Carbon Isotope Characteristics as Evidence of an External Source of High-Temperature Granitoids in Granulite Complexes

Abstract

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.