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Zhiqiang Kang - One of the best experts on this subject based on the ideXlab platform.
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geochronology and geochemistry of the sangri group Volcanic Rocks southern lhasa terrane implications for the early subduction history of the neo tethys and gangdese magmatic arc
Lithos, 2014Co-Authors: Zhiqiang Kang, Jifeng Xu, Simon A Wilde, Zuohai Feng, Jianlin Chen, Baodi Wang, Wenchun FuAbstract:Abstract The Sangri Group Volcanic Rocks are distributed along the southern margin of the Lhasa Terrane on the northern side of the Indus-Yarlung Zangbo suture zone. This Group consists of the Mamuxia and Bima formations and has long been considered to be Late Jurassic to Early Cretaceous in age. In this paper, we report for the first time zircon LA-ICPMS U-Pb ages, whole-rock major and trace element geochemistry, as well as Sr-Nd isotope data of the Bima Formation Volcanic Rocks in the Sangri County, Tibet. Two samples collected from the Bima Formation Volcanic Rocks yield zircon U-Pb ages of 195 ± 3 Ma and 189 ± 3 Ma, respectively. These data suggest that the Bima Formation Volcanic Rocks formed during the Early Jurassic rather than the Late Jurassic-Early Cretaceous as previously reported. The Volcanic Rocks of the Bima Formation are dominantly composed of basalt and andesite that are enriched in LILEs and LREEs, but depleted in HFSEs, showing typical characteristics of arc Volcanic Rocks. They also show positive e Nd (t) (+ 4.09 to + 7.02) values and low initial 87 Sr/ 86 Sr (0.7032 to 0.7050) ratios, similar to the MORB of the Indus-Yarlung Zangbo ophiolites, indicating that the Bima Formation Volcanic Rocks were derived from a depleted mantle wedge. The magmas subsequently experienced juvenile crust contamination and fractional crystallization during ascent. Geochemical features of magmas of the Bima Formation Volcanic Rocks are interpreted to be generated by the northward subduction of Neo-Tethys beneath the southern Lhasa Terrane as early as ~ 195 Ma. Coeval with a large volume of Late Triassic-Early Jurassic felsic intrusions within the Gangdese arc, the Gangdese magmatic arc is interpreted to be initiated at a juvenile continental margin during the Late Triassic-Early Jurassic, although a possible intra-oceanic arc setting cannot be excluded.
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origin of cenozoic alkaline potassic Volcanic Rocks at konglongxiang lhasa terrane tibetan plateau products of partial melting of a mafic lower crustal source
Chemical Geology, 2010Co-Authors: Jianlin Chen, Jifeng Xu, Baodi Wang, Zhiqiang KangAbstract:Abstract It is generally believed that Cenozoic potassic and ultrapotassic Volcanic Rocks of the Tibetan Plateau were generated by partial melting of enriched mantle. This paper reports new data regarding the elemental and isotopic compositions of the KonglongXiang Volcanic Rocks (KVR; K2O/Na2O > 2 and low MgO contents) in the middle–western Lhasa terrane, Tibetan Plateau. Ar–Ar isotope dating of a sample from the KVR yields an age of 21.3 Ma, indicating that the KVR lavas erupted during the Early Miocene. The KVR consists mainly of trachyte and rhyolite. A comparison of the KVR with Cenozoic potassic Volcanic Rocks of the Tibetan Plateau and the results of melting experiments involving K-rich Volcanic Rocks, as well as other K-rich Volcanic Rocks from throughout the world, reveals that the KVR trachytes originated from a mafic lower crust containing K-rich minerals rather than from a mantle source. The KVR rhyolites were probably derived from the middle–upper crust. Based on age data, compositional data, and the regional tectonic setting, we propose that the formation of the KVR and associated N–S grabens was triggered by Early Miocene E–W regional extension in the area of the southern Tibetan Plateau.
Xinyu Wang - One of the best experts on this subject based on the ideXlab platform.
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carboniferous bimodal Volcanic Rocks in the eastern tianshan nw china evidence for arc rifting
Gondwana Research, 2017Co-Authors: Yunying Zhang, Chao Yuan, Xiaoping Long, Zongying Huang, Long Du, Xinyu WangAbstract:Abstract Detailed geochronological, geochemical, and Sr–Nd isotopic data are presented for late Paleozoic Volcanic Rocks in the Dashitou area from the Eastern Tianshan, NW China, aiming to constrain their petrogenesis and tectonic implications. The Dashitou Volcanic Rocks show a bimodal distribution in composition, with dominant rhyolite and subordinate basalt. LA–ICPMS zircon U–Pb age indicates that the Volcanic Rocks were erupted at 330 ± 3 Ma. The basaltic Rocks are medium-K calc-alkaline, enriched in light rare earth element (LREE) and large ion lithophile element (LILE; Ba and U), and depleted in high field strength element (HFSE; Nb, Ta, and Ti). These features, together with their depleted isotopic signature (initial 87Sr/86Sr = 0.7035 to 0.7039, eNd(t) = 6.8 to 7.1), suggest that they were likely derived from a depleted mantle source metasomatized by subduction-related fluids. The rhyolitic Rocks are high-K calc-alkaline and exhibit characteristics of A2-type granite, with typical enrichment in alkalis, Zr, and Nb and depletion in Sr, P, and Ti. They are characterized by positive eNd(t) values (6.2–6.5) with young Nd model ages (0.57–0.58 Ga). Results of MELTS modeling imply that they were unlikely produced by fractional crystallization of coeval basaltic Rocks. Instead, they were probably generated by partial melting of juvenile basaltic crust as a result of magma underplating. The geochemical and Sr–Nd isotopic characteristics, coupled with regional geology, indicate that the formation of the Dashitou bimodal Volcanic Rocks involves an extensional regime associated with a subduction-related environment. The rifting of the Dananhu–Harlik arc in response to the retreat of the subducting Northern Tianshan oceanic lithosphere may account for the Dashitou bimodal Volcanic Rocks.
Libing Gu - One of the best experts on this subject based on the ideXlab platform.
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petrology sr nd hf isotopic geochemistry and zircon chronology of the late palaeozoic Volcanic Rocks in the southwestern tianshan mountains xinjiang nw china
Journal of the Geological Society, 2009Co-Authors: Biao Song, Lifei Zhang, Libing GuAbstract:Abstract: The Late Palaeozoic Volcanic Rocks, mainly consisting of basalt, trachyte, trachy-andesite, andesite and rhyolite, widely distributed in the southwestern Tianshan Mountains, have been proven to be formed during Late Devonian to Late Carboniferous time (>361–313 Ma) based on zircon sensitive high-resolution ion microprobe dating. The geochemistry demonstrates that the studied Volcanic Rocks represent a continental arc formed during the subduction of the Palaeo-southern Tianshan Ocean. The e Hf(T) values of zircons in these Volcanic Rocks vary from +1.4 to +15.6 with weighted average values of +9.5 (Late Devonian), +8.9 (Early Carboniferous) and +10.3 (Late Carboniferous), suggesting a depleted mantle origin. However, the Late Devonian basaltic samples have negative e Nd(T) values (from −5.16 to −3.07) and high initial 87 Sr/ 86 Sr ratios (0.7073–0.7098), whereas the Early Carboniferous Volcanic Rocks mostly have positive e Nd(T) values (from −0.18 to +3.07) with low initial 87 Sr/ 86 Sr ratios (0.7044–0.7067), and the Late Carboniferous Volcanic Rocks are characterized by high e Nd(T) values (+2.79 to +5.89) and low initial 87 Sr/ 86 Sr ratios (0.7032–0.7054). The assimilation–fractional crystallization (AFC) model is used to explain the isotope characteristics of the Late Devonian Volcanic Rocks in the southwestern Tianshan Mountains. Calculation shows that the Late Devonian samples could be formed by the AFC process between depleted mantle and continental crust. The Carboniferous basaltic Rocks originated by partial melting of the mantle wedge. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18378.
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the zircon shrimp chronology and trace element geochemistry of the carboniferous Volcanic Rocks in western tianshan mountains
Chinese Science Bulletin, 2005Co-Authors: Lifei Zhang, Libing Gu, Jing ZhouAbstract:The genesis of the Carboniferous Volcanic Rocks in the Dahalajunshan group, mainly consisting of trachytes and trachy-andesites and distributing widely in western Tianshan Mountains, remains to be controversial. It has been proposed to be relevant to “rift” or “plume”. Detailed petrology and geochemical data presented in this paper show that these Volcanic Rocks represent typical continental arc magmatism. The Volcanic Rocks are mainly trachy-andesitic, and the magma source is enriched in LILE, Th and Pb, and depleted in HFSE and Ce. Trace element geochemical study suggests that the basalts could be modeled by 7%–11% partial melt of garnet lherzolite. The Volcanic Rocks in the Dahalajunshan group are neither the products of “rift” nor so-called “plume” but represent the continental island arc of the Paleo-Southern Tianshan Ocean. The mantle wedge had been modified by the melt generating in subduction zone during a long evolution history of this island arc. The continental crust materials (i.e. mainly sediment on ocean floor) had been added into island arc through melt in subduction zone. Volcanic Rocks occurring in different regions might represent magma eruption in different time. The zircon SHRIMP dating indicates that the ages of the basalt varies between 334.0 Ma and 394.9 Ma. The 13 analyses give an average age of 353.7±4.5 Ma (MSWD = 1.7). The apparent ages of zircons in trachy-andesite vary between 293.0 Ma and 465.4 Ma. All analyses fall on the U-Pb concordant line and are divided into two groups. 8 analyses produce an average age of 312.8±4.2 Ma (MSWD = 1.7), which represents the crystallizing age of zircon rims in trachy-andesite. The acquired two ages (i.e. 354 and 313 Ma) belong to the Early Carboniferous and Late Carboniferous epochs, respectively. Thus, the Dahalajunshan group would be separated into several groups with the accumulation of high-quality age dating and data of trace element and isotopic geochemistry, in our opinion.
Jianlin Chen - One of the best experts on this subject based on the ideXlab platform.
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geochronology and geochemistry of the sangri group Volcanic Rocks southern lhasa terrane implications for the early subduction history of the neo tethys and gangdese magmatic arc
Lithos, 2014Co-Authors: Zhiqiang Kang, Jifeng Xu, Simon A Wilde, Zuohai Feng, Jianlin Chen, Baodi Wang, Wenchun FuAbstract:Abstract The Sangri Group Volcanic Rocks are distributed along the southern margin of the Lhasa Terrane on the northern side of the Indus-Yarlung Zangbo suture zone. This Group consists of the Mamuxia and Bima formations and has long been considered to be Late Jurassic to Early Cretaceous in age. In this paper, we report for the first time zircon LA-ICPMS U-Pb ages, whole-rock major and trace element geochemistry, as well as Sr-Nd isotope data of the Bima Formation Volcanic Rocks in the Sangri County, Tibet. Two samples collected from the Bima Formation Volcanic Rocks yield zircon U-Pb ages of 195 ± 3 Ma and 189 ± 3 Ma, respectively. These data suggest that the Bima Formation Volcanic Rocks formed during the Early Jurassic rather than the Late Jurassic-Early Cretaceous as previously reported. The Volcanic Rocks of the Bima Formation are dominantly composed of basalt and andesite that are enriched in LILEs and LREEs, but depleted in HFSEs, showing typical characteristics of arc Volcanic Rocks. They also show positive e Nd (t) (+ 4.09 to + 7.02) values and low initial 87 Sr/ 86 Sr (0.7032 to 0.7050) ratios, similar to the MORB of the Indus-Yarlung Zangbo ophiolites, indicating that the Bima Formation Volcanic Rocks were derived from a depleted mantle wedge. The magmas subsequently experienced juvenile crust contamination and fractional crystallization during ascent. Geochemical features of magmas of the Bima Formation Volcanic Rocks are interpreted to be generated by the northward subduction of Neo-Tethys beneath the southern Lhasa Terrane as early as ~ 195 Ma. Coeval with a large volume of Late Triassic-Early Jurassic felsic intrusions within the Gangdese arc, the Gangdese magmatic arc is interpreted to be initiated at a juvenile continental margin during the Late Triassic-Early Jurassic, although a possible intra-oceanic arc setting cannot be excluded.
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origin of cenozoic alkaline potassic Volcanic Rocks at konglongxiang lhasa terrane tibetan plateau products of partial melting of a mafic lower crustal source
Chemical Geology, 2010Co-Authors: Jianlin Chen, Jifeng Xu, Baodi Wang, Zhiqiang KangAbstract:Abstract It is generally believed that Cenozoic potassic and ultrapotassic Volcanic Rocks of the Tibetan Plateau were generated by partial melting of enriched mantle. This paper reports new data regarding the elemental and isotopic compositions of the KonglongXiang Volcanic Rocks (KVR; K2O/Na2O > 2 and low MgO contents) in the middle–western Lhasa terrane, Tibetan Plateau. Ar–Ar isotope dating of a sample from the KVR yields an age of 21.3 Ma, indicating that the KVR lavas erupted during the Early Miocene. The KVR consists mainly of trachyte and rhyolite. A comparison of the KVR with Cenozoic potassic Volcanic Rocks of the Tibetan Plateau and the results of melting experiments involving K-rich Volcanic Rocks, as well as other K-rich Volcanic Rocks from throughout the world, reveals that the KVR trachytes originated from a mafic lower crust containing K-rich minerals rather than from a mantle source. The KVR rhyolites were probably derived from the middle–upper crust. Based on age data, compositional data, and the regional tectonic setting, we propose that the formation of the KVR and associated N–S grabens was triggered by Early Miocene E–W regional extension in the area of the southern Tibetan Plateau.
Yunying Zhang - One of the best experts on this subject based on the ideXlab platform.
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carboniferous bimodal Volcanic Rocks in the eastern tianshan nw china evidence for arc rifting
Gondwana Research, 2017Co-Authors: Yunying Zhang, Chao Yuan, Xiaoping Long, Zongying Huang, Long Du, Xinyu WangAbstract:Abstract Detailed geochronological, geochemical, and Sr–Nd isotopic data are presented for late Paleozoic Volcanic Rocks in the Dashitou area from the Eastern Tianshan, NW China, aiming to constrain their petrogenesis and tectonic implications. The Dashitou Volcanic Rocks show a bimodal distribution in composition, with dominant rhyolite and subordinate basalt. LA–ICPMS zircon U–Pb age indicates that the Volcanic Rocks were erupted at 330 ± 3 Ma. The basaltic Rocks are medium-K calc-alkaline, enriched in light rare earth element (LREE) and large ion lithophile element (LILE; Ba and U), and depleted in high field strength element (HFSE; Nb, Ta, and Ti). These features, together with their depleted isotopic signature (initial 87Sr/86Sr = 0.7035 to 0.7039, eNd(t) = 6.8 to 7.1), suggest that they were likely derived from a depleted mantle source metasomatized by subduction-related fluids. The rhyolitic Rocks are high-K calc-alkaline and exhibit characteristics of A2-type granite, with typical enrichment in alkalis, Zr, and Nb and depletion in Sr, P, and Ti. They are characterized by positive eNd(t) values (6.2–6.5) with young Nd model ages (0.57–0.58 Ga). Results of MELTS modeling imply that they were unlikely produced by fractional crystallization of coeval basaltic Rocks. Instead, they were probably generated by partial melting of juvenile basaltic crust as a result of magma underplating. The geochemical and Sr–Nd isotopic characteristics, coupled with regional geology, indicate that the formation of the Dashitou bimodal Volcanic Rocks involves an extensional regime associated with a subduction-related environment. The rifting of the Dananhu–Harlik arc in response to the retreat of the subducting Northern Tianshan oceanic lithosphere may account for the Dashitou bimodal Volcanic Rocks.
