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Felsic tuff from Rutland Island - a pyroclastic flow deposit in Miocene-sediments of Andaman-Java subduction complex
T PAL, , A BHATTACHARYA, S K BHADURI
Published in INDIAN ACAD SCIENCES
2010
Volume: 119
   
Issue: 1
Pages: 19 - 25
Abstract
The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies: • white massive tuff with ill-defined bedding contacts (facies-A) and dominantly green tuff exhibiting well-developed turbidite sequence with up-section change from a massive unit to plane laminated units to ripple drift lamination (facies-B). The felsic tuff is vitric to crysto-vitric in nature and contains broken crystals of quartz, feldspar, biotite and glass shards of different shapes and sizes. The bulk chemistry indicates tra- chyte to dacite compositional range, and high values of Zr relative to Nb and Y suggest con- vergent margin tectonic setting of the tuff. Dominance of cuspate shards rather than blocky shards in both the facies indicates subaerial eruption of the pyroclasts. Recurrence of tur- bidites as well as good sorting of crystals and glass suggest that subaerially erupted ash was transported in subaqueous condition. The bed pattern supports rapid deposition of facies- A from high concentration turbidity flow whereas facies-B could be produced by decrease in grain size and suspended-load fallout rate of turbidity current. Regional correlation suggests that felsic volcanism in Sumatra was the source for such early Miocene to middle Miocene tuff. © Indian Academy of Sciences.
About the journal
JournalJournal of Earth System Science
PublisherINDIAN ACAD SCIENCES
ISSN0253-4126
Open AccessNo