Geochemistry and Petrography of Pyroxenites from Mettupalaiyam Ultramafic Complex, Tamil Nadu

Abstract

The Mettupalaiyam ultramafic complex (MUC) in Tamil Nadu is a major lithological association consisting mostly of Pyroxenites, Peridotite, Gabbro, Anorthosite gabbro in a predominantly gneissic grantite-granite terrain. Pyroxenite occurs as thin lenses and bands, at times attaining moderate thickness. Major, Trace and rear earth element geochemistry and petrography of  pyroxenites collected from well exposed outcrops near Thenkalmalai areas of this complex are presented in this paper and their Petrogenetic significance is discussed.

The geochemical signatures of the pyroxenites show a significant variation in major and trace element concentration. The pyroxenites show SiO₂ composition ranging from 49.6-55.5%, Al₂O₃ from 6-13.6%, MgO from 3.6-14.3%, CaO from 8.4-15.5% and TiO₂ from 0.24-1.7%. Bulk composition/whole rock analyses indicate that the magma type is tholeiitic but trending towards a calc-alkaline. The pyroxenites are poor in incompatible and high field strength (HFS) elements like Rb, Sr, Hf, and Ta.

Total rare earth element (∑REE) content varies in a limited range and exhibits limited REE fractionation in both LREE and HREE. The pyroxenite sample shows Negative Eu-anomalies with slight enrichment of HREE. Primitive mantle normalized multi-element spider grams suggest that the melt parental to these pyroxenites was derived from a mantle source enriched in several trace trace elements.