The Infiernillo fault, Malargüe fold and thrust belt (Andes of Mendoza), is a Miocene reverse fault: Implications for the tectonic history of the region

Abstract

The Infiernillo fault is located in the Andes of southern Mendoza province, Argentina, within the Malargüe fold and thrust belt. It has been interpreted as a normal fault active in the Miocene and the Quaternary, and is a key element in a model proposing a Quaternary extensional orogenic collapse in the region. However, recent studies have documented a contractional Quaternary deformation regime in this sector, as shown by neotectonic thrusts. Furthermore, the Miocene is the period of the main event of Andean contraction and uplift in the region. Therefore, the interpretation of the Infiernillo fault as a normal structure conflicts with the regional tectonic evolution of the Andes at these latitudes. Based on field observations and fault kinematic data, we conclude that the Infiernillo fault was a reverse out-of-sequence fault in the late Miocene, and did not have a Quaternary reactivation. This implies that the Malargüe fold and thrust belt did not undergo a collapse in the Quaternary. Our results support a model where contractional deformation can be accomodated simultaneously by several structures in different locations across the orogen during the evolution of fold and thrust belts.