Petrography And Geochemistry Of Western Tethys Mesozoic Sedimentary Covers (Alpine Corsica And Northern Apennines): A Valuable Tool In Constraining Sediment Provenance And Margin Configuration

Abstract

In the Western Tethys, the rifting processes related to the opening of the Ligure-Piemontese oceanic basin led to conjugate passive continental margins characterized by an asymmetry in their structures, lithologic composition and tectonic evolution.The asymmetry of margin configuration implicates differences between the two conjugate margins that represented the source areas of Mesozoic sedimentary cover of the Ligure-Piemontese oceanic and ocean-continent transitional domains. Up to the Late Cretaceous basin inversion, these sediments were mainly supplied by the two passive continental margins.In order to highlight the differences between the two source areas, we studied pre-late Cretaceous sedimentary units from the Balagne Nappe (Alpine Corsica) and Internal Liguride units (Northern Apennines) as representative of the Ligure-Piemontese oceanic basin located close to the Europe margin, and from the External Liguride units (Northern Apennines), that are interpreted as derived from the domain that joined the oceanic area to the Adria continental margin.This work integrates data from rudites, arenites and pelites of the studied units. Petrographic data on rudites and arenites indicates some differences in the source area composition. Particularly, only the External Liguride units contain rock fragments of medium to high grade metamorphic rocks and large chromiferous spinel fragments up to mm size. Major (XRF) and trace element (ICP-MS) data on pelite fraction show a first-order overall chemical homogeneity for all the units, with no contribution from a dissecting volcanic arc. However, significant compositional differences exist: the most striking is represented by the contribution of mafic/ultramafic rocks (e.g. high Mg#, Cr, Cr/V ratio) found only in sediments supplied from the Adria margin.Overall, petrographic and geochemical data provide matching evidence for a different composition of the two source areas, which were characterized by the occurrence of upper crustal rocks in the Europe margin and by a complete crustal and upper mantle section in the Adria margin. This configuration is probably inherited from the asymmetric opening mechanisms of the Western Tethys.