Quaternary tectonics in the southern Central Andes (37°-38° S): Retroarc compression inferred from morphotectonics and numerical models

Abstract

A neotectonic study at the transitional segment between the Central and North Patagonian Andes, in the northern part of the Neuquén province in Argentina (37°-38°S) was carried out revisiting sites previously surveyed and addressing new field evidence from a morphotectonic perspective. Particularly, fieldwork in the Guañacos fold and thrust belt (GFTB) highlighted that the inner retroarc region at these latitudes has been dominated, almost exclusively, by a Quaternary compressive regime, contrarily to previous proposals that favored a strike-slip regime. The main structures affect upper Pliocene Cola de Zorro Formation and younger deposits, developing scarps up to 60 m in height. Numerical models were performed to simulate Guañacos fault activity and to test the reliability of the scarps and deformed strata as deformation markers. From these models, shortening rates of 0.04–0.06 mm/yr were calculated. In addition, new evidence of normal faulting in Pliocene rocks was revealed. In a more regional frame, we revised two models that introduced and explained the dextral faulting in this segment of the Andes during the Quaternary, which is well constrained by focal mechanisms at the arc zone. Even though seismological data reveal strike-slip deformation along the arc, our findings suggest that at the same latitudes in the inner retroarc zone, immediately to the east, strain partitioning is negligible and, although with low deformation rates, all this transitional region between the Central and North Patagonian Andes is affected by Quaternary compressional stresses controlling surface deformation. A major crustal boundary, i.e. the Arauco transition zone, might be exerting a first-order control in this particular stress-strain distribution.