Abstract
Extension and calc-alkaline volcanism of the submerged orogen of alpine age (OAA) initiated in Early Oligocene (~33/32 Ma) and reached the stage of oceanic opening in Early-Miocene (Burdigalian), Late-Miocene and Late-Pliocene. In the Burdigalian (~20–16 Ma) period of widespread volcanism of calcalkaline type on the margins of oceanic domain, seafloor spreading originated the deep basins of north Algeria (western part of OAA) and Sardinia/Provence (European margin). Conversely, when conjugate margins’ volcanism has been absent or scarce seafloor spreading formed the plains Vavilov (7.5–6.3 Ma) and Marsili (1.87–1.67 Ma) within OAA eastern part (Tyrrhenian Sea). The contrast between occurrence and lack of margin’s igneous activity probably implies the diversity of the geotectonic setting at the times of oceanization. It appears that the Burdigalian calcalkaline volcanism on the continental margins developed in the absence of subduction. The WNW-directed subduction of African plate probably commenced at ~16/15 Ma (waning Burdigalian seafloor spreading) after ~18/16 Ma of rifting. Space-time features indicate that calcalkaline volcanism is not linked only to subduction. From this view, temporal gap would exist between the steep subduction beneath the Apennines and the previous, flat-type plunge of European plate with opposite direction producing the OAA accretion and double vergence.
Highlights
In Earth Sciences, magmatism of the calc-alkaline type is generally viewed as a result of partial melting of sources, which have undergone metasomatic modification via chemical recycling of subducted crustal material
Volcanoclastic rocks showing calc-alkaline nature, are widespread among the allochthonous sediments of the Apennines (Fig. 3; Supplementary Info S3 and Datasets S5, S6). If they have been produced from lost emission centres, which were originally sited in the Tyrrhenian OAA, their space-time distribution can be meaningful for the reconstruction of the link between calc-alkaline volcanism and tectonic setting
Post-orogenic continental extension and calc-alkaline volcanism initiated in the Oligocene, in the Burdigalian (~20–16 Ma) reached the stage of an oceanic opening in the European plate (Sardinia-Provence basin) and the western segment of the submerged orogen
Summary
Extension and calc-alkaline volcanism of the submerged orogen of alpine age (OAA) initiated in Early Oligocene (~33/32 Ma) and reached the stage of oceanic opening in Early-Miocene (Burdigalian), Late-Miocene and Late-Pliocene. The largely accepted idea considers that, since the Oligocene, extension seafloor spreading and calc-alkaline volcanism developed entirely above the WNW-directed, steep-slab-type (Island-arc-type) subduction of African plate and at the rear of the Apennine wedging[3,7] From this point of view, the West Mediterranean and the Tyrrhenian represent two distinct back-arc regions, formed above the same subduction which was retreating eastward due to slab rollback and passive sinking. Volcanoclastic rocks showing calc-alkaline nature, are widespread among the allochthonous sediments of the Apennines (Fig. 3; Supplementary Info S3 and Datasets S5, S6) If they have been produced from lost emission centres, which were originally sited in the Tyrrhenian OAA, their space-time distribution can be meaningful for the reconstruction of the link between calc-alkaline volcanism and tectonic setting. Allochthonous and “in-situ” volcanics were jointly considered
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