Origin of the Amba Dongar carbonatite complex, India and its possible linkage with the Deccan Large Igneous Province

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.

Composition and U—Pb ages of apatite in the Amba Dongar carbonatite–alkaline complex, India

“… Note . Data include those from this study and Chandra et al (), Doroshkevich et al (), and Viladkar and Wimmenauer (). The complete dataset is provided as Supporting Information.…”

“…Mapping of the complex has revealed an extensive 5‐km‐wide metasomatic aureole around the sövite ring dyke (Viladkar, ). As a result of this metasomatism, the nephelinites have undergone extensive alteration (groundmass mostly dominated by calcite) but are easily distinguished by their high melanite garnet content and the presence of hydromuscovite, phlogopite, and K‐feldspar as alteration products (Chandra et al, ; Viladkar, ). Rarely, K‐feldspar grains sourced from potassic fenite xenoliths are seen in the carbonatites (Viladkar, , ).…”

“…Apatite structural formula were calculated based on a total of 26 anions following Ketcham (), and the OH − content was estimated assuming the halogen site is filled (F − + Cl − + OH − = 2). Apatite composition data are given in Table , while apatite EPMA data from previous workers (Chandra et al, ; Doroshkevich et al, ; Viladkar & Wimmenauer, ) are summarized along with our dataset in Table . The complete EPMA dataset is given in the Supporting Information.…”

“…The evolution of the complex (based on CO isotope constraints and trace element patterns) has been described as the differentiation of a primary carbonatite melt into an initial sövite ring intrusion exhibiting different varieties (e.g., coarse‐grained, porphyritic, monomineralic, chilled, apatite‐rich, magnetite‐rich, and phlogopite‐bearing), a dolomitic carbonatite dyke and late‐stage ankerite carbonatite dykes and plugs (Viladkar, ; Viladkar & Schidlowski, ). Using trace element modelling and petrological constraints, Chandra, Paul, Viladkar, and Sensarma () described a petrogenetic model for the Amba Dongar carbonatites that involves metasomatism of carbonated garnet lherzolite at depth (>100 km, >3 GPa) aided by CO 2 ‐rich fluids and plume‐derived heat. At crustal depths, the carbonated silicate magma evolved into distinct carbonate and silicate components by concurrent liquid immiscibility, fractional crystallization, and assimilation.…”

“…Geological map of the Amba Dongar carbonatite–alkaline complex showing the various rock types, modified after Viladkar () and Chandra et al () [Colour figure can be viewed at wileyonlinelibrary.com]…”