Episodes 2020; 43(1): 312-322
Published online March 1, 2020
Copyright © International Union of Geological Sciences.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
In Indian subcontinent one active volcano and another dormant volcano of Quaternary period are present in the Andaman Java subduction complex. The active Barren volcano throughout its history is erupting mainly tholeiitic basalt whereas the dormant Norcondam volcano is domal dacite and andesite volcano. In the Barren volcano wall, of 2km wide caldera is made up of prehistoric (~35 Ka) pyroclastics whereas the polygenetic tuff cone and valley fill are the products of historic (1787 yr) to recent activities of subaerial strombolian eruption and transient lava flows. The Barren volcanics dominated by plagioclase phyric basalt, in general, show phenocrysts of plagioclase (An96–48), olivine (Fo86-67) and clinopyroxene (En48-43, Wo46-42). The geochemistry of the Barren volcanics show neither typical island arc nor NMORB tholeiitic character. Tectonic model suggests that network of low-density, low viscosity conduits facilitated rapid transport of the basaltic melt with minimum crustal contamination for the Barren volcano. In the Narcondam volcano (1.8-3.5 Ma) dacitic lava occurs at the centraltop part whereas andesite lava and pyroclastics with calcalkaline characters occur at the periphery of the island. Pyroclastic deposit occurs in the form of basal avalanche, channeled basal avalanche, ash-cloud surge and base surge deposits. The mineralogy and texture suggests that the dacite-andesite lava is evolved from the mixing of rhyolite and basalt magma.