Structure and neotectonics of the Lomas de Olmedo, a transition zone between the Subandean and Santa Bárbara Systems, province of Salta

Abstract

The present study shows evidence of neotectonic deformation in the Northwestern Argentina region of Lomas de Olmedo, province of Salta. This region is located in the orogenic front at 24°S latitude and encompasses a transition zone between the Sierras Subandinas to the north, a thin-skinned belt with east vergence, or Subandean System sensu stricto, and a southern segment corresponding to the Santa Bárbara System produced by tectonic inversion of normal faults with west vergence. Between this two segments of different behavior are the Lomas de Olmedo, which have a complex array of active faults. Paleogene deposits of the sag phases produced during thermal subsidence of the Salta rift system, and Neogene synorogenic deposits related to the Andean uplift are folded and thrust on the Quaternary deposits of the El Chorro Formation of Quaternary age. The 14C ages from gastropod shells from this unit belonging to Pomacea canaliculata yielded an age of 7,962 ± 45 BP years for these deposits. The reverse faults with east vergence indicate a shortening rate for most of the Holocene of 2.34 mm/a for the tectonic thrust front in the transition zone between the two fold and thrust belts of the Subandean area.