Geochemistry and petrogenesis of Proterozoic mafic dykes in north Kerala, southwestern Indian Shield- preliminary results

Abstract

Mafic dyke intrusions occur in three distinct orientations (NNW-SSE; NW-SE and NE-SW) in north Kerala region, the southwestern part of the Indian Shield. Dating of two NNW-SSE trending dykes by K-Ar method has yielded Middle Proterozoic ages (ca. 1660 Ma and ca. 1420 Ma respectively). Our initial geochemical results on these dyke rocks (0.65-0.15 wt% K₂O, 0.37-0.38 wt% P₂O₅, 3.30-1.00 wt% TiO₂, 11-1 p.p.m. Rb, 250-90 p.p.m. Sr, 230-40 p.p.m. Ba, 160-40 p.p.m. Zr and 30-10×chondrite rare earth elemental abundances) indicate a transitional character between abyssal and plateau tholeiites. Petrogenetic modelling suggests that the dyke compositions have been derived by different degrees of partial melting of a heterogenous source mantle. The mantle sources with accessory amphibole and/or garnet, variably enriched in LREE and LIL elements, is compatible with the observed geochemical data.