Are Deccan basalts contaminated by the continental crust?

Basalts from the Western Ghats lava sequences of the ca. 66 Ma Deccan Large Igneous Province (LIP) display substantial geochemical variability from enriched, crust-like signatures in the Late Cretaceous Kalsubai and Lonavala Subgroup basalts (e.g., ⁸⁷Sr/⁸⁶Sr_i mainly 0.705-0.715) to more depleted, mantle-like signatures in the Early Paleogene Wai Subgroup basalts (generally, ⁸⁷Sr/⁸⁶Sr_i ca. 0.703-0.706). By contrast, Os isotopic compositions are relatively uniform throughout the Western Ghats stratigraphy (¹⁸⁷Os/¹⁸⁸Os_i = 0.12 to 0.21). The lowest Os isotopic ratios are found in the Ambenali Formation of the Wai Subgroup (0.120) and may reflect a modest contribution from the subcontinental lithospheric mantle. Overall, the combined isotopic and trace-element data—particularly the Os isotopic signatures—indicate that assimilation of Proterozoic to Archean Indian crust was generally minimal (<3 wt.% of the parental magma) and did not exceed 8 wt.% in any of the analyzed samples. Comparable findings have been reported for other areas of the Deccan (Peters and Day, 2017) and other Phanerozoic LIPs. We therefore propose that the emplacement of LIPs as short-lived eruptive pulses, separated by relatively long hiatuses, limited sustained heating of the crust above its solidus and thus inhibited significant crustal contamination (Marzoli et al., 2026).

 

Marzoli, A., Reisberg, L., Capriolo, M., Callegaro, S., Renne, P. R., Chiaradia, M., Meyzen, C. M., Self, S., Vanderkluysen, L., Boscaini, A. (2026). Limited crustal contamination in large igneous province basalts: Sr-Nd-Pb-Os isotope evidence from the Western Ghats, Deccan Traps. Earth Planet. Sci. Lett. 678, 119847. doi: https://doi.org/10.1016/j.epsl.2026.119847.