中国太古宙绿岩带

ARCHEAN GREENSTONE BELTS IN CHINA

中国太古宙绿岩带主要分布在华北陆台的北缘和西南缘。绿岩带的基本地质特征可以和国外的太古宙绿岩带对比,但也具有独自的特点。根据绿岩带的地球化学特征可以将中国太古宙绿岩带划分为夹皮沟型、清原型和小秦岭型3类。绿岩带形成的古构造环境可能为与现代岛弧-大陆边缘活动带类似的裂谷型构造环境。

Chinese Archean greenstone belts are mainly exposed along the northern and south-westetn margins of the North China Platform. Seven p aleo-nuclei separated by large abyssal fauls are recognized in the North China Platform based on the geophysical data. The greenstone belts occur along the margins of the paleonuclei.On the basis of the assemblages and rock characters of the supracrustal rocks, the Chinese Archean greenstone belts can be divided into three types. The Jiapigou-type greenstone belts is composed chiefly of metamorphosed ultramafic to mafic volcanics with minor felsic volcanics and sedimentary rocks. For example, the gree nstone succession at Jiapigou consists of a lower tholeiitic rock series and an upper calc-alkaiine one, with the ratio of the two around 1.5: 1. The protoliths of the Qinyuan-type greenstone belts are those of a continuous calc-alkaline volcanosedimentary series. And the Xiaoqinling-type is composed of a lower bimodal volcanic series and an upper sedimentary rock series of tuff, tuffaceous clastic rocks, graywacke-argillite and carbonate rocks. Three granitoid associations and local minor meta-dioritic complexes have been distinguished in the granitoid-greenstone terranes in the North China Platform.The data of REE and ΣNd(t) of the mafic volcanics in some places suggest that the greenstone belts were originated from a depleted man tle and there appeared a sialic paleo-crust in the North China Platform around 1.9Ga. The granitoid-greenstone terranes of the North China Platform were formed in the Neoarchean (Ca 2.5—2.9 Ga) rift-type tectonic setting, similar to that of the moderm continental marginal mobite belts or back-arc rift. The Characteristics of the Chinese greenstone belts are basically similar to those of other countries but not in details.