Andaman–Nicobar Ophiolites, India: origin, evolution and emplacement
Biswajit Ghosh, Debaditya Bandyopadhyay, Tomoaki Morishita, 2017. "Andaman–Nicobar Ophiolites, India: origin, evolution and emplacement", The Andaman–Nicobar Accretionary Ridge: Geology, Tectonics and Hazards, P. C. Bandopadhyay, A. Carter
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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
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The Andaman–Nicobar Accretionary Ridge: Geology, Tectonics and Hazards
Rocks exposed across the hundreds of islands that belong to the 800 km long Andaman–Nicobar archipelago provide a condensed window into the active subduction zone that separates the India–Australia plate from the over-riding Burma–Sunda plate. Despite a strategic and seismically active location the Andaman-Nicobar ridge has seen comparatively little research. This Memoir provides the first detailed and comprehensive account of geological mapping and research across the island chain and adjacent ocean basins. Chapters examine models of Cenozoic rifting of the Andaman Sea and the regional tectonic and seismogenic framework. A detailed critical review of the Andaman–Nicobar stratigraphy, supported by new data, includes arc volcanism and a description of Barren Island, India’s only active volcano. Seismic history and hazards and the impacts of the 2004 earthquake and tsunami are also described. The volume ends with an examination of the region’s natural resources and hydrocarbon prospects.