Cenozoic tectonics of the Cape Roberts Rift Basin and Transantarctic Mountains Front, Southwestern Ross Sea, Antarctica

We conducted a multichannel seismic reflection survey offshore Cape Roberts , Antarctica, and combined our findings with the results of the Cape Robert s International Drilling Project (CRP). This allows us to interpret Cenozoi c tectonics in the southwest sector of the Ross Sea including the history o f uplift of the Transantarctic Mountains (TAM) and the subsidence of the Vi ctoria Land Basin (VLB). Seismic stratigraphic sequences mapped offshore Ca pe Roberts are tilted eastward and thicken into the VLB where they comprise more than half the fill seen on seismic records. Normal faults a few kilom eters offshore cut these sequences and define a north trending rift graben. Drilling results from the CRP show that these strata are latest Eocene (?) , Oligocene, and younger in age; much younger than previously inferred. We interpret this pattern to be due to an episode of E-W extension and related subsidence that occurred across the major basins in the western Ross Sea d uring the early Cenozoic. The rift graben offshore and adjacent to Cape Rob erts is bounded on the west by a major north trending to Cape Roberts is bo unded on this fault system may have from 6 to 9 km of vertical separation. This fault system is part of a larger zone along the coastline in southern Victoria Land that accommodated uplift of the TAM in Oligocene time. We nam e it here the McMurdo Sound Fault Zone. A late Oligocene angular unconformi ty that is seen in seismic data and sampled by CRP drilling marks the end o f the east tilting of the stratigraphic sequences. We interpret this as the end of the main uplift of the TAM coinciding with a change from E-W extens ion to NW-SE oblique rifting at the time. Uplift of the TAM and subsidence in the VLB may be linked with seafloor spreading on the Adare Trough to the northwest of the Ross Sea between 43 and 26 Ma. This would imply a plate b oundary between East and West Antarctica crossing through the western Ross Sea in Eocene and Oligocene time.