富氟花岗质岩浆结晶过程中高场强稀有元素的演化和成矿

F-rich leucogranitic rocks are a special type of felsic rocks enriched in fluorine and rare metal elements. They usually develop characteristic vertical zonation from a relatively potash and silica-high zone upword to a sodic and silica-low zone at the apical region of the plutons. In order to investigate their fractional crystallization process and the zonation mechanism, F-bearing protolithionite granite is used as the starting material to perform fractional crystallization experiments and to determine its crystallization sequence and melt differentiation trends at 100- 150 MPa, 850 ~ 600℃ and H2O-satuated and unsatuated conditions. The run products include quartz, alkali-feldspar, mica and quenched glass. Quartz and alkali-feldspar are the first crystallized phases and are sequentially followed by mica. There are systematic variations in the compositions of alkali feldspar and residual melt compositions with decreasing run temperature. The contents of Or (KAlSi3O8) increases and the contents of Ab (NaAlSi3O8) and An (CaAl2Si2O8) decrease. The most apparent fractionation trends in residual melt compositions are decreases in the contents of SiO2 and K2O, and increases in the contents of Na2O, Al2O3, F, and the ratios of A/NKC and Na2O/K2O. At T≦700℃, the residual melt has the compositional characteristics of natural F-rich albite granite. These experimental results indicate that the low-silica and sodic granitic melt could be derived by a relatively high-silica and potash F-rich leucogranitic magma via fractinal crystallization, which is very important for the understanding of the fractional crystallization process and the minelization mechanism of F-rich granite plutons.

本项目通过富氟花岗质熔体中含高场强稀有元素副矿物，稀有独立矿物的溶解度实验及高场强稀有元素在黑云母和花岗质熔体之间的分配实验，综合运用地球化学和现代分析测试手段，研究氟对副矿物，稀有独立矿物溶解度及高场强稀有元素在黑云母和熔体之间分配系数的影响，阐明富氟花岗质岩浆结晶过程中高场强稀有元素的分异演化行为和富集成矿机理。