Geochemical characters of Leptynite from Melur, Madurai District, Tamil Nadu, South India

Leptynite occur with minor bands of basic granulites, charnockites, calcsilicate rocks, quartzites and khondalites in the Melur area in the Southern granulite terrane (SGT), India. Interbedded grey and cream leptynite types are distinguished based on field relations and geochemistry. They are paragneisses (khondalites) comprising to quartz-felspar-sillimanite gneiss, quartz-felspar-garnet-sillimanite gneiss and their variants: charnockite series consisting of pyroxene granulites (basic) and charnockites (acidic), granites, pegmatites and aplites and dolerites. Charnockites, granites and dolerites are successfully emplaced into the basement rocks' interbanded paragneiss and pyroxene granulites. Leptynite is noticed at the contact of paragenesis and charnockite. Based on whole-rock geochemistry, it is evident that both charnockite patches and host leptynites are isochemical. The adamellite composition, per-aluminous nature with positive Europium anomaly of host leptynite and charnockite patches, suggest their co-genetic relation. Higher values of (La/Yb)N and (Gd/Lu)N of leptynites indicate the highly fractionated HREE pattern of leptynites. The total REE, LREE/HREE and Eu-Eu∗ data indicate their derivation from the post-Archaean granodioritic upper crust comprising of large proportions of impure greywackes with K-rich granitic components.