Neogene Tectonic Evolution of the Gibraltar Arc: New Paleomagnetic Constrains from the Betic Chain ⁎ M

Earth and Planetary Science Letters 250 (2006) 522–540 www.elsevier.com/locate/epsl

Neogene tectonic evolution of the Gibraltar Arc: New paleomagnetic constrains from the Betic chain ⁎ M. Mattei a, F. Cifelli a, , I. Martín Rojas b, A. Crespo Blanc c, M. Comas d, C. Faccenna a, M. Porreca a

a Dpt. Scienze Geologiche, Università degli Studi Roma TRE, Italy b Dpt. de Ciencias de la Tierra y del Medio Ambiente, Universidat de Alicante, Spain c Dpt. De Geodinamica, Universidat de Granada, Spain d CSIC — Universidat de Granada, Spain

Received 28 April 2006; received in revised form 1 August 2006; accepted 14 August 2006 Available online 27 September 2006 Editor: S. King

Abstract

New paleomagnetic results from Neogene sedimentary sequences from the Betic chain (Spain) are here presented. Sedimentary basins located in different areas were selected in order to obtain paleomagnetic data from structural domains that experienced different tectonic evolution during the Neogene. Whereas no rotations have been evidenced in the Late Tortonian sediments in the Guadalquivir foreland basin, clockwise vertical axis rotations have been measured in sedimentary basins located in the central part of the Betics: the Aquitanian to Messinian sediments in the Alcalà la Real basin and the Tortonian and Messinian sediments in the Granada basin. Moreover, counterclockwise vertical axis rotations, associated to left lateral strike-slip faults have been locally measured from sedimetary basins in the eastern Betics: the Middle Miocene to Lower Pliocene sites from the Lorca and Vera basins and, locally, the Tortonian units of the Huercal-Overa basin. Our results show that, conversely from what was believed up to now, paleomagnetic rotations continued in the Betics after Late Miocene, enhancing the role of vertical axis rotations in the recent tectonic evolution of the Gibraltar Arc. © 2006 Elsevier B.V. All rights reserved.

Keywords: Gibraltar Arc; Betics; Neogene; Paleomagnetic rotations

1. Introduction subduction slab [3–7], (3) extensional collapse of the earlier collisional Betic–Rif orogen caused by convec- The tectonic processes responsible of the shape and tive removal of deep lithospheric roots [8,9], slab evolution of the Gibraltar Arc are controversial and detachment [10], or delamination of lithospheric mantle different models have been proposed to account for its [11–13]. All these tectonic models take into account the arcuate shape: (1) presence of an intermediate micro- role played by huge opposite vertical axis rotations in plate (Alboran plate) that moved westward between shaping the narrow and tight Gibraltar Arc, through Africa and Iberia [1,2], (2) westward roll back of a progressive bending of the Betics and Rif segments. In fact, a large amount of paleomagnetic data show that the ⁎ Corresponding author. Tel.: +39 0654888058; fax: +39 0654888201. arcuate shape of the Gibraltar Arc, such as the other E-mail address: [email protected] (F. Cifelli). major arcs in the Mediterranean region, is a secondary

0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2006.08.012 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 523 feature achieved through opposite vertical axis rotations 2. Tectonic settings along the two limbs of the arc [3,14]. Most of the paleomagnetic data incorporated in these geodynamic The Gibraltar Arc is located along the complex plate models come from Mesozoic rocks of the Betic and Rif boundary between the European and the African plates. chain (see [14] for a review), whereas only a limited Together with the Rif (North Africa), the Betic Cor- amount of paleomagnetic results from Neogene rocks is dillera (southern Spain) forms the Gibraltar Arc and presently available in this region (see [15] for a recent represents the westernmost segment of the Alpine– review). Mediterranean Belt. The Betic Cordillera is traditionally In this paper we present new paleomagnetic results subdivided into three main structural domains [16]: the from an extensive sampling in the Neogene sedimentary Internal Zones ([1], similar to the Alboran Domain of basins belonging to the Betic Cordillera in order to [17]), the Flysch Trough Units, and the Prebetic and better constrain the time and the amount of paleomag- Subbetic Zones [11] (Fig. 1). netic rotations in the Gibraltar Arc. The selected basins The Internal Zones or Alboran Domain is located lie either over the Internal or the External zones, or even onshore and offshore in the inner part of the arc. It seal the Internal–External zone boundary. We discuss consists mostly of metamorphic units, which constitute ours and previously published paleomagnetic data in the remnants of a Paleogene orogen [18]. The Flysch order to provide further constrains on the geodynamic Trough Units are constituted by siliciclastic sediments models on the origin of the Gibraltar Arc and on the of Cretaceous to Early Miocene age, deposited in a deep Neogene tectonic evolution of the Betic chain. Our marine or oceanic setting near the northern African results evidence that paleomagnetic rotations in the margin [19]. They outcrop in the western part of the Gibraltar Arc may be younger than generally supposed, Betic chain and form actually an inactive accretionary as Late Miocene vertical axis rotations are evidenced in prism, whose structural trend is mainly NNW–SSE to this paper. Such differential rotations show that strike- N–S directed [20]. slip tectonics and rotations around vertical axis may The Subbetic and Prebetic Zones represent the outer have played a major role during the Late Neogene and margin of the chain and are formed by Mesozoic and Quaternary times, to accommodate the complex kine- Tertiary sediments deposited in basinal (Subbetic) and matics along the European–African boundary. shelf (Prebetic) environments of the rifted paleomargin

Fig. 1. Schematic structural map of the Betic chain showing the main structural features. The boxed areas include the study Neogene sedimentary basins. 524 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 of South Iberia. These rocks were detached from their vertical axis rotations along the two arms of the Arc, hercynian basement from Early Miocene onwards, and which are supposed to be Early Miocene in age [34]. formed a NNE–SSW to NE–SW trending fold-and- Concerning Miocene to Pliocene sites, [30] measured thrust belt, with associated foredeep and foreland basins large CW rotations in sedimentary rocks of Aquitanian along its outer margin (Guadalquivir Complex and age in eastern Betics, while no rotations were Guadalquivir Basins, respectively). measured in one Tortonian site. Platzman et al., Extensional tectonics during Miocene times played Calvo et al. and Platzman et al. [35–37] measured an important role in the development and evolution of variable amount of CW vertical axis rotation in Lower the sedimentary basins which lie over the internal or Miocene mafic dikes in the Malaga and in the external domains of the Betics (e.g., [13,17]), including Alpujarride regions. In the Murcia–Cabo de Gata the present-day Alboran Sea Basin [21,22]. In particular, region (Fig. 1), [38] measured complex vertical axis the formation of the Alboran Sea was largely coeval rotations (mainly CCW) in Upper Miocene to Pliocene with the development of the Flysch Trough, Subbetic sedimentary and volcanic rocks. This complex pattern and Prebetic fold-and-thrust belt. Finally, during the of rotations is possibly related to regional left-lateral Late Miocene, the Gibraltar region experienced a drastic strike-slip faults activity. More recently, magnetostrati- modification of the tectonic regime, possibly related graphic investigations have been carried out on Late with the halting of the roll-back processes in the Gib- Miocene to Pliocene sedimentary sections in several raltar Arc subduction system [7,23], in turn possibly internal and foreland basins of both the Betics and Rif related with a change of Africa–Eurasia plate conver- [39–45]. In that case, paleomagnetic data generally gence vector from a N-S direction to a NW-SE one (e.g., show no significant vertical axis rotations since the [24]). As a consequence, the whole Betics and the Late Tortonian [15]. Alboran Sea Basin underwent a complex pattern of compressional and strike-slip tectonics which, in some 4. Sampling and paleomagnetic methods cases, inverted previous extensional structures [21,22]. Volcanism accompanied and postdated Neogene exten- The location of the studied basins is reported in Fig. 1. sion, with calc-alkaline, potassic and basaltic volcanism We have selected sedimentary basins located in very scattered across the eastern sector of Alboran Sea and different areas of the Betics, in order to obtain paleo- Betic–Rif chain. magnetic data from structural domains that experienced According to GPS data, Africa and Europe are pre- different tectonic evolution during the Neogene. In sently undergoing convergence, which in the region of particular, we sampled Miocene sediments in: (i) the Gibraltar is about 4 mm/yr with a NW orientation [25]. Guadalquivir foreland basin, (ii) the intramontane basins Along the Southern Iberia and North Africa margin the of central Betics (Alcalá-la-Real, Granada, Guadix, African–Eurasia plate convergence is accommodated by Huercal-Overa), and (iii) the Vera, Lorca, and Mula a wide and diffuse region of deformation, mainly basins in eastern Betics, which were mainly deformed characterized by WSW oriented active thrust fronts by strike-slip tectonics. We sampled 61 sites, with 641 and NNE oriented left lateral strike-slip faults. This plate oriented samples, almost homogeneously distributed in boundary is also the source of some of the largest the different sedimentary basins. Paleomagnetic analyses earthquakes in western Europe and north Africa, such have been carried out at the paleomagnetic laboratories as the 1755 Lisbon (estimated Mw=8.5) or the 1980 of Università di Roma TRE and ETH of Zurich using Ms=7.3 El Asnam earthquakes [26,27] in northern standard methods. The samples were demagnetised Algeria. using both thermal and AF procedures. Reliable paleomagnetic results were gathered from 41 sites and are 3. Previous paleomagnetic results reported below.

Paleomagnetic data from the Gibraltar Arc come 5. Paleomagnetic results mostly from Jurassic to Late Cretaceous sedimentary units from external Betics in Spain [12,28–32] and The nature of the magnetic carriers was investigated External Rif in Morocco [33], and show mostly clock- using different rock magnetic techniques. The stepwise wise and counterclockwise rotations, respectively north acquisition of an isothermal remnant magnetization and south of the Gibraltar Strait (see [14] for a critical (IRM) was carried out by using a pulse magnetiser review). Paleomagnetic results from internal metamor- which applies magnetic fields up to 2.1–2.5 T. Different phic units also show the same opposite pattern of fields (0.12 T, 0.6 T and 1.7 T) were also applied along M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 525 the three orthogonal specimen axes and the three- Specimens were demagnetised by means of progres- component IRM was subsequently thermally demagne- sive stepwise thermal demagnetization, using temperature tised [46]. Both low coercivity and high-coercivity increments, or stepwise alternating field demagnetization, magnetic carriers were identified in the analysed sam- according to preliminary results obtained from pilot ples (Fig. 2a). In some samples, the multi-component specimens from each site. Magnetic cleaning was ter- IRM is characterized by high coercivity fractions, which minated when Natural Remnant Magnetization (NRM) show maximum unblocking temperature of 670 °C, reached the instrument sensitivity level or when a indicating hematite as main magnetic carriers (Fig. 2b). random change of the paleomagnetic direction ap- In other samples, the low coercivity fraction prevails, peared, due to mineral transformation. This change with a maximum unblocking temperature around 280°– was often accompanied by an increase in the magnetic 370° and 580 °C, which in that case indicates iron susceptibility. In some cases samples were too weakly sulphides and magnetite as the main magnetic carriers magnetized to allow a reliable, complete, stepwise (Fig. 2c). demagnetization (NRM values about 50×10− 6 A/m).

Fig. 2. IRM acquisition curves showing the presence of low coercivity and high coercivity magnetic carriers (a). Thermal demagnetization curves of composite IRM are shown for hematite-bearing (b) and magnetite-bearing (c) samples. Vector component diagrams (Zijdervald diagrams, in geographic coordinates) for the progressive thermal demagnetization of representative samples (d–m). Demagnetization step values are in degrees Celsius. Open and solid symbols represent projection on the vertical and horizontal planes, respectively. 526 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Demagnetization data were analysed using orthog- polarities have been observed which show almost onal vector diagrams (Fig. 2d–k) and directions of the antipodal directions. The mean paleomagnetic direction, remanence components were estimated using principal when all the sites are reported to the normal polarity is component analysis [47]. Samples yielding maximum D=4.8°; I=54.8°; K=66.2; α95 =11.4 (Fig. 3b), sug- angular deviation (MAD) N15° were rejected and were gesting that the Guadalquivir basin underwent no not considered for further analyses. In the other rotation since Tortonian, in agreement with published samples ChRMs or remagnetization circles were results from the western part of the same basin [15]. isolated, which in most of the samples show MAD b10°. The site mean paleomagnetic directions were 5.2. The Granada basin then calculated using the great circle method of McFadden and McElhinny (1988). In 32 sites a well The Neogene intramontane Granada basin (Fig. 1)is defined (α95 b15.0°) ChRM was isolated, while in located in the central part of the Betics, and seals the other 10 sites the ChRM is less defined (α95 b25.8°) boundary between the External and the Internal domains but is coherent with the other sites from the same (e.g., [52]), as it overlies on the Subbetic fold-and-thrust basins, and therefore has been considered for further wedge and the metamorphic rocks of the Alboran tectonic interpretations. The 42 reliable site mean Domain, north and south of the basin, respectively directions before and after tectonic correction are (Fig. 4). The sedimentary infilling of the basin took reported in Table 1. In the following subsections we place during several sedimentary cycles, evolving from report separately paleomagnetic results obtained in the marine to continental environments [53]. The marine different basins. sedimentary sequence started in the Early Tortonian with calcarenites and conglomerates. Late Tortonian fan 5.1. The Guadalquivir basin delta deposits and open marine marls, which progressively evolved to more restricted and temperate The Guadalquivir basin is located along the external environments, overlie the lowermost sequence through front of the Betic chain with a WSW–ENE orientation an angular unconformity. A transition from marine to from the Gulf of Cadiz to the west and the Prebetic arc to continental conditions began during the Late Tortonian the east (Fig. 1). The basin formed during middle as alluvial fans to shallow marine environments Miocene as a foredeep basin and evolved during the developed, associated with important evaporitic epi- Tortonian to Pliocene times as a foreland basin [48]. sodes in the deepest part of the basin. The continental Sedimentary sequences filling the foreland basin are sedimentation started at the end of the Tortonian– mainly composed by Late Miocene pelagic sediments, Messinian boundary, with deposits of fresh-water with some shallow marine episodes. The outcropping stromatolithic limestones passing upward to lutites sequences become progressively younger and thicker with gypsum and, occasionally, with lignites and towards the west, ranging respectively from Tortonian to micritic limestones. Finally, the Pliocene to Lower Late Tortonian–Messinian in the western part. They are Pleistocene sequence is characterized by alluvial fans, undeformed in the northernmost external part of the floodplains, and lacustrine basins, mostly developed in basin, where the sedimentary rocks overlie the Hercy- the central and northern part of the basin. nian rocks of the Iberian foreland. To the east, the The present day structural architecture of the sedimentary sequences of the Guadalquivir foreland Granada basin is mostly controlled by NW–SE oriented basin are overthrust by the Meso- to Cenozoic rocks normal faults. In particular, the basin is bounded to the forming the Prebetic fold-and-thrust belt [32,49]. In the east and southeast by an array of such faults, which have southern part of the Guadalquivir basin and off-shore the been shown to be active [54], and that separate the Gulf of Cadiz the Late Miocene units are overthrust by Neogene sediments from the Internal Betics metamor- the gravity driven nappes defined as olistrostrome unit phic domain. E–W oriented normal fault systems by [50]. characterize the southern border of the basin. We sampled 4 sites in the sub-horizontal Tortonian In the Granada Basin, 10 sites were sampled in con- marly clays outcropping in the eastern part of the basin, tinental marls and clays (Fig. 4a). The age of the sam- which represent the lower depositional sequence recog- pled sites ranges from Late Tortonian to Late Messinian, nized in the Guadalquivir Basin [51] (Fig. 3a). All the according to [55] and [56]. Either high and low coer- sites gained reliable results, and the main magnetic civity magnetic minerals have been identified in the carrier has been identified as a low coercivity fraction, Granada basin, which are mostly magnetite and hematite probably magnetite (Fig. 2a). Both normal and reverse (Fig. 2a). Both normal and reverse polarities have been M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 527

Table 1

Sites Age N S0 Db Ib k α95 Da Ia k α95 Guadalquivir Basin BE48 Upp. Tort. 8(14) Sub-hor. 178.4 −48.0 25.3 11.4 178.4 −48.0 25.3 11.4 BE49 Upp. Tort. 5(9) Sub-hor. 18.8 60.3 67.0 10.7 18.8 60.3 67.0 10.7 BE50 Upp. Tort. 9(10) Sub-hor. 20.1 52.9 24.0 10.1 18.0 53.1 24.0 10.1 BE51 Upp. Tort. 7(14) 275, 5 1.9 55.5 15.0 16.3 354.7 54.9 15.0 16.3 7.2 54.8 70.0 11.1 4.8 54.8 66.2 11.4

Granada Basin BE20 Upp. Mess. 9(9) 341, 31 61.2 21.5 43.1 7.90 51.6 13.3 43.1 7.9 BE21 Upp. Mess. 9(9) 230, 20 208.6 −0.1 10.1 14.40 208.0 −18.6 10.1 14.4 BE23 Upp. Tort. 7(9) 66, 20 47.4 49.0 58.3 8.00 52.0 29.8 58.3 8.0 BE24 Messinian 9(9) 0, 0 16.1 37.5 12.6 15.10 16.1 37.5 12.6 15.1 BE32 Messinian 7(9) 50, 20 5.7 31.1 43.0 9.30 11.7 15.2 43.0 9.3 BE34 Upp. Mess. 7(7) 37, 13 37.0 33.2 32.2 10.80 37.8 20.3 32.2 10.8 BE52 Messinian 9(11) 33, 14 39.8 20.0 52.6 8.0 39.4 6.1 52.6 8.0 BE53 Upp. Mess. 6(13) 306, 34 226.4 −19.5 7.85 25.8 213.2 −21.8 7.85 25.8 35.5 27.5 14.4 15.1 34.9 20.6 26.4 11.0

Guadix Basin BE54 Upp. Tort. 13(14) 358, 34 330.8 50.9 20.8 9.3 340.2 19.2 20.8 9.3 BE55 Upp. Tort. 8(9) 78, 22 16.1 46.1 39.2 9.0 31.1 33.1 39.2 9.0 BE56 Upp. Tort. 7(11) 273, 15 0.4 39.5 28.8 11.4 348.3 37.2 28.8 11.4 ⁎ BE57 Upp. Tort. 9(10) 186, 13 357.4 45.3 42.1 8.1 354.5 58.1 42.1 8.1 ⁎ BE58 Upp. Tort. 4(10) 173, 5 334.9 51.4 15.2 24.4 348.8 57.8 15.2 24.4 ⁎ BE59 Upp. Tort. 8(11) 226, 15 0.4 54.0 10.5 17.9 340.1 66.6 10.5 17.9 BE60 Upp. Tort. 10(10) 108, 27 347.4 32.3 16.3 14.3 7.0 42.2 16.3 14.3 354.7 46.6 43.6 9.2 356.7 45.8 15.3 15.9

Alcalà La Real Basin IMR20 Upp. Burdig.–Low. Langh. 12(12) 174, 27 18.5 33.4 13.7 14.5 32.5 56.7 13.8 14.4 IMR22 Upp. Burdig.–Low. Langh. 4(11) Sub-hor. 37.6 37.8 57.4 13.0 37.6 37.8 57.4 13.0 IMR23 Aquitanian 12(14) 83, 23 6.4 40.5 40.2 8.8 22.4 31.9 40.2 8.8 IMR24 Upp. Burdig.–Low. Langh. 5(15) 336, 18 70.0 59.9 5940.0 1.0 40.8 56.6 5940 1.0 IMR26 Low. Tort 10(12) 0, 10 31.9 62.6 17.5 11.9 24.3 54.2 17.5 11.9 29.5 48.6 16.2 19.6 31.1 47.7 39.4 12.3

Vera Basin BE05 Upp. Messinian 3(9) Sub-hor. 335.5 34.3 53.9 19.9 335.5 34.3 53.9 19.9 BE06 Lower Pliocene 9(9) Sub-hor. 155.2 −31.1 15.6 13.6 155.2 −31.1 15.6 13.6 BE09 Lower Pliocene 10(12) Sub-hor. 154.4 −28.6 42.5 8.0 154.4 −28.6 42.5 8.0 335.5 31.3 781.7 4.4 335.5 31.3 781.7 4.4

Huercal-Overa Basin BE61 Tort. 10(22) Variable 155.1 5.1 9.5 17.7 154.1 −40.3 10.0 17.2 BE62 Tort. 11(12) 213, 38 113.8 −27.8 11.5 14.1 98.4 −16.4 11.5 14.1 BE63 Tort. 7(8) 60, 22 171.9 −43.8 23.8 12.6 187.2 −32.7 23.8 12.6 BE66 Messinian 8(12) 354, 22 178.2 −34.2 18.0 13.5 177.5 −12.2 18.0 13.5 BE67 Tort. 6(14) 36, 18 166.8 −46.4 28.8 12.9 177.3 −33.3 28.8 12.9 156.5 −18.0 3.9 44.3 160.1 −31.1 5.8 34.6 Without BE62 167.3 −13.5 4.2 51.2 174.7 −30.2 23.4 19.4

Lorca–Tercia Basin ⁎⁎ IMR01 Upp. Serravallian 7(7) 240, 38 314.6 34.3 7.3 20.70 316.8 25.5 7.3 20.7 ⁎⁎ IMR02 Upp. Serravallian 7(7) 245, 36 209.1 −63.5 9.7 20.80 150.4 −36.4 9.7 20.8 IMR03 Upp. Serr.–Lower Tort. 5(11) 25, 63⁎⁎ 308.5 45.4 40.9 10.00 317.6 46.7 40.9 10.0 IMR04 Upp. Tort. 5(10) 83, 50 315.3 −0.6 25.8 16.4 326.1 27.4 25.8 16.4 IMR07 Lower Burdigalian 11(11) 324, 60 223.1 50.6 20.2 12.7 278.3 29.2 20.2 12.7 BE11 Serravallian 9(9) 224, 35 1.4 13.9 71.3 6.10 348.3 37.3 71.3 6.1 (continued on next page) 528 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Table 1 (continued)

Sites Age N S0 Db Ib k α95 Da Ia k α95 BE12 Lower Messinian 9(9) 57, 15 316.5 40.7 27.8 10.0 329.7 41.7 27.8 10.0 BE13 Serravallian 3(10) 0,0 335.0 27.0 97.7 12.5 335.0 27.0 97.9 12.5 BE14 Serravallian 8(10) 161, 80 111.7 5.1 23.5 12.20 85.80 −38.6 23.5 12.2 BE15 Lower Tort. 8(10) 11, 16 335.7 55.4 82.9 6.50 345.0 41.6 82.9 6.5 342.9 61.5 2.2 43.1 320.0 37.9 12.9 14.0 N=number of stable directions (total number of studied samples at a site). ⁎⁎ ⁎ S0 =bedding attitude (azimuth of the dip and dip values) Sites marked by have been also corrected for the plunging axis. Beddings marked by derives from Anisotropy of Magnetic Susceptibility tensor.

D, I site mean declinations and inclinations calculated before (Db, Ib) and after (Da, Ia) tectonic correction. k and α95, statistical parameters after Fisher (1953). Values in bold represent the sites mean for each basin. observed, which show antipodal directions. The reversal (D=35.5°, I=27.5°, K=14.4, α95 =15.1), indicating a test is of type Rc (γo=16.1°; γc=5.5°) according to pre-tilting age for the isolated component of magneti- [57]. Also in this basin the mean paleomagnetic zation. The mean paleomagnetic direction, when all the direction is better grouped after (D=34.9°, I=20.6°, sites are reported to the normal polarity, is D=34.9°; K=26.4, α95 =11.0) than before tectonic correction I=20.6°. Such result is coherent with previous data

Fig. 3. a) Schematic map of the Guadalquivir basin, location of the sampled sites and measured declinations (arrows). b) Mean paleomagnetic declinations from the basin before and after tectonic correction. M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 529

Fig. 4. a) Schematic map of the Granada basin, location of the sampled sites and measured declinations (arrows). b) Mean paleomagnetic directions from the basin before and after tectonic correction. from a magnetostratigraphic study in a Late Miocene– In this basin 7 sites were sampled in the Late Tor- Lower Pliocene sedimentary section, (D=196.5; I= tonian white marine marls (second depositional se- −39.7; K=128.4, α95 =5.9) [56] suggesting a significant quence of [58]) that outcrops in the northern part of the post Messinian CW rotation throughout the entire basin (Fig. 5a). Granada basin (Fig. 4b). The main magnetic carrier has been identified as a low coercivity fraction, probably magnetite (Fig. 2a). 5.3. The Guadix basin Notwithstanding most of the samples were characterized by low values of NRM, a stable component of mag- The Guadix Basin is located in the central part of the netization were identified for all the sites. All the Betic Cordillera (Fig. 1). As the Granada Basin, it seals samples show a normal polarity and the mean directions the Alboran Domain–Subbetic boundary. This intra- are better grouped before (D =354.7°, I =46.6°, montane basin formed in the Late Miocene after the K =43.6, α95 =9.2) than after tectonic correction main compressional events that formed the main (D=356.7°, I=45.8°, K=15.3, α95 =15.9) (Fig. 5b). tectonic structures of the Betic Cordillera [58]. The Furthermore, the mean direction in geographic coordi- stratigraphic record in the Guadix Basin covers the Late nates is almost parallel to the present-day GAD mag- Miocene up to the Quaternary with no hiatuses [59]. The netic field, suggesting that these sites have been Late Miocene sequence began with marine calcarenites remagnetized in recent times. Therefore results from and marls. It was followed by continental fluvial and the Guadix basin have not been further considered for lacustrine deposits [58]. tectonic interpretations. 530 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Messinian, as the structural architecture of the basin is characterized by hecto- to kilometric-scale, widely open NE–SW oriented folds, which deform the entire Mio- cene sequence. In this basin, eight Aquitanian to Lower Tortonian sites were sampled. One site corresponds to the youngest rocks of the deformed Subbetic domain (IMR27, Aquitanian in age according to [60]), meanwhile sample IMR23 is the oldest rocks belonging to the Alcalá-la- Real basin. Samples IMR20, 22, and 24 have been taken in Late Burdigalian to Lower Langhian calcarenites, and samples IMR21, 25 and 26 in Lower Tortonian marls (Fig. 6a). The main magnetic carrier has been identified as a low coercivity fraction, probably magnetite (Fig. 2a). Interpretable demagnetization diagrams were obtained in 6 sites, whereas 2 other sites (IMR21, IMR27) owned very weak intensity or showed an in- stable behaviour during demagnetization steps. Site IMR25 mean direction was almost parallel to the GAD magnetic field before tectonic correction and was sus- pected for recent remagnetization. This site was not considered for further tectonic considerations. The site mean paleomagnetic directions obtained from the other 5 reliable sites show a normal polarity. However the mean direction is far from the present day magnetic field in geographic coordinates and the mean basin direction is better grouped after (D=31.1°, I=47.7°, K =39.4, α95 =12.3) than before tectonic correction (D=29.5°, I=48.6°, K=16.2, α95 =19.6), indicating a pre-tilting age for the isolated component of magnetization (Fig. 6b). All the samples, from Late Burdigalian to Early Tortonian in age, show a similar clockwise rotation, and the mean paleomagnetic direction shows a 31° CW rotation. Fig. 5. a) Schematic map of the Guadix basin with the location of the sampled sites. b) Mean paleomagnetic directions from the basin before and after tectonic correction. Note that the sites show all a normal 5.5. The Huercal-Overa basin polarity and a better grouping before than after tectonic correction, suggesting a recent remagnetization. The Huercal-Overa basin, composed of Serravallian to Messinian deposits, crops out in the Eastern part of 5.4. The Alcalá-la-Real basin the Betics. It lies over the Alboran Domain rocks and is bounded by the Alpujarride units to the North and the The Alcalá-la-Real basin is characterized by outcrops Nevado–Filabride units to the South (Fig. 1). The stra- of lower Miocene to Pliocene marine sediments distri- tigraphy of the basin can be summarised as a succession buted along a NE–SW trending belt, 30 km northwest of of six main units [61], which began with a coarse con- Granada (Fig. 1). The Neogene sediments of the basin tinental sedimentary unit, attributed to the Late Serra- rest on top of the Mesozoic to Paleogene rocks of the vallian to Early Tortonian [62]. After these continental fold-and-thrust wedge of the Subbetic domain, and episodes, shallow and open marine turbidites and marls record part of the compressional events of this part of the deposited, during the entire Late Tortonian to Early Betic orogen. The youngest rocks affected by the main Messinian [61,63]. shortening event are Aquitanian in age. Although the Seven Tortonian to Messinian sites were sampled main shortening took place during Late Aquitanian (Fig. 7a), and reliable results were obtained from 5 sites. times, deformation proceeds from Early Burdigalian to Either high and low coercivity magnetic minerals have M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 531

Fig. 6. a) Schematic map of the Alcalá-la-Real basin, location of the sampled sites and measured declinations (arrows). b) Mean paleomagnetic directions from the basin before and after tectonic correction. been identified in this basin, which are mostly magnetite part of the basin in connection with the activity of left- and hematite, according to their blocking temperature of lateral strike-slip faults, whereas the rest of the basin 580° and 680° C respectively (Fig. 2a–i). All the sites only underwent small CCW rotations after Tortonian show a reverse polarity after bedding correction. The times. mean site directions is D=156.5°, I=−18.0°, K=3.9, α95 =44.3 before tectonic correction, whereas after 5.6. The Vera basin tectonic correction is D=160.1°, I=−31.1°, K=5.8, α95 =34.6, which indicates a pre-tilting age for the The N–S oriented Vera basin is located along the magnetization (Fig. 7b). The basin average inclination eastern boundary of the Sierra de los Filabres (Fig. 7). The (I=31.1°) is significantly shallower than that expected basin is filled with Upper Serravallian to Recent from its palaeolatitudinal position in the Late Miocene, sedimentary deposits, which overlie the metamorphic as for Granada basin. The mean directions sites by sites units of the Internal Betics. The sedimentary sequence show a wide dispersion (Fig. 8). Three sites were not begins with Tortonian continental and marine units, which rotated (BE 63, 66 and 67) while the 2 other sites show outcrop rarely and are strongly deformed. The Tortonian different amount of CCW rotations. Meanwhile BE61 to Messinian units are made of conglomerates, turbidites, evidence a small CCW rotation, site BE62, which has calcarenites and shallow water carbonates, which pass been sampled along the northern margin of the basin, is upward to Pliocene basinal marls and marine siliciclastic strongly rotated CCW. This rotation has a local character sediments. Late Pliocene to Pleistocene continental units and is related with the movement along left-lateral lie on top of the sequence. The tectonic–stratigraphic strike-slip faults, which characterizes this part of the evolution and the present day architecture of the basin was Betic orogen (Fig. 1). If we discard site BE62, the mean mainly controlled by the N20 oriented left-lateral grouping of the sites is strongly increased and the basin Palomares fault system, which bounds the eastern side mean paleomagnetic direction become D=174.7°, I= of the basin (Figs. 1 and 7). This fault system was active −30.2°, K=23.4, α95 =19.4 (Fig. 9). Accordingly, post since Late Miocene up to Quaternary times, and produced Tortonian CCW rotation occurred along the northern approximately 15 km of left-lateral displacement [64]. 532 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Fig. 7. a) Schematic map of the Huercal-Overa and Vera basin, location of the sampled sites and measured declinations (arrows). Mean paleomagnetic directions from the Huercal-Overa (b) and Vera (c) basins before and after tectonic correction.

Eleven sites in sub-horizontal Late Tortonian to Domain metamorphic units of Sierra de las Estancias, Lower Pliocene clays and marls were sampled (Fig. 7a). Sierra de la Tercia and Sierra Espuña (Fig. 8). To the Either high (Fig. 2a) and low coercivity (Fig. 2b) North, it is bounded by Subbetic units (Fig. 1). The magnetic minerals have been identified in this basin, sedimentary sequence reaches locally up to 2 km of which are iron-sulphides, magnetite, and hematite. Eight Burdigalian to Pliocene marine and continental sedi- sites showed low NRM values or were unstable during ments. The sedimentary sequence starts with Burdiga- demagnetization. Three other sites have given reliable lian to lower Serravallian marine units unconformably results, with antipodal normal and reverse polarities; followed by a thick continental unit, Late Serravallian to the reversal test is of type Rb (γo=9.8°; γc=4.5°) Early-Tortonian in age, formed by red conglomerates, according to [57]. When all the sites are reported to sandstones and silts with gypsum intercalations. These normal polarity, the basin mean direction is D=335.5°, units are followed by Tortonian calcirudites and by I=31.3°, K=781.7, α95 =4.4. Accordingly, the Vera open-marine marls and silts (Carivete marls, [65]) which basin underwent a significant CCW rotation after Early locally reach up to 700 m. The calcirudites lie either Pliocene (Fig. 7c). upon the Lower Tortonian marine sediments, upon the Lower to Middle Miocene rocks, or directly upon the 5.7. The Lorca basin Alboran metamorphic basement, which describes a clear angular unconformity. These Tortonian sedimentary unit The Lorca basin is a small depression located be- shows strong thickness variations, related with the tween ENE oriented anticlines formed by the Alboran position and geometry of high-angle listric growth faults M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 533

Fig. 8. a) Schematic map of the Lorca basin, location of the sampled sites and measured declinations (arrows). b) Mean paleomagnetic directions from the basin before and after tectonic correction. Geological map from [87].

that bound the ENE and WSW margins of the Lorca α95 =14.0 after correction vs. D=342.9, I=61.5, K= basin [66]. The next sedimentary unit was deposited 2.2, α95 =43.1 before correction). After tectonic correc- between the Late Tortonian and the Messinian, during tion 8 sites have a normal polarity and 2 show a reverse the uplift and emersion of the Lorca basin. It is formed polarity (reversal test is indeterminate according to by a great variety of sedimentary facies, from shallow [57]). When all the sites are reported to have normal marine (calcarenites and calcirudites) to restricted polarity, the basin mean direction is D=320.0°, I= marine, represented by organic-rich shales, cherts and 37.9°, to show 40° of CCW rotation of the basin after dolomites, and finally evaporites (mainly gypsum, halite Messinian times (Fig. 8b). in the basins depocenter). This sequence is caped by lacustrine marls, together with alluvial conglomerates 6. Discussion along the basin margins [42,65,67]. After a mostly erosional period during the Pliocene, the Quaternary is 6.1. Analysis of paleomagnetic inclinations characterized by alluvial deposits whose depocenters are strongly controlled by the position and activity of the Tilt-corrected site mean directions from the analysed Alhama de Murcia sinistral strike-slip faults [68–70]. sedimentary basins show a great scatter of inclinations, Fourteen sites were sampled in Serravallian to Mes- which in most of the sites are significantly shallower sinian sediments (Fig. 8a). Results also include one site with respect to the reference one (Table 1). As reference (IMR07) from the Mula Basin (Fig. 1). In this basin the inclination the Geocentric Axial Dipole (GAD) field main magnetic carrier is given by a low coercivity inclination (I=56°) was used since the GAD field magnetic mineral with a blocking temperature of 550– inclination must be very close to the expected Late 580 °C, identified as magnetite (Fig. 2l). In some sam- Miocene inclination for the region, not showing Iberia a ples also the presence of a high coercivity mineral has significant northward moving during Late Cenozoic. been observed, identified as hematite (Fig. 2a). We Large inclination errors can be observed in the Huercal- obtained reliable results from 10 sites. In 4 other sites Overa (generally 25° and up to 44° in difference), Vera the intensity of remanent magnetization was either too (generally 25°) and Lorca–Tercia (generally 18° and up low or the samples showed unstable behaviour during to 30° in difference) basins, and in particular in the the demagnetization steps and the results were not Granada basin (generally 36° and up to 50° in dif- reliable. The site mean directions from the analysed 10 ference). On the other hand, sites from the Guadalquivir sites show a strong increase of their grade of grouping basins do not show significant shallowing in the after tectonic correction (D=320.0, I=37.9, K=12.9, inclination (I=55°). 534 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Inclination flattening due to depositional and/or over the Internal or External Zones and in the foreland burial compaction processes has been often observed Guadalquivir Basin, evidence a complex pattern of in paleomagnetic studies from sedimentary units vertical axis rotations, which took place after the Late [71,72], and has been also observed in modern fluvial Miocene. hematite-bearing deposits from the River Soan in Menawhile no rotations have been evidenced in the Pakistan, which suffer about 25° inclination shallowing Late Tortonian sediments in the Guadalquivir foreland [73]. Tan et al. [71] showed that shallowing in incli- basin, clockwise vertical axis rotations have been nation is particularly important in sediments containing measured in basins situated in the central part of the elongate particles (such as detrital hematite), where Betics: the Aquitanian to Messinian sedimentary units in inclination flattening of more than 30° has been ob- the Alcalá-la-Real and the Tortonian and Messinian served, suggesting rock magnetism as a main factor sediments of Granada basin. By contrast, counterclock- controlling inclination shallowing. We speculate that a wise vertical axis rotations were measured in the Middle rock magnetic causes of shallow inclinations can be also Miocene to Lower Pliocene sites in the Lorca and Vera proposed in the sedimentary basin from the Betics, basins and, locally, in the Tortonian units of the Huercal- where inclination flattening is particularly important in Overa basin. Such pattern of different rotations evidence hematite-bearing sites (i.e. Granada basin), and is not that in the Betic chain, from Late Miocene onwards, observed in magnetite-bearing sites (i.e. Guadalquivir different crustal blocks with a different tectonic basin). evolution were individualized. In the following sections Ten et al. [71] used Anisotropy of Magnetic Sus- we briefly describe the main tectonic features of the ceptibility (AMS) as a tool to measure compaction, Guadalquivir foreland basin, Central Betics and Eastern due either to depositional and/or burial processes. In Betics in order to discuss the tectonic implications of particular they observed that a shallowing in inclina- paleomagnetic results presented in this study. tion of about 30° is observed for values of AMS foliation F b1.053. In our samples a strong flattening 6.2.1. The Guadalquivir foreland basin is also revealed by AMS data. In particular, sites from The tectono-stratigraphic evolution of the Guadal- Granada show a well defined magnetic foliation para- quivir foreland basin has been reconstructed mainly llel to the bedding planes, with a degree of foliation using stratigraphic, seismic and well data [26,75]. Along (F) comprised between 1.18 and 1.014, which is its eastern boundary, the Tortonian sediments of the compatible with the higher flatteningobservedinour Guadalquivir basin are overthrust by the Mesozoic sediments with respect to those studied by [71].How- sedimentary units of the Prebetic nappes, with a NW ever, no clear relationship is found between inclina- shortening direction [14,49]. Toward the west, in the tion shallowing and the AMS foliation F. This could Gulf of Cadiz, Late Miocene to Pliocene units are not be due to the fact that low-field AMS in clay sedi- involved in the main compressional deformation, clearly ments is generally controlled by the paramagnetic defining the upper time boundary of the main clayey matrix of the rock [74], suggesting that the emplacement of the allochthonous units in this region high variations in inclination errors can be related [26]. These data show that the emplacement of the to compaction processes in a complex way, being allochthonous units along the outer front of the Betics influenced either from the types and relative amount mainly occurred between Late Burdigalian and Late of magnetic carriers, in particular hematite, and com- Tortonian [14]. This compressional event has been ponents of clay matrix. Finally, the observed conspic- generally interpreted as the last episode of deformation uous inclination error confirms the primary character related to the westward transport of the Betic nappes, of the measured magnetization in all the basins (ex- which was responsible for the Gibraltar Arc bending cept Guadix which does not show significant inclina- [14]. Offshore of the Gulf of Cadiz, however, NE–SW tion flattening, due to recent remagnetization oriented active folds and thrusts have been detected by processes), since inclination shallowing can be due seismic surveys, and could be related to some of the only to events occurring during deposition and/or main big historical earthquakes, which have been diagenesis. recorded in this region [76]. These structures have been related either to the present-day NW oriented 6.2. Analysis of paleomagnetic declinations Africa–Europe convergence [26], or have been suggested as evidences of active east dipping subduction Paleomagnetic results from Neogene intramontane in the front of the Gibraltar Arc [77]. In this latter basins located in different sectors of the Betic chain, hypothesis, the east dipping subduction of the oceanic M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 535 lithosphere should be a continuous process since Early suggests that CCW rotations occurred after that time. Miocene to the present-day, controlling the present-day These CCW rotations have been observed in the geodynamics in the Betic–Rif region. different sedimentary basins located along a deforma- Our paleomagnetic results from the analysed Torto- tion belt dominated by Late Miocene–Quaternary left- nian marls, together with those from Messinian units of lateral strike-slip faults, which characterized the whole the western part of the Guadalquivir basin [15], permit South Iberian continental margin in the region of to test that this foreland basin underwent no rotations Almeria–Murcia (Fig. 1). In this region CCW rotations since the Late Miocene. Therefore, these paleomagnetic do not extend to sedimentary basins, which are located data evidence that vertical axis rotations related to the far away from the main strike-slip faults [15,38], and bending of the external part of the Gibraltar Arc were indicate the occurrence of small, fault-bounded blocks either older than Late Miocene or never reached the which rotate about vertical axis as a consequence of the foreland South Iberian sector and were confined to the activity of these faults. It is worth to note that some of Betic–Rif orogenic wedge. these faults are supposed to be active [66]. Consequent- ly, block rotation around vertical axis along left-lateral 6.2.2. Central Betics strike-slip faults could still be an active mechanism in Most of the paleomagnetic data incorporated in the the Almeria–Murcia region. geodynamic models explaining the Gibraltar Arc bending have been collected in western-central Betics. In this 6.3. Tectonic implications of paleomagnetic results region almost constant CW paleomagnetic rotations of about 60° have been measured in the Late Jurassic and Contrasting models have been proposed so far to Late Cretaceous sedimentary units of the SW–NE explain the formation of the arcuate structure of the Rif– oriented Betics thrust belt, outcropping between Gibraltar Betic belt. The concomitant formation of the compres- and Granada [78]. Such huge CW rotations have been sional structure in the external portion of the belt and the mostly measured in the allochtonous units of the Betics extensional one in the inner portion inspired the first and and have been interpreted as related either to the oblique most popular class of models where the driven engine is compression which accompanied the bending of the internal, that is derived from the instability of the dense Gibraltar Arc during the Miocene [14] or to the roll-back mantle portion of the lithosphere. This class of models of a westward retreating subducting slab (i.e. [3]). In any includes subduction and roll-back [3,4,7] and/or delam- case, paleomagnetic rotations were considered to have ination [11,79,80] or convective removal of the mantle occurred mainly during the Early Miocene and to be lithosphere [9]. In particular, subduction and/or delam- already completed in the Late Miocene [14]. In central ination process is supported by subduction-related Betics we measured significant CW rotations in Granada calcalkaline volcanism in eastern Betics, Morocco and and Alcalá-la-Real intramontane sedimentary basins. Alboran Sea which has been active in this region from These rotations are post-Tortonian in the Alcalá-la-Real 25 to 5 Ma ([7,23] and references therein), tomographic basin and post Messinian in the Granada basin. Therefore, images, showing a narrow but long east dipping slab in both basins these rotations took place after the main beneath Morocco–Gibraltar [7,76], and deep although compressional event, which lead to the formation of the isolated earthquakes [79]. In this view, the formation of Subbetic fold-and-thrust belt in the central Betics. the Gibraltar Arc is related to the westward–southwestward retreat of the trench of a small portion of the slab 6.2.3. The eastern Betics and the left-lateral strike-slip [3,7,23], producing CCW rotation in the Betics and CW fault systems rotation of the Rift. Geological data show that the main Counterclockwise paleomagnetic rotations were retreat episode vanished during the Late Miocene. measured in Vera and Lorca basins and in the north- The second class of models is related to external western sites from the Huercal-Overa basin. A single engine related to the oblique convergence along the site in Mula basin shows similar counterclockwise Africa–Iberia plate boundary. The formation of large rotations. The rotated sediments are Serravallian to scale strike-slip structure and the present day active Early Pliocene in age, and do not show any statistical tectonics in this region can be best explained by this difference or trend depending of the age or the stra- mechanism [26,27] although GPS and seismic data tigraphic position of the sampled sites. In particular in suggest that active deformation in such area is quite the Vera basin, close to the left-lateral Palomares strike- complex, and cannot simply be explained by the right slip fault, 25° of CCW rotations have been measured in lateral motion along the Iberia–Nubia plate boundary Upper Messinian–Lowermost Pliocene sites, which [25]. 536 M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540

Although geological constraints indicate that the first overriding plate. A similar pattern of rotation has been class of model prevail during the Early to Late Miocene also reconstructed in the Calabrian Arc where large while the second one from the Late Miocene onward, opposite paleomagnetic rotations are confined in the the interplay between the two main engine is difficult to orogenic wedge, while no rotations have been registered discriminate in the narrow configuration of the Gibraltar on the Adriatic and Hyblean foreland basins [82–84].In Arc. Seismological and geodetic observations show that the second class of hypothesis, the lack of vertical axis the present-day kinematics of the Iberia–Nubia bound- rotations in the Guadalquivir basin, indicates that the ary is characterized by a complex interaction between right-lateral shear belt, which marks the tectonic bound- these two main processes. In fact, GPS data suggest that ary between Iberia and north Africa, is placed to the south in central Rif an independent fault-bounded crustal of the Guadalquivir basin, as suggested by several authors block is moving southwestward, relative to Nubia, as the on the base of seismic and GPS data [77,85]. result of roll-back of a narrow slab of delaminated The interpretation of CCW paleomagnetic rotations continental lithosphere, whereas the kinematics of measured in the eastern Betics (Vera, Lorca and Huerca western and central Betics can be better explained by basins), is straightforward as they are clearly related to the oblique convergence between Nubia and Iberia [81]. the presence of a large-scale left-lateral strike-slip fault Paleomagnetic data presented in this paper gives system, which caused the western Alboran block to important constraints on the Late Miocene to Recent move southward with respect to eastern Betics. It is kinematics and deformation. The lack of rotation in the worth to note that such CCW paleomagnetic rotations Tortonian clays of the Guadalquivir basin indicates that appear to be confined in a narrow belt close to the left- the basin itself represents the northern boundary of the lateral strike-slip fault system and do not appear to rotating domains of the western Betics, confining the extend to the entire eastern Betics, where magnetostrati- rotations on the hanging wall of the outer front of the graphic data, located away from the main left-lateral chain (Fig. 9). This is not surprising if the formation of the faults, do not show significant rotations (Fig. 9). arc is related to slab roll-back, as vertical axis rotation More problematic is the interpretation of the CW related to the arc bending should be confined to the paleomagnetic rotations measured in Alcalá-la-Real and

Fig. 9. Paleomagnetic declinations (and relative confidence limits) from Neogene sediments in the Betic chain. White arrows come from this study and indicate cumulative paleomagnetic declinations for each study basin: a) Guadalquivir Basin (see Fig. 3); b) Granada Basin (see Fig. 4); c) Alcalà la Real Basin (see Fig. 6); d) Vera Basin (see Fig. 7); e) Huercal-Overa Basin (see Fig. 7), including basin paleomagnetic mean discarding BE62 (dashed paleomagnetic declination); f) Lorca–Tercia Basin (see Fig. 8). Black arrows come from previous studies and are indicative of mean paleomagnetic declination deduced in single magnetostratigraphic sections: 1) Chicamo section [40]; 2) and 3) Chorrico and Librilla section [39];La Serrata section [42]; 5) Abad section [44]; Zorreras section [88]; Galera section [89]; 8) Carmona section [15]; 9) Purcal section [56]; 10) Venta de la Virgin section [90]. (Modified from [15]). M. Mattei et al. / Earth and Planetary Science Letters 250 (2006) 522–540 537 in the Granada basins, in the central part of the Betic rotations are confined to a deformation belt related to chain (Fig. 9). Our results are coherent with previous wrench tectonics (left lateral strike-slip faults) and paleomagnetic results in the central Betics, where continued until recent times. On the other hand, CW clockwise rotations have been already documented rotations have been measured for the first time in Late [14]. However, the occurrence of such rotations in the Miocene units from intramontane basins in central Betics. Late Miocene sedimentary units demonstrates that rota- This makes substantially younger the age of CW rotation tion is younger than previously supposed and occurred in the Betic chain. Our results imply a reconsideration of after the main phases of nappe emplacement. This new the timing of paleomagnetic rotations in the Betics, and result implies either that bending process of the overall enhance the role of vertical axis rotations in the Late belt was still at work during the Late Miocene (first class Miocene to Recent tectonic evolution of the Gibraltar of models) or that these rotations are due to right-lateral Arc. Recent paleomagnetic rotations are mostly related to shear, related to the oblique plate convergence (second the complex pattern of deformation associated to the class of models) [22,25]. The first solution would imply right-lateral strike-slip component of relative motion at a revaluation of the timing of the bending process of the Africa–Iberia plate boundary, but could also imply the Gibraltar Arc as a consequence of westward slab that the bending of the Gibraltar Arc was not completely roll back. This hypothesis, recently proposed by [76], achieved in the Late Miocene. To test this hypothesis should imply the occurrence of Late Miocene to Recent detailed paleomagnetic investigations in the Neogene opposite vertical axis rotations in the Betics (CW) and in sedimentary basins from the Moroccan side of the the Rif (CCW). At the moment no paleomagnetic data Gibraltar Arc (Rif chain) should be carried out. from Late Miocene to Recent are available from the Rif chain, hindering the possibility to test successfully this Acknowledgments hypothesis. However it is important to note that active west-directed roll-back of an east-dipping slab, which Financial support for this work was provided by should cause a westward motion of Gibraltar relative to Projects: a) 01-LECEMA22F [WESTMED] by the Africa, is inconsistent with the well-defined eastward European Science Foundation under the EUROCORES motion of GPS sites observed in northwestern Morocco Programme EUROMARGINS, through contract No. [85]. ERAS-CT-2003-980409 of the European Commission, The second solution would enhance the role of the DGResearch,FP6(M.M.,F.C.,M.P.andC.F.); Nubia–Iberia oblique convergence in the recent tectonic b) BTE2003-05057-C02 (A.C–B) and c) REN2001- evolution of the Betic chain and the observed CW 3868-C03-01 (M.C.) from the MEC and FEDER rotations in western Betics should accommodate the founding (Spain). We thank G. Booth-Rea for his help right-lateral shear at the boundary between Iberia and in taking samples in the eastern Betics. M.M. and C.F. Nubia plates. This interpretation is coherent with GPS are particularly grateful to Victor Garcia Duenas who data which suggest that the the Iberia–Nubia plate introduce them to the geology of the Betics. boundary is presently located in a deformation belt located between southern Iberia and northern Morocco References [85]. CW rotations measured in central Betics could be a still active process which accommodate the complex [1] J. Andrieux, J.M. 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