Oceanic crust formation much more dynamic than previously believed

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Washington, November 26 (ANI): Earth scientists in the US have found strong evidence that the geological processes that lead to the formation of oceanic crust are not as uniformly passive as believed, and is quite dynamic.

The team found evidence in the form of a geological phenomenon known as dynamic upwelling in the underlying mantle beneath a spreading center.

Their findings may resolve a longstanding debate regarding the relative importance of passive and dynamic upwelling in the shallow mantle beneath spreading centers on the seafloor.

"We know the crust of the ocean is produced by upwelling beneath separating plates," said Don Forsyth, professor of geological sciences at Brown University.

"We just didn't know the upwelling pattern that took place, that there are concentrated upwelling centers rather than uniform upwelling," he added.

Mantle upwelling and melting beneath spreading centers has been thought to be mostly a passive response to the separating oceanic plates above.

The new finding shows there appears to be a dynamic component as well, driven by the buoyancy of melt retained in the rock or by the lighter chemical composition of rock from which melt has been removed.

The scientists from Brown and the University of Rhode Island based their findings on a high-resolution seismic study in the Gulf of California.

In that region, there are 25 seismometers spaced along the western coast of Mexico and the Baja California peninsula, which lie on either side of the Gulf of California.

Yun Wang, a Brown graduate student and the paper's lead author, tracked the velocity of seismic waves that traveled from one station to another.

She noticed a pattern.

The seismic waves in three localized centers, spaced about 250 kilometers (155 miles) apart, traveled more slowly than waves in the surrounding mantle, implying the presence of more melt in the localized centers and thus a more vigorous upwelling.

From that, the geologists determined the centers, located 40-90 kilometers (25 to 56 miles) below the surface, showed evidence of dynamic upwelling in the mantle.

"We found a pattern that was predicted by some of the theoretical models of upwelling in midoceanic ridges," Forsyth said.

According to Brian Savage, assistant professor of geophysics at the University of Rhode Island, the finding is important, because it helps to provide "a basic understanding of how a majority of the earth's crust is formed, how it emerges from the mantle below to create the oceanic crust. It's a basic science question that helps understand how crust is created." (ANI)

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