[1] We investigate the respective roles of crustal tectonic shortening and asthenospheric processes on the topography of the High Atlas and surrounding areas (Morocco). The lithospheric structure is modeled with a direct trial-and-error algorithm taking into account gravity (Bouguer and free air), geoid, heat flow, and topography. Three parallel cross sections, crossing the High Atlas and Anti-Atlas ranges, show that the lithosphere is thinned to 60 km below these mountain ranges. An analysis of the effect of the lithospheric thinning allows us to conclude that the whole topography of the Anti-Atlas, which belongs to the Sahara domain, is due to asthenospheric processes. In the High Atlas the lithospheric thinning explains a third of the relief of the western High Atlas, 500 m for a mean altitude of 1500 m, and half of the relief of the central High Atlas, 1000 m for a mean altitude of 2000 m. At the scale of Morocco the domain affected by lithospheric thinning forms an elongated NE-SW strip crossing not only the main structural zones but also the Atlantic margin to the south and the Africa-Eurasia plate boundary to the north. This major lithospheric thinning is associated with Miocene to recent alkaline volcanism and seismicity. We propose that this thermal anomaly is related to a shallow mantle plume, emplaced during middle to late Miocene time, during a period of relative tectonic quiescence.

The Greater Caucasus (GC) fold-and-thrust belt lies on the southern deformed edge of the Scythian Platform (SP) and results from the Cenozoic structural inversion of a deep marine Mesozoic basin in response to the northward displacement of the Transcaucasus (lying south of the GC) subsequent to the Arabia-Eurasia collision. A review of existing and newly acquired data has allowed a reconstruction of the GC history through the Mesozoic and Cenozoic eras. In Permo(?)-Triassic times, rifting developed along at least the northern part of the belt. Structural inversion of the basin occurred during the Late Triassic corresponding to the Eo-Cimmerian orogeny, documented SE of the GC and probably linked to the accretion of what are now Iranian terranes along the continental margin. Renewed development of extensional basin formation in the area of the present-day GC began in Sinemurian-Pliensbachian times with rift activity encompassing the Mid-Jurassic. Rifting led to extreme thinning of the underlying continental crust by the Aalenian and concomitant extrusion of mid-ocean ridge basalt lavas. A Bathonian unconformity is observed on both sides of the basin and may either correspond to the end of active rifting and the onset of post-rift basin development or be the record of collision further south along the former Mesozoic active margin. The post-rift phase began with deposition of Late Jurassic platform-type sediments onto the margins and a flysch-like unit in its deeper part, which has transgressed the basin during the Cretaceous and Early Cenozoic. An initial phase of shortening occurred in the Late Eocene under a NE-SW compressional stress regime. A second shortening event that began in the Mid-Miocene (Sarmatian), accompanied by significant uplift of the belt, continues at present. It is related to the final collision of Arabia with Eurasia and led to the development of the present-day south-vergent GC fold-and-thrust belt. Some north-vergent retrothrusts are present in the western GC and a few more in the eastern GC, where a fan-shaped belt can be observed. The mechanisms responsible for the large-scale structure of the belt remain a matter of debate because the deep crustal structure of the GC is not well known. Some (mainly Russian) geoscientists have argued that the GC is an inverted basin squeezed between deep (near)-vertical faults representing the boundaries between the GC and the SP to the north and the GC and the Transcaucasus to the south. Another model, supported in part by the distribution of earthquake hypocentres, proposes the existence of south-vergent thrusts flattening at depth, along which the Transcaucasus plunges beneath the GC and the SP. In this model, a thick-skinned mode of deformation prevailed in the central part of the GC whereas the western and eastern parts display the attributes of thin-skinned fold-and-thrust belts, although, in general, the two styles of deformation coexist along the belt. The present-day high elevation observed only in the central part of the belt would have resulted...

Accurate chronological records are critical for understanding the landformsevolution, and, in particular, of alluvial fan sequences emplaced during glocal/global climatic changes. Toward this end, we measured in-situ-produced 10Be in quartz boulders exposed on top surfaces of Sulawesian Late Quaternary alluvial fans. Combined geomorphic study(SPOT image and field analyses) indicate that this site is composed of twoalluvial fan units. In situ-produced 10Be concentrations suggest that they were emplaced during two successive major climatic events. The calculated minimum exposure ages date the younger unit abandonment at 11,000±2,000 years and seem consistent with a Late Interglacial abandonment age (~120,000years) for the older unit. This study demonstrates that using both the neutron and muon components implicated in the production of in situ10Be, surficial erosion rates can be estimated (~6 m/Ma in Sulawesi )and alluvial fan surfaces dated. In particular, it shows that10Be may be used to date fan surface emplacement during the last 120 ka under humid tropical conditions, significantly helping to constrain continental paleo-climatology in these regions