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Cenozoic Tectonics of the Cape Roberts Rift Basin,
and Transantarctic Mountains Front,
Southwestern Ross Sea, Antarctica
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Abstract
We conducted a multichannel seismic reflection survey offshore
Cape Roberts, Antarctica, and combined our findings with the results
of the Cape Roberts International Drilling Project (CRP). This allows
us to interpret Cenozoic tectonics in the southwest sector of the Ross Sea
including the history of uplift of the Transantarctic Mountains (TAM)
and subsidence of the Victoria Land Basin (VLB). Seismic
stratigraphic sequences mapped offshore Cape 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
kilometers 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 during the early Cenozoic.
The rift graben offshore and adjacent to
Cape Roberts is bounded on the west by a major north trending fault
zone. At Cape Roberts 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 Transantarctic Mountains (TAM) in Oligocene time.
We name it here the McMurdo Sound Fault Zone. A Late Oligocene
angular unconformity that is seen in seismic data and sampled by
CRP drilling marks the end of 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 extension to NW-SE oblique
rifting at that time. Uplift of the TAM and subsidence in the VLB
may be linked with sea floor spreading on the Adare Trough to the
northwest of the Ross Sea between 43 Ma and 26 Ma. This would
imply a plate boundary between East and West Antarctica crossing
through the western Ross Sea in Eocene and Oligocene time.
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