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

SANCHEZ NASSIF, ; CANELO, H.; DAVILA, F.M.

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019 vol. 758 p. 1 - 11

0040-1951

Kinematic restorations in fold and thrust belts, which are a valuable tool for studying the deformational historyof fold and thrust belts, have been poorly used to understand erosion rates. In this contribution, we estimated theamount of eroded material in thrust-belts via kinematic reconstructions. We combined kinematic restitutionswith the classic critically-tapered Coulomb wedge model, following the assumption that at times when thrustingis triggered, the surface slope was less than the angle required to reach self-similar growth, i.e. critical. Followingconservative geometrical considerations, we were able to compute a time-varying Coulomb wedge. Such un-steady wedge is used to calculatefirst-order, time dependent erosion rates, which are compared to denudationand provenance results derived from other techniques. We applied our model to the Argentine Precordillera atthe Jáchal river section, whose extensively studied outcrop data have let establish a well-constrained episodicdeformation of the thrust-belt; even though no kinematic model of the area had been presented so far. Ourresults 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. Ourfindings indicate that the amount of eroded materialmight not always be directly proportional to cumulative slip in the thrust system, as slip along Niquivil thrust isonly 22% of the total horizontal displacement, though it produced most of the uplift and erosion. Our results arein striking accordance to long-term erosion estimation proxies, like U-Th/He,10Be and sedimentological studies,which highlights the validity of the economical methodology herein proposed. Furthermore, our kinematicmodel of the evolution of the Argentine Precordillera allows us to perform 2Dflexural numerical modeling,which suggests that tectonic loading seems to not be enough to reproduce basin geometry and that additionalmechanisms, such as dynamic subsidence or lithospheric mantle thickening (among others), would be required.