Provenance evolution during progressive rifting and hyperextension using bedrock and detrital zircon U-Pb geochronology, Mauléon Basin, western Pyrenees

Abstract

The responses of sedimentary systems to rifting at continental margins are three-dimensional and involve the mixing of various sediment sources through tectonic drivers and sediment response. Such sedimentary responses have not been well studied along magma-poor, hyperextended margins where the crust is stretched and thinned to ≤10 km. The asymmetric Mauleon Basin of the western Pyrenees is the product of such magma-poor hyperextension resulting from lateral rift propagation from the Bay of Biscay during Cretaceous time. After rifting, limited shortening during Cenozoic Pyrenean inversion uplifted the basin, resulting in preservation of outcrops of rift basin fill, upper and lower crustal sections, serpentinized lithospheric mantle, and basic rift-fault relationships. In this study ~5800 new zircon U-Pb ages were obtained from prerift, synrift, and postrift strata; the ages constrain the proximal to distal evolution of the Mauleon Basin and define a general model for sediment routing during rifting. Zircon U-Pb analyses from lower crustal granulites indicate that granulite plutons crystallized at 279 ± 2 and 274 ± 2 Ma, and paragneissic granulites yielded zircon rim ages of ca. 295 Ma. Detrital zircon U-Pb ages from western Pyrenean prerift strata show age modes of ca. 615 and ca. 1000 Ma, suggesting continual recycling and/or well-mixed Gondwanan-sourced sediments throughout the Paleozoic and early Mesozoic; additional Paleozoic age components (ca. 300 and ca. 480 Ma) are also observed. The variation of detrital zircon U-Pb ages in synrift and postrift strata illustrates that during rifting, provenance varied spatially and temporally, and sediment routing switched from being regionally, to locally, and then back to regionally derived within individual structurally controlled subbasins.