Duplex at the lateral tip of a thrust fault: the "La Cagalière" example (NE Pyrenees, France)

A duplex located at the lateral tip of a thrust fault is identified and this paper aims to understand why and how such a structure developed at this particular place. The "La Cagalière" duplex is a well-exposed example of a second-order structure developed firstly as an "autochthonous roof duplex" at the front of the Lagrasse ramp-related fold (NE Pyrenees, France). During a second stage of deformation, an out-of-sequence thrusting allows the emplacement of the overturned forelimb of Lagrasse fold as an allochthonous roof above the duplex. Using geometric analysis, magnetic fabric and structural measurements, it is shown that the "La Cagalière" duplex developed as a response to the progressive inhibition of the propagation of the Lagrasse fold frontal thrust. This study provides the first natural example of a duplex acting as a "stopping structure" at a thrust tip.