Bimodal volcanism in Betul Fold Belt, central India: Implications on petrogenesis: Bimodal volcanism in Betul Fold Belt

• Published in: Journal of earth system science 2023-06, Vol.132 (3)
• Main Authors: Abhirami, Sethuraman Gomathi, Satyanarayanan, Manavalan
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics
• ISSN: 0973-774X
• DOI: 10.1007/s12040-023-02112-2

The Betul Fold Belt (BFB) present in the Central Indian Tectonic Zone (CITZ) is a mosaic of supracrustal volcano-sedimentary sequences, mafic–ultramafic rocks, and granitoid. In this belt, bimodal volcanics are represented by basalts and rhyolites from the Baragaon Group. The basalts comprise altered olivine, clinopyroxene, plagioclase, and accessory Fe–Ti oxides embedded within hypocrystalline groundmass comprising plagioclase, clinopyroxene, and amphiboles. They are characterised by high LREE, LILE over HREE, and negative Nb, Ta, Zr, and Hf anomalies. In contrast, the rhyolites comprise quartz, plagioclase, and alkali feldspar with enriched LREE and prominent negative Nb, Ta, Sr, and Ti anomalies. The low Nb/La, Th/Nb, Th/La, and Th/Ce ratios combined with consistent Nb/Th ratios favour insignificant crustal contamination for basalts. The high Ba/Nb, Ba/Th ratios and low Th content of basalts suggest the incorporation of slab-derived aqueous fluids into the mantle source. The rhyolites are classified as type-I (low ∑REE and HFSE) and type-II (high ∑REE and HFSE), in which the former follows the basaltic partial melting trend, while the latter indicates the pure crystal fractionation process. The low Sr/Y (0.4–3.5) and La/Yb (4–10.1) ratios of rhyolites depict their generation at the plagioclase stability field. Trace element modelling demonstrates that the Betul basalts erupted from ~8 to 10% partial melting of SCLM in the spinel-garnet transition zone. In contrast, the type-I rhyolites are generated by the ~10% partial melting of underplated juvenile basaltic rocks followed by separation of 75% melt generated due to crustal assimilation induced fractional crystallisation, and the type-II rhyolites are produced by ~79% fractional crystallisation of the least evolved rhyolite. The zircon saturation temperatures ( T Zr = 788°–928°C) infer the higher temperatures required for the generation of these rhyolites in the convergent margin. These bimodal volcanic rocks are generated in the arc-rifting environment of the convergent margin regime.