Apatite fission track analysis in the Argentera massif: evidence of contrasting denudation rates in the External Crystalline Massifs of the Western Alps

Apatite fission track dating from a central transect in the Argentera massif (southernmost External Crystalline Massif = ECM) yielded ages between 8.05 +/- 0.6 and 2.4 +/- 0.2 Myr, with a positive age/altitude correlation above 3 Ma, 1200 m, Recognising a thermal peak at c. 250 degreesC, 33 Ma, based on stratigraphic, metamorphic and Ar-39/Ar-40 data, the present results suggest a slow cooling rate (8-5 degreesC) for the Argentera massif during the Oligocene-early Pliocene. This rate compares with that from the Pelvoux massif, but contrasts with those observed in the northern ECM (Mont-Blanc and Aar: up to 14 degreesC Myr(-1)) for the same time interval, This can be related to the different location of the ECM within the collided European margin. At about 3-4 Ma, the denudation rate would have increased up to c, 1 mm yr(-1) in the Argentera massif, reaching the same value as in the Belledonne and northern ECM, likely a consequence of Penninic thrust inversion.