Chapter 12 Inner-arc volcanism: Barren and Narcondam islands

Abstract

Abstract 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.