Alboran Basin, Southern Spain—Part II: Neogene Tectonic

Alboran Basin, southern Spain—Part II: Neogene tectonic implications for the orogenic float model M. Ballesteros,a*, J. Riveraa, A. Muñozb, A. Muñoz-Martín c, J. Acostaa, A. Carbóc, E. Uchupid aInstituto Español de Oceanografía, Spain bSecretaría General de Pesca Marítima, Spain cUniversidad Complutense de Madrid, Spain dWoods Hole Oceanographic Institution, Spain 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. Keywords: Alboran Ridge; Alboran Basin; Carbonate mounds; Conjugate faults; Motril and Adra anticlines; Orogenic float; Stress regime (pure and simple shear); Serrata-Carboneras Fault 1. Introduction In a previous report (Muñoz et al., in press) we used multi- crustal domains, the external zones (the south-Iberian and beam echo sounding data supplemented by a few selected Maghrebian passive continental margins) composed of high resolution TOPAS seismic reflection profiles to define Mesozoic and Tertiary sedimentary rocks, the Flysch Trough the geomorphology of the marine Alboran Basin, a structure Units consisting of nappes of Cretaceous-early Miocene located within the Alpine orogen off southern Spain and sediments that were deposited on oceanic crust or very thin northern Morocco. In the present report we use these data to continental crust, and the Internal or Alboran Domain define the tectonic style of the basin. The Alpine orogen at the comprised of metamorphosed Palaeozoic and Mesozoic southern end of Spain and northern Morocco on which the sediment thrust stack (Fig. 1; Comas et al., 1999). The thrust Alboran Basin is superimposed consists of three Pre-Neogene sheets of the Alboran Domain were transported outwards onto the *Corresponding author. E-mail address: [email protected] (M. Ballesteros). ARTICLE IN PRESS 76 M. Ballesteros et al. / Marine and Petroleum Geology 25 (2008) 75–101 Fig. 1. Geologic setting of the Alboran Basin region. AG ¼ Aguilas; AL ¼ Almerıá; CA ¼ Cadiz; GR ¼ Granada; MA ¼ Malaga; ML ¼ Melilla; T ¼ Tangier. Modified from Vegas (1992; Fig. 1) by Munõz et al. (in press). passive margins of Iberia and Morocco during the the basin to a 400 Â 200 km low straddling the African and Oligocene and westward from latest Oligocene and early Eurasian plate boundary (Platt and Vissers, 1989). Miocene creating the peripheral Gibraltar Arc thrust belt. The domain underwent approximately 200 km of roughly 2. Morphology north–south convergence between the mid-Oligocene and late Miocene and 50 km of northwest–southeast conver- The area of the Alboran Basin studied during the present gence from latest Tortonian (9–8 Ma) to the present investigation extends from 351400Nto361500N and from (Comas et al., 1999 and references therein). Synchronous 21100Wto41400W(Figs. 2–4). Primary basin topographic with this shortening of the peripheral belt of the Betic and features include the northern shelf, basin slope and apron, Rif domains was extension within the Internal Domain, Habibas Escarpment, along the Yussulf Fault, and the toward the south–southwest in the West Alboran Alboran Channel and Ridge. Secondary topography Sub-Basin and toward the southeast in the East Alboran features include the submarine canyons in the basin north Sub-Basin (Comas et al., 1992). This extension led to the slope, the sides of the Alboran Ridge and Trough and formation of the Intramontane Basins within the Alboran Habibas escarpment, gravitational structures, mounds of Domain and the present marine Alboran Basin (Shipboard unknown origin along the base of the northern slope, Scientific Party, 1996). Comas et al. (1992) inferred that Miocene volcanic edifices and fault traces (Munõz et al., in extension took place during latest Aquitanian-Burdigalian, press). The northern shelf is 3–14 km wide with its seaward Langhian-Serravalian and Tortonian with the middle edge being at a depth of 100 m west of Cabo de Gata Miocene episode leading to the development of major and 150–175 m off Cabo de Gata. The 1–4.5 km wide depocenters and the creation of mud diapirs in the West and 47–90 m high upper slope extending to a depth of Alboran Sub-Basin. 150–200 m west of Cabo de Gata and to 400 m off Cabo de Extension in the Alboran Domain ended in late Gata has a gradient of 11 to 10–151. The 7.5–19 km wide Miocene. Since late Tortonian the area has been under lower slope west of Almerıá Bay extends to a depth of compression producing folding, reverse fault inversions of 600 m. On the east side of Almerıá Bay the lower slope is former normal faults and strike–slip faults. This compres- made up of two segments, an upper one extending from a sion ranged from northwest–southeast during late Torto- depth of 400–700 m having a declivity of 1–31 and a lower nian, north–south from late Tortonian to middle Pliocene one extending to a depth of 1600 with a gradient that and north–northwest–south–southeast during the rest of exceeds 241. the Pliocene and Pleistocene (Comas et al., 1999). This The basin apron on the western side of the Alboran tectonic shortening and concomitant progressive emer- Basin extends to a depth of 1500 m from the base of the gence of segments of the ancestral Alboran Basin reduced lower slope, terminates southward on the Albora ridge and ARTICLE IN PRESS M. Ballesteros et al. / Marine and Petroleum Geology 25 (2008) 75–101 77 Fig. 2. Bathymetric chart of the Alboran Basin compiled from multi-beam acquired during the present investigation. Contour interval 25 m. From Munõz et al. (in press). Fig. 3. Shaded relief map of the Alboran Basin compiled from multi-beam data. See Fig. 2 for names of prominent topographic features. From Munõz et al. (in press). has a gradient of 2–11. A low in the western side of the 41Wto21450W, the apron is dominated by an east–west apron, the West Alboran Sub-Basin, is defined by the trending 6 to 17 m wide over 900 m deep trough that we 1200 m contour. In the center of the Alboran Basin, from have tentatively named the Djibouti Trough. South of the ARTICLE IN PRESS 78 M. Ballesteros et al. / Marine and Petroleum Geology 25 (2008) 75–101 Fig. 4. The 3D diagram of Alboran Basin compiled from multi-beam data. This diagram images the northeast and northwest structures in the center of the basin. A ¼ Almerıá Canyon; AA ¼ Abra Anticline; AL ¼ Alboran Ridge; C ¼ Chella Bank; DJ ¼ Djibouti Bank; E ¼ East Alboran Sub-Basin; F ¼ Fault traces; G ¼ Graben; L ¼ Slide scar; M ¼ Motril Anticline; S ¼ South Alboran Sub-Basin; SC ¼ Serrata-Carboneras Fault; T ¼ Alboran Channel; W ¼ West Alboran Sub-Basin. trough is the o900 m deep high whose top is dominated by Habibas Escarpment and the o400 m high East and West seamounts. We have named this feature the 361100N High Cabliers ridges. (Fig. 2). The apron on the eastern side of the Alboran Basin is dominated by an over 1950 m deep 30 km wide and 3. Structural setting 57 km long low, the East Alboran Sub-Basin. The sub- basin is flanked on the south by the Habibas Escarpment. The main structural elements of the Alboran Basin, On the southern part of the Alboran Basin is the 120 km margins, basins and topographic highs, are the creation of long 4.5–8 km wide Alboran Ridge with its crest being less Miocene crustal attenuation. The south facing basin than 100 m deep. The ridge extends from Xauen Bank at margin displays a passive margin structural style consisting 4110W, 351200N on the southwest to Habibas Escarpment of sediment covered blocks that are tilted and faulted on the northeast. The base of the ridge’s northwest side is downward (Maldonado et al., 1992). The main structural 1000–1800 m deep, has a gradient of 18–241 and is indented highs in the center of the Alboran Basin are the 361100N by a 10 km wide northwest trending embayment near High and the Alboran Ridge (Figs.

Load more