Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation

Abstract

The western Mediterranean recorded subduction rollback, slab segmentation and separation.Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We kinematically reconstruct western Mediterranean geology from subduction initiation to present, using Atlantic plate reconstructions as boundary condition. We test possible reconstructions against remnants of subducted lithosphere imaged by seismic tomography. Transform motion between Africa and Iberia (including the Baleares) between~120 and 85 Ma was followed by up to 150 km convergence until 30 Ma. Subduction likely initiated along the transform fault that accommodated pre-85 Ma translation. By thẽ 30 Ma inception of rollback, up to 150 km of convergence had formed a small slab below the Baleares. Iberia was disconnected from Sardinia/Calabria through the North Balearic Transform Zone (NBTZ). Subduction below Sardinia/Calabria was slightly faster than below the Baleares, the difference being accommodated in the Pyrenees. A moving triple junction at the trench-NBTZ intersection formed a subduction transform edge propagator fault between the Baleares and Calabria slab segments. Calabria rolled back eastward, whereas the Baleares slab underwent radial (SW-S-SE) rollback. After Kabylides-Africa collision, the western slab segment retreated toward Gibraltar, here reconstructed as the maximum rollback end-member model, and a Kabylides slab detached from Africa. Opening of a slab window below the NBTZ allowed asthenospheric rise to the base of the fore arc creating high-temperature metamorphism. Western Mediterranean rollback commenced only after sufficient slab-pull was created from 100 to 150 km of slow, forced subduction before~30 Ma.

Crustal structure of the SW Iberian passive margin: The westernmost remnant of the Ligurian Tethys?

“…Gutscher et al (2009) and Martínez-Loriente et al (2014) proposed the prolongation of this oceanic crust to the east under the Gibraltar arc ( Fig. 1) (Spakman and Wortel, 2004;van Hinsbergen et al, 2014;Vergés and Fernàndez, 2012). Ma) modified after Schettino and Turco (2011), Seton et al (2012), and Sibuet et al (2012).…”

Early-stage rifting of the Southern Tyrrhenian region: The Calabria–Sardinia breakup

“…Malinverno and Ryan, 1986;Serri, 1990;Gvirtzman and Nur, 1999;Wortel and Spakman, 2000;Piromallo and Morelli, 2002;Cimini, 2004;Rosenbaum and Lister, 2004;Faccenna et al, 2007;van Hinsbergen et al, 2014). There is a general consensus that the Liguro-Provenç al , Algero-Provenç al (16-6 Ma) and Tyrrhenian Sea (12-0 Ma) are diachronous backarc basins linked to migration of the Calabria subduction zone (Dewey et al, 1989;Mauffret et al, 2004;Lepretre et al, 2013).…”

“…Boullin et al, 1986;Handy et al, 2010;van Hinsbergen et al, 2014) corresponding to a pre-30 Ma accretionary prism, formed by internal basement units, originally located south-eastwards of the Iberia and Eurasian plates. AlkaPeCa was dispersed and stretched over four regions [Alboran (Betics, Spain and Rif, Morocco), the Kabylides (Algeria), the Peloritani Mountains (Sicily) and Calabria (southern Italy)] due to post-30 Ma migration of the subduction front and contemporaneous opening of the Liguro-Provenç al, Algerian and Tyrrhenian backarc basins (Fig.…”

“…Recent geodynamical subduction models suggest that the degree of mechanical coupling between overriding continental plate and subducting oceanic plate plays a fundamental role in the distribution of extension in the overriding plate (Meyer and Bigi et al (1992), Frizon de Lamotte et al (2000), Mauffret et al (2004), Michard et al (2006), Faccenna et al (2007), Handy et al (2010), Capozzi et al (2012), Jarsve and Pedley (2012). The blue rectangle marks the location of the area shown in and Montadert, 1982;Patacca et al, 1990;Doglioni et al, 1997;Faccenna et al, 1997;Carminati et al, 1998;Guerrera et al, 2005;Schettino and Turco, 2006;Roure et al, 2012;Catalano et al, 2013;van Hinsbergen et al, 2014).…”

“…The Southern Tyrrhenian Sea passes westward to the Algerian basin (Fig. 1) that opened in a EW direction during the middle to late Miocene as the result of backarc extension (Mauffret et al, 2004;van Hinsbergen et al, 2014).…”