Petrology of Charnockites from Madurai Block of Southern Granulite Terrain, South India

Abstract

Charnockites are the most extensively studied rocks in the Southern Granulite Terrain (SGT). Charnockites are popularly known as hypersthene-bearing granite. Charnockite occurs as massive, foliated and incipient varieties in different crustal blocks of SGT. This paper presents the petrology and geochemistry of charnockite from Madurai Block. The charnockite (enderbite) studied from the Madurai Block is a medium grained rock with a mineralogy of 30–40% of quartz, 25–35% of feldspar, 15%>-20%> of ferromagnesian minerals (2-5% orthopyroxene, 2%-3% hornblende and 2%-3% biotite). Accessory minerals include Fe-Ti oxides (dominantly ilmenite), apatite, and zircon. The charnockites are dioritic to granitic in composition with high Al2O3 content and display both ferroan and magnesian characters. The REE plots of charnockites show high concentration of light rare earth elements (LREEs) and relatively low contents of heavy rare earth elements (HREEs), with significant LREE/HREE fractionation. They also show positive Eu anomalies or lack of Eu anomalies. Ba enrichment is the important characteristic of these charnockites with distinct Nb, Ta, and Ti depletion in mantle-normalized primitive mantle multi-elements diagrams, which has been considered to be one of the potential geochemical imprints of continental margin magmatism in a subduction-related environment.