Petrography and tectonic provenance of the Miocene Surma Group in parts of the Naga-Manipur hills, in and around Nungba, Northeast India

Abstract

The Miocene molassic Surma sandstones in parts of the Naga-Manipur hills, in and around Nungba, Northeast India have been studied for their tectonic provenance using petrography and heavy mineral contents. The poorly-to-moderately-sorted sub-litharenite to lithic-arkose type Surma sandstones display predominance of monocrystalline quartz (av. 61%) and include undulose and non-undulose varieties and almost equal amounts of feldspars (av. 22%) and rock fragments (av. 17%). The heavy mineral suite of Surma sandstones is dominated by transparent varieties (96%) that include garnet, zircon, tourmaline, rutile, staurolite, scapolite, phlogopite, chondrodite, humite, wollastonite, hedenbergite. sphene, chlorite, sillimanite, glauconite, glaucophane, and chloritoid. These heavy minerals characterize the granitic and silicic metamorphic complexes (GM) as well as the basic metamorphic rocks (MT) like greenstones, green schist, and amphibolites relating to passive continental margin set-up. The opaque grains constitute nearly 4% of the total heavy minerals. The presence of euhedral, as well as abraded heavy mineral grains, further supports a mixed provenance having substantial contribution from sedimentary and metamorphic rocks. A ZTR index of approximately 45% indicates mineralogically sub-mature nature of Surma sandstones. Based on the light and heavy mineral suites coupled with the type of terrain available in the vicinity of the study area, it may be visualized that the sediment supply was largely made by the Himalaya, the IMR, the Shillong plateau, and the Mikir Hills under the influence of semi-arid to semi-humid climatic conditions. An overall supply from a recycled orogen provenance has been envisaged.