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Detrital Zircon Fission-Track Thermochronology of the Present-Day Isère River Drainage System in the Western Alps: No Evidence for Increasing Erosion Rates at 5 Ma

Institut des Sciences de la Terre, CNRS, UMR 5275, Université Joseph Fourier, 1381 rue de la Piscine, Grenoble 38041, France
Geosciences 2013, 3(3), 528-542; https://doi.org/10.3390/geosciences3030528
Received: 7 May 2013 / Revised: 19 July 2013 / Accepted: 23 July 2013 / Published: 6 August 2013
(This article belongs to the Special Issue Sedimentary Basins and Orogenic Belts)
The Isère River system drains parts of the Western Alps in south-eastern France. Zircon fission-track data of the Isère River and its tributaries show a range of apparent cooling ages from about 7 to 150 Ma. Zircons with Jurassic to early Tertiary cooling ages are derived from partially reset or non-reset sedimentary cover units of the internal and external Alps, while grains belonging to the minimum age fraction are derived from areas of active river incision in the external crystalline massifs or from the Penninic front. With the absence of major normal faults, upper crustal exhumation in the Western Alps is driven by erosion. First-order long-term exhumation rate estimates based on minimum ages are about 0.5–0.6 km/Myr for the fastest exhuming areas, while drainage basin average rates based on central ages are about 0.2–0.4 km/Myr. These rates are slower than published short-term erosion rates determined from detrital quartz 10Be analyses in the Pelvoux massif. While present-day erosion is faster than the long-term average exhumation rates, the Isère River drainage zircon fission-track data do not show evidence for increasing erosion rates at 5 Ma. Exhumation has not been sufficient in this area to expose rocks with <5 Ma cooling ages today. The increase in erosion may have happened only in glaciated areas between 1 and 2 Ma. View Full-Text
Keywords: fission-track thermochronology; exhumation; erosion; Western Alps fission-track thermochronology; exhumation; erosion; Western Alps
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Bernet, M. Detrital Zircon Fission-Track Thermochronology of the Present-Day Isère River Drainage System in the Western Alps: No Evidence for Increasing Erosion Rates at 5 Ma. Geosciences 2013, 3, 528-542.

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