Mechanisms and phases of orogenic build up in the eastern Andean front

ALVAREZ CERIMEDO, J; ORTS, D; ROJAS VERA, E; FOLGUERA, A; BOTTESI, G; RAMOS, V

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Año: 2013 vol. 40 p. 1 - 20

0718-7092

The eastern Andean orogenic front at 36ºS shows unique attributes when compared to neighbor segments. Particularly it has an anomalous eastward development of the orogenic front area due to the uplift of a zone of reduced topography in the foothills constituting a pre-Andean belt. Additionally Late Oligocene to Early Miocene within-plate series are occupying an important surface in the next foreland area. This work focuses on the study of this area from extensive field mapping and analysis of seismic lines, trying to unravel its complex evolution that led to its particular morphology and geology. A pre-Late Oligocene stage of exhumation is followed by an extensional relaxation phase circumscribed to the orogenic front area. A second period of contractional deformation uplifted the pre-Andean sector. Contractional mechanisms involved deep ramps rooted into the basement, some of which are linked to inverted Late Oligocene-Miocene normal faults, to shallower detachments located in the Upper Cretaceous and Miocene incompetent layers. This last stage of orogenic construction is associated with synorogenic strata that show coarsening up sedimentary cycles with an eastward provenance.