Tectono-Stratigraphy and Emplacement History of the Ophiolite Assemblage from the Naga Hills and Andaman Island-Arc, India

The oceanic pelagic sediments from the ophiolite assemblages of Naga Hills (NHO) and Andaman islands (ANO) broadly correspond to Late Cretaneous to Paleocene age. Late Cretaceous ocean floor represented in ANO was dominantly below the carbonate-compensation-depth (CCD), whereas it was uneven but mainly above CCD during Paleocene-Early Eocene. Maestrichtian to Paleocene ocean floor appears to be dominantly above the CCD in NHO. The NHO and ANO have closely similar postemplacement ophiolite-derived mid- and mid-late Eocene cover sediments respectively. Emplacement of the Naga Hills ophiolites during mid-Eocene, was possibly caused due to initial collision of an ocean-island chain with the subduction zone beneath the Central Burmese continent. Emplacement of the Andaman ophiolites occurred during early-mid-Eocene and may have been caused by a similar situation. The Chin Hills ophiolites were also mainly emplaced during early Eocene. The accreted ophiolites of the Indo-Burman range and Andaman islands were thrust westward over the Paleogene turbidite pile, deposited on the down going Indian plate during late Oligocene, due to terminal India-Burma continent-continent collision. In the southern Manipur sector of Naga Hills, the olistostromal upper Disang Formation (mid to late mid-Eocene) tectonically flooring the NHO, stratigraphically underlies the flyschoid to molassic Barail (Oligocene) sediments. In Andaman islands, the Lipa Formation with early Eocene and older olistoliths, forms the dominant constituent of the lower tectonic sedimentary melange flooring the ophiolites. Towards west, the sedimentary melange overrides the Archipelago Group. (Neogene) which unconformably overlies the Andarnan Flysch of Eocene-Oligocene age. The ischolar_main-zone of the collisional suture appears to be concealed below younger sediments in the Central Burma basin and in the Andaman Sea, parts of the latter being created as a back-arc marginal basin. There is thus no straightforward relation between the Late Oligocene collision suture and the present subduction zone along the trench to the west of Andaman-Nicobar islands.