Petrology and mineralogy of potassic alkaline rocks from Jharia coalfields Jharkhand India

Abstract

The Jharia intrusions are classified as lamproites using the MgO K2O Al2O3 classification diagram. The bulk rock major and minor compositions of the Jharia intrusions are similar to those of cratonic lamproites. However, these intrusions show some compositional similarities with Kaapvaal orangeites and ultramafic lamprophyres. Higher TiO2 content and lower CaO content distinguishes these intrusions from Kaapvaal lamproites and aillikites, respectively. The anorogenic character of these intrusions is indicated by the negative Pb anomaly, absence of negative Nb Ta anomaly, low Al2O3/TiO2 ratio (0.8 1.4) and Th Hf Nb/2 ternary plot. The occurrence of peridotite-derived olivine-I xenocrysts and antecrystic phlogopite-I suggest that the Cretaceous lamproite magmatic event in eastern India was sourced from lithospheric mantle. The potassic sills and dykes studied indicate lamproite magma derivation from phlogopite-dominated vein assemblage and peridotite wall-rock by low degrees of partial melting. The melting event within the cratonic mantle lithosphere of eastern India may have occurred while this part of former Gondwanaland drifted in the periphery of the Kerguelen mantle plume, without any notable influence by subduction. newline