北秦岭沙河湾环斑结构花岗岩的矿物学特征及其岩石学意义

MINERALOGICAL CHARACTERISTICS OF SHAHEWAN RAPAKIVI TEXTURED GRANITE IN NORTH QINLING AND THEIR PETROLOGICAL SIGNIFICANCE

沙河湾岩体具有较典型的环斑结构。岩体中的角闪石、黑云母、斜长石、钾长石和石英均有两期 ,与典型的环斑花岗岩相似。该岩体中环斑结构花岗岩中的暗色矿物角闪石和黑云母的n(Fe) /n(Fe+Mg)分别是 0 3 3～0 3 7和 0 40～ 0 42 ,与典型环斑花岗岩中的富铁、贫镁的特点有一定差异 ,而与I A型过渡性花岗岩的暗色矿物相似 ,表明该岩体在岩浆成分和形成机理上可能与典型的稳定大陆内部的环斑花岗岩存在着差异。这可能正是产于造山带环境中的环斑结构花岗岩的特点之一。

This paper reveals that the major minerals in the Shahewan rapakivi textured gr anite can be divided into two generations, similar to those of a typical rapakiv i granite. However, the composition of biotite and hornblende, rich in Mg and po or in Fe, is different from that of the typical rapakivi granite and sh ows the features of biotite from I type to A type granite. The difference may suggest that the two kinds of granites are different in genesis.