Stress Field Evolution of the Southernmost Andean Cordillera From Paleostress Analysis (Argentine Tierra del Fuego)

Abstract

AbstractThe 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.