El descubridor de los fosfatos del Sáhara Occidental, el geólogo Manuel Alía Medina (1917-2012)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Factores litológico-geotécnicos en el peligro de movimientos cosismicos de ladera en El Salvador

Se estudia los factores geológicos y estructurales que han controlado la distribución de los movimientos de ladera disparados por los terremotos del enero y febrero 2001 en El Salvador

Kinematic models for the Variscan deformation in the Hiendelaencina shear zone (Ollo de Sapo Anticlinorium, Central Iberian Zone)

Los modelos utilizados hasta el momento para la caracterización cinemática de la zona de cizalla dúctil de Hiendelaencina, cuya actividad principal se desarrolló durante la segunda fase varisca que afectó al Anticlinorio del Ollo de Sapo (Zona Centrobérica, Macizo Ibérico), se basan en aproximaciones que no tienen en cuenta el carácter simultáneo de la actuación de las distintas componentes del flujo (cizalla simple, cizalla pura, cambio de volumen). En este trabajo se evalúa el ajuste de los datos de deformación interna y fábricas planolineares resultantes de la actuación de la dicha zona de cizalla a modelos que consideran flujos triclínicos. Como consecuencia, se han identificado dos sectores dentro de la estructura (A y B, estando el primero originariamente situado al noroeste del segundo) con características cinemáticas contrastadas. En ambos casos la componente de cizalla simple implicó desplazamiento del bloque de techo hacia el sureste (zona de cizalla sub-horizontal o suavemente buzante al NO). El sector A fue afectado simultáneamente por un acortamiento sub-vertical y un estiramiento de dirección E-O, mientras que el sector B registró un estiramiento sub-vertical y un acortamiento E-O. Estas diferencias responderían a un reparto heterogéneo de las componentes del flujo dentro de una estructura de tipo “restraining bend”.The kinematic models applied to evaluate the ductile shear zone of Hiendelaencina (second Variscan phase affecting the Ollo de Sapo Anticlinorium, Central Iberian Zone, Iberian Massif) are based on untenable assumptions about the non-simultaneous activity of the distinct acting flow components (simple shear, pure shear, volume change). In this work, the finite strain and plano-linear fabric data from the Hiendelaencina shear zone are tested against recent models considering triclinic flow histories. Two sectors (A to the NW, and B to the SE in the original arrangement of the sub-horizontal to gently NW-dipping shear zone) have been identified according to their contrasted kinematic characteristics. The simple shear component implies top-to-the-SE displacement for both sectors. The pure shear component includes sub-vertical shortening and E-W extrusion for sector A, and sub-vertical lengthening and E-W shortening at sector B. These differences are interpreted as due to heterogeneous flow partitioning within a general restraining bend structure.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)pu

Constraints from finite element modeling on the active tectonics of northern Central America and the Middle America Trench

We have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the Central American Volcanic Arc and the Chortis Block. We present synthetic focal mechanisms, maps of tectonic regime, and strain crosses to analyze the results. The models show that to achieve the observed state of stress on the volcanic arc, the arc must be modeled as a lithospheric weak zone. Also, the forces related to the eastward drift of the Caribbean plate must be higher than those related to the subduction of the Cocos plate. The coupling on the subduction interface must be low, with or without slip-partitioning due to the obliquity of the subduction at the trench. At Guatemala the western edge of the Chortis block is pinned against North America, even with low trench-normal forces, making the triple junction between the Cocos, North American, and Caribbean plates a zone of diffuse deformation. The extension in the western part of the Chortis block, from Guatemala to the Honduras depression, is explained by the geometry of the North American-Caribbean plate boundary and the direction of motion of the Caribbean plate with respect to North America. The direction of extension in the Chortis block is always E-W regardless of the magnitude of the applied forces, and the main part of the deformation is absorbed between the Ipala graben and the Honduras depression, both features being consistent with our models.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Educación y Cienciapu

Caracterización petrológica y geoquímica de las rocas ultramáficas del macizo de Herbeira, complejo de Cabo Ortegal (NO de España)

The uppermost unit in Cabo Ortegal complex is composed of ultramafic rocks that crop out in three massifs: Herbeira, Limo and Uzal. Herbeira massif shows two different areas separated by a NNE-SSW fault zone. The western area is formed by a layered complex of dunites and pyroxenites which lies on top of a basal harzburgite. Amphibole-bearing peridotites and hornblendites; with aluminous spinels (Cr#<0.4), are the main lithologies in the eastern area. Hornblende is invariably present in all types of ultramafic rocks in the Herbeira massif, but the eastern peridotites mostly contain more than 15% of amphibole. Almost all ultramafic units show light rare earth elements (LREE) enriched patterns, however the basal harzburgite shows LREE-depleted patterns with negative slope while the rocks from layered complex are LREE enriched. Both ultramafic rocks from Herbeiia present marked significant Nb and Zr negative anomalies. The mineral chemistry, the REE abundances, geological and petrological data for Herbeira suggest a open-system melting to explain the formation of ultramafic rocks. The appropriate geodynamic scenario is a mantle wedge above a supra-subduction zone where the influx of an exotic fluid/melt generated in the upper parts of the subducting slab produces melting and melt extraction in the overlying mantle wedge

Numerical modeling of the active lithospheric deformation in northern Central America, Chortís Block: Implications in the regional tectonics

Hemos desarrollado un modelo de elementos finitos de propiedades elásticas para estudiar el papel de las diferentes fuerzas tectónicas actuando en la parte noroccidental del Arco Volcánico Centroamericano y el Bloque de Chortís. Los modelos muestran que para obtener el estado de esfuerzos observado, el arco debe modelarse como una zona de debilidad litosférica, las fuerzas asociadas a la deriva relativa de la placa del Caribe deben ser superiores a las asociadas a la subducción de la placa de Cocos y el grado de acoplamiento en ésta debe ser bajo, con o sin partición del deslizamiento. El extremo occidental del Bloque de Chortís es pinzado contra la placa de Norteamérica, haciendo del punto triple entre las placas de Cocos, Caribe y Norteamérica una zona de deformación difusa. La extensión E-W en la parte occidental del Bloque de Chortís es explicada por la geometría del límite entre las placas de Norteamérica y Caribe y por la dirección de movimiento de la última. La mayor parte de la extensión en el bloqué es absorbida entre el graben de Ipala y la depresión de Honduras, siendo ambos rasgos coherentes con nuestros modelos.We have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the Central American Volcanic Arc and the Chortís Block. The models show that to achieve the observed state of stress on the volcanic arc, the arc must be modeled as a Lithospheric weak zone, the forces related to the eastward drift of the Caribbean plate must be higher than those related to the subduction of the Cocos plate and the coupling on the subduction interface must be low, with or without slip-partitioning due to the obliquity of the subduction. The western edge of the Chortís block is pinned against the North American plate, making the triple junction between the Cocos, North American, and Caribbean plates a zone of diffuse deformation. The E-W extension in the western part of the Chortís block is explained by the geometry of the North American-Caribbean plate boundary and the direction of motion of the Caribbean plate. The main part of the extension in the block is absorbed between the Ipala graben and the Honduras depression, both features being consistent with our models.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e Innovación (MICINN)Universidad Complutense de Madridpu

Aspectos tectónicos del estudio gravimétrico de la Cuenca de Málaga

This work shows the results o f a gravimetric survey carried out in the Malaga Basin (sited on the Internal Zone o f the Western Betic Chain, southern Spain). Three anomalies maps are exposed and interpreted, focusing on neotectonic aspects. In order to avoid the influence of peridotitic bodies which outcrop in the studied area, and the southward thinning of the crust, a regional anomaly map has been processed and subtracted to the Bouguer anomaly. So, a residual anomaly map has been reached, where neotectonic interpretation has been done. The main tectonic feature evidenced by gravimetric data is the Albornoque Fault. It represents the southern boundary o f the Malaga Basin with a noticeable vertical component, according to its high gradient. By other hand, the fold o f Sierra de Cartama is marked by a maximum axis. This axis continues westward giving a duplicated depocenter of the basin. It is interpreted as a reverse fault, related in depth with the folding o f Sierra de Cartama, and which affects the basement o f the basin. According with the current stress field in the zone (NNW-SSE), the proposed structures imply the existence o f a compressive neotectonic activity, where the Albornoque fault is interpreted as a high angle reverse fault o f a reverse faul