Petrogenesis of Neoarchean Mangikhuta Volcanic Complex, Dongargarh Supergroup, Central India: Insights from Relict Clino
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Petrogenesis of Neoarchean Mangikhuta Volcanic Complex, Dongargarh Supergroup, Central India: Insights from Relict Clinopyroxene Chemistry Sunil Kumar Khare1,* and Deepanker Asthana2 1
Department of Petroleum Engineering and Earth Sciences, University of Petroleum and Energy Studies, Dehradun– 248 007, India Department of Applied Geology, IIT ISM, Dhanbad,– 826 004, India *E-mail: [email protected] 2
ABSTRACT Clinopyroxene relict magmatic phases in Neoarchean Mangikhuta volcanics are described in detail in terms of their geochemistry for the first time, and their petrogenetic insights obtained. EPMA study indicates their restricted compositional range. Elemental variation diagrams show progressive variation of Al, Ca, Si, Fe+3, Ti, Cr, Aly and Aly/Alz, Ti/Al, Fe+2/Fe+3 elemental ratios with fractionation, which establishes their equilibrium conditions during crystallization differentiation. On pyroxene quadrilateral, they plot along fractionation trend of augite. Ca-Al Tschermak, esseneite and Tp are the “other components” in these clinopyroxenes. Progressive variation of other components indicates decrease of pH2O and fO 2 of the magma during fractionation. Other components of clinopyroxenes and chondrite normalized whole rock REE patterns indicate minor fractionation of plagioclase in primitive magma. However, plagioclase became a major precipitating phase in later stage of fractionation. Clinopyroxene geobarometer and geothermometer indicate 0-3 kb pressure and 1100-12500 C temperature of crystallization of Mangikhuta clinopyroxenes. Mangikhuta complex have typically high normative orthopyroxene content (35–45 vol. %) now altered to Mg-Al-Fe chlorite. The Mangikhuta magma was highly aqueous and after genesis, it ascended rapidly giving rise to silica-aluminacalc-alkaline series rocks. In the late magmatic history, there was reaction between orthopyroxene and water and plagioclase and water so that Mg(Al,Fe)SiO3 pyroxene converted to Mg(Fe, Al) chlorite and prehnite. INTRODUCTION Several workers have investigated Neoarchean Mangikhuta volcanics of Central India (Sarkar, 1957; Sarkar et al. 1994; Neogi et al. 1996; Sensarma and Mukhopadhyay, 2014, Khanna et al. 2019). Study of Asthana et al. (1996) and Jafri et al. (2007) has revealed the presence of quenched pyroxene, plagioclase and late stage formation of chlorite, zoisite, clinozoisite and prehnite in the mafic rocks of Khairagarh Group. The present study focusses on relict, fresh, medium to fine-grained clinopyroxenes from Mangikhuta volcanics, which are present as magmatic minerals. This paper presents detailed mineral chemistry of Mangikhuta clinopyroxenes. It describes for the first time, detail petrogenetic insights obtained from relict magmatic clinopyroxenes from Mangikhuta volcanics. These clinopyroxenes are reasonably useful in the estimation of pressure, temperature, pH2O, fO2 and tectonic environment of Neoarchean Mangikhuta magmatism in the Central India. MANGIKHUTA VOLCANIC COMPLEX Mangikhuta volcanic complex is a constituent of Neoarchean 0
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