Metapelite and Garnet-Bearing Leucogranites in the Namche Barwa Area,Southern Xizang,and Their Constraints on Tectonic Events
The Namche Barwa area of southern Xizang is located in the east of the Himalayan orogenic belt. This area has recorded extensive Cenozoic metamorphism and crustal anataxis,and is significant for studying the evolution process of the Himalayan orogenic belt. Based on field geological investigations and indoor microscopic petrological observations,this work analyzed the chronological significance and geochemical characteristics of metamorphic rocks and leucogranite in the Namche Barwa area through zircon U-Pb chronology and whole rock geochemistry. In this area,the garnet-bearing leucogranite parallel to schistosity intruded into metapelite in the outcrop. This metapelite is garnet-bearing biotite plagioclase gneiss,and its inherited zircon age ranges from 1617 Ma to 565 Ma,which recorded the Cenozoic metamorphism from 28.1 Ma to 16.4 Ma. The formation age of the garnet-bearing leucogranite is 23.3±0.4 Ma,and it experienced magmatic events from 18.4 Ma to 8.6 Ma. It is the product of multiple partial melting of metamorphic rocks during the tectonic decompression in the Namche Barwa area. This garnet-bearing leucogranite has higher SiO2,K2O,FeOT and A/CNK,lower AL2O3,CaO,Na2O and Na2O/K2O,which belongs to peraluminous potassium rich granite. It is enriched in Rb,K,Pb,depleted in Ba,Sr,Nb,Ta,Nd,Zr,Ti,with strong depleted Eu and gull-like REE patterns,with higher Rb/Sr,Nb/Ta and lower Zr/Hf,which may be related to plagioclase and monazite separation crystallization and the melt structure transition.
万方数据
维普
