SOUTHERNMOST SOUTH-AMERICA ANTARCTIC PENINSULA RELATIVE PLATE MOTIONSSINCE 84 MA - IMPLICATIONS FOR THE TECTONIC EVOLUTION OF THE SCOTIA ARC REGION

We have attempted to quantify the relative motion history between sout hernmost South America (SSA) and the Antarctic Peninsula (AP) by calcu lating and comparing SSA-Africa, AP-Africa and SSA-AP synthetic now li nes 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 referen ce frame has been significantly more rapid than AP's rate, Approximate ly 1320 km of east-west, left-lateral strike-slip displacement and 490 km of north-south, divergent displacement have occurred between the s outhern tip of SSA and the northern tip of AP since 84 Ma. Increased r ates of SSA-AP interplate separation and a change in the angle of plat e divergence at approximately 55-40 Ma marked the onset of accelerated continental separation that eventually led to seafloor spreading in t he western Scotia Sea at 30 Ma and the development of the Scotia Are. Increased separation rates between SSA and AP at 55-40 Ma may be relat ed to a global Eocene plate reorganization event. The northeast-southw est oriented western Scotia Sea spreading centers appear to have accom modated all of the SSA-AP interplate motion between 30 and 9 Ma. We su ggest that prior to 30 Ma and the opening of Drake Passage, components of interplate strike-slip and divergent motion were accommodated by i ntracontinental deformation that included strike-slip faulting, counte rclockwise tectonic rotation, and continental extension in the souther nmost Andes. The results indicate that the opening of the Scotia Sea w as caused by plate-scale motions as SSA and AP drifted away from Afric a at different velocities along different, nonparallel trajectories. S ubduction retreat along the South Scotia Ridge and South Sandwich are and back are spreading in the Scotia Sea contributed to the width of s eparation between SSA and AP across Drake Passage. The results place l imits on how SSA-AP relative motion has been temporally and spatially partitioned in the Scotia Are region.