Nicolas Saspiturry, Ph.D candidate at the University of Bordeaux Montaigne and Bryan Cochelin (ISTO) will give a seminar titled: "Tectono-sedimentary evolution of a rift-system controlled by Permian post-orogenic extension and MCC formation (Bidarray basin and Ursuya dome, Western Pyrenees)
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This study aims to document the sedimentary and structural response of a continental crust submitted to extension when the lithosphere is abnormally hot. We focus on the Permian rift system in the Western Pyrenees, where the Permian Bidarray Basin is now in contact with late-Variscan granulites of the Ursuya massif. We show that the basin forms a N10-20° narrow, post-orogenic intracontinental extensional basin well preserved despite the Pyrenean orogeny. The western margin of this basin preserves undeformed alluvial fans dominated by hyper-concentrated flows and interdigitating eastward with a north-south fluvial system. The structural analysis of granulites shows that they recorded longitudinal mid-crustal flow and were exhumed thanks to retrogressive strain localization within an extensional shear zone flanking an E-W elongated
domal structure. We propose that the Bidarray Basin is an extensional basin formed on the hanging wall of a southward detachment system. This extensional system develops in response to the coeval upwelling of
granulites in an immature "a-type" Metamorphic Core Complex under regional E-W extension. The present-day Ursuya granulitic unit is believed to be a remnant body of the Permian MCC, finally denudated later during Cenomanian time.