Miocene magmatic activity and tectonic implications in Yadong,southern Tibet
Himalayan leucogranites provide a natural probe to study tectonic-magmatic evolution history of continental collisional orogen.The Yadong leucogranites are located in the middle of the Higher Himalayan Sequence(HHS),and their petrogenesis and tectonic implications need to be further investigated and discussed.To address this issue,we carried out new whole-rock geochemistry and zircon geochronology study for leucogranites and granitic gneiss from Yadong area.The leucogranites are peraluminous and high-K calc-alkaline rocks,and characterized by high SiO2 and K2O concentrations(69.4％～75.5％SiO2 and 2.88％～6.70％K2O),but low CaO,FeOT,MgO concentrations(0.44％～1.74％CaO,0.29％～2.53％FeOT and 0.04％～0.57％MgO),enriched LREE patterns and obviously negative Eu anomalies,which are consistent with typical High Himalayan leucogranites.LA-ICP-MS zircon U-Pb dating yields crystallization ages of ca.21.0Ma and 23.0Ma,and partial melting in Yadong may have started as early as 36～30Ma.Yadong leucogranites have εNd(t)and(87Sr/86Sr)i values of-16.7 to-13.8 and 0.754080 to 0.791009,respectively,which are similar to those of metasedimentary rocks.The granitic gneisses have significantly higher εNd(t)and(87Sr/86Sr)ivalues of-9.0 to-8.8 and 0.847193 to 0.866306,respectively.These pieces of evidences indicate that the leucogranites were derived from partial melting of metasediments in the HHS without or with insignificant addition of granitic gneisses.Combining results from multidisciplinary studies including geochemistry,metamorphic petrology and geochronology,it is suggested that the dehydration melting of muscovite has already occurred during the burial and thickening of the HHS,and then large-scale decompression melting occurred during the tectonic extension stage,resulting in the large amounts of the Miocene leucogranites.
万方数据
维普
