Garnet mineral chemistry as a provenance indicator for the modern beach sediments of north-eastern Andhra Pradesh, east coast of India

Abstract

The provenance of garnets from coastal sediments between the Nagavali and Vamsadhara river mouths, east coast of India were studied using garnet molecular proportions. This mineral chemical electron micro probe analytical data have been correlated with published garnet chemistry from various litho units of the eastern ghats granulite belt to understand provenance. The present study reveals that the garnets with molecular proportions of almandine (Alm. 50-56%), pyrope (Py. 33-43%) and traces of grossular (Gr. <5%) were derived from khondalite suite of rocks (khondalites, leptynites and quartzo-feldspathic gneisses) and migmatites. The garnets with molecular proportions of almandine (Alm. 59-63%), pyrope (Py.<30 %) and considerable proportion of grossular (Gr.>5%) were derived from charnockite suite of rocks. The major portion (83%) of the studied garnets is derived from khondalite (metapelitic) suite of rocks susceptible for physical weathering due to large areal exposure and minor proportion (17%) is derived from charnockite suite of rocks which due to less coverage in drainage basis is not susceptible for mechanical weathering.