HR: 0800h
AN: T41A-11    [Abstracts]
TI: Revised Pacific-Antarctic rotations from anomaly 20 (~45 Ma) to present
AU: * Croon, M B
EM: mcroon@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0220, United States
AU: Cande, S C
EM: scande@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0220, United States
AU: Stock, J M
EM: jstock@gps.caltech.edu
AF: We present improved rotation parameters for the Pacific-Antarctic spreading ridge. A reconnaissance survey of swath MultiBeam bathymetry and magnetic data of the Menard fracture zone allows for significant refinement of these rotation parameters. The data were mainly collected by the NSF (Office of Polar Programs) operated RVIB Nathaniel Palmer during transits between Lyttelton, New Zealand and Punta Arenas, Chile between 1997 and 2006. In the late Cretaceous all fracture zones south of the Campbell plateau were left-stepping, whereas today most are right-stepping. The right stepping Pitman fracture zone may have developed as a response to a major plate reorganization at Chron C27 (63 Ma), which likely spawned many other right stepping fracture zones (Cande 1995). About 45 Ma ago the Pacific-Antarctic spreading ridge at this latitude nucleated within a propagating rift system that birthed the Hudson microplate and formed the conjugate Henry and Hudson Troughs, which flank the Menard fracture zone on either side (thesis B. Eakins, 2000). The Menard fracture zone experienced adaptations to changes in plate motion. Two splays, originally about 25 to 30 km apart, narrow gradually to a corridor of 5 to 10 km width, due to changes in spreading direction between roughly 32 and 23 Ma (C13 to C6b). The stagepoles, with the Antarctic plate fixed relative to the Pacific plate, experienced a period of rapid shifts in location between roughly 32 and 23 Ma (C13 to C6b). The stagepoles remained relatively stationary between C6c and C5a (24.1 to 12.3 Ma) and migrated again relatively continuously since Chron C5a (12.3 Ma). Meanwhile the transform offset of Menard fracture zone increased from about 150 to 200 km to about 200 to 250 km. The northern splay of Menard fracture zone coalesced with the southern splay slightly after Chron C3o (4.5 Ma) leaving only one transform fault. A prominent bathymetric deep at the transform fault of Menard fracture zone is possibly formed by transtension.
DE: 8155 Plate motions: general (3040)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly