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International audience; Apatite fission-track and (U-Th)/He thermochronometry have been applied to investigate the long-term topographic evolution of the French Massif Central. Located in the foreland domain of the Alpine and Pyrenean mountain belts, the French Massif Central presents enigmatic topographic features, reaching ~1700 m a.s.l. and ~1000 m of relief, that did not originate from Alpine compressional nor from extensional tectonics. The age of the present-day topography, the timing of its formation, and the underlying processes remain debated. Our new thermochronological data come from the eastern flank of the massif, where sampling profiles run from the high-elevation region down to the Rhône river valley floor with a total elevation profile of 1200 m. Age-elevation relationships, mean track-length distributions and thermal modeling indicate a two-steps cooling history: (i) a first exhumation event, already detected through previously-published thermochronology data, with an onset time during Mid-Cretaceous; and interestingly (ii) a more recent Cenozoic phase that is resolved from our data, with a likely post-Eocene onset. This second erosional event is associated with relief formation and valley incision probably induced by a long wavelength domal uplift supported by mantle upwelling. Disclaimer: This is a confidential document and must not be discussed with others, forward in any form, or posted on websites without the express written consent of the Geological Society of America.

The Calabrian-Peloritani arc represents key site to unravel evolution of surface processes on top of subducting lithosphere. During the Pleistocene, in fact the arc uplifted at rate of the order of about 1mm/yr, forming high-standing low-relief upland (figure 2). Our study is focused on the relationship between tectonic and land evolution in the Sila Massif, Messina strait and Peloritani Mts. Landforms reflect a competition between tectonic, climatic, and surficial processes. Many landscape evolution models that explore feedbacks between these competing processes, given steady forcing, predict a state of erosional equilibrium, where the rates of river incision and hillslope erosion balance rock uplift. It has been suggested that this may be the final constructive stage of orogenic systems. Assumptions of steady erosion and incision are used in the interpretation of exhumation and uplift rates from different geologic data, and in the formulation of fluvial incision and hillslope evolution models. In the Sila massif we carried out cosmogenic isotopes analysis on 24 samples of modern fluvial sediments to constrain long-term (~103 yr) erosion rate averaged on the catchment area. 35 longitudinal rivers profiles have been analyzed to study the tectonic signal on the landscape evolution. The rivers analyzed exhibit a wide variety of profile forms, diverging from equilibrium state form. Generally the river profiles show at least 2 and often 3 distinct concave-up knickpoint-bounded segments, characterized by different value of concavity and steepness indices. River profiles suggest three main stages of incision. The values of ks and θ in the lower segments evidence a decrease in river incision, due probably to increasing uplift rate. The cosmogenic erosion rates pointed out that old landscape upland is eroding slowly at ~0.1 mm/yr. In the contrary, the flanks of the massif is eroding faster with value from 0.4 to 0.5 mm/yr due to river incision and hillslope processes. Cosmogenic erosion rates mach linearly with steepness indices and with average hillslope gradient. In the Messina area the long term erosion rate from low-T thermochronometry are of the same order than millennium scale cosmogenic erosion rate (1-2 mm/yr). In this part of the chain the fast erosion is active since several million years, probably controlled by extensional tectonic regime. In the Peloritani Mts apatite fission-track and (U-Th)/He thermochronometry are applied to constraint the thermal history of the basement rock. Apatite fission-track ages range between 29.0±5.5 and 5.5±0.9 Ma while apatite (U-Th)/He ages vary from 19.4 to 1.0 Ma. Most of the AFT ages are younger than the overlying terrigenous sequence that in turn postdates the main orogenic phase. Through the coupling of the thermal modelling with the stratigraphic record, a Middle Miocene thermal event due to tectonic burial is unravel. This event affected a inner-intermediate portion of the Peloritani belt confined by young AFT data (

International audience; The Admiralty Mountains region forms the northern termination of the northern Victoria Land, Antarctica. Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the Antarctic plate, where the Admiralty Mountains region forms the northern termination of the western shoulder of the Mesozoic-Cenozoic West Antarctica Rift System. In this study we combine new low-temperature thermochronological data (apatite fission-track and (U-Th-Sm)/He analyses) with structural and topography analysis. The regional pattern of the fission-track ages shows a general tendency to older ages (80–60 Ma) associated with shortened mean track-lengths in the interior, and younger fission-track ages clustering at 38–26 Ma with long mean track-lengths in the coastal region. Differently from other regions of Victoria Land, the younger ages are found as far as 50–70 km inland. Single grain apatite (U-Th-Sm)/He ages cluster at 50–30 Ma with younger ages in the coastal domain. Topography analysis reveals that the Admiralty Mountains has high local relief, with an area close to the coast, 180 km long and 70 km large, having the highest local relief of >2500 m. This coincides with the location of the youngest fission-track ages. The shape of the area with highest local relief matches the shape of a recently detected low velocity zone beneath the northern TAM, indicating that high topography of the Admiralty Mountains region is likely sustained by a mantle thermal anomaly. We used the obtained constraints on the amount of removed crustal section to reconstruct back-eroded profiles and calculate the erosional load in order to test flexural uplift models. We found that our back-eroded profiles are better reproduced by a constant elastic thickness of intermediate values (Te = 20–30 km). This suggests that, beneath the Admiralty Mountains, the elastic properties of the lithosphere are different with respect to other TAM sectors, likely due to a stationary Cenozoic upper mantle thermal anomaly in the region.

The Kuh-e-Faghan strike-slip fault system (KFF), located to the northern edge of the Lut Block in central Iran, developed through a Neogene-Quaternary pulsed history of eastward fault propagation and fault-related exhumation. This system is a consequence of the residual stresses transmitted from the Arabia-Eurasia convergent plate boundary. Here we integrate structural and textural analysis with new and previously published apatite fission-track (AFT) and apatite (U-Th)/He (apatite He) results, chlorite thermomentry, and hematite (U-Th)/He data from hematite-coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late Miocene-Pliocene burial and exhumation associated with the propagation of the KFF. Twenty-nine hematite (U-Th)/He (hematite He) dates from three striated hematite coated slip surfaces from the KFF fault core and damage zone yield individual dates from ~12–2 Ma. Petrographic analysis and chlorite thermometry of a polyphase, fossil fluid system in the KFF fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal (T = 239 ± 10 °C) fluids and hematite formation. Hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics, no evidence of hematite comminution and similar hematite He closure temperatures (~60–85 °C) in each sample. Integration of these results with thermal history modeling of AFT and apatite He data shows that KFF activity in the late Miocene is characterized by an early stage of fault nucleation, fluid circulation, hematite mineralization, and eastward propagation not associated with vertical movement that lasted from ~12 to 7 Ma. Hematite He, AFT, and apatite He data track a second phase of fault system activity involving fault-related exhumation initiating at ~7 Ma and continuing until present time. Our new data constrain the onset of the recognized Late Miocene-Pliocene tectonic reorganization in north-central Iran.

International audience; Central Iran provides an ideal region in which to study the long-term morphotectonic response to the nucleation and propagation of intraplate faulting. In this study, a multidisciplinary approach that inte-grates structural and stratigraphic field investigations with apatite (U + Th)/He (AHe) thermochronometry is used to reconstruct the spatio-temporal evolution of the Kuh-e-Faghan Fault in northeastern central Iran. The Kuh-e-Faghan Fault is a narrow, similar to 80-km-long, deformation zone that consists of three main broadly left-stepping, E-W-trending, dextral fault strands that cut through the Mesozoic-Paleozoic substratum and the Neogene-Quaternary sedimentary cover. The AHe thermochronometry results indicate that the intrafault blocks along the Kuh-e-Faghan Fault experienced two major episodes of fault-related exhumation at ca. 18 Ma and ca. 4 Ma. The ca. 18 Ma faulting/exhumation episode is chiefly recorded by the structure and depositional architecture of the Neogene deposits along the Kuh-eFaghan Fault. A source-to-sink scenario can be reconstructed for this time frame, where topographic growth caused the synchronous erosion/exhumation of the pre-Neogene units and deposition of the eroded material in the surrounding fault-bounded continental depo-centers. Successively, the Kuh-eFaghan Fault gradually entered a period of relative tectonic quiescence and, probably, of regional subsidence, during which a thick pile of fine-grained onlapping sediments was deposited. This may have caused resetting of the He ages of apatite in the pre-Neogene and the basal Neogene successions. The ca. 4 Ma faulting episode caused the final exhumation of the fault system, resulting in the current fault zone and topography. The two faultrelated exhumation episodes fit with regional early Miocene collision-enhanced uplift/exhumation, and the late Miocene-early Pliocene widespread tectonic reorganization of the Iranian Plateau. The reconstructed longterm, spatially and temporally punctuated fault system evolution in intraplate central Iran during Neogene-Quaternary times may reflect states of far-field stress changes at the collisional boundaries.

The West Antarctic Ice Sheet is the most unstable component of the Antarctic cryosphere. Its fluctuations are well documented since the Pliocene, but its behaviour over the last 35 Ma is more controversial, particularly during periods of past high global pCO2 values similar to those predicted in future global climate scenarios. Here, we present new U-Pb dating of detrital apatite grains (previously dated by the fission-track method) from Cape Roberts Project Oligocene to Pliocene marine sediments in the Ross Sea. Two past ice-flow patterns were identified: one formed by outlet glaciers sourcing short-travelled apatites and one, northerly directed, bringing far-travelled apatite grains. The latter provides the first robust physical evidence for the presence and repeated expansion of an Oligocene West Antarctic Ice Sheet.

The opening of the Tyrrhenian Sea has been punctuated by short-lived episodes of oceanic accretion on separate small backarc basins during early Pliocene (Vavilov basin) and early Pleistocene (Marsili basin) time. These spreading pulses are related to slab rollback and are synchronous with the reduction of the subduction zone width during the formation of the narrow Calabrian arc. Using laboratory models, we investigated the long-term and transient effects of the reduction of slab width on the subduction kinematics. We found that the abrupt reduction in slab width results in a pulse of acceleration of the trench retreat velocity, as the balance between driving and resisting forces acting on the slab is temporarily modified. Our findings also show that the time scale and amplitude of spreading observed in the Tyrrhenian Sea can be experimentally fitted if the scaled viscosity of the uppermost part of the mantle ranges between 10 19 and 10 20 Pa s.