Abstract The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology ( LTT ) data ( AH e and AFT ) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT . The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada.
The exhumation history of basement areas is poorly constrained because of large gaps in the sedimentary record. Indirect methods including low temperature thermochronology may be used to estimate exhumation but these require an inverse modeling procedure to interpret the data. Solutions from such modeling are not always satisfactory as they may be too broad or may conflict with independent geological data. This study shows that the input of geological constraints is necessary to obtain a valuable and refined exhumation history and to identify the presence of a former sedimentary cover presently completely eroded. Apatite fission-track (AFT) data have been acquired on the northern part of the Ardenne Massif close to the Variscan front and in the southern Brabant, in particular for the Visean ash-beds. Apatite fission-track ages for surface samples range between 140 ± 13 and 261 ± 33 Ma and confined tracks lengths are ranging between 12.6 ± 0.2 and 13.8 ± 0.2 μm. Thermal inversion has been realized assuming that (1) samples were close to the surface (20–40 °C) during Triassic times, this is supported by remnants of detrital Upper Permian–Triassic sediments preserved in the south of the Ardenne and in the east (border of the Roer Graben and Malmédy Graben), and (2) terrestrial conditions prevailed during the Early Cretaceous for the Ardenne Massif, as indicated by radiometric ages on paleoweathering products. Inversion of the AFT data characterizes higher temperatures than surface temperatures during most of the Jurassic. Temperature range is wide but is compatible with the deposition on the northern Ardenne of a significant sedimentary cover, which has been later eroded during the Late Jurassic and/or the Early Cretaceous. Despite the presence of small outliers of Late Cretaceous (Hautes Fagnes area), no evidence is recorded by the fission-track data for the deposition of a significant chalk cover as highlighted in different parts of western Europe. These results question the existence of the London-Brabant Massif as a permanent positive structure during the Mesozoic.
<h3>The Lower Cretaceous corresponds, in northwestern Europe, to a period of significant extension with the rifting of the Bay of Biscay and its eastern prolongation, the Parentis Basin. This basin has a long history of rifting and several important discontinuities between the uppermost Jurassic and the Albian (at the top of the Jurassic, top of the Barremian and at the Aptian-Albian boundary).</h3><h3>&#160;</h3><h3>North of this basin i.e. the Aquitaine Platform, the sedimentation is very patchy, the few known Lower Cretaceous deposits suggest continental conditions during this period. Preliminary work carried out on some deep boreholes located on the Aquitaine platform reconstructed temperatures by thermochronology (apatite fission track on Triassic and Permian samples). The preliminary results show that these samples are not in equilibrium with the current sedimentary thickness taking into account a conventional geothermal gradient (35&#176;/km). All these the samples then show a significant cooling at the end of the Lower Cretaceous consistent with a regional erosion event.</h3><h3>&#160;</h3><h3>This preliminary work leads us to make two hypothesis:</h3><h3>-&#160;&#160;&#160;&#160;&#160;&#160;&#160; The deposition of a Lower Cretaceous sedimentary thickness that was then eroded form the Aptian. This hypothesis is in agreement with study carried out further east (French Massif Central) but not with the first order sedimentary outcropping characterization on the Aquitaine platform.</h3><h3>-&#160;&#160;&#160;&#160;&#160;&#160;&#160; The high palaeotemperatures recorded are controlled by an increase in the geothermal gradient (a gradient of 50&#176;/km must be considered) during the Upper Jurassic and Lower Cretaceous. This model does not consider the deposition and the erosion of a thick Cretaceous cover. This hypothesis is difficult to explain over such large area without significant crustal thinning.</h3><h3>These two-hypothesis lead to very different palaeogeographical situations and to very different vertical displacement. The answer to these questions is a key in order to understand the periods of karstification of the Jurassic carbonate platform and therefore to have a better knowledge of the water reservoir.</h3><h3>&#160;</h3><h3>We presented in this work the results of an integrated study. The results are based on a combination of field study and the interpretation of subsurface data (boreholes and seismic). A wide range of methods has been applied to this dataset (sedimentology, sequence stratigraphy, well correlation, isotopic and geochemical analysis of carbonate, sand and clay and thermochronology).</h3>
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