The Metamorphic and Deformed Characteristics of the Heilongjiang Melange in Mudanjiang Area

There is a set of structural melange of oceanic features in Mudanjiang area,Heilongjiang Province.Based on its mineral assemblage and petrographical characters,the melange is divided into three metamorphic and deformed belts,namely,the blueschist,stilpnomelane and biotite belts in turn.The existence of the two intense ductile belts separating the three belts shows they are not successive metamorphic belts but structural belts.Hence,the Heilongjiang melange of the Mudanjiang area does not belong to the normal metamorphic strata of the strictly stratigraphic meaning.The three belts are related to the thrusting from the north to the south.Based on present research and known chronological data,the structural evolution in the area can be divided into three stages:(1)before 305-296 Ma,a stage of subduction of intercontinental oceanic crust and closure of intercontinental ocean between the Jiamusi terrain and the Xingkai terrain;(2)170.26-154 Ma,a stage of collision between the Jiamusi terrain and Xingkai terrain and of an integrated continent affected by western pacific plate;(3)after 154 Ma,a stage of sinistral strike-slip and of its reworking of the Dunmi fault on Heilongjiang melange.