Articles written in Journal of Earth System Science

    • Geochemistry and petrogenesis of tholeiitic dykes from the Chotanagpur Gneissic Complex, eastern India


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      In this study, we present the geochemical analysis on 14 samples from seven distinct E–W trending mafic dykes from the Chotanagpur Gneissic Complex. These dykes have not been studied previously and highlight the importance of igneous and tectonic processes in the Chotanagpur Gneissic Complex. The dykes, in terms of modal mineralogy, do not show notable variations, but textural variations are well noticed. These dykes are characterised as basalt and basaltic andesite (SiO$_{2}$ = 45.48–54.03 wt.%; Mg# = 21–68.5), and comparable with E-MORB type tholeiitic magma series. The dykes are classified into two groups, low Mg# and high Mg# dykes, based on their Mg# and silica content. The major fractionating mineral phases are olivine, plagioclase, and pyroxene. The dykes are variably contaminated with crustal input, as shown by Nb/U vs. (Th/Nb)PM, Th/Nb vs. La/Nb, and Th/Yb vs. Nb/Yb. The dykes also underwent post-magmatic hydrothermal alteration after their emplacement. Semi-quantitative trace element modelling suggests that these dykes are derived by partial melting within spinel peridotite-rich mantle and spinel–garnet peridotite-rich mantle source in the transition zone. The low Mg# dykes are consistent with 3–15% partial melting curves, whereas high Mg# dykes are comparable with 15% melting curve. Finally, we present a conceptual and simplified model for the E–W trending mafic dykes of the CGC, based on the geochemical data of the present study and the available information.

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