Geochemistry of the late phanerozoic mafic dykes from the Moyar shear zone, South India, and its implications on the spatial extent of Deccan Large Igneous Province

Abstract

The late Phanerozoic dykes of the Moyar shear zone mark a prominent intrusive structure in the Precambrian crystalline rocks of northern Kerala. The dykes, having variable strike length and width, show a predominant NW-SE trend and basaltic composition with SiO2 ranging from 48.59 % to 49.53 % and normative quartz/olivine. The chondrite normalized REE patterns are fractionated, parallel to sub-parallel, and are generally uniform but with negative Eu-anomalies. Chemical characteristics are typical of MORB or within-plate basalts and suggest derivation of melt from a fertile or plume-related mantle source with a considerable correlation to Deccan basalts. This is consistent with the regional geological setting including the volcanism, associated with a Proterozoic crustal scale shear zone, occurring long before the onset of seafloor spreading in the Indian Ocean. The possibility of redefining the southern limit of the Deccan Large Igneous Province is examined using the characteristic features of the dykes.