ORIGIN OF PINK K-FELDSPARS IN THE PERALUMINOUS AMRITPUR GRANITE, LESSER KUMAUN HIMALAYA, INDIA

The Precambrian anatectic Peraluminous Amritpur Granite has well devel oped, deformed, pink K-feldspar phenocrysts (intermediate microcline-p erthitic) embedded in a chlorite rich groundmass. The later vein perth ite cut across the earlier exsolution perthite in them. The plagioclas es have a predominance of pericline twins. The assimilated metabasic/a mphibolite (chloritized) xenoliths (external source) have provided the necessary Fe and Mg in the granite system. The Himalayan Orogeny caus ing the associated deformation and metamorphism provided the necessary fluids and stress for the migration of Fe and Mg from the chloritized xenolithic mass into the K-feldspar phenocrysts in a closed system. T he pink K-feldspars are due to the introduction of Fe and Mg from oute r sources during the development of vein perthite, pericline twins and inversion of the higher structural mate K-feldspar to a lower structu ral state under the influence of Himalayan Orogeny. The tentative temp erature of formation of the pink K-feldspars seems to be 400 to 450 de grees C at about 4kbar pressure.