Rs. Rawat et al., ORIGIN OF PINK K-FELDSPARS IN THE PERALUMINOUS AMRITPUR GRANITE, LESSER KUMAUN HIMALAYA, INDIA, Neues Jahrbuch fur Mineralogie Monatshefte, (1), 1996, pp. 9-20
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.