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The 62.5 Ma Dongri-Uttan rhyolite sequence, Mumbai area, Panvel flexure zone: late-Deccan effusive-explosive silicic eruptions during India-Seychelles continental breakup

Arunodaya Shekhar 1, Hetu Sheth1, Anmol Naik2, B. Astha1

  • Affiliations: 1Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai 400076 India; 2School of Earth, Ocean and Atmospheric Sciences, Goa University, 403206 India 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 211

  • Programme No: 3.6.15

  • Theme 3 > Session 6

Abstract

Post-K/Pg boundary (Danian-age) Deccan magmatism is well exhibited in the western side of structurally complex Panvel flexure zone. The metropolitan city Mumbai shows multifaceted geology aligning with main Deccan magmatism like tholeiitic lava flows and dyke, and some of the atypical geological features like spilitic pillow basalts, ash constituted "intertrappean" sedimentary deposits and trachyte with or without basaltic enclaves. The study focuses on area Dongri-Uttan area, characterized as densely vegetated low-lying region in northwestern Mumbai. Most of the magmatic units dated to be of 62.5 to 61 Ma, are contemporaneous with or slightly postdate the 62.5 Ma India-Seychelles continental breakup and Panvel flexure formation. Sheth and Pande (2014) reported the 40Ar/39Ar plateau ages of the columnar rhyolites in Darkhan Quarry and near Uttan-Sagari police station (USPS) to be 62.6 ± 0.6 Ma and 62.9 ± 0.2 Ma (2σ errors). They also reported the highly altered 2-3 m thick sedimentary deposit in USPS section. Recent excavations reveal lower columnar rhyolites and, suggests the indistinguishable ages are of two distinct columnar rhyolites separated by the well-bedded silicic ash. The upper rhyolite lacks basal autobreccia, and in petrographic studies show snowflake texture without any vitroclast, but the ash present in between constitutes glass shards and pumice clasts. We interpret the ash to be explosively formed Plinian fallout deposit of low-grade vitric ash. The USPS lava-tuff-lava sequence of 62.5 Ma provides evidence for the rapid silicic eruptions switching from effusive to explosive to effusive behavior, in the western Indian rifted continental margin.