赣江断裂带中生代的演化及其地球动力学背景

赣江断裂带是江西省境内醒目的北北东向平移断裂构造带,由一系列北北东向、北东向和北西向断裂束组成,表现为一个大规模的左行走滑脆性剪切带并兼具伸展断陷和右旋走滑的成份。赣江断裂带在重力、航磁异常呈现为显著的梯度带,是一条晚中生代的岩浆岩带,控制了以鄱阳盆地为代表的一系列白垩纪-古近纪沉积盆地的形成与发育。该带在中生代的演化可分为早-中侏罗世压扭、晚侏罗早-白垩世左行平移和晚白垩世上盘斜落的右行平移3个阶段。在侏罗纪以来太平洋板块对欧亚大陆斜向俯冲的大背景下,赣江断裂带的形成和演化与华南广为发育的燕山期陆内造山作用密切相关,北北东向断裂的发育则直接受郯庐断裂早白垩世左行走滑活动控制,因而表现出“北强南弱”和“北早南晚”的特点。白垩纪时赣江断裂的活动方式与郯庐断裂一致,可认为是后者的南延。

MESOZOIC EVOLUTION OF THE GANJIANG FAULT ZONE AND RELATED GEODYNAMIC SETTINGS

The Ganjiang fault zone in Jiangxi province, composed of NNE-striking, NE-striking and NW-striking fault groups, was mainly a large scale sinistral strike slip fault; in addition, the dextral shearing and extention of the fault could be observed. Based on seismic, MT, drilling data and field survey of petroleum exploration, the paper illustrated geological and geophysical features of the fault. Three stages of the Cretaceous basins’ developing, controlled by the fault, could be distinguished: 1)the Early Cretaceous pull-apart basins controlled by the sinistral strike slipping, with sedimentary record being the Lengshuiwu Formation; 2)the trans-releasing basin in early Late Cretaceous occurring in transformation from sinistral to dextral strike slipping, the sedimentary record being the Zhoujiadian Formation; and 3)the stretch basin in middle-late period of Late Cretaceous controlled by an oblique normal faulting, with the Nanxiong Formation deposited. Under a global tectonic setting of the Pacific plate obliquely subducted the Eurasia plate since Jurassic, the Ganjiang fault experienced three-stage evolution during Juro-Cretaceous. It was a transcompressional one in Early-Middle Jurassic, whose developing of the NE-striking faults related to the Yan shanian intracontinental orogeny in South China. It became a syn-orogenic sinistral strike slip one in Late Jurassic and Early Cretaceous. The regional sinistral shearing field resulted from two events. One was closure of the Su-Lu ocean, and concurrently, an oblique convergent-shearing orogeny occurred along the Tan-Lu fault. Another was an oblique convergent-shearing orogeny along the Changle-Nan’ao fault in SE coast area. The dextral strike slip and extension in Late Cretaceous was a reflection of the Yan shanian orogens’ collapse. The evolution of the NNE-striking faults were constained by the sinistral shearing of the Tan-Lu fault, so that the sinistral strike slipping of the Ganjiang fault had a tendency of "stronger and earlier in north segment, gentle and late in south segment". The activity modes of the Ganjiang fault in Cretaceous were coincident with that of the Tan-Lu fault, and the former could be regarded as a southward extension of the Tan-Lu fault.