Petrology and geochemistry of basanite dykes and gabbro from northern Kutch, western India: Implications on source rock characteristics

Major and trace (including rare earth) element abundances, mineral compositions and Nd and Sr isotopic compositions have been determined for the mafic dykes (classified as basanite) and gabbro of the northern Island belt of Kutch rift basin. These are petrographically and geochemically distinct but have similar mantle normalized trace element patterns. Measured Sr-87/Sr-86 ratios in the mafic dykes vary from 0.70428 to 0.70593. epsilon Nd (i) varies from 0.27 to - 6.5. The isotopic compositions are broadly similar to that of Mahabaleshwar flows of western Deccan volcanic province. The geochemical character suggests the influence of fractional crystallisation in the evolution of the basanite dykes. The parent magma was enriched in K, Ti, Na and P suggesting derivations from an enriched source during the early phase of rifting. Palaeomagnetic data on the dykes show the presence of both normal polarity direction at D-m = 338 degrees, Im=-47 degrees and reverse polarity direction at D-m=141 degrees and I-m=34 degrees indicating multiple intrusion. Virtual Geomagnetic Pole (VGP) for the basanite dykes differs from Deccan Super pole suggesting a magmatic event older than the main Deccan eruption.