Barium Isotope Evidence For The Roles Of Fluid In The Origin Of Himalayan Leucogranites

Leucogranite is essential for the understanding of late stage crust evolution,magmatism and ore formation in the orogenic belt.The fluid activity during leucogranite formation process may enrich metal elements(Be,Li,Rb,etc.),which are important for ore-deposition forming.To constrain the fluid effect and source of fluid mobile elements,this study reports Ba isotope compositions of 16 leucogranite samples from the Kampa dome in Himalaya.The results show that ?138/134Ba of these samples are within-1.32?+0.12‰,which are generally lower than the values of mantle source magmatic rock,glacial diamictites and sediments.While the previous published granite show Nb/Ta ratios>5,Kampa leucogranites show lower Nb/Ta ratios and similar?138/134Ba range with A-type granite from Southern China.Therefore,the light Ba isotope compositions in the Kampa leucogranites may unlikely reflect magma crystallization or signature of the metasediment source.We suggest that Kampa leucogranite may have been affected by fluid activity with lighter barium isotopic compositions.The research implies that Ba isotope composition can potentially be a novel tool to trace magmatic evolution and formation of the metal ore-deposits.