in the southern ridge. Shackleton Fracture Zone The western edge of the plate is bounded by the Antarctic Plate, forming the Shackleton Fracture Zone and the southern Chile Trench. The Southern Chile Trench is a southern extension of the subduction of the Antarctic and Nazca plates below South America. Heading south along the ridge, the subduction rate decreases until its remaining oblique motion evolves into the Shackleton Fracture Zone transform boundary. The south-western edge of the plate is bounded by the Shetland microplate separating the Shackleton Fracture Zone and the South Scotia Ridge. North of South Shetland Islands and along the southern half of the Shackleton Fracture Zone is the remnant of the Phoenix Plate (also known as Drake or Aluk Plate). Around 47 Ma the subduction of the Phoenix Plate started as the propagation of the Pacific-Antarctic Ridge continued. The last collision between Phoenix ridge segments and the subduction zone was 6.5 Ma and at 3.3 Ma movements had stopped and the remnants of the Phoenix Plate was incorporated into the Antarctic Plate. The southern part of the Shackleton Fracture Zone is the former eastern edge of the Phoenix Plate. East Scotia Ridge The eastern edge of the Scotia Plate is a spreading ridge bounded by the South Sandwich microplate, forming the East Scotia Ridge. The East Scotia Ridge is a back-arc spreading ridge that formed due to subduction of the South American Plate below the South Sandwich Plate along the South Sandwich Island arc. Exact spreading rates are still being disputed in the literature, but it has been agreed that rates range between 60 and 90 mm/yr. The banks of northern Central Scotia Sea are superposed on oceanic basement and the spreading centre of the West Scotia Sea. Analyses of samples of volcaniclastic rocks from these sites indicate they are constructs of a continental arc and in some cases oceanic arc similar to those being formed in the currently active South Sandwich Arc. The oldest volcanic arc activity in the central and eastern regions of the Scotia Sea are 28.5 Ma. The South Sandwich forarc originated in the Central Scotia Sea at that time but has since been translated eastward by the back-arc spreading centre of the East Scotia Ridge. Timeline The timing of the formation of the Scotia Plate and opening of the Drake Passage have long been the subject of much debate due to the important