Hydrous minerals within the subducting oceanic slab are important hosts for water.Clarification of the stability field of hydrous minerals helps to understand transport and distribution of water from the surface to th...Hydrous minerals within the subducting oceanic slab are important hosts for water.Clarification of the stability field of hydrous minerals helps to understand transport and distribution of water from the surface to the Earth’s interior.We investigated the stability of brucite,a prototype of hydrous minerals,by means of electrical conductivity measurements in both open and closed systems at 3 GPa and temperatures up to 1300 K.Dramatic increase of conductivity in association with characteristic impedance spectra suggests that partial dehydration of single-crystal brucite in the open system with a low water fugacity occurs at 950 K,which is about 300 K lower than those previously defined by phase equilibrium experiments in the closed system.By contrast,brucite completely dehydrates at 1300 K in the closed system,consistent with previous studies.Partial dehydration may generate a highly defective structure but does not lead to the breakdown of brucite to periclase and water immediately.Water activity plays a key role in the stability of hydrous minerals.Low water activity(a H_(2)O)caused by the high wetting behavior of the subducted oceanic slab at the transition zone depth may cause the partial dehydration of the dense hydrous magnesium silicates(DHMSs),which significantly reduces the temperature stability of DHMS(this mechanism has been confirmed by previous study on super hydrous phase B).As a result,the transition zone may serve as a‘dead zone’for DHMSs,and most water will be stored in wadsleyite and ringwoodite in the transition zone.展开更多
We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purp...We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purpose. In-situ X-ray diffraction measurements at high pressures and composition analysis of recovered samples using an analytical transmission electron microscope showed that anorthosite consists of garnet,CaAl_4Si_2O_(11)-rich phase(CAS phase), and SiO_2 phases in the upper mantle and the mantle transition zone.Under lower mantle conditions, these minerals transform to the assemblage of bridgmanite, Ca-perovskite,corundum, stishovite, and calcium ferrite-type aluminous phase through the decomposition of garnet and CAS phase at around 700 km depth. Anorthosite has a higher density than PREM and pyrolite in the upper mantle, while its density becomes comparable or lower under lower mantle conditions. Our results suggest that ancient anorthosite crust subducted down to the deep mantle was likely to have accumulated at660-720 km in depth without coming back to the Earth's surface. Some portions of the anorthosite crust might have circulated continuously in the Earth's deep interior by mantle convection and potentially subducted to the bottom of the lower mantle when carried within layers of dense basaltic rocks.展开更多
An accurate simulation of air temperature at local scales is crucial for the vast majority of weather and climate applications.In this work,a hybrid statistical–dynamical downscaling method and a high-resolution dyna...An accurate simulation of air temperature at local scales is crucial for the vast majority of weather and climate applications.In this work,a hybrid statistical–dynamical downscaling method and a high-resolution dynamical-only downscaling method are applied to daily mean,minimum and maximum air temperatures to investigate the quality of localscale estimates produced by downscaling.These two downscaling approaches are evaluated using station observation data obtained from the Finnish Meteorological Institute over a near-coastal region of western Finland.The dynamical downscaling is performed with the Weather Research and Forecasting(WRF)model,and the statistical downscaling method implemented is the Cumulative Distribution Function-transform(CDF-t).The CDF-t is trained using 20 years of WRF-downscaled Climate Forecast System Reanalysis data over the region at a 3-km spatial resolution for the central month of each season.The performance of the two methods is assessed qualitatively,by inspection of quantile-quantile plots,and quantitatively,through the Cramer-von Mises,mean absolute error,and root-mean-square error diagnostics.The hybrid approach is found to provide significantly more skillful forecasts of the observed daily mean and maximum air temperatures than those of the dynamical-only downscaling(for all seasons).The hybrid method proves to be less computationally expensive,and also to give more skillful temperature forecasts(at least for the Finnish near-coastal region).展开更多
Volatiles in the mantle are crucial for Earth’s geodynamic and geochemical evolution.Understanding the deep recycling of volatiles is key for grasping mantle chemical heterogeneity,plate tectonics,and long-term plane...Volatiles in the mantle are crucial for Earth’s geodynamic and geochemical evolution.Understanding the deep recycling of volatiles is key for grasping mantle chemical heterogeneity,plate tectonics,and long-term planetary evolution.While subduction transfers abundant volatile elements from the Earth’s surface into the mantle,the fate of hydrous portions within subducted slabs during intensive dehydration processes remains uncertain.Boron isotopes,only efficiently fractionating near the Earth’s surface,are valuable for tracing volatile recycling signals.In this study,we document a notably large variation inδ^(11)B values(−14.3‰to+8.2‰)in Cenozoic basalts from the South China Block.These basalts,associated with a high-velocity zone beneath East China,are suggested to originate from the mantle transition zone.While the majority exhibitδ^(11)B values(−10‰to−5‰)resembling the normal mantle,their enriched Sr-Nd-Pb isotope compositions and fluid-mobile elements imply hydrous components in their source,including altered oceanic crust and sediments.The normalδ^(11)B values are attributed to the dehydration processes.Remarkably highδ^(11)B values in the basalts indicate the presence of subducted serpentinites in their mantle source.A small subset of samples with lowδ^(11)B values and radiogenic isotope enrichments suggests a contribution from recycled detrital sediments,though retaining minimal volatile elements after extensive dehydration.These findings provide compelling evidence that serpentinites within subducted slabs predominantly maintain their hydrous nature during dehydration processes in subduction zones.They may transport a considerable amount of water into deep mantle reservoirs,such as the mantle transition zone.展开更多
基金supported by CAS“Light of West China”program(Y9CR026 to X.G.)the National Natural Science Foundation of China(442072051)supported by the Ministry of Education,Culture,Sports,Science,and Technology of the Japanese Government,Grant Numbers,15H05827 and 17H01155 to T.Y.
文摘Hydrous minerals within the subducting oceanic slab are important hosts for water.Clarification of the stability field of hydrous minerals helps to understand transport and distribution of water from the surface to the Earth’s interior.We investigated the stability of brucite,a prototype of hydrous minerals,by means of electrical conductivity measurements in both open and closed systems at 3 GPa and temperatures up to 1300 K.Dramatic increase of conductivity in association with characteristic impedance spectra suggests that partial dehydration of single-crystal brucite in the open system with a low water fugacity occurs at 950 K,which is about 300 K lower than those previously defined by phase equilibrium experiments in the closed system.By contrast,brucite completely dehydrates at 1300 K in the closed system,consistent with previous studies.Partial dehydration may generate a highly defective structure but does not lead to the breakdown of brucite to periclase and water immediately.Water activity plays a key role in the stability of hydrous minerals.Low water activity(a H_(2)O)caused by the high wetting behavior of the subducted oceanic slab at the transition zone depth may cause the partial dehydration of the dense hydrous magnesium silicates(DHMSs),which significantly reduces the temperature stability of DHMS(this mechanism has been confirmed by previous study on super hydrous phase B).As a result,the transition zone may serve as a‘dead zone’for DHMSs,and most water will be stored in wadsleyite and ringwoodite in the transition zone.
基金partially supported by Grant-in-Aid for Scientific Research from the Japanese government to S.M.(JP26106002)M.N,(JP15H05469)+1 种基金S.G.(JP26287105)and T.I.(JP25220712)the Ministry of Education and Science of the Russian Federation to S.M.(14.Y26.31.0018)
文摘We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purpose. In-situ X-ray diffraction measurements at high pressures and composition analysis of recovered samples using an analytical transmission electron microscope showed that anorthosite consists of garnet,CaAl_4Si_2O_(11)-rich phase(CAS phase), and SiO_2 phases in the upper mantle and the mantle transition zone.Under lower mantle conditions, these minerals transform to the assemblage of bridgmanite, Ca-perovskite,corundum, stishovite, and calcium ferrite-type aluminous phase through the decomposition of garnet and CAS phase at around 700 km depth. Anorthosite has a higher density than PREM and pyrolite in the upper mantle, while its density becomes comparable or lower under lower mantle conditions. Our results suggest that ancient anorthosite crust subducted down to the deep mantle was likely to have accumulated at660-720 km in depth without coming back to the Earth's surface. Some portions of the anorthosite crust might have circulated continuously in the Earth's deep interior by mantle convection and potentially subducted to the bottom of the lower mantle when carried within layers of dense basaltic rocks.
基金Botnia-Atlantica, an EU-programme financing cross border cooperation projects in Sweden, Finland and Norway, for their support of this work through the WindCoE project
文摘An accurate simulation of air temperature at local scales is crucial for the vast majority of weather and climate applications.In this work,a hybrid statistical–dynamical downscaling method and a high-resolution dynamical-only downscaling method are applied to daily mean,minimum and maximum air temperatures to investigate the quality of localscale estimates produced by downscaling.These two downscaling approaches are evaluated using station observation data obtained from the Finnish Meteorological Institute over a near-coastal region of western Finland.The dynamical downscaling is performed with the Weather Research and Forecasting(WRF)model,and the statistical downscaling method implemented is the Cumulative Distribution Function-transform(CDF-t).The CDF-t is trained using 20 years of WRF-downscaled Climate Forecast System Reanalysis data over the region at a 3-km spatial resolution for the central month of each season.The performance of the two methods is assessed qualitatively,by inspection of quantile-quantile plots,and quantitatively,through the Cramer-von Mises,mean absolute error,and root-mean-square error diagnostics.The hybrid approach is found to provide significantly more skillful forecasts of the observed daily mean and maximum air temperatures than those of the dynamical-only downscaling(for all seasons).The hybrid method proves to be less computationally expensive,and also to give more skillful temperature forecasts(at least for the Finnish near-coastal region).
基金supported by the National Natural Science Foundation of China(Grant Nos.42173015 and 41702057)China Postdoctoral Science Foundation(2017M612530)the MEXT(Ministry of Education,Culture,Sports,Science and Technology).
文摘Volatiles in the mantle are crucial for Earth’s geodynamic and geochemical evolution.Understanding the deep recycling of volatiles is key for grasping mantle chemical heterogeneity,plate tectonics,and long-term planetary evolution.While subduction transfers abundant volatile elements from the Earth’s surface into the mantle,the fate of hydrous portions within subducted slabs during intensive dehydration processes remains uncertain.Boron isotopes,only efficiently fractionating near the Earth’s surface,are valuable for tracing volatile recycling signals.In this study,we document a notably large variation inδ^(11)B values(−14.3‰to+8.2‰)in Cenozoic basalts from the South China Block.These basalts,associated with a high-velocity zone beneath East China,are suggested to originate from the mantle transition zone.While the majority exhibitδ^(11)B values(−10‰to−5‰)resembling the normal mantle,their enriched Sr-Nd-Pb isotope compositions and fluid-mobile elements imply hydrous components in their source,including altered oceanic crust and sediments.The normalδ^(11)B values are attributed to the dehydration processes.Remarkably highδ^(11)B values in the basalts indicate the presence of subducted serpentinites in their mantle source.A small subset of samples with lowδ^(11)B values and radiogenic isotope enrichments suggests a contribution from recycled detrital sediments,though retaining minimal volatile elements after extensive dehydration.These findings provide compelling evidence that serpentinites within subducted slabs predominantly maintain their hydrous nature during dehydration processes in subduction zones.They may transport a considerable amount of water into deep mantle reservoirs,such as the mantle transition zone.
