The Origin of Carbonatites from Amba Dongar within the Deccan Large Igneous Province

Abstract

There are disparate views about the origin of global rift- or plume-related carbonatites. The Amba Dongar carbonatite complex, Gujarat, India, which intruded into the basalts of the Deccan Large Igneous Province (LIP), is a typical example. On the basis of new comprehensive major and trace element and Sr–Nd–Pb isotope data, we propose that low-degree primary carbonated melts from off-center of the Deccan–Réunion mantle plume migrate upwards and metasomatize part of the subcontinental lithospheric mantle (SCLM). Low-degree partial melting (∼2%) of this metasomatized SCLM source generates a parental carbonated silicate magma, which becomes contaminated with the local Archean basement during its ascent. Calcite globules in a nephelinite from Amba Dongar provide evidence that the carbonatites originated by liquid immiscibility from a parental carbonated silicate magma. Liquid immiscibility at crustal depths produces two chemically distinct, but isotopically similar magmas: the carbonatites (20% by volume) and nephelinites (80% by volume). Owing to their low heat capacity, the carbonatite melts solidified as thin carbonate veins at crustal depths. Secondary melting of these carbonate-rich veins during subsequent rifting generated the carbonatites and ferrocarbonatites now exposed at Amba Dongar. Carbonatites, if formed by liquid immiscibility from carbonated silicate magmas, can inherit a wide range of isotopic signatures that result from crustal contamination of their parental carbonated silicate magmas. In rift or plume-related settings, they can, therefore, display a much larger range of isotope signatures than their original asthenosphere or mantle plume source.

Proterozoic Alkaline rocks and Carbonatites of Peninsular India: A review

“…14. Despite disagreement on the exact nature of the mantle source, it was commonly argued that Proterozoic ARCs originated from a metasomatized SCLM. Low-degree melting of metasomatized SCLM source can generate carbonated silicate melts, which after liquid immiscibility at crustal depths, form the carbonatite and associated alkaline rocks in a locality (Chandra et al, 2019). Note that similar Sr-Nd-Pb isotopic ratios of carbonatite and associated alkaline rocks from the same complex argue in favour of a common source and that liquid immiscibility does not change the initial isotopic composition.…”

“…In the Indian context, no Proterozoic carbonatite complex has been linked to mantle-plume originated LIP, although several studies have established a link between the Phanerozoic Indian carbonatites, such as Amba Dongar, Barmer, Mundwara, Sung Valley, Swangkre, Samchampi, and Jarsa carbonatite complexes, with Deccan-Reunion and Kerguelen mantle plumes (e.g., Basu et al, 1993;Sen et al, 2009;Veena et al, 1998;Ray et al, 2000;Heaman et al, 2002;Srivastava and Sinha, 2007;Chandra et al, 2018Chandra et al, , 2019. The origin of Phanerozoic carbonatite and alkaline complexes, particularly Amba Dongar, Barmer, Mundwara, Phenai Mata, and Bhuj that occur along the Narmada-Son lineament has been linked to the mantle plume activity 68-65 Ma ago that formed the Deccan flood basalts (Basu et al, 1993;Sen et al, 2009), strengthening the argument that ARC magmatism is related to mantle plume activity.…”

India’s First Carbonatite Discovery at Amba Dongar is Sixty Years Old: An Overview and Current Status

“…Simultaneously, large-scale (decompression) melting of the rising mantle plume at depths shallower than 100 km, generated extensive tholeiitic magma (D) that gave rise to the Deccan flood basalts and associated basaltic and doleritic dykes of the area (c.f. Chandra et al, 2019, Fig.8, p. 1131. recently by Elliot et al (2018).…”

Petrologic relationship between lamprophyres, carbonatites, and heavy rare‐earth element enriched breccias at Hicks Dome

“…It is important to note that the postulated mantle source components (e.g. HIMU, EM) is only possible if interaction and chemical exchange with the overlying SCLM and continental crust can be excluded, but typically, carbonatite magmas rising through a thick lithosphere are always contaminated to some extent (Chandra et al., 2019).…”