甲基卡伟晶岩形成的温压条件:来自矿物和全岩熔融模拟实验的约束OA

Supercritical fluids are widely regarded as a key control on pegmatite genesis owing to their exceptionally high solubility,high mobility,and very low viscosity.However,it remains a matter of debate whether granitic melts and their exsolved fluids can become fully miscible and enter a supercritical state under the P-T(pressure-temperature)conditions of pegmatite formation.In this study,typical mineral assemblages and synthetic glasses prepared from whole-rock powders of the Jiajika pegmatites were investigated.In situ high-pressure and high-temperature(HP-HT)melting experiments were performed using a hydrothermal diamond-anvil cell(HDAC)to constrain the melt-fluid phase relations and evolution of natural pegmatite systems.The experimental results show that,at 0.4～0.84 GPa and 671～800℃,the melt occurs as discrete melt globules within the fluid phase,with sharp melt-fluid interfaces,in both the natural mineral assemblages and the glass systems containing abundant B-and Li-bearing fluxing components.No complete miscibility or supercritical-fluid behavior was observed.These results indicate that the critical curves for pegmatite-like systems established in previous studies using simplified H2O-albite glass systems with the excessive addition of B,F,and Na may underestimate the P-T conditions required for complete miscibility in compositionally complex natural pegmatite systems.The HP-HT experimental constraints from the Jiajika pegmatites suggest that during the petrogenesis and mineralization of ore-bearing pegmatites,the melt-fluid system likely persisted as two coexisting phases over a prolonged period.Rare-metal enrichment was controlled primarily by melt-fluid immiscibility and subsequent hydrothermal activity,rather than by supercritical processes.