Barren and Narcondam are active and now extinct, respectively, volcanic islands that belong to the inner-arc volcanic belt that extends from Java in the east to Burma in the north. Modern eruptions on Barren Island have been exclusively scoria cone-forming Strombolian-type activity in contrast to historic (1787–32) eruptions that witnessed a switch from scoria cone activity to abundant basaltic lava flows. Prehistoric (late Pleistocene) eruptions were alternating effusive and explosive events. The prehistoric events formed a mafic stratovolcano (island) and the associated large eruptions produced a c. 2.0 km diameter crater at the centre of the stratocone. Barren Island lavas are mainly basalts and basaltic andesites, whereas Narcondam rocks are dacite-andesite-rhyolite and contain evidence of magma mixing of both mantle and crustal material. The types of volcanoes and volcanism associated with Barren and Narcondam have been attributed to differences in tectonic setting and the nature of the basement below the volcanoes. It is likely that continental or transitional crust exists below Narcondam, in contrast to oceanic lithosphere below Barren Island.
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The Andaman–Nicobar Accretionary Ridge: Geology, Tectonics and Hazards
Rocks exposed across the hundreds of islands that belong to the 800 km long Andaman–Nicobar archipelago provide a condensed window into the active subduction zone that separates the India–Australia plate from the over-riding Burma–Sunda plate. Despite a strategic and seismically active location the Andaman-Nicobar ridge has seen comparatively little research. This Memoir provides the first detailed and comprehensive account of geological mapping and research across the island chain and adjacent ocean basins. Chapters examine models of Cenozoic rifting of the Andaman Sea and the regional tectonic and seismogenic framework. A detailed critical review of the Andaman–Nicobar stratigraphy, supported by new data, includes arc volcanism and a description of Barren Island, India’s only active volcano. Seismic history and hazards and the impacts of the 2004 earthquake and tsunami are also described. The volume ends with an examination of the region’s natural resources and hydrocarbon prospects.