一种刚玉夕线钾长片麻岩的岩石学矿物学特征及形成环境  

Petrology, mineralogy and formation environment ofa corundum-sillimanite-K feldspar gneiss

作　　者：沈其韩[1] 耿元生[1] 王新社[1] 吴春明[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质通报》2004年第2期99-106,共8页Geological Bulletin of China

基　　金：中国地质调查局<中国西北地区若干重点前寒武纪区构造-岩石-地层单元的划分对比及年代格架>项目(编号199913000006)的部分研究成果。

摘　　要：刚玉夕线钾长片麻岩是产于新太古代迭布斯格岩群中的一种低Si、高Al、高K的特殊岩石,主要包括刚玉钾长金红石片麻岩、黑云夕线钾长金红石片麻岩2种岩石组合,呈互层状产出。刚玉、夕线石和钾长石是通过白云母的变质分解和白云母+SiO2的变质反应而生成的。形成温度约为720～760℃,压力约为0.6～0.8GPa。由于温度和压力稍高,岩石中已开始出现重熔钾长石细脉。环带状次生白云母的出现属退变质反应。变质程度为区域中高温变质作用,达高角闪岩相,与围岩的变质程度一致。其原岩是在较短的稳定条件下由富K、富Al的花岗质岩石经强烈风化搬运进入大陆边缘沉积盆地,再经化学分解和沉积作用而形成的不同的原岩组合。Corundum-sillimanite-K feldspar gneiss, distributed at Hala Tolgoi, Alxa, Inner Mongolia, is a special rock type with low SiO2, high Al2O3 and high K2O occurring in the Lower Formation of the Neoarchean Diebusike Group-complex. It mainly includes two rock associations, corundum-K feldspar-rutile gneiss and biotite-sillimanite-K feldspar-rutile gneiss, which alternate with each other. Corundum, sillimanite and K feldspar formed by metamorphic reaction of muscovite and muscovite + SiO2 at temperature of about 720-760℃ and pressures of about 0.6-0.8 GPa. Because of higher temperatures and pressures, anatectic K feldspar veinlets occurred in the gneiss. The appearance of zoned secondary muscovite resulted from retrogressive metamorphism. The metamorphic grade of the rock is high, reaching high amphibolite facies of medium- and high-temperature regional metamorphism, which is consistent with the metamorphic grade of the country rocks. Its protolith is an association of different protoliths formed by strong weathering of Al-rich granitic rocks and their later transport into the relatively stable continental margin sedimentary basin and further chemical decomposition and deposition.

关 键 词：刚玉夕线钾长片麻岩 迭布斯格岩群 变质反应 区域中高温变质作用 原岩组合 

分 类 号：P588.345[天文地球—岩石学]