中国西部元古代蓝片岩带——世界上保存最好的前寒武纪蓝片岩  

PROTEROZOIC BLUESCHIST BELT IN WESTERN CHINA: BEST-DOCUMENTED PRECAMBRIAN BLUESCHISTS IN THE WORLD

作　　者：肖序常[1] 格雷厄姆 S.A. 

机构地区：[1]中国地质科学院 [2]美国斯坦福大学地质系

出　　处：《新疆地质》1990年第1期12-21,共10页Xinjiang Geology

摘　　要：阿克苏附近所发现的元古界阿克苏群为一完整的蓝片岩-绿片岩系列,我们通过野外调查肯定了这一认识,并认为它是高压-温相的变质块体,长40km,宽约2.5km.该变质岩由强烈片理化的绿泥石-黑硬绿泥石石墨片岩、黑硬绿泥石-多硅白云母片岩、绿片岩、蓝片岩及少量石英岩、变铁质岩组成.原岩包活泥质岩、砂岩、基性玻屑凝灰岩、块状熔岩、枕状熔岩及少量深海沉积物.蓝片岩的矿物组合:青铝闪石-绿帘石-绿泥石-钠长石-石英-阳起石.阿克苏群为世界上真正的前震旦纪蓝片岩之一,其变质年龄至少有800Ma.Near Aksu,NW China, is a coherent blueschist/greenschist terrane mapped as the Proterozoic Aksu Group by Chinese geologists. Our field investigations confirm this interpretation and indicate that the high-P/T terrane is about 40 km in length and has a structural thickness of about 2.5 km. The metamorphic rocks are uncon-.formably overlain by a thick, unmetamorphosed sedimentary sequence ranging in age from Sinian(ca. 600-800 Ma) upwards through Eo-cambrian to the Paleozoic. The basal Sinian is a transgressiye fluvial to marine sequence that contains sub-rounded to rounded clasts of the underlying schists and dike rock, clearly demonstrating the pre-Sinian age, of blueschist facies metamorphism. High-P/T metamorphic rocks: are strongly foliated chlorite-stilpnomelane gra- phite schist, stipnomelane-phengite pssammitic schist, greenschist , and blueschist with minor meta-quartzite and meta-ironstone. Protoliths include pelites, sandstone, basaltic hyaloclastite, massive lava, pillow lava, and minor pelagic sediments. Stratal continuity has been maintained. Rocks have been subjected to multi-stage deformation and transitional bluesehist/greenschist facies metamorphism.The blue-schist contains some or all of the following assemblage: crossitic amphibole+epi-dote + chlorite + albite+quartz± actinolite. The thetamorphic terrane was intruded by many weakly altered, NW-trending alkali diabase drkes. Thin thermal zones and chilled margins suggest shallow intrusion. Thus, the Aksu Group is one of the best authenticated examples of Precambrian blueschists. This occurrence demonstrates that requisite conditions for blueschist facies metamorphism existed at least 800Ma ago.

关 键 词：中国西北的阿克苏 元古代蓝片岩带 高压-温变质岩 蓝片岩-绿片岩相过渡变质类型 蓝片岩的矿物组合 蓝片岩的变质年龄(至少800Ma) 

分 类 号：P5[天文地球—地质学]