Role of rift structural inheritance in orogeny highlighted by the Western Pyrenees case-study

Abstract

It is commonly accepted that many orogens form by contractional reactivation of earlier continental rifts or rifted margins. Therefore, to better understand orogenesis, it is important to also understand how rift domains and their associated structures are incorporated into orogens.We investigate the role of rift structural inheritance during orogeny using the Western Pyrenees as a case-study. To achieve our aim, we use a kinematic forward lithosphere deformation model (RIFTER) to produce flexural isostatically compensated as well as balanced cross-sections showing the structural and stratigraphic development of both the rift and orogenic stages of the Western Pyrenees. The cross-section produced extends from the Northern to the Southern Foreland Basins and crosses the Mauléon-Arzacq Basin.Our modelling results show how rift-domains and their faults are sequentially reactivated and incorporated into the present-day Western Pyrenees architecture. Based on the results from our case-study, we identify a sequence of tectonic stages separated by critical events that record the transition between different tectonic styles by which lithosphere is deformed. The pre-orogenic extensional stage is characterized by a hyper-extended rift system that eventually led to exhumed mantle. This constitutes the pre-orogenic template. The subsequent contractional tectonics consists of two stages: (i) the inversion of the hyper-extended rift system reactivating extensional structures and (ii) the crustal shortening of the southern proximal rift domain.Results of the Western Pyrenees case-study may be used to understand the development of other Alpine-type collisional systems involving the sequential reactivation and inversion of former hyper-extended rift systems.