The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.B...The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.Based on the deep seismic tomography using long-period natural earthquake data,in this study,the deep structure and material circulation of the curved subduction system in Southeast Asia was studied,and the dynamic processes since 100 million years ago was reconstructed.It is pointed out that challenges still exist in the precise reconstruction of deep mantle structures of the study area,the influence of multi-stage subduction on deep material exchange and shallow magma activity,as well as the spatiotemporal evolution and coupling mechanism of multi-plate convergence.Future work should focus on high-resolution land-sea joint 3-D seismic tomography imaging of the curved subduction system in the Southeast Asia,combined with geochemical analysis and geodynamic modelling works.展开更多
The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less...The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less researches have addressed these deposits,and the genesis of the Zhaxikang deposit is still controversial.Based on field investigation,petrographic,microthermometric,Laser Raman Microprobe(LRM) and SEM/EDS analyses of fluid,melt-fluid,melt and solid inclusions in quartz and beryl from pegmatite,this paper documents the characteristics and the evolution of primary magmatic fluid which was genetically related to greisenization,pegmatitization,and silification in the area.The results show that the primary magmatic fluids were derived from unmixing between melt and fluid and underwent a phase separation process soon after the exsolution.The primary magmatic fluids are of low salinity,high temperature,and can be approximated by the H_2O-NaCl-CO_2 system.The presence of Mn-Fe carbonate in melt-fluid inclusions and a Zn-bearing mineral(gahnite) trapped in beryl and in inclusions from pegmatite indicates high Mn,Fe,and Zn concentrations in the parent magma and magmatic fluids,and implies a genetic link between pegmatite and Pb-Zn-Sb mineralization.High B and F concentrations in the parent magma largely lower the solidus of the magma and lead to late fluid exsolution,thus the primary magmatic fluids related to pegmatite have much lower temperature than those in most porphyry systems.Boiling of the primary magmatic fluids leads to high-salinity and high-temperature fluids which have high capacity to transport Pb,Zn and Sb.The decrease in temperature and mixing with fluids from other sources may have caused the precipitation of Pb-Zn-Sn(Au) minerals in the distal fault systems surrounding the causative intrusion.展开更多
The kinematics and dynamics of plate tectonics are frontal subjects in geosciences and the strong earthquake occurred along the plate boundary result directly from plate movement. By analyzing Ibaraki earthquake seque...The kinematics and dynamics of plate tectonics are frontal subjects in geosciences and the strong earthquake occurred along the plate boundary result directly from plate movement. By analyzing Ibaraki earthquake sequence, it has been found that the focal fault plane shows a special image of grading expansion along the direction of strike and adjustment along the dip direction respectively. With the consideration of strike, dip and slip directions of focal mechanism, we have confirmed that Ibaraki earthquake belongs to a thrust fault earthquake occurred under the Japan Trench. The cause of the earthquake sequence is discussed in the paper. The study on the temporal-spatial distribution of the earthquake sequence with a time-scale between the year-scale spatial geodetic data and the second-scale moment tensor of the strong earthquake has indicated the dynamic process of Pacific Plate subduction under the Eurasia Plate. According to the average slip distance of earthquake and the velocity of plate movement, it is predicted that a strong earthquake might occur in recent years.展开更多
The Jiama deposit is a large copper deposit in Tibet. Mineralization occurs in three different host rocks: skarn, hornfels and porphyry. A detailed fluid inclusion study was conducted for veins in the different host ...The Jiama deposit is a large copper deposit in Tibet. Mineralization occurs in three different host rocks: skarn, hornfels and porphyry. A detailed fluid inclusion study was conducted for veins in the different host rocks to investigate the relationship between fluid evolution and ore-forming processes. Based on examination of cores from 36 drill holes, three types of veins (A, B and D) were identified in the porphyries, four types (I, II, III and IV) in the skarn, and three (a, b and c) in the hornfels. The crosscutting relationships of the veins and that of the host rocks suggest two hydrothermal stages, one early and one late stage. Fluid inclusions indicate that the Jiama hydrothermal fluid system underwent at least two episodes of fluid boiling. The first boiling event occurred during the early hydrothermal stage, as recorded by fluid inclusions hosted in type A veins in the porphyries, type a veins in the hornfels, and wollastonite in the skarns. This fluid boiling event was associated with relatively weak mineralization. The second boiling event occurred in the late hydrothermal stage, as determined from fluid inclusions hosted in type B and D veins in the porphyries, type I to IV veins in the skarns, and type b and c veins in the hornfels. This late boiling event, together with mixing with meteoric water, was responsible for more than 90% of the metal accumulation in the deposit. The first boiling only occurred in the central part of the deposit and the second boiling event took place across an entire interlayered structural zone between hornfels and marble. A spatial zoning of ore-elements is evident, and appears to be related to different migration pathways and precipitation temperatures of Cu, Mo, Pb, Zn, Au and Ag.展开更多
The skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and ...The skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and layer-like bodies in permeable carbonate rocks of the Middle-Upper Carboniferous Huanglong and Chuanshan Formations which are underlain by impermeable shale or siliceous rocks of the Upper Devonian Wutong Formation. The authors study the dynamics of ore-forming processes of the ore deposits with the dynamic model of coupled transport and reaction, and the following results are obtained: The salinity gradient and flow rate of the ore-forming fluids can both promote the mixing and reaction of juvenile water and formation water, and the permeable strata are favourable sites for the intense transport-reaction of mixing and the formation of deposits. (2) As isothermal transport-reaction took place along the bedding of strata, the moving transport-reaction front formed at the contact between the ore-forming fluids and the rocks advanced slowly along the permeable strata, and then stratiform skarn and ore bodies concordant with the strata were formed. (3) The gradient transport-reaction taking place across the isotherms in the cross-bedding direction caused the mineralogical composition to alter gradually from magnesian skarn to sulphide ore bodies.展开更多
The article presents the results of study of composition, structure and properties of three genetic types of serpentinites from Ural: developed by chromite-bearing ultrabasic rocks, by metamorphic zones of carbonate r...The article presents the results of study of composition, structure and properties of three genetic types of serpentinites from Ural: developed by chromite-bearing ultrabasic rocks, by metamorphic zones of carbonate rocks and within the zone of weathering of ultrabasic rocks. The samples were selected from deposits, located along the Main Ural Fault - the Paleozoic subduction zone (named GUR). Peculiarities of microstructure, chemical composition and properties of serpentinites formed in different geological conditions were investigated and their comparative study was held. Three groups of serpentinites with oriented and non-oriented structure, which formed by different protholites, were devided: mantle, lithosphere and crust.展开更多
Southeastern China covers an extensive area from the lowerreaches of the Yangtze Riverto the southeast coastof China mainland.One of its main geological features isthe extensiveJura- Cretaceous (Yanshanian) magmatism ...Southeastern China covers an extensive area from the lowerreaches of the Yangtze Riverto the southeast coastof China mainland.One of its main geological features isthe extensiveJura- Cretaceous (Yanshanian) magmatism and related metallogenesis. Recently,some re-searchers advocate the mantle plume model as an explanation,but all of their evidences artoo ambiguous.Meanwhile,the seaward convex shape of the SE China coastline,which isdominantly composed of Jura- Cretaceous batholiths and volcanic strata,implies thatit was aconvergent margin between SE China continent and the palaeo- Pacific plate during the lateMesozoic era.Fora betterunderstanding on the relation among magmatism,tectonic regimeand dynamics,the spatial- temporal pattern of late Mesozoic (180 - 90 Ma) igneous rocks isconstructed by nearly2 0 0 isotope age valuesfrom literatures.Among these age values,mostwere obtained by Rb- Sr isochron method,and others from zircon U- Pb or40 Ar- 3展开更多
Subduction zones involve many complex geological processes, including the release of slabderived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle inte...Subduction zones involve many complex geological processes, including the release of slabderived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle interactions. Lithium(Li) isotopes(~6Li and ~7Li) have relative mass difference up to 16%, being the largest among metal elements. Thus, Li isotopes have advantage to interprete trace various geological processes. Most importantly, during crust/mantle interactions in deep subduction zones, surface materials and mantle rocks usually have distinct Li isotopic compositions. Li isotopes can be potential tracer for subduction processes, from the onset of subduction to the release of Li from subducted slabs and interaction with mantle wedge, as well as the fate of Li in slab-derived fluids and residual slabs. Moreover, the Li isotopic composition of subducting output materials can provide useful information for understanding global Li circulation. With developments in measurement and expansion of Li isotopic database, Li isotopic geochemistry will provide more inference and be a powerful tracer for understanding subduction-related processes. This work retrospected the application of Li isotopes in tracing successive subduction processes, and made some prospects for further studies of Li isotopes.展开更多
A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented fo...A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories: (i) Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and (ii) morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma (convection, turbulence, degassing, etc.). Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.展开更多
On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geolog...On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo- chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.展开更多
Since the Early Cenozoic,the Philippine Sea Plate(PSP)has undergone a complex tectonic evolution.During this period the Parece Vela Basin(PVB)was formed by seafloor spreading in the back-arc region of the proto-Izu-Bo...Since the Early Cenozoic,the Philippine Sea Plate(PSP)has undergone a complex tectonic evolution.During this period the Parece Vela Basin(PVB)was formed by seafloor spreading in the back-arc region of the proto-Izu-Bonin-Mariana(IBM)arc.However,until now,studies of the geological,geophysical,and tectonic evolution of the PVB have been rare.In this study,we obtained in situ trace element and major element compositions of minerals in basalts collected from two sites in the southern part of the PVB.The results reveal that the basalts from site CJ09-63 were likely formed via~10%partial melting of spinel-garnet lherzolite,while the basalts from site CJ09-64 were likely formed via 15%–25%partial melting of garnet lherzolite.The order of mineral crystallization for the basalts from site CJ09-64 was olivine,spinel,clinopyroxene,and plagioclase,while the plagioclase in the basalts from site CJ09-63 crystallized earlier than the clinopyroxene.Using a plagioclase-liquid hygrometer and an olivine-liquid oxybarometer,we determined that the basalts in this study have high H2O contents and oxygen fugacities,suggesting that the magma source of the Parece Vela basalts was affected by subduction components,which is consistent with the trace element composition of whole rock.展开更多
The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and develops on the continental crust.The Okinawa Trough is a natural laboratory for the study of basin ...The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and develops on the continental crust.The Okinawa Trough is a natural laboratory for the study of basin evolution,magmatism,and crustmantle processes in the early stage of back-arc spreading.Melt inclusions are small droplets of magma that are captured during the mineral crystallization process and can record the geochemical composition changes during magma evolution.In this study,the geochemical compositions of melt inclusions in host plagioclases of two volcanic rock samples at Station nos.9-1 and 9-2 from the southern Okinawa Trough are systematically analyzed.Based on previous studies,the origin and evolution of magma and the introduction of subducting materials in the study area are discussed.Results show that melt inclusions are characterized by the relative enrichment of large-ion lithophile elements,depletion of high-field-strength elements,and slight enrichment of rare earth elements.Indeed,the subduction of the Philippine Sea Plate introduced sediment-derived melts and fluids into the magma source area of the southern Okinawa Trough.Subsequently,4%to 5%partial melting of the hydrated mantle produces basaltic magma.The melt inclusions of andesite and dacite investigated in this study were formed by fractional crystallization of basaltic magma.Finally,the crystallization of plagioclase,pyroxene,and magnetite occurred during the late stage of magma evolution.The temperature-pressure data show that the melt inclusions in plagioclase have two capture periods:one is at temperatures above 1250℃and the other is at temperatures between 1180℃and 1200℃.The capture pressure of the inclusions at temperatures between 1180℃and 1200℃is between 5.6 kPa and 6.1 kPa,corresponding to the depth of 15–17 km below the seafloor.The geochemical characteristics of major and trace elements in inclusions show that the samples from two stations(i.e.,9-1 and 9-2)have similar or identical magma source areas.However,the crystallization differentiation reflected by inclusions in sample 9-1 is more obvious than that in sample 9-2.The inclusions were captured during magma evolution and were not contaminated by crustal materials.展开更多
Most metallic minerals in ore deposits are sulfides. When a sulfide mineral coexists with rock-forming minerals, its solubility is distinctly different from itself alone. The change in dissolution character of a miner...Most metallic minerals in ore deposits are sulfides. When a sulfide mineral coexists with rock-forming minerals, its solubility is distinctly different from itself alone. The change in dissolution character of a mineral with coexisting rock-forming minerals leads to particular geochemical be-havior. The concept of solubility of a metallic mineral with coexisting rock-forming minerals and its theory and model of calculation are put forward. Taking Tianmashan Cu-Au ore deposit of sulfide minerals in Tongling district as an example, solubilities of some metallic minerals with other coex-isting minerals, such as pyrite or chalcopyrite with quartz (representing sandstone) or calcite (rep-resenting limestone), are calculated. The results show the mechanism of ore-forming processes. As the ore-forming fluid flows through sandstone, it dissolves pyrite in the sandstone at first, then transports the iron and sulfur to the interface between sandstone and limestone and eventually precipitates them on the interface.展开更多
基金Support by the National Natural Science Foundation of China(No.92258303)the Project of Donghai Laboratory(No.DH-2022ZY0005)。
文摘The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.Based on the deep seismic tomography using long-period natural earthquake data,in this study,the deep structure and material circulation of the curved subduction system in Southeast Asia was studied,and the dynamic processes since 100 million years ago was reconstructed.It is pointed out that challenges still exist in the precise reconstruction of deep mantle structures of the study area,the influence of multi-stage subduction on deep material exchange and shallow magma activity,as well as the spatiotemporal evolution and coupling mechanism of multi-plate convergence.Future work should focus on high-resolution land-sea joint 3-D seismic tomography imaging of the curved subduction system in the Southeast Asia,combined with geochemical analysis and geodynamic modelling works.
基金financially supported by the State Basic Research Plan(973 project)(No.2011CB403100)IGCP/SIDA-600 project
文摘The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less researches have addressed these deposits,and the genesis of the Zhaxikang deposit is still controversial.Based on field investigation,petrographic,microthermometric,Laser Raman Microprobe(LRM) and SEM/EDS analyses of fluid,melt-fluid,melt and solid inclusions in quartz and beryl from pegmatite,this paper documents the characteristics and the evolution of primary magmatic fluid which was genetically related to greisenization,pegmatitization,and silification in the area.The results show that the primary magmatic fluids were derived from unmixing between melt and fluid and underwent a phase separation process soon after the exsolution.The primary magmatic fluids are of low salinity,high temperature,and can be approximated by the H_2O-NaCl-CO_2 system.The presence of Mn-Fe carbonate in melt-fluid inclusions and a Zn-bearing mineral(gahnite) trapped in beryl and in inclusions from pegmatite indicates high Mn,Fe,and Zn concentrations in the parent magma and magmatic fluids,and implies a genetic link between pegmatite and Pb-Zn-Sb mineralization.High B and F concentrations in the parent magma largely lower the solidus of the magma and lead to late fluid exsolution,thus the primary magmatic fluids related to pegmatite have much lower temperature than those in most porphyry systems.Boiling of the primary magmatic fluids leads to high-salinity and high-temperature fluids which have high capacity to transport Pb,Zn and Sb.The decrease in temperature and mixing with fluids from other sources may have caused the precipitation of Pb-Zn-Sn(Au) minerals in the distal fault systems surrounding the causative intrusion.
文摘The kinematics and dynamics of plate tectonics are frontal subjects in geosciences and the strong earthquake occurred along the plate boundary result directly from plate movement. By analyzing Ibaraki earthquake sequence, it has been found that the focal fault plane shows a special image of grading expansion along the direction of strike and adjustment along the dip direction respectively. With the consideration of strike, dip and slip directions of focal mechanism, we have confirmed that Ibaraki earthquake belongs to a thrust fault earthquake occurred under the Japan Trench. The cause of the earthquake sequence is discussed in the paper. The study on the temporal-spatial distribution of the earthquake sequence with a time-scale between the year-scale spatial geodetic data and the second-scale moment tensor of the strong earthquake has indicated the dynamic process of Pacific Plate subduction under the Eurasia Plate. According to the average slip distance of earthquake and the velocity of plate movement, it is predicted that a strong earthquake might occur in recent years.
基金funded by the third subject of National Natural Science Foundation of China(41302060)Geological Survey Project(12120114001304,121201004000150012)
文摘The Jiama deposit is a large copper deposit in Tibet. Mineralization occurs in three different host rocks: skarn, hornfels and porphyry. A detailed fluid inclusion study was conducted for veins in the different host rocks to investigate the relationship between fluid evolution and ore-forming processes. Based on examination of cores from 36 drill holes, three types of veins (A, B and D) were identified in the porphyries, four types (I, II, III and IV) in the skarn, and three (a, b and c) in the hornfels. The crosscutting relationships of the veins and that of the host rocks suggest two hydrothermal stages, one early and one late stage. Fluid inclusions indicate that the Jiama hydrothermal fluid system underwent at least two episodes of fluid boiling. The first boiling event occurred during the early hydrothermal stage, as recorded by fluid inclusions hosted in type A veins in the porphyries, type a veins in the hornfels, and wollastonite in the skarns. This fluid boiling event was associated with relatively weak mineralization. The second boiling event occurred in the late hydrothermal stage, as determined from fluid inclusions hosted in type B and D veins in the porphyries, type I to IV veins in the skarns, and type b and c veins in the hornfels. This late boiling event, together with mixing with meteoric water, was responsible for more than 90% of the metal accumulation in the deposit. The first boiling only occurred in the central part of the deposit and the second boiling event took place across an entire interlayered structural zone between hornfels and marble. A spatial zoning of ore-elements is evident, and appears to be related to different migration pathways and precipitation temperatures of Cu, Mo, Pb, Zn, Au and Ag.
基金MGMR Eighth Five- Year Plan Basic Geology Research Foundation Grant 8502216China National Natural Science Foundation Grant 49173169
文摘The skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and layer-like bodies in permeable carbonate rocks of the Middle-Upper Carboniferous Huanglong and Chuanshan Formations which are underlain by impermeable shale or siliceous rocks of the Upper Devonian Wutong Formation. The authors study the dynamics of ore-forming processes of the ore deposits with the dynamic model of coupled transport and reaction, and the following results are obtained: The salinity gradient and flow rate of the ore-forming fluids can both promote the mixing and reaction of juvenile water and formation water, and the permeable strata are favourable sites for the intense transport-reaction of mixing and the formation of deposits. (2) As isothermal transport-reaction took place along the bedding of strata, the moving transport-reaction front formed at the contact between the ore-forming fluids and the rocks advanced slowly along the permeable strata, and then stratiform skarn and ore bodies concordant with the strata were formed. (3) The gradient transport-reaction taking place across the isotherms in the cross-bedding direction caused the mineralogical composition to alter gradually from magnesian skarn to sulphide ore bodies.
文摘The article presents the results of study of composition, structure and properties of three genetic types of serpentinites from Ural: developed by chromite-bearing ultrabasic rocks, by metamorphic zones of carbonate rocks and within the zone of weathering of ultrabasic rocks. The samples were selected from deposits, located along the Main Ural Fault - the Paleozoic subduction zone (named GUR). Peculiarities of microstructure, chemical composition and properties of serpentinites formed in different geological conditions were investigated and their comparative study was held. Three groups of serpentinites with oriented and non-oriented structure, which formed by different protholites, were devided: mantle, lithosphere and crust.
基金the NN SFC(Grant No. 49733110 ),the Min-istry of L and and Resources of China (Project No. 2 0 0 0 10 10 2 0 6 ,2 0 0 0 10 10 2 0 2 ) ,and theostdoctoral Science Foundation of China
文摘Southeastern China covers an extensive area from the lowerreaches of the Yangtze Riverto the southeast coastof China mainland.One of its main geological features isthe extensiveJura- Cretaceous (Yanshanian) magmatism and related metallogenesis. Recently,some re-searchers advocate the mantle plume model as an explanation,but all of their evidences artoo ambiguous.Meanwhile,the seaward convex shape of the SE China coastline,which isdominantly composed of Jura- Cretaceous batholiths and volcanic strata,implies thatit was aconvergent margin between SE China continent and the palaeo- Pacific plate during the lateMesozoic era.Fora betterunderstanding on the relation among magmatism,tectonic regimeand dynamics,the spatial- temporal pattern of late Mesozoic (180 - 90 Ma) igneous rocks isconstructed by nearly2 0 0 isotope age valuesfrom literatures.Among these age values,mostwere obtained by Rb- Sr isochron method,and others from zircon U- Pb or40 Ar- 3
基金granted by the National Natural Science Foundation of China(NSFC 41273037,41673031,41473033)
文摘Subduction zones involve many complex geological processes, including the release of slabderived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle interactions. Lithium(Li) isotopes(~6Li and ~7Li) have relative mass difference up to 16%, being the largest among metal elements. Thus, Li isotopes have advantage to interprete trace various geological processes. Most importantly, during crust/mantle interactions in deep subduction zones, surface materials and mantle rocks usually have distinct Li isotopic compositions. Li isotopes can be potential tracer for subduction processes, from the onset of subduction to the release of Li from subducted slabs and interaction with mantle wedge, as well as the fate of Li in slab-derived fluids and residual slabs. Moreover, the Li isotopic composition of subducting output materials can provide useful information for understanding global Li circulation. With developments in measurement and expansion of Li isotopic database, Li isotopic geochemistry will provide more inference and be a powerful tracer for understanding subduction-related processes. This work retrospected the application of Li isotopes in tracing successive subduction processes, and made some prospects for further studies of Li isotopes.
文摘A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories: (i) Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and (ii) morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma (convection, turbulence, degassing, etc.). Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KZCX1-YW-15)the National Natural Science Foundation of China (Grant No. 90814008)parts of experimental work is supported from the Opening Funding of State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences (GPMR0506)
文摘On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo- chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.
基金supported by Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2022QNLM050201-3)the National Natural Science Foundations of China(Grants Nos.41230960,41322036,41776070)+1 种基金Aoshan Talents Program of Pilot National Laboratory for Marine Science and Technology(Qingdao)(QNLM2015ASTPES16)Taishan Scholarship from Shandong Province.
文摘Since the Early Cenozoic,the Philippine Sea Plate(PSP)has undergone a complex tectonic evolution.During this period the Parece Vela Basin(PVB)was formed by seafloor spreading in the back-arc region of the proto-Izu-Bonin-Mariana(IBM)arc.However,until now,studies of the geological,geophysical,and tectonic evolution of the PVB have been rare.In this study,we obtained in situ trace element and major element compositions of minerals in basalts collected from two sites in the southern part of the PVB.The results reveal that the basalts from site CJ09-63 were likely formed via~10%partial melting of spinel-garnet lherzolite,while the basalts from site CJ09-64 were likely formed via 15%–25%partial melting of garnet lherzolite.The order of mineral crystallization for the basalts from site CJ09-64 was olivine,spinel,clinopyroxene,and plagioclase,while the plagioclase in the basalts from site CJ09-63 crystallized earlier than the clinopyroxene.Using a plagioclase-liquid hygrometer and an olivine-liquid oxybarometer,we determined that the basalts in this study have high H2O contents and oxygen fugacities,suggesting that the magma source of the Parece Vela basalts was affected by subduction components,which is consistent with the trace element composition of whole rock.
基金the Na-tional Program on Key Basic Research of China(973 Program)(No.2013CB429702).
文摘The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and develops on the continental crust.The Okinawa Trough is a natural laboratory for the study of basin evolution,magmatism,and crustmantle processes in the early stage of back-arc spreading.Melt inclusions are small droplets of magma that are captured during the mineral crystallization process and can record the geochemical composition changes during magma evolution.In this study,the geochemical compositions of melt inclusions in host plagioclases of two volcanic rock samples at Station nos.9-1 and 9-2 from the southern Okinawa Trough are systematically analyzed.Based on previous studies,the origin and evolution of magma and the introduction of subducting materials in the study area are discussed.Results show that melt inclusions are characterized by the relative enrichment of large-ion lithophile elements,depletion of high-field-strength elements,and slight enrichment of rare earth elements.Indeed,the subduction of the Philippine Sea Plate introduced sediment-derived melts and fluids into the magma source area of the southern Okinawa Trough.Subsequently,4%to 5%partial melting of the hydrated mantle produces basaltic magma.The melt inclusions of andesite and dacite investigated in this study were formed by fractional crystallization of basaltic magma.Finally,the crystallization of plagioclase,pyroxene,and magnetite occurred during the late stage of magma evolution.The temperature-pressure data show that the melt inclusions in plagioclase have two capture periods:one is at temperatures above 1250℃and the other is at temperatures between 1180℃and 1200℃.The capture pressure of the inclusions at temperatures between 1180℃and 1200℃is between 5.6 kPa and 6.1 kPa,corresponding to the depth of 15–17 km below the seafloor.The geochemical characteristics of major and trace elements in inclusions show that the samples from two stations(i.e.,9-1 and 9-2)have similar or identical magma source areas.However,the crystallization differentiation reflected by inclusions in sample 9-1 is more obvious than that in sample 9-2.The inclusions were captured during magma evolution and were not contaminated by crustal materials.
基金NFSC (Grant No. 4933120) and State Key Project (Grant No. 95-Y-39).
文摘Most metallic minerals in ore deposits are sulfides. When a sulfide mineral coexists with rock-forming minerals, its solubility is distinctly different from itself alone. The change in dissolution character of a mineral with coexisting rock-forming minerals leads to particular geochemical be-havior. The concept of solubility of a metallic mineral with coexisting rock-forming minerals and its theory and model of calculation are put forward. Taking Tianmashan Cu-Au ore deposit of sulfide minerals in Tongling district as an example, solubilities of some metallic minerals with other coex-isting minerals, such as pyrite or chalcopyrite with quartz (representing sandstone) or calcite (rep-resenting limestone), are calculated. The results show the mechanism of ore-forming processes. As the ore-forming fluid flows through sandstone, it dissolves pyrite in the sandstone at first, then transports the iron and sulfur to the interface between sandstone and limestone and eventually precipitates them on the interface.