Andean sinistral transpression and kinematic partitioning in South Georgia

Abstract

The island of South Georgia exposes remnants of a Late Jurassic to Early Cretaceous Andean magmatic arc and marginal basin system that was compressively deformed during the mid-Cretaceous main Andean Orogeny forming widespread NW-SE trending folds and a coaxial penetrative cleavage displaying a predominantly NE-SW stretching lineation. Detailed structural studies of the Cooper Bay to Cape Vahsel area of South Georgia reveal that intense, mid-Cretaceous, polyphase deformation was strongly influenced by sinistral strike-slip shear parallel to the NW-SE regional structural grain, and along a major pre-existing fault, which we interpret as the partitioned wrench component of bulk transpressional deformation. The relationship between fold axial plane orientation and interlimb angle of widely distributed mesoscale folds is consistent with counter-clockwise rotation and fold appression as a result of sinistral simple shear deformation, suggesting kinematic strain partitioning of the wrench component was on the whole highly efficient. Locally, the modification of steep tectonic anisotropies to shallow inclinations during D 2 deformation induced imperfect or inefficient partitioning with fold arrays exhibiting fold appression characteristic of a transpressional deformation path. Our partitioned transpression model for main Andean deformation of South Georgia fits well with tectonic interpretations of the Cordillera Darwin, Patagonia.