HR: 1340h
AN: T13B-1356    [Abstracts]
TI: Magnetic Properties of Ocean Crust from the Walls of Endeavor Deep: Implications for the Source Layers of Marine Magnetic Anomalies
AU: * Richmond, R M
EM: rmrichmond@ucdavis.edu
AF: University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Pockalny, R A
EM: robp@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AU: King, J W
EM: jking@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AU: Larson, R L
EM: rlar@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AU: Popham, C T
EM: pophamc@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AB: The presence of lineated marine magnetic anomalies in the ocean basins is the foundation for plate tectonics and global plate reconstructions. The relative importance of the source layers of these anomalies, however, is still poorly constrained. Identifying the source layer(s) of the magnetic anomalies is important for present-day models of crustal accretion that require crustal rotations of up to 20-30 degrees. These rotations may result in anomalously skewed seafloor magnetic anomalies, which could significantly alter global plate reconstructions. To address the question of the magnetic sources at ultra-fast spreading rates, we have measured the magnetic properties of 135 precisely located rock samples collected with JASON II from the walls of Endeavor Deep. Endeavor Deep is the tip of a propagating rift on the Nazca/Juan Fernandez plate boundary. It exposes a 70 km-long, 40 km-wide, and 3 km-deep section of ~3 Myr old upper oceanic crust (layers 2A and 2B) created at the ultra-fast spreading (~150 km/myr) East Pacific Rise. Measurements of natural remanent magnetization, magnetic susceptibility, and median destructive field define three "stratigraphic" units and are characterized relative to similar measurements by Pariso and Johnson (1991) on samples from DSDP Hole 504B. The upper 200 m of extrusives were likely altered by low temperature oxidation, and carry a relatively low magnetization (0.4 A/m). The underlying 300 m of extrusives carry a relatively high magnetization (2.1 A/m), which likely contributes significantly to the amplitude of the magnetic anomaly signal. The transition zone from extrusive layer 2A to intrusive layer 2B (pillow basalts to dykes) and possibly the upper portion of layer 2B carries an unexpectedly high magnetization (1.6 A/m) and likely contributes to the magnetic source layer as well. A dramatic increase in susceptibility is present below the base of layer 2A that has not been previously observed.
DE: 1517 Magnetic anomaly modeling
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting