CONICET | Buscador de Institutos y Recursos Humanos

The Matagusanos-Maradona-Acequión Valley sits within the Andes Precordillera foldthrustbelt of western Argentina. It is an elongated topographic depression bounded by theroughly N-S trending Precordillera Central and Oriental in the San Juan Province.Moreover, it is not a piggy-back basin as we could have expected between two rangesbelonging to a fold-thrust belt, but a very active tectonic corridor coinciding with a thickskinnedtriangular zone, squeezed between two different tectonic domains. The twodomains converge, where the Precordillera Oriental has been incorporated to the SierrasPampeanas province, becoming the western leading edge of the west-verging broken foreland Sierras Pampeanas domain. This latter province has been in turn incorporated intothe active deformation framework of the Andes back-arc at these latitudes as a result ofenhanced coupling between the converging plates due to the subduction of the JuanFernández ridge that flattens the Nazca slab under the South American continent.This study focuses on the neotectonics of the southern tip of this N-S elongated depression,known as Acequión (from the homonym river that crosses the area), between the Del Aguaand Los Pozos rivers. This depression dies out against the transversely orientedPrecordillera Sur, which exhibits a similar tectonic style as Precordillera Occidental andCentral (east-verging fold-thrust belt). This contribution brings supporting evidence of theongoing deformation during the Late Pleistocene and Holocene of the triangular zonebounded between the two leading and converging edges of Precordillera Central andOriental thrust fronts, recorded in a multi-episodic lake sequence of the Acequión andNikes rivers. The herein gathered evidence comprise Late Pleistocene-Holocene landformsof active thrusting, fault kinematics (micro-tectonic) data and outcrop-scale (meso-tectonic)faulting and folding of recent lake and alluvial sequences. In addition, seismically-inducedeffects already reported in the literature by this working team further support the tectonicactivity of neighboring faults in the Holocene. As a concluding remark we could state thatthe ongoing deformation in the region under study is driven by a compressional regimewhose maximum horizontal stress in the late Pleistocene-Holocene is roughly east-westoriented. This is further supported by focal mechanism solutions.

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