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.
