METAMORPHISM OF THE LIAOHE GROUP

There exist four progressive metamorphic zone in the Liaohe Group.From the center to the south and north sides they are successively the kyanite zone staurolite zone,almandine zone and biotite zone.There also exist three meta- morphic facies corresponding them.The former two zones correspond to the lower amphibolite facies,while the latter two respectively correspond to the higher greensehist facies and the lower greenschist facies.That is to say,the progressive metamorphic zones in the Liaohe Group occur as E-W-trending elongated zones,the northern and southern parts being roughly symmetric.The thermal dome of the metamorphism is distributed in the Boluopu-Tongyuanbo- Hongshilazi area,with the metamorphic grade decreasing towards the northern and southern sides.The metamorphic zones are distinguished according to the principles of the isograd and isogradal reaction. The process and regularity of evolution of metamorphism of the Liaohe Group are discussed using the facies topologic diagram.The Liaohe Group is of medium-pressure metamorphic facies series and medium-pressure metamor- phism.The metamorphic temperature in the center is about 600℃. The metamorphism in the Liaohe Group reached its climax in the second deformation phase,and retrogressive metamorphism took place in the third deformation phase.This feature is very similar to that of the Dalradian rock series in the Scottic Highlands. The basic rock features of the Liaohe Group were formed by metamor- phism and deformation in the Luliang stage.It is not possible that there might be large unconformable surface.The center of the thermal flow of the Luliang-aged metamorphism coincides with the center of the Liaodong au- lacogen.