HR: 1340h
AN: GP43A-0847    [Abstracts]
TI: Evaluating Extension in the Ross Sea vs. Vertical Axis Rotation in West Antarctica as the Cause of the Offset of West and East Antarctic ca. 100 Ma Paleomagnetic Poles
AU: * DiVenere, V
EM: divenere@liu.edu
AF: C.W. Post - Long Island University, Deparment of Earth and Environmental Science 720 Northern Blvd., Brookville, NY 11548 United States
AB: Mid-Cretaceous (ca. 100 Ma) paleomagnetic poles from eastern, central, and western Marie Byrd Land (MBL) are concordant with one another and with similar age poles from the Thurston Island (TI) and Antarctic Peninsula (AP) blocks. These West Antarctic results are, however, offset from the East Antarctic Apparent Polar Wander Path. DiVenere et al. (1994) interpreted the offset as the result of opening of the Ross Sea after 100 Ma. In contrast, Luyendyk et al. (1996) proposed vertical-axis rotations in West Antarctica, as in southern California, as an alternative explanation for the offset. This was suggested to be due to transtensional separation of New Zealand from Marie Byrd Land. The scale of the proposed West Antarctic rotational corridor (~3000 km from western MBL to the northern AP) is an order of magnitude larger than the scale observed in southern California. The method used by Luyendyk et al. (1996) (decomposing the offset between the East and West Antarctic poles into separate components of vertical-axis rotation and poleward motion) is poorly suited for the study of MBL because the close proximity of the 100 Ma paleomagnetic pole to the sample sites results in greatly differing estimates of apparent rotation vs. poleward motion depending on the proposed position for the vertical rotation axis. In fact, this method implies post-100 Ma vertical axis rotation with no statistically distinguishable horizontal displacement for the northern Ford Ranges while implying large horizontal displacement with no discernible vertical axis rotation for the Ruppert/Hobbs Coast of central MBL and the Kohler Ranges of eastern MBL. Moving eastward from MBL to Thurston Island and the Antarctic Peninsula, progressively less vertical-axis rotation is required to reconcile the paleomagnetic poles with the East Antarctic poles due to the progressive increase in the distance of the rotation pole from the paleomagnetic pole. This pattern of diminishing apparent rotations does not fit a simple "rolling ball-bearings between two plates" model. Similar amounts of vertical axis rotation would have induced progressively larger amounts of offset from the East Antarctic pole from western MBL to the northern AP. It seems unlikely that a mechanism yielding the observed post-100 Ma sequence of diminishing apparent rotations would result in such a fortuitous grouping of displaced paleomagnetic poles. The offset of the mid-Cretaceous West Antarctic poles from the East Antarctic pole is more simply explained as the result of horizontal displacement between East and West Antarctica due to extension in the Ross Sea and Ross Sea Embayment.
DE: 8110 Continental tectonics--general (0905)
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting