前陆沉积与变形对郯庐断裂带同造山运动的制约

郯庐断裂带两侧的前陆沉积及其变形现象,揭示了该断裂带同造山活动的大量信息。合肥盆地东侧的郯庐断裂带旁,侏罗系沉积时出现了沉降中心与边缘相,显示这期间郯庐断裂带所处的张八岭隆起已移位至盆地东侧。砂岩的端元组份分析与碎屑白云母的电子探针分析显示,下扬子地区弧形展布的黄马青群与象山群前陆沉积的物源区为大别——苏鲁造山带,属于原地沉积,表明造山期郯庐断裂带已经出现。大别与苏鲁造山带周边都出现了强烈的前陆褶皱冲断带。合肥盆地前侏罗系基底上印支期的逆冲断层,在郯庐断裂带旁侧明显增多,指示该断裂带曾发生过同造山活动。下扬子地区前陆构造走向向郯庐断裂带方向偏转,反映它们形成时受到了郯庐断裂带左旋走滑运动的影响。这一系列前陆沉积与变形特征,指示郯庐断裂带在华北与华南板块的碰撞造山中以陆内变换断层的型式出现。该断裂带造山期运动中,东盘为主动盘,并发生了显著的逆时针旋转。独特的徐宿弧形逆冲——推覆构造,表明造山期郯庐断裂带左行平移幅度达350km。在该断裂带早白垩世的第二次平移中,断裂带向北延伸,又发生了约200km的左行平移。

CONSTRAINTS OF FORELAND SEDIMENTATION AND DEFORMATION ON SYNOROGENIC MOTION OF THE TAN-LU FAULT ZONE

The phenomena of foreland sedimentation and deformation around the Tan-Lu fault zone showed a lot of information on its synorogenic activities. The depositional center belts and marginal facies of the Jurassic strata near the fault zone in east part of the Hefei Basin suggested that the Zhangbaling uplifted belt, occupied recently by the Tan-Lu fault zone, moved to the east of the basin before Early Jurassic. The vite electronic probe analyses demonstrated Xiangshan sandstone detrital composition and detrital muscothat foreland sediments of the Huangmaqing and Groups with arcuate distribution were autochthonous in the Lower Yangtze region, and their provenance was the Dabie-Sulu orogenic belt, which implyed that the Tan-Lu fault appeared during the orogeny. The intensive foreland fold-and-thrust belts occurred on the both sides of the Dabie-Sulu orogenic belt. Increasing of the Indosinian thrusts in pre-Jurassic basement of the Hefei Basin near the Tan-Lu fault zone indicated synorogenic activities of the fault zone. Curving of the foreland structural strikes towards the Tan-Lu fault zone demonstrated that their development was affected by sinistral strike-slip movement on the fault zone. All characteristics of the foreland sedimentation and deformation suggested that the fault zone was derived from collision orogeny of the North and South China plates as an intracontinental transfer fault zone. The eastern wall of the fault zone was an active wall, and an obvious anti-clockwise rotation took place during its synorogenic movement. The unique arcuate thrust-nappe structures in Xuzhou-Suzhou area suggested a sinistral displacement about 350 km of the synorogenic fault zone. The fault zone extended northwards further during the second transcurrent faulting in Early Cretaceous and sinistral displacement of ca. 200 km took place again.