Diffusion of hydrogen in garnets reveals the rapid formation of spodumene pegmatite from Cuore in the Himalayan orogen
The Higher Himalayan leucogranite which extends east-westward for nearly 2500km is not only the product of the Cenozoic India-Asia continental collision,but also closely related to a variety of rare metal deposits.Recently,a number of spodumene pegmatite veins have been found in Cuore area in the central part of the Higher Himalayas.To study the evolution process of magma differentiation and explore the time duration of diagenesis and mineralization of these spodumene pegmatites,electron probe and Fourier transform infrared spectroscopy were used to analyze garnet from various types of granite and spodumene pegmatite in this area.The results show that the garnet in the granite-pegmatite system is an almandine-spessartine solid solution and of magmatic origin.There may be a variety of OH substitution mechanisms in pegmatite garnet.The major compositions and water content of garnet can record the evolution of magma since they can be affected by Si,Fe,Ca and Mn.In the process of magmatic differentiation and evolution from garnet muscovite granite to spodumene pegmatite,garnet is gradually rich in manganese and water.After the emplacement of pegmatite,surrounding rock contamination and fluid loss may occur,resulting in poor manganese and water on the edge of the garnet.The hydrogen diffusion simulation of garnet can be used to constrain timescales of cooling processes and pegmatite formation.The thermal simulation result shows that it takes only 24 days for the 2.5 m thick spodumene pegmatite dike to cool from the emplacement temperature of 720℃ to the central temperature of the dike below 450℃,which indicates that spodumene pegmatites in Cuore area have a rapid formation rate.Besides,the water content of garnet is positively correlated with MnO/(MnO+FeO).Therefore,the high-water-content(＞0.04％)of spessartine may be a potential sign of Li-Be mineralization of leucogranites and pegmatites in Himalayan region.
GarnetWaterDiffusion modelSpodumene pegmatite from CuoreHigher Himalayan leucogranite
万方数据
