HR: 1340h
AN: U33A-0032    [Abstracts]
TI: Paleomagnetic Data From Ontong Java Plateau are Anomalous $\sim$ Did the Plateau Form on Another Plate?
AU: * Sager, W W
EM: wsager@ocean.tamu.edu
AF: Department of Oceanography, Texas A$&$M University, College Station, TX 77843 United States
AB: A recent study of Ocean Drilling Program basalt core paleomagnetic data from Ontong Java Plateau (OJP) found paleolatitudes that disagree with previous estimates of the Early Cretaceous Pacific APWP, a result attributed to poor quality of data used in prior pole calculations [Riisager, P., S. Hall, M. Antretter, X. Zhao, Earth Planet. Sci. Lett., 208, p. 235, 2003]. My compilation of paleomagnetic data from Cretaceous Pacific basalt cores drilled by the Deep Sea Drilling Project and Ocean Drilling Program shows that paleocolatitude data in of ages 118-129 Ma display greater scatter than other age bins. The only factor that allows this data group to be coherently subdivided is whether or not the coring site is located on OJP. Without OJP data, paleocolatitude scatter is much less and gives a similar pole position (48.9$\deg$N, 327.1$\deg$E, N=40) to data in the 110-118 Ma interval. Data from the plateau give a pole that is 15$\deg$ farther north (64.9$\deg$N, 323.4$\deg$E; N=37), indistinguishable from late Jurassic and earliest Cretaceous skewness poles. The OJP and non-OJP poles are distinct at the 95$%$ confidence level despite having indistinguishable mean ages of 121.6 $\pm$1.1 Ma (OJP) and 123.4 $\pm$4.1 (non-OJP). Because Ontong Java Plateau data come from 6 different sites spread over the northern plateau, tectonic tilting is not a likely explanation for the difference. Also unlikely are systematic errors such as incomplete averaging of secular variation (large number of independent magnetic units sampled), inaccurate radiometric dates (many high quality dates), or inadequate paleomagnetic techniques (detailed studies by several different investigators). Rapid true polar wander does not seem a plausible explanation because global true polar wander curves have a different trend. Perhaps the simplest explanation is the one often used when anomalous data are found within a plate: the anomalous region had a different history of tectonic drift. In this scenario, OJP formed on a separate plate that drifted southward relative to the Pacific plate before becoming attached. This finding is similar to the AŸ’'A+ƒ_TAŸƒ_sA,A›AŸ’'A,A›AŸA›A›ƒ_sAªA.A­AŸƒ_sA,AªAŸ’'A›ƒ,ªAÝAŸA›A›ƒ_sAªA.ƒ_oStealth PlateAŸ’'A+ƒ_TAŸƒ_sA,A›AŸ’'A,A›AŸA›A›ƒ_sAªA.A­AŸƒ_sA,AªAŸ’'A,A_AŸƒ_sA,A¨AŸƒ_sA,A« hypothesis [Larson, R. L., and W. W. Sager, Proc. ODP, Sci. Res., 129, p. 471, 1992], which was formulated to explain a similar angular difference between skewness-derived paleolatitudes from the Hawaiian and Japanese magnetic lineations relative to the Phoenix lineations. The most significant challenge for this hypothesis, however, is to account for the space and plate boundaries. If true, this hypothesis implies either that much of the Jurassic Quiet Zone seafloor was created by Pacific-Stealth spreading or that an unknown plate boundary near OJP separated the plateau from the rest of the Pacific plate.
DE: 9355 Pacific Ocean
DE: 8157 Plate motions--past (3040)
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1599 General or miscellaneous
SC: Union [U]
MN: 2004 AGU Fall Meeting