Chapter 7 Andaman–Nicobar Ophiolites, India: origin, evolution and emplacement

Abstract Andaman–Nicobar Ophiolites (ANO) occur as discontinuous bodies along the eastern margin of the Andaman and Nicobar Islands, the exposed parts of the outer-arc ridge of the present Sunda subduction system. The lithospheric architecture starts with mantle rocks overlain by crustal rocks with a thin transition zone in between. The mantle peridotites and the volcanic rocks exhibit great variability all along the ridge and demonstrate influence of subduction-related magmatism in their origin. Like many Tethyan ophiolites, the ophiolitic rocks of Andaman–Nicobar had their origin in a supra-subduction zone that were juxtaposed tectonically with younger sediments, now exposed on the present outer-arc ridge. The final emplacement of this oceanic lithosphere was unlike typical Tethyan-type ophiolites because, before its final emplacement over the Indo-Burma-Andaman (IBA) microcontinent, the subduction margin was charged with huge sediments from the river delta systems to the north that accreted at the leading age of the overriding plate, similar to some extent to cordilleran-type ophiolites. We propose a two-stage subduction model that displays a sequence of events from birth to resurrection that explains the petrological, geochemical and architectural variations of ANO. Supplementary material: The geochemical tables are available at https://doi.org/10.6084/m9.figshare.c.3634331.v1