Early‐stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide‐angle and multichannel seismic study

Abstract

[1] Extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins. The mechanisms that operate during the early stage of crustal extension are still intensely debated. We present the results from coincident multichannel seismic and wide-angle seismic profiles that transect across the northern Tyrrhenian Sea Basin. The profiles cross the Corsica Basin (France) to the Latium Margin (Italy) where the early-rift stage of the basin is well preserved. We found two domains, each with a distinct tectonic style, heat flow and crustal thickness. One domain is the Corsica Basin in the west that formed before the main rift phase of the northern Tyrrhenian Sea opening ($8-4 Ma). The second domain is rifted continental crust characterized by tilted blocks and half-graben structures in the central region and at the Latium Margin. These two domains are separated by a deep ($10 km) sedimentary complex of the eastern portion of the Corsica Basin. Travel-time tomography of wide-angle seismic data reveals the crustal architecture and a subhorizontal 15-17 6 1 km deep Moho discontinuity under the basin. To estimate the amount of horizontal extension we have identified the pre-, syn-, and post-tectonic sedimentary units and calculated the relative displacement of faults. We found that major faults initiated at angles of 45 -50 and that the rifted domain is horizontally stretched by a factor of $ 1.3 ($8-10 mm/a). The crust has been thinned from $24 to $17 km indicating a similar amount of extension ($30%). The transect represents one of the best imaged early rifts and implies that the formation of crustal-scale detachments, or long-lived low-angle normal faults, is not a general feature that controls the rift initiation of continental crust. Other young rift basins, like the Gulf of Corinth, the Suez Rift or Lake Baikal, display features resembling the northern Tyrrhenian Basin, suggesting that half-graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation.

Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains

“…The WAS data do not constrain well crustal thickness beneath the island, but complementary gravity modeling indicates a ≤24 km thickness, in agreement with previous seismic estimations [ Di Stefano et al ., ]. Other WAS profiles acquired during the MEDOC‐2010 experiment in the Northern Tyrrhenian basin, across Corsica and offshore to the east, suggests a similar thickness beneath the island [ Moeller et al ., ]. The crystalline crust thins from ~15 km thick under the coastline (80 km, Figure a) to 9 km at domain 1 edge, implying a stretching factor ( ß ) of ~3 (125 km, Figure a).…”

“…From a morphotectonic point of view, the Tyrrhenian Sea can be subdivided in three different domains (Figure ); the Northern (north of ~40° 45′N), which displays shallower seafloor and rough morphology; the Central (from ~40° 45′N to ~39°N) with deeper seafloor and extended abyssal plains spotted with prominent volcanic and nonvolcanic seamounts, and the Southern Tyrrhenian with the volcanic arc along the Sicilian‐Calabrian margin. The Northern Tyrrhenian basin system of normal faults trends roughly N‐S to turn NW‐SE to the east [ Mauffret and Contruccci , ; Moeller et al ., ]. This basin is spotted by small‐scale magmatic intrusions [ Moeller et al ., ] that decrease in age eastward [ Bartole , ].…”

“…The Northern Tyrrhenian basin system of normal faults trends roughly N-S to turn NW-SE to the east [Mauffret and Contruccci, 1999;Moeller et al, 2013]. This basin is spotted by small-scale magmatic intrusions [Moeller et al, 2013] that decrease in age eastward [Bartole, 1995]. The Corsica basin in the westernmost Northern Tyrrhenian, initiated during the counterclockwise rotation of Corsica and Sardinia at least 20 Ma [Zitellini et al, 1986;Mauffret and Contruccci, 1999].…”

Oligocene-Miocene extension led to mantle exhumation in the central Ligurian Basin, Western Alpine Domain

“…The extension of the Ligurian Basin stopped and shifted to the Tyrrhenian Sea while the Apennines-Calabrian subduction zone continued to roll back further southeast until late the Messinian, ~6 Ma (Faccenna et al, 2001;Advokaat et al, 2014). The opening rate was calculated with 7.8-10.3 mm/yr (Moeller et al, 2013). In the north, extension led to continental crustal thinning (Moeller et al, 2013), while 80 further south in the centre of the Tyrrhenian Basin, mantle was exhumed and serpentinised and intruded by Mid-Ocean-Ridge type (MOR-type and intraplate basalts) (Prada et al, 2016).…”

Mantle earthquakes beneath the South Iberia continental margin and Gulf of Cadiz – constraints from an onshore-offshore seismological network

“…In continental lithosphere it has been observed that during rifting the upper crust is deformed by faulting while the lower crust generally supports ductile deformation (e.g., Odera et al, 2001;Moeller et al, 2013).The transition from brittle to ductile deformation depends on the temperature structure and the rock type. Earthquakes are generally restricted to domains of brittle deformation.…”