华北地台绿岩带地质特征类型和演化

中国绿岩带主要分布在华北地台。绿岩带产在古陆核之间或边缘，可能形成在古裂谷或古岛弧的构造环境。按原岩建造、地球化学特征和成矿作用，绿岩带可分夹皮沟型、清原型和小秦岭型。按后期的活化改造作用强度，可分基本稳定型、活化改造型和强烈活化改造型绿岩带。根据变质程度的不同，可分高级变质和中级变质为主的绿岩带。华北地台绿岩带的形成可分四个时期：中太古代、新太古代早期、新太古代晚期和早元古代。华北地台绿岩带同其他国家绿岩带相比较，其岩石类型、不一的变质程度、相似的花岗质岩石、形成在早前寒武纪和赋存丰富矿产资源等基本地质特征相似。但也具有独自的特色：１．分布面积小；２．科马提岩不甚发育；３．同构造晚期的浅成花岗岩侵入体尚未发现；４．变质程度较高；５．赋存的矿产类别有差异；６．受后期的活化改造作用强烈。

GEOLOGICAL FEATURES TYPES AND EVOLUTION OF GREENSTIONE BELTS IN THE NORTH CHINA LATFORM

Chinese greenstone belts are of widespreadly distributed in the North China Platform.The greenstone belts generally occur along the margin or in the middle of paleonuclei and havebeen formed possible in a paleo-rift or palaeo-island arc tectonic settings. In view of theirprotolithic assemblages, geochemistry and metallogenesis, the greenstone belts may be dividedinto Jiapigou type, Qingyuan type and Xiaoqialing type. According to late reworking intensity,they may be grouped intO basic stable type, activation-reworking type and intense activationreworking type, and also according to the grade of metamorphism, they may be divided into highgrade metamorphic greenstone belts and middle grade metamorphic greenstone belts. The epochof greenstone belts-forming in the North China Platform can be divided into four periods, that isMesoarchean, Early Neoarchean, Late Neoarchean and Palooproterozoic, Especially EarlyNeoarchean The greenstone belts in the North China Platform are similar to those in othercountries in basic geological features including rock types, different grade of metarnorphism,similar granitoid rocks, the Early Precambrian forming-epoch and rich in mineral resources, butthey have their own unique features, which are (1) relatively small area of distribution, (2)komatiites are not developed, (3) late stage of syntectonic thick felsic subvolcanic intrusionshavn't been discovered, (4) relatively higher grade of metamorphism, (5) rich in differentmineral resources and (6) after cratonization, intense activation-reworking.