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Geochemistry and provenance of Devono-Carboniferous volcano-sedimentary sequences from the Southern Vosges Basin and the geodynamic implications for the western Moldanubian Zone

Abstract The Southern Vosges host a volcano-sedimentary basin subdivided into a Lower Unit of Late Devonian age containing marine greywackes associated with bimodal volcanism, a marine Middle Unit (of Early Carboniferous age) and a terrestrial Upper Unit (of Late Carboniferous age), both accompanied by volcanism of intermediate to evolved composition. Petrographically and geochemically, sediments from the Lower Unit are characterized by mafic volcanic, sedimentary and metamorphic components and a positive Cr-Ni anomaly. A negative Nb anomaly weakens in the Middle and Upper Units. These units are dominated by intermediate to felsic volcanic detritus, and exhibit an enrichment in incompatible trace elements and disappearance of the Cr-Ni anomaly. The facies and composition of the volcano-sedimentary sequences indicate that an extensional basin existed in Late Devonian time (c. 360 Ma). Subduction-related volcanism and successive closure of the basin occurred in the Lower Carboniferous (c. 330 to c. 325 Ma). Sedimentation graded from flysch into molasse in Late Carboniferous time, where terrestrial conditions indicate that continental collision had occurred. The volcanism reported here coincides with arc magmatism in the Mid-German Crystalline High and closure of the Rheno-Hercynian Ocean, which was possibly responsible for the geodynamic evolution of the Southern Vosges Basin.