Carbon Isotope Characteristics as Evidence of an External Source of High-Temperature Granitoids in Granulite Complexes
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Data on the carbon isotope composition of graphite and CO2 from inclusions in quartz of granitoids of the Southern Marginal Zone (SMZ) of the Limpopo granulite belt, South Africa, are presented. The average values of δ13C for graphite and СО2 from fluid inclusions in quartz are found within the range that is typical of deep (mantle) carbon sources. The data are evidence of an external source of granitoid magmas. They are likely to be hybrid rocks that appeared during assimilation of host metapelites by trondhjemite magmas, while graphite in trondhjemites and granodiorites is a product of high-temperature (~900–1000°С) evolution of the CO2-rich fluid phase of granitoid magmas when they intrude the rocks of the granulite complex and was formed during assimilation that led to reduction of CO2 when sulfide-bearing metapelite material was contaminated by the magma.
The authors are grateful to V.B. Polyakov (Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences), L.Ya. Aranovich, and E.O. Dubinina (Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences) for discussing the results and the constructive commentary. The Raman spectra studies were supported by the Moscow State University Program of Development. The isotope studies were carried out at the the Center of Elemental and Isotope Studies, Siberian Branch, Russian Academy of Sciences, at the base of the Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences (Novosibirsk). This work was supported by the Russian Science Foundation, project no. 14-17-00581, and was conducted in cooperation with the University of Johannesburg (South Africa).