COUPLED BEDROCK AND DETRITAL THERMOCHRONOMETRY OF A HYPER-EXTENDED CONTINENTAL MARGIN, MAULéON, PYRENEES

Modern thermochronometric dating techniques have become increasingly powerful tools with a diverse range of applications in quantifying tectonic and sedimentary processes at rifted continental margins. While detrital zircon U-Pb is commonly used in detrital provenance studies, zircon (U-Th)/He (ZHe) dating is a complimentary tool that constrains sediment provenance and the exhumation history of a sediment source region. In particular, ZHe lag time is a powerful tool in elucidating the temporal and thermal evolution of tectonically active source areas. In hyper-extended margin basins, such as the Mauléon basin, inverted unroofing sequences with up-section variation in lag time record changes in either sediment source or exhumation rates during progressive continental break-up. During progressive break-up, different exhumed lithospheric levels shed zircons and also lower-crustal rutile into syn-rift basins recording progressive crustal rifting and thinning. Zircon and rutile U-Pb-He double dating studies have shown the power of coupling these data with other geochemical characteristics or fingerprints to refine provenance signatures. Rutile double dating is of particular use in hyper-extended margins, as rutile-bearing granulitic, lower-crustal rocks are exhumed during the thinning and exhumation phases. Modern detrital U-Pb-He dating of accessory phases is ideally suited to reconstruct the complete tectonic evolution of hyper-extended continental margins, as syn-rift basins archive a more complete record of margin evolution compared to bedrock thermal histories that are prone to thermal overprinting or erosion. The Mauléon Basin of the Western Pyrenees is ideal for this study due to extreme crustal thinning during Cretaceous rifting followed by Pyrenean reactivation. This area experienced less reactivation and deformation, so many pre-rift structures are preserved and can be compared to the syn- and post-rift units and structures. This study is the first major chronologic study of bedrock and detrital units completed in the Mauléon Basin. By using the discussed techniques, this study will give new insights into the evolution and structure of the Mauléon Basin and the Western Pyrenees, rifting of the Pyrenees and also plate reconstructions and kinematics of the Iberian and European plates.