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Mark T Harrison - One of the best experts on this subject based on the ideXlab platform.
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evidence for early 44 ma himalayan Crustal Thickening tethyan himalaya southeastern tibet
Earth and Planetary Science Letters, 2008Co-Authors: Amos B Aikman, Mark T HarrisonAbstract:Abstract Comprehensive understanding of Himalayan orogenesis is limited in part by a poor knowledge of the Eohimalayan episode; a phase of tectonic activity predating the better understood Neohimalayan Crustal Thickening associated with coaxial deformation along the Main Central thrust. The Cambo–Ordovician to Tertiary metasedimentary sequences outcropping within the Tethyan Himalaya are the structurally highest units of the Himalayan Fold and Thrust Belt; they and are inferred to have been the first to have accreted to Asia. A compilation of data from transects along the length of the main Himalayan arc shows that the Tethyan sequences have experienced at least five deformation events, although the timing of these episodes is poorly constrained. Emplacement of a series of undeformed granitoid bodies following the second of these events, which accounts for the majority of Crustal Thickening in the Tethyan Himalayan units, is constrained by U–Pb zircon dating to be older than 44.1 ± 1.2 Ma. Thus, significant Crustal Thickening had occurred along the length of the proto-Himalayan arc by the mid-Eocene, or within 10 to 20 myr of the initiation of Himalayan orogenesis.
M G Spagnuolo - One of the best experts on this subject based on the ideXlab platform.
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an andean tectonic cycle from Crustal Thickening to extension in a thin crust 34 37 sl
Geoscience frontiers, 2014Co-Authors: Victor A Ramos, Vanesa D Litvak, Andres Folguera, M G SpagnuoloAbstract:Abstract Several orogenic cycles of mountain building and subsequent collapse associated with periods of shallowing and steepening of subduction zones have been recognized in recent years in the Andes. Most of them are characterized by widespread Crustal delamination expressed by large calderas and rhyolitic flare-up produced by the injection of hot asthenosphere in the subduction wedge. These processes are related to the increase of the subduction angle during trench roll-back. The Payenia paleoflat-slab, in the southern Central Andes of Argentina and Chile (34°–37°S) recorded a complete cycle from Crustal Thickening and mountain uplift to extensional collapse and normal faulting, which are related to changes in the subduction geometry. The early stages are associated with magmatic expansion and migration, subsequent deformation and broken foreland. New ages and geochemical data show the middle to late Miocene expansion and migration of arc volcanism towards the foreland region was associated with important deformation in the Andean foothills. However, the main difference of this orogenic cycle with the previously described cycles is that the steepening of the oceanic subducted slab is linked to basaltic flooding of large areas in the retroarc under an extensional setting. Crustal delamination is concentrated only in a narrow central belt along the cordilleran axis. The striking differences between the two types of cycles are interpreted to be related to the Crustal thickness when steepening the subducting slab. The Crustal thickness of the Altiplano is over 60–80 km, whereas Payenia is less than 42 km in the axial part, and near 30 km in the retroarc foothills. The final extensional regime associated with the slab steepening favors the basaltic flooding of more than 8400 km 3 in an area larger than 40,000 km 2 , through 800 central vents and large fissures. These characteristics are unique in the entire present-day Andes.
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An Andean tectonic cycle: From Crustal Thickening to extension in a thin crust (34°–37°SL)
Geoscience frontiers, 2014Co-Authors: Victor A Ramos, Vanesa D Litvak, Andres Folguera, M G SpagnuoloAbstract:Abstract Several orogenic cycles of mountain building and subsequent collapse associated with periods of shallowing and steepening of subduction zones have been recognized in recent years in the Andes. Most of them are characterized by widespread Crustal delamination expressed by large calderas and rhyolitic flare-up produced by the injection of hot asthenosphere in the subduction wedge. These processes are related to the increase of the subduction angle during trench roll-back. The Payenia paleoflat-slab, in the southern Central Andes of Argentina and Chile (34°–37°S) recorded a complete cycle from Crustal Thickening and mountain uplift to extensional collapse and normal faulting, which are related to changes in the subduction geometry. The early stages are associated with magmatic expansion and migration, subsequent deformation and broken foreland. New ages and geochemical data show the middle to late Miocene expansion and migration of arc volcanism towards the foreland region was associated with important deformation in the Andean foothills. However, the main difference of this orogenic cycle with the previously described cycles is that the steepening of the oceanic subducted slab is linked to basaltic flooding of large areas in the retroarc under an extensional setting. Crustal delamination is concentrated only in a narrow central belt along the cordilleran axis. The striking differences between the two types of cycles are interpreted to be related to the Crustal thickness when steepening the subducting slab. The Crustal thickness of the Altiplano is over 60–80 km, whereas Payenia is less than 42 km in the axial part, and near 30 km in the retroarc foothills. The final extensional regime associated with the slab steepening favors the basaltic flooding of more than 8400 km 3 in an area larger than 40,000 km 2 , through 800 central vents and large fissures. These characteristics are unique in the entire present-day Andes.
Jian-lin Chen - One of the best experts on this subject based on the ideXlab platform.
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Late Cretaceous magmatism in the NW Lhasa Terrane, southern Tibet: Implications for Crustal Thickening and initial surface uplift
Geological Society of America Bulletin, 2019Co-Authors: Jian-lin Chen, Ji-feng Xu, Yun-chuan Zeng, Qiu-wei XiongAbstract:Abstract Crustal Thickening and uplift of southern Tibet have been widely associated with India-Asia continental collision during the Cenozoic. However, recent studies indicated that the crust of the northwestern (NW) Lhasa Terrane was thickened during the late Mesozoic. Here we report geochronological and geochemical data for the Gaerqiong diorite porphyries (GPs) and Xiongma plutons (XPs) in the NW Lhasa terrane, southern Tibet. Zircon U-Pb dating suggests that these intrusive rocks were generated at ca. 85 and ca. 88 Ma, respectively. The GPs are characterized by high MgO, Cr, and Ni contents, and they have adakitic affinities. These geochemical features, combined with their depleted εNd(t) (+1.7 to +2.0), 87Sr/86Sr(i) (0.705103–0.705259), and zircon εHf(t) (+5.2 to +10.2) isotopic compositions, indicate that the GPs were produced by partial melting of the delaminated juvenile continental crust. In contrast, the XPs are composed of host granites and mafic microgranular enclaves (MMEs). The MMEs have low SiO2 and high MgO contents, and low εHf(t) (–14.0 to –5.8) values, indicating that their parental magmas were derived from an enriched mantle. The host granites have high SiO2 and low MgO contents, and variable εNd(t) (–7.4 to –6.3) and zircon εHf(t) (–11 to –4.1) values. These observations, combined with the presence of MMEs in the Xiongma granites, suggest that the host granites were the result of mixing of crust- and mantle-derived magmas. Detailed study of these two plutons, combined with the previous researches, suggests that Late Cretaceous (ca. 90 Ma) magmatism in the NW Lhasa Terrane occurred in a post-collisional extensional setting related to delamination of the regionally thickened lithosphere after collision of the Lhasa-Qiangtang Terranes. We propose that the crust of the NW Lhasa Terrane reached a maximum thickness (average of >50 km) before the Late Cretaceous (ca. 90 Ma). This Crustal Thickening was caused by underplating of mafic magmas during slab roll-back and break-off of the southward-subducting Bangong-Nujiang oceanic lithosphere and subsequent tectonic thrusting during Qiangtang-Lhasa Terrane collision, respectively. Given that Crustal Thickening generally results in elevated terrain, the regional uplift (driven by isostasy due to Crustal Thickening) probably commenced before the Late Cretaceous (ca. 90 Ma).
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late cretaceous high mg granitoids in southern tibet implications for the early Crustal Thickening and tectonic evolution of the tibetan plateau
Lithos, 2015Co-Authors: Jian-lin Chen, Ji-feng Xu, Hongxia Yu, Baodi Wang, Jianbin Wu, Yuexing FengAbstract:Abstract This study presents new major and trace element, plus Sr–Nd and zircon U–Pb isotope data for the Zhongcang granitic plutons, which are located to the south of the Yongzhu–Asuo ophiolite belt within the northwestern part of the central Lhasa subterrane, Tibetan Plateau. These data provide new insights into the Late Cretaceous tectonic evolution of southern Tibet. The Zhongcang plutons are dominated by granodiorites and granites that yield zircon U–Pb emplacement ages of 94–88 Ma. They can be further divided into metaluminous and peraluminous subtypes. The metaluminous rocks have adakite-like geochemical signatures, including high SiO 2 , Al 2 O 3 , and Sr concentrations, and low Yb and Y concentrations, and high Sr/Y and (La/Yb) N ratios. These rocks also have negative eNd (t) values (− 3.17 to − 0.17), variable initial 87 Sr/ 86 Sr (i) ratios (0.705927–0.707668), and high K 2 O and Th concentrations, suggesting that they were not derived from the partial melting of subducted oceanic crust in an arc setting. The Zhongcang adakitic rocks have higher MgO and Cr concentrations and Mg# values than do contemporaneous intrusive rocks derived from a region of thickened lower crust within the central Lhasa subterrane. These data suggest that the Zhongcang adakitic rocks were generated by the partial melting of a delaminated thickened lower crust within a Late Cretaceous continental setting. In comparison with the Zhongcang adakitic rocks, the peraluminous rocks have significant negative Eu and Sr anomalies and lower eNd (t) values (− 4.06 to − 6.64). This, combined with their high Mg# values, and Cr concentrations, suggests that the peraluminous units formed from primitive magmas similar to those that formed the Zhongcang adakitic rocks, but modified by contamination with ancient Crustal material and by fractional crystallization of plagioclase and apatite during uprising and/or emplacement. The Zhongcang high-Mg# granitoids provide robust evidence for Late Cretaceous Crustal Thickening prior to India–Asia collision.
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Late Cretaceous high-Mg# granitoids in southern Tibet: Implications for the early Crustal Thickening and tectonic evolution of the Tibetan Plateau?
Lithos, 2015Co-Authors: Jian-lin Chen, Ji-feng Xu, Hongxia Yu, Baodi Wang, Jianbin Wu, Yuexing FengAbstract:Abstract This study presents new major and trace element, plus Sr–Nd and zircon U–Pb isotope data for the Zhongcang granitic plutons, which are located to the south of the Yongzhu–Asuo ophiolite belt within the northwestern part of the central Lhasa subterrane, Tibetan Plateau. These data provide new insights into the Late Cretaceous tectonic evolution of southern Tibet. The Zhongcang plutons are dominated by granodiorites and granites that yield zircon U–Pb emplacement ages of 94–88 Ma. They can be further divided into metaluminous and peraluminous subtypes. The metaluminous rocks have adakite-like geochemical signatures, including high SiO 2 , Al 2 O 3 , and Sr concentrations, and low Yb and Y concentrations, and high Sr/Y and (La/Yb) N ratios. These rocks also have negative eNd (t) values (− 3.17 to − 0.17), variable initial 87 Sr/ 86 Sr (i) ratios (0.705927–0.707668), and high K 2 O and Th concentrations, suggesting that they were not derived from the partial melting of subducted oceanic crust in an arc setting. The Zhongcang adakitic rocks have higher MgO and Cr concentrations and Mg# values than do contemporaneous intrusive rocks derived from a region of thickened lower crust within the central Lhasa subterrane. These data suggest that the Zhongcang adakitic rocks were generated by the partial melting of a delaminated thickened lower crust within a Late Cretaceous continental setting. In comparison with the Zhongcang adakitic rocks, the peraluminous rocks have significant negative Eu and Sr anomalies and lower eNd (t) values (− 4.06 to − 6.64). This, combined with their high Mg# values, and Cr concentrations, suggests that the peraluminous units formed from primitive magmas similar to those that formed the Zhongcang adakitic rocks, but modified by contamination with ancient Crustal material and by fractional crystallization of plagioclase and apatite during uprising and/or emplacement. The Zhongcang high-Mg# granitoids provide robust evidence for Late Cretaceous Crustal Thickening prior to India–Asia collision.
J Diaz - One of the best experts on this subject based on the ideXlab platform.
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Teleseismic Probing of Alpine Crustal Thickening and Wedging Beneath The Cantabrian Mountains and Western Pyrenees
2020Co-Authors: J Diaz, D Pedreira, J A Pulgar, J Gallart, Mario Ruiz, C. López, J.m. González-cortinaAbstract:The Northern part of the Iberian Peninsula involved in the Alpine tectonics has been extensively explored in the last years by seismic reflection and refraction experiments. They have revealed the existence of a Crustal Thickening and wedging, similar to that already known at the central Pyrenees since the ECORS seismic profile. A more recent, independent approach to the deep Crustal configuration is presented here. It consists of teleseismic receiver function (RF) analysis of P to S conversions at main Crustal interfaces. Two N-S transects are implemented across the eastern part of the Cantabrian Mountains and the western Pyrenees by deploying 6 Reftek stations equipped with geophones of 20s period. Teleseismic events with epicentral distances between 35◦ and 95◦ and clear P arrivals have been retained. Following the method described by Kosarev et al. (1999), the records are rotated to ray components (L,Q,T) using back azimuth and incidence angle to minimize energy on the radial and trasverse components for the P arrival. The receiver functions are then calculated by frequency domain deconvolution of the L component from the Q component. The resulting RF are processed in a similar way to Crustal reflection data, using a simple form of migration to obtain images of the lithosphere in depth domain. The western Pyrenees transect shows a clear dipping interface, interpreted as the Iberian Moho that thickens from 35 km beneath the Iberian Chain to 50 km under the Central Pyrenees, were the European Moho is also identified at less than 30 km depth. The image clearly suggests an imbrication and underthrusting of Iberia beneath the European crust. In the Cantabrian Mountains transect a similar pattern is imaged at depth, even if the European Moho is poorly defined. In both transects, intra-Crustal interfaces are identified and can be related either to the top of the lower crusts or as an evidence for highvelocity materials of European lower crust at shallow levels within the Iberian crust. The deep Crustal structure constrained by teleseismic analysis is remarkably consistent with the velocity-depth modelling results, and provides further evidence on the Crustal doubling and wedging between Iberian and European crusts throughout the Northern part of the Iberian Peninsula affected by the Alpine compressional tectonics.
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seismic evidence of alpine Crustal Thickening and wedging from the western pyrenees to the cantabrian mountains north iberia
Journal of Geophysical Research, 2003Co-Authors: D Pedreira, J A Pulgar, J Gallart, J DiazAbstract:[1] The Alpine collision between the Iberian and European plates resulted in a complex Crustal structure beneath the northern Iberian Peninsula, as revealed from a new set of seismic refraction/wide-angle reflection profiles. The study area is characterized by two major E-W ranges, the Cantabrian Mountains and the Pyrenees, which are relayed to the south by the Iberian Chain. Important variations in Crustal thickness and velocity distribution are found in a 560-km-long E-W transect. In contrast to the typical 30- to 32-km-thick European Variscan crust of the western end of the profile, a continuous Alpine Crustal root is evidenced from the Cantabrian Mountains to the central Pyrenees, with a Moho depth of 46–48 km, locally rising to ∼40 km depth in between, beneath the Basque-Cantabrian Basin. Another outstanding feature is the inferred presence of high velocities of 6.40–6.75 km/s at midCrustal depths, which can be associated with portions of a lower Crustal wedge from the northern (European) domain indenting the southern (Iberian) crust during the Alpine stage of compression. This indentation produces the delamination of the Iberian crust, with northward underthrusting of its lower half and the consequent Crustal Thickening. The indenting wedge has a discontinuous presence along the longitudinal section, as it was controlled and/or affected by N-S to NE-SW structures. Further evidence of the northward subduction of the Iberian plate is provided by another profile toward the Aquitaine Basin, while a N-S profile across the Iberian Chain reveals an Alpine midCrustal Thickening beneath this belt with Moho depths of ∼42 km.
Carlos A. Zuluaga - One of the best experts on this subject based on the ideXlab platform.
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garnet growth during Crustal Thickening in the cascades crystalline core washington usa
Journal of Metamorphic Geology, 2011Co-Authors: Harold H. Stowell, Gerrit R. Bulman, Douglas K. Tinkham, Carlos A. ZuluagaAbstract:Garnet Sm–Nd and zircon U–Pb ages, and pressure–temperature–time paths elucidate Late Cretaceous Crustal Thickening which occurred within magmatic arc rocks of the Insular Superterrane. Voluminous tonalitic magma of the Mount Stuart batholith intruded at <3 kbar into upper Crustal sedimentary rocks between 96 and 91 Ma, with initial intrusion prior to garnet growth in the metasedimentary rocks. Arc plutonism then shifted northward as Crustal Thickening commenced. Initial garnet growth, locally with kyanite and staurolite replacing andalusite, at c. 91 Ma was directly associated with intrusion of granodiorite to tonalite sheets at 7 kbar, north of the Mount Stuart batholith, within the Nason Ridge Migmatitic Gneiss. Subsequent heating and garnet growth, which postdates emplacement of large plutons, occurred between 88 and 86 Ma. This late garnet growth occurred at pressures of 6–8 kbar. The history of garnet growth and intrusion indicates that initial garnet zone and higher temperature metamorphism was restricted to contact aureoles. However, later widespread garnet growth at higher pressure probably resulted from heating as the orogenic wedge approached thermal equilibrium after Crustal Thickening. We conclude that metasedimentary rocks outside narrow contact aureoles remained at temperatures significantly below those of garnet growth and that the growth of garnet lasted <6 Myr. Heating to temperatures that stabilized garnet after pluton emplacement is compatible with intrusion of arc plutons into an accretionary wedge (Chiwaukum Schist) which was tectonically thickened and/or overthrust causing loading and thermal relaxation.
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Garnet growth during Crustal Thickening in the Cascades Crystalline Core, Washington, USA
Journal of Metamorphic Geology, 2011Co-Authors: Harold H. Stowell, Gerrit R. Bulman, Douglas K. Tinkham, Carlos A. ZuluagaAbstract:Garnet Sm–Nd and zircon U–Pb ages, and pressure–temperature–time paths elucidate Late Cretaceous Crustal Thickening which occurred within magmatic arc rocks of the Insular Superterrane. Voluminous tonalitic magma of the Mount Stuart batholith intruded at