下扬子区晚中生代逃逸构造初探

下扬子区位于秦岭大别造山带前缘,自中三叠世拉丁尼克期开始的构造活动受走滑断裂控制。在南北边界走滑断裂围限下,下扬子中生代地块呈一西南窄而东北宽的楔形。在该楔形体内,晚白垩世盆地群呈现有规律的展布,西南部盆地为长条状,NENEE走向,规模小,发育山麓相冲积扇相沉积,具有氧化条件;东北部的苏北盆地为面状展布,EW走向,规模大,湖相沉积为主,具有还原条件;中部盆地为左行斜列,NNE走向,发育特征介于前两者之间。与此相应,断裂构造及沉积岩、火成岩的发育及分布也呈现有规律的变化。上列地质事实表明,下扬子楔形地块自西南向东北方向逃逸,西南部为挤压区,东北部为引张区,中部为过渡区,形成一幅如同土耳其安那托利安新生代的构造逃逸系统。

AN APPROACH TO LATE MESOZOIC ESCAPE TECTONICS IN LOWER YANGTZE REGION

Lower Yangtze Region is situated in front of Qingling-Dabie Orogenic Belt.Its structural activities had been controlled by strike-slip faults since Ladinian Stage of Middle Triassic.Within the limit of strike-slip faults at its south and north margins,the Lower Yangtze Landmass appeared as a wedge that was narrow in the southwest part and wide in the northeast part in Late Mesozoic.Late Cretaceous basin group distributed regularly in the wedge.Basins in southwest part are in long-narrow strip-form of small scales stretching NE-NNE,foot-hill facies and alluvial-pluvial fan facies of oxidation condition devloped well;in the northeast part,Subei Basin is in planar form stretching E-W with lacustrine deposits formed under reduction condition;basins in the central part are sinistral oblique arranged striking NNE direction,their sedimentary facies and depositional environment are between those of the above mentioned two kinds.The results of geologic survey suggest that the evolution and distribution of fault structures,sedimentary and igneous rocks within this area show corresponding regularities with the above mentioned ones.This indicates that,in Late Mesozoic,the Lower Yangtze wedge landmass fled towards northeast with the southwest part to be compressional zone,the northeast part to be extensional zone,and the central part to be transitional zone,just like Anatotian tectonic escape system formed in Cenozoic in Turkey.