Stress transmission across an active plate boundary: an example from southern Mexico

Abstract

Paleostress tensors calculated from inversion of fault-slip data at 60 stations between Zihuatanejo and Tehuantepec in southern Mexico were separated into four distinct groups and assigned to time intervals between 150 Ma and Recent. The change in orientation of the maximum horizontal stress closely traces the change in direction of convergence between the North American and the Farallon/Cocos plates for the same time interval. Depending on the angle between the convergence direction and the plate margin, both thrust fault and strike-slip stress regimes were active. Based on this comparison, we infer that the stress distribution in the continental crust of southern Mexico has been controlled by interplate stress transmission. Latest Cretaceous-Early Tertiary mylonites at the northern edge of the Xolapa complex portray left-lateral oblique crustal extension and oceanward migration of the upper plate. The orientation of extension at mid-crustal level grossly correspond to the orientation of the minimum compressive stress at upper crustal level. During the last 20 Ma a tensional stress regime as a response to surface uplift has been dominant in southern Mexico.