五台山变质地体的区域变质相带和变质期次

REGIONAL METAMORPHIC ZONE AND STAGES OF THE METAMORPHIC TERRANE AT WUTAI MOUNTAINS

Comprehensive analysis of relations between unconformity interfaces and composition of basal conglomerate, characteristics of the metamorphic zone, metamorphic process, temperature-pressure conditions, metamorphic minerals (especially the X-ray analysis of muscovite), tectonic features, isotopic age and mineral generations suggests that the Early Precambrian metamorphic terrane at Wutai Mountains underwent two different types of regional metamorphisms in Wutai period of the Late Archean and Luliang period of the Early Proterozoic. The metamorphism in Wutai period recorded in the Wutai Group led to formation of sillimanite zone, staurolite-kyanite zone, almandine zone, biotite-chlorite zone and chloritoid zone, belonging to regional heat-flow metamorphism of Barrow type. The metamorphism in Luliang period mainly recorded in the Hutuo Group led to formation of sericite-chlorite zone of sandslate-phyllite level of low greenschist facies, belonging to regional low-temperature dynamic metamorphism. The metamorphism in Luliang period caused the metamorphism series of Wutai Group to produce a widely superimposed metamorphism of greenschist facies. The spatial distribution and characteristics of metamorphic zone, types, stages and evolution of the metamorphism are coincident with the crustal evolution of stable blocks formed in Early Precambrian in the Wutai Mountain region.