Constraining erosion rates in fold and thrust belts: Insights from kinematic modelling of the Argentine Precordillera: Jachal section

DÁVILA, FEDERICO M.; CANELO, HORACIO N.; SANCHEZ-NASSIF, F.; EZPELETA, M

La Rioja Capital

Simposio; XVII Reunión de Tectónica La Rioja 2018; 2018

UNLaR │ Universidad Nacional de La Rioja - COMTEC ?AGA │Comisión de Tectónica de la Asociación Geológica Argentina

Kinematic restorations, which have proved a valuable tool for studying the deformational history of fold and thrust belts, have been poorly used in constraining erosion rates. In this contribution, we pose a means of estimating the amount of eroded material in thrust-belts via kinematic restorations. Hence, we combine kinematic restitutions with the classic critically-tapered Coulomb wedge model, following the assumption that at times when thrusting is triggered, the surface slope was less than the angle required to reach self-similar growth, i.e. critical. Following conservative geometrical considerations, we are able to compute a time-varying Coulomb wedge. Such unsteady wedge is used to calculate first-order, time dependent erosion rates, which are compared to denudation and provenance results derived from other techniques. We apply our model to the Argentine Precordillera at the Jáchal river section, whose extensively studied outcrop data have let establish a well-constrained episodic deformation of the thrust-belt; even though no kinematic model of the area had been presented so far. We report two erosion rates, one previous to the movement along the last-in-sequence fault (Niquivil) and one after, 0.1 and 1.12 Km/Myr, respectively. Our results indicate that the amount of eroded material may not always be directly proportional to cumulative slip in the thrust system, as slip along Niquivil thrust is only 22% of the total horizontal displacement, though it produced most of the uplift and erosion. Our results are in striking accordance to long-term erosion estimation proxies, like U-Th/He, 10Be and sedimentological studies, which highlights the validity of the economical methodology here proposed. Furthermore, our kinematic model of the evolution of the Argentine Precordillera allows us to perform 2D flexural numerical modeling, which suggests that tectonic loading seems not to be enough to reproduce basin geometry and that additional mechanisms, such as dynamic subsidence, would be required.