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Frédéric Herman (ETH Zurich) : Quantifying erosion rates in the Alps using low temperature thermochronology

Quand ? Le 13/06/2011,
de 14:00 à 15:30
S'adresser à G. Quitté, G. Mahéo
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Several studies suggest that climate, through erosion, or the lack of it, affected the shape and dynamics of mountain belts during the Cenozoic. It is therefore critical to quantify erosion rates at various spatial and temporal scales to assess the importance of erosion on shaping the mountainous landscapes we observe today. To this end, I will present how one may quantify erosion in mountain belts during the late Cenozoic, including the recent Pliocene-Pleistocene Glaciations, using low temperature thermochronology and the European Alps as a natural laboratory.

I will first present how we have recently implemented a formal inverse procedure to extract erosion rates from spatially distributed low temperature thermochonometric data to infer exhumation rates at the Myr and orogen scales. Our method is based on a Gaussian linear inversion approach in which we set up a linear problem relating erosion rate to thermochronologic age with rates being parameterized as variable in both space and time.  I illustrate how this approach can be used to decipher the erosion history in the Alps since ca. 30 Ma.

In the second part, I will present how we developed a new thermochronometer of very low closure temperature, which is based on optically stimulated luminescence (OSL) dating. This innovative approach appears to have a closure temperature of about 300C, opening a new window of research on the latest stage of exhumation of rocks towards the surface. This system has the potential to enable quantification of geologic and/or geomorphic processes at a timescale of a Quaternary climate cycle. Besides its remarkable thermal properties, OSL-thermochronology also has the advantage of the relative ease of making measurements and the ubiquity of the minerals used: quartz and feldspar. I will show examples of application in the western Alps.

Finally, I will present how these results can be used to calibrate a large scale glacial erosion model.

In summary, our results highlight the spatial distribution of erosion across the Alps since ca. 30 Ma. They suggest an increase of erosion in the western parts of the Alps since 2-4 Ma. In particular, detailed analyses using OSL thermochronology suggest that glacial erosion rates may have been, very locally, as high as 5 mm/a during the recent the last glacial cycle.

Lien pour le projet sur les Alpes: http://www.esd.ethz.ch/research/TOPOAlps

 

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