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Abstract:

The genetic connection between Large Igneous Province (LIP) and carbonatite is controversial. Here, we present new major and trace element data for carbonatites, nephelinites and Deccan basalts from Amba Dongar in western India, and probe the linkage between carbonatite and the Deccan LIP. Carbonatites are classified into calciocarbonatite (CaO, 39.5–55.9 wt%; BaO, 0.02–3.41 wt%; ΣREE, 1025–12 317 ppm) and ferrocarbonatite (CaO, 15.6–31 wt%; BaO, 0.3–7 wt%; ΣREE, 6839–31 117 ppm). Primitive-mantle-normalized trace element patterns of carbonatites show distinct negative Ti, Zr–Hf, Pb, K and U anomalies, similar to that observed in carbonatites globally. Chondrite-normalized REE patterns reveal high LREE/HREE fractionation; average (La/Yb)N values of 175 in carbonatites and approximately 50 in nephelinites suggest very-low-degree melting of the source. Trace element modelling indicates the possibility of primary carbonatite melt generated from a subcontinental lithospheric mantle (SCLM) source, although it does not explain the entire range of trace element enrichment observed in the Amba Dongar carbonatites. We suggest that CO2-rich fluids and heat from the Deccan plume contributed towards metasomatism of the SCLM source. Melting of this SCLM generated primary carbonated silicate magma that underwent liquid immiscibility at crustal depths, forming two compositionally distinct carbonatite and nephelinite magmas.

Supplementary material: Detailed sampling locations and descriptions, major and trace element composition of apatite in carbonatite and nephelinite, analytical reproducibility for major and trace elemental analyses, and details of trace element modelling are available at https://doi.org/10.6084/m9.figshare.c.3819457

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