云南姚安碱性岩中环带状正长石

作者在研究云南姚安碱性岩的过程中,发现辉石黑云母正长斑岩和黑云母正长斑岩中正长石斑晶的环带构造广泛发育。正长石的环带构造较之斜长石和钾长石的环带构造极为罕见,研究得很少。对正长石环带的研究,能够提供很多关于岩浆结晶作用和演化方面的有用资料。

THE ZONAL TEXTURE OF ORTHOCLASE IN ALKALINE ROCK FROM YAOAN COUNTY,YUNNAN PROVINCE

In the augite biotite syenite-porphyry from Yaoan County,Yunnan province,the zonal texture of orthoclase phenocrysts and their polysynthetically twined and lamellar crystals are well developed.The number of zones in a single crystal may amount to 15-20.The form of zone is identical to that of corresponding crystal face.However,the width of zones varies with the crystal face indices.In general,the zones,parallel to {001} and {010} are narrow and dense,that parallel to {201} and {110} are the broader,and that parallel to {100} are the broadest.From inner-most zone outward,the optic angles;2V are gradually increasing.The composition of inner zone is Or₇₅Ab₂₅,and that of outer zone is Or₆₀Ab₄₀.The refractive indices are N_g=1.530.N_m=1.527,△_d (131)-(131)=0.