40Ar/39Ar geochronology of subaerial lava flows of Barren Island volcano and the deep crust beneath the Andaman Island Arc, Burma Microplate

• DOI: 10.1007/s00445-015-0944-9
• Publication Date: 2015-06-04T13:13:07Z
• Authors: Jyotiranjan S. Ray; Kanchan Pande; Rajneesh Bhutani
• Keywords: Sea; Indian-Ocean; 550; Plate; Magma; Bengal; Subduction; 15. Life on land; Andaman Ophiolite; 01 natural sciences; Andaman Island Arc; Age; Moho Transition Zone; Barren Island Volcano; Region; Ophiolite Implications; 40ar/39ar Chronology; Burma Microplate; 0105 earth and related environmental sciences

Little was known about the nature and origin of the deep crust beneath the Andaman Island Arc in spite of the fact that it formed part of the highly active Indonesian volcanic arc system, one of the important continental crust forming regions in Southeast Asia. This arc, formed as a result of subduction of the Indian Plate beneath the Burma Microplate (a sliver of the Eurasian Plate), contains only one active subaerial magmatic center, Barren Island volcano, whose evolutional timeline had remained uncertain. In this work, we present results of the first successful attempt to date crustal xenoliths and their host lava flows from the island, by incremental heating 40Ar/39Ar method, in an attempt to understand the evolutionary histories of the volcano and its basement. Based on concordant plateau and isochron ages, we establish that the oldest subaerial lava flows of the volcano are 1.58 ± 0.04 (2σ) Ma, and some of the plagioclase xenocrysts have been derived from crustal rocks of 106 ± 3 (2σ) Ma. Mineralogy (anorthite + Cr-rich diopside + minor olivine) and isotopic compositions (87Sr/86Sr 7.0) of xenoliths not only indicate their derivation from a lower (oceanic) crustal olivine gabbro but also suggest a genetic relationship between the arc crust and the ophiolitic basement of the Andaman accretionary prism. We speculate that the basements of the forearc and volcanic arc of the Andaman subduction zone belong to a single continuous unit that was once attached to the western margin of the Eurasian Plate.