Betic Internal Zone Research Articles

Tectonic framework and extensional pattern of the Malaguide Complex from Sierra Espuña (Internal Betic Zone) during Jurassic–Cretaceous: implications for the Westernmost Tethys geodynamic evolution

Mapping, lithostratigraphic, biostratigraphic and structural detailed analyses in Sierra Espuna area (Internal Betic Zone, SE Spain) have allowed us to reconstruct the Jurassic–Cretaceous evolution of the Westernmost Mesomediterranean Microplate palaeomargin and, by correlation with other sectors (Northern Rift, central and western Internal Betic Zone), to propose a geodynamic evolution for the Westernmost Tethys. Extension began from Late Toarcian, when listric normal faults activated; these faults are arranged in three categories: large-scale faults, separating hectometric cortical blocks; main faults, dividing the former blocks into some kilometre-length blocks; and secondary faults, affecting the kilometric blocks. This fault ensemble, actually outcropping, in the Sierra Espuna area, broke the palaeomargin allowing the westerly Tethyan Oceanic aperture with an extension at about 17.2%. Extension was not homogeneous in time, being the Late Toarcian to the Dogger–Malm boundary the period when blocks underwent the greatest movement (rifting phase), leading to the drowning of the area (8.2% extension). During the Malm (drifting phase) extension followed (5.7%), while during the Cretaceous a change to pelagic facies is recorded with an extension of about 3.3% (post-drift stage). This evolution in the Westernmost Tethys seems to be related to areas out of the limit of significant crustal extension in the hanging wall block of the main cortical low-angle fault of the rifting.

Jurassic biostratigraphy and paleoenvironmental evolution of the Malaguide complex from Sierra Espuña (Internal Betic Zone, SE Spain)

Jurassic studies in the Internal Zones of the Betic Cordillera are scarce since this zone is composed mainly of pre-Jurassic metamorphic rocks. Only the “Dorsal” and the Malaguide domains include fossiliferous Jurassic successions, as in Sierra Espuña (SE Spain), which is one of the bigger and well-exposed Jurassic outcrops of the Internal Zones. Collected Ammonite assemblages update and improve the precision of previous biostratigraphic data by the recognition of: the Domerian (= Upper Pliensbachian, in the Mediterranean Domain) Lavinianum (Cornacaldense Subzone), Algovianum (Ragazzoni, Bertrandi, Accuratum and Levidorsatum Subzones) and Emaciatum (Solare and Elisa Subzones) Zones; the Lower Toarcian Polymorphum and Serpentinum Zones; the Middle Toarcian, Bifrons and Gradata Zone; the Upper Toarcian Reynesi Zone; the Lower/Upper Bajocian, the Lower Callovian Bullatus and Gracilis Zones; the Middle/Upper Oxfordian Transversarium, Bifurcatus, Bimammatum and Planula Zones; and the Lower and Upper Kimmeridgian Platynota, Strombecki, Divisum and Beckeri Zones. The paleoenvironmental evolution of the Malaguide Jurassic at Sierra Espuña shows similarities with other Mediterranean Tethyan paleomargins. The biostratigraphic precision along with the litho- and biofacies analyses has enabled the interpretation that the Malaguide paleomargin evolved as a passive margin, developing shallow carbonate platforms, until the Domerian (Lavinianum Zone). Then, the platform broke up (Domerian, Lavinianum Zone–Upper Toarcian, Reynesi Zone) with the beginning of the rifting stage, beginning the development of horst–graben systems and the coeval drowning of the area. This stage ended in the upper Lower Callovian (Gracilis Zone) to the Middle Oxfordian (Transversarium Zone) interval, starting the drifting stage, which accentuated the horst–graben systems, leading to the deposition of condensed nodular limestones in the raised sea bottom.

From strike-slip to reverse reactivation: The Crevillente Fault System and seismicity in the Bullas-Mula area (Betic Cordillera, SE Spain)

Several major N80oE faults occur in the Bullas-Mula area (SE Spain). These faults and the numerous thrust slices of the Sierra de Ricote can be related to the movements of the Crevillente (or Cadiz-Alicante) fault system, which causes the westward displacement of the Betic Internal Zone and part of the External Zone. These faults moved with dextral strike-slip from Late Burdigalian to Early Tortonian. From this time on, the s1 position changed from a WNW-ESE direction to approximately N-S, giving rise to movements with a new reverse character. The focal mechanisms of the 1999 Mula earthquakes indicate a N80oE nodal plane, and their pressure axes also coincide with the s1 direction existing from the Late Miocene and deduced from mesotectonic analysis at many points of the region. There is also good coincidence between their epicentral position and the fault traces. The Bullas earthquakes that occurred in 2002 are not directly related to the Crevillente faults, although their stress-pressure axes coincide with the s1 direction reported there.

Ladinian carbonates of the Cabo Cope Unit (Betic Cordillera, SE Spain): a tethys-maláguide palaeogeographic gateway

The Cabo Cope Unit, which outcrops east of Aguilas (Murcia), belongs to the Malaguide tectonic Complex (Betic Internal Zone) and displays stratigraphic characteristics of particular interest, including Triassic bioclastic carbonate beds which are not common in the Malaguide units. Biostratigrafic fossils have been found in these beds and may correlate with Triassic alpine biofacies. Alpine fauna fossils only appeared in those palaeogeographic units of the Internal Zone of the Cordillera referred to as Alpujarride units, while the influence of the Sephardic faunal province is evident in almost all the cordillera. For these reasons it is noteworthy that new alpine fauna fossils have been found in an Internal Zone unit in which relevant fossils rarely appear. The Triassic succession of the unit studied in this paper can be subdivided into two members: a lower one, which is clastic and contains thick gypsum beds, and an upper one, consisting of carbonate rocks. The lower member has been interpreted as a fluvial-coastal deposit. The upper member is interpreted as a sequence of carbonate ramp deposits. This ramp evolved into a shallow platform with tidal flats typical of a coastal zone. The bivalve fossilsDaonella cf.lommeli (Wissmann) and “Posidonia” sp. have been found in the carbonate member, along with the conodontSephardiella mungoensis (Diebel). These fossils are of the Late Ladinian age and have been found only in this outcroup of the Betic Cordillera. The presence of this fossil assemblage, which belongs to the alpine faunal province, indicates a connection during the Late Ladinian between the Tethys sea and this area of the Malaguide palaeogeographic domain. The palaeogeographic location of the Cabo Cope Unit during the Middle Triassic was at the south-easternmost part of the Betic Basin, implying that the connection between the Tethys and the Betic Basin was established in the easternmost domains of the basin.

Alpujarride attribution of the supposed ‘Almagride Complex’ (Betic Internal Zone, Almerı́a Province, Spain)

Abstract The differentiation of units in the Sierra de Almagro has been a source of controversy. There were defined the Almagride and Ballabona–Cucharon complexes, the former considered by several authors as part of a Subbetic metamorphosed and outcropping in a tectonic window. In this study, the units of Ballabona, Almagro and Cucharon are integrated into a single one, that of Tres Pacos, because they correspond to different parts of the same stratigraphic series. This unit is tectonically over the Nevado–Filabride Complex. The existence of the Almagride and Ballabona–Cucharon complexes is discarded and their units form part of the Alpujarride Complex. To cite this article: C. Sanz de Galdeano, F.J. Garcia Tortosa, C. R. Geoscience 334 (2002) 355–362.

Thrust sequence and syntectonic sedimentation in a piggy-back basin: the Oligo-Aquitanian Mula–Pliego Basin (Internal Betic Zone, SE Spain)

The Oligo-Aquitanian deposits of the Mula–Pliego basin consist of a marine carbonate platform assemblage (bottom), transitioning into a turbidite wedge (top). This evolution was controlled by tectonics in a piggy-back basin by means of three main mechanisms: first, a flexural tectonic event created the basin; later on, blind-fault-propagation folds deformed it progressively from south to north; finally a tectonic event destroyed the basin. To cite this article: M. Martin-Martin, A. Martin-Algarra, C. R. Geoscience 334 (2002) 363–370.

Preliminary palaeomagnetic results on Oligocene–early Miocene mafic dykes from southern Spain

A preliminary palaeomagnetic study has been carried out on Oligocene–early Miocene mafic dykes intruding the Maláguide and Alpujárride complexes of the Internal Betic Zone (southern Spain). The aims of the study were to ascertain if relative perpendicular orientations (NE–SW and NW–SE) shown by different dyke families are of primary or secondary origin and to find out if palaeomagnetic rotations can be detected in that area. Ten sites with dykes showing both orientations were sampled. In addition to palaeomagnetic analysis, susceptibility-versus-temperature curves of several representative samples were measured and ore microscopic studies were carried out.Palaeomagnetic behaviour of samples was characterised by low intensities of magnetisation and alterations occurring during the demagnetisation procedure, and often also by overlapping of palaeomagnetic components. Besides an initial viscous component, two different palaeomagnetic components, named M and H were recognised. Component M is carried by pyrrothite and magnetite, and seems to record a primary palaeomagnetic direction. Component H is difficult to isolate and seems to be related to the presence of magnetite and hematite.Nine of ten studied sites offer consistent palaeomagnetic results, although in two cases statistical parameters are relatively weak. Strong clockwise rotations (approximately 90–140°) are observed. These rotations are in accordance with other block rotations observed in the Internal and External Zones of the central and western Betics, although their magnitudes are much stronger. On the other hand, both dyke families show similar rotations, independently of their original direction. Thus, their relative perpendicular orientations seem to be of primary, intrusive origin.

Présence du complexe tectonique Malaguide à l'est de Carthagène (zone interne Bétique, Espagne)

Triassic materials belonging to the Malaguide Complex east of Cartagena are described for the first time. This is the easternmost Malaguide outcrop known and it overlies the Portman Alpujarride unit. Knowledge of this outcrop contributes to the palaeogeographic reconstruction of the Betic Internal Zone in an area where the Alpujarride Complex is considerably thinned due to stratigraphic and tectonic reasons.

A high electrical conductive zone at lower crustal depth beneath the Betic Chain (Spain)

Magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the Central Betic chain. Interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two-dimensional resistivity model along a NW–SE profile from the Guadalquivir foreland basin and across the boundary between the External and the Internal Betics. Elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected. The conductors in the upper crust coincide with the areal distribution of the Cenozoic and Mesozoic sedimentary rocks from the Guadalquivir basin and the External Betics and the conductors in the middle crust with the major Miocene extensional detachments affecting the basement rocks of the Internal Betic zone. A high conductivity zone at lower crustal levels beneath the outer Internal Betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective Moho. This conductor was interpreted as partial melting of a southeast dipping subducted Iberian lower crust. The geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the Alboran domain or to the Iberian plate. In the former case it would correspond to a major plate boundary and in the latter to an intraplate feature.

La estructura del área de Sierra Espuña (contacto zonas internas-externas, sector oriental de la Cordillera Bética)

Sierra Espuna is located in the Eastern Betic Cordillera. The contact between the Malaguide Complex (Internal Betic Zone) and the External Betic Zone cropouts in this area. Sierra Espuna area is a great antiformal stack that is followed by a great synforme (Mula-Pliego Depression). In the upper part of the Malaguide Complex, two nappes, with numerous internal folding and minor thrusting, are recognized: the Morron de Totana Nappe (at the bottom) and the Perona Nappe (at the top). This structure is the result of a complex polyphasic tectonics in which two main structural events are recognized: the Intraoligocene tectonic phase, and the Lower Miocene tectonic phase.

Palaeomagnetic results from Upper Miocene and Pliocene rocks from the Internal Zone of the eastern Betic Cordilleras (southern Spain)

Palaeomagnetic and rock-magnetic studies were carried out on samples from thirteen volcanic and nine sedimentary sites of Late Miocene to Pliocene age from the Internal Zone of the eastern Betic Cordilleras. After comparing palaeomagnetic results with the expected Pliocene/Miocene direction, rotated and unrotated areas can be recognized, rotations being clockwise and counter-clockwise. Some rotations are of great magnitude. Unlike deformation in the External Betics, Late Miocene to Present block rotations in the Internal Betic Zone are non-systematic, and related to the movement of faults as local responses to the Late Miocene-Present regional stress field, due to the N140 convergence of Africa and the Iberian Peninsula.

The role of extension in the Miocene denudation of the Nevado‐Filábride Complex, Betic Cordillera (SE Spain)

The Internal Zone of the Betic Cordillera, SE Spain, consists of a nappe stack of three complexes, the deepest of which is the Nevado‐Filábride Complex. The zone is separated from the overlying Alpujárride Complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite and zircon fission track results have been obtained from the Nevado‐Filábride Complex and these have been used to define regional cooling patterns for the complex. Rapid cooling (105°C–200°C Ma−1) is spatially related to the tectonic contact with the overlying Alpujárride Complex‐Cooling to near‐surface temperatures occurred first in the east (Sierra de los Filabres) during the mid‐Serravallian (12±1 Ma) and was completed by the early Tortonian (9–8 Ma) in the west (Sierra Nevada). There is no correlation between fission track age and sample elevation. These results are consistent with tectonic unroofing of this complex, a finding that favors extension as the mechanism by which the two complexes were brought into contact. Extension spans the middle and earliest upper Miocene (12–8 Ma) in the study area and therefore lasted much longer than previously documented. A hypothesis is advanced which links oblique convergence between the Iberian plate and the Betic Internal Zones, resulting in crustal contraction at depth, with orogen parallel extension in the middle and upper crust.

Palaeogeography of the late aquitanian-early Burdigalian basin in the western Betic Internal Zone

The discovery of new outcrops of transgressive sediments in the western Betic Internal Zone belonging to the UpperAquitanian-Lower Burdigalian (Blow's N.4?, N.5 and N.6 zones of planktonic foraminifera and CN-1C calcareous nannoplankton of Okada & Bukry) shows that the basin was very large and was not restricted to the frontal part of the Internal Zone. This basin was formed in a distensive environment where marine sediments rich in siliceous materials accumulated at a depth of several hundred metres. It was tectonically controlled by faults at present showing an approximately N90 direction, which delimited several subsiding areas, between which some reliefs emerged. Sedimentation was interrupted by the tectonic superposition of the Campo de Gibraltar Complex during the Early Burdigalian. The evolution of the basin took place in the context of the important events occurring at this time in the western Mediterranean, particularly the uppermost Aquitanian-Burdigalian distension and the westward displacement of the Betic-Rifian Internal zone.

Onshore Neogene stratigraphy in the North of the Alboran Sea (Betic Internal Zones): Paleogeographic implications

The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations.

Early-middle miocene stratigraphic turning points in the Alicante region (SE Spain): Reflections of Western Mediterranean plate-tectonic reorganizations

The paper concerns the Miocene deposits of the Alicante region (SE Spain) which forms part of the Prebetic and Intermediate units, representing the former southern passive margin of the Iberian continent. From the Late Jurassic up to the Miocene, the Alicante region was the scene of a facies distribution with more continental, lagoonal or shallow marine conditions in the north and northwest, and more open or deeper marine in the south and southeast. The Early-Middle Miocene deposits can be divided in three sedimentary cycles, each one controlled by a different tectonic regime: Cycle I (Aquitanian) is deposits after a block faulting phase at about 25 Ma, related to the formation of the Ligurian and Balearic troughs. Cycle II (Burdigalian-Early Langhian) is separated from first-cycle sediments by a complete reorientation of palaeogeography at 19,5 Ma, due to the collision of Iberia with Africa: the southern part of the region is folded and uplifted and separated from a northern emerged area by a trough. Cycle III (Late Langhian-Serravallian) is controlled by strike-slip movements caused by the continuing convergence between Africa and Europe and resulting in the development of a new set of basins at 15,5 Ma. At the Middle-Late Miocene boundary the Alicante region emerges; thus, younger, important tectonics could not be dated. Our results are in conflict with several recent plate tectonic models for the Miocene history of the Western Mediterranean where the Internal Betic Zone is placed juxtaposed to the Alicante region prior to the Burdigalian.

Geologic evolution of the westernmost part of the internal Betic zone (Betic Cordilleras, Southern Spain)

The Serrania de Ronda (western Betic Cordilleras, S-Spain) is formed by different tectonic units of the Betic internal domain. Stratigraphic correlations of the “Permo-Triassic” and Triassic sedimentary sequences imply that one part of the Mesozoic carbonates of the Rondaides (Dorsale betique), namely the Cabrilla unit (Dorsale interne), is shearedoff from the frontal part of the Malaguides, and another part (Nieves unit, Dorsale externe) forms the Mesozoic cover of the alpujarride Casares unit. The first alpine compressional phases took place in the Paleogene; post-metamorphic movements followed in the time between the Upper Aquitanian and the Upper Tortonian. From geometrical considerations it can be concluded that the Malaguides originated paleogeographically from a more internal region than the Alpujarrides.