Field and Petrology of Migmatites in and around Melur Region, Madurai District, Tamil Nadu

Abstract

A petrological and structural feature of the study area rock units of the Melur region has been resulted due to the environmental variables of pressure, temperature and fluid activity. Polydeformation and polymetamorphism of the rock units has produced orientations in different directions resulting in the formation of heterogeneous silicate rock with igneous and metamorphic textures. Typically, the rock contains alternating lighter layers (leucosomes, comprised of light-colored minerals such as quartz, feldspar, and muscovite) and darker layers (melanosomes, comprised of dark-colored minerals such as amphibole and biotite). This heterogeneous nature of the rock results from partial melting that occurs when a precursor rock is exposed to high pressures and temperatures.

The present study area Madurai district falls in the latitude N10°02' and longitude of E78°16'. Strike of the formation is NN34°E and dip is 35°SW. The pegmatoidal gneiss formations are having the minor folds, several mica bandings and joints. The major intrusions of study area having Garnetiferous pegmatites and granitic composition and the augen gneiss. The mineralisations of Garnets and thick Mica banding have originated from the high pressure and high temperature. Thin veins and lenses of granitic composition measuring 2-15 cm have segregated along rock foliation.  The vein material is replacive in character as evidenced by sutured margins and interlocking relationships of Quartz and Feldspar grains, total absence of contact metamorphic effects and that of chilled margins adjacent to the granitic veins.  There is a general concordance of the veins with the foliation of the rock.  They occur as patches. The migmatites exhibit a great variety of structures has the minor and major Quartz veins were also Crystallized during the melt Segregation. The study area is highly the shearing during the crystallization.