mortuary Independent Review Subcommittee Final Report

    Science.gov (United States)

    2012-02-01

    divisions: Embalming and Transportation, Forensic and Clinical Autopsy /Investigation, Cemetery (Exhumations & Grave Openings), Embalming Consulting, and... autopsy ); improper handling and transport of fetal remains of military dependents; and improper handling of cases of missing portions of remains...lives; and providing comprehensive forensic investigative services. AFMES serves on behalf of the Secretary of Defense and under the ES2 Defense

  3. Linking time-Temperature history of the Aquitaine basin with post-orogenic evolution of the Pyrenees : new insights from borehole thermochronology

    Science.gov (United States)

    Fillon, Charlotte; Calassou, Sylvain; Mouthereau, Frédéric; Pik, Raphaël; Bellahsen, Nicolas; Gautheron, Cécile

    2017-04-01

    Within their sedimentary record, foreland basins document vertical movements of the lithosphere, climatic changes, paleogeograhic evolution but also history of exhumation of the adjacent mountain belt. Comparing vertical movements in a range and in its foreland is key to identify processes involved in growth and destruction of mountain belts. The Aquitaine basin, geomorphologically stable since the early Pyrenean orogenesis has the potential to help understanding the driving mechanisms during the late to post-orogenic phases, but the lack of outcrops makes the studies particularly difficult to achieve. To bring a new point of vue on the processes involved in the Cenozoic exhumation of this range, we present new low-Temperature thermochronology data from boreholes of the Aquitaine basin. With the objectives to study rift-related to post-orogenic processes, numerous low-T thermochronological ages ( 300 across the range) have been published, documenting pre-, syn- , and post-orogenic exhumation in the Pyrenees. Using thermal modeling of a new low-T database in the western Axial Zone, we show that a late Miocene (around 10 Ma) uplift occured in the western Pyrenees, which generalizes the post-orogenic signal already detected in the south central Pyrenees. In previous studies, we linked the post-orogenic exhumation in the Southern Pyrenees to the excavation of the foreland valleys caused by the opening of the endorheic Ebro basin towards the Mediterranean Sea. To the West, the tectonic out-of sequence reactivation of the Gavarnie thrust has been invoked to explain the late Miocene AHe ages in the Bielsa massif. These new data might lead us to re-think the causes for such an exhumation signal during "post-orogenic" times. We thus summarize all evidences for the post-orogenic phase and attempt to provide explanation for it: is exhumation driven by Aquitaine foreland basin evolution? Does it reflect a tectonic reactivation of the Pyrenees? or is the signature of a regional

  4. Active Deformation in the Greater Himalayan Zone in Western Nepal from Inversion of New (U-Th)/He Cooling Ages

    Science.gov (United States)

    Harvey, J. E.; Burbank, D.

    2015-12-01

    Much of the central Himalaya features an abrupt rise in mean elevation from ~1.5 km in the Lesser Himalaya to ~4-5 km Greater Himalaya and Tibetan Plateau. This physiographic transition is known as PT2, and is often interpreted as the surface expression of transport over a ramp in the Main Himalayan Thrust (MHT). In western Nepal, however, the same rise in elevation occurs over two distinct topographic steps (PT2-N and PT2-S). In previous work, Harvey et al. (2015) argue that this anomalous topography is the result of recent southward-migration of mid-crustal deformation along the MHT. Due to the seismogenic potential of the MHT it is important to constrain its geometry in the western Nepal seismic gap, which has not had a large earthquake in over 600 years. To test the above hypothesis, we perform [U-Th]/He dating on 39 apatite and 47 zircon samples collected along seven relief transects throughout western Nepal. We constrain exhumation histories by inverting these new cooling ages with the 3-D thermo-kinematic model Pecube. Five transects collected from the Greater Himalaya north of PT2-N are best fit by relatively rapid exhumation rates (~1-2 km/Myr) since ~4 Ma. The other two, collected from farther south near PT2-S, require rapid (~1-2 km/Myr) exhumation until around 8-11 Ma, followed by much slower (~0.1-0.2 km/Myr) exhumation until at least the late Pliocene. Assuming that exhumation rates reflect uplift rates, the rapid Plio-Pleistocene exhumation in the Greater Himalaya north of PT2-N suggest that this physiographic transition is similar to that at the foot of the Greater Himalaya in central Nepal. It follows that active deformation is occurring along a NW-trend as much as 100 km farther north than would be expected if simply projecting PT2 across western Nepal. This finding is consistent with transport over a more northerly MHT ramp or perhaps oblique slip along the recently identified, surface-breaking WNFZ. Although the geomorphology and microseismicity

  5. Late Cenozoic tectonic evolution of the Ailao Shan-Red River fault (SE Tibet): implications for kinematic change during Plateau growth

    Science.gov (United States)

    Wang, Yang; Zhang, Bo; Schoenbohm, Lindsay; Zhang, Jinjiang; Zhou, Renjie; Hou, Jianjun

    2016-04-01

    The India-Eurasia continental collision has created the Tibetan Plateau, a spectacular example of continental plateaus. Along its southeastern margin, surface uplift, river incision, shear-zone exhumation and displacement along active faults have all interacted to shape the landscape. The Ailao Shan-Red River fault, a continental-scale strike-slip fault striking over 1000 km from the Tibetan Plateau to South China Sea, is an excellent recorder for those processes, providing important insights into the evolution of the southeastern plateau margin. However, its late Cenozoic tectonic evolution still remains elusive. This work presents new structural and stratigraphic data from the Miocene basin in the bend area and apatite (U-Th)/He thermochronological data from the shear zone to put constraints on the timing and nature of structural and geomorphic evolution of the Ailao Shan-Red River fault region. Our observations indicate that the major bend in the fault was a releasing bend in the early Miocene, but became a restraining bend after the late Miocene reversal of displacement. The strata preserved in bend area record the nature and timing of exhumation of the shear zone. Apatite (U-Th)/He data show two phases of rapid exhumation in the Miocene. The first rapid exhumation occurred before 16 Ma, the timing of which is supported by the early Miocene sedimentary record and previous geochronologic results. It may have ended before the formation of a low-relief erosion surface. The second episode of rapid exhumation began at ~14-13 Ma, lasting 2-3Myr. During this interval, the Ailao Shan range may have uplift to the modern elevation and the high relief may have developed along the range due to river incision. Metamorphic clasts from the shear zone were deposited in the Red River valley. Regional compilation reveals a coincidence of tectonic events in the Tibetan Plateau and its surroundings in the middle-late Miocene, indicating dramatic kinematic change during the course

  6. Direct observation of fault zone structure and mechanics in three-dimensions: A study of the SEMP fault system, Austria

    Science.gov (United States)

    Frost, Erik Karl

    Outcrops of the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault system exhumed from depths of ˜4--17 km allow for the direct observation of fault zone structures throughout the crust, and provide insights into the way this fault, and perhaps others, distributes strain in three dimensions. At Gstatterboden, exhumed from ˜4--8 km, grain size distributions and small fault data reveal the presence of a 10-m-wide high-strain core towards which strain localized during fault evolution. Brittle fracture was accommodated via constrained comminution, which only occurs in strain-weakening rheologies and favors localization. Exposures of the SEMP at Lichtensteinklamm and Kitzlochklamm, exhumed from ˜12 km depth, bracket the brittle ductile transition. At these outcrops, the SEMP is characterized by a ˜70-m-wide, cataclastic fault core that has been altered to clays that transitions downward into a wide, ductile shear zone that has accommodated only minor amounts of strain, placing the majority of displacement on the razor-sharp fault contact. Deformation mechanisms transition from cataclasis and minor amounts of dislocation creep in calcite, to dislocation creep in quartz and calcite occurring against a background of fault-normal solution mass transfer. The ductile/ductile-brittle Rinderkarsee shear zone, exhumed from ˜17 km, marks the SEMP's continuation into the Tauern Window and is composed of three distinct shear zones. The southern, 100-m-wide shear zone has accommodated the most strain, and shows evidence for creep-accommodated grain boundary sliding in feldspar and quartz, while incipient shear zones contain ductile quartz and brittle-feldspars that undergo dislocation creep as fluids alter Kspar to muscovite, which localizes strain along felspar grain boundaries, encouraging ductility. These findings are compared to results from other faults exhumed from similar depth ranges, highlighting fundamental fault zone structures and characteristics.

  7. Rock uplift above the subduction megathrust at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

    Science.gov (United States)

    Ferguson, Kelly M.

    Deformation related to the transition from strike-slip to convergent slip during flat-slab subduction of the Yakutat microplate has resulted in regions of focused rock uplift and exhumation. In the St. Elias and Chugach Mountains, faulting related to transpressional processes and bending of fault systems coupled with enhanced glacial erosion causes rapid exhumation. Underplating below the syntaxial bend farther west in the Chugach Mountains and central Prince William Sound causes focused, but less rapid, exhumation. Farther south in the Prince William Sound, plate boundary deformation transitions from strike-slip to nearly full convergence in the Montague Island and Hinchinbrook Island region, which is ˜20 km above the megathrust between the Yakutat microplate and overriding North American Plate. Montague and Hinchinbrook Islands are narrow, elongate, and steep, with a structural grain formed by several megathrust fault splays, some of which slipped during the 1964 M9.2 earthquake. Presented here are 32 new apatite (U-Th)/He (AHe) and 28 new apatite fission-track (AFT) ages from the Montague and Hinchinbrook Island regions. Most AHe ages are Hanning Bay and Patton Bay faults during the 1964 earthquake. AFT ages range from ˜5 Ma to ˜20 Ma and are also younger at the SW end of Montague Island. These ages and corresponding exhumation rates indicate that the Montague and Hinchinbrook Island region is a narrow zone of intense deformation probably related to duplex thrusting along one or more megathrust fault splays. I interpret the rates of rock uplift and exhumation to have increased in the last ˜5 My, especially at the southwest end of the island system and farthest from the region dominated by strike-slip and transpressional deformation to the northeast. The narrow band of deformation along these islands likely represents the northwestern edge of a broader swath of plate boundary deformation between the Montague-Hinchinbrook Island region and the Kayak Island

  8. Premortal data in the process of skeletal remains identification

    Directory of Open Access Journals (Sweden)

    Marinković Nadica

    2012-01-01

    Full Text Available Background/Aim. The basic task of a forensic examiner during the exhumation of mass graves or in mass accidents is to establish identity of a person. The results obtained through these procedures depend on the level of perceptibility of post mortal changes and they are compared with premortal data obtained from family members of those missing or killed. Experience with exhumations has shown significant differences between the results obtained through exhumation and the premortal data. The aim of the study was to suggest the existance of the difference between premortal data and the results obtained by exhumation regarding the some parameters, as well as to direct premortal data colection to the specific skeletal forms. Methods. We performed comparative analysis of the results of exhumation of skeletal remains in a mass grave and the premortal data concerning the identified persons. The least number of individuals in this mass grave was calculated according to the upper parts of the right femur and it helped in calculating the smallest number of individuals in mass graves to be 48. A total of 27 persons were identified. Sex was determined by metrics and morphology of the pelvis. Personal age in the moment of death was determined by morphology features of groin symphisis and morphology of sternal edge of ribs and other parts of scelets observations. The hight was calculated as average results of length of long bones and Rollet coefficients. Results. There was a complete match in terms of sex and age matched within an interval that could be established based on the skeletal remains. All the other parameters were different, however, which made identification significantly more difficult. Conclusion. The premortal data is an important element of identification process and it should be obtained by the forensic doctor and directed towards more detailed examination of the skeletal system.

  9. Pulverization Texturein Fault Damage Zones: A result of Implosion Damage or Dynamic Compressive Stresses?

    Science.gov (United States)

    Rockwell, T. K.; Girty, G.; Whearty, J.; Mitchell, T. M.

    2015-12-01

    Micro-brecciation, or pulverization, is recognized as a fundamental component of the architecture and damage products of many large faults, although the precise mechanisms to produce this damage are debated, with both compressive and tensile mechanisms proposed. We characterized several sites along the San Jacinto fault, southern California, where the total depth of exhumation for the life history of the fault can be determined, to study the confining stresses required for pulverization. In basement rock near Anza, where exhumation is less than 100 m, granitic dikes injected into schist of the Burnt Valley Complex are pulverized out to several meters from the fault core, whereas the schist is brecciated at the macro-scale and contains narrow centimeter-thick seams of black cataclasite. Similar relationships are observed in Horse Canyon, which is exhumed about 400 m below a regional Tertiary erosion surface, where granitic dikes emplaced into schist are pulverized out to distances of several tens of meters from the fault core. These observations imply that very low confining stress is required for micro-brecciation in granitic rock. Unconsolidated sandstones (alluvial fan deposits) along the SJF in Rock House Canyon are undeformed where the deposits are exhumed by about 70 m, but show incipient pulverization (high-density, sub-grain cracking) at 120 m depth of exhumation. Cracks oriented perpendicular to the fault formed in individual quartz and feldspar grains out to a few meters from the fault core. These observations suggest that the confining stress required for onset of pulverization in unconsolidated deposits is on the order of 2-2.5 MPa. As the tensile strength of quartz is an order of magnitude higher than these confining stresses, the most likely mechanism that is producing this damage is dynamic compressive stresses during passage of the rupture front.

  10. Spatial patterns of erosion and landscape evolution in the central Menderes Massif (Western Turkey) revealed by cosmogenic ^{10}Be

    Science.gov (United States)

    Heineke, Caroline; Hetzel, Ralf; Nilius, Nils-Peter; Glotzbach, Christoph; Wölfler, Andreas; Hampel, Andrea; Akal, Cüneyt; Christl, Marcus

    2017-04-01

    In regions undergoing active crustal shortening, rock exhumation occurs exclusively by erosion, whereas in extensional tectonic settings rocks are exhumed by both erosion and normal faulting (e.g. Ring et al., 1999). An ideal region to study the relative contribution of normal faulting vs. erosion to rock exhumation is the central Menderes Massif in Western Turkey, which is bounded by the low-angle Gediz and Büyük Menderes detachment faults (e.g. Gessner et al., 2013). Recent thermochronological data show that the two detachments faults were active contemporaneously during the Pliocene (Buscher et al., 2013; Wölfler et al., in revision). Here we present 10Be erosion rates for 37 catchments to resolve the spatial pattern of erosion across the central Menderes Massif. Our results show that erosion rates for catchments located in the footwall of the Gediz detachment range from 40 to 150 mm/kyr. These relatively low rates indicate that the thick (20-50 m) cataclasites associated with this detachment fault have protected the footwall from significant erosion, which explains why the Gediz detachment is such an outstanding geomorphic feature. A comparison with thermochronological data (Buscher et al., 2013) shows that erosion contributed 10-20% to rock exhumation (0.6-2.0 km/Myr). In contrast, erosion rates from catchments in the footwall of the Büyük Menderes detachment are generally higher, with rates ranging from 140 to 400 mm/kyr. These higher rates are consistent with the observation that the respective catchments expose mechanically weak mica schists and phyllites and have rather steep hillslopes. Together with the fact that the Büyük Menderes detachment is associated with only a relatively thin layer of fault gouge and cataclasite, this explains why the Büyük Menderes detachment is less well preserved than the Gediz detachment despite the contemporaneous activity of both detachments. Furthermore, our data show that erosion contributed 20-40% to the total

  11. Discriminating Sediment Supply versus Accommodation Controls on Late Cretaceous Foreland Basin Stratigraphic Architecture in the Book Cliffs, Utah using Detrital Zircon Double Dating

    Science.gov (United States)

    Bartschi, N.; Saylor, J. E.

    2016-12-01

    Middle to late Campanian strata of the Book Cliffs, Utah record the Late Cretaceous deposition of three clastic wedges in the North American Cordilleran foreland basin east of the Sevier thrust-belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin stratal architecture. There is a significant increase in eastward progradation rate from the Lower to the Upper Castlegate Sandstone. However, the progradation rate decreases in the overlying Bluecastle and Price River formations, as well as the laterally equivalent Farrer and Tuscher formations. Rapid progradation during Upper Castlegate deposition may be caused by increased sediment supply from either rapid exhumation of the Sevier thrust-belt or introduction of a new sediment source. Alternatively, reduced accommodation within the proximal foreland basin from uplifts associated with Laramide deformation, or a transition from flexural to dynamic subsidence, could produce the observed rapid wedge progradation. Changes in sediment provenance and source-area exhumation rate can be identified using a combination of detrital zircon U-Pb geochronology and (U-Th)/He thermochronology. Quantitative comparisons between collected samples and published provenance data indicates an upsection increase in a new sediment source, revealing a significant overall shift in provenance between wedge boundaries. This change in provenance is coupled by an upsection decrease in lag time between the Lower and Upper Castlegate, consistent with an increase in exhumation rate. Conversely, there is no change in lag time between the Upper Castlegate and overlying Price River Formation, suggesting a relatively constant exhumation rate. Near-zero lag times during the Upper Castlegate is consistent with rapid exhumation associated with increased thrusting of the Sevier thrust-belt. Therefore, progradation of the Upper Castlegate can be attributed to an increase in

  12. Unravelling the long-term cooling history of the northern Pyrenees from rifting-to-orogenic evolution

    Science.gov (United States)

    Vacherat, Arnaud; Mouthereau, Frédéric; Pik, Raphaël; Bellahsen, Nicolas; Gautheron, Cécile; Bernet, Matthias; Tibari, Bouchaib; Pinna, Rosella; Daudet, Maxime; Radal, Julien

    2015-04-01

    Providing constraints on the temporal and spatial evolution of shortening in collision zones is key to reconstruct past plate motion. There are increasing evidences that the pre-orogenic architecture of the continental margins controls the development of continental accretion and therefore may be responsible for changes in the timing and rate of thrusting in collisional orogens. How this affect the thermal/exhumational record in the orogens is however little documented. Here, we study the northern Pyrenees (Ariège, Central North-Pyrenean Zone) that is exposed on the retro-wedge side of the orogen. This region developed in the vicinity of a domain that recorded hyper-extension and mantle exhumation and therefore potentially recorded the transition from rifting to collision. Apatite fission-track data from the granitic massifs of the Arize and Trois-Seigneurs Massifs indicate that collision-related exhumation started in the Early Eocene and lasted until Miocene. However, there are only scarce constraints on the former thermal history as there is not enough data from higher temperature thermochronometers. To gain a better resolution of the cooling/exhumation history from rift to mature collisional stage, we provide interpretations from new in-situ apatite and zircon fission-track and (U-Th-Sm)/He from the Arize and Trois Seigneurs massif. During extension, the studied granite recorded spatially variable thermal histories depending on the original rift-related architecture of the massifs. We show that the southern side of the Arize and 3S massif recorded significant cooling at 130-115 Ma from temperatures of 300-350°C, in agreement with RSCM temperatures obtained from the surrounding folded Mesozoic units. The northern sides recorded heating with subsidence. The massifs were rapidly cooled and exhumed between 50 and 35 Ma. Onset of convergence is only recorded in the hot basins as contraction resulted in ductile deformation. In this study, we show that the rift

  13. Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

    Science.gov (United States)

    Ferguson, Kelly M; Armstrong, Phillip A; Arkle Jeanette C,; Haeussler, Peter J.

    2014-01-01

    Megathrust splay fault systems in accretionary prisms have been identified as conduits for long-term plate motion and significant coseismic slip during subduction earthquakes. These fault systems are important because of their role in generating tsunamis, but rarely are emergent above sea level where their long-term (million year) history can be studied. We present 32 apatite (U-Th)/He (AHe) and 27 apatite fission-track (AFT) ages from rocks along an emergent megathrust splay fault system in the Prince William Sound region of Alaska above the shallowly subducting Yakutat microplate. The data show focused exhumation along the Patton Bay megathrust splay fault system since 3–2 Ma. Most AHe ages are younger than 5 Ma; some are as young as 1.1 Ma. AHe ages are youngest at the southwest end of Montague Island, where maximum fault displacement occurred on the Hanning Bay and Patton Bay faults and the highest shoreline uplift occurred during the 1964 earthquake. AFT ages range from ca. 20 to 5 Ma. Age changes across the Montague Strait fault, north of Montague Island, suggest that this fault may be a major structural boundary that acts as backstop to deformation and may be the westward mechanical continuation of the Bagley fault system backstop in the Saint Elias orogen. The regional pattern of ages and corresponding cooling and exhumation rates indicate that the Montague and Hinchinbrook Island splay faults, though separated by only a few kilometers, accommodate kilometer-scale exhumation above a shallowly subducting plate at million year time scales. This long-term pattern of exhumation also reflects short-term seismogenic uplift patterns formed during the 1964 earthquake. The increase in rock uplift and exhumation rate ca. 3–2 Ma is coincident with increased glacial erosion that, in combination with the fault-bounded, narrow width of the islands, has limited topographic development. Increased exhumation starting ca. 3–2 Ma is interpreted to be due to rock uplift

  14. Evolution of the South Atlantic passive continental margin and lithosphere dynamic movement in Southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    Science.gov (United States)

    Krob, Florian; Stippich, Christian; Glasmacher, Ulrich A.; Hackspacher, Peter C.

    2016-04-01

    Passive continental margins are important geoarchives related to mantle dynamics, the breakup of continents, lithospheric dynamics, and other processes. The main concern yields the quantifying long-term lithospheric evolution of the continental margin between São Paulo and Laguna in southeastern Brazil since the Neoproterozoic. We put special emphasis on the reactivation of old fracture zones running into the continent and their constrains on the landscape evolution. In this contribution, we represent already consisting thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4) Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 427.6 (1.8) Ma whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0) Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.52) and 92.0 (1.86) Ma. These thermochronological ages from metamorphic, sedimentary and intrusive rocks show six distinct blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos) with different evolution cut by old fracture zones. Furthermore, models of time-temperature evolution illustrate the differences in Pre- to post-rift exhumation histories of these blocks. The presented data will provide an insight into the complex exhumation history of the continental margin based on the existing literature data on the evolution of the Paraná basin in Brazil and the latest thermochronological data. We used the geological model of the Paraná basin supersequences (Rio Ivaí, Paraná, Gondwana I-III and Bauru) to remodel the subsidence and exhumation history of our consisting thermochronological sample data. First indications include a fast exhumation during the early Paleozoic, a slow shallow (northern blocks) to fast and deep (Laguna block) subduction from middle Paleozoic to Mesozoic time and a extremely fast exhumation during the opening of the South Atlantic

  15. Monazite Growth from the Eocene to the Miocene: New Interpretations of the Metamorphic History of Greater Himalayan Rocks in the Eastern Himalaya

    Science.gov (United States)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Long, S. P.; Kylander-Clark, A. R.

    2015-12-01

    Across the Himalaya, mid- to lower-crustal Greater-Himalayan (GH) rocks have been exhumed during active continent-continent collision. In the eastern Himalaya within Bhutan, GH rocks are divided into an upper and lower level by an intra-GH shear zone, the Kakthang thrust (KT). To decipher the metamorphic, melt-crystallization and exhumation history of the GH rocks exposed above and below the KT, monazite from metapelites and migmatites was dated and trace elements were analyzed by laser-ablation, split-stream ICPMS. The trace elements from the monazite were used to track when the rocks were at near-peak conditions (based on the depletion of HREE and the likely presence of garnet during monazite growth) versus likely undergoing initial exhumation and garnet breakdown (based on an increase in HREE). Samples were collected from two N-S transects that cross the KT in central and eastern Bhutan. The eastern transect reveals a progressive younging of near-peak metamorphism within the GH, with dates of ca. 23-20 Ma for the structurally-highest sample versus ca. 18-16 Ma in the structurally-lowest sample. The youngest dates from all structural levels of the eastern Bhutan metapelites are 13-15 Ma; the same analyses yield higher HREE abundances, suggesting garnet breakdown during their (re)crystallization. The migmatites yield ca. 14-16 Ma melt-crystallization ages, consistent with the GH having undergone cooling and initial exhumation to cause garnet breakdown by ca. 15 Ma. In comparison, the central Bhutan transect reveals older near-peak metamorphic ages, with garnet-stable monazite populations at ca. 48­-46 Ma within the KT zone, ca. 38-30 Ma for rocks in the middle of the upper-GH, and ca. 25-22 Ma for the structurally-highest sample. Youngest monazites from the central Bhutan transect that yield growth or recrystallization at garnet-unstable conditions range from ca. 17-26 Ma. These results suggest earlier metamorphism and exhumation of GH rocks in central Bhutan

  16. Detachment Faults and Grooved Footwalls in Diverse Magmatic and Tectonic Settings

    Science.gov (United States)

    Spencer, J. E.

    2005-12-01

    Grooved slip surfaces produced in diverse geologic settings over an enormous range of scales possibly result from the same basic physical process. Subaerial extrusion of viscous magma in 'squeeze-ups' has produced striated surfaces, as has submarine flow of basaltic magma from beneath seafloor lava-lake crusts. Striations range from mm to cm in wavelength, and decimeters to meters in length. The geologic process of producing linear forms in cooling and solidifying magmas adjacent to a slip surface is imitated in the widely used industrial process of continuous casting. Similar but much larger grooves were possibly produced by continuous casting at tectonic rates. Grooves in continental metamorphic core complexes and their bounding low-angle normal faults have wavelengths of 1-15 km and groove lengths of up to 50 km. Levels of crustal exposure change greatly along some groove axes, with shallow crustal levels indicated by non-mylonitic rocks and pre-exhumation K-Ar mica dates grading laterally into intermediate crustal levels indicated by syn-exhumation mylonitic petrofabrics and K-Ar mica dates. Grooves developed in upper crustal crystalline rocks reflect the irregular shape of the normal fault along which extension began, and are the tilted and exhumed footwalls of such faults. However, where grooves are tens of kilometers long, as in some complexes, either the fault and its down-dip continuation as a mid-crustal mylonitic shear zone formed simultaneously with a grooved form, or the most deeply exhumed rocks were molded into grooves as they flowed laterally and upward into contact with the colder and stronger, grooved underside of the hanging-wall block. In the former option, it remains unexplained why grooved shear zones would develop with identical form to a brittle fault tens of kilometers up dip. In the latter case, the grooves were produced by continuous casting at tectonic rates and scales. Deep-sea metamorphic core complexes show remarkably grooved forms

  17. A study of Central Exclusive Production

    Energy Technology Data Exchange (ETDEWEB)

    Monk, James [Univ. of Manchester (United Kingdom)

    2006-01-01

    Central exclusive production of a system X in a collision between two hadrons h is defined as hh → h + X + h with no other activity apart from the decay products of X. This thesis presents predictions for the production cross section of a CP violating supersymmetric Higgs boson and the radion of the Randall-Sundrum model. The ExHuME Monte Carlo generator was written to simulate central exclusive processes and is described and explored. A comparison to di-jet observations made by the D0 detector at the Tevatron, Fermilab between January and June 2004 is made and the distributions found support the predictions of ExHuME.

  18. Isotope provenance of Eastern Himalayan rivers draining to the south into India, Nepal and Bhutan.

    Science.gov (United States)

    Gemignani, Lorenzo; Wijbrans, Jan; Najman, Yani; van der Beek, Peter

    2015-04-01

    The two syntaxis of the Himalaya (Eastern and western) are exhuming anomalously fast compared to the rest of Himalaya , and various hypothesis and models have been proposed to explain this, including coupled tectonic-erosion model of (Tectonic Aneurism)1-2 and ductile extrusion of weak lower crust from beneath Tibet by 'channel flow' 3 . The Namche Barwa metamorphic massif constitutes the eastern syntaxis of the belt and has experienced a complex history of uplift and deformation both influenced by intense fluvial erosion associated with the Yarlung-Tzangpo. Therefore, the Himalayas represent a unique natural laboratory where the interactions between the tectonics, erosion, climate and drainage evolution can be investigated. The purpose of the work is to understand in collaboration with other PhD students and European researchers collaborating in the iTECC Marie Curie Initial training Network the importance of processes involving the complex links and feedbacks between climate, tectonics and erosion. In this multi-disciplinary and multi-technique study the mains goals will be to assess the timing of rapid exhumation, to determine provenance source area exhumation of the syntaxis in relation to the big river capture event that has implicates the Yarlung-Tsangpo by the Brahmaputra, and the effect of the dilution of the syntaxis signal 's downstream. During the work the 40Ar/39Ar dating of single-grain detrital micas technique will be used to analyze smaller and younger grains using newly developed high sensitivity multi-collection noble gas mass spectrometry. Detrital zircon fission-track is perform to provides robust cooling age time of the sources terrains. Input from eastern syntaxis has been identified in the Brahmaputra sedimentary record by the appearance of very young grains (from 10 Ma to 6 Ma)4. To compare and to increase the previously collected data, fifteen samples from the Yarlung-Brahmaputra River system and from tributaries draining the Himalaya, the

  19. Martian Spectacles

    Science.gov (United States)

    2006-01-01

    19 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a pair of partially-buried impact craters which are being exhumed on a plain east of Hellas in the Promethei Terra region Mars. Location near: 45.5oS, 256.5oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  20. Discriminating Sediment Supply Versus Accommodation Controls on Late Cretaceous Foreland Basin Stratigraphic Architecture in the Book Cliffs, Central Utah Using Double Dating

    Science.gov (United States)

    Bartschi, N.; Saylor, J. E.; Lapen, T. J.; Copeland, P.; Blum, M. D.

    2015-12-01

    Middle to late Campanian strata of the Book Cliffs, Utah record the Late Cretaceous deposition of three clastic wedges in the North American Cordilleran foreland basin east of the Sevier thrust belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin stratal architecture. There is an increase in eastward progradation rate between the Lower and Upper Castlegate Sandstone. However, the progradation rate decreases in the overlying Bluecastle and Price River formations, as well as the laterally equivalent Farrer and Tuscher formations. Rapid progradation during Upper Castlegate deposition may be caused by increased sediment supply from either rapid exhumation of the Sevier thrust belt or changes in the sediment source. Alternatively, reduced accommodation within the proximal foreland basin from uplifts associated with Laramide deformation, or a transition from flexural to dynamic subsidence, could produce the same observed rapid wedge progradation. We identify changes in sediment provenance and source-area exhumation rate using detrital zircon geochronology. Initial detrital zircon U-Pb data reveals a significant up-section and spatial shift in provenance between all wedge boundaries. Quantitative comparisons between new and previously published detrital zircon U-Pb provenance data indicates an overall up-section decrease in thrust-belt-sourced Mesozoic eolianite and North American passive-margin source areas coupled with an increase in southern magmatic arc and Mogollon Highland source. We observe an east-west diachroneity in the arrival of the southern-sourced sediment, but little to no variation from samples along a north-south transect. Initial results suggest the shift in sediment source is not consistent with an increased exhumation rate of the source area, although further work using thermochronology is required to better understand the exhumation rate.

  1. First thermochronological constraints on the Cenozoic extension along the Balkan fold-thrust belt (Central Stara Planina Mountains, Bulgaria)

    Science.gov (United States)

    Kounov, Alexandre; Gerdjikov, Ianko; Vangelov, Dian; Balkanska, Eleonora; Lazarova, Anna; Georgiev, Stoyan; Blunt, Edward; Stockli, Daniel

    2017-11-01

    The Balkan fold-thrust belt, exposed in Bulgaria and north-east Serbia, is part of the north-east vergent segment of the bi-vergent Eastern Mediterranean Alpine orogen. It was formed during two distinct compressional stages; the first one lasted from the Middle Jurassic to the Early Cretaceous and the second from Late Cretaceous to the Paleogene. Although the compressional tectonic evolution of the Balkan fold-thrust belt since the Middle Jurassic and during most of the Mesozoic is relatively well studied, the final exhumation of the rocks of the belt during the Cenozoic has remained poorly understood. Here, we present the first thermochronological constraints, based on fission-track and [U-Th-(Sm)]/He analysis, showing that along the central part of the belt syn- to post-orogenic extension could have started as early as the middle Eocene. Low-temperature thermochronological analysis of samples collected from three areas reveals at least two phases of increased cooling and exhumation during the Cenozoic. The first exhumation phase took place between 44 and 30 Ma and appears to be related to the syn- to post-orogenic collapse coeval with the earliest Cenozoic extensional stage observed across the southern Balkan Peninsula. A period of relative quiescence (between 30 and 25 Ma) is followed by the next cooling stage, between 25 and 20 Ma, which appears to be related to late Oligocene to early Miocene crustal extension across the Balkan Peninsula. Extension accommodated by the late Miocene to Recent age Sub-Balkan Graben System does not appear to have produced exhumation of rocks from beneath 2-4 km depth, as it was not detected by the low-temperature thermochronological methods applied in this study.

  2. The Diseases of the Medici Family and the Use of Phytotherapy

    OpenAIRE

    Donatella Lippi

    2007-01-01

    The Medici Project is a paleopathological and historico-medical research, based on the exhumation of corpses of the Medici Family buried in the Medici Chapels (Florence, San Lorenzo). The scientific research carried out on these remains permits us to reconstruct habits and causes of death of members of this famous family of Italian Renaissance. The comparison between the literary sources and the paleopathological evidence is also important to reconstruct different therapies. Physicians, who a...

  3. Transuranic waste assay instrumentation: new developments and directions at the Los Alamos Scientific Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Close, D.A.; Umbarger, C.J.; West, L.; Smith, W.J.; Cates, M.R.; Noel, B.W.; Honey, F.J.; Franks, L.A.; Pigg, J.L.; Trundle, A.S.

    1978-01-01

    The Los Alamos Scientific Laboratory is developing assay instrumentation for the quantitative analysis of transuranic materials found in bulk solid wastes generated by Department of Energy facilities and by the commercial nuclear power industry. This also includes wastes generated in the decontamination and decommissioning of facilities and wastes generated during burial ground exhumation. The assay instrumentation will have a detection capability for the transuranics of less than 10 nCi of activity per gram of waste whenever practicable.

  4. Controls on dryland mountain landscape development along the NW Saharan desert margin: Insights from Quaternary river terrace sequences (Dadès River, south-central High Atlas, Morocco)

    DEFF Research Database (Denmark)

    Stokes, M.; Mather, A.E.; Belfoul, M.

    2017-01-01

    between 50 and 140 m. The rock strength, stratigraphy and structure of the mountain belt influences terrace distribution. Terraces are absent in river gorges of structurally thickened limestone; whilst well-developed, laterally continuous terraces (T1-T4) form along wide valleys occupying syncline...... spacing of terraces and their distribution throughout the orogen suggests sustained base-level lowering linked to uplift-exhumation of the High Atlas. Low incision rates (

  5. Effect of the Impact of Chemical and Environmental Factors on the Durability of the High Density Polyethylene (HDPE) Geogrid in a Sanitary Landfill

    OpenAIRE

    Agnieszka Kiersnowska; Eugeniusz Koda; Wojciech Fabianowski; Jacek Kawalec

    2016-01-01

    A high density polyethylene (HDPE) uniaxial geogrid was exhumed after twenty years of service in a sanitary landfill, and its properties were examined. A geogrid installed in a landfill is exposed to mechanical and chemical factors (e.g., a wide pH range and high temperatures), as well as different weather conditions. This paper presents the results of physical and mechanical analyses of virgin and aged HDPE geogrid samples. Structural changes observed by differential scanning calorimetry and...

  6. Initiation of Extension in South China Continental Margin during the Active-Passive Margin Transition: Thermochronological and Kinematic Constraints

    Science.gov (United States)

    Zuo, X.; Chan, L. S.

    2015-12-01

    The South China continental margin is characterized by a widespread magmatic belt, prominent NE-striking faults and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from active to passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in this area. Our zircon fission-track data in this region show two episodes of exhumation: The first episode, occurring during 170-120Ma, affected local parts of the Nanling Range. The second episode, a more regional exhumation event, occurred during 115-70Ma, including the Yunkai Terrane and the Nanling Range. Numerical geodynamic modeling was conducted to simulate the subduction between the paleo-Pacific plate and the South China Block. The modeling results could explain the fact that exhumation of the granite-dominant Nanling Range occurred earlier than that of the gneiss-dominant Yunkai Terrane. In addition to the difference in rock types, the heat from Jurassic-Early Cretaceous magmatism in Nanling may have softened the upper crust, causing the area to exhume more readily than Yunkai. Numerical modeling results also indicate that (1) high lithospheric geothermal gradient, high slab dip angle and low convergence velocity favor the reversal of crustal stress state from compression to extension in the upper continental plate; (2) late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The inversion of stress regime in the continental crust from compression to crustal extension imply that the Late Cretaceous-early Paleogene red-bed basins in South China could have formed during the late stage of the subduction, accounting for the occurrence of volcanic events in some sedimentary basins. We propose that the rifting started as early as Late Cretaceous, probably before the cessation of subduction process.

  7. Controls on Erosion in the Western Tarim Basin: Implications for the Uplift of Northwest Tibet and Pamirs

    Science.gov (United States)

    Clift, P. D.; Zheng, H.; Carter, A.; Böning, P.; Jonell, T. N.; Pahnke, K.

    2016-12-01

    While the processes controlling erosion on the southern monsoon-influenced side of the Tibetan Plateau have been explored, those that dominate the drier regions north of the plateau are less well understood. We use a multiproxy approach to quantify erosion and assess variability in three rivers, the Hotan River draining the North Kunlun Block, the Yarkand River originating from the Karakoram, and the Kashgar River that flows from the eastern Pamirs. U-Pb zircon dating of modern river sands points to a strong control by topography and precipitation mediated through glaciation on erosion intensity in the Yarkand. Apatite fission track ages are younger in the Hotan River than in the Kashgar. Both rivers yield younger ages and faster exhumation rates than in the Transhimalaya and the western edge of the Tibetan Plateau. Exhumation rates are estimated at 1000 m/m.y in the North Kunlun and 500 m/m.y. in the eastern Pamirs, which are exhuming more slowly than the western Pamirs in the recent past. Our data indicate the Yarkand drainage system is relatively young as no sediment similar to the modern Yarkand River is found in older Cenozoic foreland sedimentary rocks. Uplift of the North Kunlun is interpreted to have started by 17 Ma, somewhat after uplift of the Pamirs and Songpan Garze in NW Tibet, which started before 24 Ma. Sediment eroded from the Kunlun reached the foreland basin between 14 and 11 Ma. Uplift appears to be propagating north through time with North Kunlun exhumation accelerating before 3.7 Ma, likely linked to enhanced rock uplift at that time.

  8. Zachování HP minerálů a textur ve světlých a mafických granulitech Rychlebských hor

    OpenAIRE

    Schlöglová, Kateřina

    2011-01-01

    Diploma thesis - Kateřina Schlöglová - 2011 1/2 English abstract Granulites of the Rychleby Mts. represent relics of high-pressure eclogite-facies metamorphic rocks that are scattered in various crustal and mantle segments of the Variscan orogen in central Europe. These rocks may provide important insights into early stages of Variscan plate convergence and burial as well as exhumation mechanisms. We use mineral assemblages and chemistry to reconstruct the pressure-temperature paths, mechanis...

  9. Late Cenozoic extension and crustal doming in the NE Chinese Pamir

    Science.gov (United States)

    Thiede, Rasmus C.; Sobel, Edward R.; Chen, Jie; Schoenbohm, Lindsay; Stockli, Daniel; Sudo, Masafumi; Strecker, Manfred

    2013-04-01

    The northward motion of the Pamir indenter with respect to Eurasia has resulted in coeval thrusting, strike-slip and normal faulting. The eastern Pamir is currently deformed by east-west oriented extension, accompanied by uplift and exhumation of the Kongur Shan (7719 m) and Muztagh Ata (7546 m) gneiss domes. Both domes are an integral part of the footwall of the Kongur Shan Extensional System (KES), a 250-km-long, north-south oriented graben. Why active normal faulting within the Pamir is primarily localized along the KES and not distributed more widely throughout the orogen, has remained unclear. In addition, relatively little is known about how deformation has evolved throughout the Cenozoic, despite refined estimates on present-day crustal deformation rates and microseismicity, which indicate where crustal deformation is presently being accommodated. To better constrain the spatiotemporal evolution of faulting along the KES, we present 39 new apatite fission-track, zircon U-Th-Sm/He, and 40Ar/39Ar cooling ages from a series of footwall transects along the KES graben shoulder. Combining this data with, present day topographic relief, 1D thermo-kinematic and exhumational modeling documents successive stages, rather than synchronous deformation and gneiss dome exhumation. While Kongur-Shan-exhumation started during the late Miocene, Muztagh Ata began earlier and has slowed down since the late Miocene. We present a new model, suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting Alai slab localizes extensional upper-plate deformation along the KES and decouples crustal motion between the Central/Western Pamir and Eastern Pamir/Tarim basin.

  10. Late Cenozoic extension and crustal doming in the India-Eurasia collision zone: New thermochronologic constraints from the NE Chinese Pamir

    Science.gov (United States)

    Thiede, Rasmus C.; Sobel, Edward R.; Chen, Jie; Schoenbohm, Lindsay M.; Stockli, Daniel F.; Sudo, Masafumi; Strecker, Manfred R.

    2013-06-01

    northward motion of the Pamir indenter with respect to Eurasia has resulted in coeval thrusting, strike-slip faulting, and normal faulting. The eastern Pamir is currently deformed by east-west oriented extension, accompanied by uplift and exhumation of the Kongur Shan (7719 m) and Muztagh Ata (7546 m) gneiss domes. Both domes are an integral part of the footwall of the Kongur Shan extensional fault system (KES), a 250 km long, north-south oriented graben. Why active normal faulting within the Pamir is primarily localized along the KES and not distributed more widely throughout the orogen has remained unclear. In addition, relatively little is known about how deformation has evolved throughout the Cenozoic, despite refined estimates on present-day crustal deformation rates and microseismicity, which indicate where crustal deformation is presently being accommodated. To better constrain the spatiotemporal evolution of faulting along the KES, we present 39 new apatite fission track, zircon U-Th-Sm/He, and 40Ar/39Ar cooling ages from a series of footwall transects along the KES graben shoulder. Combining these data with present-day topographic relief, 1-D thermokinematic and exhumational modeling documents successive stages, rather than synchronous deformation and gneiss dome exhumation. While the exhumation of the Kongur Shan commenced during the late Miocene, extensional processes in the Muztagh Ata massif began earlier and have slowed down since the late Miocene. We present a new model of synorogenic extension suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting Alai slab localize extensional upper plate deformation along the KES and decouple crustal motion between the central/western Pamir and eastern Pamir/Tarim basin.

  11. Haights Creek RPM Pipe Failures

    OpenAIRE

    United States Department of the Interior, Bureau of Reclamation

    1994-01-01

    In 1989, Haights Creek Irrigation Company replaced 730 linear feet of 24- and 27-inch-diameter RPM (reinforced plastic mortar) pipe because of several failures. Bureau of Reclamation personnel examined the pipe before and after exhumation, the surrounding soil conditions, and measured diametral deflections. Major longitudinal cracks in the pipe invert appear to be the result of hard spots in the pipe foundation. Some of these hard spots were caused from mounding, or using a mound of soil u...

  12. Indirect dating of deformation: a geochronological study from the Pan African Ajaj shear zone, Saudi Arabia.

    Science.gov (United States)

    Hassan, Mahmoud; Abu-Alam, Tamer; Stüwe, Kurt; Klötzli, Urs

    2013-04-01

    The metamorphic complexes of the Arabian-Nubian Shield were exhumed by different exhumation mechanisms (i.e. in extension or oblique transpression regime) during the Pan African activity of Najd Fault System - the largest pre-Mesozoic shear zone on Earth. The different exhumation mechanisms could be the consequence of (i) orientation of the complexes at slightly different angles with respect to the overall orientation of the principal stresses of the Najd Fault System, (ii) exhumation from different depths, or (iii) change of the stress regime through time. In order to test the third hypothesis, geochronological work will be applied on a representative suite of complexes across the Najd Fault System. In particular we focus on three complexes in the Arabian part of the shield named Qazaz, Hamadat and Wajh. In general, the metamorphic complexes of the Arabian part of the shield exhibit left-lateral transcurrent tectonism along the NW-SE Najd faults and right-lateral movement along conjugate NE-SW striking structures. The whole unit forms an anastomosing network of planar structures that demarcate large fish-shaped bodies of high grade metamorphics. The Hamadat complex is surrounded by a left-lateral greenshist facies WNW-ESE Ajaj shear zone. The complex consists of folds that are strongly pinched to the north and more open to the south marked by a well-developed parallel stretching sub-horizontal lineation. Granite intrusions along and across the Ajaj shear zone may allow testing the timing of the deformation. Deformed and non-deformed samples of these granites will be examined by age dating to determine the absolute timing of the metamorphism and the deformation for the complex. Some 20 samples are currently being prepared for zircon dating. Whilst no results are available at the time of writing of this abstract, they will be presented at EGU 2013.

  13. The use of forensic botany and geology in war crimes investigations in NE Bosnia.

    Science.gov (United States)

    Brown, A G

    2006-11-22

    From 1997 to 2002 the United Nations International Criminal Tribune for the former Yugoslavia (ICTY) undertook the exhumation of mass graves in NE Bosnia as part of the war crimes investigations aimed at providing evidence for the prosecution of war criminals in The Hague. This involved the location and exhumation of seven former mass graves (primary sites) dug following the fall of Srebrenica in July 1995. These primary mass graves were secretly and hurriedly exhumed three months later and most of the bodies or body parts transported and reburied in a large number of secondary sites many of which were subsequently exhumed by ICTY. The aim of the pollen and soil/sediment studies was to provide an 'environmental profile' of the original site of the samples and use this to match the relocated bodies to the original mass graves. This was part of completing the chain of evidence, providing evidence of the scale and organization of the original atrocities and the subsequent attempts to conceal the evidence related to them. All the primary sites were located in areas of contrasting geology, soils and vegetation, and this allowed matching of the sediment transported in intimate contact with the bodies to the original burial sites, which in some cases were also the execution sites. In all, over 24 sites were investigated, over 240 samples collected and analyzed under low power microscopy and 65 pollen sub-samples fully analyzed. The pollen and sediment descriptions were used in conjunction with the mineralogy (using XRD) of primary and secondary sites in order to provide matches. These matches were then compared with matching evidence from ballistic studies and clothing. The evidence has been used in court and is now in the public domain. It is believed this is the first time 'environmental profiling' techniques have been used in a systematic manner in a war crimes investigation.

  14. A long-lived Late Cretaceous-early Eocene extensional province in Anatolia? Structural evidence from the Ivriz Detachment, southern central Turkey

    Science.gov (United States)

    Gürer, Derya; Plunder, Alexis; Kirst, Frederik; Corfu, Fernando; Schmid, Stefan M.; van Hinsbergen, Douwe J. J.

    2018-01-01

    Central Anatolia exposes previously buried and metamorphosed, continent-derived rocks - the Kırşehir and Afyon zones - now covering an area of ∼300 × 400 km. So far, the exhumation history of these rocks has been poorly constrained. We show for the first time that the major, >120 km long, top-NE 'Ivriz' Detachment controlled the exhumation of the HP/LT metamorphic Afyon Zone in southern Central Anatolia. We date its activity at between the latest Cretaceous and early Eocene times. Combined with previously documented isolated extensional detachments found in the Kırşehir Block, our results suggest that a major province governed by extensional exhumation was active throughout Central Anatolia between ∼80 and ∼48 Ma. Although similar in dimension to the Aegean extensional province to the east, the Central Anatolian extensional province is considerably older and was controlled by a different extension direction. From this, we infer that the African slab(s) that subducted below Anatolia must have rolled back relative to the Aegean slab since at least the latest Cretaceous, suggesting that these regions were underlain by a segmented slab. Whether or not these early segments already corresponded to the modern Aegean, Antalya, and Cyprus slab segments remains open for debate, but slab segmentation must have occurred much earlier than previously thought.

  15. Silica Geothermometry Applications in the Taiwan Orogenic Belt

    Directory of Open Access Journals (Sweden)

    Chia-Mei Liu

    2015-01-01

    Full Text Available The silica concentrations from 130 hot spring measurements were calculated and used to indicate the heat flow distribution in the active Taiwan orgenic belt. The heat flow spatial distribution seems to be controlled by the Taiwan arc-continent collision zone tectonic development. Two abnormally high silica heat flow regions, 160 and 190 mW m-2, are identified in northeastern and southeastern Taiwan, respectively. In northeastern Taiwan, the Chingshui area, the data suggests that the anomalous heat flow distribution may be controlled mainly by hot fluids and faults. The highest heat flow in southeastern Taiwan may be generated by heat advection caused by a rapidly uplifting hot crust with a decreasing mature arc-continent collision zone exhumation rate. In addition, we estimated the exhumation rate in different tectonic zones in Southern Taiwan by applying fission track ages and silica heat flow values. The exhumation rates are 1.33, 1.72 - 3.87, and 0.51 - 1.74 mm yr-1 in the tectonic zones around Taiwan for advanced, initial arc-continent collision and accretionary wedge deformation, respectively.

  16. Erosion of the French Alpine foreland controlled by crustal thickening

    Science.gov (United States)

    Schwartz, Stéphane; Gautheron, Cécile; Audin, Laurence; Nomade, Jérôme; Dumont, Thierry; Barbarand, Jocelyn; Pinna-Jamme, Rosella; van der Beek, Peter

    2017-04-01

    In alpine-type collision belts, deformation of the foreland may occur as a result of forward propagation of thrusting and is generally associated with thin-skinned deformation mobilizing the sedimentary cover in fold-and-thrust belts. Locally, foreland deformation can involve crustal-scale thrusting and produce large-scale exhumation of crystalline basement resulting in significant relief generation. In this study, we investigate the burial and exhumation history of Tertiary flexural basins located in the western Alpine foreland, at the front of the Digne thrust-sheet (SE France), using low-temperature apatite fission-track (AFT) and (U-Th)/He (AHe) thermochronology. Based on the occurrence of partially to totally reset apatite grain ages, we document 3.3 to 4.0 km burial of these basins remnants between 12-6 Ma, related to thin-skinned thrust-sheet emplacement without major relief generation. The onset of exhumation is dated at 6 Ma and is linked to erosion associated with subsequent relief development. This evolution does not appear controlled by major climate changes (Messinian crisis) or by European slab breakoff. Rather, we propose that the erosional history of the Digne thrust-sheet corresponds to basement involvement in foreland deformation, leading to crustal thickening and the incipient formation of a new external crystalline massif. Our study highlights the control of deep-crustal tectonic processes on foreland relief development and its erosional response at mountain fronts.

  17. Miocene thrusting in the eastern Sila Massif: Implication for the evolution of the Calabria-Peloritani orogenic wedge (southern Italy)

    Science.gov (United States)

    Vignaroli, G.; Minelli, L.; Rossetti, F.; Balestrieri, M. L.; Faccenna, C.

    2012-05-01

    Alpine orogens in the central Mediterranean region have revealed the concomitance of crustal extension in back-arc domain and crustal shortening in frontal domain. Quantitative data of deformation in the frontal orogenic wedges are necessary to understand how the shortening-extension pair evolves in terms of structures, orogenic transport, timing, and exhumation rate. This paper deals with kinematics and ages of the frontal thrust systems of the Calabria-Peloritani Arc (Italy) exposed in the eastern Sila Massif. We first present structural fieldwork, onshore and offshore well log data, and new apatite fission-track (AFT) thermochronology. Then, we describe the structural architecture of the studied area as an ENE-verging stacking of thrust sheets involving basement units and syn-orogenic sediments. The AFT study documents that thrust sheets entered the partial annealing zone from 18 Ma to 13 Ma. This Early-Middle Miocene thrusting phase was coeval with exhumation of high-pressure/low temperature metamorphic rocks in the hinterland of the orogen (Coastal Chain area), mainly driven by top-to-the-W extensional tectonics. Opposite kinematic shear senses (contractional top-to-the-E and extensional top-to-the-W) and different exhumation rates (slow in the frontal, more rapid in the hinterland) are framed in a tectonic scenario of a critically tapered orogenic wedge during the eastward retreating of the Apennine slab.

  18. Metamorphic conditions and structural evolution of the Kesebir-Kardamos dome: Rhodope metamorphic complex (Greece-Bulgaria)

    Science.gov (United States)

    Moulas, Evangelos; Schenker, Filippo Luca; Burg, Jean-Pierre; Kostopoulos, Dimitrios

    2017-03-01

    The synmetamorphic nappe system of the Rhodope Metamorphic Complex has been deformed into dome-and-basin structures attributed to syn- to post-convergent exhumation. We document the deformation style and present new thermobarometric and geochronological constraints for the Kesebir-Kardamos dome in southern Bulgaria and northern Greece. The dome consists of a migmatitic core overlain by high-grade thrust sheets. Kinematic indicators indicate a continuum from ductile to brittle conditions during exhumation. Thermodynamic modeling applied to the high-grade, intermediate thrust sheets yielded peak conditions of 1.2 GPa and ca 730 °C. New U-Pb SHRIMP-II dating of zircons from rocks of the same unit revealed Late Jurassic-Early Cretaceous (145 Ma) as the time of metamorphic crystallization; some zircon rims yielded Eocene ages (53 and 44 Ma) interpreted as having been thermally reset owing to coeval granitoid magmatism. The high-grade rocks were covered by Lutetian-Priabonian marine sediments after exhumation. Slumps suggest that sedimentation took place in a tectonically active environment. Our new structural, petrological and geochronological results suggest that the major shear zone in the core of the Kesebir-Kardamos dome is equivalent to the Late Jurassic-Early Cretaceous Nestos Shear Zone. Post-Jurassic metamorphic ages recorded in the Rhodope most likely represent crustal rather than deep subduction geodynamic processes.

  19. Unearthing Truth: Forensic Anthropology, Translocal Memory, and “Provention” in Guatemala

    Directory of Open Access Journals (Sweden)

    Colette G. Mazzucelli

    2015-10-01

    Full Text Available This article deliberately examines the search for truth after decades of conflict in Guatemala. Excavations of mass gravesites and the painstaking exhumation processes carried out by professional forensic anthropology teams continue to allow families to locate lost relatives—reclaiming truth and supporting calls for justice. For Guatemalans, the search for truth now transcends national borders, especially among migrant communities in the United States. The family remains the central unit through which the work of Guatemalan forensic anthropologists is undertaken. In an effort to engender deeper insights about these exhumation processes from a social science perspective, this analysis promotes the use of specific “tools” in Guatemalan forensic anthropology investigations. The first is an exhumations concept map, which yields important questions meant to stimulate meaningful analysis. The second, Story Maps, is a technology application with the potential to mediate digital access to the emerging Guatemalan translocal space. The research in this analysis suggests that these “tools” strengthen Burton’s notion of “provention” in Guatemala.

  20. Preliminary observations of arthropods associated with buried carrion on Oahu.

    Science.gov (United States)

    Rysavy, Noel M; Goff, M Lee

    2015-03-01

    Several studies in Hawaii have focused on arthropod succession and decomposition patterns of surface remains, but the current research presents the first study to focus on shallow burials in this context. Three domestic pig carcasses (Sus scrofa L.) were buried at the depths of 20-40 cm in silty clay loam soil on an exposed ridge on the leeward side of the volcanically formed Koolau Mountain Range. One carcass was exhumed after 3 weeks, another after 6 weeks, and the last carcass was exhumed after 9 weeks. An inventory of arthropod taxa present on the carrion and in the surrounding soil and observations pertaining to decomposition were recorded at each exhumation. The longer the carrion was buried, the greater the diversity of arthropod species that were recovered from the remains. Biomass loss was calculated to be 49% at the 3-week interval, 56% at the 6-week interval, and 59% at the 9-week interval. © 2014 American Academy of Forensic Sciences.

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

    Science.gov (United States)

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

    2014-05-01

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

  2. Timing of strain localization in high-pressure low-temperature shear zones: The argon isotopic record

    Science.gov (United States)

    Laurent, Valentin; Scaillet, Stéphane; Jolivet, Laurent; Augier, Romain

    2017-04-01

    The complex interplay between rheology, temperature and deformation profoundly influences how crustal-scale shear zones form and then evolve across a deforming lithosphere. Understanding early exhumation processes in subduction zones requires quantitative age constraints on the timing of strain localization within high-pressure shear zones. Using both the in situ laser ablation and conventional step-heating 40Ar/39Ar dating (on phengite single grains and populations) methods, this study aims at quantifying the duration of ductile deformation and the timing of strain localization within HP-LT shear zones of the Cycladic Blueschist Unit (CBU, Greece). The rate of this progressive strain localization is unknown, and in general, poorly known in similar geological contexts. Critical to retrieve realistic estimates of rates of strain localization during exhumation, dense 40Ar/39Ar age transects were sampled along shear zones recently identified on Syros and Sifnos islands. There, field observations suggest that deformation progressively localized downward in the CBU during exhumation. In parallel, these shear zones are characterized by different degrees of retrogression from blueschist-facies to greenschist-facies P-T conditions overprinting eclogite-facies record throughout the CBU. Results show straightforward correlations between the degree of retrogression, the finite strain intensity and 40Ar/39Ar ages; the most ductilely deformed and retrograded rocks yielded the youngest 40Ar/39Ar ages. The possible effects of strain localization during exhumation on the record of the argon isotopic system in HP-LT shear zones are addressed. Our results show that strain has localized in shear zones over a 30 Ma long period and that individual shear zones evolve during 7-15 Ma. We also discuss these results at small-scale to see whether deformation and fluid circulations, channelled within shear bands, can homogenize chemical compositions and reset the 40Ar/39Ar isotopic record

  3. Microstructural and fabric characterization of brittle-ductile transitional deformation of middle crustal rocks along the Jinzhou detachment fault zone, Northeast China

    Science.gov (United States)

    Zhang, Juyi; Jiang, Hao; Liu, Junlai

    2017-04-01

    Detachment fault zones (DFZs) of metamorphic core complexes generally root into the middle crust. Exhumed DFZs therefore generally demonstrate structural, microstructural and fabric features characteristic of middle to upper crustal deformation. The Jinzhou detachment fault zone from the Liaonan metamorphic core complex is characterized by the occurrence of a sequence of fault rocks due to progressive shearing along the fault zone during exhumation of the lower plate. From the exhumed fabric zonation, cataclastic rocks formed in the upper crust occur near the Jinzhou master detachment fault, and toward the lower plate gradually changed to mylonites, mylonitic gneisses and migmatitic gneisses. Correspondingly, these fault rocks have various structural, microstructural and fabric characteristics that were formed by different deformation and recrystallization mechanisms from middle to upper crustal levels. At the meanwhile, various structural styles for strain localization were formed in the DFZ. As strain localization occurs, rapid changes in deformation mechanisms are attributed to increases in strain rates or involvement of fluid phases during the brittle-ductile shearing. Optical microscopic studies reveal that deformed quartz aggregates in the lower part of the detachment fault zone are characterized by generation of dynamically recrystallized grains via SGR and BLG recrystallization. Quartz rocks from the upper part of the DFZ have quartz porphyroclasts in a matrix of very fine recrystallized grains. The porphyroclasts have mantles of sub-grains and margins grain boundary bulges. Electron backscattered diffraction technique (EBSD) quartz c-axis fabric analysis suggests that quartz grain aggregates from different parts of the DFZ possess distinct fabric complexities. The c-axis fabrics of deformed quartz aggregates from mylonitic rocks in the lower part of the detachment fault zone preserve Y-maxima which are ascribed to intermediate temperature deformation (500

  4. Late Cretaceous to Miocene cooling patterns in the Eastern Alps reflecting tectonic interactions of the Alps-Adria-Carpathian system

    Science.gov (United States)

    van Gelder, Inge; Willingshofer, Ernst; Schuster, Ralf; Andriessen, Paul; Sokoutis, Dimitrios

    2017-04-01

    New structural and thermochronological (Rb-Sr biotite and zircon and apatite fission track) data constrain the deformation and exhumation history of the eastern most Alps and highlight distinct differences compared to the western Eastern Alps, including the Tauern Window. The new data has been collected along and in the surroundings of the Mur-Mürz fault (MMF), an area that hitherto had a scarce availability of low and medium temperature thermochronological data but is a key area to understand and quantify the influence of processes, such as Pannonian back-arc extension, on the Eastern Alps evolution. The obtained cooling ages document rapid (ca. 15°C/Ma) and diachronous exhumation during the Late Cretaceous to Paleocene with an eastward youngening of cooling ages across a greenschist facies normal shear zone. We interpret this cooling pattern as a post-metamorphic exhumation occurring during Campanian-Maastrichtian synorogenic extension that is characterized by an east directed migration. We suggest that oblique subduction of the Alpine Tethys or slab roll-back driven processes during final closure of the Neotethys could both be mechanisms that drive this eastward migration. Subsequently, the eastern most Alps reflect Eocene to Oligocene slow cooling (ca. 2°C/Ma) suggesting that the region was unaffected by significant crustal thickening or erosion which strongly contrasts with the units exposed in the Tauern Window and surrounding Austroalpine units. The slow cooling continued far into the Miocene and is contemporaneous with early Miocene kinematics that reflect a pre-extrusion NW-SE contraction followed by syn-extrusion NE-SW to NNE-SSW contraction recorded by middle Miocene strike-slip faulting. Field kinematics and cooling ages located on opposite sides of the MMF suggest that lateral extrusion in the eastern most Alps is not associated with significant vertical motions but is rather restricted to lateral motions along dispersed strike-slip faults. This

  5. Late Cenozoic acceleration of erosion in the Southern Central Andes revealed by low-temperature thermochronology

    Science.gov (United States)

    Franziska Stalder, Nadja; Herman, Frédéric; Reiners, Peter W.; Aguilar, German

    2017-04-01

    The Earth's topography is shaped by feedback mechanisms between tectonics, climate, and surface processes. To understand the influence of these interactions on mountain building processes, one can quantify the temporal and spatial history of exhumation using thermochronology. The Andes are a suitable natural laboratory to study such feedbacks, because they result from the steady subduction of the Nazca plate below the South American plate and their meridional extent crosses several global climate zones. Furthermore, the recent growth of regional low-temperature thermochronological studies led to an extensive data coverage, which can now be inverted to estimate the exhumation history at the scale of a mountain range. In this study, we present a total of 172 new thermochronological AHe, ZHe, and AFT bedrock ages filling remaining data gaps between 26°S and 34°S latitude. To avoid dating of emplacement ages instead of exhumation, ZHe and AFT analyses are restricted to pre-Miocene intrusions only present in the northern part of the study area. From about 31°S to 34°S, the study area covers a key transitional zone where topography decreases, precipitation increases, and the subduction regime changes from flat to steep dip angle. ZHe and AFT ages to the north of 33°S indicate erosion rates lower than 0.2 mm/yr since the Paleogene, except for few localized areas showing middle-to-late Miocene increased exhumation in their AHe ages. To the south of 33°S, two AHe age-elevation profiles reveal ages between 0.5 to 3.5 Ma and suggest intensified erosion during the Plio-Pleistocene relative to the northern area, with southward increasing rates from about 1.3 mm/yr to 3.8 mm/yr. The transition occurs more than 150 km south of the tectonic change in the subduction regime. However, the establishment of the modern atmospheric circulation pattern in the late Pliocene led to increased moisture transport to the North and the initiation of glaciations. Higher precipitation and

  6. Extreme extension across Seram and Ambon, eastern Indonesia: evidence for Banda slab rollback

    Science.gov (United States)

    Pownall, J. M.; Hall, R.; Watkinson, I. M.

    2013-09-01

    The island of Seram, which lies in the northern part of the 180°-curved Banda Arc, has previously been interpreted as a fold-and-thrust belt formed during arc-continent collision, which incorporates ophiolites intruded by granites thought to have been produced by anatexis within a metamorphic sole. However, new geological mapping and a re-examination of the field relations cause us to question this model. We instead propose that there is evidence for recent and rapid N-S extension that has caused the high-temperature exhumation of lherzolites beneath low-angle lithospheric detachment faults that induced high-temperature metamorphism and melting in overlying crustal rocks. These "Kobipoto Complex" migmatites include highly residual Al-Mg-rich garnet + cordierite + sillimanite + spinel + corundum granulites (exposed in the Kobipoto Mountains) which contain coexisting spinel + quartz, indicating that peak metamorphic temperatures likely approached 900 °C. Associated with these residual granulites are voluminous Mio-Pliocene granitic diatexites, or "cordierite granites", which crop out on Ambon, western Seram, and in the Kobipoto Mountains and incorporate abundant schlieren of spinel- and sillimanite-bearing residuum. Quaternary "ambonites" (cordierite + garnet dacites) emplaced on Ambon were also evidently sourced from the Kobipoto Complex migmatites as demonstrated by granulite-inherited xenoliths. Exhumation of the hot peridotites and granulite-facies Kobipoto Complex migmatites to shallower structural levels caused greenschist- to lower-amphibolite facies metapelites and amphibolites of the Tehoru Formation to be overprinted by sillimanite-grade metamorphism, migmatisation, and limited localised anatexis to form the Taunusa Complex. The extreme extension required to have driven Kobipoto Complex exhumation evidently occurred throughout Seram and along much of the northern Banda Arc. The lherzolites must have been juxtaposed against the crust at typical

  7. Syn- and post-rift anomalous vertical movements in the eastern Central Atlantic passive margin: a transect across the Moroccan passive continental margin.

    Science.gov (United States)

    Charton, Remi; Bertotti, Giovanni; Arantegui, Angel; Luber, Tim; Redfern, Jonathan

    2017-04-01

    Traditional models of passive margin evolution suggesting generalised regional subsidence with rates decreasing after the break-up have been questioned in the last decade by a number of detailed studies. The occurrence of episodic km-scale exhumation well within the post-rift stage, possibly associated with significant erosion, have been documented along the Atlantic continental margins. Despite the wide-spread and increasing body of evidence supporting post-rift exhumation, there is still limited understanding of the mechanism or scale of these phenomena. Most of these enigmatic vertical movements have been discovered using low-temperature geochronology and time-temperature modelling along strike of passive margins. As proposed in previous work, anomalous upward movements in the exhuming domain are coeval with higher-than-normal downward movements in the subsiding domain. These observations call for an integrated analysis of the entire source-to-sink system as a pre-requisite for a full understanding of the involved tectonics. We reconstruct the geological evolution of a 50km long transect across the Moroccan passive margin from the Western Anti-Atlas (Ifni area) to the offshore passive margin basin. Extending the presently available low-temperature geochronology database and using a new stratigraphic control of the Mesozoic sediments, we present a reconstruction of vertical movements in the area. Further, we integrate this with the analysis of an offshore seismic line and the pattern of vertical movements in the Anti-Atlas as documented in Gouiza et al. (2016). The results based on sampled rocks indicate exhumation by circa 6km after the Variscan orogeny until the Middle Jurassic. During the Late Jurassic to Early Cretaceous the region was subsequently buried by 1-2km, and later exhumed by 1-2km from late Early/Late Cretaceous onwards. From the Permian to present day, the Ifni region is the link between the generally exhuming Anti Atlas and continually subsiding

  8. From Pangaea to the present: geochronology, thermochronology and isotopic tracking of tectonic processes along the Northern Andes

    Science.gov (United States)

    Spikings, R.; Cochrane, R.; Van der Lelij, R.; Villagomez, D.

    2013-05-01

    Triassic - Tertiary rocks within the Central Cordillera of Colombia and Eastern Cordillera of Ecuador provide a record of the rift-to-drift phase of the western Tethys Wilson Cycle, Jurassic steady-state active margin magmatism, Early Cretaceous attenuation of the margin and the formation of new continental crust, and the accretion of an extensive oceanic plateau and arc sequence at ~75 Ma, which shielded juvenile continental crust from tectonic erosion during the Tertiary. The margin remained active throughout the Tertiary, and exhumed in response to changing oceanic plate kinematics and the collision of heterogeneous oceanic crust. We present geochronological, thermochronological, geochemical and Hf, Nd and O isotopic data that provide a highly-temporally resolved record of the evolution of NW Gondwana from Pangaea to the present. Migmatitic leucosomes and S-type granites were emplaced along the NW South American margin during ~275-225 Ma, and tholeiitic amphibolites intruded during ~240 - 225 Ma. These sequences formed during continental rifting in a back-arc, leading to the formation of ophiolite sequences and oceanic crust by ~216 Ma. The Maya and Oaxaquia terranes of Central America may represent parts of the conjugate margin. The NW South American margin remained passive until ~183 Ma, when subduction gave rise to calc-alkaline, I-type granitoids until ~143 Ma. Earliest Cretaceous roll-back extended and exhumed the margin, causing the arc axis to migrate oceanward while the magmatic rocks became progressively more isotopically juvenile. Arc migration opened Early Cretaceous intra-arc basins that were floored by lavas and filled with arc detritus. The arc axis stabilized at ~130-115 Ma and fringed the continental margin outboard of the Jurassic arc. Compression at 120-110 Ma closed the intra-arc basins, exhumed the buttressing continental margin and obducted variably metamorphosed rocks of the east dipping-subduction channel onto the continental margin during

  9. The Subduction of Continental Crust, the Variscan Evolution of the Bohemian Massif, and the Origin of PO Granitoids

    Science.gov (United States)

    Brueckner, H. K.

    2012-04-01

    Slices of continental crust subducted into the mantle during collisional orogeny may either undergo metamorphism and exhumation towards the surface as coherent slab-like or domal high pressure/ultrahigh pressure (HP/UHP) terranes or, if stalled or delayed in the mantle, melt and return towards the surface as magmas, or undergo a combination of exhumation and melting. Some exhumed HP/UHP terranes contain synorogenic granitoid bodies demonstrating melting does occur during exhumation. Therefore, crust that remains trapped in the mantle will also melt when temperatures reach the appropriate solidi through adiabatic decompression and/or conductive heating and/or radioactive decay. Subducted terranes with hydrous phases will undergo hydrate-breakdown melting and could melt during subduction, when stalled in the mantle or during exhumation. Terranes lacking hydrous phases probably require melting by adiabatic decompression as heated crust becomes ductile and rises as diapirs through the mantle wedge. The generated magmas will intrude through the overlying mantle wedge and into the overlying continental crust to form late orogenic and post orogenic (PO) granitoids depending on the time required to reach solidus temperatures. Geochemical characteristics will depend on P-T conditions, the age/chemistry/mineralogy of the subducted terrane (especially the presence or lack of hydrous phases), and the degree of melt interaction (i.e. the traverse length) with the mantle wedge. Melts that significantly traverse the wedge will acquire the hybrid mantle/crust nature of many PO granitoids. Melts generated by adiabatic decompression close to or within the continental crust will retain ancient crustal signatures. The Variscan evolution of the Bohemian Massif involved two episodes of subduction of continental crust: (1), the southward (present coordinates) subduction of Saxo-Thuringia beneath Bohemia (aka Tapla-Barrandia) along an east-west suture at 400-370 Ma followed by, (2), the

  10. Geodynamics of the Carpathian-Pannonian region: Insights from low temperature thermochronology of the Polish and Ukrainian Carpathians

    Science.gov (United States)

    Andreucci, Benedetta; Zattin, Massimiliano; Castelluccio, Ada; Mazzoli, Stefano; Szaniawski, Rafal; Jankowski, Leszek

    2013-04-01

    In recent years, the geodynamic evolution of the Carpathian-Pannonian region has been the subject of a heated scientific debate. This orogenic system formed between the Late Jurassic and the Neogene by the collision of the Alcapa and Tisza-Dacia microplates with the European Platform, and assumed its present-day configuration mainly during the Miocene, when the extensional Pannonian Basin formed in a retro wedge position, while compression was still active along the Carpathian front. The most common and widely accepted interpretation for the Miocene evolution of this region is based on a classical back-arc extension model and subsequent astenospheric upwelling and slab break-off. Nonetheless several authors proposed other possible driving mechanisms for the formation of the Pannonian Basin, such as lithosphere delamination or lithospheric gravitational instability. Thermochronometry provides important constrains to the depths of burial and to the timing and rates of exhumation. Each geodynamic scenario proposed for the Carpathian-Pannonian region implies a different spatial distribution of burial and a different timing of exhumation. In this work we use a compilation of several low-temperature thermochronometric datasets, referred to the Polish and Ukrainian Carpathians, to evaluate their compatibility with the different geodynamic models proposed so far. In order to achieve this goal we examine the spatial distribution of burial depths and of ages and rates of exhumation and we put them in relation with (i) the spatial trend of the relief, (ii) heat flow, (iii) crustal and lithospheric thickness, and (iv) structural setting. We propose a subdivision of the Polish and Ukrainian Carpathians in three different tectonic domains, based on geophysical and structural parameters. Each single area is characterized also by different burial-exhumation history and requires a specific explanation in terms of driving processes. In particular, we infer that exhumation occurred

  11. New insights on the geological evolution of the continental margin of Southeastern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    Science.gov (United States)

    Krob, Florian; Stippich, Christian; Glasmacher, Ulrich A.; Hackspacher, Peter

    2017-04-01

    New insights on the geological evolution of the continental margin of Southeastern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data Krob, F.C.1, Stippich, C. 1, Glasmacher, U.A.1, Hackspacher, P.C.2 (1) Institute of Earth Sciences, Research Group Thermochronology and Archaeometry, Heidelberg University, INF 234, 69120, Heidelberg, Germany (2) Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, Av. 24-A, 1515 Rio Claro, SP, 13506-900, Brazil Passive continental margins are important geoarchives related to mantle dynamics, the breakup of continents, lithospheric dynamics, and other processes. The main concern yields the quantifying long-term lithospheric evolution of the continental margin between São Paulo and Laguna in southeastern Brazil since the Neoproterozoic. We put special emphasis on the reactivation of old fracture zones running into the continent and their constrains on the landscape evolution. In this contribution, we represent already consisting thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4) Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 427.6 (1.8) Ma whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0) Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.52) and 92.0 (1.86) Ma. These thermochronological ages from metamorphic, sedimentary and intrusive rocks show six distinct blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos) with different evolution cut by old fracture zones. Furthermore, models of time-temperature evolution illustrate the differences in Pre- to post-rift exhumation histories of these blocks. The presented data will provide an insight into the complex exhumation history of the continental margin based on the existing literature data on the evolution of the Paraná basin in Brazil and the latest

  12. Uncoupled vs. coupled thrust belt-foreland deformation: a model for northern Patagonia inferred from U-Th/He and apatite fission track dating

    Science.gov (United States)

    Savignano, Elisa; Mazzoli, Stefano; Zattin, Massimiliano; Gautheron, Cécile; Franchini, Marta

    2017-04-01

    The study of the Cretaceous - Cenozoic evolution of the Patagonian Andes represents a great opportunity to investigate the effects of coupling between deep lithospheric processes and near-surface deformation. Low-temperature thermochronological systems are ideally suited for detecting events involving rocks in the uppermost part of the crust because they record time and rates of cooling related to exhumation of the top few kilometers of the crust. The Patagonia region, although characterized by a general continuity of the Andean orogen along its strike, shows an appreciable internal tectonic segmentation (marked by a variable position of the magmatic arc and of the deformation front in the retroarc area) at various latitudes. This complex structural architecture has been interpreted as the result of different processes acting since the Late Cretaceous. The present-day configuration of the southern Andes is interpreted to have been controlled by alternating stages of flat- and steep-slab subduction, which produced shortening and upper plate extension episodes,, respectively. Furthermore, the deformation in this whole retroarc sector varied not only in time (i.e. with major 'cycles' of mountain building and orogenic collapse), but also in space, due to the variable transmission of horizontal compressive stress away from the orogen, that produced an irregular unroofing pattern. In this study, we have integrated field structural observations with new apatite (U-Th)/He data (AHe) and apatite fission-track (AFT) ages in the north Patagonia region (at latitudes between 40° and 44°S) in order to analyse and compare the exhumation patterns from the frontal part of the orogen and from the adjacent foreland sector, as well as to gain new insights into the timing and modes of coupling vs. uncoupling of the deformation between the northern Patagonian fold and thrust belt and its foreland. The obtained data indicate a markedly different unroofing pattern between the 'broken

  13. Architecture of ductile-type, hyper-extended passive margins: Geological constraints from the inverted Cretaceous basin of the North-Pyrenean Zone ('Chaînons Béarnais', Western Pyrenees)

    Science.gov (United States)

    Corre, Benjamin; Lagabrielle, Yves; Labaume, Pierre; Lahfid, Abdeltif; Boulvais, Philippe; Bergamini, Geraldine; Fourcade, Serge; Clerc, Camille

    2017-04-01

    Sub-continental lithospheric mantle rocks are exhumed at the foot of magma-poor distal passive margins as a response to extreme stretching of the continental crust during plate separation. Remnants of the Northern Iberian paleo-passive margin are now exposed in the North-Pyrenean Zone (NPZ) and represent field analogues to study the processes of continental crust thinning and subcontinental mantle exhumation. The NPZ results from the inversion of basins opened between the Iberia and Europa plates during Albo-Cenomanian times. In the western NPZ, the 'Chaînons Béarnais' ranges display a fold-and-thrust structure involving the Mesozoic sedimentary cover, decoupled from its continental basement and associated with peridotite bodies in tectonic contact with Palaeozoic basement lenses of small size. Continental extension developed under hot thermal conditions, as demonstrated by the syn-metamorphic Cretaceous ductile deformation affecting both the crustal basement and the allochthonous Mesozoic cover. In this study, we present structural and geochemical data providing constraints to reconstruct the evolution of the northern Iberia paleo-margin. Field work confirms that the pre-rift Mesozoic cover is intimately associated to mantle rocks and to thin tectonic lenses of crustal basement. It also shows that the pre-rift cover was detached from its bedrock at the Keuper evaporites level and was welded to mantle rocks during their exhumation at the foot of the hyper-extended margin. The crust/mantle detachment fault is a major shear zone characterized by anastomosed shear bands defining a plurimetric phacoidal fabric at the top of the serpentinized mantle. The detachment is marked by a layer of metasomatic rocks, locally 20 meters thick, made of talc-chlorite-pyrite-rich rocks that developped under greenschist facies conditions. Raman Spectroscopy on Carbonaceous Materials (RSCM), performed on the Mesozoic cover reveal that the entire sedimentary pile underwent temperatures

  14. Sensitivity analysis of a variability in rock thermal conductivity concerning implications on the thermal evolution of the Brazilian South Atlantic passive continental margin

    Science.gov (United States)

    Stippich, Christian; Krob, Florian; Glasmacher, Ulrich Anton; Hackspacher, Peter Christian

    2017-04-01

    The aim of the research is to quantify the long-term evolution of the western South Atlantic passive continental margin (SAPCM) in SE-Brazil. Excellent onshore outcrop conditions and extensive pre-rift to post-rift archives between São Paulo and Laguna allow a high precision quantification of exhumation, and rock uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. The research integrates published (Karl et al., 2013) and partly published thermochronological data from Brazil, and test lately published new concepts on causes of long-term landscape and lithospheric evolution in southern Brazil. Six distinct lithospheric blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos), which are separated by fracture zones (Karl et al., 2013) are characterized by individual thermochronological age spectra. Furthermore, the thermal evolution derived by numerical modeling indicates variable post-rift exhumation histories of these blocks. In this context, we will provide information on the causes for the complex exhumation history of the Florianópolis, and adjacent blocks. Following up on our latest publication (Braun et al., 2016) regarding the effect of variability in rock thermal conductivity on exhumation rate estimates we performed a sensitivity analysis to quantify the effect of a differentiated lithospheric crust on the thermal evolution of the Florianópolis block versus exhumation rates estimated from modelling a lithospheric uniform crustal block. The long-term landscape evolution models with process rates were computed with the software code PECUBE (Braun, 2003; Braun et al., 2012). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameters, values, and rates can be constrained. References Braun, J., 2003. Pecube: A new finite element code to solve the 3D heat transport

  15. Magmatic and solid state structures of the Abu Ziran pluton: Deciphering transition from thrusting to extension in the Eastern Desert of Egypt

    Science.gov (United States)

    Fritz, Harald; Loizenbauer, Jürgen; Wallbrecher, Eckart

    2014-11-01

    The 606 Ma old Abu Ziran granite of the Eastern Desert of Egypt intruded the southern margin of the Meatiq dome in a sinistral shear extensional setting. Its emplacement was enabled by a system of NW-trending sinistral shears, related Riedel shears and N-S extensional shear zones and faults. Magmatic flow was east-directed and controlled by Riedel shears that progressively rotated to an orientation favourable for extension. Strain markers that document magmatic flow show eastward decreasing strain together with strain increase from pluton centre to margins. This is explained by Newtonian flow between non-parallel plates and differences in flow velocities across the pluton. Solid state fabrics including shear fabrics, orientation of late magmatic dykes and quartz tension gashes, together with quartz C-axes distributions, document southward extensional shear within the solidified pluton and adjacent host rocks. Extensional shear is correlated with exhumation of the Meatiq dome coeval and soon after pluton solidification (585 Ma). Pressure temperature evolutionary paths, derived from fluid inclusions, show a clockwise path with exhumation by isothermal decompression in the Meatiq dome. By contrast, the overlying volcanosedimentary nappes experienced an anti-clockwise path released by temperature rise due to pluton emplacement followed by isobaric cooling. Quartz fabrics indicate high-temperature coaxial N-S flow in the northern Meatiq dome and lower-temperature, non-coaxial southward flow within the overlaying superficial nappe. This is explained by the exhumation process itself that progressively localised into simple shear domains when rocks approached higher crustal levels. Late extension at ca. 580 Ma was pure shear dominated and resulted in reversal of shear, now dextral, in the western Meatiq shear zone.

  16. Relation between denudation history and sediment supply from apatite fission track thermochronology in the northeast Brazilian Margin

    Science.gov (United States)

    Jelinek, Andrea; Chemale, Farid; Bueno, Gilmar

    2014-05-01

    The aim of this study is to provide a quantitative overview of Mesozoic-Cenozoic morphotectonic evolution and sediment supply to the northeast Brazilian margin. Landscape evolution and denudation histories for the northeastern Brazilian continental margin (Sergipe, Alagoas, Bahia, and Espírito Santo states) were detailed by apatite fission track thermochronology and thermal-history modeling and related with the sedimentological record of the offshore basins of the passive margin for a comparison with their denudational history. Approximately one hundred basement samples were analyzed from the coast to the inland of the Brazilian margin. The apparent fission track ages vary from 360 to 61 Ma and confined fission track lengths vary between 10 and 14.6 µm, indicating that not all of the samples recorded the same cooling events. The results of apatite fission track ages indicate that the area has been eroded regionally since the Mesozoic (Conquista and Borborema Plateaus, and Mantiqueira Range record a Cretaceous-Paleogene onset of exhumation. This timing is consistent with the offshore sedimentary record, wherein a large clastic wedge started forming in the northeastern Sergipe-Alagoas basin, which suggests Sergipe-Alagoas basin records drainage reorganization and extension of the São Francisco River catchment. Interestingly, the Camamu basin, adjacent to the section of the margin does not record syn/post-rift exhumation, does contain a 6-km thick sedimentary succession, which should thus have been derived from more distal sources. The Neogene final denudation is observed throughout the study area and show conspicuous recent exhumation. The post-rift (<40 Ma) offshore sedimentation rates are generally lower than during preceding phases. This final sedimentary succession is thinner in all basins, consistent with limited onshore erosion during this time.

  17. Apatite (U-Th)/He Thermochronometry as an innovative Geothermal Exploration Tool - A case study from the Wassuk Range, Hawthorne, Nevada

    Science.gov (United States)

    Gorynski, K. E.; Stockli, D. F.; Walker, J. D.

    2010-12-01

    A utility-grade geothermal system requires increased, near-surface temperatures (>120°C), water to transfer heat, and structural or sedimentological fluid conduits. In extensional tectonic settings, geothermal anomalies often occur in areas with recent, high strain accumulation and complex faulting (i.e., cross-faults, accommodation zones) where exhumation and uplift of footwall rocks transfer heat, via advection, to the near-surface which is further carried by water through structural fluid conduits. Apatite helium (AHe) thermochronometric footwall age mapping can be used in conjunction with these genetic occurrence models to further focus regional-scale geothermal exploration efforts to areas of probabilistic increased fracture permeability and most recent, rapid footwall exhumation. Furthermore, partially reset apatites resulting from interaction with hydrothermal fluids (>40°C) will show which areas have been hottest most recently. This case study in the Wassuk Range, Hawthrone, NV confirms the utility of AHe thermochronometry as a geothermal exploration tool. A dense grid of footwall samples were collected adjacent to the Hawthorne geothermal anomaly (>85°C BHT) located in the hanging wall of the Wassuk Range block. Our data show that the location of the present-day geothermal anomaly correlates with the location of 1) the most recent episode of rapid footwall exhumation at 3.5-4 Ma, 2) km scale accommodation zones between differentially tilted Wassuk Range blocks, and 3) an elevated Miocene geothermal gradient. Furthermore, anomalously young AHe ages (Hawthorne geothermal anomaly and likely resulted from interaction with a deep-seated geothermal cell or hot hydrothermal fluids.

  18. Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

    Science.gov (United States)

    Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

    1997-01-01

    The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

  19. Identification process in mass graves from the Spanish Civil War I.

    Science.gov (United States)

    Ríos, Luis; Ovejero, José Ignacio Casado; Prieto, Jorge Puente

    2010-06-15

    The identification process of human skeletal remains exhumed from a mass grave from the Spanish Civil War (1936-1939) is presented. Information regarding the presumptive location of the grave and the presumptive number and identities of the persons buried in the grave was collected from interviews and written records from relatives and witnesses, as well as from research at the penitentiary archive. Antemortem individual data were collected from testimonies, and from research from penitentiary, army and civil archives. The consistency between data obtained from testimonies, archives, archaeology and osteology allowed a targeted approach to DNA typing based on the assumption of the finding of a closed synchronic group. Two were the first genetic studies requested: the first study focused in the identification of a family group presumptively buried in the grave, compatible with a group of four skeletons that were associated on the basis of dental non-metric traits; the second study focused on the identification of the youngest person presumptively buried at the grave, compatible with the biologically youngest skeleton exhumed. A complete match between 16 Y-STR loci was observed for the four skeletons, as well as a match between mtDNA profiles of the biologically youngest skeleton and the sister of the youngest person presumptively known to be buried in the grave. These results, together with the accumulated evidence, led to propose the identification of these five persons. To date, identifications have been proposed for 17 out of 46 skeletons exhumed from the grave. (c) 2010 Elsevier Ireland Ltd. All rights reserved.

  20. Landscape maturity, fold growth sequence and structural style in the Kirkuk Embayment of the Zagros, northern Iraq

    Science.gov (United States)

    Obaid, Ahmed K.; Allen, Mark B.

    2017-10-01

    The Kirkuk Embayment is located in the southwest of the Zagros fold-and-thrust belt of Iraq. Like fold-and-thrust belts worldwide, the Zagros is conventionally understood to have grown sequentially towards the foreland. Here we use landscape maturity analysis to understand anticline growth in the embayment. Digital Elevation Model (DEM)-based geomorphic indices Hypsometric Integral (HI), Surface Roughness (SR) and their combination Surface Index (SI) have been applied to quantify landscape maturity. The results inform new ideas for the sequence of anticline growth. Maturity indices are highest for the QaraChauq Anticline in the center of the Embayment, then Makhool/Himreen to the south and lastly, the Kirkuk Anticline to the north. The pattern suggests the growth sequence is not classical 'piggy back' thrusting. This result fits the exhumation record, which is loosely constrained by the stratigraphic exposure level. Favored hypotheses for fold growth order are either i) the folds have grown at different times and out of sequence (QaraChauq first, then Makhool/Himreen, and Kirkuk last), or, ii) the growth occurred with different rates of exhumation but at broadly the same time. There are few constraints from available data on syn-tectonic sedimentation patterns. Fold growth across much of the Embayment might have begun within a limited timeframe in the late Miocene-Pliocene, during the deposition of the Mukdadiyah Formation. Another hypothesis is that folds grew in sequence towards the foreland with different rates of exhumation, but we consider this less likely. We also construct a new cross-section for the Embayment, which indicates limited Cenozoic strain: 5% shortening. Analysis of topography and drainage patterns shows two previously-undescribed anticlines with hydrocarbon trap potential, between the Makhool and QaraChauq anticlines.

  1. Transient Quaternary erosion and tectonic inversion of the Northern Range, Trinidad

    Science.gov (United States)

    Arkle, Jeanette C.; Owen, Lewis A.; Weber, John; Caffee, Marc W.; Hammer, Sarah

    2017-10-01

    Cosmogenic 10Be measured in sediments from Northern Range catchments on the island of Trinidad reveals low millennial-scale rates of erosion (average 40 mm/ka) that increase roughly eightfold, from 11 to 92 mm/ka, eastward across the mountain range. These results, in conjunction with an analysis of mountain morphometrics, are consistent with Quaternary east-side-up tilting of the Northern Range, which has occurred recently ( 100 ka). The highest millennial-scale erosion rates coincide spatially with Quaternary east-side surface uplift (albeit not in magnitude), high modern rainfall rates, low topographic relief, and convex longitudinal stream profiles, indicating transient Quaternary erosion. We interpret that hillslope adjustment and erosion of the Northern Range is buffered from climatic and tectonic forcings by dense tropical vegetation cover, thick saprolite, and porous regolith. Compared with longer-term, thermochronology exhumation rates, we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the Pliocene to the Holocene. We suggest that these combined data sets highlight distinct syn- and post-collisional phases of Northern Range development that are related to a major change in relative Caribbean-South American plate motion from oblique convergence to transform motion. Oblique collision during the mid-Miocene likely caused relatively higher rates of and asymmetric exhumation of the Northern Range. Post-collisional mountain-scale tilting is likely caused by a combination of crustal extension in the Gulf of Paria and by deep subsurface lithospheric detachment processes that drives dynamic topography.

  2. Long distance transport of eclogite and blueschist during early Pacific Ocean subduction rollback

    Science.gov (United States)

    Tamblyn, Renee; Hand, Martin; Kelsey, David; Phillips, Glen; Anczkiewicz, Robert

    2017-04-01

    The Tasmanides in eastern Australia represent a period of continental crustal growth on the western margin of the Pacific Ocean associated with slab rollback from the Cambrian until the Triassic. During rollback numerical models predict that subduction products can become trapped in the forearc (Geyra et al., 2002), and can migrate with the trench as it retreats. In a long-lived subduction controlled regime such as the Tasmanides, this should result in an accumulation of subduction products with protracted geochronological and metamorphic histories. U-Pb, Lu-Hf, Sm-Nd and Ar-Ar geochronology and phase equilibria modelling of lawsonite-eclogite and garnet blueschist in the Southern New England Fold Belt in Australia demonstrate that high-P low-T rocks remained within a subduction setting for c. 40 Ma, from c. 500 to 460 Ma. High-P metamorphic rocks initially formed close to the Australian cratonic margin during the late Cambrian, and were subsequently transported over 1500 Ma oceanward, during which time subducted material continued to accumulate, resulting in the development of complex mélange which records eclogite and blueschist metamorphism and partial exhumation over 40 Ma. The duration of refrigerated metamorphism approximates the extensional evolution of the upper plate which culminated in the development of the Lachlan Fold Belt. The protracted record of eclogite and blueschist metamorphism indicates that rapid exhumation is not necessarily required for preservation of high-pressure metamorphic rocks from subduction systems. Reference: Gerya, T. V., Stockhert, B., & Perchuk, A. L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21(6), 6-1-6-19. doi:10.1029/2002tc001406

  3. Inherited weaknesses control deformation in the flat slab region of Central Argentina

    Science.gov (United States)

    Stevens, A.; Carrapa, B.; Larrovere, M.; Aciar, R. H.

    2015-12-01

    The Sierras Pampeanas region of west-central Argentina has long been considered a geologic type-area for flat-slab induced thick-skinned deformation. Frictional coupling between the horizontal subducting plate and South American lithosphere from ~12 Ma to the present provides an obvious causal mechanism for the basement block uplifts that characterize this region. New low temperature thermochronometry data show basement rocks from the central Sierras Pampeanas (~ longitude 66 ̊ W) including Sierras Cadena de Paiman, Velasco and Mazan retain a cooling history of Paleozoic - Mesozoic tectonics events. Results from this study indicate that less than 2 km of basement has been exhumed since at least the Mesozoic. These trends recorded by both apatite fission track (AFT) and apatite helium (AHe) thermochronometry suggest that recent Mio-Pliocene thick-skinned deformation associated with flat-slab subduction follow inherited zones of weakness from Paleozoic terrane sutures and shear zones and Mesozoic rifting. If a Cenozoic foreland basin exisited in this region, its thickness was minimal and was controlled by paleotopography. Pre-Cenozoic cooling ages in these ranges that now reach as high as 4 km imply significant exhumation of basement rocks before the advent of flat slab subduction in the mid-late Miocene. It also suggests that thick-skinned deformation associated with flat slab subduction may at least be facilitated by inherited crustal-scale weaknesses. At the most, pre-existing zones of weakness may be required in regions of thick-skinned deformation. Although flat-slab subduction plays an important role in the exhumation of the Sierras Pampeanas, it is likely not the sole mechanism responsible for thick-skinned deformation in this region. This insight sheds light on the interpretation of modern and ancient regions of thick-skinned deformation in Cordilleran systems.

  4. Long-term fore-arc basin evolution in response to changing subduction styles in southern Alaska

    Science.gov (United States)

    Finzel, Emily S.; Enkelmann, Eva; Falkowski, Sarah; Hedeen, Tyler

    2016-07-01

    Detrital zircon U-Pb and fission track double-dating and Hf isotopes from the Mesozoic and Cenozoic strata in the southern Alaska fore-arc basin system reveal the effects of two different modes of flat-slab subduction on the evolution of the overriding plate. The southern margin of Alaska has experienced subduction of a spreading-ridge ( 62-50 Ma) and an oceanic plateau ( 40-0 Ma). When a subducting spreading ridge drives slab flattening, our data suggest that after the ridge has moved along strike retro-arc sediment sources to the fore arc become more predominant over more proximal arc sources. Spreading-ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent, thin sedimentary strata in the fore-arc basin. When a subducting oceanic plateau drives slab flattening, our data suggest that basin catchments get smaller and local sediment sources become more predominant. Crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that, combined, create topography and increase rock exhumation rates. Consequently, the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation. The cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages. This study demonstrates the merit of double-dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large-scale tectonic processes in magmatic regions.

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

    Science.gov (United States)

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

    2015-04-01

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

  6. A history of basin inversion, scarp retreat and shallow denudation: The Araripe basin as a keystone for understanding long-term landscape evolution in NE Brazil

    Science.gov (United States)

    Peulvast, Jean-Pierre; Bétard, François

    2015-03-01

    At the border between the states of Ceará and Pernambuco (northeast Brazil), the Chapada do Araripe is a high plateau (800-1000 m a.s.l.) formed by a slab of Cenomanian fluvial sandstone. This caprock is underlain by lacustrine or marine Albian layers and older rift deposits. During the Cretaceous, the Araripe basin lay at a palaeoelevation close to sea-level. Through a presentation and discussion of original field and cartographic data we analyse the mechanisms of topographic inversion in this sedimentary basin in relation to local or regional crustal upwarp. The contrast between the plateau - a weakly dissected structural surface - and the surrounding lowlands is explained through a study of the erosional scarps - cuesta-like landforms and their outliers - that fringe the Chapada. No evidence of local tectonic inversion is found. River incision, spring sapping, landslides and other forms of mass movement are listed as efficient processes of topographic inversion and scarp retreat, the rates and patterns of which appear to be controlled by lithological contrasts and conditions of exhumation of the basement. Geometric relationships with regional stepped surfaces (e.g., the low-elevation Sertaneja Surface), exhumed palaeosurfaces and regional drainage systems are analysed. Our estimation of the amplitude of denudation and topographic inversion (0.6-0.7 km) differs significantly from apatite fission-track-derived estimates reported in recent literature, which would imply burial by considerable thicknesses of younger sediments followed by 1.5 km or more of post-rift denudation - not just in the study area, but also in the Tucano-Jatoba basin to the south. The exhumation and reworking of surrounding basement surfaces probably began during the early Cenozoic, as shown to the northwest of the Chapada by the presence of widespread laterites of probable Palaeogene age. A second stage of topographic inversion occurred during the Oligocene or later. This would correspond to

  7. Constraining lithosphere deformation modes during continental breakup for the Iberia-Newfoundland conjugate rifted margins

    Science.gov (United States)

    Jeanniot, Ludovic; Kusznir, Nick; Mohn, Geoffroy; Manatschal, Gianreto; Cowie, Leanne

    2016-06-01

    A kinematic model of lithosphere and asthenosphere deformation has been used to investigate lithosphere stretching and thinning modes during continental rifting leading to breakup and seafloor spreading. The model has been applied to two conjugate profiles across the Iberia-Newfoundland rifted margins and quantitatively calibrated using observed present-day water loaded subsidence and crustal thickness, together with observed mantle exhumation, subsidence and melting generation histories. The kinematic model uses an evolving prescribed flow-field to deform the lithosphere and asthenosphere leading to lithospheric breakup from which continental crustal thinning, lithosphere thermal evolution, decompression melt initiation and subsidence are predicted. We explore the sensitivity of model predictions to extension rate history, deformation migration and buoyancy induced upwelling. The best fit calibrated models of lithosphere deformation evolution for the Iberia-Newfoundland conjugate margins require; (1) an initial broad region of lithosphere deformation with passive upwelling, (2) lateral migration of deformation, (3) an increase in extension rate with time, (4) focussing of the deformation and (5) buoyancy induced upwelling. The model prediction of exhumed mantle at the Iberia-Newfoundland margins, as observed, requires a critical threshold of melting to be exceeded before melt extraction. The preferred calibrated models predict faster extension rates and earlier continental crustal separation and mantle exhumation for the Iberia Abyssal Plain-Flemish Pass conjugate margin profile than for the Galicia Bank-Flemish Cap profile to the north. The predicted N-S differences in the deformation evolution give insights into the 3D evolution of Iberia-Newfoundland margin crustal separation.

  8. Tracing Landscape Evolution of the Sila Massif using 10Be

    Science.gov (United States)

    Raab, Gerald; Ruppli, Annina; Brandová, Dagmar; Scarciglia, Fabio; Norton, Kevin; Christl, Marcus; Egli, Markus

    2017-04-01

    Erosion distinctly shapes earth's surface and therefore influences landscape and, in particular, also soils. The evolution of landscapes and soils are known to evolve in discontinuous ways over thousands of years. Several studies have tried to compare erosion rates over different time periods, thereby trying to derive a chronology of process rates. These studies, however, often had a catchment-wide approach and, thus, basically lack in a distinction of soil erosion from erosion as a general landscape process. To decipher soil erosion rates over millennia time-scales, new approaches are therefore needed. Landscapes affected by intense erosion and denudation may be characterised by boulder fields or "tor" landforms, i.e. tower-like or dome-shaped, often castellated, residual rock boulders (resistant to erosion) "growing" from gentle landforms. Determining the speed of boulder exhumation, soil erosion rates over different time periods can be deduced. The Sila Massif upland plateau in Calabria (Italy) exhibits boulder fields that seemed to be exhumed over time. 10Be-dating along vertical profiles of such granitic boulders was now used as a new approach to unravel long-term erosional phases and to reconstruct the lowering of the surface. The results cover a time span of the last 140 ka and revealed several phases of their exhumation. The different trends could be connected to specific climate conditions, yet a major tectonic influence could be excluded, as the main uplift ended about 400 ka ago. This new approach provides a new insight into soil erosion and denudation rates during the Pleistocene and Holocene.

  9. Thermochronology of the Sulu ultrahigh-pressure metamorphic terrane: Implications for continental collision and lithospheric thinning

    Science.gov (United States)

    Liu, Li-Ping; Li, Zheng-Xiang; Danišík, Martin; Li, Sanzhong; Evans, Noreen; Jourdan, Fred; Tao, Ni

    2017-08-01

    The thermal history of the Dabie-Sulu orogenic belt provides important constraints on the collision process between the South China and North China blocks during the Mesozoic, and possible lithospheric thinning event(s) in the eastern North China Block. This study reports on the thermal evolution of the Sulu ultrahigh-pressure metamorphic (UHP) terrane using zircon U-Pb geochronology and multiple thermochronology methods such as mica and hornblende 40Ar/39Ar, zircon and apatite fission track, and zircon and apatite (U-Th)/He dating. 40Ar/39Ar and zircon (U-Th)/He data show that the UHP terrane experienced accelerated cooling during 180-160 Ma. This cooling event could be interpreted to have resulted from extensional unroofing of an earlier southward thrusting nappe, or, more likely, an episode of northward thrusting of the UHP rocks as a hanging wall. A subsequent episode of exhumation took place between ca. 125 Ma and 90 Ma as recorded by zircon (U-Th)/He data. This event was more pronounced in the northwest section of the UHP terrane, whereas in the southeast section, the zircon (U-Th)/He system retained Jurassic cooling ages of ca. 180-160 Ma. The mid-Cretaceous episode of exhumation is interpreted to have resulted from crustal extension due to the removal of thickened, enriched mantle. A younger episode of exhumation was recorded by apatite fission track and apatite (U-Th)/He ages at ca. 65-40 Ma. Both latter events were linked to episodic thinning of lithosphere along the Sulu UHP terrane in an extensional environment, likely caused by the roll-back of the Western Pacific subduction system.

  10. The influence of burial heating on the (U-Th)/He system in apatite: Grand Canyon case study

    Science.gov (United States)

    Fox, Matthew; Shuster, David L.

    2014-07-01

    Thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1-2 km of earth's crust, and have thus been pivotal in illuminating topographic development over timescales >0.1 Ma. However, in some cases, different methods have led to conflicting conclusions about timing of valley-scale exhumation. Here, we investigate the case of Western Grand Canyon, USA, where different thermochronological datasets have been interpreted to record very different timings of canyon incision (∼70 Ma versus ∼5 Ma). We present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the Mesozoic can result in incomplete annealing of radiation damage in apatite. In turn, this has a dramatic effect on the temperature sensitivity of the apatite (U-Th)/He system and its ability to record post-burial exhumation. The possibility of incomplete annealing resolves the apparent conflict in time-temperature paths inferred over the last 70 Ma, although it requires temperatures during burial that are lower than predicted by apatite fission track data. A refinement of parameters that prescribe the kinetics of damage annealing and related control on 4He diffusivity in apatite would account for this discrepancy, specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature. These effects will be important for any application of the apatite (U-Th)/He system in geologic settings that experienced prolonged residence (>10 Ma) between 50-150 °C; the approaches developed here provide means to assess these effects.

  11. U-Pb zircon geochronology and phase equilibria modelling of a mafic eclogite from the Sumdo complex of south-east Tibet: Insights into prograde zircon growth and the assembly of the Tibetan plateau

    Science.gov (United States)

    Weller, O. M.; St-Onge, M. R.; Rayner, N.; Waters, D. J.; Searle, M. P.; Palin, R. M.

    2016-10-01

    The Sumdo complex is a Permian-Triassic eclogitic metamorphic belt in south-east Tibet, which marks the location of a suture zone that separates the northern and southern Lhasa terranes. An integrated geochronological and petrological study of a mafic eclogite from the complex has constrained its tectonometamorphic history and provides a case study of zircon growth in eclogite as a product of prograde dissolution-precipitation. In situ U-Pb geochronology indicates that the eclogite contains a single population of zircon with a crystallisation age of 273.6 ± 2.8 Ma. The morphology and chemistry of the zircon grains are consistent with growth by dissolution-precipitation of protolith magmatic zircon. The presence of zircon grains as inclusions in the cores of peak phases indicates that zircon dissolution-precipitation occurred during prograde metamorphism, and calculated pressure and temperature conditions over which mineral inclusions in zircon are stable suggest that the zircon most likely precipitated at 15.5-16.5 kbar and 500-560 °C. Subsequent peak metamorphism is calculated to have reached pressure-temperature conditions of 27 ± 1 kbar and 670 ± 50 °C. Previous studies, which have documented a range of peak metamorphic conditions from high- to ultrahigh-pressure at c. 266-230 Ma, indicate that the Sumdo complex is a composite belt that experienced protracted eclogite exhumation. The results of this study are consistent with this interpretation, and extend the age range of high-pressure metamorphism in the complex to over 40 Myr. Analysis of published pressure-temperature-time data indicates two systematic behaviours within this spread. First, peak metamorphic temperatures declined over time. Second, eclogite exhumation occurred in two discrete intervals: soon after formation, and during the demise of the subduction zone. The latter behaviour serves as a reminder that eclogite exhumation is the exception rather than the rule.

  12. Transitional time of oceanic to continental subduction in the Dabie orogen: Clues from the Triassic age for oceanic eclogites

    Science.gov (United States)

    Cheng, H.; Dufrane, S.; Nakamura, E.; Vervoort, J. D.

    2009-12-01

    Low-temperature and high-pressure eclogites with an oceanic affinity in the western part of the Dabie orogen have been investigated with combined Lu-Hf and U-Pb geochronology. These eclogites formed over a range of temperatures (482-565°C and 1.9-2.2 GPa). Three eclogites, which were sampled from the Gaoqiao country, yield Lu-Hf ages of 240.7 ± 1.2 Ma, 243.3 ± 4.1 Ma and 238.3 ± 1.2 Ma, with a corresponding lower-intercept U-Pb zircon age of 232 ± 26 Ma. Despite the well-preserved prograde major- and trace-element zoning in garnets, mineralogical and petrologic studies suggest that Lu-Hf ages mostly reflect a later garnet growth episode. These ages mark the termination of high-pressure eclogite-facies metamorphism instead of representing the early phase of garnet growth. An upper-intercept zircon U-Pb age of 765 ± 24 Ma is defined for the Gaoqiao eclogite, which is consistent with the weighted mean age of 768 ± 21 Ma for the country gneiss. This suggests an analogue protolith origin; however, the gneiss has not been subjected to successive high-pressure metamorphism. The new Triassic ages are thus either an estimate of the involvement of oceanic fragments in the continental subduction or a milestone of the termination of oceanic subduction. The latter implies that different oceanic crustal slices/fragments reached peak metamorphism and started to exhume at diverse times, rather than being subducted and exhumed as a whole. Despite these results, many fundamental questions regarding the multi-slices subduction and exhumation hypothesis remain unanswered.

  13. The thermal evolution of Chinese central Tianshan and its implications: Insights from multi-method chronometry

    Science.gov (United States)

    Yin, Jiyuan; Chen, Wen; Hodges, Kip V.; Xiao, Wenjiao; Cai, Keda; Yuan, Chao; Sun, Min; Liu, Li-Ping; van Soest, Matthijs C.

    2018-01-01

    The Chinese Tianshan is located in the south of the Central Asian Orogenic Belt and formed during final consumption of the Paleo-Asian Ocean in the late Palaeozoic. In order to further elucidate the tectonic evolution of the Chinese Tianshan, we have established the temperature-time history of granitic rocks from the Chinese Tianshan through a multi-chronological approach that includes U/Pb (zircon), 40Ar/39Ar (biotite and K-feldspar), and (U-Th)/He (zircon and apatite) dating. Our data show that the central Tianshan experienced accelerated cooling during the late Carboniferous- to early Permian. Multiple sequences of complex multiple accretionary, subduction and collisional events could have induced the cooling in the Tianshan Orogenic Belt. The new 40Ar/39Ar and (U-Th)/He data, in combination with thermal history modeling results, reveal that several tectonic reactivation and exhumation episodes affected the Chinese central Tianshan during middle Triassic (245-210 Ma), early Cretaceous (140-100 Ma), late Oligocene-early Miocene (35-20 Ma) and late Miocene (12-9 Ma). The middle Triassic cooling dates was only found in the central Tianshan. Strong uplift and deformation in the Chinese Tianshan has been limited and localized. It have been concentrated in around major fault zone and the foreland thrust belt since the early Cretaceous. The middle Triassic and early Cretaceous exhumation is interpreted as distal effects of the Cimmerian collisions (i.e. the Qiangtang and Kunlun-Qaidam collision and Lhasa-Qiangtang collision) at the southern Eurasian margin. The Cenozoic reactivation and exhumation is interpreted as a far field response to the India-Eurasia collision and represents the beginning of modern mountain building and denudation in the Chinese Tianshan.

  14. Structural and petrological analyses of the Frido Unit (southern Italy): New insights into the early tectonic evolution of the southern Apennines-Calabrian Arc system

    Science.gov (United States)

    Vitale, Stefano; Fedele, Lorenzo; Tramparulo, Francesco D'Assisi; Ciarcia, Sabatino; Mazzoli, Stefano; Novellino, Alessandro

    2013-05-01

    This study provides new data on the deformation and metamorphic evolution of the Jurassic to Upper Oligocene Frido Unit, an Ocean Continent Transition (OCT) Unit belonging to the Ligurian Accretionary Complex (LAC), by means of the integration of structural analysis, petrological investigations and a revision of the stratigraphical setting. The Frido Unit, representing the main metamorphic component of the Lower-Middle Miocene LAC in southern Italy, is characterized by a multistage tectonic evolution including: (i) two progressive deformation phases involving the development, under relatively high-pressure metamorphic conditions, of an early cleavage associated with isoclinal folds within the framework of a dominant SE-ward tectonic transport; (ii) a third deformation stage involving the growth of lower-pressure Na-amphibole along extensional shear surfaces (therefore probably marking the onset of tectonic exhumation); and (iii) two very low-temperature deformation phases characterized by the development of kink folds and associated thrusts, probably related to the late tectonic emplacement of the accretionary wedge onto the outer sectors of the Apennine domain (with a prevailing tectonic transport first toward the NE and then toward the NW). In order to clarify the metamorphic evolution of the Frido Unit, petrologic analyses were focused on its metasedimentary pelitic succession. Here, mineral parageneses including carpholite (well-documented for the first time in this study) and potassic white mica yielded peak pressure of ~ 1.2-1.4 GPa and temperature around 350 °C, thus indicating a high pressure/very low temperature metamorphism and a P-T-t path characterized by a rapid exhumation without any greenschist-facies overprint. In comparison with similar units cropping out in northern Calabria, Tuscany and Corsica, the Frido Unit experienced one of the coldest burial-exhumation histories.

  15. Mountain building, strike-slip faulting, and landscape evolution in the Marlborough Fault System, NZ: Insights from new low-temperature thermochronology and modeling

    Science.gov (United States)

    Duvall, A. R.; Collett, C.; Flowers, R. M.; Tucker, G. E.; Upton, P.

    2016-12-01

    The 150 km wide Marlborough Fault System (MFS) and adjacent dextral-reverse Alpine Fault accommodate oblique convergence of the Australian and Pacific plates in a broad transform boundary that extends for much of the South Island New Zealand. Understanding the deformation history of the Marlborough region offers the opportunity to study topographic evolution in a strike-slip setting and a fuller picture of the evolving New Zealand plate boundary as the MFS lies at the transition from oceanic Pacific plate subduction to oblique continental collision. Here we present low-temperature thermochronology from the MFS to place new limits on the timing and style of mountain building. We sampled a range of elevations spanning 2 km within and adjacent to the Kaikoura Mountains, which stand high as topographic anomalies above active strike-slip faults. Young apatite (U-Th)/He ages ( 2-5 Ma) on both sides of range-bounding faults are consistent with regional distributed deformation since the Pliocene initiation of strike-slip faulting. However, large differences in both zircon helium and apatite fission track ages, from Paleogene/Neogene ages within hanging walls to unreset >100 Ma ages in footwalls, indicate an early phase of fault-related vertical exhumation. Thermal modeling using the QTQt program reveals two phases of exhumation within the Kaikoura Ranges: rapid cooling at 15-12 Ma localized to hanging wall rocks and regional rapid cooling reflected in all samples starting at 4-5 Ma. These results and landscape evolution models suggest that, despite the presence of active mountain front faults, much of the topographic relief in this region may predate the onset of strike-slip faulting and that portions of the Marlborough Faults are re-activated thrusts that coincide with the early development of the transpressive plate boundary. Regional exhumation after 5 Ma likely reflects increased proximity to the migrating Pacific plate subduction zone and the buoyant Chatham Rise.

  16. Origin and role of fluids involved in the seismic cycle of extensional faults in carbonate rocks

    Science.gov (United States)

    Smeraglia, Luca; Berra, Fabrizio; Billi, Andrea; Boschi, Chiara; Carminati, Eugenio; Doglioni, Carlo

    2016-09-01

    We examine the potentially-seismic right-lateral transtensional-extensional Tre Monti Fault (central Apennines, Italy) with structural and geochemical methods and develop a conceptual evolutionary model of extensional faulting with fluid involvement in shallow (≤3 km depth) faults in carbonate rocks. In the analysed fault zone, multiscale fault rock structures include injection veins, fluidized ultracataclasite layers, and crackle breccias, suggesting that the fault slipped seismically. We reconstructed the relative chronology of these structures through cross-cutting relationship and cathodoluminescence analyses. We then used C- and O-isotope data from different generations of fault-related mineralizations to show a shift from connate (marine-derived) to meteoric fluid circulation during exhumation from 3 to ≤1 km depths and concurrent fluid cooling from ∼68 to barriers within the sedimentary sequence created a semi-closed hydrological system, where prevalently connate fluids circulated within the fault zone at temperatures between 60° and 75 °C. During fault zone exhumation, at depths ≤1 km and temperatures <30 °C, the hydrological circulation became open and meteoric-derived fluids progressively infiltrated and circulated within the fault zone. The role of these fluids during syn-exhumation seismic cycles of the Tre Monti Fault has been substantially passive along the whole fault zone, the fluids being passively redistributed at hydrostatic pressure following co-seismic dilatancy. Only the principal fault has been characterized, locally and transiently, by fluid overpressures. The presence of low-permeability clayey layers in the sedimentary sequence contributed to control the type of fluids infiltrating into the fault zone and possibly their transient overpressures. These results can foster the comprehension of seismic faulting at shallow depths in carbonate rocks of other fold-thrust belts involved in post-collisional seismogenic extensional

  17. Study of the geodynamic evolution of the Chinese Tianshan metamorphic belt to unravel deep processes occurring at the plate interface.

    Science.gov (United States)

    Bayet, L.; John, T.; Agard, P.; Becker, H.; Gao, J.

    2016-12-01

    Field-based studies of fossil plate interfaces can be used to provide constraints on the mechanical behaviour of subduction channel processes at depth. The Chinese Tianshan metamorphic belt (TMB) represents a suitable test area to study such processes since it contains fresh high-pressure rocks and well exposed structures in its central part. Lithologies composed of intercalated metasediments and volcanoclastics are likely derived from the trench during subduction with incorporation of first metapelitic-rich components and then increasing amounts of psammitic- and mafic-rich components and few carbonates. During burial, this material as well as pieces of the upper oceanic crust (pillow basalts) were scrapped off the slab and stacked to the upper plate and/or to the subduction channel at depth. During exhumation most of the deformation was accommodated by shearing and schistosity developed at blueschist-facies conditions (glaucophane lineations). A systematic sampling survey was carried out in the area through two N-S transects in order to reconstruct the P-T-t history of the central part of the TMB. Peak pressures and temperatures were estimated independently using Raman spectroscopy (quartz inclusions in garnet (P) and carbonaceous material (T)) and electron microprobe analysis (Zr-in rutile) on metasediments and metabasites. These yield coherent peak conditions of 530±30°C and 2.3±3 GPa. We combined these results with new geochronological Rb-Sr data to constrain the age of underplating and exhumation. We finally propose a tentative model for the geodynamic evolution of the TMB, based on field observations and P-T-t conditions. The TMB is interpreted to represent an erosive margin with accretion and stacking of tectonic slices at depths of 70 km, implying strong coupling/decoupling processes around this depth. During later exhumation this stack of detached material was brought back to the surface as a single unit undergoing shearing with minor internal

  18. Constructing victimhood in post-Franco‘s Spain: The recovery of memory by the grandchildren of victims of the civil war and dictatorship

    OpenAIRE

    Valverde Estela

    2012-01-01

    Since the end of the Spanish Civil War their victims have lived in a state of repression and terror that did not allow them to claim victimhood or any restitution to the State. Furthermore, the post-Franco Amnesty Law in 1977 made a blanket statement about the issue: there were no winners or losers, no victims or perpetrators. Everything had to be forgiven and forgotten. This paper will analyze the new Spanish movement for exhumation focused on the disappeared during the Civil War and t...

  19. L’Afrique solaire ou le récit oublié. Représentations sociales et expérimentations en matière d’énergie solaire en Afrique 19ème - 20ème siècles

    OpenAIRE

    Caille, Frédéric

    2016-01-01

    Ce texte évoque l’importance encore méconnue de l’Afrique comme terre d’accueil des premiers projets d’expérimentation de l’énergie solaire (dès les années 1860), ainsi que les enjeux en termes de représentations sociales et d’imagination politique d’un autre mode de « développement » que peut recouvrir aujourd’hui l’exhumation et la mise en récit de cette histoire.

  20. Very low temperature OSL-thermochronometry applied to the Siwalik deposits in Nepal and Bhutan

    Science.gov (United States)

    King, G. E.; Grujic, D.; Coutand, I.; Herman, F.

    2016-12-01

    The Himalayan foreland fold-and-thrust belt is made of Neogene synorogenic sediments of the Siwalik Group and accommodates a large fraction of the India-Eurasia convergence. This region receives high precipitation and experiences seismic events of M8 and larger. Along the strike of the 2500-km-long orogenic arc, the eastward narrowing of the fold-and-thrust belt has been attributed to increasing annual rainfall and specific stream power, rather than to lateral changes in shortening rates. However, exhumation/erosion rates of this unit remain unknown. Precisely constraining the erosion rates of this unit at the scale of the orogen would allow an estimate of the relative contributions of tectonic and climatic processes to the erosion of the youngest and frontal part of the Himalayan orogen. Thermochronometry enables the cooling, and therefore exhumation/erosion histories of rocks to be determined. However the exhumation histories of the Siwalik Group, which have experienced limited burial heating not exceeding 100-50 °C remain very difficult to constrain using traditional thermochronometers. Optically stimulated luminescence (OSL)-thermochronometry is a recently developed very low temperature thermochronometer sensitive to temperatures of 30-90 °C. Consequently, its application to the Siwalik deposits may provide insights into their cooling and exhumation histories. K-feldspar extracts from 18 sandstones samples of the Siwalik Group were investigated using a multi-OSL-thermochronometry approach, whereby four different signals, with different thermal stabilities were measured for each sample. The sandstone samples were collected along two traverses across the Himalayan fold-and-thrust belt in western Nepal, and eastern Bhutan. Using signals with different thermal sensitivities enables high precision Quaternary cooling histories to be derived. These data were inverted using a Bayesian approach resulting in preliminary cooling rates of 100 °C/Myr during the last 0

  1. Tectonic geomorphology of the Andes with SIR-A and SIR-B

    Science.gov (United States)

    Bloom, Arthur L.; Fielding, Eric J.

    1986-01-01

    Data takes from SIR-A and SIR-B (Shuttle Imaging Radar) crossed all of the principal geomorphic provinces of the central Andes between 17 and 34 S latitude. In conjunction with Thematic Mapping images and photographs from hand-held cameras as well as from the Large Format Camera that was flown with SIR-B, the radar images give an excellent sampling of Andean geomorphology. In particular, the radar images show new details of volcanic rocks and landforms of late Cenozoic age in the Puna, and the exhumed surfaces of tilted blocks of Precambrian crystalline basement in the Sierras Pampeanas.

  2. Initiation of extension in South China continental margin during the active-passive margin transition: kinematic and thermochronological constraints

    Science.gov (United States)

    ZUO, Xuran; CHAN, Lung

    2015-04-01

    The southern South China Block is characterized by a widespread magmatic belt, prominent NE-striking fault zones and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from an active to a passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in this area. In this study, we used zircon fission-track dating (ZFT) and numerical modeling to examine the timing and kinematics of the active-passive margin transition. Our ZFT results on granitic plutons in the SW Cathaysia Block show two episodes of exhumation of the granitic plutons. The first episode, occurring during 170 Ma - 120 Ma, affected local parts of the Nanling Range. The second episode, a more regional exhumation event, occurred during 115 Ma - 70 Ma. Numerical geodynamic modeling was conducted to simulate the subduction between the paleo-Pacific plate and the South China Block. The modeling results could explain the observation based on ZFT data that exhumation of the granite-dominant Nanling Range occurred at an earlier time than the gneiss-dominant Yunkai Terrane. In addition to the difference in geology between Yunkai and Nanling, the heating from Jurassic-Early Cretaceous magmatism in the Nanling Range may have softened the upper crust, causing the area to exhume more readily. Numerical modeling results also indicate that (1) high slab dip angle, high geothermal gradient of lithosphere and low convergence velocity favor the subduction process and the reversal of crustal stress state from compression to extension in the upper plate; (2) the late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The inversion of stress regime in the continental crust from compression to crustal extension has shed light on the geological condition producing the red bed basins during Late Cretaceous

  3. Bach and His.

    Science.gov (United States)

    Beasley, Wyn

    2014-12-01

    This paper examines the career of Johann Sebastian Bach (1685-1750) and the role played by Wilhelm His I (who was, with Albert von Haller, a noted pioneer of physiology) in the exhumation of Bach's remains in 1894. His's examination of these remains allowed the sculptor Carl Seffner to produce the celebrated statue of Bach which stands outside the church of St Thomas in Leipzig, where the composer was employed from 1723 until his death. Modern forensic techniques have recently enabled Bach's image to be reconstructed in even more spectacular detail. © 2014 Royal Australasian College of Surgeons.

  4. Uplift in the Fiordland region, New Zealand: implications for incipient subduction.

    Science.gov (United States)

    House, M A; Gurnis, M; Kamp, P J J; Sutherland, R

    2002-09-20

    Low-temperature thermochronometry reveals regional Late Cenozoic denudation in Fiordland, New Zealand, consistent with geodynamic models showing uplift of the overriding plate during incipient subduction. The data show a northward progression of exhumation in response to northward migration of the initiation of subduction. The locus of most recent uplift coincides with a large positive Bouguer gravity anomaly within Fiordland. Thermochronometrically deduced crustal thinning, anomalous gravity, and estimates of surface uplift are all consistent with approximately 2 kilometers of dynamic support. This amount of dynamic support is in accord with geodynamic predictions, suggesting that we have dated the initiation of subduction adjacent to Fiordland.

  5. Sub-aqueous sulfur volcanos at Waiotapu, New Zealand

    Energy Technology Data Exchange (ETDEWEB)

    Grimes, S.; Rickard, D. [University of Wales, Cardiff (United Kingdom). Dept. of Earth Sciences; Browne, P.; Simmons, S. [University of Auckland (New Zealand). Geothermal Institute and Geology Dept.; Jull, T. [University of Arizona, Tucson (United States). AMS Facility

    1999-12-01

    Exhumed, sub-aqueous sulfur mounds occur in the Waiotapu geothermal area, New Zealand. The extinct mounds are < 2 m high and composed of small (< 0.5 cm) hollow spheres, and occasional teardrop-shaped globules. They are located within a drained valley that until recently was connected to Lake Whangioterangi. They were formed a maximum of 820 {+-} 80 years BP as a result of the rapid sub-aqueous deposition of sulfur globules, formed when fumarolic gases discharged through molten sulfur pools. Similar globules are now being formed by the discharge of fumarolic gases through a sub-aqueous molten sulfur pool in Lake Whangioterangi. (author)

  6. Tissue preservation and projectile context in a Spanish Civil War victim.

    Science.gov (United States)

    Ferllini, Roxana

    2010-07-01

    Exhumations of mass graves containing the remains of those executed during the Spanish Civil War and the subsequent Franco regime are currently being conducted at the request of surviving relatives. This individual case report illustrates how soft tissue preservation, through copper ion contact in one particular victim aided in preserving the projectile in an anatomical context, thereby permitting the correct interpretation of the projectile's path and angle, which otherwise would not have been possible as no bone tissue was affected. The information obtained has important relevance for human rights investigations and the work of the forensic anthropologist. Copyright 2010 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.

  7. Phanerozoic burial, uplift and denudation of the Equatorial Atlantic margin of South America

    Science.gov (United States)

    Japsen, Peter; Bonow, Johan M.; Green, Paul F.; dall'Asta, Massimo; Roig, Jean-Yves; Theveniaut, Hervé

    2017-04-01

    We have initiated a study aimed at understanding the history of burial, uplift and denudation of the South American Equatorial Atlantic Margin (SAEAM Uplift) including the Guiana Shield to provide a framework for investigating the hydrocarbon prospectivity of the offshore region. We report first results including observations from fieldwork at the northern and southern flank of the Guiana Shield. The study combines apatite fission-track analysis (AFTA) and vitrinite reflectance data from samples of outcrops and drillcores, sonic velocity data from drill holes and stratigraphic landscape analysis (mapping of peneplains) - all constrained by geological evidence, following the methods of Green et al. (2013). The study will thus combine the thermal history from AFTA data with the denudation history from stratigraphic landscape analysis to provide magnitudes and timing of vertical movements (Japsen et al. 2012, 2016). Along the Atlantic margin of Suriname and French Guiana, tilted and truncated Lower Cretaceous strata rest on Precambrian basement (Sapin et al. 2016). Our AFTA data show that the basement underwent Mesozoic exhumation prior to deposition of the Lower Cretaceous cover. Sub-horizontal peneplains define the landscape of the Guiana Shield at elevations up to 500 m a.s.l. As these sub-horizontal peneplains truncate the tilted, sub-Cretaceous surface along the Atlantic margin, these peneplains were therefore formed and uplifted in post-Cretaceous time. This interpretation is in good agreement with our AFTA data that define Paleogene exhumation along the margin and with the results of Theveniaut and Freyssinet (2002) who used palaeomagnetic data to conclude that bauxitic surfaces across basement at up to 400 m a.s.l. on the Guiana Shield formed during the Palaeogene. Integration of the results from AFTA with stratigraphic landscape analysis (currently in progress) and geological evidence will provide a robust reconstruction of the tectonic development of the

  8. New data and contributions to the cultural sequence of Lancia (Villasabariego, León, Spain

    Directory of Open Access Journals (Sweden)

    Jesús LIZ GUIRAL

    2013-05-01

    Full Text Available We try in our work to show the advances in the investigation of Lancia. In the last years we have worked in Roman downtown, presumably very near the forum, two architectural groups: some small thermal baths and a macellum, already discovered and partly exhumed in the years fifty and sixty of last century. The new contribution affects so much to the advance in the knowledge of the functionality of this structures as well as to their chronology and construction phases. It is important also the location of archaeological units belonging to the prerroman moment of the city that they had never been found in situ.

  9. Reptiles escamosos (Squamata del Pleistoceno Medio del Norte de la ciudad de Mar del Plata (provincia de Buenos Aires, Argentina

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    Santiago Brizuela

    2015-05-01

    Full Text Available In this study, we describe two fossil remains of squamate reptiles found in Middle Pleistocene outcrops at the northern marine cliffs of the city of Mar del Plata (Buenos Aires province. The specimens were found forming a taphocenosis with remains of other microvertebrates (amphibians, mammals and birds. The reptiles recognized in the association are represented by remains of an undetermined colubrid, and the anguid Ophiodes sp. This latter finding represents the first fossil record for the family Anguidae exhumed in Argentina.

  10. Accretion of a Small Continental Fragment to a Larger Continental Plate: Mesozoic Ecuador as a Case-Study Area

    Science.gov (United States)

    Massonne, H.

    2013-05-01

    Only a few regions on Earth are appropriate to study processes that have happened in deeper crustal levels during the accretion of a microplate to a larger continental plate. Ecuador is one of these regions where in middle Mesozoic times a small continental fragment collided with the South-American plate. Along the suture between both plates, which occurs close to the present volcanic belt of Ecuador, high-pressure (HP) metamorphic rocks developed. These rocks, which are metapelites, metabasites, and metagranitoids, record processes during the microcontinent-continent collision (Massonne and Toulkeridis, 2012, Int. Geol. Rev. 54). The pressures, determined for the HP rocks, were as high as 14 kbar at temperatures somewhat above 500°C. The HP stage was followed by slight heating at the early exhumation. Peak temperatures up to 560°C were reached at pressures ≥10 kbar. This HP metamorphism was caused by the collision of the microplate with the South-American plate resulting in crustal thickening. The ascent of the HP rocks occurred in an exhumation channel. Before the collision, an oceanic basin existed between these plates. Probably, it was narrow as eclogite bodies are lacking in the N-S trending HP belt of Ecuador. Such bodies, especially if the eclogites had experienced pressures in excess of 20 kbar, are markers of a collision of major continental plates in Phanerozoic times with originally extended oceanic basins between these plates. In a more global context, the narrow ocean between the microplate and the South American continent is assumed to have been the westernmost portion of the Neo-Tethys which had extended to completely separate the two major fragments of former Pangaea before the opening of the southern Atlantic Ocean. This opening caused the closure of the narrow Neo-Tethys segment between the colliding microplate and the South American plate. This segment was bordered by E-W trending transform faults. A fault system (La Palma - El Guayabo fault

  11. Nationalcatholicism and education in the postwar Spain. Notes about a reading and a A. Mayordomo 's preliminary study

    Directory of Open Access Journals (Sweden)

    Herminio BARREIRO RODRIGUEZ

    2013-11-01

    Full Text Available More than ever, history is today a subject which must be proyected towards the most realistic comprehension of our roots and to a better knowledge of the world where we live. In that sense, what Spain urgently needs is an holistic criticism of Franco's dictatorship and its consequences. It is important to exhumate texts. But to do it in a critical way is important too. From the perspective of classical historial studies —although not enough in number and quality— this paper tries to determine the main steps of Franco's period from an educational historical point of view

  12. Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

    Science.gov (United States)

    Teixell, A.; Labaume, P.; Ayarza, P.; Espurt, N.; de Saint Blanquat, M.; Lagabrielle, Y.

    2018-01-01

    This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian ( 84 Ma) to early Miocene times ( 20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised. The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above

  13. Structure and tectonic evolution of the southwestern Trinidad dome, Escambray complex, Central Cuba: Insights into deformation in an accretionary wedge

    Science.gov (United States)

    Despaigne-Díaz, Ana Ibis; García Casco, Antonio; Cáceres Govea, Dámaso; Wilde, Simon A.; Millán Trujillo, Guillermo

    2017-10-01

    The Trinidad dome, Escambray complex, Cuba, forms part of an accretionary wedge built during intra-oceanic subduction in the Caribbean from the Late Cretaceous to Cenozoic. The structure reflects syn-subduction exhumation during thickening of the wedge, followed by extension. Field mapping, metamorphic and structural analysis constrain the tectonic evolution into five stages. Three ductile deformation events (D1, D2 and D3) are related to metamorphism in a compressional setting and formation of several nappes. D1 subduction fabrics are only preserved as relict S1 foliation and rootless isoclinal folds strongly overprinted by the main S2 foliation. The S2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts, suggesting thrust stacks and underthrusting at mantle depths. Thrusting caused an inverted metamorphic structure with higher-grade on top of lower-grade nappes. Exhumation started during D2 when the units were incorporated into the growing accretionary wedge along NNE-directed thrust faults and was accompanied by substantial decompression and cooling. Folding and thrusting continued during D3 and marks the transition from ductile to brittle-ductile conditions at shallower crustal levels. The D4-5 events are related to extension and contributed to the final exhumation (likely as a core complex). D4 is associated with a regional spaced S4 cleavage, late open folds, and numerous extension veins, whereas D5 is recorded by normal and strike-slip faults affecting all nappes. The P-t path shows rapid exhumation during D2 and slower rates during D3 when the units were progressively incorporated into the accretionary prism. The domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development. These results support tectonic models of SW subduction of the Proto-Caribbean crust under the Caribbean plate during the latest Cretaceous and provide

  14. Tectonics and sedimentology of post-rift anomalous vertical movements: the rifted margin of Morocco

    Science.gov (United States)

    Bertotti, Giovanni; Charton, Remi; Luber, Tim; Arantegui, Angel; Redfern, Jonathan

    2016-04-01

    Roughly 15 years ago it was discovered that substantial parts of the Morocco passive continental margin experienced km-scale, post-rift exhumation. It was predicted that the sands resulting from the associated erosion would be present in the offshore and potentially form hydrocarbon reservoirs. At the same time, anomalous post-rift vertical movements have been documented in various localities of the world and rifted continental margins are at present exciting objects of research. Following intense research efforts the knowledge of the kinematics of vertical movements and their implications for sedimentary systems is increasing. The low-T geochronology initially limited to the classical Meseta-Massif Ancien de Marrakech transect has been expanded reaching the Reguibate Massif to the S and covering, possibly more importantly, one transect in E-W direction along the Anti Atlas. Exhumation occurred along two dominant trends. In N-S direction a several hundred-kilometers long exhuming domain developed roughly parallel to the Atlantic margin. Changes in magnitude and timing of exhumation are observed along this elevated domain associated with E-W trending undulations. The timing of main stage of upward movement of E-W trending highs seems to be Late Jurassic-Early Cretaceous in the Meseta and High Atlas and somewhat older, Early to Middle Jurassic, in the Anti-Atlas and Reguibate. The discovery of E-W trending highs and lows has major implication for sediment distribution and dispersal. At the large scale, it means that the drainage basins were smaller than initially predicted. This seems to be compatible with the paucity of sands encountered by recent exploration wells drilled offshore Morocco. At the scale of several kilometers, W-E trending anticlines and synclines developed in a generally subsiding coastal environment. These folds often had an expression at the sea floor documented by ravinement surfaces and (Jurassic) reef build-ups on top of the anticlines

  15. More on Darwin's illness: comment on the final diagnosis of Charles Darwin.

    Science.gov (United States)

    Sheehan, William; Meller, William H; Thurber, Steven

    2008-06-20

    Without the possibility of confirmatory exhumation, diagnostic inferences about Darwin's illness must remain speculative. A diagnosis of Darwin's aggregate symptoms must account for not only gastrointestinal distress but also his predominant and excessive retching and the conglomerate of other heterogeneous symptoms. We opine that Crohn's disease, posited as the 'final diagnosis', is not sufficient for subsuming his pleiomorphic symptomatology. An additional proposal is outlined that may help to explain his presentation with heterogeneous symptoms. It incorporates constitutional vulnerabilities, psychosomatic influences and Pavlovian conditioning as explanatory variables.

  16. Tectonic evolution of the Northern Pyrenees. Results of the PYRAMID project

    Science.gov (United States)

    Ford, Mary; Mouthereau, Fredéric; Christophoul, Fredéric; de Saint Blanquat, Michel; Espurt, Nicolas; Labaume, Pierre; Vergés, Jaume; Teixell, Antonio; Bellahsen, Nicolas; Vacharat, Arnaud; Pik, Raphael; Pironon, Jacques; Carpentier, Cédric; Angrand, Paul; Grool, Arjan; Salardon, Roland; Huismans, Ritske; Bader, Anne-Gaëlle; Baudin, Thierry; Aubourg, Charles

    2017-04-01

    The aims of the PYRAMID project funded by the Agence Nationale de la Recherche of France, were to investigate and constrain the 3D structural style and architecture of the North Pyrenean retrowedge and foreland basin, their evolution through time, to define the character and role of inherited crustal geometries, to investigate the interactions between deformation, fluids and thermicity in the different structural units, and to carry out source to sink studies In this talk we present a series of restored cross sections through the central and eastern Pyrenean retrowedge to illustrate structural style, amount and type of deformation and how it was accommodated within the upper crust along the orogen. The total amount of convergence appears to have been constant and the timing of onset of convergence was synchronous. However, in the retrowedge the complexity of the Cretaceous oblique rift system has led to high lateral structural variability. Inherited vertical late Variscan faults trending NE-SW to ENE-WSW segment the European crust and have strongly compartmentalised both retrowedge and foreland basin evolution along the orogen. Crustal scale restorations provide new evolutionary models for the geometry and style of inversion of the pre-orogenic hyper-extended rift system where mantle was exhumed in the most distal domain. Numerical models provide insight into retrowedge inversion. A new stratigraphic scheme has been developed for the eastern and central foreland. Subsidence analyses and foreland basin reconstructions document two pulses of convergence (Late Santonian to Early Paleocene and Eocene to Oligocene) separated by a quiet phase during the Paleocene. These phases can be linked to deformation in the North Pyrenean Zone thrust belt. The first phase was caused mainly by inversion and emplacement of the Metamorphic Internal Zone onto external zones associated with subduction of the exhumed mantle domain. Little or no relief was created during this phase

  17. Short preliminary considerations on some funeral arrangements in the light of Government Decision no. 741/2016

    Directory of Open Access Journals (Sweden)

    S.-D. ŞCHIOPU

    2017-07-01

    Full Text Available Nowadays, the new ʻTechnical and Health Rules regarding the funeral services, burial, cremation, transport, exhumation and reburial of human corpses, cemeteries, human crematoriums, and also the professional criteria that must be met by the providers of funeral services’, govern some key aspects following one’s death. For a better understanding of this new legislation concerning the death care industry, this short overview attempts, on the one hand, to highlight certain aspects of the present-day configuration of thanatopraxy, burial, cremation and funerals, and on the other hand, to examine the effectiveness of determining one’s own funeral.

  18. Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

    Science.gov (United States)

    Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

    2017-09-01

    Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge

  19. Metamorphic evolution of the Frido Unit from the southern Apennines (Italy): consequences for the subduction processes in the western Mediterranean area

    Science.gov (United States)

    Laurita, Salvatore; Prosser, Giacomo; Altenberger, Uwe; Bousquet, Romain; Oberhänsli, Roland; Cavalcante, Francesco

    2013-04-01

    in the stability field of aragonite, implying extremely cool exhumation conditions, followed the PT peak. Significant cooling during decompression implies that exhumation took place during active subduction of the cold oceanic lithosphere of the Tethyan domain. In addition, exhumation was slow enough to equilibrate the temperature of the exhuming body with the ambient conditions. Summarizing, the evolution of the Frido Unit fits the HP-LT evolution of metasediments of the Alpine-Apennine System during subduction and closure of the Piedmont-Ligurian Ocean.

  20. The afterlife of Laurence Sterne (1713-1768): Body snatching, dissection and the role of Cambridge anatomist Charles Collignon.

    Science.gov (United States)

    Dittmar, Jenna M; Mitchell, Piers D

    2016-11-01

    This paper aims to highlight the practice of body snatching from graves in the 1700s for the purpose of providing corpses for anatomical dissection, and for stocking anatomy museums. To do this, we examine the exhumation and dissection of the famous eighteenth-century novelist Laurence Sterne and explore the involvement of Charles Collignon, Professor of Anatomy at the University of Cambridge. We also show that osteological and cut-mark analysis of a skull purported to be that of Sterne, currently housed in the Duckworth Collection at Cambridge, provides the key to solving the mystery surrounding why Sterne was resurrected. © The Author(s) 2015.

  1. Thermodynamic modelling of metamorphic processes: state of the art in pseudosection approach

    Science.gov (United States)

    López-Carmona, A.; Gutiérrez-Alonso, G.; Tishin, P. A.; Gertner, I. F.

    2017-12-01

    Understanding global-scale orogenic processes related to supercontinents, and their relationship to the secular evolution of the Earth’s lithosphere, represent important challenges for Earth scientists today. The record of these processes is preserved in the microstructures, mineral assemblages and mineral compositions of lithospheric rocks exhumed to the Earth’s surface. Given a well-characterized microstructural evolution, thermodynamic modelling is the key to quantifying changes in pressure and temperature, with the rate of these changes being provided by rock-forming and accessory mineral-based geochronology. Thus, metamorphic rocks provide Pressure–Temperature–time–deformation (P–T–t–d) data that help to parameterize orogenic processes.

  2. Las abarcas de Fontanosas, o cuando la memoria/escritura es la memoria/escritura de uno mismo

    Directory of Open Access Journals (Sweden)

    Francisco Caudet

    2006-11-01

    Full Text Available Making a story about the past may be a challenging task, because of the existing tensions between memory and writing, especially when a society carries a traumatic experience in its recent past. Focusing on the tensions between memory and writing, this article puts forward a reflection about the possibilities of telling the recent past in Spain around the named "pact of silence". The starting point of this analysis is the anonymous letter from a soldier of Franco's army, written in a confessional tone, which, appearing half a century later, helped to find and exhume the remains of a group of shot soldiers.

  3. Passer à la télé ! Le rêve de l’homme de gouvernement ?

    Directory of Open Access Journals (Sweden)

    Christian Ruby

    2007-06-01

    Full Text Available Fouiller et exhumer les archives (celles de la « voix de la France », notamment, regarder des heures d’enregistrement d’émissions produites par la télévision (dans « sa mission d’informer » officielle, analyser des images électroniques et des bandes sonores, retenir des intonations, des contractions et des décontractions de candidats, des performances inédites ou des bons mots de présidents de la République, enfin observer l’évolution des attitudes des personnels de ...

  4. Breastfeeding and weaning in renaissance Italy: the Medici children.

    Science.gov (United States)

    Giuffra, Valentina; Fornaciari, Gino

    2013-06-01

    Abstract Exploration of the Medici Chapels in the Basilica of San Lorenzo in Florence, Italy, revealed the burials of nine infantile members of the Medici family. Eight children were found in the intact tomb of the last Grand Duke GianGastone (1671-1737), and another child was exhumed from the Chapel of Grand Duke Ferdinando I (1549-1609). Skeletal ages ranged from newborn to 5 years, suggesting an identification with infantile members of the family. A paleonutritional study has been performed on the bone samples of all members of the Medici family exhumed so far. Carbon and nitrogen stable isotope analysis of bone collagen was used to detect the timing of the weaning process in this population. The (15)N values of the Medici children are significantly higher than those of adults, indicating that these infants were breastfed for a long time period. In particular, the levels of (15)N are high before the second year but decrease in older children, evidently after weaning, reaching the levels of adults. During the Renaissance, it was the common opinion that children should not be weaned before the second year of life. Archival documents suggest that the Medici children were never weaned before that age and, in most cases, even some months later. Combination of paleonutritional data and historical sources allowed reconstruction of the breastfeeding and weaning patterns of this aristocratic Renaissance class.

  5. Geological evolution of the southwestern part of the Veporic Unit (Western Carpathians: based on fission track and morphotectonic data

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    Vojtko Rastislav

    2017-08-01

    Full Text Available Zircon and apatite fission track (FT and morphotectonic analyses were applied in order to infer quantitative constraints on the Alpine morphotectonic evolution of the western part of the Southern Veporic Unit which is related to: (1 Eo-Alpine Cretaceous nappe stacking and metamorphism of the crystalline basement in the greenschist facies. (2 Exhumation phase due to underthrusting of the northerly located Tatric-Fatric basement (~ 90–80 Ma, followed by a passive en-block exhumation with cooling through ~ 320–200 °C during the Palaeocene (ZFT ages of ~ 61–55 Ma. (3 Slow Eocene cooling through ~ 245–90 °C, which most likely reflected erosion of the overlying cover nappes and the Gosau Group sediments. Cooling reached up to 60 °C till the Oligocene (AFT ages of ~ 37–22 Ma in association with erosion of cover nappes. The efficient Eocene erosion led to the formation of the first Cenozoic planation surface with supergene kaolinization in many places. (4 The early Miocene erosion coincided with surface lowering and resulted in the second planation surface favourable for kaolinization. (5 In the middle Miocene, the study area was covered by the Poľana, Javorie, and Vepor stratovolcanoes. (6 The late Miocene stage was related to the erosion and formation of the third Cenozoic planation surface and the final shaping of the mountains was linked to a new accelerated uplift from the Pliocene.

  6. Modelling the geomorphic history of the Tribeč Mts. and the Pohronský Inovec Mts. (Western Carpathians with the CHILD model

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    Staškovanová Veronika

    2016-06-01

    Full Text Available Numerical models were developed in order to provide a suitable computational framework for exploring research questions related to long-term landscape evolution. We used the Channel-Hillslope Integrated Landscape Development (CHILD model to prove three hypotheses concerning the processes contributing to the neotectonic landscape evolution of the Tribeč Mts. and the Pohronský Inovec Mts. (Western Carpathians: (1 simultaneous planation and uplift; (2 temporally and spatially varying uplift; (3 exhumation of a part of the area from below Neogene sediments. Given the size of the area, its lithological variability and the insufficient knowledge of the palaeogeographical settings, using a detachment-limited model to express river incision into bedrock as well as water (rill erosion on hillslopes proved the best solution. Results of the simulations were compared with real topography through hypsographic curves and the distribution of remnants of planation surfaces. The real surface corresponds best to a combination of the hypotheses (2 and (3, with more intensive Quaternary tectonic uplift of the Pohronský Inovec Mts. and the adjacent Rázdiel part of the Tribeč Mts., and exhumation of a mature palaeosurface from below Miocene sediments in the east of the Tribeč Mts.

  7. Polar poisons: did Botulism doom the Franklin expedition?

    Science.gov (United States)

    Horowitz, B Zane

    2003-01-01

    In 1845 the Franklin expedition left London with 2 ships and 134 men on board in an attempt to find the route through the Northwest Passage. The ships were built with state-of-the-art technology for their day, but provisioned with supplies from the lowest bidder. After taking on fresh provisions in the Whalefish Islands, off the coast of Greenland, the entire crew was never heard from again. Graves found on remote Beechey Island indicate that three able-bodied seamen died during the first winter. A note written on a ship's log, later found in a cairn, indicate that the expedition's leader, Sir John Franklin, died during the second winter entrapped on the ice, by which time 24 men had also perished. The remaining crew failed in their attempt to walk out of the Arctic by an overland route. In 1981 Owen Beattie, from the University of Alberta, exhumed the remains of the sailors from the three graves on Beechey Island. Elevated lead levels were found in all three sailors. While lead poisoning has been a leading theory of the cause of the crew's deaths, blamed on the crudely tinned provisions the ships carried with them from England, chronic lead exposure may only have weakened the crew, not necessarily killed them. One of three exhumed sailors also had in his intestine the spores of an unspecified Clostridium species. The theory put forth by this article is that Botulism, type E, which is endemic in the Arctic, may have been responsible for their deaths.

  8. The effects of lower crustal strength and preexisting midcrustal shear zones on the formation of continental core complexes and low-angle normal faults

    KAUST Repository

    Wu, Guangliang

    2016-08-22

    To investigate the formation of core complexes and low-angle normal faults, we devise thermomechanical simulations on a simplified wedge-like orogenic hinterland that has initial topography, Moho relief, and a preexisting midcrustal shear zone that can accommodate shear at very low angles (<20°). We mainly vary the strength of the lower crust and the frictional strength of the preexisting midcrustal shear zone. We find that the strength of the lower crust and the existence and strength of a preexisting shear zone significantly affect the formation and evolution of core complexes. With increasing lower crustal strength, we recognize varying extensional features with decreasing exhumation rate: these are characterized by bivergent metamorphic massifs, classic Cordilleran metamorphic core complexes, multiple consecutive core complexes (or boudinage structures), and a flexural core complex underlined by a large subsurface low-angle detachment fault with a small convex curvature. Topographic loading and mantle buoyancy forces, together with divergent boundaries, drive a regional lower crustal flow that leads to the exhumation of the lower crust where intensive upper crustal faulting induces strong unloading. The detachment fault is a decoupling zone that accommodates large displacement and accumulates sustained shear strain at very low angle between upper and lower crust. Though the regional stress is largely Andersonian, we find non-Andersonian stress in regions adjacent to the preexisting shear zone and those with high topographic gradient. Our new models provide a view that is generally consistent with geological and geophysical observations on how core complexes form and evolve.

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

    CERN Document Server

    Roda, Manuel; Marotta, Anna Maria

    2012-01-01

    A numerical modelling approach is used to validate the physical and ge- ological reliability of the ablative subduction mechanism during Alpine con- vergence in order to interpret the tectonic and metamorphic evolution of an inner portion of the Alpine belt: the Austroalpine Domain. The model pre- dictions 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 evolu- tion 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 config- uration of this part of the Alps. There is less agreement between the model predictions and the natural data for the Austr...

  10. Detection of Mercury in Human Organs and Hair in a Case of a Homicidal Poisoning of a Woman Autopsied 6 Years After Death.

    Science.gov (United States)

    Lech, Teresa

    2015-09-01

    In the described case of the death of a 53-year-old woman, no toxicological examination was performed directly after death (only an anatomopathological autopsy), although symptoms of serious gastrointestinal disturbances had been present (the woman had been hospitalized twice in the course of several months). It was assumed that the cause of death was myocardial infarction. Five years later, some new circumstances came to light which suggested that somebody could have administered some poison (metals, cyanides) to the woman. Toxicological analysis of postmortem samples from the corpse, exhumed 6 years after death by order of the public prosecutor's office, revealed high tissue mercury contents in biological material (cold vapor atomic absorption spectrometry): small intestine, 1516 ng/g; large intestine, 487 ng/g; liver, 1201 ng/g; heart muscle, 1023 ng/g; and scalp hair, 227 ng/g. In samples of soil from places near the coffin, negligible traces of mercury were found (0.5-1.5 ng/g); contamination by mercury from the environment was ruled out. The presented case is a rare example of recognition of mercury poisoning on the basis of the results of analysis of biological material from an exhumed cadaver.

  11. Normal faulting in the forearc of the Hellenic subduction margin: Paleoearthquake history and kinematics of the Spili Fault, Crete, Greece

    Science.gov (United States)

    Mouslopoulou, Vasiliki; Moraetis, Daniel; Benedetti, Lucilla; Guillou, Valery; Bellier, Olivier; Hristopulos, Dionisis

    2014-09-01

    The late-Cenozoic kinematic and late-Pleistocene paleoearthquake history of the Spili Fault is examined using slip-vector measurements and in situ cosmogenic (36Cl) dating, respectively. The Spili Fault appears to have undergone at least three successive but distinct phases of extension since Messinian (˜7 Ma), with the most recent faulting resulting in the exhumation of its carbonate plane for a fault-length of ˜20 km. Earthquake-slip and age data show that the lower 9 m of the Spili Fault plane were exhumed during the last ˜16,500 years through a minimum of five large-magnitude (Mw > 6) earthquakes. The timing between successive paleoearthquakes varied by more than one order of magnitude (from 800 to 9000 years), suggesting a highly variable earthquake recurrence interval during late Pleistocene (CV = 1). This variability resulted to significant fluctuations in the displacement rate of the Spili Fault, with the millennium rate (3.5 mm/yr) being about six times faster than its late-Pleistocene rate (0.6 mm/yr). The observed variability in the slip-size of the paleoearthquakes is, however, significantly smaller (CV = 0.3). These data collectively suggest that the Spili Fault is one of the fastest moving faults in the forearc of the Hellenic subduction margin.

  12. Improving the apatite fission-track annealing algorithm

    Science.gov (United States)

    Luijendijk, Elco; Andriessen, Paul; ter Voorde, Marlies; van Balen, Ronald

    2017-04-01

    Low-temperature thermochronology is a key tool to quantifying the thermal history and exhumation of the crust. The interpretation of one of the most widely-used thermochronometers, apatite fission-track analysis, relies on models that relate fission track density to temperature history. These models have been calibrated to fission-track data from the Otway basin, Australia. We discuss geological evidence that the current benchmark dataset is located in a basin in which rocks may have been warmer in the past than previously assumed. We recalibrate the apatite fission-track annealing algorithm to a dataset from Southern Texas with a well-constrained thermal history. We show that current models underestimate the temperature at which fission tracks anneal completely by 19 ˚C to 34 ˚C. Exhumation rates derived from fission-track data have been underestimated; at normal geothermal gradients estimates may have to be revised upward by 500 to 2000 m. The results also have implications for the (U-Th)/He thermochronometer, because radiation damage influences the diffusivity of helium in apatites. The difference in modelled (U-Th)/He ages is approximately 10% for samples that have undergone a long cooling history. We also present a new Python code that can be used for forward or inverse modelling of fission track data using the new annealing algorithm.

  13. From nappe stacking to extensional detachments at the contact between the Carpathians and Dinarides - The Jastrebac Mountains of Central Serbia

    Science.gov (United States)

    Erak, Dalibor; Matenco, Liviu; Toljić, Marinko; Stojadinović, Uroš; Andriessen, Paul A. M.; Willingshofer, Ernst; Ducea, Mihai N.

    2017-07-01

    Reactivation of inherited nappe contacts is a common process in orogenic areas affected by back-arc extension. The amount of back-arc extension is often variable along the orogenic strike, owing to the evolution of arcuated mountain chains during stages of rapid slab retreat. This evolution creates low rates of extension near rotation poles, where kinematics and interplay with the pre-existing orogenic structure are less understood. The amount of Miocene extension recorded by the Pannonian Basin of Central Europe decreases SE-wards along the inherited Cretaceous - Paleogene contact between the Dinarides and Carpathian Mountains. Our study combines kinematic data obtained from field and micro-structural observations assisted with fission track thermochronological analysis and U-Pb zircon dating to demonstrate a complex poly-phase evolution in the key area of the Jastrebac Mountains of Serbia. A first event of Late Cretaceous exhumation was followed by latest Cretaceous - Eocene thrusting and magmatism related to a continental collision that sutured the accretionary wedge containing contractional trench turbidites. The suture zone was subsequently reactivated and exhumed by a newly observed Miocene extensional detachment that lasted longer in the Jastrebac Mountains when compared with similar structures situated elsewhere in the same structural position. Such extensional zones situated near the pole of extensional-driven rotation favour late stage truncations and migration of extension in a hanging-wall direction, while directions of tectonic transport show significant differences in short distances across the strike of major structures.

  14. Slab flattening, dynamic topography and normal faulting in the Cordillera Blanca region (northern Peru)

    Science.gov (United States)

    Margirier, A.; Robert, X.; Laurence, A.; Gautheron, C.; Bernet, M.; Simon-Labric, T.; Hall, S. R.

    2015-12-01

    Processes driving surface uplift in the Andes are still debated and the role of subduction processes as slab flattening on surface uplift and relief building in the Andes is not well understood. Some of the highest Andean summits, the Cordillera Blanca (6768 m) and the Cordillera Negra (5187 m), are located above a present flat subduction zone (3-15°S), in northern Peru. In this area, both the geometry and timing of the flattening of the slab are well constrained (Gutscher et al., 1999; Rosenbaum et al., 2005). This region is thus a perfect target to explore the effect of slab flattening on the Andean topography and uplift. We obtained new apatite (U-Th)/He and fission-track ages from three vertical profiles located in the Cordillera Blanca and the Cordillera Negra. Time-temperature paths obtained from inverse modeling of the thermochronological data indicates a Middle Miocene cooling for both Cordillera Negra profiles. We interpret it as regional exhumation in the Cordillera Occidental starting in Middle Miocene, synchronous with the onset of the subduction of the Nazca ridge (Rosenbaum et al., 2005). We propose that the Nazca ridge subduction at 15 Ma and onset of slab flattening in northern Peru drove regional positive dynamic topography and thus enhanced exhumation in the Cordillera Occidental. This study provides new evidence of the impact subduction processes and associated dynamic topography on paleogeography and surface uplift in the Andes.

  15. ESTIMATING THE SIZE OF LATE VENEER IMPACTORS FROM IMPACT-INDUCED MIXING ON MERCURY

    Energy Technology Data Exchange (ETDEWEB)

    Rivera-Valentin, E. G.; Barr, A. C., E-mail: rivera-valentin@brown.edu [Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, RI 02912 (United States)

    2014-02-10

    Late accretion of a ''veneer'' of compositionally diverse planetesimals may introduce chemical heterogeneity in the mantles of the terrestrial planets. The size of the late veneer objects is an important control on the angular momenta, eccentricities, and inclinations of the terrestrial planets, but current estimates range from meter-scale bodies to objects with diameters of thousands of kilometers. We use a three-dimensional global Monte Carlo model of impact cratering, excavation, and ejecta blanket formation to show that evidence of mantle heterogeneity can be preserved within ejecta blankets of mantle-exhuming impacts on terrestrial planets. Compositionally distinct provinces implanted at the time of the late veneer are most likely to be preserved in bodies whose subsequent geodynamical evolution is limited. Mercury may have avoided intensive mixing by solid-state convection during much of its history. Its subsequent bombardment may have then excavated evidence of primordial mantle heterogeneity introduced by the late veneer. Simple geometric arguments can predict the amount of mantle material in the ejecta blanket of mantle-exhuming impacts, and deviations in composition relative to geometric predictions can constrain the length-scale of chemical heterogeneities in the subsurface. A marked change in the relationship between mantle and ejecta composition occurs when chemically distinct provinces are ∼250 km in diameter; thus, evidence of bombardment by thousand-kilometer-sized objects should be readily apparent from the variation in compositions of ejecta blankets in Mercury's ancient cratered terrains.

  16. CIL II 4977 (Mondragón, Guipúzcoa. Una inscripción romana enterrada por la Inquisición y conservada en Segobriga

    Directory of Open Access Journals (Sweden)

    Manuel Abascal, Juan

    2010-12-01

    Full Text Available The CIL II 4977 inscription, for Hübner of unknown origin , really comes from a hermitage close to Mondragon, from where it was removed and buried by order of the Inquisition in 1787. It was exhumed by José Vargas Ponce between 1800 and 1803 and transported to the Royal Academy of History (Madrid. In 1907 the monument was moved to the National Archaeological Museum and in 1974 to the Museum of Segobriga. The Vargas Ponce manuscripts of the Royal Academy of History now allow its provenance to be confirmed.La inscripción CIL II 4977, de procedencia desconocida para Hübner, viene en realidad de una ermita cercana a Mondragón, de donde fue retirada y enterrada por orden de la Inquisición en 1787. Allí la exhumó José Vargas Ponce entre 1800 y 1803 y la trasladó a la Real Academia de la Historia (Madrid, desde donde pasó en 1907 al Museo Arqueológico Nacional y en 1974 al Museo de Segobriga. Los manuscritos de Vargas Ponce de la Real Academia de la Historia permiten asegurar ahora su procedencia.

  17. Genetic Identification of Communist Crimes' Victims (1944-1956) Based on the Analysis of One of Many Mass Graves Discovered on the Powazki Military Cemetery in Warsaw, Poland.

    Science.gov (United States)

    Ossowski, Andrzej; Diepenbroek, Marta; Kupiec, Tomasz; Bykowska-Witowska, Milena; Zielińska, Grażyna; Dembińska, Teresa; Ciechanowicz, Andrzej

    2016-11-01

    As the result of the communist terror in Poland, during years 1944-1956 more than 50,000 people died. Their bodies were buried secretly, and most places are still unknown. The research presents the results of identification of people buried in one of many mass graves, which were found at the cemetery Powązki Military in Warsaw, Poland. Exhumation revealed the remains of eight people, among which seven were identified genetically. Well-preserved molars were used for the study. Reference material was collected from the closest living relatives. In one case, an exhumation of victim's parents had to be performed. DNA from swabs was extracted with a PrepFiler® BTA Forensic DNA Extraction Kit and organic method. Autosomal, Y-STR amplification, and mtDNA sequencing were performed. The biostatistical calculations resulted in LR values from 1608 to 928 × 1018 . So far, remains of more than 50 victims were identified. © 2016 American Academy of Forensic Sciences.

  18. Dormancy cycles in buried seeds of three perennial Xyris (Xyridaceae) species from the Brazilian campo rupestre.

    Science.gov (United States)

    Oliveira, T G S; Diamantino, I P; Garcia, Q S

    2017-09-01

    Dormancy cycles are an important mechanism for avoiding seed germination under unfavourable periods for seedling establishment. This mechanism has been scarcely studied in tropical species. Here, we studied three tropical and perennial species of Xyris, X. asperula, X. subsetigera and X. trachyphylla, to investigate in situ longevity and the existence of seasonal seed dormancy cycles. Seeds of three species of Xyris were buried in their natural habitat, with samples exhumed bimonthly for 18 months. Germination of exhumed seeds was assessed under a 12-h photoperiod over a broad range of temperatures. Seeds of X. trachyphylla were also subjected to treatments to overcome secondary dormancy. Seeds of all species are able to form a persistent seed bank and exhibit seasonal changes in germinability. Secondary dormancy was acquired during the rainy summer and was overcome during the subsequent dry season (autumn/winter). Desiccation partially overcomes secondary dormancy in X. trachyphylla seeds. Soil seed bank persistence and synchronisation of seed germination under favourable conditions for seedling establishment contribute to the persistence and regeneration of X. asperula, X. subsetigera and X. trachyphylla in their natural environment. © 2017 German Botanical Society and The Royal Botanical Society of the Netherlands.

  19. Leucogranite geochronological constraints on the termination of the South Tibetan Detachment in eastern Himalaya

    Science.gov (United States)

    Liu, Zhi-Chao; Wu, Fu-Yuan; Qiu, Zhi-Li; Wang, Jian-Gang; Liu, Xiao-Chi; Ji, Wei-Qiang; Liu, Chuan-Zhou

    2017-11-01

    The South Tibetan Detachment System (STDS) developed between the very-low-grade Tethyan Himalayan Sequence (THS) and the high-grade metamorphic Greater Himalayan Sequence (GHS) over an along-strike distance exceeding 2000 km within the Himalayan orogen. Motion along the STDS has been associated with the exhumation of the GHS and the uplift of the Himalayan Mountains. Geological field mapping and U-Th-Pb geochronological analyses were performed to trace and date the STDS in the Yadong region of southern Tibet, where it is a top-to-the-north shear zone juxtaposing the Yadong klippe of the THS with the high-grade GHS. This shear zone is intruded by multiple generations of leucogranites emplaced mainly at ca. 23 Ma, ca. 20-18 Ma and ca. 17-16 Ma. The undeformed textures of the leucogranites and their cross-cutting relationships with the shear zone indicate that ductile motion along the STDS terminated by ca. 20 Ma. This is largely consistent with the deformation history of the STDS in central and western Himalaya. The termination of shearing along the STDS during the Early Miocene occurred well before the rapid cooling of the GHS during the Middle Miocene, suggesting that exhumation and decompression of the GHS was still ongoing after the cessation of motion along the STDS.

  20. Petrographic study of the Miocene-Pleistocene sandstone in the Western Foothills, northern Taiwan: implication for the unroofing history of Taiwan orogenic belt

    Science.gov (United States)

    Jia-Jhih, Yeh; Wen-Shan, Chen

    2017-04-01

    The Taiwan orogeny belt developed due to the arc-continental collision since about 6 Ma. Plio-Pleistocene foreland basin deposits are eroded from adjacent orogenic belt that provides much information about orogenic tectonics. In this study, sandstone petrography is enabled to trace orogenic exhumation history of the northern Taiwan. It indicates that late Miocene-early Pliocene strata were composed dominantly of monocrystalline quartz and feldspar deriving from the Eurasia continent. Late Pliocene-early Pleistocene sandstone (3.6-2Ma) contains lithic fragments which consist dominantly of sandstone fragments. It suggests that the sediments were derived from sedimentary province (Miocene strata) of the orogenic belt. The middle Pleistocene sandstone (1.5Ma) consists of argillite and metasandstone fragments (Oligocene strata) deriving from low-grade metamorphic province (the Hsuehshan Range). The late Pleistocene sandstone consists of quartzite fragments (Eocene strata) which were derived from metamorphic province (the Hsuehshan Range). The exhumation history of orogenic belt is revealed significant changes from sedimentary to metamorphic provinces during the middle Pleistocene. It suggests that the Hsuehshan Range exposed since middle Pleistocene. Lithic fragments derived from the Taiwan orogenic belt that corresponded with the unroofing history of the northern Hsuehshan Range by apatite and zircon fission track dating (1.2-2.6Ma and 4.6-6.4Ma).

  1. Late Palaeozoic to Triassic formations unconformably deposited over the Ronda peridotites (Betic Cordilleras): Evidence for their Variscan time of crustal emplacement

    Energy Technology Data Exchange (ETDEWEB)

    Sanz de Galdeano, C.; Ruiz Cruz, M.D.

    2016-07-01

    The age of the emplacement of the Ronda Peridotites has been widely debated during recent decades, and ages ranging from the Palaeozoic to the early Miocene have been proposed, although most of the current interpretations suggest an Oligocene-Miocene age. In this article, we describe two meta-sedimentary formations (the lower one formed by detrital sediments and the upper one by marbles) that were unconformably deposited over the Ronda peridotites and now record low-grade metamorphism. The detrital formation contains layers of acidic rocks with an age of 269±9 Ma and the overlying marbles are assumed to be Triassic. The existence of these unconformable formations over the peridotites is crucial for the dating of the exhumation of the latter. The presence of peridotite clasts in the detrital formation indicates that peridotites were exposed during the Permian and other data suggest that peridotites were exhumed during the late Carboniferous. During the Alpine cycle, the peridotites operated as an element situated at the bottom of the tectonically higher Alpujarride/Sebtide unit (the Jubrique unit) and forming part of it, then being incorporated to the Alpine thrusts of this unit. (Author)

  2. Rift-to-collision transition recorded by tectonothermal evolution of the northern Pyrenees

    Science.gov (United States)

    Vacherat, Arnaud; Mouthereau, Frédéric; Pik, Raphaël.; Bellahsen, Nicolas; Gautheron, Cécile; Bernet, Matthias; Daudet, Maxime; Balansa, Jocelyn; Tibari, Bouchaib; Pinna Jamme, Rosella; Radal, Julien

    2016-04-01

    The impact of rift-related processes on tectonic and thermal evolution of collisional orogens is poorly documented. Here, we study the northern Pyrenees, a region that has preserved a geological record of the transition from rifting to collision. Using modeling of new low-temperature thermochronological data, including fission track and (U-Th)/He on apatite and zircon, we propose a temporal reconstruction of the inversion of the European rifted margin. Our data confirm that rifting and related cooling started in the Late Paleozoic-Triassic. Throughout the Jurassic and Early Cretaceous the European margin recorded slow heating during postrift subdsidence. Modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130-110 Ma. Following onset of convergence at 83 Ma, shortening accumulated into the weak and hot Albian-Cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle. The lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient. The onset of exhumation-related cooling is recognized in the whole Pyrenean region at 50-35 Ma. This timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred.

  3. Gypsum veins in Triassic Moenkopi mudrocks of southern Utah: Analogs to calcium sulfate veins on Mars

    Science.gov (United States)

    Young, B. W.; Chan, M. A.

    2017-01-01

    Well-exposed gypsum veins in the Triassic Moenkopi formation in southern Utah, USA, are similar to veins at Endeavour and Gale Craters on Mars. Both Moenkopi and Mars veins are hydrated calcium sulfate, have fibrous textures, and crosscut other diagenetic features. Moenkopi veins are stratigraphically localized with strontium and sulfur isotope ratios similar to primary Moenkopi sulfate beds and are thus interpreted to be sourced from within the unit. Endeavour veins seem to be distributed by lithology and may have a local source. Gale veins cut across multiple lithologies and appear to be sourced from another stratigraphic interval. Evaluation of vein network geometries indicates that horizontal Moenkopi veins are longer and thicker than vertical veins. Moenkopi veins are also generally oriented with the modern stress field, so are interpreted to have formed in the latest stages of exhumation. Endeavour veins appear to be generally vertical and oriented parallel to the margins of Cape York and are interpreted to have formed in response to topographic collapse of the crater rim. Gale horizontal veins appear to be slightly more continuous than vertical veins and may have formed during exhumation. Abrupt changes in orientation, complex crosscutting relationships, and fibrous (antitaxial) texture in Moenkopi and Mars veins suggest emplacement via hydraulic fracture at low temperatures. Moenkopi and Mars veins are interpreted as late-stage diagenetic features that have experienced little alteration since emplacement. Moenkopi veins are useful terrestrial analogs for Mars veins because vein geometry, texture, and chemistry record information about crustal deformation and vein emplacement.

  4. Passive Neutron Non-Destructive Assay for Remediation of Radiological Waste at Hanford Burial Grounds- 13189

    Energy Technology Data Exchange (ETDEWEB)

    Simpson, A.; Pitts, M. [Pajarito Scientific Corporation, 2976 Rodeo Park Drive East, Santa Fe, NM 87505 (United States); Ludowise, J.D.; Valentinelli, P. [Washington Closure Hanford, 2620 Fermi Ave., Richland, WA 99354 (United States); Grando, C.J. [ELR Consulting, Inc., 15247 Wilbur Rd., La Conner, WA 98257 (United States); Haggard, D.L. [WorleyParsons Polestar, 601 Williams Blvd., Richland, WA 99354 (United States)

    2013-07-01

    The Hanford burial grounds contains a broad spectrum of low activity radioactive wastes, transuranic (TRU) wastes, and hazardous wastes including fission products, byproduct material (thorium and uranium), plutonium and laboratory chemicals. A passive neutron non-destructive assay technique has been developed for characterization of shielded concreted drums exhumed from the burial grounds. This method facilitates the separation of low activity radiological waste containers from TRU waste containers exhumed from the burial grounds. Two identical total neutron counting systems have been deployed, each consisting of He-3 detectors surrounded by a polyethylene moderator. The counts are processed through a statistical filter that removes outliers in order to suppress cosmic spallation events and electronic noise. Upon completion of processing, a 'GO / NO GO' signal is provided to the operator based on a threshold level equivalent to 0.5 grams of weapons grade plutonium in the container being evaluated. This approach allows instantaneous decisions to be made on how to proceed with the waste. The counting systems have been set up using initial on-site measurements (neutron emitting standards loaded into surrogate waste containers) combined with Monte Carlo modeling techniques. The benefit of this approach is to allow the systems to extend their measurement ranges, in terms of applicable matrix types and container sizes, with minimal interruption to the operations at the burial grounds. (authors)

  5. Eclogite inclusions from subducted metaigneous continental crust (Malpica-Tui Allochthonous Complex, NW Spain): Petrofabric, geochronology, and calculated seismic properties

    Science.gov (United States)

    Puelles, P.; Beranoaguirre, A.; Ábalos, B.; Gil Ibarguchi, J. I.; García de Madinabeitia, S.; Rodríguez, J.; Fernández-Armas, S.

    2017-07-01

    This study describes the strain geometry, crystal-plastic deformational features, isotopic age of metamorphism, and calculated seismic properties of two medium-temperature eclogite types from the Malpica-Tui Allochthonous Complex of Variscan NW Iberia. The eclogite types are eclogites with coronitic garnets and eclogites with a planolinear fabric. Both of them were buried, deformed and recrystallized under maximum pressure and temperature of 2.6 GPa and 610-640°C, and subsequently exhumed in a late Devonian subduction channel. The metamorphic peak of the subduction-exhumation cycle occurred 375 Ma ago. Omphacite petrofabric ties eclogites with coronitic garnet to noncoaxial constrictional strain and eclogites with planolinear fabrics to noncoaxial flattening strain and stretching along the lineation. We also used omphacite crystallographic preferred orientations to calculate and constrain the seismic properties of the eclogites. The slight variations in petrophysical properties observed are interpreted to result from variations in the strain regime recorded by pristine eclogites, or from variations in the modal proportions of the constituent high-pressure minerals. We foresee that eclogite in subduction metamorphic complexes might be either seismically undetectable or detected as planar features with high impedance contrasts relative to their host rocks.

  6. Post-rift vertical movements and horizontal deformations in the eastern margin of the Central Atlantic: Middle Jurassic to Early Cretaceous evolution of Morocco

    Science.gov (United States)

    Bertotti, Giovanni; Gouiza, Mohamed

    2012-11-01

    Wide regions of Morocco, from the Meseta to the High Atlas, have experienced km-scale upward vertical movements during Middle Jurassic to Early Cretaceous times following the appearance of oceanic crust in the Central Atlantic. The area experiencing exhumation was flanked to the W by a domain of continuous subsidence, part of which is named the Essaouira-Agadir basin. Comparison with vertical movement curves predicted by lithospheric thinning models shows that only 50-60 % of the subsidence documented in the Essaouira basin can be explained by post-rift thermal relaxation and that <30-40 % of the observed exhumation can be explained by processes (in)directly related to the evolution of the Central Atlantic rifted margin. Syn-sedimentary structures in Middle Jurassic to Lower Cretaceous formations of the Eassouira-Agadir basin are common and range from m-scale folds and thrusts to km-scale sedimentary wedges. These structures systematically document coeval shortening generally oriented at high angle to the present margin. As a working hypothesis, it is suggested that regional shortening can explain the structural observations and the enigmatic vertical movements.

  7. A stable isotope record of late Cenozoic surface uplift of southern Alaska

    Science.gov (United States)

    Bill, Nicholas S.; Mix, Hari T.; Clark, Peter U.; Reilly, Sean P.; Jensen, Britta J. L.; Benowitz, Jeffrey A.

    2018-01-01

    Although the timing of an acceleration in late-Cenozoic exhumation of southern Alaska is reasonably well constrained as beginning ∼5-∼6 Ma, the surface uplift history of this region remains poorly understood. To assess the extent of surface uplift relative to rapid exhumation, we developed a stable isotope record using the hydrogen isotope composition (δD) of paleo-meteoric water over the last ∼7 Ma from interior basins of Alaska and Yukon Territory. Our record, which is derived from authigenic clays (δDclay) in silicic tephras, documents a ∼50-60‰ increase in δD values from the late Miocene (∼6-∼7 Ma) through the Plio-Pleistocene transition (∼2-∼3 Ma), followed by near-constant values over at least the last ∼2 Ma. Although this enrichment trend is opposite that of a Rayleigh distillation model typically associated with surface uplift, we suggest that it is consistent with indirect effects of surface uplift on interior Alaska, including changes in aridity, moisture source, and seasonality of moisture. We conclude that the δDclay record documents the creation of a topographic barrier and the associated changes to the climate of interior Alaska and Yukon Territory.

  8. Geometry and kinematics of shear zones formed during continental extension in eastern Papua New Guinea

    Science.gov (United States)

    Hill, E. J.

    1994-08-01

    The D'Entrecasteaux Islands, eastern Papua New Guinea, lie in an area of continental extension that has been active since the mid-Miocene. During the last 4 Ma the metamorphic basement rocks composing most of the islands have been uplifted and tectonically exhumed from depths of approximately 35 km. Tectonic exhumation appears to have been controlled by deformation in broad (kilometre-scale) mylonitic shear zones. A progressive evolution is documented in the shear zones, characterized by: increasing localized deformation; a change from dominantly ductile to dominantly brittle processes; and decreasing metamorphic grade (i.e. retrograde metamorphism). The evolution is believed to be the result of uplift and cooling of the basement accompanying shear zone movement. The kinematic history of the shear zones is complex. A number of sinistrally offset extensional detachment zones separate a multiply deformed, high-grade metamorphic basement from a cover of largely undeformed ultramafic and mafic cover rocks. The detachment zones are connected by transverse shear zones. These transverse zones appear to act as sinistral strike-slip zones which also accommodate transfer motion between the detachment zones.

  9. Raman spectroscopy of detrital garnet from the (U)HP terrane of eastern Papua New Guinea

    Science.gov (United States)

    Andò, Sergio; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Malusà, Marco G.; Aliatis, Irene; Vezzoli, Giovanni; Garzanti, Eduardo

    2013-04-01

    Garnet is one of the most widespread heavy minerals in sediments derived from orogenic systems. Its chemical composition varies systematically with temperature and pressure conditions, and thus provides information on the metamorphic evolution of source areas that is crucial in tectonic and geodynamic reconstructions. Garnet is easily identified in mineral grain mounts and is relatively stable during burial diagenesis. Raman spectroscopy allows rapid determination of garnet compositions in grain mounts or thin sections of sand and sandstone samples, and can be used to assess their density and chemical composition quite accurately ("MIRAGEM" method of Bersani et al., 2009; Andò et al., 2009). In the D'Entrecastreaux Islands of southeastern Papua New Guinea, the world's youngest (U)HP rocks are exposed. There, mafic rocks and their felsic host gneisses were metamorphosed under eclogite facies conditions from late Miocene to Pliocene, before being exhumed from depths of ~90 km (Baldwin et al., 2004, 2008). The eclogite preserves a peak assemblage of garnet, omphacite, rutile, phengite and Si02 (Hill and Baldwin, 1993). A coesite-eclogite has been found in one small island outcrop. In order to sample garnet populations representative of a larger geographical area, we sampled and studied a heavy-mineral-dominated placer sand (HMC 80) from a beach from SE Goodenough Island. Garnet grains in beach sand are associated with blue-green to subordinately green-brown amphibole and minor epidote, omphacitic clinopyroxene, titanite, apatite and rutile. The subordinate low-density fraction is feldspatho-quartzose with high-rank metamorphic rock fragments and biotite (Q62 F35 Lm2; MI 360). Detrital garnets are mostly classified as almandine with relatively high Mg and Ca and lacking Mn, typical of the eclogite facies (Win et al., 2007; type Ci garnets of Mange and Morton 2007; Andò et al., 2013). In well-described stratigraphic sequences within syn-and post-tectonic basins

  10. Evaluation of a self-guided transport vehicle for remote transportation of transuranic and other hazardous waste

    Energy Technology Data Exchange (ETDEWEB)

    Rice, P.M.; Moody, S.J.; Peterson, R. [and others

    1997-04-01

    Between 1952 and 1970, over two million cubic ft of transuranic mixed waste was buried in shallow pits and trenches in the Subsurface Disposal Area at the Idaho National Engineering Laboratory`s Radioactive Waste Management Complex. Commingled with this two million cubic ft of waste is up to 10 million cubic ft of fill soil. The pits and trenches were constructed similarly to municipal landfills with both stacked and random dump waste forms such as barrels and boxes. The main contaminants are micron-sized particles of plutonium and americium oxides, chlorides, and hydroxides. Retrieval, treatment, and disposal is one of the options being considered for the waste. This report describes the results of a field demonstration conducted to evaluate a technology for transporting exhumed transuranic wastes at the Idaho National Engineering and Environmental Laboratory (INEEL) and at other hazardous or radioactive waste sites through the U.S. Department of Energy complex. The full-scale demonstration, conducted at the INEEL Robotics Center in the summer of 1995, evaluated equipment performance and techniques for remote transport of exhumed buried waste. The technology consisted of a Self-Guided Transport Vehicle designed to remotely convey retrieved waste from the retrieval digface and transport it to a receiving/processing area with minimal human intervention. Data were gathered and analyzed to evaluate performance parameters such as precision and accuracy of navigation and transportation rates.

  11. Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria)

    Science.gov (United States)

    Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Vitale-Brovarone, Alberto; Fernandez, Laure; Hammor, Dalila; Laouar, Rabah; Ouabadi, Aziouz; Abdallah, Nachida; Mechati, Mehdi

    2017-09-01

    Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

  12. The stratigraphy and evolution of lower Mount Sharp from spectral, morphological, and thermophysical orbital data sets.

    Science.gov (United States)

    Fraeman, A A; Ehlmann, B L; Arvidson, R E; Edwards, C S; Grotzinger, J P; Milliken, R E; Quinn, D P; Rice, M S

    2016-09-01

    We have developed a refined geologic map and stratigraphy for lower Mount Sharp using coordinated analyses of new spectral, thermophysical, and morphologic orbital data products. The Mount Sharp group consists of seven relatively planar units delineated by differences in texture, mineralogy, and thermophysical properties. These units are (1-3) three spatially adjacent units in the Murray formation which contain a variety of secondary phases and are distinguishable by thermal inertia and albedo differences, (4) a phyllosilicate-bearing unit, (5) a hematite-capped ridge unit, (6) a unit associated with material having a strongly sloped spectral signature at visible near-infrared wavelengths, and (7) a layered sulfate unit. The Siccar Point group consists of the Stimson formation and two additional units that unconformably overlie the Mount Sharp group. All Siccar Point group units are distinguished by higher thermal inertia values and record a period of substantial deposition and exhumation that followed the deposition and exhumation of the Mount Sharp group. Several spatially extensive silica deposits associated with veins and fractures show that late-stage silica enrichment within lower Mount Sharp was pervasive. At least two laterally extensive hematitic deposits are present at different stratigraphic intervals, and both are geometrically conformable with lower Mount Sharp strata. The occurrence of hematite at multiple stratigraphic horizons suggests redox interfaces were widespread in space and/or in time, and future measurements by the Mars Science Laboratory Curiosity rover will provide further insights into the depositional settings of these and other mineral phases.

  13. Apatite fission track thermochronology in the Kuluketage and Aksu areas, NW China: Implication for tectonic evolution of the northern Tarim

    Directory of Open Access Journals (Sweden)

    Zhiyong Zhang

    2016-03-01

    Full Text Available Tarim Precambrian bedrocks are well exposed in the Kuluketage and Aksu areas, where twenty four samples were taken to reveal the denudation history of the northern Tarim Craton. Apatite fission track dating and thermal history modeling suggest that the northern Tarim experienced multi-stage cooling events which were assumed to be associated with the distant effects of the Cimmerian orogeny and India-Eurasia collision in the past. But the first episode of exhumation in the northern Tarim, occurring in the mid-Permian to Triassic, is here suggested to be induced by docking of the Tarim Craton and final amalgamation of the Central Asian Orogenic Belt. The cooling event at ca. 170 Ma may be triggered by the Qiangtang-Eurasia collision. Widespread Cretaceous exhumation could be linked with docking of the Lhasa terrane in the late Jurassic. Cenozoic reheating and recooling likely occurred because of the north-propagating stress, however, this has not affected the northern Tarim much because the Tarim is characterized by rigid block-like motion.

  14. Documenting feedbacks between surface processes and structural deformation in East Timor using stream profile and drainage network analysis

    Science.gov (United States)

    Tate, G. W.; Willett, S.; McQuarrie, N.; Goren, L.; Fox, M.

    2013-12-01

    While river profile analyses have long been used to evaluate the development of landforms, recent advances in analyzing drainage networks have significantly improved the ability to positively link stream profiles with surface uplift. In one such method, Perron and Royden (2012) define the value chi, an integral quantity based on the steady-state stream power equation which aids in determining the conformity of rivers and drainage basins to steady-state behavior. East Timor is an ideal location to test new methods using chi, as it is an active and unglaciated orogen with independent constraints of the deformational history through thermochronology and structural geology. We utilize the calculation of chi in our analyses of the drainage network to provide new constraints on the most recent uplift history of the island of Timor. Discontinuities in chi across drainage divides imply different steady state baselevel for hillslopes and therefore active migration of the divide. We confirm this by noting visible landslides in satellite images and asymmetries in hillslope steepness. Analyses of chi and elevation reveal in some locations that tributaries within a single basin have experienced distinctly different histories, documenting instances where previous river capture has occurred. In other locations the relationships between chi and elevation along single rivers denote spatial changes in surface uplift rate. Many of these observations from the drainage network correspond well to patterns of recent exhumation identified from thermochronologic analyses as well as structural constraints from field mapping and balanced cross-sections. Much of the fastest exhumation on the island (as indicated by zircon (U-Th)/He ages of 1.5-3.8 Ma and modeled exhumation rates of 1-3 mm/yr) is in the hinterland slate belt, which also contains the most stream profile remnants of paleo-capture events. Many locations of active river capture correspond well to independently constrained

  15. The Central Pamir domes as tracer of gravitational disequilibrium and deformation phases forced by deep-seated lithospheric processes

    Science.gov (United States)

    Rutte, Daniel; Fox, Matthew; Ratschbacher, Lothar

    2017-04-01

    Miocene gneiss domes in the Pamir allow unique insight into crustal-scale processes forming the Asian crust of the Pamir-Tibet Plateau. They were exhumed along normal-sense shear zones in an intermittent phase of N-S extension while earlier and later structures document N-S shortening. Recently, Schmidt et al. (2011), Stearns et al., (2013; 2015), Rutte et al. (a & b, accepted), and Hacker et al. (submitted) established a vast structural, petrologic, and geochronologic dataset for the Central Pamir domes. These studies interpreted the domes as a product of gravitational collapse. The dataset includes (micro)structural observations constraining the mechanism of exhumation, thermobarometry of the metamorphic rocks, petrochronologic data constraining timing of pro- and retrogression, a vast multi-method thermochronometric dataset including age-elevation and age-distance data, dates for normal-sense shear zones and barometric data on intrusive rocks. These data constrain the time-temperature, pressure-temperature, and time-pressure history of the dome rocks. We explore the dataset using one-dimensional thermal models. Our code solves the heat transfer equation and gives a transient solution allowing for variation of the geothermal gradient and thermal diffusivity. At this stage, our models suggest that exponential decay of an initially high exhumation rate of 6 km/Myr at 22 Ma to 0.5km/Myr at 13 Ma best explains the dataset. This suggests a one-time input of gravitational potential energy (GPE) that is successively decaying through crustal extension. Both, Asian crustal foundering or Indian slab breakoff may concur with this result. While the Central Pamir domes extend >400 km along strike of the orogen, little variation in timing of most of exhumation during N-S extension is observed. This suggests that the underlying mechanism - be it crustal foundering or slab breakoff - varied little along strike as well. References Hacker, B.R., Ratschbacher, L., Rutte, D

  16. Variable shortening rates in the Bhutan thrust belt: implications for strain partitioning in the eastern Himalayan-Tibetan orogenic system

    Science.gov (United States)

    Long, S. P.; McQuarrie, N.; Tobgay, T.; Coutand, I.; Cooper, F. J.; Reiners, P. W.; Wartho, J.; Hodges, K.

    2012-12-01

    We present data on the burial, displacement and exhumation history of the Himalayan fold-thrust belt in eastern Bhutan, which highlight temporal variability in shortening rates. 8 new 40Ar/39Ar ages from white mica (MAr), 32 new zircon (U-Th)/He ages (ZHe), 7 new apatite fission-track (AFT) ages, and one new U-Pb zircon (LA-MC-ICP-MS) metamorphic rim growth age are combined with published cooling ages and deformation temperatures, and incremental restorations of two published balanced cross-sections, to constrain a four-part record of shortening rates from ~23 Ma to the present. Previous work indicates that the Main Central thrust (MCT) sheet was emplaced between ~23-18 Ma, and that proximal Lesser Himalayan (LH) rocks were buried under the MCT sheet at ~20 Ma. After burial, LH rocks were deformed in two duplex systems, the lower LH duplex, with the MCT acting as the roof thrust and the Shumar thrust (ST) acting as the floor thrust, and the upper LH duplex, with the ST acting as the roof thrust. U-Pb zircon rim growth as young as ~15 Ma and a ~15 Ma MAr neoblastic mica growth age from rocks beneath the ST are interpreted as prograde metamorphism due to thrust burial via displacement on the ST. These data bracket construction of the lower LH duplex between 20-15 Ma. Thrust sheets of the lower LH duplex yield MAr ages (325-400°C) between 13-8 Ma, ZHe ages (185-195°C) between 6-10 Ma, and AFT ages (120-130°C) between 3-5 Ma, which are interpreted as the result of passive transport, uplift and erosion during translation over a subsurface footwall ramp and younger deformation of upper LH rocks. Exhumation rates for lower LH rocks were as high as 1.3-2.6 mm/yr, and slowed to 0.4-0.9 mm/yr after passing over the footwall ramp. Thrust sheets of the upper LH duplex were exhumed from peak temperatures of 350-400°C to 185-195°C between 15 and ~9.5-10.5 Ma (ZHe ages). We attribute this pulse of rapid cooling, which corresponds to exhumation rates of 1.1-1.7 mm/yr, to

  17. Constraining the timing of Shillong Plateau uplift from a study of the palaeo-Brahmaputra deposits, Siwalik Group, Samdrup Jongkhar, Eastern Bhutan

    Science.gov (United States)

    Govin, G.; Najman, Y.; Grujic, D.; Van Der Beek, P.; Davenport, J.; Huyghe, P.

    2015-12-01

    The ~400 km long and two km high Shillong Plateau is the only major raised topography in the Himalayan foreland. Debates over the timing of uplift and implication for erosion-climate-tectonic couplings, strain partitioning within the Himalaya and the palaeodrainage history of the palaeo-Brahmaputra are important. Grujic et al, (2006) proposed that the uplift of the plateau has affected the exhumation of Himalayan rocks to the north in Bhutan, due to the creation of a regional climatic change in the plateau's rain shadow. By contrast, Coutand et al. (2014) suggest that the local decrease in erosion rates in the eastern Bhutan Himalaya is best explained by the decrease in overthrusting rates at 5-6 Ma, which might be potentially related to late Miocene to Pliocene changes in the India-southern Eurasia convergence partitioning, with shortening taken up by faults bounding the Shillong Plateau, i.e. by its uplift. The exhumation of the Shillong Plateau has been proposed to initiate by 8-15 Ma (Biswas et al, 2007; Clark & Bilham, 2008) whilst surface uplift, decoupled from exhumation, of Miocene (Chirouze et al 2013), Pliocene (Johnson and Nur Alam 1991; Biswas et al., 2007) and Early Quaternary (Najman et al, in review) have been proposed. Our study uses the foreland basin Siwalik sedimentary record preserved to the north of the Shillong Plateau in Bhutan, to constrain the plateau's uplift history. Provenance is characterized by U-Pb dating on detrital zircons, which allows specifically documenting an Indus-Yarlung suture-zone and therefore paleo-Brahmaputra signature. We document the timing that the palaeo-Brahmaputra was shunted north and west by the rising plateau, using this U/Pb provenance technique to detect first appearance of the river and to a minor degree the Namche Barwa syntaxe signature. The results allow to better constrain the period of uplifting of the Shillong Plateau and thus better inform the implications through a study of the palaeodrainage of the

  18. Depositional and provenance record of the Paleogene transition from foreland to hinterland basin evolution during Andean orogenesis, northern Middle Magdalena Valley Basin, Colombia

    Science.gov (United States)

    Moreno, Christopher J.; Horton, Brian K.; Caballero, Victor; Mora, Andrés; Parra, Mauricio; Sierra, Jair

    2011-10-01

    The Central Cordillera and Eastern Cordillera of the northern Andes form the topographic flanks of the north-trending Magdalena Valley Basin. Constraining the growth of these ranges and intervening basin has implications for Andean shortening and the transformation from a foreland to hinterland basin configuration. We present sedimentological, paleocurrent, and sandstone petrographic results from Cenozoic type localities to provide insights into the tectonic history of the northern Middle Magdalena Valley Basin of Colombia. In the Nuevo Mundo Syncline, the mid-Paleocene transition from marine to nonmarine deposystems of the Lisama Formation corresponds with a paleocurrent shift from northward to eastward transport. These changes match detrital geochronological evidence for a contemporaneous shift from cratonic (Amazonian) to orogenic (Andean) provenance, suggesting initial shortening-related uplift of the Central Cordillera and foreland basin generation in the Magdalena Valley by mid-Paleocene time. Subsequent establishment of a meandering fluvial system is recorded in lower-middle Eocene strata of the lower La Paz Formation. Eastward paleocurrents in mid-Paleocene through uppermost Eocene fluvial deposits indicate a continuous influence of western sediment source areas. However, at the upper middle Eocene (˜40 Ma) boundary between the lower and upper La Paz Formation, sandstone compositions show a drastic decrease in lithic content, particularly lithic volcanic fragments. This change is accompanied by a facies shift from mixed channel and overbank facies to thick, amalgamated braided fluvial deposits of possible fluvial megafans, reflecting changes in both the composition and proximity of western sediment sources. We attribute these modifications to the growing influence of exhumed La Cira-Infantas paleohighs in the axial Magdalena Valley, features presently buried beneath upper Eocene-Quaternary basin fill along the western flank of the Nuevo Mundo Syncline. In

  19. Erosional Reduction of an Orogenic Wedge: Structural Response to Neogene Climate Change within the St. Elias Orogen, Alaska

    Science.gov (United States)

    Berger, A. L.; Spotila, J. A.; Chapman, J. B.; Pavlis, T. L.; Enkelmann, E.; Buscher, J. T.

    2007-12-01

    The kinematics and architecture of orogenic systems may be heavily influenced by climate, but little research has focused on the long term effects of glacial erosion on orogenesis. Apatite and zircon (U-Th)/He thermochronometry on >75 bedrock samples across the St. Elias orogen, one of the best examples of a glaciated orogenic wedge, is the basis for a new kinematic model and demonstrates an association between glacial denudation and orogenic architecture. The spatial pattern of low temperature cooling indicates that exhumation and deformation are focused within a thin-skinned fold and thrust belt on the windward flank, whereas the leeward flank of the orogen functions as a deformational backstop. A previously unrecognized structure beneath the Bagley ice field must separate these domains with south-side-up motion. We propose this structure is a backthrust making the orogen doubly-vergent. Suggestive of accelerated backthrust motion in response to climate change, cooling rates within the hanging wall block and across the entire windward flank of the orogen accelerated ten-fold coeval with enhanced glaciation. As backthrust motion increased, glacial unroofing also coincided with a regional shift in deformation away from prominent forethrusts including the North American-Yakutat terrane suture (Chugach St. Elias fault) and the seaward deformation front (Pamplona zone). Across the windward flank of the orogen, exhumation, at rates of up to 5 mm/yr, is focused within a narrow zone, where the glacial equilibrium line altitude (ELA) intersects the orogenic wedge. This zone of rapid exhumation, not present prior to the onset of enhanced glaciation, cuts across the structural trend of the orogen and is more narrowly focused than orographic precipitation. Accelerated denudation at the ELA thus appears to have redistributed strain along a series of forethrusts that lie at the zone of heaviest glacial flux, while the backthrust progressively truncates the southward

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

    Science.gov (United States)

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

    2017-04-01

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

  1. Structural and rheological evolution of the Laramide subduction channel in southern California

    Science.gov (United States)

    Xia, Haoran; Platt, John P.

    2017-03-01

    The Pelona Schist in the San Gabriel Mountains, southern California, formed in the Laramide subduction channel, exhibits multiple phases of deformation/metamorphism and provides valuable insights into the rheological properties of the subduction channel. Petrological and microstructural analysis indicates that the Pelona Schist has undergone three major deformational/metamorphic events. Subduction of volcanic and sedimentary protoliths during D1 was recorded by aligned mineral inclusions in albite and epidote porphyroblasts. Metamorphic temperature and pressure at the end of subduction yielded by Raman spectroscopy of carbonaceous material and phengite barometry were 519 ± 20 °C and 10.5 ± 0.4 kbar, respectively. During D1 the dominant deformation mechanism was quartz pressure solution, and the estimated shear stress at the end of D1 was less than 10 MPa. D2, the first stage exhumation of the Pelona Schist along the upper section of the subduction channel during return flow, was recorded by retrogressive metamorphism, isoclinal folding, and a pervasive schistosity that wraps around earlier porphyroblasts. Metagreywacke was deformed mainly by quartz pressure solution and metachert was deformed dominantly by dislocation creep during D2. The shear stress in metagreywacke was less than 10 MPa and that in metachert was between 8.3 + 2.7/- 1.5 and 12.9 + .9/- 2.3 MPa, resulting in a strain rate of 1.4 × 10-13 to 5.5 × 10-13 s-1. A topography driven model is proposed as the main driving force of D2 exhumation. D3 records normal-sense movement on the Vincent Fault, which separates the schist from overlying arc and continental basement. This resulted in the second stage of exhumation, creating a major synform and associated mylonitic fabric in the upper section of the Pelona Schist. Conditions at the beginning of D3 were 390 ± 13 °C and 5.8 ± 0.8 kbar given by the TitaniQ thermometer and phengite geobarometer. The deformation was dominated by quartz dislocation

  2. Key role of Upper Mantle rocks in Alpine type orogens: some speculations derived from extensional settings for subduction zone processes and mountain roots

    Science.gov (United States)

    Müntener, Othmar

    2016-04-01

    Orogenic architecture and mountain roots are intrinsically related. Understanding mountain roots largely depends on geophysical methods and exhumed high pressure and high temperature rocks that might record snapshots of the temporal evolution at elevated pressure, temperatures and/or fluid pulses. If such high pressure rocks represent ophiolitic material they are commonly interpreted as exhumed remnants of some sort of 'mid-ocean ridge' processes. Mantle peridotites and their serpentinized counterparts thus play a key role in understanding orogenic architecture as they are often considered to track suture zones or ancient plate boundaries. The recognition that some mantle peridotites and their serpentinized counterparts are derived from ocean-continent transition zones (OCT's) or non-steady state (ultra-)slow plate separation systems question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. Among these are: (i) the commonly held assumption of a simple genetic link between mantle melting and mafic (MORB-type) magmatism, (ii) the commonly held assumption that mélange zones represent deep subduction zone processes at the plate interface, (iii) that pre-collisional continental crust and oceanic crust can easily be reconstructed to their original thickness and used for reconstructions of the size of small subducted oceanic basins as geophysical data from rifted margins increasingly indicate that continental crust is thinned to much less than the average 30-35 kilometers over a large area that might be called the 'zone of hyperextension', and (iv) the lack of a continuous sheet of mafic oceanic crust and the extremely short time interval of formation results in a lack of 'eclogitization potential' during convergence and hence a lack of potential for subsequent slab pull and, perhaps, a lack of potential for 'slab-breakoff'. Here we provide a synopsis of mantle rocks from the

  3. Transfer/transform relationships in continental rifts and margins and their control on syn- and post-rift denudation: the case of the southeastern Gulf of Aden, Socotra Island, Yemen

    Science.gov (United States)

    Pik, Raphael; Bellahsen, Nicolas; Leroy, Sylvie; Denele, Yoann; Razin, Philippe; Ahmed, Abdulhakim; Khanbari, Khaled

    2013-04-01

    Transfer zones are ubiquist features in continental rifts and margins, as well as transform faults in oceanic lithosphere. Here, we present the structural study of such a structure (the Hadibo Transfer Zone, HTZ) from the southeastern Gulf of Aden, in Socotra Island, Yemen. There, from field data, the HTZ is interpreted as being reactivated, obliquely to divergence, since early rifting stages. Then, from a short review of transfer/transform fault zone geometries worldwide, we derive a classification in terms of relative importance (1st, 2nd, 3rd order), geometry, and location. We suggest that the HTZ is a 1st order transfer fault zone as it controls the initiation of a 1st order oceanic transform fault zone. We then investigate the denudation history of the region surrounding the HTZ in order to highlight the interplay of normal and transfer/transform tectonic structures in the course of rift evolution. Samples belong from two distinct East and West domains of the Socotra Island, separated by the (HTZ). Tectonic denudation started during the Priabonian-Rupelian along flat normal faults and removed all the overlying sedimentary formations, allowing basement exhumation up to the surface (~ 1.2 - 1.6 km of exhumation). Forward t-T modelling of the data requires a slightly earlier date and shorter period for development of rifting in the E-Socotra domain (38 - 34 Ma), compared to the W-Socotra domain (34 - 25 Ma), which suggests that the HTZ was already active at that time. A second major event of basement cooling and exhumation (additional ~ 0.7 - 1 km), starting at about ~ 20 Ma, has only been recorded on the E-Socotra domain. This second denudation phase significantly post-dates local rifting period but appears synchronous with Ocean Continent Transition (OCT: 20 - 17.6 Ma). This late syn-OCT uplift is maximum close to the HTZ, in the wedge of hangingwall delimited by this transfer system and the steep north-dipping normal faults that accommodated the vertical

  4. Spatial variations in cooling rate in the mantle section of the Samail ophiolite in Oman: Implications for formation of lithosphere at mid-ocean ridges

    Science.gov (United States)

    Dygert, Nick; Kelemen, Peter B.; Liang, Yan

    2017-05-01

    To understand how the mantle cools beneath mid-ocean ridge spreading centers, we applied a REE-in-two-pyroxene thermometer and major element thermometers to peridotites from the Wadi Tayin massif in the southern part of the Samail ophiolite in the Sultanate of Oman, which represent more than 10 km of structural depth beneath the paleo-Moho. Closure temperatures for REEs in pyroxenes deduced from the REE-in-two-pyroxene thermometer (TREE) decrease smoothly and systematically with depth in the section, from >1300 °C near the crust to <1100 °C near the metamorphic sole, consistent with previously observed, similar variations in mineral thermometers with lower cooling temperatures. Estimated cooling rates decrease from ∼0.3 °C/y just below the crust-mantle transition zone (MTZ) to ∼10-3 °C/y at a depth of six km below the MTZ. Cooling rates derived from Ca-in-olivine thermometry also decrease moving deeper into the section. These variations in cooling rate are most consistent with conductive cooling of the mantle beneath a cold overlying crust. In turn, this suggests that hydrothermal circulation extended to the MTZ near the axis of the fast-spreading ridge where the igneous crust of the Samail ophiolite formed. These observations are consistent with the Sheeted Sills model for accretion of lower oceanic crust, and with previous work demonstrating very rapid cooling rates in the crust of the Wadi Tayin massif. Our observations, combined with previous results, suggest that efficient hydrothermal circulation beneath fast spreading centers cools the uppermost mantle from magmatic temperatures to <1000 °C as quickly as tectonic exhumation at amagmatic spreading centers. In contrast, thermometers sensitive to cooling over lower temperature intervals indicate that the Wadi Tayin peridotites cooled more slowly than tectonically exhumed peridotites sampled near the seafloor along mid-ocean ridges. Hydrothermal cooling of the crust may have waned, so that the crust

  5. Numerical Modelling of Subduction Plate Interface, Technical Advances for Outstanding Questions

    Science.gov (United States)

    Le Pourhiet, L.; Ruh, J.; Pranger, C. C.; Zheng, L.; van Dinther, Y.; May, D.; Gerya, T.; Burov, E. B.

    2015-12-01

    The subduction zone interface is the place of the largest earthquakes on earth. Compared to the size of a subduction zone itself, it constitutes a very thin zone (few kilometers) with effective rheological behaviour that varies as a function of pressure, temperature, loading, nature of the material locally embedded within the interface as well as the amount of water, melts and CO2. Capturing the behaviour of this interface and its evolution in time is crucial, yet modelling it is not an easy task. In the last decade, thermo-mechanical models of subduction zone have flourished in the literature. They mostly focused on the long-term dynamics of the subduction; e.g. flat subduction, slab detachment or exhumation. The models were validated models against PTt path of exhumed material as well as topography. The models that could reproduce the data all included a mechanically weak subduction channel made of extremely weak and non cohesive material. While this subduction channel model is very convenient at large scale and might apply to some real subduction zones, it does not capture the many geological field evidences that point out the exhumation of very large slice of almost pristine oceanic crust along localised shear zone. Moreover, modelling of sismological and geodetic data using short term tectonic modelling approach also point out that large localised patches rupture within the subduction interface, which is in accordance with geological data but not with large-scale long-term tectonic models. I will present how high resolution models permit to produce slicing at the subduction interface and give clues on how the plate coupling and effective location of the plate interface vary over a few millions of year time scale. I will then discuss the implication of these new high-resolution long-term models of subduction zone on earthquake generation, report progress in the development of self-consistent thermomechanical codes which can handle large strain, high resolution

  6. Direct Observation of Depth Variation in Fault Zone Structure Through and Below the Seismogenic Crust: Preliminary Results From the SEMP Fault System in Austria

    Science.gov (United States)

    Frost, E. K.; Dolan, J.; Sammis, C.; Hacker, B.; Ratschbacher, L.

    2004-12-01

    One of the most exciting and important frontiers in earthquake science is the linkage between the internal structure and the mechanical behavior of fault zones. In particular, little is known about how fault-zone structure varies as a function of depth, from near-surface conditions down through the seismogenic crust and into the ductile lower crust. Such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This imperative has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria. The SEMP system is an extremely rare example of a major strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. This exhumed fault system thus provides a unique opportunity to systematically examine depth-dependent changes in fault-zone geometry and structure along a single fault. Our ongoing field studies focus on structural transects across the SEMP fault zone at exhumation levels ranging from the near-surface at the eastern end of the fault (Vienna pull-apart basin), within the seismogenic crust (central Austria), and down into the ductile lower crust exposed in the Tauern window of western Austria. In addition to detailed field mapping of structural fabrics, fluid-rock interactions, relative timing relationships, and variations in fault geometry, we are also conducting detailed analyses of fault-zone rocks designed to explore deformation at a wide range of scales using petrographic microscopy, cathodoluminescence microscopy, fluid-inclusion studies, scanning-electron microscopy, and transmission/analytical-electron microscopy. Preliminary results from one of our first detailed study sites, at Gesäuse in central Austria, reveal strikingly asymmetric damage across the fault. The limestones exposed south of the fault are fractured, but relatively coherent to within a few meters of the main fault

  7. Constraints on the thermal evolution of the Adriatic margin during Jurassic continental break-up from U-Pb dating of rutile (Ivrea-Verbano Zone, Italy)

    Science.gov (United States)

    Ewing, T. A.; Rubatto, D.; Hermann, J.; Beltrando, M.

    2015-12-01

    U­-Pb dating of rutile is an ideal tool for exploring the cooling and exhumation history of the lower crust, given its moderate closure temperature and the occurrence of rutile in relevant lithologies. We present an example from the Ivrea-Verbano Zone (IVZ, Italy), a classic section through the Permian lower crust that records high-temperature metamorphism followed by extension and exhumation associated partly with the Jurassic opening of the Alpine Tethys ocean. Granulite facies metapelites collected across ~35 km have Zr-in-rutile temperatures that record crystallisation during Permian metamorphism and anatexis, but SHRIMP U-Pb dating of rutile records cooling through 650-550 °C in the Jurassic. Rutile age distributions are dominated by a peak at ~160 Ma, with a subordinate peak at ~175 Ma. Both age populations show excellent agreement between samples, indicating that the two distinctive cooling stages they record were synchronous on a regional scale. The ~175 Ma population is interpreted to record cooling in the footwall of rift-related faults and shear zones, for which widespread activity in the Lower Jurassic has been documented along the western margin of the Adriatic plate. The ~160 Ma age population postdates the activity of all known rift-related structures within the Adriatic margin, but coincides with extensive gabbroic magmatism and exhumation of sub-continental mantle to the floor of the Alpine Tethys, west of the IVZ. We propose that this ~160 Ma early post-rift age population records regional cooling following episodic heating of the distal Adriatic margin. The partial preservation of the ~175 Ma age cluster suggests that the post-rift (~160 Ma) heating pulse was of short duration. The regional consistency of the rutile U-Pb data is in contrast to many other thermochronometers in the IVZ, demonstrating the value of this technique for probing the thermal evolution of high-grade metamorphic terranes. The decoupling between Zr-in-rutile temperatures

  8. Phase Equilibria Modeling of Coesite Eclogite from the Sulu Belt, Eastern China

    Science.gov (United States)

    Xia, B.; Brown, M.; Wang, L.; Wang, S.; Piccoli, P. M.

    2016-12-01

    Modeling of phase equilibria and tectonic processes are essential components to understand controls on P-T paths of UHPM rocks. However, diffusion at higher temperatures (> 700 °C), and issues with determination of Fe3+ in minerals and estimating H2O contents limit our ability to determine prograde, peak P and retrograde P-T data. Also, the lack of an appropriate activity-composition model for melt in basic rocks has limited the application of phase equilibria modeling to understand partial melting associated with exhumation. Here we apply phase equilibria modeling to coesite eclogite from Yangkou to assess the influence of Fe3+ and fluid during metamorphism, monitor reactions and phase relations in eclogite during deep subduction and exhumation and investigate partial melting at HP conditions. The modeling used the THERMOCALC software and the new internally consistent thermodynamic dataset for basic rocks (http://www.metamorph.geo.uni-mainz.de/thermocalc/dataset6/index.html). Here we investigate bimineralic (gt+omp+coe/qz+ru/ilm), phengite-bearing (gt+omp+phen (2 samples, 5 vol%) +coe/qz+ru/ilm) and kyanite-bearing (gt+omp+phen+ky+coe/qz+ru/ilm) eclogites. Coesite in the matrix is the hallmark of the Yangkou eclogite. For each sample, we use an iterative process to estimate the H2O and O content in the bulk composition, and then calculate a P-T pseudosection. The results suggest that some prograde information (670-770 °C, > 3.0 GPa) is retained in large garnet cores in bimineralic and phengite-bearing eclogite. The peak P-T conditions are a challenge because in the field of gt+omp+coe/qz±phen+H2O at T > 750 °C and P > 3.5 GPa mode and compositional changes are small. However, isopleths of Si in phengite suggest that the peak P could have been > 5-6 GPa. Re-equilibration of garnet and omphacite compositions occurred during exhumation, yielding P-T conditions of 700-790 °C at 3.1-2.0 GPa. Amphibolite facies metamorphism occurred at 630-710 °C, 1.3-1.2 GPa. The

  9. The relationship between orogenesis, terrane accretion and the subduction of oceanic ridges in the Ecuadorian andes

    Science.gov (United States)

    Spikings, R.; Winkler, W.; Seward, D.; Hughes, R.; Handler, R.; Crowhurst, P.

    2003-04-01

    Oceanic hotspot activity, generating large oceanic igneous plateau provinces, plate rearrangements and the generation of new spreading centers since at least 90 Ma have formed large structural, thickness and density heterogeneities in the approaching and subducting oceanic crust offshore NW South America (SOAM). Various oceanic allochthonous terranes comprise western Ecuador and the relatively thick and buoyant Carnegie Ridge is being subducted. We present 40Ar/39Ar, fission track (FT) and (U-Th/He) data from i) the Eastern Cordillera and the Amotape Complex, which define the palaeo-continental margin, ii) the Western Cordillera, which is built upon allochthonous, oceanic crust and iii) a tectonic mélange at the ocean-continent suture. 40Ar/39Ar ages and FT data from exotic, Triassic blocks within the ocean-continent suture record elevated cooling rates of plateau basalts and the continental margin. 40Ar/39Ar ages and FT data from the palaeo-continental margin show that the entire contemporaneous continental margin was being cooled by rapid tectonic exhumation (combined with geochemical analyses, suggest that these periods of orogenesis were driven by stress imposed by the collision of terranes that originated at the Caribbean Plateau. Distinct periods of rapid cooling and exhumation of fault blocks in the W. Cordillera and the northern E. Cordillera occurred at ˜15 and ˜9 Ma. Cooling at ˜15 Ma was driven by the collision of the Carnegie Ridge with the trench at ˜15 Ma. The elevated, compressive stress field gave rise to a complex transcurrent system, resulting in uplift, exhumation and cooling in the northern E. Cordillera and extension in the southern E. Cordillera. Finally, FT and (U-Th)/He data record rapid cooling in the northern E. Cordillera and parts of the W. Cordillera at ˜6-5 Ma, suggesting that the middle Miocene transcurrent system was reactivated by thrust tectonics during the late Miocene, giving rise to the Interandean Valley, which split the

  10. Flattening of the Greater Himalayan Zone within the Eastern Himalaya: Insights from Pressure-Temperature-Structural Distance Trends from Central and Eastern Bhutan

    Science.gov (United States)

    Agustsson, K. S.; Gordon, S. M.; Long, S. P.; Seward, G.; Zeiger, K. J.; Penfold, M. L.

    2014-12-01

    Quantifying pressure-temperature (P-T) trends across structural thickness provides insight into the tectonic mechanisms for emplacement and exhumation of orogen-scale ductile thrust sheets in active continental collision zones. Furthermore, these trends can reveal, via metamorphic discontinuities, the presence or absence of intra-thrust sheet structures. The Greater Himalayan zone (GHZ) contains mid-crustal rocks exhumed during Neogene convergence between India and Asia; however, the mechanisms that drove their emplacement and exhumation are debated. Within the Bhutan Himalaya, an intra-GHZ structure, the Kakhtang thrust (KT) is proposed to separate the GHZ into structurally upper and lower levels, and is interpreted to extend across much of the eastern Himalaya. In this investigation, peak P-T conditions were determined for rocks from two transects through both levels of the GHZ in north-central and northeastern Bhutan, in order to evaluate the significance of the KT, and to better understand the emplacement mechanism of GHZ rocks. The composition of the phases Grt + Pl + Bt ± Ms ± St ± Amp ± Kfs from twelve metapelite and orthogneiss samples were analyzed using the electron microprobe at UC-Santa Barbara. Peak P-T estimates, determined via THERMOCALC and supplemented by Ti-in-biotite thermometry, show similar T- but differing P versus structural distance trends across each transect. A gradual decrease in temperatures structurally upsection (~750 ºC to 600 ºC) was observed on both transects, and in northeast Bhutan, a steep decreasing pressure trend (0.40 ± 0.08 kbar/km) is documented. In comparison, in north-central Bhutan, a super-lithostatic pressure gradient (0.74 ± 0.16 kbar/km) is observed across >5.5 km of structural thickness, and is interpreted to represent >60 % layer-normal flattening strain, similar in magnitude to flattening documented in GHZ rocks in south-central Bhutan. The documented gradients show no significant change in P-T conditions

  11. Petrology, geochemistry and modelling of the granulitic-ultramafic rocks in Beni Bousera (Rif, Morocco): implications for direct crust-mantle interactions and melt-extraction systems

    Science.gov (United States)

    Manthei, C. D.; Álvarez-Valero, A.; Jagoutz, O. E.

    2011-12-01

    The Beni Bousera (N. Morocco) and Ronda (S. Spain) ultramafic massifs of the Betic-Rif orogenic belt are two of the most pristine exposures of upper-mantle/lower crustal material on Earth's surface. Unlike other samples of the mantle, they are relatively unaltered and preserve a record of ultra-high pressure conditions, within the diamond-stability field (e.g. Slodkevich, 1980; Pearson et al., 1989). The process of removing of the massifs from the diamond-stability field, and the ensuing emplacement into the continental crust, is an ongoing area of research in regional tectonics. Here, we focus specifically on Beni Bousera, and note that the up-risen material is of higher density than its host, prompting the development of models that use melt-induced buoyancy forces as the primary driver of exhumation (Jagoutz et al., 2006; Gerya and Burg, 2007). We find evidence for discrete reaction zones in the ultramafic rocks that were formed by pervasive infiltration of melt, which may have channelized, lowered the integrated bulk density of the massif (e.g., Jagoutz et al., 2006), and driven exhumation. Since key questions concerning the emplacement mechanisms are still unanswered, complementary studies of the surrounding crustal material -granulitic rocks, which are mostly metapelitic with local intercalation of mafic composition-, assist in deepening our understanding crust-mantle processes. We will discuss our ongoing research at Beni Bousera, focusing on: (1) the petrological, structural, geochronological and physical relationships between mantle and crust by combining field petrology, petrography and phase diagram modeling, geochemistry, zircons/monazite dating, and numerical modeling; (2) the emplacement mechanisms of ultramafic and granulitic rocks by proposing a new hypothesis of very rapid exhumation of the mantle material. This rapid ascent is currently being constrained/tested by combining geobarometric calculations and high precision U-Pb zircon geochronology on

  12. Pemeriksaan Odontologi Forensik pada Identifikasi Korban Masal di Medan

    Directory of Open Access Journals (Sweden)

    Amri Amir

    2015-09-01

    Full Text Available Forensic odontology (FO has played an important role in the process of identification of unknown victims. This has help doctor dentist and forensic expert to a great extents. The process of identification of 2 plane crash victims of Garuda DC 10 in 1987 and Garuda Air-Bus in 1995, and 41 murder victims executed by Dukun AS after exhumationed are discussed here. The need of a well trained dentists in the field of FO is imperative as a companion of doctors and forensic experts in the process of examining cases of unknown origin criminal cases and mass disasters victims. It is expected in the future that the demand of Forensic Odontologist is a must in several health service centers in Indonesia.

  13. Reconstructing the transport history of pebbles on Mars

    Science.gov (United States)

    Szabó, Tímea; Domokos, Gábor; Grotzinger, John P.; Jerolmack, Douglas J.

    2015-01-01

    The discovery of remarkably rounded pebbles by the rover Curiosity, within an exhumed alluvial fan complex in Gale Crater, presents some of the most compelling evidence yet for sustained fluvial activity on Mars. While rounding is known to result from abrasion by inter-particle collisions, geologic interpretations of sediment shape have been qualitative. Here we show how quantitative information on the transport distance of river pebbles can be extracted from their shape alone, using a combination of theory, laboratory experiments and terrestrial field data. We determine that the Martian basalt pebbles have been carried tens of kilometres from their source, by bed-load transport on an alluvial fan. In contrast, angular clasts strewn about the surface of the Curiosity traverse are indicative of later emplacement by rock fragmentation processes. The proposed method for decoding transport history from particle shape provides a new tool for terrestrial and planetary sedimentology. PMID:26460507

  14. Cenozoic topographic build-up of the Iranien plateau: first constraints from low-temperature thermochronology

    Science.gov (United States)

    François, Thomas; Agard, Philippe; Meyer, Bertrand; Zarrinkoub, Mohammad; Chung, Sun-Lin; Bernet, Matthias; Burov, Evgueni

    2013-04-01

    The Iranian plateau is a smooth topographic high at the rear of the Zagros mountains, with average elevation of c. 1.5 km. Its formation is thought to result from the collision between the Arabian and Eurasian plates since ~35 Myrs, following a long-standing subduction, and represents an interesting analogue to the so far better documented Tibetan plateau. Yet, while the Zagros orogeny was reappraised by numerous authors over the past few years, the topographic build-up of both the Zagros and the Iranian plateau remains ill-constrained. We herein present (U-Th)/He and fission track (FT) thermochronology results to reconstruct the Cenozoic tectonic evolution of the Iranien plateau and quantify the age and amount of vertical movements. Apatite and zircon single grain cooling age data were collected on plutonic rocks (for which crystallization ages were already available: Chiu et al., 2010) from the internal domains of Sanandaj-Sirjan Zone (SSZ), Urumieh-Doktar magmatic arc (UDMA), Central Iran and, for comparison, Kopet Dagh. We stress that an important milestone for topographic build-up is the presence of the marine Qom formation (coeval with the external Asmari formation) in the UDMA and part of the SSZ, indicating that the plateau was at or near sea level at 20 Ma. Temperature time paths inferred from low temperature thermochronology suggest a spatial and temporal separation of exhumation processes. The results show that the SSZ was exhumed very early in the collision process (essentially before 20 Ma), with a likely acceleration around the Oligocene (i.e., at the onset of continental collision) from 0.05 to 0.3 mm/yr. Post-collision cooling along the UDMA is marked by an average, constant exhumation rate of 0.3-0.4 mm/yr, which suggests that no significant increase or decrease of erosion occurred since continental collision. In Central Iran, the overlap (within error) of ZrFT, AFT and AHe ages from gneissic samples points to their rapid cooling during the upper

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

    Science.gov (United States)

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

    2016-04-01

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

  16. Rapid middle Miocene extension and unroofing of the southern Ruby Mountains, Nevada

    Science.gov (United States)

    Colgan, Joseph P.; Howard, Keith A.; Fleck, Robert J.; Wooden, Joseph L.

    2010-01-01

    Paleozoic rocks in the northern Ruby Mountains were metamorphosed during Mesozoic crustal shortening and Cenozoic magmatism, but equivalent strata in the southern Ruby Mountains were never buried deeper than stratigraphic depths prior to exhumation in the footwall of a west dipping brittle normal fault. In the southern Ruby Mountains, Miocene sedimentary rocks in the hanging wall of this fault date from 15.2 to 11.6 Ma and contain abundant detritus from the Paleozoic section. Apatite fission track and (U-Th)/He samples of the Eocene Harrison Pass pluton record rapid cooling that peaked ca. 17–15 Ma, while apatite fission track data from Jurassic plutons east and west of the southern Ruby Mountains indicate near-surface temperatures (period of rapid extension (ca. 17–15 to 12–10 Ma) documented widely across the northern Basin and Range Province.

  17. Where are the bodies? A transnational examination of state violence and its consequences.

    Science.gov (United States)

    Keene, Judith

    2010-02-01

    This special issue of The Public Historian will examine what is a pressing, pervasive, traumatic, and very public contemporary issue in which history and historians are heavily involved in many countries around the globe. Authors will investigate a range of issues around the state involvement in death, including the role of the state as perpetrator and its responsibilities to the victims and their families; the process and significance of exhumation, of identification, and of repatriation; the status of refugees and displaced peoples who die when legally stateless and so without state protection; the differing transnational stances in tracing and punishing the perpetrators; the fraught issue of personal and official reparation; and the role and efficacy of international justice.

  18. Laboratory observations of artificial sand and oil agglomerates video and velocity data

    Science.gov (United States)

    Jenkins, Robert; Dalyander, P. Soupy; Penko, Allison; Long, Joseph W.; Nelson, Timothy

    2017-01-01

    The U.S. Geological Survey conducted experiments during March of 2014 to expand the available data on sand and oil agglomerate motion; test shear stress based incipient motion parameterizations in a controlled, laboratory setting; and directly observe sand and oil agglomerate exhumation and burial processes. Experiments were carried out at the Naval Research Laboratory, Stennis Space Center, Stennis, Mississippi using a small-oscillatory flow tunnel. HD Video data was collected by two Canon 7D DSLR cameras. 3D flow velocity data was captured by a Vectrino acoustic Doppler current profiler. Additional video data was captured by a GoPro camera placed within the small-oscillatory flow tunnel. For the false-floor incipient motion experiment, movies which combine video data, flow velocity data, calculations of shear stress, and the instant of incipient motion were created. For the movable bed sea-floor interaction experiment, movies which combine video data and flow velocity data were created.

  19. Discovery of Upper Oligocene-Lower Miocene brown coal deposits (Kosh-Agach formation) in the Dzhazator River valley (Southeastern Russian Altai): Neotectonic and paleogeographical aspects

    Science.gov (United States)

    Agatova, A. R.; Nepop, R. K.; Rudaya, N. A.; Khazina, I. V.; Zhdanova, A. N.; Bronnikova, M. A.; Uspenskaya, O. N.; Zazovskaya, E. P.; Ovchinnikov, I. Y.; Panov, V. S.; Shurygin, B. N.

    2017-08-01

    Results of complex paleontological and geochemical analysis are reported for a new locality of the Upper Oligocene-Lower Miocene Kosh-Agach carbonaceous formation in the Dzhazator River valley. This find specifies the scales of lacustrine-marsh sedimentation at the end of the Paleogene and beginning of the Neogene, as well as the character and amplitude of post-Neogene neotectonic movements in the southeastern highest mountain part of Russian Altai. Systematic rejuvenation of the radiocarbon age of the sequences studied, which has been established for the first time in Altai, is related to influx of young carbon during the subsequent complex geological history. This fact is of great importance for deciphering the chronology of Pleistocene glacial-dammed lakes in the intermontane basins of Altai and Tuva, the erosion zone of which spanned exhumed Tertiary deposits.

  20. Identification process in mass graves from the Spanish Civil War II.

    Science.gov (United States)

    Ríos, Luis; García-Rubio, Almudena; Martínez, Berta; Alonso, Andrea; Puente, Jorge

    2012-06-10

    The identification process of a mass grave from the Spanish Civil War (1936-1939) is presented. The presumed location of the grave, as well as the presumed number and identities of the persons buried in the grave were obtained exclusively from witnesses' and relatives' testimonies. In agreement with the testimonies, the grave was located at the indicated location and five skeletons were exhumed. Also in agreement with the testimonies, the osteological and DNA study led investigators to propose the identification of two kin groups, a father and his son and a pair of brothers. But the genetic study did not support the identification of a fifth man presumed to have been buried in the grave. The differences and similarities between this case and another case reported earlier are discussed. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

  1. Identification of two fire victims by comparative nuclear DNA typing of skeletal remains and stored umbilical tissues.

    Science.gov (United States)

    Calacal, Gayvelline C; De Ungria, Maria Corazon A; Delfin, Frederick C; Lara, Myra C; Magtanong, Danilo L; Fortun, Raquel

    2003-06-01

    We describe here our collaborative efforts in identifying 2 fatalities of a fire disaster by using a variety of identification techniques. Postmortem findings in both cases were reinforced using Short Tandem Repeat (STR) DNA technology to establish with a high degree of certainty the identities of 2 child victims. STR markers used in the present study include HUMAMEL, HUMCSFIPO, HUMTHO1, HUMvWA, HUMFES/FPS, HUMF13A01, HUMFOLP23, D8S3O6, HUMFGA, and HUMTPOX. Unambiguous identification was made possible through matching DNA profiles generated from skeletal remains with those from umbilical tissues. These tissues were kept by their mothers in accordance with a Philippine tradition and were submitted for DNA analysis. Of the DNA profiles generated from exhumed bone samples of 21 child victims, comparison with the genetic profiles of children A and B obtained from umbilical tissues showed consistent DNA matches with remains 1756 and 1758, respectively.

  2. A historical case of amelogenesis imperfecta: Giovanna of Austria, Grand Duchess of Tuscany (1547-1578).

    Science.gov (United States)

    Giuffra, Valentina; Panetta, Daniele; Salvadori, Piero A; Fornaciari, Gino

    2014-02-01

    The skeletal remains of Giovanna of Austria (1547-1578), daughter of the Emperor Ferdinand I of Habsburg (1503-1564) and first wife of the Grand Duke of Tuscany, Francesco I (1541-1587), exhumed from the Basilica of San Lorenzo in Florence, were submitted to paleopathological study. Examination of the dentition, which was in a good state of preservation, showed maxillary retrognathism, together with a caries lesion, moderate periodontal disease, malposition of the upper second premolars and tooth wear. Furthermore, several horizontal grooves were observed in both the buccal and the lingual crown surfaces of almost all teeth, especially the anterior ones. The orthopantomogram showed hypomineralized enamel and alveolar bone loss. Two third-molar teeth were investigated using micro-computed tomography (micro-CT) analysis, revealing highly irregular enamel caps with reduced average thickness. The observed features suggest a diagnosis of hypoplastic amelogenesis imperfecta, a developmental condition affecting enamel formation. © 2013 Eur J Oral Sci.

  3. The diseases of the medici family and the use of phytotherapy.

    Science.gov (United States)

    Lippi, Donatella

    2007-09-01

    The Medici Project is a paleopathological and historico-medical research, based on the exhumation of corpses of the Medici Family buried in the Medici Chapels (Florence, San Lorenzo). The scientific research carried out on these remains permits us to reconstruct habits and causes of death of members of this famous family of Italian Renaissance. The comparison between the literary sources and the paleopathological evidence is also important to reconstruct different therapies. Physicians, who assisted the most important persons of the Medici Family, have left a rich literature about their patients: the treatments were based on the use of plants and natural substances. Analyzing these sources is of unique importance and throws light on the therapeutical choices of the time.

  4. The Diseases of the Medici Family and the Use of Phytotherapy

    Directory of Open Access Journals (Sweden)

    Donatella Lippi

    2007-01-01

    Full Text Available The Medici Project is a paleopathological and historico-medical research, based on the exhumation of corpses of the Medici Family buried in the Medici Chapels (Florence, San Lorenzo. The scientific research carried out on these remains permits us to reconstruct habits and causes of death of members of this famous family of Italian Renaissance. The comparison between the literary sources and the paleopathological evidence is also important to reconstruct different therapies. Physicians, who assisted the most important persons of the Medici Family, have left a rich literature about their patients: the treatments were based on the use of plants and natural substances. Analyzing these sources is of unique importance and throws light on the therapeutical choices of the time.

  5. Geology of the Petersburg batholith, eastern Piedmont, Virginia

    Science.gov (United States)

    Owens, Brent E.; Carter, Mark W.; Bailey, Christopher M.

    2017-01-01

    The 295-300 Ma Petersburg batholith in east-central Virginia forms one of the largest and northernmost of the Alleghanian plutonic complexes in the southern Appalachian Piedmont. The batholith is primarily composed of granite including massive and foliated (both magmatic and solid-state fabrics) varieties. The plutonic complex intruded medium-grade metamorphosed volcanic/plutonic rocks of the Roanoke Rapids terrane. The western edge of the batholith experienced right lateral transpressional deformation associated with movement on the Hylas fault zone during the Alleghanian orogeny; this was followed by normal faulting and exhumation during the development of the Triassic Richmond basin. Much of the batholith was buried by a thin veneer of primarily Cenozoic siliciclastic sediments at the western edge of the Atlantic Coastal Plain. Granite rocks of the Petersburg batholith have long been quarried for both dimension and crushed stone. The purpose of this trip is to discuss the age, origin, and tectonic significance of the Petersburg batholith.

  6. Performance of geotextiles in landfills covers

    Energy Technology Data Exchange (ETDEWEB)

    Reitz, L.J.; Holtz, R.D.

    1997-11-01

    As part of the research into the performance of geotextiles in landfill covers, 14 test pits were excavated in five landfill covers constructed between 1988 and 1992 in Washington State. Materials used in the drainage system were examined and documented. Specimens of geotextiles (all 8 oz/yd{sup 2}, needle punched nonwovens) as well as samples of the vegetative and sand drainage soils, were obtained for laboratory analyses. Laboratory tests indicated that the geotextiles satisfactorily performed their intended filtration function. No apparent migration of fines into the drainage layer was detected. The degree of clogging was evaluated by performing permittivity tests on specimens of the exhumed geotextiles, as retrieved and after washing. Washing typically resulted in permittivity increases on the order of 30 to 90 percent.

  7. SOME FUNDAMENTAL PROBLEMS OF TECTONICS AND GEODYNAMICS OF THE CENTRAL ASIAN FOLDED BELT

    Directory of Open Access Journals (Sweden)

    I. V. Gordienko

    2014-01-01

    Full Text Available This study addresses some fundamental problems of tectonics and geodynamics of the Central Asian folded belt, the largest tectonic structure in Eurasia. The article presents results of long-term researches conducted by scientists and geologists specialized in various disciplines which contribute to the knowledge of the origin and breakup of Rodinia and formation of the Paleo-Asian Ocean. It considers problems of development of the Central Asian folded belt that was formed in the area of the Paleo-Asian Ocean and describes its subduction magmatism and marginal-marine sedimentation, formation of island arcs, processes of exhumation of the oceanic crust and formation of high-pressure blueschist and eclogite-blueschist complexes. Outstanding fundamental issues of the geodynamic evolution of the Central Asian folded belt are noted. 

  8. Human identification and analysis of DNA in bones.

    Science.gov (United States)

    Iwamura, Edna Sadayo Miazato; Soares-Vieira, José Arnaldo; Muñoz, Daniel Romero

    2004-12-01

    The introduction of molecular biology techniques, especially of DNA analysis, for human identification is a recent advance in legal medicine. Substantial effort has continuously been made in an attempt to identify cadavers and human remains after wars, socio-political problems and mass disasters. In addition, because of the social dynamics of large cities, there are always cases of missing people, as well as unidentified cadavers and human remains that are found. In the last few years, there has also been an increase in requests for exhumation of human remains in order to determine genetic relationships in civil suits and court action. The authors provide an extensive review of the literature regarding the use of this new methodology for human identification of ancient or recent bones.

  9. A variant of incaprettamento (ritual ligature strangulation) in East Timor.

    Science.gov (United States)

    Pollanen, Michael S

    2003-03-01

    Incaprettamento is a ritualized form of ligature strangulation often associated with the Italian Mafia. The hallmarks include ligature strangulation and binding of the body in a highly stereotyped fashion. The bindings include tying the wrists and ankles together, with the body in the prone position (similar to "hogtying"), and an additional ligature encircling the neck and attached to the bindings of the extremities. The binding of the body may be performed after death is inflicted by ligature strangulation, or it may be associated with self-strangulation, as shown by the arrangement of ligatures and the position of the body. A case with great similarities to incaprettamento, in which the body was exhumed from a grave in East Timor, is described in detail. However, in addition to prone-position binding and a hyoid fracture, chopping wounds of a knee and blunt trauma to the posterior torso were found. The implication of these wounds is discussed in relation to incaprettamento.

  10. Uplift history of the Villány Hills (SW Hungary) based on paleontological data

    Science.gov (United States)

    Sebe, Krisztina; Pazonyi, Piroska; Gasparik, Mihály; Lajos Szujó, Gábor

    2015-04-01

    Villány Hills are the southernmost basement outcrop in Hungary, along the northern margin of the Drava Basin. They comprise part of a Cretaceous nappe in the Tisza structural unit. Data on their young tectonic evolution are scarce, mostly due to the almost complete lack of Cenozoic sediments. Though somewhat debated, indirect data suggest that most of the area was covered by Upper Miocene (Lake Pannon) clastic sediments. Uplift and exhumation of the basement was driven by Late Miocene to post-Miocene basin inversion. A unique opportunity to study the uplift history is offered by paleontological data, by small but numerous terrestrial vertebrate sites, which cover a long time span in the Pliocene and Pleistocene. Faunas accumulated in fissure fillings of karstified limestone and thus provide a minimum age for the subaerial exposure (exhumation) of the bedrock at the given site. For some sites it has been proposed that water-linked species in the fauna refer to the existence of an alluvial plain on the clastic cover, in immediate proximity to the bedrock. If true, this would give an exact elevation of the surrounding terrain at the time indicated by the fauna. If exhumation of the basement happened during the time interval covered by the vertebrate faunas, then a relationship is expected to exist between the age and elevation of the the fossil sites, with the youngest faunas lying at lowest elevation. This relationship is expected to be strictly valid primarily in the case of water-linket faunas, but as a trend also for all fossil sites. We collected the age data and ecological requirements of the reliably datable vertebrate faunas and their locations with the possible precision. Then the relationship between the elevation and age was studied and compared to the available geomorphological, sedimentological and tectonic data. The age-elevation distribution of vertebrate faunas did not show the expected relationship. Based on the results, exhumation of the Vill

  11. The Medici syndrome: a medico-historical puzzle.

    Science.gov (United States)

    Weisz, George M; Matucci-Cerinic, Marco; Albury, William R; Lippi, Donatella

    2010-05-01

    The historical significance of the Medici family of Florence is widely recognised, but the diseases which afflicted leading members of this family have only been scientifically studied in recent decades. Paleopathological findings on exhumed skeletons, supplemented by medical descriptions in historical documents, have permitted a retrospective diagnosis of a triple pathological syndrome in the senior branch of the Medici family. Peripheral joint and spinal conditions, with the presence of skin disease, are identified in several generations of the family in the 15th century and are presented as the 'Medici syndrome'. Radiological findings are compared with macro- and microscopical descriptions in the diagnosis of the peripheral joint disease and spinal ankylosis/stenosis within the syndrome.

  12. Farallon slab detachment and deformation of the Magdalena Shelf, southern Baja California

    Science.gov (United States)

    Brothers, Daniel S.; Harding, Alistair J.; Gonzalez-Fernandez, Antonio; Holbrook, W.S. Steven; Kent, Graham M.; Driscoll, Neal W.; Fletcher, John M.; Lizarralde, Daniel; Umhoefer, Paul J.; Axen, Gary

    2012-01-01

    Subduction of the Farallon plate beneath northwestern Mexico stalled by ~12 Ma when the Pacific-Farallon spreading-ridge approached the subduction zone. Coupling between remnant slab and the overriding North American plate played an important role in the capture of the Baja California (BC) microplate by the Pacific Plate. Active-source seismic reflection and wide-angle seismic refraction profiles across southwestern BC (~24.5°N) are used to image the extent of remnant slab and study its impact on the overriding plate. We infer that the hot, buoyant slab detached ~40 km landward of the fossil trench. Isostatic rebound following slab detachment uplifted the margin and exposed the Magdalena Shelf to wave-base erosion. Subsequent cooling, subsidence and transtensional opening along the shelf (starting ~8 Ma) starved the fossil trench of terrigenous sediment input. Slab detachment and the resultant rebound of the margin provide a mechanism for rapid uplift and exhumation of forearc subduction complexes.

  13. Biotechnology and bioforensics new trends

    CERN Document Server

    Kumar, Amit

    2015-01-01

    This Brief covers broad areas of Applied Biology specifically into the domains of Biotechnology/Biomedicine and Forensic Science. Chapters included here would also explain the role of bioinformatics in protein and gene characterization, modeling of the protein structure, survey related to the chromosomal effect on Human Disorders like Diabetes and Cardiac Problems. This Brief is full of Innovative Literature like Use of Microbes in Electricity Production, Brain connection to Type 2 Diabetes etc. Interesting issues in Forensic biology and the aspects of Bioforensics like STR profiling of exhumed bones makes this brief truly useful and informative for Researchers. It also includes the advancements and new ideologies in understanding crop improvements & crop quality. This Brief witnesses Innovative Research related to the Bio and Agri software development too which are capable of accelerating Insilico biological data analysis.

  14. Stratigraphic architecture of Devonian lacustrine basins of northern Scotland

    DEFF Research Database (Denmark)

    Kristiansen, Thorben; Moreau, Julien; Andrews, Steven D.

    interpretations. The studied deposits have been deeply buried then exhumed so that they are exposed widely onshore. Post Caledonian tectonism has faulted and folded the Devonian succession making it challenging to reconstruct the stratigraphy and the basin architecture from geological data only. The Devonian...... sediments were deposited in a continental environment and fluvial and alluvial deposits are interbedded with lacustrine units. These lacustrine facies contain fishbeds which are organic rich mudstones with moderate source potential. Variations in burial history have resulted in variations in the source rock...... profiles. Correlations made to deep borehole data (Tain-1 well) have allowed marker beds to be attributed to specific seismic reflections. Finally, gravimetric data are used to calculate the depth to basement. The main focus of this work is to fully interpret the seismic architecture of the Devonian basins...

  15. Geotechnical and geomechanical characterization of the "fault gouge" of the "Alhama de Murcia" active fault, SE Spain.

    Science.gov (United States)

    Rodriguez-Soto, Pablo; Tsige, Meaza; Insua-Arevalo, Juan M.; Martinez-Diaz, Jose J.; Rodriguez-Escudero, Emilio; Jurado, M. ª Jose; Crespo, Elena; Jiménez Molina, David

    2017-04-01

    Here we present the results of the mechanical and mineralogical study of the fault rock of the Alhama de Murcia fault. This fault is one of the most active faults in the Iberian Peninsula. It shows segments partially formed by exhumed fine grained fault rocks (fault gouge FG) with a thickness of more than 50 m developed mainly in a brittle regime. Several strength and strain tests have been carried out, both in-situ and in laboratory, considering different stress orientations in relation to the tectonic fabric. Undisturbed samples encountered from two fault observatory boreholes drilled near Lorca, (FAM-1 and FAMSIS-IGN, of 174 and 40 m depth, respectively) has been used for the laboratory tests. The FG shows a hard soil and soft rock like mechanical behavior with uniaxial compressive strength 1.19) for planes unfavourably oriented.

  16. Assessing mobility and redistribution patterns of sand and oil agglomerates in the surf zone.

    Science.gov (United States)

    Dalyander, P Soupy; Long, Joseph W; Plant, Nathaniel G; Thompson, David M

    2014-03-15

    Heavier-than-water sand and oil agglomerates that formed in the surf zone following the Deepwater Horizon oil spill continued to cause beach re-oiling 3years after initial stranding. To understand this phenomena and inform operational response now and for future spills, a numerical method to assess the mobility and alongshore movement of these "surface residual balls" (SRBs) was developed and applied to the Alabama and western Florida coasts. Alongshore flow and SRB mobility and potential flux were used to identify likely patterns of transport and deposition. Results indicate that under typical calm conditions, cm-size SRBs are unlikely to move alongshore, whereas mobility and transport is likely during storms. The greater mobility of sand compared to SRBs makes burial and exhumation of SRBs likely, and inlets were identified as probable SRB traps. Analysis of field data supports these model results. Published by Elsevier Ltd.

  17. GRS evidence and the possibility of paleooceans on Mars

    Science.gov (United States)

    Dohm, J.M.; Baker, V.R.; Boynton, W.V.; Fairen, A.G.; Ferris, J.C.; Finch, M.; Furfaro, R.; Hare, T.M.; Janes, D.M.; Kargel, J.S.; Karunatillake, S.; Keller, J.; Kerry, K.; Kim, K.J.; Komatsu, G.; Mahaney, W.C.; Schulze-Makuch, D.; Marinangeli, L.; Ori, G.G.; Ruiz, J.; Wheelock, S.J.

    2009-01-01

    The Gamma Ray Spectrometer (Mars Odyssey spacecraft) has revealed elemental distributions of potassium (K), thorium (Th), and iron (Fe) on Mars that require fractionation of K (and possibly Th and Fe) consistent with aqueous activity. This includes weathering, evolution of soils, and transport, sorting, and deposition, as well as with the location of first-order geomorphological demarcations identified as possible paleoocean boundaries. The element abundances occur in patterns consistent with weathering in situ and possible presence of relict or exhumed paleosols, deposition of weathered materials (salts and clastic minerals), and weathering/transport under neutral to acidic brines. The abundances are explained by hydrogeology consistent with the possibly overlapping alternatives of paleooceans and/or heterogeneous rock compositions from diverse provenances (e.g., differing igneous compositions). ?? 2008 Elsevier Ltd.

  18. Recovery and identification of human remains in post-conflict environments: A comparative study of the humanitarian forensic programs in Cyprus and Kosovo.

    Science.gov (United States)

    Mikellide, Maria

    2017-10-01

    This study follows the humanitarian forensic programs in Cyprus and Kosovo over a ten-year period with an emphasis on the role of local capacity building. It begins by providing an in-depth historical account of forensic activities, followed by a comparison of the rate of excavations, exhumations and identifications. Through this analysis, a repeated pattern emerges whereby forensic activities in Kosovo start with a surge in values, which drop drastically in the first few years of operations, followed by a steadily declining productivity curve. By contrast, in Cyprus, activities begin modestly, with lower values allowing for some modest growth. Close observation of the two programs provides indications as to the factors that may influence the development of forensic programs as well as the elements that need to be set in place to create an environment conducive to greater sustainability through local ownership and responsibility. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. What did Avicenna (Ibn Sina, 980-1037A.D.) look like?

    Science.gov (United States)

    Erolin, Caroline; Shoja, Mohammadali M; Loukas, Marious; Shokouhi, Ghaffar; Rashidi, Mohammada Reza; Khalili, Majid; Tubbs, R Shane

    2013-09-01

    We present a reconstruction of Avicenna's face from the only photograph of his skull available today. The photograph is more than 50 years old, and was obtained during the exhumation of Avicenna's tomb in Hamadan for relocation. The reconstruction procedure was performed by the Centre for Anatomy and Human Identification at the University of Dundee, UK. This is probably the first scholarly attempt to reconstruct Avicenna's face. Historians and clinicians who are interested in the history of medicine may find the current craniofacial analysis of Avicenna and the final output interesting and worth recording. The life, achievements and contributions of Avicenna to medical sciences and the influence of his "Canon" on Renaissance medicine are discussed. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  20. Thermal modeling and geomorphology of the south border of the Sao Francisco Craton: thermochronology by fission tracks in apatites;Modelagem termica e geomorfologia da borda sul do Craton do Sao Francisco: termocronologia por tracos de fissao em apatita

    Energy Technology Data Exchange (ETDEWEB)

    Hackspacher, Peter Christian [UNESP, Rio Claro, SP (Brazil). Inst. de Geociencias e Ciencias Exatas; Godoy, Daniel Francoso de; Franco, Ana Olivia Barufi [UNESP, Rio Claro, SP (Brazil). Pos-Graduacao em Geologia Regional; Ribeiro, Luiz Felipe Brandini [NUCLEARGEO, Rio Claro, SP (Brazil); Hadler Neto, Julio Cesar [Universidade Estadual de Campinas (IFGW/UNICAMP), SP (Brazil). Inst. de Fisica Gleb Wataghin

    2007-12-15

    Recent developments in Fission Track thermochronology associated to mesozoic-cenozoic erosion and tectonic presented trough thematic maps (isotemperature), permit to model the landscape evolution in the southern border of the Sao Francisco craton, southeastern Brazil. Paleotemperature, obtained by fission track analysis in apatite, is closely related to geomorphologic interpretations. The area suffered a complex imprint of endogenous and exogenous processes resulting diversified and differentiated relieves. The landscape is strongly controlled by exhumation between Jurassic and Lower Cretaceous, uplift with tectonic denudation related to crustal heating at the Upper Cretaceous and reactivation of faults until the Miocene. This scenario is a result of reactivations of different brittle structures that accommodate the deformation in the southern border of the Sao Francisco craton. The landscape reflects denudations of up to 3 km with preserved remains of erosive surfaces in the topographical tops and chronocorrelates deposits in the basins of the region. (author)

  1. Large-scale recumbent isoclinal folds in the footwall of the West Cycladic Detachment System (Greece)

    Science.gov (United States)

    Rice, A. Hugh N.; Grasemann, Bernhard

    2017-04-01

    The Pindos Zone in the Cyclades underwent Eocene high-pressure metamorphism and syn-orogenic exhumation, overprinted by Miocene low-angled extension. Although this represents a combination of likely high-strain-events, structural evidence of large-scale folding is rare. Here potential examples of such folding on Kea and Kythnos, in the Western Cyclades, are evaluated. These islands lie within the Cycladic Blueschist Nappe (lower nappe) of the Pindos Zone and in the footwall of the top-to-SSW West Cycladic Detachment System (WCDS). On Kea, no lithostratigraphy can be established in the 450 m thick greenschist facies mixed sedimentary-volcanoclastic-marble mylonite/phyllonite succession. On the east side of the island, lensoid marble layers frequently bifurcate, which might be reflecting early, sheared-out isoclinal folding, although no evidence of folded compositional layering has been found in potential fold-hinge zones and the bifurcation points are not arranged in a way suggestive of a fold axes parallel to the NNE-SSW oriented stretching lineation. However, at two localities, medium-scale recumbent isoclinal folding has been mapped, with NNE-SSW fold-axes exposed for up to 250 m and amplitudes of up to 170 m. On Kythnos, stretching lineations in greenschist facies rocks show a rotation from ENE-WSW in the north to NNE-SSW in the south, taken to represent a reorientation of the Eocene exhumation strain during block rotation coincident with top-to-SSW movement of the WCDS. The distribution of the three marble units that crop out in central/southern Kythnos suggest large-scale, likely isoclinal folding occurred. (1) Petroussa Lithodeme - a blue-grey calcite (BGC) marble with quartz-calcite-white-mica (QCWM) schists, forming a continuous outcrop around the island, thinning from >16m in the SE to cropping out above the Flabouria Lithodeme south of Aghios Dimitrios, directly below the WCDS; (3) Mavrianou Lithodeme - mylonitic QCWM schists with lenses of BGC mylonites

  2. How piecemeal is your caldera? Going beyond modelling to investigate the structural evolution of explosive caldera volcanoes

    Energy Technology Data Exchange (ETDEWEB)

    Willcox, Chris; Branney, Mike [University of Leicester, UK, LE1 7RH (United Kingdom); Carrasco-Nunez, Gerardo [Centro de Geociencias Campus Juraquilla, UNAM, Apdo. Postal 1-742 Queretaro, Qro. 76001 (Mexico)], E-mail: cpw14@le.ac.uk

    2008-10-01

    Despite a profusion of analogue models relatively little is known about the internal structure and temporal evolution of explosive caldera volcanoes. So how can modellers test their predictions given that the internal structures of many young calderas are concealed? Mapping ancient exhumed calderas has proven advantageous, yet this requires a large investment of time and expertise to constrain the structural evolution in sufficient detail. We aim to investigate the interplay between the structural evolution and eruption style over time at a modern caldera. We have selected Los Humeros (Mexico) because it is thought to be an example of a caldera with some piecemeal development, and it also has a well-exposed pyroclastic succession and abundant borehole data.

  3. Blueschists of the Inner Makran accretionary wedge, SE Iran: Petrography, geochemistry and thermobarometry

    Science.gov (United States)

    Hunziker, Daniela; Burg, Jean-Pierre; Caddick, Mark; Reusser, Eric; Omrani, Jafar

    2010-05-01

    Blueschist facies rocks are an essential element in all discussions related to subduction processes. Some incertitude concerns their depth of burial and subsequent exhumation mechanisms, which should involve tectonic processes sufficiently rapid to preserve mineral phases stable under high pressure - low temperature conditions. It has become crucial to understand and ascertain the thermobarometric conditions under which such rocks recrystallize in order to provide a precise record of vertical movements and thermal variations in accretionary wedges and related subduction zones. Fe3+/Fe2+ ratios of mineral phases, sodic amphiboles in particular, are important for metamorphic pressure and temperature calculations. However, these ratios are poorly known for most minerals. We approached the problem by studying the petrography, geochemistry and thermobarometry of scarcely surveyed blueschists, in northern Makran, comparing the influence of both bulk and mineral ferric/ferrous iron ratios on recalculated pressure and temperature conditions. The regional and thematic consequences of these preliminary results are discussed.

  4. Huygens Crater: Insights into Noachian Volcanism, Stratigraphy, and Aqueous Processes

    Science.gov (United States)

    Ackiss, S. E.; Wray, J. J.; Seelos, K. D.; Niles, P. B.

    2015-01-01

    Huygens crater is a well preserved peak ring structure on Mars centered at 13.5 deg S, 55.5 deg E in the Noachian highlands between Terras Tyrrhena and Sabaea near the NW rim of Hellas basin. With a diameter of approximately 470 km, it uplifted and exhumed pre-Noachian crustal materials from depths greater than 25 km, penetrating below the thick, ubiquitous layer of Hellas ejecta. In addition, Huygens served as a basin for subsequent aqueous activity, including erosion/deposition by fluvial valley networks and subsurface alteration that is now exposed by smaller impacts. Younger mafic-bearing plains that partially cover the basin floor and surrounding intercrater areas were likely emplaced by later volcanism.

  5. Metamorphic evolution of LT-UHP eclogite from the south Dabie orogen, central China: An insight from phase equilibria modeling

    Science.gov (United States)

    Wei, Chunjing; Cui, Ying; Tian, Zuolin

    2015-11-01

    suggests a flat P-T vector dominated by heating, representing a slower subduction process, and the mantle-rim zoning indicates a steep P-T vector dominated by increasing pressure, pointing to a faster subduction process. The post-peak exhumation of the LT-UHP eclogite involves two stages: the early-stage exhumation is dominated by lawsonite dehydrations, forming the porphyroblasts of epidote, paragonite and glaucophane under fluid-present conditions, and the late-stage exhumation occurs under fluid-absent conditions, forming hornblendic amphibole and plagioclase triggered by fluid-infiltration. As a consequence of the metamorphic evolution especially during the early-stage exhumation, the observed mineral assemblages in LT-UHP eclogites cannot well match those at their peak stages.

  6. The blueschits from the Kopina Mt., West Sudetes, Poland - what do they tell us about accretion of the Variscides?

    Science.gov (United States)

    Majka, Jarosław; Mazur, Stanisław; Kośmińska, Karolina; Dudek, Krzysztof

    2015-04-01

    cool subduction of the oceanic crust. Therefore, the origin of the studied rocks dates back to the time preceding accretion of the eastern Variscides and defines one of the key tectonic boundaries in the Bohemian Massif. A mechanism for syn-collisional emplacement and exhumation of the Kopina blueschists can be tentatively explained through activation of the double subduction system operating towards the east. First subduction commenced already in the Early Devonian and operated beneath an island arc located in proximity to the Saxothuringian margin, within the Rheic Ocean. After the mid-Devonian exhumation of the Central Sudetes allochthon, another subduction system was initiated along the eastern margin of the Rheic Ocean, beneath the Brunia microplate. Subducted oceanic crust of the Rheic Ocean (including the Kopina Mt. blueschists) reached peak metamorphic conditions in the Late Devonian, the event pronounced by a continental arc volcanism along the Brunian margin. Exhumation of the subducted oceanic crust was accommodated by the slab roll-back, which is inferred from the bimodal age and spatial distribution of the volcanic activity within the Brunian active margin. Shortly after the Kopina Mt. blueschists exhumation this eastern subduction system became probably inactive. In contrast, the western one involving the Saxothuringian margin was still operating leading to the subsequent collision with Brunia in the Early Carboniferous that produced a widespread high temperature overprint mostly wiping up the earlier metamorphic history.

  7. Upright folding during extensional and transtensional tectonics

    Science.gov (United States)

    Teyssier, Christian; Fossen, Haakon; Rey, Patrice F.; Whitney, Donna L.

    2017-04-01

    Upright folds are common structures that develop in response to horizontal shortening in layered material, for example in foreland basins that surround orogens. While the contractional nature of these folds is not in doubt, interpretation of their tectonic setting needs careful consideration. Here we focus on two examples: (1) folds developed in transtension; and (2) folds developed during the flow of deep crust in response to lithospheric extension. In both cases we consider folding of nearly horizontal layers that are either primary (bedding) or secondary (foliation). Strain theory inspired by John Ramsay's work makes predictions for the behavior of material lines and planes as well as strain axes (instantaneous, finite) during transtensional deformation. Results show: folds can form in transtension; fold hinges rotate toward the direction of divergence (and not the shear zone boundary as they do in transpression), providing unique insight into ancient plate motions; fold tightness is controlled by the obliquity of divergence and not finite strain; hinge parallel stretching is always greater than hinge-perpendicular shortening, resulting in constriction strain and boudinage of fold hinges. Taken together these results provide a rigorous framework for interpreting field observations where structures are complex and boundary conditions unclear. These principles are applied to various tectonic settings ranging from active tectonic regions of oblique divergence in western North America to ancient folding that developed during oblique extension of the Western Gneiss Region, deposition of Devonian basins, and exhumation of ultrahigh-pressure rocks in the Norwegian Caledonides. The other class of upright folds that form during extension may require revision of the tectonic interpretation of structural overprints in orogenic cores, for example in gneiss/migmatite domes. Dynamic modeling of extension of thick/hot crust predicts a positive feedback between extension of

  8. Le métamorphisme Tardi-Crétacé à Éocène des zones internes de la chaîne Indo-Birmane (Myanmar occidental) : implications géodynamiquesLate Cretaceous to Eocene metamorphism of the internal zone of the Indo-Burma range (western Myanmar): geodynamic implications

    Science.gov (United States)

    Socquet, Anne; Goffé, Bruno; Pubellier, Manuel; Rangin, Claude

    Metamorphic study on Triassic schists in the internal zone of the Indo-Burma range, essentially based on chlorite-mica equilibrium in metapelites, allows a P- T path to be quantified. During the prograde metamorphism, the geothermic gradient evolves from that of a 'normal' crust (30 °C km -1) to that of a thickened crust (18 °C km -1). The peak conditions are around 8 kbar and 450 °C. This thickening (25-30 km) is probably made in a wedge set up between the Late Cretaceous and the Eocene, in front of the obduction. The obtained cold retrograde path requires a mechanism allowing thermal re-equilibration, implying slow exhumation. It occurred along a shear zone that put into contact the micaschists of the core with the Triassic schists of the roof. To cite this article: A. Socquet et al., C. R. Geoscience 334 (2002) 573-580.

  9. Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

    Science.gov (United States)

    Townend, John; Sutherland, Rupert; Toy, Virginia G.; Doan, Mai-Linh; Célérier, Bernard; Massiot, Cécile; Coussens, Jamie; Jeppson, Tamara; Janku-Capova, Lucie; Remaud, Léa.; Upton, Phaedra; Schmitt, Douglas R.; Pezard, Philippe; Williams, Jack; Allen, Michael John; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin M.; Boulton, Carolyn; Broderick, Neil; Carpenter, Brett; Chamberlain, Calum J.; Cooper, Alan; Coutts, Ashley; Cox, Simon C.; Craw, Lisa; Eccles, Jennifer D.; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Henry, Gilles; Howarth, Jamie; Jacobs, Katrina; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Tim; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luis; Mori, Hiroshi; Niemeijer, André; Nishikawa, Osamu; Nitsch, Olivier; Paris, Jehanne; Prior, David J.; Sauer, Katrina; Savage, Martha K.; Schleicher, Anja; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Zimmer, Martin

    2017-12-01

    Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP-2). We present observational evidence for extensive fracturing and high hanging-wall hydraulic conductivity (˜10-9 to 10-7 m/s, corresponding to permeability of ˜10-16 to 10-14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP-2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging-wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off-fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.

  10. Cretaceous—Quaternary tectonic evolution of the Tatra Mts (Western Carpathians: constraints from structural, sedimentary, geomorphological, and fission track data

    Directory of Open Access Journals (Sweden)

    Králiková Silvia

    2014-08-01

    Full Text Available The Tatra Mts area, located in the northernmost part of Central Western Carpathians on the border between Slovakia and Poland, underwent a complex Alpine tectonic evolution. This study integrates structural, sedimentary, and geomorphological data combined with fission track data from the Variscan granite rocks to discuss the Cretaceous to Quaternary tectonic and landscape evolution of the Tatra Mts. The presented data can be correlated with five principal tectonic stages (TS, including neotectonics. TS-1 (~95-80 Ma is related to mid-Cretaceous nappe stacking when the Tatric Unit was overlain by Mesozoic sequences of the Fatric and Hronic Nappes. After nappe stacking the Tatric crystalline basement was exhumed (and cooled in response to the Late Cretaceous/Paleogene orogenic collapse followed by orogen-parallel extension. This is supported by 70 to 60 Ma old zircon fission track ages. Extensional tectonics were replaced by transpression to transtension during the Late Paleocene to Eocene (TS-2; ~80-45 Ma. TS-3 (~45-20 Ma is documented by thick Oligocene-lowermost Miocene sediments of the Central Carpathian Paleogene Basin which kept the underlying Tatric crystalline basement at elevated temperatures (ca. > 120 °C and < 200 °C. The TS-4 (~20-7 Ma is linked to slow Miocene exhumation rate of the Tatric crystalline basement, as it is indicated by apatite fission track data of 9-12 Ma. The final shaping of the Tatra Mts has been linked to accelerated tectonic activity since the Pliocene (TS-5; ~7-0 Ma.

  11. Along-Axis Structure and Crustal Construction Processes of Spreading Segments in Iceland: Implications for Magmatic Rifts

    Science.gov (United States)

    Siler, D. L.; Karson, J. A.

    2017-10-01

    Magmatic rift systems are composed of discrete spreading segments defined by morphologic, structural, and volcanic features that vary systematically along strike. In Iceland, structural features mapped in the glaciated and exhumed Miocene age upper crust correlate with analogous features in the seismically and volcanically active neovolcanic zone. Integrating information from both the active rift zones and ancient crust provides a three-dimensional perspective of crustal structure and the volcanic and tectonic processes that construct crust along spreading segments. Crustal exposures in the Skagi region of northern Iceland reveal significant along-strike variations in geologic structure. The upper crust at exhumed magmatic centers (segment centers) is characterized by a variety of intrusive rocks, high-temperature hydrothermal alteration, and geologic evidence for kilometer-scale subsidence. In contrast, the upper crust along segment limbs, which extend along strike from magmatic centers, is characterized by thick sections of gently dipping lava flows, cut by varying proportions of subvertical dikes. This structure implies relatively minor upper crustal subsidence and lateral dike intrusion. The differing modes of subsidence beneath segment centers and segment limbs require along-axis mass redistribution in the underlying upper, middle, and lower crust during crustal construction. This along-axis material transport is accomplished through lateral dike intrusion in the upper crust and by along-axis flow of magmatic to high-temperature solid-state gabbroic material in the middle and lower crust. These processes, inferred from outcrop evidence in Skagi, are consistent with processes inferred to be important during active rifting in Iceland and at analogous magmatic oceanic and continental rifts.

  12. U-Pb Geochronology, Geochemistry and Kinematic Analyses of Subduction-Related Late Triassic Basins in Northern Chile (24.5º-26ºS).

    Science.gov (United States)

    Espinoza, M. E.

    2015-12-01

    In northern Chile (24.5°-26°S) two Pre-Andean depocenters crop out: the Cifuncho basin in the Coastal Cordillera and the Profeta basin in the Precordillera. These basins have been classically interpreted as a continental rifting unrelated to subduction during the period prior to the Andean orogenic cycle. However, recent petrographic and geochemical data suggest the development of these basins in an active subduction system. In order to test this hypothesis and to establish the geologic evolution of the basins and the strain field during the rifting process, we present preliminary U-Pb geochronological and geochemical data together with structural analyses of synrift structures. The geochronological data along the Cifuncho and Profeta basins, show a main continental sedimentary deposition during the Norian to Raethian. Volcanosedimentary rocks show a main detrital supply of Early Permian age (~297-283 Ma). This input can be associated with the volcanic La Tabla Formation and/or the exhumation of Permian granitoids. A minor supply close to ~478 Ma is related to a source from the Lower Ordovician arc (~480 Ma), suggesting the tectonic exhumation of this source to the east of the Profeta basin during the Late Triassic. On the other hand, structural analysis was carried in third and four order extensional faults (<10 m of slip) along the Profeta basin. Most of the faults show a clear synrift character with the development of fault controlled growing strata. The kinematic analyses evidence a variability in the orientation of the maximum strain axes from a main northwest to a subordinate northeast direction of extension. Thus, the intimate relation between the continental sedimentary deposition and a proximal volcanism of intermediate composition and calk-alkaline affinity, suggests the development of these basins in a supra-subduction setting during the Late Triassic. Structural data probably reflect local variation in the strain field across the basins.

  13. Influence of thrust belt geometry and shortening rate on thermochronometer cooling ages: Insights from thermokinematic and erosion modeling of the Bhutan Himalaya

    Science.gov (United States)

    McQuarrie, Nadine; Ehlers, Todd A.

    2015-06-01

    Advancements in thermochronology and numerical modeling offer the potential to associate the age of thermochronometric samples to both exhumational and deformational processes. However, understanding how these components are related in compressional systems requires linking the geometry and magnitude of fault slip to the distribution and amount of erosion. To address this, we apply a 2-D thermokinematic model to a forward modeled balanced cross section to quantify the cooling history in fold-thrust belt settings. The restored cross section provides a kinematic path of rocks and structures necessary to reproduce the surface geology. By assigning ages to displacement amounts, we produced a range of potential velocity vectors used to calculate heat transport, erosion, and rock cooling. We test the predicted ages against a suite of previously published thermochronometric data from the Bhutan Himalaya to explore the utility of the data to constrain the timing, rate, and geometry of fault motion as well as variations in the exhumation rate. We evaluate the cooling history associated with a constant rate of shortening of 18 mm/yr, rates that are 2.0, 1.5, 0.75, and 0.5 times the constant rate, and rates that vary with time to determine which kinematic history best matches the measured cooling ages. The combination of relatively old apatite fission track and zircon (U-Th)/He measured ages and younger (15-9 Ma) 40Ar/39Ar ages from white mica is best matched with faster rates (relative to constant rates) between 11.5 and 8 Ma and slower than constant rates from 17 to 11.5 Ma and 8 Ma to present.

  14. Discriminating Sediment Supply versus Accommodation Controls on Foreland Basin Stratigraphic Architecture in the Book Cliffs, central Utah using Detrital Double Dating

    Science.gov (United States)

    Bartschi, N.; Saylor, J. E.; Blum, M. D.

    2014-12-01

    Middle-late Campanian strata of the Book Cliffs record the deposition of three clastic wedges in the foreland basin east of the Sevier fold-thrust belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin architecture. There is an increase in eastward progradation rate between the L. and M. Castlegate Sandstone, followed by a return to slower progradation rates in the overlying Bluecastle Tongue, and Price River Formation, as well as their lateral equivalents. Rapid progradation may be caused by increased sediment supply, due either to rapid exhumation in the Sevier fold-thrust belt, or changes in the sediment source. Alternatively, reduced accommodation within the foreland basin due to uplift during initial Laramide deformation could produce the same rapid progradation. In this scenario, decreased progradation would be coincident with enhanced foreland basin subsidence and rapid sediment accumulation in the proximal foredeep. We test these hypotheses using thermo- and geochronology to double date individual detrital grains, enabling identification of changes in lag time and sediment provenance. Upsection decreases or increases in lag time correspond to increased or decreased exhumation rates, respectively, or introduction of a new upper crustal sedimentary source. We focus on 21 samples from 7 measured sections along depositional strike and dip. Samples were collected from the upper Blackhawk Formation, L. and M. Castlegate Sandstone, Bluecastle Tongue, Price River Formation, and their lateral equivalents. Initial results indicate major sediment provenance changes associated with the transition between slow and rapid wedge progradation, as well as minor provenance changes within individual wedges. There is also a significantly greater proportion of Cordilleran magmatic arc grains in distal locations than in proximal locations, interpreted as sediment mixing during transport.

  15. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang

    2015-07-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  16. Observations of an aeolian landscape: From surface to orbit in Gale Crater

    Science.gov (United States)

    Day, Mackenzie; Kocurek, Gary

    2016-12-01

    Landscapes derived solely from aeolian processes are rare on Earth because of the dominance of subaqueous processes. In contrast, aeolian-derived landscapes should typify Mars because of the absence of liquid water, the long exposure times of surfaces, and the presence of wind as the default geomorphic agent. Using the full range of available orbital and Mars Science Laboratory rover Curiosity images, wind-formed features in Gale Crater were cataloged and analyzed in order to characterize the aeolian landscape and to derive the evolution of the crater wind regime over time. Inferred wind directions show a dominance of regional northerly winds over geologic time-scales, but a dominance of topography-driven katabatic winds in modern times. Landscapes in Gale Crater show a preponderance of aeolian features at all spatial scales. Interpreted processes forming these features include first-cycle aeolian abrasion of bedrock, pervasive deflation, organization of available sand into bedforms, abundant cratering, and gravity-driven wasting, all of which occur over a background of slow physical weathering. The observed landscapes are proposed to represent a spectrum of progressive surface denudation from fractured bedrock, to retreating bedrock-capped mesas, to remnant hills capped by bedrock rubble, to desert pavement plains. This model of landscape evolution provides the mechanism by which northerly winds acting over ∼3 Ga excavated tens of thousands of cubic kilometers of material from the once sediment-filled crater, thus carving the intra-crater moat and exhuming Mount Sharp (Aeolis Mons). The current crater surface is relatively sand-starved, indicating that potential sediment deflation from the crater is greater than sediment production, and that most exhumation of Mount Sharp occurred in the ancient geologic past.

  17. [Correlation between the lengths of the long bones of the forearm and the fibula with body height in our population].

    Science.gov (United States)

    Marinković, Nadica; Vilić, Jasenka Vasić

    2012-05-01

    The task of a forensic examiner during exhumation of skeletal remains is to calculate antemortem height of a person whose skeletal remains were found. Anthropological investigations which provided formulae for calculating ante-mortem body height date back from XIX or from the first half of XX centuries. The most commonly used formulae are those of Trotter-Gleser, which were used to investigate skeletal remains from the World War II. Those investigations were conducted on skeletal remains of various ages and degrees of decay. Our experience with exhumation have shown that the present formulae do not deliver reliable values of antemortem height. The aim of this study was to investigate if there is a correlation of the length of long bones of leg and forearm with body height within our population and to establish the formulae for calculating ante-mortem body height within our population based on the obtained values. The lengths of ulna, radius, fibula and tibia were determined precisely by measuring bones on living individuals using a digital X-ray system. The height of individuals whose bones were measured was determined using an anthropometer. The highest degree of correlation between bone length and body height was found for tibia in males (r = 0.859, p population the length of long bones of the forearm and the leg are characterized by various degree of correlation with body height. The formulae that we set, make less distinction between the measured and the calculated body height as compared with the Trotter-Gleser formulae. We do hope that their implementation will facilitate identification of sceletal remains in our population.

  18. Meso-/Cenozoic long-term landscape evolution at the southern Moroccan passive continental margin, Tarfaya Basin, recorded by low-temperature thermochronology

    Science.gov (United States)

    Sehrt, Manuel; Glasmacher, Ulrich A.; Stockli, Daniel F.; Jabour, Haddou; Kluth, Oliver

    2017-10-01

    This paper presents the first regional study of low-temperature thermochronology to be undertaken in the Tarfaya Basin at the southern Moroccan passive continental margin. The basin is characterised by vast subsidence since Mid-Triassic times, whereby up to 12 km of Meso- to Cenozoic sedimentary rocks accumulated. The study focused on the post-rift vertical movements along a typical ;passive; margin and besides dealt with the timing and maximum temperature reached by potential source rocks of the basin. To unravel the t-T development, thermochronological analyses were performed on 50 outcrop and well samples from Meso-Cenozoic rocks. Thermochronological data reveal a continuous subsidence phase in the offshore basin from Mid-Triassic to recent times. In contrast, apatite (U-Th-Sm)/He and apatite fission-track data as well as thermal modelling point to an inversion of the northeastern onshore basin starting in the Palaeogene at 65-55 Ma. The rock uplift and exhumation period resulted in the erosion of a 1.0-1.4 km thick Cretaceous-Palaeogene sedimentary pile contemporaneously with peak Atlas surface uplift in the Cenozoic. The exhumation stage could be an explanation for the increasing periodic influx of detrital material into the offshore and southern onshore Tarfaya Basin since Palaeocene. Detrital apatite fission-track ages from 92 (± 16) to 237 (± 35) Ma of the Upper Cretaceous-Neogene succession indicate no heating above 60 °C confirming immature to early mature Cenomanian to Campanian and Eocene source rocks in the onshore Tarfaya Basin.

  19. Autopsia social de un subtierro

    Directory of Open Access Journals (Sweden)

    Ferrándiz, Francisco

    2011-12-01

    Full Text Available This paper proposes a conceptualization of the mass graves of defeat, mostly derived from the Spanish Civil War (1936- 1939 and the early Postwar years, understanding them as a radical form of a below ground internal exile. Once the bodies in the mass graves and the violence inscribed in them have been characterized, the paper engages in a social autopsy of how this memory has evolved in contemporary Spain since the year 2000, when the first exhumation of the most recent cycle of Civil War graves took place. The analysis follows the political, judicial, scientific, media and associative impact of these exhumed bodies.

    Este artículo propone una conceptualización de las fosas comunes de la derrota derivadas de la Guerra Civil española (1936- 1939 y la posguerra utilizando la noción del subtierro —asimilable a una forma extrema de exilio interior bajo tierra—, cuyo origen histórico sería el mismo que el de los exiliados, desterrados o transterrados que tuvieron que abandonar España, pero cuyas condiciones de producción y cuya historia social, política, simbólica y judicial desde la guerra hasta el presente tiene características específicas. A partir de ahí, una vez definidos los cuerpos que se encuentran en estas fosas y el tipo de violencia que se inscribió sobre ellos, se realiza una autopsia social de su evolución histórica y del recorrido que su apertura desde el año 2000 está teniendo en la sociedad española contemporánea desde el punto de vista político, judicial, científico, mediático y asociativo.

  20. Building the Pamir-Tibetan Plateau—Crustal stacking, extensional collapse, and lateral extrusion in the Central Pamir: 2. Timing and rates

    Science.gov (United States)

    Rutte, Daniel; Ratschbacher, Lothar; Khan, Jahanzeb; Stübner, Konstanze; Hacker, Bradley R.; Stearns, Michael A.; Enkelmann, Eva; Jonckheere, Raymond; Pfänder, Jörg A.; Sperner, Blanka; Tichomirowa, Marion

    2017-03-01

    Geothermochronologic data outline the temperature-deformation-time evolution of the Muskol and Shatput gneiss domes and their hanging walls in the Central Pamir. Prograde metamorphism started before 35 Ma and peaked at 23-20 Ma, reflecting top-to- N thrust-sheet and fold-nappe emplacement that tripled the thickness of the upper 7-10 km of the Asian crust. Multimethod thermochronology traces cooling through 700-100°C between 22 and 12 Ma due to exhumation along dome-bounding normal-sense shear zones. Synkinematic minerals date normal sense shear-zone deformation at 22-17 Ma. Age-versus-elevation relationships and paleoisotherm spacing imply exhumation at ≥3 km/Myr. South of the domes, Mesozoic granitoids record slow cooling and/or constant temperature throughout the Paleogene and enhanced cooling (7-31°C/Myr) starting between 23 and 12 Ma and continuing today. Integrating the Central Pamir data with those of the East (Chinese) Pamir Kongur Shan and Muztaghata domes, and with the South Pamir Shakhdara dome, implies (i) regionally distributed, Paleogene crustal thickening; (ii) Pamir-wide gravitational collapse of thickened crust starting at 23-21 Ma during ongoing India-Asia convergence; and (iii) termination of doming and resumption of shortening following northward propagating underthrusting of the Indian cratonic lithosphere at ≥12 Ma. Westward lateral extrusion of Pamir Plateau crust into the Hindu Kush and the Tajik depression accompanied all stages. Deep-seated processes, e.g., slab breakoff, crustal foundering, and underthrusting of buoyant lithosphere, governed transitional phases in the Pamir, and likely the Tibet crust.

  1. A Bayesian Hierarchical Modeling Scheme for Estimating Erosion Rates Under Current Climate Conditions

    Science.gov (United States)

    Lowman, L.; Barros, A. P.

    2014-12-01

    Computational modeling of surface erosion processes is inherently difficult because of the four-dimensional nature of the problem and the multiple temporal and spatial scales that govern individual mechanisms. Landscapes are modified via surface and fluvial erosion and exhumation, each of which takes place over a range of time scales. Traditional field measurements of erosion/exhumation rates are scale dependent, often valid for a single point-wise location or averaging over large aerial extents and periods with intense and mild erosion. We present a method of remotely estimating erosion rates using a Bayesian hierarchical model based upon the stream power erosion law (SPEL). A Bayesian approach allows for estimating erosion rates using the deterministic relationship given by the SPEL and data on channel slopes and precipitation at the basin and sub-basin scale. The spatial scale associated with this framework is the elevation class, where each class is characterized by distinct morphologic behavior observed through different modes in the distribution of basin outlet elevations. Interestingly, the distributions of first-order outlets are similar in shape and extent to the distribution of precipitation events (i.e. individual storms) over a 14-year period between 1998-2011. We demonstrate an application of the Bayesian hierarchical modeling framework for five basins and one intermontane basin located in the central Andes between 5S and 20S. Using remotely sensed data of current annual precipitation rates from the Tropical Rainfall Measuring Mission (TRMM) and topography from a high resolution (3 arc-seconds) digital elevation map (DEM), our erosion rate estimates are consistent with decadal-scale estimates based on landslide mapping and sediment flux observations and 1-2 orders of magnitude larger than most millennial and million year timescale estimates from thermochronology and cosmogenic nuclides.

  2. Nature of the Mantle in the Iberia/Newfoundland Magma-poor Rifted Margin on the Basis of Radiogenic Isotopes in Separates Clinopyroxenes: Preliminary Results.

    Science.gov (United States)

    Amann, M.; Ulrich, M.; Autin, J.; Manatschal, G.; Pelt, E.; Boiron, M. C.; Sauter, D.

    2016-12-01

    The conjugate Iberia-Newfoundland margins represent the type example of a magma-poor rift system characterized by a zone of exhumed continental mantle (ZECM). Although the ZECM has been investigated in numerous studies, there are still little known on the nature and timing of emplacement of the magmatic rocks and the geochemical nature of the mantle section. In particular the lack of radiogenic isotope data makes the interpretation of the origin of the mantle in the ZECM difficult to constrain. In this study we present new in situ analytical data from mantle clinopyroxenes (CPX) derived from ODP Sites 1070 (Iberia) and 1277 (Newfoundland). Although these sites are at present separated by the N-Atlantic Ocean, the two sites are assumed to represent adjacent parts of the ZECM before being separated by lithospheric break-up and following seafloor spreading. On one hand, CPX from plagioclase-bearing harzburgites and related websterites from Iberia Abyssal Plain (IAP) are characterized by very low Na content and a strong depletion in light Rare Earth Elements (REE). Websterites have a 143Nd/144Nd ratio much lower than the Depleted Mantle (DMM). Pyroxenite layers in the IAP are thus the result of the partial melting of the subcontinental lithospheric mantle due to the asthenosphere upwelling during the incipient rifting. On the other hand, CPX from spinel harzburgites in the Newfoundland margin mantle are highly depleted in REE and have undergone higher partial melting degree. New radiogenic Pb-Nd-Sr analyzes on separates clinopyroxenes will provide new evidence to argue whether or not the exhumed mantle was geochemically homogeneous on both side of the incipient mid-oceanic ridge and if the subsequent break-up is related to a mantle inheritance such as the former Caledonian subduction zone.

  3. Reinterpretation of adcoh and cocorp seismic reflection data with constraints from detailed forward modeling of potential field data - Implications for Laurentia-Peri-Gondwana suture

    Science.gov (United States)

    Duff, Patrick D.; Kellogg, James N.

    2017-08-01

    To better constrain the structure of the Laurentian - Peri-Gondwana suture zone, maps and a 2-dimensional regional cross-section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields. The Central Piedmont Suture (CPS), the boundary between the Laurentian Inner Piedmont and the Peri-Gondwanan Carolina terrane is a low-angle thrust fault ( 30°) ramping up from an Alleghanian mid-crustal detachment at depths of about 12 km. ADCOH and COCORP seismic data image anticlinal structures in the footwalls of the Hayesville thrust and the CPS, above the Alleghanian decollement. The footwall rocks have previously been interpreted as Paleozoic shelf strata on the basis of sub-horizontal seismic reflectors; however, the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of Grenvillian basement. The Appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the Carolina Terrane toward the Appalachian core. A change in lower crustal density is not required, so that Grenville basement rocks may extend farther to the southeast than previously thought. The 5 to 10 km of Alleghanian uplift and exhumation predicted by P-T crystallization data compiled in this paper can be easily accommodated by thrusting on four major low-angle thrust systems: Great Smoky Mountain Thrust (GSMT), Hayesville, Brevard, and CPS. Unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation. Alleghanian collision along the southeastern Appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter-clockwise rotation of Gondwanan West Africa, creating head-on collision in the southern

  4. (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone

    Science.gov (United States)

    Moser, Amy C.; Evans, James P.; Ault, Alexis K.; Janecke, Susanne U.; Bradbury, Kelly K.

    2017-10-01

    The timing, tempo, and processes of punctuated deformation in strike-slip fault systems are challenging to resolve in the rock record. Faults in the Mecca Hills, adjacent to the southernmost San Andreas Fault, California, accommodate active deformation and exhumation in the Plio-Pleistocene sedimentary rocks and underlying crystalline basement. We document the spatiotemporal patterns of San Andreas Fault-related deformation as recorded in crystalline basement rocks of the Mecca Hills using fault microstructural observations, geochemical data, and hematite (n = 24) and apatite (n = 44) (U-Th)/He (hematite He, apatite He) thermochronometry data. Reproducible mean hematite He dates from minor hematite-coated fault surfaces in the Painted Canyon Fault damage zone range from ∼0.7-0.4 Ma and are younger than ∼1.2 Ma apatite He dates from adjacent crystalline basement host rock. These data reveal concomitant Pleistocene pulses of fault slip, fluid flow, and synkinematic hematite mineralization. Hematite textures, crystal morphology, and hematite He data patterns imply some damage zone deformation occurred via cyclic crack-seal and creep processes. Apatite He data from crystalline basement define distinct date-eU patterns and indicate cooling across discrete fault blocks in the Mecca Hills. Uniform ∼1.2 Ma apatite He dates regardless of eU are located exclusively between the Painted Canyon and Platform faults. Outside of this fault block, samples yield individual apatite He dates from ∼30-1 Ma that define a positive apatite He date-eU correlation. These patterns reveal focused exhumation away from the main trace of the San Andreas Fault at ∼1.2 Ma. Low-temperature thermochronometry of fault-related rocks provides an unprecedented window into the 105-106-yr record of San Andreas Fault-related deformation in the Mecca Hills and documents hematite deformation mechanisms that may be operative in other strike-slip faults world-wide.

  5. An Electrochemical Method to Predict Corrosion Rates in Soils

    Energy Technology Data Exchange (ETDEWEB)

    Dafter, M. R. [Hunter Water Australia Pty Ltd, Newcastle (Australia)

    2016-10-15

    Linear polarization resistance (LPR) testing of soils has been used extensively by a number of water utilities across Australia for many years now to determine the condition of buried ferrous water mains. The LPR test itself is a relatively simple, inexpensive test that serves as a substitute for actual exhumation and physical inspection of buried water mains to determine corrosion losses. LPR testing results (and the corresponding pit depth estimates) in combination with proprietary pipe failure algorithms can provide a useful predictive tool in determining the current and future conditions of an asset{sup 1)}. A number of LPR tests have been developed on soil by various researchers over the years{sup 1)}, but few have gained widespread commercial use, partly due to the difficulty in replicating the results. This author developed an electrochemical cell that was suitable for LPR soil testing and utilized this cell to test a series of soil samples obtained through an extensive program of field exhumations. The objective of this testing was to examine the relationship between short-term electrochemical testing and long-term in-situ corrosion of buried water mains, utilizing an LPR test that could be robustly replicated. Forty-one soil samples and related corrosion data were obtained from ad hoc condition assessments of buried water mains located throughout the Hunter region of New South Wales, Australia. Each sample was subjected to the electrochemical test developed by the author, and the resulting polarization data were compared with long-term pitting data obtained from each water main. The results of this testing program enabled the author to undertake a comprehensive review of the LPR technique as it is applied to soils and to examine whether correlations can be made between LPR testing results and long-term field corrosion.

  6. Cenozoic tectono-thermal history of the Tordrillo Mountains, Alaska: Paleocene-Eocene ridge subduction, decreasing relief, and late Neogene faulting