Tasmania and adjoining continental blocks, the South Tasnam Rise (STR) and East Tasman Plateau (ETP), are central components of a major fragmentation of east Gondwana that began in early Late Cretaceous. The tectonic development of the Tasmanian region is key to understanding (i) the kinematics and geological evolution of adjacent plates and former neighboring continents and microcontinents that have now dispersed, (ii) formation of the extensive sedimentary basins off Tasmania, and (iii) major changes in ocean circulation, climate and sedimentation patterns associated with the opening of a deep-water seaway between Tasmania and Antarctica at the end of the Eocene. The Australian and Antarctic continents separated at the SW tip of the STR at 33.5 Ma, Opening a deep seaway that led to circum-Antarctic circulation circulation as the continents continued to drift apart. Significant flow-through may have begun several million years earlier across passages in the southern Ninene Basin and South Tasman Saddle, due to basin extension and increased margin subsidence. (mod. journ. abst.)