Paleoproterozoic alkaline-carbonatite magmatism in the convergent tectonic setting: Evidences from 2.07 Ga Dubravinsky complex in the Eastern Sarmatia

Abstract

The Dubravinsky alkaline-carbonatite complex (ACC) include two relatively large plutons: the arcuate shape Dubravinka pluton and linear Chernyanka pluton intruding the Paleoarchean TTG of the Kursk block of Sarmatia and consisting of three main lithologies: alkaline pyroxenites, carbonatites (together with silicocarbonatites and phoscorites) and syenites (including alkaline granites). The carbonatites and silicocarbonatites are enriched in trace and rare earth elements, which contents vary significantly.The source for the alkaline pyroxenites and carbonatites could be enriched protoliths from the subcontinental lithospheric mantle, produced by melting and release of fluids from the subducted oceanic slab at c. 2.1 Ga. The primary igneous C and O isotope composition is preserved in the carbonatite: δ13C (‰ VPDB) = (−4.9) - (−6.4), δ18O (‰ VSMOW) = (+8.0) – (+9.8). The alkaline granites display well preserved isotope markers of a long-lasting crustal prehistory indicating Paleoarchean source. The syenites have a lesser contribution of Paleoarchean crustal material.The alkaline pyroxenites and carbonatites are undoubtedly initially igneous rocks that have undergone c. 2.07 Ga-old high-temperature metamorphism. The Dubravinsky ACC is most likely 2.07–2.08 Ga-old, not much older than the metamorphic event. The Dubravinsky ACC has been formed in a suprasubduction setting from both mantle and crustal sources. It is the earliest known carbonatite complex in the World resulted from subduction-collision processes, and the first sign of transition to deep subduction of the modern style.