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Eastern Dharwar Craton,India:continental lithosphere growth by accretion of diverse plume and arc terranes

Geoscience Frontiers 2012年第3期3卷 225-240页

作者： C.Manikyamba Robert Kerrich National Geophysical Research Institute Council of Scientific and Industrial ResearchHyderabad 500 007India Department of Geological Sciences University of SaskatchewanSaskatoonSaskatchewan S7N 5E2Canada

Abstract Greenstone belts of the eastern Dharwar Craton, India are reinterpreted as composite tecto- nostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new high-precision elemental data. The former are dominated by a komatiite plus Mg-tholeiitic basalt volcanic association, with deep water siliciclastic and banded iron formation （BIF） sedimentary rocks. Plumes melted at 〈90 km under thin rifted continental lithosphere to preserve intrao- ceanic and continental margin aspects. Associated alkaline basalts record subduction-recycling of Me- soarchean oceanic crust, incubated in the asthenosphere, and erupted coevally with Mg basalts from a heterogeneous mantle plume. Together, komatiites-Mg basalts-alkaline basalts plot along the Phanero- zoic mantle array in Th/Yb versus Nb/Yb coordinate space, representing zoned plumes, establishing that these reservoirs were present in the Neoarchean mantle. Convergent margin magmatic associations are dominated by tholeiitic to calc-alkaline basalts compo- sitionally similar to recent intraoceanic arcs. As well, boninitic flows sourced in extremely depleted mantle are present, and the association of arc basalts with Mg-andesites-Nb enriched basalts-adakites documented from Cenozoic arcs characterized by subduction of young （〈20 Ma）, hot, oceanic litho- sphere. Consequently, Cenozoic style ＂hot＂ subduction was operating in the Neoarchean. These diverse volcanic associations were assembled to give composite terranes in a subduction-accretion orogen at -2.7 Ga, coevally with a global accretionary orogen at -2.7 Ga, and associated orogenic gold mineralization.

关键词： continental lithospheregrowth Zoned plume Subduction-accretion Neoarchean mantle Geodynamics Eastern Dharwar Craton

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