The Birth History of Two Granitic Plutons of the Bhilangna Valley of Garhwal Himalaya: A Geochemical Approach

On the basis of geochemical study, two granitic plutons are identified in the Bhilangna valley of the Garhwal Himalaya, viz. the Chaili porphyritic granite gneiss (CPGG) and the Ingedinala granite gneiss (IGG). Both, CPGG and IGG rocks fall in the quartz rich zone (QRZ) of chemical-mineralogical typology of Dcbon and Le Fort, 1982. CPGG and IGG are strongly peraluminous, S-type granites and enriched in Si and K and depleted in Ca and Sr. The unusually high K₂O suggests introduction of LILE during metasomatic processes. Both, CPGG and IGG are crustally derived and produced due to the partial melting of psammo-pelitic sediments. Probably the source materials for CPGG and IGG are same, attested by the geochemical similarities. The Q-Ab-Or plots of CPGG and IGG revealed that the temperature higher than that of the 'minimum' melt was attained during anatexis. During the Himalayan orogeny, intracontinental subduction took place along MCT and provided channels for the metasomatic fluids which induced K and Rb metasomatism and subsequently modified the nature of CPGG and IGG.