The Nansha Block(NB)is one of the blocks separated from the southern margin of the South China Craton(SCC)by the western Pacific subduction,which contains rich information of geodynamic and tectonic transformation.To ...The Nansha Block(NB)is one of the blocks separated from the southern margin of the South China Craton(SCC)by the western Pacific subduction,which contains rich information of geodynamic and tectonic transformation.To reveal the essence of western Paleo-Pacific subduction during the Triassic period,Well NK-1 in this block was selected for petrographic study,and published research data from other cooperative teams were compared.A double-cycle pattern of basic to neutral magmatic volcanism was established,and 36 lithological rhythmic layers and representative cryptoexplosive breccia facies and welded tuff bands were identified.Combined with a reanalysis of published geochronological data,geochemical elements,and isotope geochemistry,we found that the rock assemblages could be divided into an intermediate-acid dacite(DA)series(SiO_(2)>65%)and basaltic(BA)series(Co<40μg/g),which was formed during the early Late Triassic((218.6±3.2)–(217.9±3.5)Ma).BA exhibits obvious calc-alkaline island-arc magmatic properties:(^(87)Sr/^(86)Sr)_i ratio ranging 0.70377–0.71118(average:0.70645),^(147)Sm/^(144)Nd ratio ranging 0.119–0.193(average:0.168),and chondrite-normalized rare earth element(REE)curves being flat,while DA exhibits remarkable characteristics of subducted island-arc andesitic magma:(^(87)Sr/^(86)Sr)_i ratio(0.70939–0.71129;average:0.71035),εNd(t)value(-6.2–-4.8;average:-5.6)andε_(Hf)(t)value(-2.9–-1.7,average:-2.2)show obvious crust-mantle mixing characteristics.BA and DA reveal typical characteristics of island-arc magma systems and typeⅡenriched mantle(EM-Ⅱ)magma.BA magma was likely resulted from the process whereby the continental crust frontal accretionary wedge was driven by the Paleo-Pacific slab subduction into the deep and began to melt,resulting in a large amount of melt(fluid)joined the asthenosphere on the side of the continental margin.In contrast,DA magma was likely resulted from the process whereby the plate front was forced to bend with increasing subduction distance,which triggered the upwelling of the asthenosphere near the continent and subsequently led to the partial melting of the lithospheric mantle and lower crust due to continuous underplating.The lithospheric thinning environment in the study area at the end of Triassic created suitable conditions for the separation between the NB and SCC,which provided an opportunity for the formation of the early intracontinental rift during the later expansion of the South China Sea(SCS).展开更多
The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from t...The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.展开更多
The study presents the results of U-Pb dating of zircons and whole-rock geochemical analyses of syenogranite in Angeer Yinwula area, China, with the aim of determining its formation time, petrogenesis and regional set...The study presents the results of U-Pb dating of zircons and whole-rock geochemical analyses of syenogranite in Angeer Yinwula area, China, with the aim of determining its formation time, petrogenesis and regional setting. Zircon U-Pb data obtained by LA-ICP-MS indicate that the syenogranite formed in the Early Cretaceous(136.1±0.9 Ma). Geochemically, the rock is characterized by high SiO_2(76.63%--77.58%) and Na_2O+K_2O(8.00%--8.32%), low MgO(0.02%--0.04%) and TFe_2O_3(0.51%--0.84%), and is enriched in LREEs and LILEs, depleted in HREEs and HFSEs. It belongs to high-K calc-alkaline, metaluminous-weakly peraluminous, exhibiting an affinity to I-type granite. All these characteristics implied that the syenogranite in this region derived from crust-mantle mixed source. Overall, the regional geology, geochronology and geochemical features suggest that the formation of the syenogranite was related to the subduction of the Paleo-Pacific Ocean.展开更多
基金the National Natural Science Foundation of China(No.42206073)the National Key R&D Program of China(No.2021YFC3100600)+5 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515110782)the China Post-doctoral Science Foundation(No.2021M703296)the Open Fund of the Key Laboratory of Tectonic Controlled Mineralization and Oil Reservoir of the Ministry of Natural Resources(No.gzck202101)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2019ZD0206)the K.C.Wong Education Foundation(No.GJTD-2018-13)。
文摘The Nansha Block(NB)is one of the blocks separated from the southern margin of the South China Craton(SCC)by the western Pacific subduction,which contains rich information of geodynamic and tectonic transformation.To reveal the essence of western Paleo-Pacific subduction during the Triassic period,Well NK-1 in this block was selected for petrographic study,and published research data from other cooperative teams were compared.A double-cycle pattern of basic to neutral magmatic volcanism was established,and 36 lithological rhythmic layers and representative cryptoexplosive breccia facies and welded tuff bands were identified.Combined with a reanalysis of published geochronological data,geochemical elements,and isotope geochemistry,we found that the rock assemblages could be divided into an intermediate-acid dacite(DA)series(SiO_(2)>65%)and basaltic(BA)series(Co<40μg/g),which was formed during the early Late Triassic((218.6±3.2)–(217.9±3.5)Ma).BA exhibits obvious calc-alkaline island-arc magmatic properties:(^(87)Sr/^(86)Sr)_i ratio ranging 0.70377–0.71118(average:0.70645),^(147)Sm/^(144)Nd ratio ranging 0.119–0.193(average:0.168),and chondrite-normalized rare earth element(REE)curves being flat,while DA exhibits remarkable characteristics of subducted island-arc andesitic magma:(^(87)Sr/^(86)Sr)_i ratio(0.70939–0.71129;average:0.71035),εNd(t)value(-6.2–-4.8;average:-5.6)andε_(Hf)(t)value(-2.9–-1.7,average:-2.2)show obvious crust-mantle mixing characteristics.BA and DA reveal typical characteristics of island-arc magma systems and typeⅡenriched mantle(EM-Ⅱ)magma.BA magma was likely resulted from the process whereby the continental crust frontal accretionary wedge was driven by the Paleo-Pacific slab subduction into the deep and began to melt,resulting in a large amount of melt(fluid)joined the asthenosphere on the side of the continental margin.In contrast,DA magma was likely resulted from the process whereby the plate front was forced to bend with increasing subduction distance,which triggered the upwelling of the asthenosphere near the continent and subsequently led to the partial melting of the lithospheric mantle and lower crust due to continuous underplating.The lithospheric thinning environment in the study area at the end of Triassic created suitable conditions for the separation between the NB and SCC,which provided an opportunity for the formation of the early intracontinental rift during the later expansion of the South China Sea(SCS).
基金supported by the National Natural Science Foundation of China(Grant No.41688103)the International Cooperation Program of the Chinese Academy of Sciences(Grant No.GJHZ1776)。
文摘The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.
基金Supported by Joint Project of Geological Survey of Jilin University and Shandong Gold Group Co.,Ltd(No.MJDK2016005)
文摘The study presents the results of U-Pb dating of zircons and whole-rock geochemical analyses of syenogranite in Angeer Yinwula area, China, with the aim of determining its formation time, petrogenesis and regional setting. Zircon U-Pb data obtained by LA-ICP-MS indicate that the syenogranite formed in the Early Cretaceous(136.1±0.9 Ma). Geochemically, the rock is characterized by high SiO_2(76.63%--77.58%) and Na_2O+K_2O(8.00%--8.32%), low MgO(0.02%--0.04%) and TFe_2O_3(0.51%--0.84%), and is enriched in LREEs and LILEs, depleted in HREEs and HFSEs. It belongs to high-K calc-alkaline, metaluminous-weakly peraluminous, exhibiting an affinity to I-type granite. All these characteristics implied that the syenogranite in this region derived from crust-mantle mixed source. Overall, the regional geology, geochronology and geochemical features suggest that the formation of the syenogranite was related to the subduction of the Paleo-Pacific Ocean.
