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

Abstract

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.