Sediment routing system evolution within a diachronously uplifting orogen: Insights from detrital zircon thermochronological analyses from the South-Central Pyrenees

Abstract

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 (ϳ78 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 (ϳ30 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 exhumational 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.

Erosion rates in the source region of an ancient sediment routing system: comparison of depositional volumes with thermochronometric estimates

“…Palaeocurrent data show that the dominant palaeoslope was towards the west (Fig. 2), supporting previous palaeogeographical reconstructions (Bentham et al 1992;Nijman 1998;Dreyer et al 1999;remacha et al 2005;Das Gupta & Pickering 2008;Caja et al 2010;Whitchurch et al 2011). Palaeocurrent data also indicate that two major palaeovalley systems (Sis and Gurb-Pobla) dispersed sediment towards the south from the Pyrenean mountain belt (Mellere 1993;Vincent 2001;Whittaker et al 2011;Parsons et al 2012;Michael 2013), swinging towards the west in the southern Tremp Basin owing to deflection by the topography caused by the Montsec thrust system (Millán et al 1994;Allen et al 2013).…”

“…The effect of (1) is minimal, as the main thick-skinned thrust sheets had been emplaced by 30-35 Ma (Beaumont et al 2000). The effect of (2) may be considerable, but the easterly extension of the Gurb catchment is limited by structural barriers along the Segre line, which guided the input of sediment from the eastern Pyrenees into the Ebro foredeep (Vergés 2007;Whitchurch et al 2011).…”

“…There was a diachronous westwards progradation (Bentham et al 1993;Whitchurch et al 2011), so that by time interval 3 (36.5-33.9 Ma), the Ainsa and Jaca Basins were filled with fluvial sediments (Turner 1992;Hogan & Burbank 1996;Teixell 1998). At this stage, uplift of the western Pyrenees caused additional source regions to contribute to the sediment budget of the Escanilla system, represented principally by the fanglomerates of the Santa orasia source (Jolley 1987).…”

“…Hercynian granites are abundant throughout the Pyrenees, whereas pre-Hercynian granites are located and restricted close to the North Pyrenean Fault Zone and to the Eastern Pyrenees. If compartmentalization of the late Eocene Pyrenean fold-thrust belt prevented longitudinal flow from the Eastern Pyrenees to the Tremp Basin (Filleaudeau et al 2012;Whitchurch et al 2011), the source of the pre-Hercynian zircons found at Gurb must have been close to the drainage divide of the central Pyrenees. The provenance signals in both Sis and Gurb therefore imply catchment areas extending well into the Axial Zone.…”

“…Lag-time estimates in the south Pyrenean area have been made by a number of workers (Beamud et al 2010;Filleaudeau et al 2012;rahl et al 2011;Whitchurch et al 2011;Michael 2013). Importantly, the value of exhumation rate obtained refers to the erosion rate averaged over the time scale of the lag time immediately preceding deposition.…”