Abstract:
Mafic dykes of Rewa basin occur along the Son-Narmada lineament between the Deccan volcanics of western India and the mafic and ultramafic dykes of the Gondwana coalfields in eastern India. In the present area of study, Umaria is from the western part, Shahdol from the central and the Chirimiri dykes are from the eastern extremity. Palaeomagnetic determinations on the Shahdol and Chirimiri dykes of the Rewa basin obtain a palaeomagnetic pole at 40.40°N and 286.62°E, which is very close to Deccan, super pole. The dykes are medium to coarse grained, porphyritic with phenocrysts of clinopyroxene (Wo31–39 Fs14–25 En42–46), plagioclase (An 43–78) set in a groundmass of clinopyroxene (Wo28–39Fs21–54 En17–39), plagioclase (An 63–65), olivine and opaque minerals. The mafic dykes have a restricted composition in the basaltic field. The Umaria dykes intruding the Deccan lavas are more evolved than the others. ΣREE varies from 86.8 to 141.8 ppm in the dykes with a weak Eu anomaly (Eu/Eu* varies from 0.82 to 1.13). Initial 87Sr/86Sr ratios in the mafic dykes vary from 0.704625 to 0.714403 and 143Nd/144Nd varies from 0.511677 to 0.512802. The (εNd)i values of five dykes are positive varying from + 1.46 to + 4.83; two dykes samples have negative εNd values. In a 143Nd/144Nd vs 87Sr/86Sr plot, the dykes do not fall in any of the fields established for the Deccan stratigraphic formations of the Western Ghats. The Sr and Nd isotopic ratios of the dykes require complex contamination of a depleted source with an end member having high Rb/Sr and low Sm/Nd. It is suggested that these dykes are late stage intrusions of Deccan magma along the Narmada lineament and were possibly emplaced along intrabasinal faults in Rewa and other Gondwana basins of eastern India.
