GEOLOGICAL FEATURE AND EVOLUTION OF THE EARLY PRECAMBRIAN CONTINENTAL CRUST IN NORTHERN LIAONING PROVINCE AND SOUTHERN JILIN PROVINCE

The region of northern Liaoning Province and southern Jilin Province is one of the regions where typical Early Precambrian continental crust is exposed.It is composed of the granite greenstone belt and high grade metamorphic terrain,which contain abundant mineral resources such as gold,copper,zinc and iron.Single zircon U Pb, 40 Ar / 39 Ar,Sm Nd and Rb Sr isochron ages suggest that the greenstone belt was formed 2700—2800 Ma ago.The ages of three types of syntectonic granites associated with the greenstone belt are （2555±35）Ma,（2515±4）Ma and 2505—2400Ma,respectively.The formation ages of supracrustal rocks and granites in the high grade terrain are 3018 Ma and 2950 Ma.Metallogenic epochs of syntectonic and post tectonic gold deposits in the greenstone belt are 2409—2475 Ma and 180—190 Ma.The Early Precambrian crust can be divided into two types in the study area:one type is primaty crust which was formed by direct mantle partial melting,while the other is reworked crust which was formed by anatexis or partial melting of preexisting crust.Four periods of Early Precambrian continental crust formation may be distinguished,they are 3500—3700Ma,3000 Ma,2700—2900 Ma,respectively.