Thermal imprint of rift-related processes in orogens as recorded in the Pyrenees

The extent to which heat recorded in orogens reflects thermal conditions inherited from previous rift-related processes is still debated and poorly documented. As a case study, we examine the Mauléon basin in the north-western Pyrenees that experienced both extreme crustal thinning and tectonic inversion within a period of ∼30 Myrs. To constrain the time–temperature history of the basin in such a scenario, we provide new detrital zircon fission-track and (U–Th–Sm)/He thermochronology data. The role of rift-related processes in subsequent collision is captured by inverse modeling of our thermochronological data, using relationships between zircon (U–Th–Sm)/He ages and uranium content, combined with thermo-kinematic models of a rift-orogen cycle. We show that the basin recorded significant heating at about 100 Ma characterized by high geothermal gradients (∼80 °C/km). Our thermo-kinematic modeling and geological constraints support the view that subcontinental lithospheric mantle was exhumed at that time below the Mauléon basin. Such a high geothermal gradient lasted 30 Myr after onset of convergence at ∼83 Ma and was relaxed during the collision phase from ∼50 Ma. This study suggests that heat needed for ductile shortening during convergence, is primarily inherited from extension rather than being only related to tectonic and/or sedimentary burial. This should have strong implications on tectonic reconstructions in many collision belts that resulted from inversion of hyper-extended rift basins.