HR: 1340h
AN: T33B-1352 INVITED    [Abstracts]
TI: Implications for Magma Supply to Overlapping Spreading Centers at 9N East Pacific Rise from Widespread Low Effusion Rate Eruptions for the Past 2 M.Y.
AU: * White, S M
EM: swhite@geol.sc.edu
AF: Dept Geological Sciences, Univ South Carolina, Columbia, SC 29208, United States
AU: Macdonald, K C
EM: macdonald@geol.ucsb.edu
AF: Dept Earth Science, UCSB, Santa Barbara, CA 93106, United States
AB: Zero-age seafloor along the crest of mid-ocean ridges deepens in the vicinity of over 95% of well-mapped ridge axis discontinuities such as transform faults and overlapping spreading centers. Ever since the discovery that the ridge axis deepens at ridge axis discontinuities, there has been vigorous debate about whether ridge axis depth and shape reflects magma supply. The East Pacific Rise (EPR) is an ideal location to investigate the processes taking place at ridge discontinuities because the fast-spreading rate combined with long spreading segments and relatively little off-axis deformation provides a clear record of the history of a discontinuity by preserving the seafloor on the ridge flank. Here we report evidence, from one of the most thoroughly studied ridge discontinuities on a fast-spreading mid-ocean ridge, that volcanic eruption effusion rates have been low relative to the mid- segment regions for at least the past 2 million years since the discontinuity began. This is inferred from the distribution of fields of mounds which are much more abundant in the off-axis discordant zone of the EPR 9° N overlapping spreading centers than on typical EPR seafloor. These mounds are constructed primarily by pillow lava which is erupted at lower effusion rates along the EPR than lobate and sheet lavas. This new observation, combined with a host of previously reported measurements ranging from the distribution of hydrothermal faunal communities to crustal magnetization and geochemistry, supports the hypothesis that segmentation of fast-spreading mid-ocean ridges reflects the pattern of melt generation and supply from the underlying mantle. These new observations indicate that this pattern was sustained on the EPR at 9-10° N for at least 2 My.
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3075 Submarine tectonics and volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting