Development of kinematic partitioning in a pure-shear dominated dextral transpression zone: the southern Ellsworth Mountains, Antarctica

The Heritage Range of the southern Ellsworth Mountains, West Antarctica, is composed of Cambrian to Permian sedimentary and volcanic rocks, which were deformed during the Permo-Triassic Gondwanian orogeny. The structural grain of the Heritage Range exhibits a previously unrecognized 18° swing from 333-153° in the north to 315-135° in the south. A change in structural and kinematic style accompanies this strike-swing, with a structure consistent with near-orthogonal shortening present in the south, and a structural style consistent with dextral transpression within the central and northern Heritage Range. Kinematic partitioning is present within the central Heritage Range, where strikeparallel, contemporaneous domains of dextral and reverse shear have developed simultaneously with the regional cleavage. Comparison of the structure and kinematics within both structural domains suggests that the central and northern Heritage Range experienced pure-shear dominated dextral transpression, with an approximate angle of relative shortening (α) of 65-70°. Results derived by integrating field data into a published kinematic partitioning model suggest relatively efficient kinematic partitioning has occurred. However, such efficient partitioning cannot be explained by strain partitioning models based purely on plate boundary conditions. Therefore, it is proposed that pre-existing weak structures were present within the unexposed basement facilitating the apparent high percentage of kinematic partitioning.