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Microstructural and geochemical studies of Higher Himalayan Leucogranite: implications for geodynamic evolution of Tertiary Leucogranite in the Eastern Himalaya

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Abstract

The Higher Himalayan Leucogranites (HHLG) intruded into the high grade rocks of the Higher Himalayan Crystallines (HHC) in Arunachal Himalaya of the Eastern Himalaya, yield distinctive field data, petrography, microstructures, geochemical and mineral chemistry data. The Arunachal HHLG are characterized by the presence of two micas; normative corundum; high contents of SiO2 (67–78 wt.%), Al2O3 (13–18 wt.%), A/CNK (0.98–1.44) and Rb (154–412 ppm); low contents of CaO (0.33–1.91 wt.%) and Sr (19–171 ppm), and a high ratio of FeO(tot)/MgO in biotite (2.54–4.82). These distinctive features, along with their strong depletion in high field strength elements (HFSE), suggest their affinity to peraluminous S-type granite generated by the partial melting of crustal material. Geothermobarometric estimations and mineral assemblages of the HHC metapelites confirm that the HHLG were probably generated in the middle crust (~20 km) and the produced melts intruded the HHC in the form of sills/dykes. Microstructurally, the HHLG shows high temperature deformation features including chessboard extinction in quartz and cuspate/lobate grain boundaries between quartz and feldspars (plagioclase and K-feldspar). The deformation microstructures suggest that the HHLG was deformed under early high temperature ductile deformation conditions. These fabrics were subsequently superimposed by later brittle deformation features associated with decreasing temperatures during the exhumation of the HHLG towards shallow structural levels at the time of Himalayan orogeny. Copyright © 2013 John Wiley & Sons, Ltd.

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