From extension to transpression during the final exhumation of the Pelvoux and Argentera massifs, Western Alps

Like the other “external crystalline massifs” (ECM) of the Western Alps, the Pelvoux and Argentera massifs record a late and important uplift of the Prealpine basement in the immediate foreland of the internal nappes. Recently published structural and fission track data indicate distinctly different final stages of exhumation for the two massifs. The last main exhumation of the SE Pelvoux basement took place in the Late Miocene, when an extensional tectonic regime widely affected the internal arc. This exhumation occurred mainly through extensional denudation below the inverted Briançonnais Frontal Thrust. Final exhumation of the NE Argentera basement, however, took place in the Pliocene, while it was thrust southward in a transpressive regime. This exhumation mainly resulted from erosion of the created relief. Late orogenparallel faulting within the High Durance Fault Zone records this two-stage late history, which is coeval with the outward propagation of compressional structures in the external arc. The last, dominantly transpressive, stage could be common to all the ECM around the western Alpine arc, explaining the striking similarities regarding their present-day structural setting.