A compressive system overimposed to an oblique rift: Applications in the Malargüe fold and thrust belt, southern Mendoza.

Abstract

Analogue modelling experiments were performed to simulate the evolution that results from the application of compressive stresses oblique to the axis of a pre-existing extensional system. Granular materials were used to represent brittle upper crustal rocks. Two asymmetric halfgrabens linked by a transfer fault were created in the base of the models, and were subsequently compressed moving a piston in oblique sense to the halfgrabens' strike. The aim of these experiments was to analyze the structural pattern that results from a change of tectonic regime, studying the influence that exerts the preexisting extensional structures over the style of latter compressive deformation. Even though the obtained results show limited reactivation of normal faults, the final geometric arrangement of the new reverse faults was strongly controlled by them. Increasing the distance between the underlying extensional system and the advancing thrust front results in a loss of its influence over the newly formed thrusts. Associated with the imposed structural control, strike changes of the thrusts, length variations of the thrust sheets, differential uplifting near the basal structure and out of sequence thrusting localized in certain sectors of the system were found. These results have been compared with the structural architecture of the southern sector of the Malargüe fold and thrust belt, suggesting analogies that allow interpreting the presence of NE and NW oriented extensional trends for the Jurassic extensional event in this region.