Alboran Basin, southern Spain—Part II: Neogene tectonic implications for the orogenic float model

Abstract

We infer that the Alboran Basin, the first western Mediterranean Basin found after crossing Gibraltar, is an orogenic float underlained by a de´ collement system, a multi-layered ductile shear extending from 10 km to between 30 and 40 km below sea level. This float was formed as consequence of the collision of the African-Eurasian plates in the Oligocene-late Miocene. Synchronous with this compression the float experienced basin wide crustal thinning and subsidence about 25 m/year ago by subcrustal processes. Since latest Miocene the float has undergone compression due to the continuous convergence of Eurasia and Africa. The faults created as a result of this compression are dominated by a conjugate system of northeast trending left-lateral and northwest right-lateral strike-slip faults. This deformation is taking place under a simple shear mechanism. Associated with the northwest and northeast lateral faults are zones of compression trending west and east of north extending from the base of the basin's north upper slope to the Alboran Ridge. The initial morphology of the Alboran Ridge on the southern side of the Alboran Basin was due to the construction of a volcanic edifice at the northeast end of the ridge and igneous activity along northeast trending fractures southwest of the edifice. At the northeast end of the Alboran Ridge motion along a right-lateral fault cutting across the ridge led to sediment collapse and the creation of a prominent embayment on the ridge's northwest flank. Deformation is more subdued in the western than in the eastern part of the Alboran Basin, a tectonic style due either to differences in sediment rheology or that the accommodation of the convergence of Africa and Iberia is more diffused and attenuated in the west than in the east.

Acoustic and seismic imaging of the Adra Fault (NE Alboran Sea): in search of the source of the 1910 Adra earthquake

“…Incised on the shelf edge (100 m depth), the NE-SW trending 11.3 km long Adra Channel obliquely cuts the upper slope and stops around 650 m depth. At the base of the shelf edge, between 2 • 56 W and 2 • 52 W, a cluster of small rounded monticules correspond to coral mounds, first described by Ballesteros et al (2008) (Fig. 2).…”

Active mud volcanism in the West Alboran Basin: Geochemical evidence of hydrocarbon seepage

“…1) is situated at the boundary of the African and Eurasian plates, which have had varied directions of relative motion since the late Cretaceous. Plate-tectonics reconstruction suggests that this segment was a convergent margin during the mid-Oligocene and late Miocene, followed by approximately 50 km of NNW-directed oblique convergence since the late Miocene (Dewey et al, 1989;Morley, 1992;Ballesteros et al, 2008).…”

The South-Western Alboran Earthquake Sequence of January-March 2016 and Its Associated Coulomb Stress Changes

“…[12] [13] [14]. The main physiographic lows are: the almost-radial West Alboran basin, the narrow Alboran channel (ENE-WSW), prolonged by the also volcanic Tofiño bank and the sedimentary Xauen bank [6] [12] [15] [16], the Algarrobo-Herradura-Djibouti banks off the Spanish margin [17], the Pytheas-Cabliers-Provençaux banks [12], and the WNW-ESE Yusuf-Habibas lineament consisting of a ridge and a scarp [18].…”

“…Along the Spanish margin, there are conspicuous structures such as the NE-SW Adra and Serrata-Carboneras faults [17] and smaller structures described in detail [19], while along the Moroccan margin, some surface expressions of the Bousekkour-Aghbal and Trougout faults were described by [13] [14] [20].…”

“…This fault zone consists of numerous almost-vertical normal faults which are relayed to the north by a major sinistral strike-slip fault offsetting the western termination of the Alboran Ridge and the Tofiño bank for about 28 km [12]. The northern continuation of the TASZ is not as simple as suggested by [1]; for instance, other authors [8] [12] extend it northwards to the Djibouti bank area, but detailed analysis by [17] show that it continues in a diffuse manner as linear depressions, and more northwards by small segments until it reaches the land east of Motril. The relationship with the NE-SW trending Serrata-Carboneras segment is not obvious as they are separated from each other by the Adra anticline [17].…”