New isotopic,geochemical and geochronological data justify the widespread occurrence of middle Paleocene to early Eocene(60–53 Ma)post-subduction felsic magmatism across the entire Sikhote-Alin territory(southeastern...New isotopic,geochemical and geochronological data justify the widespread occurrence of middle Paleocene to early Eocene(60–53 Ma)post-subduction felsic magmatism across the entire Sikhote-Alin territory(southeastern Russia),conform with previous observations in Northeast China,the southern Korean Peninsula,and the Inner Zone of Japan.This igneous activity in East Asia coincided with the reactivation(after tectonic quiescence between~93–60Ma)of left-lateral strike-slip displacements along the Tan-Lu and Central Sikhote-Alin faults and with the post-60 Ma cessation of subduction/accretion recorded in the Shimanto belt of SW Japan.The Sikhote-Alin post-subduction igneous A-type rocks present diverse mineralogical and geochemical features that suggest interactions of the subducting plate with anhydrous mantle upwelling through slab tears in the continental margin.The middle Paleocene–early Eocene magmatismis not related to subduction but is synchronous with strikeslip tectonics and the termination of accretionary prism development,suggesting a shift in tectonic regime from oceanic plate subduction at a convergent margin to parallel sliding and initiation of a transformcontinental margin.These new observations are inconsistent with the current tectonic model of 60–50 Ma Izanagi-Pacific ridge subduction beneath East Asian continental margin.展开更多
Global geodynamic reconstruction models of the Pacific margin of Asia refer to materials collected throughout Japan,Korea and northeastern China,but they lack data on southern Sikhote-Alin.Therewith,the Sikhote-Alin o...Global geodynamic reconstruction models of the Pacific margin of Asia refer to materials collected throughout Japan,Korea and northeastern China,but they lack data on southern Sikhote-Alin.Therewith,the Sikhote-Alin orogenic belt(NE Asia)constituted a single eastern margin of the paleo-Asian continent with the abovementioned territories in the Paleocene.New isotopic,geochemical,and geochronological data show that Paleocene igneous activity(-61-55 Ma)is widely developed in south-ern Sikhote-Alin.Bulk rock compositions of the igneous rocks of this period yield ferroan,peraluminous,calc-alkaline to alkaline affinities,highly abundant LILE and HFSE(with pronounced Ba,Sr,Eu,and Ti neg-ative anomalies)and depleted HREE.The initial melts,displaying Zr+Y+Ce+Nb>350 ppm and 10,000×Ga/Al>2.6,derived from an OIB-like mantle source crystallised under fairly reducing conditions(below FMQ buffer),and yield high temperature of zircon saturation(>850℃),indicating typical A-type granite and related volcanic rock features.It is logical to associate variations in A-type rock geochemical composition with an enrichment of the upper part of the magma chamber with fluid-mobile components involving a reditribution of major and trace elements through fluid-magmatic differentiation.Strong depletion in Ca,Mg,Ba,Sr,Eu in the A-type rocks is caused by an outflow of these elements by an oxi-dizing,initially reduced,acidic fluid beyond the zone of magma generation.Whole-rock Sr-Nd isotope data argue for the generation of the A-type rocks by melting of dominantly a juvenile mantle component with a subordinate component of the ancient crust.Isotope variations of igneous rocks of the reference area:^(87)Sr/^(86)Sr(t)(0.7024-0.7118),ε_(Nd)(t)(-0.9 to-5.1)and T_(DM2)(934-1277 Ma),result from the mixing of the OIB-like mantle source with selective melts or from the metapelite contamination of the Samarka terrane accretionary prism and of the Zhuravlevka-Amur turbidite basin,later followed by fluid-magmatic differentiation that led to the formation of anatectic or hybrid melts.We further suggest that the origin of the A-type granites and related volcanic rocks is the result of the oblique interaction of ocea-nic and continental plates.This interaction accounts for the simultaneous formation of tears in the slab,enabling sub-slab asthenospheric upwelling,and strike-slip fault-related extensional structures in the overriding continental plate.展开更多
基金by the Russian Foundation for Basic Research and the National Natural Science Foundation of China for scientific project No.19-55-53008by the partial financial support of the Russian Foundation for Basic Research(No.19-05-00100).
文摘New isotopic,geochemical and geochronological data justify the widespread occurrence of middle Paleocene to early Eocene(60–53 Ma)post-subduction felsic magmatism across the entire Sikhote-Alin territory(southeastern Russia),conform with previous observations in Northeast China,the southern Korean Peninsula,and the Inner Zone of Japan.This igneous activity in East Asia coincided with the reactivation(after tectonic quiescence between~93–60Ma)of left-lateral strike-slip displacements along the Tan-Lu and Central Sikhote-Alin faults and with the post-60 Ma cessation of subduction/accretion recorded in the Shimanto belt of SW Japan.The Sikhote-Alin post-subduction igneous A-type rocks present diverse mineralogical and geochemical features that suggest interactions of the subducting plate with anhydrous mantle upwelling through slab tears in the continental margin.The middle Paleocene–early Eocene magmatismis not related to subduction but is synchronous with strikeslip tectonics and the termination of accretionary prism development,suggesting a shift in tectonic regime from oceanic plate subduction at a convergent margin to parallel sliding and initiation of a transformcontinental margin.These new observations are inconsistent with the current tectonic model of 60–50 Ma Izanagi-Pacific ridge subduction beneath East Asian continental margin.
基金This work was financially supported by the Russian Science Foundation(No.22-27-00223)。
文摘Global geodynamic reconstruction models of the Pacific margin of Asia refer to materials collected throughout Japan,Korea and northeastern China,but they lack data on southern Sikhote-Alin.Therewith,the Sikhote-Alin orogenic belt(NE Asia)constituted a single eastern margin of the paleo-Asian continent with the abovementioned territories in the Paleocene.New isotopic,geochemical,and geochronological data show that Paleocene igneous activity(-61-55 Ma)is widely developed in south-ern Sikhote-Alin.Bulk rock compositions of the igneous rocks of this period yield ferroan,peraluminous,calc-alkaline to alkaline affinities,highly abundant LILE and HFSE(with pronounced Ba,Sr,Eu,and Ti neg-ative anomalies)and depleted HREE.The initial melts,displaying Zr+Y+Ce+Nb>350 ppm and 10,000×Ga/Al>2.6,derived from an OIB-like mantle source crystallised under fairly reducing conditions(below FMQ buffer),and yield high temperature of zircon saturation(>850℃),indicating typical A-type granite and related volcanic rock features.It is logical to associate variations in A-type rock geochemical composition with an enrichment of the upper part of the magma chamber with fluid-mobile components involving a reditribution of major and trace elements through fluid-magmatic differentiation.Strong depletion in Ca,Mg,Ba,Sr,Eu in the A-type rocks is caused by an outflow of these elements by an oxi-dizing,initially reduced,acidic fluid beyond the zone of magma generation.Whole-rock Sr-Nd isotope data argue for the generation of the A-type rocks by melting of dominantly a juvenile mantle component with a subordinate component of the ancient crust.Isotope variations of igneous rocks of the reference area:^(87)Sr/^(86)Sr(t)(0.7024-0.7118),ε_(Nd)(t)(-0.9 to-5.1)and T_(DM2)(934-1277 Ma),result from the mixing of the OIB-like mantle source with selective melts or from the metapelite contamination of the Samarka terrane accretionary prism and of the Zhuravlevka-Amur turbidite basin,later followed by fluid-magmatic differentiation that led to the formation of anatectic or hybrid melts.We further suggest that the origin of the A-type granites and related volcanic rocks is the result of the oblique interaction of ocea-nic and continental plates.This interaction accounts for the simultaneous formation of tears in the slab,enabling sub-slab asthenospheric upwelling,and strike-slip fault-related extensional structures in the overriding continental plate.
