试论汾渭“S”型旋转拉分构造体系及其影响

汾渭地堑系位于我国东部阴山与秦岭纬向带之间,自北向南,由集宁、怀来、大同、蔚县、忻州、太原、晋中、汾渭、天水、礼县、西和、成县等10余个NE向斜列的新生代断陷盆地组成,它们呈“S”形展布,反映华北地块在新生代时期发生了顺时针旋转,使古老地块发生裂解,可称之为“S”型旋转拉分构造体系。这个构造体系对中国东部构造格局和构造发展有广泛和深远的影响,强烈改造了秦岭—大别山纬向构造带和江南地块北缘的构造格局,使新华夏系形成分段特征,启动了华北地块伸展构造发展模式,影响所及直达琉球海沟。无独有偶,亚洲中部俄罗斯、蒙古境内有贝加尔地堑系,由反“S”形分布的新生代断陷盆地组成,它们也发育于古老结晶地块之中,可与之对比,是逆时针旋转的反“S”型旋转拉分构造体系。说明它们是同一类型的旋转构造型式,是古老地块裂解的一种方式。

“S”-Type Rotation and Pull-apart Tectonics of the Fen-Wei Graben

The Fen-Wei graben system is located between the Yinshan and Qinling tectonic belts in Eastern China, and comprises (from north to south) over 10 Cenozoic downfaulted basins in the NE syncline, such as the Jining, Huailai, Datong, Yuxian, Xinzhou, Taiyuan, Jinzhong, Fen-Wei, Tianshui, Lixian, Xihe, and Chengxian. This shows that the North China block rotated clockwise in the Cenozoic and caused its rifting, which can be called “S”-type rotation and pull-apart tectonic system. This system had a broad and far-reaching influence on the tectonic framework and development of Eastern China, and strongly modified the tectonic framework of the Qinling-Dabieshan belts and the northern margin of the Jiangnan massif. This may have resulted in the segmentation of the Neo-Cathaysian tectonic system, and initiated the extensional tectonics of the North China Block that reached as far as the Ryukyu trench. Similarly, the Baikal graben system in Russia and Mongolia is composed of Cenozoic rift basins with an inverted-“S”-shaped pattern, and was also developed in ancient crystalline blocks. This represents anti-clockwise rotation of the reversed “S”-type rotation pull-apart tectonic system. Our study shows that they belong to the same tectonic type, and a way of ancient continental block rifting.