The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,rev...The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures.Being unusual nowadays,this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area.The tiny grains of 10 μm are forming in the microscopic voids in the rock.Also,large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170μm.The titanites of second type often coexist with chalcedony and barite.No carbonate minerals were found in the weathering profile.Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly,increased Al2 O3 content and low content of trace elements.Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase.The titanite precipitation is controlled by slow diffusion in poorly-aerated,highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2.However,the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite.We demonstrate a complex feedback between CO2 and soil carbonates.The rise in pCO2 triggers the precipitation of calcite in the weathering regolith,but the greenhouse effect increasing the temperature can cease carbonate deposition.Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.展开更多
The research is devoted to the multicomponent system CaTiSiO5-YFeSnO5. The synthesis of solid solutions Ca1-xYxTi1-xSnxSi1-xFexO5 (x = 0 - 1.0, Δx = 0.1) was conducted in low-temperature plasma of hydrogen-oxygen fla...The research is devoted to the multicomponent system CaTiSiO5-YFeSnO5. The synthesis of solid solutions Ca1-xYxTi1-xSnxSi1-xFexO5 (x = 0 - 1.0, Δx = 0.1) was conducted in low-temperature plasma of hydrogen-oxygen flame. It was found that ions Ca2+, Ti4+ and Si4+ in the molecule of titanit may be substituted with t ions Y3+, Fe3+ and Sn4+. In this case, the system produces two phases of variable composition with broad regions of homogeneity. There were defined the boundaries of formed phases, crystallographic and electrical parameters of the solid solutions. All solid solutions have a semiconductor conductivity type, whose value is linearly dependent on the temperature and com- position of the sample.展开更多
文摘The stability of titanite is sensitive to temperature and partial pressure of CO2.The finding of authigenic titanite grains in weathering regolith formed on Parana basalts,Brazil,under tropical climatic conditions,reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures.Being unusual nowadays,this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area.The tiny grains of 10 μm are forming in the microscopic voids in the rock.Also,large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170μm.The titanites of second type often coexist with chalcedony and barite.No carbonate minerals were found in the weathering profile.Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly,increased Al2 O3 content and low content of trace elements.Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase.The titanite precipitation is controlled by slow diffusion in poorly-aerated,highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2.However,the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite.We demonstrate a complex feedback between CO2 and soil carbonates.The rise in pCO2 triggers the precipitation of calcite in the weathering regolith,but the greenhouse effect increasing the temperature can cease carbonate deposition.Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.
文摘The research is devoted to the multicomponent system CaTiSiO5-YFeSnO5. The synthesis of solid solutions Ca1-xYxTi1-xSnxSi1-xFexO5 (x = 0 - 1.0, Δx = 0.1) was conducted in low-temperature plasma of hydrogen-oxygen flame. It was found that ions Ca2+, Ti4+ and Si4+ in the molecule of titanit may be substituted with t ions Y3+, Fe3+ and Sn4+. In this case, the system produces two phases of variable composition with broad regions of homogeneity. There were defined the boundaries of formed phases, crystallographic and electrical parameters of the solid solutions. All solid solutions have a semiconductor conductivity type, whose value is linearly dependent on the temperature and com- position of the sample.
