The partitioning behavior of trace elements is of key importance for understanding the geochemical process and material cycle mechanism in subduction zones.This paper focuses on the advances and prospects on the studi...The partitioning behavior of trace elements is of key importance for understanding the geochemical process and material cycle mechanism in subduction zones.This paper focuses on the advances and prospects on the studies of trace element partitioning in subduction zones from the following four aspects.(1)The properties of fluids derived from subducting slabs and their ability in element transport.How slab-derived solute-rich fluids and supercritical fluids are formed and what the roles and key control factors of these fluids are in transferring of elements(especially the high field strength elements)from slab to wedge are discussed.We point out that the detailed investigations of supercritical fluids may provide a new perspective for the element migration mechanism,material cycle process,arc magma genesis and so on.(2)The behavior of transition elements during mantle wedge melting.The behavior of the first row transition elements(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn)in the mantle partial melting process is compatible or incompatible,depending on residual mineral assemblage and physicochemical conditions.The partitioning behavior of the elements such as Sc,Ti,Co,Ni and Zn whose valence states do not change in the melting process mainly depends on the residual mineral assemblage and temperature,whereas the partitioning behavior of the multivalent elements such as V and Fe is also the function of oxygen fugacity(fO_(2))in addition to mineral assemblage and temperature.Therefore,the partitioning behavior of transition elements has important applications in tracing lithologic inhomogeneity and fO_(2)of the mantle wedges.(3)The specificity of element partitioning behavior during arc magma evolution.Garnet has Dy/Yb partitioning behavior different from amphibole,and rutile has Nb/Ta partitioning behavior different from amphibole.Dy/Yb and Nb/Ta partitioning differences for these minerals enable to distinguish the specific evolution process of arc magmas.The Dy/Yb and Nb/Ta generally decrease with the increase of SiO_(2)in arc magmas,indicating that amphibole fractionation should be the most important during arc magma differentiation.(4)The behavior of sulfur and chalcophile elements and porphyry metallogeny.In subduction zones,the behavior of chalcophile elements such as Cu and Au is controlled by sulfide and fluid.Therefore,the stability of sulfide,the time at which the fluid exsolves from the melt relative to sulfide saturation,the fluid/sulfide mass ratio and fluid/melt Cu and Au partition coefficients in intermediate-felsic magma-H_(2)O systems are especially important in understanding Cu and Au enrichment in magma-hydrothermal processes.Intermediate-felsic magmas mainly originate from the differentiation of arc magmas at lower crustal reservoirs,and thus the fluid exsolution from the lower crustal reservoirs and the fluid/melt and fluid/sulfide partition coefficients of Cu and Au should be the keys to understanding quantitatively how Cu and Au are migrated from the deep crust to the shallow site of mineralization.展开更多
The solubility of Au in silicate melts and fluids governs the enrichment and migration of Au during the formation of magmatic-hydrothermal Au deposits.Large Au deposits require vast amounts of Au to migrate from the u...The solubility of Au in silicate melts and fluids governs the enrichment and migration of Au during the formation of magmatic-hydrothermal Au deposits.Large Au deposits require vast amounts of Au to migrate from the upper mantle-lower crust to the shallow crust,and high Au solubility in magma and hydrothermal fluid facilitates the formation of Au-rich magma and fluid in the crust and mantle source and efficient transport.This paper reviews recent high-pressure and high-temperature experimental studies on Au species in magmas and hydrothermal fluids,the partitioning behavior of Au between silicate melts and fluids,and the effects of temperature,pressure,oxygen fugacity,sulfur fugacity,silicate melt composition,and volatiles(H2O,CO2,chlorine,and sulfur)on the solubility of Au in magma.We show that the solubility of Au in magma is largely controlled by the volatiles in the magma:the higher the content of reduced sulfur(S2-and HS-)in the magma,the higher the solubility of Au.Under high-temperature,high-pressure,H2O-rich,and intermediate oxygen fugacity conditions,magma can dissolve more reduced sulfur species,thus enhancing the ability of the magma to transport Au.If the ore-forming elements of the Au deposits in the North China Craton originate from mantle-derived magmas and fluids,we can conclude,in terms of massive Au migration,that these deep Au-rich magmas might have been generated under H2 O-rich and moderately oxidized conditions(S2-coexists with S6+).The big mantle wedge beneath East Asia was metasomatized by melts and fluids from the dehydration of the Early Cretaceous paleo-Pacific stagnant slab,which not only caused thinning of the North China Craton,but also created physicochemical conditions favorable for massive Au migration.展开更多
基金the National Key Research and Development Program of China(Grant No.2018YFA0702704)the National Natural Science Foundation of China(Grant Nos.41573053&41921003)the Key Research Project of Frontier Science of the Chinese Academy of Sciences(Grant No.QYZDJ-SSW-DQC012).
文摘The partitioning behavior of trace elements is of key importance for understanding the geochemical process and material cycle mechanism in subduction zones.This paper focuses on the advances and prospects on the studies of trace element partitioning in subduction zones from the following four aspects.(1)The properties of fluids derived from subducting slabs and their ability in element transport.How slab-derived solute-rich fluids and supercritical fluids are formed and what the roles and key control factors of these fluids are in transferring of elements(especially the high field strength elements)from slab to wedge are discussed.We point out that the detailed investigations of supercritical fluids may provide a new perspective for the element migration mechanism,material cycle process,arc magma genesis and so on.(2)The behavior of transition elements during mantle wedge melting.The behavior of the first row transition elements(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn)in the mantle partial melting process is compatible or incompatible,depending on residual mineral assemblage and physicochemical conditions.The partitioning behavior of the elements such as Sc,Ti,Co,Ni and Zn whose valence states do not change in the melting process mainly depends on the residual mineral assemblage and temperature,whereas the partitioning behavior of the multivalent elements such as V and Fe is also the function of oxygen fugacity(fO_(2))in addition to mineral assemblage and temperature.Therefore,the partitioning behavior of transition elements has important applications in tracing lithologic inhomogeneity and fO_(2)of the mantle wedges.(3)The specificity of element partitioning behavior during arc magma evolution.Garnet has Dy/Yb partitioning behavior different from amphibole,and rutile has Nb/Ta partitioning behavior different from amphibole.Dy/Yb and Nb/Ta partitioning differences for these minerals enable to distinguish the specific evolution process of arc magmas.The Dy/Yb and Nb/Ta generally decrease with the increase of SiO_(2)in arc magmas,indicating that amphibole fractionation should be the most important during arc magma differentiation.(4)The behavior of sulfur and chalcophile elements and porphyry metallogeny.In subduction zones,the behavior of chalcophile elements such as Cu and Au is controlled by sulfide and fluid.Therefore,the stability of sulfide,the time at which the fluid exsolves from the melt relative to sulfide saturation,the fluid/sulfide mass ratio and fluid/melt Cu and Au partition coefficients in intermediate-felsic magma-H_(2)O systems are especially important in understanding Cu and Au enrichment in magma-hydrothermal processes.Intermediate-felsic magmas mainly originate from the differentiation of arc magmas at lower crustal reservoirs,and thus the fluid exsolution from the lower crustal reservoirs and the fluid/melt and fluid/sulfide partition coefficients of Cu and Au should be the keys to understanding quantitatively how Cu and Au are migrated from the deep crust to the shallow site of mineralization.
基金Project of China(Grant No.2016YFC0600104),the National Natural Science Foundation of China(Grant No.41573053)the Youth Innovation Promotion Association CAS(Grant No.2019344)。
文摘The solubility of Au in silicate melts and fluids governs the enrichment and migration of Au during the formation of magmatic-hydrothermal Au deposits.Large Au deposits require vast amounts of Au to migrate from the upper mantle-lower crust to the shallow crust,and high Au solubility in magma and hydrothermal fluid facilitates the formation of Au-rich magma and fluid in the crust and mantle source and efficient transport.This paper reviews recent high-pressure and high-temperature experimental studies on Au species in magmas and hydrothermal fluids,the partitioning behavior of Au between silicate melts and fluids,and the effects of temperature,pressure,oxygen fugacity,sulfur fugacity,silicate melt composition,and volatiles(H2O,CO2,chlorine,and sulfur)on the solubility of Au in magma.We show that the solubility of Au in magma is largely controlled by the volatiles in the magma:the higher the content of reduced sulfur(S2-and HS-)in the magma,the higher the solubility of Au.Under high-temperature,high-pressure,H2O-rich,and intermediate oxygen fugacity conditions,magma can dissolve more reduced sulfur species,thus enhancing the ability of the magma to transport Au.If the ore-forming elements of the Au deposits in the North China Craton originate from mantle-derived magmas and fluids,we can conclude,in terms of massive Au migration,that these deep Au-rich magmas might have been generated under H2 O-rich and moderately oxidized conditions(S2-coexists with S6+).The big mantle wedge beneath East Asia was metasomatized by melts and fluids from the dehydration of the Early Cretaceous paleo-Pacific stagnant slab,which not only caused thinning of the North China Craton,but also created physicochemical conditions favorable for massive Au migration.
