扬子地区晋宁期板块构造的探讨

THE PLATE TECTONICS OF YANGTZI BLOCK REGION DURING JINNING OROGENIC PERIOD

扬子地区在晋宁造山期(1.05—0.85 Ga)发生过板块俯冲活动,其活动模式为青康滇古大洋板块向东南扬子古大陆板块俯冲,浙赣粤古大洋板块向西北的扬子古大陆板块俯冲。两个不平行的古大洋板块相对俯冲所产生的合应力,造成扬子古大陆板块朝北北东向移动,而与华北古大陆板块发生碰撞。

Whether the plate subduction had occurredin Yangtzi Block region during the Precambrian is an important geological question in dispute. Based on the study of the stratigraphy, magmatic formation, ophiolite suite, sedimentary formation and deep fractures in the Precambian basement in southern China, it is suggested that the plate subduction has taken place in the Yangtzi Block region during the Jinning orogenic period (1.05-0.85Ga). The Qingkangdiari paleo-oceanic plate has subducted beneath the Yangtzi paleo-continental plate to the south-east, resulted in formation of a volcanic arc and trench system on the active continental margin in the Kangdian mountain system-Longmen mountain-Micang mountain area located in the north-west margin of the Yangtzi Block, and the Zheganyue paleo-oceanic plate subducted beneath the Yangtzi paleo-continental plate to the north-west, resulted in formation of an island arc and trench system in the Jiuwangda mountain-Xuefeng mountain-Jiuling mountain-Huiji mountain area located in the south-east margin of the Yangtzi Block. The opposite movement of these two un-parallel palao-oceanic plates toward the Yangtzi palao-continental plate produced a composite stress in north-northeast direction and brought abovt the movement of Yangtzi paleo-continental plate in north-north-east direction, and collided with the North China plaeo-contin-nental plate.