 Corresponding author: G. R. Senthil Kumar 0000-0002-8647-1959 Copyright © 2023 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution Liscense 4.0. Petrographic, mineralogical and microstructural studies in the mafic dyke occurred in the area of Mettur, Salem District, Tamil Nadu, India Hari Prasad S., Senthil Kumar G.R. * and Faisal Abass Padder Department of Earth Sciences, Annamalai University, Annamalainagar – 608 002, Tamil Nadu,, India. GSC Advanced Research and Reviews, 2023, 14(03), 241–253 Publication history: Received on 09 February 2023; revised on 18 March 2023; accepted on 21 March 2023 Article DOI: https://doi.org/10.30574/gscarr.2023.14.3.0088 Abstract A mafic dyke is a mass of rock generated in either sedimentary or igneous terrain and intrudes in pre-existing cracks. It was common to see many enormous dyke swarms in the southern granulitic landscape made up of archean rocks. Dykes tend to be younger than the surrounding rock body. Generally, mafic dolerite dyke has an ophitic texture and is medium to fine grained. In the study area country rock and dolerite dyke rocks petrographical microscope, XRD, and FE-SEM techniques were analysed. Plagioclase feldspar, augite, biotite, hornblende, and quartz minerals presented in the study area rocks. Alternating wedges, augite/labradorite grain boundaries are shown in the microstructure as a white rectangle. Two augite wedges were observed with rounded ends. The mineral percentage of quartz is rich in dolerite rock because of its intergrowth texture and low cooling temperature and pressure. So, the magma crystallized rapidly on the surface thus, the crystallizing temperature of the quartz is low. Thus, the rock mineral shows a high percentage of quartz. The rock is quartz-dolerite. Keywords: Dyke; Petrography; Mineralogy; Microstructure; Quartz-Dolerite. 1. Introduction Many of the Archaean gneissic terrains contain early Proterozoic dyke swarms as a common unit. The widespread occurences is that partial melting in the mantle produced mafic dykes. However, little or microscale differences in various mafic dykes and other mantle-derived rocks, such as mantle xenoliths, have shown that the composition of mantle-derived rocks can differ greatly from the source. In general, there are two possible causes for variations in the composition of mafic rocks: first, variations in the source mantle; and second, variations in the processes of magma generation, such as the degree of partial melting or variations in the magmatic processes, such as fractional crystallisation and crustal assimilation. Typically, mafic dykes are connected to the extension of the continental lithosphere [1, 2, 3, 4] and their parent magmas came from sources in the deep mantle, opening a window to study the nature of the deep mantle and the development of the lithosphere [5] . The primary pathway by which mantle melts are delivered to the crustal levels is through the mafic dykes. These are important features, and in some cases, the sole significant Proterozoic geologic event that affected the Archaean cratons [6] . Although a few intrude Paleozoic sedimentary strata of the valley and ridge province, the majority of dykes are found in the Piedmont province. Individual dykes can be up to 100 km long, and local swarms can be up to 225 km long [7] . Although 300 m ± thick dykes exist [8] , the majority are less than 30 m wide [9, 10] . Dykes occur in a wide variety of geological and tectonics settings and their detailed study through space and time is imperative for understanding several geological events. Dykes are believed to be an integral part of continental rifting and when they occur as spatially extensive swarms of adequate size can be of immense utility in continental reconstructions. This also helps to identify large igneous provinces (LIPs) [11] . Dykes are particularly important for serving as conduits for the transfer of voluminous magma from the mantle to the upper crust and thereby constitute a common expression of crustal extension. It is also well acknowledged that the continental flood basalts and major dyke swarms have their origin related in some way to the up-rise of hot mantle plumes which may