Computation of Parent Magma Compositions of a Layered Gabbro Suite around Kuliana, Orissa, Eastern India: Implications for Magmatic Evolution and Paleotectonic Setting

Abstract

A layered gabbro suite was emplaced around Kuliana (lat 22°3ʹN and long 86°38ʹE), Orissa, eastern India, within deformed metasedimentary rocks of the north Singhbhum mobile belt. This magmatic suite does not have any exposures of feeder dikes, chilled margins, or other evidence for an intrusive character. Because the cumulate layers do not provide information about the parent magma of this suite, the equilibrium distribution method has been utilized in this study to estimate trace element concentrations of melts in equilibrium with the cumulate solid products. The mineralogical and chemical evolution of the layered suite has been carried out on the basis of both calculated parent magmas and chemical data of cumulate layers. The magmatic differentiation of the layered suite was guided by fractional crystallization and punctuated by an event of magma chamber replenishment. The calculated parent melts exhibit enriched light rare earth elements and large ion lithophile elements, marked depletion of Ti and Y, and successive total rare earth element depletion through progressive differentiation. Plotting several immobile trace element diagrams—Nb/Yb versus Th/Yb, La/Nb versus Th/Nb, Nb/La versus Ba/La, and Zr versus Zr/Y—reveals their chemical affinity to enriched mid-ocean ridge basalt–like magmas. The La versus La/Sm plot of mantle sources affected by partial melting shows a relatively low degree (8%–30%) of melting and indicates a deeper (garnet facies) mantle as the possible source region of the parent magmas of the Kuliana layered mafic suite.