April 1, 2013
Geologists Say Earth’s Tectonic Movements Sometimes Get Congested
Brett Smith for redOrbit.com - Your Universe Online
According to a new study from a team of German researchers, geological forces are stagnating in certain regions because of pressure-induced phase transitions.
The Earth´s crust is in a constant state of flux, with solid slabs diving hundreds of miles down into the mantle as hot liquid magma rises up to fill the gaps. According to study author“¯Falko Langenhorst from the Friedrich Schiller University Jena, these forces are constantly changing the face of the Earth as we know it.
"In 100 million years' time Africa will be pulled apart and North Australia will be at the equator," he said.
While these forces normally take millennia for their effects to be seen, the team of German scientists found that congestion at certain points in the crust and mantle will stall the geological forces in some regions, according to their study, which appeared in a recent edition of Nature Geoscience.
"Seismic measurements show that in some mantle regions, where one slab is subducted underneath another one, the movement stagnates as soon as the rocks have reached a certain depth," Langenhorst explained.
Based on a series of laboratory experiments simulating different temperatures and pressures, the researchers say the problems occur at depths of around 250 to 350 kilometers between two different layers of the Earth´s mantle.
"The reason for that can be found in the slow diffusion and transformation of mineral components," Langenhorst said.
The German scientist explained that the melting and chemical reactions that occur at shallower depths — primarily between the main minerals of pyroxene and garnet — cause the submerging rocks to become denser. In turn, this causes the submerging plate to become buoyant and the increased buoyancy essentially stalls subduction, the process whereby one tectonic plate slips beneath another and sinks into the Earth´s mantle.
"The diffusion of a pyroxene-component in garnet is so slow, that the submerging rocks don't become denser and heavier, and therefore stagnate," Langenhost said.
The scientist noted that this buoyancy is particularly noticeable where the ocean floor appears to be submerging into the Earth at a particularly high rate.
"In the Tonga rift off Japan for example, the speed of subduction is very high," Langenhorst said. He added that the speed of such a subduction doesn´t allow for the sinking crust to heat and melt effectively.
"It takes about 100 million years for pyroxene crystals which are only 1 mm in size to diffuse into the garnet. For this amount of time the submerging plate stagnates," he said.
In their report, the authors said that pyroxene undergoes another phase transformation at the base of the mantle transition zone, at a depth of around 350 miles. As the higher pressures of these depths cause pyroxene to change into the mineral akimotoite, the rock slab becomes denser.
"This could lead to an immediate rise in the rock density and would enable the submerging into greater depths,” Langenhorst said.
Geologists from the Friedrich Schiller University Jena have also been focused on monitoring the Hawaiian volcano Kilauea. Using cutting-edge radar technology, the scientists are able to track the shifting and elevation changes that occur within the volcano.