Asymmetric growth of the Pyrenees revealed through measurement and modeling of orogenic fluxes

Abstract

ABSTRACT. Orogenic asymmetry is ubiquitous in terms of topography, structure and metamorphism, but the relative influences of climate and tectonics in determining such asymmetry remain contentious. This study demonstrates that for the case of the European Pyrenees, orogenic asymmetry is not defined by inherited structural asymmetry, nor by orographic asymmetry of precipitation, but is the simple consequence of the inherent tectonic growth of a doubly-vergent orogen.The Discrete element model experiments are used to explore the natural tendency of the system towards asymmetry. Model output demonstrates that during active frontal accretion to the pro-wedge of an orogen, the maxima in erosional denudation is offset towards the pro-wedge relative to the maximum depths of exhumation. This asymmetry is fundamentally driven by the progressive reduction in advection velocities of material within the orogen from the pro-wedge into the retro-wedge. Hence, for an efficient erosional regime, a dynamic coupling between erosion and structural uplift of the pro-wedge will reduce activity of the retro-wedge and hence drive asymmetry in terms of low temperature thermochronometry, erosion and sedimentation. The models also demonstrate the tendency for pro-wedge growth through frontal accretion to slow. However, the cessation of frontal accretion as recorded by the South Pyrenean Thrust Belt (phases 3 and 4) requires additional forcing; it is proposed that the thick wedge-top sedimentation recorded at this time, increased taper angles and hence stabilized the wedge. Accretionary influx into the orogen at this time was accomplished through underplating. These processes governing asymmetry do not require a spatially variable climate or a laterally heterogeneous underthrust plate.

Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

“…These cycles last on the order of 15 -200,000 model years. Our models, along with other numerical [Naylor and Sinclair, 2007] and analog models [Hoth et al, 2006; and some well dated examples from active orogens [Masaferro et al, 2002;Hubert-Ferrari et al, 2005;Sinclair et al, 2005], suggest that transient accommodation of strain may be common. Thus, caution should be applied when extrapolating long-term slip rates from varying temporal scales.…”

“…Masaferro et al [2002] showed that the Neogene-Quaternary growth of the Santaren anticline (Cuban fold and thrust belt) is characterized by several tectonic uplift pulses of different duration and intensity, interrupted by periods of variable duration in which no fold growth occurred. The Pyrenees show a punctuated pattern of exhumation [Sinclair et al, 2005]. Given these examples and results from both numerical [Naylor and Sinclair, 2007; this study] and analog [Hoth et al, 2006[Hoth et al, , 2007 modeling, it appears that transient accommodation of strain may be a rather common process.…”

Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

“…16), which produced major crustal thickening, surface uplift and expansive molasse sedimentation in both foreland basins (Beaumont et al, 2000;Vergés et al, 2002;Biteau et al, 2006;Teixell et al, 2016). In parallel, rapid exhumation-related cooling, recorded by thermochronology, took place in the Axial Zone, and continued until the Miocene (Fitzgerald et al, 1999;Sinclair et al, 2005;Jolivet et al, 2007;Metcalf et al, 2009;Bosch et al 2016;Labaume et al, 2016a,b). Teixell et al (2016) propose that by late-mid to late Eocene times the stretched and pulled-apart tracts of lower crust (Fig.…”

Late Paleozoic low-angle southward-dipping thrust in the Züünharaa area, Mongolia: tectonic implications for the geological structures in the Sayan-Baikal and Hangai-Daur belts

“…The doubly vergent asymmetric structure characterizes a ~150-km-wide surface expression of the Hercynian basement, thin-skinned fold-thrust belts shown by the 250-km-long deep seismic survey (ECORS Pyrenees profile; Choukfoune 1989) from the Aquitaine basin to the Ebro basin of the Pyrenees (Sinclair et al 2005). This structure is considered to have formed in the Pyrenees as a result of northward subduction of the Iberian plate beneath the East European craton during Late Cretaceous to early Miocene times (Roest and Srivastava 1991;Sinclair et al 2005).…”