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Ocean basins form when the sections of Earth's crust, known as tectonic plates, move apart. By studying surface rocks from areas where oceans were formed long ago, scientists have learned that large fault-like areas (shear zones) play a critical role in this process. Now Geoff Abers, associate professor of earth sciences and doctoral student Aaron Ferris (GRS '05) have new data from an active region in Papua New Guinea that provides fresh insight into this process.
Abers, Ferris, and their colleagues recorded and analyzed earthquake data from the Woodlark Rift, the site of the fastest opening continental rift and one that exhibits spectacular surface geology related to tectonic motion. In this area, the northern islands of Trobriand and Woodlark are moving north at the rate of four to five centimeters per year relative to the southern islands such as Misima.
By recording signals from remote earthquakes the team gleaned valuable information about the thickness of the crust and the temperature of the underlying mantle in the rift area. Contrary to expectations they found that both the crust and the mantle are both thinning in the same area, creating a possible basin for some future ocean. The large shear zones visible on the surface seem to be directly controlled by the large-scale changes occurring deep below the surface.
Earlier models, which still may apply to other, more longstanding rifts, predict that the thinning of the crust and mantle would be offset rather than so closely aligned in position.
These findings were reported in the August 22, 2002 issue of the journal Nature.
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