Abstract

Analysis of the polyphase fault population of southeastern Livingston Island led us to establish three brittle deformation phases characterized by homoaxial stress tensors. One of the horizontal axes trends NW-SE, parallel to the transform faults governing the relative movement between the Phoenix and Antarctic plates. On the basis of the principles of symmetry these tensors are interpreted as corresponding to the regional stress field, and the transition between the phases is seen as reflecting changes in the relative values of the principal axes of their corresponding stress tensors. Phases 1 and 2 correspond to strike slip regimes, the first having NW-SE-oriented (σl (maximum principal compressive stress), whereas σ1 of phase 2 has a NE-SW trend. Phases 2 and 3 show a NW-SE-oriented σ3 (minimum principal compressive stress). The decreasing magnitude of the NW-SE stress axis during the recorded history is interpreted as being related to the decreasing velocities of the interacting plates caused by the cessation of the accretion at the Antarctic-Phoenix Ridge. The kinematic evolution of the analysed fault population can be understood assuming that faults form according to the Anderson model, that extensional dykes and veins form perpendicular to u3, and that fault slip on pre-existing fractures occurs parallel to the maximum shear stress direction on those planes.

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