Isocon Analysis of Layered Migmatite in Qinling Group
秦岭群中条带状混合岩质量等比线分析

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.