HR: 1340h
AN: T33B-1349    [Abstracts]
TI: Deep-tow Investigation of Crustal Magnetization at the 9N Overlapping Spreading Centers on the East Pacific Rise
AU: * O'Brien, J F
EM: jobrien@geol.sc.edu
AF: University of South Carolina, Dept of Geological Sciences 701 Sumter Street, EWS 617 University of South Carolina, Columbia, SC 29208, United States
AU: White, S M
EM: swhite@geol.sc.edu
AF: University of South Carolina, Dept of Geological Sciences 701 Sumter Street, EWS 617 University of South Carolina, Columbia, SC 29208, United States
AB: Previous estimations of crustal thickness at OSCs have been determined by using seismic velocity models to determine the location of seismic layer 2A in the subsurface. These estimations may be inaccurate due to accretionary processes and alteration of the rocks at the OSC which place the base of layer 2A at depths that do not coincide with the base of the extrusive volcanic layer. A more accurate estimation of the true crustal thickness can be made by measuring the magnetic fields present in the extrusive rock layer of the region. Determination of thickness of the extrusive layer beneath both limbs and overlap basin of the OSC can aid in understanding the geomorphology and ongoing processes of these ridge axis discontinuities. A recent research expedition was conducted in Spring 2007 to study the OSC at 9°03'N on the East Pacific Rise. A fluxgate magnetometer was attached to the deep-towed DSL-120A towfish to measure the magnetic field at a 110 meter altitude above the sea floor. A total of 10 track lines were run in a north-south orientation covering the 20 km length of the OSC with an average spacing of 1 km. Computational inversions were performed on the magnetic fields using the Fourier approach of Parker and Huestis to solve for magnetism of the rocks and to constrain for the thickness of the underlying extrusive volcanic rock layer. Results of the inversions show magnetic anomalies of up to 600 nT near the tip of the southward propagating eastern limb. The ROV Jason 2 collected over 200 rock samples at the OSC of which 25 were subsequently analyzed for NRM, susceptibility and stability. Results of the rock sample analyses show consistently high stability from both limbs and central basin and lack of secondary alteration. NRM and susceptibility measurements show two distinct zones of high anomalies on the eastern limb located between 9°05'N and 9°08'N and on the western limb between 9°00'N and 9°01'N.
DE: 0925 Magnetic and electrical methods (5109)
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 3035 Midocean ridge processes
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting