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Xiao Yang - One of the best experts on this subject based on the ideXlab platform.
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Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: a paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle
'Geological Society of America', 2019Co-Authors: Zheng Hao, Huang Qiangtai, Kapsiotis Argyrios, Lenaz Davide, Velicogna Matteo, Xu Chi, Cheng Chen, Xia Bin, Liu Weiliang, Xiao YangAbstract:The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the Zhongba-Zhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 \ub1 2.0 Ma (Valanginian). These dolerites show Ocean Island Basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)N = 13\u201316], high initial 87Sr/86Sr ratios (0.70598\u20130.70765), and low \u3b5Nd(t) values (\u20132.6 to \u20132.3). Zircons separated from this group of dolerites have slightly radiogenic \u3b5Hf(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 \ub1 2.5 Ma and 124.4 \ub1 3.2 Ma (Aptian). These East Purang dolerites show normal mid-Ocean ridge Basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)N = 0.6\u20130.9] with noticeable negative Nb and Th (\ub1Ti) anomalies, and have high 87Sr/86Sr(i) (0.70295\u20130.70618) and high \u3b5Nd(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic \u3b5Hf(t) values (+3.5 to +17.0). Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5%\u201310% polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORBtype mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent Oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-Oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous
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Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: a paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle
'Geological Society of America', 2019Co-Authors: Zheng Hao, Huang Qiangtai, Kapsiotis Argyrios, Lenaz Davide, Velicogna Matteo, Xu Chi, Cheng Chen, Xia Bin, Liu Weiliang, Xiao YangAbstract:The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the ZhongbaZhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 +/- 2.0 Ma (Valanginian). These dolerites show Ocean Island Basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)(N )= 13-16], high initial Sr-87/Sr-86 ratios (0.70598-0.70765), and low epsilon(Nd)(t) values (-2.6 to -2.3). Zircons separated from this group of dolerites have slightly radiogenic epsilon(Hf)(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 +/- 2.5 Ma and 124.4 +/- 3.2 Ma (Aptian). These East Purang dolerites show normal mid-Ocean ridge Basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)(N) = 0.6-0.9] with noticeable negative Nb and Th (+/- Ti) anomalies, and have high Sr-87/Sr-86((i)) (0.70295-0.70618) and high epsilon(Nd)(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic epsilon(Hf)(t) values (+3.5 to +17.0).Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5 %-10 % polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORB-type mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent Oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-Oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous
Lili Tong - One of the best experts on this subject based on the ideXlab platform.
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petrogenesis and tectonic implications of early carboniferous alkaline volcanic rocks in karamay region of west junggar northwest china
International Geology Review, 2016Co-Authors: Gaoxue Yang, Lili Tong, Zuopeng WangAbstract:ABSTRACTZircon U–Pb geochronological and geochemical analyses are reported for a suite of the early Carboniferous volcanic rocks from West Junggar (Northwest China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded concordant weighted mean 206Pb/238U age of 345 ± 3 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The early Carboniferous volcanic rocks consist of Basalt, Basaltic andesite, and andesite. Geochemically, all the samples bear the signature of Ocean Island Basalt (OIB), and are characterized by alkaline affinity with minor variations in SiO2 compositions (45.13–53.05 wt.%), high concentrations of Na2O + K2O (5.08–8.89 wt.%) and TiO2 (1.71–3.35 wt.%), and LREE enrichment and HREE depletion ((La/Yb)N = 7.1–12.4), with weak Eu anomalies (Eu/Eu* = 0.9–1.1) and no obvious Nb, Ta, ...
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, M Santosh, Yongjun Li, Baokai Yang, Bing Zhang, Lili TongAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, Lili Tong, M Santosh, Baokai Yang, Bing ZhangAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.
M Santosh - One of the best experts on this subject based on the ideXlab platform.
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the role of recycled Oceanic crust in magmatism and metallogeny os sr nd isotopes u pb geochronology and geochemistry of picritic dykes in the panzhihua giant fe ti oxide deposit central emeishan large igneous province sw china
Contributions to Mineralogy and Petrology, 2013Co-Authors: Zhaochong Zhang, John Encarnacion, M SantoshAbstract:The picritic dykes occurring within fine-grained gabbro in the marginal zone and in the surrounding Prote- rozoic wall-rock marbles of the Panzhihua Fe-Ti oxide deposit closely correspond in bulk composition with the nearby Panzhihua intrusion. These dykes offer important constraints on the nature of the mantle source of the Panzh- ihua ore-bearing intrusion and its possible link to the Emeishan plume. U-Pb zircon dating of the picritic dyke yields a crystallization age of 261.4 ± 4.6 Ma, coeval with the timing of the main Panzhihua gabbroic intrusion and Late Permian Emeishan flood Basalts. The Panzhihua picritic dykes contain 37.63-43.41 wt% SiO2, 1.15-1.56 wt% TiO2, 11.43-13.25 wt% TFe2O3, and 20.96-28.87 wt% MgO. Primitive-mantle-normalized patterns of the rocks are comparable to those of Ocean Island Basalt. The rocks define a relatively small range of Os isotopic compositions and a low Os signature of -0.13 to ?2.76 for cOs (261 Ma). In combination with their Sr-Nd-Os isotopic compositions, we interpret that these rocks were derived from the Emeishan plume sources as well as the interactions of plume melts with the overlying lithosphere which had been extensively affected by eclogite-derived melts from the deep-subducted Oceanic slab. Partial melting induced by an upwelling mantle plume that involved an eclogite or pyroxenite component in the lithospheric mantle could have produced the parental Fe-rich magma. Our study suggests that plume-lithosphere interaction might have played a key role in generating many world-class Fe-Ti oxide deposits clustered in the Panxi area.
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, M Santosh, Yongjun Li, Baokai Yang, Bing Zhang, Lili TongAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, Lili Tong, M Santosh, Baokai Yang, Bing ZhangAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.
Zheng Hao - One of the best experts on this subject based on the ideXlab platform.
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Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: a paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle
'Geological Society of America', 2019Co-Authors: Zheng Hao, Huang Qiangtai, Kapsiotis Argyrios, Lenaz Davide, Velicogna Matteo, Xu Chi, Cheng Chen, Xia Bin, Liu Weiliang, Xiao YangAbstract:The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the Zhongba-Zhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 \ub1 2.0 Ma (Valanginian). These dolerites show Ocean Island Basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)N = 13\u201316], high initial 87Sr/86Sr ratios (0.70598\u20130.70765), and low \u3b5Nd(t) values (\u20132.6 to \u20132.3). Zircons separated from this group of dolerites have slightly radiogenic \u3b5Hf(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 \ub1 2.5 Ma and 124.4 \ub1 3.2 Ma (Aptian). These East Purang dolerites show normal mid-Ocean ridge Basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)N = 0.6\u20130.9] with noticeable negative Nb and Th (\ub1Ti) anomalies, and have high 87Sr/86Sr(i) (0.70295\u20130.70618) and high \u3b5Nd(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic \u3b5Hf(t) values (+3.5 to +17.0). Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5%\u201310% polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORBtype mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent Oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-Oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous
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Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: a paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle
'Geological Society of America', 2019Co-Authors: Zheng Hao, Huang Qiangtai, Kapsiotis Argyrios, Lenaz Davide, Velicogna Matteo, Xu Chi, Cheng Chen, Xia Bin, Liu Weiliang, Xiao YangAbstract:The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the ZhongbaZhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 +/- 2.0 Ma (Valanginian). These dolerites show Ocean Island Basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)(N )= 13-16], high initial Sr-87/Sr-86 ratios (0.70598-0.70765), and low epsilon(Nd)(t) values (-2.6 to -2.3). Zircons separated from this group of dolerites have slightly radiogenic epsilon(Hf)(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 +/- 2.5 Ma and 124.4 +/- 3.2 Ma (Aptian). These East Purang dolerites show normal mid-Ocean ridge Basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)(N) = 0.6-0.9] with noticeable negative Nb and Th (+/- Ti) anomalies, and have high Sr-87/Sr-86((i)) (0.70295-0.70618) and high epsilon(Nd)(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic epsilon(Hf)(t) values (+3.5 to +17.0).Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5 %-10 % polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORB-type mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent Oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-Oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous
Gaoxue Yang - One of the best experts on this subject based on the ideXlab platform.
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petrogenesis and tectonic implications of early carboniferous alkaline volcanic rocks in karamay region of west junggar northwest china
International Geology Review, 2016Co-Authors: Gaoxue Yang, Lili Tong, Zuopeng WangAbstract:ABSTRACTZircon U–Pb geochronological and geochemical analyses are reported for a suite of the early Carboniferous volcanic rocks from West Junggar (Northwest China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded concordant weighted mean 206Pb/238U age of 345 ± 3 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The early Carboniferous volcanic rocks consist of Basalt, Basaltic andesite, and andesite. Geochemically, all the samples bear the signature of Ocean Island Basalt (OIB), and are characterized by alkaline affinity with minor variations in SiO2 compositions (45.13–53.05 wt.%), high concentrations of Na2O + K2O (5.08–8.89 wt.%) and TiO2 (1.71–3.35 wt.%), and LREE enrichment and HREE depletion ((La/Yb)N = 7.1–12.4), with weak Eu anomalies (Eu/Eu* = 0.9–1.1) and no obvious Nb, Ta, ...
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, M Santosh, Yongjun Li, Baokai Yang, Bing Zhang, Lili TongAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.
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geochronology and geochemistry of Basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra Oceanic accretionary tectonics of the southern altaids
Geological Society of America Bulletin, 2013Co-Authors: Gaoxue Yang, Lili Tong, M Santosh, Baokai Yang, Bing ZhangAbstract:New laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon ages and geochemical data are reported for the Karamay ophiolitic melange in the West Junggar area at the southwestern margin of the Altaids (or Central Asian orogenic belt), northwestern China. The data were used to identify the petrogenesis of the melange, and to evaluate its tectonic significance. In addition, this study aimed to assess the possible presence of Devonian mantle plume in the region. The Karamay ophiolitic melange crops out at the boundary of the Junggar Basin but is partly hidden by Mesozoic sediments, with an exposure area of ∼40 km 2 . The site contains ultramafic rocks, cumulates, gabbros, pillow lavas, abyssal radiolarian cherts, turbidites, and tuffs, which show typical block-in-matrix structures. Zircon U-Pb analyses from the Basalt and gabbro by LA-ICP-MS yielded weighted mean ages of 395 ± 3 Ma and 387 ± 8 Ma, respectively. These ages suggest a Middle Devonian emplacement. All Basalts bear the signature of Ocean-Island Basalt (OIB) and are characterized by alkaline compositions with high concentrations of Na 2 O + K 2 O (3.7–8.5 wt%) and TiO 2 (1.5–3.1 wt%); large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion; very weak or no Eu anomalies (Eu/Eu ∗ = 0.9–1.0); and no obvious Nb, Ta, or Ti negative anomalies. We propose that these Basaltic rocks were derived from mantle plume–related magmatism associated with the evolution of the Paleoasian Oceanic system. The enriched mantle source could have contained 2%–5% garnet and ∼3% spinel. The rocks also display strong geochemical similarities with the Xigaze seamount Basalts, which formed in intra-Oceanic settings. Compared to the Basalts, the gabbros display mid-Ocean-ridge-Basalt–type tholeiitic Basalt features, derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction-zone environment. These observations are supported by previous work, and they indicate Devonian mantle plume–related magmatism within the Paleoasian Ocean. However, as these rocks are mainly parts of accretionary complexes, whether the Karamay and Darbut ophiolitic melange formed in a single belt remains equivocal, and further work is required to resolve this issue. Thus, there was a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous before final amalgamation and docking to the northern Siberian block.