HR: 16:30h
AN: T14A-03    [Abstracts]
TI: Constraints on Late Cretaceous and Cenozoic Extension in the Ross Sea from the Southwest Pacific Plate Circuit
AU: * Cande, S C
EM: scande@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Code 0220, La Jolla, CA 92093-0220 United States
AU: Stock, J M
EM: jstock@gps.caltech.edu
AF: Caltech, 252-21, Pasadena, CA 91125 United States
AB: Magnetic anomalies and fracture zone trends north of the Ross Sea associated with Australia-Antarctic, Pacific-Antarctic and Lord Howe Rise-Antarctic sea floor spreading place strong constraints on Late Cretaceous and Cenozoic motion between East and West Antarctica. There appear to be two episodes of extension in the Western Ross Sea in this time period. The younger episode, starting about 45 Ma and ending around 25 Ma, is well constrained by differences in spreading rates on the Southeast Indian Ridge (SEIR) on either side of the Balleny FZ and by magnetic anomalies straddling the Adare Trough (Cande et al., 2000). These data document about 150 km of ENE-WSW directed extension across the Adare Basin just north of the Ross Sea. An earlier (80 to 55 Ma) episode of extension is not well constrained in large part because the spreading rate between Australia and East Antarctica was very slow and identifications of magnetic anomalies older than anomaly 24 on the SEIR are problematical. However, there are useful constraints imposed by fitting magnetic anomalies and fracture zone traces from north of the Iselin Bank, from southwest of the Campbell Plateau and from the South Tasman Sea. These features form a network of tectonic constraints that have to be fit by any proposed model of East - West Antarctic motion. A reconstruction of the conjugate splays of the Emerald FZ shows that the Iselin Trough, a fossil rift structure northeast of the Iselin Bank, formed by a local ccw rotation of 12 degrees about 72.6ø S, 183ø E of the Iselin Bank between anomalies 27 and 24, thus constraining East-West Antarctic extension in this period to the corridor west of the Iselin Bank. These features also enable us to test the plate circuit formed by closing the Campbell Plateau and Challenger Plateau to its pre-rift (50 Ma) configuration and closing the Tasman Sea, SEIR and Pacific-Antarctic ridge. Rotations for the SEIR which treat the older Australia-Antarctic magnetic anomalies as isochrons (Tikku and Cande, 1999) are not appropriate for this test since they produce a large overlap of the South Tasman Rise and Tasmania with Northern Victoria Land. The SEIR rotations of Royer and Rollett (1997), which do not fit the Australia-Antarctic anomalies very well, produce a reasonable closure of the Iselin Bank with Northern Victoria Land and predict about 100 km of additional (pre-55 Ma) extension in the northern Ross Sea.
DE: 9310 Antarctica
DE: 8155 Plate motions--general
DE: 8157 Plate motions--past (3040)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting