Kinematics of a backthrust system in the Agrio fold and thrust belt, Argentina: Insights from structural analysis and analogue models

Abstract

The Agrio fold and thrust belt is an orogenic belt located in the Southern Central Andes (37°-38°S latitude). A set of thin-skinned thrust-related folds with opposite vergence to the tectonic push, occur in front of major thick-skinned structures. Seven west-vergent anticlines that involve the Late Jurassic - Early Cretaceous sequences of the Mendoza Group were mapped. These folds were formed by imbricate faults detached on underlying Jurassic evaporites (Auquilco Formation). A regional balanced-cross section shows that this backthrust system accommodates part of the shortening transferred by major east-directed basement-involved thrusts developed in the inner zone of the Agrio fold and thrust belt. Analogue model was constructed to reproduce the structures and to understand their kinematic evolution. The model illustrates that the individual backthrusts develop in a normal sequence of faulting; it means that successively younger backthrusts are formed in the footwall to the west of previous faults. The comparison between field structures and those obtained in laboratory allows to analyze the close relationship between the thick and thin-skinned structures during the development of the Agrio fold and thrust belt and to discuss possible causes that favoured the generation of the studied backthrust system.