Geochemistry and petrography of Western Tethys Cretaceous sedimentary covers (Corsica and Northern Apennines): From source areas to configuration of margins
Laura Bracciali, Michele Marroni, Pandolfi Luca, Rocchi Sergio, 2007. "Geochemistry and petrography of Western Tethys Cretaceous sedimentary covers (Corsica and Northern Apennines): From source areas to configuration of margins", Sedimentary Provenance and Petrogenesis: Perspectives from Petrography and Geochemistry, José Arribas, Mark J. Johnsson, Salvatore Critelli
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Provenance studies most commonly apply the classical approach based on petrographic modal analysis of arenites. In this paper, a modal analysis of arenites is combined with both a petrographic study on conglomerate clasts and a geochemical investigation of major and trace elements of pelites. The Ligure-Piemontese oceanic basin, a branch of Western Tethys, and its continental margins were consumed during the Eocene collisional events that led to the formation of the Alpine-Apennine belt. Remnants of Cretaceous sedimentary successions supplied by the continental margins are today preserved as tectonic units in the Alpine-Apennine belt: Balagne Nappe in Alpine Corsica and Internal and External Ligurian units in the Northern Apennines. The petrography of pebbles from rudites and lithic fragments from are-nites shows that Corsica and Internal Ligurian units contain debris from granitoids, low-grade metamorphic rocks, and carbonate platform rocks, while the External Ligurian units contain debris from low- to high-grade metamorphic rocks, a mantle-rock source, carbonate platform, and pelagic siliceous and carbonate rock sources. Geochemical data on pelites indicate a more mafic-ultramafic character for External Ligurian units (enrichment in Cr, Co, Ni, and Th/Sc/Cr/V/Ni relationships that show a systematic shift toward an ultramafic contribution). Petrographic and chemical data indicate that the source for sediments of Corsica and Internal Ligurian units was made up of the upper part of a continental basement and its carbonate sedimentary cover (the Corsica-Europe continental margin). On the other hand, the External Ligurian units were supplied by a source area where a complete lithospheric section was exposed, from the upper mantle up to the deep-sea sedimentary cover (the Adria continental margin).
These findings are useful in order to unravel the processes related to the opening mechanisms of the Ligure-Piemontese oceanic basin: among the different rifting models in existence, our data support an asymmetric mechanism dominated by a west-dipping detachment fault, with the Adria margin acting as the lower plate.