Geochemical characterization and geodynamic implication of N-trending mafic dyke swarm from the western Dharwar craton and their possible link to the ca. 2.22 Ga large igneous province

摘要

Several N-trending mafic dykes are exposed in the western Dharwar craton (WDC) and they are thought to be coeval with the ca. 2.22 Ga N- to NNW-trending Kandlamadugu dyke swarm of the eastern Dharwar craton (EDC). Geochemical characterization of these dykes is presented here to understand their genetic aspects and likely correlation with their counterpart in the EDC. Petrographic examinations suggest mineralogical and textural variations from dolerite to meta-dolerite types. Geochemically they are classified either as sub-alkaline tholeiitic basalt or basaltic andesite. Geochemical variations suggest evolution of mantle melt and demonstrate prominent clinopyroxene fractionation, however, minor role of olivine, orthopyroxene and plagioclase fractionation cannot be discarded at initial stages of crystallization. Fractionation trends of trace elements suggest crystallization of accessory phases like ilmenite, apatite and zircon, at later stages. Although observed geochemical nature suggests a little effect of involvement of crust, however, its role in the genesis of the studied mafic dykes cannot be ignored. Conversely, it is suggested that they are derived from a melt generated in a sub-continental lithospheric mantle (SCLM), which was metasomatized during an ancient subduction event before its cratonization. Based on the petrogenetic models of incompatible trace elements, it is inferred that they were likely to be derived from a melt generated by a lower percentage of melting within the garnet or garnet-spinel transition zone. Their connection to the ca. 2.22 Ga large igneous province (LIP) indicates as an integral part of the ca. 2.22 Ga N- to NNW-trending Kandlamadugu dyke swarm of the EDC. The existence of a mantle plume, substantiated by mantle potential temperature (T-p) estimate, is well-supported by higher thermal regime in the upper mantle. Although there is no direct age data available for the studied mafic dykes, however, their geochemical similarities with the ca. 2.22 Ga Kandlamadugu swarm suggest that they are co-genetic and could be linked to the same event. The likely age correlation of the ca. 2.22 Ga Kandlamadugu swami with mafic dykes of North Atlantic and Superior cratons, support their link with the Superia supercraton.