Role of rift maturity on the architecture and shortening distribution in mountain belts

Abstract

Many relics of passive margin are found in mountain belts sometimes together with pristine exhume mantle. The reasons why these structures are preserved from tectonic reworking and whether the piece of mantle that accompanies them is exhumed during extension or collision remains a question. Using thermo-mechanical modelling we find on the one hand that, the strain distribution in the orogenic wedge is controlled by the original position of crustal domains across the rifted margin. In the upper plate, the structural relationships acquired during the rifting phase between the upper mantle and surrounding units are never reactivated during compression due to crustal strain localization. Mantle exhumation on the other hand can occur either during the collision or rifting phase depending on the thermal regime at the onset of the inversion. Applying these general rules to the Pyrenees, we show that exhumed mantle domain in the former passive margin could not exceed a width of 50 km to 70 km; otherwise obduction would have occurred due to the high thermal regime at the onset of the inversion.