La transversal de Gavarnie-Guara. Estructura y edad de los mantos de Gavarnie, Guara-Gèdre y Guarga (Pirineo centro-occidental)

Abstract

The structure of the eastern extreme of the Jaca Basin is defined by the Gavarnie, Guara-Gèdre and Guarga thrust sheets. The Guara-Gèdre thrust was active during mid Luttetian-earliest Chattian and the Gavarnie thrust, that results from the inversion of a normal fault, developed at least from early Bartonian to mid Rupelian. During the latter, the southward translation of the cover rocks occurred along parallel detachment horizons located at the Lower Eocene and Triassic incompetent levels. The movement of the Guarga thrust gave rise to both the reactivation of old structures in the External Sierras, previously originated by the Guara-Gèdre thrust, and the formation of new ones. Along the studied transect the Guarga thrust sheet evolved from early Chattian to Aquitanian times, consumed ~ 5 km of horizontal shortening, and in the Jaca Basin produced a tectonic uplift not smaller than 8 km. The latter is interpreted to be partially related with a significant amount of Alpine ductile shortening of the basement allochthonous units. Comparison of the translation values of the Guara-Gèdre and the Guarga thrusts between the Ansó and Gavarnie- Guara transects indicate that the translation related to the Guara-Gèdre thrust decreases westward whereas the one associated to the Guarga thrust decreases eastward