四川会理—米易—盐边一带前震旦系变质岩特征及时代问题

THE CHARACTERISTICS OF PRE-SINIAN METAMORPHIC ROCKS IN THE HUILI-MIYI-YANBIAN AREA,SICHUAN PROVINCE,AND THEIR AGE

在四川省会理、米易、盐边一带,发育有一套前震旦纪变质岩,以含矽线石、十字石、铁铝榴石、红柱石等特征矿物的云母片岩,云母石英片岩,钠长石英岩为主,并夹少量绿片岩、变粒岩及白云大理岩。作者提出建立下村群,自下而上划分为汞山组、吴家沟组、小荒田组、核桃湾组.本文从岩石组合、沉积建造、变质作用特征、同位素地质年龄资料等方面,与前人已建立的会理群、盐边群、河口群、康定群进行了详细对比与分析.认为下村群应位于康定群之上,会理群及盐边群之下,其时限在2000—1700Ma 之间,它与河口群的关系还有待进一步研究.

There is a sequence of miea-schist, mica-quartz schist and albite quartzite with small amount of greenschist,granulitite and dolomite marble containing such diagnostic minerals as silimanite,staurolite,andalusite and almandine in the Huili-Miyi-Yanbian area,Sichuan Province.The authors name this sequence of metamorphic rocks the Xiacun Grnup and divide it from below upwards into the Gongshan,Wujiagou,Huanglian and Hetaowan Formations. A detailed correlation is made between it and the Huili,Yanbian,Hekou and Kangding Groups established by the predecessors in respect to the rock associations,sedimentary formations,metamorphism and isotopic ages.The authors consider that the Xiacun Group lies above the Kangding Group and below the Huili and Yanbian Groups,with an age range between 2000 and 1700 Ma.Its relationship with the Hekou Group awaits further study.