TEMPORAL AND SPATIAL EVOLUTION OF METAMORPHISM IN ALTAIDE OROGENIC BELT,CHINA

Chinese Altaide coinciding geographically with Altay mountain is located in the southwest margin of Siberia plateform.It extends northwestly to Kazakhstan Gornyi and Rudnyi Altay and southeastly to Mongolia Gobi Altay.Junggar block and surrounding geosyncline fold region is located to the south of Chinese Altaide and they are divided from each other by Irtysh fault. Chinese Altaide is a typical orogenical belt and experienced three episode of tectono-metamorphism in Hercynian orogenical cycle.The main episode metamorphism,granitization and deformation developed on the basis of early episode metamorphism and deformation.The main episode metamorphism is characteristed by typical progressive metamorphic belt from biotite to sillimanite belt.In the process of prograde metamorphic reaction,a sequential porphyroblastic phase formed on the basis of primary assemblage.The higher grade metamorphic assemblage neither developed directly from primary assemblage(chlorite+sericite) nor from the predecessor equilibrium assemblage.The rocks of a higher grade metamorphic zone had undergone each P-T range from lower to higher in turn,but it did not reach the equilibrium assemblages each of metamorphic zone because reaction time were very short and only little part could react when the rock underwent each P-T range of prelude lower metamorphic zones.And so,a series sub-equilibrium minerals such as biotite,garnet,staurolite,kyanite coexists in the rocks of higher grade metamorphic zone After peak of metamorphism of each metamorphic zone in main episode,the rocks subjected static retrograde metamorphism more or less.Aluminosilicate minerals retrograded into muscovite and garnet,staurolite,cordierite and biotite into chlorite and muscovite.And in late deformatiom episode,the metamorphic rocks were subjected dynamic retrograde metamorphism along the shear zone.