OCCURRENCE OF FLUORAPATITE IN GRANITIC VEINS FROM THE KERALA KHONDALITE BELT, SOUTHERN INDIA

This paper presents the first description of fluorapatite in rocks of the Kerala Khondalite Belt in southern India. The fluorapatites occur either dispersed or aggregated in granitic and pegmatitic veins which intruded into high-grade metamorphic garnet-biotite gneisses. Microtex tures indicate an exclusively magmatic origin for the fluorapatites an d the strong zoning of F and OH points to a change in fluid/melt compo sition during apatite crystallization. The P-T conditions of melt crys tallization are estimated to be in the range of 750-800 degrees C and less than or equal to 5 kbar. The origin of the fluorapatite bearing m elts is poorly known. It is suggested that they formed either through fluid-absent incongruent melting of a F-rich biotite or during a late stage of fractional crystallization of a granitic parent magma. Additi onally, we report a single occurrence of a monazite-rich quartzmonzodi orite vein. Field observations indicate an emplacement subsequent to t he fluorapatite bearing granites and pegmatites. The occurrence of mag matic andalusite and cordierite in this rock points to a crystallizati on at low pressures (P less than or equal to 3 kbar).