The Experts below are selected from a list of 44193 Experts worldwide ranked by ideXlab platform
Alex Copley - One of the best experts on this subject based on the ideXlab platform.
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evidence for mechanical coupling and strong indian lower Crust beneath southern tibet
Nature, 2011Co-Authors: Alex Copley, Jean Philippe Avouac, Brian P WernickeAbstract:How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The Upper Crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian Crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the Upper Crust of southern Tibet and the underthrusting Indian Crust. Such coupling is inconsistent with the presence of active ‘channel flow’ beneath southern Tibet, and suggests that the Indian Crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet.
Kurt Bucher - One of the best experts on this subject based on the ideXlab platform.
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hydraulic conductivity of fractured Upper Crust insights from hydraulic tests in boreholes and fluid rock interaction in crystalline basement rocks
Geofluids, 2015Co-Authors: Ingrid Stober, Kurt BucherAbstract:The permeability (κ[m2]) of fractured crystalline basement of the Upper continental Crust is an intrinsic property of a complex system of rocks and fractures that characterizes the flow properties of a representative volume of that system. Permeability decreases with depth. Permeability can be derived from hydraulic well test data in deep boreholes. Only a handful of such deep wells exist on a worldwide basis. Consequently, few data from hydraulically tested wells in crystalline basement are available to the depth of 4–5 km. The permeability of Upper Crust varies over a very large range depending on the predominant rock type at the studied site and the geological history of the drilled crystalline basement. Hydraulic tests in deep boreholes in the continental crystalline basement revealed permeability (κ) values ranging over nine log-units from 10−21 to 10−12 m2. This large variance also decreases with depth, and at 4 km depth, a characteristic value for the permeability κ is 10−15 m2. The permeability varies with time due to deformation-related changes of fracture aperture and fracture geometry and as a result of chemical reaction of flowing fluids with the solids exposed along the fractures. Dissolution and precipitation of minerals contribute to the variation of the permeability with time. The time dependence of κ is difficult to measure directly, and it has not been observed in hydraulic well tests. At depths below the deepest wells down to the brittle ductile transition zone, evidence of permeability variation with time can be found in surface exposures of rocks originally from this depth. Exposed hydrothermal reaction veins are very common in continental Crustal rocks and witness fossil permeability and its variation with time. The transient evolution of permeability can be predicted from models using fictive and simple starting conditions. However, a geologically meaningful quantitative description of permeability variation with time in the deeper parts of the brittle continental Crust resulting from combined fracturing and chemical reaction appears very difficult.
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Hydraulic Properties of the Upper Continental Crust: data from the Urach 3 geothermal well
Hydrogeology of Crystalline Rocks, 2000Co-Authors: Ingrid Stober, Kurt BucherAbstract:The 4500m deep research borehole at Urach (South Germany) has been extensively used for hydraulic testing of the crystalline basement. The data permit a general interpretation of the hydraulic properties of crystalline continental Upper Crust. The typical granitic and gneissic basement contains an interconnected fluid-filled fracture system and behaves hydraulically like a confined fractured aquifer. Thus standard hydraulic well-tests can be used in the basement. The conclusions are based on data from the central part of the Upper Crust and are, therefore, believed to be characteristic and significant for the brittle Upper continental Crust in general.The performed tests (including a > 500 hours long-term injection test) revealed a hydraulically effective porosity of the basement of typically 0.5% and an average permeability of about 10−9 m/s. NaCl-rich brine with > 100 g/kg total dissolved solids (TDS) occupies the fracture pore space at depth. The basement can be best described as a homogeneous, isotropic aquifer and this characteristic hydraulic behavior persists to at least several hundred meters around the borehole. No evidence for hydraulic infiltration or the existence of impervious boundaries was found in the test data. The homogeneity of the aquifer, together with the highly saline water present in an interconnected system of abundant fractures appear to be characteristic of continental Upper Crust in general. Similar general aquifer properties were found in other deep boreholes into the crystalline basement of the Black Forest area, in the “Hot-Dry-Rock” well of Soultzsous-Forêts (France), NAGRA deep wells (N-Switzerland), KTB wells (SE-Germany) and the Kola well (Kola, Russia).
Alexey Shebanov - One of the best experts on this subject based on the ideXlab platform.
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Prolonged postcollisional shoshonitic magmatism in the southern Svecofennian domain – a case study of the Åva granite–lamprophyre ring complex
Lithos, 2005Co-Authors: Olav Eklund, Alexey ShebanovAbstract:Abstract The Ava ring complex is one of four Paleoproterozoic postcollisional shoshonitic ring complexes in southwestern Finland. It is composed of ring dykes of K-feldspar megacryst-bearing granite, mingled in places with a shoshonitic monzonite, and lamprophyre dykes crosscutting all the rocks in a radial pattern. A survey was undertaken to trace the magma chamber beneath the ring complex to date it and measure some intensive parameters to clarify the crystallisation conditions at depth before the granite was emplaced in the Upper Crust. Mineral separates were extracted from the core zones of K-feldspar megacrysts in the granite, heavy mineral fractions (including zircons) from these separates were used for P - T assessment and age determinations, and the results were compared to data obtained from bulk rock samples. It appears that magma differentiation took place in a midCrustal magma chamber (at 4 to 7 kbar) possibly ∼30 Ma before the emplacement of the ring complex in the Upper Crust (deep assemblage ∼1790 Ma, shallow assemblage ∼1760 Ma). Relatively high activity of the alkalies and a low oxygen fugacity characterised the midCrustal chamber. The juvenile Svecofennian Crust was invaded by shoshonitic magmas from an enriched lithospheric mantle over a long period of time. Some of these magmas were stored and differentiated in the middle Crust before transportation to the Upper Crust. The results also show that coarse-grained granites may provide evidence for several magmatic evolutionary episodes, e.g., differentiation and crystallisation in different environments prior to final emplacement.
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prolonged postcollisional shoshonitic magmatism in the southern svecofennian domain a case study of the ava granite lamprophyre ring complex
Lithos, 2005Co-Authors: Olav Eklund, Alexey ShebanovAbstract:Abstract The Ava ring complex is one of four Paleoproterozoic postcollisional shoshonitic ring complexes in southwestern Finland. It is composed of ring dykes of K-feldspar megacryst-bearing granite, mingled in places with a shoshonitic monzonite, and lamprophyre dykes crosscutting all the rocks in a radial pattern. A survey was undertaken to trace the magma chamber beneath the ring complex to date it and measure some intensive parameters to clarify the crystallisation conditions at depth before the granite was emplaced in the Upper Crust. Mineral separates were extracted from the core zones of K-feldspar megacrysts in the granite, heavy mineral fractions (including zircons) from these separates were used for P - T assessment and age determinations, and the results were compared to data obtained from bulk rock samples. It appears that magma differentiation took place in a midCrustal magma chamber (at 4 to 7 kbar) possibly ∼30 Ma before the emplacement of the ring complex in the Upper Crust (deep assemblage ∼1790 Ma, shallow assemblage ∼1760 Ma). Relatively high activity of the alkalies and a low oxygen fugacity characterised the midCrustal chamber. The juvenile Svecofennian Crust was invaded by shoshonitic magmas from an enriched lithospheric mantle over a long period of time. Some of these magmas were stored and differentiated in the middle Crust before transportation to the Upper Crust. The results also show that coarse-grained granites may provide evidence for several magmatic evolutionary episodes, e.g., differentiation and crystallisation in different environments prior to final emplacement.
Youguo Deng - One of the best experts on this subject based on the ideXlab platform.
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Crustal p wave velocity structure beneath the se margin of the tibetan plateau from deep seismic sounding results
Tectonophysics, 2019Co-Authors: Walter D. Mooney, Xiaofeng Tian, Fuyun Wang, Yonghong Duan, Tao Xu, Youguo DengAbstract:Abstract The Crust and Uppermost mantle beneath the southeastern (SE) margin of Tibetan Plateau record the lateral expansion of Tibet and far-field effects from the ongoing continental collision and convergence. In order to obtain constraints on the deep structure and the eastward expansion of the plateau, we synthesized Deep Seismic Sounding (DSS) results in this region and constructed the P wave velocity models for each terrane. The principal characteristics of the Crustal velocity model and tectonic significance are: (1) Crustal thickness decreases from 53 km beneath the Songpan-Ganzi terrane (SGT) to 34 km in the south direction beneath Simao terrane (SMT), and 42 km in the east direction beneath Chengdu area. The Crust is dominantly felsic in Upper Crust, with a small percentage of mafic composition in the lower Crust. (2) The Crustal structure is very heterogeneous in this region. The Indochina Block is characterized by low seismic velocities in the Upper Crust, while the west Yangtze terrane (WYZT) and SGT show higher velocities in the Upper Crust. The lower Crust beneath WYZT is relatively thicker than other terranes. (3) We deduce that the high velocity in the Upper Crust and relatively thick lower Crust beneath the SGT and WYZT can be associated with magmatic processes that generated the Emeishan flood basalts which may have been triggered by rifting or mantle plume. The lateral variations of the Crustal thickness in SE Tibet may be due to lower Crustal flow from the Tibetan Plateau to the SE direction after blocked by the cold and rigid Yangtze craton in the east direction.
Tao Xu - One of the best experts on this subject based on the ideXlab platform.
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Crustal p wave velocity structure beneath the se margin of the tibetan plateau from deep seismic sounding results
Tectonophysics, 2019Co-Authors: Walter D. Mooney, Xiaofeng Tian, Fuyun Wang, Yonghong Duan, Tao Xu, Youguo DengAbstract:Abstract The Crust and Uppermost mantle beneath the southeastern (SE) margin of Tibetan Plateau record the lateral expansion of Tibet and far-field effects from the ongoing continental collision and convergence. In order to obtain constraints on the deep structure and the eastward expansion of the plateau, we synthesized Deep Seismic Sounding (DSS) results in this region and constructed the P wave velocity models for each terrane. The principal characteristics of the Crustal velocity model and tectonic significance are: (1) Crustal thickness decreases from 53 km beneath the Songpan-Ganzi terrane (SGT) to 34 km in the south direction beneath Simao terrane (SMT), and 42 km in the east direction beneath Chengdu area. The Crust is dominantly felsic in Upper Crust, with a small percentage of mafic composition in the lower Crust. (2) The Crustal structure is very heterogeneous in this region. The Indochina Block is characterized by low seismic velocities in the Upper Crust, while the west Yangtze terrane (WYZT) and SGT show higher velocities in the Upper Crust. The lower Crust beneath WYZT is relatively thicker than other terranes. (3) We deduce that the high velocity in the Upper Crust and relatively thick lower Crust beneath the SGT and WYZT can be associated with magmatic processes that generated the Emeishan flood basalts which may have been triggered by rifting or mantle plume. The lateral variations of the Crustal thickness in SE Tibet may be due to lower Crustal flow from the Tibetan Plateau to the SE direction after blocked by the cold and rigid Yangtze craton in the east direction.
