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 setof thin-skinned thrust-related folds with opposite vergence to the tectonic push, occur in front of major thickskinnedstructures. Seven west-vergent anticlines that involve the Late Jurassic - Early Cretaceous sequences ofthe Mendoza Group were mapped. These folds were formed by imbricate faults detached on underlying Jurassicevaporites (Auquilco Formation). A regional balanced-cross section shows that this backthrust system accommodatespart of the shortening transferred by major east-directed basement-involved thrusts developed in theinner zone of the Agrio fold and thrust belt. Analogue model was constructed to reproduce the structures and tounderstand their kinematic evolution. The model illustrates that the individual backthrusts develop in a normalsequence of faulting; it means that successively younger backthrusts are formed in the footwall to the west ofprevious faults. The comparison between field structures and those obtained in laboratory allows to analyze theclose relationship between the thick and thin-skinned structures during the development of the Agrio fold andthrust belt and to discuss possible causes that favoured the generation of the studied backthrust system.