River sand detrital geo-thermochronology record contrasting thermal histories across the Pyrenees of Spain and France

Abstract:

Understanding feedbacks and relationships among lithospheric and surface processes in doubly-vergent orogenic systems and associated foreland basin records are fundamental to reconstructing thermal and tectonic histories of orogens. Here we leverage modern river sand geo-thermochronometry to constrain differences in catchment-averaged thermal histories, exhumation, and downstream provenance signatures across pro-and retro-wedge domains of the Pyrenees collisional-orogenic system. High-and medium-temperature zircon, apatite, and rutile U-Pb geochronology provide a temporal record of magmatism, metamorphism, and exhumation of lower crustal levels, and low-temperature apatite and zircon (U-Th)/He thermochronology record upper-crustal tectonic inversion, orogenic growth, and post-orogenic decay. Detrital zircon U-Pb ages from the north flowing Ariège river (France) and south flowing Segre river (Spain) show downstream provenance signatures that exhibit the controlling nature of hinterland basement bedrock sources where zircon fertile Carboniferous-Permian Variscan plutons and metamorphic rocks dominate the retro-wedge and pro-wedge fluvial systems. Detrital thermochronology results from Spanish pro-wedge predominately preserves punctuated cooling events during Pan-African (>600 Ma), Variscan (420-240 Ma), and Pyrenean (85-20 Ma) orogenesis, whereas the French retro-wedge records a protracted thermal history that not only preserves cooling during orogenesis but also Cadomian subduction (600-520 Ma), Rheic rifting (520-420 Ma), Mesozoic rifting (240-85 Ma), and Pyrenean decay (<20 Ma). Contrasting thermal histories across the Pyrenees doubly-vergent orogenic system suggest inherited structures and thermal crustal architecture control subsequent deformation and exhumation. Linking tectonic, thermal, and provenance signatures to the geomorphic expression of landscapes across comparable fluvial systems provides new tools and insights for interpreting the long-term thermal evolution, deformation, and detrital thermochronometric records of convergent margins.