As a minor phase, kyanite has been repeatedly shown to have experienced ultrahigh pressure （UHP） metamorphism together with its host eclogites. Thus, it could play some role in trans- porting water into the deep ear...As a minor phase, kyanite has been repeatedly shown to have experienced ultrahigh pressure （UHP） metamorphism together with its host eclogites. Thus, it could play some role in trans- porting water into the deep earth. Here we present a detailed investigation of water concentrations of kyanite, and for reference, of garnet and omphacite from four Maobei eclogites in the Sulu orogenic belt, eastern China. Fourier transform infrared （FTIR） measurements show that kyanites, garnets, and omphacites all have distinct hydroxyl absorption bands due to OH groups bound in their crystal struc- ture. The FTIR profile analyses on ten grains from different samples reveal a homogeneous distribution of water across kyanite, suggesting insignificant water loss during exhumation. The calculated water concentrations in kyanite （21 wt ppm-41 wt ppm） are comparable to those reported previously for kyanite from various geological occurrences when using the most recent calibration. They are however much lower compared with those in garnet （46 wt ppm-83 wt ppm） and omphacite （302 wt ppm-548 wt ppm） from the Maobei eclogites. This implies that kyanite is not a major water carrier in eclogites con- sidering its low volume fraction and contributes negligibly to transport water into the deep mantle ac- companying subducted oceanic crust until its possible transformation to AISiO3OH.展开更多
Intracrystalline distortions(like undulose extinction,dislocations,and subgrain boundaries)in olivine from naturally-deformed peridotites are generally taken as signs of dislocation creep.However,similar features in o...Intracrystalline distortions(like undulose extinction,dislocations,and subgrain boundaries)in olivine from naturally-deformed peridotites are generally taken as signs of dislocation creep.However,similar features in olivine phenocrysts that have been found in basaltic magmas are still not well understood.In particular,whether subgrain boundaries in olivine phenocrysts arise from plastic deformation or grain growth is still debated(in the latter case,they are essentially grain boundaries but not subgrain boundaries.Therefore,we used hereinafter subgrain-boundary-like structures instead of subgrain boundaries to name this kind of intracrystalline distortion).Here we carried out a detailed study on dislocations and subgrainboundary-like(SG-like)structures in olivine phenocrysts from two Hawaiian basaltic lavas by means of petrographic microscopy,scanning electron microscopy,and transmission electron microscopy(TEM).Abundant and complex dislocation substructures(free dislocations,dislocation walls,and dislocation tangles)were observed in the decorated olivine grains,similar to those in olivine from peridotite xenoliths entrained by the Hawaiian basalts.The measured average dislocation density is(2.9±1.3)×1011 m-2,and is three to five orders of magnitude higher than that in laboratory-synthesized,undeformed olivine.TEM observations on samples cut across the SG-like structures by FIB(focused ion beam)demonstrated that this kind of structures is made of an array of dislocations.These observations clearly indicate that these structures are real subgrain boundaries rather than grain boundaries.These facts suggest that the observed high dislocation densities and subgrain boundaries cannot result from crystal crystallization/growth,but can be formed by plastic deformation.These deformation features do not prove that the olivine phenocrysts(and implicitly mantle xenoliths)were deformed after their capture by the basaltic magmas,but can be ascribed to a former deformation event in a dunitic cumulate,which was formed by magmatic fractionation,then plastically deformed,and finally disaggregated and captured by the basaltic magma that brought them to the surface.展开更多
It is proposed in the subduction channel model that the plate interface interaction is a basic mechanism for the mass and energy exchange between Earth’s surface and interior.The significant difference in composition...It is proposed in the subduction channel model that the plate interface interaction is a basic mechanism for the mass and energy exchange between Earth’s surface and interior.The significant difference in composition and nature between continental lithosphere and oceanic lithosphere inevitably leads to variations in deep physical and chemical processes as well as crust-mantle interaction products in these two settings.Many studies of experimental petrology have provided constraints on the potential partial melting and crust-mantle interaction in oceanic subduction channels for silicate and carbonate rocks.The partial melts of mafic and felsic compositions are adakitic or non-adakitic granitic melts depending on melting pressure or depth.A trivial amount of CO2 can lower significantly the melting temperature of peridotites and lead to pronounced enrichment of incompatible elements in carbonate melt.The silica saturated or unsaturated melts can react with mantle-wedge peridotites in subduction channels to generate complex products.However,the existing experiments are mostly dedicated to island arc settings above oceanic subduction zones rather than dehydration melting above continental subduction zones.It is crucial to conduct high pressure and high temperature experiments to investigate all possible reactions between peridotites and crustal materials and their derivatives under the conditions responsible for the slab-mantle interface in continental subduction channels.Experimental results,combined with natural observations,are possible to elucidate the processes of metamorphic dehydration,partial melting and mantle metasomatism in continental subduction channels.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 41372224 and 41590623)
文摘As a minor phase, kyanite has been repeatedly shown to have experienced ultrahigh pressure （UHP） metamorphism together with its host eclogites. Thus, it could play some role in trans- porting water into the deep earth. Here we present a detailed investigation of water concentrations of kyanite, and for reference, of garnet and omphacite from four Maobei eclogites in the Sulu orogenic belt, eastern China. Fourier transform infrared （FTIR） measurements show that kyanites, garnets, and omphacites all have distinct hydroxyl absorption bands due to OH groups bound in their crystal struc- ture. The FTIR profile analyses on ten grains from different samples reveal a homogeneous distribution of water across kyanite, suggesting insignificant water loss during exhumation. The calculated water concentrations in kyanite （21 wt ppm-41 wt ppm） are comparable to those reported previously for kyanite from various geological occurrences when using the most recent calibration. They are however much lower compared with those in garnet （46 wt ppm-83 wt ppm） and omphacite （302 wt ppm-548 wt ppm） from the Maobei eclogites. This implies that kyanite is not a major water carrier in eclogites con- sidering its low volume fraction and contributes negligibly to transport water into the deep mantle ac- companying subducted oceanic crust until its possible transformation to AISiO3OH.
基金the National Natural Science Foundation of China(Nos.41590623,41972231,41872230)。
文摘Intracrystalline distortions(like undulose extinction,dislocations,and subgrain boundaries)in olivine from naturally-deformed peridotites are generally taken as signs of dislocation creep.However,similar features in olivine phenocrysts that have been found in basaltic magmas are still not well understood.In particular,whether subgrain boundaries in olivine phenocrysts arise from plastic deformation or grain growth is still debated(in the latter case,they are essentially grain boundaries but not subgrain boundaries.Therefore,we used hereinafter subgrain-boundary-like structures instead of subgrain boundaries to name this kind of intracrystalline distortion).Here we carried out a detailed study on dislocations and subgrainboundary-like(SG-like)structures in olivine phenocrysts from two Hawaiian basaltic lavas by means of petrographic microscopy,scanning electron microscopy,and transmission electron microscopy(TEM).Abundant and complex dislocation substructures(free dislocations,dislocation walls,and dislocation tangles)were observed in the decorated olivine grains,similar to those in olivine from peridotite xenoliths entrained by the Hawaiian basalts.The measured average dislocation density is(2.9±1.3)×1011 m-2,and is three to five orders of magnitude higher than that in laboratory-synthesized,undeformed olivine.TEM observations on samples cut across the SG-like structures by FIB(focused ion beam)demonstrated that this kind of structures is made of an array of dislocations.These observations clearly indicate that these structures are real subgrain boundaries rather than grain boundaries.These facts suggest that the observed high dislocation densities and subgrain boundaries cannot result from crystal crystallization/growth,but can be formed by plastic deformation.These deformation features do not prove that the olivine phenocrysts(and implicitly mantle xenoliths)were deformed after their capture by the basaltic magmas,but can be ascribed to a former deformation event in a dunitic cumulate,which was formed by magmatic fractionation,then plastically deformed,and finally disaggregated and captured by the basaltic magma that brought them to the surface.
基金supported by the National Basic Research Program of China(Grant No.2015CB856101)the National Natural Science Foundation of China(Grant Nos.41172070,41425012)the Ministry of Education of China and the State Administration of Foreign Expert Affairs of China(Grant No.B07039)
文摘It is proposed in the subduction channel model that the plate interface interaction is a basic mechanism for the mass and energy exchange between Earth’s surface and interior.The significant difference in composition and nature between continental lithosphere and oceanic lithosphere inevitably leads to variations in deep physical and chemical processes as well as crust-mantle interaction products in these two settings.Many studies of experimental petrology have provided constraints on the potential partial melting and crust-mantle interaction in oceanic subduction channels for silicate and carbonate rocks.The partial melts of mafic and felsic compositions are adakitic or non-adakitic granitic melts depending on melting pressure or depth.A trivial amount of CO2 can lower significantly the melting temperature of peridotites and lead to pronounced enrichment of incompatible elements in carbonate melt.The silica saturated or unsaturated melts can react with mantle-wedge peridotites in subduction channels to generate complex products.However,the existing experiments are mostly dedicated to island arc settings above oceanic subduction zones rather than dehydration melting above continental subduction zones.It is crucial to conduct high pressure and high temperature experiments to investigate all possible reactions between peridotites and crustal materials and their derivatives under the conditions responsible for the slab-mantle interface in continental subduction channels.Experimental results,combined with natural observations,are possible to elucidate the processes of metamorphic dehydration,partial melting and mantle metasomatism in continental subduction channels.
