Spatio-temporal variation of the strain field in the southern Central Andes broken-foreland (27°30′S) during the Late Cenozoic

QUIROGA, R; PEÑA, M; POBLETE, F.; GIAMBIAGI, L; MESCUA, J; GOMEZ, I

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020

0895-9811

We present an integrated structural and Anisotropy of Magnetic Susceptibility (AMS) study focused on the characterization of the spatio-temporal variation of the strain field during the main Neogene deformation, documented in Argentine Precordillera and the northern Sierras Pampeanas, immediately to the south of the Puna plateau (27°30´S). The AMS from 43 sites and fault-slip data analysis from mesoscale faults (n=540) were carried out in Early Miocene to Middle Pliocene sedimentary and volcaniclastic rocks. The AMS results show that the magnetic susceptibility is mainly controlled by paramagnetic minerals, with high values of anisotropy degree near to deformation zones, while the values diminished far away from these areas. The magnetic sedimentary fabric is recorded in undeformed or slightly-deformed areas. In areas where the rocks are deformed, the incipient magnetic lineation is well-developed, they are subparallel to the regional structural trend, and they present a main N-S orientation in the Precordillera and Fiambala basin, while in the Sierras Pampeanas they are mostly NE-oriented. Combining these results with kinematic analysis from fault-slip data, we identify, in the Precordillera and Fiambalá basin areas, a contractional event with E-W main direction, from ~23 Ma to 5 Ma, mostly active from the onset of deposition of Neogene sequences. During this period, in the NW Sierras Pampeanas, the contraction directions follow a NW orientation. The onset of N-S to NNW contraction directions, mostly recognized in rocks younger than 5 Ma, exposed in the northern areas of Precordillera and Sierra Pampeanas, document a change of the strain field during the early-to-middle Pliocene from E-W to N-S. We relate the change in the strain field to a major contraction direction influenced by the rapid uplift of the Puna, generating a juxtaposition of an area under N-S extension affecting the topographically-higher Puna with the other area under contraction in the adjacent Precordillera and Sierras Pampeanas. We associate the events documented in this work as a part of the evolution of this segment of the Andes, where the broken foreland setting is active during this time. By combining the AMS and kinematic analysis results, we obtain a timing for the spatio-temporal change of contraction directions, which allows us to compare both the broken-foreland and foreland basins to understand spatio-temporal strain variations.