Two different parental melt trends for the Deccan Trap main sequence

The lava flows of the Deccan Large Igneous Province (DLIP) cover at least one million years of continuous magmatic activity across the Cretaceous-Paleogene boundary (Schoene et al. 2021) likely representing the initial stage of the Réunion plume. Earlier studies suggested that the geochemical signatures of basaltic rocks from the DLIP main sequence originated from melts of the depleted upper mantle and Réunion plume that mixed within magma chamber systems (e.g. Peng et al. 1994). In this scenario, the compositional range of the DLIP is best explained by subsequent assimilation of varying proportions of crustal and lithospheric components during ascent.The major and trace element as well as Sr-Nd-Hf-Pb isotope data of this study covers the entire stratigraphy of the DLIP main sequence and casts doubt on the generally accepted interpretation. Most notably, Pb isotopes as well as high field strength element systematics suggest two separate magma differentiation trends in the petrogenetic pathway of DLIP melts. The observed trends are best explained by two mafic endmembers that tap different mantle source reservoirs. Our isotope and trace element data suggests that melts from these reservoirs, namely the depleted upper mantle and lower mantle (Réunion plume) assimilated crustal and lithospheric components to a variable degree. Consequently, lava flows within single volcano-stratigraphic formations of the DLIP likely originated from different parental melts that did not interact during ascent. Previously, such fast-changing contributions from different mantle reservoirs have been underestimated for the Deccan volcanic rocks.

Peng et al. 1994. GCASchoene et al. 2021, GChron