Geometric and kinematic model for basement-involved backthrusting at Diamante River, southern Andes, Mendoza province, Argentina

Abstract

At the confluence of the Las Aucas stream with the Diamante River (69°30′W Long.; 34°40′S Lat.), kilometer-scale structures affecting basement rocks were surveyed. Andean deformation involved both Cordillera Principal and Cordillera Frontal rocks, whose structures probably were locally contemporaneous and intimately related. The Cordón del Carrizalito, a huge structure interpreted as a rigid basement block raised by a reverse fault on the eastern edge, which produced intense deformation in the sedimentary cover, can be explained by a geometric and kinematic model for basement-involved structures in the upper crustal levels. The Lomas Bayas structure is considered a west-vergent anticline associated with a backthrust, which branches out from the basement block's eastern edge. A new kinematic quantitative model, based on the Lomas Bayas structure, explains basement-involved backthrusts. Shearing of the basement rocks produced progressive rotation of the backthrust's hangingwall block, whose upper toe is bent but sedimentary cover is delaminated and detached. These retrodeformable models are applied to two cross-sections to test their viability and calculate the structural shortening.