Paleoproterozoic Andesite−Dacite−Rhyolite Volcanism in the Tim Backarc Basin of Sarmatia: Sources of the Melts, Crustal Evolution, and Geodynamic Scenarios

The study is focused on the petrogenesis of Paleoproterozoic volcanic rocks in the active continental margin of the Archean Kursk block. The largest Paleoproterozoic syncline of eastern Sarmatia is the Tim backarc basin (terrane), which hosts metamorphosed rocks of the calc-alkaline andesite−dacite−rhyolite (ADR) rock association, dated at 2.07–2.08 Ga. The ADR rocks formed via the differentiation of parental basaltic melt. The enriched mafic melts of the ADR association might have been derived from a mantle wedge metasomatized by fluids during the descent of the lower oceanic slab in the course of low-angle subduction. These enriched basaltic andesite melts entered the crust and continued differentiating in crustal intermediate chambers to give rise to the dacites and rhyolites.