Evidence for the activity and paleoseismicity of the Padul fault (Betic Cordillera, southern Spain)

There is evidence of recent tectonic activity in the proximity of Padul, in the central sector of the Betic Cordillera. The principal active fault in this region is the Padul normal fault, running NW-SE, which displays spectacular geomorphological and structural features owing to its recent activity. However, there is no evidence of earthquakes of moderate-high magnitude occurring in this area during the historical or the instrumental period. In the vicinity of Padul we identified various soft-sediment deformation structures produced by liquefaction which we attributed to seismic shocks of a moderate-high magnitude. These structures are situated in detritic sediments, intercalated with layers of peat, which have enabled dating of these paleoearthquakes to the late Pleistocene (approx. 30,000 to 35,000 yr BP). Moreover, field observations in sediments of alluvial fans in the vicinity of the Padul fault, together with a retrodeformation analysis of an outcrop, enabled various deformation events to be dated to the recent Quaternary period.En el área de Padul, localizada en el sector central de la Cordillera Bética, existen numerosas evidencias de actividad tectónica reciente. La principal falla activa de la región es la falla normal de Padul, de dirección NW-SE, que presenta evidencias geomorfológicas y estructurales espectaculares de su actividad reciente. Sin embargo, no se tiene constancia de la ocurrencia de terremotos de magnitud moderada-alta en el área de Padul ni durante el periodo histórico ni el instrumental. En este sector hemos identificado varias estructuras sedimentarias de deformación producidas por licuefacción que interpretamos como resultado de sacudidas sísmicas de magnitud moderada-alta. Estas estructuras se localizan en sedimentos detríticos intercalados con niveles de turba que han permitido datar estos paleoterremotos como Pleistoceno superior (aproximadamente entre 30.000 y 35.000 años B.P.). Por otra parte, las observaciones de campo realizadas en algunos sedimentos de los abanicos aluviales de la zona de falla de Padul y el análisis de retrodeformación en un afloramiento han permitido identificar varios eventos de deformación durante el Cuaternario reciente

Evidence for the activity and paleoseismicity of the Padul fault (Betic Cordillera, southern Spain)

There is evidence of recent tectonic activity in the proximity of Padul, in the central sector of the Betic Cordillera. The principal active fault in this region is the Padul normal fault, running NW-SE, which displays spectacular geomorphological and structural features owing to its recent activity. However, there is no evidence of earthquakes of moderate-high magnitude occurring in this area during the historical or the instrumental period. In the vicinity of Padul we identified various soft-sediment deformation structures produced by liquefaction which we attributed to seismic shocks of a moderate-high magnitude. These structures are situated in detritic sediments, intercalated with layers of peat, which have enabled dating of these paleoearthquakes to the late Pleistocene (approx. 30,000 to 35,000 yr BP). Moreover, field observations in sediments of alluvial fans in the vicinity of the Padul fault, together with a retrodeformation analysis of an outcrop, enabled various deformation events to be dated to the recent Quaternary period

Reply to the comment by Michard et al. on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : The Tanger-Ketama Unit (External Rif, northern Morocco) by Vázquez et al., Geologica Acta 11 (2013), 277-293"

Michard et al. (this issue) commented on certain aspects of the Alpine metamorphism and structural evolution of the Rif belt (Morocco) that were briefly noted in Vázquez et al. (2013). In particular, they criticize our interpretation of an extensional setting during the main metamorphic recrystallization of the Tanger-Ketama Unit that we considered related to slaty cleavage (S1) parallel to the lithological layering generated during the Cretaceous. Michard et al. (this issue) interpret the S1 syn-metamorphic foliation as being related to compressional folds, and the peak metamorphism temperatures, in the Lower Cretaceous sediments, as ranging between 200-300°C. Therefore, they conclude that recrystallization of the Ketama Unit occurred during Miocene thrust nappe tectonics. We explain our view in the following sections

Reply to the comment by Michard et al. on “Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: the Tanger-Ketama Unit (External Rif, Northern Morocco) by Vázquez et al., GeologicaActa 11 (2013)...

Non

Regional assessment of seismically induced slope instabilities in the Lorca Basin (Murcia): Implementation of Newmark’s method in a GIS

La Cuenca de Lorca (Murcia, SE España) constituye un territorio de gran interés para estudios de sismicidad y fenómenos inducidos ya que en ella se registra una elevada actividad sísmica, se localizan algunas de las fallas activas con mayor potencial sísmico de España y existen casos reconocidos de desprendimientos asociados a terremotos (e.g., Mula 1999, Bullas 2002, La Paca 2005). En esta área, se ha desarrollado una aplicación a escala regional del método del “bloque rígido deslizante” de Newmark en un sistema de información geográfica (SIG). Además, en este trabajo hemos propuesto una modificación del método de Newmark para tener en cuenta los efectos de amplificación sísmica relacionados con el suelo y con la topografía. Posteriormente, se han generado los mapas de desplazamiento de Newmark considerando tanto escenarios sísmicos deterministas como probabilistas para la Cuenca de Lorca. El cálculo del factor de seguridad estático para cada píxel del área de estudio ha permitido obtener un mapa de aceleración crítica (ac), el cual representa la susceptibilidad de las laderas a inestabilidades inducidas sísmicamente. Los mapas de desplazamiento de Newmark obtenidos permiten identificar las áreas con mayor peligrosidad así como zonas de interés para posteriores estudios de detalle. Los resultados predicen la mayoría de las inestabilidades observadas en trabajos previos (principalmente, desprendimientos) y los desprendimientos asociados a terremotos concretos con valores de desplazamiento de Newmark menores de 2 cm. Inestabilidades de mayor entidad y deslizamientos ocurrirían con desplazamientos de Newmark mayores de 2 cm para lo que se requeriría un terremoto de gran magnitud (Mw=6.7-6.8).The Lorca Basin (Murcia, SE Spain) exhibits a high seismic activity because some of the most active faults in Spain have been identified in the surroundings of this basin and there are well known cases of rock-falls associated to specific earthquakes (e.g., Mula 1999, Bullas 2002, La Paca 2005). In this area, we have used a geographic information system (GIS) to develop an implementation for the Newmark’s sliding rigid block method at a regional scale. In addition, we have particularly proposed a new small variation of Newmark’s method to consider soil and topographic amplification effects. Subsequently, we produce “Newmark displacement” maps for both deterministic and probabilistic seismic scenarios in the Lorca Basin. The estimation of static safety factor for each pixel of study area has allowed obtaining the critical acceleration (ac) map that represents seismically induced slope instability susceptibility. The obtained Newmark displacement maps allowed us to identify areas with the highest potential seismic hazard as well as interesting areas for future particular studies. The results predict the majority of identified instabilities in previous studies (mainly, rock-falls) and rock-falls associated with specific earthquakes with values of Newmark displacement lower than 2 cm. Larger instabilities and landslides occur with Newmark displacement higher than 2 cm assuming that a great earthquake (Mw=6.7-6.8) take place.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEAndalucia. Juntapu

High-P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

The transition between antigorite-serpentinite and chlorite-harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite-metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the antigorite-serpentinite domain and has three generations of garnet. Grossular-rich Grt-1 formed during rodingitization at the seafloor (10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO ~HM buffer) released by brucite breakdown in the host antigorite-serpentinite. Type 2 Epidote-metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite-harzburgite. Type 2 formed by increasing μSiO (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high-P antigorite breakdown in serpentinite. The growth of Grt-4, with low-grandite and high-pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite-metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite-harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite-rich garnet (Grt-5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe/Fe ratios of antigorite-serpentinite and chlorite-harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle.“Ministerio de Economía, Industria y Competitividad” (MINECO), Grant/Award Number: CGL2012-32067, CGL201675224-R; Junta de Andalucía, Grant/ Award Number: RNM-145, P12-RNM3141; Ramón y Cajal, Grant/Award Number: RYC-2012-11314; MINECO, Grant/Award Number: CGL2016-81085-R, PCIN-2015-05

EXCAVACIONES EN DÓLMENES DE ÍLLORA (GRANADA)

El grupo de sepulturas que aquí presentamos fueron localizadas por don Manuel Argüelles, vecino de Íllora y asiduo colaborador del Museo Arqueológico de Granada, entre 1980 y 1983. En 1982 una de las estructuras localizadas cerca de Puerto Lope fue destruida al poner en cultivo nuevas tierras; ante ello el Museo Arqueológico de Granada, decidió crear un plan de documentación de todas las estructuras inéditas, para ir excavándolas sistemáticamente, habiendo sido excavadas una en el verano de 1982 y otras en marzo de 1983.El municipio de Íllora se encuentra enclavado en la región natural de Los Montes. Todas las sepulturas se sitúan en una estrecha zona entre las Sierras de Parapanda y Pelada al W y NW y la Sierra de Madrid y Cerros de las Coronas al E. Es por tanto una zona muy montañosa, en oposición marginal con respecto a los pasillos que unen la Vega de Granada con el Alto Guadalquivir, uno de los cuales es el sistema formado por los ríos Frailes-Velillos, situado al este de la Sierra de Madrid. Toda la zona tiene una altitud mínima de 800 m., situándose las necrópolis entre los 900 y 1.200 m

Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : the Tanger- Ketama Unit (External Rif, northern Morocco)

The distribution pattern of diagenetic conditions to very low-grade metamorphism in the eastern Rif has been determined based on a study of clay-mineral assemblages and illite crystallinity of Mesozoic metapelites. Low-grade conditions were reached in marbles and also in the Beni-Malek serpentinites, as suggested by the mineral assemblages present in the marbles and antigorite growth in serpentinites. Previous thermochronological data are based on i) 40Ar/39Ar in amphiboles from greenschists, ii) K/Ar in white micas from metasandstones, and iii) fission tracks in apatites and zircons from metasandstones. These data indicate a Late Cretaceous age (∼80 Ma) for the very low- to low-grade metamorphism. We propose an evolutionary model for the Tanger-Ketama Unit consisting of a Lower Cretaceous sequence deposited in half-graben basins over an exhumed serpentinized mantle in a setting similar to the West Galician non-volcanic margin. The sediments underwent diagenesis to very low-grade metamorphism under relatively high heat flow in this extensional setting. Miocene contractional deformation of the Tanger-Ketama Unit resulted in a penetrative crenulation cleavage associated to asymmetric inclined folds. This crenulation developed, mostly by solution-transfer processes, without significant mineral growth. Miocene metamorphism reset the apatite fission-tracks, but metamorphic conditions were not high enough to reset either the K/Ar ages or the zircon fission track

EL YACIMIENTO PREIBÉRICO DEL CERRO DEL CENTINELA

Don Rafael Utrilla, vecino de Domingo Pérez, y descubridor de un tesorillo de monedas árabes adquirido recientemente por el Estado, localizó mientras araba en una zona próxima al lugar del primer hallazgo, una sepultura, de la que dio cuenta al Museo Arqueológico de Granada el 15 de marzo de 1983.Dos días después, se realizó una visita de prospección, comprobándose la existencia de una sepultura de inhumación, así como la documentación, en las proximidades, de varias manchas de ceniza, que habían sido puestas al descubierto también por el arado, y en las que se recogieron algunos fragmentos de cerámica a torno y a mano. Dado que el propietario de las tierras necesitaba continuar con las labores agrícolas, se procedió a realizar una excavación de urgencia, limpiando la sepultura y excavando dos de las manchas de ceniza. Dicha excavación se realizó entre el 18 de marzo y el 6 de abril de 1983.La sepultura, de la que no vamos a ocuparnos ahora aquí, puede fecharse globalmente en época medieval. Las manchas de tierra quemada y cenizas son fondos de cabaña de época protohistórica

Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta