Geochemistry and Petrography of Western Tethys Cretaceous sedimentary covers (Corsica and Northern Apennines): from source areas to configuration of margins

Provenance studies most commonly apply the classical approach based on petrographic modal analysis of arenites. In this this is combined to both petrographic study on conglomerate clasts and to geochemical investigation on major and trace elements of pelites. This work is aimed to: i) understand the nature of the source areas of the Mesozoic sedimentary covers of the Ligure-Piemontese oceanic basin, a branch of Western Tethys; these sedimentary successions are preserved as tectonic units in the Alpine-Apennine belt (Balagne Nappe in Alpine Corsica and Internal and External Ligurian units in Northern Apennines); ii) provide further constraints to the understanding of the Jurassic rifting process. Petrographic and geochemical results indicate significant differences between Corsica and Internal Ligurian units against External Ligurian units. Petrography of pebbles from rudites and lithic fragments from arenites shows that Corsica and Internal Ligurian units contain a debris of low-grade metamorphic rocks and carbonate platform rock fragments, while the External Ligurian units are represented by low-, medium- and high-grade metamorphic rocks; mm-sized Cr-spinel probably derived from a mantle-rock source; additionally, both carbonate platform and pelagic siliceous/carbonatic rock fragments have been found. Geochemical data on pelites show that samples from External Ligurian units suggest a more mafic/ultramafic character: they are enriched in elements such as Cr, Co, Ni (abundant in mafic-ultramafic rocks), and the Th/Sc/Cr/V/Ni relationships show a systematic shift towards ultramafic contribution. On the whole, petrographic and chemical data collected in this paper indicate that the source for sediments of Corsica and Internal Ligurian units were similar, and made up by the upper part of a continental basement and its carbonatic sedimentary cover (the Europe continental margin). On the other hand, the sedimentary cover of the External Ligurian units was 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 to unravel the processes related to the opening mechanisms of the Ligure-Piemontese oceanic basin: among the different rifting models existing, our data support an asymmetric mechanism dominated by a west-dipping detachment fault, with the Adria margin acting as the lower plate.