The Metamorphism,Times And Tectonic Significance Of High-Grade Metamorphic Rocks In Xiwulangbulang Area Inner Mongolia

Daqingshan-Wulashan region Located in the central Inner Mongolia widely distributed the early Precambrian metamorphic basement,This is the ideal place to study Precambrian geology. Since the beginning of the last century, Chinese and foreign geologists began to study in the region。Although a great many achievements have been made, there are still some puzzles and arguments. The main contradictions on high-grade metamorphic terrane in the region is the different understanding of tectonothermal-evolution's mode and time. Xiwulanbulang area is located in the northern Slope of Daqingshan.The earlier Precambrian metamorphic basement distributed in Xiwulangbulang area is divided into Xinghe group,Wulashan group and Langyashan hypersthere granitic gneiss. The granulite of Xinghe xinghe group and the Langyashan hypersthere granitic gneiss are a set of high-grade metamorphic stratigraphy, They have a close relationship,a nd the detailed study of them can Help to solve the contradictions.In order to study the causes of they are formed and the relationship between them. we study the the geochemistry, metamorphic mineralogy,Characteristics of metamorphism and SHRIMP geochronology of region's high-grade metamorphic rocks . The results showed that:①Regional high-grade metamorphic rocks have complex geochemical characteristics , Samples of different locations have different geochemical characteristics, but the adjacent granulite sample and granitic gneiss sample have similar geochemical characteristics.It show that Xinghe group and Langyashan gneiss rock Share a common source rock,and they are formed by by the metamorphism, In the process of metamorphism, anatexis occurred and the Melt did not flow.②Metamorphic mineralogy and Characteristics of metamorphism show that the highgrade metamorphic rocks in the region experienced granulite facies metamorphism and suffered a later additional metamorphism.The metamorphism have a clockwise P-T paths which is considered to be the Continental collision type. The calculations from geothermobaromerers (geothermometers and geobarometers) indicate that the peak metamorphic condition is 800~850℃±,1.0~1.2Gpa. Judge from the characteristics of metamorphism,the anatexis occurred in the isothermal and decompression time after peak.③SHRIMP geochronology Research provides constraints for the metamorphism. The Zircon age of the core is 2550~2700Ma,It represents the formation time of the Xinghe group and langyashan gneiss's protoliths.The time which is not entirely consistent prove their protoliths is a complex. The Zircon age of the Mantle and edge department recorded continuous large-scale regional metamorphism which caused by continental collision occurred in 2450Ma~2550Ma ago.