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Geochemistry of an ENE-WSW to NE-SW trending ~2.37 Ga mafic dyke swarm of the eastern Dharwar craton, India: Does it represent a single magmatic event?

( 2014-01-01) Srivastava, Rajesh K. ; Jayananda, M. ; Gautam, Gulab C. ; Gireesh, V. ; Samal, Amiya K.

A vast tract of ENE-WSW to NE-SW trending mafic dyke swarm transects Archaean basement rocks within the eastern Dharwar craton. Petrographic data reveal their dolerite/olivine dolerite or gabbro/ olivine gabbro composition. Geochemical characteristics, particularly HFSEs, indicate that not all these dykes are co-genetic but are probably derived from more than one magma batch and different crystallization trends. In most samples the LaN/LuN ratio is at ~2, whereas others have a LaN/LuN ratio >2 and show higher concentrations of high-field strength elements (HFSEs) than the former group. As a consequence, we assume that the ENE-WSW to NE-SE trending mafic dykes of the eastern Dharwar craton do not represent one single magmatic event but were emplaced in two different episodes; one of them dated at about 2.37 Ga and another probably at about 1.89 Ga. Trace element modelling also supports this inference: older mafic dykes are derived from a melt generated through ~25% melting of a depleted mantle, whereas the younger set of dykes shows its derivation through a lower degree of melting (~15%) of a comparatively enriched mantle source. © 2013 Elsevier GmbH.