No abstract

[1] Three cross sections of the Moroccan High Atlas illustrate the structural geometry and relationship between tectonic shortening and topography in this Cenozoic intracontinental mountain range. The structure is dominated by thick-skinned thrusting and folding, essentially by inversion of Mesozoic extensional faults and by buckling of both preMesozoic basement and its sedimentary cover. Detached, thin-skinned thrusting is limited and apparently related to basement underthrusting, which did not always create structural relief. Despite the high topography, tectonic shortening is moderate, with faults and folds being spaced and separated by broad tabular areas. Section restoration indicates that shortening decreases along strike from east to west in the High Atlas, while topographic elevation generally increases. This inverse correlation suggests that crustal thickening does not fully explain the observed topography and suggests a mantle contribution to uplift. This is supported by geophysical indications of a thin lithosphere and by alkaline volcanism in the vicinity. Mantle-related uplift, which occurs in a broad region, may also explain the scarce foreland basin record adjacent to the High Atlas. The relief of the Atlas Mountains is interpreted as a combination of crustal isostatic and dynamic topography.

New evolutionary models for the Pyrenean orogeny must consider feedbacks between the midCretaceous hyperextension postulated recently and the Pyrenean inversion. We present a new crustal section of the Pyrenees through the Jaca basin, the western Axial Zone and the Chaînons Béarnais which allows identifying the ancient continental margins of the Iberian and European plates and a suture. A sequential restoration allows a reassessment of the style of convergence through time. Restoration leads to a progressively thinned crust in narrow continental margins separated by a domain of exhumed mantle peridotite and overlain by a detached sedimentary lid. Early convergence during the late Cretaceous and earliest Paleogene was accommodated by subduction of the peridotite domain. This was followed in the Eocene by initial collision involving overriding of the Iberian margin onto the European margin along the deep ramp of the NorthPyrenean Frontal thrust, which defines the suture. Subsequent full collision and strong relief generation from the late Eocene to the early Miocene were associated to thrust accretion of the Iberian plate, underlain by wedging and northward subduction of decoupled Iberian lower crust.

No abstract

International audienceThis paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record

We discuss the implications of a lithospheric model of the Moroccan Atlas Mountains based on topography, heat flow, gravity and geoid anomalies, taking into account the regional geology. The NW African cratonic lithosphere, some 160-180 km thick, thins to c. 80 km beneath the Atlas fold-thrust belts, in contrast with the shortening regime prevailing there since the early Cenozoic. This fact explains several geological and geophysical features as high topography with modest tectonic shortening, the occurrence of alkaline magmatism contemporaneous to compression, the absence of large crustal roots to support elevation, the scarce development of foreland basins, and a marked geoid high. The modelled lithosphere thinning is related to a thermal upwelling constrained between the Iberia-Africa convergent plate boundary and the Saharan craton.

No abstract

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 toward the basin borders, especially toward the eastern, N‐S trending, Llastarri salt weld. The 90° 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 130° bed fanning attitude from overturned Cenomanian carbonate platform strata to upright Campanian turbidite beds. The Sant Gervàs flap development since 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.