藏北羌塘中部冈塘错花岗岩体中环带条纹钾长石巨斑晶的特征

Characteristics of giant annulus stripe K-feldspar phenocryst of Gangtangcuo granitic pluton in central Qiangtang, northern Tibet, China

冈塘错花岗岩体是分布于西藏双湖角木日地区的一套晚三叠世酸性侵入岩。于2008年1∶5万区域地质调查填图中首次发现该岩体中的中粗粒巨斑状含黑云母二长花岗岩中的巨斑晶为环带条纹钾长石。主要描述了该岩体中环带条纹钾长石巨斑晶的矿物学、岩石学特征,利用电子探针详细分析了环带条纹钾长石巨斑晶从核部到边缘的成分变化特征,运用二长石温度计简单地计算了斑晶的结晶温度。根据斑晶的化学成分变化特征和结晶温度,结合岩体的岩石学、地质学特征,初步确定该岩体为岩浆混合作用的产物。

Gangtangcuo granite widely distributes in Shuanghujiaomuri area, Tibet and it is a set of Late Triassic felsic intrusive rock. In 2008, during regional 1∶50000 geological mapping, we found that the coarse-grained phenocryst in biotite adamellite belongs to annulus stripe K-feldspar. In this paper,we described the mineralogy, petrology characteristics of the giant K-feldspar phenocryst. By using electronic microprobe method, a detailed analysis of the component variation from the edge to the core within this phenocryst was also conducted out, and through two-feldspar geologic thermometer, crystallization temperature of phenocryst was also calculated. Finally, based on the chemical composition changes of the phenocryst and crystallization temperature, combined with the petrology and geology characteristics, we made a primary conclusion that the granite was formed because of magma mixing.