Oxygen isotope fractionation between coexisting minerals in slowly cooled rocks conveys information about their cooling history. By using the fast grain boundary(FGB) model to simulate closed-system diffusive exchange...Oxygen isotope fractionation between coexisting minerals in slowly cooled rocks conveys information about their cooling history. By using the fast grain boundary(FGB) model to simulate closed-system diffusive exchange of oxygen isotopes between coexisting minerals, I show that the apparent equilibrium temperatures(Tae) by the mineral pair with the largest isotopic fractionation(PLIF) always lies between the closure temperatures(Tc) of those two minerals. Therefore, when the rate of oxygen diffusion and hence Tc for the PLIF chance to be comparable(such as in the case of quartz and magnetite), Tae will serve as a good approximation of Tc regardless of variation in mineral proportions. The specialty of the PLIF in constraining Tae within their Tc range can be generalized to other stable isotope systems and element partitioning. By approximating Tc with Tae and inverting Dodson's equation, the cooling rate of plutonic or metamorphic rocks can be inferred.展开更多
The combination of magnetotelluric survey and laboratory measurements of electrical conductivity is a powerful approach for exploring the conditions of Earth's deep interior. Electrical conductivity of hydrous sil...The combination of magnetotelluric survey and laboratory measurements of electrical conductivity is a powerful approach for exploring the conditions of Earth's deep interior. Electrical conductivity of hydrous silicate melts and aqueous fluids is sensitive to composition, temperature, and pressure, making it useful for understanding partial melting and fluid activity at great depths. This study presents a review on the experimental studies of electrical conductivity of silicate melts and aqueous fluids, and introduces some important applications of experimental results. For silicate melts, electrical conductivity increases with increasing temperature but decreases with pressure. With a similar Na^+ concentration, along the calc-alkaline series electrical conductivity generally increases from basaltic to rhyolitic melt, accompanied by a decreasing activation enthalpy. Electrical conductivity of silicate melts is strongly enhanced with the incorporation of water due to promoted cation mobility. For aqueous fluids, research is focused on dilute electrolyte solutions. Electrical conductivity typically first increases and then decreases with increasing temperature, and increases with pressure before approaching a plateau value. The dissociation constant of electrolyte can be derived from conductivity data. To develop generally applicable quantitative models of electrical conductivity of melt/fluid addressing the dependences on temperature, pressure, and composition, it requires more electrical conductivity measurements of representative systems to be implemented in an extensive P-T range using up-to-date methods.展开更多
Water plays a crucial role in the melting of Earth's mantle. Mantle magmatisms mostly occur at plate boundaries(including subduction zones and mid-ocean ridges) and in some intraplate regions with thermal anomaly....Water plays a crucial role in the melting of Earth's mantle. Mantle magmatisms mostly occur at plate boundaries(including subduction zones and mid-ocean ridges) and in some intraplate regions with thermal anomaly. At oceanic subduction zones, water released by the subducted slab may induce melting of the overlying mantle wedge or even the slab itself, giving rise to arc magmatism, or may evolve into a supercritical fluid. The physicochemical conditions for the formation of slab melt and supercritical fluid are still under debate. At mid-ocean ridges and intraplate hot zones, water and CO_2 cause melting of the upwelling mantle to occur at greater depths and in greater extents. Low degree melting of the mantle may occur at boundaries between Earth's internal spheres, including the lithosphere-asthenosphere boundary(LAB), the upper mantletransition zone boundary, and the transition zone-lower mantle boundary, usually attributed to contrasting water storage capacity across the boundary. The origin for the stimulating effect of water on melting lies in that water as an incompatible component has a strong tendency to be enriched in the melt(i.e., with a mineral-melt partition coefficient much smaller than unity), thereby lowering the Gibbs free energy of the melt. The partitioning of water between melt and mantle minerals such as olivine, pyroxenes and garnet has been investigated extensively, but the effects of hydration on the density and transport properties of silicate melts require further assessments by experimental and computational approaches.展开更多
基金the financial support from the Recruitment Program of Global Experts(Thousand Talents),Chinathe Natural Science Foundation of China(41322015)
文摘Oxygen isotope fractionation between coexisting minerals in slowly cooled rocks conveys information about their cooling history. By using the fast grain boundary(FGB) model to simulate closed-system diffusive exchange of oxygen isotopes between coexisting minerals, I show that the apparent equilibrium temperatures(Tae) by the mineral pair with the largest isotopic fractionation(PLIF) always lies between the closure temperatures(Tc) of those two minerals. Therefore, when the rate of oxygen diffusion and hence Tc for the PLIF chance to be comparable(such as in the case of quartz and magnetite), Tae will serve as a good approximation of Tc regardless of variation in mineral proportions. The specialty of the PLIF in constraining Tae within their Tc range can be generalized to other stable isotope systems and element partitioning. By approximating Tc with Tae and inverting Dodson's equation, the cooling rate of plutonic or metamorphic rocks can be inferred.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41402041 & 41322015)the Fundamental Research Funds for the Central Universities of China
文摘The combination of magnetotelluric survey and laboratory measurements of electrical conductivity is a powerful approach for exploring the conditions of Earth's deep interior. Electrical conductivity of hydrous silicate melts and aqueous fluids is sensitive to composition, temperature, and pressure, making it useful for understanding partial melting and fluid activity at great depths. This study presents a review on the experimental studies of electrical conductivity of silicate melts and aqueous fluids, and introduces some important applications of experimental results. For silicate melts, electrical conductivity increases with increasing temperature but decreases with pressure. With a similar Na^+ concentration, along the calc-alkaline series electrical conductivity generally increases from basaltic to rhyolitic melt, accompanied by a decreasing activation enthalpy. Electrical conductivity of silicate melts is strongly enhanced with the incorporation of water due to promoted cation mobility. For aqueous fluids, research is focused on dilute electrolyte solutions. Electrical conductivity typically first increases and then decreases with increasing temperature, and increases with pressure before approaching a plateau value. The dissociation constant of electrolyte can be derived from conductivity data. To develop generally applicable quantitative models of electrical conductivity of melt/fluid addressing the dependences on temperature, pressure, and composition, it requires more electrical conductivity measurements of representative systems to be implemented in an extensive P-T range using up-to-date methods.
基金supported by the National Natural Science Foundation of China(Grant Nos.41590622&41473058)the 111 Project of Ministry of Education,China+1 种基金the Fundamental Research Funds for the Central Universities of Chinathe Recruitment Program of Global Experts(Thousand Talents),China
文摘Water plays a crucial role in the melting of Earth's mantle. Mantle magmatisms mostly occur at plate boundaries(including subduction zones and mid-ocean ridges) and in some intraplate regions with thermal anomaly. At oceanic subduction zones, water released by the subducted slab may induce melting of the overlying mantle wedge or even the slab itself, giving rise to arc magmatism, or may evolve into a supercritical fluid. The physicochemical conditions for the formation of slab melt and supercritical fluid are still under debate. At mid-ocean ridges and intraplate hot zones, water and CO_2 cause melting of the upwelling mantle to occur at greater depths and in greater extents. Low degree melting of the mantle may occur at boundaries between Earth's internal spheres, including the lithosphere-asthenosphere boundary(LAB), the upper mantletransition zone boundary, and the transition zone-lower mantle boundary, usually attributed to contrasting water storage capacity across the boundary. The origin for the stimulating effect of water on melting lies in that water as an incompatible component has a strong tendency to be enriched in the melt(i.e., with a mineral-melt partition coefficient much smaller than unity), thereby lowering the Gibbs free energy of the melt. The partitioning of water between melt and mantle minerals such as olivine, pyroxenes and garnet has been investigated extensively, but the effects of hydration on the density and transport properties of silicate melts require further assessments by experimental and computational approaches.
