Perquè hi ha serralades dins les plaques tectòniques

L'aixecament de les serralades de muntanyes a l'interior de les plaques, lluny de les seves vores, és una de les assignatures pendents de la tectònica global. Investigadors del Departament de Geologia han mostrat com una conjunció singular de processos superficials i profunds han aixecat les serralades intracontinentals de l'Atlas del Marroc.La ampliación de las cordilleras montañosas al interior de las placas, lejos de su superficie, es una de las asignaturas pendientes en la tectónica global. Un equipo de investigadores del Departamento de Geología han demostrado como una conjunción singular de procesos superficiales y profundos han ampliado las cordilleras intracontinentales del Atlas de Marruecos

El relieve de los Pirineos

La evolución del relieve de los Pirineos es un buen ejemplo de la interacción entre procesos superficiales y profundos. La elevada topografía media de la cadena es fruto del acortamiento y engrosamiento cortical, hoy inactivo, que se produjo principalmente durante el Paleógeno. Aunque la topografía es antigua, el escarpado relieve local es moderno. La etapa paleógena culminó con la formación de superficies de erosión con bajo relieve, formadas ya desde su inicio a gran altitud, en relación con el aumento de nivel de base fluvial causado por la sedimentación continental en los piedemontes o antepaíses de la cadena. La formación de superficies en altitud comportó la preservación de la raíz cortical y de la topografía elevada a pesar del allanamiento. Los valles que caracterizan la red de drenaje actual y el relieve joven disectan profundamente los restos de la superficie de erosión, y se deben a cambios en la conexión de la red fluvial remota y, sobre todo, a los cambios climáticos del Plio-Cuaternario (ciclos glaciares).The landscape evolution in the Pyrenees is a good example of the interactions between surface and deep earth processes. The high topography is relatively old, resulting from crustal shortening and thickening during Palaeogene times, now inactive. However, the local relief is relatively young. The palaeogene stage produced a high-elevation, low-relief erosional surface in relation to the fluvial base level rise associated to the continental sedimentary aggradation in the forelands. This permitted the preservation of the Pyrenean crustal roots and the high topography, in spite of the lowering of the local relief. The incision of the present drainage network with high relief is due to changes in the connections of the distal fluvial network and the climate changes initiated during the Plio-Quaternary (i.e., the glacial cycles)

Influència de la sal en el desenvolupament tectònic de la Cordillera Oriental dels Andes de Colòmbia

La presència de capes de sal en conques sedimentàries no sempre és fàcil d'observar a causa de processos geològics posteriors com ara la compressió. Un estudi recent ha trobat evidències d'antigues estructures salines a la regió de Guaitiquía, al front d'encavalcament de la Cordillera Oriental dels Andes de Colòmbia, que no havien estat mai detectades fins ara. Aquests resultats obren nous conceptes d'exploració rellevants per a altres sectors dels Andes i en general per als sistemes d'encavalcaments productius d'hidrocarburs arreu del món.La presencia de capas de sal en cuencas sedimentarias no siempre es fácil de observar debido a procesos geológicos posteriores como la compresión. Un estudio reciente ha hallado evidencias de antiguas estructuras salinas en la región de Guaitiquía, en el frente de cabalgamiento de la Cordillera Oriental de los Andes de Colombia, que no habían sido detectadas hasta ahora. Estos resultados abren nuevos conceptos de exploración que tienen relevancia para otros sectores de los Andes y en general para los sistemas de cabalgamientos productivos de hidrocarburos en el mundo

Experiment sísmic a l'Atlas : finalitza la primera fase de la recerca

Coordinats per la UAB i el CSIC, 70 investigadors han participat durant el mes de maig en el projecte SIMA, registrant el perfil sísmic de la serralada de l'Atlas al llarg de 700 kilòmetres. L'experiment, un dels més importants de Ciències de la Terra que s'ha realitzat a Àfrica, forma part d'una recerca que té com a objectiu l'estudi de l'estructura profunda de l'escorça terrestre i del mantell superior en el nord-oest de la placa africana.Coordinados por la UAB y el CSIC, 70 investigadores han participado durante el mes de mayo en el proyecto SIMA, registrando el perfil sísmico de la cordillera del Atlas a lo largo de 700 kilómetros. El experimento, uno de los más importantes de Ciencias de la Tierra que se ha realizado en África, forma parte de una investigación que tiene como objetivo el estudio de la estructura profunda de la corteza terrestre y del manto superior en el noroeste de la placa africana

Influence of salt in the tectonic development of the frontal thrust belt of the eastern Cordillera (Guatiquía area, Colombian Andes)

Geological maps, seismic lines and data from a dry exploration well are used to develop a new structural model for a segment of the eastern foothills of the Eastern Cordillera of Colombia, emphasizing the role of salt tectonics. Milestones in the deformation history of the Guatiquía foothills are illustrated by sequential section restoration to selected steps. Uncommon structural geometries and sparse salt occurrences are interpreted in terms of a kinematic evolution in which Cretaceous salt migration in extension produced a diapiric salt wall, which was subsequently welded during the main episodes of the Andean compression, when the salt wall was squeezed generating a large overturned flap. Salt-weld strain hardening resulted in break-through thrusting across the overturned flap in late deformation stages. This research puts forward a pattern of salt tectonics previously unrecognized in the foothills thrust belt, which may be significant in other parts of the external Colombian Andes

Magnitude of rift-related burial and orogenic contraction in the Marrakech High Atlas revealed by zircon (U-Th)/He thermochronology and thermal modelling

The Atlas of Morocco is a continental rift developed during the Triassic-Jurassic and moderately inverted during the Cenozoic. The High Atlas south of Marrakech, with exposures of basement and Triassic early synrift deposits, has been viewed as a high during the Mesozoic rifting. First zircon (U-Th)/He ages and thermal models obtained from 42 samples in the Marrakech High Atlas following two NNW-SSE transects across the mountain belt reveal that in contrast to previous models, the Triassic-Jurassic rift was well developed in the Marrakech High Atlas (with more than 4.5-6 km of rift-related deposits). Middle Jurassic-Early Cretaceous zHe cooling ages obtained indicate that rift-related subsidence in the Marrakech High Atlas finished in the Middle Jurassic and was followed by a period of exhumation where 2-3 km of rock were eroded. Thermal models from zHe data provide the first thermochronologic clue for a Late Cretaceous initiation of the Atlas compression-driven exhumation in the inner parts of the Marrakech High Atlas. The Triassic-Jurassic basin reconstruction assisted by thermochronology highlights a key role of inherited basement anisotropy in rift orientation and evolution, and on its subsequent inversion. Comparison of present-day and restored sections to the rifting stage aided by thermochronology suggests minimum values of total orogenic shortening in the Marrakech High Atlas of 13 to 14 km (21 to 17%), with exhumation of 1 to more than 5 km of rocks. Similar zHe ages on both sides of the Tizi n'Test fault evince minor vertical movements along the fault during the Atlas orogeny

Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

The Eastern Cordillera of Colombia is a thick-skinned thrust-fold belt that is characterized by two topographic domains: (1) the axial zone, a high altitude plateau (the Sabana de Bogotá, 2500 masl) with low local relief and dominated by longitudinal rivers, and (2) the Cordillera flanks, where local relief exceeds 1000 m and transverse rivers dominate. On the basis of an analysis of digital topography and river parameters combined with a review of paleodrainage data, we show that the accumulation of shortening and crustal thickening during the Andean orogeny triggered a process of fluvial reorganization in the Cordillera. Owing to a progressive increase of the regional slope, the drainage network evolves from longitudinal to transverse-dominated, a process that is still active at present. This study provides the idea of progressive divide migration toward the inner part of the mountain belt, by which the area of the Sabana de Bogotá plateau is decreasing, the flanks increase in area, and ultimately transverse rivers will probably dominate the drainage of the Cordillera

Rising and falling diapirs, shifting depocenters and flap overturning in the Cretaceous Sopeira and Sant Gervàs subbasins (Ribagorça basin, Southern Pyrenees)

The halokinetic structure of inverted salt-related continental margins is frequently obliterated by compressional overprinting. The Cretaceous Sopeira and Sant Gervàs subbasins of the Ribagorça basin (South-Central Pyrenees) show evidence of salt-related extensional tectonics and diapiric growth along the Iberian margin of the Mesozoic Pyrenean rift. We present an integrated field-based tectonic-sedimentary study to reconstruct the evolution of the Ribagorça basin system previous to, and in the early stages of, the Pyrenean orogeny. The ~4 km-thick Albian-Cenomanian Sopeira minibasin infill thins towards the basin borders, especially towards the eastern N-S trending Llastarri salt weld. The 90º tilt to the south of the Sopeira basin bottom records the growth of the buried north-dipping Sopeira listric fault from Albian to Santonian times, when it evolved as an extensional rollover associated with the Aulet salt roller. The ~3 km thick Cenomanian-Campanian succession filling the Sant Gervàs flap displays 130º bed fanning attitude from overturned Cenomanian carbonate platform strata to upright Campanian turbidite beds. The Sant Gervàs flap development during Cenomanian times was related to the fall of a large salt pillow after the main Soperia minibasin stage. Jurassic-Campanian diachronous subsidence is also observed in the adjacent Montiberri, Faiada and Tamurcia depocenters. Correlation with the Pedraforca, Cotiella and Basque-Cantabrian basins along the Southern Pyrenees suggests that a significant segment of the Iberian side of the Pyrenean rift experienced a gravity-driven extension from Albian to late Santonian. The Ribagorça basin provides an excellent field analogue for presently buried salt-related structures of extended passive margins

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

Alpine Ductile Deformation of the Upper Iberian Collided Margin (Eaux-Chaudes Massif, West-Central Pyrenean Hinterland, France)

Altres ajuts: acords transformatius de la UABThe Eaux-Chaudes massif provides keys to unravel the deep-seated deformation of the Iberian rifted margin during the Alpine orogeny in the Pyrenees. The massif conforms to an inlier of upper Cretaceous carbonate rocks within the Paleozoic basement of the western Axial Zone, originally deposited in the upper margin shelf before the Cenozoic collision. New geological mapping and cross-section construction lead to the description of the lateral structural variation from a km-scale fold nappe in the west to a ductile, imbricate fold-thrust fan in the east. The transition from a Variscan pluton to Devonian metasediments underlying the autochthonous Cretaceous induced this structural change. Recumbent folding, which involved upper Paleozoic rocks, was facilitated by a lower detachment in Silurian slates and an upper detachment in an overlying Keuper shale and evaporite thrust sheet. Remnants of this allochthonous sheet form shale and ophite bodies pinched within the upper Cretaceous carbonates, conforming unusual tertiary welds. Ductile shear in the overturned limb of the Eaux-Chaudes fold nappe imparted strong mylonitic foliation in carbonate rocks, often accompanied by N-S stretching lineation and top-to-the-south kinematic indicators. The burial of the massif by basement-involved thrust sheets and the Keuper sheet, along with their Mesozoic-Cenozoic cover, account for ductile deformation conditions and a structural style not reported hitherto for the Alpine Pyrenees. A hypothesis for the tectonic restoration of this part of the Pyrenean hinterland is finally proposed