THE VARIATION OF THERMODYNAMICAL CONDITIONS OF METAMORPHISM AND THE EVOLUTION CHARACTERISTICS OF THE NORTH CHINA PLATFORM

Archaean-Proterozoic metamorphic rock seriesis extensively distributed in the North China Platform.The difference of thermodynamical conditions of metamorphism shows evolution characteristics of the North china platform. Study of thermodynamical conditions of a few typical metamorphic regions indicates that these areas,such as eastern Hebei,Fuping,Miyun,Hengshan, Zuozi-Yanggao,Jining and Qianlishan,belong to Archaean metamorphic regions of granulite facies. The difference of thermodynamical conditions and rocks associations demon- strates that they are products at different erosion depths.Metamorphic temper atures in these areas are over 750℃,and pertain to regional high-temperature metamorphism.Various pressures show that these rocks were formed at different of the crust.During the late Archaean-early Proterozoic,there were amphibolite facies and greenschist facies of regional dynamical thermal flow metamorphism,and in the late Proterozoic,regional dynamical metamorphism of sub-greenschist facies developed in the North China platform.With time, from Archaean to Proterozoic,the thermal flow of the crust had a tendenog to decrease,and the strength of metamorphism weakened obviously. The changes from regional high-temperature metamorahism through regional dynamical thermal flow metamorphism to regional dynamical met- amorphism again represent the processor variation of thermal dynamical conditions during the history of the crust.They demonstrate all the evolution history of the crust from activity to stability