Offshore Oligo-Miocene volcanic fields within the Corsica-Liguria Basin: Magmatic diversity and slab evolution in the western Mediterranean Sea

Abstract

The European and Corsica-Sardinia margins of the Ligurian Sea (western Mediterranean) have been affected by a geochemically diverse igneous activity, offshore and onshore, since the Eocene. This magmatism occurred in a global subduction-related framework. On the European side, the oldest Tertiary magmatism dated at ca. 35 Ma was mainly calc-alkaline. It included the emplacement of plutonic bodies of adakitic affinity, such as the quartz microdiorite laccolith locally referred to as "esterellite". Younger magmatic events on-land within the whole Ligurian domain were mostly medium-K or K-rich calc-alkaline. Miocene volcanic activity was important in Sardinia, where andesites and ignimbrites were erupted during several magmatic cycles. In Corsica, it was minor although it emplaced lamprophyres near Sisco at 15 Ma.Dredging and diving cruises conducted in the Ligurian Sea during the last thirty years allowed us to collect a number of submarine samples. We discuss here their geochemistry (major and trace elements) and their whole-rock K-Ar ages and mineral 40 Ar-39 Ar plateau ages.Around 15 Ma, minor amounts of adakitic lavas were emplaced off southwestern Corsica, in the deepest part of the Liguria-Corsica Basin. They rested over the thinnest southwestern Corsica Hercynian continental crust. Closer to the coast, contemporaneous calc-alkaline rocks erupted 2 on a less thinned crust. The adakitic events could be indicative of either the final stages of active subduction, or alternatively of a slab tearing linked to the southeastern retreat and steepening of the slab. The latter event could be connected with the end of the Corsica-Sardinia block drifting and its correlative eastern collision.Younger volcanic effusions, dated at 14-6 Ma, occurred mostly northwest and north of Corsica. K-rich calc-alkaline basalts, shoshonites and K-rich trachytes were emplaced during this period, and alkali basalts erupted as early as 12 Ma in Sardinia. In the Toulon area, alkali basalts dated at 7-6 Ma represent the last onshore activity just before the Messinian crisis, and the Pliocene alkali basaltic outpouring in Sardinia. We propose to link these latter volcanic events to the development of a slab window in a post-collisional tectonic framework.

Pb and Hf isotope evidence for mantle enrichment processes and melt interactions in the lower crust and lithospheric mantle in Miocene orogenic volcanic rocks from Monte Arcuentu (Sardinia, Italy)

“…The geodynamics of the western Mediterranean are complex, but essentially involve subduction with different polarities of the Alpine Tethys oceanic lithosphere due to northward migration of Africa during the Mesozoic (Réhault et al, 1984(Réhault et al, , 2012Carminati et al, 2010). Detailed reviews of the geologic evolution of the region are given by Carminati et al (2012), Lustrino et al (2013) and references therein, so only essential aspects will be mentioned here.…”

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

“…[], and Réhault et al . []). Note the contrasting physiography and basement lithology in the northern and southern Tyrrhenian and the drastic change in basement lithology across the central Fault.…”

“…During early Miocene rifting, the crust beneath the Ligurian‐Provençal basin, now floored by oceanic crust [ Mauffret et al ., ; Rollet et al ., ], was thinned from ∼25 to ∼5 km [ Bois , ; Chamot‐Rooke et al ., ]. Seafloor spreading was broadly coeval with the climax of orogenic volcanism in Sardinia [ Lustrino et al ., ], but magmatism is also documented north of Corsica and along the northern offshore continuation of the Sardinia rift [ Réhault et al ., ] (Figure ).…”

Magmatism, mantle evolution and geodynamics at the converging plate margins of Italy

“…Orogenic magmatism related to Apennine subduction processes started in Provence (about 33-19 Ma; Rehault et al 2012) and progressively shifted to , the Tyrrhenian Sea basin and the Italian peninsula (about 8 Ma to present), following the eastward retreat of the Apennine subduction front. Petrological compositions of magmas are mainly calc-alkaline, but the younger activity becomes enriched in potassium, with shoshonitic to ultrapotassic magmas abundantly erupted over the last million years (e.g.…”