中国西北部南北向伸展构造存在的新证据——酒泉早白垩世半地堑断陷成因初探

New evidences for the presence of the NS-trending extensional structures in northwestern China: An example from the Early Cretaceous half-graben fault depressions in Jiuquan, Gansu

酒泉早白垩世半地堑断陷呈南北向或北东向展布,进一步分为多米诺骨牌式、对倾式和背倾式三种。其充填物明显地受近南北向或北东向正断裂控制,其中的火山岩均为碱性玄武岩,可能由地幔熔融形成。初步认为,酒泉半地堑断陷是早白垩世陆内地幔热隆诱发的近南北向伸展构造。在新生代,由于印度板块的挤压作用,北祁连山前展式北向推覆作用可能使早白垩世半地堑断陷的南部地区转换成山脉,现今的半地堑南部边界被掩伏于北祁连山之下;同时,印度板块的挤压作用使控制半地堑沉积体系的近南北向或北东向正断裂转换为逆冲断裂,发生反转。

The Early Cretaceous halfgraben fault depressions in Jiuquan are aligned along the NS or NE directions, and classified into three types: Domino, opposite dip and trailing dip types. The filling material is obviously constrained by the NS or NEtrending normal faults. The volcanic rocks are composed, without exception, of alkaline basalts that may be of mantlemelted origin. The half graben fault depressions in Jiuquan are interpreted to be built up of nearly NStrending extensional structures triggered by the intracontinental mantle thermal upwelling during the Early Cretaceous. Till the Cenozoic, the compressional processes of the Indian plate and the northward thrusting of the North Qilian Mountains may give rise to the transition of the southern parts of these Early Cretaceous halfgraben fault depressions into mountain ranges. The presentday southern boundaries of the halfgraben fault depressions have been overlain by the North Qilian Mountains. Furthermore, the compression of the Indian plate caused the NS or NEtrending normal faults to be overturned to form the thrusts.