The 2005 Eruption of Barren Volcano: an Explosive Inner Arc Volcanism in Andaman Sea

The 2005 eruption of Barren Volcano was explosive and pulsative Strombolian type (15-30 seconds interval). A thick column of grey smoke along with red-hot pyroclasts was found ejecting out with rumbling sound from the crater. The eruption column of ash particles attained a height of more than 300 m, whereas larger pyroclasts were ejecting out to about 100 m above the crater. The assorted mixture of air fall tephra in the form of blocks, cinders, lapilli and spatter along with ash formed two cinder cones. Pyroclasts are of basaltic composition and show vitrophyric texture with phenocrysts of plagioclase, olivine and diopside set in a glassy groundmass. EPMA of the mineral phases shows that plagioclase phenocrysts are represented by anorthite (An 94.5) and bytownite (An8 1.6-89.0),whereas in the groundmass, feldspar microlites are labradorite (An57.3). Compositionally olivines are forsteritic (Fo72-79), and the clinopyroxenes as phenocrysts are diopside and clinopyroxenes in groundmass as pigeonite. Major oxide analyses of the bulk pyroclastics show that the basalts are high alumina basalt of Island Arc Tholeiitic (IAT) affinity Mineralogical as well as chemical similarities of these basalts with lavas of earlier eruptions from Barren Volcano suggests no major change in magmatic evolution with time in the inner arc setting of Andaman subduction complex.