EUGENE, Ore. -- After years of results that repeatedly dogged him, University of Oregon geologist Douglas R. Toomey decided to follow the trail of data surfacing from the Pacific Ocean. In doing so, he and his collaborators may have altered long-held assumptions involving plate tectonics on the ocean floor.
Reporting in the March 22 issue of Nature, Toomey and co-authors from four other institutions propose that, one, the flow in the Earth's mantle is rotated beneath the East Pacific Rise, causing the plate boundary to change orientation with time. Secondly, they argue that deep-sea hydrothermal vents frequently form above volcanoes where upwelling of the mantle and spreading of the plates are aligned.
Surprisingly, Toomey added, the amount of magma produced by volcanoes under both aligned and non-aligned mantle-plate regions is relatively equal, but that magma only in aligned sections regularly breaches the crust. When the volcanic plumbing between the mantle and crust is not aligned, magma cools and volatiles are lost as the magma moves laterally, he said. Most of the magma then remains under the sea floor.
For years, geologic theory has predicted that magma production alone is vital to fuel hydrothermal vents, or the hot smokers where microorganisms such as the Archaea thrive. These new findings indicate that the volcanic-plumbing system better explains why one volcano hosts hot smokers, while another does not, Toomey said.
We've had the data since 1997 and the germ of our results for the last six years, said Toomey, whose funding came through the Ridge 2000 initiative of the National Science Foundation. We've really solidified our findings in the last 18 months. The mantle is moving or flowing in one direction, and the plate boundary is trying to catch up. We've talked for years about passive flow models for ocean ridges - the mantle upwells as a passive response to plate motion. Now we see the mantle flow
Contact: Jim Barlow
University of Oregon