THE TECTONIC EVOLUTION OF THE LIAODONG RIET

The Liaodong rift refers to an early Proterozoic sedimentary hasin located in eastern Liaoning and southern Jilin. It originated from dextral strike-slip movement of the ancient Tancheng-Lujiang fault and its development lasted from about 2300±100 to 1700±100Ma. Tce volcanic-sedimentary series accummulating ia the rift may be divided into the Liaoyang Group in the lower part and the Liaohe Group in the upper part. The boundary between the groups lies between the Gaojiayu Formation and the Dashiqiao Formation. The geological structure in the rift shows the characteristics of polycyclic development, The early and late cycles went through a process of development from extensional fault depression-compressive uplift. In the early cyclethere occurred intermediate-acid and occasionally basic magmatic eruption and distinct structural differentiation. The Liaoyang Group deposited at that time may be laterally divided into three different structural lithofacies areas. In the late cycle there occurred intrusion of basic rocks, and structural differentiation weakened. The lithofacies formations are essentially consistent in the whole region. The age of the upper limit of the Liaohe Group is 1700±100 Ma, when there occurred an important event of deformation and metamorphism.