Gravity collapse structures in the Central Precordillera fold-and-thrust belt, Argentina

Several landforms found in the fold-and-thrust belt area of the Andean Central Precordillera of Argentina, which were often associated with tectonic shortening, are in fact related to superficial gravity tectonic structures. These gravitational collapse structures have developed in the western flank of sierras de La Dehesa and Talacasto. These include rock-slides, rock falls, wrinkle folds, slip sheets and flaps, among others; which together constitute a monoclinal fold dipping between 30 degrees and 60 degrees to the west. Gravity collapse structures are parallel to the regional strike of the sierras de la Dehesa and Talacasto are placed in Ordovician limestones and dolomites. Their sloping towards the west, the presence of bed planes, fractures and joints; and the lithology (limestone interbedded with incompetent argillaceous layers) would have favored their occurrence. Detachment and initial transport of gravity collapse structures and rockslides in the western flank of the Sierra de la Dehesa were tightly controlled by three structural elements: 1) the bedding, when It is dipping > 30 degrees in the slope direction; 2) joint sets that constitute lateral and transverse traction cracks which release extensional stresses; and 3) discontinuities fragmenting sliding surfaces. Some other factors that could be characterized as local (lithology, structure and topography) and as regional (high seismic activity and possibly wetter conditions during the postglacial period) were determinant in favoring the steady loss of the western mountain side in the easternmost foothills of the Central Precordillera.