NEOGENE TECTONIC FRAMEWORK OF THE ROSS EMBAYMENT, ANTARCTICA

The main tectonic elements of the Ross embayment region, the West Antarctic rift system and the Transantarctic Mountains (TAM) rift shoulder, were established in Mesozoic and early Cenozoic times. In Neogene times, the rift regime changed and the inception of major volcanism modified the pre-existing paleogeography. Regional arguments indicate that Cretaceous rifting was important in the Ross embayment, however, the Cape Roberts Project (CRP) stratigraphic drilling showed that the main phase of rifting in the western Ross Sea adjacent to the TAM occurred in Oligocene times. The stratigraphic record from CRP shows that growth faulting associated with an east-tilting half-graben continued at least until 17 Ma, and that a regional episode of transtension and strike-slip faulting must be younger than this time, forming the Terror Rift. The Terror Rift may link with major strike-slip faults crossing the TAM in northern Victoria Land, and may either terminate in southern McMurdo Sound or be offset across a transfer zone and continue southward into the Ross embayment. The Transantarctic Mountains attained much of their current form prior to the Neogene, as indicated by thermochronology and the unroofing history recorded in Oligo-Miocene strata cored by CRP. Geomorphic studies in the Transantarctic Mountains adjacent to McMurdo Sound, combined with dating of landscape features, indicate that the current mountain landscape has existed with only minor glacial modification since at least 14 Ma. To the north, however, glacial geomorphic evidence is interpreted to indicate substantial late Neogene-Recent uplift. The regional paleogeography changed dramatically by construction of the archipelago of major volcanoes and volcanic islands in southern McMurdo sound in the Neogene.