HR: 0800h
AN: GP11D-0867    [Abstracts]
TI: Paleomagnetic Paleolatitudes of the Ontong Java Plateau From 120 Ma to 55 Ma: Implications for the Apparent Polar Wander Path of the Pacific Plate.
AU: * Hall, S A
EM: sahgeo@uh.edu
AF: Dept of Geosciences, University of Houston, Houston, TX 77204-5007 United States
AU: Riisager, P
AF: Earth Sciences Department, University of California at Santa Cruz, Santa Cruz, CA University United States
AU: Riisager, P
AF: Geological Museum, University of Copenhagen,$\O$ster Voldgade 5-7, Copenhagen, DK-1350 Denmark
AB: Paleomagnetic analyses of Late Cretaceous- early Tertiary deep-water carbonates obtained during ODP Leg 192 drilling have been used to document the latitudinal motion of the Ontong Java Plateau (OJP). Paleolatitude estimates were obtained for the following periods: magnetochrons 25n-25r (55.9-57.5 Ma), 27r-31n (61.3-68.7 Ma), 32n-32r (71.1-73.6 Ma) and 33n (73.6-79.1 Ma). The broad agreement between our new sedimentary paleomagnetic data and those recently obtained from OJP basement rocks suggests that possible compaction-induced inclination shallowing in the studied sediments is negligible. Anisotropy of anhysteretic remanent magnetization measurements further support this argument, yielding magnetic fabrics that appear poorly correlated with individual characteristic remanent magnetization inclinations. \ Our results when combined with other OJP paleomagnetic data yield an internally consistent data set that describes the northward motion of the plateau from its formation $\sim$120 Ma until 55 Ma. Between 120 Ma and 76 Ma the plateau is located near $24\deg$S and is either stationary or exhibits a slow northward movement. From 76 Ma until 68 Ma the plateau moves rapidly through approximately $10\deg$ of latitude to $\sim10\deg$S. From 68 Ma until 56 Ma the plateau is again almost stationary before moving slowly northward. Our data therefore support previous suggestions for a Cretaceous "standstill" of the Pacific plate and provide additional constraints upon proposed episodes of rapid plate movement. Our new OJP paleomagnetic paleolatitudes are generally lower than those predicted by indirect data from seamount magnetization studies and deskew analyses for chron 27r/31n but are higher than those predicted from deskew analyses for chrons 32 and 33n. More direct paleomagnetic data are necessary to define Pacific plate motion, drift of hotspots, and possible true polar wander events. We suggest that deep-water carbonates, if carefully analysed, can yield reliable paleomagnetic inclinations.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting