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      https://www.ias.ac.in/article/fulltext/jess/130/0152

    • Keywords

       

      Flood basalt; rifted margin; Deccan Traps; gabbro; granophyre; magmatic differentiation.

    • Abstract

       

      The western Indian volcanic rifted margin, and its large-scale tectonic feature called the Panvel flexure, formed at 62.5 Ma during the late stages of Deccan Traps flood volcanism. We present a geological account of late-stage ($\leq$ 62.5 Ma) Deccan volcanism and plutonism in the relatively poorly studied Thane–Vasai region in the Panvel flexure zone. The study area shows west-dipping basaltic sequences up to hundreds of meters thick, overlain by pyroclastic deposits of various types. The volcanic units are intruded by gabbro plutons, and all these units are in turn intruded by dykes of varied compositions (including tholeiitic basalt, lamprophyre, and granophyre). There are also early tholeiitic dykes, some of which may be feeders to the basaltic sequence. We focus on the gabbro intrusions and provide extensive petrographic and mineral chemical data on them. The gabbros are tholeiitic, and of considerable interest in commonly containing interstitial silicic melts (granophyre or silicic glass). One of the intrusions, the Chena pluton, shows clear outcrop transitions from gabbro, and gabbro with interstitial granophyre, to transitional gabbro-granophyre, and then to a distinct upper zone of granophyre and microgranite. Granophyre is common in mafic intrusions in continental flood basalt provinces of the world (e.g., the Palisades Sill and the Skaergaard Intrusion), where its genesis is ascribed to mechanisms such as fractional crystallisation, liquid immiscibility, or crustal melting, typically based on geochemical data. The Chena gabbro outcrops are valuable in providing direct evidence for a fractional crystallisation origin of the granophyres (and silicic glasses) found in the Thane–Vasai gabbro intrusions, with which the mineral chemical compositions are also consistent.

    • Author Affiliations

       

      ANMOL NAIK1 JANISAR M SHEIKH1 2 HETU SHETH1 HRISHIKESH SAMANT3 SHAWN D’SOUZA3 4

      1. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai, India.
      2. Centre of Advanced Study in Geology, Institute of Science, Banaras Hindu University (BHU), Varanasi 221 005, India.
      3. Department of Geology, St. Xavier’s College, Mumbai 400 001, India.
      4. Cybertech Software and Systems Ltd., Thane, Mumbai 400 604, India.
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  • Journal of Earth System Science | News

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