Strike‐slip faults in the southernmost andes and the development of the Patagonian orocline

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Abstract
The Patagonian orocline is the 90° bend in the southernmost Andes between 50°S and 56°S. Paleomagnetic and structural data indicate that the orocline is, at least in part, the product of tectonic rotation. Recent field work in the Beagle Channel region of southernmost Chile provides evidence for widespread left‐lateral strike‐slip faulting in the internal zones of the mountain belt. Both arms of the Beagle Channel are interpreted to be left‐lateral strike‐slip faults based on detailed study of mesoscale strike‐slip faults (Riedel shears) observed in coastal outcrops. Although much of the evidence indicates Cenozoic brittle strike‐slip faulting, other fabric data, including vertical foliation zones containing horizontal quartz stretching lineations and ductile left‐lateral kinematic indicators, suggest that Mesozoic ductile strike‐slip or oblique‐slip shearing also occurred. The implication is that the mid‐Cretaceous Andean orogeny involved the transpressional inversion of the Rocas Verdes marginal basin and that transpression has been the dominant deformational regime in the region for the last 120 Ma. Regional left‐lateral strike‐slip faults are now recognized in all lithotectonic provinces of the southernmost Andes. A statistical study of regional lineament trends using aerial photographs and satellite imagery suggests that many unstudied lineaments are also strike‐slip faults. A new model is proposed that integrates the development of strike‐slip faulting and the structural evolution and uplift of the southernmost Andes with the rotational development of the orocline. The Patagonian orocline appears to be the product of broad interplate shearing accommodated by strike‐slip faulting, block rotation, and contraction and is probably continuing to evolve today.