Petrogenesis of Hudupahar-Gitilgarh Metabasic Rocks in Chhotanagpur Granite Gneiss, Eastern India

Hypersthene- to minor olivine-normative low K-quartz tholelites occurring in Hudupahar-Gitigarh area of Chhotanagpur Granite Gneissic Complex appear to have formed at low pressure (<10Kb) conditions. Small range and mutually coherent, regular patterns of distribution of the major and trace elements in Harker-Type and other variation diagrams and tight clustering of all data points in Pearce Element Ratio plots indicate unaltered and uncontaminated and comagmatic nature of the melt for the (meta)-basic rocks subjected to clinopyroxene, plagioclase and minor olivine fractionation. Multielement spidergrams and trace element modelling for a number of Compatible-Incompatible pars suggest that these rocks are products of partial melting of depleted mantle which possibly has been metasomatically slightly enriched in some but depleted in other elements prior to melting. Approximately -15% partial melting of the mantle followed by fractional crystallization of up to 20-30% in the melt appears to have been the probable mechanism for the generation of these tholeutes.