秦岭群中条带状混合岩质量等比线分析

对采自秦岭群中的五块条带状混合岩所作的质量等比线分析显示了两种情况：（１）古成体或围岩与脉体加暗色体确定的质量等比线揭示古成体或围岩是脉体加暗色体的原岩。脉体加暗色体有小的质量剩余，主要是Ｎａ＋Ｋ的带入，一块标本有Ｃａ的带出，而另一块标本有Ｆｅ的带出。后一标本的古成体与暗色体确定的质量等比线表明这类条带状混合岩的形成还涉及分异作用，它由分异作用和交代作用共同形成。（２）古成体与脉体加暗色体确定的质量等比线表明脉体加暗色体有大的质量剩余，剩余物质是花岗岩成分，没有物质的损失。这一情况存在两种解释：其一是原岩有不同的成分层，富长英质的成分层发育为脉体加暗色体；其二是原岩均匀，脉体加暗色体的形成中有大量外来物质的加入。本文倾向于第一种解释。

Isocon Analysis of Layered Migmatite in Qinling Group

Isocon analysis has been applied to five samples of layered migmatites in Qinling Group. Two cases have been distinguished. (1) Isocon between paleosome (P) or country rock and leucosome (L) plus selvage (S) shows that paleosome or country rock is protolith of leucosome plus selvage. L S has a small excess mass: K Na was gained, and Ca was lost in a sample, and Fe was lost in another sample. The selvage paleosome isocon in the latter sample indicates that formation of this migmatite was involved in differentiation. The differentiation and metasomatism are jointly responsible for the formation of migmatites. (2) Isocon between P and L S shows that L S has a great excess mass that its compositions is granitic, and none of components was lost. There are two explanations about the excess mass that agree with isocon analysis: introduction of foreign material and original compositional difference between the present paleosome and leucosome selvage. The authors suggest that the latter reason is mainly responsible for the excess mass.