SEDIMENT ROUTING SYSTEM EVOLUTION WITHIN A DIACHRONOUSLY UPLIFTING OROGEN: INSIGHTS FROM DETRITAL ZIRCON THERMOCHRONOLOGICAL ANALYSES FROM THE SOUTH-CENTRAL PYRENEES

The Pyrenees represents an orogen that developed diachronously, from east to west, between the Late Cretaceous and Miocene. Here, we use detrital zircon fission-track thermochronological analyses and U-Pb geochronology, interpreted within the context of the thermal and tectono-sedimentary development of the orogen, to construct a 3-stage model for south-central Pyrenean sediment routing system evolution as follows: (1) Late Cretaceous to Paleocene: Oblique convergence and topographic growth initiates in the eastern Pyrenees. After erosion and removal of the cover layer, south-central Pyrenean basins are supplied with zircons cooled during the Late Cretaceous (similar to 78 Ma), with a fission-track lag time of ca. 15 Myr, that record early Pyrenean exhumation. The zircons are sourced from the eastern, not central, Pyrenees. Orogen-parallel sediment routing systems dominate; (2) Early to Middle Eocene: After a period of quiescence, plate convergence rates increase. Uplift of the central Pyrenees supplies the south-central Pyrenean basins with zircons sourced from the central Pyrenean cover layer. Out-of-sequence thrusting recycles the early foredeep deposits and their associated thermochronological signals. The sediment routing systems begin to transition from orogen-parallel to orogen-transverse states; (3) Late Eocene to Miocene: Uplift and exhumation of the western Pyrenees begins. Zircons exhumed and cooled during the Oligocene (similar to 30 Ma) in response to duplex stacking in the central Axial Zone, reach the south-central Pyrenean wedge-top and foreland basins with a lag time of ca. 3 Myr. Orogen-transverse sediment routing systems become fully established. Our results extend the exhumationa1 history of the Pyrenees beyond that shown from bedrock studies and reveal that significant topography existed in the Pyrenees in the Paleocene. Furthermore, our data demonstrate the successive change from orogen-parallel to orogen-transverse sediment dispersal along strike, coeval with diachronous mountain growth. This study has implications for understanding the evolution of synorogenic sediment routing systems, migrating depocenters and the redistribution of mass by surface processes that may drive any coupling with tectonics during oblique orogenic development.