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Richard Walshaw - One of the best experts on this subject based on the ideXlab platform.

  • mid crustal deformation of the annapurna dhaulagiri himalaya central nepal an atypical example of channel flow during the Himalayan Orogeny
    Geosphere, 2016
    Co-Authors: A J Parsons, M P Searle, Geoffrey E. Lloyd, R J Phillips, Richard Walshaw
    Abstract:

    The channel-flow model for the Greater Himalayan Sequence (GHS) of the Himalayan orogen involves a partially molten, rheologically weak, mid-crustal layer “flowing” southward relative to the upper and lower crust during late Oligocene–Miocene. Flow was driven by topographic overburden, underthrusting, and focused erosion. We present new structural and thermobarometric analyses from the GHS in the Annapurna-Dhaulagiri Hima­laya, central Nepal; these data suggest that during exhumation, the GHS cooled, strengthened, and transformed from a weak “active channel” to a strong “channel plug” at greater depths than elsewhere in the Himalaya. After strengthening, continued convergence resulted in localized top-southwest (top-SW) shortening on the South Tibetan detachment system (STDS). The GHS in the Annapurna-Dhaulagiri Himalaya displays several geological features that distinguish it from other Himalayan regions. These include reduced volumes of leucogranite and migmatite, no evidence for partial melting within the sillimanite stability field, reduced structural thickness, and late-stage top-southwest shortening in the STDS. New and previously published structural and thermobarometric constraints suggest that the channel-flow model can be applied to mid-Eocene–early Miocene mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya. However, pressure-temperature-time (PTt) constraints indicate that following peak conditions, the GHS in this region did not undergo rapid isothermal exhumation and widespread sillima­nite-grade decompression melting, as commonly recorded elsewhere in the Hima­laya. Instead, lower-than-typical structural thickness and melt volumes suggest that the upper part of the GHS (Upper Greater Himalayan Sequence [UGHS]—the proposed channel) had a greater viscosity than in other Hima­layan regions. We suggest that viscosity-limited, subdued channel flow prevented exhumation on an isothermal trajectory and forced the UGHS to exhume slowly. These findings are distinct from other regions in the Himalaya. As such, we describe the mid-crustal evolution of the GHS in the Annapurna-­Dhaulagiri Himalaya as an atypical example of channel flow during the Himalayan Orogeny.

  • mid crustal deformation of the annapurna dhaulagiri himalaya central nepal an atypical example of channel flow during the Himalayan Orogeny
    Geosphere, 2016
    Co-Authors: A J Parsons, M P Searle, Geoffrey E. Lloyd, R J Phillips, Richard Walshaw
    Abstract:

    The channel-flow model for the Greater Himalayan Sequence (GHS) of the Himalayan orogen involves a partially molten, rheologically weak, mid-crustal layer “flowing” southward relative to the upper and lower crust during late Oligocene–Miocene. Flow was driven by topographic overburden, underthrusting, and focused erosion. We present new structural and thermobarometric analyses from the GHS in the Annapurna-Dhaulagiri Hima­laya, central Nepal; these data suggest that during exhumation, the GHS cooled, strengthened, and transformed from a weak “active channel” to a strong “channel plug” at greater depths than elsewhere in the Himalaya. After strengthening, continued convergence resulted in localized top-southwest (top-SW) shortening on the South Tibetan detachment system (STDS). The GHS in the Annapurna-Dhaulagiri Himalaya displays several geological features that distinguish it from other Himalayan regions. These include reduced volumes of leucogranite and migmatite, no evidence for partial melting within the sillimanite stability field, reduced structural thickness, and late-stage top-southwest shortening in the STDS. New and previously published structural and thermobarometric constraints suggest that the channel-flow model can be applied to mid-Eocene–early Miocene mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya. However, pressure-temperature-time (PTt) constraints indicate that following peak conditions, the GHS in this region did not undergo rapid isothermal exhumation and widespread sillima­nite-grade decompression melting, as commonly recorded elsewhere in the Hima­laya. Instead, lower-than-typical structural thickness and melt volumes suggest that the upper part of the GHS (Upper Greater Himalayan Sequence [UGHS]—the proposed channel) had a greater viscosity than in other Hima­layan regions. We suggest that viscosity-limited, subdued channel flow prevented exhumation on an isothermal trajectory and forced the UGHS to exhume slowly. These findings are distinct from other regions in the Himalaya. As such, we describe the mid-crustal evolution of the GHS in the Annapurna-­Dhaulagiri Himalaya as an atypical example of channel flow during the Himalayan Orogeny.

Lee Jeffrey - One of the best experts on this subject based on the ideXlab platform.

  • Tibetan Garnet Records Early Eocene Tectonics in the Himalaya
    'Geological Society of America', 2014
    Co-Authors: Smit, Matthijs A., Hacker, Bradley R., Lee Jeffrey
    Abstract:

    Tectonic reconstructions of the Himalayan Orogeny depend on the age at which crustal thickening commenced. To investigate this age, we analyzed garnet from middle crustal rocks exposed in the north Himalayan Mabja and Kangmar gneiss domes of Tibet using Lu-Hf geochronology. Garnet yielded Lu-Hf ages of 54–52 Ma in Mabja and 51–49 Ma in Kangmar samples. On the basis of microstructural and major element and rare earth element zoning observations, the Lu-Hf ages are interpreted as recording garnet growth during contractional deformation in the middle crust at 54.3 ± 0.6 Ma, followed by variable recrystallization during subsequent high-temperature ductile extension. The new Lu-Hf ages are the first to confirm that crustal thickening and contraction in the Tibetan Himalaya was broadly synchronous with the early Eocene collision between Greater India and the Eurasian plate. This article is available from the Geological Society of America website

  • Tibetan garnet records early Eocene initiation of thickening in the Himalaya
    'Geological Society of America', 2014
    Co-Authors: Smit, Matthijs A., Hacker, Bradley R., Lee Jeffrey
    Abstract:

    Tectonic reconstructions of the Himalayan Orogeny depend on the age at which crustal thickening commenced. To investigate this age, we analyzed garnet from middle crustal rocks exposed in the north Himalayan Mabja and Kangmar gneiss domes of Tibet using Lu-Hf geochronology. Garnet yielded Lu-Hf ages of 54–52 Ma in Mabja and 51–49 Ma in Kangmar samples. On the basis of microstructural and major element and rare earth element zoning observations, the Lu-Hf ages are interpreted as recording garnet growth during contractional deformation in the middle crust at 54.3 ± 0.6 Ma, followed by variable recrystallization during subsequent high-temperature ductile extension. The new Lu-Hf ages are the first to confirm that crustal thickening and contraction in the Tibetan Himalaya was broadly synchronous with the early Eocene collision between Greater India and the Eurasian plate

  • The Malashan Gneiss Dome in South Tibet: Comparative Study with the Kangmar Dome with Special Reference to Kinematics of Deformation and Origin of Associated Granites
    ScholarWorks@CWU, 2006
    Co-Authors: Aoya Mutsuki, Lee Jeffrey, Kawakami Tetsuo, Yu Wang, Wallis Simon, Maeda H.
    Abstract:

    Despite the importance of Tethys Himalayan or North Himalayan gneiss domes for discussing extrusive flow of the underlying Greater Himalayan Sequence, these metamorphic domes in general remain poorly documented. The main exception is the Kangmar dome. The Malashan metamorphic complex, a newly documented North Himalayan gneiss dome, is shown to have strong similarities with the Kangmar dome, suggesting that the North Himalayan gneiss domes have the following features in common: (i) Barrovian-type metamorphism with grade increasing towards a centrally located two-mica granite; (ii) the presence of two dominant ductile deformation stages, D(1) and D(2), with D(2) showing an increasing strength towards the granite contacts; and (iii) the development of a strong D(2) foliation (gneissosity) in the outermost part of the granite cores. In addition, field and bulk-chemical studies show: (i) D(2) is associated with a dominant top-to-the-north sense of shear (in disagreement with the most recent kinematic studies in Kangmar dome); (ii) the deposition age of associated metasediments is upper Jurassic suggesting that the Malashan dome is located not at the base, but within the middle section of the Tethys Himalaya; and (iii) in contrast to the Kangmar granitic gneiss that is interpreted as Indian basement, three granitic bodies in Malashan all formed as young intrusive bodies during the Himalayan Orogeny. These results suggest that the formation mechanism of the North Himalayan gneiss domes needs to be re-evaluated to test the rigidity of the hanging wall assumed in channel flow models

  • North-South Extension in the Tibetan Crust Triggered by Granite Emplacement
    'Geological Society of America', 2005
    Co-Authors: Aoya Mutsuki, Wallis, Simon R., Terada Kentaro, Lee Jeffrey, Kawakami Tetsuo, Heizler Matt, Yu Wang
    Abstract:

    We combine zircon sensitive high-resolution ion microprobe U-Pb spot dating and mica 40Ar-39Ar plateau ages with field-geological and geochemical constraints from the Mala shan area of Southern Tibet to show that the deformed granite core of the North Himalayan metamorphic domes in this area is not Indian basement, but was intruded and deformed during the Himalayan Orogeny. Microstructural observations reveal that a transition from top-to-the-south thrust-related to top-to-the-north extension-related deformation occurred during granite intrusion and related metamorphism. This suggests that intrusion triggered the onset of extensional tectonics in the Tibetan middle to upper crust. Expected positive feedback mechanisms between decompression melting leading to more intrusion and more extensional deformation suggest that this mechanism may have been important on a regional scale

A J Parsons - One of the best experts on this subject based on the ideXlab platform.

  • mid crustal deformation of the annapurna dhaulagiri himalaya central nepal an atypical example of channel flow during the Himalayan Orogeny
    Geosphere, 2016
    Co-Authors: A J Parsons, M P Searle, Geoffrey E. Lloyd, R J Phillips, Richard Walshaw
    Abstract:

    The channel-flow model for the Greater Himalayan Sequence (GHS) of the Himalayan orogen involves a partially molten, rheologically weak, mid-crustal layer “flowing” southward relative to the upper and lower crust during late Oligocene–Miocene. Flow was driven by topographic overburden, underthrusting, and focused erosion. We present new structural and thermobarometric analyses from the GHS in the Annapurna-Dhaulagiri Hima­laya, central Nepal; these data suggest that during exhumation, the GHS cooled, strengthened, and transformed from a weak “active channel” to a strong “channel plug” at greater depths than elsewhere in the Himalaya. After strengthening, continued convergence resulted in localized top-southwest (top-SW) shortening on the South Tibetan detachment system (STDS). The GHS in the Annapurna-Dhaulagiri Himalaya displays several geological features that distinguish it from other Himalayan regions. These include reduced volumes of leucogranite and migmatite, no evidence for partial melting within the sillimanite stability field, reduced structural thickness, and late-stage top-southwest shortening in the STDS. New and previously published structural and thermobarometric constraints suggest that the channel-flow model can be applied to mid-Eocene–early Miocene mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya. However, pressure-temperature-time (PTt) constraints indicate that following peak conditions, the GHS in this region did not undergo rapid isothermal exhumation and widespread sillima­nite-grade decompression melting, as commonly recorded elsewhere in the Hima­laya. Instead, lower-than-typical structural thickness and melt volumes suggest that the upper part of the GHS (Upper Greater Himalayan Sequence [UGHS]—the proposed channel) had a greater viscosity than in other Hima­layan regions. We suggest that viscosity-limited, subdued channel flow prevented exhumation on an isothermal trajectory and forced the UGHS to exhume slowly. These findings are distinct from other regions in the Himalaya. As such, we describe the mid-crustal evolution of the GHS in the Annapurna-­Dhaulagiri Himalaya as an atypical example of channel flow during the Himalayan Orogeny.

  • mid crustal deformation of the annapurna dhaulagiri himalaya central nepal an atypical example of channel flow during the Himalayan Orogeny
    Geosphere, 2016
    Co-Authors: A J Parsons, M P Searle, Geoffrey E. Lloyd, R J Phillips, Richard Walshaw
    Abstract:

    The channel-flow model for the Greater Himalayan Sequence (GHS) of the Himalayan orogen involves a partially molten, rheologically weak, mid-crustal layer “flowing” southward relative to the upper and lower crust during late Oligocene–Miocene. Flow was driven by topographic overburden, underthrusting, and focused erosion. We present new structural and thermobarometric analyses from the GHS in the Annapurna-Dhaulagiri Hima­laya, central Nepal; these data suggest that during exhumation, the GHS cooled, strengthened, and transformed from a weak “active channel” to a strong “channel plug” at greater depths than elsewhere in the Himalaya. After strengthening, continued convergence resulted in localized top-southwest (top-SW) shortening on the South Tibetan detachment system (STDS). The GHS in the Annapurna-Dhaulagiri Himalaya displays several geological features that distinguish it from other Himalayan regions. These include reduced volumes of leucogranite and migmatite, no evidence for partial melting within the sillimanite stability field, reduced structural thickness, and late-stage top-southwest shortening in the STDS. New and previously published structural and thermobarometric constraints suggest that the channel-flow model can be applied to mid-Eocene–early Miocene mid-crustal evolution of the GHS in the Annapurna-Dhaulagiri Himalaya. However, pressure-temperature-time (PTt) constraints indicate that following peak conditions, the GHS in this region did not undergo rapid isothermal exhumation and widespread sillima­nite-grade decompression melting, as commonly recorded elsewhere in the Hima­laya. Instead, lower-than-typical structural thickness and melt volumes suggest that the upper part of the GHS (Upper Greater Himalayan Sequence [UGHS]—the proposed channel) had a greater viscosity than in other Hima­layan regions. We suggest that viscosity-limited, subdued channel flow prevented exhumation on an isothermal trajectory and forced the UGHS to exhume slowly. These findings are distinct from other regions in the Himalaya. As such, we describe the mid-crustal evolution of the GHS in the Annapurna-­Dhaulagiri Himalaya as an atypical example of channel flow during the Himalayan Orogeny.

Xiao Zhongyao - One of the best experts on this subject based on the ideXlab platform.

  • iodine 129 chronological study of brines from an ordovician paleokarst reservoir in the lunnan oilfield tarim basin
    Applied Geochemistry, 2016
    Co-Authors: Jian Chen, Pingan Peng, Hou Xiaolin, Zhang Baoshou, Dayong Liu, Chen Ning, Xiao Zhongyao
    Abstract:

    Abstract Previous studies have shown that brines in an Ordovician paleokarst reservoir of the Lunnan oilfield in the Tarim Basin, China, are the product of mixing of paleo-evaporated seawater in the east with paleometeoric waters in the west. In order to put time constraints on the brine and related hydrocarbons in this field, 10 brine samples were collected, for which the iodine concentrations and 129 I/I ratios were measured and discussed. The iodine concentration (3.70–31.2 mg/L) and the 129 I/I ratio (189–897 × 10 −15 ) show that the iodine in the paleoseawater and meteoric water (MW) had different origins and 129 I characteristics. The paleoseawater has a high iodine content (∼31 mg/L), indicating that iodine was introduced into the reservoir along with thermally generated hydrocarbons, possibly in the Cretaceous, from the Caohu Sag in the eastern area. Based on consideration of all possible origins of iodine and 129 I in the brines, it is suggested that the meteoric water maintained its initial iodine content (0.01 mg/L) and 129 I/I ratio (1500 × 10 −15 ), whereas the iodine-enriched paloseawater (IPSW) exhibited a secular 129 I equilibrium (N sq  = 39 atom/μL) as a result of fissiogenic 129 I input in the reservoir over a long period of time. The model of brine evolution developed on that basis confirmed that meteoric water entered the reservoir in the Miocene at about 10 Ma, and partially mixed with the iodine-enriched paleoseawater. The movement of meteoric water was facilitated by faults created during the Himalayan Orogeny, then became more dense after dissolving Paleogene halite and infiltrated into the reservoir at high pressure. The iodine and 129 I concentration in the brine contains information about the path and history of the fluid in the reservoir. This may be useful in oil exploration, since the movement of water was, to some extent, related to hydrocarbon migration.

  • Iodine-129 chronological study of brines from an Ordovician paleokarst reservoir in the Lunnan oilfield, Tarim Basin
    'Elsevier BV', 2016
    Co-Authors: Chen Jian, Liu Dayong, Peng Ping'an, Ning Chen, Hou Xiaolin, Zhang Baoshou, Xiao Zhongyao
    Abstract:

    Previous studies have shown that brines in an Ordovician paleokarst reservoir of the Lunnan oilfield in the Tarim Basin, China, are the product of mixing of paleo-evaporated seawater in the east with paleo-meteoric waters in the west. In order to put time constraints on the brine and related hydrocarbons in this field, 10 brine samples were collected, for which the iodine concentrations and I-129/I ratios were measured and discussed. The iodine concentration (3.70-31.2 mg/L) and the I-129/I ratio (189 -897 x 10(-15)) show that the iodine in the paleoseawater and meteoric water (MW) had different origins and I-129 characteristics. The paleoseawater has a high iodine content (similar to 31 mg/L), indicating that iodine was introduced into the reservoir along with thermally generated hydrocarbons, possibly in the Cretaceous, from the Caohu Sag in the eastern area. Based on consideration of all possible origins of iodine and I-129 in the brines, it is suggested that the meteoric water maintained its initial iodine content (0.01 mg/L) and I-129/I ratio (1500 x 10(-15)), whereas the iodine-enriched paloseawater (IPSW) exhibited a secular I-129 equilibrium (N-sq = 39 atom/mu L) as a result of fissiogenic I-129 input in the reservoir over a long period of time. The model of brine evolution developed on that basis confirmed that meteoric water entered the reservoir in the Miocene at about 10 Ma, and partially mixed with the iodine-enriched paleoseawater. The movement of meteoric water was facilitated by faults created during the Himalayan Orogeny, then became more dense after dissolving Paleogene halite and infiltrated into the reservoir at high pressure. The iodine and I-129 concentration in the brine contains information about the path and history of the fluid in the reservoir. This may be useful in oil exploration, since the movement of water was, to some extent, related to hydrocarbon migration. (C) 2015 Elsevier Ltd. All rights reserved

Smit, Matthijs A. - One of the best experts on this subject based on the ideXlab platform.

  • Tibetan garnet records early Eocene initiation of thickening in the Himalaya
    'Geological Society of America', 2014
    Co-Authors: Smit, Matthijs A., Hacker, Bradley R., Lee Jeffrey
    Abstract:

    Tectonic reconstructions of the Himalayan Orogeny depend on the age at which crustal thickening commenced. To investigate this age, we analyzed garnet from middle crustal rocks exposed in the north Himalayan Mabja and Kangmar gneiss domes of Tibet using Lu-Hf geochronology. Garnet yielded Lu-Hf ages of 54–52 Ma in Mabja and 51–49 Ma in Kangmar samples. On the basis of microstructural and major element and rare earth element zoning observations, the Lu-Hf ages are interpreted as recording garnet growth during contractional deformation in the middle crust at 54.3 ± 0.6 Ma, followed by variable recrystallization during subsequent high-temperature ductile extension. The new Lu-Hf ages are the first to confirm that crustal thickening and contraction in the Tibetan Himalaya was broadly synchronous with the early Eocene collision between Greater India and the Eurasian plate

  • Tibetan Garnet Records Early Eocene Tectonics in the Himalaya
    'Geological Society of America', 2014
    Co-Authors: Smit, Matthijs A., Hacker, Bradley R., Lee Jeffrey
    Abstract:

    Tectonic reconstructions of the Himalayan Orogeny depend on the age at which crustal thickening commenced. To investigate this age, we analyzed garnet from middle crustal rocks exposed in the north Himalayan Mabja and Kangmar gneiss domes of Tibet using Lu-Hf geochronology. Garnet yielded Lu-Hf ages of 54–52 Ma in Mabja and 51–49 Ma in Kangmar samples. On the basis of microstructural and major element and rare earth element zoning observations, the Lu-Hf ages are interpreted as recording garnet growth during contractional deformation in the middle crust at 54.3 ± 0.6 Ma, followed by variable recrystallization during subsequent high-temperature ductile extension. The new Lu-Hf ages are the first to confirm that crustal thickening and contraction in the Tibetan Himalaya was broadly synchronous with the early Eocene collision between Greater India and the Eurasian plate. This article is available from the Geological Society of America website