The Neocomian of Chachahuén (Mendoza, Argentina): Evidence of a broken foreland associated with the Payenia flat-slab.

SAGRIPANTI, L; AGUIRRE URRETA, B; FOLGUERA, A; RAMOS, V

Geodynamic Processes in the Andes of Central Chile and Argentina.

Geological Society of London.

Año: 2013;

Isolated marine sedimentary Lower Cretaceous deposits crop out in the foreland flank of the Neuquén Basin in west-central Argentina. The detailed examination of these outcrops in the field, together with seismic subsurface data, shows that they are the result of an anomalous uplift of the Sierra de Chachahuén in the far foreland region, disconnected to the Andes. These outcrops, known from several decades, are assigned to the middle and upper part of Agrio Formation based on their rich fossil contents though show some distinctive proximal facies in the study area. In particular, the study of the upper Agrio Formation reveals a unique outcrop of continental facies along the eastern margin of the basin that even though are known in core wells, constitutes the first expose evidence at the surface. These deposits, which are deformed by the Andean compression, are exposed 70 km far away from the Andean orogenic front. The 2 km uplift of these is interpreted as produced by high angle reverse faults that are the product of selective inversion of a previous early Mesozoic rift system. The combination of the strain field imposed by the emplacement of a large and unique calcalkaline late Miocene volcanic centre, associated with the expansion of the magmatic activity to the foreland, related to a period of shallowing of the subduction zone and the stress field imposed by the plate convergence; has produced the Mesozoic exposures controlled by a broken foreland. This broken foreland has been formed by localized heating of the Miocene volcanic center, that produced the rising of the brittle-ductile transitions, and led to compression in the foreland zone during formation of the Payenia flat-slab.