HR: 0830h
AN: GP21A-0033    [PDF]
TI: Magnetic Anomalies Associated With Fracture Zones in the Cretaceous Magnetic Quiet Zone in the North Pacific Ocean
AU: * Ishihara, T
EM: t-ishihara@aist.go.jp
AF: Geological Survey of Japan, AIST Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AB: The existence of magnetic anomalies along east-west trending fracture zones in the north Pacific is well known. These anomalies are particularly prominent in the Cretaceous magnetic quiet zone, where no comparable anomalies are observed other than those associated with the Hawaiian Ridge and the Musician Seamounts in a newly compiled magnetic anomaly map. Model calculation was conducted using old magnetic and bathymetric data collected in the Cretaceous magnetic quiet zone. Two-dimensional simple models along north-south lines, which cross the Mendocino, Pioneer, Murray, Molokai and Clarion Fracture Zones, were constructed in order to clarify the sources of these magnetic anomalies. In these model calculations, it was assumed that the source bodies have normal remanent magnetizations with their inclinations of about $<$ETH$>$5 (for Mendocino FZ) to -25 degrees (for Clarion FZ), corresponding to the latitudes 40 degrees south of the present locations, as was suggested to have been in the late Cretaceous by some of paleomagnetic studies. This assumption is consistent with the dominance of negative anomalies in the observation. The model calculations suggest that under assumption of 0.5 km thick magnetic source bodies, remanent magnetizations more than 10 A/m should occur below some of the ridges and troughs in these fractures zones. Alternatively, in more plausible models with a remanent magnetization of 3 A/m, the magnetic source bodies should have thicknesses of up to about 5 km there.
DE: 0903 Computational methods, potential fields
DE: 0925 Magnetic and electrical methods
DE: 0930 Oceanic structures
DE: 1517 Magnetic anomaly modeling
DE: 9355 Pacific Ocean
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting