花岗岩块状样品的熔融实验研究

EXPERIMENTAL STUDIES OF PARTIAL MELTING OF MASSIVE GRANITES

以粉末样品的熔融实验为基础的花岗岩体系相平衡理论,在花岗岩成因研究方面具有一定的局限性。天然花岗岩块状样品的熔融实验表明,赋存于矿物颗粒间的熔体成分主要受控于不同矿物边界的局部熔融体系。较低温条件下的熔体基本属于花岗岩体系的低熔点成分,而较高温度下的熔体则远离同熔线转变为非平衡熔体。

Phase equilibrium relations in the melting granite system are the basis ofmodern petrology.At present this phase-equilibrium theory has been establishedon the basis of the results of melting experiments on powder samples.Becauseof the destruction of the original fabrics,the experiments cannot provide eviden-ce for variations in mineral composition,fabric,composition and distribution of melt,so they have many limitations in petrogenesis.Experimental results indicated thatthe melts exist mainly at the boundaries of quartz/plagioclase and quartz/potash fel-dspar,their compositions being essentially controlled by local melting systems amongdifferent minerals and having nothing to do with the bulk composition of the rock.At lower temperatures(740—760℃,0.2GPa),the melt plots at or near the eutecticpoint in the Q-Ab-Or-An-H_2O diagram,revealing a mechanism of equilibrium mel-ting.At higher temperatures(790—800℃,0.2GPa),the melt becomes lower inSiO_2 and higher in Na_2O,it is not situated on the eutectic line in the Q-Ab-Or-An-H_2O diagram,but at the same time no mineral disappeared due to melting,sug-gesting that the melting at higher temperatures is of nonequilibrium.It is obviousthat the phase-equilibrium relations in natural massive granite samples are greatlydifferent from those in powder samples,which would provide new clues to thephase-equilibrium relations in the granite system.