Rift-to-collision sediment routing in the Pyrenees: A synthesis from sedimentological, geochronological and kinematic constraints

Abstract

Reconstructing long-term drainage evolution in collisional setting is key to deciphering between the drivers controlling landscape and time scales of syn-orogenic sediment transfer processes. Provenance studies in orogenic systems often exploit the geochronological record of past magmatic events in sediments to infer their source rocks. However, detrital age distribution may be difficult to be directly related to a specific source rock because it depends on whole rock composition and a robust stratigraphic and sedimentologic framework. Description of the provenance signal over the orogenic cycle from rift basin to its inversion as an orogenic prism may therefore appear to be a very challenging task. Here, we take advantage of an extensive set of geochronological dates in combination with sedimentological data in well-dated stratigraphic units to resolve uncertainties on grain provenance.We focus on the Pyrenees Mountains that developed in response to the inversion of European and Iberian continental margins from the Late Cretaceous to the Miocene. Inversion of hyper-extended rift basins in the Northern Pyrenees is recorded by specific cooling histories contrasting with the Southern Pyrenees where crustal extension was minor.We review and compile all available detrital thermochronological and geochronological data sets and provide new U/Pb and (U-Th-Sm)/He analyses on detrital zircon grains. This new data set allows us to re-examine the evolution of the sediments routing in the Pyrenees from rift-related Mesozoic basin evolution to tectonic inversion during Cenozoic foreland development. Together with sedimentological and petrographical constraints from syn-rift Mesozoic and syn-orogenic Cenozoic sediments, and within the frame of quantitative kinematic plate reconstructions based on existing rotation data, and balanced cross-sections, we examine the temporal and spatial evolution of sediment routing in the entire Pyrenean realm from rift to collision. Our paleogeographic reconstructions of the sediment dispersal pattern are presented for four key time steps at ~100, 70, 55, and 40Ma, accounting for Iberia's plate motion.Early Cretaceous extension on the European margin led to the formation of multiple and narrow basins that were fed locally. This contrasts with the larger-scale pattern of sediment dispersal on the southern Iberia margin. The differences in sediments dispersal are shown to reflect first-order N-S asymmetry of extension. The asymmetry is maintained during the earliest stages of convergence in Late-Cretaceous – Paleocene. The southern foreland basin exhibits large-scale longitudinal drainage patterns while sediments dispersal in the northern basin is controlled by inherited pre-orogenic E-W-striking basin architecture. In the Paleocene, the southwards migration of thrust sheets and underplating below the Axial Zone led to increasing exhumation at the origin of the emplacement of the first transverse drainage network in the Southern Pyrenees. Changes from dominant longitudinal to transverse drainage in the north occurred in the middle Eocene.Our study emphasizes the role played by the rifted margin on the syn-collisional sediment routing system. We anticipate that this main result could be transposed to other orogens that have resulted from rift basin inversion.