HR: 14:32h
AN: GP33B-04 INVITED     [Abstracts]
TI: Geomagnetic paleointensity results from 9° - 10°N on the East Pacific Rise and models of lava accretion at fast-spreading ridges
AU: * Bowles, J
EM: jbowles@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego 9500 Gilman Dr., MC 0220, La Jolla, CA 92093 United States
AU: Gee, J S
EM: jsgee@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego 9500 Gilman Dr., MC 0220, La Jolla, CA 92093 United States
AU: Kent, D V
EM: dvk@rci.rutgers.edu
AF: Rutgers University, Department of Geology 610 Taylor Road, Piscataway, NJ 08854 United States
AU: Perfit, M R
EM: perfit@geology.ufl.edu
AF: University of Florida, Geological Sciences PO BOX 112120, Gainesville, FL 32611 United States
AU: Soule, A
EM: ssoule@whoi.edu
AF: Woods Hole Oceanographic Institution, Mailstop 24, Woods Hole, MA 02543 United States
AU: Fornari, D J
EM: dfornari@whoi.edu
AF: Woods Hole Oceanographic Institution, Mailstop 24, Woods Hole, MA 02543 United States
AB: Our understanding of the neovolcanic zone at fast spreading ridges has become more sophisticated in recent years, but placing accurate age constraints on many near-axis flows remains difficult. Geomagnetic paleointensity recorded in submarine basaltic glass (SBG) holds promise for placing quantitative age constraints on near-axis flows. Based on the results of over 500 SBG paleointensity estimates from 189 near-axis (< 4 km) sites at the East Pacific Rise, 9° - 10°N, we evaluate the temporal and spatial variability in lava accretion. Paleointensities range from 6 - 53 μT and are distributed spatially as would be expected from known temporal variations in the geomagnetic field: samples within and adjacent to the axial summit trough (AST) have values approximately equal to or slightly higher than the present day; off-axis samples out to 1-3 km from the AST have values higher than the present day; and samples farther off-axis have values lower than the present day. Paleointensity values are also generally consistent with rough age interpretations based on sidescan data. While along-axis data (< 500 m from the AST) provide constraints on eruptive recurrence intervals, the cross-axis data contain valuable information regarding variability in spatial scales of lava accretion. Spatial patterns in paleointensity data suggest that the width of the lava emplacement zone must vary significantly in time and in space, locally remaining quite narrow (< 1 km half-width) for extended periods of time. This implies that extensive off-axis flow emplacement may occur infrequently, with recurrence intervals of 10-20 kyr. Results of a stochastic model of lava emplacement show that this can be achieved by modeling the eruptive recurrence interval as a Poisson process, which results in a standard gamma distribution of wait times. Flow size is directly or indirectly linked to wait time through an available magma budget. A median wait time of 70 years most closely matches the patterns seen in the paleointensity data, and such a flow distribution results in a flow > 3.5 km total width once ever ~20 kyr on average.
DE: 1521 Paleointensity
DE: 1527 Paleomagnetism applied to geologic processes
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 3035 Midocean ridge processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005