Paleogene tectonic and sedimentation history of the Andaman-Nicobar Accretionary Arc, Northeast Indian Ocean

The Andaman-Nicobar archipelago in the northeastern Indian Ocean is a nonvolcanic outer arc island chain developed by tectonic accretion of sediments and ocean crust along the eastern margin of the subducting Indian lithosphere. The Paleogene stratigraphy of the island chain comprises olistostromes, olistoliths and coarse-grained volcaniclastic turbidite facies, and reefal limestones of late Paleocene- Eocene MithakhariMelange and finer-grained siliciclastic turbidites (Andaman Flysch) of Oligocene age. The lower Paleogene sedimentary rocks were deposited in shallow-water basins formed on the upper trench slope and growing accretionary wedge and contain material sourced from a local volcanic arc and eroded ophiolite. By contrast, the Oligocene continent-derived siliciclastic sediments were originally deposited outside of the accretionary wedge as part of a large submarine fan system. Subsequent deformation and thrusting juxtaposed these different formations as trench rollback progressed and the accretionary wedge expanded westwards