Science.gov

Sample records for exhumed permian mudstone-dominated

  1. Exhuming Landforms

    NASA Technical Reports Server (NTRS)

    2005-01-01

    26 October 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a crater and adjacent terrain that have been exhumed from beneath a wind-eroded material. The sharp, pointy ridges inside and immediately adjacent to the crater are the remains of a material that once covered the entire scene. Wind has stripped these materials away, forming yardangs. Inside the crater, the erosion has revealed an older, eroded layered material. This smooth-surfaced layered feature inside the crater was already eroded to nearly its present shape before the yardang-forming material was deposited (and then eroded away).

    Location near: 7.2oN, 156.4oW Image width: width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

  2. Late Permian vertebrate community of the Pranhita Godavari valley, India

    NASA Astrophysics Data System (ADS)

    Ray, Sanghamitra; Bandyopadhyay, Saswati

    2003-03-01

    The Kundaram Formation of the Pranhita-Godavari valley yields the only Late Permian multispecies terrestrial vertebrate assemblage from India. This includes various medium and small dicynodonts such as Endothiodon, Oudenodon, Kingoria, Emydops, Cistecephalus and Pristerodon. At present two species of Endothiodon ( E. mahalanobisi and E. uniseries) are known. Apart from these dicynodonts, the Kundaram vertebrate fauna also contains a medium-sized gorgonopsian and a small captorhinid. The material, from the red mudstone dominated Kundaram Formation, includes numerous isolated, disarticulated skulls and lower jaws. Postcranial elements are relatively rare except for a few broken limb ends and vertebrae. The bones are encrusted by iron rich matrix and most of them had suffered deformation. This skull dominant accumulation is attributed to prolonged aerial exposure prior to burial resulting in disarticulation of the skeletons and subsequent inundation by floodwater. The limb bones and other postcranial elements of the already disarticulated skeletons were winnowed out by shallow competent flow while the relatively heavier skulls and lower jaws resisting transportation were buried near the site of death. The Late Permian scenario of the Pranhita-Godavari valley was characterised by the dominance of herbivores. This abundance of herbivores at the base and the presence of relatively few carnivores and omnivores at the top of the Kundaram food pyramid indicate a trophic structure similar to that of the modern-day terrestrial ecosystem.

  3. Modern Pearl River Delta and Permian Huainan coalfield, China: A comparative sedimentary facies study

    USGS Publications Warehouse

    Suping, P.; Flores, R.M.

    1996-01-01

    Sedimentary facies types of the Pleistocene deposits of the Modern Pearl River Delta in Guangdong Province, China and Permian Member D deposits in Huainan coalfield in Anhui Province are exemplified by depositional facies of anastomosing fluvial systems. In both study areas, sand/sandstone and mud/mudstone-dominated facies types formed in diverging and converging, coeval fluvial channels laterally juxtaposed with floodplains containing ponds, lakes, and topogenous mires. The mires accumulated thin to thick peat/coal deposits that vary in vertical and lateral distribution between the two study areas. This difference is probably due to attendant sedimentary processes that affected the floodplain environments. The ancestral floodplains of the Modern Pearl River Delta were reworked by combined fluvial and tidal and estuarine processes. In contrast, the floodplains of the Permian Member D were mainly influenced by freshwater fluvial processes. In addition, the thick, laterally extensive coal zones of the Permian Member D may have formed in topogenous mires that developed on abandoned courses of anastomosing fluvial systems. This is typified by Seam 13-1, which is a blanket-like body that thickens to as much as 8 in but also splits into thinner beds. This seam overlies deposits of diverging and converging, coeval fluvial channels of the Sandstone D, and associated overbank-floodplain deposits. The limited areal extent of lenticular Pleistocene peat deposits of the Modern Pearl River Delta is due to their primary accumulation in topogenous mires in the central floodplains that were restricted by contemporaneous anastomosing channels.

  4. Exhuming South Polar Crater

    NASA Technical Reports Server (NTRS)

    2004-01-01

    7 February 2004 The large, circular feature in this image is an old meteor impact crater. The crater is larger than the 3 kilometers-wide (1.9 miles-wide) Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, thus only part of the crater is seen. The bright mesas full of pits and holes--in some areas resembling swiss cheese--are composed of frozen carbon dioxide. In this summertime view, the mesa slopes and pit walls are darkened as sunlight causes some of the ice to sublime away. At one time in the past, the crater shown here may have been completely covered with carbon dioxide ice, but, over time, it has been exhumed as the ice sublimes a little bit more each summer. The crater is located near 86.8oS, 111.6oW. Sunlight illuminates this scene from the upper left.

  5. Exhumed Arabian Crater

    NASA Technical Reports Server (NTRS)

    2004-01-01

    26 August 2004 Eastern Arabia Terra shares many attributes with western Arabia and Sinus Meridiani. In particular, it is a region of vast layered rock within which are interbedded filled and buried craters and valleys. Erosion has subsequently re-exposed many of these landforms, including the exhumed and eroded crater shown in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. Following the period in which erosion occurred, the region was blanketed by dust. This image is located near 22.5oN, 318.4oW, and covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the left/lower left.

  6. Permian karst topography in the Wichita uplift, southwestern Oklahoma

    SciTech Connect

    Donovan, R.N. Busbey, A.B. . Geology Dept.)

    1993-02-01

    The Wichita uplift in southwestern Oklahoma is one part of a record of Pennsylvania and early Permian deformation that affected the Southern Oklahoma aulacogen. As a result of a partial inversion, the Lower Paleozoic section of this aulacogen was sequentially stripped off an uplift between the Wichita uplift and the Anadarko basin, resulting in the exposure of ultrabasic rocks deep in the Cambrian igneous fill of the aulacogen. Following the late Paleozoic tectonism, the topography of the uplift was entombed beneath Permian sediments and remained essentially undisturbed until exhumation during the present erosional cycle. Modern erosion is gradually exposing this topography, permitting morphometric analysis of the Permian hill forms. Because of the variation of lithology in the uplift, it is possible to isolate the effects of weathering processes such as intense hydrolysis of the igneous rocks (producing, among other features, or topography) and limestone dissolution, in the form of a surface and subsurface karst imprint. The latter process resulted in a network of small caves that are essentially fissures eroded along tectonic fractures. These small caves can be found in all the exposed areas of limestone. They are particularly noteworthy for three reasons: in at least five examples they contain a complex fauna of Permian vertebrates (mostly fragmentary), speleothems in some examples contain hydrocarbon inclusions, derived from the underlying Anadarko basin, some of the caves yield evidence of post burial evolution in the form of clay infiltration from the surface and brine flushing from the underlying Anadarko basin.

  7. Permian chronostratigraphy in Kansas

    SciTech Connect

    Baars, D.L. )

    1990-08-01

    Correlations between the type Permian System of Russia and North American strata have been difficult for decades because of biostratigraphic and nomenclatural confusion. Consequently, a standard Permian section was established in west Texas that is widely accepted throughout North America. Series of the North American standard section are, in ascending order, Wolfcampian, Leonardian, Guadalupian, and Ochoan. This nomenclature was adopted for usage in Kansas in 1951, but was later abandoned in favor of local terminology. However, direct biostratigraphic correlations between Kansas and the west Texas standard section have now been firmly established, and local chronostratigraphic names, i.e., Big Blue, Lyon, Geary, Cimarron, and Custer, have not been widely accepted. The Kansas Geological Survey has now readopted usage of the Wolfcampian Series for rocks of the Admire, Council Grove, and Chase Groups; the Leonardian Series for rocks of the Summer and Nippewalla Groups; and the Guadalupian Series for rocks of the Whitehorse, Day Creek, and Big Basin Formations. The Wolfcampian Series in Kansas (and elsewhere in North America) contains post-Virgilian (latest Carboniferous) strata that predate the classical Permian System of the Russian type section. Consequently, the Pennsylvanian/Permian boundary will probably have to be raised stratigraphically to conform to global usage.

  8. Composition of Permian seawater

    SciTech Connect

    Lazar, B.; Friedmann, T.J.; Holland, H.D.

    1985-01-01

    The authors demonstrated that fluid inclusions in Miocene halite can be used to define the composition of contemporary Miocene seawater. During the past year the authors, have extracted inclusion fluids from halite in the Lower Permian Wellington Formation near Lyons, Kansas and from the Upper Permian Salado Formation near Carlsbad, New Mexico to define the composition of Permian seawater. The extracted inclusion fluids were analyzed by ion chromatography. The concentration of Na/sup +/, Cl/sup -/, and Mg/sup +2/ in these fluids along the evaporation path of present-day seawater. Compared to evaporated modern seawater the solutions are slightly enriched with respect to Br/sup -/ and K/sup +/. The excess of these ions is probably due to heir transfer from enclosing halite to the inclusion fluids during recrystallization. The concentration of SO/sub 4//sup -2/ in the inclusion fluids is lower than in evaporated modern seawater. The SO/sub 4//sup -2/ deficit in the fluids from halite in the Wellington Formation is almost certainly due to dolomitization followed by gypsum and/or anhydrite precipitation. No difference between the SO/sub 4//sup -2/ concentration of lower Permian and present-day seawater is required to explain the SO/sub 4//sup -2/ deficit in these fluids. This explanation does not account for the SO/sub 4//sup -2/ deficit in the inclusion fluids from the Salado Formation. The concentration of Li/sup +/ in the inclusion fluids is higher by a factor of ca. 4 than the concentration to be expected from the evaporation of modern seawater. With this exception, the composition of Permian seawater appears to have been remarkably similar to that of modern seawater.

  9. Exhumation of an unusually large, ~3000 km3 coherent block of oceanic crust from >40 km depth

    NASA Astrophysics Data System (ADS)

    Barrow, Wendy; Metcalf, Rodney; Fairhurst, Robert

    2010-05-01

    The Central Metamorphic terrane (CMt) is an unusually large (~3000 km3) coherent block of mid-ocean ridge (MOR) metabasites; the first one of this scale reported with eclogite facies relicts, decompression assemblages, and thermobarometry indicating exhumation of the entire block from >40 km depth. The CMt is exposed in the eastern Klamath Mountains of northern California and is dominantly an amphibolite facies metabasite which represents remnant oceanic crust subducted in a mid-Paleozoic Pacific-type margin. Thermochronology indicates that the CMt was subsequently exhumed along the Trinity fault during an early Permian extensional event. Newly discovered relict textures with new thermobarometry results suggest the CMt metabasites record the retrograde segment of the P-T-deformation-time path during exhumation from hornblende eclogite facies P-T conditions. A decompression and cooling sequence consisting of rutile cores within ilmenite crystals mantled by titanite is observed in CMt amphibolite samples. Zr-in-rutile thermometry combined with experimental data for rutile stability in metabasites suggests that relict rutile crystals preserve early P-T conditions of ~600° C and >1.3 GPa. Transition from eclogite facies is further supported by ilmenite-plagioclase-amphibole symplectites suggesting replacement of garnet or omphacite during decompression. The dominant mineral assemblages and metamorphic fabrics indicate dynamic recrystallization of metabasites during declining P-T conditions through amphibolite - epidote amphibolite facies. Exhumation via extension along the Trinity fault is suggested by the coplanar relationship between metabasite decompression-related deformation fabrics and the Trinity fault. We propose that subducted oceanic crust (CMt) was subsequently exhumed as a large coherent block from depths >40 km. This is significant because the conversion of mafic oceanic crust to eclogite produces the negative buoyancy (relative to mantle peridotite) that

  10. Phanerozoic orogeny triggers reactivation and exhumation in the northern part of the Archean-Paleoproterozoic North China Craton

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Fu; Zou, Dong-Ya; Santosh, M.; Zhu, Bin

    2016-09-01

    Cratons and orogenic belts are integral components of ancient continents. In some cases, stable continents can be reactivated and even largely destroyed by younger events. The mechanisms of reactivation or destruction of ancient cratons remain equivocal. Here we compile zircon U-Pb data from the metamorphic rocks of the Hongqiyingzi Group in the northern part of the North China Craton (NCC) to evaluate this problem. The results reveal episodic tectonothermal events related to three major periods of Latest Neoarchean-Earliest Paleoproterozoic (2.6-2.4 Ga), Paleoproterozoic (1.85-1.95 Ma) and Phanerozoic (480-220 Ma, with peak at 360-320 Ma). The Neoarchean-Paleoproterozoic crust as represented by the Hongqiyingzi Group was subducted to eclogite facies at ca. 1.95 Ga, followed by the final collision between the Eastern and Western Blocks at ca. 1.85 Ga to produce the Trans-North China Orogen (TNCO). The ubiquitous presence of Phanerozoic concordant zircons in the Hongqiyingzi Group suggests the episodic exhumation of the TNCO in the northern segment during the Phanerozoic. The 460-420 Ma concordant zircons record the onset of exhumation, triggered by the Ordovician-Silurian southward subduction of the Paleoasian Ocean. Widespread occurrence of 360-320 Ma metamorphic and magmatic zircons in the Hongqiyingzi Group demonstrates that the Carboniferous-Permian was an important period of exhumation for the TNCO, possibly related to back-arc extension. A few Permian-Triassic concordant zircons record late Permian accretion and Triassic post-accretional uplifting. Our study demonstrates that the young orogeny during the formation of the Central Asian Orogenic Belt resulted in extensive reactivation of not only the Archean continental crust but also the Paleoproterozoic orogen in the northern NCC.

  11. Early Cenozoic "dome like" exhumation around the Irish Sea

    NASA Astrophysics Data System (ADS)

    Doepke, Daniel; Cogné, Nathan; Chew, David; Stuart, Fin

    2016-04-01

    Despite decades of research the Early Cenozoic exhumation history of Ireland and Britain is still poorly understood and subject to contentious debate (see Davis et al., 2012 and subsequent comments). Previous studies have attributed the Cenozoic exhumation history of Ireland and Britain mainly to: (a) Paleogene - Neogene far-field stress between the opening of the North Atlantic Ocean and the Alpine collision (Ziegler et al., 1995; Hillis et al., 2008) or (b) early Paleogene mantle driven magmatic underplating associated with the development of the proto-Iceland mantle plume beneath the Irish Sea (Brodie and White, 1994; Al-Kindi et al., 2003). The major differences between the two hypotheses are the pattern and timing of spatial exhumation. This project thus seeks to investigate the timing and mechanisms of late Mesozoic - early Cenozoic exhumation on the onshore part of the British Isles by using a combination of apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) data, which we then model using the QTQt program of Gallagher (2012) to better constrain the modelled thermal histories. Our studied area centres on the margins of the Irish Sea, but includes all Ireland and western Britain. Overall we analysed 74 samples for AFT and 66 samples for AHe dating. In particular, our results include ten pseudo-vertical profiles. The AFT ages display a wide range of ages from early Carboniferous in Scotland to early Eocene in central Ireland. Our AHe ages range from mid Permian on Shetland to Eocene Ft-corrected. The AFT data do not show any specific spatial distribution, however, the Ft-corrected AHe ages around the Irish Sea only focus around late Cretaceous to Eocene suggesting an important thermal event around this time. The modelled thermal histories of samples located around the Irish Sea and western Scotland show a clear late Cretaceous to early Paleogene cooling event which is not present elsewhere. The distribution of this cooling event is broadly consistent

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

    NASA Astrophysics Data System (ADS)

    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

  13. Petrology of exhumed mantle rocks at passive margins: ancient lithosphere and rejuvenation processes

    NASA Astrophysics Data System (ADS)

    Müntener, Othmar; McCarthy, Anders; Picazo, Suzanne

    2014-05-01

    , an alternative is that these depleted domains represent snapshots of melting processes that are related to Permian and/or even older crust forming processes. The findings of the these refractory mantle rocks over the entire Western Alpine arc and the similarity in model ages of depletion suggests a connection to the Early Permian magmatic activity. Shallow and deep crustal magmatism in the Permian is widespread over Western Europe and the distribution of these mafic rocks are likely to pre-determine the future areas of crustal thinning and exhumation during formation of the Thethyan passive margins.

  14. Thermal and exhumation history of the central Tianshan (NW China): Constraints by U-Pb geochronology and Ar-Ar and (U-Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Yin, J.; Chen, W.; Hodges, K. V.; Xiao, W.; Van Soest, M. C.; Cai, K.; Zhang, B.; Mercer, C. M.; Yuan, C.

    2015-12-01

    Geochronology and thermochronology using multiple mineral-isotopic chronometers reveals the thermo-tectonic history of the central Tianshan (NW China) from emplacement to exhumation. Granites from the central Tianshan, which are associated with the southward subduction of the northern Tianshan Ocean, have been dated at 362-354 Ma using the LA-ICP-MS Zircon U-Pb method. A younger diorite sample (282 ± 1 Ma, Zircon U-Pb method by LA-ICP-MS) from northern Tianshan formed during the final closure of the Northern Tianshan Ocean when the Junggar Block collided with the Yili-Central Tianshan Block. 40Ar/39Ar step-wise heating plateau dates (biotite Ar/Ar: 312-293 Ma; Plagioclase Ar/Ar: 270-229 Ma) from the Central Tianshan show rapid post-magmatic cooling during the Late Carboniferous-Early Permian followed by a more modest rate of cooling from the middle Permian to the middle Jurassic. The northern Tianshan diorite (biotite Ar/Ar: 240 ± 1 Ma) also reveals a middle Jurassic cooling. Apatite (U-Th )/He dates from the central Tianshan samples range from ca. 130 Ma to ca. 116 Ma. The Apatite (U-Th )/He date for the northern Tianshan sample is ca. 27 Ma. Previous studies also reported Apatite (U-Th)/He ages of ca. 44 Ma-11 Ma in the Baluntai area of the southern Central Tianshan[1]. Two episodes of cooling are distinguished by thermal history modelling: (1) Mesozoic cooling occurred as the result of the exhumation and tectonic reactivation of the central Tianshan; and (2) The Tianshan orogenic belt has been rapidly exhumed since the Middle Cenozoic. References [1] Lü, H.H., Chang, Y., Wang, W., Zhou, Z.Y., 2013. Rapid exhumation of the Tianshan Mountains since the early Miocene: Evidence from combined apatite fission track and (U-Th)/He thermochronology. Science China: Earth Sciences, 43(12): 1964-1974 (in Chinese).

  15. Reconstructing Late Paleozoic exhumation history of the Inner Mongolia Highland along the northern edge of the North China Craton

    NASA Astrophysics Data System (ADS)

    Ma, Shouxian; Meng, Qingren; Duan, Liang; Wu, Guoli

    2014-06-01

    The Inner Mongolia Highland (IMH), along the northern edge of the North China Craton, was considered to be a long-standing topographic highland, whose exhumation history remains elusive. The aim of this study is to reveal Late Paleozoic exhumation processes of the IMH based on an integrated analysis of stratigraphy, petrography of clastic rocks, and U-Pb ages and Hf isotopes of detrital zircons from Permian-Triassic succession in the middle Yanshan belt. The results of the study show that the Benxi Formation, which was originally regarded as a Late Carboniferous unit, proves to be Early Permian in age because it contains detrital zircons as young as ∼298 Ma. The Lower Shihezi Formation is demonstrated to be a unit whose age spans the boundary of the Middle and Upper Permian, constrained by a U-Pb age of 260 ± 2 Ma from a dacite layer. Clastic compositions of conglomerate and sandstone change markedly, characterised by the predominance of sedimentary components in the Benxi-Shanxi Formations, by large amounts of volcanic clastics in the Lower and Upper Shihezi Formations, and by the presence of both metamorphic and igneous clastics in the Sunjiagou-Ermaying Formations. Sedimentary clastics include chert, carbonate, sandstone and quartzite, which may have been derived from Proterozoic to Lower Paleozoic sedimentary covers. Volcanic clasts were directly related to volcanic eruptions, while granite and gneiss grains were sourced from exhumed Late Paleozoic intrusive rocks and basement rocks. Detrital zircon U-Pb ages can be divided into five populations: 2.6-2.4 Ga, 1.9-1.7 Ga, 400-360 Ma, 325-290 Ma and 270-250 Ma. Precambrian detrital zircons are typically subrounded to rounded in shape, implying a recycling origin. Late Paleozoic zircons show oscillatory zones and their Th/U ratios >0.4, suggesting a magmatic origin. Most Phanerozoic zircons have negative εHf(T) values of -3.2 to -25.5, which are compatible with those of Late Paleozoic plutons in the IMH. The

  16. Exhumation, cooling and deformation history of the necking zone of the fossil Adriatic rifted margin: the Campo/Grosina section (S-Switzerland and N-Italy)

    NASA Astrophysics Data System (ADS)

    Petri, Benoît; Mohn, Geoffroy; Wijbrans, Jan R.; Manatschal, Gianreto; Beltrando, Marco

    2016-04-01

    The Austroalpine units in SE Switzerland and N-Italy preserve remnants of the fossil Adriatic rifted margin. Notably the Campo-Grosina units represent the necking zone where major crustal thinning was accommodated during the Jurassic rifting. This contribution aims to unravel the complex tectonic evolution recorded in these units from the late Carboniferous - early Permian to the Jurassic rifting. The cooling and exhumation of the Campo and overlying Grosina units, separated by the Eita shear zone are explored by the acquisition of 40Ar/39Ar on hornblende, muscovite and biotite. New geochronological data on the Grosina unit present 40Ar/39Ar ages between 273 and 261 Ma for muscovite and between 248 and 246 Ma for biotite. The Campo unit shows clearly younger ages between 210 and 177 Ma on hornblende, between 186 and 176 Ma on muscovite and between 174 and 171 Ma on biotite. Numerous data were discarded due to frequent excess 40Ar on amphiboles, probably associated to the emplacement of the Sondalo gabbro with a high 40Ar/36Ar ratio in Permian times. These new ages, together with a compilation of existing ages obtained with different chronometers (U-Pb, Sm-Nd, Rb-Sr, K-Ar, 40Ar/39Ar) and performed on different lithologies from both the Campo and the Grosina units allow an estimation of the cooling rates for these units to be done. The new results show that both the Campo and the Grosina units underwent a cooling rate around 10°C/Ma in Permian time. The Grosina unit, being in a shallower crustal level, did not record the Jurassic cooling, reaching up to 50°C/Ma in the Campo unit. The notable difference in cooling rates between the Permian and the Jurassic events attests of a cooling without being associated to an exhumation in Permian times, whereas the Campo unit cooled rapidly in Jurassic times, due to an exhumation and an emplacement in shallow crustal levels. The latter tectonic event was likely caused by shearing along the Eita or other greenschist facies

  17. Low-temperature thermochronology of the northern Thomson Orogen: Implications for exhumation of basement rocks in NE Australia

    NASA Astrophysics Data System (ADS)

    Verdel, Charles; Stockli, Daniel; Purdy, David

    2016-01-01

    The Tasmanides of eastern Australia record much of the Phanerozoic tectonic development of the retreating Pacific-Australia plate boundary and are an oft-cited example of an orogen that has undergone "tectonic mode switching." To begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the NE Tasmanides, we measured apatite and zircon (U-Th)/He ages from the Thomson Orogen and overlying Paleozoic strata in the back-arc of the New England Orogen in NE Australia. Zircon (U-Th)/He ages from basement samples (including those recovered from boreholes at depths of up to 1.1 km) are characterized by large inter- and intra-sample variability and range from approximately 180 Ma (Early Jurassic) to 375 Ma (Late Devonian). (U-Th)/He zircon ages from several individual samples are negatively correlated with effective uranium (eU), a pattern that is also true of the dataset as a whole, suggesting that variations in U and Th zoning and radiation damage are partially responsible for the age variability. The oldest zircon (U-Th)/He cooling ages coincide with the formation of regionally extensive Late Devonian-early Carboniferous back-arc basins, suggesting that Late Devonian extension played a significant role in exhumation of parts of the northern Thomson Orogen. Apatite (U-Th)/He ages from a basement sample and a late Permian sandstone in the overlying Bowen Basin, which are also marked by intra-sample variability and age-eU correlations, span from the Early Cretaceous through Oligocene, in general agreement with previous apatite fission track data. In conjunction with observations of key geologic relationships and prior K-Ar and 40Ar/39Ar data, our results suggest four overall phases in the thermal history of the northern Thomson Orogen: (1) Cambrian-early Silurian metamorphism during the Delamerian and Benambran Orogenies; (2) protracted cooling during the Late Devonian through mid-Permian that likely resulted from extensional

  18. New Permian fauna from tropical Gondwana.

    PubMed

    Cisneros, Juan C; Marsicano, Claudia; Angielczyk, Kenneth D; Smith, Roger M H; Richter, Martha; Fröbisch, Jörg; Kammerer, Christian F; Sadleir, Rudyard W

    2015-01-01

    Terrestrial vertebrates are first known to colonize high-latitude regions during the middle Permian (Guadalupian) about 270 million years ago, following the Pennsylvanian Gondwanan continental glaciation. However, despite over 150 years of study in these areas, the biogeographic origins of these rich communities of land-dwelling vertebrates remain obscure. Here we report on a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Northeastern Brazil hosted an extensive lacustrine system inhabited by a unique community of temnospondyl amphibians and reptiles that considerably expand the known temporal and geographic ranges of key subgroups. Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian. PMID:26537112

  19. New Permian fauna from tropical Gondwana

    PubMed Central

    Cisneros, Juan C.; Marsicano, Claudia; Angielczyk, Kenneth D.; Smith, Roger M. H.; Richter, Martha; Fröbisch, Jörg; Kammerer, Christian F.; Sadleir, Rudyard W.

    2015-01-01

    Terrestrial vertebrates are first known to colonize high-latitude regions during the middle Permian (Guadalupian) about 270 million years ago, following the Pennsylvanian Gondwanan continental glaciation. However, despite over 150 years of study in these areas, the biogeographic origins of these rich communities of land-dwelling vertebrates remain obscure. Here we report on a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Northeastern Brazil hosted an extensive lacustrine system inhabited by a unique community of temnospondyl amphibians and reptiles that considerably expand the known temporal and geographic ranges of key subgroups. Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian. PMID:26537112

  20. Permian geology of Gondwana countries: An overview

    SciTech Connect

    Dickins, J.M. )

    1992-10-01

    Earliest Permian sequences of Antarctica, southern and east-central Africa, the southern part of the Arabian Peninsula, Pakistan, peninsular and Himalayan India, Tibet, western and eastern Australia, New Zealand, and South America are all characterized by glacial deposits and cold-water marine faunas. In the course of the Permian, considerable faunal (and floral) and climatic divergence occurred. Although folding is not necessarily present, the effects of the strong compressive tectonic phase (Hunter-Bowen Orogenic Folding Phase of Dickins) beginning in the mid-Permian (traditional two-fold subdivision) and of acidic and intermediate volcano-magmatic activity are apparent in all these regions as in other parts of the world. The progressive continentality of the Upper Permian (worldwide regression) culminates at the Permian-Triassic (Changxingian-Griesbachian) boundary.

  1. The composition of Permian seawater.

    PubMed

    Horita, J; Friedman, T J; Lazar, B; Holland, H D

    1991-01-01

    Forty-nine brine inclusions in marine halite from the Ochoan Salado Formation in the Delaware Basin and fifteen inclusions in halite from the Leonardian Wellington Formation in the Kansas Basin were extracted, and their chemical compositions were determined. The brines are of the Na-K-Mg-Cl-SO4 type; their compositions resemble those of evaporated modern seawater. The values of (mCl(-) - mNa+)/mBr- and (mMg(2+) + mCa(2+) - mSO4(2-) - 1/2mHCO3-)/mBr- of the inclusion brine from the two formations are equal to or slightly higher than those of modern seawater. The original mNa+/mBr- and mCl-/mBr- ratios of the inclusion brines were probably equal to or slightly larger than those of modern seawater. The values of mMg2+/mBr- of the inclusion brines from the Salado Formation are very close to that of modern seawater; the ratios of inclusion brines from the Wellington Formation are slightly lower, probably due to the formation of dolomite/magnesite. The mMg2+/mBr- ratio in the initial seawater was probably close to the parent seawater of the Salado brines. The values of (mSO4(2-) - mCa(2+) + 1/2mHCO3-)/mBr- of the inclusion brines appear to be reduced by the formation of dolomite/magnesite, and the value of this ratio in Permian seawater was probably similar to that of modern seawater. The mK+/mBr- ratios of the inclusion brines are variable, but the original ratios are probably close to or slightly larger than that of modern seawater. If the Br- concentration of Permian seawater was equal to that of modern seawater, the composition of Permian seawater can be narrowly constrained; in mmol/kg H2O, 460 < or = mNa+ < 630, 550 < or = mCl- < 730, mMg2+ = 54 +/- 6, mK+ approximately equal to 11, (mSO4(2-) - mCa(2+) + 1/2mHCO3-) > or = 17, 20 < mSO4(2-) < 45, 5 < mCa2+ < 20, and 0.15 < mHCO3- < 5. The composition of Permian seawater was therefore quite similar to that of modern seawater. PMID:11537200

  2. Late Paleozoic structural evolution of Permian basin

    SciTech Connect

    Ewing, T.E.

    1984-04-01

    The southern Permian basin is underlain by the NNW-trending Central Basin disturbed belt of Wolfcamp age (Lower Permian), the deep Delaware basin to its west, and the shallower Midland basin to its eat. The disturbed belt is highly segmented with zones of left-lateral offset. Major segments from south to north are: the Puckett-Grey Ranch zone; the Fort Stockton uplift; the Monahans transverse zone; the Andector ridges and the Eunice ridge; the Hobbs transverse zone; and the Tatum ridges, which abut the broad Roosevelt uplift to the north. The disturbed belt may have originated along rift zones of either Precambrian or Cambrian age. The extent of Lower and Middle Pennsylvanian deformation is unclear; much of the Val Verde basin-Ozona arch structure may have formed then. The main Wolfcamp deformation over thrust the West Texas crustal block against the Delaware block, with local denudation of the uplifted edge and eastward-directed backthrusting into the Midland basin. Latter in the Permian, the area was the center of a subcontinental bowl of subsidence - the Permian basin proper. The disturbed belt formed a pedestal for the carbonate accumulations which created the Central Basin platform. The major pre-Permian reservoirs of the Permian basin lie in large structural and unconformity-bounded traps on uplift ridges and domes. Further work on the regional structural style may help to predict fracture trends, to assess the timing of oil migration, and to evaluate intrareservoir variations in the overlying Permian giant oil fields.

  3. Exhumation of the Shackleton Range, Antarctica

    NASA Astrophysics Data System (ADS)

    Lucka, Nicole; Lisker, Frank; Läufer, Andreas; Spiegel, Cornelia

    2013-04-01

    The Shackleton Range is situated between 80° - 81°S and 19° - 31°W, where it forms the continuation of the Transantarctic Mountains in the Weddell Sea sector of Antarctica. There, Precambrian igneous and metamorphic basement is overlain by (meta-) sedimentary rocks of an Early Paleozoic nappe stack and post-orogenic red beds. Nappe stacking resulted from the collision of East and West Gondwana due to the closure of the Mozambique Ocean in pan-African times. The uplift and exhumation history of the Shackleton Range has been analysed earlier based on a series of vertical fission track profiles (Schäfer, 1998; Lisker et al., 1999). Zircon ages range from ~160 to 210 Ma while apatite ages between ~95 and ~170 Ma comprise a break in slope of the altitude regression at ~110 Ma, and are accompanied by mean track lengths of 12.7 - 14.1 µm (standard deviation 1.0 - 1.4 µm). These data have been interpreted qualitatively in terms of two cooling/ exhumation stages during Jurassic and mid-Cretaceous times. However, the recognition of Jurassic volcaniclastic rocks associated with the ~180 Ma Ferrar event in the vicinity of the sample locations (Buggisch et al., 1994) challenges this exhumation concept. Moreover, new fission track proxy data (Dpar) and apatite (U-Th-Sm)/He ages between 88 and 171 Ma allow thermal history modelling of the combined thermochronological data. First tentative thermal history models suggest early Mesozoic cooling followed by (post-) Jurassic heating and final cooling since the Late Cretaceous. This scenario requires burial of the Shackleton Range region, and therefore the existence of a sedimentary basin at least during the Jurassic-Early Cretaceous, and subsequent basin inversion. The thickness of the now vanished sedimentary strata did unlikely exceed 2 - 3 km. Future work including additional apatite fission track analyses will help to quantifying geometry, depth and timing of this depocentre and evaluating potential links with the coeval

  4. Zircon and apatite fission-track evidence for an Early Permian thermal peak and relatively rapid Late Permian cooling in the Appalachian Basin

    SciTech Connect

    Roden, M.K. . Dept. of Earth and Environmental Science); Wintsch, R.P. . Dept. of Geological Sciences)

    1992-01-01

    New zircon fission-track ages compliment published apatite fission-track ages in the Appalachian Basin to narrowly constrain its thermal history. Geologic evidence can only constrain timing of the thermal peak to be younger than late Pennsylvanian sediments ([approximately] 300 Ma) and older than Mesozoic sediments in the Newark and Gettysburg Basins ([approximately] 210 Ma). Apatite fission-track ages as old as 246 Ma require the Alleghanian thermal peak to have been pre-Triassic. Preliminary data on reset zircon fission-track ages from middle Paleozoic sediments range from 255 to 290 Ma. Zircon fission-track apparent ages from samples younger and structurally higher than these are not reset. Thus, the oldest reset zircon fission-track age constraints the time of the Alleghanian thermal peak to be earliest Permian. Rates of post-Alleghanian cooling have not been well-constrained by geologic data and could be very slow. The difference between apatite and zircon fission-track ages for most of the samples range from 100--120 m.y. reflecting Permo-Triassic cooling of only 1 C/m.y. However, one sample with one of the oldest apatite ages, 245 Ma, yields one of the younger zircon ages of 255 Ma. This requires cooling rates of 10 C/m.y. and uplift rates of [approximately] 0.5 mm/yr. Collectively, these data support an early Permian thermal peak and a two-stage cooling history, consisting of > 100 C cooling (> 8 km denundation) in the Permian followed by relatively slow cooling and exhumation throughout the Mesozoic.

  5. Long-term landscape evolution, cooling and exhumation history at the Moroccan passive continental margin, Western Anti-Atlas

    NASA Astrophysics Data System (ADS)

    Sehrt, Manuel; Glasmacher, Ulrich A.

    2014-05-01

    The ENE-trending Anti-Atlas of Morocco is located at the northwestern fringe of the West African Craton and south of the High Atlas and represents the Phanerozoic foreland of the Late Palaeozoic North African Variscides and the Cenozoic Atlas Belt. The Anti-Atlas mountain belt extends from the Atlantic Ocean over 500 km into the Moroccan interior and shows a rugged topography with elevations of about 2700 m. The exhumation of the Precambrian basement and the deformation and erosion of the Palaeozoic cover is mainly related to the Variscan orogeny in the Upper Carboniferous-Lower Permian. Subsequently, exhumation of the inliers occurred in the Triassic-Jurassic, as the Anti-Atlas formed the shoulder of the Atlantic rift and finally in the Upper Eocene-Pleistocene, contemporaneously with the uplift of the Atlas belt. In Morocco, a large amount of Mesozoic terrigenous sedimentary rocks are deposited in most of the basins along the continental margin indicating a major episode of erosion during the rift and early post-rift period in the Central Atlantic. In the Tarfaya-Laâyoune-Dakhla Basin, south of the Anti-Atlas, the sedimentary cover reach a thickness of up to 12 km. The presence of high surface elevations in the Anti-Atlas mountain belt indicates a potential source area for the surrounding basins. Currently, phases of exhumation in the Anti-Atlas during the Central Atlantic rifting and places where the associated erosion products are deposited are poorly constrained and there is little quantitative data available at present. The present study was focused on the thermal and exhumation history of the Western Anti-Atlas, the burial and inversion history of the Tarfaya-Laâyoune-Dakhla Basin and on provenance analysis of the Meso-Cenozoic sedimentary rocks in the basin. In order to characterize the t-T history, apatite and zircon fission-track dating, apatite and zircon (U-Th-Sm)/He dating and furthermore 2-D modelling with 'HeFTy' software has been carried out at

  6. Subduction and exhumation of continental crust: insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Bialas, Robert W.; Funiciello, Francesca; Faccenna, Claudio

    2011-01-01

    When slivers of continental crust and sediment overlying oceanic lithosphere enter a subduction zone, they may be scraped off at shallow levels, subducted to depths of up to 100-200 km and then exhumed as high pressure (HP) and ultra-high pressure (UHP) rocks, or subducted and recycled in the mantle. To investigate the factors that influence the behaviour of subducting slivers of continental material, we use 3-D dynamically consistent laboratory models. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. A sliver of continental material, also composed of silicone putty, overlies the subducting lithosphere, separated by a syrup detachment. The density of the sliver, viscosity of the detachment, geometry of the subducting system (attached plate versus free ridge) and dimensions of the sliver are varied in 34 experiments. By varying the density of the sliver and viscosity of the detachment, we can reproduce a range of sliver behaviour, including subduction, subduction and exhumation from various depths and offscraping. Sliver subduction and exhumation requires sufficient sliver buoyancy and a detachment that is strong enough to hold the sliver during initial subduction, but weak enough to allow adequate sliver displacement or detachment for exhumation. Changes to the system geometry alter the slab dip, subduction velocity, pattern of mantle flow and amount of rollback. Shallower slab dips with more trench rollback produce a mantle flow pattern that aids exhumation. Steeper slab dips allow more buoyancy force to be directed in the up-dip direction of the plane of the plate, and aide exhumation of subducted slivers. Slower subduction can also aide exhumation, but if slab dip is too steep or subduction too slow, the sliver will subduct to only shallow levels and not exhume. Smaller slivers are most easily subducted and exhumed and influenced by the mantle flow.

  7. Late Permian to Early Triassic magnetostratigraphy

    NASA Astrophysics Data System (ADS)

    Haag, Maja; Heller, Friedrich

    1991-10-01

    A Late Permian to Early Triassic magnetostratigraphic reference section is presented. The Lower Triassic part is based on results from marine limestone sections in South China published earlier [1,2]. Reliable new Permian data are added here which have been collected in the Nammal gorge (Salt Range, Northwest Pakistan) where marine sediments have been deposited quasi-continuously with occasional minor hiatuses during the late Palaeozoic to early Mesozoic. About 50% of the Permian samples from the Nammal section contain, hidden beneath a strong recent or Tertiary overprint, a characteristic remanent magnetization (ChRM) which is very likely of Permian age. This component, which was imprinted on the southern hemisphere, has normal as well as reversed polarity with a normal mean direction (Decl. = 289.3°, Incl. = -50.3°, α 95 = 4.3° , N = 113) which is in close agreement with the palaeofield direction expected for a site belonging to the Indian plate as part of Gondwanaland during the Permian. In the lower Upper Permian several normal polarity zones are recognized. This contradicts the current assumption that rocks of this age belong to the long, reversely polarized Kiaman hyperzone. The Kiaman interval must end and the Illawarra hyperzone of mixed polarity must begin in or prior to the lowermost Upper Permian. The Permian/Triassic boundary at Nammal as well as in the Chinese sections is situated very close to a transition from a reversed to a normal polarity zone. The Upper Permian at Nammal together with the Lower Triassic South China sections is estimated to cover about 20 Ma. Nearly 30 polarity changes are observed which result in an average reversal frequency very similar to that observed during the early Tertiary. The reversal rate after the end of the long-lasting reversed Kiaman hyperchron apparently increases in a manner similar to that after the end of the Cretaceous Long Normal Superchron. Only a few polarity zones are found in the lower Upper Permian

  8. Late Cenozoic Exhumation of the Terskey Range, Kyrgyz Tien Shan

    NASA Astrophysics Data System (ADS)

    Sobel, E. R.; Macaulay, E. A.; Mikolaichuk, A.; Kohn, B. P.

    2008-12-01

    The glaciated, granitic Terskey range and the associated foreland basin within the Kyrgyz Tien Shan is an ideal region to examine whether Plio-Pleistocene climate change has led to enhanced erosion. Three ca. 1000m vertical profiles were collected in the hanging wall of the main, north-vergent thrust, spaced 25 km apart along strike. AFT analysis have been conducted from the westernmost-transect; all profiles have been analyzed using apatite (U-Th-Sm)/He analysis. AFT and Helium data from the Barskoon gorge profile define parallel trends on the age-elevation plot with apparent exhumation rates of ca. 0.08 km/Myr. The uppermost AFT sample resided for a long period within the partial annealing zone (PAZ); hence, the onset of rapid exhumation defined by the base of the exhumed PAZ appears to be 31±5 Ma. This is earlier than expected from the known regional geology. An alternative interpretation is that the next lowest sample has also been partially reset, such that the onset of exhumation is later and the initial exhumation is more rapid. Helium data from the Kichikyzulsu and Turgenaksu profiles define linear trends on age-elevation plots with apparent exhumation rates of 0.1-0.25 km/Myr and 0.2 km/Myr, respectively. Much older ages at high elevations along the former profile suggest that the base of the Helium partial retention zone (PRZ) has been sampled; the onset of exhumation is roughly constrained to be between 10 and 20 Ma. The onset of rapid exhumation at the latter profile can only be constrained as prior to 11 Ma. Combining the apparent exhumation rate with the age of the youngest samples from each transect provides an estimate of the amount of exhumation since that sample cooled through the PRZ. For the 3 profiles, this implies 1 to 1.2 km, 0.7 to 1.8 km, and 1.5 km of exhumation, assuming that the exhumation rate remained constant. The observed small magnitude and slow rate of exhumation suggests that there has been only limited advection and hence

  9. Neogene Extension and Exhumation in NW Sulawesi

    NASA Astrophysics Data System (ADS)

    Advokaat, E. L.; Hall, R.; White, L. T.; Armstrong, R. A.; Kohn, B. P.; BouDagher-Fadel, M. K.

    2014-12-01

    The unusual K-shaped island of Sulawesi, located in the convergent zone between the Eurasian, Australian and Pacific plates, has traditionally been interpreted as the consequence of collision and accretion. New data challenge this idea and indicate that crustal extension has played an important role in its Neogene development. In the north of the Sulawesi North Arm are Eocene-Lower Miocene basalts intercalated with radiolarian chert and volcaniclastic sediments, which were deformed during collision of the Sula Spur with the North Arm. Undeformed granitoids derived from lower crustal rocks intrude the sequence and preliminary LA-ICP-MS U-Pb zircon ages decrease from 9.44±0.43 Ma in the north to 8.19±0.20 Ma in the south. Structurally beneath all these rocks is the Malino Metamorphic Complex (MMC) which exposes dominantly quartzo-feldspathic muscovite schists to gneisses, with subordinate amphibolites and garnet schists. The MMC is a metamorphic core complex, surrounded by a discontinuous greenschist carapace and shear zones with opposite shear senses on the northern and southern sides of the complex. Metamorphic rocks from the MMC yield SHRIMP U-Pb ages on zircon rims of 15.42±0.62 Ma and 15.36±0.53 Ma. Locally these metamorphic rocks are intruded by undeformed granitoids with SHRIMP U-Pb zircon ages of 4.85 ± 0.07 to 3.78±0.04 Ma. Late stage exhumation accommodated by high angle oblique normal faults is indicated by apatite (U-Th)/He ages between 3.26±0.23 Ma and 1.43±0.24 Ma, at a rate of 0.27 mm/a based on age-elevation plots. Lower Pliocene-Lower Pleistocene syn-extensional shallow marine siliciclastic and carbonate sediments are crosscut by normal faults. The timing of faulting and lack of metamorphic detritus in these young sediments support rapid and recent regional uplift. We interpret two phases of extension in North Sulawesi, one during the Middle Miocene and another during the Late Pliocene-Pleistocene, exhuming the granitic and metamorphic rocks.

  10. The Silurian to Permian history of a metamorphic core complex in Lofoten, northern Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Steltenpohl, Mark G.; Hames, Willis E.; Andresen, Arild

    2004-02-01

    , Permian extension in Lofoten is largely characterized by brittle structures that formed at conditions substantially less than 300°C. Compared to the exhumation history of the southern Western Gneiss Region, the depth of Caledonian, continental (A-type) subduction and subsequent unroofing of Lofoten are of lesser magnitude, and the present erosional level remained in the middle crust for a much longer interval of time. The Permian 40Ar/39Ar mineral ages documented in this study are the youngest such ages yet identified in Scandinavia. These ages relate to episodes of deformation and cooling in response to extensional tectonic events that occurred roughly 100 m.y. after comparable effects identified on the Caledonian mainland. Our preferred explanation for the Carboniferous-Permian radiometric ages, structural evolution, and stratigraphic data for Lofoten is that they all developed in the context of a long-lived Cordilleran-style metamorphic core complex.

  11. Porosity formation in deep-burial environment: overview, with examples, from Permian basin

    SciTech Connect

    Mazzullo, S.J.; Harris, P.M.

    1989-03-01

    Porosity formation accompanying deep burial is ubiquitous and widespread in the Permian basin, particularly but not exclusively in offshore platform and resedimented basinal carbonates of Pennsylvanian and Permian age. Hydrocarbon reservoirs in such platform carbonate examples locally contain evidence of subaerial exposure and meteoric diagenesis. Commonly, much of the porosity formed during exposure is ultimately reduced by compaction and cementation during early burial. By contrast, no evidence of meteoric diagenesis is observed in associated basinal carbonates, although compaction and cementation accompanying progressive burial are readily evident. In both cases, however, such early diagenesis is overprinted by late burial dissolution, sometimes coincident with hydrocarbon emplacement, creating rocks of high porosity. The formation of porosity by cement dissolution may exhume occluded pores or enhance relict pores that formed in the eogenetic zone, the result being a preponderance of interparticle and moldic pores and residual cements that mimic vadose and phreatic products. In other cases, nonfabric selective dissolution, locally associated with fractures or stylolites, creates vuggy porosity which may resemble that formed during eodiagenesis. Multiple phases of deep-burial dissolution and partial cementation or replacement (by calcite or dolomite) are indicated for many of these diagenetic systems and result in a complex suite of different pore types.

  12. Magnitude and spatial patterns of erosional exhumation in the Nevadaplano, eastern Nevada and western Utah: insights from a Paleogene paleogeologic map

    NASA Astrophysics Data System (ADS)

    Long, S. P.

    2011-12-01

    Neoproterozoic and Permian in the Central Nevada thrust belt (CNTB), indicating significant structural relief. Isolated segments of CNTB structures can be correlated by their subcrop patterns, and can be traced southward to connect with thrust faults in southern Nevada. The exhumation map can be divided into three zones that exhibit significant across-strike magnitude changes: 1) high exhumation magnitudes (4-8 km) characterize the deeply-eroded hanging wall of the DWC thrust system and Sevier Culmination, which display little variability for a 350 km along-strike distance; 2) the CNTB displays high magnitudes (4-8 km) in its southern extent, and moderate magnitudes (2-5 km) in its northern extent; 3) the DWC thrust system and CNTB bound a large region that exhibits low (1-3 km) exhumation magnitudes. The close spatial association of high exhumation magnitudes with the hanging walls of thrust faults highlights the first-order control deformation and structural elevation has on exhumation patterns, and suggests that erosional exhumation is a response to relief generation accompanying contractional deformation in orogenic plateaus. The lack of significant exhumation variability within each structural zone implies that relief generation was relatively uniform along-strike.

  13. CONSTRAINTS ON EXHUMATION AND SEDIMENTS PROVENANCE DURING PALEOGENE IN THE NORTHERN PYRENEES (FRANCE) USING DETRITAL AFT, ZHe AND Z(U/Pb) THERMOCHRONOLOGY

    NASA Astrophysics Data System (ADS)

    Filleaudeau, P.; Mouthereau, F.; Fellin, M.; Pik, R.; Lacombe, O.

    2009-12-01

    The Pyrenees are a doubly vergent orogenic wedge built by the convergence between the subducting Iberian microplate and the European plate lasting from late Cretaceous to early Miocene. The backbone of the Pyrenean belt (Axial Zone) consists in a stack of thrusts units composed of Paleozoic series intruded by late-Variscan granitoids. Both pro- and retro-wedge sides of the Pyrenees are fold-and-thrust belts made of Meso-Cenozoic sediments thrusted onto the Ebro and Aquitaine foreland basins. The deep structure, highlighted by the ECORS profile, shows a strong asymmetry caused by the southward migration of deformation associated with the development of a Paleogene antiformal stack emplaced during wedge growth in the Iberian plate. The present study focuses on the synorogenic deposits of the retro-foreland basin in the northern part of the belt. To examine the source rocks and quantify the exhumation rates, we combine fission track thermochronometry on detrital apatites with Helium diffusion and U/Pb thermochronometry on zircons. Due to the very high closure temperature of the U/Pb system and the wide range of age distribution, the U/Pb method, that provides zircon crystallisation ages, is a powerful tool to distinguish the various eroded sources feeding the North Pyrenean basin. Thus, we can separate grains coming from Variscan intrusive basement with ages around 310 Ma from younger grains coming from Permian or Triassic to lower Jurassic volcanics. Zircon ages of 220 Ma found in the Paleocene sandstones point to the Triassic volcanic rocks (the so-called “ophites”) as the main source of detrital grains. We infer that Paleozoic units of the Axial Zone were not outcropping in the Paleocene catchments. Exhumation rates are estimated through apatite fission track grain-age distributions and (U-Th)/He dating for two Lutetian and Bartonian synorogenic sandstone samples of the North Pyenean foreland basin. The first results obtained with AFT dating show two main grain

  14. Permian insect wing from antarctic sentinel mountains.

    PubMed

    Tasch, P; Riek, E F

    1969-06-27

    A homopterous insect wing was found in micaceous graywacke from the Polarstar Formation, Sentinel Mountains. The unusual venation is reminiscent of family Stenoviciidae known from the Permian and Triassic of Eastern Australia and elsewhere. This first documented account of Paleozoic insects in Antarctica bears on drift questions. PMID:17748532

  15. Starting a Business in the Permian Basin.

    ERIC Educational Resources Information Center

    Harrison, Danny

    The business and economic development center of Midland College provides assistance to small businesses. Written for use by future and current small business owners and entrepreneurs living in a 17-county area of the Permian Basin of Texas, this guidebook describes the procedures for developing a business plan and for successfully starting and…

  16. Permian depositional history, Leach Mountains, northeastern Nevada

    SciTech Connect

    Martindale, S.G. . EMA/Construction Div.)

    1993-04-01

    The 4,000 m thick Permian sequence in the Leach Mountains consists of carbonate rock, chert, terrigenous clastic rock and phosphatic rock. These rocks, in ascending order, comprise the Third Fork Fm., Badger Gulch Fm., Trapper Creek Fm., Grandeur Fm., Meade Peak Phosphatic Shale Tongue of the Phosphoria Fm., Murdock Mountain Fm. and Gerster Limestone. This sequence disconformably overlain by Triassic strata. Initial Permian deposition, represented by the late Wolfcampian to early Leonardian Third Fork Fm., was on a slope, at a water depth of about 50 m. Subsequently, a shallowing trend occurred during the early Leonardian to late Leonardian with deposition of the Badger Gulch, Trapper Creek and Grandeur Fms. The Trapper Creek and Grandeur Fms. were deposited on the shelf, in very shallow subtidal to supratidal environments. The shelf persisted through the remainder of the Permian. In the late leonardian, the Meade Peak Tongue was deposited in very shallow subtidal and intertidal environments. A supratidal environment was re-established in latest Leonardian( ) to early Guadalupian with deposition of the lower Murdock Mountain Fm. The upper Murdock Mountain Fm. was deposited in very shallow subtidal to supratidal environments. Later during the early Guadalupian, intertidal to shallow subtidal deposition of the Gerster Limestone occurred. Angular phosphatic pebbles that were derived from phosphatic strata at the top of the Gerster Limestone are contained in the Triassic basal conglomerate. These pebbles indicate that the last Permian event was probably emergence and erosion of the top of the Gerster Limestone.

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

    NASA Astrophysics Data System (ADS)

    Warren, C. J.

    2013-02-01

    The formation and exhumation of high and ultra-high-pressure, (U)HP, rocks of crustal origin appears to be ubiquitous during Phanerozoic plate subduction and continental collision events. Exhumation of (U)HP 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 (U)HP assemblages, to be subducted to (U)HP 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 all affect

  18. Exhumation and continental strike-slip fault systems: Introduction

    USGS Publications Warehouse

    Roeske, S.M.; Till, A.B.; Foster, D.A.; Sample, J.C.

    2007-01-01

    Metamorphic rocks adjacent to and within strike-slip faultsystems occur in a wide range of tectonic settings. Detailed studies show that for a number of these locales a significant part of the exhumation occurred during strike-slip fault motion, but the specific processes involved are often cryptic. Although some sites share characteristic features, such as metamorphic rocks exhumed in extensional step-overs within overall transtensional systems, no one common theme emerges from all of the studies. Our understanding of the variables that control continental strike-slip faults' interaction with mid- to lower-crustal structures is still primitive.

  19. Alpine exhumation of the central Cantabrian Mountains, Northwest Spain

    NASA Astrophysics Data System (ADS)

    Fillon, C.; Pedreira, D.; Beek, P. A.; Huismans, R. S.; Barbero, L.; Pulgar, J. A.

    2016-02-01

    The Cantabrian Mountains extend along the Atlantic coast of northern Spain and are known to have experienced an Alpine phase of deformation, reactivating well-expressed Variscan structures. They form the westward continuation of the Pyrenean range and were similarly uplifted consequently to the convergence between the Iberian and European plates. Nevertheless, due to the scarcity of syntectonic sediments and structural markers in a large outcrop of Variscan basement, little is known about the precise timing and amount of the Alpine exhumation phase in the Cantabrian Mountains. We present a new low-temperature thermochronology data set, composed of nine apatite fission track (AFT) and six zircon (U-Th)/He (ZHe) ages, sampled along structurally well-constrained N-S profiles through the central part of the Cantabrian Mountains and complemented by 3-D thermokinematic modeling. The occurrence of Eocene-Oligocene AFT and ZHe ages in the center of the profiles allows us to frame the period of Alpine exhumation from 39 to 29 Ma, at a rate of 0.24-0.3 km Myr-1. Moreover, the reset ZHe ages imply significant burial of the samples, by up to 8-10 km in the center of the range. Therefore, the Alpine exhumation phase was significant, and synchronous to the main phase of exhumation in the central Pyrenees, although exhumation rates were an order of magnitude lower. Three-dimensional thermokinematic modeling of the data confirms the timing of uplift of this area, but its resolution is limited by the relatively small number of reset ages over a large area.

  20. The terminal Permian in European Russia: Vyaznikovian Horizon, Nedubrovo Member, and Permian-Triassic boundary

    NASA Astrophysics Data System (ADS)

    Lozovsky, V. R.; Balabanov, Yu. P.; Karasev, E. V.; Novikov, I. V.; Ponomarenko, A. G.; Yaroshenko, O. P.

    2016-07-01

    The comprehensive analysis of the data obtained on terrestrial vertebrata, ostracods, entomologic fauna, megaflora, and microflora in deposits of the Vyaznikovian Horizon and Nedubrovo Member, as well as the paleomagnetic data measured in enclosing rocks, confirms heterogeneity of these deposits. Accordingly, it is necessary to distinguish these two stratons in the terminal Permian of the East European Platform. The combined sequence of Triassic-Permian boundary deposits in the Moscow Syneclise, which is considered to be the most complete sequence in the East European Platform, is as follows (from bottom upward): Vyatkian deposits; Vyaznikovian Horizon, including Sokovka and Zhukovo members; Nedubrovo Member (Upper Permian); Astashikha and Ryabi members of the Vokhmian Horizon (Lower Triassic). None of the sequences of Permian-Triassic boundary deposits known in the area of study characterizes this sequence in full volume. In the north, the Triassic deposits are underlain by the Nedubrovo Member; in the south (the Klyazma River basin), the sections are underlain by the Vyaznikovian Horizon. The Permian-Triassic boundary adopted in the General Stratigraphic Scale of Russia for continental deposits of the East European platform (the lower boundary of the Astashikha Member) is more ancient than the one adopted in the International Stratigraphic Chart. The same geological situation is observed in the German Basin and other localities where Triassic continental deposits are developed. The ways of solving this problem are discussed in this article.

  1. Succession of Permian and Mesozoic metasomatic events in the eastern Pyrenees with emphasis on the Trimouns talc-chlorite deposit

    NASA Astrophysics Data System (ADS)

    Boutin, Alexandre; de Saint Blanquat, Michel; Poujol, Marc; Boulvais, Philippe; de Parseval, Philippe; Rouleau, Caroline; Robert, Jean-François

    2016-04-01

    Recent studies proposing pre-orogenic mantle exhumation models have helped renew the interest of the geosciences community in the Pyrenees, which should be now interpreted as a hyper-extended passive margin before the convergence between Iberia and Eurasia occurred. Unresolved questions of the Pyrenean geology, as well as the understanding of the formation of hyper-extended passive margins, are how the crust was thinned, and when, where and how the crustal breakoff occurred. The study of the Variscan and pre-Variscan Pyrenean basement is thus critical to document and understand this Cretaceous crustal thinning. In order to specify the timing of Mesozoic metasomatism and the associated deformation in the pre-Mesozoic basement of the Pyrenees, we carried out a U-Th-Pb laser ablation ICP-MS study on a large panel of REE and titanium-rich minerals (titanite and rutile) from talc-chlorite ores from the eastern Pyrenees, with a special emphasis on the Trimouns deposit, the world's largest talc quarry. Our results suggest that the Trimouns talc formation was restricted to the upper Aptian-Cenomanian time, while the talc and chlorite formation in the eastern Pyrenees occurred during several distinct Permian, Jurassic and Cretaceous episodes. These results give strong constraints on the tectonic setting of the Pyrenean domain during the transition between the Variscan and Alpine orogenic cycles, and particularly on when and how the upper crust was thinned before the crustal breakoff and the final mantle exhumation.

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

    NASA Astrophysics Data System (ADS)

    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. Clarification and changes in Permian stratigraphic nomenclature in Kansas

    USGS Publications Warehouse

    Sawin, R.S.; Franseen, E.K.; West, R.R.; Ludvigson, Greg A.; Watney, W.L.

    2008-01-01

    This paper outlines Permian nomenclature changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Permian System/ Period, Cisuralian Series/Epoch, and Asselian Stage/Age are established at the base of the Bennett Shale Member of the Red Eagle Limestone. Series/epoch names Wolfcampian, Leonardian, and Guadalupian are retained and usage of Gearyan, Cimarronian, and Custerian is abandoned. The repositioned Carboniferous-Permian boundary divides the Council Grove Group into Carboniferous (Upper Pennsylvanian Series/Epoch; Virgilian Stage/Age) and Permian (Wolfcampian Series Epoch) segments.

  4. Southwest USA Exhumation History Recorded Below the Great Unconformity

    NASA Astrophysics Data System (ADS)

    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

  5. The timing of exhumation of the Lesser Himalaya

    NASA Astrophysics Data System (ADS)

    Najman, Yani; Foster, Gavin; Millar, Ian; Parrish, Randy; Bickle, Mike; Mark, Darren; Reisberg, Laurie; McKenzie, Ryan; Thiede, Rasmus

    2013-04-01

    Knowledge of the exhumation of the Lesser Himalaya (LH) is important to the development of models of crustal deformation and to testing whether erosion of the LH has contributed to changes in ocean geochemistry, (e.g. Pierson-Wickmann et al 2000; Chesley et al 2000). Since most of the LH is unmetamorphosed, using bedrock to determine the timing of exhumation has been confined to fission track studies, whilst detrital work has concentrated on using the earliest isotopic / petrographic detection of LH detritus in the dated foreland basin sedimentary record to constrain the timing of exhumation (DeCelles et al 1998; Robinson et al 2001; Huyghe et al 2001; Szulc et al 2006; Najman et al 2009). Bulk Sm-Nd analyses of foreland basin mudstones, and U-Pb analyses of detrital zircons were used since the LH and Higher Himalaya (HH), which was exhuming previously, were considered to differ in their Sm-Nd characteristics and zircon age spectra. However, the HH, exhumed earlier and of high topography, continues to dominate the detrital load to the basin, thus hindering detection of the subordinate LH due to dilution effects when bulk isotopic analyses are used. Additionally, emerging work shows that there is some overlap in the U-Pb age spectra of zircons and bulk Nd from the HH and LH (McKenzie et al 2011). Thus there is ambiguity in the detection of the earliest LH detritus in the foreland basin; erosion of the LH occurred by 11 Ma, but may have begun by 16 Ma (Bernet et al 2006). In addition to Ar-Ar analyses on detrital micas and Sm-Nd analyses on conglomerate clasts, we employed new techniques to the foreland basin succession in order to detect LH input: - Re-Os analyses on mudstones. Material of high 187Os/188Os is found in the LH (e.g. Pierson-Wickmann et al 2000) but has not so far been found in the HH. - U-Pb analyses on detrital rutiles. HH and LH rutiles are distinguishable by their different cooling ages (Bracciali et al - poster in this session; this study). - Sm

  6. Concretions in Exhumed Channels Near Hanksville Utah: Implications for Mars

    NASA Technical Reports Server (NTRS)

    Clarke, Jonathan; Stoker, Carol R.

    2011-01-01

    The landscape near Hanksville, Utah, contains a diversity of Mars analogue features. These included segmented and inverted anatasomosing palaeochannels exhumed from the Late Jurassic Brushy Basin Member of the Morrison Formation that hosts abundant small carbonate concretions. The exhumed and inverted channels closely resemble many seen on the surface of Mars in satellite imagery and which may be visited by surface missions in the near future. The channels contain a wealth of palaeo-environmental information, but intrinsically difficult terrain would make their study challenging on Mars. We show that an unexhumed channel feature can be detected geophysically, this may allow their study in more easily accessed terrain. The concretions morphologically and in their surface expression parallel the haematite blue berries that are strewn across the surface of Meridiani Planum on Mars. They are best developed in poorly cemented medium to coarse channel sandstones and appear to have formed early in the diagenetic history.

  7. [Identification of an exhumed unknown infant through DNA analysis].

    PubMed

    Jopp, Eilin; Püschel, Klaus; Warschke, Christian; Kaufmann, Richard; Krebs, Oliver

    2014-01-01

    The article reports on the exhumation and subsequent DNA analysis of the skeletal remains of an unknown male newborn from 1988. Molecular biological methods confirmed the maternity of a woman who was already convicted of infanticide. Since homicide could not be clearly proven and manslaughter becomes barred by the statute of limitation after 20 years, the woman cannot be held accountable for the alleged killing of her first child. PMID:25004622

  8. Permian polar forests: deciduousness and environmental variation.

    PubMed

    Gulbranson, E L; Isbell, J L; Taylor, E L; Ryberg, P E; Taylor, T N; Flaig, P P

    2012-11-01

    Forests are expected to expand into northern polar latitudes in the next century. However, the impact of forests at high latitudes on climate and terrestrial biogeochemical cycling is poorly understood because such forests cannot be studied in the modern. This study presents forestry and geochemical analyses of three in situ fossil forests from Late Permian strata of Antarctica, which grew at polar latitudes. Stem size measurements and stump spacing measurements indicate significant differences in forest density and canopy structure that are related to the local depositional setting. For forests closest to fluvial systems, tree density appears to decrease as the forests mature, which is the opposite trend of self-thinning observed in modern forests. We speculate that a combination of tree mortality and high disturbance created low-density mature forests without understory vegetation near Late Permian river systems. Stable carbon isotopes measured from permineralized wood in these forests demonstrate two important points: (i) recently developed techniques of high-resolution carbon isotope studies of wood and mummified wood can be applied to permineralized wood, for which much of the original organic matter has been lost and (ii) that the fossil trees maintained a deciduous habit at polar latitudes during the Late Permian. The combination of paleobotanical, sedimentologic, and paleoforestry techniques provides an unrivaled examination of the function of polar forests in deep time; and the carbon isotope geochemistry supplements this work with subannual records of carbon fixation that allows for the quantitative analysis of deciduous versus evergreen habits and environmental parameters, for example, relative humidity. PMID:22845834

  9. Permian age from radiolarites of the Hawasina nappes, Oman Mountains

    SciTech Connect

    Wever, P.D. ); Grissac C.B. ); Bechennec, F. )

    1988-10-01

    The Hawasina napper of the Oman Mountains yielded Permian radiolarians from cherts stratigraphically overlying a thick volcanic basement (Al Jil Formation) at the base of the Hamrat Duru Group. This fauna represents the first Permian radiolarians and radiolarites in the central and western Tethyan realm. A Permain age for pelagic sequences within the Hawasina Complex of Oman has major significance for regional paleogeographic reconstruction. A clear differentiation between platform (reefal sediments) and basin (radiolarites) from the base of the Late Permian (255 Ma) is implied. It suggests a flexure of the platform during Permian time; the present data implies that a zone of rifting was already developed adjacent to the northeast Gondwana platform margin during the Late Permian. The Hamrat Duru Basin corresponds to an opening intracontinental rift area (sphenochasm) between Arabia and northeast Gondwana, a reentrant of the paleo-Tethys.

  10. The Major-ion Composition of Permian Seawater

    SciTech Connect

    Lowenstein, T K.; Timofeeff, Michael N.; Kovalevych, Volodymyr M.; Horita, Juske

    2005-01-01

    The major-ion (Mg{sup 2+}, Ca{sup 2+}, Na{sup +}, K{sup +}, SO{sub 4}{sup 2-}, and Cl{sup -}) composition of Permian seawater was determined from chemical analyses of fluid inclusions in marine halites. New data from the Upper Permian San Andres Formation of Texas (274--272 Ma) and Salado Formation of New Mexico (251 Ma), analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy-dispersive spectrometry (EDS) method, along with published chemical compositions of fluid inclusions in Permian marine halites from North America (two formations of different ages) and the Central and Eastern European basins (eight formations of four different ages) show that Permian seawater shares chemical characteristics with modern seawater, including SO{sub 4}{sup 2-} > Ca{sup 2+} at the point of gypsum precipitation, evolution into Mg{sup 2+}-Na{sup +}-K{sup +}-SO{sub 4}{sup 2-}-Cl{sup -} brines, and Mg{sup 2+}/K{sup +} ratios {approx} 5. Permian seawater, however, is slightly depleted in SO{sub 4}{sup 2-} and enriched in Ca{sup 2+}, although modeling results do not rule out Ca{sup 2+} concentrations close to those in present-day seawater. Na{sup +} and Mg{sup 2+} in Permian seawater are close to (slightly below) their concentrations in modern seawater. Permian and modern seawater are both classified as aragonite seas, with Mg{sup 2+}/Ca{sup 2+} ratios >2, conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements. The chemistry of Permian seawater was modeled using the chemical composition of brine inclusions for three periods: Lower Permian Asselian-Sakmarian (296--283 Ma), Lower Permian Artinskian-Kungurian (283--274 Ma), and Upper Permian Tatarian (258--251 Ma). Parallel changes in the chemistry of brine inclusions from equivalent age evaporites in North America, Central Europe, and Eastern Europe show that seawater underwent secular variations in chemistry over the 50 million years of the Permian. Modeled SO{sub 4}{sup 2

  11. Miocene to Pleistocene Exhumation of the Southern European Alps

    NASA Astrophysics Data System (ADS)

    Reverman, R. L.; Fellin, M. G.; Herman, F.; Willett, S. D.

    2012-04-01

    We apply apatite fission-track, (U-Th-Sm)/He dating, 4He/3He diffusion profiles, and OSL thermochronometry to construct a complete thermal history and constrain the exhumation and topographic evolution of the Adamello complex in the Southern European Alps. The Adamello complex is an Eocene-Oligocene pluton emplaced at a depth of 7 km, now exposed at the intersection of two major fault systems and dissected by deep valleys, which drain into larger fluvial systems overdeepened during the Messinian Salinity Crisis. All our ages span the Miocene and display a normal age-elevation relationship, where age increases with elevation, until 2300m, below which all AHe ages are within error of each other. We interpret this break in slope as the onset of a period of rapid cooling initiating at 8.5 Ma and continuing till at least 6 Ma, our youngest age. Further insight is provided by helium diffusion profiles, which constrains the cooling history of the grain from 80°C-20°C. Our results confirm that rapid cooling began at ~8.5 Ma and continued until 4 Ma. We estimate exhumation rates using age-elevation relationships and cooling histories. We compare these estimates with those predicted from a 3-D heat conduction model including topographic relief and erosion (Pecube; Braun, 2002) paired with the Neighborhood Algorithm, which is a two stage mathematical procedure that finds models, or parameters, which minimize the misfit to the data (Sambridge, 1999a,b). The predicted tectono-geomorphic history is tested for feasibility through comparison with known timing of tectonic and erosional events and the thermal history determined by helium diffusion profiles. We also discuss how our results compare to results from elsewhere in the Alps and the implications for the exhumational/erosional history of the Alps.

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Permian magmatism, Permian detachment faulting, and Alpine thrusting in the Orobic Anticline, southern Alps, Italy

    NASA Astrophysics Data System (ADS)

    Pohl, Florian; Froitzheim, Niko; Geisler-Wierwille, Thorsten; Schlöder, Oliver

    2014-05-01

    The Grassi Detachment Fault is located in the Orobic Alps east of Lake Como and was described by Froitzheim et al. (2008) as an Early Permian extensional structure. Many issues still remained unclear, like the exact timing of faulting and the extension from the well-exposed part of the detachment towards west. The Grassi Detachment Fault separates the Variscan Basement in its footwall from the volcanic and sedimentary rocks of the Early Permian Collio Formation within its hanging wall, marked by a mylonitic and cataclastic layer whose textures indicate top-to-the-southeast displacement. The footwall basement is formed by the Variscan Morbegno Gneiss and two granitic intrusions, the Val Biandino Quarz Diorite (VBQD) and the Valle Biagio Granite (VBG). The former is syntectonic with respect to the detachment, whereas for the latter, the relation to the detachment is unknown. The age of the VBQD is poorly defined as 312 Ma ± 48 Ma (Thöni et al. 1992); the VBG has not been dated. Volcanic rocks of the Collio Formation in the hanging wall may represent the extrusive part of the magmatic system. In our study area west of Val Biandino, several faults and shear zones are exposed: (1) The Grassi Detachment Fault is represented by mylonites and cataclasites with top-SE shear sense, between basement rocks and the Collio Volcanics. Towards NW, it is truncated by the unconformably overlying Late Permian Verrucano Lombardo. This may reflect the eroded culmination of a Permian metamorphic core complex. (2) A steeply NW-dipping, brittle normal fault is found further west in the footwall between VBQD and VBG. It is sealed by the basal unconformity of the Verrucano Lombardo and therefore should also be of Early Permian age (Sciunnach, 2001). It may represent an antithetic fault with respect to the detachment, accommodating the uplift of the magmatically inflated core complex. (3) The Biandino Fault is a steeply SE-dipping reverse fault, affecting also the Late Permian Verrucano

  14. Surface uplift, uplift of rocks, and exhumation of rocks

    SciTech Connect

    England, P. ); Molnar, P. )

    1990-12-01

    Uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion, and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges. Rates of uplift of the surfaces of mountain ranges have not, however, been quantified sufficiently well that they provide useful constraints on those processes. Many reports of surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift, and provide no information whatsoever on the rates of surface uplift.

  15. Exhumation Depths of the Lower Crustal Domes of the Pamir

    NASA Astrophysics Data System (ADS)

    McGraw, J. L.; Hacker, B. R.; Ratschbacher, L.

    2009-12-01

    Large-scale orogenic plateaux are important geodynamic features within continental collision systems. In this context, the indo-asian collision and the Tibetan plateau have been the focus of numerous studies aimed at understanding the development of these areas of over-thickened crust. However, the Pamir plateau may provide a better opportunity to understand the mechanics of plateau formation. Because of greater exhumation within the Pamir in the Cenozoic, deeper crustal rocks are exposed which may shed light on the crustal-scale processes occurring within the plateau interior. Examination of lower crustal exposures within the Pamir therefore provides an opportunity to understand the pressure-temperature history of the lower crust that is otherwise not directly observable in the Tibetan Plateau. Samples from three lower crustal domes from the Pamir plateau were analyzed by electron probe microanalysis. The sampled Kurgovat, Yazgulem, and Shakdhara domes likely formed diachronously as the Pamir grew northward, as they are dispersed north to south across the western half of the plateau. Exhumation depths determined from the pressure-temperature history of the rocks were obtained through quantitative thermobarometry. Well-established thermobarometers such as GASP, GHPQ, GBMP and GARB were used on the mainly metapelitic rocks. The typical peak pressure assemblage, garnet + kyanite + biotite + An20 plagioclase ± K-white mica, replaced staurolite, and is itself overgrown by sillimanite and more anorthitic plagioclase. Garnet cores are chemically homogeneous and rims are partially resorbed with long-wavelength rimward increases in Mn. Preliminary data indicate south to north variation in peak metamorphic pressures, which range from 9-11 kbar at temperatures of 700-800°C in the south to ~5 kbar at 500°C in the north; exhumation from peak pressures to 4-6 kbar occurred at temperatures of 500-700°C. These data imply exhumation depths of 32-40 km in the south and ~20 km

  16. An exhumed Late Paleozoic canyon in the rocky mountains

    USGS Publications Warehouse

    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.

  17. Comparative Earth history and Late Permian mass extinction

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Bambach, R. K.; Canfield, D. E.; Grotzinger, J. P.

    1996-01-01

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  18. Upper Permian fluviolacustrine deposits of southern Africa and the late Permian climate southern Gondwana

    SciTech Connect

    Yemane, K. . Dept. of Geology Bryn Mawr Coll., PA . Dept. of Geology)

    1993-03-01

    Upper Permian-age fluviolacustrine deposits are widespread throughout southern Africa. In the southern part of the subcontinent, where deposition took place in foreland basin settings, the sequences are thicker and fluvial-dominated whereas, lacustrine-dominated deposits accumulated in settings of low relief, broad warping and mild faulting at the northern end. The geographic extent and lateral correlatability of these deposits suggest the existence of concurrent, perhaps interconnected, giant lakes within major fluvial frameworks throughout the subcontinent, thousands of miles inland from the sea. This period of major lake development within fluvial depositional settings suggests climatic conditions that sustained a uniquely wet continental environment, deep in the heart of the Gondwanan supercontinent. Simulations based on various general circulation and energy balance climate models predict extreme seasonal temperatures and aridity for Gondwana at the palaeolatitudes of southern Africa during the Late Permian. On the other hand, distribution of climate-sensitive rocks, palynologic and palaeobotanic data and vertebrate fossils, coroborate the temperature climate documented by sedimentologic studies. The erroneous modeling results may have arisen from the fact that the models do not employ palaeogeographies that accommodate the existence of the vast lakes and rivers of Gondwana. The Late Permian palaeogeography of series of giant lakes within major fluvial frameworks would have had considerable influences on the regional climate. This suggests that it is imperative that numerical modeling studies incorporate accurate palaeogeographies, constructed based on available geological data, in order to recreate past climates with acceptable degree of accuracy.

  19. Upper Permian (Guadalupian) facies and their association with hydrocarbons - Permian basin, west Texas and New Mexico

    SciTech Connect

    Ward, R.F.; Kendall, C.G.S.C.; Harris, P.M.

    1986-03-01

    Outcrops of Guadalupian sedimentary rocks in the Permian basin of west Texas and southeastern New Mexico are a classic example of the facies relationships that span a carbonate shelf. In the subsurface, these rocks form classic hydrocarbon-facies taps. Proceeding from basin to the updip termination of the shelf, the facies are (1) deep-water basin, (2) an apron of allochthonous carbonates, (3) carbonate shelf margin or reef, (4) carbonate sand flats, (5) carbonate barrier islands, (6) lagoon, and (7) coastal playas and supratidal salt flats (sabkhas). Over a half century of exploration drilling has shown that hydrocarbons in the Permian rocks of the Permian basin have accumulated at the updip contact of the lagoonal dolomites and clastics with the coastal evaporites, and in the basinal channel-fill clastics. The shelf marginal (reef) facies contain cavernous porosity, but commonly are water saturated. These facies relationships and hydrocarbon occurrences provide an exploration model with which to explore and rank hydrocarbon potential in other carbonate provinces. 16 figures, 3 tables.

  20. Quantification of tertiary exhumation in the United Kingdom southern North Sea using sonic velocity data

    SciTech Connect

    Hillis, R.R.

    1995-01-01

    Sonic velocities from the Upper and Middle Chalk (Upper Cretaceous), the Bunter Sandstone and the Bunter Shale (both Lower Triassic) were used to independently quantify apparent exhumation (height above maximum burial depth) in the United Kingdom (UK) southern North Sea. Apparent exhumation is the displacement, on the depth axis, of a given velocity/depth trend from the normal (unaffected by exhumation) trend. Apparent exhumation results derived from the Upper and Middle Chalk, the Bunter Sandstone, and the Bunter Shale are statistically similar. The consistency of results from carbonate and clastic units suggests that, at a formational and regional scale, over-compaction (i.e., anomalously high sonic velocity) in all three units analyzed reflects previously greater burial depth, rather than sedimentological and/or diagenetic processes, and validates the use of lithologies other than shale in maximum burial depth studies. The consistency of results from units of Early Triassic to Late Cretaceous age suggests that Tertiary exhumation was of sufficiently great magnitude to mask any earlier Mesozoic periods of exhumation, and the maximum Mesozoic-Cenozoic burial depth in the southern North Sea was attained prior to Tertiary exhumation. The proposed magnitudes of exhumation are generally greater than those previously published for the southern North Sea, but they are consistent with recent estimates from apatite fission track analysis. Cretaceous-Tertiary burial prior to exhumation must have been of great magnitude and more rapid than suggested by the preserved stratigraphy. The effect of this extra burial and subsequent exhumation on sedimentary rock decompaction procedure and thermal maturation modeling is illustrated for the Cleethorpes-1 and 44/7-1 wells, and must also be incorporated in modeling reservoir diagenesis. The regional, Tertiary tectonic uplift associated with exhumation must have had a thick-skinned origin.

  1. Extreme mantle uplift and exhumation along a transpressive transform fault

    NASA Astrophysics Data System (ADS)

    Maia, Marcia; Sichel, Susanna; Briais, Anne; Brunelli, Daniele; Ligi, Marco; Ferreira, Nicolas; Campos, Thomas; Mougel, Bérengère; Brehme, Isa; Hémond, Christophe; Motoki, Akihisa; Moura, Denise; Scalabrin, Carla; Pessanha, Ivo; Alves, Eliane; Ayres, Arthur; Oliveira, Pedro

    2016-08-01

    Mantle exhumation at slow-spreading ridges is favoured by extensional tectonics through low-angle detachment faults, and, along transforms, by transtension due to changes in ridge/transform geometry. Less common, exhumation by compressive stresses has been proposed for the large-offset transforms of the equatorial Atlantic. Here we show, using high-resolution bathymetry, seismic and gravity data, that the northern transform fault of the St Paul system has been controlled by compressive deformation since ~10 million years ago. The long-lived transpression resulted from ridge overlap due to the propagation of the northern Mid-Atlantic Ridge segment into the transform domain, which induced the migration and segmentation of the transform fault creating restraining stepovers. An anticlockwise change in plate motion at ~11 million years ago initially favoured extension in the left-stepping transform, triggering the formation of a transverse ridge, later uplifted through transpression, forming the St Peter and St Paul islets. Enhanced melt supply at the ridge axis due to the nearby Sierra Leone thermo chemical anomaly is responsible for the robust response of the northern Mid-Atlantic Ridge segment to the kinematic change. The long-lived process at the origin of the compressive stresses is directly linked to the nature of the underlying mantle and not to a change in the far-field stress regime.

  2. How Orogen-scale Exhumed Strike-slip Faults Initiate

    NASA Astrophysics Data System (ADS)

    Cao, S.; Neubauer, F.

    2015-12-01

    Orogen-scale strike-slip faults present one the most important geodynamic processes affecting the lithosphere-asthenosphere system. In specific subtypes, faulting is virtually initiated along hot-to-cool boundaries, e.g. at such of hot granite intrusions or metamorphic core complexes to cool country rocks. Such fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust and are stacked within each other ("telescoping"). Exhumation of rocks is, therefore, a common feature of such strike-slip faults implying major transtensive and/or transpressive processes accompanying pure strike-slip motion. The hot-to-cool thermal structure across the fault zone significantly influences the physical fault rock properties. One major question is how and where a major strike-slip initiates and further development. Here, we propose a model in which major continental exhumed strike-slip faults potentially evolve along rheologically weak zones such as plutons or margins of metamorphic complexes. As an example, we propose a model for the Ailao Shan-Red River (ASRR) fault, SE Asia, which initiated along the edge of a plutonic belt and evolved in response to India-Asia collision with four tectonic phases.

  3. Tectonic evolution of the Montagne Noire and a possible orogenic model for syncollisional exhumation of deep rocks, Variscan belt, France

    NASA Astrophysics Data System (ADS)

    Aerden, Domingo G. A. M.

    1998-02-01

    Namurian times (D4) producing a 2 km wide subhorizontal shear zone in which orogen-parallel stretching continued. At the surface, deformation was accommodated by decollements, normal faulting, and basin formation. Gneissic rocks below the shear zone were not affected by the collapse because a stronger rheology and horizontal shortening was probably continuous here. Retrograde cooling of the cover restored gravitational equilibrium and caused its renewed upright folding during late-Variscan times (D5). Permian postorogenic extension (D6) oriented at a high angle to the previous orogen-parallel stretching completed exhumation of the gneiss dome. The dome structure of the Montagne Noire metamorphic core complex was acquired during compressional tectonics and later modified (flattened) by synorogenic and postorogenic extensional events. A similiar polyphase origin appears not to be excluded for other metamorphic core complexes with poorly constrained preextension histories.

  4. Permian of Norwegian-Greenland sea margins: future exploration target

    SciTech Connect

    Surlyk, F.; Hurst, J.M.; Piasecki, S.; Rolle, F.; Stemmerik, L.; Thomsen, E.; Wrang, P.

    1984-09-01

    Oil and gas exploration in the northern North Sea and the southern Norwegian shelf has mainy been concentrated on Jurassic and younger reservoirs with Late Jurassic black shale source rocks. New onshore investigations in Jameson Land, central East Greenland, suggest that the Permian of the Norwegian-Greenland Sea margins contains relatively thick sequences of potential oil source rocks interbedded with carbonate reefs. The East Greenland, Upper Permian marine basin is exposed over a length of 400 km (250 mi) from Jameson Land in the south to Wollaston Forland in the north, parallel with the continental margin. The Upper Permian black shale is relatively thick, widely distributed, has a high organic carbon content, and a favorable kerogen type. Consequently, the possibilities for a Permian play in the northern part of the Norwegian shelf and along parts of the Norwegian-Greenland Sea margins are worth evaluating.

  5. Life in the end-Permian dead zone

    PubMed Central

    Looy, Cindy V.; Twitchett, Richard J.; Dilcher, David L.; Van Konijnenburg-Van Cittert, Johanna H. A.; Visscher, Henk

    2001-01-01

    The fossil record of land plants is an obvious source of information on the dynamics of mass extinctions in the geological past. In conjunction with the end-Permian ecological crisis, ≈250 million years ago, palynological data from East Greenland reveal some unanticipated patterns. We document the significant time lag between terrestrial ecosystem collapse and selective extinction among characteristic Late Permian plants. Furthermore, ecological crisis resulted in an initial increase in plant diversity, instead of a decrease. Paradoxically, these floral patterns correspond to a “dead zone” in the end-Permian faunal record, characterized by a paucity of marine invertebrate megafossils. The time-delayed, end-Permian plant extinctions resemble modeled “extinction debt” responses of multispecies metapopulations to progressive habitat destruction. PMID:11427710

  6. Diachronous burial and exhumation of a single tectonic unit during collision orogenesis (Sulitjelma, central Scandinavian Caledonides)

    NASA Astrophysics Data System (ADS)

    Boyle, Alan P.; Burton, Kevin W.; Westhead, R. Keith

    1994-11-01

    The Sulitjelma fold nappe represents part of a Caledonian marginal basin obducted during the closure of the Iapetus Ocean and collision between Laurentia and Baltica. Metamorphic pressure-temperature (P-T) paths indicate that various parts of the Sulitjelma fold nappe followed characteristic clockwise P-T paths involving prograde burial followed by prograde exhumation and then near-isothermal exhumation prior to cooling. Geochronological results indicate that foreland rocks followed this general P-T path before more hinterlandward rocks, such that foreland rocks underwent exhumation while hinterlandward rocks were still being buried. This is consistent with the fold nappe passing through a collisional orogen; burial and ultimately prograde metamorphism were terminated sequentially by exhumation as a given part of the fold nappe came into contact with the lower plate, basement ramp (Baltica) and was driven upward. Burial, heating, exhumation, and cooling were thus diachronous within a single tectonic unit.

  7. Exhumation and extrusion of the Great Himalaya Complex (GHC)

    NASA Astrophysics Data System (ADS)

    Xu, Zhiqin; Wang, Qi; Cao, Hui

    2013-04-01

    The predominant stretching lineation in the Great Himalaya Complex (GHC) trends perpendicular orogen, which has been attributed to southward exhumation of these mid-crustal rocks between the South Tibet Detachment (STD) and Main Central Thrust (MCT) in wedge extrusion (e.g., Burchfiel and Royden, 1985; Grujic et al., 1996) and channel flow models (e.g., Beaumont et al., 2001; Hodges et al., 2001; Grujic et al., 2002), or to emplacement of the GHC between the MCT and STD in tectonic wedging models (Yin, 2006; Webb et al., 2007, 2011a, b). Our new structural and geochronological data from southern Tibet demonstrate widespread lateral flow marked by orogen-parallel stretching lineation in the upper part of the GHC, which corresponds to decoupling between the high-grade GHC rocks and the overlying Tethyan Himalayan Sequence (THS). The kinematic framework reveals a top-to-the-east shear sense in the eastern GHC, both top-to-the-east and top-to-the-west shearing in the central GHC, and a top-to-the-west shear sense in the western GHC during the late Oligocene and Miocene. Geological observations along the Butwal-Pokhara- Jomsom cross section of the Central Nepal-Himalaya indicate that the STD is characterized by small-scale ductile normal shearing at the top part of the GHC and large-scale listric folding structures at the lower part of the Tethys Himalaya unit (TH) composed by Paleozoic- Mesozoic sediments. But the very wide thrusting deformation domain with about 8 km thickness existed in the both sides of the MCT shows possible ductile thrust shearing occurred earlier than We propose that exhumation and extrusion of the GHC probably experienced following complex processes: (1) Early Partial melting occurred at the deep part of the GHC at Eocene; (2) Orogen-parallel gravitational collapse in the late Oligocene and Miocene; (3) Exhumation of the GHC caused by thrusting and extrusion of the GHC between the MCT and STD at Miocene.

  8. Late Cretaceous and Cenozoic exhumation history of the Malay Peninsula

    NASA Astrophysics Data System (ADS)

    François, Thomas; Daanen, Twan; Matenco, Liviu; Willingshofer, Ernst; van der Wal, Jorien

    2015-04-01

    The evolution of Peninsular Malaysia up to the collisional period in the Triassic is well described but the evolution since the collision between Indochina and the Sukhothai Arc in Triassic times is less well described in the literature. The processes affecting Peninsular Malaysia during the Jurassic up to current day times have to explain the emplacement multiple intrusions (the Stong Complex, and the Kemahang granite), the Jurassic/Cretaceous onland basins, the Cenozoic offshore basins, and the asymmetric extension, which caused the exhumation of Taku Schists dome. The orogenic period in Permo-Triassic times, which also formed the Bentong-Raub suture zone, resulted in thickening of the continental crust of current day Peninsular Malaysia due to the collision of the Indochina continental block and the Sukhothai Arc, and is related to the subduction of oceanic crust once present between these continental blocks. The Jurassic/Cretaceous is a period of extension, resulting in the onland Jurassic/Cretaceous basins, synchronous melting of the crust, resulting in the emplacement Stong Complex and the Kemahang granite and thinning of the continental crust on the scale of the Peninsular, followed by uplift of the Peninsular. Different models can explain these observations: continental root removal, oceanic slab detachment, or slab delamination. These models all describe the melting of the lower crust due to asthenospheric upwelling, resulting in uplift and subsequent extension either due to mantle convective movements or gravitational instabilities related to uplift. The Cenozoic period is dominated by extension and rapid exhumation in the area as documented by low temperature thermocrological ages The extension in this period is most likely related to the subduction, which resumed at 45 Ma, of the Australian plate beneath the Eurasian plate after it terminated in Cretaceous times due to the collision of an Australian microcontinental fragment with the Sunda margin in the

  9. Rapid Oligocene Exhumation of the Western Canadian Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Szameitat, A.; Parrish, R. R.; Stuart, F. M.; Carter, A.; Fishwick, S.

    2014-12-01

    As part of the North American Cordillera the Rocky Mountains of Canada impact the deflection of weather systems and the jet stream and form a distinct barrier to Pacific moisture reaching the continental interior. The extent to which this climatic pattern extended into the past is at present uncertain, so improving our understanding of the elevation history of the Rockies is critical to determining the controls on climate change within the Northern Hemisphere. We have undertaken a comprehensive apatite (U-Th-Sm)/He and fission track study of the southeastern Canadian Cordillera, i.e. the southern Canadian Rocky Mountains, in order to provide insight into the mid to late Cenozoic uplift and exhumation history of this region. Thermal history and exhumation models of widespread low elevation samples in combination with 6 vertical profiles covering elevations from 500 up to 3100 m a.s.l. show at least 1500 m of rapid exhumation west of the Rocky Mountain Trench (RMT) during the Oligocene (Figure 1). In contrast, the ranges east of the RMT low elevation samples provide Eocene ages throughout. The data show a very different history of recent uplift of the Canadian Rockies compared to what is currently known from published work, which mostly infer that the eastern Canadian Cordillera has not experienced significant uplift since the Eocene. We propose that the most likely cause of this rock uplift was upwelling of asthenosphere around the eastward subducting Farallon Plate. This also led to the eruption of the nearby mainly Miocene Chilcotin Group flood basalts and could have caused underplating of the thin lithosphere west of the RMT, adding to the buoyancy of the plate and lifting the range. Because the Trench marks the edge of the normal thickness craton which was underthrust beneath the Rocky Mountains during the initial upper Cretaceous orogeny, the eastern Rockies have a normal lithosperic thickness. This would impede recent uplift and provides an explanation for the

  10. Omphacite breakdown reactions and relation to eclogite exhumation rates

    NASA Astrophysics Data System (ADS)

    Anderson, Eric D.; Moecher, David P.

    2007-09-01

    Clinopyroxene + plagioclase (±Hbl ± Qtz) symplectites after omphacite are widely cited as evidence for prior eclogite-facies or high-pressure (HP) metamorphism. Precursor omphacite compositions of retrograde eclogites, used for reconstructing retrograde P- T paths, are commonly estimated by reintegrating symplectite phases with the assumption that the symplectite-forming reactions were isochemical. Comparisons of broadbeam symplectite compositions to adjacent unreacted pyroxene from various symplectites after clinopyroxene from the Appalachian Blue Ridge (ABR) and Western Gneiss Region (WGR) suggest that the symplectite forming reactions are largely isochemical. Endmember calculations based on reintegrated symplectite compositions from the ABR and WGR suggest that a minor Ca-Eskola (CaEs) component (XCaEs = 0.04-0.15) was present in precursor HP clinopyroxene. WGR symplectites consist of fine-grained (˜1 μm-scale), vermicular intergrowths of Pl + Cpx II ± Hbl that occur at grain boundaries or internally. ABR symplectites contain coarser (˜10 μm-scale) planar lamellae and rods of Pl + Cpx II + Qtz + Hbl within clinopyroxene cores. The contrasting textures correlate with decompression and cooling rate, and degree of overstepping of the retrograde reaction (lamellar: slow, erosionally controlled exhumation with slow/low overstepping; fine-grained, grainboundary symplectite: rapid, tectonic exhumation with rapid/high overstepping). Variations in XCaEs, Xjd, and XCaTs of precursor HP omphacite are related to the symplectic mineral assemblages that result from decompression. Quartz-normative symplectities indicate quartz-producing retrograde reactions (e.g., breakdown of precursor CaEs); quartz-free symplectities (e.g., diopside + plagioclase after omphacite) indicate quartz-consuming reactions (jd, CaTs breakdown) outpaced quartz-producing reactions.

  11. Revised exhumation history of the Wind River Range, WY, and implications for Laramide tectonics

    NASA Astrophysics Data System (ADS)

    Stevens, Andrea L.; Balgord, Elizabeth A.; Carrapa, Barbara

    2016-05-01

    A reanalysis of apatite fission track (AFT) thermochronology coupled with thermal-kinetic modeling of samples from the Wind River Range document Late Cretaceous to early Eocene episodic cooling and exhumation of one of the largest basement-cored ranges in the western United States. Three vertical transects taken at different latitudes along the length of the 145 km Wind River Range reveal that exhumation is uniform along strike suggesting steady displacement along the Wind River Fault, and significant exhumation and relief in the Wind River Range by the early Eocene. Thermal modeling of AFT ages, lengths, and compositional proxies document rapid exhumation from ~65 to 50 Ma. This rapid exhumation episode matches a period of accelerated subsidence in the adjacent Green River and Wind River basins. At ~50 Ma, exhumation dramatically slowed by an order of magnitude coincident with decreasing subsidence in the adjacent basins. No signal of Oligocene cooling is apparent in either AFT cooling ages or thermal modeling suggesting that a possible later phase of reactivation of structures and uplift, as previously suggested, was limited to less than approximately 1 km of exhumation.

  12. A climate signal in exhumation patterns revealed by porphyry copper deposits

    NASA Astrophysics Data System (ADS)

    Yanites, Brian J.; Kesler, Stephen E.

    2015-06-01

    The processes that build and shape mountain landscapes expose important mineral resources. Mountain landscapes are widely thought to result from the interaction between tectonic uplift and exhumation by erosion. Both climate and tectonics affect rates of exhumation, but estimates of their relative importance vary. Porphyry copper deposits are emplaced at a depth of about 2 km in convergent tectonic settings; their exposure at the surface therefore can be used to track landscape exhumation. Here we analyse the distribution, ages and spatial density of exposed Cenozoic porphyry copper deposits using a global data set to quantify exhumation. We find that the deposits exhibit young ages and are sparsely distributed--both consistent with rapid exhumation--in regions with high precipitation, and deposits are older and more abundant in dry regions. This suggests that climate is driving erosion and mineral exposure in deposit-bearing mountain landscapes. Our findings show that the emplacement ages of porphyry copper deposits provide a means to estimate long-term exhumation rates in active orogens, and we conclude that climate-driven exhumation influences the age and abundance of exposed porphyry copper deposits around the world.

  13. Testing models of orogen exhumation using zircon (U-Th)/He thermochronology: Insight from the Ligurian Alps, Northern Italy

    NASA Astrophysics Data System (ADS)

    Maino, Matteo; Dallagiovanna, Giorgio; Dobson, Katherine J.; Gaggero, Laura; Persano, Cristina; Seno, Silvio; Stuart, Finlay M.

    2012-08-01

    Testing models of orogen exhumation requires precise constraint of the time-temperature paths of the exhumed rocks. The zircon (U-Th)/He (ZHe) thermochronometer has a closure temperature of ~ 140-210 °C, and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen. We performed ZHe analyses to test the existing contradictory models for the exhumation of the Ligurian Alps. The ZHe ages indicate a very rapid (1.3-6.8 mm/yr) and southward migrating exhumation of the orogen between ~ 32 and 25 Ma. These high exhumation rates are unique within the Alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the Ligurian Alps. We propose a model of tectonic denudation via detachment accomplished in the shallowest crust (< 5 km) as a result of the last orogenic phase of extension.

  14. Middle-Late Permian mass extinction on land

    SciTech Connect

    Retallack, G.J.; Metzger, C.A.; Greaver, T.; Jahren, A.H.; Smith, R.M.H.; Sheldon, N.D.

    2006-11-15

    The end-Permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years. We propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land, one terminating the Middle Permian (Guadalupian) at 260.4 Ma and a later one ending the Permian Period at 251 Ma. Our evidence comes from new paleobotanical, paleopedological, and carbon isotopic studies of Portal Mountain, Antarctica, and comparable studies in the Karoo Basin, South Africa. Extinctions have long been apparent among marine invertebrates at both the end of the Guadalupian and end of the Permian, which were also times of warm-wet greenhouse climatic transients, marked soil erosion, transition from high- to low-sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the end-Guadalupian Emeishan Basalt and end-Permian Siberian Traps.

  15. Permian paleoclimate data from fluid inclusions in halite

    USGS Publications Warehouse

    Benison, K.C.; Goldstein, R.H.

    1999-01-01

    This study has yielded surface water paleotemperatures from primary fluid inclusions in mid Permian Nippewalla Group halite from western Kansas. A 'cooling nucleation' method is used to generate vapor bubbles in originally all-liquid primary inclusions. Then, surface water paleotemperatures are obtained by measuring temperatures of homogenization to liquid. Homogenization temperatures ranged from 21??C to 50??C and are consistent along individual fluid inclusion assemblages, indicating that the fluid inclusions have not been altered by thermal reequilibration. Homogenization temperatures show a range of up to 26??C from base to top of individual cloudy chevron growth bands. Petrographic and fluid inclusion evidence indicate that no significant pressure correction is needed for the homogenization temperature data. We interpret these homogenization temperatures to represent shallow surface water paleotemperatures. The range in temperatures from base to top of single chevron bands may reflect daily temperatures variations. These Permian surface water temperatures fall within the same range as some modern evaporative surface waters, suggesting that this Permian environment may have been relatively similar to its modern counterparts. Shallow surface water temperatures in evaporative settings correspond closely to local air temperatures. Therefore, the Permian surface water temperatures determined in this study may be considered proxies for local Permian air temperatures.

  16. Basin development, petrology, and paleogeography - Early Permian carbonates, northwestern Bolivia

    SciTech Connect

    Canter, K.L.; Isaacson, P.E. )

    1990-05-01

    Early Permian carbonate rocks of the Yaurichambi Formation in northwestern Bolivia demonstrate in-situ, low-paleolatitude development within a complexly interbedded sequence punctuated by siliciclastics apparently derived from a western source. The Yaurichambi Formation (Copacabana Group) occurs above a regional caliche surface that caps Upper Carboniferous quartzarenites. Lower beds of the formation are characterized by interbedded carbonate and quartz-rich lithologies. This interval is gradationally overlain by a shallowing-upward, carbonate-dominated sequence. Mud-rich wackestones and packstones grade upward to bioclastic packstones and grainstones. Common allochems in bioclastic-rich lithologies include echinoderms, brachiopods, fenestrate bryozoans, intraclasts, and less common corals. Uppermost beds contain abundant siliciclastic interbeds. Where exposed, this carbonate sequence is terminated by the Tiquina Sandstone. Permian rocks were deposited in a northwest-southeast-oriented basin. Siliciclastic flooding from the western and southwestern margin of the basin dominated throughout the Carboniferous and occurred intermittently during the Permian, with apparent shallowing to the south. A low-latitude paleogeographic setting for these rocks is indicated by the carbonate lithologies dominating the Lower Permian sequence. Sedimentary and diagenetic features diagnostic of semi-arid warm-water deposition include penecontemporaneous dolomites, fenestral fabric, and calcretes. Furthermore, the faunas are similar to those found in equivalent strata of the Permian basin area of west Texas, indicating that deposition occurred at relatively low latitudes.

  17. 40 CFR 81.242 - Pecos-Permian Basin Intrastate Air Quality Control Region.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 17 2010-07-01 2010-07-01 false Pecos-Permian Basin Intrastate Air... Air Quality Control Regions § 81.242 Pecos-Permian Basin Intrastate Air Quality Control Region. The Pecos-Permian Basin Intrastate Air Quality Control Region (New Mexico) consists of the territorial...

  18. 40 CFR 81.242 - Pecos-Permian Basin Intrastate Air Quality Control Region.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 17 2011-07-01 2011-07-01 false Pecos-Permian Basin Intrastate Air... Air Quality Control Regions § 81.242 Pecos-Permian Basin Intrastate Air Quality Control Region. The Pecos-Permian Basin Intrastate Air Quality Control Region (New Mexico) consists of the territorial...

  19. Interpretation of "fungal spikes" in Permian-Triassic boundary sections

    NASA Astrophysics Data System (ADS)

    Hochuli, Peter A.

    2016-09-01

    Abundant occurrences of the palynomorph Reduviasporonites have been described as "fungal spike" from several Permian/Triassic boundary sections and related to the supposed destruction of woody vegetation by fungal pathogens during the Permian/Triassic extinction event. The biological affinity of this taxa considered by some authors of fungal origin is still controversially discussed since there is geochemical evidence that it is most probably related to algae. The abundance peak of this species is used by some authors as a stratigraphic marker, notably in terrestrial Permian/Triassic boundary sections from South China. Illustrations of the reported fungal remains however show potentially erroneous taxonomic identification of Reduviasporonites, and, based on differences in thermal maturation, they may represent recent contamination. Here Reduviasporonites chalastus of Early Triassic age is illustrated together with recent fungal remains originating from a strongly weathered and otherwise barren sample from a Middle Triassic section.

  20. Late Neogene exhumation patterns in Taranaki Basin (New Zealand): Evidence from offset porosity-depth trends

    NASA Astrophysics Data System (ADS)

    Armstrong, Phillip A.; Allis, Richard G.; Funnell, Robert H.; Chapman, David S.

    1998-12-01

    Taranaki Basin, New Zealand, is located adjacent to the Australian-Pacific Plate boundary where the tectonic regime changes from dominantly subduction-related to the north to transpression-related along the Alpine Fault to the south. During the Neogene, burial and exhumation varied extensively, in both time and space, in response to subsidence and uplift along this evolving plate boundary zone. The basin can be divided into two regions: (1) the Western Platform outside the plate boundary deformation zone where no uplift nor exhumation has occurred and (2) the Eastern Mobile Belt, which lies inside the deformation zone and has been variably uplifted and exhumed. Exhumation magnitudes for sedimentary deposits of the basin are estimated from offset porosity-depth trends. The analysis is based on correlating sonic log travel times with compensated density logs, permitting sonic travel time to be used as a proxy for porosity. Twelve Western Platform wells are used to define a standard exponential porosity-depth trend with an extrapolated surface porosity of 50% and an exponential decay factor of 2265 m, valid for mudstone/shale sections spanning a depth range of 300-3000 m. This curve is a calibration curve against which offset porosity-depth trends from wells in exhumed regions can be compared to determine apparent exhumation amounts. Porosity-depth trends for 43 Eastern Mobile Belt wells are offset 0-2800 m shallower relative to the Western Platform trend but generally are parallel to it. In the southern region of the Eastern Mobile Belt, net exhumation amounts, which are the sum of the porosity-depth trend offset and depth to unconformity, range from 850 to 3000 m; most of this exhumation occurred on discrete contractional structures in late Miocene to early Pliocene time, probably associated with an increased rate of convergence across the Alpine Fault system to the south. In the eastern region of the Eastern Mobile Belt, net exhumation progressively increases from

  1. Hypoxia, global warming, and terrestrial late Permian extinctions.

    PubMed

    Huey, Raymond B; Ward, Peter D

    2005-04-15

    A catastrophic extinction occurred at the end of the Permian Period. However, baseline extinction rates appear to have been elevated even before the final catastrophe, suggesting sustained environmental degradation. For terrestrial vertebrates during the Late Permian, the combination of a drop in atmospheric oxygen plus climate warming would have induced hypoxic stress and consequently compressed altitudinal ranges to near sea level. Our simulations suggest that the magnitude of altitudinal compression would have forced extinctions by reducing habitat diversity, fragmenting and isolating populations, and inducing a species-area effect. It also might have delayed ecosystem recovery after the mass extinction. PMID:15831755

  2. Exhumation by gravitational sliding up an inclined plane

    NASA Astrophysics Data System (ADS)

    Podladchikov, Yury; Schmalholz, Stefan; Burg, Jean-Pierre

    2015-04-01

    Gravity causes sliding down an inclined plane if pressure is near lithostatic. If metamorphic pressures are lithostatic pressures, the approximation is inconsistent with pressure-temperature exhumation histories of thrust nappes stacked during compression to form the thickened crust of mountain belts. Overthickened mountain roots and foreland basin-type sedimentation accompanying the downward movement component of the Moho require significant non-lithostatic pressure perturbations within the mountain belts. Relaxation of the subsequent pressure gradients can be achieved by nappe-like thrusting up an inclined plane recording near isothermal decompression and carrying young sediments to high altitudes. We present results of fully dynamic numerical modelling documenting feasibility of this process. Neither thrusting, nor large weakness zones nor S-point-type boundary conditions are kinematically prescribed in our models. Thrusting emerges spontaneously as an instability, strain localization process that may follow preexisting lithological layering or thermal gradients and able to form new zones of weakness by shear heating mechanism. The non-prescribed nature of our modeled deformation modes makes them feasible, even probable as a leading response to continental shortening. In that case, non lithostatic pressure 'cycle' is an alternative or a complement to the classical Wilson cycle invoked alone to explain elevated occurrences of deep-water sediments.

  3. Late Cenozoic exhumation of New Zealand: inversion from bedrock thermochronological ages

    NASA Astrophysics Data System (ADS)

    Jiao, Ruohong; Herman, Frédéric; Seward, Diane

    2016-04-01

    In the SW Pacific, the present subaerial land area of New Zealand straddles the boundary between the Australian and Pacific Plates. This margin has been converging since the mid-Eocene-late Oligocene, leading to a period of widespread crustal deformation and exhumation. During the past decades, the exhumation of the New Zealand basement has been the basis of many thermochronological studies, resulting in a large number of data from the Palaeozoic and Mesozoic bedrocks. We compiled the cooling ages from multiple thermochronological systems (i.e. apatite and zircon (U-Th)/He, apatite and zircon fission-track, K-feldspar, muscovite, biotite and hornblende 40Ar/39Ar or K-Ar) that yielded cooling events younger than 25 Ma, and formally inverted this data set to estimate the large-scale temporal and spatial variations in the exhumation rates of New Zealand during the late Cenozoic. The exhumation results show good agreement with the predicted off-shore sedimentation rates, while the thermal model used in the inversion is in part constrained by the present-day observed surface heat flow. The modelling results indicate crustal exhumation from the earliest Miocene (just prior to 20 Ma). But from ~10 Ma, a moderate acceleration of exhumation is observed at most sites, coincident with an important change in the orientation of the Pacific motion relative to the Australian Plate. Since the Quaternary, rapid exhumation has occurred in the Southern Alps along the west coast of South Island, with the highest rates in the central part of range. In this region, our estimates of the million-year-scale exhumation rates are in general coincidence with those previously estimated over shorter (i.e. 0.1 Ma and 10 ka) time scales, as well as with the contemporary rock uplift rates derived from GPS data, confirming exhumational steady-state in the orogeny. In contrast in eastern North Island, the predicted Quaternary exhumation rates are much lower than the recent rock uplift rates measured

  4. Chronological constraints on the Permian geodynamic evolution of eastern Australia

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Rosenbaum, Gideon; Vasconcelos, Paulo

    2014-03-01

    The New England Orogen in eastern Australia developed as a subduction-related orogen in the Late Devonian to Carboniferous, and was modified in the Permian by deformation, magmatism and oroclinal bending. The geodynamics associated with the development of the New England oroclines and the exact timing of major tectonic events is still enigmatic. Here we present new 40Ar/39Ar results from metasedimentary and volcanic rocks from the southern New England Orogen. Eight grains from four metasedimentary samples (Texas beds) that originated in the Late Devonian to Carboniferous accretionary wedge yielded reproducible plateau ages of ~ 293, ~ 280, ~ 270 and ~ 260 Ma. These results suggest a complex thermal history associated with multiple thermal events, possibly due to the proximity to Permian intrusions. Two samples from mafic volcanic rocks in the southernmost New England Orogen (Alum Mountain Volcanics and Werrie Basalt) yielded eruption ages of 271.8 ± 1.8 and 266.4 ± 3.0 Ma. The origin of these rocks was previously attributed to slab breakoff, following a period of widespread extension in the early Permian. We suggest that this phase of volcanism marked the transition from backarc extension assisted by trench retreat to overriding-plate contraction. The main phase of oroclinal bending has likely occurred during backarc extension in the early Permian, and terminated at 271-266 Ma with the processes of slab segmentation and breakoff.

  5. Terrestrial Permian - Triassic boundary sections in South China

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Vajda, Vivi

    2016-08-01

    The Permian-Triassic boundary interval in China comprises a significant record of faunal and floral changes during this important extinction event. Here we discuss the details of palynomorph preservation at the classical Western Guizhou and Eastern Yunnan sections in an effort to expand the stratigraphy and paleontology from these earlier studies.

  6. The Great End Permian Tsunamis: Recognition, Extent and Generation

    NASA Astrophysics Data System (ADS)

    Brookfield, M. E.; Algeo, T. J.; Hannigan, R.; Williams, J. C.; Bhat, G. M.

    2013-12-01

    At least three coarse intrabioclastic limestones at the base of the Khunamuh Formation (latest Permian to early Triassic) in Kashmir show features typical features of wave reworking of sediments too deep to be affected by storm waves. These are now interpreted as the deposits of large tsunamis by inferring the wavelengths and amplitudes of the waves from basic wave theory. The same three beds are found in latest Permian shallow marine to moderately deep slope environments throughout the southern Neotethy, as well as further afield in the Alps, East Greenland, and possibly even in the lowland deposits of the European Buntsandstein. Such tsunamis can also account for the contemporary marine erosion surfaces in China and elsewhere in shelf and slope environments. Tsunami waves, unlike storm waves, can also cause reworking of fine sediment and ventilation in deep-sea deposits, and there is some evidence for this in latest Permian oceanic sediments in Japan, New Zealand and western North America. The inferred huge size of the tsunami waves requires marine extraterrestrial impacts or large slumps into and/or under the sea, to generate them. The lack of good evidence for marine extraterrestrial impacts in the latest Permian, and the presence of seismically disturbed beds below the tsunami deposits in some sections suggest that large earthquakes preceded the formation of the tsunamis. These earthquakes might have triggered tsunami-generating large submarine landslides, such as are seen in Quaternary deposits at continental margins and around the Hawaiian and other oceanic volcanic islands. Large slumps of the appropriate age occur in some latest Permian sections in East Greenland and New Zealand.

  7. Thermochronological record of long term faulting, burial and exhumation history in the Sudetes (Bohemian Massif, Central Europe): a multi-system thermochronological approach

    NASA Astrophysics Data System (ADS)

    Štěpančíková, P..; Danišík, M.; Evans, N. J.

    2012-04-01

    Reconstructing erosional and faulting history in the old crystalline basement terrains, with lacking or sparse post-tectonic geological records, is a challenging task where even radiometric data on the basement rocks need not to provide ultimate answers. NE part of the Bohemian Massif (known as the Sudetes) represents a classic example where numerous attempts to constrain denudation, faulting and relief formation on the Variscan basement, often based on incomplete lines of evidence, led to formulation of controversial models. In this study we aim to reconstruct the post-orogenic exhumation history of the Rychlebské hory Mts. in the eastern Sudetes and constrain paleo-activity along the Sudetic Marginal Fault (SMF) - one of the morphologically most prominent, but poorly understood features of Central Europe, forming a >140 km long escarpment separating the Sudetic Mountains from the foreland in the northeast. We do so by applying zircon (U-Th)/He (ZHe), apatite fission track (AFT) and apatite (U-Th)/He (AHe) dating methods to the basement samples from different fault-bounded blocks and sparsely preserved post-orogenic sedimentary samples. New thermochronological data reveals that in the Late Cretaceous at ~95-80 Ma, the Carboniferous-Permian basement blocks SW and NE of the SMF were buried to ~4-7 km and >6.5 km depths, respectively, by sediments of the Bohemian Cretaceous Basin System. This finding contradicts the traditional paleogeographic reconstructions suggesting exposure of large portions of the Sudetes for most of the Mesozoic-Cenozoic. During the burial, the SMF acted as a normal fault as documented by offset in ZHe ages across the fault. At 85-70 Ma, the basin was inverted, Cretaceous strata eroded and basement blocks were exhumed to the near-surface at exhumation rate of ~300 m/Ma as evidenced by Late Cretaceous-Paleocene AFT ages and thermal modelling results. There is no appreciable difference in AFT and AHe ages across the fault suggesting that the

  8. Isotopic age constraints on provenance of exotic terranes, latest Permian collision and fast Late Triassic post-collisional cooling and tectonic exhumation of the Korean collision belt

    NASA Astrophysics Data System (ADS)

    de Jong, Koenraad; Han, Seokyoung; Ruffet, Gilles; Yi, Keewook

    2016-04-01

    The Korean peninsula is located in the eastern margin of the Eurasian continent where major late Palaeozoic to early Mesozoic continental collision zones, like the Central Asian Orogenic Belt and the Central China Orogen, merge with circum-Pacific subduction-accretion systems. We present an integrated view of the Korean collision belt using recent Ar/Ar laser-probe step-heating single grain ages from the uppermost Gyeonggi Massif, central Korea's Palaeoproterozoic high-grade granite-gneiss terrane affected by Permo-Triassic metamorphism, the bordering Hongseong zone and the overlying Imjingang belt and the correlative Taean Formation, as well as SHRIMP isotopic ages of detrital zircons from meta-sandstones from the latter metamorphic marine turbidite sequences. We show that early Paleozoic isolated exotic terranes form part of the collision belt and were reworked in Permo-Triassic time. Age spectra of zircons from mature meta-sandstones in the Misan Formation (Imjingang Belt) and Taean Formation do not match the age distribution of the Gyeonggi Massif, to which both are usually assigned, as they show only subordinate 1.9-1.8 Ga and ~2.5 Ga age modes but dominant 441-426 Ma and 978-919 Ma peaks. Much of the sediment appears to have been derived from distant, exotic middle Paleozoic and Early Neoproterozoic magmatic sources, not present in Gyeonggi or other Korean basement massifs. The youngest concordant zircon ages are: 394, 398 and 402 Ma, showing that both formations are at least of Early Devonian age. Terranes with a substratum with Early Neoproterozoic and Silurian-Devonian granitoids are present in the South Chinese Cathaysia Terrane and in the Qinling Terrane (Central China Orogen). Both formations may, hence, represent the submarine fan part of a routing system and a delta-shelf system originally situated in China. The Taean Formation and Imjingang Belt are thus exotic Paleozoic terranes tectonically emplaced in the Korean collision belt. Muscovite, biotite and amphibole from different units of the Imjingang Belt yielded tightly clustered Ar/Ar plateau ages between 255±1 and 249±1 Ma, dating fast cooling after peak temperature conditions. Slightly younger 243±1 and 240±1 Ma muscovite plateau ages in strongly retrogressed mylonites in the top of the Gyeonggi Massif and 241-237 Ma age components (Taean Formation) point to collisional tectonism. Concordant 233-229 Ma isotopic ages of titanite, hornblende and mica in Hongseong zone and Taean Formation, and detrital muscovite in Jurassic Gimpo sandstones reveal a regional thermal event affecting large portions of the peninsula's crust, also manifested in widespread 237-226 Ma mantle-sourced Mg-rich potassic magmatism and associated mafic dykes truncating folds and tectonic foliations. The Late Triassic thermal pulse implies rapid advective-conductive asthenospheric heat transport promoted by extension and magmatic underplating during post- or late-collisional lower crust and uppermost mantle delamination and/or oceanic slab break-off. The efficiency of cooling is underlined by identical biotite (228±1 Ma) and hornblende (230±1 Ma) plateau ages in Hongseong amphibolites that are partly concordant with 243-229 Ma (average: ˜235 Ma) U-Pb zircon ages in the Gyeonggi Massif and the Hongseong zone, in the literature. This indicates that the Gyeonggi Massif is a Late Triassic core complex.

  9. Concept of the exhumed partial annealing (retention) zone in thermochronology: An appraisal

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.

    2013-12-01

    The concept of an exhumed partial annealing zone (PAZ) in fission track (FT) thermochronology has been a widely used and successful interpretative tool since the 1980s. This 1D-interpretative approach is typically applied to samples collected over significant relief, with best results if the sampling is undertaken in steep short-wavelength topography and samples collected parallel to topography (perpendicular to curved isotherms), and for samples following a vertical exhumation path. While annealing of fission tracks occurs even at low ambient temperatures the PAZ is defined as the zone between where tracks are annealed 'geologically' instantaneously and where the rate of annealing slows dramatically; between ~60 and ~110°C for tracks in apatite depending on composition. The shape and average slope of a PAZ varies depending on the paleogeothermal gradient and its stability, and the length of time over which a PAZ forms. PAZs and partial retention zones (PRZ) are now known for different minerals for various techniques. Single grain age dispersion can be significantly magnified in a PAZ/PRZ depending on composition, grain size, [eU], radiation damage and zoning for the FT and (U-Th)/He methods. An exhumed PAZ/PRZ may be revealed in an age-elevation ('vertical') profile when, following a period of uplift/exhumation, the form of the PAZ/PRZ is retained with a 'sharp' convex inflexion (the 'break in slope') marking the base of the exhumed PAZ/PRZ with reset samples structurally beneath. The break in slope represents a minimal age for the transition from 'relative thermal stability' to rapid cooling, as the rock column has to cool through the PAZ/PRZ, with the underestimate greater if the change in cooling rate is not significant. The base of an exhumed PAZ/PRZ is a curve, but we approximate it with straight lines, with less precision with fewer samples. The break in slope may not be distinguishable if the cooling/exhumation was long ago and/or of low magnitude. The

  10. Style of exhumation and rheological evolution of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Behr, W. M.

    2011-12-01

    We examine the style of exhumation and rheological evolution of a subduction complex forming part of the Betic Cordillera in the Western Mediterranean. Rocks within the Nevado-Filabride complex (NFC) were subducted and exhumed to the surface within ~10 m.y. in the Miocene. Ti-in-quartz thermobarometry, Raman spectroscopy on graphite, and chlorite thermometry indicate that the exhumation path of the NFC was close to linear, reaching peak T and P of 550 ± 50°C and 15 ± 3 kbar. Two-dimensional thermal modeling allows us to fit this P-T-t path using exhumation rate and exhumation geometry as free parameters. We find that the P-T-t path is best fit by a model in which the rocks are subducted to > 50 km depth, exhumed rapidly along the same trajectory within a subduction channel, then captured by a low angle detachment fault cutting through the overlying crust. This model can be reconciled with the thermal history preserved in the overlying plate and is supported by the kinematics recorded in high strain fabrics within the NFC itself. We also link the exhumation history of the NFC subduction channel to the rheology of quartz-rich rocks within it by tracking changes in deformation mechanism, stress, strain rate, water content, and crystallographic preferred orientation (CPO) over time. Increasing localization during cooling allowed earlier microstructures to be preserved, such that the rocks record several stages in their exhumation history. Early deformation during initial subduction was accommodated by pressure solution under low-stress (<6 MPa), low-strain-rate, variable T conditions, and produced an inverted metamorphic gradient within the NFC. At the early stages of exhumation, the deformation mechanism at the top of the channel switched to dislocation creep at stresses of ~6-20 MPa, strain rates of < 5E-13/s and temperatures of 500-550°C. Both stress and strain rate increased with decreasing T in the channel margin, culminating in stresses of ~180 MPa, strain

  11. Style of exhumation and rheological evolution of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Behr, W. M.; Platt, J. P.

    2012-04-01

    We examine the style of exhumation and rheological evolution of a subduction complex forming part of the Betic Cordillera in the Western Mediterranean. Rocks within the Nevado-Filabride complex (NFC) were subducted and exhumed to the surface within ~10 m.y. in the Miocene. Ti-in-quartz thermobarometry, Raman spectroscopy on graphite, and chlorite thermometry indicate that the exhumation path of the NFC was close to linear, reaching peak T and P of 550 ± 50°C and 15 ± 3 kbar. Two-dimensional thermal modeling allows us to fit this P-T-t path using exhumation rate and exhumation geometry as free parameters. We find that the P-T-t path is best fit by a model in which the rocks are subducted to > 50 km depth, exhumed rapidly along the same trajectory within a subduction channel, then captured by a low angle detachment fault cutting through the overlying crust. This model can be reconciled with the thermal history preserved in the overlying plate and is supported by the kinematics recorded in high strain fabrics within the NFC itself. We also link the exhumation history of the NFC subduction channel to the rheology of quartz-rich rocks within it by tracking changes in deformation mechanism, stress, strain rate, water content, and crystallographic preferred orientation (CPO) over time. Increasing localization during cooling allowed earlier microstructures to be preserved, such that the rocks record several stages in their exhumation history. Early deformation during initial subduction was accommodated by pressure solution under low-stress (<6 MPa), low-strain-rate, variable T conditions, and produced an inverted metamorphic gradient within the NFC. At the early stages of exhumation, the deformation mechanism at the top of the channel switched to dislocation creep at stresses of ~6-20 MPa, strain rates of < 5E-13/s and temperatures of 500-550°C. Both stress and strain rate increased with decreasing T in the channel margin, culminating in stresses of ~180 MPa, strain

  12. Testing exhumation models using PTt paths: an Alpine perspective based on deformation ages

    NASA Astrophysics Data System (ADS)

    Reddy, S.; Butler, R.; Wheeler, J.; Cliff, B.; Freeman, S.; Biggs, A.

    2005-12-01

    Geochronological data are now commonly used to establish the timing and rates of exhumation of high pressure metamorphic rocks, critical for testing geodynamic models of orogenic belts. Such approaches must be used with care. Ages of peak pressure metamorphic assemblages allied to younger cooling ages give a general insight into the rates of exhumation when tied to PT paths. However, the results of this workflow are difficult to relate to the kinematic history and therefore maybe of limited use in the critical testing of exhumation models. An alternative strategy is to date directly synkinematic mineral phases in characterised deformation zones. Examples are drawn from the deformed and variably subducted "European" continental crust now exposed in the Western Alps to illustrate this, chiefly using Rb-Sr mica dating, applied to greenschist facies shear zones. Some structures are synchronously active for c. 100km along strike (e.g. the regional "retrocharriage" shear system of the Eastern Brianconnais: 34 Ma). However, UHP terrains of the basement massifs attained peak pressures and were exhumed diachronously (38 Ma - 32 Ma). These results indicate that tectono-metamorphic histories based on single orogenic transects may give misleading pictures of geodynamic evolution. In an Alpine context it appears that exhumation of UHP and shallower parts of the evolving continental subduction channel occurred as variably detached flakes rather than relate to the dynamics of larger scale plate processes.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Tracing trends in erosion and exhumation during the Middle-Late Paleozoic tectonic evolution of the Farewell terrane, SW Alaska

    NASA Astrophysics Data System (ADS)

    Hampton, B. A.; Malkowski, M. A.; Bradley, D. C.; Fujita, K.; O'Sullivan, P. B.

    2010-12-01

    The Farewell terrane of southwest and west-central Alaska is located at the northernmost endpoint of the North American Cordillera and is just beyond the present-day margin of the Amerasia Basin. The initial geologic framework of this region has been constrained, yet the origin, Paleozoic tectonic development, and paleogeography of the Farewell terrane prior to opening of the Arctic Ocean remain unknown. In southwestern Alaska, the Farewell is defined by a three-part succession that consist of (1) Neoproterozoic-Devonian carbonate rocks and subordinate clastic strata of the Nixon Fork subterrane, (2) Cambrian-Devonian clastic and carbonate units of the Dillinger subterrane, and (3) Devonian-Permian(?) siliciclastic strata of the Mystic subterrane. Although previous studies have suggested a Siberian origin for the oldest parts of the Farewell based on faunal data, it has yet to be determined if the Dillinger and Mystic subterranes share links with regions to the north (e.g. Siberia, Baltica, Greenland) or with the northern and western regions of Laurentia. Here we present U-Pb detrital zircon data as well as modal composition trends from Paleozoic strata of the Dillinger and Mystic subterranes that reflect an upsection transition in detrital contribution from middle to top of the Farewell terrane. U-Pb detrital zircon age spectra from Silurian-Devonian strata of the Dillinger subterrane reveal a range of Precambrian and Paleozoic ages with primary occurrences between 400-440 and 1000-2000 Ma. Isolated age peaks occur at 430, 500, 890, 1100, and1400 Ma. The oldest strata from the overlying Mystic subterrane contain primary peaks at 380, 420, 925 Ma with an elevated occurrence of Proterozoic ages between 500-2000 Ma. Younger Devonian-Permian age strata of the Mystic subterrane yield primary age peaks between 300-350 and 420-450 Ma with smaller peaks between 1800-2000 Ma. Modal composition trends from the Dillinger and Mystic subterranes reveal pervasive occurrences of

  15. Mechanisms of mantle exhumation at oceanic core complexes

    NASA Astrophysics Data System (ADS)

    MacLeod, C. J.; Escartin, J.; Dick, H. J. B.; Allerton, S.

    2003-04-01

    Mantle rocks are exposed on the seafloor at many slow-spreading mid-ocean ridges as well as at the ocean-continent transitions of rifted continental margins. Similarities in morphology are evident in the two environments and it is likely that the mechanisms that give rise to exhumation of the mantle are comparable to some degree. We review the processes of deformation and magmatism in two contrasting modern oceanic core complexes and compare it with observations from the Lizard Complex (SW England), which is variously interpreted either as an ancient fragment of slow-spread ocean lithosphere or as a piece of lithosphere from a rifted continental margin. Mantle and lower crustal rocks are exposed at Atlantis Bank, on the SW Indian Ridge, and on corrugated highs north of the Fifteen-Twenty fracture zone on the Mid-Atlantic Ridge. Wireline rock drilling has shown that these ‘oceanic core complex’ massifs are the footwalls of large detachment fault systems. Despite their general similarities the two examples exhibit very different mechanisms of strain localisation, and may represent end-members of a range of processes by which detachment faults may form. At Atlantis Bank widespread high-temperature crystal-plastic (and locally syn-magmatic) deformation of gabbros indicates that the detachment fault did not form and move only during amagmatic phases: instead, a continuous gabbro layer was being formed and accreting in the footwall at the same time as the detachment was active, implying that the 'hot' detachment rooted within or near an active magma chamber. In contrast, evidence for high-temperature deformation on the Fifteen-Twenty detachment fault is absent: fault rocks are instead composed of talc-chlorite-tremolite schists, indicating that deformation took place under greenschist facies conditions and suggesting that fluid circulation accompanied and assisted strain localisation. This 'cold' detachment fault must therefore have rooted and slipped in the shallow

  16. Complex Burial and Exhumation of South Polar Cap Pitted Terrain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This image is illuminated by sunlight from the upper left. The two prominent bright stripes at the left/center of the image are covered with bright frost and thus create the illusion that they are sunlit from the lower left.

    The large pits, troughs, and 'swiss cheese' of the south polar residual cap appear to have been formed in the upper 4 or 5 layers of the polar material. Each layer is approximately 2 meters (6.6 feet) thick. Some Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of this terrain show examples in which older pitted and eroded layers have been previously buried and are now being exhumed. The example shown here includes two narrow, diagonal slopes that trend from upper left toward lower right at the left/center portion of the frame. Along the bottoms of these slopes are revealed a layer that underlies them in which there are many more pits and troughs than in the upper layer. It is likely in this case that the lower layer formed its pits and troughs before it was covered by the upper layer. This observation suggests that the troughs, pits, and 'swiss cheese' features of the south polar cap are very old and form over long time scales.

    The picture is located near 84.6oS, 45.1oW, and covers an area 3 km by 5 km (1.9 x 3.1 mi) at a resolution of about 3.8 meters (12 ft) per pixel. The image was taken during southern spring on August 29, 1999.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  17. Significance of "stretched" mineral inclusions for reconstructing P- T exhumation history

    NASA Astrophysics Data System (ADS)

    Ashley, Kyle T.; Darling, Robert S.; Bodnar, Robert J.; Law, Richard D.

    2015-06-01

    Analysis of mineral inclusions in chemically and physically resistant hosts has proven to be valuable for reconstructing the P- T exhumation history of high-grade metamorphic rocks. The occurrence of cristobalite-bearing inclusions in garnets from Gore Mountain, New York, is unexpected because the peak metamorphic conditions reached are well removed (>600 °C too cold) from the stability field of this low-density silica polymorph that typically forms in high temperature volcanic environments. A previous study of samples from this area interpreted polymineralic inclusions consisting of cristobalite, albite and ilmenite as representing crystallized droplets of melt generated during a garnet-in reaction, followed by water loss from the inclusion to explain the reduction in inclusion pressure that drove the transformation of quartz to cristobalite. However, the recent discovery of monomineralic inclusions of cristobalite from the nearby Hooper Mine cannot be explained by this process. For these inclusions, we propose that the volume response to pressure and temperature changes during exhumation to Earth's surface resulted in large tensile stresses within the silica phase that would be sufficient to cause transformation to the low-density (low-pressure) form. Elastic modeling of other common inclusion-host systems suggests that this quartz-to-cristobalite example may not be a unique case. The aluminosilicate polymorph kyanite also has the capacity to retain tensile stresses if exhumed to Earth's surface after being trapped as an inclusion in plagioclase at P- T conditions within the kyanite stability field, with the stresses developed during exhumation sufficient to produce a transformation to andalusite. These results highlight the elastic environment that may arise during exhumation and provide a potential explanation of observed inclusions whose stability fields are well removed from P- T paths followed during exhumation.

  18. Late-Quaternary exhumation of Namche Barwa constrained using low-temperature multi-OSL-thermochronometry

    NASA Astrophysics Data System (ADS)

    King, Georgina; Herman, Frederic

    2016-04-01

    The influence of climate on tectonic processes remains a controversial concept. Exhumation rates of >5 mm/yr make Namche Barwa, Tibet, one of the most rapidly exhuming places on earth, and two main hypotheses have developed to explain the very high rates of exhumation there. The tectonic aneurysm model (Zeitler et al., 2001) proposes that crustal weakening coupled with extremely active surface processes causes a spatial stationarity of exhumation. Alternatively, a northward plunging antiform that is progressively migrating north-eastward (Seward and Burg, 2008) may explain the concentration of extremely low cooling ages and rapid exhumation that characterise the Namche Barwa massif. Here we use multi-OSL-thermochronometry of feldspar, which comprises a series of different systems with closure temperatures ranging from 30 to 70 C, to quantify spatial and temporal changes in exhumation rates. We have applied this new technique to a suite of samples from the Namche Barwa massif and inverting our data enables us to precisely resolve cooling histories over 0.1 Ma timescales. Our data indicate propagation of a knick-point along the Parlung river, which can be explained by progressive north-eastward migration of a northward plunging antiform. We suggest that river incision does not therefore feedback onto tectonics, as proposed by the aneurysm model. Zeitler, P.K., Meltzer, A.S., Koons, P.O., et al., 2001. Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism. GSA Today 11, 4-9 Seward, D., Burg, J-P., 2008. Growth of the Namche Barwa Syntaxis and associated evolution of the Tsangpo Gorge: Constraints from structural and thermochronological data. Tectonophysics 451, 282-289.

  19. Decoupling of long-term exhumation and short-term erosion rates in the Sikkim Himalaya

    NASA Astrophysics Data System (ADS)

    Abrahami, Rachel; van der Beek, Peter; Huyghe, Pascale; Hardwick, Elisabeth; Carcaillet, Julien

    2016-01-01

    Understanding the relative strengths of tectonic and climatic forcing on erosion at different spatial and temporal scales is important to understand the evolution of orogenic topography. To address this question, we quantified exhumation rates at geological timescales and erosion rates at millennial timescales in modern river sands from 10 sub-catchments of the Tista River drainage basin in the Sikkim Himalaya (northeast India) using detrital apatite fission-track thermochronology and cosmogenic 10Be analyses, respectively. We compare these rates to several potential geomorphic or climatic forcing parameters. Our results show that millennial erosion rates are generally higher and spatially more variable than long-term exhumation rates in Sikkim. They also show strongly contrasting spatial patterns, suggesting that the processes controlling these rates are decoupled. At geological timescales, exhumation rates decrease from south to north, with rates up to 1.2 ± 0.6 mm/yr recorded in southwest Sikkim and as low as 0.5 ± 0.2 mm/yr in the northernmost catchment. Long-term exhumation rates do not correlate with any geomorphic or climatic parameter. We suggest they are tectonically controlled: high rates in southwest Sikkim may be linked to the building of the Lesser Himalaya Rangit Duplex, whereas low rates in north Sikkim are consistent with cessation of extensional exhumation along the South Tibetan Detachment after 13 Ma. The highest apparent erosion rates recorded by cosmogenic nuclides (˜5 mm/yr) occur in catchments spanning the Main Central Thrust Zone, but these appear to be strongly influenced by recent landsliding. High millennial erosion rates (1-2 mm/yr) also occur in north Sikkim and may be climatically driven through strong glacial inheritance of the landscape, as attested by high channel-steepness values close to the maximum extent of glaciers during the Last Glacial Maximum. In contrast, variations in rainfall rate do not seem to strongly influence

  20. Thermal structure, rock exhumation, and glacial erosion of the Namche Barwa Peak, constraints from thermochronological data

    NASA Astrophysics Data System (ADS)

    Tu, Ji-Yao; Ji, Jian-Qing; Sun, Dong-Xia; Gong, Jun-Feng; Zhong, Da-Lai; Han, Bao-Fu

    2015-06-01

    In this paper, we report thermochronological data from the southwest slope of Namche Barwa Peak, the core region of the eastern Himalayan syntaxis. The data include apatite fission track (AFT) ages of ten bedrock samples ranging from 0.5 ± 0.1 to 3.5 ± 0.5 Myr and biotite 40Ar/39Ar ages from 2.53 ± 0.14 to 5.57 ± 0.19 Myr, corresponding to elevations from 5370 to 3060 m. These ages are characterized by inverted age-elevation relationships (AERs), and the AERs of the AFT ages and the biotite 40Ar/39Ar ages are approximately parallel. Numerical modeling suggests that a possible change in the surface topography or faulting in this region could not have led to the observed inverted AERs. These observed ages demonstrate that a field of nonuniform exhumation rates existed in the relatively shallow crust (above the 110 °C isotherm) of the Namche Barwa Peak region. The exhumation rates increase significantly from 0.3 km/Myr to 5 km/Myr with increasing proximity to the peak. However, the exhumation rates in the relatively deep crust (below the 110 °C isotherm) of the same area are uniform at approximately 1.7 km/Myr. This distinctive exhumation field and the strong spatial correlation between the intense glacial erosion and high rock exhumation rate of Namche Barwa Peak suggest that glacial erosion most likely drives the rapid exhumation of Namche Barwa Peak.

  1. Effect of horseshoe crab spawning density on nest disturbance and exhumation of eggs: A simulation study

    USGS Publications Warehouse

    Smith, D.R.

    2007-01-01

    Because the Delaware Bay horseshoe crab (Limulus polyphemus) population is managed to provide for dependent species, such as migratory shorebirds, there is a need to understand the process of egg exhumation and to predict eggs available to foraging shorebirds. A simple spatial model was used to simulate horseshoe crab spawning that would occur on a typical Delaware Bay beach during spring tide cycles to quantify density-dependent nest disturbance. At least 20% of nests and eggs were disturbed for levels of spawning greater than one third of the average density in Delaware Bay during 2004. Nest disturbance increased approximately linearly as spawning density increased from one half to twice the 2004 level. As spawning density increased further, the percentage of eggs that were disturbed reached an asymptote of 70% for densities up to 10 times the density in 2004. Nest disturbance was heaviest in the mid beach zone. Nest disturbance precedes entrainment and begins the process of exhumation of eggs to surface sediments. Model predictions were combined with observations from egg surveys to estimate a snap-shot exhumation rate of 5-9% of disturbed eggs. Because an unknown quantity of eggs were exhumed and removed from the beach prior to the survey, cumulative exhumation rate was likely to have been higher than the snap-shot estimate. Because egg exhumation is density-dependent, in addition to managing for a high population size, identification and conservation of beaches where spawning horseshoe crabs concentrate in high densities (i.e., hot spots) are important steps toward providing a reliable food supply for migratory shorebirds. ?? 2007 Estuarine Research Federation.

  2. Environmental mutagenesis during the end-Permian ecological crisis.

    PubMed

    Visscher, Henk; Looy, Cindy V; Collinson, Margaret E; Brinkhuis, Henk; van Konijnenburg-van Cittert, Johanna H A; Kürschner, Wolfram M; Sephton, Mark A

    2004-08-31

    During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism. PMID:15282373

  3. Environmental mutagenesis during the end-Permian ecological crisis

    PubMed Central

    Visscher, Henk; Looy, Cindy V.; Collinson, Margaret E.; Brinkhuis, Henk; van Konijnenburg-van Cittert, Johanna H. A.; Kürschner, Wolfram M.; Sephton, Mark A.

    2004-01-01

    During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism. PMID:15282373

  4. Zircon (U-Th)/He thermochronometry and modeling of Cenozoic exhumation of the West Spitsbergen Fold Belt: a HeFTy task

    NASA Astrophysics Data System (ADS)

    Barnes, Chris; Schneider, David; Majka, Jaroslaw; Lorenz, Henning; Kosminska, Karolina; Manecki, Maciej

    2015-04-01

    The West Spitsbergen Fold Belt (WSFB) is part of a ca. 55 Ma Eurekan deformation zone which trends N-S along the western margin of the Svalbard archipelago and is largely comprised of Meso- to Neoproterozoic metasediments and metavolcanics. (U-Th)/He thermochronometry is being conducted from three different regions within the fold belt to resolve the time-temperature history: Wedel Jarlsberg Land, Prins Karls Forland, and Sorkapp Land. Preliminary data obtained from Wedel Jarlsberg Land (amphibolite facies Eimfjellet Group and greenschist facies Sofiebogen Group) yield zircon (U-Th)/He (ZHe) ages indicative of Late Cretaceous to Early Paleogene cooling. It is apparent from the cooling ages that these Neoproterozoic rocks were >200°C before Eurekan deformation. Despite no clear trend between cooling age and grain size, the zircons exhibit a large range of eU values (51 to 826), viewed as a proxy for radiation damage, corresponding to a Gaussian distribution with age. Preliminary ZHe ages obtained from the Macnairrabbane unit of Prins Karls Forland suggests slightly younger cooling, as young as Late Eocene. HeFTy inversion models suggest the possibility that these rocks were at near-surface conditions through much of the Carboniferous and Permian as part of the Sorkapp-Hornsund High as a consequence of the Late Devonian Svalbardian Event. A moderate-temperature burial or heating event is therefore required to explain the Late Cretaceous /Early Paleogene ZHe cooling ages. With the current data, it is difficult to resolve whether this heating event was the result of pre-Eurekan sedimentation or syn-Eurekan over-thrusting. Nonetheless, the data strongly suggest fast cooling (and exhumation) through the He partial-retention zone during Eurekan tectonism, which may have commenced prior to 55 Ma. Similar thermochronometry results have been produced from Mesozoic rocks of the Sverdrup Basin exposed on Axel Heiberg and Ellesmere Islands of Canada; apatite fission-track and

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

    NASA Astrophysics Data System (ADS)

    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

  6. Precollisional, multistage exhumation of subducted continental crust: The Sesia Zone, western Alps

    NASA Astrophysics Data System (ADS)

    Babist, J.; Handy, M. R.; Konrad-Schmolke, M.; Hammerschmidt, K.

    2006-12-01

    The Sesia Zone within the Tertiary arc of the western Alps is a relic of the subducted part of the Adriatic continental margin along the SE border of the Tethyan ocean. The Sesia Zone comprises three basement nappes which individuated during Late Cretaceous (65-80 Ma) subduction to different depths at high-pressure (HP, blueschist, eclogite facies) conditions (peak pressures of 1.0-1.2, 1.0-1.5, and 1.5-2.0 GPa). The thrusts bounding these nappes developed where the crust was previously thinned during Jurassic rifting. Crustal-scale shear zones partly overprinted these early thrusts and exhumed coherent slices of crust containing HP rocks. Initial exhumation of the internal part of the accreted margin involved thrusting (D1) and transpressional shearing (D2) along a subvertical, E-W trending mylonitic shear zone under retrograde blueschist- to greenschist-facies conditions. This exhumation was nearly isothermal to a depth of about 25 km, where the basement nappes were juxtaposed. Subsequent exhumation of these nappes to a common depth of about 15-20 km occurred in the footwall of a greenschist-facies, top-SE extensional shear zone (D3) preserved in some of the highest mountain peaks of the Sesia Zone. New Rb-Sr mineral ages constrain D2 to have occurred at about 60-65 Ma and D3 at about 45-55 Ma. Thus top-SE extensional exhumation was broadly coeval with Eocene, SE directed subduction of the Liguro-Piemont oceanic lithosphere beneath the Adriatic margin. Slow cooling and erosional denudation of the Sesia Zone from 45 to 30 Ma occurred in the hanging wall of the Gressoney extensional shear zone (D4), which itself contributed to the exhumation of Eocene HP and ultra-HP oceanic rocks in its footwall. By 30 Ma, HP rocks of the Sesia Zone were intruded by shallow granitic plutons which were eroded and redeposited within volcanoclastic sediments. Oligo-Miocene Insubric backfolding and thrusting (D5) only exhumed northeastern parts of the Sesia Zone, where HP metamorphism

  7. Thecamoebians from Late Permian Gondwana sediments of peninsular India.

    PubMed

    Farooqui, Anjum; Aggarwal, Neha; Jha, Neerja

    2014-02-01

    The evolutionary history of thecamoebians (testate amoebae) extends back to the Neoproterozoic Era. However, until now, these have had a restricted, discontinuous and modest record across the world. The studied sediment of Raniganj Formation (Godavari Graben), Andhra Pradesh, India has been assigned as Late Permian on the basis of co-occurring age-diagnostic Late Permian palynomorphs. About sixteen thecamoebian species and one taxon incertae sedis have been recorded here in the palynological slides on the basis of shell morphology and morphometry. Out of these, five belong to the family Arcellidae, seven to Centropyxidae, two to Trigonopyxidae, one to Difflugiidae, one to Plagiopyxidae, and one is regarded incertae sedis. The morphometric characteristics of fossil forms resemble their corresponding extant species studied from ecologically diverse fresh water wetlands in India. In general, the ratio of shell diameter and aperture diameter of Late Permian fossil and extant specimens show significant correlation in all the studied species. Except that, the ratio of shell length and breadth is the distinguishing feature between Centropyxis aerophila and C. aerophila 'sylvatica', rather than the ratio of shell length and longest diameter of the shell aperture in both fossil and extant forms. The study elucidates the minimal morphological evolution in thecamoebians and their survival during mass extinction periods and stressful environmental conditions over the geological timescale. PMID:23876495

  8. Hooked: Habits of the Chinese Permian gigantopterid Gigantonoclea

    NASA Astrophysics Data System (ADS)

    Seyfullah, Leyla J.; Glasspool, Ian J.; Hilton, Jason

    2014-04-01

    Based upon anatomical evidence, Permian aged gigantopterid fossils are in general reconstructed as climbing or scrambling plants. Gigantonoclea, a genus of adpressed gigantopterid foliage from the Permian of northern China, has been reported to co-occur with hook-like organs that were interpreted as indicating a scrambling/climbing habit. We reinvestigated these hook-like structures and re-evaluated the nature of the co-occurrences in context with the flora preserved in each plant-bearing fossil 'bed' in the North China sedimentary succession. New findings show that the species Gigantonoclea hallei probably climbed using specially adapted clusters of compound grappling hook-like shoots borne on the stems. This structural arrangement comprising shoots of hooks is new to the scrambling/climbing concept in gigantopterids. However, a key figured specimen previously reported as showing intermediate hook-tipped leaf morphology on a sole pinnule tip is discounted as such and is reinterpreted as a 'normal' pinnule partially hidden under sediment that results in an unusual appearance to this pinnule tip. Adaptations for climbing or scrambling based upon 'hooked leaves' observed in Gigantonoclea lagrelii are no longer supported and are reinterpreted as incompletely expanded leaves where the vernation process was interrupted. These data weaken prior interpretations of G. lagrelii as a climber/scrambler and raise doubts about the ubiquity of hooks amongst the gigantopterids as structures enabling them to climb or scramble their way through the Permian world.

  9. Pennsylvanian-Permian Antler foreland of eastern Nevada

    SciTech Connect

    Snyder, W.S. . Dept. of Geosciences); Trexler, J.H. Jr. . Dept. of Geological Sciences)

    1993-04-01

    Models for the Antler foreland generally assume that it was a Mississippian feature dominated by a single, large basin (the Antler foredeep). Recent work indicates that the foreland, as a tectonic region, is longer-lived, and is better described as a series of sub-basins separated by intervening structural highs. Long sections reveal space/time changes in depositional facies and sedimentologic features indicative or suggestive of this repeated tectonism. For example, in the southern Pancake Range, the fluvial-deltaic clastic units of the Late Mississippian-earliest Pennsylvanian Neward Canyon sequence are overlain by 540 m of cyclical Pennsylvanian Ely Limestone. The flooding event that marks the boundary between these units occurs during a long-term 2nd order eustatic low stand and thus reflects the regional tectonism that created the Ely basin'. Further, tectonically driven subsidence seems necessary to sustain deposition of the thick of marginal marine-open shelf Ely Limestone at this locality. Regionally, Early Permian deposition within the Dry Mountain trough was dominated by a complex series of local tectonic controls. Within eastern Nevada, tectonic influences on the stratigraphy continued through at least the Middle Permian, and this tectonism perhaps merged with that of the classic Late Permian-Early Triassic Sonoma orogeny. One consequence of this protracted tectonism was development or reactivation of zones of structural weakness that fragmented the foreland into a series of basins and highs and that accommodated differing geometries and styles of deformation.

  10. Spiral-shaped graphoglyptids from an Early Permian intertidal flat

    NASA Astrophysics Data System (ADS)

    Minter, Nicholas J.; Buatois, Luis A.; Lucas, Spencer G.; Braddy, Simon J.; Smith, Joshua A.

    2006-12-01

    Spiral-shaped foraging trace fossils, assigned to the grapho glyptid cf. Spirorhaphe azteca, are reported from an Early Permian intertidal flat in the Robledo Mountains of southern New Mexico, USA. Remarkably similar spiral-shaped structures are produced in modern intertidal flats by the paraonid polychaete Paraonis fulgens, and function as traps to capture mobile microorganisms migrating in the sediment in response to tides. We envisage a similar function for the Early Permian trace fossils. Previous studies have suggested that the lack of P. fulgens type traces from ancient intertidal deposits indicates that such behavior only evolved geologically recently in such settings. However, this report demonstrates that such specialized foraging behavior was present in intertidal settings by at least the Early Permian. Graphoglyptids are typical of deep-marine settings, and characteristic of the Nereites ichnofacies. This represents their first undoubted occurrence in intertidal facies in the geological record. We postulate that the occurrence of graphoglyptids in deep-marine and intertidal settings is related to the predictability of resources. The scarcity of intertidal graphoglyptids in the geological record is most likely a preservational effect.

  11. Lower Permian Dry Mountain trough, eastern Nevada: preliminary basin analysis

    SciTech Connect

    Schwarz, D.L.; Snyder, W.S.; Spinosa, C.

    1987-08-01

    The Lower Permian Dry Mountain trough (DMT) is one of several basins that developed during the Late Pennsylvanian to Permian along the western edge of the North American continent. A tectonic mechanism has been suggested for the subsidence of the DMT, possibly due to reactivation of the Antler orogenic belt during the waning stages of Ancestral Rocky Mountain deformation. The DMT records marked subsidence with the appearance during the Artinskian (latest Wolfcampian) of a deeper water facies that consists of thin-bedded silty micrites and micritic mudstones rich in radiolarians and sponge spicules, characterized by a relative abundance of ammonoids, and rarer conodonts and Nereites ichnofacies trace fossils. Taxa recovered from a distinctive concretionary horizon at various locations provide an Artinskian datum on which to palinspastically reconstruct the DMT paleogeography. These taxa include ammonoids: Uraloceras, Medlicottia, Marathonites, Crimites, Metalegoceras, properrinitids; and conodonts: Neogondolella bisselli, Sweetognathus whitei, S. behnkeni, and Diplognathodus stevensi. The western margin facies of the DMT consists of Permian Carbon Ridge/Garden Valley Formations. Here, lowermost black Artinskianage euxinic micrites, considered a potential source rock for petroleum generation, are overlain by base-of-slope carbonate apron deposits, which, in turn, are overlain by base-of-slope carbonate apron deposits, which, in turn, are overlain by a thick, eastwardly prograding conglomerate wedge. Seismic profiles across Diamond Valley indicate a 3.0-4.6-km thick Tertiary sequence above the Paleozoic strata.

  12. Episodic exhumation and relief growth in the Mont Blanc massif, Western Alps from numerical modelling of thermochronology data

    NASA Astrophysics Data System (ADS)

    Glotzbach, C.; van der Beek, P. A.; Spiegel, C.

    2011-04-01

    The Pliocene-Quaternary exhumational and topographic evolution of the European Alps and its potential climatic and tectonic controls remain a subject of controversy. Here, we apply inverse numerical thermal-kinematic modelling to a spatially dense thermochronological dataset (apatite fission-track and (U-Th)/He) of both tunnel and surface samples across the Mont Blanc massif in the Western Alps, complemented by new zircon fission-track data, in order to better quantify its Neogene exhumation and relief history. Age-elevation relationships and modelling results show that an episodic exhumation scenario best fits the data. Initiation of exhumation in the Mont Blanc massif at 22 ± 2 Ma with a rate of 0.8 ± 0.15 km/Myr is probably related to NW-directed thrusting during nappe emplacement. Exhumation rates decrease at 6 ± 2 Ma to values of 0.15 ± 0.65 km/Myr, which we interpret to be the result of a general decrease in convergence rates and/or extensive exposure of less erodible crystalline basement rocks from below more easily erodible Mesozoic sediments. Finally, local exhumation rates increase up to 2.0 ± 0.6 km/Myr at 1.7 ± 0.8 Ma. Modelling shows that this recent increase in local exhumation can be explained by valley incision and the associated increase in relief at 0.9 ± 0.8 Ma, leading to erosional unloading, isostatic rebound and additional rock uplift and exhumation. Given the lack of tectonic activity as evidenced by constant thermochronological ages along the tunnel transect, we suggest that the final increase in exhumation and relief in the Mont Blanc massif is the result of climate change, with the initiation of mid-Pleistocene glaciations leading to rapid valley incision and related local exhumation.

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

    NASA Astrophysics Data System (ADS)

    Tate, Garrett W.; McQuarrie, Nadine; 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.

  14. Strontium isotope evolution of Late Permian and Triassic seawater

    NASA Astrophysics Data System (ADS)

    Korte, Christoph; Kozur, Heinz W.; Bruckschen, Peter; Veizer, Ján

    2003-01-01

    The 87Sr/ 86Sr values based on brachiopods and conodonts define a nearly continuous record for the Late Permian and Triassic intervals. Minor gaps in measurements exist only for the uppermost Brahmanian, lower part of the Upper Olenekian, and Middle Norian, and only sparse data are available for the Late Permian. These 219 measurements include 67 brachiopods and 114 conodont samples from the Tethyan realm as well as 37 brachiopods and one conodont sample from the mid-European Middle Triassic Muschelkalk Sea. The Late Permian/Lower Triassic interval is characterized by a steep 1.3 × 10 -3 rise, from 0.7070 at the base of the Dzhulfian to 0.7082 in the late Olenekian, a rate of change comparable to that in the Cenozoic. In the mid-Triassic (Anisian and Ladinian), the isotope values fall to 0.7075, followed again by a rise to 0.7081 in the Middle/Late Norian. The 87Sr/ 86Sr values decline again in the Late Norian (Sevatian) and Rhaetian to 0.7076. The sharp rise in the 87Sr/ 86Sr values during the Late Permian/Early Triassic was coincident with widespread clastic sedimentation. Because of the paucity of tectonic uplifts, the enhanced erosion may have been due to intermittent humid phases, during mainly an arid interval, coupled with the absence of a dense protective land plant cover following the mass extinction during the latest Permian. The apex of the 87Sr/ 86Sr curve at the Olenekian/Anisian boundary coincides with cessation of the large-scale clastic sedimentation and also marks the final recovery of land vegetation, as indicated by the renewed onset of coal formation in the Middle Triassic. The rising 87Sr/ 86Sr values from the Middle Carnian to the Late Norian coincide with the uplift and erosion of the Cimmeride-Indosinian orogens marking the closure of the Palaeotethys. The subsequent Rhaetian decline that continues into Jurassic (Pliensbachian/Toarcian boundary), on the other hand, coincides with the opening of the Vardar Ocean and its eastern continuation

  15. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea.

    PubMed

    Baldwin, Suzanne L; Monteleone, Brian D; Webb, Laura E; Fitzgerald, Paul G; Grove, Marty; Hill, E June

    2004-09-16

    As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (> 1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence. PMID:15372021

  16. A revised thermal history of the Ronda peridotite, S. Spain: New evidence for excision during exhumation

    NASA Astrophysics Data System (ADS)

    Johanesen, Katharine; Platt, John P.; Kaplan, Michael S.; Ianno, Adam J.

    2014-05-01

    The Ronda peridotite massif of southern Spain exposes subcontinental lithospheric mantle that records pressure-temperature data and microstructures formed during exhumation beneath the rapidly extending Alboran domain. The peridotite is zoned from garnet- and spinel-bearing mylonites at the structural top, to spinel-bearing tectonites, to melt-percolated spinel-bearing granular peridotites, to plagioclase-bearing tectonites at the structural base. We find microstructural evidence of melt present in the spinel zones prior to the deformation event which exhumed the peridotites, and we therefore reinterpret the spinel tectonites as being a result of deformational overprinting of part of the granular domain. We also reinterpret garnet intergrown with spinel in the mylonite zone as part of the pre-mylonitic porphyroclast assemblage, rather than as a syn-mylonite assemblage. This places mylonite formation within the spinel field, rather than right on the garnet-spinel transition (18 kb). Two-dimensional thermal modeling indicates that these conditions require removal of lithospheric mantle below 100 km followed by exhumation along a low angle shear zone. Excision of material during exhumation is required to explain the steep thermal gradients observed. These results shed light on the mechanisms of back-arc extension, as well as the emplacement of orogenic lherzolites.

  17. Late-Quaternary exhumation rates constrained by OSL thermochronometry at the Franz Josef Glacier, New Zealand

    NASA Astrophysics Data System (ADS)

    Duverger, Arnaud; King, Georgina; Valla, Pierre; Cox, Simon; Herman, Frederic

    2016-04-01

    The Southern Alps of New Zealand are often cited as the primary example of a mountain range that has reached exhumation and topographic steady state, especially on the West Coast where exhumation rates reach up to about 10 mm/yr. However, cyclic climatic changes, throughout the Quaternary period have meant that the Alps cycled between being completely glaciated and ice free. The impact that such glacial cycles may have had on the spatial variability of erosion rates remains poorly constrained. Here we use Optically Stimulated Luminescence (OSL) as a very low temperature thermochronometer to constrain rock cooling histories at 10-100 kyr timescales on samples collected near the Franz Josef glacier. OSL-thermochronometry is based on the amount of electrons accumulated in the lattice defects of natural minerals such as quartz or feldspar, due to the competing effects of charge trapping due to the natural radioactivity within the rock and charge detrapping due to thermal loss during rock exhumation towards the surface. We collected 9 samples along the Waiho valley (crossing the Alpine Fault) and the Franz Josef glacier to quantify late-Quaternary exhumation rates and their potential spatial variations. Bedrock samples have been crushed to extract the light-safe rock interiors which have then been processed to isolate potassium-rich feldspars (K-feldspars). We used the Infra-Red Stimulated Luminescence at 50°C (IRSL50) protocol, including the measurement of the natural IRSL50 trapped charge population and the laboratory characterization of sample-specific thermal and athermal kinetic parameters. Once measured, the luminescence signal can be inverted into cooling histories. We also explored the potential of the recently developed multi-OSL-thermochronometer (King et al., accepted) to better constrain the cooling path. Our first OSL measurements show that samples are not in saturation and thus contain useful thermochronometric information over the last ~100 kyr. Inverse

  18. Efficient exhumation of (ultra) high-pressure rocks by slab extraction

    NASA Astrophysics Data System (ADS)

    Zhao, Zhongbao; Bons, Paul; Gomez-Rivas, Enrique; Soesoo, Alvar; Evgueni, Burov

    2015-04-01

    A range of mechanisms has been proposed for the enigmatic exhumation of (ultra) high-pressure (UHP) rocks from great depths. These include channel flow, wedge extrusion, diapiric rise, metamorphic core complexes and eduction. Most current models envisage exhumation to occur in a subduction setting, where exhumation of UHP rocks takes place in the context of the downward movement of the subducting slab. In addition, removal of the downward pull on the subducting slab (by slab break-off and slab retreat) may lead to buoyant rise of the UHP material, especially in case of subduction of continental crust. Here we consider the alternative scenario of slab extraction, where subduction is reversed and the slab is pulled up and away from the overriding plate, instead of sliding down into the mantle. UHP rocks are then exhumed together with the ascending plate. Slab extraction occurs when the downward pull of the subducted slab is exceeded by an opposite force, for example in case of plate divergence. Another case is a divergent double subduction zone (DDSZ), where the two hinges inevitably converge by rollback. At some point the pull of one slab can exceed that of the other one if it is short enough, leading to the extraction of the shorter slab and concomitant exhumation of UHP rocks. The evolution of a DDSZ with one short slab was modelled with the thermo-mechanical code FLAMAR, varying the relative movement of the two overriding plates. If the two overriding plates do not converge too fast, the short slab is pulled up and away from its suture and is eventually pulled down at the opposite suture. UHP rocks are exhumed at rates exceeding cms/yr in what is effectively a lithospheric-scale core complex. This mechanism may explain the exhumation of UHP rocks in the Tibetan Qiangtang Metamorphic Belt and the d'Entercasteaux Islands. If the sutures converge slower than the long slab slides down, an oceanic basin forms, which we suggest is the cause for the rapid opening of the

  19. Cyclostratigraphy and duration of the Yates Formation (Permian, Late Guadalupian) of the Permian Basin

    SciTech Connect

    Borer, J.M.; Harris, P.M. )

    1990-05-01

    Using log, core, and outcrop data, the authors have identified patterns in cyclic sequences of the mixed siliciclastic-carbonate Yates Formation of the Permian basin. A composite well log, representing the entire formation through a single sea level-sensitive facies tract, exhibits two orders of cyclicity with Milankovitch band periodicity. At the shelf margin, large-scale cycles consist of subequal dolomite- and siliciclastic-rich intervals. Small-scale cycles are carbonate and siliciclastic couplets that exhibit regular changes in lithology and thickness (bundling) that define the large-scale cycles. Cycle packaging changes across the shelf due to the updip (landward) pinch-out of high frequency carbonate intervals. Several lines of evidence suggest that the depositional cycles are the product of orbitally forced sea level fluctuations with 100- and 400-k.y. periods (Milankovitch eccentricity cycles). This implies that the five large-scale cycles present in the Yates represent about 2 m.y. of deposition. A lower frequency (third-order) sea level cycle was also active during Yates deposition. This 1.5- to 2-m.y. cycle is apparent from Fischer plots and a lithofacies cross section. The third-order cycle may be related to a low-frequency Milankovitch signal or tectonics. Fischer plots and stratigraphic analysis suggest that all the sea level fluctuations had relatively low magnitudes ranging from approximately 2 m for the 100-k.y. cycles, 8-12 m for the 400-k.y. cycles, and 5 m for the 1.5- to 2-m.y. cycle. The architecture of Yates Formation reservoirs is related to the stacking of depositional sequences during the three orders of sea-level fluctuations. In general, the low frequency (1.5-2 m.y.) cycle controlled the lateral position and reservoir quality of 400-k.y. depositional cycles (reservoir units); whereas, high-frequency (100 k.y.) sea level cycles controlled heterogeneity within reservoir units.

  20. Processes of subduction and exhumation of continental blocks in collisional orogeny

    NASA Astrophysics Data System (ADS)

    Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

    2009-12-01

    Understanding the mechanism of accretion, subduction and exhumation of rocks during orogeny is a fundamental issue for plate tectonics. Numerous models have been proposed in order to explain the tectonic events that accompany continental subduction. Here, in order to examine the different processes in a simple, self-consistent manner, the fully coupled thermo-mechanical numerical code PARAFLAM is used to perform a parametric study on the subduction mode and, particularly, on the continental subduction processes. A wide range of parameters including slab-pull magnitude, temperature and viscosity distribution, initial geometry of the subduction zone and rheology, is explored to understand the dynamics of accretion, the different processes of exhumation, the deformation of the slab and the deformation of the overriding plate. The first results of this study show the evolution of one or two small continental blocks (terranes) reaching the subduction-zone continental margin. A set of experiments demonstrates that the progressive incorporation of a continental block into the over-riding plate is governed by the dynamics of subduction. Initially, the continental block is partly or entirely subducted, which increases its buoyancy and induces its detachment from the subducting slab. By the time the emplacement of the block into the continental margin is completed, exhumation is likely to have occurred, depending mainly on the slab pull magnitude and the rheology of the continental block itself. As an example, some experiments show the continuous subduction of a continental block followed by an UHP-HP exhumation and a metamorphic-core-complex type of exhumation. These cases can be compared with the pattern of deformation observed in the Aegean-Sea domain or in the Tyrrhenian one.

  1. Cenozoic Exhumation History and Evolutionary Model For The Central Catalan Coastal Ranges (ne Spain)

    NASA Astrophysics Data System (ADS)

    Gaspar-Escribano, J. M.; Garcia-Castellanos, D.; Roca, E.; Juez-Larre, J.; Cloetingh, S.

    We have studied the Cenozoic exhumation history of the Catalan Coastal Ranges (NE Spain) and propose a model for its kinematic evolution. Two difficulties appear when reconstructing the geological evolution of the study area: (1) Neogene fault extensional reactivation overrides former compressional structures, leading to uncertainties of fault slips and amounts of exhumation and hence misinter- pretation of basin evolution; (2) Absence of parts of the sedimentary record impedes a complete description of timing and significance of erosion-sedimentation during the corresponding time interval. We address these problems by using multiple data sets as constraints for a kinematic model. The observations accounted for in the model consist of: (1) Partially reconstructed geological sections based on seismics and/or sedimentological studies; and (2) New fission track data, that were translated in terms of exhumation to validate the evolu- tionary model. In order to quantitatively link these observations, we use a fault block model that as- sumes vertical shear and incorporates flexural isostasy and surface transport (erosion and sedimentation). Modifying input fault geometries and velocities we can adjust modeling predictions with the observed geometry and exhumation-time diagrams. A gradual variation of effective elastic thickness (low value~5 km offshore, higher value ~25 km in the Ebro Basin) is required to fit exhumation curves derived and the topog- raphy in the Littoral Range. Results of our model provide constraints on the evolution of the region in terms of topography and fault activity. The mass balance between deposition and erosion is also calculated, indicating significant out-of-plane surface transport.

  2. Putting it all together: Exhumation histories from a formal combination of heat flow and a suite of thermochronometers

    USGS Publications Warehouse

    d'Alessio, M. A.; Williams, C.F.

    2007-01-01

    A suite of new techniques in thermochronometry allow analysis of the thermal history of a sample over a broad range of temperature sensitivities. New analysis tools must be developed that fully and formally integrate these techniques, allowing a single geologic interpretation of the rate and timing of exhumation and burial events consistent with all data. We integrate a thermal model of burial and exhumation, (U-Th)/He age modeling, and fission track age and length modeling. We then use a genetic algorithm to efficiently explore possible time-exhumation histories of a vertical sample profile (such as a borehole), simultaneously solving for exhumation and burial rates as well as changes in background heat flow. We formally combine all data in a rigorous statistical fashion. By parameterizing the model in terms of exhumation rather than time-temperature paths (as traditionally done in fission track modeling), we can ensure that exhumation histories result in a sedimentary basin whose thickness is consistent with the observed basin, a physically based constraint that eliminates otherwise acceptable thermal histories. We apply the technique to heat flow and thermochronometry data from the 2.1 -km-deep San Andreas Fault Observatory at Depth pilot hole near the San Andreas fault, California. We find that the site experienced <1 km of exhumation or burial since the onset of San Andreas fault activity ???30 Ma.

  3. The Permian-Triassic boundary & mass extinction in China

    USGS Publications Warehouse

    Metcalfe, I.; Nicoll, R.S.; Mundil, R.; Foster, C.; Glen, J.; Lyons, J.; Xiaofeng, W.; Cheng-Yuan, W.; Renne, P.R.; Black, L.; Xun, Q.; Xiaodong, M.

    2001-01-01

    The first appearance of Hindeodus parvus (Kozur & Pjatakova) at the Permian-Triassic (P-T) GSSP level (base of Bed 27c) at Meishan is here confirmed. Hindeodus changxingensis Wang occurs from Beds 26 to 29 at Meishan and appears to be restricted to the narrow boundary interval immediately above the main mass extinction level in Bed 25. It is suggested that this species is therefore a valuable P-T boundary interval index taxon. Our collections from the Shangsi section confirm that the first occurrence of Hindeodus parvus in that section is about 5 in above the highest level from which a typical Permian fauna is recovered. This may suggest that that some section may be missing at Meishan. The age of the currently defined Permian-Triassic Boundary is estimated by our own studies and a reassessment of previous worker's data at c. 253 Ma, slightly older than our IDTIMS 206Pb/238U age of 252.5 ??0.3 Ma for Bed 28, just 8 cm above the GSSP boundary (Mundil et al., 2001). The age of the main mass extinction, at the base of Bed 25 at Meishan, is estimated at slightly older than 254 Ma based on an age of >254 Ma for the Bed 25 ash. Regardless of the absolute age of the boundary, it is evident that the claimed <165,000 y short duration for the negative carbon isotope excursion at the P-T boundary (Bowring et al., 1998) cannot be confirmed. Purportedly extraterrestrial fullerenes at the boundary (Hecker et al., 2001) have equivocal significance due to their chronostratigraphic non-uniqueness and their occurrence in a volcanic ash.

  4. Forward stratigraphic modeling of the Permian of the Delaware Basin

    SciTech Connect

    Qiucheng, Ye; Kerans, C.; Bowman, S.

    1996-12-31

    Permian platform-to-basin strata of the Delaware Basin In west Texas and New Mexico represent one of the world`s most complete, best studied, and most hydrocarbon productive records of this geologic period in the world. This superb marriage of a refined stratigraphic framework and active exploration provided impetus to develop a forward stratigraphic model of this section to better predict the distribution of reservoir and seal relationships. The approximately 30 m.y. interval modeled is composed of 2 km of platform strata and 3 km of basinal strata divided into 8 composite sequences (average 3 m.y. duration) and 45 high-frequency sequences (400 ky m.y. duration). A 130 km dip section through the basin margin Guadalupe/Deleware Mountain outcrop is inversely modeled to derive local tectonic subsidence and a sea level curve for the Permian. In this process, the highest and lowest shoreline positions of each sequence are interpreted based on facies description which are assumed to approximate the highest and lowest relative sea level. A eustatic sea level curve is calculated by restoring these shoreline positions and removing local tectonic subsidence using a polynomial fit to the derived relative sea level curve. The quantitatively constrained curve for the Permian contains 2nd, 3rd, and 4th order 180m. This quantitatively constrained accommodation history (calculated eustatic curve and subsidence history) are input into the PHIL forward modeling program. Model variables of sediment supply are depositional system are adjusted to match known outcrop relations. The resulting model is potentially capable of predicting stratigraphy elsewhere in the basin using only subsidence history data from the inverse model.

  5. Forward stratigraphic modeling of the Permian of the Delaware Basin

    SciTech Connect

    Qiucheng, Ye; Kerans, C.; Bowman, S. )

    1996-01-01

    Permian platform-to-basin strata of the Delaware Basin In west Texas and New Mexico represent one of the world's most complete, best studied, and most hydrocarbon productive records of this geologic period in the world. This superb marriage of a refined stratigraphic framework and active exploration provided impetus to develop a forward stratigraphic model of this section to better predict the distribution of reservoir and seal relationships. The approximately 30 m.y. interval modeled is composed of 2 km of platform strata and 3 km of basinal strata divided into 8 composite sequences (average 3 m.y. duration) and 45 high-frequency sequences (400 ky m.y. duration). A 130 km dip section through the basin margin Guadalupe/Deleware Mountain outcrop is inversely modeled to derive local tectonic subsidence and a sea level curve for the Permian. In this process, the highest and lowest shoreline positions of each sequence are interpreted based on facies description which are assumed to approximate the highest and lowest relative sea level. A eustatic sea level curve is calculated by restoring these shoreline positions and removing local tectonic subsidence using a polynomial fit to the derived relative sea level curve. The quantitatively constrained curve for the Permian contains 2nd, 3rd, and 4th order 180m. This quantitatively constrained accommodation history (calculated eustatic curve and subsidence history) are input into the PHIL forward modeling program. Model variables of sediment supply are depositional system are adjusted to match known outcrop relations. The resulting model is potentially capable of predicting stratigraphy elsewhere in the basin using only subsidence history data from the inverse model.

  6. Controls on reservoir development in Devonian Chert: Permian Basin, Texas

    SciTech Connect

    Ruppel, S.C.; Hovorka, S.D.

    1995-12-01

    Chert reservoirs of the Lower Devonian Thirtyone Formation contain a significant portion of the hydrocarbon resource in the Permian basin. More than 700 million bbl of oil have been produced from these rocks, and an equivalent amount of mobile oil remains. Effective exploitation of this sizable remaining resource, however, demands a comprehensive appreciation of the complex factors that have contributed to reservoir development. Analysis of Thirtyone Formation chert deposits in Three Bar field and elsewhere in the Permian basin indicates that reservoirs display substantial heterogeneity resulting from depositional, diagenetic, and structural processes. Large-scale reservoir geometries and finer scale, intra-reservoir heterogeneity are primarily attributable to original depositional processes. Despite facies variations, porosity development in these cherts is principally a result of variations in rates and products of early silica diagenesis. Because this diagenesis was in part a function of depositional facies architecture, porosity development follows original depositional patterns. In reservoirs such as Three Bar field, where the Thirtyone Formation has been unroofed by Pennsylvanian deformation, meteoric diagenesis has created additional heterogeneity by causing dissolution of chert and carbonate, especially in areas of higher density fracturing and faulting and along truncated reservoir margins. Structural deformation also has exerted direct controls on heterogeneity that are particularly noteworthy in reservoirs under waterflood. High-density fracture zones create preferred flow paths that result in nonuniform sweep through the reservoir. Faulting locally creates compartments by offsetting reservoir flow units. As such, the processes and models defined here improve understanding of the causes of heterogeneity in all Thirtyone chert reservoirs in the Permian basin and aid recovery of the sizable hydrocarbon resource remaining in these rocks.

  7. Spatial Variations in Deformation and Exhumation at the Yakutat plate corner, SE Alaska

    NASA Astrophysics Data System (ADS)

    Enkelmann, E.; Ehlers, T. A.; Falkowski, S.; Grabowski, D.

    2012-12-01

    Quantification of exhumation processes near plate boundaries provides insights into the mechanics and history of deformation along transpressional structures. Here we present an analysis of regional variations in plate deformation near the corner of the obliquely converging Yakutat Terrane and North American plate. Techniques used include an integration of bedrock and detrital thermochronometer ages collected around the major faults in the region. The Yakutat Terrane is transported northward along the western margin of North America and is colliding with the southern margin of Alaska, forming the St. Elias Mountains. The boundaries of the Yakutat Terrane to North America are formed by the dextral Fairweather transform fault in the east and the Chugach-St. Elias thrust and the fold-and thrust belt to the north. One of the major questions is how stress from the Fairweather transform is transferred and distributed inboard when the transform fault runs into the continent and deformation style changes to convergent. This region of change in deformation is called the St. Elias syntaxis and is characterized by a 90° bend of the major structures, the highest mountain peaks (5959 m), high local relief (5000 m), and it is mainly covered by thick ice fields and glaciers. This ice cover hampers field observations, structural measurements, and rock sampling and thus it is unclear how strain is distributed in the syntaxis region. Observed cooling ages indicate that the region of the St. Elias syntaxis contains 3-2 Ma detrital zircon fission track (ZFT) ages in the Seward-Malaspina Glacier outwash, indicating cooling rates of >100°C/Ma somewhere in the catchment. We revisited the Malaspina Glacier and investigated the petrology and cooling ages of clast-size material. Zircon U-Th/He ages of 3-2 Ma are observed in clasts of various lithologies including amphibolite, granulite, gneiss, and undeformed granite and granodiorite. This variety in rock types suggest that rapid

  8. New Permian durhaminid cerioid corals from east-central California

    USGS Publications Warehouse

    Stevens, C.H.; Stone, P.

    2009-01-01

    Permian colonial corals from Artinskian to Kungurian strata in the Conglomerate Mesa area, Inyo Mountains, east-central California, include five new species, one of which is assigned to a new genus. The new taxa are: Malpaisia maceyi n. gen. and n. sp., Pararachnastraea bellula n. sp., P. delicata n. sp., P. owensensis n. sp., and Cordillerastraea inyoensis n. sp. These species, several of which compare most closely with other Artinskian and Kungurian species from eastern Nevada and northern Mexico, represent three distinct stocks that differentiated on an isolated submarine uplift offshore from the main part of the Cordilleran carbonate shelf.

  9. A sudden end-Permian mass extinction (Invited)

    NASA Astrophysics Data System (ADS)

    Shen, S.

    2013-12-01

    The end-Permian mass extinction is the largest of the Phanerozoic. In the immediate aftermath the marine ecosystem was dominated by microbial and communities with disaster taxa. Plausible kill mechanism includes an extremely rapid, explosive release of gases such as carbon dioxide, methane and hydrogen sulfide. Siberian flood volcanism has been suggested as the most possible mechanism to trigger the massive release of greenhouse gases from volcanic eruptions and interaction of magmas with carbon from thick organic-rich deposits or rapid venting of coal-derived methane or massive combustion of coal. A sharp δ13C isotopic excursion, rapid disappearance of carbonate benthic communities and δ18O data from conodont apatite suggest rapid global warming. The end-Permian mass extinction occurred in less than 200,000 years. This extinction interval is constrained by two ash beds (Beds 25 and 28) at the Meishan section. However, the extinction patterns remain controversial largely due to the condensed nature of the Meishan sections. Geochemical signals and their interpretations are also contentious. Thus, the level of achievable stratigraphic resolution becomes crucial to determine the nature of the event and a detailed study of the extinction interval is essential to unravel the extinction pattern, chemostratigraphy, and the causes. However, the extinction interval at Meishan is only 26 cm thick and contains distinct gaps at the Permian-Triassic boundary (PTB) and possibly the base of Bed 25. Thus, it is impossible to resolve a detailed extinction pattern. Studying expanded sections is crucial to understand the detailed events before, during and after the main extinction. In this report, we show a highly-expanded Permian-Triassic boundary section in Guangxi Province, South China. The last 4.5 m between beds 22 and 28 of the Meishan sections is represented by a sequence of ~560 m at the section and the extinction interval between beds 24e and 28 at Meishan is represented

  10. A Thermochronometric Approach to Understanding Exhumation in the Southern Colorado Rockies

    NASA Astrophysics Data System (ADS)

    Abbey, A. L.; Niemi, N. A.; Geissman, J. W.; Heizler, M. T.

    2015-12-01

    We use 40Ar/39Ar thermochronometry of hornblende, biotite and feldspar, coupled with apatite (U-Th-Sm)/He thermochronometry, to refine emplacement age and exhumation history of the latest Cretaceous Whitehorn Granodiorite, in the SW Front Range east of the Arkansas River Valley. The pluton intrudes Pennsylvanian and Precambrian wall rocks and has a surface exposure of ~8 km (E-W) by ~25 km (N-S). 40Ar/39Ar analysis on Whitehorn samples from two locations (2920 m and 2890 m) yield dates of 68.2 Ma and 69.1 Ma (hbl), 68.4 Ma and 68.9 Ma (bt), and 67.1 Ma and 74.2 Ma (kfs), respectively. AHe dates from 4 samples collected in Proterozoic wall rocks northwest of the Whitehorn pluton along a 625 m vertical transect, range from 56.9 Ma to 63.4 Ma, and 3 samples in a 345 m vertical transect east of the pluton range from 67.3Ma to 135.3Ma. Previous thermochronometric, paleomagnetic, and petrologic studies indicate Whitehorn pluton was emplaced at paleodepths of 8-10 km with ambient host rock temperatures of ~200°C, and insignificant tilting since then. We infer that, the biotite and hornblende Ar40/Ar39 dates record timing of pluton emplacement, and K-feldspar MDD modeling records post-emplacement cooling to ambient temperatures by 66 Ma. AHe dates record lower temperature (<60°C) cooling of the wall rocks and must reflect post-emplacement exhumation of the pluton and host rocks. The SW Front Range thus appears to have experienced rapid, large magnitude (~6-8 km) exhumation and differential uplift at ca. 60 Ma with respect to the SE Front Range. Presently, the southern Front Range is overlain by horizontal Oligocene volcanic rocks, deposited on a widespread regional erosion surface across the central CO Rockies. The preservation of Paleocene AHe dates below this regional surface suggests that it formed shortly after exhumation, and experienced < 2 km of reburial, or exhumation, from ~55 Ma until deposition of the Wall Mountain tuff at ca. 34 Ma. The Arkansas River cuts

  11. An integrated approach to study the exhumation of rocks in Neelum valley, NW Himalayas, Pakistan.

    NASA Astrophysics Data System (ADS)

    Turab, Syed Ali; Stüwe, Kurt; Stuart, Finlay M.; Chew, David M.

    2016-04-01

    Tectonics and erosion have both been suggested as alternative driving mechanisms for rapid exhumation of rocks in the western Himalayan syntaxis. This debate could be resolved by understanding the plan view-geometry of the exhumation of rocks in the region: does it follow the major structures?, or is it related to the drainage geometry? In order to resolve this geometry we have undertaken a low-temperature thermochronologic study, using crystalline rocks, of a critical region of the western syntaxis: Neelum valley region, Pakistan. Apatite (U-Th-Sm)/He (AHe), fission track (AFT) and U-Pb dating has been combined with geomorphic stream power analysis in order to discern the relationship of exhumation of rocks to tectonics (main faults) or erosion. Pooled AFT ages show a range of 2.2 ± 0.4 to 7.0 ± 0.4 Ma (1σ). Recoil corrected AHe ages exhibit a range from 2.0 ± 0.1 to 8.7 ± 0.5 Ma (1σ). U-Pb ages could be used to divide the samples in three groups: ages that are completely-, partly- and not- affected by Himalayan tectonics. The range of apatite U-Pb ages displayed by both completely- and partly- affected samples is from 17.0 to 43.0 Ma (2σ, unanchored, i.e. constrained by isochrones alone) and 6.0 to 48.3 Ma (2σ, anchored using the Stacey and Kramers terrestrial Pb evolution model). Stream power analysis of the Neelum river catchment indicates a region with high steepness index (Ksn, normalized to reference concavity, θref = 0.45) values of > 500 m0.9 which coincides well the region sampled. In combination with earlier published ages, our data indicate that exhumation contours run more or less parallel to the major structures in the region. The boundary between samples with unaffected and affected U-Pb ages as well as transition from high Ksn to lower Ksn values along the main Neelum river fits well with the mapped trace of the Main Central Thrust (MCT), corroborating the presence of the MCT in the southeastern parts of our study area. Thermal history

  12. Volcanism, mantle exhumation and spreading at the axial zone of a fossil slow spreading ocean

    NASA Astrophysics Data System (ADS)

    Chalot-Prat, F.; Coco, E.

    2003-04-01

    Within an axial zone of a slow spreading ocean, the mechanisms checking together volcano emplacement, mantle exhumation and ocean enlargement are poorly known. In order to better assess how they could be linked , a detailed mapping of a fossil ocean-floor structure, preserved from alpine tectonic and metamorphism, was performed in the Chenaillet unit (Franco-Italian Alps)(Chalot-Prat &Coco, submit.). The detailed 3D geometry of the ophiolite evidences that from its dimensions, topography, morphology, and the architecture of the volcanic cover at different scales, the Chenaillet unit is a witness of an axial zone of Atlantic type. The basement (serpentinized peridotites and gabbros), below and in the prolongation of the volcanic cover (le50 m), is capped by a tectonic breccias horizon (Chalot-Prat and Manatschal, 2002), underlining detachment faults responsible for its exhumation at the seafloor. Clasts of dolerite, found within the fault zone, indicate that basement exhumation had to be active during and even after volcano emplacement. Stair- and comb-type volcanic systems check the distribution of individual volcanoes; the higher the edifice, the younger it is relative to the others. In the stair-type (up to 600 m of height difference between base and top), each step is formed with a pillow and tube tongue stacking fed from fissural conduits located at the root of each step. This system formed by uplift, step by step fracturation of an already exhumed basement, and magma injection along the fissures once formed. The comb-type (up to 200 m of height difference between base and top) consists in well-defined alignments of pillow and tube conic edifices. Their central feeder dykes are emplaced on the crossing of two types of fractures, oblique (tooth) and parallel (line) to the main branch of the comb. Along a same line, eruptions are coeval as proved by rhythmic variations of major and trace element contents of basalts from one line to another. The comb formation

  13. Thermochronologic evidence for Miocene mid-crustal tectonic exhumation of the Huachuca Mountains, southeast Arizona

    NASA Astrophysics Data System (ADS)

    King, C. C.; Orme, D. A.; Biswas, A.; Reiners, P. W.

    2011-12-01

    Zircon double dating of detrital grains from the northward flowing upper San Pedro river valley at Murray Springs in southeastern Arizona yields abundant zircons with variable U/Pb crystallization ages of ~70-1400 Ma, but a restricted range of (U-Th)/He cooling ages of ~18-25 Ma. This combination of diverse formation ages but uniform mid-Miocene cooling ages is characteristic of zircons from the core complexes and deeply exhumed Santa Catalina, Rincon, and Pinaleno Mountains, which experienced tectonic exhumation from mid-crustal depths during mid-Miocene extension. But all these sources are far downstream or outside the watershed of the upper San Pedro valley. To trace the source of these detrital grains and understand the implications for regional tectonics, we also measured U/Pb and (U-Th)/He dates of zircons from the Tombstone Hills and Huachuca Mountains, proximal to the Murray Springs site. Magmatic rocks in the Tombstone Hills yielded U/Pb dates of 76-83 Ma and zircon He ages of 53-60 Ma. In contrast, crystalline basement of the Huachucas yields Cretaceous through 1.5-Ga U/Pb ages and zircon He ages of 17-25 Ma, with most between 21-22 Ma. These data require that a large region of the Huachucas contains rocks that cooled rapidly below temperatures of at least 180 oC in the mid-Miocene. Assuming typical geothermal gradients of 20-30 oC, this requires exhumation of at least 7-9 km of crust, likely within 1-2 Myr. While it is possible that erosion contributed, it is more likely that denudation was accommodated by deep tectonic exhumation. Faults are observed on the basin-bounding east-side of the Huachucas, but most are inferred to accommodate Laramide-age thrusting, and the normal faults have been interpreted as high-angle and unlikely to cause significant tectonic exhumation. Our new data suggest that a large part of the presently exposed Huachucas was exhumed from depths at least as great as ~7-9 km, requiring a considerable revision of structural

  14. Reconciling Geodetic Deformation and Long-term Exhumation Rates Across the Western Greater Caucasus

    NASA Astrophysics Data System (ADS)

    Avdeev, B.; Niemi, N. A.

    2011-12-01

    Low modern geodetic strain rates and minimal instrumentally recorded seismicity in the western Greater Caucasus contradict the the high topography, deep exhumation, and young low-temperature thermochronometric ages indicative of active tectonic deformation in this mountain range. We use new and existing low-temperature thermochronometric data to show that the rate of present-day convergence across the range is sufficient to sustain observed rates of long-term exhumation and topographic growth. Thus, it is possible that the western Greater Caucasus has existed in an erosional steady state since shortly after the onset of exhumation of the range in Pliocene. We employ a Markov chain Monte Carlo algorithm to estimate the parameters of a thermokinematic model constrained by thermochronometric data and a focal mechanism solution from the 1991 Racha earthquake. We find that the thermochronometric data are best fit by exhumation commencing at ~4 Ma and driven by 3-5 mm/y of overthrusting on the Main Caucasus thrust dipping 40-45° at the surface and becoming flat at a depth of 15-20 km. This long-term exhumation model was compared with active rates of convergence in the western Greater Caucasus using an elastic half-space deformation model to estimate the geometry and rate of slip on a buried dislocation that best fits the observed geodetic velocity field. The estimated active slip of 4-7 mm/y is comparable to the long-term rate of overthrusting and is, therefore, sufficient to produce the observed rock uplift. Up to 4 mm/y excess of active convergence may potentially be consumed by underthrusting of the Transcaucasus or on faults south of the Main Caucasus thrust. We conclude that high rates of rock uplift observed in the western Greater Caucasus are the result of focused shortening occurring on a single fault. This differs from the deformation style of the eastern Greater Caucasus, where a larger amount of shortening is distributed across the width of the range with

  15. Depositional Environment of Permian Tak Fa Formation, Nakhonsawan, Northern Thailand

    NASA Astrophysics Data System (ADS)

    Ketwetsuriya, Chatchalerm; Nützel, Alexander; Kanjanapayont, Pitsanupong

    2016-04-01

    The carbonate rocks of the study area at Amphoe Tak Fa and Amphoe Takhli, Changwat Nakhon Sawan belong to the Tak Fa Formation, Saraburi Group. This formation crops out in the Khao Khwang Platform and consists of late Palaeozoic carbonate platform deposits. It reaches a thickness of 900 meters and crops out in a vast area. The exposures have been measured and samples were collected for petrographic study. The rock consists of limestones, argillaceous limestones, mudstones and dolomites with nodular and banded cherts, which comprise many invertebrate fossils such as fusulinids, ammonoid, pelecypod, gastropod, coral and bryozoa. Many of the fossils are silicified. The gastropod assemblage is currently under study and represents one of the most diverse faunas reported from SE Asia. The age of the rock is Yakhtashian or Artinskian (late Early Permian) to Midian or Capitanian (late Middle Permian). The study of carbonate facies and fauna indicates that the depositional environment was on shelf lagoon within the carbonate platform varying from shallow marine to barrier bar.

  16. The end-Permian mass extinction: A complex, multicausal extinction

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.

    1994-01-01

    The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction.

  17. The Permian and Triassic in the Albanian Alps

    NASA Astrophysics Data System (ADS)

    Gaetani, Maurizio; Meço, Selam; Rettori, Roberto; Henderson, Charles M.; Tulone, Accursio

    2015-09-01

    The sedimentary succession of the Permian to Middle Triassic of the Albanian Alps is described, as part of the eastern Adria passive margin towards the Tethys. A carbonate ramp deepening towards NE in present day coordinates developed during the Middle Permian and was affected by block faulting with the deposition of carbonate breccia. The Early Triassic was characterized by intense terrigenous deposition with several cobble conglomerate units up to 80 m-thick, and by oolitic carbonate shoals. The fine clastic deposition ended gradually during the earliest Anisian and a wide calcarenitic ramp occupied the area, with small local carbonate mounds. Basinward, the red nodular limestone of the Han Bulog Formation was interbedded with calcarenitic material exported from the ramp. Drowning to more open conditions occurred towards the end of the Pelsonian. Subsequently, cherty limestone and tuffitic layers spread over the entire area. Towards the end of the Ladinian, with the end of the volcanic activity, red pelagic limestone was deposited locally for a short period. By the latest Ladinian most of the area returned to shallow-water conditions, with a peritidal carbonate platform. In the Theth area, in contrast, a basin with black organic-rich dolostone and limestone developed which seems to be unique in that part of the Adria passive margin. The occurrence of cobble conglomerate units in the Lower Triassic testifies to very active block faulting and high accommodation, not yet described for the area.

  18. Flourishing ocean drives the end-Permian marine mass extinction.

    PubMed

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-08-18

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian-Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness. PMID:26240323

  19. A potential biomarker for the Permian Triassic ecological crisis

    NASA Astrophysics Data System (ADS)

    Grice, Kliti; Twitchett, Richard J.; Alexander, Robert; Foster, C. B.; Looy, Cindy

    2005-07-01

    A unique biomarker, a C 33n-alkylcyclohexane ( n-heptacosylcyclohexane), which strongly increases in abundance within the extinction interval of the end-Permian ecological crisis, is here reported from the key Permian-Triassic (P-Tr) marine section in Greenland. Prior to this study, this compound had been known from Early Triassic organic-rich marine rocks and oils from the northern Perth Basin, Western Australia for two decades. We have identified the compound in high relative abundance in 29 samples from P-Tr marine sections from two separate paleogeographic localities, from Laurasia and Gondwana. Relative concentrations of the C 33n-alkylcyclohexane show similar changes to the relative abundances of extinct spinose acritarchs ( Veryhachium and Micrhystridium) indicating that the source organism of the C 33n-alkylcyclohexane is associated with the depositional environments/facies in which the acritarchs are identified. These organisms probably formed the cornerstone of the unique marine ecosystem that thrived in the extinction aftermath in the Early Triassic Ocean.

  20. Calcium isotope constraints on the end-Permian mass extinction

    PubMed Central

    Payne, Jonathan L.; Turchyn, Alexandra V.; Paytan, Adina; DePaolo, Donald J.; Lehrmann, Daniel J.; Yu, Meiyi; Wei, Jiayong

    2010-01-01

    The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (δ13C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (δ44/40Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report δ44/40Ca across the Permian-Triassic boundary from marine limestone in south China. The δ44/40Ca exhibits a transient negative excursion of ∼0.3‰ over a few hundred thousand years or less, which we interpret to reflect a change in the global δ44/40Ca composition of seawater. CO2-driven ocean acidification best explains the coincidence of the δ44/40Ca excursion with negative excursions in the δ13C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average δ13C of CO2 released was heavier than -28‰ and more likely near -15‰; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction. PMID:20421502

  1. Western Tibet: Low-temperature thermochronology data and interpretation on exhumation history.

    NASA Astrophysics Data System (ADS)

    Gourbet, L.; Shuster, D. L.; Maheo, G.; Leloup, P. H.; Paquette, J.

    2013-12-01

    The Tibetan plateau is the highest and largest orogenic plateau in the world. Uplift of the plateau is related to the India-Asia collision. However, recent studies [1] suggest that peneplanation predates collision. This implies that a low-relief, low-elevation surface could have existed prior to the uplift and have therefore gained elevation following the India-Asia collision. Some models of long timescale, regional topographic evolution have been mostly based on low-temperature thermochronometry, but so far most data have been obtained in Central and Southern Tibet, where " plateau " conditions, (i.e. low exhumation rates), seem to have been reached prior to the collision [1,2]. Our study focuses on Western Tibet, where the landscape is internally drained and characterized by high local relief on the order of 2 km. We performed (U-Th)/He dating on 21 granitic samples collected in Western Tibet, between the Karakoram fault and the Pangong Co. Apatite (U-Th)/He ages from a vertical transect in the Rutog granite vary between 13.11 +/- 0.14 and 29.25 +/- 0.31 Ma and reveal a clear ages-elevation correlation. Based on the crystallization age of the sampled granite (74.4 +/- 1.9 Ma, U/Pb on zircons), apatite ages are not related to post-intrusion cooling but rather record exhumation or relief evolution. Mean apparent exhumation rate is ~67 m/Ma, which is significatively higher than rates estimated in central Tibet [1,2]. Western Tibet, as Central Tibet, is currently a cold, arid environment with low rates of river incision; modern exhumation rates are presumably similar to Central Tibet and extremely low (< 0.003 mm/a) [3]. Apparent exhumation rates are at least one-order-of-magnitude greater than modern exhumation rates; this suggests that exhumation slowed down after 13 Ma. A possible hypothesis to explain the cooling age difference between Central and Western Tibet is that internal drainage, responsible for low exhumation rates, was established later in Western Tibet

  2. Cooling and exhumation of continents at billion-year time scales

    NASA Astrophysics Data System (ADS)

    Blackburn, T.; Bowring, S. A.; Perron, T.; Mahan, K. H.; Dudas, F. O.

    2011-12-01

    The oldest rocks on Earth are preserved within the continental lithosphere, where assembled fragments of ancient orogenic belts have survived erosion and destruction by plate tectonic and surface processes for billions of years. Though the rate of orogenic exhumation and erosion has been measured for segments of an orogenic history, it remains unclear how these exhumation rates have changed over the lifetime of any terrane. Because the exhumation of the lithospheric surface has a direct effect on the rate of heat loss within the lithosphere, a continuous record of lithosphere exhumation can be reconstructed through the use of thermochronology. Thermochronologic studies have typically employed systems sensitive to cooling at temperatures <300 °C, such as the (U-Th)/He and 40Ar/39Ar systems. This largely restricts their application to measuring cooling in rocks from the outer 10 km of the Earth's crust, resulting in a thermal history that is controlled by either upper crustal flexure and faulting and/or isotherm inflections related to surface topography. Combining these biases with the uplift, erosion and recycling of these shallow rocks results in a poor preservation potential of any long-term record. Here, an ancient and long-term record of lithosphere exhumation is constructed using U-Pb thermochronology, a geochronologic system sensitive to cooling at temperatures found at 20-50 km depth (400-650 °C). Lower crustal xenoliths provide material that resided at these depths for billions of years or more, recording a thermal history that is buried deep enough to remain insensitive to upper crustal deformation and instead is dominated by the vertical motions of the continents. We show how this temperature-sensitive system can produce a long-term integrated measure of continental exhumation and erosion. Preserved beneath Phanerozoic sedimentary rocks within Montana, USA, the Great Falls Tectonic Zone formed when two Archean cratons, the Wyoming Province and Medicine

  3. Exhumation of high-pressure rocks beneath the Solund Basin, Western Gneiss Region of Norway

    USGS Publications Warehouse

    Hacker, B.R.; Andersen, T.B.; Root, D.B.; Mehl, L.; Mattinson, J.M.; Wooden, J.L.

    2003-01-01

    The Solund-Hyllestad-Lavik area affords an excellent opportunity to understand the ultrahigh-pressure Scandian orogeny because it contains a near-complete record of ophiolite emplacement, high-pressure metamorphism and large-scale extension. In this area, the Upper Allochthon was intruded by the c. 434 Ma Sogneskollen granodiorite and thrust eastward over the Middle/Lower Allochthon, probably in the Wenlockian. The Middle/Lower Allochthon was subducted to c. 50 km depth and the structurally lower Western Gneiss Complex was subducted to eclogite facies conditions at c. 80 km depth by c. 410-400 Ma. Within 100. Exhumation to upper crustal levels was complete by c. 403 Ma. The Solund fault produced the last few km of tectonic exhumation, bringing the near-ultrahigh-pressure rocks to within c. 3 km vertical distance from the low-grade Solund Conglomerate.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

    NASA Astrophysics Data System (ADS)

    Lease, Richard O.; Haeussler, Peter J.; O'Sullivan, Paul

    2016-04-01

    Cenozoic growth of the Alaska Range created the highest topography in North America, but the space-time pattern and drivers of exhumation are poorly constrained. We analyzed U/Pb and fission-track double dates of detrital zircon and apatite grains from 12 catchments that span a 450 km length of the Alaska Range to illuminate the timing and extent of exhumation during different periods. U/Pb ages indicate a dominant Late Cretaceous to Oligocene plutonic provenance for the detrital grains, with only a small percentage of grains recycled from the Mesozoic and Paleozoic sedimentary cover. Fission-track ages record exhumation during Alaska Range growth and incision and reveal three distinctive patterns. First, initial Oligocene exhumation was focused in the central Alaska Range at ~30 Ma and expanded outward along the entire length of the range until 18 Ma. Oligocene exhumation, coeval with initial Yakutat microplate collision >600 km to the southeast, suggests a far-field response to collision that was localized by the Denali Fault within a weak Mesozoic suture zone. Second, the variable timing of middle to late Miocene exhumation suggests independently evolving histories influenced by local structures. Time-transgressive cooling ages suggest successive rock uplift and erosion of Mounts Foraker (12 Ma) through Denali (6 Ma) as crust was advected through a restraining bend in the Denali Fault and indicate a long-term slip rate ~4 mm/yr. Third, Pliocene exhumation is synchronous (3.7-2.7 Ma) along the length of the Alaska Range but only occurs in high-relief, glacier-covered catchments. Pliocene exhumation may record an acceleration in glacial incision that was coincident with the onset of Northern Hemisphere glaciation.

  6. Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica)

    NASA Astrophysics Data System (ADS)

    Malusà, Marco G.; Faccenna, Claudio; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Rossetti, Federico; Balestrieri, Maria Laura; Danišík, Martin; Ellero, Alessandro; Ottria, Giuseppe; Piromallo, Claudia

    2015-06-01

    Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary.

  7. Post-orogenic exhumation history of a Variscan mid-crustal basement in Galicia (NW Spain)

    NASA Astrophysics Data System (ADS)

    Grobe, Rene; Alvarez-Marrón, Joaquina; Glasmacher, Ulrich A.; Stuart, Finlay; Castañeda-Zarauz, A.

    2010-05-01

    The present study aims to quantify the complex post-orogenic history of cooling, denudation, and long-term landscape evolution of a mid-crustal section of Variscan basement in Galicia (NW Spain). We use apatite fission-track and apatite (U-Th)/He thermochronological techniques combined with time-temperature (t-T) path modelling using the software code HeFTy©. The topography is characterized by an extensive, low relief area at ~500 m elevation in central Galicia, and a WNW-ESE ridge that reaches up to 1000 m to the North. The area experienced two major tectonic events since the end of the Variscan orogeny in the Late Palaeozoic: 1) continental break-up and Mesozoic rifting leading to the opening of the Atlantic Ocean and the Bay of Biscay, and 2) limited convergence between Iberia and Eurasia since Middle Eocene times. Apatite fission-track ages range from 68.1 ± 5.0 Ma to 174.5 ± 7.7 Ma and apatite (U-Th)/He ages range from 73.6 ± 5.4 to 147.1 ± 16.6 Ma. Age-elevation plots and t-T path modelling suggest a tectonothermal evolution with faster exhumation associated to faulting during Mesozoic rifting. In particular, two major fault systems trending WNW-ESE and NNE-SSW, the As Pontes and the Lugo faults respectively separate areas with the fastest exhumation around 115 Ma from areas with overall slow exhumation since 200-150 Ma. A landscape of subdued topography in central Galicia was acquired prior to Eocene convergence. The higher elevation areas along the northern ridge formed since Middle Eocene times due to fault reactivation and minor exhumation occurred along the fault escarpment.

  8. Exhumation of an eclogite terrane as a hot migmatitic nappe, Sveconorwegian orogen

    NASA Astrophysics Data System (ADS)

    Möller, Charlotte; Andersson, Jenny; Dyck, Brendan; Antal Lundin, Ildiko

    2015-06-01

    We demonstrate a case of eclogite exhumation in a partially molten, low-viscosity fold nappe within high-grade metamorphosed crust in the Eastern Segment of the Sveconorwegian orogen. The nappe formed during tectonic extrusion, melt-weakening assisted exhumation and foreland-directed translation of eclogitized crust, and stalled at 35-40 km depth within the collisional belt. The eclogites are structurally restricted to a regional recumbent fold in which stromatic orthogneiss with pods of amphibolitized eclogite make up the core. High-temperature mylonitic gneiss with remnants of kyanite eclogite (P > 15 kbar) composes a basal shear zone 50 km long and < 4 km wide. Heterogeneously sheared and partly migmatized augen gneiss forms a tectonostratigraphic marker in front of and beneath the nappe, and is in turn structurally enveloped by a composite sequence of orthogneisses and metabasites. The entire tectonostratigraphic pile underwent near-pervasive deformation and recrystallization under high-pressure granulite and upper amphibolite conditions. U-Pb SIMS metamorphic zircon ages of eclogite and stromatic orthogneiss constrain the time of eclogitization at 988 ± 6 Ma and 978 ± 7 Ma. Migmatization, concomitant deformation, and exhumation are dated at 976 ± 6 Ma, and crystallization of post-kinematic melt at 956 ± 7 Ma. Orthogneiss protoliths are dated at 1733 ± 11 and 1677 ± 10 Ma (stromatic gneiss) and 1388 ± 7 Ma (augen gneiss in footwall), demonstrating origins indigenous to the Eastern Segment. Eclogitization and exhumation were coeval with the Rigolet phase of the Grenvillian orogeny, reflecting the late stage of continental collision during construction of the supercontinent Rodinia.

  9. Burial, Uplift and Exhumation History of the Atlantic Margin of NE Brazil

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Bonow, Johan M.; Green, Paul F.; Cobbold, Peter R.; Chiossi, Dario; Lilletveit, Ragnhild

    2010-05-01

    We have undertaken a regional study of landscape development and thermo-tectonic evo-lution of NE Brazil. Our results reveal a long history of post-Devonian burial and exhuma-tion across NE Brazil. Uplift movements just prior to and during Early Cretaceous rifting led to further regional denudation, to filling of rift basins and finally to formation of the Atlantic margin. The rifted margin was buried by a km-thick post-rift section, but exhumation began in the Late Cretaceous as a result of plate-scale forces. The Cretaceous cover probably extended over much of NE Brazil where it is still preserved over extensive areas. The Late Cretaceous exhumation event was followed by events in the Paleogene and Neogene. The results of these events of uplift and exhumation are two regional peneplains that form steps in the landscape. The plateaux in the interior highlands are defined by the Higher Surface at c. 1 km above sea level. This surface formed by fluvial erosion after the Late Cretaceous event - and most likely after the Paleogene event - and thus formed as a Paleogene pene-plain near sea level. This surface was reburied prior to the Neogene event, in the interior by continental deposits and along the Atlantic margin by marine and coastal deposits. Neo-gene uplift led to reexposure of the Palaeogene peneplain and to formation of the Lower Surface by incision along rivers below the uplifted Higher Surface that characterise the pre-sent landscape. Our results show that the elevated landscapes along the Brazilian margin formed during the Neogene, c. 100 Myr after break-up. Studies in West Greenland have demonstrated that similar landscapes formed during the late Neogene, c. 50 Myr after break-up. Many passive continental margins around the world are characterised by such elevated plateaus and it thus seems possible, even likely, that they may also post-date rifting and continental separation by many Myr.

  10. Ancestral Rocky Mountian Tectonics: A Sedimentary Record of Ancestral Front Range and Uncompahgre Exhumation

    NASA Astrophysics Data System (ADS)

    Smith, T. M.; Saylor, J. E.; Lapen, T. J.

    2015-12-01

    The Ancestral Rocky Mountains (ARM) encompass multiple crustal provinces with characteristic crystallization ages across the central and western US. Two driving mechanisms have been proposed to explain ARM deformation. (1) Ouachita-Marathon collision SE of the ARM uplifts has been linked to an E-to-W sequence of uplift and is consistent with proposed disruption of a larger Paradox-Central Colorado Trough Basin by exhumation of the Uncompahgre Uplift. Initial exhumation of the Amarillo-Wichita Uplift to the east would provide a unique ~530 Ma signal absent from source areas to the SW, and result in initial exhumation of the Ancestral Front Range. (2) Alternatively, deformation due to flat slab subduction along a hypothesized plate boundary to the SW suggests a SW-to-NE younging of exhumation. This hypothesis suggests a SW-derived Grenville signature, and would trigger uplift of the Uncompahgre first. We analyzed depositional environments, sediment dispersal patterns, and sediment and basement zircon U-Pb and (U-Th)/He ages in 3 locations in the Paradox Basin and Central Colorado Trough (CCT). The Paradox Basin exhibits an up-section transition in fluvial style that suggests a decrease in overbank stability and increased lateral migration. Similarly, the CCT records a long-term progradation of depositional environments from marginal marine to fluvial, indicating that sediment supply in both basins outpaced accommodation. Preliminary provenance results indicate little to no input from the Amarillo-Wichita uplift in either basin despite uniformly westward sediment dispersal systems in both basins. Results also show that the Uncompahgre Uplift was the source for sediment throughout Paradox Basin deposition. These observations are inconsistent with the predictions of scenario 1 above. Rather, they suggest either a synchronous response to tectonic stress across the ARM provinces or an SW-to-NE pattern of deformation.

  11. Evolution of a complex behavior: the origin and initial diversification of foliar galling by Permian insects

    NASA Astrophysics Data System (ADS)

    Schachat, Sandra R.; Labandeira, Conrad C.

    2015-04-01

    A central notion of the early evolution of insect galling is that this unique behavior was uncommon to rare before the diversification of angiosperms 135 to 125 m.yr. ago. However, evidence accumulated during recent years shows that foliar galls were diverse and locally abundant as early as the Permian Period, 299 to 252 m.yr. ago. In particular, a diversity of leaf galling during the Early Permian has recently been documented by the plant-damage record of foliar galls and, now, our interpretation of the body-fossil record of culprit insect gallers. Small size is a prerequisite for gallers. Wing-length measurements of Permian insects indicate that several small-bodied hemipteroid lineages originated early during the Permian, some descendant lineages of which gall the leaves of seed plants to the present day. The earliest foliar gallers likely were Protopsyllidiidae (Hemiptera) and Lophioneuridae (Thripida). Much of the Early Permian was a xeric interval, and modern galls are most common in dry, extra-tropical habitats such as scrubland and deserts. Plant-damage, insect body fossils, and the paleoclimate record collectively support the ecological expansion of foliar galling during the Early Permian and its continued expansion through the Late Permian.

  12. Evolution of a complex behavior: the origin and initial diversification of foliar galling by Permian insects.

    PubMed

    Schachat, Sandra R; Labandeira, Conrad C

    2015-04-01

    A central notion of the early evolution of insect galling is that this unique behavior was uncommon to rare before the diversification of angiosperms 135 to 125 m.yr. ago. However, evidence accumulated during recent years shows that foliar galls were diverse and locally abundant as early as the Permian Period, 299 to 252 m.yr. ago. In particular, a diversity of leaf galling during the Early Permian has recently been documented by the plant-damage record of foliar galls and, now, our interpretation of the body-fossil record of culprit insect gallers. Small size is a prerequisite for gallers. Wing-length measurements of Permian insects indicate that several small-bodied hemipteroid lineages originated early during the Permian, some descendant lineages of which gall the leaves of seed plants to the present day. The earliest foliar gallers likely were Protopsyllidiidae (Hemiptera) and Lophioneuridae (Thripida). Much of the Early Permian was a xeric interval, and modern galls are most common in dry, extra-tropical habitats such as scrubland and deserts. Plant-damage, insect body fossils, and the paleoclimate record collectively support the ecological expansion of foliar galling during the Early Permian and its continued expansion through the Late Permian. PMID:25783809

  13. Permian and Triassic rocks near Quinn River Crossing, Humboldt County, Nevada

    NASA Astrophysics Data System (ADS)

    Ketner, Keith B.; Wardlaw, Bruce R.

    1981-03-01

    Permian and Triassic rocks near Quinn River Crossing, Humboldt County, Nevada, consist of four structural blocks: (1) a Lower Permian volcanic block; (2) a Permian(?) chert-arenite block; (3) a Lower Permian limestone block; and (4) a Permian and Triassic block. The contacts between the Permian volcanic block and the others are interpreted as thrust faults or glide surfaces. None of these rocks are metamorphosed, in contrast to those of the surrounding mountain ranges. Each of the blocks is lithically similar in some respects to rocks of the Osgood Mountains area 80 km to the southeast. The fusulinid and brachiopod faunas of two of the blocks display affinities to those of the McCloud Limestone of northern California and the Coyote Butte Limestone of central Oregon, and the fauna of another block has elements in common with autochthonous rocks of eastern Nevada and Utah. All four blocks probably are allochthonous with respect to the rocks exposed in the surrounding mountain ranges, but their points of origin remain obscure. The rocks at Quinn River Crossing provide a link among the Permian rocks of north-central Nevada, northern California, and central Oregon and a possible key to their original relations, but more comparative data are needed.

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

    NASA Astrophysics Data System (ADS)

    Rosenberg, C. L.; Berger, A.; Bellahsen, N.; Bousquet, R.

    2015-06-01

    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 the TALP diminishes during ongoing shortening, indicating that the erosional flux outpaced the accretionary flux. Higher amounts of collisional shortening systematically coincide with smaller widths of the TALP and dramatic increases of the reconstructed eroded rock column. Higher amounts of shortening also coincide with larger amplitudes of orogen-scale, upright folds, with higher exhumation and with higher exhumation rates. Hence, erosion did play a major role in reducing by >30 km the vertical crustal thickness in order to accommodate and allow shortening by folding. Long-term climate differences cannot explain alternating changes of width by a factor of almost 2 along straight segments of the orogen on length scales less than 200 km, as observed from the western Central Alps to the easternmost Eastern Alps. Sedimentary or paleontological evidences supporting such paleo-climatic differences are lacking, suggesting that erosional processes did not directly control the width of the orogen.

  15. Exhumation history of the Mindoro, Philippine and its implication to mountain building process.

    NASA Astrophysics Data System (ADS)

    Wei, S. C.

    2014-12-01

    Exhumation history of the Mindoro, Philippine and its implication to mountain building process Chung-Wei Shiu1,Yuan-Hsi Lee1, Reuy-juin Rau2, Toto Bacolcol3 Department of Earth and Environmental Sciences, National Chung-Cheng university, Taiwan Department of earth science, National Cheng Kung University, Taiwan Department of science and technology, Philippine institute of volcanology and seismology The Mindoro orogenic belt is result from the collision between the Palawan continental crust and Philippine Mobile zone. In this study we report the zircon fission track ages to identify the timing of rapid exhumation of Mindoro orogenic belt. The NNW striking East Mindoro fault (EMF) separates the mountain belt and Luzon arc block. The highest mountain reaches to 2500m on hanging wall of the EMF. In the western side of the EMF the mountain belt can be separate into two blocks by NW trending Mindoro suture zone. To the north and south are Mindoro block and north Palawan block, respectively. The Mindoro block is major comprised of unmetamorphic Eocene strata and Mindoro metamorphic complex. The oldest zircon reset fission track ages shows 4-5 Ma in eastern and western side of the Mindoro metamorphic complex which infers the timing of rapid exhumation since ca. 5Ma which indicate the timing of collision between the Palawan block and Luzon arc.

  16. Regional flow perturbation folding within an exhumation channel: A case study from the Cycladic Blueschists

    NASA Astrophysics Data System (ADS)

    Xypolias, P.; Alsop, G. I.

    2014-05-01

    Kilometre-scale cylindrical folds and associated parasitic folds that trend at small angles to the transport lineation are analysed along a 100-km-long transport-normal segment of the Cycladic Blueschists in an attempt to reconstruct the 3D structural architecture within an exhumation channel. Reversals in the polarity of both fold vergence and the hinge/lineation obliquity occur in a flow-normal direction, defining transport-parallel culmination and depression surfaces that root downwards onto an underlying detachment. Fold patterns generated around culmination and depression surfaces support models of flow-perturbation folding where folds initiate at small angles or sub-parallel to transport in response to wrench-dominated differential shearing. Successive culmination and depression surfaces are separated from one another by along strike distances of ˜20 km, although atypical fold geometries developed in the flanks of major culmination and depressions follow their own patterns, revealing that smaller perturbations occur within the larger scheme. Major culminations are interpreted to reflect regions of surging flow marked by increased velocity during exhumation, whilst the opposite is true for depressions. This behaviour implies that on a regional scale, differential shear varies laterally in an irregular-sinusoidal manner defining areas of relative high and relative low displacement within the exhumation channel.

  17. Regional structural cross sections, mid-permian to quaternary strata, Texas Panhandle and Eastern New Mexico

    SciTech Connect

    McGookey, D.A.; Gustavson, T.C.; Hoadley, A.D.

    1989-01-01

    Twelve regional cross sections (with text) of the Palo Duro, Dalhart, and Anadarko Basins illustrating the tabular geometry of Permian evaporite beds, areas where salt has been lost by dissolution, and the effects of dissolution-induced subsidence on Permian and post-Permian strata. The authors identify areas of dissolution beneath the High Plains, the Caprock Escarpment, the Rolling Plains, the Pecos Plains, and along the Canadian River valley. The cross sections are printed at a vertical scale of 1 inch equals 400 feet and a horizontal scale of 1 inch equals approximately 8 miles and were constructed using geophysical logs, sample logs, and surficial geologic data.

  18. Appalachian Piedmont landscapes from the Permian to the Holocene

    NASA Astrophysics Data System (ADS)

    Cleaves, Emery T.

    1989-09-01

    Between the Potomac and Susquehanna Rivers and from the Blue Ridge to the Fall Zone, landscapes of the Piedmont are illustrated for times in the Holocene, Late Wisconsin, Early Miocene, Early Cretaceous, Late Triassic, and Permian. Landscape evolution took place in tectonic settings marked by major plate collisions (Permian), arching and rifting (Late Triassic) and development of the Atlantic passive margin by sea floor spreading (Early Cretaceous). Erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity. Atlantic Outer Continental Shelf sediments record three major erosional periods: (1) Late Triassic-Early Jurassic; (2) Late Jurassic-Early Cretaceous; and (3) Middle Miocene-Holocene. The Middle Miocene-Holocene pulse is related to neotectonic activity and major climatic fluctuations. In the Piedmont upland the Holocene landscape is interpreted as an upland surface of low relief undergoing dissection. Major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies. The Fall Zone has apparently evolved from a combination of warping, faulting, and differential erosion since Late Miocene. The periglacial environment of the Late Wisconsin (and earlier glacial epochs) resulted in increased physical erosion and reduced chemical weathering. Even with lowered saprolitization rates, geochemical modeling suggests that 80 m or more of saprolite may have formed since Late Miocene. This volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence. Greatly subdued relief characterized the Early Miocene time, near the end of a prolonged interval of tropical morphogenesis. The ancestral Susquehanna and Potomac Rivers occupied approximately their present locations. In Early Cretaceous time local relief may have been as much as 900 m, and a major axial river draining both the Piedmont and Appalachians flowed southeast

  19. Appalachian Piedmont landscapes from the Permian to the Holocene

    USGS Publications Warehouse

    Cleaves, E.T.

    1989-01-01

    Between the Potomac and Susquehanna Rivers and from the Blue Ridge to the Fall Zone, landscapes of the Piedmont are illustrated for times in the Holocene, Late Wisconsin, Early Miocene, Early Cretaceous, Late Triassic, and Permian. Landscape evolution took place in tectonic settings marked by major plate collisions (Permian), arching and rifting (Late Triassic) and development of the Atlantic passive margin by sea floor spreading (Early Cretaceous). Erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity. Atlantic Outer Continental Shelf sediments record three major erosional periods: (1) Late Triassic-Early Jurassic; (2) Late Jurassic-Early Cretaceous; and (3) Middle Miocene-Holocene. The Middle Miocene-Holocene pulse is related to neotectonic activity and major climatic fluctuations. In the Piedmont upland the Holocene landscape is interpreted as an upland surface of low relief undergoing dissection. Major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies. The Fall Zone has apparently evolved from a combination of warping, faulting, and differential erosion since Late Miocene. The periglacial environment of the Late Wisconsin (and earlier glacial epochs) resulted in increased physical erosion and reduced chemical weathering. Even with lowered saprolitization rates, geochemical modeling suggests that 80 m or more of saprolite may have formed since Late Miocene. This volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence. Greatly subdued relief characterized the Early Miocene time, near the end of a prolonged interval of tropical morphogenesis. The ancestral Susquehanna and Potomac Rivers occupied approximately their present locations. In Early Cretaceous time local relief may have been as much as 900 m, and a major axial river draining both the Piedmont and Appalachians flowed southeast

  20. Eocene extensional exhumation of basement and arc rocks along southwesternmost Peru, Central Andes.

    NASA Astrophysics Data System (ADS)

    Noury, Mélanie; Bernet, Matthias; Sempéré, Thierry

    2014-05-01

    The overthickened crust of the current Central Andes is commonly viewed as the result of tectonic shortening. However, in the present-day terrestrial forearc and arc of southwesternmost Peru, crustal thickness increases from 30 km along the coastline to >60 km below the active arc, whereas the upper crust exhibits little to no evidence of crustal shortening and, in constrast, many extensional features. How (and when) crustal overthickness was acquired in this region is thus little understood. Because crustal overthickening often results in extensional collapse and/or significant erosion, here we address this issue through a regional-scale study of exhumation using fission-track thermochronology. The limited fission-track data previously available in the area suggested that exhumation began during the Mesozoic. In this study, we present new apatite and zircon fission-track data obtained along the current terrestrial forearc of southwesternmost Peru. This relatively restricted area presents the interest of providing extensive outcrops of Precambrian to Ordovician basement and Early Jurassic to Late Cretaceous arc plutons. In order to compare the chronology of exhumation of these units, we performed extensive sampling for fission-track dating, as well as structural mapping. Our results indicate that the basement rocks and Jurassic plutons that crop out in the Arequipa region, where the crust is now >50 km-thick, experienced a rapid cooling through the 240-110°C temperature range between ~65 and ~35 Ma. This period of rapid exhumation coincided in time with the accumulation of terrestrial forearc deposits (the Lower Moquegua Group), that exhibit many syn-sedimentary extensional features and are bounded by conspicuous normal faults, specifically along the region where intense activity of the main arc between ~90 and ~60 Ma had led to voluminous magma emplacement. This close succession of (1) intense magmatic activity and (2) regional-scale exhumation associated with

  1. Cenozoic exhumation history of Sulu terrane: Implications from (U-Th)/He thermochrology

    NASA Astrophysics Data System (ADS)

    Wu, Lin; Monié, Patrick; Wang, Fei; Lin, Wei; Ji, Wenbin; Bonno, Michael; Münch, Philippe; Wang, Qingchen

    2016-03-01

    The Qinling-Dabie-Sulu orogen is the most prominent Phanerozoic orogenic belt in China. The discovery of ultra-high pressure (UHP) minerals in zircon inclusions suggests that the crust was subducted to deeper than 120 km into the mantle and then exhumed to shallow crustal. Recently, low temperature thermochronology has been applied to constrain the final exhumation of Dabie Shan, while there are few studies describing the Cenozoic exhumation history of the Sulu belt. Here we report some (U-Th)/He ages for various lithologies from Sulu Orogenic belt and its northern part-Jiaobei terrane. The single grain He ages range between 18 and 154 Ma, and most of the samples having large intra-sample age scattering. Several reasons such as invisible U/Th-rich inclusions, grain size effect, slow cooling rate, and zonation of parent nuclide or radiation damage effect may account for this dispersion. For all samples, the pattern of the single grain age data exhibits a peak at ~ 45 Ma which is consistent with the borehole fission-track age pattern in adjacent Hefei Basin. Both (U-Th)/He and fission track ages of the Sulu area suggest an enhanced exhumation/cooling in Early-Middle Eocene in the southern part of Tan-Lu fault zone. This enhanced cooling event coincides with rapid subsidence of North China Basin and rapid uplift of its surrounding reliefs, which indicates basin-mountain coupling. This Eocene event is widespread in central China and could be far-field consequence of India-Asia collision. The convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary and reached a minimum in Eocene (~ 30-40 mm/yr) while at the same time the collision between India and Asia was completed. Therefore, the Cenozoic exhumation history of the Sulu Orogenic Belt was a combined result of far-field effect of India-Asia collision and declined subduction rate of the Pacific Plate under Eurasia.

  2. Burial and exhumation history of the Polish Outer Carpathians: Discriminating the role of thrusting and post-thrusting extension

    NASA Astrophysics Data System (ADS)

    Andreucci, B.; Castelluccio, A.; Jankowski, L.; Mazzoli, S.; Szaniawski, R.; Zattin, M.

    2013-11-01

    Several tectonic processes have been proposed to be important in the Alpine to the recent evolution of the Polish Outer Carpathians, i.e., Paleogene-Neogene thrusting, post-thrusting extension, Quaternary reactivation of compression. This work tests the effect of these processes on exhumation of the wedge, in order to verify their timing and relative role in shaping the Polish Outer Carpathians. AFT, AHe and ZHe analyses were performed on samples collected along the study region. This allowed the reconstruction of their post-depositional minimum heating, depth of burial and timing of cooling and exhumation. After deposition samples from the innermost units were heated up to temperatures of ca. 60-120 °C (ca. 4-9 km), whereas samples from the outer units were heated to temperatures lower than 60 °C (ca. 4 km). Cooling and exhumation occurred progressively later from west to east (between ca. 25 and 10 Ma in the western sector, between ca. 15 and 5 Ma in the eastern sector). These results have been put in relationship with single structural features to understand the relative role of thrusts and normal faults. In the eastern sector of the study region samples at the footwall of significant normal faults show a higher degree of reset and younger ages than samples located at the hangingwall. This implies that, in this sector, extensional tectonics played an important role in exhumation. However, proper tectonic exhumation only had a minor role, the major exhumation mechanism being erosion, which is enhanced in the footwalls and reduced in the hangingwalls. In the western sector of the Polish Outer Carpathians only in few cases evidence of enhanced erosion to the footwall of major normal faults could be observed based on the present data. In this region the wedge exhumed mainly as a response to thrusting and normal faulting only played a minor role, locally modifying the pattern of erosion. Finally no major exhumation events occurred after Miocene, pointing to a minor

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

    NASA Astrophysics Data System (ADS)

    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

  4. Neogene exhumation of the Internal Rif units (Northern Morocco) evidenced by low- temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Romagny, Adrien; Munch, Philippe; Corsini, Michel; Azdimoussa, Ali; Arnaud, Nicolas; Monié, Patrick; Bonno, Michael; Vazquez, Mercedes

    2013-04-01

    The Rif Chain (Northern Morocco) belongs, with the Betic Cordillera (Southern Spain) to the westernmost part of the Alpine belt. There, the Beni Bousera peridotite massif is exhumed and corresponds to one of the deepest exhumed lithospheric rocks of the chain. Tectono-metamorphic studies showed that the internal units were subjected to very fast exhumation during the late Oligocene - early Miocene interval in relation with a crustal thinning and the Alboran sea rifting (synthesis in Chalouan et al., 2008). However, no data are available for the subsequent period despite that Neogene uplift sediments are well known in the internal domain since the work of Wildi and Wernli (1977) and predicted during the Messinian by thermomecanical modelling (Duggen et al., 2003). We present here for the first time a low temperature thermochronologic study (apatite (U-Th)/He and fission tracks; AHe and AFT) of these rocks in order to date and quantify the Neogene exhumation history of internal units of the Rif Chain. Most AHe ages are comprised between 14.25 ± 0.21 and 21.32 ± 0.31 Ma however some are younger (e.g. 6.92 ± 0.14 Ma). AHe ages are closed to fission tracks ages, indicating a very rapid cooling. Moreover they do not show any clear age-elevation relationship that is consistent with a very rapid cooling. Youngest ages correspond to apatite with low eU concentration and thus are interpreted in terms of lower closure temperatures. We performed thermal modelling with HeFTy software (Ehlers et al., 2005; Ketcham et al., 2007) on fission tracks lengths and He diffusion data as they provide a statistical but more complete temperature-time history for the samples. We also used available 40Ar/39Ar data on biotite and field data to better constrain thermal modelling. Exhumation occurred in two main steps: i) a very rapid cooling between 22 and 17 Ma until rocks reached the top of the PAZ (80 to 60°C) at a rate of ~70 to 120°C/Ma) and ii) a very slow cooling between 17 and 4 Ma

  5. Multiple broadly synchronous km-scale exhumation episodes on different continents: implications for controlling processes

    NASA Astrophysics Data System (ADS)

    Green, Paul; Duddy, Ian; Japsen, Peter

    2015-04-01

    Numerous low temperature thermochronology studies have defined regional cooling episodes which imply removal of several km of section over areas of several 104 km2. The origin of such events has long been the subject of debate, while their reality has sometimes been questioned because of the lack of a viable mechanism. Kilometre-scale denudation at rifted margins has traditionally been interpreted as related to rifting and breakup, magnified by the flexural response to denudation of the uplifted rift flanks. But it is now clear that at many margins the post-breakup history is more complex, with km-scale uplift and erosion commonly post-dating breakup by 10s of Myr and often affecting regions many 100s of kilometres inland of the margins (Green et al., 2013; Brown et al., 2014). Numerous examples around the world of km-scale exhumation affecting regions distant from continental margins, including cratonic regions traditionally regarded as stable over Phanerozoic time (e.g. Ault et al., 2009; Flowers & Kelley, 2011), cannot be explained by margin-related mechanisms. It has also become clear that periods of exhumation are separated by episodes of burial, defining a series of positive and negative vertical movements. Previous studies have defined a broad synchroneity of Early, Middle and Late Cenozoic exhumation events in regions from Alaska to Greenland, Norway and Svalbard (Green and Duddy, 2010). New results from SE Australia define a series of exhumation episodes ranging in time from Carboniferous to Cenozoic which are broadly synchronous with similar events previously defined in Brazil and South Africa (Green et al. 2013). While estimates of the timing of exhumation in different areas are subject to some uncertainty, data across three southern hemisphere continents show a broad synchronicity in similar fashion to the northern hemisphere examples cited above. Dynamic topography has been invoked as a possible mechanism for producing uplift, the effects of which

  6. Karst in Permian evaporite rocks of western Oklahoma

    SciTech Connect

    Johnson, K.S. )

    1993-02-01

    Bedded evaporites (gypsum and salt) of Permian age have been dissolved naturally by ground water to form a major evaporite-karst region in western Oklahoma. The Blaine Formation and associated evaporites comprise 100--800 ft of strata that dip gently into broad, structural basins. Outcropping gypsum, dolomite, and red-bed shales of the Blaine display typical karstic features, such as sinkholes, caves, disappearing streams, and springs. Large caves are developed in gypsum beds 10--30 ft thick at several places, and a major gypsum/dolomite karst aquifer provides irrigation water to a large region in southwestern Oklahoma, where salt layers above and below the Blaine Formation have been partly dissolved at depths of 30--800 ft below the land surface. Salt dissolution causes development of brine-filled cavities, into which overlying strata collapse, and the brine eventually is emitted at the land surface in large salt plains.

  7. Methanogenic burst in the end-Permian carbon cycle

    PubMed Central

    Rothman, Daniel H.; Fournier, Gregory P.; French, Katherine L.; Alm, Eric J.; Boyle, Edward A.; Cao, Changqun; Summons, Roger E.

    2014-01-01

    The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation. PMID:24706773

  8. Mg Isotopes of the Late Permian Evaporites, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Feng, C.; Gao, C. H.; Chang, S. C.

    2015-12-01

    Mg isotope holds promise to decipher the evaporative environment of evaporites. High-precision Mg isotope compositions of the late Permian langbeinites have been measured by using MC-ICPMS. The equilibrium Mg isotope fractionation factor between langbeinite and aqueous Mg2+ solutions has been determined using quantum chemistry calculations. All computations are employed at B3LYP/6-311++G(2d,2p) level and solvation effects are treated by solvent model ("water-droplet" approach), mineral structures are constructed using volume variable cluster models (VVCM). The Mg isotope compositions of the langbeinite samples, whose total formation thickness ranges up to 100 meters, are extremely isotopically lighter than that of modern seawater and relatively homogeneous (δ26MgDSM3 is from -4.12±0.03‰ to -3.81±0.07‰ v.s. -0.83‰ of modern seawater). The computed equilibrium Mg isotope fractionation factors between langbeinite and aqueous Mg2+ solutions are -2.73‰, -2.66‰ and -2.53‰ at 25, 30 and 40 ℃, respectively. These significant equilibrium fractionation factors indicate that a huge equilibrium Mg isotope fractionation between langbeinite and its parent brine can happen during langbeinite depositions, and langbeinites are enriched in isotopically light 24Mg comparing to the brine. Using the computed fractionation factors to simulate a Rayleigh fractionation process of langbeinite Mg precipitation, we find that a significant Mg isotope difference between langbeinite and its growing brine (seawater) is indeed present but the Mg isotope composition of langbeinite merely increase monotonically in a closed system. Because of that, the homogenous Mg isotope compositions of such a thick evaporite sequence suggest a disequlibrium effect rather than an equilibrium Mg isotope fractionation behavior during its formation. Combined with its prevailing Mg-bearing character, the homogenous Mg isotope compositions reveal that this the late Permian langbeinite sequence has

  9. Exhumation of Basement-cored Uplifts: Example of the Kyrgyz Range Quantified with Apatite Fission-track Thermochronology

    NASA Technical Reports Server (NTRS)

    Sobel, Edward R.; Oskin, Michael; Burbank, Douglas; Mikolaichuk, Alexander

    2005-01-01

    The Kyrgyz Range, the northernmost portion of the Kyrgyzstan Tien Shan, displays topographic evidence for lateral propagation of surface uplift and exhumation. The highest and most deeply dissected segment lies in the center of the range. To the east, topography and relief decrease, and preserved remnants of a Cretaceous regional erosion surface imply minimal amounts of bedrock exhumation. The timing of exhumation of range segments defines the lateral propagation rate of the range-bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology. New apatite fission-track (AFT) data from three transects from the eastern Kyrgyz Range, combined with published AFT data, demonstrate that the range has propagated over 110 km eastwards over the last 7-11 Myr. Based on the thermal and topographic evolutionary history, we present a model for a time-varying exhumation rate driven by rock uplift and changes in erodability and the time scale of geomorphic adjustment to surface uplift. Easily eroded, Cenozoic sedimentary rocks overlying resistant basement control early, rapid exhumation and slow surface upliftrates. As increasing amounts of resistant basement are exposed, exhumation rates decrease while surface uplift rates are sustained or increase, thereby growing topography. As the range becomes high enough to cause ice accumulation and develop steep river valleys, fluvial and glacial erosion become more powerful and exhumation rates once again increase. Independently determined range-noma1 shortening rates have also varied over time, suggesting a feedback between erosional efficiency and shortening rate.

  10. No reff-rimmed margins to the Permian carbonate platforms of Thailand

    NASA Astrophysics Data System (ADS)

    Dawson, Orapin; Baird, Angus; Bosence, Dan

    In the central Thailand platform, marginal buildups (Early Permian) are formed mainly by fossiliferous grainstones with boundstones occurring only as small biostrome. Boundstones have a dominant skeletal element of encrusting Archaelithoporella and Tubiphytes with calcisponges and abundant syndepositional marine cements. This boundstone texture is similar to that of many other well documented Permian examples, such as El Capitan, U.S.A. and Trogkofel, Austria. In the Ratburi area of Peninsular Thailand, small bioherms (Middle Permian) are interbedded within grainstone shoals. Boundstone textures are matrix rich, with bryozoa, the main skeletal element and Tubiphytes, the main binding element. The Peninsular Thailand buildups formed on platform interior ridges and not in a shelf marginal position. These small biostromal and biohermal buildups in central and Peninsular Thailand did not form massive shelf-margin reef bodies as have been described from Permian platforms in western U.S.A. and southern China.

  11. New evidence for 250 Ma age of halotolerant bacterium from a Permian salt crystal

    NASA Astrophysics Data System (ADS)

    Satterfield, Cindy L.; Lowenstein, Tim K.; Vreeland, Russell H.; Rosenzweig, William D.; Powers, Dennis W.

    2005-04-01

    The purported oldest living organism, the spore-forming bacterium Virgibacillus sp. Permian strain 2 9-3, was recently cultured from a brine inclusion in halite of the 250 Ma Permian Salado Formation. However, the antiquity of Virgibacillus sp. 2 9-3 has been challenged; it has been argued that the halite crystal and the fluid inclusion from which the bacterial spores were extracted may be younger than the Permian Salado salts. Here we report that brine inclusions from the same layer of salt that housed Virgibacillus sp. 2 9-3 are composed of evaporated Late Permian seawater that was trapped in halite cement crystals precipitated syndepositionally from shallow groundwater brines at temperatures of 17 37 °C. These results support the 250 Ma age of the fluid inclusions, and by inference, the long-term survivability of microorganisms such as Virgibacillus sp. 2 9-3.

  12. Fungal event and palynological record of ecological crisis and recovery across the Permian-Triassic boundary

    NASA Astrophysics Data System (ADS)

    Eshet, Yoram; Rampino, Michael R.; Visscher, Henk

    1995-11-01

    The end of the Permian Period was marked by the most severe mass extinction in the geologic record. Detailed quantitative study of pollen and spores from shallow-marine deposits spanning the Permian-Triassic (P-Tr) boundary in Israel reveals a sequence of palynological-ecological stages reflecting a major crisis among land plants. The disappearance of the gymnosperm-dominated palynoflora of the Late Permian Lueckisporites virkkiae Zone is recorded at a claystone horizon containing almost exclusively abundant fungal remains and carbonized terrestrial plant debris. This “fungal spike” is followed by a zone dominated by marine acritarchs and a succession showing ecological recovery with abundant lycopod spores and eventual reappearance of bisaccate gymnosperm pollen in the Early Triassic. The latest Permian proliferation of fungi is recognizable worldwide and can be correlated with other paleontological and geochemical markers of a global ecological disaster.

  13. The history of the Arabian platform evolution in the Late Permian and Triassic

    SciTech Connect

    Bebeshev, I.I.

    1995-03-01

    On the basis of comprehensive investigations of the Upper Permian and Triassic sequences of the Arabian platform, three stages were recognized, corresponding to distinct time intervals. The first stage corresponds to the Latest Permian-Early Triassic, the second - to the Early-Middle Triassic, the third - to the Late Triassic. Special maps were plotted for the second and third stages, reflecting major paleogeographic and paleotectonic events. An effort was made to test the oil potential of the sequences.

  14. Feasibility study of heavy oil recovery in the Permian Basin (Texas and New Mexico)

    SciTech Connect

    Olsen, D.K.; Johnson, W.I.

    1993-05-01

    This report is one of a series of publications assessing the feasibility of increasing domestic heavy oil production. Each report covers select areas of the United States. The Permian Basin of West Texas and Southeastern New Mexico is made up of the Midland, Delaware, Val Verde, and Kerr Basins; the Northwestern, Eastern, and Southern shelves; the Central Basin Platform, and the Sheffield Channel. The present day Permian Basin was one sedimentary basin until uplift and subsidence occurred during Pennsylvanian and early Permian Age to create the configuration of the basins, shelves, and platform of today. The basin has been a major light oil producing area served by an extensive pipeline network connected to refineries designed to process light sweet and limited sour crude oil. Limited resources of heavy oil (10`` to 20`` API gravity) occurs in both carbonate and sandstone reservoirs of Permian and Cretaceous Age. The largest cumulative heavy oil production comes from fluvial sandstones of the Cretaceous Trinity Group. Permian heavy oil is principally paraffinic and thus commands a higher price than asphaltic California heavy oil. Heavy oil in deeper reservoirs has solution gas and low viscosity and thus can be produced by primary and by waterflooding. Because of the nature of the resource, the Permian Basin should not be considered a major heavy oil producing area.

  15. Feasibility study of heavy oil recovery in the Permian Basin (Texas and New Mexico)

    SciTech Connect

    Olsen, D.K.; Johnson, W.I.

    1993-05-01

    This report is one of a series of publications assessing the feasibility of increasing domestic heavy oil production. Each report covers select areas of the United States. The Permian Basin of West Texas and Southeastern New Mexico is made up of the Midland, Delaware, Val Verde, and Kerr Basins; the Northwestern, Eastern, and Southern shelves; the Central Basin Platform, and the Sheffield Channel. The present day Permian Basin was one sedimentary basin until uplift and subsidence occurred during Pennsylvanian and early Permian Age to create the configuration of the basins, shelves, and platform of today. The basin has been a major light oil producing area served by an extensive pipeline network connected to refineries designed to process light sweet and limited sour crude oil. Limited resources of heavy oil (10'' to 20'' API gravity) occurs in both carbonate and sandstone reservoirs of Permian and Cretaceous Age. The largest cumulative heavy oil production comes from fluvial sandstones of the Cretaceous Trinity Group. Permian heavy oil is principally paraffinic and thus commands a higher price than asphaltic California heavy oil. Heavy oil in deeper reservoirs has solution gas and low viscosity and thus can be produced by primary and by waterflooding. Because of the nature of the resource, the Permian Basin should not be considered a major heavy oil producing area.

  16. Brittle deformation and exhumation mechanisms in the core of the Eastern Alps, The Tauern Window

    NASA Astrophysics Data System (ADS)

    Bertrand, Audrey; Garcia, Sebastian; Rosenberg, Claudio

    2010-05-01

    The Tauern Window (TW) is a Tertiary structural and thermal dome located in the core of the Eastern Alpine orogen and in front of the Dolomite indenter. The Penninic basement and cover units within the TW attained their thermal peak about 30 Myr ago (e.g., Selverstone et al., 1992) followed by cooling and exhumation from Early Oligocene to late Miocene time (e.g., Grundmann and Morteani, 1985). Most exhumation was partly accommodated by two normal faults at the western and eastern ends of the TW (Brenner and Katschberg faults, respectively). Although these normal faults are well described in the literature, their roles in the exhumation of the TW are still under debate: Exhumation accommodated primarily by folding and erosion (e.g., Rosenberg et al., 2004) versus exhumation mainly accommodated by Brenner and Katschberg normal faulting (e.g., Selverstone, 1988; Ratschbacher et al., 1989). New fault-slip data from the TW allow us to reconstruct paleostress axes by inversion and to constrain the relative roles of the folding and orogen-parallel extension during the late deformation history of the TW, in the brittle-field. Our results show little evidence of compression and a clear zoning of the paleostress field in the TW. In the central part of the TW, the σ1 direction is sub-horizontal N-S to NE-SW (strike-slip), whereas it is steep in the footwall of the Brenner and the Katschberg normal faults. Local variability of the σ3 direction are observed; indeed, the σ3 direction varies from E-W to WNW-ESE along the Brenner fault, to NW-SE along the Jaufen fault, the inferred southern continuation of the Brenner fault (Schneider et al., this session). Along the Katschberg fault, the σ3 direction is mainly NNW-SSE oriented, which is consistent with extension in front of a triangular dead zone shape induced by the WSW-striking Dolomites indenter. Nearly no evidence of a stress field compatible with upright folding (D2 phase of deformation) was found in the brittle domain

  17. Recent Exhumation in the Chugach, St. Elias, and Fairweather Ranges, Alaska

    NASA Astrophysics Data System (ADS)

    Spotila, J. A.; Berger, A. L.; McAleer, R. J.

    2006-12-01

    The motion of the Yakutat block into North America has produced a band of crustal deformation that begins near the tip of the Aleutian megathrust, continues through the eastern Chugach Range and St. Elias Mountains, and wraps southeastward along the Fairweather transform. Because of the extreme climate of the southern Alaska margin, this oblique collision has developed under the intense action of glacial erosion for the past few million years. This makes this orogen suitable for investigating the nature of feedbacks between climate, tectonics, and topography. We have measured the spatial and temporal patterns of exhumation at scales of orogenic evolution using apatite (U-Th)/He dating. In conjunction with previously published (U-Th)/He and fission-track ages (O'Sullivan and Currie, 1996; O'Sullivan et al., 1997; Buscher et al., 2002; Spotila et al., 2004; Johnston, 2005; Meigs et al., 2006; Perry et al., 2006), our new low-temperature cooling ages are beginning to reveal patterns of vertical strain localization on individual structures and in climatic zones, as well as the balance between tectonic influx and erosional efflux in the orogen. Data obtained thus far form a rough bull's eye pattern of concentric rings of cooling ages in the core of the orogen that become older with distance away from focused exhumation near the bend in the plate boundary. A similar bull's eye of young ages occurs along the Fairweather Range southeast of the bend and continuing to Glacier Bay, such that the zone of rapid exhumation is actually boomerang in shape. This is surprising, given that geologic and geodetic data indicate the Fairweather fault is pure strike-slip. Uplift and exhumation of the Fairweather corridor instead implies plate motion is oblique, with a significant component of partitioned shortening. Further west within the core of the Yakutat collision, the youngest apatite helium ages, less than 1 Ma, occur in a band along the coast that extends westwards from Mt. St

  18. Oblique divergence and exhumation of giant ultrahigh-pressure terrains (Western Gneiss Region, Norway)

    NASA Astrophysics Data System (ADS)

    Teyssier, Christian; Whitney, Donna L.; Gordon, Stacia M.; Renedo, Roxanne; Fossen, Haakon

    2013-04-01

    The subduction of continental rocks to ultrahigh-pressure (UHP) conditions is an integral part of the evolution of many orogens, but the processes that exhume these rocks are still highly debated. Syn-convergence exhumation can explain the forced and/or buoyant return of relatively small UHP bodies in a subduction channel. However, we propose that the exhumation of giant UHP terrains, such as the Western Gneiss Region (WGR) of Norway, is consistent with oblique divergence, not convergence. Oblique divergence is expected to produce transtensional structures, including extension-parallel fold hinges and boudins as well as constrictional fabrics. The structural style of the WGR is dominated by transtension strain from UHP to low P conditions. We propose that the timing of exhumation of UHP rocks is tied to a large transform-detachment system along the western coast of southern and central Norway. The UHP WGR is bounded to the north by the SW-NE trending Møre-Trøndelag Fault Zone (MTFZ), a ~10 km wide transform shear zone that connects two extensional systems over a distance of several hundred kilometers. The extensional system to the S of the MTSZ consists of the W-directed Nordfjord-Sogn detachment that exhumed the UHP terrain. The extensional system on the northern side of the MTFZ is defined by the SW-directed Høybakken and NE-directed Kollstraumen detachments that bound a bivergent extensional core complex, the Central Norway Basement Window (CNBW). South of the MTFZ, UHP and HP eclogite is dispersed in an extensively deformed gneissic and migmatitic host with strong linear fabrics, lineation-parallel folds, and variably oriented shear zones that accommodated strike-slip to normal sense (top-to-W) shear. Omphacite CPO in layered eclogite indicates that fabrics developed in constriction (consistent with transtension) at HP and possibly UHP conditions. U-Pb ICPMS dating of zircon from leucosome in the gneissic host of UHP eclogite reveals dates between 410 and

  19. Accretion/underplating, detachment and exhumation: short/long-term rheology of the subduction plate interface

    NASA Astrophysics Data System (ADS)

    Agard, Philippe; Angiboust, Samuel; Plunder, Alexis; Guillot, Stéphane; Yamato, Philippe; Oncken, Onno; Ruh, Jonas; Burov, Evgueni; Bonnet, Guillaume

    2016-04-01

    The presence of km-scale accreted terranes/units in both ancient and present-day subduction zones attests to changes in strain localization along the plate interface, whereby these terranes/units get detached from the downgoing slab (or, in places, are eroded away from the tip of the upper plate) and either directly exhumed or accreted/underplated below the upper plate before final exhumation. The rock record (P-T-t data) indicates that, for a given subduction zone, exhumation is episodic: no more than a few My compared to the ~100 My lifetime of typical subduction zones. Not much is known, however, regarding this process and important open questions remain: what exactly is episodic (i.e., detachment from the slab and/or exhumation?), for how long and where? How is mechanical coupling impacted by the initial structure of the incoming plates (structural/lithological heterogeneities, thermo-fluid regime, geodynamic boundary conditions, etc...)? We herein present both new and literature structural and P-T-t data ranging from shallow (i.e., 15-20 km) to intermediate depths (~100 km) along the subduction interface, that span a range from long-term to short-lived events of underplating and/or exhumation, and confront them with the recent wealth of geophysical data gathered on subduction zones. Structural and petrological data indicate that the slicing of km-scale units mostly occurs at specific depths where major mechanical changes occur along the plate interface: at 30-40 km (downdip of the seismogenic zone) and 70-80 km (where mechanical coupling between the two plates resumes and where eclogites get critically dense). This suggests that switches in mechanical coupling (i.e., in the rheology of the material) are key in controlling the ability to detach pieces from the slab (and that later exhumation is rather controlled by large-scale, lithospheric-scale boundary conditions). The study of rock remnants detached from the slab and underplated during subduction infancy (i

  20. Rifting and UHP exhumation in Eastern Papua New Guinea: Temperature and pressure constraints from primitive magmas

    NASA Astrophysics Data System (ADS)

    Ruprecht, P.; Plank, T. A.; Jin, G.; Abers, G. A.

    2013-12-01

    The area east and northeast of the Papuan peninsula is one of the most tectonically complex regions worldwide, with three different processes superimposed. The rock record on the peninsula provides evidence for multiple episodes of arc collisions over the Cenozoic. Simultaneously ocean spreading in the Woodlark Basin has progressed westward and impinges on Papuan mainland, leading to rifting at the easternmost extension of the peninsula. This complex plate reconfiguration coincides with the exhumation of the youngest HP/UHP rocks on Earth, 5-6 Ma, in the D'Entrecasteaux Islands. The dynamic controls between those three processes are unknown. The thermal structure in the mantle is one of the most fundamental constraints for any dynamic model and as well as for seismic studies. Primitive magmas that erupted around the rift provide estimates of mantle temperatures beneath the volcanoes and in the vicinity of the exhuming HP/UHP rocks. Trace elements and volatiles in olivine-hosted melt inclusions provide new insights into the geochemical make-up of the mantle source region and the influence of subduction and/or rifting on magma generation. We present data primarily from two Holocene volcanic centers (Wagifa and Goropu) that erupted basaltic andesites containing primitive olivines (> Fo89). Thermobarometry on these tephras suggest that the magmas equilibrated prior to their extraction from the mantle at temperatures and pressures of ~1150-1200 degree C and 0.55-0.75 GPa, respectively. If these estimates represent equilibrium below the Moho then, in particular, results from Wagifa suggest that crustal thicknesses in the area of the D'Entrecasteaux islands do not exceed ~23 +/-6 km, which is somewhat thinner than currently proposed average Moho depth estimates from receiver functions and and SsPmP phases (23-24 +/- 3km). Moreover, local mantle temperatures are well above the melting point of exhumed felsic HP/UHP rocks, suggesting that either (1) the thermal pulse that

  1. Cenozoic uplift, exhumation and deformation in the north Kuqa Depression, China as constrained by (U-Th)/He thermochronometry

    NASA Astrophysics Data System (ADS)

    Yu, Shun; Chen, Wen; Evans, Noreen J.; McInnes, Brent I. A.; Yin, Jiyuan; Sun, Jingbo; Li, Jie; Zhang, Bin

    2014-09-01

    Placing spatial and temporal constraints on deformation, uplift and exhumation using thermochronology methods can shed light on Cenozoic orogenic evolution in the Kuqa foreland. New apatite (U-Th)/He and previously published apatite fission track thermochronology are combined with vitrinite reflectance data and modeling to compile a low temperature, multi-stage thermal history of tectonic uplift/thrust and exhumation. A rapid uplift and exhumation event originated in South Tianshan during the Eocene (~ 46 Ma), with systematic younging of mean apatite (U-Th)/He ages from north to south (from the margin towards the interior). Uplift and exhumation south edge of the Biyoulebaoguzi anticline in the northern monocline belt at ~ 36 Ma with more than 3400 m of stratum denuded. Subsequently, deformation and uplift south edge of the Biyoulebaoguzi anticline in the northern monocline belt at ~ 36 Ma with more than 3400 m of stratum denuded. Subsequently, deformation and uplift extended to the northern edge of Kelasu-Yiqikelike at ~ 10 Ma and then at ~ 6 Ma, the Kanyaken anticline formed and uplifted resulting in 3000-3700 m of overburden erosion. The data support sequential southward propagating deformation and uplift (inferred exhumation) in the north Kuqa Depression during the Cenozoic, probably as a result of the collision of India with Asia far to the south of the Tianshan.

  2. Constraining the deformation and exhumation history of the Ronda Massif, Southern Spain

    NASA Astrophysics Data System (ADS)

    Myall, Jack; Donaldson, Colin

    2016-04-01

    The Ronda peridotite, southern Spain is comprised of four peridotite units hosted within metasedimentary units of the Betic Cordillera, Western Alps. These four areas of differing mineral facies are termed: the Garnet Mylonite , the Foliated Spinel Peridotite, the Granular Spinel Peridotite and the Foliated Plagioclase Peridotite. Whilst two of these units show a strong NE-SW foliation, the granular unit has no foliation and the Plagioclase facies shows a NW-SE foliation. The massif is separated from the metasedimentary host through a mylonite shear zone to the NW and thrust faults to the SE. The Garnets contain rims of Kelyphite which when combined with the rims of Spinel on the Plagioclase crystals illustrate the complicated exhumation of this massif. The Kelyphite shows the breakdown of garnet back to spinel and pyroxene showing the deeper high pressure high temperature mineral is under shallowing conditions whereas in contrast to this the low pressure low temperature plagioclase crystals have spinel rims showing that they have been moved into deeper conditions. The P-T-t pathway of the massif suggests slow exhumation to allow for partial recrystallisation of not only the garnets and plagioclases but of a 100m band of peridotite between the Foliated Spinel Peridotite and the Granular Spinel Peridotite facies. The tectonic model for the Ronda Peridotite that best describes the field data and subsequent lab work of this study is Mantle Core complex and slab roll back models. These models support mantle uprising during an extensional event that whereby slab roll back of the subducting lithosphere provides uplift into a void and emplacement into the crust. Further extension and final exhumation causes rotation of a mantle wedge into its present day position.

  3. Constraints and inferences of conditions of seismic slip from analyses of exhumed faults

    NASA Astrophysics Data System (ADS)

    Evans, J. P.

    2008-12-01

    The study of exhumed faults, where constrained by geochemical or geochronologic evidence for depth of deformation, has provided abundant insights into the processes by which the upper crust accommodates strain. What remains elusive in these studies are: a] what evidence do we have for diagnosing [paleo] seismic slip, b ] how do we extrapolate the textures and composition of formerly active faults to constraining the conditions at depth, c] determining the conditions that promote seismic vs. aseismic slip, and d] to what degree do interseismic [healing] and post-slip processes exhumation affect what we see at the surface. Field evidence for the conditions that promote or are of diagnostic seismic vs. aseismic slip, is elusive, as there are few ways to determine seismic rates of slip in faults other than the presence of pseudotachylytes. Recent work on these rocks in a variety of settings and the increase in recognition of the presence of fault- related melts document the relationships between pseudotachylytes and cataclastically deformed rocks in what is thought to be the frictional regime, or with ductily deformed rocks at the base of a fault. Conditions that appear to promote seismic slip are alteration of granitic host rock to lower melting temperature phases and the presence of geometric complexities that may act as stress risers in the faults. Drilling into portions of faults where earthquakes occur at the top of the seismogenic zone have sampled fault-related rocks that have striking similarities to exhumed faults, exhibiting narrow slip surfaces, foliated cataclasites, injected gouge textures, polished slip surfaces, and thermally altered rocks along slip surfaces. We review the recent work from a wide range of studies to suggest that relatively small changes in conditions may initiate seismic slip, and suggest further avenues of investigation.

  4. Fault slip analysis and late exhumation of the Tauern Window, Eastern Alps

    NASA Astrophysics Data System (ADS)

    Bertrand, Audrey; Rosenberg, Claudio; Garcia, Sebastian

    2015-05-01

    Exhumation of the Eastern Alps from the early Tertiary to the late Miocene was localized mainly in the Tauern Window, a thermal and structural dome located in front of the Dolomites indenter. Stress inversions based on new structural investigations over the entire Tauern Window indicate a regional zoning of the paleostress field with a predominance of strike-slip states of stress in the core of the investigated area, and dominant extensional regimes in the eastern and western borders of the dome. Few inverse fault structures have been highlighted. We propose a two-stage deformation history in order to explain the different types of structures that characterise the ductile and the brittle domains. During the first stage of exhumation of the Tauern Window, corresponding to the folding event, the brittle crust was probably dominated by N-S shortening and compression. The second stage of exhumation was marked by normal faulting at the borders of the dome and strike-slip faulting in the core. During the second stage, the brittle part of the crust that was previously affected by compressive structures belonging to the first stage was eroded. Normal faulting associated to E-W extension along the eastern and western borders of the Tauern Window was accommodated by strike-slip faulting located in the core of the Tauern Window, yielding E-W extension and N-S shortening. The orientation of the extensional axes and the nature of the stress tensors are similar to the ones inferred for the late-stage, brittle overprint of the internal basement massifs of the Central Alps pointing to a possible common, large-scale, state of stress acting well beyond the area of the Eastern Alps.

  5. Kinematics of Cretaceous subduction and exhumation in the western Rhodope (Chalkidiki block)

    NASA Astrophysics Data System (ADS)

    Kydonakis, Konstantinos; Brun, Jean-Pierre; Sokoutis, Dimitrios; Gueydan, Frédéric

    2015-12-01

    In the Chalkidiki Peninsula of northern Greece a thrust complex made of a basement (Vertiskos Unit), a cover (Circum-Rhodope belt) and arc/back-arc units (Chortiatis Magmatic Suite and eastern Vardar Ophiolites) is exposed in the Chalkidiki Peninsula of northern Greece. The complex forms the western part of the Rhodope Metamorphic Province and lies on the hanging-wall of the Kerdylion Detachment, the structure responsible for the exhumation of the Southern Rhodope Core Complex and the most prominent and visible ductile structure related to the Tertiary Aegean extension. The Chalkidiki thrust complex arguably preserves a complete record of Cretaceous deformation and related fabrics. In this contribution we describe the geometry of foliation, stretching lineation and shear sense(s) on a regional scale. The regional foliation strikes NW-SE and displays different patterns in the three studied units: (i) dominantly dipping at low angle in the Vertiskos Unit, (ii) affected by upright folding in the Circum-Rhodope belt and (iii) systematically steeply dipping to the NE in the Chortiatis Magmatic Suite. Stretching lineation trend dominantly SW-NE in the three mentioned units. On the basis of new mapping, neglecting local perturbations and deformation related to Tertiary extension, we infer the regional kinematics of Cretaceous syn-metamorphic thrusting and subsequent exhumation of the metamorphic units. Thrusting took place toward the SW (in present-day coordination) and the related fabrics are recorded throughout the metamorphic pile. On the contrary, exhumation-related fabrics are related to shear toward the NE and are preferentially recorded in the uppermost part of the metamorphic pile suggesting that extension was more localised and of less finite intensity compared to thrusting.

  6. Influence of paleo-heat flow variations on estimates of exhumation rates

    NASA Astrophysics Data System (ADS)

    von Hagke, Christoph; Luijendijk, Elco

    2016-04-01

    Deriving exhumation estimates from thermochronological data requires assumptions on the paleo-thermal field of the Earth's crust. Existing thermal models take into account heat transfer by diffusion and advection caused by the movement of the crust and erosion as well as changes in geothermal gradient over time caused by changes in structure or thermal properties of the crust, surface temperature and elevation. However, temperature field of mountain belts and basins may vary not only due to tectonic activity or landscape evolution. We present a high-resolution thermochronology data set from the foreland fold-and-thrust belt of the European Alps that shows substantial variation of cooling rates probably caused by hydrothermal flow in the subsurface in the past. Tectonic blocks with uniform exhumation history show variations in cooling of up to 50°C. In addition, changes in cooling between two different fault blocks show opposite trend than expected by models of their tectonic history. The observed historic changes in paleo-geothermal gradients are equal in magnitude to a present-day thermal anomaly caused by the upward flow of warm fluids in the distal part of the foreland basin. The strong variations in geothermal gradients by fluid flow imply that straightforward interpretation of landscape evolution rates using thermochronology is not possible, unless the thermal effects of fluid flow are taken into account. This is of particular importance to studies where the amount of thermochronology data is limited and local hydrothermal anomalies could easily be interpreted as regional exhumation signals. On the other hand, our findings suggest that thermochronology offers new opportunities to constrain magnitude and timing of paleo-heat flow variations in the upper crust.

  7. Peneplains on Tibetan Plateau: a long-term archive of exhumation and slow erosion

    NASA Astrophysics Data System (ADS)

    Haider, Vicky; Dunkl, István; von Eynatten, Hilmar; Lin, Ding

    2010-05-01

    Peneplains are not only representative and well recognizable geomorphological features but also archives of slow erosion and long-term exhumation. In the Lhasa terrane between the Banggong Suture in the north and the Nyaingentangtha Mountain range in the south, especially in the area around lake Nam Co, peneplains were graved into Jurassic and Cretaceous granitic intrusions. Some peneplains are crossing massive Jurassic sandstone. Characteristic outstanding paleosurfaces are wide planar surfaces that extend over 1 km at different elevation. They are not to mix up with also present sub-recent, smaller sized plane surfaces which were formed by abrasion processes of the local lakes. We used low-temperature chronological methods such as (U-Th)/He and fission track (FT) for dating heavy minerals such as apatite and zircon to measure and extract information about processes like erosion and exhumation that are closely related to orogenic stacking and uplift. Around hundred samples in particular from Cretaceous to Eocene granites, volcanics and sedimentary rocks were taken from the peneplains and their surroundings. Apatite crystals from more than 25 samples and zircon crystals from ten samples have been successfully analysed by (U-Th)/He method. While (U-Th)/He apatite ages cluster in Paleocene and Eocene ranging from 38 to 60 Ma, apatite and zircon FT ages cluster in Late Cretaceous. The age clusters are internally consistent in areas smaller than 100 km2. This first thermochronological data lead us most surely to a Late Cretaceous to Early Tertiary thermotectonical event which is probably connected to erosion and planation of the paleosurface. The deposition of Late Cretaceous to Eocene siliciclastic sediments close to the currently exhumed peneplains are also evidence of such an event.

  8. Collision in the Central Alps: 2. Exhumation of high-pressure fragments

    NASA Astrophysics Data System (ADS)

    Brouwer, F. M.; Burri, T.; Berger, A.; Engi, M.

    2003-04-01

    In the Central Alps high-pressure metamorphic rocks are confined to but a few tectonic units. In the Adula nappe pressures range from about 12 kbar in the north, to 20 kbar in the south [1]. The Southern Steep Belt (SSB) is a high-strain zone at the contact between rocks deriving from Apulia and Eurasia. The SSB contains a tectonic composite of ortho and paragneisses, with widespread bands and lenses of mafic and ultramafic composition. Many of the mafic fragments are garnet-amphibolites or eclogites, with a highly variable degree of retrogression. Our petrological studies indicate that the HP rocks in the SSB show extensive variation in metamorphic pressure. In mafic fragments, pressures retained by assemblages predating the amphibolite facies overprint range from 8 to 21 kbar, while pressure estimates for some peridotites are >30 kbar. Some HP fragments show evidence of substantial heating during decompression. New Lu-Hf and Sm-Nd geochronology, in conjunction with previously published data, indicates a spread in ages obtained from the high-pressure metamorphic assemblage. Thermal models based on simplified kinematics produce computed PTt histories that resemble those documented in individual HP fragments [2]. The SSB is interpreted to represent an exhumed part of a Tectonic Accretion Channel (TAC, cf. [3]), assembled of numerous, relatively small fragments which reflect a variety of paths. The different residence times and exhumation rates reflect a protracted history of subduction and extrusion, in which the fragments moved independently from their current neighbours. Combination of thermal modelling and field-based studies improve our conceptual thinking on the dynamics of exhumation of high-pressure rocks in a convergent orogen. [1] Heinrich (1986) J. Pet. 27: 123-154 [2] Roselle et al. (2002) Amer. J. Sci. 302: 381-409 [3] Engi et al. (2001) Geology 29: 1143-1146

  9. Seismic valve as the main mechanism for sedimentary fluid entrapment within extensional basin: example of the Lodève Permian Basin (Hérault, South of France).

    NASA Astrophysics Data System (ADS)

    Laurent, D.; Lopez, M.; Chauvet, A.; Imbert, P.; Sauvage, A. C.; Martine, B.; Thomas, M.

    2014-12-01

    During syn-sedimentary burial in basin, interstitial fluids initially trapped within the sedimentary pile are easily moving under overpressure gradient. Indeed, they have a significant role on deformation during basin evolution, particularly on fault reactivation. The Lodève Permian Basin (Hérault, France) is an exhumed half graben with exceptional outcrop conditions providing access to barite-sulfides mineralized systems and hydrocarbon trapped into rollover faults of the basin. Architectural studies shows a cyclic infilling of fault zone and associated S0-parallel veins according to three main fluid events during dextral/normal faulting. Contrasting fluid entrapment conditions are deduced from textural analysis, fluid inclusion microthermometry and sulfide isotope geothermometer: (i) the first stage is characterized by an implosion breccia cemented by silicifications and barite during abrupt pressure drop within fault zone; (ii) the second stage consists in succession of barite ribbons precipitated under overpressure fluctuations, derived from fault-valve action, with reactivation planes formed by sulphide-rich micro-shearing structures showing normal movement; and (iii) the third stage is associated to the formation of dextral strike-slip pull-apart infilling by large barite crystals and contemporary hydrocarbons under suprahydrostatic pressure values. Microthermometry, sulfide and strontium isotopic compositions of the barite-sulfides veins indicate that all stages were formed by mixing between deep basinal fluids at 230°C, derived from cinerite dewatering, and formation water from overlying sedimentary cover channelized trough fault planes. We conclude to a polyphase history of fluid trapping during Permian synrift formation of the basin: (i) a first event, associated with the dextral strike-slip motion on faults, leads to a first sealing of the fault zone; (ii) periodic reactivations of fault planes and bedding-controlled shearing form the main mineralized

  10. Low temperature thermochronological constrains on the late exhumation of the Alpine foreland (Digne nappe, France).

    NASA Astrophysics Data System (ADS)

    Schwartz, S.; Gautheron, C.; Audin, L.; Dumont, T.; Nomade, J.; Pinna-Jamme, R.

    2015-12-01

    The frontal part of the southwestern Alpine belt is characterized by important compressional deformation marked by the emplacement of the Digne nappe and the formation of the Valavoire thrust-sheet. The final emplacement of this nappe is dated Late Miocene thanks to Tertiary continental molasses of the foreland basin that are involved in the famous Vélodrôme recumbent syncline and exposed in erosional windows. The stratigraphic series of the Digne nappe is made of ~5000 m thick Liassic to Eocene deposits, which overthrust the vélodrôme syncline. We performed a low temperature apatite fission tracks (AFT) and (U-Th)/He (AHe) study on detrital grains of Tertiary molasses in order to (i) characterize the thermal conditions during burial and exhumation and to (ii) propose a late tectonic evolution in the front of the European Alpine foreland. Tertiary molasses were sampled in two sites of the erosional windows at different elevations. Samples present dispersed AHe and AFT ages due to an incomplete resetting of both thermochronometers, expected for the lowest elevation samples. In detail, AHe ages ranges from 2±0.2 to 60.4±5.4 Ma, whereas central AFT ages range from 11±1 to 67±16 Ma. On both sites, the total and partial reset of the thermochronological data suggests a heating event after the sediment deposition. Using QTQt inverse modeling and He damage codes, we determined the samples thermal history. The results implied a common burial temperature at 110±5°C during ~5Ma and a similar exhumation starting at 6±1 Ma. From these results, we conclude that the thermal conditions during burial associated with the Digne nappe thrusting were sufficient to reset the detrital apatites. Using mean surface temperature of 10°C and typical thermal gradient from 25°C/km, our new data show that the Digne Nappe reached at least 4.5 to 3.6 km-thick on both sites before further erosion. We propose that the late exhumation occurred at ~6 Ma ago, before the Messinian incision

  11. Structural and thermochronometric evidence for multi-stage exhumation of southern Syros, Cycladic islands, Greece

    NASA Astrophysics Data System (ADS)

    Soukis, Konstantinos; Stockli, Daniel F.

    2013-06-01

    The Attic-Cycladic metamorphic-core complex province was formed during Miocene to recent regional back-arc extension in response to slab-rollback and gravitational collapse. The development of several metamorphic-core complexes along extensional low-angle detachment faults resulted in the exhumation of lower-plate rocks and the tectonic denudation of the upper plate that is only sparsely exposed throughout the Aegean Sea. One of these areas is in southern Syros where the tectonic configuration includes three tectonometamorphic units separated by two detachment faults. The lower-plate Cycladic Blueschist Unit underwent late Cretaceous-Eocene HP/LT metamorphism and subsequent greenschist-facies overprint during Oligo-Miocene times. The tectonically overlying greenschist-facies Upper Unit is a tectonic sliver between the Cycladic Blueschist Unit and the structurally highest unit, the Vari Unit, which is dominated by quartzofeldspathic gneisses that are affected by four distinct deformation events (D1-D4). The late Cretaceous upper greenschist-facies D1 episode is related to late Cretaceous-Eocene subduction while D2-D4 fabrics were formed in response to late Cenozoic extension and exhumation. Field relations and structural data suggest that the late Miocene brittle Vari Detachment juxtaposes both Vari Unit and Upper Unit against the Cycladic Blueschist Unit. Mylonitic rocks observed at the base of Vari Unit along the contact with Upper Unit and zircon and apatite (U-Th)/He thermochronometry corroborate this scenario with lower-plate Cycladic Blueschist Unit rocks recording rapid cooling at ~ 8-10 Ma. In contrast, cooling ages from the Vari Unit cluster at ~ 13-15 Ma, indicating rapid exhumation coeval with activity along the Livadi Detachment on the neighboring island of Tinos. These data document new evidence that Vari Unit was affected by a major middle Miocene phase of exhumation and an older semi-brittle episode, both unrelated to late Miocene detachment faulting

  12. The Tyrrhenian Basin: fault activity migration, focusing of deformation, break up, magmatism and fast mantle exhumation

    NASA Astrophysics Data System (ADS)

    Ranero, Cesar R.; Sallarés, Valenti; Vendrell, Montserrat G.; Prada, Manuel; Grevemeyer, Ingo; Zitellini, Nevio

    2015-04-01

    We present a new interpretation of the creation of the geological domains and the processes forming the Tyrrhenian basin by rifting of Cratonic Variscan lithosphere. The basin is not presently extending, but its crustal structure preserves information of the temporal evolution of rifting processes. Our work is based on the tectonic structure and stratigraphy of over 3000 km of calibrated multichannel seismic data and full coverage multibeam bathymetry of the basin. From these data circa 2000 km are new and about 1000 are vintage data. The seismic data are used to understand the formation of the domains (continental, backarc magmatism, exhumed mantle) defined with our recently published, under review, or submitted 5 across-the-basin wide-angle reflection and refraction transects. The 5 transects provide the Vp distribution of the crust and upper mantle. This information has allowed defining the petrological nature and distribution of the geological domains, and to infer the importance of magmatism in the rifting process, to constrain the location of break up and the expanse of the region of mantle exhumation. The seismic reflection images have been interpreted to map in time and space the evolution of the deformation across the basin. We analyzed the tectonic structure and mapped the calibrated stratigraphy across the basin to understand the temporal evolution and styles of faulting processes. The stratigraphy provides also constraints on the rates at which the different processes of extension, magmatism, break up and mantle exhumation have occurred. The basin has opened with different extension factors from north to south. The northern region stopped opening after a relatively low extension factors. Towards the south extension increased up to full crustal separation. Here extension in some areas was coeval with abundant magmatism. Changing in the locus of faulting and rates of extension led to break up and to a surprisingly fast mantle exhumation. Subsequent

  13. Progressive Extensional Exhumation of the Ultrahigh-Pressure Tso Morari Terrain, NW Indian Himalaya

    NASA Astrophysics Data System (ADS)

    Hodges, K.; Clark, R.; Monteleone, B.; Sachan, H.; Mukherjee, B. K.; Ahmad, T.

    2011-12-01

    The core of the Tso Morari dome in the Ladakh region of NW India (roughly 33 °10'N; 78°10'E) is one of only two known ultrahigh-pressure (UHP) terrains in the Himalayan-Tibetan orogenic system. The quartzofeldspathic Puga Orthogneiss from the structurally deepest portions of the terrain does not contain UHP mineralogy but surrounds dismembered lenses of mafic eclogite with accessory coesite, confirming that at least the eclogite lenses experienced UHP metamorphic conditions (Mukherjee et al., 2003, International Geology Review; Sachan et al., 2004, European Journal of Mineralogy). U-Pb zircon dates from the Puga orthogneiss (53.3 ± 0.7 Ma: Leech et al., 2007, International Geology Review) provide what appear to be the most precise available constraints on the age of UHP metamorphism at Tso Morari provided we presume that the UHP assemblages in the eclogite lenses developed at the same time as the 53.3 ± 0.7 Ma metamorphic zircon in the orthogneiss. However, other components of the zircon population studied by Leech and co-workers, as well as the results obtained using other thermochronometers and geochronometers (de Sigoyer et al., 2004, Tectonics), demonstrate that a series of lower pressure metamorphic events also affected the Tso Morari terrain between ca. 53 Ma and ca. 45 Ma, implying rapid decompression at elevated temperatures (ca. 800 - 350°C). Our 1:50000-scale geologic mapping at Tso Morari provides evidence that this exhumation was largely accommodated by two previously unrecognized low-angle ductile detachments that separate the terrain into three tectonostratigraphic units with distinctive metamorphic histories. The structurally lowest shear zone (Karla detachment) separates the Puga Orthogneiss from overlying lower amphibolite facies metasedimentary rocks of the Zoboshisha Unit, which contains no UHP assemblages. Structurally higher and demonstrably younger detachments separate the Zoboshisha Unit and the Puga Orthogneiss from greenschist to

  14. Does Late Miocene Exhumation Along the Western Slope of the Colorado Rockies Reflect Differential Rock Uplift?

    NASA Astrophysics Data System (ADS)

    Rosenberg, R. H.; Kirby, E.; Aslan, A.; Karlstrom, K. E.; Heizler, M. T.; Kelley, S. A.; Piotraschke, R. E.; Furlong, K. P.

    2011-12-01

    It is increasingly recognized that dynamic effects associated with changes in mantle flow and buoyancy can influence the evolution of surface topography. In the Rocky Mountain province of the western United States, recent seismic deployments reveal intriguing correlations between anomalies in the velocity structure of the upper mantle and regions of high topography. Here, we investigate whether regional correlations between upper-mantle structure and topography are associated with the history of Late Cenozoic fluvial incision and exhumation. Major tributaries of the upper Colorado River, including the Gunnison and Dolores Rivers, which drain high topography in central and western Colorado overlie upper mantle with slow seismic wave velocities; these drainages exhibit relatively steep longitudinal profiles (normalized for differences in drainage area and discharge) and are associated with ~1000-1500 m of incision over the past 10 Ma. In contrast, tributaries of the Green River that drain the western slope in northern Colorado (White, Yampa, and Little Snake Rivers) overlie mantle of progressively higher seismic wave velocities. River profiles in northern Colorado are two to three times less steep along reaches with comparable bedrock lithologies. New Ar39/Ar40 ages on ~11 Ma basalt flows capping the Tertiary Brown's Park Formation in northern Colorado indicate that the magnitude of exhumation along these profiles ranges from ~400 - 600 m over this time interval. The correspondence of steep river profiles in regions of greater incision implies that the fluvial systems are dynamically adjusting to an external forcing. New constraints on the exhumation history of the upper Colorado River from apatite fission track ages in boreholes near Rifle, Colorado are best explained by an onset of exhumation at ca. 8-10 Ma. Thus, relative base level fall associated with development of Grand Canyon (ca. 6-5 Ma) does not explain the regional onset of incision along the western slope

  15. Grain-rimming kaolinite in Permian Rotliegend reservoir rocks

    NASA Astrophysics Data System (ADS)

    Waldmann, Svenja; Gaupp, Reinhard

    2016-04-01

    Upper Rotliegend sediments of Permian age from the northeast Netherlands show moderate to good reservoir qualities. The predominant control is by the presence of authigenic grain-rimming kaolinite, which has a negative, but in some parts also a positive, effect on reservoir quality. To better understand the formation and distribution of grain-rimming kaolinite, reservoir rocks were studied in terms of composition and diagenetic processes. Petrographic evidence, summarized as a paragenetic sequence, is integrated with geochemical modeling results to identify early mesodiagenetic water-rock interactions under the participation of gases, i.e., CO2 and H2S, released from underlying Carboniferous source rocks. The sediments investigated were deposited at varying distance from the southern flank of the Southern Permian Basin. Sediments near the basin margin are mainly attributed to a fluvial environment and comprise medium to coarse-grained sandstones and conglomerates. There, vermicular kaolinite occurs with a lath-like structure. Distal to the basin margin, mainly in sandstones intercalated with fine-grained playa sediments, comparatively high amounts of grain-rimming kaolinite occur. There, the presence of this mineral has a significant influence on the rock properties and the reservoir quality. Geochemical modeling suggests that the formation of such kaolinites cannot be explained exclusively by in situ feldspar dissolution. The modeling results support evidence that kaolinite can be formed from precursor clay minerals under the presence of CO2-rich formation waters. Such clay minerals could be corrensite, smectite-chlorite mixed-layer minerals, or chlorite that is potentially present in Rotliegend sediments during early diagenesis. Furthermore, the geochemical modeling can reflect several mineral reactions that were identified from petrographic analysis such as the formation of illite and kaolinite at the expense of feldspar dissolution and consequent silica

  16. CENOZOIC EXHUMATION OF THE ANTIOQUEÑO PLATEAU, NORTHERN ANDES, COLOMBIA, FROM APATITE LOW-TEMPERATURE THERMOCHRONOLOGY

    NASA Astrophysics Data System (ADS)

    Restrepo-Moreno, S. A.; Foster, D. A.; O'Sullivan, P. B.; Donelick, R.; Stockli, D. F.

    2009-12-01

    The Antioqueño plateau (AP), in the northernmost Cordillera Central, Colombia, is the most extensive and best preserved relict surface in the Northern Andes. Apatite (U-Th)/He (AHe) and fission track (AFT) results from twenty two samples, collected from paleocrustal depths along two vertical profiles in canyons dissecting the AP, constrain Cenozoic erosional exhumation of this segment of the Andean range. The two profiles exhibit excellent reproducibility of AHe and AFT data. Helium ages increase with elevation from ~22-49 Ma. A marked inflection point in the AHe age-elevation plots at 25 Ma defines the bottom of the post-Oligocene He partial retention zone (PRZ). Virtually invariant ages at ~25 Ma record onset of rapid exhumation in the AP. A more subtle slope change in the PRZ at ~43 Ma is interpreted as a minor exhumation pulse. AFT better defines timing and intensity of Eocene exhumation. AFT ages for both profiles vary from ~30-49 Ma and are consistently older than AHe ages. AFT data display invariant ages (±2σ) between 1500-2400 m elevations while confined track length data exhibit uni-modal distributions with a mean track length of ~14.2 μm. Both facts indicate rapid cooling. This is further supported by virtually concordant AFT and AHe ages for both profiles between 1500 to 2200 m implying that rocks were exhumed from temperatures >120°C to below AHe closure temperature 60°C. Assuming a geothermal gradient of ~25°C/km this corresponds to exhumation rates in the order of 0.5 mm/y, comparable in intensity to the Miocene pulse defined by AHe. Integrated thermal modeling show an episode of rapid cooling at ~43-49 Ma. AFT profiles show an apparent inflection point at ~1400 m, which defines the upper boundary of an apatite partial annealing zone (PAZ) exhumed during the 43-49 Ma cooling event. The position of the PAZ and PRZ relative to the present erosional surface point to average erosion rates of ~0.03 mm/yr, which constitute very low denudation rates

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Eduction, extension, and exhumation of ultrahigh-pressure rocks in metamorphic core complexes due to subduction initiation

    NASA Astrophysics Data System (ADS)

    Petersen, Kenni Dinesen; Buck, W. Roger

    2015-09-01

    The controversy over the exhumation of ultrahigh-pressure (UHP) rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes "eduction," i.e., reverse subduction. We present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together: crust subducted deep enough is heated and weakened, causing limited diapiric rise, while crust subducted to shallower depths retains strength and is exhumed only by eduction. The model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence. This occurs spontaneously when subduction of buoyant crust causes a subduction zone to "lock up" in one place causing a new subduction zone to form in another. The model is consistent with many features of the youngest region of UHP rock exhumation on earth: the D'Entrecasteaux Islands. UHP exhumation and the amount of regional extension, as well as the seismic structure around the islands, can be explained by eduction. Ductile flow fabrics, seen on the islands, would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting. Reversal of motion on the north-dipping continental subduction zone, required by this model, was likely triggered by initiation of the New Britain Trench, as suggested previously. Our model implies that the crust of Goodenough Basin, south of the islands, was exhumed by eduction in the last 5 Ma and this hypothesis can be tested by drilling.

  19. An Early Permian fusuline fauna from southernmost Peninsular Thailand: Discovery of Early Permian warming spikes in the peri-Gondwanan Sibumasu Block

    NASA Astrophysics Data System (ADS)

    Ueno, Katsumi; Arita, Michiko; Meno, Satomi; Sardsud, Apsorn; Saesaengseerung, Doungrutai

    2015-05-01

    An Early Permian fusuline fauna is reported from the Tarn To Formation of the Yala area in southernmost Peninsular Thailand, which geotectonically belongs to the peri-Gondwanan Sibumasu Block. The fauna consists of Pseudofusulina and Praeskinnerella? species, including forms closely resembling Tethyan and Panthalassan Pseudofusulina fusiformis and Pseudofusulina ex gr. kraffti. A Yakhtashian-Bolorian age is estimated for this fauna. In Sibumasu, shallow-marine biotas showing similar Tethyan affinities, such as the fusulines Misellina and alatoconchid bivalves, also occur in the Early Permian succession of the Kinta Valley area in western Peninsular Malaysia. These unusual Tethyan faunas within Early Permian peri-Gondwanan fossil records suggest episodic influences from paleo-tropical Tethyan biotas. They are here interpreted as showing short-term warming spikes during the late Yakhtashian-Bolorian transgression, which would facilitate sporadic migration and temporal inhabitation of warm-water dwellers into the eastern Cimmerian areas. The Yala and Kinta Valley fusuline and other invertebrate faunas would give us a new insight for the Permian geohistory and environmental change of the peri-Gondwanan Sibumasu Block.

  20. Late-orogenic heating during exhumation: Alpine PTt trajectories and thermomechanical models

    NASA Astrophysics Data System (ADS)

    Brouwer, F. M.; van de Zedde, D. M. A.; Wortel, M. J. R.; Vissers, R. L. M.

    2004-03-01

    During the Alpine orogeny, the Penninic zone of the Alps was affected by Eoalpine high-pressure metamorphism. In the central and western Alps, this was followed by Lepontine medium-pressure, high-temperature metamorphism during exhumation. We compare the pressure-temperature-time (PTt) trajectories established in two key areas in the central and western Alps with 2-D numerical models of two possible causes of Lepontine metamorphism: (1) detachment or breakoff of a subducting slab, and (2) the presence of a wedge of accreted radiogenic material. Numerical models show that both mechanisms are capable of producing significant heating during orogeny. Heating by slab detachment is fast and transient (more than 100°C in up to 10 million years, depending on the location), whereas radiogenic heating requires time spans of the order of tens of millions of years and cessation of the subduction process. The combination of PTt trajectories and synthetic PT paths deduced from our thermomechanical modelling results suggests that the metamorphism observed in the central Alps has not been caused by radiogenic heating alone. Slab breakoff, on the other hand, seems a viable mechanism to account for the documented rise in metamorphic temperatures during exhumation. In view of the time constraints posed by the geological data, and acknowledging the effects of large-scale block rotations and out-of-section transport, slab detachment is also a more likely mechanism to have provided sufficient heat to cause re-heating in the western Alps.

  1. Deformation history of a subducted continental crust (Gran Paradiso, Western Alps): continuing crustal shortening during exhumation

    NASA Astrophysics Data System (ADS)

    Le Bayon, Benjamin; Ballèvre, Michel

    2006-05-01

    Eclogite-facies continental basement in the Western Alps outcrops as tectonic windows below the oceanic units. In the Gran Paradiso massif, eclogite-facies assemblages in mafic rocks display a N-S stretching lineation (D A1). The main-phase foliation formed under epidote amphibolite-facies conditions (D A2) and defines a regional dome structure for the whole Gran Paradiso massif. Structural data, including new detailed mapping, microstructural analyses and metamorphic studies in the northern part of the Gran Paradiso (Cogne valley) reveal the occurrence of major thrusts in this continental basement associated with the D A2 deformation. E-W-trending stretching lineations and fold axes are associated with this second and main deformation. Nappe stacking of the different units was achieved by top-to-the-west shearing during exhumation of the eclogite-facies basement. The antiformal doming of the Gran Paradiso basement is thus produced by the nappe stacking during exhumation, under epidote amphibolite facies.

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

    PubMed

    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. PMID:22687773

  3. Nb-Ta mobility and fractionation during exhumation of UHP eclogite from southwestern Tianshan, China

    NASA Astrophysics Data System (ADS)

    Zhang, Lijuan; Zhang, Lifei; Lü, Zeng; Bader, Thomas; Chen, Zhenyu

    2016-05-01

    In order to study the behavior of high field strength elements (HFSE) during retrograde overprint of ultrahigh-pressure (UHP) eclogites, analysis of Nb and Ta concentrations was carried out on bulk rock, rutile (in both veins and host rocks) and titanite in the host eclogite. The studied samples were collected from the UHP metamorphic belt of southwestern Tianshan, China. Petrographic observation and phase equilibria modeling show that the host eclogites have experienced UHP metamorphism and the rutile-bearing veins are thought to be originated from an internal fluid source, probably by lawsonite dehydration during exhumation. The presence of vein rutile indicates HFSE could be mobilized from host eclogites to veins, which is probably facilitated by complexation with dissolved Na-Al silicates and fluorine-rich fluids. Changes in fluid composition (e.g., F-1, X(CO2)) may trigger the precipitation of rutile. Rutile/fluid partitioning may be the key to fractionating Nb and Ta, with preference for Ta in the fluid, resulting in Nb/Ta ratio of rutile in the veins lower than that in the host eclogite. Besides, the transformation of rutile into titanite also might be an effective mechanism for fractionating Nb from Ta, resulting in the intra-grain Nb-Ta zonations in vein rutile. The Nb-Ta mobility and fractionation can happen during exhumation of the UHP eclogite, which should be very important for understanding the behavior of HFSE in subduction zone metamorphism.

  4. From nappe stacking to exhumation: Cretaceous tectonics in the Apuseni Mountains (Romania)

    NASA Astrophysics Data System (ADS)

    Reiser, Martin Kaspar; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard

    2016-05-01

    New Ar-Ar muscovite and Rb-Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on the timing and kinematics of deformation during the Cretaceous. Time-temperature paths from the structurally highest basement nappe of the Apuseni Mountains in combination with sedimentary data indicate exhumation and a position close to the surface after the Late Jurassic emplacement of the South Apuseni Ophiolites. Early Cretaceous Ar-Ar muscovite ages from structurally lower parts in the Biharia Nappe System (Dacia Mega-Unit) show cooling from medium-grade conditions. NE-SW-trending stretching lineation and associated kinematic indicators of this deformation phase (D1) are overprinted by top-NW-directed thrusting during D2. An Albian to Turonian age (110-90 Ma) is proposed for the main deformation (D2) that formed the present-day geometry of the nappe stack and led to a pervasive retrograde greenschist-facies overprint. Thermochronological and structural data from the Bihor Unit (Tisza Mega-Unit) allowed to establish E-directed differential exhumation during Early-Late Cretaceous times (D3.1). Brittle detachment faulting (D3.2) and the deposition of syn-extensional sediments indicate general uplift and partial surface exposure during the Late Cretaceous. Brittle conditions persist during the latest Cretaceous compressional overprint (D4).

  5. The thermal and structural evolution of the Ronda peridotite during exhumation

    NASA Astrophysics Data System (ADS)

    Johanesen, Katharine Elizabeth

    The Ronda peridotite massif of southern Spain exposes subcontinental lithospheric mantle that records pressure-temperature data and microstructures formed during exhumation beneath the rapidly extending Alboran domain. The peridotite is zoned from garnet- and spinel-bearing mylonites at the structural top, to spinel-bearing tectonites, to melt-percolated spinel-bearing granular peridotites, to plagioclase-bearing tectonites at the structural base. I find microstructural evidence of melt present in the spinel zones prior to the deformation event which exhumed the peridotites, and I, therefore, reinterpret the spinel tectonites as being a result of deformational overprinting of part of the granular domain. I also reinterpret garnet intergrown with spinel in the mylonite zone as part of the pre-mylonitic porphyroclast assemblage, rather than as a syn-mylonite assemblage. This places mylonite formation within the spinel field, rather than right on the garnet-spinel transition (18 kb). Two-dimensional thermal modeling indicates that these conditions require removal of lithospheric mantle below 100 km followed by exhumation along a low angle shear zone. Olivine crystallographic lattice preferred orientations (LPO) from these samples fall into three categories: A-type with a maximum of (010) poles normal to foliation and bands of (100) and (001) parallel to foliation, B-type with (010) poles normal to foliation and (100) parallel foliation and normal to lineation, and E-type with (100) parallel to lineation and (010) parallel foliation and normal to lineation. The garnet- and spinel-bearing mylonites and recrystallized grains in the spinel tectonites show A-type LPO, indicating dry conditions and moderate stresses during deformation. Coarse grains in the spinel tectonites and granular peridotites have a B-type LPO indicative of higher stresses and possible water contents. A shear zone that cross-cuts the granular peridotites has an E-type LPO, which suggests high water

  6. Plio-Pleistocene exhumation of the eastern Himalayan syntaxis and its domal 'pop-up'

    NASA Astrophysics Data System (ADS)

    Bracciali, Laura; Parrish, Randall R.; Najman, Yani; Carter, Andrew; Wijbrans, Jan R.; Smye, Andrew

    2016-04-01

    The eastern termination of the Himalayan orogen at the southern margin of the Tibetan Plateau forms a syntaxial antiform that folds the suture zone between the Indian and Asian plates and is characterised by 10 to < 1 Ma dates of various geo- and thermo-chronometers. These document Late Miocene to Pleistocene structural, metamorphic, igneous and exhumation events and a recent history of very rapid cooling. The northern third of the syntaxis corresponds to a steep domal 'pop-up' structure bounded by the India-Asia suture on three sides and a thrust zone to the south. One of the major rivers of the eastern Himalaya-Tibet region, the Yarlung Tsangpo, dissects the eastern syntaxis. The river becomes the Brahmaputra River in the Indian foreland basin before emptying into the Bay of Bengal. Exceptionally high relief and one of the deepest gorges on Earth have developed where the river's tortuous route crosses the Namche Barwa-Gyala Peri massif (> 7 km in elevation) in the core of the syntaxis. Downstream of the gorge very high erosion rates contribute ~ 50% of total detritus to the sediment load of the river. The initiation of the exceptional exhumation has been attributed either to the extreme erosive power of a river flowing across a deforming indentor corner and the positive feedback that would establish between the two, or to subduction geometry of a stiffened indentor corner. It has also been suggested that the growth of the antiformal structure and the exhumation of its high grade metamorphic core resulted from buckling as a means to accommodate shortening in the indentor corner. In this study [1] we provide new chronological data on the bedrock of the eastern syntaxis and its erosion products to date the inception of very rapid uplift and erosion and discuss its cause, with the ultimate aim to reconstruct the structural and exhumation history of the syntaxis. We use U-Pb zircon and rutile, white mica Ar-Ar and fission track zircon dating of bedrock, modern

  7. Continental subduction and exhumation of UHP rocks. Structural and geochronological insights from the Dabieshan (East China)

    NASA Astrophysics Data System (ADS)

    Faure, Michel; Lin, Wei; Schärer, Urs; Shu, Liangshu; Sun, Yan; Arnaud, Nicolas

    2003-10-01

    In the Dabieshan, the available models for exhumation of ultrahigh-pressure (UHP) rocks are poorly constrained by structural data. A comprehensive structural and kinematic map and a general cross-section of the Dabieshan including its foreland fold belt and the Northern Dabieshan Domain (Foziling and Luzenguang groups) are presented here. South Dabieshan consists from bottom to top of stacked allochtons: (1) an amphibolite facies gneissic unit, devoid of UHP rocks, interpreted here as the relative autochton; (2) an UHP allochton; (3) a HP rock unit (Susong group) mostly retrogressed into greenschist facies micaschists; (4) a weakly metamorphosed Proterozoic slate and sandstone unit; and (5) an unmetamorphosed Cambrian to Early Triassic sedimentary sequence unconformably covered by Jurassic sandstone. All these units exhibit a polyphase ductile deformation characterized by (i) a NW-SE lineation with a top-to-the-NW shearing, and (ii) a southward refolding of early ductile fabrics. The Central Dabieshan is a 100-km scale migmatitic dome. Newly discovered eclogite xenoliths in a Cretaceous granitoid dated at 102 Ma by the U-Pb method on titanite demonstrate that migmatization post-dates HP-UHP metamorphism. Ductile faults formed in the subsolidus state coeval to migmatization allow us to characterize the structural pattern of doming. Along the dome margins, migmatite is gneissified under post-solidus conditions and mylonitic-ultramylonitic fabrics commonly develop. The north and west boundaries of the Central Dabieshan metamorphics, i.e. the Xiaotian-Mozitan and Macheng faults, are ductile normal faults formed before Late Jurassic-Early Cretaceous. A Cretaceous reworking is recorded by synkinematic plutons. North of the Xiaotian-Mozitan fault, the North Dabieshan Domain consists of metasediments and orthogneiss (Foziling and Luzenguang groups) metamorphosed under greenschist to amphibolite facies which never experienced UHP metamorphism. A rare N-S-trending lineation

  8. Recrystallized microbial trace fossils from metamorphosed Permian basalt, southwestern Japan

    NASA Astrophysics Data System (ADS)

    Sugawara, H.; Sakakibara, M.; Ikehara, M.

    2014-05-01

    Microbial trace fossils on terrestrial basalts can be used as an analogue in the search for traces of life on other terrestrial planets. This study reports on microbial trace fossils within Permian greenstones in the Maizuru Terrane, southwest Japan, which is recognized as back-arc basin oceanic crust that consists mainly of metabasalt and metagabbro. The trace fossils have been studied by means of morphology, mineralogy, elemental mapping, and carbon isotope analysis. Although minute original textures of trace fossils are recrystallized in these rocks, Granulohyalichnus vulgaris isp., Tubulohyalichnus spiralis isp., and Tubulohyalichnus annularis isp. were identified. Significant concentration of C within the trace fossils implies these are organic remnants from microbes. The δ13CPDB values <-7‰ of calcite within the greenstones indicates that the bacterial activity took place prior to the formation of calcite veins. The results support that microbial trace fossils within low-grade metamorphic basalt can be reliably identified based on their morphology and chemical composition, as reveled by elemental mapping. In this context, glassy Martian basalt may be the best rock type to investigate in terms of searching for signs of microbial activity on Earth and other planets.

  9. Time-calibrated Milankovitch cycles for the late Permian

    PubMed Central

    Wu, Huaichun; Zhang, Shihong; Hinnov, Linda A.; Jiang, Ganqing; Feng, Qinglai; Li, Haiyan; Yang, Tianshui

    2013-01-01

    An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic–Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U–Pb dating. The evidence extends empirical knowledge of Earth’s astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic–Mesozoic transition. PMID:24030138

  10. Time-calibrated Milankovitch cycles for the late Permian.

    PubMed

    Wu, Huaichun; Zhang, Shihong; Hinnov, Linda A; Jiang, Ganqing; Feng, Qinglai; Li, Haiyan; Yang, Tianshui

    2013-01-01

    An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic-Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U-Pb dating. The evidence extends empirical knowledge of Earth's astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic-Mesozoic transition. PMID:24030138

  11. Extremely acid Permian lakes and ground waters in North America

    USGS Publications Warehouse

    Benison, K.C.; Goldstein, R.H.; Wopenka, B.; Burruss, R.C.; Pasteris, J.D.

    1998-01-01

    Evaporites hosted by red beds (red shales and sandstones), some 275-265 million years old, extend over a large area of the North American mid- continent. They were deposited in non-marine saline lakes, pans and mud- flats, settings that are typically assumed to have been alkaline. Here we use laser Raman microprobe analyses of fluid inclusions trapped in halites from these Permian deposits to argue for the existence of highly acidic (pH < 1) lakes and ground waters. These extremely acidic systems may have extended over an area of 200,000 km2. Modern analogues of such systems may be natural acid lake and groundwater systems (pH ~2-4) in southern Australia. Both the ancient and modern acid systems are characterized by closed drainage, arid climate, low acid-neutralizing capacity, and the oxidation of minerals such as pyrite to generate acidity. The discovery of widespread ancient acid lake and groundwater systems demands a re-evaluation of reconstructions of surface conditions of the past, and further investigations of the geochemistry and ecology of acid systems in general.

  12. A review of the Carboniferous and Permian trilobites of Australia.

    PubMed

    Vanderlaan, Tegan A; Ebach, Malte C

    2015-01-01

    The first complete review of the Carboniferous and Permian trilobite species found within Australia is presented to assess the current standing of Australian taxa in a modern systematic context. The review consists of four families, 20 genera and 61 known species from the early Tournaisian to Moscovian (358.9 Ma to 304 Ma), throughout New South Wales, Tasmania, Western Australia and Queensland. The revision also includes a revised anatomical nomenclature for Australian Carboniferous trilobites. Emended diagnoses are provided for seven genera and 28 species. The genus Thalabaria is placed within the subfamily Archegoninae, and the genera Australokaskia and Planokaskia are placed within Cummingellinae. The subgenera Brachymetopus (Spinimetopus), Bollandia (Capricornia), Australokaskia (Longilobus) and Australokaskia (Planilobus) are suppressed within Brachymetopus, Bollandia, Australokaskia, respectively. All Brachymetopus (Brachymetopus) maccoyi subspecies are elevated to species. Species of Linguaphillipsia are considered sensu lato until there is adequate revision of the entire genus. New combinations include the following: Aprathia semicircularis is reassigned to Weania; Aprathia applanata is questionably reassigned to Carbonocoryphe; and Phillipsia squamata is tentatively reassigned to Palaeophillipsia. The following have been synonymised: Conophillipsia with Monodechenella; Megaproetus with Pudoproetus; Weberiphillipsia with Palaeophillipsia; Weania (Rosehillia) with Schizophillipsia; Conophillipsia breviceps dungogensis with Monodechenella breviceps; Linguaphillipsia raglanensis with Linguaphillipsia stanvellensis; and Weberiphillipsia girvanensis with Palaeophillipsia collinsi. Carbonocoryphe (Winterbergia) elegans, Carbonocoryphe (Winterbergia) keepitensis and Winterbergia? waterhousei are considered representatives of indeterminate genera. PMID:25781767

  13. Permian nonmarine bivalve zonation of the East European platform

    NASA Astrophysics Data System (ADS)

    Silantiev, V. V.

    2014-01-01

    New finds and revision of available collections of nonmarine bivalves provided grounds for development of a zonal scale for terrestrial sequences of the Permian System based on species belonging to the genus Palaeomutela Amalitzky, 1891, which are characterized by regular changes in the structure of the shell hinge. The scale includes two parallel zonal successions that are based on the stratigraphic distribution and evolutionary trends of two morphological lineages of the genus. The zonal succession based on development of the P. umbonata group (dwellers of mobile waters and silty-psammitic substrates) includes 11 range zones: stegocephalum, ovatiformis, umbonata, quadriangularis, krotowi, wohrmani, numerosa, ulemensis, keyserlingi, curiosa, golubevi. The zonal succession based on development of the P. castor group (dwellers of calm waters and silty-pelitic substrates) includes eight range zones: larae, castor, olgae, doratioformis, marposadica, fischeri, obunca, amalitzkyi. The proposed zonal units are correlated with scales based on ostracod, fish, and tetrapod fossils. New species Palaeomutela golubevi sp. nov. and P. amalitzkyi sp. nov. are described with the extended diagnosis of the genus Palaeomutela.

  14. Complete tylosis formation in a latest Permian conifer stem

    PubMed Central

    Feng, Zhuo; Wang, Jun; Rößler, Ronny; Kerp, Hans; Wei, Hai-Bo

    2013-01-01

    Background and Aims Our knowledge of tylosis formation is mainly based on observations of extant plants; however, its developmental and functional significance are less well understood in fossil plants. This study, for the first time, describes a complete tylosis formation in a fossil woody conifer and discusses its ecophysiological implications. Methods The permineralized stem of Shenoxylon mirabile was collected from the upper Permian (Changhsingian) Sunjiagou Formation of Shitanjing coalfield, northern China. Samples from different portions of the stem were prepared by using the standard thin-sectioning technique and studied in transmitted light. Key Results The outgrowth of ray parenchyma cells protruded into adjacent tracheids through pits initially forming small pyriform or balloon-shaped structures, which became globular or slightly elongated when they reached their maximum size. The tracheid luminae were gradually occluded by densely spaced tyloses. The host tracheids are arranged in distinct concentric zones representing different growth phases of tylosis formation within a single growth ring. Conclusions The extensive development of tyloses from the innermost heartwood (metaxylem) tracheids to the outermost sapwood tracheids suggests that the plant was highly vulnerable and reacted strongly to environmental stress. Based on the evidence available, the tyloses were probably not produced in response to wound reaction or pathogenic infection, since evidence of wood traumatic events or fungal invasion are not recognizable. Rather, they may represent an ecophysiological response to the constant environmental stimuli. PMID:23532049

  15. The Alashan Terrane did not amalgamate with North China block by the Late Permian: Evidence from Carboniferous and Permian paleomagnetic results

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Yang, Zhenyu

    2015-05-01

    Rock magnetic and paleomagnetic studies have been carried out on the early Carboniferous limestones and the Late Permian purple sandstones sampled in the eastern Alashan Terrane (ALT), northwest of China. Two components were isolated from the Early Carboniferous limestone by thermal progressive demagnetisation: a low unblocking temperature component (LTC) of recent origin; a pre-folding medium temperature component (MTC) (the paleomagnetic pole is λ = 13.1°N, Ф = 11.0°E, A95 = 7.0°) that is probably the result of the hydrothermal fluids from the Qilian Orgenic Belt acquired during the Late Carboniferous-Early Permian. Also, two components were separated from the Late Permian purple sandstone by thermal progressive demagnetisation: the LTC with the recent viscous remanent magnetisation, and the higher temperature component (HTC) revealed from three sections which has passed a regional fold test at the 95% probability level and reversal test, suggesting a primary characteristic magnetisation. The corresponding paleomagnetic pole is λ = 27.2° N, Ф = 18.8° E, A95 = 12.0°. The apparent polar wander path (including early Carboniferous, late Carboniferous-Early Permian, Late Permian and Early-middle Triassic poles) of the ALT is significantly different with those of the NCB. Comparison of the APWPs between the ALT and NCB shows a strong similarity. If the APWP of Hexi Corridor-Alashan rotated counterclockwise around an Euler pole at 44°N, 84°E by 32°, then the coeval APW path of the ALT overlaps to that of the NCB. This result indicates that the ALT migrated to the NCB after the Early-Middle Triassic along a tectonic boundary located between Helanshan Mountain and Zhuozishan Mountain, and finally amalgamated to the NCB before the Early Cretaceous.

  16. Permian and Triassic microfloral assemblages from the Blue Nile Basin, central Ethiopia

    NASA Astrophysics Data System (ADS)

    Dawit, Enkurie L.

    2014-11-01

    Palynological investigation was carried out on surface samples from up to 400 m thick continental siliciclastic sediments, here referred to as “Fincha Sandstone”, in the Blue Nile Basin, central Ethiopia. One hundred sixty species were identified from 15 productive samples collected along a continuous road-cut exposure. Six informal palynological assemblage zones have been identified. These assemblage zones, in ascending order, are: “Central Ethiopian Permian Assemblage Zone - CEPAZ I”, earliest Permian (Asselian-Sakmarian); “CEPAZ II”, late Early Permian (Artinskian-Kungurian); CEPAZ III - Late Permian (Kazanian-Tatarian); “CETAZ IV”, Lower Triassic (Olenekian Induan); “CETAZ V”, Middle Triassic (Anisian Ladinian); “CETAZ VI”, Late Triassic (Carnian Norian). Tentative age ranges proposed herein are compared with faunally calibrated palynological zones in Gondwana. The overall composition and vertical distribution of miospores throughout the studied section reveals a wide variation both qualitatively and quantitatively. The high frequency of monosaccate pollen in CEPAZ I may reflect a Glossopterid-dominated upland flora in the earliest Permian. The succeeding zone is dominated by straite/taeniate disaccate pollen and polyplicates, suggesting a notable increase in diversity of glossopterids. The decline in the diversity of taeniate disaccate pollen and the concomitant rise in abundance of non-taeniate disaccates in CEPAZ III may suggest the decline in Glossopteris diversity, though no additional evidence is available to equate this change with End-Permian extinction. More diverse and dominant non-taeniate, disaccate, seed fern pollen assignable to FalcisporitesAlisporites in CETAZ IV may represent an earliest Triassic recovery flora. The introduction of new disaccate forms with thick, rigid sacci, such as Staurosaccites and Cuneatisporites, in CETAZ V and VI may indicate the emergence of new gymnospermous plants that might have favourably

  17. Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution.

    PubMed

    Romano, Carlo; Koot, Martha B; Kogan, Ilja; Brayard, Arnaud; Minikh, Alla V; Brinkmann, Winand; Bucher, Hugo; Kriwet, Jürgen

    2016-02-01

    The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end-Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian-Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian-Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, 'Palaeopterygii', 'Subholostei', Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the Permian to higher levels in the Triassic. Diversity dynamics in the Permian are marked by a decline in freshwater taxa during the Cisuralian. An extinction event during the end-Guadalupian crisis is not evident from our data, but 'palaeopterygians' experienced a significant body size increase across the Guadalupian-Lopingian boundary and these fishes upheld their position as large, top predators from the Late Permian to the Late Triassic. Elevated turnover rates are documented at the Permian-Triassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the Early Triassic (dipnoans, actinistians, 'palaeopterygians', 'subholosteans') and a second one during the Middle Triassic ('subholosteans', neopterygians). The origination of new, small taxa predominantly among these groups during the Middle Triassic event caused a

  18. Bioessential element-depleted ocean following the euxinic maximum of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Takahashi, Satoshi; Yamasaki, Shin-ichi; Ogawa, Yasumasa; Kimura, Kazuhiko; Kaiho, Kunio; Yoshida, Takeyoshi; Tsuchiya, Noriyoshi

    2014-05-01

    We describe variations in trace element compositions that occurred on the deep seafloor of palaeo-superocean Panthalassa during the end-Permian mass extinction based on samples of sedimentary rock from one of the most continuous Permian-Triassic boundary sections of the pelagic deep sea exposed in north-eastern Japan. Our measurements revealed low manganese (Mn) enrichment factor (normalised by the composition of the average upper continental crust) and high cerium anomaly values throughout the section, suggesting that a reducing condition already existed in the depositional environment in the Changhsingian (Late Permian). Other redox-sensitive trace-element (vanadium [V], chromium [Cr], molybdenum [Mo], and uranium [U]) enrichment factors provide a detailed redox history ranging from the upper Permian to the end of the Permian. A single V increase (representing the first reduction state of a two-step V reduction process) detected in uppermost Changhsingian chert beds suggests development into a mildly reducing deep-sea condition less than 1 million years before the end-Permian mass extinction. Subsequently, a more reducing condition, inferred from increases in Cr, V, and Mo, developed in overlying Changhsingian grey siliceous claystone beds. The most reducing sulphidic condition is recognised by the highest peaks of Mo and V (second reduction state) in the uppermost siliceous claystone and overlying lowermost black claystone beds, in accordance with the end-Permian mass extinction event. This significant increase in Mo in the upper Changhsingian led to a high Mo/U ratio, much larger than that of modern sulphidic ocean regions. This trend suggests that sulphidic water conditions developed both at the sediment-water interface and in the water column. Above the end-Permian mass extinction horizon, Mo, V and Cr decrease significantly. On this trend, we provide an interpretation of drawdown of these elements in seawater after the massive element precipitation event

  19. Development of the Permian-Triassic unconformity in southwestern Utah, southeastern Nevada and northwestern Arizona

    SciTech Connect

    Nielson, R.L. . Dept. of Geology)

    1993-04-01

    Development of positive areas, that are oriented northwest-southeast in south-western Utah, southeastern Nevada, and northwestern Arizona, are indicated by the depositional patterns of the Rock Canyon Conglomerate and facies changes produced by on-lapping during the deposition of the Timpoweap, Lower Red, and Virgin Limestone Members of the Moenkopi Formation. The lack of facies change in the Kaibab Formation indicates that uplift of the positive areas did not start during the early Permian. The Fossil Mountain Member of the Kaibab Formation, is a marker of continuous shallow marine sedimentation across the area. The Harrisburg Member contains three limestone units, separated by gypsum and shale units, that represent regressions and transgressions. Where the gypsum in the Kaibab Formation thins, collapse breccia and deformed shale units are present indicating that the gypsum was deposited and then removed by dissolution. Channels cut during the late Permian and early Triassic Periods do not cut through the Harrisburg Member of the Kaibab Formation. West of St. George, Utah, where the gypsum deposits are thickest, is the location where Timpoweap, Lower Red, and Virgin Limestone members thin and are absent. Late Permian and early Triassic topography may have in part been controlled by dissolution of the gypsum deposits in the Kaibab Formation. The low angle of discordance between Permian and Triassic units indicated that the area was not subjected to major deformation during the late Permian and early Triassic, but was gently tilted and uplifted.

  20. The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa

    NASA Astrophysics Data System (ADS)

    Modesto, Sean P.; Smith, Roger M. H.; Campione, Nicolás E.; Reisz, Robert R.

    2011-12-01

    We report on a partial varanopid skull and mandible from the Pristerognathus Assemblage Zone of the Beaufort Group, in the South African Karoo Basin, which is probably latest Middle Permian (Capitanian) in age. This mycterosaurine is not only the youngest known varanopid from the Southern Hemisphere, but it is also the youngest known "pelycosaur" (i.e., non-therapsid synapsid). Like all other members of this clade of hypercarnivores, the teeth are strongly flattened, recurved, and have finely serrated cutting edges. The anterior dentary teeth form a caniniform region, and the splenial features a foramen intermandibularis oralis, the first ever to be described in a "pelycosaur." The last varanopids were the smallest carnivores of latest Middle Permian continental faunas. Occupation of the small carnivore guild appears to have allowed varanopids to achieve a nearly cosmopolitan distribution throughout the Middle Permian, between the great Early Permian radiation of basal synapsids and the spectacular diversification of therapsid synapsids in the Late Permian and Early Triassic.

  1. Permian tectonism in Rocky Mountain foreland and its importance in Exploration for Minnelusa and Lyons sandstones

    SciTech Connect

    Moore, W.R.

    1985-05-01

    Permian sandstones are important producers of oil in the Powder River and Denver basins of the Rocky Mountain foreland region. In the Powder River basin, Wolfcampian Minnelusa Sandstone produces oil from structural and stratigraphic traps on both sides of the basin axis, whereas in Denver basin, the Leonardian Lyons Sandstone produces oil mainly from structural traps on the west flank of the basin. Two fields, North Fork-Cellars Ranch in the Powder River basin, and Black Hollow in the Denver basin, are examples of Permian growth of structural features. At North Fork-Cellars Ranch, a period of Permian structural growth and resultant differential sedimentation is documented by structure and isopach maps of the Minnelusa and overlying Goose Egg Formation. Structural growth began at the end of Minnelusa deposition and resulted in deposition of a much thicker Goose Egg section on the west flank of the field. At Black Hollow, mapping indicates structural growth was initiated before deposition of the Lyons Sandstone and continued throughout Leonardian time. In both fields growth abruptly ceased in the Late Permian. Both North Fork-Cellars Ranch and Black Hollow are located on structural highs, or arches, which trend east-west across the Powder River and Denver basins. These arches were present during the pre-Laramide migration of Paleozoic-sourced hydrocarbons into the basins and acted as pathways for migration. Exploration for Permian reservoirs in the two basins should be concentrated on the arches, as the early formed traps were present when migration began.

  2. Paleomagnetism and question of original location of the Permian Brook Street Terrane, New Zealand

    NASA Astrophysics Data System (ADS)

    Haston, Roger B.; Luyendyk, Bruce P.; Landis, C. A.; Coombs, D. S.

    1989-08-01

    Over 400 rock samples from 30 sites were collected for paleomagnetic study from the volcanogenic section in the Brook Street terrane within the Takitimu Mountains in western Southland, New Zealand. The section includes igneous and sedimentary rocks of the Permian Takitimu Group and White Hill Intrusive Suite. Many of the samples show a partial or complete remagnetization in the present field because of a recent acquisition of viscous remanent magnetization. An Early Permian direction (inclination = 46.1°, declination = 257°), isolated from the Heartbreak and Chimney Peaks formations of the Takitimu Group, indicates a low paleolatitude to midpaleolatitude, position (27° ± 5°) for the Brook Street terrane. Directions from the Late Permian (?) White Hill Intrusives (inclination = 64.6°, declination = 173.3°) suggest a slightly higher paleolatitude than the Early Permian Takitimu Group directions and 70°-90° of intervening clockwise rotation. Plate reconstructions and paleomagnetic data predict a high paleolatitude for the New Zealand margin of Gondwana throughout the late Paleozoic and Mesozoic. The low paleolatitude to middle paleolatitude, implied by the Early Permian Brook Street result, together with the oceanic nature of the Brook Street arc, suggest that the Brook Street terrane is allochthonous to the margin of Gondwana. A published Late Triassic/Early Jurassic paleomagnetic pole from the adjacent Murihiku terrane indicates a high paleolatitude. This suggests that the Brook Street and Murihiku terranes are genetically distinct.

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

    NASA Astrophysics Data System (ADS)

    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

  4. Time and duration of metamorphism and exhumation of the central Rhodopian core complex, Bulgaria

    NASA Astrophysics Data System (ADS)

    Ovtcharova, M.; von Quadt, A.; Peytcheva, I.; Neubauer, F.; Heinrich, C. A.; Kaiser, M.

    2003-04-01

    The evolution of central Rhodopian dome (Bulgaria) is interpreted in terms of an extensional collapse of thickened crust (Ivanov at al., 2000). U-Pb isotope dating (single Zr and Mnz), Rb-Sr (W.R., Bt and Ap) and Ar-Ar (on Bt) were carried out on different rocks from the central Rhodope, Bulgaria, to constrain the timing and duration of the metamorphism and exhumation of the core complex. The beginning of extensional stage is marked by intrusion of earliest non-penetratively deformed granite bodies at 53Ma (U-Pb on single Zr and Mnz). The late Alpine extensional evolution of the massif is marked by a detachment system connected with exhumation of the migmatites in the core part of the dome (lower plate). U-Pb analyses on Mnz and Zr from mesosome and discordant leucosome yield a Variscan protolith age of the gneiss (311 Ma) and Eocene age (37Ma) of crystallization of the newly formed anatectic melt that corresponds with the peak of the Alpine metamorphic event (P 4.5-6kbar and T 720-750^oC; Georgieva et al., 2002). Rb-Sr mineral system of the weakly deformed gneisses from lower plate of the core complex gives evidence for a cooling age of 34.5±0.34Ma. This result is confirmed by Ar-Ar on Bt from the same rock: 35.5±0.4Ma. Ar-Ar data on biotite from gneisses of the upper plate yield an age of 34.9±0.6Ma. The same age is reflected by an Rb-Sr isochron (W.R., Bt and Ap) of 35.22±0.35Ma. The post-collisional extension was followed by graben depressions filled with sediments of Eocene-Oligocene age and active volcanism and ore mineralization (Zn-Pb and Cu-Pb-Zn ore deposits). Connected with the most intensively "stretched" sections of the extensional system is emplacement of rhyolitic dikes at 32.8±0.41Ma (U-Pb on single Zr, Xe). The available data constrain narrow time bracket between timing of high-grade metamorphism event (37Ma, >600^oC), cooling (35Ma, 300ºC) of the core complex and volcanic activity (32Ma) that corresponds with rapid exhumation tectonic regime

  5. Dynamics of subduction, accretion, exhumation and slab roll-back: Mediterranean scenarios

    NASA Astrophysics Data System (ADS)

    Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

    2010-12-01

    A dynamic orogen reveals various tectonic processes brought about by subduction: accretion of oceanic and continental crust, exhumation of UHP-HP rocks, and often, back-arc extension. In the Mediterranean, orogeny is strongly affected by slab retreat, as in the Aegean and Tyrrhenian Seas. In order to examine the different dynamic processes in a self-consistent manner, we perform a parametric study using the fully coupled thermo-mechanical numerical code PARAFLAM. The experiments reproduce a subduction zone in a slab pull mode, with accretion of one (the Tyrrhenian case) and two continental blocks (the Aegean case) that undergo, in sequence, thrusting, burial and exhumation. The modeling shows that despite differences in structure between the two cases, the deformation mechanisms are fundamentally similar and can be described as follows. The accretion of a continental block at the trench beneath the suture zone begins with its burial to UHP-HP conditions and thrusting. Then the continental block is delaminated from its subducting lithosphere. During the subduction-accretion process, the angle of the subducting slab increases due to the buoyancy of the continental block. When the oceanic subduction resumes, the angle of the slab decreases to reach a steady-state position. The Aegean and Tyrrhenian scenarios diverge at this stage, due naturally to the differences of their accretion history. When continental accretion is followed by oceanic subduction only, the continental block that has been accreted and detached stays at close to the trench and does not undergo further deformation, despite the continuing rollback. The extensional deformation is located further within the overriding plate, resulting in continental breakup and the development of an oceanic basin, as in the Tyrrhenian domain. When the continental accretion is followed first by oceanic subduction and then by accretion of another continental block, however, the evolution of the subduction zone is

  6. Evolution of Continental Lower Crust Recorded By an Exhumed Deep Crustal Intracontinental Shear Zone

    NASA Astrophysics Data System (ADS)

    Dumond, G.; Mahan, K. H.; Regan, S. P.; Williams, M. L.; Goncalves, P.; Wood, V. R.

    2014-12-01

    Exposures of deep crustal shear zones are fundamental records of strain localization and the temporal evolution of ductile to brittle behavior as these tectonites were exhumed to the surface. We present results from a decade of field-based research on a deeply exhumed (~35 km-paleodepths) strike-slip shear zone in the western Churchill province of the Canadian Shield. The Grease River shear zone is a >400 km-long and 7 km-thick structure that cuts the Athabasca granulite terrane, North America's largest exposure of continental lower crust (>20,000 km2). The shear zone is dominated by granulite- to amphibolite-grade L-S and L>S tectonites characterized by penetrative NE-striking steeply-dipping foliations with gently-plunging to sub-horizontal stretching and intersection lineations. These fabrics are locally overprinted by pseudotachylyte and narrow (<500 m-thick) greenschist-grade zones of cataclasite. Dextral kinematics are defined by deflected foliation trajectories, C' shear bands, and well-developed σ- and δ-type porphyroclasts of Kfs + Pl + Opx + Grt + Hb in felsic to intermediate granulite paragneisses and orthogneisses. Data collected along a well-exposed, nearly 150 km-long segment of the shear zone documents a >100 m.y. episodic record of transpressive to strike-slip intracontinental strain accumulation that coincided with two oppositely convergent orogenies: the east-vergent arc-continent collision of the 1.94-1.90 Ga Taltson orogen and the west-vergent continent-continent collision of the 1.9-1.8 Ga Trans-Hudson orogen. Deformation mechanisms evolved from distributed ductile dynamic recrystallization and grain-size reduction to localized pseudotachylyte development, cataclastic flow, and brittle faulting. Lower crustal behavior during strain localization was dynamic. Melt-weakened mono-cyclic crust was juxtaposed against strong isobarically-cooled poly-cyclic crust along the shear zone at 1.92-1.90 Ga. Brittle-ductile reactivation of the structure

  7. How does the lithosphere deformation mode during continental breakup affect mantle exhumation and subsidence history?

    NASA Astrophysics Data System (ADS)

    Jeanniot, L.; Kusznir, N.; Manatschal, G.

    2012-04-01

    Mantle exhumation at magma-poor rifted continental margin requires that continental crust ruptures prior to the onset of significant decompression melting. Both the relative timing of crustal rupture and melting, and therefore mantle exhumation, and rifted margin subsidence are dependent on the deformation mode of the continental lithosphere stretching and thinning leading to breakup. Fletcher et al. (2009) showed that for the Iberia-Newfoundland rifted margin, modelling of continental lithosphere stretching and thinning by pure-shear resulted in decompression melt initiation before continental crustal-rupture, while stretching and thinning by upwelling-divergent "corner flow" resulted in crustal-rupture before melt initiation. Observations at rifted continental margins (including Iberia-Newfoundland rifted margin) suggest a complex rifting evolution that cannot be explained by simplistic end-member pure-shear or "corner flow" deformation modes of lithosphere thinning and stretching (Péron-Pinvidic and Manatschal, 2009). By analogy with the deformation processes occurring at slow spreading ocean-ridges (Cannat, 1996), a more realistic lithosphere deformation mode for magma-poor continental breakup is extensional faulting for the colder brittle upper 12-15km above upwelling-divergent "corner flow" for the remaining lithosphere and asthenosphere. We use a kinematic numerical model of continental lithosphere thinning and stretching to examine decompression melt initiation, continental crustal rupture and subsidence for such a hybrid lithosphere deformation model represented by pure-shear deformation in the topmost brittle lithosphere above upwelling-divergent flow. We explore the relative contributions of pure-shear and upwelling-divergent "corner flow" deformation and its sensitivity to deformation rate, pure-shear half-width, the "corner flow" Vz/Vx ration and mantle potential temperature. The kinematic numerical model that we use represents lithosphere and

  8. Glacial morphology in the Chinese Pamir: Connections among climate, erosion, topography, lithology and exhumation

    NASA Astrophysics Data System (ADS)

    Schoenbohm, Lindsay M.; Chen, Jie; Stutz, Jamey; Sobel, Edward R.; Thiede, Rasmus C.; Kirby, Benjamin; Strecker, Manfred R.

    2014-09-01

    Modification of the landscape by glacial erosion reflects the dynamic interplay of climate through temperature, precipitation, and prevailing wind direction, and tectonics through rock uplift and exhumation rate, lithology, and range and fault geometry. We investigate these relationships in the northeast Pamir Mountains using mapping and dating of moraines and terraces to determine the glacial history. We analyze modern glacial morphology to determine glacier area, spacing, headwall relief, debris cover, and equilibrium line altitude (ELA) using the area x altitude balance ratio (AABR), toe-to-headwall altitude ratio (THAR) and toe-to-summit altitude method (TSAM) for 156 glaciers and compare this to lithologic, tectonic, and climatic data. We observe a pronounced asymmetry in glacial ELA, area, debris cover, and headwall relief that we interpret to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers of the upwind, fault-controlled side of the range. We explain this by the transfer of moisture deep into the range as wind-blown or avalanched snow and by limitations imposed on glacial area on the upwind side of the range by the geometry of the Kongur extensional system (KES). The correspondence between rapid exhumation along the KES and maxima in glacier debris cover and headwall relief and minimums in all measures of ELA suggest that taller glacier headwalls develop in a response to more rapid exhumation rates. However, we find that glaciers in the Muji valley did not extend beyond the range front until at least 43 ka, in contrast to extensive glaciation since 300 ka in the south around the high peaks, a pattern which does not clearly reflect uplift rate. Instead, the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) with flanking glaciers likely reflects

  9. From crustal thinning to mantle exhumation: what the Pyrenean breccia formations tell us.

    NASA Astrophysics Data System (ADS)

    Clerc, C.; Chauvet, A.; Lagabrielle, Y.; Reynaud, J.-Y.; Boulvais, P.; Bousquet, R.; Lahfid, A.; Vauchez, A.; Mahé, S.

    2012-04-01

    Several formations with various breccia types occur in Mesozoic basins disseminated along the North Pyrenean fault, on the northern flank of the French Pyrenees. Due to their location along the Iberia-Europa plate boundary, the North Pyrenean breccia formations represent complex archives documenting the tectonic and sedimentary evolution of the Pyrenean realm during the Aptian-Albian period. In particular, the North Pyrenean breccia formations have recorded the main stages of crustal thinning, continental break-up and mantle exhumation, which occurred along the North Pyrenean Zone (NPZ). We will review the main sedimentary, structural, metamorphic and geochemical characters of these breccias, based on new field investigations conducted in both the Western and Eastern Pyrenées (Agly, Aulus, Moncaup-St Béas and Urdach localities). Based on our new founding, we re-intrepret the significance of the breccia formations in the light of the most recent models developed for the pre-orogenic evolution of the Pyrenees. In several places and mostly close to the contact between Paleozoic basement and Mesozoic cover, we systematically recognized the following three types of breccias: i) Semi-ductile syn-metamorphic breccias resulting from the boudinage of silicic or dolomitic beddings in ductily deformed marbles. ii) Cataclastic breccias disturbing the neighbouring host rocks and displaying a relatively monogenetic character. These tectonic breccias result from the disruption of the Mesozoic metamorphic platform under cooling conditions. They are dominated by cataclastic levels mainly located in the Triassic and Liassic weaker levels, iii) Polymictic sedimentary breccias, which composition is dominated by clasts of Mesozoic metasediments. Locally, close to subcontinental mantle bodies, the sedimentary breccias include numerous clasts of ultramafic and/or crustal basement rocks. Such breccias are the witness of the disruption of the sedimentary cover of the North Pyrenean Zone

  10. Uplift, exhumation and erosion along the Angolan continental margin: an integrated approach

    NASA Astrophysics Data System (ADS)

    Gröger, Heike R.; Machado, Vladimir; Di Pinto, Giuseppe

    2013-04-01

    The topographical development along the SW African margin is not exclusively rift-related. In addition to the onset of rifting in the Early Cretaceous, additional Late Cretaceous and Cenozoic events of uplift, exhumation and erosion are discussed. Thermochronology has proven to be a valuable tool to constrain phases of exhumation in passive continental margins. For South Africa and Namibia a large number of thermochronological data are available. Angola on the other hand is still scarcely investigated. This study is based on thermochronological data from onshore Angola, integrated with quantitative morphotectonic analysis and the on- and offshore stratigraphic record. In South Africa and Namibia published thermochronological data document pronounced Early and Late Cretaceous cooling events, which can be related to 2.5-3.5 km of removed section during the Cretaceous. An additional 1-2 km of removed section are estimated during the Cenozoic. In Angola predominantly Permo-Triassic apatite fission track ages indicate significantly less Cretaceous to Cenozoic erosion (< 2.5 km). The apatite fission track data do not provide high resolution constraints on the syn-post rift topographical development along the Angolan margin. However, thermal modelling points to a pronounced Miocene final cooling event. River bed topography upstream the Angolan escarpment is in equilibrium, while the escarpment itself forms a major knick zone. Downstream the main knick point towards the coast, river long-profiles are characterised by convex reaches which are the evidence of an immature, non steady-state topography. Estimation from knick point migration reveals about 1 km uplift within the Cenozoic (< 57 Ma). Published basin reconstructions offshore South Africa and Namibia confirm the general picture of pronounced Cretaceous erosion in the offshore sedimentary record of the basins south of the Walvis ridge (Walvis, Lüderitz and Orange basin). More pronounced Cenozoic erosion in Angola

  11. A new permopsocidan genus and species from the Late Permian of Australia (Insecta: Acercaria: Psocidiidae).

    PubMed

    Prokop, Jakub; Garrouste, Romain; Nel, André

    2016-01-01

    The psocidiid Hypopsylla belmontensis gen. et sp. nov., new psocidiid genus and species, is described and figured from the Late Permian of New South Wales in Australia. This discovery extends the knowledge on the diversity of the small order Permopsocida whose members passed the Permian-Triassic boundary and became extinct in Cretaceous. PMID:27515638

  12. Exhumation of Wistar rats experimentally exposed to the carbamate pesticides aldicarb and carbofuran: A pathological and toxicological study.

    PubMed

    de Siqueira, Adriana; Rodrigues, Karina Borges Almeida; Gonçalves-Júnior, Vagner; Calefi, Atilio Sersun; Fukushima, André Rinaldi; Cuevas, Silvia Elena Campusano; Spinosa, Helenice de Souza; Maiorka, Paulo César

    2016-06-01

    Exhumation is required for the investigation of suspicions deaths when a body is buried and is usually performed under court order. Exhumation of animals is not a routine practice in forensic pathology. In this study, 30 male 70-day-old Wistar rats were experimentally exposed to the carbamate pesticides aldicarb and carbofuran. Toxicological, macroscopic and microscopic examinations were performed. Groups of 3 animals (2 exposed and 1 control) were evaluated at 24h, 3days, 5days, 7days and 10days post-mortem. In histopathological examination, the brain, liver, lungs and kidneys were assessed, and for toxicological analysis, the gastric contents, liver, vitreous humor, skeletal muscle and larvae (when available) were collected. The pesticides were detected by HPLC and quantified in the analyzed matrices, and a possible delay in tissue putrefaction due to the pesticides was observed. This study has revealed that it is possible to exhume animals for investigations of possible poisoning by carbamates and has demonstrated that the exhumation of an animal in a suspected case of poisoning should not be ruled out. The increasing demand for investigations of suspicious animal deaths, e.g., in cases of poisoning, will likely lead to an increase in the use of this type of procedure in veterinary pathology. PMID:27020045

  13. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, M.; Steck, A.; Carter, A.; Cosca, M.; Epard, J.-L.; Hunziker, J.

    2011-01-01

    New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55. Ma and metamorphosed by ca. 48-40. Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10. km) by 40-30. Ma in the Tso Morari dome (northern section of the transect) and by 30-20. Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene. High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26. Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19. Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10. km) between 20 and 6. Ma, while its southern front reached this depth at 10-5. Ma. ?? 2010 Elsevier Ltd.

  14. Ocean anoxia did not cause the Latest Permian Extinction

    NASA Astrophysics Data System (ADS)

    Proemse, Bernadette C.; Grasby, Stephen E.; Wieser, Michael E.; Mayer, Bernhard; Beauchamp, Benoit

    2014-05-01

    The Latest Permian Extinction (LPE, ~252 million years ago) was a turning point in the history of life on Earth with a loss of ~96% of all marine species and ~70% of all terrestrial species. While, the event undoubtedly shaped the evolution of life its cause remains enigmatic. A leading hypothesis is that the global oceans became depleted in oxygen (anoxia). In order to test this hypothesis we investigated a proxy for marine oxygen levels (molybdenum isotopic composition) in shale across the LPE horizon located on the subtropical northwest margin of Pangea at that time. We studied two sedimentary records in the Sverdrup basin, Canadian High Arctic: Buchanan Lake (eastern Axel Heiberg Island; 79° 26.1'N, 87° 12.6'W), representing a distal deep-water slope environment, and West Blind Fiord (southwest Ellesmere Island; 78° 23.9'N, 85° 57.2'W), representing a deep outer shelf environment (below storm wave base). The molybdenum isotopic composition (δ98/95Mo) of sediments has recently become a powerful tool as a paleo-oceanographic proxy of marine oxygen levels. Sample preparation was carried out in a metal-free clean room facility in the isotope laboratory of the Department of Physics and Astronomy, University of Calgary, Canada, that is supplied by HEPA-filtered air. Molybdenum isotope ratios were determined on a Thermo Scientific multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) with an uncertainty better than ±0.10o for δ98/95Mo values. Results from the Buchanan Lake section show a large shift in δ98/95Mo values from 2.02o to +2.23o at the extinction horizon, consistent with onset of euxinic conditions. In contrast, West Blind Fiord shales, representing the sub-storm wave base shelf environment, show little change in the molybdenum isotopic composition (1.34o to +0.05), indicating ongoing oxic conditions across the LPE (Proemse et al., 2013). Our results suggest that areas of the Pangea continental shelf (North West Pangea) experienced

  15. Permian-Triassic plutonism and tectonics, Death Valley region, California and Nevada

    SciTech Connect

    Snow, J.K.; Asmerom, Y. ); Lux, D.R. )

    1991-06-01

    Significant contractional structures that deform Permian rocks but predate an Early Triassic overlap sequence are recognized within the Cordilleran orogen, western US. Thrusting in the Death Valley region of the orogen, however, has been regarded as Middle Triassic or younger and thus kinematically distinct. The authors present new isotopic age limits on two posttectonic stocks that intrude major structures of the Death Valley thrust belt. The stocks are no younger than Middle Triassic, but are likely Late Permian in age, consistent with stratigraphic and structural data suggesting that thrusting predates the overlap sequence. The authors hypothesize that Permian shortening may have affected more than 700 km of the Cordilleran orogen at the same time arc activity began within cratonic North America but prior to Early Triassic emplacement of the structurally higher Sonomian arc terrane.

  16. Chondritic meteorite fragments associated with the Permian-Triassic boundary in Antarctica.

    PubMed

    Basu, Asish R; Petaev, Michail I; Poreda, Robert J; Jacobsen, Stein B; Becker, Luann

    2003-11-21

    Multiple chondritic meteorite fragments have been found in two sedimentary rock samples from an end-Permian bed at Graphite Peak in Antarctica. The Ni/Fe, Co/Ni, and P/Fe ratios in metal grains; the Fe/Mg and Mn/Fe ratios in olivine and pyroxene; and the chemistry of Fe-, Ni-, P-, and S-bearing oxide in the meteorite fragments are typical of CM-type chondritic meteorites. In one sample, the meteoritic fragments are accompanied by more abundant discrete metal grains, which are also found in an end-Permian bed at Meishan, southern China. We discuss the implications of this finding for a suggested global impact event at the Permian-Triassic boundary. PMID:14631038

  17. Permian reptilian fauna from the Kundaram Formation, Pranhita-Godavari Valley, India

    NASA Astrophysics Data System (ADS)

    Ray, Sanghamitra

    1999-07-01

    The Kundaram Formation of the Pranhita-Godavari Valley yields the only Permian reptilian fauna in India. It is composed essentially of a dicynodont assemblage and includes Endothiodon, Cistecephalus, Pristerodon, Oudenodon and Emydops-like forms. The only non-dicynodont member is a captorhinid reptile. These taxa allow the correlation of the Kundaram Formation with the Tropidostoma and/or Cistecephalus Assemblage Zones of the Beaufort Group of South Africa, the basal beds of Madumabisa Mudstones of Zambia, the Ruhuhu and lower part of the Kawinga Formation of Tanzania and the Morro Pelado member of the Rio do Rasto Formation of Brazil, indicating a Late Permian (Tatarian) age. The Kundaram fauna helps in fixing the upper age of the coal-bearing Damuda Group more precisely at Tatarian. The distribution of the Late Permian dicynodonts in the now widely separated geographic areas suggests the close proximity of the continents and a lack of endemism or provinciality.

  18. Permian tetrapods from the Sahara show climate-controlled endemism in Pangaea.

    PubMed

    Sidor, Christian A; O'Keefe, F Robin; Damiani, Ross; Steyer, J Sébastien; Smith, Roger M H; Larsson, Hans C E; Sereno, Paul C; Ide, Oumarou; Maga, Abdoulaye

    2005-04-14

    New fossils from the Upper Permian Moradi Formation of northern Niger provide an insight into the faunas that inhabited low-latitude, xeric environments near the end of the Palaeozoic era (approximately 251 million years ago). We describe here two new temnospondyl amphibians, the cochleosaurid Nigerpeton ricqlesi gen. et sp. nov. and the stem edopoid Saharastega moradiensis gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40-90 million years earlier. Coupled with a scarcity of therapsids, the new finds suggest that faunas from the poorly sampled xeric belt that straddled the Equator during the Permian period differed markedly from well-sampled faunas that dominated tropical-to-temperate zones to the north and south. Our results show that long-standing theories of Late Permian faunal homogeneity are probably oversimplified as the result of uneven latitudinal sampling. PMID:15829962

  19. Polish permian basin: Lithofacies traps for gas within the Rotliegende deposits as a new exploration potential

    SciTech Connect

    Karnkowski, P.H. )

    1993-09-01

    Rotliegende deposits are the most prospective reservoir gas rocks in the Polish Permian basin. Thirty years of their exploration have led to location of numerous gas fields in the upper-most part of these series, particularly in the area of the Fore-Sudetic monocline. Up to this time, exploration studies concentrated mainly on structural objects, and most of the structures were positive gas traps. Well and seismic data also indicate an occurrence of lithofacies gas traps; they occur mainly in the sandstone zones within the fanglomerates surrounding the Wolsztyn Ridge. When comparing the facies regularities in the known gas fields in the German Permian basin (interfingering sandstones and claystones) to the facies patterns of the Polish Permian basin, one may suspect similar exploration possibilities. These are the first promising results. Advances in analysis of the Rotliegende depositional systems will enable us to create a new exploration potential.

  20. Trouble Upstairs: Reconstructing Permian-Triassic Climate during Siberian Traps Magmatism

    NASA Astrophysics Data System (ADS)

    Black, B. A.; Neely, R. R., III; Lamarque, J. F.; Elkins-Tanton, L. T.; Mills, M. J.

    2014-12-01

    The eruption of large igneous provinces can transfer significant masses of volatiles from Earth's interior to the atmosphere. What are the consequences of this degassing for habitability and extinction? In this presentation, we consider this question in the context of Siberian Traps magmatism, which has been shown to overlap within geochronologic uncertainty with catastrophic deterioration of Permian-Triassic marine and terrestrial ecosystems. To investigate the impacts of endogenic gases on climate, atmospheric chemistry, and ocean circulation, we conducted a series of numerical experiments with a comprehensive global model for the Permian-Triassic. Our simulations predict the intensity and distribution of acid rain and ozone depletion, with implications for terrestrial biota. We further explore feedbacks between sulfur emissions, transient cooling, and shifts in ocean circulation. We suggest that Siberian Traps magmatism may have triggered several distinct kill mechanisms in the oceans and on land, contributing to a complex combined pattern of environmental stress and latest Permian ecological failure.

  1. The Pennsylvanian and Permian Oquirrh-Wood River basin

    SciTech Connect

    Geslin, J.K. . Dept. of Earth and Planetary Sciences)

    1993-04-01

    Strata of the Middle Pennsylvanian to Lower Permian Oquirrh-Wood River Basin (OWRB) lie unconformably above the Antler orogenic belt and flysch trough/starved basin in NW Utah, NE Nevada, and SC Idaho. Strata of the basin, now separated geographically by the Neogene Snake River Plain, show similar subsidence histories, identical mixed carbonate-siliciclastic sedimentary fill, and identical chert pebble conglomerate beds supplied by one or more DesMoinesian uplifts containing Lower Paleozoic strata. This conglomerate, of the lower Sun Valley Group, Snaky Canyon Formation, and parts of the Oquirrh Formation, was reworked progressively southward, to at least the Idaho-Utah border. It is present in strata as young as Virgilian. Virgilian to Leonardian rocks are ubiquitously fine-grained mixed carbonate-siliciclastic turbidites. These rocks contain cratonal, well-sorbed subarkosic and quartzose sand and silt in part derived from the Canadian Shield. This siliciclastic fraction is intimately mixed with arenaceous micritized skeletal material and peloids derived from an eastern carbonate platform represented by the Snaky Canyon Formation in east-central Idaho, an eastern facies of the Eagle Creek Member, Wood River Formation in the Boulder Mountains, and the Oquirrh Formation in the Deep Creek Mountains. Subsidence of the OWRB may have been caused by two phases (DesMoinesian and Wolfcampian to Leonardian) of crustal loading by continental margin tectonism to the west. An elevated rim separated the OWRB from coeval volcanogenic basins to the west. Earlier, Antler-age structures may have been reactivated. A new pulse of tectonism occurred in Leonardian to Guadalupian time as in most places carbonatic and phosphatic strata of the Leonardian to Guadalupian Park City and Phosphoria Formation overlie OWRB strata, with different geographic arrangement of basinal, slope, and shelf depocenters.

  2. Flourishing ocean drives the end-Permian marine mass extinction

    PubMed Central

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-01-01

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian−Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth’s history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness. PMID:26240323

  3. Two pulses of oceanic environmental disturbance during the Permian-Triassic boundary crisis

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Feng, Qinglai; Algeo, Thomas J.; Li, Chao; Planavsky, Noah J.; Zhou, Lian; Zhang, Mingliang

    2016-06-01

    Pyrite morphology, iron speciation, and pyrite sulfur isotope data from the Xiakou section (Hubei Province, South China) were integrated to explore oceanic environmental variations through the Permian-Triassic transition and their possible relations to the largest mass extinction in Earth history. High ratios of highly-reactive iron to total iron (FeHR/FeT > 0.6) and pyrite iron to highly-reactive iron (FePy/FeHR > 0.7) together with a high abundance of small (mean diameter <5 μm) framboidal pyrite show that euxinic conditions existed in the late Permian (pre-extinction interval). High ratios of FeHR/FeT (mostly >0.6) along with lower values of FePy/FeHR (<0.7) and more variable framboid content among samples indicate anoxic but dominantly ferruginous conditions punctuated by episodic euxinic events in the latest Permian to earliest Triassic (post-extinction interval). The largest fluctuations of these redox proxies are observed in the ∼1.0 m of strata directly overlying the first (latest Permian) extinction horizon, indicating unsettled marine environmental conditions marked by frequent perturbations during the ∼60-kyr interval immediately following the mass extinction. The two largest redox events at Xiakou coincided with deposition of volcanic ash layers that have been correlated with Beds 25 and 28 of the Meishan D section, each of which was associated with an extinction pulse (the first and second extinction horizons of latest Permian and earliest Triassic age, respectively). Thus, our observations document two pulses of oceanic environmental change during the Permian-Triassic transition, each associated with a faunal crisis and possibly triggered by contemporaneous volcanic activity.

  4. Ochoan (upper Permian) stratigraphy and age determinations, southeastern New Mexico and west Texas

    SciTech Connect

    Lucas, S.G. ); Anderson, O.R. )

    1994-03-01

    Upper Permian strata, which are the stratotype of the Ochoan State (Series), have an extensive subsurface distribution and limited outcrop area in southeastern New Mexico and west Texas. The oldest strata are alternating laminae of anhydrite and calcite of the Castile Formation and are as much as 700 m thick. The closely related and overlying Salado Formation is a much as 600 m thick and is mostly halite and argillaceous halite with minor anhydrite. The overlying Rustler Formation is as much as 150 m thick and consists of anhydrite, red silty shale and magnesian limestone. Overlying red beds are the Quartermaster Formation (Dewey Lake Formation is a synonym, as is the term Pierce Canyon red beds), which is as much as 106 m thick and consist of fine sandstones, siltstones, and minor gypsum. The Castile rests disconformably on the Capitanian (middle Permian) Lamar Limestone Member of the Bell Canyon Formation and its equivalent, the Tansill Formation of the Artesia Group. Counting of Castile-Salado laminae and their posited relationship to astronomical cycles suggests that Castile-Salado deposition took only 200,000-300,000 yr. Limited assemblages of brachiopods and conodonts from the Rustler Formation indicate a Late Permian age, but are no more precise age indicators. A small assemblage of bivalves, K-Ar ages and magnetostratigraphy indicate a late Permian age for the Quartermaster Formation. There is no evidence to support a Triassic age assignment for the Quarter-master; it is disconformably overlain by the Upper Triassic (Carnian) Chinle group. Most workers us the Ochoan as a Late Permian Stage-Age, although its typical strata generally lack good age indicators and may represent relatively short and sporadic intervals of the Late Permian. We prefer recognition of the Ochoan as a lithostratigraphic unit (group) without regional or global geochronologial significance.

  5. Terrestrial paleoenvironment characterization across the Permian-Triassic boundary in South China

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Cui, Ying; Forel, Marie-Béatrice; Yu, Jianxin; Vajda, Vivi

    2015-02-01

    Well-preserved marine fossils in carbonate rocks permit detailed studies of the end-Permian extinction event in the marine realm. However, the rarity of fossils in terrestrial depositional environments makes it more challenging to attain a satisfactory degree of resolution to describe the biotic turnover on land. Here we present new sedimentological, paleontological and geochemical (X-ray fluorescence) analysis from the study of four terrestrial sections (Chahe, Zhejue, Mide and Jiucaichong) in Western Guizhou and Eastern Yunnan (Yangtze Platform, South China) to evaluate paleoenvironmental changes through the Permian-Triassic transition. Our results show major differences in the depositional environments between the Permian Xuanwei and the Triassic Kayitou formations with a change from fluvial-lacustrine to coastal marine settings. This change is associated with a drastic modification of the preservation mode of the fossil plants, from large compressions to small comminuted debris. Plant fossils spanning the Permian-Triassic boundary show the existence of two distinct assemblages: In the Xuanwei Formation, a Late Permian (Changhsingian) assemblage with characteristic Cathaysian wetland plants (mainly Gigantopteris dictyophylloides, Gigantonoclea guizhouensis, G. nicotianaefolia, G. plumosa, G. hallei, Lobatannularia heinanensis, L. cathaysiana, L. multifolia, Annularia pingloensis, A. shirakii, Paracalamites stenocostatus, Cordaites sp.) is identified. In the lowermost Kayitou Formation, an Early Triassic (Induan) Annalepis-Peltaspermum assemblage is shown, associated with very rare, relictual gigantopterids. Palynological samples are poor, and low yield samples show assemblages almost exclusively represented by spores. A ∼1 m thick zone enriched in putative fungal spores was identified near the top of the Xuanwei Formation, including diverse multicellular forms, such as Reduviasporonites sp. This interval likely corresponds to the PTB "fungal spike

  6. Early Permian volcano-sedimentary successions, Beishan, NW China: Peperites demonstrate an evolving rift basin

    NASA Astrophysics Data System (ADS)

    Chen, Shi; Guo, Zhaojie; Qi, Jiafu; Zhang, Yuanyuan; Pe-Piper, Georgia; Piper, David J. W.

    2016-01-01

    The Lower Permian volcano-sedimentary Zhesi Group has been investigated in the Hongliuhe and Liuyuan areas in Beishan, China, which is significant for the reconstruction of Late Paleozoic evolution in the southern part of the Central Asian Orogenic Belt. A variety of volcanic facies were distinguished in the Upper Zhesi Group: pillow basalt with interstitial limestone, thin-interbedded limestone and basalt, closely packed pillows, pillow-fragmented hyaloclastite breccia, and peperite. Laser 40Ar/39Ar whole-rock dating of the basalt yielding an age of 277 ± 11 Ma, as well as Early Permian brachiopod fossils in the limestone interbedded with the basalt, indicate that basalt was erupted in the Early Permian. The identification of the peperite and other facies originating from magma-sediment mingling reveals that the basaltic lava flows were derived from autochthonous basaltic magmatism and formed as part of the Lower Permian succession. The peperite also indicates that these subaqueous basaltic lava flows are not dismembered ophiolitic components, but formed in an autochthonous extensional setting in the Early Permian. The clastic rocks in the Lower Zhesi Group underlying the basaltic flows and peperites in the Hongliuhe and Liuyuan areas show a general fining-upwards sequence, indicating that they were deposited in a progressively deepening basin overlying the Devonian Hongliuhe suture zone. Subaqueous volcanism in a rift basin or basins, accompanied by coeval deposition of carbonate sediment and mud, built up the peperite-bearing volcanogenic-sedimentary successions. From among the various tectonic hypotheses for the Beishan region, this study demonstrates that by Early Permian the region was developing post-collisional rift basins.

  7. Surface water paleotemperatures and chemical compositions from fluid inclusions in Permian Nippewalla Group halite

    SciTech Connect

    Benison, K.C. )

    1996-01-01

    Quantitative climatic data for the Permian have been determined from Nippewalla Group halite. The middle Permian Nippewalla Group of Kansas and Oklahoma consists of several hundred feet of bedded halite, anhydrite, and red beds. Study of core and surface samples suggest that this halite was deposited by ephemeral lakes. Fluid inclusions provide evidence for the geochemistry of these Permian saline lake waters, including temperatures, salinities, and chemical compositions. Primary fluid inclusions are well-preserved in the Nippewalla halite. They are 5 - 30 [mu]m cubic inclusions situated along chevron and cornet growth bands. Most are one phase aqueous inclusions, but some also contain anhydride [open quote]accidental[close quotes] crystals. Rare two phase liquid-vapor inclusions may have formed by subaqueous outgassing or trapping of air at the water surface. Fluid inclusion freezing-melting behavior and leachate analyses suggest that Nippewalla halite precipitated from Na-Cl-rich waters with lesser quantities of SO[sub 4], Mg, K, Al, and Si. This composition may be a product of long-term weathering. Surface water paleotemperatures were determined from one phase aqueous fluid inclusions. Homogenization temperatures range from 32 to 46[degrees]C in primary fluid inclusions and are consistent (within 3[degrees]C) along individual chevrons and cornets. These homogenization temperatures are interpreted to represent maximum surface water temperatures. These fluid inclusion data are significant in addressing global change problems. Temperatures and chemistries in these Permian lake waters agree with some modern shallow saline lake waters and with Permian climate models. This study suggests that this Permian environment was relatively similar to its modern counterparts.

  8. Surface water paleotemperatures and chemical compositions from fluid inclusions in Permian Nippewalla Group halite

    SciTech Connect

    Benison, K.C.

    1996-12-31

    Quantitative climatic data for the Permian have been determined from Nippewalla Group halite. The middle Permian Nippewalla Group of Kansas and Oklahoma consists of several hundred feet of bedded halite, anhydrite, and red beds. Study of core and surface samples suggest that this halite was deposited by ephemeral lakes. Fluid inclusions provide evidence for the geochemistry of these Permian saline lake waters, including temperatures, salinities, and chemical compositions. Primary fluid inclusions are well-preserved in the Nippewalla halite. They are 5 - 30 {mu}m cubic inclusions situated along chevron and cornet growth bands. Most are one phase aqueous inclusions, but some also contain anhydride {open_quote}accidental{close_quotes} crystals. Rare two phase liquid-vapor inclusions may have formed by subaqueous outgassing or trapping of air at the water surface. Fluid inclusion freezing-melting behavior and leachate analyses suggest that Nippewalla halite precipitated from Na-Cl-rich waters with lesser quantities of SO{sub 4}, Mg, K, Al, and Si. This composition may be a product of long-term weathering. Surface water paleotemperatures were determined from one phase aqueous fluid inclusions. Homogenization temperatures range from 32 to 46{degrees}C in primary fluid inclusions and are consistent (within 3{degrees}C) along individual chevrons and cornets. These homogenization temperatures are interpreted to represent maximum surface water temperatures. These fluid inclusion data are significant in addressing global change problems. Temperatures and chemistries in these Permian lake waters agree with some modern shallow saline lake waters and with Permian climate models. This study suggests that this Permian environment was relatively similar to its modern counterparts.

  9. Colorado Plateau rock strength, exhumation, and river knickzones - spatial datasets relating erodability to topographic metrics

    NASA Astrophysics Data System (ADS)

    Tressler, C.; Pederson, J. L.

    2009-12-01

    Bedrock resistance to erosion has a fundamental role in controlling topography and surface processes. This has been recognized since the birth of geomorphology, yet measurements and datasets quantifying rock strength are rare. This is despite it being an essential parameter in tectonic, fluvial, and hillslope process geomorphology, where erodability is commonly marginalized within the diffusivity constant, as well as the K coefficient in stream-power formulations and the channel-concavity and steepness indexes derived from it. The Colorado Plateau landscape, because of its semiarid climate and extensive exhumation, is strongly influenced by variations in bedrock. It is a prime setting to complete such a dataset of rock strength and analyze it in the context of erosion and topography because of both its historic scientific importance and the fact that all bedrock units are exposed for study. We are completing the measurement and mapping of the erodability of all major bedrock units at over 150 sites across the plateau through several approaches, including traditional Schmidt-hammer compressive strength, fracture spacing, and other characteristics associated with Selby rock-mass strength (RMS). These measures may specifically relate to erosion by mass-movement and fluvial plucking processes. Results highlight two problems with these basic data: they overestimate the strength of rock with massive bedding because of the heavy weighting of fracture spacing in Selby RMS, and they don’t include the extensive shale bedrock of the region. To address these issues, we are measuring sample tensile strength (Brazilian splitting test) to capture disintegration and fluvial abrasion erosion of massive units, and we are utilizing the stratigraphic proportion of shale within geologic units as a scaling factor in RMS. We are then exploring spatial relations of these strength measures to topography, exhumation, stream power, and steepness within the Colorado River drainage basin

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

    USGS Publications Warehouse

    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).

  11. The exhumed ``Carlin-type'' fossil oil reservoir at Yankee Basin

    NASA Astrophysics Data System (ADS)

    Hulen, Jeffrey B.; Collister, James W.; Stout, Bill; Curtiss, David K.; Dahdah, Nicolas F.

    1998-12-01

    The Carlin-type disseminated gold orebodies of Yankee basin in the southern part of the Alligator Ridge mining district in Nevada contain widespread oil as smears, open-space fillings, and fluid inclusions in syn- and pre-mineral calcite veins. These unusual oils are the relicts of an exhumed and deeply oxidized oil reservoir that encom-passes the orebodies at the crest of a dissected, anticlinal trap. Results of fluid-inclusion microthermometry and organic geochemistry demonstrate that the oils experienced peak paleotemperatures of no more than about 150°C, a temperature unusually low for Carlin-type mineralization, but ideal for the transport, entrapment, and preservation of liquid hydrocarbon. Similar geothermal systems are actively circulating at three of Nevada’s producing oil fields—Grant Canyon, Bacon Flat, and Blackburn. Accordingly, concealed Carlin-type fossil hydrothermal systems of this type, even if subeconomic for gold, could contain commercial concentrations of oil.

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

    PubMed

    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

    2015-10-01

    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). PMID:26450214

  13. Late exhumation of the Alpine foreland (Digne nappe, France) constrained by low temperature thermochronology

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The frontal part of the southwestern Alpine belt is characterized by important compressional deformation marked by the emplacement of the Digne nappe and the formation of the Valavoire thrust-sheet. The final displacement of this nappe is dated Late Miocene thanks to continental molasses of the foreland basin, which are folded in its footwall and form the famous Vélodrôme recumbent syncline. The stratigraphic series of the Digne nappe is made of more than 5000 m thick Liassic to Eocene deposits a part of which overthrust the vélodrôme syncline. In order to quantify this overburden and the timing of the subsequent exhumation and erosion of the Valavoire thrust-sheet we performed a low temperature apatite fission tracks (AFT) and (U-Th)/He (AHe) study on the Tertiary molasses sampled at Faucon du Caire and Esclangon area in order to (i) characterize the thermal conditions during burial and exhumation (ii) and to propose a coherent evolution of the European foreland in the front of the Digne nappe. AHe and AFT data obtained on detrital grains present for Faucon du Caire and Esclangon molasses minimum ages ranging of 3-5 Ma. From these data we determine than the Faucon du Caire molasses have been totally reset for He system and whereas the Esclangon molasses have been only partially reset. Using QTQt inverse modeling and He damage codes (Gallagher et al., 2012), the thermal history results implied a burial at 90-100°C for the Esclangon molasses and >120°C for the Faucon du Caire molasses and a similar exhumation starting at 5.5±0.5 Ma. From these results, we conclude that the thermal conditions during burial associated with the Digne nappe thrusting were enough sufficient to reset the detrital apatites in Miocene sediments. This implies several kilometers of tectonic overload. Maximum burial occurred at ~6 Ma ago, which precludes the occurrence of any Messinian incision overlain by the nappe in the Barles half-window as recently proposed (Hippolyte et al., 2011

  14. Long-term coupling along the subduction plate interface: insights from exhumed rocks and models

    NASA Astrophysics Data System (ADS)

    Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

    2012-04-01

    Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Combining evidence from exhumed rocks worldwide and the results of recently published thermo-mechanical models, we herein investigate how long-term mechanical coupling takes place along deep portions of the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. Geological evidence indicates that, unlike subduction, exhumation is highly discontinuous. Besides, eclogites worldwide are found in essentially two types of tectonic setting, either as large scale (>km) slices with coherent PT estimates (W. Alps) or as isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial in some localities; Franciscan, Cuba, Sistan). This latter type tends to show warmer equilibration paths (although minor lawsonite-eclogite blocks can be found), whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive. Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (hydrated crust and mantle top), thereby

  15. Kinks in subducted slabs: Petrological evidence points to additional hindrance to the exhumation of UHP rocks

    NASA Astrophysics Data System (ADS)

    John, T.; Klemd, R.; Scherer, E. E.; Rondenay, S.; Gao, J.

    2012-12-01

    Sudden changes in the dip of subducted oceanic plates have been resolved by seismic imaging [1, 2]. Such kinking often coincides with the seismic disappearance of the low-velocity subducted oceanic crust, i.e., at a depth where eclogitization (dehydration) of the upper oceanic crust is nearly complete and the oceanic crust becomes almost seismically indistinguishable from mantle peridotite. We present petrological evidence for this phenomenon derived from oceanic blueschist- and eclogite-facies rocks from the Chinese Tianshan. The peak-metamorphic conditions of the samples range between 330 and 580°C at 1.5 to 2.3 GPa. Such a wide range of peak conditions for intercalated high- and ultrahigh-pressure rocks has also been reported from other Tianshan localities. These observations suggest that the rocks were derived from different depths within the subduction zone and later juxtaposed during exhumation within the subduction channel. Multi-point Lu-Hf isochrons from four high-pressure rocks yield consistent garnet-growth ages of around ~315 Ma, confirming that the eclogite-facies metamorphism of the Tianshan high-pressure rocks resulted from a single subduction event in the Late Carboniferous. These ages, in conjunction with the ~311 Ma cluster of 40Ar-39Ar and Rb-Sr white mica ages from the same localities imply rapid exhumation. Previously reported peak P-T estimates from UHP metasediments and eclogites all lie on a lower geothermal gradient—and thus on a colder P-T path at the slab-wedge interface—than that defined by the HP eclogites and meta-volcaniclastic rocks studied here. This suggests that the slab-subduction angle steepened sharply at approximately 90 km depth, just between the depths at which the HP and UHP rocks equilibrated. The increase in subduction angle may result from a greater slab pull resulting from eclogitization densification. An additional factor may be an ephemeral weakening of the slab as it undergoes eclogitization reactions [3, 4]. We

  16. Using Digital Topography to Differentiate Erosionally Exhumed and Tectonically Active Mountains Fronts

    NASA Astrophysics Data System (ADS)

    Frankel, K. L.; Pazzaglia, F. J.

    2003-12-01

    Mountain ranges in the southern Rocky Mountains have departed on unique landscape evolutionary pathways in the late Cenozoic that are directly dependent upon the degree of post-orogenic tectonic activity they have experienced. The topography of Sierra Nacimiento, a Laramide uplift in west-central New Mexico lacking an active range-front fault, is shaped primarily by erosional exhumation that is continuous, but not steady, being driven by distal base level fall from Rio Grande incision and resultant south to north knickpoint migration. In contrast, the topography of the Taos Range, a rift flank uplift in north-central New Mexico is shaped by contrasting active stream incision and aggradation astride an active range front normal fault. The distinction between exhumation-dominated and tectonically-dominated mountain fronts is best quantified by analyses of a new metric we call the drainage basin volume to drainage basin area ratio (V-A ratio) as well as the gradients of first-order streams. Drainage basin volume and area are calculated by constructing topographic envelope maps from 10 m resolution digital elevation models (DEM). The envelope maps are pinned by the watershed divide and cover the maximum elevations in each drainage basin. Subtracting the original DEM from the maximum elevation envelope map produces a topographic residual map from which area and volume data can be obtained. The erosionally exhumed Sierra Nacimiento has a mean V-A ratio of 88 m while the tectonically active Taos Range has a mean V-A ratio of 140 m. Similarly, there are systematic differences in the gradients of first order streams measured both in the range block and approximately 5 km of adjacent piedmont. Streams were defined and subsequently Strahler ordered by a flow accumulation threshold of 250 water-equivalent grid cell units. First order stream channel long profiles were extracted from the DEM at 30 meter increments and gradients were calculated by a FORTRAN program. Gradients of

  17. The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models

    NASA Astrophysics Data System (ADS)

    Penniston-Dorland, Sarah C.; Kohn, Matthew J.; Manning, Craig E.

    2015-10-01

    The maximum-pressure Psbnd T conditions (Pmax- T) and prograde Psbnd T paths of exhumed subduction-related metamorphic rocks are compared to predictions of Psbnd T conditions from computational thermal models of subduction systems. While the range of proposed models encompasses most estimated Pmax- T conditions, models predict temperatures that are on average colder than those recorded by exhumed rocks. In general, discrepancies are greatest for Pmax < 2 GPa, where only a few of the highest-T model paths overlap petrologic observations and model averages are 100-300 °C colder than average conditions recorded by rocks. Prograde Psbnd T paths similarly indicate warmer subduction than typical models. Both petrologic estimates and models have inherent biases. Petrologic analysis may overestimate temperatures at Pmax where overprinting occurs during exhumation, although Psbnd T paths suggest that relatively warm conditions are experienced by rocks on the prograde subduction path. Models may underestimate temperatures at depth by neglecting shear heating, hydration reactions and fluid and rock advection. Our compilation and comparison suggest that exhumed high-P rocks provide a more accurate constraint on Psbnd T conditions within subduction zones, and that those conditions may closely represent the subduction geotherm. While exhumation processes in subduction zones require closer petrologic scrutiny, the next generation of models should more comprehensively incorporate all sources of heat. Subduction-zone thermal structures from currently available models appear to be inaccurate, and this mismatch has wide-reaching implications for our understanding of global geochemical cycles, the petrologic structure of subduction zones, and fluid-rock interactions and seismicity within subduction zones.

  18. Driving mechanisms for >40 km of exhumation during contraction and extension in a continental arc, Cascades core, Washington

    NASA Astrophysics Data System (ADS)

    Paterson, Scott R.; Miller, Robert B.; Alsleben, Helge; Whitney, Donna L.; Valley, Peter M.; Hurlow, Hugh

    2004-06-01

    In the NW North American Cordillera, the Cascades core region of the Coast Plutonic Complex underwent Late Cretaceous (>96 Ma to locally 73 Ma) SW-NE contraction and crustal thickening followed by dextral transpression (˜73 to 55 Ma), then transtension (<55 Ma). Exhumation occurred during all three phases. During contraction, slow exhumation (˜0.6 mm/yr) occurred along the margins of the core, driven by isostatic rebound and erosion, and faster exhumation (>3 mm/yr) by local thrusting in regions undergoing crustal thickening. In the central part of the core (Chelan block), >40 km of exhumation occurred between 91 and 45 Ma, about half of which occurred during early contraction (driven by thrusting) and half during top-to-north, arc-oblique shear during reactivation of a midcrustal Cretaceous thrust, the Dinkelman decollement. The footwall of this thrust consists of the Swakane Biotite Gneiss, a Cretaceous, metaclastic assemblage with recorded pressures of 10-12 kbar, no arc-related magmatism, and structures dominated by pervasive top-to-north shearing. The hanging wall consists of the Napeequa Complex, an oceanic assemblage with recorded pressures of 6-12 kbar, voluminous arc-related magmatism, and complex structures indicating early top-to-WSW shearing, younger top-to-north shearing, and widespread folding. In the Napeequa, top-to-north shearing started by 73 Ma during melt-present conditions at pressures ≥6 kbar. Top-to-north shearing in both hanging wall and footwall continued during exhumation (˜1.6 mm/yr) and cooling to greenschist facies conditions during which slip became increasingly localized, eventually resulting in formation of pseudotachylite on discrete slip surfaces. We suggest that arc-oblique extension was driven by along-arc heterogeneity in displacements/erosion, initially during transpression and underplating of continental sediments, and later during transtension.

  19. Exhumed analogues of seismically active carbonate-bearing thrusts: fault architecture and deformation mechanisms

    NASA Astrophysics Data System (ADS)

    Tesei, T.; Collettini, C.; Viti, C.; Barchi, M. R.

    2012-12-01

    In May 2012 a M = 5.9 earthquake followed by a long aftershock sequence struck the Northern Italy. The sequence occurred at 4-10 km depth within the active front of Northern Apennines Prism and the major events nucleate within, or propagate through, a thick sequence of carbonates. In an inner sector of the Northern Apennines, ancient carbonate-bearing thrusts exposed at the surface, represent exhumed analogues of structures generating seismicity in the active front. Here we document fault architecture and deformation mechanisms of three regional carbonate bearing thrusts with displacement of several kilometers and exhumation in the range of 1-4 km. Fault zone structure and deformation mechanisms are controlled by the lithology of the faulted rocks. In layered limestones and marly-limestones the fault zone is up to 200 m thick and is characterized by intense pressure solution. In massive limestones the deformation generally occurs along thin and sharp slip planes that are in contact with fault portions affected by either cataclasis or pressure solution. SEM and TEM observations show that pressure solution surfaces, made of smectite lamellae, with time tend to form an interconnected network affected by frictional sliding. Sharp slipping planes along massive limestones show localization along Y shear planes that separate an extremely comminuted cataclasites from an almost undeformed protolith. The comparison of the three shear zones depicts a fault zone structure extremely heterogeneous as the result of protolith lithology, geometrical complexities and the presence of inherited structures. We observe the competition between brittle (cataclasis, distributed frictional sliding along phyllosilicates and extremely localized slip within carbonates) and pressure solution processes, that suggest a multi-mode of slip behaviour. Extreme localization along carbonate-bearing Y shear planes is our favorite fault zone feature representing past seismic ruptures along the studied

  20. Deep-tow magnetic survey above large exhumed mantle domains of the eastern Southwest Indian ridge

    NASA Astrophysics Data System (ADS)

    Bronner, A.; Munschy, M.; Carlut, J. H.; Searle, R. C.; Sauter, D.; Cannat, M.

    2011-12-01

    The recent discovery of a new type of seafloor, the "smooth seafloor", formed with no or very little volcanic activity along the ultra-slow spreading Southwest Indian ridge (SWIR) shows an unexpected complexity in processes of generation of the oceanic lithosphere. There, detachment faulting is thought to be a mechanism for efficient exhumation of deep-seated mantle rocks. We present here a deep-tow geological-geophysical survey over smooth seafloor at the eastern SWIR (62-64°N) combining magnetic data, geology mapping from side-scan sonar images and results from dredge sampling. We introduce a new type of calibration approach for deep-tow fluxgate magnetometer. We show that magnetic data can be corrected from the magnetic effect of the vehicle with no recourse to its attitude (pitch, roll and heading) but only using the 3 components recorded by the magnetometer and an approximation of the scalar intensity of the Earth magnetic field. The collected dredge samples as well as the side-scan images confirm the presence of large areas of exhumed mantle-derived peridodites surrounded by a few volcanic constructions. This allows us to hypothesis that magnetic anomalies are caused by serpentinized peridotites or magmatic intrusions. We show that the magnetic signature of the smooth seafloor is clearly weaker than the surrounding volcanic areas. Moreover, the calculated magnetization of a source layer as well as the comparison between deep-tow and sea-surface magnetic data argue for strong East-West variability in the distribution of the magnetized sources. This variability may results from fluid-rocks interaction along the detachment faults as well as from the repartition of the volcanic material and thus questions the seafloor spreading origin of the corresponding magnetic anomalies. Finally, we provide magnetic arguments, as calculation of block rotation or spreading asymmetry in order to better constrain tectonic mechanisms that occur during the formation of this

  1. Thermochronologic constraints on Late Cretaceous to Cenozoic exhumation of the Bendeleben Mountains, Seward Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    McDannell, Kalin T.; Toro, Jaime; Hourigan, Jeremy K.; Harris, Daniel

    2014-10-01

    the Bendeleben Mountains, Seward Peninsula, mid-Cretaceous granites are exposed in an uplifted block bounded on its south side by an E-W striking normal fault. The Bendeleben fault has well-preserved scarps 4-7 m in height that offset Holocene moraines. Seismic activity, young normal faulting, and Quaternary basaltic volcanism are all evidence of active extension. South of the Bendeleben fault, there is a 3-4 km deep basin. Fifteen apatite (U-Th)/He ages from granitic samples of the footwall yield an Eocene weighted mean age of 41.3±4.8 Ma. Biotite 40Ar/39Ar ages from the country rock of the Bendeleben pluton are 81-83 Ma. In spite of the young fault scarps, HeFTy and Pecube thermal modeling results illustrate that rapid exhumation of the Bendeleben Mountains occurred in the Late Cretaceous-Eocene and slowed since the Oligocene. A weak age-elevation relationship of apatite He ages and a lack of correlation between age and distance from the fault indicate that exhumation was accomplished with minimal block rotation on a steeply dipping, long-lived normal fault. Timing of extension in the Seward Peninsula can be correlated with deformation in the offshore Hope Basin where seismic reflection lines document Early Tertiary large-magnitude normal faulting followed by minor post-Miocene reactivation. The faulting observed in the Bendeleben Mountains is part of an extensional system that spans a large portion of the Bering Strait region. The tectonic model proposed in previous studies suggests that clockwise rotation of the Bering block relative to North America is the cause of extensional deformation in western Alaska.

  2. Exhumation history of the Tatry Mountains, Western Carpathians, constrained by low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Śmigielski, M.; Sinclair, H. D.; Stuart, F. M.; Persano, C.; Krzywiec, P.

    2016-01-01

    This study tests alternative models for the growth of the Tatry Mountains (Central Western Carpathians) by the application of low-temperature thermochronology. Zircon (U + Th)/He ages from the north of the range are mostly between 48 and 37 Ma and indicate cooling prior to the onset of fore-arc sedimentation in the region (42-39 Ma). In contrast, zircon (U + Th)/He ages in the south of the range are around 22 Ma. Apatite fission track ages across the sampled sites range from 20 to 15 Ma. Apatite (U + Th)/He ages range from 18 to 14 Ma with little variation with elevation or horizontal location. Based on thermal modeling and tectonic reconstructions, these Miocene ages are interpreted as cooling in the hanging wall of a northward dipping thrust ramp in the current location of the sub-Tatric fault with cooling rates of ~20°C/Myr at ~22-14 Ma. Modeled cooling histories require an abrupt deceleration in cooling after ~14 Ma to <5°C/Myr. This is associated with termination of deformation in the Outer Carpathians and is synchronous with the transition of the Pannonian Basin from a syn-rift to a postrift stage and with termination of N-S compression in the northern part of the Central Western Carpathians. Overall, the timing of shortening and exhumation is synchronous with the formation of the Outer Carpathian orogen and so the Miocene exhumation of the Tatry records retrovergent thrusting at the northern margin of the Alcapa microplate.

  3. Events during Early Triassic recovery from the end-Permian extinction

    NASA Astrophysics Data System (ADS)

    Tong, Jinnan; Zhang, Suxin; Zuo, Jingxun; Xiong, Xinqi

    2007-01-01

    The Palaeozoic-Mesozoic transition is characterized not only by the biggest Phanerozoic mass extinction, at the end of Permian, but also a prolonged period of recovery of the biota during the succeeding Early Triassic. The delayed recovery is generally attributed to the effects of extreme environmental conditions on the Early Triassic ecosystem. However, there has been very little study of the cause and mechanism of the environmental conditions that prevailed during the period of extinction and subsequent recovery. Research on the Permian-Triassic boundary and Lower Triassic, especially that on environmental events at the beginning of the Triassic in South China, indicates that the slowness of the recovery may be the result of three factors: (1) extreme environmental conditions that persisted through the transitional period and which were maintained by, for example, intermittent contemporary volcanism; (2) a passive evolutionary and ecologic strategy of the biota, in which r-selection taxa were dominant and K-selection forms insignificant; (3) an immature, poorly functioning ecosystem, which had difficulty in responding to and withstanding extreme environmental changes. According to data from South China, environmental changes were frequent during the Late Permian, and especially serious at the Permian-Triassic boundary. The Late Permian ecosystem was well structured and fully functioning as a result of a long period of steady development during the late Palaeozoic, and was capable of resisting general environmental changes. However, increasingly frequent and probably more extreme environmental events in the latest Permian may have led to a general collapse of this ecosystem and to the mass extinction at the end of the Permian. The Early Triassic ecosystem was immature, functioned poorly, and was unable to respond effectively to environmental changes, so that persisting extreme environmental conditions slowed ecosystem reconstruction considerably, and the recovery

  4. Permian continental basins in the Southern Alps (Italy) and peri-mediterranean correlations

    NASA Astrophysics Data System (ADS)

    Cassinis, Giuseppe; Perotti, Cesare R.; Ronchi, Ausonio

    2012-01-01

    The Late Carboniferous to Permian continental successions of the Southern Alps can be subdivided into two main tectono-sedimentary Cycles, separated by a marked unconformity sealing a Middle Permian time gap, generally estimated at over 10 Ma. The lower cycle (1), between the Variscan crystalline basement and the Early Permian, is mainly characterised by fluvio-lacustrine and volcanic deposits of calc-alkaline acidic-to-intermediate composition, which range up to a maximum thickness of more than 2,000 m. The upper cycle (2), which is devoid of volcanics, is mostly dominated through the Mid?-Late Permian by alluvial sedimentation which covered the previous basins and the surrounding highs, giving rise to the subaerial Verrucano Lombardo-Val Gardena (Gröden) red-beds, up to about 800 m thick. The palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro- and microfloras and tetrapod footprints. The age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings; however, some sections are also controlled by radiometric calibrations. The comparison with some selected continental successions in southern Europe allows to determine their evolution and set up correlations. A marked stratigraphic gap shows everywhere between the above-mentioned Cycles 1 and 2. As in the Southern Alps, the gap reaches the greatest extent during the Mid-Permian, near the Illawarra Reversal geomagnetic event (265 Ma). In western Europe, however, such as in Provence and Sardinia, the discussed gap persists upwardly to Late Permian and Early Triassic or slightly younger times, i.e. to the onset of the "Alpine sedimentary Cycle", even though in northeastern Spain (Iberian Ranges, Balearic Islands) this gap results clearly interrupted by late Guadalupian-Lopingian deposits. The above two major tectonosedimentary cycles reflect, in our view, two main

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

    USGS Publications Warehouse

    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.

  6. Records of Late Permian surface temperatures in continental Gondwana in isotope geochemistry of upper Permian early diagenetic calcite concretions

    SciTech Connect

    Yeman, E.; Kelts, K.

    1996-12-31

    We present geochemical and isotopic evidence of paleotemperatures from freshwater continental deposits from 55{degrees}S in interior southern Gondwana. Lacustrine shales host spheroidal concretions with abundant septarian cracks. Cement carbonate varies from 65% at the centre to 15% at the edges. Cistraccide remains are preserved. Septarian calcite occurs in dull and bright bands, with three distinct generations of vein-fills. Early-formed cement both in concretions and septarian veins is magnesium-rich whereas, later-formed carbonates are pure calcite. Carbon- and oxygen-isotope ratios (PDB) are: host shales, {delta}{sup 13}C= -4.36 to o.77{per_thousand}, {delta}{sup 18}O= -12.73 to -17.12{per_thousand}; concretion cements, {delta}{sup 13}C=+0.26 to {delta}{sup 18}O= -9.34{per_thousand}; and vein-fills, {delta}{sup 13}C= -7.05 to +1.09{per_thousand}, {delta}{sup 18}O= -8.28 to -18.24{per_thousand}. 13C and 18O ratios are depleted from the center of concretions to the periphery, as well as from the centre of veins to the tip. Near-surface cementation is suggested by textural evidence. {delta}18O in the range of -12.636{per_thousand} to -8.989 SMOW is calculated for the meteoric palaeowaters, from which average annual surface temperatures of 5-8{degrees}C are inferred. {delta}18O of early-formed cements also yields a mean annual surface temperature of 2-6{degrees}C. Based on continentality and palaeolatitudes of northern Malawi during the Late Permian, we propose that mean annual surface palaeotemperatures may have been as high as 10{degrees}C, similar to those found in modern continental temperate climates.

  7. Records of Late Permian surface temperatures in continental Gondwana in isotope geochemistry of upper Permian early diagenetic calcite concretions

    SciTech Connect

    Yeman, E. ); Kelts, K. )

    1996-01-01

    We present geochemical and isotopic evidence of paleotemperatures from freshwater continental deposits from 55[degrees]S in interior southern Gondwana. Lacustrine shales host spheroidal concretions with abundant septarian cracks. Cement carbonate varies from 65% at the centre to 15% at the edges. Cistraccide remains are preserved. Septarian calcite occurs in dull and bright bands, with three distinct generations of vein-fills. Early-formed cement both in concretions and septarian veins is magnesium-rich whereas, later-formed carbonates are pure calcite. Carbon- and oxygen-isotope ratios (PDB) are: host shales, [delta][sup 13]C= -4.36 to o.77[per thousand], [delta][sup 18]O= -12.73 to -17.12[per thousand]; concretion cements, [delta][sup 13]C=+0.26 to [delta][sup 18]O= -9.34[per thousand]; and vein-fills, [delta][sup 13]C= -7.05 to +1.09[per thousand], [delta][sup 18]O= -8.28 to -18.24[per thousand]. 13C and 18O ratios are depleted from the center of concretions to the periphery, as well as from the centre of veins to the tip. Near-surface cementation is suggested by textural evidence. [delta]18O in the range of -12.636[per thousand] to -8.989 SMOW is calculated for the meteoric palaeowaters, from which average annual surface temperatures of 5-8[degrees]C are inferred. [delta]18O of early-formed cements also yields a mean annual surface temperature of 2-6[degrees]C. Based on continentality and palaeolatitudes of northern Malawi during the Late Permian, we propose that mean annual surface palaeotemperatures may have been as high as 10[degrees]C, similar to those found in modern continental temperate climates.

  8. Cooling and Exhumation of the Coastal Batholith in the Peruvian Andes (5-12°S)

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The South American Andes exhibit strong morphological differences along strike, shaped by a combination of tectonic forces and surface processes. In the central Peruvian Andes (~12°S) a major morphological transition occurs; to the north, the spines of the Western and Eastern Cordilleras come together into a relatively narrow configuration of high topography. In Southern Peru, the region of high topography widens, where the Western and Eastern Cordilleras flank the broad, Altiplano plateau. Despite this morphological change, the Mesozoic-early Cenozoic Coastal Batholith outcrops continuously from 0°-18°S along the western margin of the Peruvian Andes, emplaced along a trench-parallel marginal basin in the Mesozoic. The Coastal Batholith is an ideal geologic setting to investigate potential differences in rock exhumation and cooling histories along the western margin of Peru. While the cooling history of the southern Coastal Batholith has been previously used to estimate timing and magnitude of rock exhumation in Southern Peru, north of 12°S it is poorly constrained. We present 16 zircon and 7 apatite (U-Th)/He mean-ages from three sites, across seven degrees of latitude (5°S to 12°S). In general, ZHe and AHe ages capture two stages of cooling, Oligocene-to-mid-Miocene and mid-to-late Miocene, respectively. We model time-temperature histories of samples with paired AHe and ZHe ages using a Monte-Carlo inversion of HeFTy® (Ketcham, 2005); best fit time-temperature pathways show cooling rates ranging from ~2-24°C/my, where fastest cooling rates are generally observed in the mid-Miocene. To estimate exhumation rates, we apply a simple thermal model to account for nonuniform geothermal gradients expected in a trench-arc setting. Exhumation rates range from ~0.2mm/yr in the north, to 0.4-0.7mm/yr in the south, and rates increase orogenward, where mean elevation is highest. These results, particularly the predominance of Miocene ZHe and AHe data, and the younging

  9. Thermochronological constraints on the multiphase exhumation history of the Ivrea-Verbano Zone of the Southern Alps

    NASA Astrophysics Data System (ADS)

    Wolff, R.; Dunkl, I.; Kiesselbach, G.; Wemmer, K.; Siegesmund, S.

    2012-12-01

    The Ivrea-Verbano Zone of the western Southern Alps (NW Italy) exposes a well-preserved tilted section across the lower continental crust, making it a key region for studying deep crustal and exhumation processes. This paper refines the cooling and exhumation history of the Ivrea-Verbano Zone using K/Ar dating of mica and illite-rich fault gouges as well as zircon fission track and (U-Th)/He thermochronology. The adjacent Strona-Ceneri Zone, Sesia-Lanzo Zone and Lower Penninic nappes are included in the study to derive a broader picture of the low-temperature history of the area. In the Strona profile of the Ivrea-Verbano unit the biotite K/Ar, zircon fission track and (U-Th)/He geochronometers show well preserved, but unusually wide partial retention zones. The youngest ages, representing the formerly deepest position, are situated along the Insubric Line. The main foliation of the Ivrea-Verbano Zone is vertical. The exhumation of the Ivrea-Verbano Zone, which section has a horizontal position on the surface now - took place in three steps. During Jurassic time the Ivrea-Verbano Zone was exhumed to a shallow to mid-crustal position by continental-scale extension. In this displacement the Pogallo Line probably played a dominant role. The studied section occupied an oblique position with a calculated angle of ca. 15 to 23° in the Jurassic. Later the Ivrea-Verbano Zone experienced a minor cooling event in the Late Eocene (~ 38 Ma zircon fission track ages) that was probably related to thrusting and erosion. The final exhumation towards the surface took place in the mid-Miocene as documented by the ca. 14 Ma zircon (U-Th)/He ages and a 12.8 Ma K/Ar fault gouge age. The magnitude and the high rate of final exhumation suggest orogen-parallel extension as a driving force, which is widespread in the Alps in the Lower to Middle Miocene and is most probably connected to orogenic collapse.

  10. Development of the Permian-Triassic sequence in the basin Fringe area, southern Netherlands

    SciTech Connect

    Geluk, M.; Van Doorn, D.; Plomp, A.; Duin, E. )

    1993-09-01

    Geological studies in the fringe area of the southern Permian basin led to new insights in the distribution and development of the Permian-Triassic sequence. During the Permian, the fringe area formed a platform, attached to the London-Brabant Massif, while during the Triassic it is characterized by strongly subsiding half grabens. In the southern Netherlands, Rotliegende sandstones and conglomerates have a much wider distribution than previously recognized. The Rotliegende deposits are capped by claystones and carbonates of the Upper Permian Zechstein. In the offshore, an important feeder system of clastics from the London-Brabant Massif was active during deposition of the Rotliegende and the Zechstein. In course of time, the location of major sandstone deposition shifted westward. Deposition of the Triassic Buntsandstein was controlled by the development of a large feeder system, which transported clastics from the Vosges northward, through the Roer Valley Graben and West netherlands Basin into the Off Holland Low. This system was responsible for the deposition of the economically important sheet sandstones of the Volpriehausen, Detfurth, Hardegsen, and Solling formations. A regional unconformity occurs below the Solling Formation. The sandstones are capped by claystones, evaporites, and sandstones of the Rot Formation. During deposition of the Muschelkalk, the differences in subsidence decreased and shallow marine sediments are interbedded with evaporites. Several unconformities occur within the Keuper. In the previous half grabens in the southern Netherlands, the Keuper is incomplete, which may be indicative for a possible reversal of the tectonic movements during this period.

  11. Marine anoxia and delayed Earth system recovery after the end-Permian extinction.

    PubMed

    Lau, Kimberly V; Maher, Kate; Altiner, Demir; Kelley, Brian M; Kump, Lee R; Lehrmann, Daniel J; Silva-Tamayo, Juan Carlos; Weaver, Karrie L; Yu, Meiyi; Payne, Jonathan L

    2016-03-01

    Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and (238)U/(235)U isotopic compositions (δ(238)U) of Upper Permian-Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ(238)U across the end-Permian extinction horizon, from ∼3 ppm and -0.15‰ to ∼0.3 ppm and -0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans-characterized by prolonged shallow anoxia that may have impinged onto continental shelves-global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe. PMID:26884155

  12. Permian and Pennsylvanian tectonic events in eastern California in relation to major plate motions

    SciTech Connect

    Stevens, C.H.; Sedlock, R. ); Stone, P. )

    1993-04-01

    Northwest-trending basins cutting across older northeast-trending facies belts in eastern California opened by Middle Pennsylvanian time and continued to develop and expand into the Early Permian. Basin development was accompanied by east-vergent thrust-faulting in the Early Permian and was followed by development of northeast-trending folds and regional uplift in middle and Late Permian time. These events have been considered products of long-tern sinistral truncation of the western North American continental margin. Later, in the Late Permian, extensional faulting created small northeast-trending basins in which deposition of terrestrial and shallow-marine rocks occurred. The author consider all late Paleozoic tectonism in eastern California to have been driven by plate interactions along the western margin of North America and to be only indirectly related to the late Paleozoic collision between North America and Gondwana. They propose that the truncated part of North America was part of the Paleo-pacific plate. In Nevada the margin of this plate, along which the Havallah assemblage eventually was emplaced, was convergent, but in California the margin bent sharply and became transform. This fault continued as the Mojave-Sonora mega-shear into Mexico where the oceanic part of the Paleopacific plate was subducted under Gondwana, forming an extensive arc now represented by rocks in S. America.

  13. Has the utility of Dicynodon for Late Permian terrestrial biostratigraphy been overstated?

    NASA Astrophysics Data System (ADS)

    Angielczyk, Kenneth D.; Kurkin, Andrey A.

    2003-04-01

    Dicynodont therapsids have long played an important role in global Late Permian and Triassic biostratigraphy, including recent studies of the effects of the extinction at the Permian-Triassic boundary on terrestrial vertebrates. In particular, the last appearance of the Late Permian taxon Dicynodon has been used to mark the Permian-Triassic boundary in the Karoo Basin of South Africa and to correlate this basin with others in Africa, Europe, and Asia. These practices assume that the named taxon Dicynodon corresponds to a biologically real entity. Here we present the results of a phylogenetic analysis that suggests that this is not the case. Our analysis includes two species referred to Dicynodon that occur only in Russia and the type species that occurs in southern Africa. Our results suggest that these three species do not form a clade to the exclusion of all other dicynodonts; the alternative hypothesis of a monophyletic Dicynodon is more weakly supported. Although preliminary, our analysis challenges the use of Dicynodon for biostratigraphic correlations between Russia and South Africa, and we urge caution in using this taxon to correlate other widely separated basins. This study also emphasizes that without phylogenetic information, there is no guarantee that named taxa represent biologically real entities, and the uncritical use of named taxa can easily lead to spurious biostratigraphic correlations.

  14. Unayzah Formation: a new Permian-Carboniferous unit in Saudi Arabia

    SciTech Connect

    Al-Laboun, A.A.

    1987-01-01

    The sandstones, shales, and thin beds of argillaceous limestone previously included as the basal part of the Permian Khuff Formation were described as the Unayzah Formation by al-Laboun in 1982 and 1986. The type locality (stratotype.) of this formation is in the town of Unayzah, and a reference section was established in the Qusayba area, al-Qasim district, Saudi Arabia. Fossil flora collected from outcrops and palynomorphs obtained from boreholes support a Late Carboniferous-Early Permian age for these strata. The Unayzah Formation is conformably overlain by the massive carbonates of the Khuff Formation, whereas its basal contact is marked by a regional angular unconformity with various older units. The Unayzah Formation is widespread in the Greater Arabian basin. The formation represents cyclic transgressive and regressive deposits preceding the Permian regional marine transgression, during which the massive carbonates of the Khuff Formation were deposited. This Permian transgression marked a major change in the Sedimentation and evolution of the Greater Arabian basin. The porous sandstones of the Unayzah Formation are important exploration targets because several fields in the eastern and southeastern parts of the Greater Arabian basin produce hydrocarbons from the Unayzah. 11 figures, 1 table.

  15. Unique organic remains from an upper Permian coal bearing sequence in the Talcher Coalfield, Orissa, India

    SciTech Connect

    Tripathi, A.

    2004-07-01

    The playnological assemblage of coal bearing upper Permian sequence of Talcher Coalfield registers presence of some peculiar organic remains. These are described as Orissiella gen. nov., which is characterized by a vesicle with collar-like structure at the oral end, spines and or corrugations on the body. The affinity and palaeoecological significance of Orissiella is also discussed. 12 refs., 4 figs., 2 plates.

  16. Tectonic controls on Upper Permian lacustrine oil shales in the Junggar basin, NW China

    SciTech Connect

    Carroll, A.R.; Brassell, S.C.; Graham, S.A. )

    1991-03-01

    Collision of the Tarim craton with the southern margin of Asia during the Late Carboniferous-Early Permian resulted in uplift of an ancestral Tian Shan range and geographic isolation of the previously marine Junggar basin. Dramatic shifts from marine to nonmarine sedimentation took place in both the southern Junggar and northern Tarim basins during the Permina. Paleocurrent analysis indicate that by the Late Permian, coarse-grained sediments in both basins were being supplied predominantly from the area of the Tian Shan. During the Late Permian, the southern Junggar received in excess of 5,000 m of nonmarine sediments, including approximately 1,000 m of laminated, highly organic-rich lacustrine mudstones (oil shales). These deposits commonly have TOCs of 20-30%, and Rock-Eval pyrolitic yields reaching 2,000 mg/g, ranking them among the most prolific petroleum source rocks in the world. Based on a comparison of the distribution of steranes and extended tricyclic terpanes, these Upper Permian oil shales appear to be the primary source of oils in the giant Karamay field in the northwestern Junggar basin. Ancestral uplift of the Tian Shan thus produced a complex tectono-hydrologic partitioning of the Late Permina Junggar basin, which exerted a strong influence on the character of petroleum source rocks deposited within the basin.

  17. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea

    NASA Astrophysics Data System (ADS)

    Cisneros, Juan Carlos; Abdala, Fernando; Atayman-Güven, Saniye; Rubidge, Bruce S.; Celâl Şengör, A. M.; Schultz, Cesar L.

    2012-01-01

    The medial Permian (∼270-260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian "mammal-like reptile" member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction.

  18. Provincialization of terrestrial faunas following the end-Permian mass extinction.

    PubMed

    Sidor, Christian A; Vilhena, Daril A; Angielczyk, Kenneth D; Huttenlocker, Adam K; Nesbitt, Sterling J; Peecook, Brandon R; Steyer, J Sébastien; Smith, Roger M H; Tsuji, Linda A

    2013-05-14

    In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic. PMID:23630295

  19. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea

    PubMed Central

    Cisneros, Juan Carlos; Abdala, Fernando; Atayman-Güven, Saniye; Rubidge, Bruce S.; Şengör, A. M. Celâl; Schultz, Cesar L.

    2012-01-01

    The medial Permian (∼270–260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian “mammal-like reptile” member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction. PMID:22307615

  20. Taeniopterid lamina on Phasmatocycas megasporophylls (Cycadales) from the Lower Permian of Kansas, U.S.A.

    USGS Publications Warehouse

    Gillespie, W.H.; Pfefferkorn, H.W.

    1986-01-01

    New specimens of Phasmatocycas and Taeniopteris from the original Lower Permian locality in Kansas demonstrate organic attachment of the two and corroborate Mamay's hypothesis that Phasmatocycas and Taeniopteris were parts of the same plant. These forms also suggest that cycads evolved from taxa with entire leaves; i.e. Taeniopteris, rather than from pteridosperms with compound leaves. ?? 1986.

  1. Upper Permian vertebrates and their sedimentological context in the South Urals, Russia

    NASA Astrophysics Data System (ADS)

    Tverdokhlebov, Valentin P.; Tverdokhlebova, Galina I.; Minikh, Alla V.; Surkov, Mikhail V.; Benton, Michael J.

    2005-02-01

    Fossil fishes and tetrapods (amphibians and reptiles) have been discovered at 81 localities in the Upper Permian of the Southern Urals area of European Russia. The first sites were found in the 1940s, and subsequent surveys have revealed many more. Broad-scale stratigraphic schemes have been published, but full documentation of the rich tetrapod faunas has not been presented before. The area of richest deposits covers some 900,000 km 2 of territory between Samara on the River Volga in the NW, and Orenburg and Sakmara in the SW. A continental succession, some 3 km thick, of mudstones, siltstones, and sandstones, deposited on mudflats and in small rivers flowing off the Ural Mountain chain, span the last two stages of the Permian (Kazanian, Tatarian). The succession is divided into seven successive units of Kazanian (Kalinovskaya, Osinovskaya, and Belebey svitas, in succession) and Tatarian age, which is further subdivided into the early Tatatian Urzhumian Gorizont (Bolshekinelskaya and Amanakskaya svitas, in succession), and the late Tatarian Severodvinian (Vyazovskaya and Malokinelskaya svitas, of equivalent age) and Vyatkian gorizonts (Kulchumovskaya and Kutulukskaya svitas, of equivalent age). This succession documents major climatic changes, with increasing aridity through the Late Permian. The climate changes are manifested in changing sedimentation and the spread of dryland plants, and peak aridity was achieved right at the Permo-Triassic (PTr) boundary, coincident with global warming. Uplift of the Urals and extinction of land plants led to stripping of soils and massive run-off from the mountains; these phenomena have been identified at the PTr boundary elsewhere (South Africa, Australia) and this may be a key part of the end-Permian mass extinction. The succession of Late Permian fish and tetrapod faunas in Russia documents their richness and diversity before the mass extinction. The terminal Permian Kulchomovskaya and Kutulukskaya svitas have yielded

  2. Pangean Reconstruction of the Yucatan Block and its Permian, Triassic, and Jurassic Geologic and Tectonic History

    NASA Astrophysics Data System (ADS)

    Steiner, M.

    2004-12-01

    Paleomagnetic studies of Paleozoic sedimentary and plutonic rocks demonstrate that the Yucatan Block lay inverted off the NW coast of South America (SA) in Pangea, and rotated in a series of clockwise motions as SA and NA separated. Mid-Permian Yucatan was a fragment of the western margin of Pangea, just south of the equator. By 230 Ma, Yucatan rotated ˜20° clockwise and moved to the equator. Clockwise rotation continued through the Jurassic: ˜54° between 230 Ma and about Oxfordian, and another ˜32° between ˜Oxfordian and Tithonian, when the approximate present orientation was achieved. Passage of the Yucatan Block into the gap created by the separation of North and South America requires left-lateral motion relative to North America, perhaps by translation along the Mojave Sonora megashear. One remanence, carried by magnetite in red bed strata from the margins of the marine Santa Rosa basin (Maya Mtns), decays exceedingly linearly to the origin of orthogonal-axes plots. Biostratigraphy indicates a Late Pennsylvanian to Middle Permian age, and the presence of dual polarities in a 110 m, four polarity, magnetostratigraphic sequence demonstrates a post-Late Paleozoic Reversed Superchron (i.e., Middle Permian) age. Plutonic rocks exhibit a second, also dual-polarity, remanence, which corresponds to a paleopole 60° clockwise of the mid-Permian pole. The spatial relationship between the Permian and pluton paleopoles is very similar to that of the North American Permian and Late Triassic poles. Moreover, exceedingly uniform K/Ar ages of 231±7 Ma characterize all Maya Mtns plutons and the southern volcanic complex, indicating a 230 Ma resetting of the K/Ar radiometric systems of plutons dated by U/Pb as Late Silurian (Steiner and Walker, 1996). Metamorphic aureoles developed in the Pennsylvanian-Permian Santa Rosa strata bordering the Silurian plutonic complexes suggest the occurrence of a post-intrusion hydrothermal event. The 230 Ma reset K/Ar systems

  3. Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy): constraints on the exhumation of Zermatt-Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust

    NASA Astrophysics Data System (ADS)

    Kirst, Frederik; Leiss, Bernd

    2016-03-01

    Kinematic analyses of shear zones at Lago di Cignana in the Italian Western Alps were used to constrain the structural evolution of units from the Piemont-Ligurian oceanic realm (Zermatt-Saas and Combin zones) and the Adriatic continental margin (Dent Blanche nappe) during Palaeogene syn- and post-exhumational deformation. Exhumation of Zermatt-Saas (U)HP rocks to approximately lower crustal levels at ca. 39 Ma occurred during normal-sense top-(S)E shearing under epidote-amphibolite-facies conditions. Juxtaposition with the overlying Combin zone along the Combin Fault at mid-crustal levels occurred during greenschist-facies normal-sense top-SE shearing at ca. 38 Ma. The scarcity of top-SE kinematic indicators in the hanging wall of the Combin Fault probably resulted from strain localization along the uppermost Zermatt-Saas zone and obliteration by subsequent deformation. A phase of dominant pure shear deformation around 35 Ma affected units in the direct footwall and hanging wall of the Combin Fault. It is interpreted to reflect NW-SE crustal elongation during updoming of the nappe stack as a result of underthrusting of European continental margin units and the onset of continental collision. This phase was partly accompanied and followed by ductile bulk top-NW shearing, especially at higher structural levels, which transitioned into semi-ductile to brittle normal-sense top-NW deformation due to Vanzone phase folding from ca. 32 Ma onwards. Our structural observations suggest that syn-exhumational deformation is partly preserved within units and shear zones exposed at Lago di Cignana but also that the Combin Fault and Dent Blanche Basal Thrust experienced significant post-exhumational deformation reworking and overprinting earlier structures.

  4. Total petroleum systems of the Bonaparte Gulf Basin area, Australia; Jurassic, Early Cretaceous-Mesozoic; Keyling, Hyland Bay-Permian; Milligans-Carboniferous, Permian

    USGS Publications Warehouse

    Bishop, M.G.

    1999-01-01

    The Bonaparte Gulf Basin Province (USGS #3910) of northern Australia contains three important hydrocarbon source-rock intervals. The oldest source-rock interval and associated reservoir rocks is the Milligans-Carboniferous, Permian petroleum system. This petroleum system is located at the southern end of Joseph Bonaparte Gulf and includes both onshore and offshore areas within a northwest to southeast trending Paleozoic rift that was initiated in the Devonian. The Milligans Formation is a Carboniferous marine shale that sources accumulations of both oil and gas in Carboniferous and Permian deltaic, marine shelf carbonate, and shallow to deep marine sandstones. The second petroleum system in the Paleozoic rift is the Keyling, Hyland Bay-Permian. Source rocks include Lower Permian Keyling Formation delta-plain coals and marginal marine shales combined with Upper Permian Hyland Bay Formation prodelta shales. These source-rock intervals provide gas and condensate for fluvial, deltaic, and shallow marine sandstone reservoirs primarily within several members of the Hyland Bay Formation. The Keyling, Hyland Bay-Permian petroleum system is located in the Joseph Bonaparte Gulf, north of the Milligans-Carboniferous, Permian petroleum system, and may extend northwest under the Vulcan graben sub-basin. The third and youngest petroleum system is the Jurassic, Early Cretaceous-Mesozoic system that is located seaward of Joseph Bonaparte Gulf on the Australian continental shelf, and trends southwest-northeast. Source-rock intervals in the Vulcan graben sub-basin include deltaic mudstones of the Middle Jurassic Plover Formation and organic-rich marine shales of the Upper Jurassic Vulcan Formation and Lower Cretaceous Echuca Shoals Formation. These intervals produce gas, oil, and condensate that accumulates in, shallow- to deep-marine sandstone reservoirs of the Challis and Vulcan Formations of Jurassic to Cretaceous age. Organic-rich, marginal marine claystones and coals of the

  5. New Thermochronologic Data Constraining the Exhumation History of the Pangong Range, Ladakh, NW India

    NASA Astrophysics Data System (ADS)

    Bohon, W.; Tripathy, A.; Hodges, K.; Arrowsmith, R.; Van Soest, M. C.

    2011-12-01

    Major transcurrent fault systems have played a fundamental role in the late Cenozoic evolution of the Himalayan-Tibetan orogenic system. One of the most dramatic of these is the NW-SE striking, dextral-oblique Karakoram fault system (KFS), which effectively serves as the SW boundary of the Tibetan Plateau. In the Ladakh region of NW India, the fault system bifurcates into 2 fault strands bounding the Pangong Range (PR), a lozenge-shaped region of high elevation that is commonly regarded as a transpressional uplift. We are studying the partitioning of slip over time between shortening and translational components during transpression along both KFS strands. An important aspect of this work is a study of the differential exhumation history of the PR relative to two other high elevation regions to the north and south: the Karakoram Range (KR) and the Ladakh Range (LR), respectively. Although a variety of thermochronometric data will be reported for the LR, PR, and KR in our presentation, we focus here on (U-Th)/He zircon (ZHe) data for the KR and LR. Four published ZHe dates for the northern margin of the LR (Kirstein et al., 2009, Geological Society of London, special pub.) range from 12.9 ± 2.0 Ma to 19.2 ± 3.0 Ma (2 σ) with a rough correlation of older dates at higher elevations. Our new dates for samples collected nearer to the SW strand of the KFS are substantially younger: 7.5 ± 0.12 Ma. It is unclear if the combined datasets are indicative of protracted cooling of the northern part of the LR during rotational exhumation of the LR to the south, as postulated by Kirstein et al., or if the ca. 7.5 Ma dates represent local resetting during KFS activity. Interestingly, detrital ZHe data for modern sands from large catchments that drain the KR range to the north of the NE strand of the KFS indicate cooling of the KR below the nominal bulk closure temperature of the ZHe system (ca. 190C) within a narrow time range of 5.5-7.8 Ma. This range includes the ZHe cooling

  6. Exhumation history of the eastern Periadriatic fault - linkage to the Tauern metamorphic core complex

    NASA Astrophysics Data System (ADS)

    Heberer, Bianca; Neubauer, Franz; Dunkl, István; Genser, Johann

    2014-05-01

    Indentation of rigid blocks into rheologically weak orogens is generally associated with lateral and vertical extrusion of rocks. In this study, we report an example from the Eastern Alps, in which subvertical extrusion of crustal blocks associated with exhumation in distant areas is connected by a transfer fault, which likely corresponds to a block boundary in the deeper crust or even lithosphere. We applied apatite (U-Th)/He (AHe) dating to Triassic granites and Oligocene tonalites from the Karawanken plutonic belts located in the immediate vicinity of the eastern Periadriatic fault near the Austrian-Slovenian border. The eastern Periadriatic fault is segmented into three portions: a straight segment west of the Hochstuhl-Möll Valley (HVM) fault system, a central segment between the NW-trending HVM and Lavant Valley faults with a Neogene positive flower structure separating the north-vergent North Karawanken from the south-vergent South Karawanken unit, and an eastern segment largely buried underneath Neogene Pannonian basin sediments. In the central segment, the Periadriatic fault is dextrally displaced by the HVM and Lavant Valley faults and the North Karawanken unit is thrust over the Neogene flexural, intra-orogenic Klagenfurt basin, which contains sediments ranging from Sarmatian (ca. 11 Ma) to Pliocene or possibly even Quaternary. In the central segment, we find AHe ages mostly ranging from 6 to 9 Ma. This is in contrast to older ages west of the HVM directly at the PAF, where an age of 20 ± 1 Ma has been found. The basement north of the Klagenfurt basin yields also older AHe and apatite fission track ages ranging from c. 25 to 30 Ma. This age pattern confirms and constrains the positive flower structure as an area of young exhumation. Young AHe ages similar to the central segment of the eastern Periadriatic fault were reported from the Tauern window (Foeken et al., 2007; Wölfler et al., 2012). We suggest that the HVM fault system acts as a transfer

  7. Uppermost Permian to Lower Triassic Conodont Zonation from Enshi area, western Hubei Province, South China

    NASA Astrophysics Data System (ADS)

    Lyu, Z.; Zhao, L.; Chen, Z. Q.; Ma, D.; Yan, P.; Zhan, P.

    2015-12-01

    The Permian-Triassic transition witnessed the largest biotic turnover of Earth life during the Phanerozoic history. Ecosystems in sea and on land have also experienced the most protected restoration following the end-Permian mass extinction. These biocrises were also associated with climatic and environmental extremes through the latest Permian to Middle Triassic. In order to uncover the links among these extreme events, we need to establish high-resolution biochronostratigraphy, which offers precise timescales for reconstructing event sequences and probing the possible causes. Of these, conodont biostratigraphy is an operational tool in enhancing stratigraphic resolution. Although their ancestors and phylogeny remain unclear, conodonts are a rapid evolutionary lineage and extremely abundant in the Triassic marine carbonate successions. Here, we present recent study results of the Lower Triassic conodont zonation from the Ganxi and Jianshi areas, western Hubei Province, South China, which were situated on a carbonate ramp at the southern northern margin of the Upper Yangtze Platform. Therein, the uppermost Permian to Lower Triassic successions are well exposed and yield abundant conodonts. A total of nine conodont zones was established: (1) Clarkina yini-Clarkina zhangi Zone, (2) Hindeodus changxingensis Zone, (3) Hindeodus parvus Zone, (4) Isarcicella staeschei Zone, (5) Clarkina planata Zone, (6) Neoclarkina discrete Zone, (7) Neospathodus dieneri Zone, (8) Novispathodus waageni Zone, and (9) Triassospathodus homeri Zone. The Ns. dieneri M1, Ns. dieneri M2 and Ns. dieneri M3 subzones have also been distinguished from the Ns. dieneri Zone. Both Nv. waageni eowaageni subzones and Nv. waageni waageni subzones are also recognizable from the Nv. waageni Zone. The first occurrence of H. parvus marks the Permian-Triassic boundary(PTB), while the first occurrence of Nv. waageni eowaageni defines the Induan-Olenekian boundary. These conodont zones correlate well with

  8. Paleoenvironment of the Permian rocks: a comparison between central and eastern Alborz, Iran

    NASA Astrophysics Data System (ADS)

    Lankarani, M.; Amini, A.; Mosadegh, H.

    2009-04-01

    The succession of Permian rocks in Alborz region is composed of siliciclastic and carbonate facies. All of the sediments were deposited in the Paleotethyan passive continental margin but they show different facies architecture and paleoenvironmental condition in various parts of the region. This study, as part of a wider project, has investigated sedimentary facies and paleoenvironment of the Permian rocks in central and eastern Alborz. The Permian rocks in central Alborz are dominated by siliciclastic facies (Doroud Formation) in the lower, and carbonate facies (Ruteh Formation) in the upper half. Field studies and laboratory measurements resulted in recognition of 4 terrigenous and 13 carbonate facies in the succession. A siliciclastic shallow marine system was determined as depositional environment of the terrigenous facies. A homoclinal carbonate ramp, with scattered patch reefs, was determined as depositional environment of the carbonate facies. Dasycladacean green algae, ancestral red algae, hermatypic corals and bryozoans were the major bioconstructors of the ramp. The abundance of skeletal shoals respect to ooidal shoals in the ramp margin was high. The Permian rocks in eastern Alborz are dominated by mixed siliciclastic-carbonate facies (Ruteh Formation) in the lower, and siliciclastic facies (Nesen Formation) in the upper half. The studies resulted in recognition of 5 terrigenous and 6 carbonate facies in the succession. A mixed siliciclastic-carbonate shelf with high sediment influx was determined as depositional environment of the mixed siliciclastic-carbonate facies. Occurrence of the small patch reefs with high coral diversity in this mixed shelf indicates normal marine (hyposaline) condition. Upper terrigenous facies were deposited in fluvial-flood plain system. Difference in paleoclimate and tectonic activity of two sub-basins seems to be the major cause of the differences between the Permian facies in central and eastern Alborz.

  9. Tectonic rotations south of the Bohemian Massif from palaeomagnetic directions of Permian red beds in Hungary

    USGS Publications Warehouse

    Marton, E.; Elston, D.P.

    1987-01-01

    Palaeomagnetic studies were carried out in Permian red beds of the Balaton Highlands, the Mecsek Mountains and the Bu??kk Mountains of Hungary. Statistically well defined directions were obtained from six localities in the Balaton Highlands and two localities in the Mecsek Mountains. No meaningful results were obtained from the Bu??kk Mountains. Three magnetic components were identified from red beds of the Balaton Highlands: (1) in haematite with a very high unblocking temperature (700??C), interpreted as a Permian magnetization (Dc= 79??, Ic=-11??, k = 24, ??95 = 13.6 ??), in six samples from three beds in a single locality (2) a secondary but ancient component residing mainly inmaghemite (D = 314??, I = 49??, k = 48, ??95 = 10.0??), in 84 samples from six localities with a within-locality scatter increasing on unfolding; and (3) a direction parallel to the present field (D = 7??, I = 62??, k = 46, ??95 = 7.7 ??), in nine samples from a single locality. For the Balaton Highlands, the component 1 direction agrees with directions obtained from Permian red beds and volcanics in the eastern part of the Southern and Eastern Alps and the Inner West Carpathians. All show large, apparent rotations relative to stable Europe since the Permian. Component 2 is of post-folding (post-Aptian) age. Its direction agrees with known Late Cretaceous directions from the Transdanubian Central Mountains, which also show significant counterclockwise rotation relative to stable Europe. The characteristic magnetization for the Mecsek Mountains resides in haematite and may be primary. The directions indicate only a slight net counterclockwise rotation of the Mecsek Mountains with respect to stable Europe since the Permian. ?? 1987.

  10. Coring and High-Resolution Imaging of the Permian-Triassic Boundary in Deltadalen, Svalbard

    NASA Astrophysics Data System (ADS)

    Planke, Sverre

    2016-04-01

    The Permian-Triassic extinction was likely triggered by the voluminous igneous activity of the Siberian Traps. There are, however, limited information available about the effects of the Siberian Traps volcanism in Permian to Triassic sedimentary successions outside Siberia. We drilled two boreholes across the Permian-Triassic boundary (PTB) in Deltadalen, Svalbard, in August 2014, to better document the extinction event and environmental changes in the sedimentary succession in this region. Even though the PTB event is studied in several outcrops to varying degree if scrutiny on Svalbard, a scientific core is important for understanding the details of the PTB event, as outcrops may not permit studies at the appropriate levels of resolution, exposure or confidence. The Deltadalen site was chosen as an optimal drilling location after field work in the Isfjorden area in 2013 and early 2014. The almost 100 m deep holes were fully cored and penetrated the Triassic Vikinghøgda Formation (about 85 m recovered) and the Permian Kapp Starostin Formation (about 15 m). The main lithologies include Permian chert-rich green glauconitic sandstones and Triassic mudstones. A 10 m thick sedimentary reference outcrop section across the PTB was further logged and sampled in a nearby river valley. A comprehensive core analysis program is now underway. High-resolution XRF, MST and hyperspectral core scanning has been completed along the entire core surface, while high-resolution CT scanning has been carried out for whole core sections. The DD-1 core has subsequently been split, photographed, described, and sampled for geochemical, micropaleontological, petrological and magnetic analyses. Almost 10 bentonite layers have furthermore been sampled for volcanological and geochronological studies. Our goal is that the cores will become an important future reference section of the PTB in Svalbard and the high-Arctic, and help constrain the extent of the regional effects of explosive volcanism

  11. Species of the medullosan ovule Stephanospermum from the Lopingian (late Permian) floras of China

    NASA Astrophysics Data System (ADS)

    Spencer, Alan R. T.; Wang, Shi-Jun; Dunn, Michael T.; Hilton, Jason

    2013-10-01

    The medullosan pteridosperm ovule Stephanospermum Brongniart is a well-known component of Carboniferous aged coal-ball and siderite nodule floras from North America and Europe but also occurs in the Permian floras of Cathaysia where it is represented by the Lopingian (late Permian) aged species Stephanospermum trunctatum (Li) Wang et al. (2009) from coal-balls in the Wangjiazhai Formation in Southern China. We provide a detailed emendation of S. trunctatum and illustrate it comprehensively for the first time, and document an additional specimen from the Wangjiazhai Formation coal-ball assemblage that we assign to Stephanospermum shuichengensis sp. nov. S. shuichengensis is distinguished from S. trunctatum by the absence of apical teeth in the sclerotesta and non-obovate base. The two species of Stephanospermum from the Wangjiazhai Formation are important as they extend the stratigraphic and geographical range of the genus from the Pennsylvanian of Euramerica into the Lopingian of Southern China, and demonstrate that the genus persisted in wetland, peat forming environments in the run up to the end-Permian mass extinction event. The 44 MY stratigraphic discontinuity between the Euramerican and the Cathaysian species, here named the Stephanospermum gap, leads us to infer that the genus was likely to have occurred in the Pennsylvanian-Permian successions of southern Russia and northern China that are geographically and stratigraphically intermediate to the known occurrences but from which the genus has yet to be discovered. Medullosan pteridosperms appear to have become extinct at or immediately prior to the Permian-Triassic boundary that coincides with the Permo-Trias mass extinction event; although the exact causes of this loss in plant diversity remains unknown, a response to regional climatic drying is likely to have been a contributing factor.

  12. Post-Variscan basin evolution in the central Pyrenees: Insights from the Stephanian-Permian Anayet Basin

    NASA Astrophysics Data System (ADS)

    Rodríguez-Méndez, Lidia; Cuevas, Julia; Tubía, José María

    2016-03-01

    The Anayet Basin, in the central Pyrenees, records a Stephanian-Permian continental succession including three Permian volcanic episodes. The absolute chronology of these rocks has allowed us to better constrain the early post-Variscan evolution of the Pyrenees. The transtensional regime responsible for the formation of the pull-apart Anayet Basin began at least in Stephanian times, the age of the first post-Variscan deposits in the area, and lasted until Late Permian. During Middle Eocene times, the Alpine Orogeny inverted the Anayet Basin and led to the formation of south-vergent chevron folds and axial plane penetrative cleavage.

  13. New parametric implementation of metamorphic reactions limited by water content, impact on exhumation along detachment faults

    NASA Astrophysics Data System (ADS)

    Mezri, L.; Le Pourhiet, L.; Wolf, S.; Burov, E.

    2015-11-01

    Metamorphic phase changes have a strong impact on the physical and mechanical properties of rocks including buoyancy (body forces) and rheology (interface forces). As such, they exert important dynamic control on tectonic processes. It is generally assumed that phase changes are mainly controlled by pressure (P) and temperature (T) conditions. Yet, in reality, whatever the PT conditions are, phase changes cannot take place without an adequate amount of the main reactant - water. In present day geodynamic models, the influence of water content is neglected. It is generally assumed that water is always available in quantities sufficient for thermodynamic reactions to take place at minimal Gibbs energy for given P and T conditions and a constant chemical composition. If this assumption was correct, no high-grade metamorphic rocks could to be found on the Earth's surface, since they would be retro-morphed to low-grade state during their exhumation. Indeed, petrologic studies point out that water, as a limiting reactant, is responsible for the lack of retrograde metamorphic reactions observed in the rocks exhumed in typical MCC contexts. In order to study the impact of fluid content on the structure of metamorphic core complexes, we have coupled a geodynamic thermo-mechanical code Flamar with a fluid-transport and water-limited thermodynamic phase transition algorithm. We have introduced a new parameterization of Darcy flow that is able to capture source/sink and transport aspects of fluid transport at the scale of the whole crust with a minimum of complexity. Within this model, phase transitions are controlled by pressure temperature and the local amount of free fluid that comes from both external (meteoric) and local (dehydration) sources. The numerical experiments suggest a strong positive feedback between the asymmetry of the tectonic structures and the depth of penetration of meteoric fluids. In particular, bending-stress distribution in asymmetric detachment zones

  14. Subsidence in Gorontalo Bay, Sulawesi (Indonesia) and metamorphic core complex exhumation on land

    NASA Astrophysics Data System (ADS)

    Pezzati, Giovanni; Hennig, Juliane; Advokaat, Eldert; Hall, Robert; Burgess, Peter; Perez-Gussinye, Marta

    2015-04-01

    data suggest that the northern flank of the complex continues under the basin, linked to a potential low-angle normal fault under the basin. Similar structures have been identified in the Palu Metamorphic Complex to the west of the bay. Strongly deformed mid to lower crustal rocks are exposed in high mountains along the Neck of Sulawesi and were rapidly exhumed along mylonitic shear zones due to northward extension associated with development of the North Sulawesi Trench during the Pliocene. We propose that the rapid subsidence of the Poso and Tomini Basins is related to extension associated with the exhumation of metamorphic core complex on land.

  15. Imaging high-pressure rock exhumation along the arc-continent suture in eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Brown, Dennis; Feng, Kuan-Fu; Wu, Yih-Min; Huang, Hsin-Hua

    2015-04-01

    Imaging high-pressure rock exhumation in active tectonic settings is considered to be one of the important observations that could potentially help to move forward the understanding of how this process works. Petrophysical analyses carried out along a high velocity zone imaged by seismic travel time tomography along the suture zone between the actively colliding Luzon Arc and the southeastern margin of Eurasia in Taiwan suggests that high-pressure rocks are being exhumed from at least a depth of 50 km below the arc-continent suture to the shallow subsurface where they coincide with an outcropping tectonic mélange called the Yuli Belt. The Yuli Belt comprises mainly greenschist facies quartz-mica schist, with lesser metabasite, metamorphosed mantle fragments and, importantly, minor blueschist. Modeling of published data bases of measured seismic velocities for a large suite of rocks suggests that all of the Yuli belt lithologies fit well with the measured Vp, Vs, and Vp/Vs at ambient pressures and temperatures (a 20 oC/km geotherm is used) from 10 to about 20 km depth. With the exception of hornblendite, mantle rocks need 30% to 40 % serpentinization to approximate the in situ range of Vp and and Vs at these depths. From about 20 km to 30 km, most continental crust and volcanic arc lithologies move out of the range of velocities measured by the tomography model at these depths. Blueschist (including the calculated Vp and Vs for the Yuli Belt samples), pyroxenite, and harzburgite, lherzolite, and dunite with around 20% to 30% serpentinization now enter into the range of velocities for these depths. From 40 km to 50 km depth, the mantle rocks pyroxenite, and weakly to unserpentinized harzburgite, lherzolite, and dunite, together with mafic eclogite velocities best fit the range of Vp, Vs and Vp/Vs at these depths. Seismicity along the arc-continent suture, the upper bounding fault of the high velocity zone examined here, indicate that it is a moderately oblique

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Exhumation in the Bendeleben Mountains, Seward Peninsula, Alaska constrained by radiogenic helium thermochronometry

    NASA Astrophysics Data System (ADS)

    McDannell, K. T.; Toro, J.; Hourigan, J. K.

    2010-12-01

    system to form through the Seward Peninsula. This study is focused on recreating the thermal history and magnitude of exhumation within the extensional regime using radiogenic helium thermochronometry. Over 24 Granitic samples were collected throughout the Bendeleben range for apatite (U-Th/He) analysis along age-elevation profiles extending from the fault scarp to over 600 meters of relief. The apatite low-temperature cooling ages were input into a forward modeling sequence within Pecube which derived an applicable model to suggest an exhumation history of the Bendeleben Mountains in accordance with the apatite apparent ages.

  20. Deep-tow geophysical survey above large exhumed mantle domains of the eastern Southwest Indian ridge

    NASA Astrophysics Data System (ADS)

    Bronner, A.; Munschy, M.; Sauter, D.; Carlut, J.; Searle, R.; Cannat, M.

    2012-04-01

    The recent discovery of a new type of seafloor, the "smooth seafloor", formed with no or very little volcanic activity along the easternmost part of the ultra-slow spreading Southwest Indian ridge (SWIR) shows an unexpected complexity in processes of generation of the oceanic lithosphere. There, detachment faulting is thought to be a mechanism for efficient exhumation of deep-seated mantle rocks. We present here a deep-tow geological-geophysical survey over smooth seafloor at the eastern SWIR (62-64°N) combining multibeam bathymetric data, magnetic data, geology mapping from sidescan sonar (TOBI) images and results from dredge sampling. We introduce a new type of calibration approach for deep-tow fluxgate magnetometer. We show that magnetic data can be corrected from the magnetic effect of the vehicle with no recourse to its attitude (pitch, roll and heading) but only using the 3 components recorded by the magnetometer and an approximation of the scalar intensity of the Earth magnetic field. The collected dredge samples as well as the sidescan sonar images confirm the presence of large areas of exhumed mantle-derived peridodites surrounded by a few volcanic constructions. We investigate the possibility that magnetic anomalies are either caused by serpentinized peridotites and/or magmatic intrusions. We show that the magnetic signature of the smooth seafloor is clearly weaker than the surrounding volcanic areas. Moreover, the calculated magnetization of a source layer as well as the comparison between deep-tow and sea-surface magnetic data argue for strong East-West variability in the distribution of the magnetized sources. This variability may result from fluid-rock interactions along the detachment faults as well as from the occurrence of small sized and thin volcanic patches and thus questions the seafloor spreading origin of the corresponding magnetic anomalies. Finally, we provide magnetic arguments, as calculation of block rotation or spreading asymmetry in

  1. Exhumation By Landslide-Initiated Debris Flows in the 2013 Colorado Front Range Storm

    NASA Astrophysics Data System (ADS)

    Anderson, R. S.; Anderson, S. W.; Anderson, S. P.; Schellhase, D. A.

    2014-12-01

    What is the role of rare events in the exhumation of steep landscapes? We use the "millennial" storm that hit the Front Range, Colorado, USA, in September 2013 to explore this question in a semi-arid landscape. More than 250 mm of rain fell over a ~100 km swath of the Front Range in a 5 day period; totals in some areas exceeded average annual precipitation. The storm triggered over 1300 landslides and debris flows in four major Front Range watersheds (Coe et al., 2014). We created a DEM of difference in the 102 km2 area of overlap using aerial LiDAR surveys, acquired in August 2010 by the Boulder Creek CZO and in November 2013 by FEMA. The study region covers the Boulder Creek watershed from the middle of the Rocky Mountain Surface to the western edge of the Plains, and encompasses Boulder Canyon, Fourmile Canyon, and the 26-km2 2010 Fourmile Canyon Fire. Precambrian crystalline rocks underlie most of the area, although the eastern margin includes sedimentary rocks in hogbacks along the mountain front. We computed site characteristics and volumes for 120 failures. Within the crystalline terrain, most failures occurred at or near the bedrock interface at 0.5-1 m depth, often near the ridgelines downslope of bedrock outcrops. Failures occurred on slopes of 25-40°, and show no slope aspect bias. Failures evolved into debris flows that scoured chutes from the initiation site down to the master stream, traveling at up to 10 m/s. We saw little evidence of deposition; most debris was entrained in the flooding master streams and exited the mountain front. Evacuated sediment volumes represent several hundred years of exhumation within the source basins, based on published long-term erosion rates calculated from 10Be concentrations. We infer that, even in this semi-arid environment, debris flows initiated by rare shallow landslides are a dominant process for evacuating sediment from steep channels and delivering it to the plains.

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

    NASA Astrophysics Data System (ADS)

    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

  3. Long-term exhumational history and Neogene reactivation of the Brooks Ranges, Alaska : Insights from low-T thermochronology

    NASA Astrophysics Data System (ADS)

    Bigot-Buschendorf, Maelianna; Fillon, Charlotte; Mouthereau, Frédéric; Labrousse, Loïc; Auxiètre, Jean-Luc; Moore, Thomas; van der Beek, Peter; Stockli, Daniel; Ehlers, Todd

    2013-04-01

    The Brooks Ranges, northern Alaska, result from the Mesozoic collision of continental arcs with the Arctic continental margin. The foreland basin deposits indicating exhumation and creation of topography dates the formation of an orogenic wedge from 160 Ma onward. Discrete events of rapid exhumation occurred from 140 to 25 Ma, likely reflecting changes in the dynamics of the orogenic wedge, linked to rate and geometry of the subduction in the southern Alaska margin and/or climate changes. Our study aims at quantifying rates and duration of exhumational events in the Brooks Ranges through new low-temperature thermochronology analyses, using (U-Th)/He on apatites and zircons along the Trans-Aslaskan Crustal Transect (TACT) profile from the Ruby Mountains to the North Slope, and integrating whole sediments from the basement to the Tertiary cover (Franklin Bluffs and Sagwon Bluffs). We also combined these new thermochronological data to existing dataset in the Colville Basin and Central Brooks Ranges to unravel the thrusting sequence through a 3-D thermo-kinematic model (Pecube). The modeling of the main thrust activation sequences shows that a thick-skinned out-of-sequence thrust system must have been active from 30 to 15 Ma along the TACT, and from 40 to 15 Ma in the Shublik mountain, to reproduce the data. Preliminary results from inverse modeling show evidences for two main exhumational events at 100-85 Ma and 35-20 Ma. The latter Neogene event appears to be related to out-of-sequence duplexing in the Doonerak mountains. Reasons for the reactivation of the Mesozoic Brooks Ranges during the Neogene must include far-field accommodation of deformation induced by subduction of the Yakutat terranes in southern Alaska coupled with transcurrent movements in the Beaufort Sea, and coeval increase in sediment yields as evidenced in the McKenzie delta.

  4. The thermal, metamorphic and magmatic evolution of a rapidly exhuming terrane: the Nanga Parbat Massif, northern Pakistan

    NASA Astrophysics Data System (ADS)

    Whittington, A. G.

    The Nanga Parbat-Haramosh Massif (NPHM) is the most northerly outcrop of Indian Plate rocks in the Himalayan orogen, exposed by rapid recent exhumation through the structurally overlying Kohistan Island Arc in northern Pakistan. Exhumation has been achieved by erosion in the apparent absence of extensional tectonics. Metabasaltic dykes intruded into polymetamorphic basement rocks provide time markers that distinguish early from late fabrics that probably correlated with Precambrian and Himalayan deformation respectively. Nanga Parbat is anomalous within the Himalayan orogen for both the timing and nature of metamorphism and anatexis. A multidisciplinary approach allows the thermal history to be tightly constrained. Metamorphism is characterised by cordierite growth during near-isothermal decompression. Garnet inclusion assemblages record P-T conditions of 720 +/- 50 deg C and 7.5 +/- 1.5 kbar, while spinel-cordierite intergrowths unique to the massif interior formed at 710 +/- 60 deg C and 5.0 +/- 1.1 kbar. Lower grade assemblages are exposed towards the massif margins. Tourmaline leucogranite plutons and sheets are characterised by similar trace element geochemistry to Miocene High Himalayan granites, indicative of vapour-absent crustal melting as would result from rapid decompression, but were emplaced more than 10 million years later. More recently, fluid infiltration into conjugate shear zones accommodating vertical stretching in the core of the massif resulted in anatexis and the formation of restitic cordierite-bearing pods. 40Ar-39Ar studies indicate regional cooling below 400 deg C as recently as 1 Ma, and the distribution of excess 40Ar in basement samples is indicative of magmatic/metamorphic fluids at depths > 10 km. One-dimensional thermal modelling indicates that increasing cooling rates through time do not require increasing exhumation rates because advection of heat results in a steepened near-surface geotherm. These models predict both the style and

  5. Apatite fission-track evidence of widespread Eocene heating and exhumation in the Yukon-Tanana Upland, interior Alaska

    USGS Publications Warehouse

    Dusel-Bacon, C.; Murphy, J.M.

    2001-01-01

    We present an apatite fission-track (AFT) study of five plutonic rocks and seven metamorphic rocks across 310 km of the Yukon-Tanana Upland in east-central Alaska. Samples yielding ???40 Ma AFT ages and mean confined track lengths > 14 ??m with low standard deviations cooled rapidly from >120??C to 40 Ma suggest partial annealing and, therefore, lower maximum temperatures (???90-105??C). A few samples with single-grain ages of ???20 Ma apparently remained above ???50??C after initial cooling. Although the present geothermal gradient in the western Yukon-Tanana Upland is ???32??C/km, it could have been as high as 45??C/km during a widespread Eocene intraplate magmatic episode. Prior to rapid exhumation, samples with ???40 Ma AFT ages were >3.8-2.7 km deep and samples with >50 Ma AFT ages were >3.3-2.0 km deep. We calculate a 440-320 m/Ma minimum rate for exhumation of all samples during rapid cooling. Our AFT data, and data from rocks north of Fairbanks and from the Eielson deep test hole, indicate up to 3 km of post-40 Ma vertical displacement along known and inferred northeast-trending high-angle faults. The predominance of 40-50 Ma AFT ages throughout the Yukon-Tanana Upland indicates that, prior to the post-40 Ma relative uplift along some northeast-trending faults, rapid regional cooling and exhumation closely followed the Eocene extensional magmatism. We propose that Eocene magmatism and exhumation were somehow related to plate movements that produced regional-scale oroclinal rotation, northward translation of outboard terranes, major dextral strike-slip faulting, and subduction of an oceanic spreading ridge along the southern margin of Alaska.

  6. Titanite petrochronology of the Pamir gneiss domes: Implications for middle to deep crust exhumation and titanite closure to Pb and Zr diffusion

    NASA Astrophysics Data System (ADS)

    Stearns, M. A.; Hacker, B. R.; Ratschbacher, L.; Rutte, D.; Kylander-Clark, A. R. C.

    2015-04-01

    The Pamir Plateau, a result of the India-Asia collision, contains extensive exposures of Cenozoic middle to lower crust in domes exhumed by north-south crustal extension. Titanite grains from 60 igneous and metamorphic rocks were investigated with U-Pb + trace element petrochronology (including Zr thermometry) to constrain the timing and temperatures of crustal thickening and exhumation. Titanite from the Pamir domes records thickening from ~44 to 25 Ma. Retrograde titanite from the Yazgulem, Sarez, and Muskol-Shatput domes records a transition from thickening to exhumation at ~20-16 Ma, whereas titanite from the Shakhadara dome records prolonged exhumation from ~20 to 8 Ma. The synchronous onset of exhumation may have been initiated by breakoff of the Indian slab and possible convective removal of the Asian lower crust and/or mantle lithosphere. The prolonged exhumation of the Shakhdara and Muztaghata-Kongur Shan domes may have been driven by continued rollback of the Asian lithosphere concurrent with shortening and northwestward translation of the Pamir Plateau.

  7. Chlorine isotope constraints on fluid-rock interactions during subduction and exhumation of the Zermatt-Saas ophiolite

    NASA Astrophysics Data System (ADS)

    Selverstone, J.; Sharp, Z. D.

    2013-10-01

    Chlorine isotope compositions of high-pressure (˜2.3 GPa) serpentinite, rodingite, and hydrothermally altered oceanic crust (AOC) differ significantly from high- and ultrahigh-pressure (> 3.2 GPa) metasedimentary rocks in the Aosta region, Italy. Texturally early serpentinites, rodingites, and AOC have bulk δ37Cl values indistinguishable from those of modern seafloor analogues (δ37Cl = -1.0 to +1.0‰). In contrast, serpentinites and AOC samples that recrystallized during exhumation have low δ37Cl values (-2.7 to -0.5‰); 37Cl depletion correlates with progressive changes in bulk chemistry. HP/UHP metasediments have low δ37Cl values (median = -2.5‰) that differ statistically from modern marine sediments (median = -0.6‰). Cl in metasedimentary rocks is concentrated in texturally early minerals, indicating modification of seafloor compositions early in the subduction history. The data constrain fluid sources during both subduction and exhumation-related phases of fluid-rock interaction: (1) marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction. (2) No pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial. (3) Localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel. Most samples, however, preserved protolith signatures during subduction to near-arc depths.

  8. Pulsed exhumation of interior eastern Tibet: Implications for relief generation mechanisms and the origin of high-elevation planation surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Huiping; Oskin, Michael E.; Liu-Zeng, Jing; Zhang, Peizhen; Reiners, Peter W.; Xiao, Ping

    2016-09-01

    River incision into a widespread, upland low-relief landscape, and related patterns of exhumation recorded by low-temperature thermochronology, together underpin geodynamic interpretations for crustal thickening and uplift of the eastern Tibetan Plateau. We report results from a suite of 11 (U-Th-Sm)/He cooling-age samples. Eight samples comprise a 1.2 km relief section collected from elevations up to 4800 m in the Jiulong Shan, an elevated, rugged region located in the hinterland of the Yalong-Longmen Shan Thrust Belt, and surrounded on three sides by upland low-relief landscape surfaces. Zircon and apatite cooling ages record two episodes of rapid exhumation in the early Oligocene and late Miocene, that were separated by a period of stability from ∼30 to 15 Ma. The first episode is consistent with a similar pulse evident from the Longmen Shan. The second episode is ongoing, and when integrated with adjacent cooling-age data sets, shows that doming of the Jiulong Shan has resulted in 2 to 4 km of differential exhumation of the plateau interior. We show from a compilation of glacial landform-mapping that the elevation of the plateau surface closely tracks global last glacial maximum equilibrium line altitude. We hypothesize that smoothing of highlands by efficient glacial and periglacial erosion, coupled with potential river captures and conveyance of sediments via external drainage, can yield an apparently continuous low-relief plateau landscape formed diachronously at high elevation.

  9. Exhumation of the Panama basement complex and basins: Implications for the closure of the Central American seaway

    NASA Astrophysics Data System (ADS)

    Ramírez, Diego A.; Foster, David A.; Min, Kyoungwon; Montes, Camilo; Cardona, Agustín.; Sadove, Gephen

    2016-05-01

    The emergence of the Central American isthmus occurred episodically from Eocene to Pliocene time and was caused by a series of tectonic and volcanic processes. Results from zircon U-Pb geochronology, zircon (U-Th)/He (ZHe) and apatite (U-Th)/He (AHe) thermochronology, and zircon Lu-Hf isotopic data from sedimentary (sandstones and recent river sands) and plutonic rocks from the Azuero Peninsula and Central Panama document the exhumation and uplift history of the Panamanian basement complex. Our data support previous paleobotanical and thermochronological studies that suggest that by middle Eocene time some areas of Central Panama and Azuero Peninsula were exposed above sea level as a series of islands surrounded by shallow open marine waters. The Gatuncillo, Cobachón and Tonosí formations were deposited during this partial emergence. Transtension in the Oligocene-early Miocene produced various pull-apart basins (e.g., the Canal Basin) and local uplift that exhumed the Eocene strata (Gatuncillo and Cobachón formations). This event probably reduced circulation between the Pacific Ocean and the Caribbean Sea. The Tonosí Formation records late Miocene to Pleistocene cooling and exhumation, which may be related to uplift above the subducting Coiba Ridge. These results suggest that the emergence of the Isthmus of Panama followed a series of diachronous events that led to the final closure of the Central American seaway.

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

    USGS Publications Warehouse

    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.

  11. Exhumation of Greater Himalayan rock along the main central thrust in Nepal: Implications for channel flow

    USGS Publications Warehouse

    Robinson, D.M.; Pearson, O.N.

    2006-01-01

    South-vergent channel flow from beneath the Tibetan Plateau may have played an important role in forming the Himalaya. The possibility that Greater Himalayan rocks currently exposed in the Himalayan Fold-Thrust Belt flowed at mid-crustal depths before being exhumed is intriguing, and may suggest a natural link between orogenic processes operating under the Tibetan Plateau and in the fold-thrust belt. Conceptual and numeric models for the Himalayan-Tibetan Orogen currently reported in the literature do an admirable job of replicating many of the observable primary geological features and relationships. However, detailed observations from Greater Himalayan rocks exposed in the fold-thrust belt's external klippen, and from Lesser Himalayan rocks in the proximal footwall of the Main Central Thrust, suggest that since Early Miocene time, it may be more appropriate to model the evolution of the fold-thrust belt using the critical taper paradigm. This does not exclude the possibility that channel flow and linked extrusion of Greater Himalayan rocks may have occurred, but it places important boundaries on a permissible time frame during which these processes may have operated. ?? The Geological Society of London 2006.

  12. Structural control of weathering processes within exhumed granitoids: Compartmentalisation of geophysical properties by faults and fractures

    NASA Astrophysics Data System (ADS)

    Place, J.; Géraud, Y.; Diraison, M.; Herquel, G.; Edel, J.-B.; Bano, M.; Le Garzic, E.; Walter, B.

    2016-03-01

    In the latter stages of exhumation processes, rocks undergo weathering. Weathering halos have been described in the vicinity of structures such as faults, veins or dykes, with a lateral size gradually narrowing with depth, symmetrically around the structures. In this paper, we describe the geophysical characterisation of such alteration patterns on two granitoid outcrops of the Catalan Coastal Ranges (Spain), each of which is affected by one major fault, as well as minor faults and fractures. Seismic, electric and ground penetrating radar surveys were carried out to map the spatial distribution of P-wave velocity, electrical resistivity and to identify reflectors of electromagnetic waves. The analysis of this multi-method and complementary dataset revealed that, at shallow depth, geophysical properties of the materials are compartmentalised and asymmetric with respect to major and subsidiary faults affecting the rock mass. This compartmentalisation and asymmetry both tend to attenuate with depth, whereas the effect of weathering is more symmetric with respect to the major structure of the outcrops. We interpret such compartmentalisation as resulting from the role of hydraulic and mechanical boundaries played by subsidiary faults, which tend to govern both the chemical and physical alterations involved in weathering. Thus, the smoothly narrowing halo model is not always accurate, as weathering halos can be strongly asymmetrical and present highly irregular contours delimiting sharp contrasts of geophysical properties. These results should be considered when investigating and modelling fluid storage and transfer in top crystalline rock settings for groundwater applications, hydrocarbon or geothermal reservoirs, as well as mineral deposits.

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

    PubMed

    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. PMID:24767546

  14. Late Neogene tectonically driven crustal exhumation of the Sikkim Himalaya: Insights from inversion of multithermochronologic data

    NASA Astrophysics Data System (ADS)

    Landry, Kyle R.; Coutand, Isabelle; Whipp, David M.; Grujic, Djordje; Hourigan, Jeremy K.

    2016-03-01

    Apatite fission track and zircon (U-Th)/He data are reported for 34 bedrock samples distributed between the foothills and the topographic crest of the Darjeeling-Sikkim Himalaya. The pattern of observed cooling ages does not correlate with topography, rainfall distribution, and the deeply incised high-relief Tista window, indicating that tectonic processes are mainly responsible for their spatial distribution. Inversion of this thermochronometric data set using 3-D thermokinematic modeling constrained by independent geological and geophysical observations was performed to evaluate the contribution of slip partitioning, duplex development, and relief growth on the evolution of the thermal structure of the Himalaya during the last 12 Ma. Models involving significant relief growth do not show a substantial influence of topography evolution on the cooling age distribution, while models involving duplex growth demonstrate that tectonic processes exert a dominant influence on their distribution. In concert with equivalent studies in Bhutan, central Nepal, and NW India, our results attest that the lateral variation of the geometry and kinematics of the Himalayan basal décollement locally associated with duplex formation exert a leading influence on lateral variations of middle to upper crustal long-term exhumation rates documented along the strike of the Himalaya.

  15. The northern Sacramento Mountains, southwest United States. Part II: Exhumation history and detachment faulting

    USGS Publications Warehouse

    Pease, V.; Foster, D.; Wooden, J.; O'Sullivan, P.; Argent, J.; Fanning, C.

    2000-01-01

    Thermochronologic and thermobarometric data reveal the timing, distribution and intensity of thermal events associated with detachment faulting in the Sacramento Mountains metamorphic core complex. In the northwest Sacramento Mountains, cooling rates of c. 100°C Ma−1 are associated with Late Cretaceous plutonism followed by cooling of the crust by thermal conduction. Post-Late Cretaceous cooling slowed to c. 1–6°C Ma−1. Finally, the region records average cooling rates of 38–53°C Ma−1 between c. 20 and 15 Ma. In contrast, the thermal profile of the northeast Sacramento Mountains is dominated by syntectonic Tertiary plutonism followed by very rapid cooling. A granodioritic suite intruded at c. 680°C and c. 3 kbar at c. 20 Ma, records cooling to <100°C by c. 15 Ma. Such rapid cooling and exhumation suggests that unroofing by tectonic denudation was the driving mechanism for the final cooling. The similarity of the miocene cooling profiles between these two areas clearly suggests that the Sacramento Mountains experienced a regional cooling event associated with tectonic unroofing driven by regional Miocene crustal extension. Estimates of the initial angle of the Sacramento Mountains detachment fault using palaeothermal gradients suggest that it was active at a dip of 25°.

  16. Emplacement, rapid burial, and exhumation of 90-Ma plutons in southeastern Alaska

    USGS Publications Warehouse

    Himmelberg, G.R.; Haeussler, P.J.; Brew, D.A.

    2004-01-01

    In southeastern Alaska, granodiorite-tonalite plutons of the Admiralty-Revillagigedo belt intruded the Jurassic-Cretaceous Gravina belt along the eastern side of the Alexander terrane around 90 Ma. These plutons postdate some deformation related to a major contractional event between the previously amalgamated Wrangellia and Alexander terranes and the previously accreted terranes of the North American margin. We studied the aureole mineral assemblages of these plutons near Petersburg, Alaska, determined pressure and temperature of equilibration, and examined structures that developed within and adjacent to these plutons. Parallelism of magmatic and submagmatic fabrics with fabrics in the country rock indicates synchroneity of pluton emplacement with regional deformation and suggests that magma transport to higher crustal levels was assisted by regional deformation. Replacement of andalusite by kyanite or sillimanite indicates crustal thickening soon after pluton emplacement. Regional structural analysis indicates the crustal thickening was accomplished by thrust burial. Thermobarometric analyses indicate the aureoles reached near-peak temperatures of 525 to 635 ??C at pressures of 570 to 630 MPa. Consideration of the rate of thermal decay of the aureoles suggests that burial was rapid and occurred at rates around 5 to 8 mm/year. Structural observations indicate there was contractional deformation before, during, and after emplacement of the 90-Ma plutons. Initial exhumation of the Admiralty-Revillagedo belt in the Petersburg area may have occurred along a thrust west of the pluton belt within the Gravina belt. ?? 2004 NRC Canada.

  17. Exhumation of serpentinized peridotite in the northern Manila subduction zone inferred from forward gravity modeling

    NASA Astrophysics Data System (ADS)

    Doo, Wen-Bin; Lo, Chung-Liang; Kuo-Chen, Hao; Brown, Dennis; Hsu, Shu-Kun

    2015-10-01

    The Taiwan Integrated Geodynamic Research program (TAIGER) collected two wide-angle and reflection seismic transects across the northern Manila subduction zone that provide constraints on the seismic velocity structure of the crust. Two-dimensional gravity modeling along these two transects shows a significant, relatively high density (3.12 and 3.02 g/cm3) in the fore-arc region, at the interface between the subducting Eurasian Plate and the accretionary prism in front of the Luzon arc on the overriding Philippine Sea Plate. The anomalous density in this zone is higher than that in the fore-arc crust and the accretionary prism but lower than that in mantle. Numerous geophysical and geological data, together with numerical models, have indicated that serpentinization of the fore-arc mantle is both expected and observed. Serpentinization of mantle rocks can dramatically reduce their seismic velocity and therefore their seismic velocity in a density to velocity conversion. Therefore, the source of the high-density material could be serpentinized fore-arc mantle, with serpentinization caused by the dehydration of the subducting Eurasian Plate. We interpret that positive buoyancy combined with weak plate coupling forces in the northern Manila subduction zone is resulting in this serpentinized fore-arc mantle peridotite being exhumed.

  18. Assessment of potential unconventional Carboniferous-Permian gas resources of the Liaohe Basin eastern uplift, Liaoning Province, China, 2011

    USGS Publications Warehouse

    Pollastro, Richard M.; Potter, Christopher J.; Schenk, Christopher J.; Charpentier, Ronald R.; Cook, Troy A.; Klett, Timothy R.; Kirschbaum, Mark A.

    2012-01-01

    The U.S. Geological Survey estimated a mean of 448 billion cubic feet of potential technically recoverable unconventional natural gas in Carboniferous and Permian coal-bearing strata in the eastern uplift of the Liaohe Basin, Liaoning Province, China.

  19. A feasibility study for an emergency medical services system to serve the Permian basin in the state of Texas

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The development of an Emergency Medical Services System grant application for the Permian Basin Region of West Texas is described along with the application of NASA-developed technology. Conclusions and recommendations are included.

  20. Paleomagnetic studies of Carboniferous and Permian in the U. K. Southern North Sea: Core orientation, paleocurrent analysis, and diagenetic application

    SciTech Connect

    Turner, P. ); Hartley, A.J. )

    1991-03-01

    The U.K. southern North Sea is a major gas province with production from Carboniferous and Permian reservoirs. It was a foreland basin in Carboniferous times uplifted to form a Lower Permian desert basin and subsequently deeply buried during the Mesozoic. Paleomagnetic methods have been used for burial analysis, core orientation, and paleocurrent studies. VRM is shown to be of only limited value for core orientation; problems relating to drilling effects and deflection by ChRM will be discussed. Detailed thermal demagnetization studies are most valuable. Blocking temperature spectra can be related to burial history curves, and ChRM directions isolated and compared with Carboniferous and Permian reference directions. ChRM is a valuable parameter for core orientation and thus paleocurrent studies. Examples will be shown from the Carboniferous and Lower Permian.

  1. Sandstone petrofacies expressions of multiphase basinal tectonics and arc magmatism: Permian Triassic north Bowen Basin, Australia

    NASA Astrophysics Data System (ADS)

    Michaelsen, P.; Henderson, R. A.

    2000-10-01

    Modal analyses of 209 sandstone samples from the Permian-Triassic succession of the northern Bowen Basin, eastern Australia, identify two stratigraphically and compositionally distinct petrofacies. The Lower to Mid Upper Permian Back Creek Group is characterised by Petrofacies A which is quartz-rich (Q 82F 8L 10). It was sourced primarily from cratonic basement terranes to the west, where relief was subdued, and the quartz content of the sandstones may also reflect some reworking in the marine realm with a consequent loss of labile grains. Petrofacies B is volcanolithic and characterises alluvial sediments of the Upper Permian Blackwater and Lower Triassic Rewan Groups. It was sourced from an undissected to transitional magmatic arc provenance located in the contemporary New England Orogen to the east, which supplied abundant pyroclastic debris to the depositional complex. Petrofacies B of the northern Bowen Basin was derived primarily from felsic volcanics, compared to an intermediate association recorded for the southern basinal sector, indicating significant along-arc variation in volcanic style. As a consequence, its framework grain population is enriched in quartz and is not readily accommodated in the schemes of provenance interpretation currently in use. The consistency of framework detrital modes for sandstones distributed throughout the Blackwater Group (Q 24F 10L 66) allows the recognition of subpetrofacies B1 and shows that the volcanism associated with the magmatic arc system was remarkably uniform in character and activity during deposition of the entire group. The magmatic arc delivered almost identical sedimentary debris over a period of some 9 My in the Late Permian. Relative enrichment of quartz within the Early Triassic Rewan Group (Q 49F 6L 45) relative to the Blackwater Group discriminates subpetrofacies B2 and is attributed to a climatic change and shift in palaeotemperature at the Permian-Triassic boundary. The contact between the marine Back

  2. Chemo- and palyno-stratigraphy of the Permian-Triassic transition in the Boreal region

    NASA Astrophysics Data System (ADS)

    van Soelen, Els; Planke, Sverre; Svensen, Henrik; Twitchett, Richard; Polozov, Alexander; Kürschner, Wolfram

    2016-04-01

    Late Permian and early Triassic sediments from Boreal regions are studied using palynological and organic geochemical tools. We present preliminary results from two sites: a Norwegian site which is represented by a 100-m long borehole core and outcrops from Deltadalen on Spitsbergen, and a Russian site which is represented by outcrops and short cores collected near Norilsk in northern Siberia. The main goals of the project are to improve the stratigraphy and to study the environmental changes at high resolution. There is a growing scientific consensus that end Permian biotic crisis was linked to the Siberian Traps Large Igneous Province (LIP) event. However, direct evidence for a stratigraphic correlation of the marine and terrestrial extinction events, with the volcanic successions in the Siberian basin, is rather limited. The Permian-Triassic boundary successions in the Arctic are crucial for direct correlation eastwards to the Siberian Traps. The magnitude and timing of a carbon isotope excursion near the Permian-Triassic boundary is an important stratigraphical tool that may help to unravel the sequence of the events happening during this important period. Preliminary results from the Deltadalen core near the base of the Vikinghøgda Formation show shifts in δ13C from -24.5 to -32.7‰ in the interval expected to span the Permian/Triassic boundary. New Rock-Eval pyrolysis data will shed further light on the origin of the organic matter (e.g. marine versus terrestrial) and may help to understand how much of the δ13C signal can be explained by changes in organic matter source and how much may be attributed to a global change in the carbon isotope signature. Furthermore, compound specific isotope analysis will be done on terrestrial derived lipids (long chain n-alkanes) to reconstruct changes in atmospheric carbon isotopes. In addition to chemostratigraphy, the palynological record will be used for biostratigraphical studies at both Deltadalen and Norilsk

  3. The Permian antitropical fusulinoidean genus Monodiexodina: Distribution, taxonomy, paleobiogeography and paleoecology

    NASA Astrophysics Data System (ADS)

    Ueno, Katsumi

    2006-03-01

    All the documented occurrences with illustration of specimens of the Permian fusulinoidean genus Monodiexodina from a total of 33 areas in 11 regions are reviewed and their taxonomic positions are reexamined in this paper. Among 17 species (including two subspecies) of Monodiexodina in the current taxonomy, the following 10 species are recognized as valid: M. kattaensis, M. wanneri, M. caracorumensis, M. sutchanica, M. shiptoni, M. kumensis, M. wanganensis, M. neimongolensis, M. delicata, and M. rhaphidoformis. In addition, species once referred to Monodiexodina but now should be excluded from the genus are also investigated in terms of their generic positions. In reconstructed mid-Permian paleomap, Monodiexodina-bearing areas can be restored to either northern or southern middle latitudes between high latitudinal cool/cold-water climatic realm and paleo-tropical warm-water realm. These two middle latitudinal areas, each corresponding to the Northern and Southern Transitional Zones, respectively, can be best interpreted climatologically as mesothermal, warm temperate belts in both hemispheres, thus suggesting the genus to be a paleobiogeographically typical antitropical fusulinoidean taxon. Moreover, the genus is generally found in a monotypic, crowded manner in sandy sediments with their shells being often aligned uni-directionally. This mode of occurrence of Monodiexodina strongly suggests that it was adapted to shallow-marine, high-energy environments, which would probably be essentially maintained by the acquisition of highly elongated fusiform/subcylindrical shells with well-developed polar torsion. This morphological feature is adapted to increase septal pores per unit area in polar regions, thus increasing possibility to develop more pseudopodia on both sides of test. It probably has a functional significance for not only locomotion but also anchoring their tests on the surface of bottom sediments in agitated water conditions. The genus itself is considered

  4. Euxinia prior to end-Permian main extinction at Xiaojiaba section, Sichuan Province, South China

    NASA Astrophysics Data System (ADS)

    Wei, H.; Algeo, T. J.; Chen, D.; Yu, H.

    2013-12-01

    Redox conditions in the global ocean prior to, during, and following the end-Permian mass extinction at 252.28 Ma remain contentious. Previous studies in western Australia, South China, and East Greenland have shown that photic-zone euxinia was present at least intermittently from the early Changhsingian through the Dienerian1-3. Here we report a study of organic carbon isotopes, pyrite sulfur isotopes, TOC, pyritic sulfur content, REE, and major and trace elements from the Upper Permian Xiaojiaba section in the Chaotian district of Guangyuan City, Sichuan Province, China. During the Permian-Triassic transition, this section was located on the northwestern margin of the South China Block, facing the Paleo-Tethys Ocean. Our results indicate that suboxic conditions prevailed during the Wuchiapingian and suboxic to anoxic conditions with several pulses of euxinia during the Changhsingian. δ13Corg values are mostly -28‰ to -26‰ but show three positive excursions (to -22‰) prior to the end-Permian mass extinction horizon. These positive excursions are associated with higher Spy concentrations (to ~1%). δ34Spy values are variable (from -41‰ to +5‰) but show a sharp negative excursion in the late Changhsingian (to -43.4‰) that coincided with the most positive δ13Corg values. This horizon is also associated with increases in Eu/Eu*, Baxs, ∑REE, Si, and redox-sensitive metals such as V. These patterns reflect linkage of the C and S cycles during the latest Permian, possibly in response to redox controls. The observed positive excursions in δ13Corg may be due to organic inputs from green sulfur bacteria, which exhibit a smaller photosynthetic fractionation (-12.5‰4) than eukaryotic algae. The pronounced negative excursion of δ34Spy corresponds to a sulfate-sulfide S isotope fractionation of about -60‰, suggesting a large flux of syngenetic framboidal pyrite, which would be indicative of euxinic water-column conditions. We infer that the euxinia prior

  5. Life crises on land across the Permian-Triassic boundary in South China

    NASA Astrophysics Data System (ADS)

    Peng, Yuanqiao; Shi, G. R.

    2009-02-01

    The western Guizhou and eastern Yunnan area of southwest China commands a unique and significant position globally in the study of Permian-Triassic boundary (PTB) events as it contains well and continuously exposed PTB sections of marine, non-marine and marginal-marine origin in the same area. By using a range of high-resolution stratigraphic methods including biostratigraphy, eventostratigraphy, chronostratigraphy and chemostratigraphy, not only are the non-marine PTB sections correlated with their marine counterparts in the study area with high-resolution, the non-marine PTB sections of the study area can also be aligned with the PTB Global Stratotype Section and Point (GSSP) at Meishan in eastern China. Plant megafossils ("megaplants") in the study area indicate a major loss in abundance and diversity across the PTB, and no coal beds and/or seams have been found in the non-marine Lower Triassic although they are very common in the non-marine Upper Permian. The megaplants, however, did not disappear consistently across the whole area, with some elements of the Late Permian Cathaysian Gigantopteris flora surviving the PTB mass extinction and locally even extending up to the Lower Triassic. Palynomorphs exhibit a similar temporal pattern characterized by a protracted stepwise decrease from fern-dominated spores in the Late Permian to pteridosperm and gymnosperm-dominated pollen in the Early Triassic, which was however punctuated by an accelerated loss in both abundance and diversity across the PTB. Contemporaneous with the PTB crisis in the study area was the peculiar prevalence and dominance of some fungi and/or algae species. The temporal patterns of megaplants and palynomorphs across the PTB in the study area are consistent with the regional trends of plant changes in South China, which also show a long-term decrease in species diversity from the Late Permian Wuchiapingian through the Changhsingian to the earliest Triassic, with about 48% and 77% losses of

  6. Lower crust exhumation and ongoing continental convergence in the Variscan Maures-Tanneron Massif, France, geological synthesis and numerical models

    NASA Astrophysics Data System (ADS)

    Gerbault, Muriel; Schneider, Julie; Corsini, Michel; Reverso-Peila, Alexandre

    2015-04-01

    The Maures-Tanneron Massif together with Corsica and Sardinia compose the present day southeastern part of the Variscan belt. Pressure-temperature-time patterns were compiled to adress how rocks once forming a thick orogenic crust were exhumed, from burial conditions of ca. 10 kb and ca. 800°C. A continuous evolution from subduction to collision, from ca. 420 Ma to 290 Ma has recently been proposed by Schneider et al., 2014, ending with orthogonal Permean rifting. Here we complement this study by exploring the thermo-mechanical conditions prevailing during the massive exhumation of this orogenic crust. Based on field observations and petrological analysis indicative of the acceleration of partial melting during ongoing convergence, our numerical models test a scenario in which pre-thickened units located at 40-60 km depth, would have molten due to internal heating and burrial, and were progressively exhumed by gravitationally-driven instabilities to the surface, within ~15-25 Myrs. Assuming temperature dependent elasto-visco-plastic behavior, we have tested rheological layering including mafic or felsic units, far-field convergence and surface processes, as well as temperature-dependent melting conditions and density and viscosity evolution. In order to reproduce asymmetrical exhumation over the given time-scales and over an extent area of more than 50 km synchroneous with the development of compressional folds in the upper crust, a best fit was obtained for an applied far-field convergence of 0.5 cm/yr, equivalent to present day Alpine convergence rates, and a bulk crustal viscosity of at least 102° Pa.s. Crustal heat source had to contribute significantly, whereas a too shallow mantle heat source triggers exceedingly warm and fast exhumation. We propose that the evolution from transpressional to tensile conditions perpendicular to the orogenic axis (north-south Permean rifting versus East-West vergence of the orogenic structures), occurred progressively as

  7. Late Cenozoic exhumation and timing of the deformation front of the Kashmir Himalayas from U-Th/(He) thermochronometry

    NASA Astrophysics Data System (ADS)

    Gavillot, Y. G.; Meigs, A.; Stockli, D. F.; Malik, M. M.

    2013-12-01

    Apatite and zircon (U-Th)/He cooling ages are used to quantify the recent exhumation pattern associated with fault activity across the Kashmir Himalayas. Here we present data from thirty samples, totaling of 74 individual single-grain apatite and zircon dated aliquots. Cooling age data were collected from (1) molasse sediments of the Murree and Siwalik Formations from structures in the Sub-Himalayan belt (deformed foreland) and from (2) metasediments and plutonic rocks exhumed in the 'hinterland'. Structures of the Sub-Himalayan belt include the Suruin-Mastgarh anticline (SMA) at the deformation front, equivalent to the Himalayan Frontal thrust (HFT), and emergent local faults to the north (e.g. the Riasi thrust (RT)). In the hinterland, the Main Boundary (MBT) and Main Central (MCT) thrust sheets bound the Sub-Himalayan belt to the north. Apatite (U-Th)/He (AHe) cooling ages for the molasses sediments are consistently younger than the sediment age indicating that Sub-Himalayan belt samples are reset. Mean cooling age data based on the single grain populations from each sample ranges from ~1-10 Ma. Single grain and mean age probability density plots reveal a period of rapid cooling and exhumation between 1.8-2.75 Ma throughout the Sub-Himalaya. Distributed deformation associated with northward underthrusting along the MHT, and the onset of folding related to the SMA explains the regional exhumation of the Sub-Himalaya after ~2.75 Ma. Four samples from the hinterland MBT and MCT thrust sheets yield AHe cooling ages between ~5-21 Ma. Three of the samples have cooling ages between 4.7-7.2 Ma, likely coeval with activity of the MBT. Zircon (U-Th)/He (ZHe) samples from the hinterland are younger than the ages of the metasedimentary or plutonic source rocks. Most sample ages from the Sub-Himalaya are older or the same to the depositional age and are therefore detrital. Probability density plots of hinterland ZHe data show a pronounced spike in cooling between 16-21 Ma

  8. Detrital apatite (U-Th)/He constraints on the exhumational histories of the Arunachal Pradesh Himalaya and the Shillong Plateau

    NASA Astrophysics Data System (ADS)

    Staisch, L. M.; Clark, M. K.; Niemi, N. A.; Avdeev, B.

    2010-12-01

    Erosion in the Himalaya is driven largely by a strongly coupled system of extreme climatic conditions and active tectonic processes. Spatial and temporal variations in erosion rates along strike are presumably controlled by differences in local climate, seismicity, deformation rates, and lithology. Quantifying the contribution of each of these parameters to the erosional budget of the Himalaya, however, is a nontrivial problem. The easternmost portion of the Himalayan arc offers a natural laboratory to explore the role of climatic influence on erosion rates. Deformation and uplift of the Shillong Plateau since ~8 Ma has created an orographic barrier ~400 km long that shields the eastern Himalaya, in Arunachal Pradesh, India, from a significant proportion of the precipitation carried by the South Asian Monsoon. Long-term exhumation rates derived from the Himalaya west and east of this orographic barrier have been shown to differ by a factor of ~2, a difference ascribed to reduced climatic forcing of erosion in the lee of the Shillong Plateau. Here we present apatite (U-Th)/He thermochronology data from modern detrital samples collected from northeast India. Between 18-20 single grain ages from each catchment were analyzed in order to calculate erosion rates on a 106 yr timescale. Recently developed Bayesian techniques for the inverse modeling of detrital data were used to derive time-temperature histories for each sample. Recent erosion rates modeled for a single south-facing catchment on the Shillong Plateau are modest, ~0.25 km Myr-1, and show a clear increase in exhumation rates at ~8 Ma from rates of <0.01 km Myr-1. These results are consistent with published estimates based on bedrock thermochronology sampling. Detrital data from the Arunachal Himalaya also reveal an increase in exhumation rate, from ~0.01 to ~0.55 km Myr-1, at ~7 Ma. While these rates are consistent with erosion rates derived from bedrock samples in the lee of the Shillong Plateau in the

  9. Exhumation History of the Taebaek Mountain Range in Korean Peninsula: Implications for Miocene Tectonic Evolution of East Asia

    NASA Astrophysics Data System (ADS)

    Min, K. K.; Cho, M.; Reiners, P. W.

    2008-12-01

    The Taebaek mountain range is the major, N-S trending belt running along the eastern margin of the Korean Peninsula. This range has a relatively gentle slope to the west (inland) whereas its eastern side is significantly steeper being bounded by the East Sea (or Japan Sea). The Daegwanryeong, a ~850-m- high mountain located approximately in the middle (latitude 37.5°N) of the Taebaek range, is mainly composed of a single body of Jurassic granite. In order to study exhumation histories of the Taebaek mountain range, we applied single-grain apatite (U-Th)/He thermochronometry to the eastern crustal section of the Daegwanryeong. Apatite samples from the elevation of 25 - 500 m yielded average (U-Th)/He ages in the range of ~21 - 26 Ma with an overall weighted mean age of ~23 Ma. The variation of ages over this elevation span is negligible. In contrast, two samples collected at higher elevations show apparently older ages of 30 Ma (770 m) and 36 Ma (840 m). The elevation-independent ages below 500 m suggest a pulse of rapid exhumation at ~23 Ma, and the positive correlation between age and elevation detected above 700 m indicates a less intense cooling event prior to ~23 Ma. By extrapolating the observed patterns for the low (<500 m) and high (>700 m) elevation data in the age-elevation plot, we inferred a breakage of the slope near the elevation of 600 - 700 m which is interpreted as the base of the previous He partial retention zone (He- PRZ) of apatite. The inferred onset of rapid exhumation in the Daegwanryeong is coeval with the opening of East Sea (or Japan Sea). Although the exact timing of initial separation of the Japanese islands from the Eurasian continent is controversial, several lines of evidence support Late Oligocene - Early Miocene development of initial rift as a precursor of the East Sea. The remarkable temporal match between the exhumation of Daegwanryeong and the opening of East Sea provides an example for the coupled development of mountain

  10. Petrogenesis of greenstones from the Mino Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau

    NASA Astrophysics Data System (ADS)

    Ichiyama, Yuji; Ishiwatari, Akira; Koizumi, Kazuto

    2008-01-01

    Permian greenstones in the Jurassic Mino-Tamba accretionary complex, southwest Japan, are divided into three distinct series on the basis of their geological occurrence, mineralogy, and geochemistry. A low-Ti series (LTS) is associated with Lower Permian chert and limestone, and is the most voluminous of the three series. The LTS shows slightly more enriched geochemical and isotopic characteristics than MORB. A transition series (TS) is mainly associated with Lower Permian chert, and has more enriched geochemical signatures than MORB. Its isotopic characteristics are divided into enriched and depleted types. A high-Ti series (HTS) occurs as sills and hyaloclastites within Middle Permian chert and as dikes intruding the TS. Some HTS rocks have high MgO contents. The HTS is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to HIMU-type basalt. The geochemistry of the voluminous LTS is similar to that of the oceanic basalt series of the Kerguelen plateau, suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in Early Permian time. We infer that the TS formed simultaneously at the margins of the mantle plume head. In contrast, the HTS may have resulted from partial melting of a deep mantle plume tail in Middle Permian time. Permian greenstones in the Mino-Tamba belt may have thus formed by superplume activity in an intra-oceanic setting. Given the presence of two known contemporary continental flood basalt provinces (Siberia and Emeishan) and some accreted oceanic plateau basalts, the vast magmatism of the Mino-Tamba oceanic plateau suggests a large-scale superplume pulse in Permian time. Accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in Japan and elsewhere in the circum-Pacific region.

  11. First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

    NASA Astrophysics Data System (ADS)

    Vozárová, Anna; Presnyakov, Sergey; Šarinová, Katarína; Šmelko, Miloš

    2015-10-01

    Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44-0.27) and for the Nb/U ratio at (9.55-4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U-238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

  12. Sedimentation of shelf sandstones in Queen Formation, McFarland and Means fields, central basin platform of Permian basin

    SciTech Connect

    Malicse, A.; Mazzullo, J.; Holley, C.; Mazzullo, S.J.

    1988-01-01

    The Queen Formation is a sequence of carbonates, evaporites, and sandstones of Permian (Guadalupian) age that is found across the subsurface of the Central Basin platform of the Permian basin. The formation is a major hydrocarbon reservoir in this region, and its primary reservoir facies are porous shelf sandstones and dolomites. Cores and well logs from McFarland and Means fields (on the northwest margin of the Central Basin platform) were examined to determine the sedimentary history of the shelf sandstones.

  13. Palaeomagnetism and magnetostratigraphy of uppermost Permian strata, southeast New Mexico, USA: correlation of the Permian-Triassic boundary in non-marine environments

    NASA Astrophysics Data System (ADS)

    Molina Garza, Roberto S.; Geissman, John W.; Lucas, Spencer G.

    2000-06-01

    Continental red sandstone and siltstone rocks of the Dewey Lake (Quartermaster) Formation at Maroon Cliffs, near Carlsbad, New Mexico, are characterized by two components of magnetization with partially overlapping laboratory unblocking temperature spectra. Both magnetizations display high coercivities (>100mT), probably residing in haematite. A north-directed magnetization with steep positive inclination unblocks between 100 and 650°C, isolating a predominantly northwest-directed magnetization, with shallow inclination, of near uniform normal polarity and maximum unblocking temperatures of 680°C. We collected samples from 24 palaeomagnetic sites (i.e. individual beds) from a ~60m thick section of flat-lying strata disconformably overlying carbonate and evaporite rocks of the Rustler Formation. The upper member of the Rustler Formation contains a Late Permian (early Changxingian) marine invertebrate and conodont fauna. Of the sampled sites, four yield only steep magnetizations, interpreted to be recent overprints. Eight sites did not yield well-grouped site means and were excluded from the final calculations. The formation mean (dec=337.7°, inc=9.2° k=31.6, α95=7.8°, N=12 sites) defines a palaeomagnetic pole located at 55.2°N, 117.5°E, in good agreement with other Late Permian North American cratonic poles. Correlation of the short polarity sequence of this section of Dewey Lake strata is unambiguous. Compared with the polarity stratigraphy of marine sections in Asia, and supported by isotopic age determinations on a widespread bentonite bed in Dewey Lake strata in west Texas (approximately 251Ma) and fossil data for the underlying Rustler Formation, the magnetostratigraphy is consistent with deposition of the Dewey Lake Formation during the latest Changxingian (Late Permian) stage.

  14. Late exhumation of the Bergell pluton (Italian Alps): tectonics, climate change or Messinian base level drop? Insights from apatite (U-Th)/He ages determination and modeling.

    NASA Astrophysics Data System (ADS)

    Mahéo, Gweltaz; Gautheron, Cécile; Hervé Leloup, Philippe; Tassant-Got, Laurent; Douville, Eric

    2010-05-01

    The Bergell pluton, is an elongated-shape granodioritic to tonalitic body emplaced during Oligocene time at 30-32 Ma along the Insubric Line in the south-central Alps. This intrusion is located immediately north of the Insubric fault, within a bloc delimited by a major strike slip and normal faults related to the eastward extrusion of the central and eastern Alps. The range lies north of the Italian great lakes, an area where the erosion related to the Messinian base-level drop is supposedly strong. In order to reconstruct the Miocene exhumation history of this pluton and to place constraints on the effect of Messinian base-level drop on erosion and uplift, we performed (U-Th)/He dating of 10 apatite samples from the Bergell area. Data from horizontal (constant elevation) profiles indicate that no significant E-W tilting occurred after ~9 Ma and that the present day relief, especially in the valley where the Insubric/Tonale line is located, is at least 9 Ma old. Apatite (U-Th)/He age versus elevation data from a vertical transect in the core of the pluton suggests a three phases exhumation/cooling history: (1) fast exhumation/cooling until 16-12 Ma, (2) slow exhumation/cooling and (3) fast exhumation/cooling after ~6 Ma. Simulations of the apatite He ages versus elevation relationship, using a trial and error method, confirm these three exhumation/cooling phases. It furthermore suggests that the final exhumation stage initiated between 4 and 6 Ma ago, and continued at a relatively high rate until present time. By comparing this timing with the onset of major climatic, tectonic and base level drop events recognized in the Southern Alps, we propose that the Messinian base-level drop has initiated the late exhumation of the Bergell. However, as this event is relatively short (less than 1 Myr) it cannot explain the post 4 Ma-high exhumation rate. It is thus suggested that the transition to a more variable climate initiating at 3-4 Ma might have maintained high erosion

  15. Heterogeneous extrusion and exhumation of deep-crustal Variscan assembly: Geochronology of the Western Tatra Mountains, northern Slovakia

    NASA Astrophysics Data System (ADS)

    Moussallam, Y.; Schneider, D. A.; Janák, M.; Thöni, M.; Holm, D. K.

    2012-07-01

    The nature and style of mid-crustal assembly and exhumation during continental collision has been investigated in the Tatra Mountains of the Western Carpathians. The pre-Alpine basement of the Western Carpathians represents the easternmost exposure of the Variscan orogen in Europe, which marks the collision of Laurasia with Gondwanian-affiliated terranes during the Palaeozoic. The Tatric crystalline unit of the Western Tatra in northern Slovakia displays an inverted metamorphic sequence where a high-grade unit comprising migmatites with relicts of eclogite has been thrust over a lower-grade mica schist unit. New geochronological and thermochronological data together with published thermobarometry illuminate the metamorphic history of the Western Tatra. The Upper Unit eclogites with occasionally preserved omphacite record near isothermal decompression from 1.6 GPa to 1.0-1.2 GPa at 750-800 °C which lead to intensive re-equilibration at high-pressure granulite facies conditions, comparable to the peak metamorphic conditions of the host migmatite. Both eclogite and migmatite shared a retrograde P-T path following the insertion of the eclogite assemblage into the migmatites. The metamorphic evolution of the Lower Unit mica schist is constrained to peak P-T conditions of 0.6-0.8 GPa and 640 and 660 °C followed by retrogression. This suggests that different rock types of the Western Tatra metamorphic core shared only their exhumation path from mid-crustal levels. ID-TIMS Sm-Nd dating of garnet from eclogite yields a whole rock-garnet isochron age of 337 ± 10 Ma, with an initial ɛNd isotopic composition of + 8.3. In situ U-Pb dating of monazite from a migmatite surrounding the eclogite shows one age population of c. 380 Ma whereas monazite from a migmatite away from the eclogite preserves a robust 340 ± 11 Ma age which is indistinguishable from Sm-Nd garnet age and U-Pb age of zircons in the anatectic leucosome of the migmatite (347 ± 7 Ma). A younger monazite age

  16. Benthic aquatic ecosystems across the Permian-Triassic transition: record from biogenic structures in fluvial sandstones, central Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Miller, M. F.

    2000-07-01

    The effect of the Permian extinction in communities inhabiting sandy stream bottoms can be evaluated using trace fossils as proxies for body fossils. Permian and Triassic sandstones exposed in the Beardmore and Shackleton Glacier areas (central Transantarctic Mountains) were deposited in sandy braided streams and contain four types of trace fossils (vertical shafts and horizontal, bilobed and chevron traces). These traces were produced by a single type of animal that moved in the top 30 cm of sediment and dominated the benthic community. Evidence for a single producer includes similar size (diameter) of all traces and change within single specimens from one trace type to another. The animal was not affected by the Permian extinction event, as evidenced by its equal abundance within the Permian (Buckley Formation) and Triassic (Fremouw Formation) fluvial sandstones in the Beardmore Glacier area. Based on trace morphology and on domination of modern sandy river ecosystems by insects, the producer most likely was an insect, although its more precise identity is problematic. Although families of insects with modern aquatic burrowers are not known before the Jurassic, these trace fossils may show that these burrowers were present earlier than the insect body-fossil record suggests. Alternatively, archaic insect groups, many of which became extinct at the end-Permian and are known to have been aquatic but not infaunal, may have included some active burrowers that were unscathed by the Permian extinction.

  17. Palynological assemblages of non-marine rocks at the Permian Triassic boundary, western Guizhou and eastern Yunnan, South China

    NASA Astrophysics Data System (ADS)

    Peng, Yuanqiao; Yu, Jianxin; Gao, Yongqun; Yang, Fengqing

    2006-12-01

    Marine and non-marine facies of the Permian-Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian-Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage.

  18. Tubiphytes-archaeolithoporella-girvanella reefal facies in Permian buildup, Mino terrane, central Japan

    NASA Astrophysics Data System (ADS)

    Sano, Hiroyoshi; Horibo, Kenji; Kumamoto, Yasuko

    1990-10-01

    The Lower to Middle Permian Okumino buildup of the Mino terrane, central Japan, formed a carbonate cap on a seamount which was sitting in an open-ocean realm. Microscopic examination reveals considerable amounts of Tubiphytes, Archaeolithoporella, and Girvanella in these rocks. These low laminar encrusting organisms together with cystopore bryozoa and syndepositional radial-fibrous cements formed bindstones. The bindstones are interpreted as having formed wave-resistant algal reefal mounds on the marginal terrace of the Okumino buildup which also has the lagoonal flat, sand bar or shoal, and foreslope facies. The Okumino buildup is closer in its biotic association of major encrusting organisms to the Trogkofel buildup in southern Alps than to the Capitan Reef Complex in New Mexico and Texas. The similarity implies that Tubiphytes and Archaeolithoporella were the most predominant and significant rock-forming encrusting organisms in Early to early Middle Permian times.

  19. Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida)

    NASA Astrophysics Data System (ADS)

    Benoit, Julien; Abdala, Fernando; Van den Brandt, Marc J.; Manger, Paul R.; Rubidge, Bruce S.

    2015-12-01

    The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the parietal foramen. The parietal foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the parietal foramen in a specimen of Cynosaurus suppostus, a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae, a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus, possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.

  20. Paleomagnetic and rock-magnetic studies of the Permian Cutler and Elephant Canyon formations in Utah.

    NASA Technical Reports Server (NTRS)

    Gose, W. A.; Helsley, C. E.

    1972-01-01

    Study of the Permian Cutler formation and the upper 15 meters of the Permian Elephant Canyon formation at 0.6-meter stratigraphic intervals southwest of Moab in eastern Utah. The directions of natural remanent magnetization show a pronounced streak distribution, but thermal demagnetization successfully isolates the stable paleomagnetic direction. All directions are reversed, and no significant long-term change in pole position is observed throughout the entire section. The pole calculated from the Elephant Canyon data lies at 43.6 N, 119.6 E; the Cutler pole lies at 44.4 N, 116.2 E. Rock-magnetic analyses suggest that the secondary magnetization results from the iron hydroxides and was acquired after recent surface exposure.

  1. Organic geochemistry of Pennsylvanian-Permian oils and black shales, northern Denver basin

    SciTech Connect

    Clayton, J.L.; King, J.D.

    1984-04-01

    Organic geochemical analyses were performed on Paleozoic shales and oils from the northern Denver basin to determine oil-source bed relationships. Two general oil types were recognized: oil produced from reservoirs of Virgilian and Wolfcampian age in northeastern Colorado and Nebraska, and oil produced form the Lower Permian Lyons Sandstone near the basin axis in Colorado. Low-gravity oil (20/sup 0/ API) produced from the Virgilian-age reservoir at the Amazon field (Nebraska) and a higher gravity oil (37/sup 0/ API) produced from a well near the Amazon field (Wespro 1-23 Lyngholm) can be distinguished geochemically from the other Virgilian-Wolfcampian oils studied and may be genetically unrelated to them. For comparison, oils were analyzed from the Minnelusa Formation (Permian-Pennsylvanian) in the Powder River basin. These oils are geochemically unlike any Paleozoic oils analyzed in this study in southeastern Wyoming and Colorado.

  2. A Martian analog in Kansas: Comparing Martian strata with Permian acid saline lake deposits

    NASA Astrophysics Data System (ADS)

    Benison, Kathleen C.

    2006-05-01

    An important result of the Mars Exploration Rover's (MER) mission has been the images of sedimentary structures and diagenetic features in the Burns Formation at Meridiani Planum. Bedding, cross-bedding, ripple marks, mud cracks, displacive evaporite crystal molds, and hematite concretions are contained in these Martian strata. Together, these features are evidence of past saline groundwater and ephemeral shallow surface waters on Mars. Geochemical analyses of these Martian outcrops have established the presence of sulfates, iron oxides, and jarosite, which strongly suggests that these waters were also acidic. The same assemblage of sedimentary structures and diagenetic features is found in the salt-bearing terrestrial red sandstones and shales of the middle Permian (ca. 270 Ma) Nippewalla Group of Kansas, which were deposited in and around acid saline ephemeral lakes. These striking sedimentological and mineralogical similarities make these Permian red beds and evaporites the best-known terrestrial analog for the Martian sedimentary rocks at Meridiani Planum.

  3. Multiple S-isotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction

    PubMed Central

    Shen, Yanan; Farquhar, James; Zhang, Hua; Masterson, Andrew; Zhang, Tonggang; Wing, Boswell A.

    2011-01-01

    Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes (32S, 33S, 34S and 36S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ34S with negative Δ33S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction. PMID:21343928

  4. Carbon Capture and Storage in the Permian Basin, a Regional Technology Transfer and Training Program

    SciTech Connect

    Rychel, Dwight

    2013-09-30

    The Permian Basin Carbon Capture, Utilization and Storage (CCUS) Training Center was one of seven regional centers formed in 2009 under the American Recovery and Reinvestment Act of 2009 and managed by the Department of Energy. Based in the Permian Basin, it is focused on the utilization of CO2 Enhanced Oil Recovery (EOR) projects for the long term storage of CO2 while producing a domestic oil and revenue stream. It delivers training to students, oil and gas professionals, regulators, environmental and academia through a robust web site, newsletter, tech alerts, webinars, self-paced online courses, one day workshops, and two day high level forums. While course material prominently features all aspects of the capture, transportation and EOR utilization of CO2, the audience focus is represented by its high level forums where selected graduate students with an interest in CCUS interact with Industry experts and in-house workshops for the regulatory community.

  5. Multiple S-isotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction.

    PubMed

    Shen, Yanan; Farquhar, James; Zhang, Hua; Masterson, Andrew; Zhang, Tonggang; Wing, Boswell A

    2011-01-01

    Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes ((32)S, (33)S, (34)S and (36)S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ(34)S with negative Δ(33)S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction. PMID:21343928

  6. Sandrewia, n. gen., a problematical plant from the Lower Permian of Texas and Kansas

    USGS Publications Warehouse

    Mamay, S.H.

    1975-01-01

    Sandrewia, n. gen., monotypified by S. texana, n. sp., is a plant from Lower Permian beds of north-central Texas and east-central Kansas. It is characterized by stout axes with spirally disposed, laxly inserted, petiolate leaves; the laminae are broadly flabelliform with coarse, open venation. The leaves are reminiscent of the vojnovskyalean Nephropsis, of the Permian Petchora Basin, U.S.S.R., but biologic relationships are only speculative because of limited material. However, leaf characteristics render Sandrewia easily identifiable. Its presently limited stratigraphic range, along with floristic associations, indicates it may be a useful guide fossil and supports the author's beliefs regarding important times and places in Paleozoic plant evolution. ?? 1975.

  7. The End-Permian mass extinction: What really happened and did it matter?

    PubMed

    Erwin, D H

    1989-08-01

    Marine communities of the Paleozoic differ markedly from those of the post-Paleozoic, a dichotomy long recognized as the most fundamental change between the Cambrian metazoan radiation and the present. The end-Permian mass extinction of about 54% of marine families eliminated many of the groups that dominated Paleozoic communities. Correlative changes occurred in terrestrial vertebrate and plant communities, but there is no clear evidence that these changes are related to the marine extinction. The marine extinction occurred during a period of physical change, and a variety of extinction mechanisms have been proposed, most related to a major Late Permian marine regression or to climatic changes. Unfortunately, the regression has made it difficult to gather data on the rate, timing and pattern of extinction, and the available data exclude only a few hypotheses. Thus the largest mass extinction, and the one with the greatest evolutionary importance, is also the most poorly understood. PMID:21227355

  8. Episodic perturbations of end-Permian atmosphere recorded in plant spore chemistry

    NASA Astrophysics Data System (ADS)

    Fraser, Wesley; Lomax, Barry; Beerling, David; James, David; Pyle, John; Self, Stephen; Sephton, Mark; Wellman, Charles

    2016-04-01

    The largest marine Phanerozoic extinction occurred 251 million years ago at the end of the Permian period with a contemporaneous major reorganisation of terrestrial. Previous work suggests the eruption of the Siberian Traps large igneous province could have generated substantial volumes of ozone depleting substances; the result being a partial collapse of the stratospheric ozone layer, and commensurate increase in ultraviolet-B (UV-B, 280-315nm) radiation. Increased UV-B flux would contribute additional pressures to an already stressed environment and flora and fauna. Here we present data utilising a new biogeochemical proxy for UV-B radiation to analyse clubmoss (lycophyta) megaspores to track UV-B radiation across the end-Permian interval. Our biogeochemical data when combined with published work on spore and pollen mutations suggests a highly dynamic global atmospheric system, oscillating between episodes of high and low UV-B flux, most likely driven by pulsed eruptive phases of the Siberian Traps.

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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

  11. Exhumation of high-pressure rocks in a Variscan migmatite dome (Montagne Noire, France)

    NASA Astrophysics Data System (ADS)

    Whitney, Donna; Roger, Francoise; Rey, Patrice; Teyssier, Christian

    2015-04-01

    of garnet rims presents a challenge for ascribing the zircon rim age to hydrothermal alteration. Of the 5 reported eclogite localities in the MN, 4 are located near a high-strain zone along the long axis of the dome and one is located in a shear zone at the SSW margin of the gneissic core. 2D and 3D numerical models show that migmatite domes may form in response to extension of the upper crust, as the partially molten deep crust ascends along a steep, axial high strain zone and then flows into subdomes flanking this zone, forming a double dome such as the MN. This mode of dome formation is an efficient mechanism for rapid exhumation of deep crust. Migmatite dome rocks equilibrate at LP/HT, but eclogite inclusion in migmatite preserve their deep origin, track exhumation, and inform the internal dynamics of domes. Domes like the MN demonstrate that the opportunistic low-viscosity deep crust flows readily to fill gaps created by extensional/ transtensional domains in the collapsing late-Variscan orogen.

  12. Volatile-organic molecular characterization of shale-oil produced water from the Permian Basin.

    PubMed

    Khan, Naima A; Engle, Mark; Dungan, Barry; Holguin, F Omar; Xu, Pei; Carroll, Kenneth C

    2016-04-01

    Growth in unconventional oil and gas has spurred concerns on environmental impact and interest in beneficial uses of produced water (PW), especially in arid regions such as the Permian Basin, the largest U.S. tight-oil producer. To evaluate environmental impact, treatment, and reuse potential, there is a need to characterize the compositional variability of PW. Although hydraulic fracturing has caused a significant increase in shale-oil production, there are no high-resolution organic composition data for the shale-oil PW from the Permian Basin or other shale-oil plays (Eagle Ford, Bakken, etc.). PW was collected from shale-oil wells in the Midland sub-basin of the Permian Basin. Molecular characterization was conducted using high-resolution solid phase micro extraction gas chromatography time-of-flight mass spectrometry. Approximately 1400 compounds were identified, and 327 compounds had a >70% library match. PW contained alkane, cyclohexane, cyclopentane, BTEX (benzene, toluene, ethylbenzene, and xylene), alkyl benzenes, propyl-benzene, and naphthalene. PW also contained heteroatomic compounds containing nitrogen, oxygen, and sulfur. 3D van Krevelen and double bond equivalence versus carbon number analyses were used to evaluate molecular variability. Source composition, as well as solubility, controlled the distribution of volatile compounds found in shale-oil PW. The salinity also increased with depth, ranging from 105 to 162 g/L total dissolved solids. These data fill a gap for shale-oil PW composition, the associated petroleomics plots provide a fingerprinting framework, and the results for the Permian shale-oil PW suggest that partial treatment of suspended solids and organics would support some beneficial uses such as onsite reuse and bio-energy production. PMID:26802271

  13. Nitrogen Limitation and Productivity in the Permian-Triassic Greenhouse Ocean

    NASA Astrophysics Data System (ADS)

    Schoepfer, S.; Algeo, T. J.

    2013-12-01

    Marine primary productivity is an important ecological variable with major implications for the end-Permian carbon cycle. While numerous studies have examined relative changes in productivity across the Permian-Triassic boundary, we have less constraint on absolute rates of carbon export from the surface ocean, or qualitative comparison to modern marine environments. The HEATT model suggests that under sufficiently warm conditions, an increase in denitrification and decrease in P burial efficiency could lead to replacement of P by N as the ultimate limiting nutrient in marine systems, although the implications of such limitation on primary productivity are not clear. The Gujo Hachiman and Ubara sections, located in the Mino-Tamba accretionary complex of Japan, record sedimentation in the equatorial Panthalassic ocean across the Permian-Triassic boundary, an interval experiencing potentially the most intense greenhouse conditions of the Phanerozoic. Nitrogen isotope measurements of sedimentary organic matter in the Japanese accreted sections show values consistently close to 0, suggesting that the planktonic ecosystem relied on direct N fixation from the atmosphere by cyanobacteria to supply its nutrient requirements. Calculated organic carbon fluxes are comparable to those seen in the modern equatorial Pacific, however these results are complicated by preservational effects, suggesting an approach that includes several proxies for productivity with different modes of preservation. In this study, we attempt to constrain productivity in the late-Permian/earliest-Triassic equatorial Panthalassic Ocean and make comparisons with analogous environments in the modern equatorial Pacific. We compare calculated mass fluxes of inorganic productivity proxies to the modern equatorial Pacific Ocean, as well as areas of known local N limitation due to denitrification, such as the Cariaco Basin.

  14. Geochemical anomalies near the Eocene-Oligocene and Permian-Triassic boundaries

    SciTech Connect

    Asaro, F.; Alvarez, L.W.; Alvarez, W.; Michel, H.V.

    1981-10-01

    Evidence is presented to support the theory that several mass extinctions, i.e., those that define the Permian-Triassic boundary, the Cretaceous-Tertiary boundary, and the Eocene-1 Oligocene boundary, were caused by impact on the earth of extraterrestrial objects having the composition of carbonaceous chondrites and diameters of about 10 km. The evidence consists of anomalously high concentrations of iridium and other siderophile elements at the stratigraphic levels defining the extinctions. (ACR)

  15. Tectonic implications of facies patterns, Lower Permian Dry Mountain trough, east-central Nevada

    SciTech Connect

    Gallegos, D.M.; Snyder, W.S.; Spinosa, C. )

    1991-02-01

    Paleozoic tectonism is indicated by a study of a west-east facies analysis transect across the northern portion of the Lower Permian Dry Mountain trough (DMT). In an attempt to characterize the Early Permian basin-filling sequences, three broadly recognizable facies packages have been identified across the DMT: the western margin facies and the central basin facies of the DMT and an eastern shelf facies. In the western margin facies of the basin, pulses of tectonic activity are recorded at McCloud Spring in the Sulphur Springs Range. Here, shallow open-marine carbonate overlies eroded Vinini Formation and, in turn, is unconformably overlain by basinal marine carbonate. An unconformity also marks the contact with the overriding prograding coarse clastic facies. These abrupt transitions suggest the sediments were deposited in a tectonically active area where they preservation of Waltherian sequences is unlikely to occur. Similarly abrupt transitions are evident in the western part of the central basin facies. At Portuguese Springs n the Diamond Range, a thin basal marine conglomerate delineates Lower Permian sedimentation over the Pennsylvanian Ely Formation. Coarsening-upward basinal carbonate strata of pelagic, hemipelagic, and turbidite components overlie the basal conglomerate. this progression of sediments is unconformably overlain by a subaerial sequence of coarse clastic deposits. Within the eastern part of the central basin facies in the Maverick Spring Range, the Lower Permian sediments are open-marine siltstone, wackestone, packstone, and grainstone. The sediments are assigned to a gradually sloping ramp, indicating the effects of tectonism on this margin of the basin were subdued.

  16. Permian reefs of Texas and New Mexico: history of their study and scientific influence

    SciTech Connect

    Rigby, J.K.

    1985-01-01

    No fossil reef has more influenced thinking on carbonate and evaporite deposition, paleontology, paleoecology, and accumulation of petroleum than the Permian reefs of Texas and New Mexico. Study of the reefs can be divided into six fairly distinct periods. Little attention was given these Permian rocks, following discovery in 1855, until work by Girty and Richardson resulted in the monumental Guadalupian Fauna. Their study and those of Udden, Darton, Baker and others typify the first period. Discovery of oil in Permian rocks in Winkler County, Texas in 1926 initiated the second period, one when outcrops in the Guadalupe Mountains and elsewhere were examined to help explain puzzling stratigraphic relationships seen in the subsurface. E.R. Lloyd published in 1929 that the Capitan Limestone was a reef. The third period was dominated by P.B. and R.E. King and their colleagues. It was a time of geologic mapping and stratigraphic study. Adams et al. proposed Permian series based on sections in the Glass and Guadalupe Mountains. The fourth period is characterized by the classic study of Newell and his associates and was a time of paleoecologic and paleontologic work. Seminal studies by industry geologists, such as Dunham (Shell) and Pray and Tyrrell (Amoco) typify the fifth period. Dunham's work, in particular, spurred study of massive reef and bedded shelf facies and reef profiles. The sixth period is characterized by continuing detailed study of physical aspects of reef and shelf rocks by University of Wisconsin students and faculty, although they have also included work on algae and conodonts.

  17. Geology of the oil and gas bearing Permian formation in the Polish Lowlands

    SciTech Connect

    Pokorski, J.; Wagner, R. )

    1993-09-01

    Permian rocks occur over more than 80% of the Polish territory and, in middle Poland, they occur at considerable depth, from 2 to 6 km. The Early Permian was a period of long-lasting intensive volcanic activity. The Late Permian and Zechstein began with desert deposition which was followed by evaporitic deposition of a shallow epicontinental sea. The middle Polish trough (MPT) constituted the central part of the late Permian basin and was the site of the earliest and longest deposition with the most intensive periodical subsidence not compensated by sedimentation. Subsidence rate and syndepositional faulting substantially controlled the paleogeographic pattern. The final structure of the oil and gas fields was caused by late diagenesis and Upper Cretaceous structural remodeling. The upper Rotliegendes have the biggest natural gas fields. Reservoir rocks are sandstone and sandstones interfingering with conglomerates in tectonically active zones. The most promising areas for hydrocarbon exploration are the marginal parts of the basin (UPL) and the contact zone between MPT and the adjacent platforms. In the central part of the basin, the most promising are sandstone complexes on elevated tectonic blocks. Zechstein hydrocarbon fields occur in carbonate horizons of the first three cycles (PZ1, PZ2, and PZ3). In some areas, the Zechstein limestones (Cal), constitute the natural gas reservoir. Main dolomite (Ca2), oil, gas, and condensate fields are connected with the carbonate platform or its slope. Source rocks for oil occur in the Ca2 basinal facies or in the deeper parts of the platform-type lagoons. Oil migration is short and lateral, from either the basin or lagoon, toward the carbonate platform. Gas in Ca2 derived from the sub-Zechstein basement and migrated vertically along fault zones. The most prospective areas are reservoir horizons of the carbonate platform occurring in the near source rocks. The play dolomite Ca3 is not very promising.

  18. Tectono-eustatic controls on carbonate platform development, Permian basin outcrop-subsurface

    SciTech Connect

    Sarg, J.F.; Romine, K.; Vail, P.R.

    1987-05-01

    Integration of seismic stratigraphic concepts, detailed field studies, and geohistory analysis provides powerful interpretation leverage for deciphering the geologic history of the Permian carbonate platform complexes. The structural history of the Permian basin during the Permian shows two subsidence cycles of 10 to 20 m.y. duration. These subsidence cycles played a major role in the long-term (millions to tens of millions of years) development of the Permian carbonate platforms. During periods of relatively rapid subsidence, aggradation was dominant; during times of slow subsidence, major basinward platform progradation occurred. Superimposed on the long-term tectonic cycles are a series of third-order eustatic cycles (0.5-3 m.y.) which controlled development of 23 depositional sequences. Each sequence is composed of three depositional systems tracts: (1) a lower basin-restricted wedge interpreted to have been deposited during a relative fall and lowstand of sea level; (2) a transgressive systems tract of variable thickness; and (3) an upper aggradational to progradational carbonate platform system interpreted to have been deposited during a relative highstand in sea level. The lowstand systems tracts are composed dominantly of quartz sandstone, commonly intercalated with carbonate debris beds at the toe-of-slope. Two highstand depositional styles are differentiated here: (1) a keep-up system which maintains pace with periodic rises in relative sea level and displays a mounded-oblique stratal geometry at the platform margin and (2) a catch-up system which represents a relatively slow rate of accumulation and displays a sigmoid profile at the platform margin. Sequence boundaries display erosional truncation (subaerial on shelf or at shelf edge; subaqueous on slope) and/or subaerial exposure.

  19. Behavior of lophophorates during the end-Permian mass extinction and recovery

    NASA Astrophysics Data System (ADS)

    Powers, Catherine M.; Bottjer, David J.

    2009-11-01

    The end-Permian mass extinction devastated most marine communities and the recovery was a protracted event lasting several million years into the Early Triassic. Environmental and biological processes undoubtedly controlled patterns of recovery for marine invertebrates in the aftermath of the extinction, but are often difficult to single-out. The global diversity and distribution of marine lophophorates during the aftermath of the end-Permian mass extinction indicates that stenolaemate bryozoans, rhynchonelliform brachiopods, and lingulid brachiopods displayed distinct recovery patterns. Bryozoans were the most susceptible of the lophophorates, experiencing relatively high rates of extinction at the end of the Permian, and becoming restricted to the Boreal region during the Early Triassic. The recovery of bryozoans was also delayed until the Late Triassic and characterized by very low diversity and abundance. Following the final disappearance of Permian rhynchonelliform brachiopod survivors, Early Triassic rhynchonelliform brachiopod abundance remained suppressed despite a successful re-diversification and a global distribution, suggesting a decoupling between global taxonomic and ecological processes likely driven by lingering environmental stress. In contrast with bryozoans and rhynchonelliforms, lingulid brachiopods rebounded rapidly, colonizing shallow marine settings left vacant by the extinction. Lingulid dominance, characterized by low diversity but high numerical abundance, was short-lived and they were once again displaced back into marginal settings as environmental stress changed through the marine recovery. The presence in lingulid brachiopods of the respiratory pigment hemerythrin, known to increase the efficacy of oxygen storage and transport, when coupled with other morphological and physiological adaptations, may have given lingulids a survival advantage in environmentally stressed Early Triassic settings.

  20. Variation in Magnitude of Differential Stress Across an Exhumed Continental-scale Thrust Zone

    NASA Astrophysics Data System (ADS)

    Lusk, A. D.; Platt, J. P.

    2015-12-01

    The Moine Thrust Zone (MTZ), located in NW Scotland, formed as a result of the closing of the Iapetus Ocean and docking of various terranes and arcs (Scandian Phase of the Caledonian Orogeny, ca. 445-420 Ma). The MTZ as defined here comprises three major foreland-propagating thrust faults, the latest of which is the Moine Thrust itself, which emplaced Proterozoic Moine Supergroup psammites westward onto Cambro-Ordovician shelf sequence rocks and Lewisian basement gneiss. Presently, the north-south striking Moine Thrust Zone is exposed for more than 200 km along strike, and Scandian deformation can be traced up to 40 km eastward from the Moine Thrust towards the hinterland. The thrust system is thought to have been exhumed while still active, resulting in the exposure of deep structural levels of the MTZ. As part of an ongoing project to study how the stress, rheology, and width of continental-scale faults vary with depth, we use the piezometer based on the grainsize of dynamically recrystallized quartz to determine the variation in magnitude of differential stress across the MTZ. We present a transect from the head of Loch Eriboll in the footwall, eastward to the base of Ben Hope in the hangingwall. Grainsize generally decreases westward and structurally downward to the Moine Thrust, where ultramylonites have grainsizes on the order of 10 μm. Higher stresses towards the foreland likely reflect lower temperatures of deformation in rocks that before thrusting were at higher structural levels, and may have triggered a switch to grainsize sensitive creep, thus resulting in localization of strain and narrowing of shear zone width.

  1. Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

    NASA Astrophysics Data System (ADS)

    Lang, Helen M.; Gilotti, Jane A.

    2015-06-01

    Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

  2. Upper Cretaceous exhumation of the western Rhodope Metamorphic Province (Chalkidiki Peninsula, northern Greece)

    NASA Astrophysics Data System (ADS)

    Kydonakis, Konstantinos; Gallagher, Kerry; Brun, Jean-Pierre; Jolivet, Marc; Gueydan, Frédéric; Kostopoulos, Dimitrios

    2014-06-01

    The Vertiskos Unit of northern Greece is an elongated basement belt with a complex poly-metamorphic history. It extends from Greece (Chalkidiki peninsula), to the south, up to Serbia, in the north, and arguably represents the westernmost part of the Rhodope Metamorphic Province (northern Greece to southern Bulgaria). The Vertiskos Unit experienced a medium pressure lower amphibolite-facies metamorphic overprint during the Alpine Orogeny. The available medium-temperature geochronology implies that it remained at temperature of approximately 300°C (or slightly higher) during Lower Cretaceous. In order to constrain its post-Lower Cretaceous thermal history, until near-surface exposure, we applied apatite fission track analysis. The central ages obtained range from 68.5 ± 3.8 to 46.6 ± 3.6 Ma (uppermost Cretaceous to Middle Eocene) and mean track lengths between 13 and 13.5 µm. We applied two inverse thermal modeling approaches using either each sample independently (high degree of freedom in the thermal history, better data fit) or all samples together interpreting them as a vertical profile (simpler thermal history, worse data fit). Irrespective of the modeling approach, we conclude that the bulk thermal history of the Vertiskos Unit crosses the high-temperature limit of the apatite partial annealing zone by the uppermost Cretaceous and reaches near-surface conditions as early as lower/middle Eocene. These results contrast with the thermal history of the other domains of the Rhodope Metamorphic Province further east (namely the Southern Rhodope Core Complex and the Northern Rhodope Complex) and establish the Vertiskos basement complex as the oldest exhumed coherent basement fragment of the Rhodope Metamorphic Province and Greece.

  3. Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust

    PubMed Central

    Ernst, W. G.; Maruyama, S.; Wallis, S.

    1997-01-01

    Preservation of ultrahigh-pressure (UHP) minerals formed at depths of 90–125 km require unusual conditions. Our subduction model involves underflow of a salient (250 ± 150 km wide, 90–125 km long) of continental crust embedded in cold, largely oceanic crust-capped lithosphere; loss of leading portions of the high-density oceanic lithosphere by slab break-off, as increasing volumes of microcontinental material enter the subduction zone; buoyancy-driven return toward midcrustal levels of a thin (2–15 km thick), low-density slice; finally, uplift, backfolding, normal faulting, and exposure of the UHP terrane. Sustained over ≈20 million years, rapid (≈5 mm/year) exhumation of the thin-aspect ratio UHP sialic sheet caught between cooler hanging-wall plate and refrigerating, downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces. The intracratonal position of most UHP complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone. UHP metamorphic terranes consist chiefly of transformed, yet relatively low-density continental crust compared with displaced mantle material—otherwise such complexes could not return to shallow depths. Relatively rare metabasaltic, metagabbroic, and metacherty lithologies retain traces of phases characteristic of UHP conditions because they are massive, virtually impervious to fluids, and nearly anhydrous. In contrast, H2O-rich quartzofeldspathic, gneissose/schistose, more permeable metasedimentary and metagranitic units have backreacted thoroughly, so coesite and other UHP silicates are exceedingly rare. Because of the initial presence of biogenic carbon, and its especially sluggish transformation rate, UHP paragneisses contain the most abundantly preserved crustal diamonds. PMID:11038569

  4. Mantle exhumation at the Southwest Indian Ridge; preliminary results of the SMOOTHSEAFLOOR cruise

    NASA Astrophysics Data System (ADS)

    Sauter, D.; Cannat, M.; Andreani, M.; Birot, D.; Bronner, A.; Brunelli, D.; Carlut, J. H.; Delacour, A.; Guyader, V.; Mendel, V.; Ménez, B.; MacLeod, C. J.; Pasini, V.; Rouméjon, S.; Ruellan, E.; Searle, R. C.

    2011-12-01

    The eastern Southwest Indian Ridge (SWIR) is among the deepest part of the oceanic ridge system, and it is thus inferred to represent a melt-poor end-member for this system. It displays the widest expanses known to date of seafloor with no evidence for a volcanic upper crustal layer. This nonvolcanic ocean floor has no equivalent at faster spreading ridges and has been called "smooth seafloor" because it occurs in the form of broad ridges up to 2000 m high with a smooth, rounded topography with no resolvable volcanic cones on bathymetric data (Cannat et al., 2006). On R/V Marion Dufresne cruise "SMOOTHSEAFLOOR" in October 2010, we conducted a detailed geological-geophysical survey of such smooth seafloor areas, determining the rock types exposed at these ridges, searching for hydrothermal activity and mapping the volcanic, tectonic and sedimentary structures. 35 dredges and 15 CTDs have been realized and more than 1000 km long TOBI sidescan sonar images and deep towed magnetometer profiles have been collected over two contrasting survey areas up to magnetic anomaly C5n (10 Ma). The main result of our cruise is that serpentinized mantle-derived peridotites were dredged widely throughout the smooth seafloor areas while gabbros and basalts were rare. Mantle rocks were found on moderate slopes (20-35°), facing toward and away from the axial valley, at ridges with symmetric shape, as well as on gentle slopes (<15°) facing the axis at asymmetric ridges whose outward facing steeper slopes may be covered with volcanics. TOBI sidescan sonar images show that these hillsides are ancient large low angle normal faults which were covered locally by small amount of volcanics and dismembered by landslide activity. These results show that mantle exhumation has been the main process which shaped the smooth seafloor areas of the eastern SWIR for the last 10 Myrs.

  5. Exploring the Variability of Late Cenozoic Exhumation Rates across the Himalayan Rain Shadow

    NASA Astrophysics Data System (ADS)

    Schultz, M.; Hodges, K. V.; Ehlers, T. A.; Van Soest, M. C.; Wartho, J. A.; McDonald, C.

    2015-12-01

    The Himalayan ranges of South Asia form one of the world's most impressive rain shadows. Data from the NASA - Japan Aerospace Exploration Agency Tropical Rainfall Measurement Mission (TRMM) suggest that precipitation in the central Himalaya drops from more than four meters per year along the southern flanks of the Higher Himalaya (falling mostly as rain during the summer monsoon) to about half a meter per year north of the range crest on the southern Tibetan Plateau. While a correlation between modern precipitation and erosion seems intuitive, important questions remain regarding how far backward in time the correlation might extend. Previous investigations of the relationships between precipitation patterns and thermochronologic cooling dates south of the Himalayan range crest have yielded discrepant results, partly due to the fact that many were conducted along deep trans-Himalayan gorges that serve to channel monsoon storms locally northward, sometimes obscuring broader trends. We are addressing this problem through the comparative studies of bedrock exhumation on million-year timescales north and south of the range crest in transects that are not along major trans-Himalayan gorges. Our low-temperature thermochronology dataset from Greater Himalayan Sequence leucogranites and sillimanite gneisses north of the range crest indicate cooling through the white mica 40Ar/39Ar closure isotherm between 15.5 - 14.5 Ma with zircon (U-Th)/He ages ranging from 14.5 - 11 Ma. Though (U-Th)/He systematics of apatites from these samples is complex, our data point to 9 - 8 Ma cooling through the ~70°C isotherm. Our developing dataset from the Khumbu Himal region south of the range crest thus far indicates cooling through ApHe closure occurred more recently at 3 - 2 Ma, about 5 - 6 million years later those from southern Tibet. We will be investigating this dataset further using the 1-D thermal model QTQt as well as the 1-D thermal-kinematic model Pecube.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Exploring the Variability of Late Cenozoic Exhumation Rates Across the Himalayan Rain Shadow

    NASA Astrophysics Data System (ADS)

    Schultz, M.; Hodges, K. V.; Van Soest, M. C.

    2013-12-01

    The Himalayan ranges of South Asia form one of the world's starkest rain shadows. Data from the NASA - Japan Aerospace Exploration Agency Tropical Rainfall Measurement Mission (TRMM) suggest that precipitation in the central Himalaya drops from more than four meters per year along the southern flanks of the Higher Himalaya (falling mostly as rain during the summer monsoon) to about half a meter per year north of the range crest on the southern Tibetan Plateau. While a correlation between modern precipitation and erosion seems intuitive, important questions remain regarding how far backward in time the correlation might extend. Previous investigations of the relationships between precipitation patterns and thermochronologic cooling dates south of the Himalayan range crest have yielded discrepant results, partly due to the fact that many were conducted along deep trans-Himalayan gorges that serve to channel monsoon storms locally northward, sometimes obscuring broader trends. We are addressing this problem through the comparative studies of bedrock exhumation on million-year timescales north and south of the range crest in transects that are not along major trans-Himalayan gorges. In this presentation, we review a developing (U-Th)/He dataset for metamorphic and intrusive igneous samples of the Greater Himalayan sequence from the north side of the Himalaya at the approximate longitude of Mount Everest (Qomolangma). Results thus far include Middle Miocene (U-Th)/He zircon and apatite dates that are one to two orders of magnitude older than Pliocene-Pleistocene dates typically obtained on similar units from the southern flank of the Himalaya. If this trend continues, and if planned studies south of Everest in 2014 yield very young cooling ages as expected, the simplest explanation is that the modern correlation between monsoon precipitation and erosion rates extends at least as far back as the Miocene Epoch.

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

    NASA Astrophysics Data System (ADS)

    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

  9. Facies comparison of autochthonous and allochthonous Permian and Triassic units, north-central Brooks Range, Alaska

    SciTech Connect

    Adams, K.E.

    1985-04-01

    Eight stratigraphic sections of Permian and Triassic rocks have been studied over a 30 km by 150 km area in the Endicott and Philip Smith Mountains of the central Brooks Range. Six of the sections are located on the Endicott Mountains allochthon, and the remaining two are parautochthonous columns in the Mount Doonerak area. The sections record a facies transition between the autochthonous Sadlerochit Group and Shublik Formation of the northeastern Brooks Range and the characteristically siliceous rocks of the allochthonous Siksikpuk and Otuk formations of the western Brooks Range. Laterally continuous and bioturbated beds of fine-grained sandstone, siltstone, and shale dominantly compose the Permian sequence, whereas the Triassic rocks consist of black shales, thin rhythmically bedded siliceous mudstones, and fossiliferous limestones. When the allochthonous sections are restored to a position south of the Mount Doonerak area, a general shallowing trend from southwest to northwest becomes evident within the reconstructed marine basin. To the south and west, the Permian sediments show a marked increase in silica content, with the occurrence of barite and a corresponding decrease in the thickness of the basal, coarser grained clastics. The Triassic formations also document an increase in silica and the presence of barite to the south and west, while becoming significantly sooty and phosphatic to the north and east. Ongoing petrographic and micropaleontologic studies of the field data will clarify these general paleogeographic relationships.

  10. Marine anoxia and delayed Earth system recovery after the end-Permian extinction

    PubMed Central

    Lau, Kimberly V.; Maher, Kate; Altiner, Demir; Kelley, Brian M.; Kump, Lee R.; Lehrmann, Daniel J.; Silva-Tamayo, Juan Carlos; Weaver, Karrie L.; Yu, Meiyi; Payne, Jonathan L.

    2016-01-01

    Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and 238U/235U isotopic compositions (δ238U) of Upper Permian−Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ238U across the end-Permian extinction horizon, from ∼3 ppm and −0.15‰ to ∼0.3 ppm and −0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans—characterized by prolonged shallow anoxia that may have impinged onto continental shelves—global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe. PMID:26884155

  11. The Late Permian - Early Triassic Evolution of the Western Barents Sea

    NASA Astrophysics Data System (ADS)

    Planke, S.; Svensen, H.; Faleide, J.; Myklebust, R.

    2013-12-01

    The Permian-Triassic boundary was temporarily associated with formation of the Siberian Traps Large Igneous Province. Major Late Permian and Early Triassic subsidence is documented by seismic reflection data in the East Barents Basin. Further west, basin subsidence and an abrupt change from carbonate and evaporite deposition to clastic sedimentation is recorded by industry seismic and well data in the south and onshore Svalbard in the north. The Permian-Triassic boundary is commonly not preserved either due to non-deposition or erosion, but could be locally preserved in depocenters. A major northwestward prograding clastic delta sourced from the Uralian hinterland reached the Norwegian (western) part of the Barents Sea in the earliest Triassic (Induan). We suggest that the large-scale changes in paleoenviroment, vertical motions, and sedimentary processes in the Barents Sea region were strongly influenced by large-scale changes in mantle dynamics and paleoclimate caused by the Siberian Traps igneous event. By analogy with other Large Igneous Provinces, such as the North Atlantic Volcanic Province, regional uplift and subsidence associated with a rising mantle plume may precede the arrival of the plume at the base of the lithosphere with 10's of millions of years. In contrast, the paleoenvironmental changes and the associated extinction were mainly caused by rapid intrusion of magma into sedimentary basins and voluminous igneous eruptions.

  12. A new Early Permian reptile and its significance in early diapsid evolution.

    PubMed

    Reisz, Robert R; Modesto, Sean P; Scott, Diane M

    2011-12-22

    The initial stages of evolution of Diapsida (the large clade that includes not only snakes, lizards, crocodiles and birds, but also dinosaurs and numerous other extinct taxa) is clouded by an exceedingly poor Palaeozoic fossil record. Previous studies had indicated a 38 Myr gap between the first appearance of the oldest diapsid clade (Araeoscelidia), ca 304 million years ago (Ma), and that of its sister group in the Middle Permian (ca 266 Ma). Two new reptile skulls from the Richards Spur locality, Lower Permian of Oklahoma, represent a new diapsid reptile: Orovenator mayorum n. gen. et sp. A phylogenetic analysis identifies O. mayorum as the oldest and most basal member of the araeoscelidian sister group. As Richards Spur has recently been dated to 289 Ma, the new diapsid neatly spans the above gap by appearing 15 Myr after the origin of Diapsida. The presence of O. mayorum at Richards Spur, which records a diverse upland fauna, suggests that initial stages in the evolution of non-araeoscelidian diapsids may have been tied to upland environments. This hypothesis is consonant with the overall scant record for non-araeoscelidian diapsids during the Permian Period, when the well-known terrestrial vertebrate communities are preserved almost exclusively in lowland deltaic, flood plain and lacustrine sedimentary rocks. PMID:21525061

  13. Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia.

    PubMed

    Wang, Jun; Pfefferkorn, Hermann W; Zhang, Yi; Feng, Zhuo

    2012-03-27

    Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m(2) of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time. PMID:22355112

  14. Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia

    PubMed Central

    Wang, Jun; Pfefferkorn, Hermann W.; Zhang, Yi; Feng, Zhuo

    2012-01-01

    Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m2 of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time. PMID:22355112

  15. Mid-Permian Phosphoria Sea in Nevada and the Upwelling Model

    USGS Publications Warehouse

    Ketner, Keith B.

    2009-01-01

    The Phosphoria Sea extended at least 500 km westward and at least 700 km southwestward from its core area centered in southeastern Idaho. Throughout that extent it displayed many characteristic features of the core: the same fauna, the same unique sedimentary assemblage including phosphate in mostly pelletal form, chert composed mainly of sponge spicules, and an association with dolomite. Phosphoria-age sediments in Nevada display ample evidence of deposition in shallow water. The chief difference between the sediments in Nevada and those of the core area is the greater admixture of sandstone and conglomerate in Nevada. Evidence of the western margin of the Phosphoria Sea where the water deepened and began to lose its essential characteristics is located in the uppermost part of the Upper Devonian to Permian Havallah sequence, which has been displaced tectonically eastward an unknown distance. The relatively deep water in which the mid-Permian part of the Havallah was deposited was a sea of probably restricted east-west width and was floored by a very thick sequence of mainly terrigenous sedimentary rocks. The phosphate content of mid-Permian strata in western exposures tends to be relatively low as a percentage, but the thickness of those strata tends to be high. The core area in and near southeastern Idaho where the concentration of phosphate is highest was separated from any possible site of upwelling oceanic waters by a great expanse of shallow sea.

  16. Earth's biggest 'whodunnit': unravelling the clues in the case of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    White, Rosalind V.

    2002-12-01

    The mass extinction that occurred at the end of the Permian period, 250 million years ago, was the most devastating loss of life that Earth has ever experienced. It is estimated that ca.96% of marine species were wiped out and land plants, reptiles, amphibians and insects also suffered. The causes of this catastrophic event are currently a topic of intense debate. The geological record points to significant environmental disturbances, for example, global warming and stagnation of ocean water. A key issue is whether the Earth's feedback mechanisms can become unstable on their own, or whether some forcing is required to precipitate a catastrophe of this magnitude. A prime suspect for pushing Earth's systems into a critical condition is massive end-Permian Siberian volcanism, which would have pumped large quantities of carbon dioxide and toxic gases into the atmosphere. Recently, it has been postulated that Earth was also the victim of a bolide impact at this time. If further research substantiates this claim, it raises some intriguing questions. The Cretaceous-Tertiary mass extinction, 65 million years ago, was contemporaneous with both an impact and massive volcanism. Are both types of calamity necessary to drive Earth to the brink of faunal cataclysm? We do not presently have enough pieces of the jigsaw to solve the mystery of the end-Permian extinction, but the forensic work continues.

  17. Severest crisis overlooked-Worst disruption of terrestrial environments postdates the Permian-Triassic mass extinction.

    PubMed

    Hochuli, Peter A; Sanson-Barrera, Anna; Schneebeli-Hermann, Elke; Bucher, Hugo

    2016-01-01

    Generally Early Triassic floras are believed to be depauperate, suffering from protracted recovery following the Permian-Triassic extinction event. Here we present palynological data of an expanded East Greenland section documenting recovered floras in the basal Triassic (Griesbachian) and a subsequent fundamental floral turnover, postdating the Permian-Triassic boundary extinction by about 500 kyrs. This event is marked by a swap in dominating floral elements, changing from gymnosperm pollen-dominated associations in the Griesbachian to lycopsid spore-dominated assemblages in the Dienerian. This turnover coincides with an extreme δ(13)Corg negative shift revealing a severe environmental crisis, probably induced by volcanic outbursts of the Siberian Traps, accompanied by a climatic turnover, changing from cool and dry in the Griesbachian to hot and humid in the Dienerian. Estimates of sedimentation rates suggest that this environmental alteration took place within some 1000 years. Similar, coeval changes documented on the North Indian Margin (Pakistan) and the Bowen Basin (Australia) indicate the global extent of this crisis. Our results evidence the first profound disruption of the recovery of terrestrial environments about 500kyrs after the Permian-Triassic extinction event. It was followed by another crisis, about 1myrs later thus, the Early Triassic can be characterised as a time of successive environmental crises. PMID:27340926

  18. Carboniferous-Lower Permian carbonate reservoirs of the Timan-Pechora Basin

    SciTech Connect

    Zhemchugova, V.A.; Schamel, S.

    1994-01-01

    The Carboniferous-Lower Permian carbonate succession of the Timan-Pechora basin is a major hydrocarbon-bearing complex, hosting about half of the oil and nearly a third of the gas reserves of the basin. The succession represents the last episode of carbonate deposition on the northeastern margin of the Russian platform before the closure of the Ural seaway in the mid-Permian. The lower part of the succession (upper Visean-Moscovian) contains three major transgressive-regressive sequences. Depositional facies ranged from nearshore carbonate-shale-evaporite through shallow shelf detrital carbonates to outer-shelf carbonate-siliceous shale. The most pronounced regression during this interval occurred during the Serpukhovian, when marine sabkhas covered vast portions of the carbonate platform. Late Carboniferous-Early Permian sedimentation was complicated by the onset of Uralian tectonism. Flysch from the encroaching orogen accumulated initially in the east, advanced westward across the passive margin, and finally covered the carbonate platform in Artinskian-Kungurian time. Simultaneously, structural inversion along the Pechora-Kolva aulacogen and elsewhere provided sites for bioherm growth, in addition to exposing parts of the lower succession to erosion and karstification. Overall polarity of the basin switched as the eastern margin was elevated in the frontal thrusts of the Urals. The carbonate succession was terminated by increased clastic input from the advancing Ural orogen. 6 refs., 9 figs.

  19. A paleoclimatic simulation of the Late Permian greenhouse world and its consequences

    SciTech Connect

    Moore, G.T.; Jacobson, S.R.; Hayashida, D.N. )

    1991-03-01

    Sea-floor spreading assembled all the major cratonic blocks into a single supercontinent once in the Phanerozoic Eon. This unique Late Permian crustal tectonic event produced Pangaea and an enormous oceanic basin volume that dropped sea level to a global lowstand unrivaled in the Phanerozoic. Two paleoclimatic simulations using a numerical three-dimensional general circulation model tested changes in the greenhouse effect. The authors conclude that for a simulation to fit the Late Permian geologic record, the paleoatmosphere must contain an enhanced greenhouse gas effect. A third simulation tested changes of paleogeography in southern Pangaea (Gondwana) that did not appreciably alter the harsh continental paleoclimate. The simulated paleoclimatic changes provide extraordinarily warm ocean and atmosphere, and a significant reduction in continental rainfall and runoff. These conditions inevitably lead to more aridity and less vegetation on land, gradually reduce the delivery of vital nutrients from continental sources to marine margins, systematically liberate CO{sub 2} dissolved in ocean water, and incrementally increase stress on marine and terrestrial biotas. These consequences severely disrupted rates of oxygen and carbon cycling. Their quantitative paleoclimatic simulation is consistent with distributions of red beds, evaporites, coals, marine shelf areas, seawater isotope trends, and paleontologic originations and extinctions. Thus, the Pangaean plate assembly probably triggered an inexorable sequence of geophysical, geochemical, and biological events that forced an elevated greenhouse effect in the Late Permian, nearly annihilating the Phanerozoic biota.

  20. Earth's biggest 'whodunnit': unravelling the clues in the case of the end-Permian mass extinction.

    PubMed

    White, Rosalind V

    2002-12-15

    The mass extinction that occurred at the end of the Permian period, 250 million years ago, was the most devastating loss of life that Earth has ever experienced. It is estimated that ca. 96% of marine species were wiped out and land plants, reptiles, amphibians and insects also suffered. The causes of this catastrophic event are currently a topic of intense debate. The geological record points to significant environmental disturbances, for example, global warming and stagnation of ocean water. A key issue is whether the Earth's feedback mechanisms can become unstable on their own, or whether some forcing is required to precipitate a catastrophe of this magnitude. A prime suspect for pushing Earth's systems into a critical condition is massive end-Permian Siberian volcanism, which would have pumped large quantities of carbon dioxide and toxic gases into the atmosphere. Recently, it has been postulated that Earth was also the victim of a bolide impact at this time. If further research substantiates this claim, it raises some intriguing questions. The Cretaceous-Tertiary mass extinction, 65 million years ago, was contemporaneous with both an impact and massive volcanism. Are both types of calamity necessary to drive Earth to the brink of faunal cataclysm? We do not presently have enough pieces of the jigsaw to solve the mystery of the end-Permian extinction, but the forensic work continues. PMID:12626276

  1. Permian {open_quotes}Wolfcamp{close_quotes} limestone reservoirs: Powell Ranch field, Eastern Midland Basin

    SciTech Connect

    Montgomery, S.L.

    1996-09-01

    Deep-water carbonate channel reservoirs form important oil reservoirs along the toe of the Eastern Shelf of the Permian basin in west Texas. In northwestern Glasscock County, these `Wolfcamp` reservoirs are Leonardian (Early Permian) in age and define high-energy channels incised into surrounding carbonate detritus and basinal shale. Porous grain-flow material filling these channels, along with encasing detritus, was derived from the shallow shelf located six miles to the east. Reservoirs are in packstone and grainstone facies and have significant interparticle and moldic porosity. Relevant exploration began in the 1960s, but expanded slowly thereafter due to lack of success caused by complex patterns of channel occurrence. Results of a three-dimensional (3-D) seismic survey conducted in 1990 have greatly enhanced the identification and mapping of productive channels in the Powell Ranch field complex. Wells in this complex are capable of flowing 400-1200 bbl of oil per day, and have reserves ranging from 0.2 to 1.3 MBO. The new 3-D data have improved the relevant geologic model and dramatically increased rates of drilling success. Application of such data to this setting offers a potential model for other parts of the Permian basin.

  2. Far-travelled permian chert of the North Fork terrane, Klamath mountains, California

    USGS Publications Warehouse

    Mankinen, E.A.; Irwin, W.P.; Blome, C.D.

    1996-01-01

    Permian chert in the North Fork terrane and correlative rocks of the Klamath Mountains province has a remanent magnetization that is prefolding and presumably primary. Paleomagnetic results indicate that the chert formed at a paleolatitude of 8.6?? ?? 2.5?? but in which hemisphere remains uncertain. This finding requires that these rocks have undergone at least 8.6?? ?? 4.4?? of northward transport relative to Permian North America since their deposition. Paleontological evidence suggests that the Permian limestone of the Eastern Klamath terrane originated thousands of kilometers distant from North America. The limestone of the North Fork terrane may have formed at a similar or even greater distance as suggested by its faunal affinity to the Eastern Klamath terrane and more westerly position. Available evidence indicates that convergence of the North Fork and composite Central Metamorphic-Eastern Klamath terranes occurred during Triassic or Early Jurassic time and that their joining together was a Middle Jurassic event. Primary and secondary magnetizations indicate that the new composite terrane containing these and other rocks of the Western Paleozoic and Triassic belt behaved as a single rigid block that has been latitudinally concordant with the North American craton since Middle Jurassic time.

  3. Impact of Siberian Trap volcanism on the end-Permian and Early Triassic carbon cycle

    NASA Astrophysics Data System (ADS)

    Meyer, K. M.; Kump, L.; Cui, Y.; Ridgwell, A. J.; Payne, J.

    2011-12-01

    The Siberian Traps are the largest of the large igneous provinces, covering approximately 5 million km2. The timing of this volcanic episode is indistinguishable from the end-Permian mass extinction, and the event likely both directly and indirectly impacted marine ecosystems, leading to the largest extinction of Earth history. Recent studies suggest record volumes of carbon dioxide and other greenhouse gases were released from both lava degassing and degassing due to heating of Tunguska Basin sediments. In this study, we use Genie-1, an Earth system model of intermediate complexity (http://wwww.genie.ac.uk), to examine the impact of volcanic volatile release on the sedimentary carbon isotope record and end-Permian carbonate system under a wide range of volumes, rates, and isotope compositions of CO2 input. These model experiments place quantitative constraints on the magnitude and rates of CO2 addition that can account for the sedimentary and C isotope records of the end-Permian and Early Triassic.

  4. Geology of the Pennsylvanian and Permian Culter Group and Permian Kaibab Limestone in the Paradox Basin, southeastern Utah and southwestern Colorado

    USGS Publications Warehouse

    Condon, Steven M.

    1997-01-01

    The Cutler Formation is composed of thick, arkosic, alluvial sandstones shed southwestward from the Uncompahgre highlands into the Paradox Basin. Salt tectonism played an important role in deposition of the Cutler in some areas. In the northeast part of the basin, more than 8,000 ft, and as much as 15,000 ft, of arkose was trapped between rising salt anticlines - this arkose is thin to absent over the crests of some anticlines. In the western and southern parts of the basin, the Cutler is recognized as a Group consisting of, in ascending order: the lower Cutler beds, Cedar Mesa Sandstone, Organ Rock Formation, White Rim Sandstone, and De Chelly Sandstone. The aggregate thickness of these formations is less than 2,000 ft. The formations of the Cutler Group were deposited in a complex system of alluvial, eolian, and marine environments characterized by abrupt vertical and lateral lithologic changes. The basal Cutler is Pennsylvanian in age, but the bulk of the Group was deposited during the Permian. The Cutler is conformably underlain by the Pennsylvanian Hermosa Group across most of the basin. It is overlain unconformably by the Permian Kaibab Limestone in the western part of the Paradox Basin. The Cutler or Kaibab are overlain unconformably by the Triassic Moenkopi or Chinle Formations.

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

    NASA Astrophysics Data System (ADS)

    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 (<10 Ma) high grade metamorphism, melting and unusually high rates of exhumation (~10mm/yr), compared to the main arc of the range where peak metamorphism / melting occurred in the Early Miocene and exhumation rates of ca 2mm/yr are more common 1. The history of the young metamorphism and rapid exhumation of the eastern syntaxis is debated. Bedrock studies have been interpreted to imply rapid exhumation since either 3-4 Ma 2 or 8-10 Ma 3. However, the earlier history of the sampled region is removed by erosion and should be preserved in the sedimentary record. Bracciali et al 4 focused on distal detrital deposits and suggested a much more recent onset, during the Quaternary. A number of models have been proposed to explain the syntaxial evolution, supporting different 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

  6. Long-term erosion and exhumation of the “Altiplano Antioqueño”, Northern Andes (Colombia) from apatite (U Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Restrepo-Moreno, Sergio A.; Foster, David A.; Stockli, Daniel F.; Parra-Sánchez, Luis N.

    2009-02-01

    The Antioqueño Plateau (AP) in the northern Cordillera Central, Colombia, is the largest high elevation erosional surface in the Northern Andes. Apatite (U-Th)/He thermochronometry (AHe) of samples collected from two elevation profiles spanning ˜ 2 km of exhumed crustal sections reveal the long-term erosional exhumation of the AP. Sample profiles exhibit AHe ages that increase with elevation from ca. 22 Ma (˜ 760 m) at the bottom of regional scarps to ca. 49 Ma (˜ 2350 m) on top of the AP. A marked inflection point in age versus elevation data at ca. 25 Ma defines the bottom of the exhumed post-Oligocene He partial retention zone (He-PRZ). Elevation-invariant ages below ca. 25 Ma record the onset of rapid exhumation and surface uplift of the AP that led to river incision. A subtle change in slope within the He-PRZ, ca. 41 Ma, is interpreted as a less intense, exhumation-related cooling episode. These two exhumation pulses coincide with the Proto-Andina and Pre-Andina orogenic phases previously proposed for the Colombian Andes, and are synchronous with tectonically driven exhumation events reported for the Peruvian, Bolivian and Argentinean Andes, and for some orogenic systems in the Caribbean. The pulses are correlated with variations in the rates of convergence between Nazca (Farallon) and South America documented for the Middle Eocene and the Late Oligocene suggesting continental-scale controls on uplift and denudation throughout the Andean range. AHe data provide an average erosion rate of ˜ 0.04 mm/yr for the last 25 million years. Erosion rates during the exhumation pulses were in the order of ˜ 0.2-0.4 mm/yr. Similarity between AHe profiles indicates the whole AP was uplifted and exhumed as a coherent structural block, corroborating previous structural evidence for the rigidity and coherence of this crustal block in the Northern Andes. Our results are in agreement with tectonostratigraphic data in the Magdalena and Cauca basins and with proposed

  7. Variscan to Neogene thermal and exhumation history at the Moroccan passive continental margin assessed by low temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Sehrt, M.; Glasmacher, U. A.; Stockli, D. F.; Kluth, O.; Jabour, H.

    2012-04-01

    In North Africa, a large amount of Mesozoic terrigenous sedimentary rocks are deposited in most of the basins along the continental margin indicating a major episode of erosion occurred during the rift and early post-rift period in the Central Atlantic. In the Tarfaya-Dakhla Basin, Morocco the sedimentary cover reaches thicknesses of up to 9000 m. The presence of high surface elevations in the Anti-Atlas mountain belt (2500 m) indicates a potential source area for the surrounding basins. The NE-SW oriented Anti-Atlas of Morocco is located at the northwestern fringe of the West African Craton and south of the High Atlas and represents the Phanerozoic foreland of the Late Paleozoic North African Variscides and the Cenozoic Atlas Belt. Variscan deformation affected most of Morocco. Paleozoic basins were folded and thrusted, with the major collision dated as late Devonian to Late Carboniferous. Zircon fission-track ages of 287 (±23) to 331 (±24) Ma confirmed the main exhumation referred to the Variscan folding, followed by rapid exhumation and the post-folding erosion. Currently, phases of uplift and exhumation in the Anti-Atlas during the Central Atlantic rifting and places where the associated erosion products are deposited are poorly constrained and there is little quantitative data available at present. The objective of the study is to determine the thermal and exhumation history of the Anti-Atlas and the connected Tarfaya-Dakhla Basin at the Moroccan passive continental margin. Besides zircon fission-track dating, apatite and zircon (U-Th-Sm)/He and apatite fission-track analyses and furthermore 2-D modelling with 'HeFTy' software has been carried out at Precambrian rocks of the Western Anti-Atlas and Cretaceous to Neogene sedimentary rocks from the Northern Tarfaya-Dakhla Basin. The apatite fission-track ages of 120 (±13) to 189 (±14) Ma in the Anti-Atlas and 176 (±20) to 216 (±18) Ma in the Tarfaya Basin indicate very obvious a Central Atlantic opening

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

    NASA Astrophysics Data System (ADS)

    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

  9. Further paleomagnetic results for lower Permian basalts of the Baoshan Terrane, southwestern China, and paleogeographic implications

    NASA Astrophysics Data System (ADS)

    Xu, Yingchao; Yang, Zhenyu; Tong, Ya-Bo; Wang, Heng; Gao, Liang; An, Chunzhi

    2015-05-01

    The Baoshan Terrane of southwestern China is considered to have been part of the Cimmerian block during the late Paleozoic; consequently, knowledge of its paleoposition and geological evolution can provide constraints on the Permian breakup of northern East Gondwana. Therefore, we conducted paleomagnetic and rockmagnetic studies on lower Permian basalts from four localities in the Baoshan Terrane. The basalts hold a stable characteristic remanent magnetization (ChRM) at high temperatures (300-680 °C) that is carried by magnetite, maghemite, and hematite with both pseudo-single and multiple domains. To test the reliability of data from these volcanic rocks, we analyzed the geomagnetic secular variation (GSV) and reliability of both the present data and previous paleomagnetic data. The results from 23 sites yield a single reversed polarity directed downwards to the southwest, giving a site-mean direction of Dg/Ig = 156.7°/56.6° (kg = 8.0, α95 = 11.4°) before tilt correction, and Ds/Is = 218.3°/60.1° (ks = 14.1, α95 = 8.4°) after tilt correction. The result passed the fold test, but the GSV was able to be averaged out in only two sections. All available data were examined section-by-section using the angular dispersion (SB) of virtual geomagnetic poles (VGPs) to ensure that the GSV was completely averaged out. Because the dispersion in declinations is likely to have been affectedby subsequent tectonic deformation, the paleosecular variation (PSV) could not be evaluated from all the data amassed from different sections, and the PSV was able to be removed from only four (combined) sections. A small-circle fit of these VGPs gives an averaged paleocolatitude of 51.9° ± 3.7° (N = 31 sites) centered on 24°N, 99°E. The result indicates that the sampled area of the Baoshan Terrane was located at a latitude of 38°S ± 3.7° during the late early Permian. A comparison of this result with early Permian data from Gondwanan blocks suggests that the Baoshan Terrane

  10. The carbon and sulfur cycles and atmospheric oxygen from middle Permian to middle Triassic

    NASA Astrophysics Data System (ADS)

    Berner, Robert A.

    2005-07-01

    The results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering-plus-degassing fluxes within the combined long-term carbon and sulfur cycles. Averaged data for oceanic δ 13C and δ 34S were entered for every million years from 270 to 240 Ma (middle Permian to middle Triassic) to study general trends across the Permian-Triassic boundary. Results show a drop in the rate of global organic matter burial during the late Permian and a predominance of low values during the early-to-middle Triassic. This overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris. Additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late Permian which led to smaller areas of low-lying coastal wetlands suitable for coal and peat deposition. Mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite, and a dramatic increase in the calculated global mean ratio of pyrite-S to organic-C. High S/C values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low-pyrite associated terrestrial organic matter. The prediction of increased oceanic anoxia during the late Permian and early Triassic agrees with independent studies of the composition of sedimentary rocks. Weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen. The striking result is a continuous drop in O 2 concentration from ˜30% to ˜13% over a twenty million year period. This drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter. but with a possible contribution from the weathering of older organic matter on land. It must have exerted a considerable influence on

  11. Illawarra Reversal: the onset of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Isozaki, Y.

    2008-12-01

    The Permian magnetostratigraphic records demonstrate that a remarkable change occurred in geomagnetism in the Late Guadalupian (Middle Permian; ca. 265 Ma) from the long-term stable Kiaman Reverse Superchron (throughout the Late Carboniferous and Early-Middle Permian) to the Permian-Triassic Mixed Superchron with frequent polarity change (in the Late Permian and Triassic). This unique episode called the Illawarra Reversal probably reflects a significant mode change in geodynamo in the outer core of the planet after a 50 million year-long stable geomagnetism. The Illawarra Reversal was likely led by the appearance of thermal instability at the 2,900 km-deep core-mantle boundary in connection with mantle superplume activity. The Illawarra Reversal and the Guadalupian-Lopingian boundary event recorded the significant transition from the Paleozoic to Mesozoic-Modern world. Major global environmental changes in the Phanerozoic occurred almost simultaneously in the latest Guadalupian, e.g., 1) mass extinction, 2) ocean redox change, 3) sharp isotopic excursions (C and Sr), 4) sea-level drop, and 5) plume-related volcanism. In addition to the claimed possible link between the above-listed various environmental changes and mantle superplume activity, here I propose an extra explanation that a change in the core's geodynamo may have played another important role in determining the surface climate of the planet and the course of biotic evolution. When a superplume is launched from the core-mantle boundary, resultant thermal instability makes the geodynamo's dipole of the outer core unstable, and lowers the geomagnetic intensity. Being modulated by geo- and heliomagnetism, cosmic ray flux from the outer space into the Earth's atmosphere changes along time. The more cosmic ray penetrates through the atmosphere, the more cloud develops to increase albedo, thus enhances cooling the Earth's surface. The Illawarra Reversal, the Kamura cooling event, and other unique geologic

  12. Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge: results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor

    NASA Astrophysics Data System (ADS)

    Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.

    2013-12-01

    We investigate the magnetic signature of an ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myrs, exhumed large areas of mantle derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62° E and 65° E. We show that, despite an ultraslow spreading rate, volcanic areas within robust magmatic segments are characterized by well defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.

  13. Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge - results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor

    NASA Astrophysics Data System (ADS)

    Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.

    2014-05-01

    We investigate the magnetic signature of ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myr, exhumed large areas of mantle-derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62° E and 65° E. We show that, despite an ultra-slow spreading rate, volcanic areas within robust magmatic segments are characterized by well-defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.

  14. Spatial variation in exhumation rates across Ladakh and the Karakoram: New apatite fission track data from the Eastern Karakoram, NW India

    NASA Astrophysics Data System (ADS)

    Wallis, David; Carter, Andrew; Phillips, Richard J.; Parsons, Andrew J.; Searle, Michael P.

    2016-03-01

    Characterization of low-temperature cooling histories and associated exhumation rates is critical for deciphering the recent evolution of orogenic regions. However, these may vary significantly over relatively short distances within orogens. It is pertinent therefore to constrain cooling histories and hence exhumation rates across major tectonic boundaries. We report the first apatite fission track ages from the Karakoram Fault Zone in the Eastern Karakoram range, which forms part of the western margin of the Tibetan Plateau. Ten samples, from elevations of 3477-4875 m, have apatite fission track dates from 3.3 ± 0.3 Ma to 7.4 ± 1.1 Ma. The ages correspond to modeled average erosional exhumation rates of 0.67 + 0.27/-0.18 mm/yr across the Eastern Karakoram. The results are consistent with a trend northward from the Indus suture zone, across the Ladakh terrane and into the Karakoram, in which tectonic uplift associated with crustal thickening increases toward the north, raising elevation and promoting glaciation and generation of extreme relief. As a result, erosion and exhumation rates increase south to north. Present-day precipitation on the other hand varies little within the study area and on a larger scale decreases southwest to northeast across this portion of the orogen. The Eastern Karakoram results highlight the diverse patterns of exhumation driven by regional variations in tectonic response to collision along the western margin of Tibet.

  15. Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration melting during exhumation in response to continental collision

    NASA Astrophysics Data System (ADS)

    Song, Shuguang; Niu, Yaoling; Su, Li; Wei, Chunjing; Zhang, Lifei

    2014-04-01

    Modern adakite or adakitic rocks are thought to result from partial melting of younger and thus warmer subducting ocean crust in subduction zones, with the melt interacting with or without mantle wedge peridotite during ascent, or from melting of thickened mafic lower crust. Here we show that adakitic (tonalitic-trondhjemitic) melts can also be produced by eclogite decompression during exhumation of subducted and metamorphosed oceanic/continental crust in response to continental collision, as exemplified by the adakitic rocks genetically associated with the early Paleozoic North Qaidam ultra-high pressure metamorphic (UHPM) belt on the northern margin of the Greater Tibetan Plateau. We present field evidence for partial melting of eclogite and its products, including adakitic melt, volumetrically significant plutons evolved from the melt, cumulate rocks precipitated from the melt, and associated granulitic residues. This “adakitic assemblage” records a clear progression from eclogite decompression and heating to partial melting, to melt fractionation and ascent/percolation in response to exhumation of the UHPM package. The garnetite and garnet-rich layers in the adakitic assemblage are of cumulate origin from the adakitic melt at high pressure, and accommodate much of the Nb-Ta-Ti. Zircon SHRIMP U-Pb dating shows that partial melting of the eclogite took place at ∼435-410 Ma, which postdates the seafloor subduction (>440 Ma) and temporally overlaps the UHPM (∼440-425 Ma). While the geological context and the timing of adakite melt formation we observe differ from the prevailing models, our observations and documentations demonstrate that eclogite melting during UHPM exhumation may be important in contributing to crustal growth.

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

    NASA Astrophysics Data System (ADS)

    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

  17. Differential exhumation rates in the High Himalaya perpendicular to the orogenic convergence: from Mt. Everest to the Arun River gorge

    NASA Astrophysics Data System (ADS)

    Haviv, I.; Avouac, J.; Farley, K. A.; Harrison, M.; Neupane, P. C.; Heizler, M. T.

    2011-12-01

    Long-term localization of tectonic strain in response to erosion by surface processes is an intriguing hypothesis with implications ranging from flexural isostasy and river anticlines to tectonic aneurysm and channel flow. We examine geomorphic indices and thermochronologic constraints along the Barun river in Eastern Nepal flowing entirely within the High Himalaya and perpendicular to the orogenic convergence, from Mt. Everest and Mt. Makalu in the west, to the confluence with the Arun River gorge in the east. Apatite (U-Th)/He valley bottom ages decrease from ~ 2 Ma at the Makalu base camp to ~0.8 Ma at the Arun gorge. Along the same transect Zircon (U-Th)/He ages decrease from ~ 4 Ma to ~ 1.9 Ma. The two ends of this transect delineate cooling rates which are different by more than a factor of two. 3D thermo-kinematic modeling suggests that this difference can be translated to an exhumation rate delta of around 1 km/Ma which is supported further by a sub-vertical age-elevation transect along the slopes of Mt. Makalu. Previously published AFT data from the peak of Mt. Everest suggests that less than 3-5 km of rock were removed at the peak setting over the last 14 Ma. In addition, our own (U-Th)/He data from the Everest base camp in Tibet supports < 3 km of valley bottom exhumation over the last 10 Ma. We demonstrate that our data requires differential uplift with lower long-term uplift rates at the Everest and Makalu area, vs. higher uplift at the Arun gorge. In addition, we discuss stratigraphic and thermochronologic observations which suggest that other prominent Himalaya peaks such as Shisha Pangma, Annapurna and Manaslu have also experienced long-term exhumation rates which are much lower than those of adjacent valleys.

  18. Underthrusting and exhumation: A comparison between the External Hellenides and the ``hot'' Cycladic and ``cold'' South Aegean core complexes (Greece)

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, D. J. J.; Zachariasse, W. J.; Wortel, M. J. R.; Meulenkamp, J. E.

    2005-04-01

    After their emplacement in the course of the late Mesozoic and the Cenozoic, the Hellenic nappes became fragmented during late orogenic extension since the late Eocene. Here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension. To this end, we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the Tripolitza and Ionian nappes, which were exhumed in the Cycladic and South Aegean windows, with newly obtained data on the sedimentary, stratigraphic, and structural development of the part of these nappes in the foreland, in front of the subduction thrust. The results allow the identification of two major events: Event 1 took place around the Eocene-Oligocene transition and marks the onset of underthrusting of the Tripolitza nappe below the Pindos nappe and the Ionian nappe below the Tripolitza nappe, respectively. This led to the uplift and erosion of the Pindos unit and the onset of deposition of the Tripolitza and Ionian flysch in front of the Pindos thrust, together with the formation of mylonites at the base of the metamorphosed portions of the Pindos unit related to the underthrusting of the Tripolitza unit. Event 2 occurred in the latest Oligocene to earliest Miocene and marks the decoupling of the Ionian unit from the underthrusting plate, the accretion of the Tripolitza and Ionian units to the overriding plate, and the onset of late orogenic extension and exhumation in the overriding plate. This led to the formation of the South Aegean and Cycladic core complexes and the subsidence of the Klematia-Paramythia half-graben throughout the early Miocene.

  19. Timing and rate of exhumation along the Litang fault system, implication for fault reorganization in Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Zhang, Yuan-Ze; Replumaz, Anne; Wang, Guo-Can; Leloup, Philippe Hervé; Gautheron, Cécile; Bernet, Matthias; Beek, Peter; Paquette, Jean Louis; Wang, An; Zhang, Ke-Xin; Chevalier, Marie-Luce; Li, Hai-Bing

    2015-06-01

    The Litang fault system that crosses the Litang Plateau, a low relief surface at high elevation (~4200-4800 m above sea level) that is not affected by regional incision, provides the opportunity to study exhumation related to tectonics in the SE Tibetan Plateau independently of regional erosion. Combining apatite and zircon fission track with apatite (U-Th)/He thermochronologic data, we constrain the cooling history of the Litang fault system footwall along two transects. Apatite fission track ages range from 4 to 16 Ma, AHe ages from 2 to 6 Ma, and one zircon fission track age is ~99 Ma. These data imply a tectonic quiet period sustained since at least 100 Ma with a slow denudation rate of ~0.03 km/Ma, interrupted at 7 to 5 Ma by exhumation at a rate between 0.59 and 0.99 km/Ma. We relate that faster exhumation to the onset of motion along the left-lateral/normal Litang fault system. That onset is linked to a Lower Miocene important kinematic reorganization between the Xianshuihe and the Red River faults, with the eastward propagation of the Xianshuihe fault along the Xiaojiang fault system and the formation of the Zhongdian fault. Such strike-slip faults allow the sliding to the east of a wide continental block, with the Litang fault system accommodating differential motion between rigid blocks. The regional evolution appears to be guided by the strike-slip faults, with different phases of deformation, which appears more in agreement with an "hidden plate-tectonic" model rather than with a "lower channel flow" model.

  20. Thrusting between exhumed mantle blocks at the Gorringe Bank (SW Iberian margin): Evidence from combined seismic and gravity modeling

    NASA Astrophysics Data System (ADS)

    Sallarès, V.; Martinez-Loriente, S.; Prada, M.; Gailler, A.; Gutscher, M.-A.; Bartolome, R.; Gracia, E.

    2012-04-01

    The Gorringe Bank is a massive seamount located offshore the SW Iberian margin that displays one of the largest gravity anomalies on Earth's oceans. To determine its deep seismic structure, a wide-angle seismic transect with OBS/H crossing it from the Tagus to Horseshoe Abyssal plains, was acquired in 2008. The corresponding velocity model, obtained by joint refraction and reflection travel-time inversion, displays a variably-thick sedimentary layer on top of a basement showing a strong vertical velocity gradient and no evidence for a crust-mantle boundary, not only in the Gorringe Bank but also in the adjacent segments of the deep oceanic basins. The seismic structure closely resembles that of exhumed mantle sections described along the Western Iberian margin and largely differs from that of either oceanic or extended continental crust. A velocity-derived density model assuming that the basement is made of serpentinized peridotite matches well the observed gravity anomaly, showing a basement with a variable degree of serpentinization, decreasing from ~90 % at the seafloor to ~20 % at 10 km deep. Our preferred interpretation is that the Gorringe Bank was initially the central segment of an exhumed mantle band that included also the present-day Eastern Tagus and Western Horseshoe basins. This band, which constitutes the southernmost and oldest section of the Western Iberia oceanic domain, was probably exhumed in the Earliest Cretaceous, during the onset of the North Atlantic opening. During the WNW-ESE Neogene compression, the westernmost Horseshoe basin was thrust on top of the easternmost Tagus basin, uplifting the Gorringe Bank.

  1. Late Cretaceous-early Eocene Laramide uplift, exhumation, and basin subsidence in Wyoming: Crustal responses to flat slab subduction

    NASA Astrophysics Data System (ADS)

    Fan, Majie; Carrapa, Barbara

    2014-04-01

    Low-angle subduction of the Farallon oceanic plate during the Late Cretaceous-early Eocene is generally considered as the main driver forming the high Rocky Mountains in Wyoming and nearby areas. How the deformation was transferred from mantle to upper crust over the great duration of deformation (~40 Myr) is still debated. Here, we reconstruct basin subsidence and compile paleoelevation, thermochronology, and provenance data to assess the timing, magnitude, and rates of rock uplift during the Laramide deformation. We reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information. The amount (and rate) of rock uplift of individual Laramide ranges was less than 2.4-4.8 km (~0.21-0.32 mm/yr) during the early Maastrichtian-Paleocene (stage 1) and increased to more than ~3 km (~0.38-0.60 mm/yr) during the late Paleocene-early Eocene (stage 2). Our quantitative constraints reveal a two-stage development of the Laramide deformation in Wyoming and an increase of rock uplift during stage 2, associated with enhanced intermontane basin subsidence. Exhumation and uplift during stage 1 is consistent with eastward migration of Cordilleran deformation associated with low-angle subduction, whereas the change in exhumation during stage 2 seems to follow a southwestward trend, which requires an alternative explanation. We here suggest that the increase of rock uplift rate during the late Paleocene-early Eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the Farallon oceanic slab.

  2. Paleomagnetism and Thermal History of the Permian Succession of the Velebit Mts (Dinarides, Croatia)

    NASA Astrophysics Data System (ADS)

    Lewandowski, M.; Werner, T.; Vlahovic, I.; Srodon, J.; Anczkiewicz, A.; Velic, I.; Sidorczuk, M.

    2012-12-01

    The studied area of Velebit Mts, a part of the Adria Microplate, belonged to a NE margin of Gondwana during the Carboniferous and Permian. While Permian is characterised by clastics, post-Permian sedimentation is dominated by a thick sequence of carbonate rocks. Today, the entire sequence, representing a stratigraphic range from Carboniferous to Recent, is in places more than 10,000 m thick. The mid-Permian deposits of the core part of the Velebit Mt. at Kosna and Crne Grede localities were investigated using paleomagnetic and rock magnetic measurements, supported by XRD, AFT and K-Ar studies of the clastic part of the profile (Carboniferous to Triassic). Hysteresis studies revealed that magnetic susceptibility of reddish siltstones/sandstones as well as underlying conglomerates is mostly carried by the paramagnetic matrix with a significant but varying contribution of hematite and some SP/SD magnetite. AMS fabric with low anisotropy ratio (1-3%) is strongly oblate at Kosna and weakly prolate at Crne Grede, reflecting differences in the contribution of magnetic phases. Thermal enhancement of AMS results in substantial increase of susceptibility, anisotropy ratio and more oblate fabric due to growth of SP magnetite fraction,.Enhanced AMS fabric tends to mimic tectonic fabric supporting that SP/SD magnetite is younger syntectonic phase more prone to record younger remagnetization. The paleotemperatures have been estimated by clay minerals analyses of the Carboniferous, Permian and Triassic shales. K-Ar and apatite fission track analyses (AFT) provided time constraints for the maximum paleotemperature and the uplift event, respectively. The paleotemperature estimates gave a range from ca. 140 to more than 200°C. Generally, the highest paleotemperatures are recorded within the Carboniferous rocks. K-Ar measurements of multiple fractions of illite-smectite separated from Triassic bentonites gave a consistent range of the Late Cretaceous ages of the maximum

  3. Timing of Emeishan magmatic activity and implications for the end-Middle Permian biotic crisis

    NASA Astrophysics Data System (ADS)

    Mundil, R.; Denyszyn, S. W.; Shellnutt, J. G.; Jost, A. B.; Payne, J. L.; Renne, P. R.; He, B.; Zhong, Y.; Xu, Y.

    2012-04-01

    Evidence from high-resolution geochronology combined with fossil records and proxies for changes in the paleoenvironment suggest that there is a link between large-scale (but short-term) volcanic events and mass extinctions. Synchroneity has been shown between large-scale volcanic events and three of the five most severe mass extinctions: the end-Permian extinction (P-T) coincides with Siberian Traps LIP; the end-Triassic extinction (Tr-J) with Central Atlantic Magmatic Province; and the end-Cretaceous (K-P) with the Deccan Traps LIP. Recent studies also show that the magnitude of the extinction is not a simple function of the size (volume) of the igneous event; rather, the eruption rate and nature of the host rock that is intruded exert important controls on the rate and magnitude of the release of gases that affect climate and ocean chemistry. Consequently, high-resolution geochronological constraints on LIP volcanism, biotic extinctions, and climatic change are essential to understanding the role of magmatism in these evolutionary catastrophes. The end-Guadalupian (latest Middle Permian) extinction event shows a selectivity pattern similar to the better-studied end-Permian extinction. Single zircon U-Pb ages from intrusions related to the late Middle Permian ca 260 Ma Emeishan LIP (central and southwest China) have recently been shown to have intruded within a very narrow time interval between 260 and 257 Ma, broadly overlapping the timing of end-Guadalupian biotic change. New zircon U-Pb ages from felsic volcanic rocks overlying the youngest Emeishan related basalts show that effusive volcanism was terminated between 258 and 259 Ma, suggesting that the main stage of volcanism was very short. Unfortunately, 40Ar/39Ar analyses applied to minerals extracted from basalts have proven notoriously difficult because of thermal overprint in the studied area. Whereas the timing of Emeishan related magmatic activity is now better constrained by our new U-Pb zircon

  4. Modes of deformation in ultramafic rocks exhumed in the footwall of detachment faults at the Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Picazo, S. M.; Cannat, M.; Delacour, A.; Silantiev, S.; Fouquet, Y.

    2010-12-01

    Mantle exhumation by detachment faulting is common at slow spreading mid-ocean ridges. We present deformation structures related to exhumation in ultramafic and associated mafic rocks which were dredged and sampled by ROV during the SERPENTINE cruise (2007) in the footwall of detachments along the Mid-Atlantic Ridge: next to the Ashadze vent field at 13°N, and to the Logatchev vent field at 14°45'N. At these two locations, the main fault zones have been eroded by rockslides. However, we infer that our samples come from < 200m of these main faults. The exhumed rocks belong to 4 lithological types in varying proportions: metabasalts and metadolerites (0,5 to 54%), metagabbros (0,1 to 18%), and serpentinized peridotites with (25 to 49%) and without (2 to 74%) gabbroic injections. We focused our study on these last two types and identified 4 types of deformation. For each type of deformation, we use the weight % of affected samples as an indicator of the distributed character of this deformation in the detachment footwall. Only 0,2% of the ultramafic rocks is affected to some degree by lithospheric ductile deformation with recrystallization of primary minerals (olivine, pyroxenes). 17% presents brittle-ductile shear zones. Most of these shear zones contains mineral assemblages typical of greenschist facies hydrous alteration of gabbroic material (tremolite after hornblende, chlorite after plagioclase, and occasional zircon). These minerals, with serpentine and less common talc are recrystallized, or kinked and fractured. A small number of shear zones are comprised of strongly oriented tremolite fibbers with post-kinematic replacement by talc and carbonates. These are interpreted as sheared hydrothermal veins. Matrix-supported cataclasites are observed in samples collected near the Logatchev vent field, where they represent 13% of the ultramafics. These cataclasites contain serpentinized and gabbroic clasts in a matrix of sheared and/or fractured chlorite, serpentine

  5. Polar gypsum on Mars : wind-driven exhumation from the North Polar Cap and redistribution in the Circumpolar Dune Field

    NASA Astrophysics Data System (ADS)

    Masse, M.; Bourgeois, O.; Le Mouélic, S.; Verpoorter, C.; Le Deit, L.; Mercier, E.; Bibring, J.

    2010-12-01

    The North Polar Cap of Mars is associated with different kinds of superficial sediments, including the Circumpolar Dune Field and sedimentary veneers scattered over the ice cap. In order to resolve the mineralogical composition of these sediments, we processed OMEGA and CRISM hyperspectral data with an original method based on spectral derivation (Huguenin and Jones, 1986). We find that gypsum is present in all areas where undefined hydrated minerals had been previously detected (Poulet et al., 2008; Horgan et al., 2009; Calvin et al., 2010), including the superficial sedimentary veneers found on the North Polar Cap and the whole Circumpolar Dune Field. Integrated morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap (Massé et al., 2010). The source of sedimentary veneers is the dust that was previously contained in the upper part of the ice cap, the ice-rich North Polar Layered Deposits (NPLD). This gypsum-bearing dust was exhumed, on south-facing slopes of spiral troughs and arcuate scarps, by ice ablation induced by katabatic winds. By the analysis of all associations of erosional scarps and dune fields over the North Polar Cap, we also demonstrate that the source of the polar dunes are sand-sized particles that were previously contained in the sediment-rich BU (Basal Unit), corresponding to the lower part of the ice cap. These particles were exhumed from the BU, by regressive ablation of the ice at marginal scarps that border the North Polar Cap, or by vertical ablation of the ice on Olympia Planum. From a reconstruction of wind flow lines over and around the ice cap, we infer that katabatic winds descending from the polar high and rotating around the North Polar Cap are responsible for the exhumation of this gypsum-bearing sand and for its redistribution in the Circumpolar Dune Field. The intensity of gypsum diagnostic spectral absorption bands decreases along wind flow lines in the

  6. Exhumation of Triassic HP-LT rocks by upright extrusional domes and overlying detachment faults, Ishigaki-jima, Ryukyu islands

    NASA Astrophysics Data System (ADS)

    Osozawa, Soichi; Wakabayashi, John

    2012-10-01

    The Tomuru Formation of Ishigaki-jima in the southernmost part of the Ryukyu arc, comprises blueschist facies subduction complex rocks metamorphosed in Triassic time. D1 structures related to subduction, blueschist facies mineral growth, and possibly early stages of exhumation, are deformed by D2 structures that appear to reflect the last stage of exhumation. D2 structures define several anticlines with parasitic overturned folds verging away from anticlinal axes. The shortening recorded by this deformation appears to reflect upward extrusion relative to flanking material. The anticlines are flanked by detachment faults with normal sense-of-shear parallel to D2 vergence. Hanging wall rocks that include the Fusaki Formation, an accretionary prism with early Cretaceous metamorphic ages, and late Eocene limestone, conglomerate, and andesitic volcanics. The Eocene strata contain metamorphic detritus derived from the Tomuru and Fusaki Formations indicating pre-late Eocene surface exposure of these units. Ultramafic rocks and gabbro blocks of the Tomuru Formation were incorporated by sedimentary sliding into the trench prior to subduction and high-pressure metamorphism rather than being emplaced as diapirs along a post-metamorphic fault as previously proposed. Geochronologic, metamorphic, and thermal considerations suggest exhumation of the Tomuru Formation to relatively shallow crustal depths prior to or concurrent with early Cretaceous metamorphism of the Fusaki Formation. Arcward-vergent thrusting may have placed the younger, and formerly structurally lower, subduction complex (Fusaki Formation) over the older one (Tomuru Formation). D2 extrusional doming began after the emplacement of the Fusaki Formation at high structural levels. The D2 transport directions are subparallel to the strike of the orogen suggesting that the upright extrusion may have occurred along a forearc strike-slip fault system. This final stage of exhumation concluded in the late Eocene with

  7. An exhumation history of Hall Peninsula, Baffin Island, Canada derived from low-temperature thermochronology and 3D thermokinematic modeling

    NASA Astrophysics Data System (ADS)

    Creason, C. Gabriel; Gosse, John; Whipp, David; Young, Michael; Kislitsyn, Roman

    2014-05-01

    The eastern Canadian Arctic Rim (eCAR) is a rugged, high-relief terrain, spanning from southeastern Ellesmere Island to northern Labrador. While much of the relief along the eCAR may be related to rift-flank uplift and incision during and after rifting between Canada and Greenland, there has recently been much debate over our understanding of passive margin evolution and the processes responsible for the development of their modern landscape. Furthermore, thermal histories derived from previous thermochronologic studies from the northern and southern regions of the eCAR, as well as in West Greenland, are incompatible with a single, continuous exhumation history for the eCAR. This study aims to characterize the long-term exhumation history of Hall Peninsula, and, by linking together previous thermochronologic studies in the eCAR, we will test various models of tectonic and climate-driven landscape evolution of Baffin Island. In total, 33 samples have been analyzed by low-temperature (U-Th)/He thermochronometry (26 apatite-He (AHe), 7 zircon-He (ZHe); 5 aliquots each) to help define the cooling history of the rocks on Hall Peninsula. Results from these samples reveal cooling ages that are heavily influenced by the effects of radiation damage, with strong positive or negative correlations between effective U concentration (eU = U + 0.235Th) and He age for AHe and ZHe, respectively. Preliminary modeling of the t-T path of individual samples using thermal modeling program HeFTy suggests a history of protracted, slow cooling across Hall Peninsula, with cooling events initiating from middle Paleozoic to late Mesozoic. However, many samples cannot be modeled using HeFTy, likely due to the large dispersion in the age data. Thus, to aid the thermal model in adjusting the cooling ages for the effects of radiation damage, select samples will also be analyzed using apatite fission track thermochronometry. A three-dimensional thermokinematic finite-element modeling code, Pecube

  8. Unraveling the geochemistry of melts in exhumed mantle domains in present-day and fossil magma-poor rifted margins

    NASA Astrophysics Data System (ADS)

    Amann, Méderic; Ulrich, Marc; Autin, Julia; Manatschal, Gianreto; Epin, Marie-Eva; Müntener, Othmar; Boiron, Marie-Christine; Sauter, Daniel

    2016-04-01

    The role of magmatic processes occurring during the continental break-up and the onset of steady-state seafloor spreading are still a matter of debate. Beside the tectonic processes like stretching, thinning and exhumation, magmatic processes also play a key role in the evolution and breakup of magma-poor rifted margins. To unravel the impact of such processes, Ocean-Continent-Transitions (OCTs) are of particular interest. OCTs are complex areas where hyper-extended continental crust, exhumed mantle and proto-oceanic crust occur. All these domains have been identified and sampled in both present-day (Iberia/Newfoundland margins) and fossil margins (Platta/Err nappes). In this study, we present preliminary results that enable to characterize the nature of the mantle rocks and the melts found in the OCTs of these paleo- and present-day margins with the aim to investigate how the mantle evolves from initial exhumation to final lithospheric breaks. In OCTs two types of mantle rocks can be observed: (i) a « sub-continental type » free of syn-exhumation melt imprint preserving the early geochemical evolution, and (ii) a « refertilized type » characterized by melt infiltration and mantle-melt interaction. Melts from these domains have different major, trace element and isotopic compositions and can therefore be used to constrain how melt interacts with the mantle and to understand the role of magmatic processes in the break-up. We therefore summarized whole-rock, in-situ and isotopic analysis available in the literature from the Iberia/Newfoundland present-day margin system and completed the existing database with new additional data from the Iberia margin. These new data have been obtained using in-situ technics mainly on clinopyroxenites, serpentinized peridotites and gabbros of ODP drill cores. Around 200 new data have been acquired using the LA-ICPMS technic. Preliminary results show that clinopyroxenes in serpentinized peridodite breccia from ODP site 637A and

  9. From dust to dust: ethical and practical issues involved in the location, exhumation, and identification of bodies from mass graves.

    PubMed

    Williams, Erin D; Crews, John D

    2003-06-01

    There are many potential purposes served by the investigation of human remains: criminal fact-finding, archaeological exploration, forensic research, and others. This paper focuses on the identification of remains from mass graves to find missing persons. The primary goal of such efforts is to honor the memory of the dead by bringing closure to living family members, thus supporting the human rights of both the living and the deceased. Cultures, customs, political, and interpersonal specifics will vary, but that singular goal should remain the central guiding principle. This article presents ethical and practical issues resulting from efforts to locate, exhume, and identify the remains of mass fatalities. PMID:12808715

  10. Subducted sedimentary serpentinite mélanges: Record of multiple burial-exhumation cycles and subduction erosion

    NASA Astrophysics Data System (ADS)

    Wakabayashi, John

    2012-09-01

    Serpentinite matrix mélanges give insight into large-scale convergent plate margin processes, particularly because of the derivation of the serpentinite from oceanic mantle. Similar to shale-matrix mélanges, a field geologist may easily recognize the sedimentary origins of little-deformed serpentinite matrix mélanges, but mélanges within accretionary prisms have undergone significant deformation and recrystallization of matrix. Serpentinite mélanges of the Franciscan subduction complex of California have a seemingly intact and foliated matrix. Such exposures contrast sharply with the granular undeformed sedimentary serpentinite mélanges of the coeval Great Valley Group (GVG) forearc basin deposits that depositionally overlie Coast Range Ophiolite (that structurally overlies the Franciscan). Nonetheless, Franciscan serpentinite mélanges display evidence of sedimentary origins, including sedimentary breccia composed of exotic block material (Tolay Ridge), sedimentary serpentinite breccia (Panoche Pass Road), basal serpentinite conglomerate with exotic clasts (Sunol Regional Wilderness), and serpentinite sandstones and conglomerates, including a basal conglomerate overlying coherent metagraywacke (Tiburon Peninsula). These examples record two burial-exhumation cycles to blueschist facies depths. In addition, a mélange/breccia in the Panoche Pass area may have components that record three burial-exhumation cycles to blueschist (or greater) depth. Exhumation rates for various cycles ranged from about 1.2 to 10 mm/year. The Tiburon Peninsula serpentinite mélange occupies the structurally highest horizon in the Franciscan of the San Francisco Bay area, and regional field relationships indicate deposition at ca. 100 Ma. Apparently, about 65 Ma of subduction erosion/non accretion followed initiation of Franciscan subduction in this region. The oldest Franciscan serpentinite mélanges are at least 35 Ma younger than sedimentary serpentinites of the GVG. Subduction

  11. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, Micha; Steck, Albrecht; Carter, Andrew; Cosca, Michael; Epard, Jean-Luc; Hunziker, Johannes

    2011-01-01

    High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26 Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19 Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (

  12. Source and mode of the Permian Panjal Trap magmatism: Evidence from zircon U-Pb and Hf isotopes and trace element data from the Himalayan ultrahigh-pressure rocks

    NASA Astrophysics Data System (ADS)

    Rehman, Hafiz Ur; Lee, Hao-Yang; Chung, Sun-Lin; Khan, Tahseenullah; O'Brien, Patrick J.; Yamamoto, Hiroshi

    2016-09-01

    We present an integrated study of LA-ICP-MS U-Pb age, Hf isotopes, and trace element geochemistry of zircons from the Himalayan eclogites (mafic rocks) and their host gneisses (felsic rocks) from the Kaghan Valley in Pakistan in order to understand the source and mode of their magmatic protoliths and the effect of metamorphism. Zircons from the so-called Group I (high-pressure) eclogites yielded U-Pb mean ages of 259 ± 10 Ma (MSWD = 0.74), whereas those of Group II (ultrahigh-pressure) eclogites yielded 48 ± 3 Ma (MSWD = 0.71). In felsic gneisses the central or core domains of zircons yielded ages similar to those from Group I eclogites but zircon overgrowth domains yielded 47 ± 1 Ma (MSWD = 1.9). Trace element data suggest a magmatic origin for Group I-derived (having Th/U ratios: > 0.5) and metamorphic origin for Group II-derived (Th/U < 0.07) zircons, respectively. Zircon Hf isotope data, obtained from the same dated spots, show positive initial 176Hf/177Hf isotopic ratios referred to as "ƐHf(t)" of around + 10 in Group I eclogites; + 7 in Group II eclogites; and + 8 in felsic gneisses zircons, respectively, thus indicate a juvenile mantle source for the protolith rocks (Panjal Traps) with almost no contribution from the ancient crustal material. The similar ƐHf(t) values, identical protolith ages and trace element compositions of zircons in felsic (granites or rhyolites) and mafic (basalt and dolerite) rocks attest to a bimodal magmatism accounting for the Panjal Traps during the Permian. Later, during India-Asia collision in Eocene times, both the felsic and mafic lithologies were subducted to mantle-depths (> 90 km: coesite-stable) and experienced ultrahigh-pressure metamorphism before their final exhumation.

  13. Seismic evidence for hyper-stretched crust and mantle exhumation offshore Vietnam.

    NASA Astrophysics Data System (ADS)

    Savva, D.; Meresse, F.; Pubellier, M.; Chamot-Rooke, N.; Franke, D.; Steuer, S.; Sapin, F.; Auxietre, J. L.

    2012-04-01

    - 10.5 Ma, at variance with models derived from magnetic anomalies recognized over the oceanic portions of the South China Sea (15.5 to 20 Ma). keywords : South China Sea, Vietnam, Phu Khan Basin, mantle exhumation, polyphased rifting

  14. Pliocene Core Complex Exhumation on Land and Rapid Subsidence in Gorontalo Bay, Sulawesi (Indonesia)

    NASA Astrophysics Data System (ADS)

    Pezzati, G.; Hall, R.; Burgess, P.; Perez-Gussinye, M.

    2014-12-01

    Gorontalo Bay is a semi-enclosed sea between the North and East Arms of Sulawesi. It is surrounded by land on three sides, separating a northern volcanic province from metamorphic rocks to the south and west, and ophiolites to the southeast. Recently acquired multibeam bathymetry and 2D seismic data suggest a link between core complex exhumation on land and offshore subsidence driven by major young extension. In western Gorontalo Bay are two sub-basins with different histories: Tomini Basin in the north and Poso Basin in the south. In Tomini Basin six major seismic sequences (Units A to F) have a total thickness over 5 sec TWT. Ages are based on interpreted correlations with events on land. Basement Unit A subsided from the Early Miocene, with deposition of Units B and C, largely in a deep marine environment. There was regional uplift in the Middle Miocene. Carbonate platforms were thereafter deposited in shallow marine environments (Units D-E). The platforms show a wedge geometry that suggests tilting of the basin during their deposition. Subsidence accelerated during the deposition of Unit E in the Early Pliocene, causing backstepping of the shelf edge, formation of pinnacle reefs and then drowning of the carbonate platforms, leading to present depths of 2 km in the basin centre (Unit F). Poso Basin is younger than Tomini Basin and forms the southern part of western Gorontalo Bay. The deeper part of its sedimentary sequence is probably the time equivalent of Unit D in Tomini Basin. It contains a complex deformed sequence of sediments, up to 3 sec TWT, that are the probable equivalent of Units E and F to the north. On land to the south of Poso Basin is a large metamorphic core complex. Seismic data suggest that the northern flank of the complex can be traced into a potential low angle normal fault under the basin that caused subsidence offshore. Low T thermochronology and alluvial sediment records on land suggest major uplift and subsidence occurred in the

  15. Two radically different exhumation models for the Qiangtang Terrane, Central Tibet

    NASA Astrophysics Data System (ADS)

    Zhao, Zhongbao; Bons, Paul D.

    2014-05-01

    A century after the discovery of blueschist rocks in the central Qiangtang Terrane, the debate on their origin is still ongoing. Although all authors agree that the blueschists derive from subduction of oceanic crust, two radically different models are proposed. The "underthrust model" envisages early Mesozoic subduction mélange to have been thrust southwards (from the Jinsa Suture Zone, 200 km to the North) under Paleozoic crust of the Qiangtang Terrane. The subduction mélange, with high-pressure rocks, are thought to have exhumed by normal faulting in a large metamorphic core complex. The alternative "in-situ subduction model" puts the suture with northward subduction closer by at the Longmu Co-Shuanhu Suture Zone that separates the North and South Qiangtang terranes. In this model, allochtonous mélange is thrust over autochtonous Paleozoic basement in a south-vergent imbricate thrusts system. The models have far-reaching consequences for the crustal structure of central Tibet, as the first predicts the middle and lower crust to consist of subduction mélange overlain by Qiangtang basement and onshore Carboniferous-Triassic sediments, whereas the second predicts these rocks to overlie the Qiangtang basement of North-Gondwana provenance. To resolve this issue we combined detailed mapping in the central Qiangtang Terrane with 3D structural modelling using ASTER satellite images and the software package Move(TM). The high topography makes it possible to constrain the location and orientation of large-scale (>kms) structures, such as major faults. We found that Ordovician to Carboniferous sediments unconformably overly low-metamorphic grade pre-Ordovician basement rocks, together forming the autochtonous Paleozoic basement. This is overlain by a stack of shallowly dipping thrust sheets of subduction mélange, high-pressure rocks, as well as Permo-Triassic sediments. With the subduction mélange overlying the autochtonous basement, we prefer the in-situ subduction

  16. Mantle exhumation and OCT architecture dependency on lithosphere deformation modes during continental breakup: Numerical experiments

    NASA Astrophysics Data System (ADS)

    Jeanniot, Ludovic; Kusznir, Nick; Manatschal, Gianreto; Cowie, Leanne

    2013-04-01

    The initiation of sea-floor spreading, during the continental breakup process, requires both the rupture of the continental crust and the initiation of decompression melting. This process results in mantle upwelling and at some point decompressional melting which creates new oceanic crust. Using numerical experiments, we investigate how the deformation mode of continental lithosphere thinning and stretching controls the rupture of continental crust and lithospheric mantle, the onset of decompression melting, their relative timing, and the circumstances under which mantle exhumation may occur. We assume that the topmost continental and ocean lithosphere, corresponding to the cooler brittle seismogenic layer, deforms by extensional faulting (pure-shear deformation) and magmatic intrusion, consistent with the observations of deformation processes occurring at slow spreading ocean ridges (Cannat, 1996). We assume that deformation beneath this topmost lithosphere layer (approximately 15-20 km thick) occurs in response to passive upwelling and thermal and melt buoyancy driven small-scale convection. We use a 2D finite element viscous flow model (FeMargin) to describe lithosphere and asthenosphere deformation. This flow field is used to advect lithosphere and asthenosphere temperature and material. The finite element model is kinematically driven by Vx for the topmost upper crust inducing passive upwelling beneath that layer. A vertical velocity Vz is defined for buoyancy enhanced upwelling as predicted by Braun et al. (2000). Melt generation is predicted by decompression melting using the parameterization and methodology of Katz et al. (2003). Numerical experiments have been used to investigate the dependency of continental crust and lithosphere rupture, decompression melt initiation, rifted margin ocean-continent transition architecture and subsidence history on the half-spreading rate Vx, buoyancy driven upwelling rate Vz, the relative contribution of these deformation

  17. The Cora Lake Shear Zone, an Exhumed Deep Crustal Lithotectonic Discontinuity, Western Churchill Province, Canada

    NASA Astrophysics Data System (ADS)

    Regan, S.; Leslie, S.; Holland, M. E.; Williams, M. L.; Mahan, K. H.; Jercinovic, M. J.

    2011-12-01

    Deep crustal flow is a fundamental tectonic process that may serve to reduce topographic gradients, especially in overthickened collisional orogens. Recent studies have utilized numerical models and seismic interpretations, but generally in two dimensions. Although useful, two dimensional models can not fully characterize lower crustal flow or coupling of crustal layers because they cannot fully incorporate lateral heterogeneity in the flow field. The Athabasca Granulite terrane, in northern Saskatchewan, is an exposed deep crustal terrane that underwent granulite grade deformation during the Neoarchean (ca. 2.55), then cooled isobarically for 600 m.y., and then was reactivated during the Paleoproterozoic (ca. 1.9 Ga). Regional exhumation occurred at roughly 1.85 Ga. This exposure, is a field laboratory for studying lower crustal flow, stabilization, and reactivation. Recent work suggests that the northwestern domain, dominated by the multiphase, opx-bearing, Mary batholith, underwent top-to-the-east lower crustal flow during the Neoarchean. The Chipman domain, to the SE , is primarily underlain by the 3.2 Ga, Chipman tonalite straight gneiss, which was likely restitic, and rheologically strong during the 2.6 Ga flow event. The Cora Lake shear zone (CLsz), which divides the two domains, is interpreted to represent a lithotectonic, compositional, and rheologic boundary within the deep crust. Recent mapping of the western gradient of the CLsz has provided insight into the role and evolution of the rheologic discontinuity and its relationship to crustal flow. The Mary granite (gneiss) contains excellent assemblages for P-T and pseudosection analysis. Interlayered felsic granulite contain abundant monazite for in-situ geochronology. An intense subhorizontal tectonic fabric (S1), interpreted to be the product of crustal flow, is present in both units. This early fabric was locally crenulated, folded, and transposed, by a sub-vertical S2 fabric. Current work involves

  18. A 10 Myrs long record of mantle exhumation at the eastern Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Sauter, D.; Cannat, M.; Andreani, M.; Birot, D.; Bronner, A.; Brunelli, D.; Carlut, J. H.; Delacour, A.; Guyader, V.; Mendel, V.; Ménez, B.; MacLeod, C. J.; Pasini, V.; Rouméjon, S.; Ruellan, E.; Searle, R. C.

    2011-12-01

    Although detachment faulting is thought to be a fundamental, widespread style of accretion of oceanic lithosphere, the kinematic evolution of faulting and the link between deformation and magmatic emplacement are still poorly known. Here we use newly acquired geological and geophysical data from the eastern Southwest Indian Ridge (SWIR) to address this question. The eastern SWIR displays the widest expanses known to date of seafloor with no evidence for a volcanic upper crustal layer. Deep tow TOBI sidescan sonar images and dredged rock samples were collected over two areas with contrasting styles of non volcanic seafloor. In the first survey area (centered at 62°30'E) several broad smooth elongated and symmetric ridges are oriented SW-NE, oblique to the spreading direction (~NS). TOBI images show that the hillsides of these ridges, facing toward and away from the axial valley, correspond to smooth surfaces with mass wasting features and almost no evidence of volcanism. Some of these ridges display highly backscattering fuzzy textures with rounded shape features of unknown origin. Serpentinized mantle-derived peridotites were systematically dredged in those areas. Volcanic textures are only observed at the eastern and western ends of these ridges. The second survey area (centered at 64°35'E) covers the edge between volcanic and non volcanic seafloor. There, ridges are perpendicular to the spreading direction and display mainly an asymmetric shape. TOBI sidescan sonar images show that the inward facing gentle slope of these ridges are smooth and sedimented surfaces covered locally by small sized volcanic patches. Outward facing slopes are steeper and may be covered with volcanic textures. Serpentinized mantle-derived peridotites were also systematically dredged outside these volcanic areas. We interpret the successive non volcanic ridges as the result of large low angle normal faults which exhume mantle rocks alternatively to the northern and to the southern flank

  19. Geomorphic and exhumational response of the Central American Volcanic Arc to Cocos Ridge subduction

    NASA Astrophysics Data System (ADS)

    Morell, Kristin D.; Kirby, Eric; Fisher, Donald M.; van Soest, Matthijs

    2012-04-01

    The timing of collision of the Cocos Ridge at the Middle America Trench remains one of the outstanding questions in the tectonic evolution of the Central American convergent margin. New analyses of the tectonic geomorphology of the Cordillera de Talamanca, the extinct volcanic arc inboard of the Cocos Ridge, coupled with low temperature thermochronometry data, provide insight into the cooling and erosional history of the arc from late Miocene to present. We identify a low-relief surface at high elevation along the northeastern flanks of the range, which represents a relict erosional landscape cut across shallow plutonic rocks of the arc edifice. Longitudinal profiles of rivers on this surface are isolated from steep downstream sections by prominent knickzones that are interpreted to reflect a migrating wave of transient incision generated during differential rock uplift of the range. Reconstruction of pre-incision profiles suggests that rock uplift during the growth of the Cordillera de Talamanca is no greater than ˜2 km. This inference is corroborated by results from our apatite (U-Th)/He and apatite fission track analyses along an elevation transect on Mt. Chirripó, the highest mountain in the Cordillera de Talamanca. Low-temperature cooling ages overlap significantly with published high-temperature40Ar/39Ar ages; the combined results imply that rapid cooling in the late Miocene was related to secular cooling of a shallow pluton, rather than exhumation. Our results imply that rapid incision along downstream channel segments, differential rock uplift, and growth of the Talamanca as a bivergent orogenic wedge associated with the onset of Cocos Ridge subduction are relatively young characteristics of the range. A review of previously published radiometric ages and revised plate reconstructions for the late Miocene further suggest that the cessation of arc volcanism in both the Cordillera de Talamanca and the Cordillera Central of western Panama was coeval with the

  20. Chondritic Meteoritic Fragments Associated With the Permian-Triassic (P-T) Boundary in Antarctica: Evidence for an end-Permian Bolide Impact.

    NASA Astrophysics Data System (ADS)

    Basu, A. R.; Petaev, M. I.; Poreda, R. J.; Jacobsen, S. B.; Becker, L.

    2003-12-01

    We report the discovery of meteoritic fragments, as large as 400μ m in size, in an end-Permian sedimentary bed in Graphite Peak, Central Transantarctic Mountains, Antarctica. Here, the P-T boundary is well constrained isotopically and paleontologically, and its lithology is well documented. The boundary at this site is also characterized by fullerenes containing extraterrestrial 3He and shocked quartz grains. We found meteoritic fragments in two samples of a claystone-breccia bed (separated stratigraphically by 23cm) that rests directly above the coal horizon with the last occurrence of Glossopteris. The meteoritic fragments display poikilitic or granular texture with euhedral-subhedral forsterite crystals enclosed in larger clinoenstatite grains showing polysynthetic twinning. Some silicate grains contain tiny inclusions of Fe, Ni-metal grains with chondritic Ni/Fe and Co/Ni ratios. Overall, Ni/Fe, Co/Ni and P/Fe ratios in the metal grains, Fe/Mg and Mn/Fe ratios in olivines and pyroxenes, and the chemistry of Fe, Ni, P, S-bearing oxides within the meteoritic fragments are typical of CM chondritic meteorites. The meteoritic grains found in magnetic separates of the sediments are accompanied by abundant metal nuggets, which are also found in an end-Permian bed from Meishan, south China. The common occurrence of these Fe-Ni-Si metal grains at Graphite Peak and at the Meishan P-T section provides further evidence that we sampled the P-T boundary at Graphite Peak. The association of metal grains with discrete meteoritic fragments at the Graphite Peak P-T boundary along with previous reports of such metal grains from other P-T localities leads us to support a catastrophic collision of a celestial body with the Earth at the end-Permian. We believe that this is what caused the global extinction event at the P-T boundary. Thus it appears that the two largest mass extinctions in Earth history at the K-T and P-T boundaries were both caused by catastrophic collisions with

  1. The Central European Permian Basins; Rheological and structural controls on basin history and on inter-basin connectivity

    NASA Astrophysics Data System (ADS)

    Smit, Jeroen; Van Wees, Jan-Diederik; Cloetingh, Sierd

    2014-05-01

    We analyse the relative importance of the major crustal-scale fault zones and crustal architecture in controlling basin formation, deformation and the structural connections between basins. The North and South Permian Basins of Central Europe are usually defined by the extend of Rotliegend sedimentary and volcanic units and not by a common tectonic origin or development. Instead, the sub-basins that together form the Permian Basins are each controlled by different structural and/or rheological controls that are inherited from Early Paleozoïc and older geodynamic processes, they are even located in different crustal/lithospheric domains. The North Permian basin is located on Baltic crust that was thinned during Late Proterozoïc - Early Paleozoïc times. South of the Thor suture, the South Permian basin and its sub-basins are located on Avalonian crust (Southern North Sea and North German Basins) and on the transition of East European cratonic and Avalonian crust (Polish Through). The size of crustal domains and of the faults that govern basin formation requires a regional-scale to assess their impact on basins and sub-basins. In the case of the Permian Basins this encompasses East Avalonia and surroundings, roughly speaking the area north of the Variscan Rheïc suture, east of the Atlantic and southwest of the Teisseyre-Tornquist line. This approach sheds light on the effects of long lived differences in crustal fabric which are responsible for spatial heterogeneity in stress and strain magnitudes and zonations of fracturing, burial history and temperature history. The focus on understanding the geomechanical control of large crustal-scale fault structures will provide the constraints and geometrical and compositional input for local models of stress and strain. Considering their fundamentally different structural and rheological controls, the Permian (sub)basins have a remarkably common history of subsidence and inversion, suggesting a more or less continuous

  2. Global coal gap between Permian-Triassic extinction and Middle Triassic recovery of peat-forming plants

    SciTech Connect

    Retallack, G.J.; Veevers, J.J.; Morante, R.

    1996-02-01

    Early Triassic coals are unknown, and Middle Triassic coals are rare and thin. The Early Triassic coal gap began with extinction of peat-forming plants at the end of the Permian (ca. 250 Ma), with no coal known anywhere until Middle Triassic (243 Ma). Permian levels of plant diversity and peat thickness were not recovered until Late Triassic (230 Ma). Tectonic and climatic explanations for the coal gap fail because deposits of fluctuating sea levels and sedimentary facies and paleosols commonly found in coal-bearing sequences are present also in Early Triassic rocks. Nor do we favor explanations involving evolutionary advances in the effectiveness of fungal decomposers, insects or tetrapod herbivores, which became cosmopolitan and much reduced in diversity across the Permian-Triassic boundary. Instead, we favor explanations involving extinction of peat-forming plants at the Permian-Triassic boundary, followed by a hiatus of some 10 m.y. until newly evolved peat-forming plants developed tolerance to the acidic dysaerobic conditions of wetlands. This view is compatible not only with the paleobotanical record of extinction of swamp plants, but also with indications of a terminal Permian productivity crash from {delta}{sup 13}C{sub org} and total organic carbon of both nonmarine and shallow marine shales. 205 refs., 3 figs., 3 tabs.

  3. From wetlands to wet spots: Environmental tracking and the fate of carboniferous elements in early permian tropical fl oras

    USGS Publications Warehouse

    DiMichele, W.A.; Tabor, N.J.; Chaney, D.S.; Nelson, W.J.

    2006-01-01

    Diverse wetland vegetation flourished at the margins of the Midland Basin in north-central Texas during the Pennsylvanian Period. Extensive coastal swamps and an ever-wet, tropical climate supported lush growth of pteridosperm, marattialean fern, lycopsid, and calamite trees, and a wide array of ground cover and vines. As the Pennsylvanian passed into the Permian, the climate of the area became drier and more seasonal, the great swamps disappeared regionally, and aridity spread. The climatic inferences are based on changes in sedimentary patterns and paleosols as well as the general paleobotanical trends. The lithological patterns include a change from a diverse array of paleosols, including Histosols (ever-wet waterlogged soils), in the late Pennsylvanian to greatly diminished paleosol diversity with poorly developed Vertisols by the Early-Middle Permian transition. In addition, coal seams were present with wide areal distribution in the late Pennsylvanian whereas beds of evaporates were common by the end of the Early Permian. During this climatic transition, wetland plants were confi ned to shrinking "wet spots" found along permanent streams where the vegetation they constituted remained distinct if increasingly depauperate in terms of species richness. By Leonardian (late Early Permian) time, most of the landscape was dominated by plants adapted to seasonal drought and a deep water table. Wetland elements were reduced to scattered pockets, dominated primarily by weedy forms and riparian specialists tolerant of flooding and burial. By the Middle Permian, even these small wetland pockets had disappeared from the region. ?? 2006 Geological Society of America.

  4. Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

    NASA Astrophysics Data System (ADS)

    José Fernández, Francisco; Llana-Fúnez, Sergio; Valverde-Vaquero, Pablo; Marcos, Alberto; Castiñeiras, Pedro

    2016-04-01

    High-grade, highly deformed gneisses crop out continuously along the Masanteo peninsula and constitute the upper part of the lower crustal section in the Cabo Ortegal nappe (NW Spain). The rock sequence formed by migmatitic quartzo-feldspathic (qz-fsp) gneisses and mafic rocks records the early Ordovician (ca. 480-488 Ma) injection of felsic dioritic/granodioritic dykes at the base of the qz-fsp gneisses, and Devonian eclogitization (ca. 390.4 ± 1.2 Ma), prior to its exhumation. A SE-vergent ductile thrust constitutes the base of quartzo-feldspathic gneissic unit, incorporating mafic eclogite blocks within migmatitic gneisses. A NW-vergent detachment displaced metasedimentary qz-fsp gneisses over the migmatites. A difference in metamorphic pressure of ca. 0.5 GPa is estimated between both gneissic units. The tectono-metamorphic relationships of the basal ductile thrust and the normal detachment bounding the top of the migmatites indicate that both discrete mechanical contacts were active before the recumbent folding affecting the sequence of gneisses during their final emplacement. The progressive tectonic exhumation from eclogite to greenschist facies conditions occurred over ca. 10 Ma and involved bulk thinning of the high-grade rock sequence in the high pressure and high temperature (HP-HT) Cabo Ortegal nappe. The necessary strain was accommodated by the development of a widespread main foliation, dominated by flattening, that subsequently localized to a network of anastomosing shear bands that evolved to planar shear zones. Qz-fsp gneisses and neighbouring mafic granulites were exhumed at > 3 mm yr-1, and the exhumation path involved a cooling of ˜ 20 °C/100 MPa, These figures are comparable to currently active subduction zones, although exhumation P-T trajectory and ascent rates are at the hotter and slower end in comparison with currently active similar settings, suggesting an extremely ductile deformation environment during the exhumation of qz

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

    NASA Astrophysics Data System (ADS)

    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.

  6. H2O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

    NASA Astrophysics Data System (ADS)

    Labrousse, L.; Duretz, T.; Gerya, T.

    2015-10-01

    We present two-dimensional numerical models of plate subduction and collision inspired by the Scandinavian Caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra-high pressure metamorphic rocks. Three possible reactions were tested: low temperature solidus representing H2O-fluid-saturated partial melting, and two end-member reaction curves for dehydration melting. Thermo-mechanical effects of partial melting were implemented as (1) a viscosity decrease as a determined rheologically critical melt percentage was reached (here 0.1), (2) a change in effective heat capacity and adiabatic heating/cooling accounting for a latent heat term in the heat equation. Among the 3 tested reactions, only H2O-fluid-saturated partial melting drastically modifies the collision dynamics from the non-melting reference model holding all other parameters constant. A substantially low general viscosity truncation (here 1017 Pa s) is needed to properly resolve the effect of partial melting on deep collision processes. Low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment, where migmatites exhume from UHP conditions at rates and with pressure-temperature paths similar to the natural values acknowledged for the Norwegian Caledonides. High temperature melting has no drastic influence on early collision dynamics. While positive buoyancy remains the first order driver for the exhumation of buried continental rocks, exhumation initiates in these cases with eduction subsequent to slab detachment. Melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 °C. Some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone. Even if minor in terms of amount of magma produced, H2O-fluid-saturated partial melting

  7. Very high geothermal gradient during mantle exhumation recorded in mylonitic marbles and carbonate breccias from a Mesozoic Pyrenean palaeomargin (Lherz area, North Pyrenean Zone, France)

    NASA Astrophysics Data System (ADS)

    Lagabrielle, Yves; Clerc, Camille; Vauchez, Alain; Lahfid, Abdeltif; Labaume, Pierre; Azambre, Bernard; Fourcade, Serge; Dautria, Jean-Marie

    2016-03-01

    Although they are famous among Earth scientists, the Lherz peridotites are exposed within geological formations of the North Pyrenean Zone (NPZ) still lacking detailed investigations. Our study focuses on the metasediments of the Aulus basin hosting the Lherz peridotite body and associated ultramafic fragments of smaller size. The new data set comprises of structural analysis and detailed geological mapping of the massive Mesozoic marbles that form the prerift sequence typical of the NPZ and of the ultramafic-rich clastic breccia formations surrounding the peridotite bodies. The massive marbles display an evolution from hot and ductile to cold and brittle deformation, indicative of an exhumation process ending with the sedimentary reworking of both the deformed Mesozoic metasediments and the exhumed ultramafic rocks. Crystal Preferred Orientations (CPO) measured in the marbles support a deformation mechanism by dislocation creep of calcite, which is dominant between 400 °C and 600 °C; these deformation temperatures are within the range determined earlier by Clerc et al. (2015), using RSCM (Raman Spectroscopy of Carbonaceous Material) geothermometry. As a consequence, we better describe the transition from ductile to brittle deformation in the prerift marbles and clarify the origin of the syn-rift breccias. Due to continuous exhumation along detachments' faults, the brecciated metamorphic carbonates of the prerift NPZ sedimentary cover were passively uplifted towards shallower levels and progressively unroofed, while transported passively on the back of the exhumed ultramafic footwall. These results are consistent with the recent interpretations of the North Pyrenean peridotites as remnants of subcontinental mantle rocks exhumed within the pre-Pyrenean rift system. We emphasize the importance of tectonic decoupling between the Mesozoic sedimentary cover and the Palaeozoic basement, which leads to the juxtaposition of metamorphosed and deformed Mesozoic sediments

  8. New structural field data on the timing and kinematics of deformation and exhumation of the Mont Blanc massif

    NASA Astrophysics Data System (ADS)

    Egli, Daniel; Mancktelow, Neil

    2010-05-01

    The Mont Blanc massif is one of the external crystalline massifs, which represent the basement of the former European continental margin and therefore belong to the Helvetic domain. It mainly consists of polymetamorphic Late Proterozoic to Early Paleozoic gneisses intruded by the Variscan Mont Blanc granite (Von Raumer et al. 1993). The timing and kinematics of deformation and exhumation of the Mont Blanc massif is a controversial topic and various models have been proposed. Low-temperature thermochronology studies provide an extensive data set for estimating exhumation rates in Neogene times (e.g. Seward & Mancktelow 1994; Leloup et al. 2005; Glotzbach et al. 2008), but detailed structural studies to critically asses and constrain the proposed kinematic models are largely lacking. Glotzbach et al. (2008) show that the exhumation is episodic, with rates changing from relatively fast (~2.5 km/Ma before 6 Ma) to a slow phase (<0.5 km/Ma between 6 and 3.5 Ma), in turn followed by acceleration to ~1 km/Ma after 3 Ma. Our study presents new structural data from the south-eastern side of the Mont Blanc massif and the adjacent sediments and addresses the tectonic evolution and late stage exhumation history of the massif. The goal is to assess the importance of tectonics versus climate for controlling exhumation, as well as to establish the overall geometry of uplift (2D pop-up, 3D dextral transpressive model, large scale backfolding). A major back-thrust was proposed by previous authors ("Mont Blanc back-thrust", e.g. Leloup et al. 2005, Rolland et al. 2007), characterized as a relatively steeply north-west dipping thrust bringing the Mont Blanc basement back over the tectonostratigraphically higher Helvetic and Ultrahelvetic metasediments. 40Ar¬-39Ar dating of white micas interpreted to have grown during movement on the Mont Blanc back-thrust indicates an initiation of movement around 16 Ma (Rolland et al. 2007). Leloup et al. (2005) suggest a reactivation of this

  9. Garnet-quartz/coesite graphic texture and expansion in the early exhumation of silica-rich UHP crustal rocks

    NASA Astrophysics Data System (ADS)

    Theunissen, K.; Korsakov, A. V.; Smirnova, L. V.

    2003-04-01

    Relying on existing thermobarometric data for garnets (Grtw) from nearby whiteschists, both the compositional and optical zonation patterns of different garnet types (Grt1--3), their relation with fabric-forming minerals and their occurrence in different micaschistous rocks, are explored as a tool in unravelling early stage exhumation mechanisms of ultrahigh-pressure (UHP) metamorphic rocks. Within kyanite-phengite-garnet (Grt1) micaschists, silica-rich lenses are composed of quartz, Grt2 and Grt3 porphyroblasts and minor phengite. Grt3 and quartz granoblasts (Q3) depict a particular Grt3-Q3 graphic texture. All garnet types are prograde zoned with coesite pseudomorphs included in their rim, but only Grt3 bears coesite in its core. Q3 develops as Q3m in the matrix and overprints as large Q3g the densely cracked Grt3 cores, where traces of coesite relics are preserved. In the matrix Q3m is in textural equilibrium with HP phengite, depicting a differentiated S2 schistose fabric. The Grt3-Q3 graphic texture is ascribed to expansion due to coesite-quartz (C-Q) transformation and is considered to occur under HP conditions. Destabilization through expansion is discussed as a suitable deep-seated process or mechanism, contributing in the early stage exhumation of UHP and silica-rich supracrustal Kulet rocks (Kokchetav massif, Kazakhstan). This study was supported by the Russian Foundation for Basic Research (N 01-05-65093) and by the Belgian Government (BOSTCA).

  10. Poisson's Ratio Structure Through a Zone of Exhumed Mantle at the Goban Spur Rifted Margin, Southwest of the UK.

    NASA Astrophysics Data System (ADS)

    Bullock, A. D.; Minshull, T. A.

    2004-12-01

    Zones of exhumed mantle have been identified at the west Iberia and Goban Spur rifted margins in the eastern North Atlantic where they form a transition zone up to 130 km wide between thinned continental crust and oceanic crust further seaward. P-wave velocities range from ˜4~km~s-1 at top basement to 7.2-7.6~km~s-1 at 4-6~km depth into basement and taken in isolation are consistent with a wide range of contrasting lithologies. Poisson's ratio may be used as a discriminator between possible compositions as, for P-wave velocities <6~km~s-1, serpentinite can be clearly distinguised from basalt. We present here the Poisson's ratio structure through the zone of exhumed mantle at the Goban Spur margin up to 4~km into basement. Velocities are constrained by seven ocean-bottom hydrophones and six sonobuoys across this region at a separation of ˜15~km; S-wave arrivals are observed on five ocean-bottom hydrophones in this region as P-to-S conversions occurring at top basement. A regularised inversion with smoothing constraints was used to define the P- and S-wave velocity structures individually and the Poisson's ratio computed from these models.

  11. Relief and drainage evolution during the exhumation of the Sierra Nevada (SE Spain): Is denudation keeping pace with uplift?

    NASA Astrophysics Data System (ADS)

    Azañón, J. M.; Galve, J. P.; Pérez-Peña, J. V.; Giaconia, F.; Carvajal, R.; Booth-Rea, G.; Jabaloy, A.; Vázquez, M.; Azor, A.; Roldán, F. J.

    2015-11-01

    We have performed a geomorphic analysis of the Sierra Nevada, the highest range of the Betic Cordillera (SE Spain), with the aim to elucidate its late Miocene to present-day exhumation history. The qualitative and quantitative analysis is based on filtered topography, local relief, swath-profile analysis, anomalies on stream orientation, bulk erosion volume, hypsometry, and steepness index (ksn). All these parameters are intimately linked to river incision and development of drainage pattern, having been calculated to assess the role of folding and faulting on the evolution of the Sierra Nevada. Moreover, uplift rates in the core of the Sierra Nevada have been deduced from an extrapolation of the position of Late Tortonian to Pliocene coastline deposits. These data have been compared to apatite (U-Th)/He, fission-track and 10Be cosmogenic data from SE Spain in order to evaluate the consistency among uplift, thermal histories and denudation rates. Our preferred tectonic scenario is one that favors fast exhumation of the western Sierra Nevada in a NW-SE overall compressive setting produced by the convergence between the Nubia and Africa plates. Sub-perpendicular to this compression, a westward 4 mm/year extensional hanging-wall displacement promotes uplift and unroofing of the western part of Sierra Nevada.

  12. Subduction, peak and multi-stage exhumation metamorphism: Traces from one coesite-bearing eclogite, Tso Morari, western Himalaya

    NASA Astrophysics Data System (ADS)

    Wilke, Franziska D. H.; O'Brien, Patrick J.; Schmidt, Alexander; Ziemann, Martin A.

    2015-08-01

    Ultrahigh-pressure (UHP), coesite-bearing eclogites in the Himalaya have been documented from the Kaghan Valley in Pakistan and the Tso Morari area in northwest India. These complexes are part of the northern edge of the Indian plate that has been subducted to, and metamorphosed at, mantle depths of more than 100 km before being exhumed. Both UHP complexes are located today directly adjacent to the Indus-Tsangpo suture zone and are not separated by non-metamorphosed sequences of Tethyan sediments from the Asian margin. Herein, we present new data for one fresh coesite-bearing eclogite from the Tso Morari massif. Therein, garnets are zoned reflecting their growth during prograde and peak metamorphism and showing a thin retrograde overgrowth. Inclusions can be directly correlated to the compositional zoning and are seen as either relicts of the protolith mineral paragenesis and as "snap shots" of the mineral paragenesis during subduction and under peak conditions. Rare earth element concentrations (REE) were obtained for garnet, mineral inclusions in garnet and matrix minerals. The REE pattern in garnet reflects a sequential change in matrix minerals and their proportions due to net transfer reactions during subduction and peak metamorphism. Using conventional geothermobarometry, a peak pressure of ca. 44-48 kbar at 560-760 °C followed by an S-shaped exhumation curve has been deduced. Gibbs free energy minimization modelling was used to supplement our analytical findings.

  13. Hydrothermal alteration products of gabbros help accommodate exhumation-related deformation in mantle-derived ultramafics exposed at the Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Picazo, S.; Cannat, M.; Escartin, J.; Gibert, B.; Delacour, A.; Silantyev, S.

    2011-12-01

    Outcrops of deeply-derived ultramafic rocks and gabbros are widespread along slow spreading ridges but the rheology and dynamics of the exhumation faults and of their uplifted footwalls are still poorly known. Previous studies of samples collected within meters of exposed exhumation fault surfaces in the Atlantic have shown that a gabbroic component was added to the primarily ultramafic material in the fault zone, allowing for the growth of abundant amphibole, chlorite and talc. The nature of this component (altered magmatic intrusions or metasomatic hydrothermal fluids) could not, however, be ascertained in the pervasively sheared fault material. In this abstract we report on a set of 474 samples collected at the Mid-Atlantic Ridge (MAR) during the Serpentine cruise (2007; RV Pourquoi Pas? PI Y. Fouquet) next to the ultramafic-hosted Ashadze (13°N) and Logatchev (14°45'N) vent fields. Most of these 474 samples are weakly to moderately deformed and are interpreted as representing the upper few hundred meters below their respective exhumation fault zone, rather than the fault zone itself. The large number of samples, and their overall moderate degree of deformation gives us a chance to propose a semi-statistical study of plastic, brittle-plastic and brittle deformation in ultramafic rocks next to a MAR exhumation system, in relation with the magmatic and hydrothermal history. Our primary finding is that significant brittle-plastic deformation systematically involves amphibole±chlorite±talc-bearing ultramafic lithologies. Serpentine is commonly present in these deformed assemblages, but we did not find serpentine-only shear zones. Amphibole (in successive generations ranging from hornblende to tremolite) and chlorite occur in veins, many of which also contain zircon and some relict plagioclase, indicating a magmatic origin. Relicts of primary peridotite minerals in the most amphibole-rich samples indicate that magmatic injection followed on an episode of

  14. Recent (0-8 Ma) tectonics and exhumation processes in Cordilleras Blanca and Negra, Central Peru: Constraints from (U-Th)/He dating

    NASA Astrophysics Data System (ADS)

    Margirier, Audrey; Robert, Xavier; Gautheron, Cécile; Audin, Laurence

    2014-05-01

    The Central Andes are a classical example of topography building in front of an oceanic subduction. However, many first order questions are still debated: How do subduction processes and observed tectonic uplift interact along the Andean margin? What is the impact of tectonic, magmatism and climate on exhumation? The Cordilleras Blanca (6768 m) and Negra (5181 m), in north Central Peru, belong to the highest Andean reliefs. Both ranges trend parallel to the subduction zone and are separated by the NW-SE Rio Santa valley. The Cordillera Blanca pluton formed in an active subduction context at 8-5 Ma and renders an abnormal magmatic activity over a planar subduction. In contrast with the Cordillera Blanca, the Cordillera Negra is an older relief, which evolution and exhumation history has never been studied. A remarkable ~200 km-long normal fault system showing ~4500 m of vertical displacement since 5 Ma edges the western flank of the Cordillera Blanca. This region is a perfect target to study the impact of magmatism and subduction processes on exhumation. We perform a morphotectonic study on both cordilleras coupled with low-temperature thermochronology apatite (U-Th)/He dating to quantify these processes. Geomorphic parameters and altitude contrasts between these two ranges indicate a differential uplift. The Cordillera Negra displays a smooth and asymmetric relief from the West to the East whereas the Cordillera Blanca shows higher and sharper relief with North/South and East/West contrasts. We obtain apatite (U-Th)/He ages for twenty samples located along vertical and horizontal profiles at different latitudes of the Cordilleras Blanca and Negra. The (U-Th)/He ages range from 13.4 ± 1.3 to 5.6 ± 0.6 Ma in the Cordillera Negra and range from 11.8 ± 1.2 to 2.0 ± 0.2 Ma in the Cordillera Blanca. We use them as inputs in QTQt tools for time-temperature reconstructions and thus to constrain the exhumation history. Whole ages evidence a more regional exhumation than

  15. Extension, disruption and translation of an orogenic wedge by exhumation of large ultrahigh pressure terranes: Two examples from the Norwegian Caledonides

    NASA Astrophysics Data System (ADS)

    Brueckner, H. K.; Cuthbert, S. J.

    2012-12-01

    We propose the thrust-dominated accretion of an orogenic wedge during continental subduction can be succeeded by stretching, disruption and passive transport of the frontal part of the wedge on top of an exhuming high pressure/ultrahigh pressure (HP/UHP) metamorphic terrane. Initial thrusting occurs when cratons collide and one subducts beneath the other into the mantle. The subducted craton undergoes HP/UHP metamorphism while an accretionary orogenic wedge develops at its junction with the overlying craton. The subsequent exhumation of the HP/UHP terrane either by true extension and/or buoyancy-driven extrusion reverses the shear traction along its upper boundary from its earlier foreland-directed thrust motion to hinterland-directed normal displacement. This normal-sense shear stretches the orogenic wedge and can potentially detach a fragment of its frontal part away from the rearward part, allowing it to be carried passively towards the foreland on the exhuming plate with the length of displacement a function of the amount of exhumation of the HP/UHP terrane. The Jotun and Trondheim Basin Nappe Complexes of the Caledonide orogenic wedge in southern and central Scandinavia were thrust (sensu stricto) E/SE onto the Baltic Shield during the Scandian Orogeny when the western edge of Baltica subducted into the mantle beneath Laurentia to form the HP/UHP Western Gneiss Complex (WGC). Kinematic indicators along the basal décollements of orogenic wedge allochthons indicate a change in shear sense from top-E/SE to top-W/NW at the same time (≈415 Ma) radiometric ages indicate the WGC began exhumation from the mantle. The shear traction along the top of the exhuming WGC stretched the Jotun and Trondheim Basin allochthons, then broke them into segments, and finally separated the frontal part of some of the allochthons away from the main body, causing them to be carried passively E/SE as the WGC continued to exhume out of the mantle. The lack of fragmentation and absence

  16. Fluvial and deltaic facies and environments of the late permian