The Tyrrhenian back-arc basin and subduction of the Ionian lithosphere

Abstract

A deep, narrow, and distorted Benioff zone, plunging from the Ionian Sea towards the southern Tyrrhenian basin, is the remnant of a long and eastward migrating subduction of eastern Mediterranean lithosphere. From Oligocene to Recent, subduction generated the Western Mediterranean and the Tyrrhenian back-arc basins, as well as an accretionary wedge constituting the Southern Apenninic Arc. In the Tyrrhenian Sea, stretching started in late Miocene and eventually produced two small oceanic areas: the Vavilov Plain during Pliocene (in the central sector) and the Marsili Plain during Quaternary (in the southeastern sector). They are separated by a thicker crustal sector, called the Issel Bridge. Back-arc extension was rapid and discontinuous, and affected a land locked area where continental elements of various sizes occurred. Discontinuities in extension were mirrored by changes in nature of the lithosphere scraped off to form the Southern Apenninic Arc. Part of the tectonic units of the southern Apennines, accreted into the wedge from late Miocene to Pliocene, had originally been laid down on thinned continental lithosphere, which should constitute the deep portion of the present slab. After Pliocene, only Ionian oceanic lithosphere was subducted, because the large buoyancy of the wide and not thinned continental lithosphere of Apulia and Africa (Sicily) preserved these elements from roll back of subduction. After Pliocene, the passively retreating oceanic slab had to adjust and distort according to the geometry of these continental elements. The late onset of arc volcanism in respect to the duration of extension in the Tyrrhenian-Ionian system may find an explanation considering an initial stage of subduction of thinned continental lithosphere. The strong Pleistocene vertical movements that occurred in the whole southeastern system (subsidence in the back-arc basin and uplift in the orogenic arc) may instead be related to the distortion of the oceanic slab.

The Calabrian Orocline: buckling of a previously more linear orogen

“…Crust underlying the basin varies between 'transitional' (15-km thick) to true oceanic crust (6-km thick) (Sartori 2003). The northtapering, triangular shape of the basin implies that it opened about a pole of rotation to the north, consistent with the restricted development of oceanic crust in the southern Tyrrhenian sea (the region farthest from the Euler pole), the north-south trend of spreading ridges (e.g.…”

“…Tortonian rift deposits fringing the sea imply initial opening of the basin at 8 -9 Ma and indicate that the sea is the youngest in the Mediterranean region (Sartori 2003). Crust underlying the basin varies between 'transitional' (15-km thick) to true oceanic crust (6-km thick) (Sartori 2003).…”

An analytical model for the geotherm in the Basilicata oil fields area (southern Italy)

“…These processes involved the consumption of most of the Neo-Tethyan oceanic lithosphere originally interposed between the two continental palaeomargins. Remnants of the overriding plate are preserved as continental crust units of the Calabrian Arc (FACCENNA et alii, 2001;MINELLI & FACCENNA, 2010;CIARCIA et alii, 2012;VITALE et alii, 2013), while back-arc extension produced the Liguro-Provençal Basin (Late Oligocene to Early Miocene) and then, in Late Miocene-Quaternary times, the southern Tyrrhenian Sea (FACCENNA et alii, 1997;SARTORI, 2003, and references therein).…”

Seismic velocity structures of southern Italy from tomographic imaging of the Ionian slab and petrological inferences

“…At that time lithospheric rifting separated the Calabrian block from the Sardinian basement (Goes et al 2004). This event led to the formation of new oceanic crust, which formed the Vavilov Basin to the west (4.3–2.6 Myr, Sartori 2003; 8.5–4.5 Myr, Argnani 2000), and the Marsili Basin to the south east (2.0–1.7 Ma, Argnani 2000; 1.6 Myr, Kastens et al 1988).…”