Adakitic rocks are intermediate-acid magmatic rocks characterized by enrichment in light rare-earth elements,depletion in heavy rare-earth elements,positive to negligible Eu and Sr anomalies,and high La/Yb and Sr/Y ra...Adakitic rocks are intermediate-acid magmatic rocks characterized by enrichment in light rare-earth elements,depletion in heavy rare-earth elements,positive to negligible Eu and Sr anomalies,and high La/Yb and Sr/Y ratios.Cenozoic adakitic rocks generated by partial melting of subducted oceanic crust(slab)under eclogite-facies conditions(i.e.,the original definition of“adakite”)occur mainly in Pacific Rim volcanic arcs(intra-oceanic,continental,and continental-margin island arcs),whereas those generated by partial melting of thickened lower crust occur mainly in Tethyan Tibetan collisional orogens.In volcanic arcs,adakitic melts derived from the melting of subducted oceanic crust metasomatize the mantle wedge to form a unique rock suite comprising adakite-adakite-type high-Mg andesite-Piip-type high-Mg andesite-Nb-rich basalt-boninite.This suite differs from the basalt-andesite-dacite-rhyolite suite formed from mantle wedge metasomatized by fluids derived from subducted oceanic crust.Previously published data indicate that partial melting of mafic rocks can generate adakitic magmas under pressure,temperature,and hydrous conditions of 1.2-3.0 GPa,800-1000℃,and 1.5-6.0 wt.%H_(2)O,respectively,leaving residual minerals of garnet and rutile with little or no plagioclase.Cenozoic Au and Cu deposits occur proximally to adakitic rocks,with host rocks of some deposits actually being adakitic rocks.Adakitic rocks thus have important implications for both deep-Earth dynamics and Cu-Au mineralization/exploration.Although studies of Cenozoic adakitic rocks have made many important advances,there remain weaknesses in some important areas such as their tectonic settings,petrogenesis,magma sources,melt-mantle interactions of pre-Cenozoic adakitic rocks,and their relationship with the onset of plate tectonics and crustal growth.Future research directions are likely to involve(1)the generation of adakitic magmas by experimental simulations of partial melting of different types of rock(including intermediate-acid rocks)and magma fractional crystallization at different temperatures and pressures,(2)the relationship between magma reservoir evolution and the formation of adakitic rocks,(3)the tectonic setting and petrogenesis of pre-Cenozoic adakitic rocks and related geodynamic processes,(4)interactions between slab melts and the mantle wedge,(5)the formation of Archean adakitic tonalite-trondhjemite-granodiorite and its link to the onset of plate tectonics and crustal growth,and(6)the relationship between the formation of adakitic rocks and metal mineralization in different tectonic settings.展开更多
Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floo...Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floor.These bathymetric highs may be subducted,and such processes are commonly referred to as ridge subduction.Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics,they also play an important role in the generation of arc magmatism,material recycling,the growth and evolution of continental crust,the deformation and modification of the overlying plates,and metallogenesis at convergent plate boundaries.Therefore,these events have attracted widespread attention.The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window,and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt(OIB)or a mid-oceanic ridge basalt(MORB)-type rock suite,and is closely associated with Au mineralization.Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct,to typically collide with arcs or continents or to induce flat subduction(low angle of less than 10°)due to the thickness of their underlying normal oceanic crust(>6–7 km)and high topography.However,the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic.On the eastern side of the Pacific Ocean,aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents,which may cause a magmatic gap.But slab melting can occur and adakites,or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing.Cu-Au mineralization is commonly associated with such flat subduction events.On the western side of the Pacific Ocean,however,aseismic ridges and oceanic plateaus are subducted at relatively high angles(>30°).These subduction processes can generate large scale eruptions of basalts,basaltic andesites and andesites,which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge.In addition,some inactive arc ridges are subducted beneath Southwest Japan,and these subduction processes are commonly associated with the production of basalts,high-Mg andesites and adakites and Au mineralization.Besides magmatism and Cu-Au mineralization,ridge subduction may also trigger subduction erosion in subduction zones.Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events,clarifying the associated geodynamic mechanisms,quantifying subduction zone material recycling,establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization,establishing criteria to recognize pre-Cenozoic ridge subduction,the onset of modernstyle plate tectonics and the growth mechanisms for Archean continental crust.展开更多
Whether arc magmatism occurs above oceanic subduction zones is the forefront of studies on convergent plate margins.The most important petrologic issue related to the evolution of arc systems is the origin of arc magm...Whether arc magmatism occurs above oceanic subduction zones is the forefront of studies on convergent plate margins.The most important petrologic issue related to the evolution of arc systems is the origin of arc magmatism,among which arc basalts are the most important one because they provide insights into mantle enrichment mechanism and crust-mantle interaction at oceanic subduction zones.Fluids or melts released either by dehydration or by melting of subducting oceanic slab infiltrate and metasomatize the overlying mantle wedge at varying depth,leading to the formation of source regions of arc basalts.Such processes make most of arc basalts commonly enriched in large ion lithosphile elements and light rare earth elements,but depleted in high-field strength elements and heavy rare earth elements.Small amounts of arc basalts are characterized by relatively high Nb contents or by Nb enrichment.Rare basalts with compositions similar to ocean island basalts or mid-ocean ridge basalt also occur in arc systems.For these peculiar rocks,it remains debated whether their source is affected by subduction-related components.During their ascent and before their eruption,arc basaltic magmas are subjected to crystal fractionation,mixing and crustal contamination.In addition to the contribution of subducting slab components to the mantle source of arc basalts,the materials above the subducting slab at forearc depths would have been transported either by drag or by subduction erosion into the subarc mantle and into the source of arc magmas.Heats and materials brought by corner flows also play important roles in the generation of arc basalts.Despite the important progresses made in recent studies of arc basalts,further efforts are needed to investigate subarc mantle metasomatism,material recycling,the formation of arc magma sources,geodynamic mechanism in generating arc basalts,and their implicationd s for the initiation of plate tectonics on Earth.展开更多
基金the National Natural Science Foundation of China(Grant Nos.41630208 and 91855215)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0702)+2 种基金the National Key R&D Program of China(Grant No.2016YFC0600407)the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(Grant No.XDA2007030402),the Key Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWDQC026)the Key Program of Guangzhou City(Grant No.201707020032).
文摘Adakitic rocks are intermediate-acid magmatic rocks characterized by enrichment in light rare-earth elements,depletion in heavy rare-earth elements,positive to negligible Eu and Sr anomalies,and high La/Yb and Sr/Y ratios.Cenozoic adakitic rocks generated by partial melting of subducted oceanic crust(slab)under eclogite-facies conditions(i.e.,the original definition of“adakite”)occur mainly in Pacific Rim volcanic arcs(intra-oceanic,continental,and continental-margin island arcs),whereas those generated by partial melting of thickened lower crust occur mainly in Tethyan Tibetan collisional orogens.In volcanic arcs,adakitic melts derived from the melting of subducted oceanic crust metasomatize the mantle wedge to form a unique rock suite comprising adakite-adakite-type high-Mg andesite-Piip-type high-Mg andesite-Nb-rich basalt-boninite.This suite differs from the basalt-andesite-dacite-rhyolite suite formed from mantle wedge metasomatized by fluids derived from subducted oceanic crust.Previously published data indicate that partial melting of mafic rocks can generate adakitic magmas under pressure,temperature,and hydrous conditions of 1.2-3.0 GPa,800-1000℃,and 1.5-6.0 wt.%H_(2)O,respectively,leaving residual minerals of garnet and rutile with little or no plagioclase.Cenozoic Au and Cu deposits occur proximally to adakitic rocks,with host rocks of some deposits actually being adakitic rocks.Adakitic rocks thus have important implications for both deep-Earth dynamics and Cu-Au mineralization/exploration.Although studies of Cenozoic adakitic rocks have made many important advances,there remain weaknesses in some important areas such as their tectonic settings,petrogenesis,magma sources,melt-mantle interactions of pre-Cenozoic adakitic rocks,and their relationship with the onset of plate tectonics and crustal growth.Future research directions are likely to involve(1)the generation of adakitic magmas by experimental simulations of partial melting of different types of rock(including intermediate-acid rocks)and magma fractional crystallization at different temperatures and pressures,(2)the relationship between magma reservoir evolution and the formation of adakitic rocks,(3)the tectonic setting and petrogenesis of pre-Cenozoic adakitic rocks and related geodynamic processes,(4)interactions between slab melts and the mantle wedge,(5)the formation of Archean adakitic tonalite-trondhjemite-granodiorite and its link to the onset of plate tectonics and crustal growth,and(6)the relationship between the formation of adakitic rocks and metal mineralization in different tectonic settings.
基金supported by the National Natural Science Foundation of China(Grant Nos.41630208 and 91855215)the National Key R&D Program of China(Grant No.2016YFC0600407)+3 种基金the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(Grant No.XDA2007030402)the Key Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWDQC026)the Key Program of Guangzhou City(Grant No.201707020032)No.IS-2873 from GIGCAS。
文摘Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floor.These bathymetric highs may be subducted,and such processes are commonly referred to as ridge subduction.Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics,they also play an important role in the generation of arc magmatism,material recycling,the growth and evolution of continental crust,the deformation and modification of the overlying plates,and metallogenesis at convergent plate boundaries.Therefore,these events have attracted widespread attention.The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window,and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt(OIB)or a mid-oceanic ridge basalt(MORB)-type rock suite,and is closely associated with Au mineralization.Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct,to typically collide with arcs or continents or to induce flat subduction(low angle of less than 10°)due to the thickness of their underlying normal oceanic crust(>6–7 km)and high topography.However,the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic.On the eastern side of the Pacific Ocean,aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents,which may cause a magmatic gap.But slab melting can occur and adakites,or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing.Cu-Au mineralization is commonly associated with such flat subduction events.On the western side of the Pacific Ocean,however,aseismic ridges and oceanic plateaus are subducted at relatively high angles(>30°).These subduction processes can generate large scale eruptions of basalts,basaltic andesites and andesites,which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge.In addition,some inactive arc ridges are subducted beneath Southwest Japan,and these subduction processes are commonly associated with the production of basalts,high-Mg andesites and adakites and Au mineralization.Besides magmatism and Cu-Au mineralization,ridge subduction may also trigger subduction erosion in subduction zones.Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events,clarifying the associated geodynamic mechanisms,quantifying subduction zone material recycling,establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization,establishing criteria to recognize pre-Cenozoic ridge subduction,the onset of modernstyle plate tectonics and the growth mechanisms for Archean continental crust.
基金State Ocean Bureau International Collaboration Program(Grant No.GASI-GEOGE-02)the National Natural Science Foundation of China(Grant Nos.91855215,41630208)CAS Strategy Program B(Grant No.XDB18000000).
文摘Whether arc magmatism occurs above oceanic subduction zones is the forefront of studies on convergent plate margins.The most important petrologic issue related to the evolution of arc systems is the origin of arc magmatism,among which arc basalts are the most important one because they provide insights into mantle enrichment mechanism and crust-mantle interaction at oceanic subduction zones.Fluids or melts released either by dehydration or by melting of subducting oceanic slab infiltrate and metasomatize the overlying mantle wedge at varying depth,leading to the formation of source regions of arc basalts.Such processes make most of arc basalts commonly enriched in large ion lithosphile elements and light rare earth elements,but depleted in high-field strength elements and heavy rare earth elements.Small amounts of arc basalts are characterized by relatively high Nb contents or by Nb enrichment.Rare basalts with compositions similar to ocean island basalts or mid-ocean ridge basalt also occur in arc systems.For these peculiar rocks,it remains debated whether their source is affected by subduction-related components.During their ascent and before their eruption,arc basaltic magmas are subjected to crystal fractionation,mixing and crustal contamination.In addition to the contribution of subducting slab components to the mantle source of arc basalts,the materials above the subducting slab at forearc depths would have been transported either by drag or by subduction erosion into the subarc mantle and into the source of arc magmas.Heats and materials brought by corner flows also play important roles in the generation of arc basalts.Despite the important progresses made in recent studies of arc basalts,further efforts are needed to investigate subarc mantle metasomatism,material recycling,the formation of arc magma sources,geodynamic mechanism in generating arc basalts,and their implicationd s for the initiation of plate tectonics on Earth.
