METAMORPHOSED BASIC AND ULTRABASIC DYKE SWARMS IN TAIPINGZHAI REGION,EAST HEBEI
Song Shuguang(Xi'an Institute of Geology and Mineral Resources)
Five varieties of basic and ultrabasic metamorphosed dyke swarms have been recognised in the high-grade gneiss terrain in Taipingzai region , East Hebei Province. They are Ⅰ. pyroxene-granulite dykes and amphibole-pyroxenite dykes intruded in per- or syn-D2 deformation phase and metamorphosed by pyroxenegranulite facies; Ⅱ.garnet amphibole anorthositic diopsidite dykes metamorphosed by high- grade amphibolite facies; Ⅲ. diabase-porphyrite dykes metamorphosed by amphibole- granulite facies;Ⅱ.amphibolite dykes metamorphosed by low-grade amphibolite facies andⅢ.diabase dykes metamorphosed by greenschist facies. The latter four types of dyke intruded in the ending of Archaean.According to the feature of deformation and metamorphism of dyke Ⅱ.Ⅲ. and Ⅳ., the author have determined D4 deformation phase in the early precambrian deformation history and high-grade amphibolitefacies to amphibole-granulite facies. This is a new tectonic-magmati-cmetamorphic event of crustal evolution. So, at least two granulite facies metamorphic events have taken place in this area.The intrusion of numerous dyke swarms is one of the marks of ending andstabilization of cratonic orogenic movement.The characteristics of dyke swarm reflected the evolution regularity that crustal temperature gradually lowered and deformation changed from ductile to brittle.