Constraining erosion rates in thrust belts: Insights from kinematic modeling of the Argentine Precordillera, Jachal section

Abstract

Kinematic restorations in fold and thrust belts, which are a valuable tool for studying the deformational history of fold and thrust belts, have been poorly used to understand erosion rates. In this contribution, we estimated the amount of eroded material in thrust-belts via kinematic reconstructions. We combined 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 were 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 applied 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. Our results show two contrasting erosion rates, one prior to the movement along the last-in-sequence fault (Niquivil) and one after, 0.1 and 1.34 Km/Myr, respectively. Our findings indicate that the amount of eroded material might 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, 10 Be and sedimentological studies, which highlights the validity of the economical methodology herein 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 to not be enough to reproduce basin geometry and that additional mechanisms, such as dynamic subsidence or lithospheric mantle thickening (among others), would be required.