Variable thermal histories across the Pyrenees orogen recorded in modern river sand detrital geo-/thermochronology and PECUBE thermokinematic modelling

The Pyrenees Mountains are a classic example of a doubly-verging collisional orogenic system with flanking retro- and pro-foreland basin systems. Previous bedrock and detrital geo-/thermochronologic studies have observed magmatic and exhumation-related ages that reflect a complex thermo-tectonic evolution of the European and Iberian plate margins related to break-up and assembly of the Gondwana, Pangea and Pyrenean-Alpine orogenic cycles. This study integrates detrital zircon, rutile and apatite U-Pb dating and, detrital zircon and apatite (U-Th)/He dating from modern river sands from the northern and southern Pyrenees, with PECUBE thermokinematic modelling of bedrock cooling ages to simulate detrital age distributions in order to evaluate: (1) regional patterns in long-term crustal processes associated with pre-Pyrenean crustal shortening, crustal thinning and magmatism along the Iberian and European plate margin; (2) timing of regional cooling and inferred erosion related to Pyrenean orogenesis; and (3) the exhumation processes associated with post-orogenic decay and erosion. Modern river multimineral detrital geo-/thermochronometry results are consistent with previous bedrock thermal history models and records punctuated Variscan and Pyrenean cooling events in the pro-wedge that contrasts with protracted Permian to Pliocene thermal history preserved in the retro-wedge of the orogen. Detrital age distributions from PECUBE modelling predict the Pyrenean age component in both detrital apatite and zircon (U-Th)/He age distributions, indicating the modelled exhumation patterns in the Axial Zone and Northern Pyrenean Zone can predict observed Pyrenean thermochronology ages. The presence of strong Pyrenean age peaks amongst the modern river sand and modelled detrital cooling age distributions suggests retro-wedge deformation and exhumation remained active during the main phase of pro-wedge activity and experienced significant orogenic decay. Isolated Miocene apatite He ages from the North Pyrenees modern river record post-orogenic cooling, due to tectonic mode switch to extension and (or) climate-driven enhanced exhumation.