A cross section of the eastern Betic Cordillera (SE Spain) according field data and a seismic reflection profile

(2007) 97–126www.elsevier.com/locate/tecto

Tectonophysics 433

A cross section of the eastern Betic Cordillera (SE Spain) accordingfield data and a seismic reflection profile

A. Jabaloy-Sánchez ⁎, E.M. Fernández-Fernández, F. González-Lodeiro

Dpto. Geodinámica, Univ. Granada, 18071 Granada, Spain

Received 6 July 2006; received in revised form 9 November 2006; accepted 15 November 2006Available online 18 January 2007

Abstract

The BT3 multichannel seismic profile was acquired by the C.G.G. (Compagnie General de Géophysique) in 1977 forhydrocarbon exploration in the eastern Betic Cordillera. REXIMseis Ltd scanned and vectorized a paper copy and then performedpost-stack processing, including coherence filtering and deconvolution. The receiver functions of a broad-band seismic stationlocated near the village of Vélez Rubio, at the SE end of the profile, were analysed by Julia et al. [Julia, J., Mancilla, F., Morales, J.,2005. Seismic signature of intracrustal magmatic intrusions in the Eastern Betics (Internal Zone), SE Iberia, Geophysical ResearchLetters 32, L16304, doi:10.1029/2005GL023274.] to determine the structure of the underlying crust. We have used these Vp datato convert the profile to depth. The profile has a mean SE–NW trend, with a SE-Section 44 km in length followed by a NW-Section20 km in length. The record includes the first 4 s (twtt), which corresponds to 11 km.

Two main areas can be seen in the profile. At the SE-end, a band of high-amplitude discontinuous reflectors dips towards thenorth. The band is 100 to 200 ms thick, increasing even more northwards. This band reaches the surface at the top of the MaláguideComplex (the upper complex of the Internal Zones). Above these reflectors, an area with chaotic seismic facies and no reflectorscorresponds to the outcrops of the olistostromes and turbidites of the Solana Formation, and it is in turn overlain by discontinuousreflectors of the Subbetic rocks.

At the NW-end of the profile, a set of high-amplitude continuous reflectors with SE dips point to the location of the Prebetic.Below this section, oblique reflectors of intermediate amplitude indicate the Variscan basement. Over the Prebetic, we have markedthe basal thrusts of the Intermediate Units and the Subbetic. Using this seismic data, as well as field observations, we propose ageological cross-section of the upper crust of the eastern Betic Cordillera and a model of the most recent evolution of the orogen. Inthis model, the Internal Zones and the Subbetic have been welded together from the Middle Burdigalian to the present day andacted as an orogenic wedge that deformed the Intermediate Units and the Prebetic.© 2006 Elsevier B.V. All rights reserved.

Keywords: Multichannel seismic profile; Geological cross section; Betic Cordillera; Thrust system

1. Introduction

The Betic Cordillera is characterised by folds withsmall axial immersion and by high- and low-angle normal

⁎ Corresponding author.E-mail address: [email protected] (A. Jabaloy-Sánchez).

0040-1951/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.tecto.2006.11.004

faults and extensional detachments. Therefore, geologicalcross-sections of the area are usually superficial and it isdifficult to determine the structure of the rocks in depth.Several authors have proposed cross-sections of thecordillera that include the upper crust, but the proposedstrucures in the intermediate and lower depths ofthese cross-sections cannot be confirmed by surfaceobservations.

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http://dx.doi.org/10.1016/j.tecto.2006.11.004

98 A. Jabaloy-Sánchez et al. / Tectonophysics 433 (2007) 97–126

In this work we present a NW–SE geological cross-section of the eastern Betic Cordillera using field dataand a seismic-reflection profile (profile BT-3), whichenables us to obtain an image of the upper crust to adepth of 11 km. This geological cross-section is also anaid to discussing previous cross-sections proposed forthe eastern Betic Cordillera and to presenting a model ofthe evolution of the chain from the Early Miocene to thepresent day.

2. Geological setting

The rocks of the Betic Cordillera have been subdividedinto the External Zones, or South Iberian Domain, and theInternal Zones, orAlboranDomain (Fallot, 1948; Balanyáand García Dueñas, 1987) (Fig. 1). The External Zonesinclude rocks deposited in the southern and easternmargins of the Iberian Massif during the Mesozoic–Cainozoic. These rocks were deformed during the

Fig. 1. Geological sketch of the Betic Cordillera.

Neogene as a thrust-and-fold belt, and have traditionallybeen subdivided into a Prebetic Zone to the north and aSubbetic Zone to the south (García-Hernández et al.,1980).

The Internal Zones comprise metamorphic andsedimentary rocks deformed in a wide range of pressuresand temperatures during the Alpine orogeny. Three maintectono-metamorphic complexes are recognised in therocks of the Internal Zones: the lower one is the Nevado–Filábride Complex, the intermediate is the AlpujárrideComplex, and the upper one is the Maláguide Complex(Fig. 1).

The eastern Betic Cordillera has several features thatdifferentiate it from the central and western traverseof the orogenic belt. In the central and western BeticCordillera, the chain is separated from the Variscanforeland by the Guadalquivir foreland basin. However,this basin disappears east of the 3° W meridian and isreplaced by the thrust-and-fold belt of the Prebetic

The rectangle marks the area of the Fig. 2.

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Zone (Fig. 1). Moreover, the outcrops with chaoticfacies in the Subbetic (Olistostromes of the Guadalqui-vir and similar facies) are less abundant in the easterntraverse than in the rest of the chain. Another majordifference is that the eastern traverse contains the out-crops of the Nevado–Filábride and the extensional

Fig. 2. Geological sketch of the eastern Betic Cordillera, with the location ostructure near Vélez Rubio.

detachment that separates this complex from theoverlying Alpujárride Complex (Jabaloy et al., 1993).In addition, the Flyschs facies of the Flyschs TroughUnits are mainly found in the western sector of thechain, while the Neogene volcanism centres in theeastern Betic Cordillera (Fig. 1).

f the reflection seismic profile BT-3 and also the main features of the


Paquet (1967) determined the main characteristics ofthe configuration in his study of the eastern BeticCordillera. The Subbetic is essentially a large pop-upstructure limited by a NW-directed thrust to the north anda SE-directed back-thrust to the south. In the InternalZones, theMaláguide Complex was deformed by a thrustsystem during the Middle Eocene. De Smet (1984)identified the Crevillente Fault Zone as a major dextralstrike-slip fault cutting the structures of the Subbetic.

Banks andWarburton (1991) proposed the first cross-section of the Eastern Betic Cordillera using data fromseismic-reflection profiles (Profile Río-Segura 15) anddrills (Río Segura-1), confirming the previous interpre-tation by Paquet (1967) of the Subbetic as a major pop-up. These authors also interpreted the southern part of thePrebetic as a triangle zone (“a combination of two thrustswith the same basal detachment and with opposingvergence such that they form a triangular zone, McClay,1992). The works of Lonergan (1991, 1993) on the areaextended the knowledge of the geometry and kinematicsof the Maláguide Complex structures and the Subbeticback-thrust. Lonergan (1991, 1993) also managed toprovide more precise information on the timing of thedeformations, dating the backthrust of the Subbetic overthe Maláguide Complex as Middle Burdigalian and thedeformations in the Maláguide as Middle Eocene toOligocene. Platt et al. (2003) included a cross-section ofthe study area that assumes that the thrust and foldsystem of the Prebetic Zone is composed mainly of NW-directed thrusts, and the Subbetic is a pop-up with all thethrusts south of the Barrunda Basin directed towards thesouth-east.

3. Field data

The field data derive mainly from the sector aroundVélez Rubio (Figs. 2, 3, and 4). The rocks of theSubbetic Zone that crop out in this sector thrust over thehighest rocks of the Internal Zones, those of theMaláguide Complex.

3.1. Description of the Subbetic Zone rocks

The Subbetic sequence in the Vélez Rubio beginswith nearly 1500 m of Early to Middle Jurassiclimestones and dolostones with shallow marine facies(Gavilán and Camarena Formations, Rey, 1993). Therelationship of these rocks with syn-sedimentary normalfaults cutting the sequence indicates that they are a pre-rift succession (Rey, 1998).

The pre-rift succession is overlain by several LateJurassic to Early Cretaceous formations, which are

discontinuous and usually wedge-shaped (Rey, 1993,1998; Fernández-Fernández et al., 2003). The forma-tions normally onlap the lower rocks and are frequentlyunconformable; moreover, the upper formations areexpansive over the lower ones. The Upper Jurassic rocksare marls and radiolarites (Radiolaritas del CharcoFormation) and nodular limestones (Ammonítico RossoSuperior Formation). The Lower Cretaceous formationscomprise mainly marls, marly limestones, and clays(Carretero and Fardes Formations) that evolve laterallyto olistostromes (Conglomerados Calcáreos de PuertoFormation). These rocks were deposited in half-grabenand graben basins associated with normal faults(Fernández-Fernández et al., 2003) and represent asyn-rift succession. All these formations have pelagicfacies, indicating subsidence with respect to the Lower–Middle Jurassic rocks. Maximum depth was reachedduring the Late Barremian–Early Cenomanian with thedeposition of the Fardes Formation near the CarbonateCompensation Level (near the −3200 to −3500 waterdepth in the Middle Atlantic during the Albian–Cenomanian, Van Andel, 1975).

The syn-rift succession is covered by marls andmarly limestones (Capas Blancas and Capas RojasFormations) of Upper Cretaceous–Middle Eocene age,which in turn are overlain by the marls and sandstonesof the Barahona Formation (Palaeogene–Aquitanian).These formations, usually continuous, have marinepelagic facies and frequent changes in thickness. Theycover most of the syn-sedimentary normal faults and weinterpret them as a post-rift succession. The post-riftsuccession is unconformable over the syn- and pre-riftsuccessions and in several places all the Late Jurassicand Early Cretaceous rocks are missing (Fernández-Fernández et al., 2003).

The aforementioned rocks are folded and uncon-formably covered by Lower to Middle Miocene rocks.From bottom to top, these upper unconformableformations are: the conglomerates and sandstones ofthe Marín (Middle Burdigalian, Fernández-Fernández,2003), Maíz (Upper Burdigalian-Langhian, Aguado andRey, 1997; Geel and Roep, 1998), and Tala (Langhian,Aguado and Rey, 1997; Geel and Roep, 1998)Formations. These rocks have shallow marine faciesand their relationships with the folds and thrusts aid innarrowing the age of the structures.

In the north of the study area there is a megabrecciawith fragments of the Subbetic sequence within a matrixof deformed Triassic rocks with Keuper facies. Thismegabreccia is called the Trias with Blocks Formation(Allerton et al., 1993; Fernández-Fernández, 2003).These rocks are primarily found at two locations: within

Fig. 3. Geological map of the area near Vélez Rubio with the trace of the SE end of the seismic profile. The Southern border of the Barrunda Basin isrepresented in the northern part of the map.



subvertical bodies associated to the Crevillente FaultZone and as wedge-shaped bodies that root into thesubvertical fault zone and overlie the Upper Eocene toMiddle Burdigalian rocks of the Barahona and MarínFormations. We interpret these former bodies as flows ofthe materials being outwardly displaced from theCrevillente Fault Zone, although this interpretationdoes not implies that there is not major tectonic sheetsof this melange within the thrust stack, as other authorsinterpret (i.e. Platt et al., 2003).

This Subbetic sequence has abundant lateral changesof facies and variations in the thicknesses of the rockformations.

3.2. Structure of the Subbetic Zone

The syn-sedimentary normal faults that developedduring the Late Jurassic–Early Cretaceous are associat-ed with half-grabens and grabens (Fig. 4). These faultsare arranged in two sets of conjugate faults with nearlynormal strikes: ENE–WSW to E–Wand NNW–SSE toN–S. The ENE–WSW to E–W set is better developedand has major slips (Fernández-Fernández et al., 2003).These faults were contemporaneous with the tectonicsubsidence that positioned the basins at the CarbonateCompensation Level (CCL) during the Aptian–Albian.The Capas Blancas and Capas Rojas Formations beganto cover the palaeo-reliefs and the faults in the UpperCretaceous, suggesting that the rifting stage ended atthis time.

The older compressive structures are a trend of foldsdeforming the Aquitanian rocks of the upper BarahonaFormation. The major folds have amplitudes rangingbetween 500 to 700 m and wave lengths that varybetween 1000 and 1500 m (Fig. 4). They are double-plunging non-cylindrical folds that, in a map view, showaxial surfaces folded in an arc. The folds trend N10° Eand are E-vergent in the northeast of the study area; inthe central and western parts of the zone, in contrast, thefolds trend N50° to N115° E and are S-SE-vergent.Fernández-Fernández et al. (2004) describe internalunconformities within the Marín Formation (MiddleBurdigalian) that are associated with the nucleus of asynform, indicating that fold formation began during theEarly Burdigalian and tightened during the MiddleBurdigalian. The deformation seems to have taken placewith area reduction, as indicated by the tightening of thefolds, their double-plunging non-cylindrical character,and the arcuate pattern of the axial traces.

The palaeomagnetic studies of Allerton et al. (1993)and Platt et al. (2003) indicate that the present-dayorientation of the folds is the result of vertical axis

rotations. The arcuate pattern of the folds agrees with therotations described by these authors. When the foldstrend E–W to ENE–WSW, the palaeomagnetic dataindicate about 60° of clockwise rotation; however, whenthe folds trend NNW–SSE, then the rotations areanticlockwise with a value of around 15°. These datasuggest that the folds were generated with an N–S trendand an E-vergent character and later underwent verticalaxis rotations. The most probable age for these rotationsis the transition between the Middle to Upper Burdiga-lian, because it must have occurred after the formationand tightening of the folds and prior to or during themovement of the Vélez Blanco Thrust, since the striae ofthe thrust do not record the rotations. The fault rock ofthe Vélez Blanco Thrust has striations with trendsranging from N20° E to N150° E and most of thekinematic criteria show a top-to-the-SSE sense ofmovement (Fernández-Fernández et al., 2004). Howev-er, we can distinguish two areas with slightly differenttrends along the thrust fault: in the western region of thethrust surface, the main trend of the striations variesfrom N145° E to N200° E, while in the eastern region,the main trends of the striations are E–W to N190° E.These small differences in the slip direction cannotaccommodate the vertical axis clockwise rotations of74° determined for the Sierra de María Range (Plattet al., 2003).

The Vélez Blanco Thrust superposes the Subbeticover the Solana Formation. The thrust has a frontal splaythat places the Upper Cretaceous–Aquitanian rocks overthe Solana Formation (attributed to the Aquitanian).This frontal splay is overthrust by the main surface,which places the Lower Jurassic rocks on top (crossSection 1-1′, Fig. 4). The thrust surface and the frontalsplay are folded by E–Wand NNE–SSW trending folds.The culminations of these folds allow the formation oftectonic windows in which the Solana Formation cropsout (Figs. 3 and 4). The thrust surface is cut by the NW–SE normal faults that bound the Lorca Basin. East of theLorca Basin, the thrust continues as the basal thrustingof the Subbetic over the Maláguide rocks (Paquet, 1967;Lonergan, 1993).

The Vélez Blanco thrust has a fault rock with striaeranging from N20° E to N150° E. The kinematic criteriausually indicate a top-to-the-SE sense of movement(maximum around N150° E). However, in several placesyounger N–S striae develop with a northward sense ofmovement of the hanging wall. The thrust surface cutsrocks of the Marín Formation (Middle Burdigalian) andis eroded; it is unconformably overlain by the conglom-erates of the Maíz Formation (Upper Burdigalian). TheVélez Blanco thrust is cut by a lower thrust system (the

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Fig. 4. Geological cross sections of the studied area. See Fig. 3 for location. The legend is the same as in Fig. 3.


Parroquia Thrust) responsible for the superposition ofthe Solana Formation and the Subbetic over the InternalZones. The splay of this lower thrust system cuts theVélez Blanco Thrust, generating breaching duplexes(Butler, 1987) (Fig. 4). The breaching duplexes areparallel to the folds deforming the Vélez Blanco thrust,suggesting that these folds are associated to blind thrustsof the Parroquia Thrust system.

In the northern part of the study area, the folds arecut by a subvertical fault zone around 2 km thick andan ENE–WSW strike that affects the Subbetic sequenceand the Trias with Blocks megabreccia (Fig. 3). Themain fault surfaces are subvertical with ENE–WSWstrikes and contain strike-slip striae. Kinematic criteriaare abundant (mainly S–C, steps and calcite fibres) andnormally indicate a right-handed sense of movement,although there is also left-handed sense of movement,mainly on R′ planes [see Platt et al. (2003) for sliplineations on thrust faults in the area, while lineationdata within the Crevillente Fault zone are provided byAllerton et al. (1994) and Bousquet (1979)]. Within thegypsum bodies inside the megabreccia, a planar-linearfabric developed with subhorizontal stretching linea-tion. The kinematic criteria (trails of crushed clasts)also indicate a right-handed sense of movement. The

Fig. 5. Location of the main CDPs along the trace of the BET-3 seismic proflocated near the Vélez Rubio village, in the SE end of the profile.

structure was termed the Crevillente fault by De Smet(1984) and interpreted as a major subvertical dextralstrike-slip fault. This fault zone extends for a hundredkilometers and has a displacement of 60 km (Nieto andRey, 2004).

However, two observations suggest that the originalorientation of the fault zone was not vertical. The firstindication is found in the northern border of the faultzone (Fig. 2), which comprises the SE border of theBarrunda Basin, a small rectangular basin located overthe External Zones of the chain (Figs. 2 and 3). Thisbasin is filled by a shallow marine succession of UpperBurdigalian to Messinian rocks including two levels ofgypsum, which are overlain by continental Pliocenesediments. The different levels of the sedimentary fillingof the basin can be observed in the northern border of theCrevillente Fault Zone; they are vertical and define aNW-vergent synform in the SE border of the basin (Figs.3 and 4). The second observation is that this major foldand the associated antiform can be followed in seismicprofile BT-3. We will discuss this profile below, but italso indicates that the fault zone dips NW. We proposethat the Crevillente Fault Zone had an original diptowards the NW and that its present-day orientation isdue to the late NW-folds.

ile. The broad band seismic station mentioned by Julia et al. (2005) is


3.3. The syn-orogenic deposits of the Solana Formation

The rocks of the Solana Formation can be observedbetween the Internal and the External Zones. Theserocks are green–brown marls with interlayered levelsof quartzitic sandstones and calcarenites. The sandstoneclasts mainly derive from the rocks of the Maláguideand the Subbetic (Geel, 1973). The sandstones andthe calcarenites are turbiditic levels with a Bouma se-quence. Fossils are scarce and show evidence of re-working (Soediono, 1971). Moreover, microfauna agesvary widely, ranging between the Late Jurassic andBasal Miocene; however, as the younger age of thefossils is Oligocene–Basal Miocene, most authorssuggest an Aquitanian age (e.g. Geel and Roep, 1998).

These rocks represent pelagic turbidites deposited ina trough between the Maláguide and the Subbetic withclastic input from both zones (Geel, 1973; Geel andRoep, 1998). Martín-Algarra (1987) suggests that theyare similar to the Algeciras Formation (Late Oligocene)and the Aljibe Sandstones of the Flyschs Trough Units.However, another hypothesis is that these rocks rep-resent gravitational deposits associated to deformationsof the Maláguide Complex and the convergence of theSubbetic during the Early Miocene.

The Parroquia Thrust system (top-to-the-SE sense ofmovement) has forced the Solana Formation to thrustover the Burdigalian rocks of the Maláguide Complex(Fuente–Espejos Formation).

3.4. Description of the Maláguide Complex rocks

The Maláguide sequence in the Vélez Rubio sectorbegins with a Palaeozoic basement (Piar Group, LateSilurian–Late Carboniferous) deformed during theVariscan orogeny and overlain by a Mesozoic–Caino-zoic cover that is usually detached.

The cover begins with the red pelites, sandstones,and conglomerates of the Saladilla Formation (Middle-Late Triassic), which are overlain by Jurassic–LowerEocene limestones and dolostones. The brown calcar-enites, sandstones and pelites of the Ciudad GranadaFormation (Early-Middle Aquitanian, González Donosoet al., 1988) unconformably cover the above formations.These sandstones and calcarenites contain only clastsfrom the Maláguide Complex (Mac Gillavry et al.,1963; Geel, 1973).

The top of the succession, the Fuente-Espejos For-mation, is Early Burdigalian to lower-Late Burdigalian(González Donoso et al., 1988; Geel and Roep, 1998),which is unconformable over all the above-describedrocks. This formation is formed of calcarenites, brec-

cias, and conglomerates with clasts from the Maláguideand Alpujárride Complexes. Moreover, the upper part ofthe formation contains clasts from the Subbetic and theSolana Formation.

3.5. Structure of the Maláguide Complex

The oldest Alpine structure in theMaláguide is a slatycleavage that developed in the pelites of the SaladillaFormation (Middle to Upper Triassic) in the deepestareas of the complex. Another ancient Alpine structure isthe décollement between the Palaeozoic basement andthe cover. The striae within this surface have a NNW–SSE trend and the kinematic criteria (S–C structures)indicate a top-to-the-NNW sense of movement. In thenorthern outcrops of the complex, this décollement thinsthe sedimentary cover, and the Jurassic–Lower Eocenerocks lie directly over the Palaeozoic rocks of thebasement. However, the most conspicuous structures inthe field and on the map are a set of ENE–WSW reversefaults with dips ranging between 45° and 90° towards thenorth. The striae within the fault rocks have NW–SE toWNW–ESE trends and the kinematic criteria indicate asense of movement of the hanging wall towards the ESE.These reverse and right-handed reverse faults cut theCiudad Granada Formation (Early-Middle Aquitanian),while the map shows that the Fuente-Espejos Formation(Burdigalian) caps the faults. This circumstance indi-cates that these faults predate the Vélez Blanco andParroquia thrusts and records right-handed transpressionsuch as that proposed for the Subbetic during the Early-Middle Burdigalian (Lonergan and White, 1997; Fer-nández-Fernández et al., 2004).

The basal contact of the Maláguide with the Alpu-járride is a low-angle normal fault with a top-to-the-ENEsense of movement (Aldaya et al., 1991; Lonergan andPlatt, 1995). This fault is folded by a NW-vergentantiform, and it is mainly the subvertical limb of thisfold that crops out in the study area. The AlpujárrideComplex, which crops out in the footwall of this fault, hasundergone HP-LT Alpine metamorphism (Goffé et al.,1989). Fission-track ages on zircons and apatites(Johnson, 1993; Platt et al., 2005) indicate cooling ofthe footwall rocks from 21–18Ma, which agrees with thedeposition of Alpujárride clasts within the Fuente-EspejosFormation (Burdigalian) and their absence within theCiudad Granada Formation (Early-Middle Aquitanian).

4. Seismic reflection profile BT-3

Multichannel seismic profile BT-3 was acquired bythe CGG (Compagnie General de Géophysique) in 1977

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Fig. 6. The BET-3 multichannel seismic profile represented in milliseconds (twtt), and a line drawing interpretation, illustrating the structure of the upper crust of the studied area. The resultant conversions of twtt (milliseconds) to depth (in meters) calculated using three Vp velocity profiles obtained using reasonable Poisson's ratios (0.2, 0.25 and0.3) are represented to the right of the seismic line. UMRS: Upper Maláguide Reflectors; VBR: Variscan Basement top reflector.


for hydrocarbon exploration. In accordance with Spanishlaw, a copy of this profile was deposited in the “InstitutoGeológico y Minero de España” (IGME), where it isavailable for public use in the SIGEOF (InternetGeophysical Information System; http://www.igme.es/internet/sigeof/INICIOsiGEOF.htm).

A paper copy was scanned and vectorized byREXIMseis Ltd., and was then post-stack processed,including coherence filtering and deconvolution. Theprofile is a slalom line with a curve trajectory (Fig. 5). Themean trend of the profile is NW–SE, with a SE-Section45 km in length followed by a NW-Section 20 km inlength. The record includes the first 4 s (twtt, Fig. 6).

Julia et al. (2005) studied the receiver functions of abroadband seismic station located in Vélez Rubio (verynear CDP 100 of the seismic profile, Fig. 5) and deter-mined the structure of its underlying crust and uppermostmantle with their respective Vp and Vs values. The onlyavailable study about velocity structure in the study areacomes from receiver functions. These receiver functionsare mainly sensitive to the Vs profile, and it is commonpractice in receiver function studies to generate the P-wave velocities after assuming a uniform Poisson's ratiofor the whole crust. In the work of Julia et al. (2005), anaverage Poisson ratio of 0.26 was considered as anaverage of the standard crustal composition to obtain theVp velocity profile. To test the validity of the model, wehave calculated several Vp velocity profiles using variousreasonable Poisson ratios from a minimum value of 0.2 toa maximum value of 0.3, and an intermediate value of0.25 and the changes in the Vp law do not showsignificant variations in the resultant conversion of TTWTto depth (Fig. 6). Therefore, we have used the Vp velocitymodel of the crust published by Julia et al. (2005) toconvert the seismic profile to depths (Fig. 7).

The resultant profile shows practically the entire uppercrust (11 km, Fig. 7). The conversion was performedusing PROMAX software in the Instituto Andaluz deCiencias de la Tierra (CSIC) at the University of Granada.

5. Interpretation of seismic profile BT-3

The data from the profile are not very good. Therecord is contaminated by noise and very lowfrequencies were recorded (15 to 49 MHz). However,several reflectors can be identified in the upper crust,which is usually transparent in the deep seismic profilesof the Betics (see ESCI-Betics profiles in García-Dueñaset al., 1994; Galindo-Zaldívar et al., 1997).

It can be seen on the map that, at its southeastern end(Figs. 6 and 8), the profile cuts the Maláguide complexnear Vélez Rubio (Fig. 3). The Fuente-Espejos Forma-

tion crops out in CDPs 130 to 140, and north-westwardsthe profile cuts the synforms affecting the frontal splayof the Vélez Blanco Thrust and the antiforms with thetectonic windows of the Solana Formation. BetweenCDPs 150 and 350, a band of high-amplitude discon-tinuous reflectors dips towards the north; thicknessranges from 100 to 200 ms and increases northwards(UMRS in Figs. 6, 7 and 8). This band reaches thesurface at the Fuente-Espejos Formation (Early Burdi-galian–lower part of the Late Burdigalian) outcrops,thus very plausibly representing these rocks. Over thesereflectors, an area with chaotic seismic facies with noreflectors comprises outcrops of the olistostromes andturbidites of the Solana Formation (assumed to beAquitanian). These chaotic seismic facies are coveredby high-amplitude continuous reflectors that mark thegeometry of the southern synform affecting the frontalsplay of the Vélez Blanco Thrust, composed essentiallyof the Capas Rojas Formation (Late Cretaceous–EarlyEocene).

Below the high-amplitude reflectors interpreted asthe Fuente-Espejos Formation, a series of high-ampli-tude discontinuous reflectors correspond to the Malá-guide Complex. The Parroquia Thrust system has beenrelated with the displacement of the high-amplitudeband of reflectors interpreted as the Fuente-EspejosFormation. This system is a blind thrust responsible forthe folds where the tectonic windows develop.

On the geological map, between CDPs 330 and 490,the profile cuts the syncline with the unconformableMaíz (Late Burdigalian–Basal Langhian) and Tala(Langhian) Formations, which erode and cap theVélez Blanco thrust surface. North-westwards, betweenCDPs 500 and 900, the seismic profile cuts the post-riftsuccession of the Subbetic, which is affected by the SE-vergent folds. However, this cut is oblique to the meantrend of the folds.

The formation outcrops help to identify the seismicfacies of the rocks. The marls and marly limestones of theCapas Blancas and Capas Rojas Formations (LateCretaceous–Early Eocene) correspond to a band of dis-continuous reflectors with high amplitude and a thicknessof 100 ms (Fig. 8). Over and under this band, there is amore transparent seismic facies with few reflectors andintermediate amplitudes. We interpret this facies asequivalent to the Barahona Formation (Middle Eocene–Basal Burdigalian) upsection and to the marly formationsof the syn-rift succession (Radiolaritas del Charco, Am-monítico Rosso Superior, Carretero, Fardes, and Con-glomerados Calcáreos del Puerto Formations, LateJurassic–Early Cretaceous) downsection (Fig. 8). Belowthis aforementioned facies, a band of discontinuous high-

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Fig. 7. The line drawing of the BET-3 seismic profile converted to depth (km) according the Vp data form Julia et al. (2005). UMRS: Upper Maláguide Reflectors; VBR: Variscan Basement topreflector.

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97–126

Fig. 8. Awindow of the SE end of the BET-3 MCS profile (see Fig. 6 for location) and a line drawing interpretation, illustrating the structure of the Vélez Blanco and La Parroquia thrusts surfaces.UMRS: Upper Maláguide Reflectors.


amplitude reflectors has been interpreted as the pre-riftsuccession (Gavilán and Camarena Formations, Early-Middle Jurassic), in accordance with their location in theprofile (Fig. 8).

The prolongation of the Crevillente Fault Zone cutsthe seismic profile between CDPs 800 to 1000. In theseismic profile, this sector shows a band of continuoushigh-amplitude reflectors dipping towards the NW;therefore, we have represented the Crevillente FaultZone over these reflectors.

At the NW end of the profile, from CDP 1800onwards, a set of high-amplitude continuous reflectorsshows the location of the Prebetic with SE dips. This setis thick, about 2200ms (twtt) and 5.5 to 7 km in depth. Ataround 1600 ms (twtt) and 4000 m (depth), the reflectorsincrease in amplitude. Based on seismic profile RíoSegura 15 and drillhole RS-1 (see Banks andWarburton,1991), we interpret this seismic facies as the Triassic andJurassic rocks of the Prebetic, covered by a thickCretaceous–Palaeogene succession. Below these reflec-tors, intermediate-amplitude oblique reflectors indicatethe location of the Variscan basement (VBR in Figs. 6and 7). Over the Prebetic, we havemarked the location ofthe basal thrusts of the Intermediate Units and theSubbetic. Towards the centre of the profile, we havelocated the top of the Iberian basement at 6 km of depth(Fig. 7), which agrees with the magnetotelluric data fromMartí (2006) that indicates the presence of a conductor(C20 Conductor) associated with the rocks of the

Fig. 9. A window of BET-3 MCS profile and a line drawinginterpretation (see Fig. 6 for location) illustrating the accommodationfolds with southeastward vergence developed in the Prebetic.

External zones that reach 7 km depth near the center ofthe profile.

Within the seismic facies of the Cretaceous–Palaeo-gene Prebetic succession, we have interpreted theobliquity between the reflectors as due to listric faultsdipping towards the SE. We interpret these faults as beinga result of the Late Jurassic–Early Cretaceous riftingstage. Banks and Warburton (1991) deduced, in the RíoSegura seismic profile 15, NWof the considered section, asyn-sedimentary normal listric fault that thins the rocksequence.

At the NW end of the seismic profile, several back-thrusts (Fig. 9) and accommodation folds can be easilyidentified; the back-thrusts can be correlated with the Se-gura Back-Thrust Zone of Banks and Warburton (1991).

Over the Prebetic Zone we have located the basalthrusts of the Intermediate Units and the Subbetic nearPuebla de Don Fadrique (Fig. 10). The prolongation ofthese structures has been drawn based on the klippes ofthese units. We have not represented the internalstructure of the northern Subbetic because it is almostentirely covered by the Late Miocene–Quaternarydeposits of the Guadix–Baza Basin.

6. Discussion and conclusions

Field structures (thrusts and folds) suggest theexistence of two main stages of evolution from the EarlyMiocene to the present day in the study area. The olderstage corresponds to the development of the reverse andright-reverse faults in the Maláguide during the UpperAquitanian, the formation of N-folds with eastwardvergence in the Subbetic during the Early Burdigalian,and their tightening and refolding during the MiddleBurdigalian by vertical axis rotation. This stage seems toend with the thrusting of the Subbetic and the SolanaFormation over the Malaguide Complex and the devel-opment of the right-handed Crevillente Fault (Fig. 11). Allthese structures indicate right-handed transpression as themechanism for the convergence of the Internal andExternal Zones (Lonergan and White, 1997; Fernández-Fernández et al., 2004). The last deformations of this stagestrongly resemble the model proposed by Dewey (1982)for strain partitioning in a transpressive regime where thedeformations parallel to the orogen are accommodated bystrike-slip faults and the shortening normal to the orogen isaccommodated by thrusts.We propose that, althoughmostof the transpression is accommodated mainly by verticalaxis rotations, the deformation is somewhat partitionedbetween the thrusts (which accommodated the shortening)and theCrevillente Fault (which accommodated part of themovement parallel to the orogen) (Fig. 11).


The younger stage (Upper Burdigalian to the presentday) corresponds to the deformation of the Subbetic andInternal Zones, which now seem to act as a weldedblock. These deformations include the development ofthe NW vergent folds and also normal faults that boundthe Lorca Basin (Fig. 11). This stage has a primarilyNW–SE shortening direction recorded by NW-vergentfolds and NE–SW extensional trending marked by thenormal faults. The development of the strike-slip faultsof Alhama de Murcia, Carrascoy, Palomares, andCarboneras, as well as their related faults and folds(see, for example, Montenat and Ott d'Estevou, 1990;Martínez-Díaz et al., 2001; Masana et al., 2005), canalso be included in this event.

Fig. 10. Geological map of the area around the NWend of the profile (Dabrioand Baena-Pérez, 1978). Violet, blues, and greens represent the Triassic to Cred colours represent the Cainozoic Prebetic rocks. The klippes in the northerYellow and grey colours represent the Neogene rocks of the Guadix-Baza d

Seismic profile BT3, although not of good quality,does allow us to propose a model for the structure of theupper crust (nearly 11 km thick), especially whencombined with the field data, since its trend is parallel tothe shortening direction of the structures. However, thestructures that accommodated the NE–SWextension arecut along the strike and perpendicular to their sense ofmovement. These faults can be seen best in a NE–SWgeological cross-section.

We can deduce the evolution of the compressivestructures involved in the convergence of the Internal andExternal Zones from the profile and the field data. Theolder structures that developed during the LateAquitanianin theMaláguide Complex were a set of reverse and right-

and López-Garrido, 1977; Baena-Pérez et al., 1978; Guzmán del Pinoretaceous Subbetic and Intermediate Units rocks, while the orange andn part of the map show the northernmost location of the Subbetic front.epression.


Fig. 11. Sketch showing the proposed evolution of the main compressional structures during the Neogene in the eastern Betic Cordillera. Theapproximation between the Internal Zones and the South Iberian Domain produced an orogenic wedge that advanced towards the foreland producingthe thrusting of the intermediate units and the Prebetic.

handed reverse faults with a top-to-the-ESE sense ofmovement. These right-handed reverse faults can beproduced by right-handed transpression, and this trans-pression may also explain the large vertical axisdetermined in the area (Allerton et al., 1993; Platzmanet al., 2000; Platzman and Platt, 2004). These faults firstrecorded the right-handed transpression and also indicatea major characteristic of the orogen: the fact that theInternal Zones are less resistant than the Iberian crust as awhole and were, therefore, the first material deformedduring the convergence. This characteristic has, of course,remained constant during the evolution of the easternBetic Cordillera to the present day, and now the activestructures (i.e. Alhama de Murcia Fault, CarbonerasFaults, etc.) are all located within the Internal Zones.

The deformation of the Subbetic began later, duringthe Early Burdigalian, and it included the formationof N–S folds and their rotation during the MiddleBurdigalian. The first syn-orogenic deposits seem to bethe Solana Formation, which was originally located be-tween the two zones and received material from both.These syn-orogenic deposits were overthrust by the

Subbetic during the Middle Burdigalian and weredetached from their basement (probably the NWMaláguide, now below the Subbetic). Sedimentationthen migrated to the Fuente-Espejos Formation, whichrecorded the convergence of the Subbetic and the SolanaFormation during the Early Burdigalian–Lower partof the Late Burdigalian. These rocks also show theexhumation of the Alpujárride Complex due to move-ment across the low-angle normal fault separating theMaláguide from the Alpujárride. The age of the ex-humation of the Alpujárride also agrees with the coolingages obtained from zircons and apatites by Johnson(1993) and Platt et al. (2005).

The Internal Zones and the Subbetic were shortenedduring the Late Burdigalian and from that moment onformed a single ensemble that acted as an orogenic wedgeand pushed the Intermediate units and the Prebetic.

Acknowledgements

We would like to thank Carlos Sanz de Galdeanoand José Rodríguez-Fernández for their help in


obtaining the BT3 profile. Also, we wish to thankCarlos for his help during the interpretation anddiscussion of the results. We would like also to thankFlor de Lis Mancilla, José Morales and Teresa Teixidófrom the I.A.G. (Instituto Andaluz de Geofísica) fortheir help with the data of the receiver functions of thebroad-band seismic station of Vélez Rubio and thedepth conversion, and Anna Martí from the Universityof Barcelona for her Ph. Doctoral Thesis. Thegeological maps of the Fig. 11 come from the digitalcartographic system in the web page of the I.G.M.E.(Instituto Geológico y Minero de España). The aid ofEmilia Gurmezova and Ivan Boronov was indispens-able in order to vectorize the seismic profile and toprocess it. Eduard Roca's discussion on the initialinterpretation helped to constrain the geometry of thecross-section. Christine Laurin revised the English text.This work was financed by the Spanish research projectnumber BTE2003-01699 from C.I.C.Y.T. and theSpanish CONSOLIDER-INGENIO 2010 project num-ber CSD2006-0041.

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