Fission-track grain-age distributions for detrital zircon are used in this study to resolve the late Cenozoic exhumation history of the European Alps. Grain-age distributions were determined for six sandstone samples and one modern river sediment sample, providing a record from 15 Ma to present. All samples can be traced to sources in the Western and Central Alps. The grain-age distributions are dominated by two components, P1 (8-25 Ma) and P2 (16-35 Ma), both of which show steady lag times (cooling age minus depositional age), with an average of 7.9 m.y. for P1 and 16.7 m.y. for P2. These results indicate steady-state exhumation in the source region at rates of ϳ0.4-0.7 km/m.y. since at least 15 Ma.

The collision between the Eurasian and Arabian plates along the 2400-km-long Bitlis-Zagros thrust zone isolated the Mediterranean from the Indian Ocean and has been linked to extension of the Aegean, rifting of the Red Sea, and the formation of the North and East Anatolian fault systems. However, the timing of the collision is poorly constrained, and estimates range from Late Cretaceous to late Miocene. Here, we report the fi rst apatite fissiontrack\ud (AFT) ages from the Bitlis-Zagros thrust zone. The AFT samples are distributed over the 450 km length of the Bitlis thrust zone in southeast Turkey and include metamorphic\ud rocks and Eocene sandstones. Despite the disparate lithology and large distance, the AFT ages point consistently to exhumation between 18 and 13 Ma. The AFT ages, along with a critical appraisal of regional stratigraphy, indicate that the last oceanic lithosphere between the Arabian and Eurasian plates was consumed by the early Miocene (ca. 20 Ma). The results imply that Aegean extension predated the Arabia-Eurasia collision

In the southern Apennines fold-and-thrust belt, thermal indicators record exhumation of sedimentary units from depths locally in excess of 5 km. The thrust belt is made of allochthonous sedimentary units that overlie a 6-8-km-thick, carbonate footwall succession. The latter, continuous with the foreland Apulian Platform, is deformed by reverse faults involving the underlying basement. Therefore, a switch from thin-skinned to thick-skinned thrusting occurred as the Apulian Platform carbonates-and the underlying thick continental lithosphere-were deformed during the latest shortening stages. Apatite fi ssion track data, showing cooling ages ranging between 9.2 ± 1.0 and 1.5 ± 0.8 Ma, indicate that exhumation marks these late tectonic stages, probably initiating with the buttressing of the allochthonous wedge against the western margin of the Apulian Platform. Pliocene-Pleistocene foreland advancing of the allochthonous units exceeds the total amount of slip that, based on cross-section balancing and restoration, could be transferred to the base of the allochthon from the underlying thick-skinned structures. This suggests that emplacement of the allochthon above the western portion of the Apulian Platform carbonates was followed by gravitational readjustments within the allochthonous wedge, coeval-and partly associated with-thick-skinned shortening at depth. The related denudation processes are interpreted to have played a primary role in tectonic exhumation.

Analysis of cooling age patterns yielded by low-temperature thermochronometers provides key information about the role played by tectonic discontinuities during the late stages of exhumation of metamorphic belts. In the Western Alps, fission track data published so far are heterogeneously scattered and concentrated in few structural domains, preventing analyses at the scale of the whole belt. The new apatite fission track data reported in this work, obtained with the external detector method as well as the population method in very low U content samples, fill this gap. They constrain the postmetamorphic evolution of the Western Alps along two transects from the foreland to the retroforeland, unraveling the effective role played by some major faults during the exhumation of the belt at shallow crustal levels. A clear regional pattern, characterized by decreasing ages moving from the axial sector to the European external sector of the belt and by an along-strike gradient with increasing ages from north to south, has been unraveled. Evident breaks in this age pattern have been detected in correspondence of faults that are near-parallel to the trend of the belt, pointing to the occurrence of active tectonics during and after exhumation. The most apparent breaks have been observed in the axial sector of the belt, where the postmetamorphic deformation would have been negligible according to classic tectonic models. Faults located in the axial sector split the belt into two major blocks (eastern and western). Since the Miocene, the western block experienced higher exhumation rates than the eastern one. Such differential exhumation was accommodated in the northern portion of the belt thanks to reverse motion along the Internal Houiller Fault, which occurred in a convergent transcurrent framework. To the south, it was accommodated instead by normal reactivation of the Brianc¸onnais Front and by activity of the Longitudinal Fault System, which occurred in a divergent transcurrent framework. The tectonic activity affecting the axial sector of the belt, in a context of regional dextral strike slip, is coeval with the forward propagation of the external thrusts, and of similar magnitude. We suggest that the contrasting kinematic regimes (i.e., convergent versus divergent transcurrence) observed in the Western Alps moving along strike were responsible of the increasing exhumation rates toward the north, revealed in both blocks by the along-strike age gradient. The higher exhumation rates recognized northward would be related to an increasing importance of crustal shortening that promoted erosion during the late stages of exhumation of the belt

Analysis of 146 new apatite (U-Th)/He ages, six new apatite fi ssion-track ages, and 165 previously published apatite fission track (AFT) ages from the northern Apennine extending convergent orogen reveals a signifi cant along-strike change in post-late Miocene wedge kinematics and exhumation history. East of ~11°30 E, age patterns and age-elevation relationships are diagnostic of ongoing frontal accretion and slab retreat consistent with a northeastward-migrating “orogenic wave.” Enhanced erosion rates of ~1 mm/yr over a period of ~3–5 Ma are recorded on the contractional pro-side of the orogen and ~0.3 mm/yr on the extending retro-side. West of ~11°30 E, ongoing exhumation has been restricted to the range core since at least ca. 8 Ma at rates of ~0.4 mm/yr increasing to ~1 mm/yr in the Pliocene (ca. 3 Ma) accompanied by post-Pliocene tilting and associated faulting. This pattern can be attributed to either continued convergence (but a switch in the transfer of material into the wedge to a regime dominated by underplating or out-of-sequence shortening), or a slowdown or cessation of frontal accretion and slab retreat with enhanced Pliocene uplift and erosion triggered by a deeper seated process such as lithospheric delamination, complete slab detachment, or slab tear. These fi ndings emphasize that no single model of wedge kinematics is likely appropriate to explain long-term northern Apennine orogenesis and synconvergent extension, but rather that different lithospheric geodynamic processes have acted at different times in different lateral segments of the orogen

The European Alps are a mountain belt that is characterized by a series of discrete orogenic events, which have long been recognized. Despite the inherent episodic nature of orogenic evolution, the Alps have been continuously exhumed, mainly by erosion, but also by normal faulting. Since continental collision started in the late Eocene/Early Oligocene evidence for ongoing erosional exhumation has been preserved in synorogenic sediments that accumulated in basins adjacent to the pro- and retro - side of this double-vergent mountain belt. This long-term erosion record can be used to determine exhumation rates. Lag-times calculated from fission-track (FT) ages of detrital zircon from synorogenic sediments are fairly constant for the European Alps since the Oligocene-Late Miocene. Although the fast exhuming areas were unroofed at rates of 0.4^0.7 kmMyr_1, the overall average exhumation rate is between 0.2 and 0.3 kmMyr_1on a regional scale. The detrital and bedrock zircon FT data of the Alps do not detect the increase in erosion rates since the Pliocene over the past _5Myr, as shown elsewhere. This increase cannot be detected yet with the detrital zircon FT method because not enough rock has been removed to widely expose zircons with Pliocene or younger cooling ages in the Alps. Long term(30Myr) exhumation rates appear to have been approximately constant when averaged over a sliding time window of about 8Myr, or depth window of 5 to10 km(ZFT closure depths); shorter-term fluctuations are not identified using this metho

In the Northern Apennines foreland, the Marnoso-arenacea Formation (MA Fm) records post-depositional burial temperatures overlapping with those of the zone of partial annealing of apatite fission tracks. Because the stratigraphy, sedimentology, petrography and structural evolution of this turbidite succession has been intensively studied over the last 40 years, the MA Fm provides an ideal case to apply the apatite fission-track method. The data show a general decrease of the maximum paleotemperature undergone by the MA samples toward the foreland area. The maximum burial, calculated using a geothermal gradient of 20°C/km, spans from more than 5 km to less than 2.5 km and indicates that the reconstructed total thickness of the MA succession is not enough to justify the determined burial values. Stratigraphic data indicates that the missing section consisted of a lower component (foredeep successions) and an upper allocthonous component composed of disrupted and chaotic oceanic sediments and minor ophiolites (Ligurian unit). The Ligurian unit overrode the foredeep succession during deposition. Its advancement toward the foreland area was associated with subsidence and only locally contrasted by thrust growth. The reconstructed wedge shape of the Ligurian unit, in its final and preerosional configuration at time of the maximum burial of the MA succession, shows a flat upper surface, which corresponds to a paleosurface of Early Pliocene age. This surface marks at 4 to 5 Ma the onset of the exhumation phase, which occurred at a mean rate of 1.2 mm/yr.

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