Some of the highest quality images ever taken of the Earth's lowercrust reveal that the upper and lower crust form in two distinctlydifferent ways.
"This new way of studying the ocean crust is the equivalent of a newtelescope in astronomy," said Bruce Malfait, head of the NationalScience Foundation (NSF)'s marine geosciences section, which funded theresearch. "It allows us to look at Earth processes and composition at aremarkable new level of detail."
To form the images, the researchers, led by a team from ColumbiaUniversity's Lamont-Doherty Earth Observatory (LDEO), analyzed soundwaves bounced off structures deep in the Earth, a process similar tocreating an ultrasound image. They published the results of their workin the Aug. 25 issue of the journal Nature.
The Earth's oceanic crust is formed from molten rock, or magma,located beneath mid-ocean ridges. Magma chambers located in themid-crust are known to be responsible for generating the upper-oceaniccrust. But it has so far been unclear if the lower crust is formed fromthe same magma source, or if it arises primarily from "magmalenses"--smaller bodies located at or near the base of the crust.
The resulting images are the first of their kind to show solidifiedlenses and sills--narrow lateral intrusions of magma--embedded withinthe crust-mantle boundary known as the Moho transition zone. Thepresence of such lenses and sills deep near a mid-ocean ridge suggeststhe lower crust is at least partially formed from several smallersources of magma rather than from a single large source located in themiddle of the crust.
"This demonstrates that the process of crustal formation is morecomplex than believed," said LDEO scientist and lead author of thestudy, Mladen Nedimovic. "It also favors the emerging view thatvolcanoes have a complicated plumbing system consisting of manyinterconnected sills and magma conduits. We still have a lot to learnabout what goes on beneath the surface of the Earth."
Researchers from LDEO as well as the Scripps Institution ofOceanography and the Woods Hole Oceanographic Institution collectedseismic data from the oceanic crust beneath the sea floor off the coastof Wash., Ore., and northern Calif.
The study was also funded by a grant from the Doherty Foundation.
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