Southernmost South America-Antarctic Peninsula relative plate motions since 84 Ma: Implications for the tectonic evolution of the Scotia Arc region

We have attempted to quantify the relative motion history between southernmost South America (SSA) and the Antarctic Peninsula (AP) by calculating and comparing SSA-Africa, AP-Africa and SSA-AP synthetic flow lines for 84–0 Ma. The flow lines were created using published poles of rotation and plate reconstruction software. The results indicate that since 84 Ma, SSA and AP have moved approximately westward relative to a fixed Africa; however, SSA's rate of westerly motion in that reference frame has been significantly more rapid than AP's rate. Approximately 1320 km of east-west, left-lateral strike-slip displacement and 490 km of north-south, divergent displacement have occurred between the southern tip of SSA and the northern tip of AP since 84 Ma. Increased rates of SSA-AP interplate separation and a change in the angle of plate divergence at approximately 55–40 Ma marked the onset of accelerated continental separation that eventually led to seafloor spreading in the western Scotia Sea at 30 Ma and the development of the Scotia Arc. Increased separation rates between SSA and AP at 55–40 Ma may be related to a global Eocene plate reorganization event. The northeast-southwest oriented western Scotia Sea spreading centers appear to have accommodated all of the SSA-AP interplate motion between 30 and 9 Ma. We suggest that prior to 30 Ma and the opening of Drake Passage, components of interplate strike-slip and divergent motion were accommodated by intracontinental deformation that included strike-slip faulting, counterclockwise tectonic rotation, and continental extension in the southernmost Andes. The results indicate that the opening of the Scotia Sea was caused by plate-scale motions as SSA and AP drifted away from Africa at different velocities along different, nonparallel trajectories. Subduction retreat along the South Scotia Ridge and South Sandwich arc and back arc spreading in the Scotia Sea contributed to the width of separation between SSA and AP across Drake Passage. The results place limits on how SSA-AP relative motion has been temporally and spatially partitioned in the Scotia Arc region.