Geochemistry of calc-silicate rocks around Lunavada region, NE Gujarat: Implications for their protolith, provenance and
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Geochemistry of calc-silicate rocks around Lunavada region, NE Gujarat: Implications for their protolith, provenance and tectonic setting GAYATRI N AKOLKAR and MANOJ A LIMAYE* Department of Geology, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat 390 002, India. *Corresponding author. e-mail: manoj˙[email protected] MS received 18 October 2019; revised 13 May 2020; accepted 19 June 2020
In this work, the calc-silicate rocks aDliated to the ‘Kadana Formation’, a youngest formation of the Lunavada Group have been investigated. These rocks are found to be embedded within associated rock types, viz., quartzites and metapelites in the form of isolated lensoidal bodies. Contact metamorphic textures and the typical mineral assemblage, viz., Act +Di + Cal + Qtz + Ttn ± Mc ± Pl ± Bt ± Ep ± Scp ± Chl with minor proportion of apatite, zircon and opaques can be observed in these calc-silicates. Major oxides, trace and rare earth elements were analysed to investigate the protolith type, provenance and tectonic setting of these rocks. Protolith must be calcareous sandstone with varied proportion of clay and deposited in shallow water environment as revealed by CaO, Al2O3 and FeO+MgO and Al–Zr–Ti ternary diagram, respectively. Low to moderate weathering of source rocks has been indicated by A–CN–K ternary diagram. Th/Sc vs. Zr/Sc and Th/Co vs. La/Sc plots conBrm the continental source with felsic nature for these rocks and the calc-silicate samples fall within the active continental margin region of Sc–Th–Zr/10 diagram which also justify the kind of provenance for primary sediments. Keywords. Calc-silicate rocks; Lunavada; Kadana; geochemistry; protolith; tectonic setting.
1. Introduction Calc-silicate rocks are the type of metamorphic rocks primarily composed of calc-silicate minerals and contain less than 5% volume of carbonate minerals, i.e., calcite and/or aragonite and/or dolomite, as per the ‘subcommission on the systematics of metamorphic rocks’ (SCMR) classiBcation scheme. The calc-silicates being investigated here belong to the Lunavada Group which is a second youngest group of the Aravalli Supergroup comprising an extension of the Southern Aravalli Mountain Belt (SAMB), which occupies the NE part of the Gujarat state. These rocks comprise youngest formation of Lunavada Group known as
Kadana Formation having Meso-proterozoic age (Iqbaluddin 1989; Gupta et al. 1992, 1997). The area around Lunavada has been variously investigated on the basis of their lithological (Gupta and Mukherjee 1938), sedimentological (Iqbaluddin and Venkataramaiah 1976) and structural (Mamtani et al. 1999, 2000) aspects. However, the calcsilicate rocks did not receive much attention. Therefore, present paper makes a maiden attempt to characterize this rock based on its major, trace and rare earth elements geochemistry. These data have been used to constrain the protolith characteristic and investigate the depositional environment, weathe
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