Provenance, tectonic settings and diagenetic evolution of sandstones along the Mangkolemba – Mongchen section, Mokokchung district, Nagaland: Insights from petrography and heavy mineral assemblages

Abstract

The Barail and Tipam Group sandstone sequences of the Mangkolemba–Mongchen section, Mokokchung District, Nagaland, were analyzed using field, petrographic and heavy mineral studies to determine their provenance, tectonic setting, diagenetic modifications and paleoclimate of provenance areas. Petrography impart that the quartz is the superior framework grain and they are sub-angular to sub-rounded in shape. Both plagioclase and orthoclase feldspars have been observed. Rock fragments are second most abundant in proportion after quartz and are represented by volcanic, sedimentary and metamorphic fragments. Based on petrographic investigation and modal counting, the sandstones are classified as subarkose to sublitharenite. The heavy minerals suite of the studied sandstones comprises of sub-angular to sub-rounded grains of kyanite, tourmaline, rutile, zircon, sphene, chloritoid, chlorite, apatite, staurolite and opaques. Petrographic composition and heavy mineral assemblages indicate that the sandstones were derived from a mixed provenance where sediments have combindly been supplied by different sources in response to the tectonics of the region. Regional tectonics reorganized local drainage, forcing sediment input from multiple directions and sources such as from Indian craton, Naga Ophiolites, and Naga Metamorphic complexes. The tectonic analyses suggest that most of the sediments were deposited in a passive margin setting. The high Zircon–Tourmaline–Rutile (ZTR) index values (75.42–91.66%) indicate that the sediments are compositionally mature and were transported over long distances prior to deposition. Paleoclimatic analysis indicates that the provenance area was subjected to humid climatic conditions. The sandstones preserve a comprehensive diagenetic suite, recording an evolution from shallow to deep burial regimes, followed by overprinting telogenetic feature. Together provenance and diagenetic analyses offer critical insights into the tectono-sedimentary evolution of the Barail and Tipam Group of sandstones within the Indo–Myanmar orogenic system that can be used for regional correlation.