Episodes 2020; 43(1): 249-277
Published online March 1, 2020
Copyright © International Union of Geological Sciences.
Debajyoti Paul1*, Jyoti Chandra2, Mahesh Halder1
1Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
2CSIR-National Geophysical Research Institute, Hyderabad 500007, Telangana, India
*Corresponding author, E-mail address: email@example.com (D. Paul), Tel: +91-512-259-6169, Fax: +91-512-259-6469
Correspondence to:E-mail address: firstname.lastname@example.org (D. Paul), Tel: +91-512-259-6169, Fax: +91-512-259-6469
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The alkaline rocks and carbonatites (ARCs) of the Great Indian Proterozoic belt bear the testimony of tectonic processes operating in the Proterozoic during the continental assembly and breakup of both Columbia and Rodinia. We present a comprehensive review, mainly focused on the petrology, geochemistry, and geochronology of 38 ARCs of Peninsular India, which are mostly concentrated within the Eastern Ghats Mobile Belt and Southern Granulite Terrain. Available geochronologic data reveals three distinct alkaline magmatic phases (2533–2340 Ma, 1510–1242 Ma, 833–572 Ma) and two metamorphic events (950–930 Ma and 570–485 Ma) that correlate with the Grenvillian and Pan-African orogeny events. Whereas clinopyroxene, amphibole, titanite and apatite fractionation seems to have affected the nephelinite, nepheline syenite and syenite, carbonatite is affected by fractionation of calcite, dolomite, ankerite, pyroxene, apatite, magnetite, mica, and pyrochlore. Trace elements and Sr-Nd-Pb-C-O isotopic compositions of these ARCs strongly suggest a subcontinental lithospheric mantle source, that is enriched either by distribution of subducted crustal material or by metasomatism of mantle-derived fluids, for the generation of ARCs. Despite some isotopic variability that can result from crustal contamination, a trend showing enrichment in 87Sr/86Sri (0.702 to 0.708) and depletion in εNd(i) (–1.3 to –14.1) over a 2 Gyr duration indicates temporal changes in the lithospheric/asthenospheric source of ARCs, due to periodic enrichment of the source by mantle-derived fluids. ARC generation starts in an intracontinental rift setting (beginning of Wilson cycle). These early-formed ARCs are carriedto 100 km depths during continental collision (termination stage of Wilson cycle) and undergo extensive melting because of renewed rifting along suture zones to form new generation of ARCs.