Three-Phased Temporal Evolution of the Jhirgadandi Granite Complex, Sonbhadra District, Uttar Pradesh

Field observations, petromineralogical and geochemical studies on the locks of Jhirgadanpdi pluton indicate three phases of igneous activity, compositionally ranging from gianodiorite, Quartz-Monzonite to granite. The wide spread intermediate phase of this suite shows anomalous concentration of U, Ce and Th as compared to average granite and enrichment of K, Rb, Ba relative to Zr, Nb and Y. The radioactive minerals identified are thorite, uranothorite, allanite monazite and samaiskite Molybdenite and chalcopyite are the other are minerals Presence of REE (1 are earth element) minerals, distibution pattern of LIL (large Ion lithophile) elements, various elemental ratios and increasing metaluminous tendency indicate moderate degree of differentiation Petromineralogical study of rocks suggests partial melting of a magic source of lower crustal rocks Geochemical data suggests that the granitic rocks of the three phases are comagmatic. Available age data together with tectonic considerations indicate that the magmatic activity is relaled to the development of Mahakoshal greenstone belt which might have culminated with the emplacement of Post-Tectonic Jhirgadandi sulte (∼ 1800 Ma), possibly under the influence of a mantle plume.