Late orogenic extension of the Betic Cordillera and the Alboran Domain: A lithospheric view

Abstract

The Betic Cordillera of southern Spain provides a clear example of a collisional orogen that has undergone large‐scale extensional collapse while convergent motion of the bounding plates continued. Extension was accommodated by coeval shortening in thin‐skinned fold and thrust belts around the periphery of the system, and much of the region has now subsided to form a large marine basin. The thermal and deformational record of these processes is preserved in rocks from the upper mantle, crystalline crust, and sedimentary cover. Upper mantle peridotites record evidence for exhumation in several stages from asthenospheric depths to the surface. Early stages of exhumation probably occurred during Mesozoic rifting. Cooling at midlithospheric depths reflects continental convergence, and subsequent heating indicates loss of most of the underlying lithosphere and ascent of asthenosphere, whilst the final stages of exhumation in early Miocene time reflect extensional collapse. Crustal rocks in the internal zone of the Betic Cordillera were metamorphosed down to 50 km depth and are now exposed beneath major low‐angle normal detachment zones that separate them from heavily faulted low‐grade rocks above. Cooling ages of associated mylonites indicate that these detachments were active during the early to middle Miocene. Fault‐bounded intramontane basins, developed during the early to middle Miocene, contain coarse continental sediments heavily affected by normal fault systems, followed by a less deformed late Miocene marine succession. All of these phenomena can be explained by convective removal of the lithospheric root beneath a Paleogene collisional orogen, leading to large‐scale extension followed by thermal subsidence of the center of the system.

Mechanisms for folding of high-grade rocks in extensional tectonic settings

“…the Betic Cordillera, Spain, which, with the exception of Platt (1982) and Vissers et al (1995), had previously been attributed to contractional nappe stacking, have been shown by Orozco et al (1998) to have formed synchronous with displacement on low-angle normal faults during crustal extension. One such fold can be followed axially for over 50 km (Orozco et al, 1998).…”

Scenarios for earthquake-generated tsunamis on a complex tectonic area of diffuse deformation and low velocity: The Alboran Sea, Western Mediterranean

“…Different processes have been proposed to explain this evolution and the thinning of the crust: westward displacement due to the opening of the Algero-Provenc;al Basin (Sanz de Galdeano, 1990); subduction of Africa under Iberia, being the Alboran Basin a back-arc basin (Morley, 1993); subduction of Iberia under the Betic Cordillera and the Alboran Basin (Morales et al, 1999); east dipping subduction of the Atlantic, Iberia and Africa under the Alboran domain (Royden, 1993;lonergan and White, 1997); and thinning of the crust due to convection processes in the mantle (Weijermars, 1985;Doblas and Oyarzun. 1989;Platt and Vissers, 1989;Vissers et al, 1995). In addition to these hypotheses to explain the shallow tectonics, there are also a number of hypotheses to explain the intermediate and deep focus earthquakes that take place in the area, divided into delamination processes (Garcia-Duefias et al" 1992;Watts et aI., 1993;Docherty and Banda, 1995;Seber et al, 1996;Buforn et al, 1997;Mezcua and Rueda, 1997;Morales et al, 1997) and subducted slab processes (Royden, 1993;Gutscher et aI., 2002;Thiebot and Gutscher, 2006); maybe being both active for deep and intermediate earthquakes respectively (Bufom et aI., 1991;L6pez Dsado et aI., 2001).…”

Punctuated Neogene tectonics and stratigraphy of the African-Iberian plate-boundary zone: concurrent development of Betic-Rif basins (southern Spain, northern Morocco)

“…Extension of the continental crust due to convective removal of (cold and dense) lithosphere beneath a fixed depocentre (Platt & Vissers, 1989;Vissers et al, 1995) or by (asymmetric) delamination of the lithosphere beneath an eastwardmigrating depocentre (García-Dueñas et al, 1992;Docherty & Banda, 1995;Seber et al, 1996). This was associated with the simultaneous gravitational collapse of thickened continental crust as well as extension-driven thrusting.…”

“…It was open to the North Algerian Basin in the east and closed to the west by the Gibraltar Arc, i.e. the Atlantic-facing collision front of the 'Alboran Block' (Platt & Vissers, 1989;García-Dueñas et al, 1992;Morley, 1993;Vissers et al, 1995;Lonergan & White, 1997;Rosenbaum & Lister, 2004; see Tandon et al (1998) for a discussion of later rifting in part of the basin, inferred to have been due to time-transgressive migration of delaminating lithosphere). After the late Aquitanian-early Burdigalian, the main period of migration, thinning and fragmentation of the 'Alboran Block', subduction-related magmatism occurred abundantly as testified by numerous post-Burdigalian seamounts (generally ~22-6 Ma; Hernández et al, 1987;Lonergan & White, 1997;Fernández-Soler, 2001) and the Alboran Ridge (Fig.…”

“…The Internal Zone, the outcropping Spanish part of which is also called 'Betic Zone', consists essentially of fragments (allochthonous terranes) derived from a linear, collisional mountain chain (thick-skinned nappe stack) that originated in a distant northeastern position. Probably mostly during the Late Eocene 'Atlas Event' of enhanced collision of Africa and Europe in combination with increased NE-SW striking lithosphere-scale underthrusting (Vissers et al, 1995;Frizon de Lamotte et al, 2000). The 'Betic Zone' collapsed in 'mid-Oligocene' time at the beginning of S and W directed back-arc extension in the Western Mediterranean (Rosenbaum & Lister, 2004).…”