Mineral assemblages and tectono-provenance of the Oligocene Barail sandstones in parts of Naga Hills of the Assam-Arakan Orogenic Belt, North-east India

Oligocene Barail sandstones in parts of the Naga Hills, west of Kohima town, Nagaland, north-east India have been studied for their provenance and tectonic environments using mineral assemblages and heavy mineral contents. Moderate to well-sorted litharenite to sublith-arenite Barail sandstones are dominated by monocrystalline quartz and are represented by both undulose and non-undulose varieties. Of the two feldspars, plagioclase dominates over K-feldspar. Rock fragments are second in abundance and constituted of chert, siltstones, schist, and volcanic fragments. The heavy mineral assemblage of Barail sandstones is represented by euhedral, subhedral/subrounded, and well-rounded zircon, tourmaline, rutile, staurolite, sillimanite, and kyanite. Opaques are represented by rounded iron oxides. Detailed petrography coupled with heavy mineral assemblage points towards a mixed provenance dominated by a sedimentary source of recycled orogenic provenance in a foreland basinal set-up. Our study further reveals that sediments were mainly supplied from a north-east direction. However, at the higher stratigraphic levels, contributions were also made from the west. In response to changing plate interaction with time, contributions were made from the Indo-Myanmar Ranges, the Shillong Plateau and/or the Karbi-Anglong Massif, and also from the sediments formed under earlier tectonic regimes of the Assam-Arakan Orogenic Belt.