¹⁰Be surface exposure dating reveals unexpected high deformation rates in the central Andean wedge interior

Abstract

Understanding deformation associated with active thrust wedges is essential to evaluate seismic hazards. In this study, we investigate the spatial distribution, timing, and rates of deformation across the central Andean backarc of Argentina, where deformation and shortening have been assumed to occur within a narrow wedge‐front zone. The combined results of our geomorphic mapping, topographic surveying, and 10Be exposure dating demonstrate that fault activity related to the growth of the Andean orogenic wedge is not only limited to a narrow thrust front zone but also occurs in the Andean wedge interior. There, internal structures with deformation rates of ca. 1.3 mm/year have been active during the last ~140 ka. Widely distributed deformation implies that seismic hazards may have been underestimated in the internal part of the Andean orogen.

Late Quaternary Intraplate Deformation Defined by the Las Chacras Fault Zone, West‐Central Argentina

“…Figure 1. (a) Map showing tectonic features(Costa et al, 2000;Siame et al, 2002), GPS velocity uncertainty ellipses(Brooks et al, 2003), and Quaternary slip rates(Costa et al, 2015a(Costa et al, , b, 2018(Costa et al, , 2019García Morabito et al, 2020;Rimando et al, 2019;Rockwell et al, 2014;Salomon et al, 2013;Schmidt et al, 2011a;Siame et al, 1997Siame et al, , 2002Siame et al, , 2006Siame et al, , 2015 in the Pampean flat-slab segment of the Central Andes. Numbers in white boxes indicate faults with known Quaternary slip rates (shortening rates except for those followed by the letter "U," which correspond to uplift rates): 1-El Tigre (strike slip SS) Fault, 2-La Laja Fault, 3-Las Tapias segment of Villicum-Zonda-Pedernal Thrust, 4-Barreal Fault, 5-La Rinconada Fault Zone, 6-Cerro Salinas Fault 7-Las Peñas Thrust, 8-Las Higueras Thrust, 9-La Cal Thrust, 10-Northern Sierra Pie de Palo (Pajaritos) Fault, 11-Eastern Sierra Pie de Palo Fault, and 12-Los Molinos branch of the Comechingones Fault.…”