History of subduction and back-arc extension in the Central Mediterranean

Abstract

Summary Geological and geophysical constraints to reconstruct the evolution of the Central Mediterranean subduction zone are presented. Geological observations such as upper plate stratigraphy, HP–LT metamorphic assemblages, foredeep/trench stratigraphy, arc volcanism and the back‐arc extension process are used to define the infant stage of the subduction zone and its latest, back‐arc phase. Based on this data set, the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross‐sections from the northern Apennines and from Calabria to the Gulf of Lyon can be derived. Further, the reconstruction is used to unravel the main evolutionary trends of the subduction process. Results of this analysis indicate that (1) subduction in the Central Mediterranean is as old as 80 Myr, (2) the slab descended slowly into the mantle during the first 20–30 Myr (subduction speeds were probably less than 1 cm year− 1), (3) subduction accelerated afterwards, producing arc volcanism and back‐arc extension and (4) the slab reached the 660 km transition zone after 60–70 Myr. This time‐dependent scenario, where a slow initiation is followed by a roughly exponential increase in the subduction speed, can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull. Finally, the third stage is controlled by the interaction between the slab and the 660 km transition zone. In the southern region, this results in an important re‐shaping of the slab and intermittent pulses of back‐arc extension. In the northern region, the decrease in the trench retreat can be explained by the entrance of light continental material at the trench.

Collisional model for rapid fore‐arc block rotations, arc curvature, and episodic back‐arc rifting in subduction settings

“…[42] To date, the slab rollback hypothesis has proven the most popular and durable model to explain the formation of back-arc basins, especially in areas of strongly curved arcs [e.g., Garfunkel et al, 1986;Kincaid and Olson, 1987;Dvorkin et al, 1993;Royden, 1993 Taylor and Karner [1983] are (1) they are unable to explain why some subduction zones have back-arc basins, while others do not (although Sdrolias and Mueller [2006] do point out that absolute upper plate motion can explain the lack of back-arc basins at some subduction margins) and (2) none of the 2-D models can explain the highly episodic character of most backarc systems where the main pulse of back-arc opening commonly lasts only several million years [e.g., Faccenna et al, 2001aFaccenna et al, , 2001b (Table 1).…”

“…[43] Advocates of mantle-controlled 2-D models for back-arc basin opening have proposed shortlived mechanisms that could produce the observed style of episodic opening, namely, (1) slab detachment [Faccenna et al, 2006] or (2) the intersection of the subducted slab with the 660-km-deep transition zone between the upper and lower mantle [Faccenna et al, 2001a[Faccenna et al, , 2001bSchellart, 2004]. However, it is not yet proven that these mechanisms actually are responsible for back-arc episodicity.…”

Origin and evolution of Cenozoic magmatism of Sardinia (Italy). A combined isotopic (Sr–Nd–Pb–O–Hf–Os) and petrological view

“…Osmium is qualitatively considered to be a strongly compatible element in peridotitic assemblages, whereas Re is moderately incompatible (e.g., Shirey and Walker, 1998;Meisel et al, 2001;Hauri, 2002 We propose that the earliest (~43-23 Ma) subduction-related igneous phases in the western Mediterranean are not directly related to the metamorphic dehydration processes of the subducting Alpine Tethys plate, but rather to the pushing effects of this plate over the ancient lower crust of the upper plate. Assuming a convergence rate between the upper (i.e., Europe) and lower plates (i.e., western branch of the Alpine Tethys) as slow as 1-3 cm/yr (e.g., Gueguen et al, 1998;Faccenna et al, 2001;Carminati et al, 2010Carminati et al, , 2012) and a 45° angle of the subducting plate ), the front of the Alpine Tethys slab would have reached the depth at which the amphibole is expected to breakdown (~80-120 km; Schmidt and Poli, 1998;Niida and Green, 1999;Syracuse and Abers, 2006) between 3.8 Myr (3 cm/yr, 80 km depth) and 17 Myr (1 cm/yr, 120 km depth) later.…”

Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)

“…In particular, being the thermal structure in subduction channels and orogenic convergence zones modulated by the relative importance of heat advection to diffusion (e.g. Peackock et al, 1994;Peackock and Wang, 1999;Faccenna et al, 2001;Sandiford, 2002), conduction-dominated (the nascent and warm Proto-Sabzevar subduction, thermal gradient of ca. 25 • C km −1 ) and advection-dominated (the mature and cold Neotheyan subduction, thermal gradient of ca.…”

“…The metamorphic record of the ocean-derived units marking orogenic suture zones provides key elements to decipher modes and regimes of oceanic subduction and to constrain paleotectonic reconstructions at (paleo-)convergent margins (e.g. Scambelluri et al, 1995;Peacock, 1996;Faccenna et al, 2001;Hacker et al, 2003;Jolivet et al, 2003;Brown, 2006Brown, , 2010Bebout et al, 2007;Agard et al, 2009).…”