Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular.This paper aims to understand the me...Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular.This paper aims to understand the melt source and emplacement age of the leucogranites from Sikkim in order to decipher the deep geodynamic processes of the eastern Himalayas.Zircon U-Pb analysis of the Higher Himalayan Sequence(HHS)metamorphic core reveals a prolonged period of crustal melting between>33 Ma and ca.14 Ma.Major and trace element abundances are presented for 27 leucogranites from North Sikkim that are classified into two-mica and tourmaline leucogranite types.They are peraluminous in composition,characterized by high SiO2(70.91-74.9 wt.%),Al2O3(13.69-15.82 wt.%),and low MgO(0.13-0.74 wt.%).Elemental abundances suggest that Sikkim Himalayan leucogranites are derived from crustal melts.The two-mica leucogranites are derived from a metagreywacke source,whereas the tourmaline leucogranites are sourced from metapelitic sources,with inherited zircons indicating an HHS origin for both types.U-Pb zircon geochronology of the two mica leucogranites indicates ages of ca.19-15 Ma,consistent with crustal melting recorded in HHS gneisses from Darjeeling.Monazites from both the two-mica and tourmaline leucogranites yield a crystallization age of ca.15-14 Ma,coeval with movement on the Main Central Thrust and South Tibetan Detachment System which further provides constraints on the timing and mechanism of petrogenesis of leucogranites in the Sikkim Himalayas.展开更多
Geochemical and Pb-Sr-Nd isotopic compositions of five Indosinian granitoid intrusions from the western Qinling belt provide insights into basement nature and tectonic affinity. The results show that the western Qinli...Geochemical and Pb-Sr-Nd isotopic compositions of five Indosinian granitoid intrusions from the western Qinling belt provide insights into basement nature and tectonic affinity. The results show that the western Qinling granitoids incline towards basic in their bulk chemical composition. The granitoids belong to high-K to shoshonitic series with K2O/Na2O=1.04-1.86 and are dominantly metaluminous with A/CNK=0.90-1.05 (most samples have A/CNK of <1.0). They have similar trace elemental compo- sitional patterns. In Sr-Nd isotopic compositions, they display some extent heterogeneity with Isr=0.70682-0.70845, εNd(t)=?4.85 to ?9.17 and TDM=1.26-1.66 Ga. They are characterized by high ra- diogenic Pb isotopic compositions. Their initial Pb isotopic ratios are 206Pb/204Pb=17.996-18.468, 207Pb/204Pb=15.565-15.677 and 208Pb/204Pb=38.082-38.587. Geochemical and Sr-Nd isotopic composi- tions reveal that magma for the granitoids was derived from partial melting of high-K (Rb) basaltic rocks, which might be formed in 900-1400 Ma. It is suggested that a large amount of the Proterozoic high-K (Rb) basaltic rocks, which underlie the Phanerozoic sedimentary cover, constitute the crustal basement of the western Qinling belt. Pb-Sr-Nd isotopic compositional comparison between the east- ern Qinling and the western Qinling Indosinian granitoids indicates that the crustal basement of the western Qinling is distinct from that of the eastern Qinling. The Baoji-Chengdu railway close to south-north orientation can be taken as an approximate boundary between both basements. The Pb-Nd isotopic compositional characteristics of the western Qinling granitoids suggest that the basement of the western Qinling belt has an affinity with the Yangtze block.展开更多
基金supported by Innovation in Science Pursuit for Inspired Research (INSPIRE)No.DST/INSPIRE Fellowship/2016/IF160729,。
文摘Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular.This paper aims to understand the melt source and emplacement age of the leucogranites from Sikkim in order to decipher the deep geodynamic processes of the eastern Himalayas.Zircon U-Pb analysis of the Higher Himalayan Sequence(HHS)metamorphic core reveals a prolonged period of crustal melting between>33 Ma and ca.14 Ma.Major and trace element abundances are presented for 27 leucogranites from North Sikkim that are classified into two-mica and tourmaline leucogranite types.They are peraluminous in composition,characterized by high SiO2(70.91-74.9 wt.%),Al2O3(13.69-15.82 wt.%),and low MgO(0.13-0.74 wt.%).Elemental abundances suggest that Sikkim Himalayan leucogranites are derived from crustal melts.The two-mica leucogranites are derived from a metagreywacke source,whereas the tourmaline leucogranites are sourced from metapelitic sources,with inherited zircons indicating an HHS origin for both types.U-Pb zircon geochronology of the two mica leucogranites indicates ages of ca.19-15 Ma,consistent with crustal melting recorded in HHS gneisses from Darjeeling.Monazites from both the two-mica and tourmaline leucogranites yield a crystallization age of ca.15-14 Ma,coeval with movement on the Main Central Thrust and South Tibetan Detachment System which further provides constraints on the timing and mechanism of petrogenesis of leucogranites in the Sikkim Himalayas.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40234052 and 40521001)the State Key Laboratory of Geological Process and Mineral Resources,China University of Geosciences and the Key Laboratory of Continental Dynamics, Northwest University
文摘Geochemical and Pb-Sr-Nd isotopic compositions of five Indosinian granitoid intrusions from the western Qinling belt provide insights into basement nature and tectonic affinity. The results show that the western Qinling granitoids incline towards basic in their bulk chemical composition. The granitoids belong to high-K to shoshonitic series with K2O/Na2O=1.04-1.86 and are dominantly metaluminous with A/CNK=0.90-1.05 (most samples have A/CNK of <1.0). They have similar trace elemental compo- sitional patterns. In Sr-Nd isotopic compositions, they display some extent heterogeneity with Isr=0.70682-0.70845, εNd(t)=?4.85 to ?9.17 and TDM=1.26-1.66 Ga. They are characterized by high ra- diogenic Pb isotopic compositions. Their initial Pb isotopic ratios are 206Pb/204Pb=17.996-18.468, 207Pb/204Pb=15.565-15.677 and 208Pb/204Pb=38.082-38.587. Geochemical and Sr-Nd isotopic composi- tions reveal that magma for the granitoids was derived from partial melting of high-K (Rb) basaltic rocks, which might be formed in 900-1400 Ma. It is suggested that a large amount of the Proterozoic high-K (Rb) basaltic rocks, which underlie the Phanerozoic sedimentary cover, constitute the crustal basement of the western Qinling belt. Pb-Sr-Nd isotopic compositional comparison between the east- ern Qinling and the western Qinling Indosinian granitoids indicates that the crustal basement of the western Qinling is distinct from that of the eastern Qinling. The Baoji-Chengdu railway close to south-north orientation can be taken as an approximate boundary between both basements. The Pb-Nd isotopic compositional characteristics of the western Qinling granitoids suggest that the basement of the western Qinling belt has an affinity with the Yangtze block.
