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Junmeng Zhao - One of the best experts on this subject based on the ideXlab platform.
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structure of crust and upper mantle beneath nw himalayas pamir and hindukush by multi scale double difference seismic tomography
Physics of the Earth and Planetary Interiors, 2018Co-Authors: Zahid Imran Bhatti, Junmeng Zhao, Nangyal Ghani Khan, Syed Tallataf Hussain ShahAbstract:Abstract The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017. The northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian Plate under the Hindukush beyond 71°E longitude. The Indian Plate overturns due south after interacting with the Asian Plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian Plate. The Asian Plate is also imaged as a southward subducting seismic zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian Plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.
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p wave tomography and dynamics of the crust and upper mantle beneath western tibet
Gondwana Research, 2014Co-Authors: Junmeng Zhao, Dapeng Zhao, Heng Zhang, Hongbing Liu, Ying Huang, Honggang Cheng, Wei WangAbstract:Abstract The continental collision between the Indian and Asian Plates plays a key role in the geologic and tectonic evolution of the Tibetan Plateau. In this article we present high-resolution tomographic images of the crust and upper mantle derived from a large number of high-quality seismic data from the ANTILOPE project in western Tibet. Both local and distant earthquakes were used in this study and 35,115 P-wave arrival times were manually picked from the original seismograms. Geological and geochemical results suggested that the subducting Indian Plate has reached northward to the Lhasa terrane, whereas our new tomography shows that the Indian Plate is currently sub-horizontal and underthrusting to the Jinsha river suture at depths of ~ 100 to ~ 250 km, suggesting that the subduction process has evolved over time. The Asian Plate is also imaged clearly from the surface to a depth of ~ 100 km by our tomography, and it is located under the Tarim Basin north of the Altyn Tagh Fault. There is no obvious evidence to show that the Asian Plate has subducted beneath western Tibet. The Indian and Asian Plates are separated by a prominent low-velocity zone under northern Tibet. We attribute the low-velocity zone to mantle upwelling, which may account for the warm crust and upper mantle beneath that region, and thus explain the different features of magmatism between southern and northern Tibet. But the upwelling may not penetrate through the whole crust. We propose a revised geodynamic model and suggest that the high-velocity zones under Lhasa terrane may reflect a cold crust which has interrupted the crustal flow under the westernmost Tibetan Plateau.
Syed Tallataf Hussain Shah - One of the best experts on this subject based on the ideXlab platform.
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structure of crust and upper mantle beneath nw himalayas pamir and hindukush by multi scale double difference seismic tomography
Physics of the Earth and Planetary Interiors, 2018Co-Authors: Zahid Imran Bhatti, Junmeng Zhao, Nangyal Ghani Khan, Syed Tallataf Hussain ShahAbstract:Abstract The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017. The northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian Plate under the Hindukush beyond 71°E longitude. The Indian Plate overturns due south after interacting with the Asian Plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian Plate. The Asian Plate is also imaged as a southward subducting seismic zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian Plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.
Abdul Salam Khan - One of the best experts on this subject based on the ideXlab platform.
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active tectonic deformation of the western Indian Plate boundary a case study from the chaman fault system
Journal of Asian Earth Sciences, 2017Co-Authors: Wanda E Crupa, Shuhab D. Khan, Abdul Salam Khan, Jingqiu Huang, Aimal Khan KasiAbstract:Abstract Collision of the Eurasian and Indian Plates has resulted in two spatially offset subduction zones, the Makran subduction zone to the south and the Himalayan convergent margin to the north. These zones are linked by a system of left-lateral strike-slip faults known as the Chaman Fault System, ∼1200 km, which spans along western Pakistan. Although this is one of the greatest strike-slip faults, yet temporal and spatial variation in displacement has not been adequately defined along this fault system. This study conducted geomorphic and geodetic investigations along the Chaman Fault in a search for evidence of spatial variations in motion. Four study areas were selected over the span of the Chaman Fault: (1) Tarnak-Rud area over the Tarnak-Rud valley, (2) Spinatizha area over the Spinatizha Mountain Range, (3) Nushki area over the Nushki basin, and (4) Kharan area over the northern tip of the Central Makran Mountains. Remote sensing data allowed for in depth mapping of different components and faults within the Kohjak group. Wind and water gap pairs along with offset rivers were identified using high-resolution imagery and digital-elevation models to show displacement for the four study areas. The mountain-front-sinuosity ratio, valley height-to-width-ratio, and the stream-length-gradient index were calculated and used to determine the relative tectonic activity of each area. These geomorphic indices suggest that the Kharan area is the most active and the Tarnak-Rud area is the least active. GPS data were processed into a stable Indian Plate reference frame and analyzed. Fault parallel velocity versus fault normal distance yielded a ∼8–10 mm/yr displacement rate along the Chaman Fault just north of the Spinatizha area. InSAR data were also integrated to assess displacement rates along the fault system. Geodetic data support that ultra-slow earthquakes similar to those that strike along other major strike-slip faults, such as the San Andreas Fault System, are possible along the northern segments of the Chaman Fault zone. Geomorphic data suggest that the Chaman Fault along southern part is not very active now but may have gone through high tectonic activity in the past.
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Slip-rates along the Chaman fault: Implication for transient strain accumulation and strain partitioning along the western Indian Plate margin
Tectonophysics, 2013Co-Authors: Shams Ul-hadi, Shuhab D. Khan, Lewis A. Owen, Abdul Salam Khan, Kathryn A. Hedrick, Marc W. CaffeeAbstract:Abstract The Chaman fault in Western Pakistan marks the western collision boundary between the Indian and Eurasian Plates and connects the Makran subduction zone to the Himalayan convergence zone. Geomorphic-scale slip-rates along an active strand of the Chaman fault are added to the sporadic data set of this poorly investigated transform system. Field investigations coupled with high-resolution GeoEye-1 satellite data of an alluvial fan surface (Bostankaul alluvial fan) show ~ 1150 m left-lateral offset by the fault since the formation of the alluvial fan surface. A weighted mean 10Be exposure age of 34.8 ± 3 kyr for the Bostankaul alluvial surface yields a slip-rate of 33.3 ± 3.0 mm/yr. This rate agrees with the geologically defined slip-rates along the Chaman fault, but is approximately twice as large as that inferred from the decade-long global positioning system measurements of 18 ± 1 mm/yr. The contrast in geomorphic and geodetic slip-rates along the Chaman fault, like other major intra-continental strike–slip faults, has two major implications: 1) the geodetic rates might represent a period of reduced displacement as compared to the averaged Late Pleistocene rate because of transient variations in rates of elastic strain accumulation; or 2) strain partitioning within the Plate boundary zone. While strain partitioning could be the reason of slip-rate variations within the western Indian Plate boundary zone, transient strain accumulation could explain contrasting slip-rates along the Chaman fault at this stage in its poorly understood seismic cycle.
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contrasting late cretaceous palaeocene lithostratigraphic successions across the bibai thrust western sulaiman fold thrust belt pakistan their significance in deciphering the early collisional history of the nw Indian Plate margin
Journal of Asian Earth Sciences, 2009Co-Authors: Akhtar M Kassi, Gilbert Kelling, Aimal Khan Kasi, Mohammad Umar, Abdul Salam KhanAbstract:Abstract The Sulaiman Fold–Thrust Belt is a significant tectonic element in northwest Pakistan, located on the NW margin of the Indian Plate having a rift–drift-collision Plate tectonic history. Late Cretaceous–Palaeocene successions in the western sector of this Belt conventionally comprise strata above the widespread pelagic Parh Limestone (Albian–Campanian) and below the fluvio-deltaic Ghazij Formation (Early Eocene). These successions display marked lithostratigraphic variations across the Bibai Thrust, long known to be an important structural feature in the western Sulaiman Belt. The successions on the foot wall, to the east and southeast of the Bibai Thrust (Quetta, Spera Ragha and Chinjun areas), exhibit the most variable lithostratigraphy, were deposited exclusively in shallow marine conditions and include volcanics associated with a local submarine edifice. They also display several internal disconformities, locally accompanied by oxidised units that attest to intermittent emergence. By contrast, coeval successions on the hanging wall, to the north and northwest of the Bibai Thrust (Urghargai–Mazu Ghar and Kach–Ziarat areas) are the products of deposition in deeper marine conditions and also include important volcanigenic contributions. These contrasting lithofacies accumulated respectively in widely separated proximal and distal sectors of the north-western margin of the Indian Plate and their current proximity is attributed to tectonic juxtaposition by relative southward translation of the distal facies along the Bibai and related thrusts. Involvement of Late Eocene limestones in these thrusts and their sealing by Mio-Pliocene fluvial sediments demonstrates that active translation on these thrusts continued at least into Late Eocene or Oligocene times.
Aimal Khan Kasi - One of the best experts on this subject based on the ideXlab platform.
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active tectonic deformation of the western Indian Plate boundary a case study from the chaman fault system
Journal of Asian Earth Sciences, 2017Co-Authors: Wanda E Crupa, Shuhab D. Khan, Abdul Salam Khan, Jingqiu Huang, Aimal Khan KasiAbstract:Abstract Collision of the Eurasian and Indian Plates has resulted in two spatially offset subduction zones, the Makran subduction zone to the south and the Himalayan convergent margin to the north. These zones are linked by a system of left-lateral strike-slip faults known as the Chaman Fault System, ∼1200 km, which spans along western Pakistan. Although this is one of the greatest strike-slip faults, yet temporal and spatial variation in displacement has not been adequately defined along this fault system. This study conducted geomorphic and geodetic investigations along the Chaman Fault in a search for evidence of spatial variations in motion. Four study areas were selected over the span of the Chaman Fault: (1) Tarnak-Rud area over the Tarnak-Rud valley, (2) Spinatizha area over the Spinatizha Mountain Range, (3) Nushki area over the Nushki basin, and (4) Kharan area over the northern tip of the Central Makran Mountains. Remote sensing data allowed for in depth mapping of different components and faults within the Kohjak group. Wind and water gap pairs along with offset rivers were identified using high-resolution imagery and digital-elevation models to show displacement for the four study areas. The mountain-front-sinuosity ratio, valley height-to-width-ratio, and the stream-length-gradient index were calculated and used to determine the relative tectonic activity of each area. These geomorphic indices suggest that the Kharan area is the most active and the Tarnak-Rud area is the least active. GPS data were processed into a stable Indian Plate reference frame and analyzed. Fault parallel velocity versus fault normal distance yielded a ∼8–10 mm/yr displacement rate along the Chaman Fault just north of the Spinatizha area. InSAR data were also integrated to assess displacement rates along the fault system. Geodetic data support that ultra-slow earthquakes similar to those that strike along other major strike-slip faults, such as the San Andreas Fault System, are possible along the northern segments of the Chaman Fault zone. Geomorphic data suggest that the Chaman Fault along southern part is not very active now but may have gone through high tectonic activity in the past.
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contrasting late cretaceous palaeocene lithostratigraphic successions across the bibai thrust western sulaiman fold thrust belt pakistan their significance in deciphering the early collisional history of the nw Indian Plate margin
Journal of Asian Earth Sciences, 2009Co-Authors: Akhtar M Kassi, Gilbert Kelling, Aimal Khan Kasi, Mohammad Umar, Abdul Salam KhanAbstract:Abstract The Sulaiman Fold–Thrust Belt is a significant tectonic element in northwest Pakistan, located on the NW margin of the Indian Plate having a rift–drift-collision Plate tectonic history. Late Cretaceous–Palaeocene successions in the western sector of this Belt conventionally comprise strata above the widespread pelagic Parh Limestone (Albian–Campanian) and below the fluvio-deltaic Ghazij Formation (Early Eocene). These successions display marked lithostratigraphic variations across the Bibai Thrust, long known to be an important structural feature in the western Sulaiman Belt. The successions on the foot wall, to the east and southeast of the Bibai Thrust (Quetta, Spera Ragha and Chinjun areas), exhibit the most variable lithostratigraphy, were deposited exclusively in shallow marine conditions and include volcanics associated with a local submarine edifice. They also display several internal disconformities, locally accompanied by oxidised units that attest to intermittent emergence. By contrast, coeval successions on the hanging wall, to the north and northwest of the Bibai Thrust (Urghargai–Mazu Ghar and Kach–Ziarat areas) are the products of deposition in deeper marine conditions and also include important volcanigenic contributions. These contrasting lithofacies accumulated respectively in widely separated proximal and distal sectors of the north-western margin of the Indian Plate and their current proximity is attributed to tectonic juxtaposition by relative southward translation of the distal facies along the Bibai and related thrusts. Involvement of Late Eocene limestones in these thrusts and their sealing by Mio-Pliocene fluvial sediments demonstrates that active translation on these thrusts continued at least into Late Eocene or Oligocene times.
Qing Wang - One of the best experts on this subject based on the ideXlab platform.
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potassic volcanic rocks and adakitic intrusions in southern tibet insights into mantle crust interaction and mass transfer from Indian Plate
Lithos, 2017Co-Authors: Zhidan Zhao, Donald J Depaolo, Fanyi Meng, Qing WangAbstract:Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rock types have contrasting temporal–spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K2O/Na2O tend to display lower Y and higher SiO2, suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, the unradiogenic 143Nd/144Nd and the dramatic decrease of zircon eHf(t) values since ~ 35 Ma shown by postcollisional adakites should be interpreted as reflecting the crustal input from Indian Plate. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian continental crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that special caution is needed if we attempt to probe into the nature of mantle lithosphere using isotopic tracers of the Tibetan ultrapotassic rocks.
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potassic volcanic rocks and adakitic intrusions in southern tibet insights into mantle crust interaction and mass transfer from Indian Plate
Lithos, 2017Co-Authors: Dong Liu, Zhidan Zhao, Donald J Depaolo, Fanyi Meng, Dicheng Zhu, Qingshang Shi, Qing WangAbstract:Abstract Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rock types have contrasting temporal–spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K2O/Na2O tend to display lower Y and higher SiO2, suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, the unradiogenic 143Nd/144Nd and the dramatic decrease of zircon eHf(t) values since ~ 35 Ma shown by postcollisional adakites should be interpreted as reflecting the crustal input from Indian Plate. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian continental crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that special caution is needed if we attempt to probe into the nature of mantle lithosphere using isotopic tracers of the Tibetan ultrapotassic rocks.