Geochemistry and zircon U-Pb geochronology of diabase, gabbros, anorthosites and ultramafic rocks from the South Andaman Island ophiolite suite on the South-Eastern margin of the Indian plate.

The South Andaman Island is located on the southeastern fringe of the Indian plate. Tectonically, the islands are associated with the Burma-Andaman-Java subduction zone of the Indonesian arc system. Several Mesozoic ophiolitic exposures are preserved in the Burma-Andaman-Java subduction zone. This study reports new petrological, geochemical, and zircon U-Pb geochronological data for the diabases, gabbros, anorthosites, and harzburgites of the ophiolite suite exposed in the South Andaman Island. The diabase is composed of plagioclase and clinopyroxene exhibiting ophitic textures. Anorthosite mainly contains plagioclase (> 90 vol%), pyroxenes and Fe-oxides. Gabbros have plagioclases and clinopyroxenes occurring as the major minerals. Harzburgites consist of olivine, orthopyroxene, clinopyroxene and spinel. Geochemical investigation reveals that these rocks were formed through crystal fractionation and accumulation processes from partial melt generated from a spinel lherzolite source. Gabbro, diabase, and anorthosites are formed by ∼1–5% melting of the, whereas depleted harzburgites were generated by slightly higher degrees of partial melting (∼10–20%) of the spinel lherzolite source. Trace element modelling reveals the influence of mid-oceanic ridge basalt (MORB)-melt interaction and subduction-related mantle alterations. The anorthosite and gabbro samples yield zircon 206Pb / 238U weighted mean ages of 93.2 ± 1.0 Ma and 442.5 ± 4.0 Ma, 383.9 ± 3.3 Ma respectively. However, the harzburgite sample records multiple age population including Paleo-Mesoproterozoic grains ranging in age from 1216 to 1931 Ma as well as Neoproterozoic and Phanerozoic grains of 607 Ma, 594 Ma, 237 Ma, 105 Ma, and 85 Ma suggesting a long-lived supra subduction zone in the Burma-Andaman-Java subduction zone where the South Andaman ophiolite suite was formed, evolved, and was emplaced. [Display omitted] • First report on the geochemical characteristics of diabase and anorthosites from the South Andaman Ophiolite suite. • Magmatic zircons from the anorthosite yields an age of 93.2 ± 1.0 Ma • First report on age of an ophiolitic anorthosite from the Indian ophiolite occurrences. • Additional novel geochemical and geochronological data on gabbros and harzburgites South Andaman Ophiolite suite. • Geochronological results imply a long lived supra subduction zone in the Burma-Andaman-Java subduction zone. [ABSTRACT FROM AUTHOR]