The South Sandwich plate (or Sandwich plate) is a small oceanic microplate located south of the South American plate in the Southern Ocean; the volcanic South Sandwich Islands are situated on this microplate. It is flanked by three larger plates: the South American plate to the east (which subducts beneath the microplate), the Antarctic plate to the south, and the Scotia plate to the west.
The plate’s eastern margin is a classic convergent boundary where subduction has produced the South Sandwich Trench and the volcanic arc and trench morphology typical of oceanic subduction systems. On the western side, the East Scotia Rise represents a back-arc spreading center that developed in response to processes linked to this eastern subduction, forming the spreading locus between the South Sandwich and Scotia plates.
Tectonically, subduction along the South Sandwich margin began around 66 Ma in response to regional convergence between the Antarctic and South American plates, establishing a long-lived convergent regime. Continued regional deformation—characterized by back-arc extension of the Scotia Sea and rollback (trench retreat) of South American oceanic lithosphere—produced an ancestral Scotia plate through trench retreat and extension. The South Sandwich microplate separated from that ancestral Scotia domain roughly 15 Ma as a back-arc basin opened and the East Scotia Rise developed, producing the present plate geometry. Geodynamic explanations for this separation emphasize either subducting-slab rollback, the absolute motion of the Scotia plate away from the trench, or a combination of both; regional mapping and plate-kinematic studies document the plate relationships and relative motions along the East Scotia Rise, South Sandwich Trench and adjacent boundaries.