El terratrèmol de l'11 de març del 2011 al Japó

El març passat un intens terratrèmol va sacsejar la costa oriental del Japó, produint un tsunami que va originar un nombre molt gran de víctimes i enormes danys materials. Vegem què va succei

The inverted Triassic rift of the Marrakech High Atlas : a reappraisal of basin geometries and faulting histories

The High Atlas of Morocco is an aborted rift developed during the Triassic-Jurassic and moderately inverted during the Cenozoic. The Marrakech High Atlas, with large exposures of basement and Triassic early syn-rift deposits, is ideal to investigate the geometries of the deepest parts of a rift, constituting a good analogue for pre-salt domains. It allows unraveling geometries and kinematics of the extensional and compressional structures and the influence that they exert over one another. A detailed structural study of the main Triassic basins and basin-margin faults of the Marrakech High Atlas shows that only a few rift faults were reactivated during the Cenozoic compressional stage in contrast to previous interpretations, and emphasizes that fault reactivation cannot be taken for granted in inverted rift systems. Preserved extensional features demonstrate a dominant dip-slip opening kinematics with strike-slip playing a minor role, at variance to models proposing a major strike-slip component along the main basin-bounding faults, including faults belonging to the Tizi n'Test fault zone. A new Middle Triassic paleogeographic reconstruction shows that the Marrakech High Atlas was a narrow and segmented orthogonal rift (sub-perpendicular to the main regional extension direction which was ~ NW-SE), in contrast to the central and eastern segments of the Atlas rift which developed obliquely. This difference in orientation is attributed to the indented Ouzellarh Precambrian salient, part of the West African Craton, which deflected the general rift trend in the area evidencing the major role of inherited lithospheric anisotropies in rift direction and evolution. As for the Cenozoic inversion, total orogenic shortening is moderate (~ 16%) and appears accommodated by basement-involved large-scale folding, and by newly formed shortcut and by-pass thrusting, with rare left-lateral strike-slip indicators. Triassic faults commonly acted as buttresses

Structural and facies architecture of a diapir-related carbonate minibasin (lower and middle Jurassic, High Atlas, Morocco)

We report the structural geometry and facies architecture of a small diapir-related carbonate-dominated basin from the Jurassic rift of the Moroccan High Atlas. The Azag minibasin is a lozenge-shaped depocenter completely enclosed by tectonic boundaries that we interpret as welds after former salt anticlines or salt walls. The exposed ca. 3000 m-thick infill of the Azag minibasin is asymmetric; layers are tilted to the W defining a rollover geometry. Areally-restricted sedimentary discontinuities and wedges of growth strata near the basin margins indicate sedimentation contemporaneous with diapiric rise of a Triassic ductile layer. Facies evolution through the basin reflects local accommodation by salt withdrawal and regional events in the High Atlas rift. The early basin infill in the Sinemurian and Pliensbachian shows thickness variations indicative of low-amplitude halokinetic movements, with reduced exposed thicknesses compared to surrounding areas. The exposed Toarcian and Aalenian deposits are also reduced in thickness compared to areas outside the basin. Subsidence increased dramatically in the Bajocian-early Bathonian (?), the main phase of downbuilding, when over 2600 m of carbonates and shales accumulated at a rate > 0.5 mm/a in the depocentral area of the minibasin governed by W-directed salt expulsion. The stratigraphic units distinguished often show maximum thicknesses and deeper facies in the depocentral area, and rapidly change to shallower facies at the basin margins. The Bajocian carbonate facies assemblage of the minibasin include: reservoir facies as microbialite-coral reefs in the basin margins (formed during periods of strong diapir inflation and bathymetric relief), basin-expansive oolite bars (formed during episodes of subdued relief), and organic-rich, dark lime mudstones and shales that show source-rock characteristics. The Azag basin is a good analog for the exploration of salt-related carbonate plays in rifts and continental margins where source-rock and reservoir can form in a same minibasin

Creació de recursos digitals per a la innovació docent en geologia estructural i tectònica

Aquest projecte consisteix en l'elaboració d'una sèrie de recursos didàctics en format digital per a l'ensenyament de les matèries de Geologia Estructural i de Tectònica en titulacions relacionades amb les Ciències de la Terra. L'objectiu és la millora de la formació i del rendiment dels estudiants mitjançant l'elaboració d'activitats de suport no presencials que fomentin l'autoaprenentatge i l'autoregulació per part de l'estudiant. Les activitats intenten aprofitar les noves eines informàtiques disponibles i fomentar-ne l'accés mitjançant la xarxa. El material que s'elabora en el marc del projecte consisteix en: 1) un fons documental d'imatges relacionades amb la Geologia Estructural i la Tectònica amb explicació, disponibles en xarxa i accessibles mitjançant motors específics de cerca, 2) un conjunt d'exercicis i casos pràctics, alguns dels quals resolts, i 3) sortides de camp virtuals a una regió geològica que permeten proposar activitats prèvies a una pràctica presencial de camp o desenvolupar la pràctica de manera completament autònoma.Este proyecto consiste en la elaboración de una serie de recursos didácticos en formato digital para la enseñanza de las materias de Geología Estructural y Tectónica en titulaciones relacionadas con las Ciencias de la Tierra. El objetivo es la mejora de la formación y del rendimiento de los estudiantes mediante la elaboración de actividades de apoyo no presenciales que fomenten el autoaprendizaje y la autorregulación por parte del estudiante. Las actividades intentan aprovechar las nuevas herramientas informáticas disponibles y fomentar el acceso mediante la red. El material que se elabora en el marco del proyecto consiste en: 1) un fondo documental de imágenes relacionadas con la Geología Estructural y la Tectónica con explicación, disponibles en red y accesibles mediante motores específicos de búsqueda, 2) un conjunto de ejercicios y casos prácticos, algunos de ellos resueltos, y 3) salidas de campo virtuales de una región geológica que permiten proponer actividades previas a una práctica presencial de campo o desarrollar la práctica de forma completamente autónoma.This project consisted of developing a series of teaching resources in digital format to teach the subjects of Structural Geology and Tectonics in degree programmes related to the Earth Sciences. The goal was to improve students' training and performance by developing out-of-classroom support activities that foster independent learning and self-regulation on the part of the students. The activities aim to take advantage of the new IT tools available and to foster their access via the Web. The material that was developed in this project consisted of: 1) a documentary collection of images related to Structural Geology and Tectonics with explanations, available on the Web and accessible from specific search engines, 2) a series of exercises and practical case studies, some of them already solved, and 3) virtual field trips to a geological region that enabled us to propose activities prior to a visit to the field or to develop the practice totally independently

De la tectónica de placas a la cordillera del Atlas : qué estudia un geólogo para interpretar las cadenas de montañas

Conferència pronunciada a la sala d'actes de les Fac. Biociències i Ciències amb motiu de la celebració de Sant Albert Magne, UAB, 201

Geodinámica de las cordilleras del Alto y Medio Atlas : síntesis de los conocimientos actuales

Se presenta una síntesis geodinámica de las cadenas de intraplaca del Alto y Medio Atlas de Marruecos. Estas cadenas derivan de la inversión tectónica de cuencas extensionales Jurásicas, con un acortamiento orogénico modesto (máximo del 24% en el Alto Atlas y del 10% en el Medio Atlas) heterogéneamente distribuido en el tiempo y en el espacio. Las relaciones entre tectónica y sedimentación en el margen sur del Alto Atlas indican que la deformación compresiva tuvo lugar entre el Eoceno medio y el Cuaternario. Consecuentemente con los valores de acortamiento, el espesor de la corteza detectado por gravimetría no supera los 40 km. A pesar de ello, la topografía de las cadenas del Atlas es elevada, y el modelado de campos potenciales sugiere que está causada por un marcado adelgazamiento litosférico, independiente de la tectónica compresiva regional. Un abundante magmatismo alcalino indica que el adelgazamiento litosférico coexistió con el acortamiento en los últimos 15 Ma, aunque los indicadores geomorfológicos sugieren que la mayor parte del levantamiento de origen mantélico es relativamente reciente (últimos 5 Ma). La termocronología indica que la cantidad de erosión es generalmente pequeña en el Atlas, registrándose de manera notable solo en los últimos 20-25 Ma

3D variation of shortened salt walls from the Moroccan Atlas : Influence of salt inclusions and suprasalt sedimentary wedges

Altres ajuts: acords transformatius de la UABWe present a field study of salt ridges and minibasins of the Moroccan High Atlas near Rich that shows the along- and across-strike variability of such structures. Salt walls evolved from halokinesis during Jurassic rifting, to shortening during Cenozoic orogeny. Salt wall segments exhibit variable degrees of welding due primarily to the local presence of intrasalt inclusions (basalt and gabbro) rather than orientation with respect to the shortening or position along the ridge. Flanking Jurassic minibasins may be upright and symmetric or tilted; tilting may have started during halokinesis but was largely acquired during shortening. Minibasins tilt away from welded diapiric segments towards inclusion-rich segments, indicating differential diapir rise. The structure of the central parts of the salt walls differs from the lateral terminations. While the central parts are relatively simple with aperture or welding governed by the inclusions, many salt walls end buried by suprasalt sedimentary wedges. These perched wedges were not arched upward during diapir squeezing but were unexpectedly folded into synclines. The folding was formed by the flanking minibasin tilting in one limb and by inhomogeneous diapir rise and lateral salt escape in the other, thus defining a new modality of roof and shoulder folding above salt diapirs

Structural control on present-day topography of a basement massif: the Central and Eastern Anti-Atlas (Morocco)

The Anti-Atlas basement massif extends South of the High Atlas, and, despite a very mild Cenozoic deformation, its altitude exceeds 1500m in large areas, reaching 3305m in Jbel Sirwa. Structural contours of the present elevation of a polygenic planation surface (the High Erosional surface) and of the base of Cretaceous and Neogene inliers have been performed to characterize the major tectonic structures. Gentle Cenozoic WSW-ENE- and N-Strending folds, of 60 to100km wavelength, reactivate Variscan structures, being the major contributors to the local topography of the Anti-Atlas. Reactivated thrusts of decakilometric to kilometric-scale and E-W trend involving the Neogene rocks exhibit a steep attitude and a small displacement, but they also produce a marked topographic expression. The resulting Cenozoic horizontal shortening along N-S sections across the Anti-Atlas is about 1%. The position of the major anticlinal hinges determines the location of the fluvial divides of the Warzazat basin and the Anti-Atlas, and a structural depression on one of these hinges (Jbel Saghro anticline) allowed the formerly endorheic Warzazat basin to drain southwards. The first Cenozoic structures generating local topography are of pre-mid Miocene age (postdated by 6.7Ma volcanic rocks at the Jbel Saghro), whereas the youngest thrust movements postdate the Pliocene sedimentary and volcanic rocks (involving 2.1Ma volcanic rocks at Jbel Sirwa). In addition to these features, the mean elevation of the Anti-Atlas at the regional scale is also the result of a mantle thermal anomaly reported in previous works for the entire Atlas system