Superposed deformation in the Peninsula Mitre recess (Fuegian thrust-fold belt, Southern Argentina), and implications for orogenic curve kinematics

摘要

A detailed study of the structure of the Peninsula Mitre recess in the Fuegian thrust-fold belt of southern Argentina reveals superposed deformation related to contrasting shortening directions. One group of structures trend parallel to the recess and verge either towards the foreland or towards the hinterland. A second group of structures accommodate contraction superposed on the previous group. Analysis of fault-slip data reveals that the first group is related to sigma 1 perpendicular to the surface traces of thrusts and/or fold axes, and are therefore compressive structures. In contrast, the paleostress tensors of the second group of structures show sigma 1 orientations parallel or at a low angle with respect to local structural trends. The style of the superposed structures of the second group, which mostly indicate contraction subparallel to the trend of the recess, is consistent with structures resulting from tangential longitudinal shortening associated with oroclinal bending. This scenario implies that the Peninsula Mitre recess formed as a progressive curve involving rotation due to slip trajectories convergent toward the recess, causing the observed tangential contraction. This kinematic model supports previous interpretations of buttressing of the thrust-fold belt against a basement promontory.