Palomares Fault Zone Research Articles

Gravimetric survey and modelling of a tectonic indenter boundary: The Palomares Fault Zone (Betic Cordillera, Iberia)

New gravimetric data are improving our understanding of the Palomares Fault Zone (PFZ) that accommodates the Águilas Arc tectonic indentation (eastern Betic Cordillera, SE Iberia) in the context of the Eurasia-Africa convergence. The PFZ limits the sedimentary infill geometry of the Vera and Pulpí Basins, and the western Guadalentín Corridor, which are located along the western boundary of the arc. Gravity anomaly models are in agreement with previous tectonic interpretations that suggest that the PFZ fragments and bends the depocenters of those basins, as it has been proposed for the antiforms (ranges) that are located eastwards. Furthermore, the gravity anomaly models show that the PFZ extends from the Cabrera Range to the Almagrera Range and ends in the north at the Pulpí Basin, where the basin infill is only deformed by a gentle symmetrical synform. As a consequence, the PFZ is (i) confined to the southern zone, where the deformation is most intense due to the displacement of the tectonic indenter, and (ii) disconnected from the front of the Águilas Arc and the Alhama de Murcia Fault (part of the Eastern Betic Shear Zone, EBSZ). The new extend of the PFZ we have documented supposes the structural segmentation of the EBSZ and reduces both seismotectonic and structural significances of the PFZ. The study of the PFZ shows that the boundaries of the indenter are the locus for diffused deformation accommodated by local-scale faulting along with structural rotations and deflections, rather than localized strike-slip faulting along the whole indenter margin.

Shearing in an Indenter Boundary: The Case of the Palomares Fault Zone (Betic Cordillera, Iberia)

Shearing in an Indenter Boundary: The Case of the Palomares Fault Zone (Betic Cordillera, Iberia)

Shearing in an Indenter Boundary: The Case of the Palomares Fault Zone (Betic Cordillera, Iberia)

Shearing in an Indenter Boundary: The Case of the Palomares Fault Zone (Betic Cordillera, Iberia)

Analysis of faulted fan surfaces and paleosols in the Palomares Fault Zone (Betic Cordillera, SE Spain): Paleoclimatic and paleoseismic implications

This study presents a multidisciplinary approach to the tectonic geomorphology and history of the Palomares strike-slip fault in the Eastern Betic Cordillera (SE Spain). Analysis combines geomorphological mapping of fan-surfaces, pedological studies of faulted sedimentary successions, geoelectrical prospection and typical paleoseismological routines of structural analyses. Combined application of these methods together with the existing geochronological databases offer probable paleoclimatic and paleoseismic scenarios for the zone from Middle Pleistocene to Holocene. This study segments the Palomares Fault (PLF) in three overlapping “en echelon” N–S trends (PLF1, PLF2, PLF3). The older PLF1 controls the main faulted Almenara-Almagro range fronts. The younger PLF2 cuts and beheads crusted fan surfaces in the Aljibejo zone (ABJ). The intermediate PLF3 controls the development of intervening tectonic reliefs and offset paleosol sequences in alluvial-colluvial deposits. Our analysis focuses on the PLF3 at the La Escarihuela site (ESCH), where outcrops display eight faulted paleosols developed on overlapped Middle Pleistocene colluvial-alluvial deposits, with variable vertical slip of between 21 and 12 cm (bulk accumulated offset: 33 cm), evidence of two surface faulting events. After the structural analysis of the fault planes (striae plunges) net left-lateral displacements of 120.9 ± 3.3 cm (Event 1) to 69.1 ± 5.2 cm (Event 2), associated with maximum magnitudes of c. 6.7–6.5 Mw. However, the faulted sequence is sealed by a thick mature calcrete horizon of similar characteristics to that faulted at the ABJ1 site. Regional chronological data on calcic soils and calcretes in SE Spain assign this mature calcrete to Oxygen isotopic stages (OIS) 9 (c. 300 ka). With this age fixed at the uppermost of the faulted paleosol sequence at the ESCH site (PLF3), soil development features (clay and carbonate contents, thickness, reddishness, etc.) were used as paleoclimatic proxies to correlate soil horizons with conventional OIS. Correlation indicates that clayey Bt soil horizons primarily occurred during warm isotopic stages followed by recalcification and carbonate accumulation (Btk; Bk; Ck horizons) during latter warmer stages. A proposed theoretical geochronological framework suggests that the sedimentary sequence at the ESCH site (PLF3) was deposited between OIS 18 and 9. Major environmental change towards the present semi-arid climate occurred during OIS 13 (c. 500 ka). During this same stage, paleoseismic event 1 also occurred, but paleoseismic event 2 took probably place during OIS 10 (c. 350 ka), before development of the uppermost calcrete sealing the deformation in this fault segment. However, this OIS 9 calcrete is faulted in the ABJ1 and a younger less developed calcrete is faulted in ABJ2 on the PLF2 segment. Chronology proposed in this paper suggests theoretical ages for these events of between OIS 8-OIS 5 for ABJ1 (c. 200 ka) and between OIS 4 -OIS 2 for ABJ2 (c. 40 ka). This last paleoseismic event triggered major landscape changes with still-visible fault scarps, linear tectonic reliefs, alluvial fan beheading and active drainage shuttering. This present work illustrates the use of soil/paleosol analyses in paleoseismology as a useful tool to build paleoclimatic analogues and develop relative chronological frameworks from existing regional age data.

Mountain front migration and drainage captures related to fault segment linkage and growth: The Polopos transpressive fault zone (southeastern Betics, SE Spain)

The Polopos E–W- to ESE–WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE–SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene.

Recent and active faults and folds in the central-eastern Internal Zones of the Betic Cordillera

The most recent tectonic structures of the central-eastern Internal Zones of the Betic Cordillera (from 3.1ºW to 1.7ºW and to the south of 37.525ºN) include fault and folds developed from the Late Miocene onwards, which are related to N-S/NW-SE directed continental collision and moderate thickening of a crust that is relatively hot at depth. In this setting, E-W to WSW-ENE folds, with locally associated E-W transpressive right-lateral and reverse faults, favoured the emersion of the northern Alborán basin palaeomargin and the progressive intramontane basin disconnection. The NNE-SSW to NE-SW trending regional left-lateral Palomares and Carboneras fault zones are dominant structures in the easternmost part of the cordillera. In addition, NW-SE to WNWESE trending normal and oblique-slip normal faults are widespread. The collision is still active and continues to drive active folds and faults, some probably being the likely source of moderate-sized earthquakes. The Campo de Dalías and surrounding sectors, deformed by active ENE-WSW folds and NW-SE to WNW-ESE oblique-slip normal faults, are probably the sites with the largest concentration of significant earthquakes during recent years. Moderate-magnitude earthquakes (Mw 5.0 to 6.5) have occurred there at fairly regular intervals, in 1804, 1910, and 1994. Toward the east, NW-SE trending normal faults extending from Almería to the Tabernas basin deform the Quaternary rocks with associated moderate seismicity (the 2002 Gergal Mw 4.7 earthquake, and possibly the 1894 Nacimiento earthquake, felt with intensity VII). In the Sorbas-Vera basin, the Palomares fault zone is also responsible for moderate-sized earthquakes (1518 Vera earthquake). In the Almanzora corridor, NW-SE to WNW-ESE trending Lúcar-Somontín faults also could be considered one of the possible source of moderate-magnitude seismicity (1932 Lúcar, Mw 4.8 earthquake felt with intensity VIII). Toward the east, between Albox and Partaloa, several small reverse faults and associated compressive structures deform Quaternary alluvial and fluvial sediments. Although some of these folds reveal a slow and progressive deformation from the Middle Pleistocene onwards, some of these reverse fault segments that deform the western Huércal-Overa basin could host the 1972 NW Partaloa, mbLg 4.8 earthquake, felt with intensity VII.

Geomorphic analysis of the Sierra Cabrera, an active pop-up in the constrictional domain of conjugate strike-slip faults: The Palomares and Polopos fault zones (eastern Betics, SE Spain)

The NNE–SSW sinistral Palomares and the conjugate dextral WNW–ESE striking Polopos fault zones terminate in the Sierra Cabrera antiform. In order to test the Quaternary activity and topographic relief control in the termination of these fault zones, here we present new qualitative and quantitative geomorphic analyses supported by a new structural map of the region. The main mountain fronts of the Cabrera antiform are formed by the North and South Cabrera reverse faults that merge laterally into the Palomares and Polopos faults, respectively. These faults produce knickpoints, stream deflections, complex basin hypsometric curves, high SLk anomalies and highly eroded basins in their proximity. Furthermore, the drainage network shows an S-shaped pattern reflecting progressive anticlockwise rotation related to the sinistral Palomares fault zone. The estimated uplift rates determined by the integration between mountain front sinuosity index and valley floor width to height ratio are larger than those obtained for strike-slip faults in the eastern Betics. These larger uplift rates with our geomorphic and structural dataset indicate that the topographic relief of the Sierra Cabrera antiform is controlled by reverse faults that form a pop-up structure in the constrictional domain between the larger Palomares–Polopos conjugate strike-slip faults. Existing GPS geodetic data suggest that the North and South Cabrera reverse faults probably accommodate a large part of Africa–Iberia convergence in the region.

Plio-Pleistocene drainage development in an inverted sedimentary basin: Vera basin, Betic Cordillera, SE Spain

The Vera basin is one of a series of interconnected Neogene–Quaternary sedimentary basins located within the Internal Zone of the Betic Cordillera (southeast Spain). Since the Pliocene the Vera basin has been subjected to low uplift rates (11–21 m Ma − 1 ) and inverted via compressive tectonics that are related to the ongoing oblique collision between the African and Iberian plates. Within this paper the sedimentary and geomorphic response to basin inversion is explored. Sedimentary processes and environments are established for key stratigraphic units of the Pliocene/Plio-Pleistocene basin fill and Pleistocene dissectional landscape. These data are subsequently utilised to reconstruct an evolving basin palaeogeography. Fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development. During the Early-Mid Pliocene the Vera basin was characterised by shallow marine shelf conditions (Cuevas Formation). A major palaeogeographic reorganisation occurred during the Mid-Late Pliocene. Strike-slip movement along the eastern basin margin, coupled with uplift and basin emergence created a protected, partially enclosed marine embayment that was conducive for Gilbert-type fan-delta sedimentation from fluvial inputs along the northern and eastern basin margins (Espíritu Santo Formation). The Vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the Late Pliocene to Early Pleistocene. Alluvial fans developed along the northern and western basin margins, grading to a bajada and terminating in a playa lake in central basin areas (Salmerón Formation). During the Early-Mid Pleistocene a switch from basin infilling to dissection took place, recorded by alluvial fan incision, a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography. Fluvial incision, headwards erosion, expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms. Fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins. The relatively low Plio-Pleistocene uplift rate of the Vera basin (11–21 m Ma − 1 ) in comparison to adjacent basins (Sorbas: 80–160 m Ma − 1 ; Huercal–Overa: > 50 m Ma − 1 ) resulted in a switch from internal to external basin drainage. Ancestral forms of the principal drainage systems within the Vera basin: the Ríos Almanzora, Aguas and Antas, captured basins and mountain catchment areas to the north (Huercal–Overa basin), southwest (Sorbas basin) and west (Sierra de los Filabres range). The switch from basin infilling to fluvial dissection is coincident with a phase of Early-Mid Pleistocene compressional tectonics, expressed by extensional faulting. This deformation is probably linked to accelerated strike-slip movement along the Palomares Fault Zone. The faulting is superimposed onto the longer term pattern of Plio-Pleistocene uplift and basin inversion.

Influence of strike-slip fault segmentation on drainage evolution and topography. A case study: the Palomares Fault Zone (southeastern Betics, Spain)

The Palomares Fault Zone (PFZ) is one of the main sinistral strike-slip faults in the Betics (SE Spain), with approximately 16 km of north–south displacement. The PFZ initiated during the Tortonian–Messinian as a transfer structure linking areas subject to NW/SE shortening. During the Plio-Quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of Sierra Almagrera–Sierra Almenara. These Sierras, which show moderate uplift rates of 0.05–0.15 m/ka, formed in response to the oblique-slip regime of the PFZ. The drainage system in the vicinity of the PFZ is asymmetric with respect to a main axial valley that runs parallel to the PFZ on the downthrown fault block. In this block, the drainage density is lower and the streams are longer than in the uplifted block. Furthermore, west of the main axial valley the streams describe eastward directed deflections, indicating the progressive eastward migration of the main axial valley during the Pleistocene. The drainage system on the uplifted ranges shows a consequent pattern, indicating recent uplift and folding under NNW/SSE convergence. Recent activity along segments of the PFZ has increased topographical gradients, favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments.

Uppermost Tortonian to Quaternary depocentre migration related with segmentation of the strike-slip Palomares Fault Zone, Vera Basin (SE Spain)

The Palomares Fault Zone (PFZ) is one of the main strike-slip brittle shear zones found in the Betics. It is segmented in several faults that have been active between the Upper Tortonian and present day. Data from drill cores in the Palomares area have permitted us to define the geometry and location of sedimentary depocentres related with the PFZ. These data show an eastward displacement between the Upper Tortonian to Messinian and the Pliocene–Quaternary sedimentary depocentres, towards the presently active Arteal fault, which bounds the western mountain front of Sierra Almagrera, showing that deformation along this fault zone has migrated towards the east, from the Palomares segment, with its main activity during the Upper Tortonian and Messinian, towards the Arteal fault, active during the Pliocene and Quaternary. To cite this article: G. Booth-Rea et al.,

Deformation in Neogene sediments of the Sorbas and Vera Basins (SE Spain): constraints on simple-shear deformation and rigid body rotation along major strike-slip faults

Detailed structural analyses are presented of the Neogene Sorbas Basin adjacent to the E–W striking Gafarillos fault zone and the Vera Basin adjacent to the 020° striking Palomares fault zone in southeastern Spain. A stress regime with an E–W oriented subhorizontal maximum principal stress ( σ 1) existed in pre-Tortonian (>11.3 Ma) time. A strike-slip regime with NW–SE oriented compression during Tortonian and earliest Messinian time caused dextral displacement along the E–W trending Gafarillos fault of approximately 10 km. Structural analysis indicates that most displacement took place in the Early Tortonian. Deformational patterns within the adjacent pull-apart basin reflect a dextral simple shear-zone of at least 500 m width. Kinematical analysis of folds in the Sorbas Basin suggests, however, that rotational effects are largely caused by rigid-body rotation without much internal deformation. Sinistral strike-slip displacements occurred along the Palomares fault zone under the influence of the same stress-regime. An abrupt change in the orientation of the stress field to N–S directed compression in earliest Messinian time (6.5 Ma) caused the termination of displacements along the Gafarillos fault zone, whereas the 020° trending Palomares fault zone continued to accumulate sinistral strike-slip displacements of about 25 km. Volcanism occurred along splays of the fault zone. A wider shear-zone of a few kilometers width evolved, in which considerable anti-clockwise rotation of folds occurred. Kinematic analysis of these folds shows that these rotational effects are again dominantly rigid-body rotations. Assuming rotations are merely caused by simple-shear deformation overestimates the amounts of strain. A better way to deal with simple-shear deformation is to compare observed shortening caused by folding with the magnitude of rotation of fold-hinges.

Palaeostress analysis of the northern Nijar and southern Vera basins: constraints for the Neogene displacement history of major strike-slip faults in the Betic Cordilleras, SE Spain

This paper presents the results of a detailed structural analysis of the northern Nijar and southern Vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the Serrata, Gafarillos and Palomares strike-slip fault zones. These major fault zones control the Neogene deformation of the SE Internal Betic Cordilleras in Spain. Detailed stress analysis on Neogene sediments of the Vera and Nijar basins shows a strike-slip regime with NW–SE-oriented subhorizontal maximum principal stress ( σ 1) during Tortonian and earliest Messinian times. Under the influence of this stress field, dextral displacement along the N090E-trending Gafarillos fault zone resulted in deformation of the sediments of the southern Sorbas and northeastern Nijar basins. During the early Messinian a clock-wise rotation of the stress field occurred. Stress analysis in rocks with late–early Messinian up to Quaternary ages in the Nijar and Vera basins indicates a strike-slip regime with N–S-oriented subhorizontal maximum principal stress ( σ 1). Under the influence of this stress field the main activity along the N010E-striking Palomares strike-slip fault zone took place, resulting in deformation of the Neogene sediments of the southeastern Vera basin and culminating in a maximum sinistral displacement of more than 20 km. At the same time the stress field was not suitably oriented to exert a large shear component on the Gafarillos fault zone, which activity ended after the earliest Messinian. Fault and outcrop patterns of syntectonic Neogene sediments in the Vera basin show that displacement along the Palomares fault zone decreased at the end of the Middle Miocene although minor displacement phases may still have occurred during the Late Miocene and possibly even Pliocene. From the Middle Miocene onward, deformation in the Nijar basin was controlled by sinistral displacement along the N040E-trending Serrata strike-slip fault zone.

Neogene evolution of the Sorbas basin (SE Spain) determined by paleostress analysis

The Neogene subsidence history of the Sorbas basin, situated in the Internal Zone of the Betic Cordilleras of southeastern Spain, is strongly controlled by strike-slip deformation. The sedimentary sequence of the basin offers a good control on the timing of separate phases of fault activation. The southern border of the Sorbas basin is formed by a major east-west trending fault zone (the Gafarillos fault zone) which consists of intermixed slivers of pre-Neogene basement blocks and Neogene basin sediments. Fault patterns and paleostress analysis both indicate that major displacement along this fault zone was dextral with a N310E-oriented maximum principal stress axis. Strike-slip movement along the east-west-oriented faults ended during the earliest Messinian after a minimum of 6 Ma of activation. Paleostress analysis indicates a subsequent phase of strike-slip fault movement present in sites of up to Early Pliocene age. The maximum principal stress axis orientation is N350E for this phase. This deformation is synchronous with sinistral displacement along the Palomares fault zone situated directly to the east of the study area. Subsequently, our paleostress analysis indicates an extensional regime during the Late Pliocene to Quaternary. However, extensional tensors were calculated at a number of sites possibly representing local stress regimes coexisting with the main strike-slip deformation and Sorbas basin subsidence. Folding of Tortonian sediments points out that local compressional deformation took place as well during the Neogene basin history. Observed wide ranges for the ellipsoid shapes of the calculated tensors support the existence of lateral stress variations.