华北地台的元古宙构造演化

华北地台在前寒武纪经历过三个大构造阶段,即太古初始克拉通、早元古代原地台和中—晚元古代地台的形成阶段,每个阶段都有各具特点的构造演化史。发生在太古宙末期的阜平运动,是一次强烈的构造-热事件,造成太古岩层的变质、变形等和形成初始的克拉通基底,早元古时出现了裂陷形成了克拉通内或边缘的内硅铝盆地或海槽。早元古末期的吕梁-中条运动是另一次重要的构造-热事件,此后,原地台最终固化,华北地台的主要构造格架基本成型。中—晚元古时期在华北地台的不同部位发育了三个主要构造盆地。

PROTEROZOIC TECTONIC EVOLUTION OF THE NORTH CHINA PLATFORM

Three tectonic megastages of the North China Platform, including the formation of Archaean craton, early Proterozoic Protoplatform and middlelate Proterozoic platform, during the long span of Precambrian are recognized each with a distinct tectonic history.The Fupingian Orogeny (Ca. 2.5 Ga) at the end of Archaean was an intensive tectono-thermal event that caused Archaean rocks becoming metamorphosed and deformed, giving rise to an extensive basement, the North China craton (Fig. 1, Fig. 2).Some ensialic basins and troughs, somewhat varing in diamension and othen features, formed by riftingsagging occured within the primary consolidated craton during the early Proterozoic. The difference in controlling factors including depth, nature and activity of faults and feature; of sialic crust gave rise to the difference between calcalkaline and subalkaline volcanics, poor-sorted tarbidite in deep water and well-sorted sediments in shallow water as well as BIF of Algoma-like and Superior-like types in different basins and troughs, at the early stage of early Proterozoic. characteristics of some stra-tigraphic sequences are similar to those of the Proterozoic greenstone belts. Their metamorphic facies ranges from amphibolite to greenschist facies and synorogenic granites were intruded. After the Wutaian orogeny (Ca. 2.3Ga) which took place at the middle of early Proterozoic, molasse occured at first, and was followed by neritic and lagoon sediments with minor mafic volcanic rocks. Nevertheless, extensive mobile belts, where metamorphic facies of rocks been up to granulite facies locally, were situated in the northern border and northeastern part of the North China protoplatform during the early Protero- zoic.The Luliangian-Zhongtiaoan orogeny (Ca. 1.9-1.8Ga) was anotheri mpor-tant tectono-thermal event at the end of early Proterozoic. During the pano-rogenic period, terminal consolidation of the protoplatform was achieved, and consequently the principal tectonic framework of the North China Platform acquired it pattern.Three main tectonic basins occured at different portions of the platform during the middle-late Proterozoic. The largest intracontinental basin was located within the centra] part of the platform. At the early graben stage, fluvial facies was accumulated, and then was followed by orthoquartz-sandstone, shale and dolomite in shallow water. The anorogenic magmatic events were represented by ultrapotassium volcanics and rapakivi granite (Ca. 1.6 Ga) respectively. The widest transgression took place and brought about carbonate sedimentation with a huge thickness. After the frequent elevation and subsidence of the late Proterozoic, the main parts of the intracontinental basin uplifted, however a few small taphrogenic basins located at the eastern part of the basin continued to receive sediments. A platfornm marginal basin occured at the sorthern border of the North China platform. Its tectonic evolutionary characteristics and stages are very similar to those of the above-mentioned intracontinental basin. But a failed arm of a triple rift system was developed and filled with subalkaline and calcalkaline volcanics during the first stage of middle Proterozoic. Another continental marginal basin enlongated in E-W direction, occuring in the northern border of the platform, in which such a sequence of flysh association and carbonates as well as intercalations of volcanics with complicate composition was properly accumulated in the middle Proterozoic. Subsequently, only smaller basins were preserved at the late Proterozoic.