Stress field evolution of the southernmost Andean Cordillera from paleostress analysis (Argentine Tierra del Fuego).

Abstract

The Argentine Tierra del Fuego comprises part of the roughly east-west trending southern end of the Andean Cordillera intensely deformed since the Mesozoic. Mesostructures have been measured in Late Jurassic to Miocene rocks. Taking into account statistical criteria to provide a representative stress tensor from a fault population, this study defines 28 paleostress tensors pertaining to 22 sites. The orientation of σ1 shows two main modes trending E-W to ESE-WNW and NE-SW. In addition, extensional sites reveal N-S, NE-SW, ESE-WNW, and NW-SE horizontal σ3 and vertical σ1. The stress fields obtained are congruous with a regional NE-SW compressive stress direction active in the study zone since the Late Cretaceous. Shortening was coeval with a 30° counterclockwise rotation of the Patagonian orogenic curve and the indentation of the orogenic wedge against a basement high, the Río Chico Arch, up to the early Miocene. The indentation caused a modification in the orientation of the compressive stress trajectories, showing NE-SW direction in Sorondo Range sector and NW-SE in Mitre Peninsula area. Since the late Miocene, left-lateral activity along the Magallanes-Fagnano Fault System produced local deviations of the NE-SW compressive stress toward an E-W direction. The present-day stress field is also characterized by NE-SW subhorizontal P axis derived from earthquake focal mechanisms and geodetic studies.