川西—滇东地区早元古宙变质岩系及其区域变质作用与地壳演化

在川西—滇东地区,前人一直将会理群、昆阳群等作为该区所出露的最古老的地层,并认为它们代表了扬子地台的最老基底。笔者通过对该区详细的变质地质研究认为,在它们之下还存在着一套与之完全不同的层状变质岩系,我们将其称为康定群,推测其时代至少为早元古宙或晚太古宙。它与中、晚元古宙的会理群、昆阳群等共同构成了扬子地台的古老基底,为基底的两个重要的地质构造单元,分别代表了本区早期地壳演化的不同阶段。

EARLY PROTEROZOIC METAMORPHIC ROCK SERIES,WEST SICHUAN AND EAST YUNNAN, CHINA. METAMORPHISM AND CRUSTAL EVOLUTION

The metamorphic rock series of early proterozoic distributed in west Sichuan and east Yunnan is a set of layer metamorphic complex which different from Huili Group or Kunyang Group. It is called Kangding Group in west Sichuan and Julin Group in east Yunnan. The metamorphic rock series consists of much amphibolites, leptynites, mica-quartz schist and less granulites,marble, quartzite. The priimary rock formation is tholeiitic-calc-alkallinic-basic volcanic rock formationin the loher,intermed iate-ac itic wlcan ic rock forma-tion,or intemediate-acidic tuffs rich in carbon and aluminium pelite formation in the middle,and clastic flyschformation in the upper part.The metamorphism of Kangding Group and Julin Group blongs to regional dynamic-thermal metamorphism. The metamorphic facies are mainly of amphibolite facies and locally of granulite facies, high green schist facies and low green schist facies. There is distinct incremental metamorphic zones which are concordant with stratification of the sedimentary sequence. The metamorphic facies series is dominated by low pressure facies series but towards south transferring to medium pressure type.They set up commonly the old basement of Yangtze Platform. Including Huili Group and Kunyang Group there are two important geological tectonic units of the Yangtze Platform basement,that is, the early proterozoic craton and the middle-late proterozoic mobile belt. They represent two different periods of early crustal evolution in this area and the type of metamorphism appears cyclic change from regional dynamic-thermal metamorphism to regional low temperature dynamic metamorphism.