Mineralogical and geochemical signatures of the Malaguide-Ghomaride Culm Facies (Betic Cordillera and Rif Chain: Western Mediterranean): new constraints for the northern Gondwana plate tectonics

This study investigates the mineralogical and chemical composition of 25 slate samples and the petrography of four coarse-grained slates from seven sectors of the Carboniferous Culm Facies in the Malaguide (S Spain) and Ghomaride (N Morocco) domains (Betic Cordillera and Rif Chain). The succession comprises the lower Almogía Formation (Retamares and Greywacke-Slate members) and the upper Marbella Conglomerate Formation. Protoliths originated from shale sediments, consisting of quartz, feldspars, micas and Fe-oxides. An upward increase in quartz content, observed from the Malaguide to the Ghomaride domains, indicates increasing sediment maturity, due to erosion after a pre-depositional tectonic phase and sediment recycling. The rocks experienced post-burial very low-grade metamorphism (200–300°C). Geochemical signatures show increasing upward felsic components, decreasing mafic content, suggesting erosion of a volcanic arc and/or relict oceanic suture in the hinterland. Detrital chlorite and illite/muscovite testify low-grade metamorphic detrital signatures in the source area. Moderate oxidizing climatic conditions were dominant during sedimentation. Integrating our findings with recent researches, we propose that multiple Paleotethys Ocean branches separated the Paleo-Mesomediterranean microplate from the Iberian-Central French Domain, to the north, and from the Paleo-Atlas-Saharian Domain, to the south, during the Carboniferous. The Malaguide and Ghomaride domains, located along one of the southern Paleotethys branches, received detritus from a northern, pre-Carboniferous metamorphic zone, as well as, from an oceanic suture belt and/or magmatic arc. These hinterland source terranes were structured prior to Culm Facies deposition, which was subsequently structured during the latest Carboniferous Paleotethyan phase, contributing to the Pangaea final assembly.