Earth Mantle: Strangely stable flow points discovered

Upstream flows between Africa and the Central Pacific have been in place for 250 million years

Location of the Two Stable Upstreams in the Earth's Mantle (Red) © Clint Conrad / University of Hawaii
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The earth's crust is in constant motion: continents merge and break again. But there are two places on Earth that have been stable for at least 250 million years: two ascent zones in the Earth's mantle where hot material has been rising since then. Today, they are under Africa and under the Central Pacific, but in the course of geological history, this geological heat source burned even by prehistoric crust of the primal continent Pangea, as researchers report in the journal "Nature".

"The supercontinent Pangea formed and then gradually broke apart - but despite these dramatic transformations on the surface, the two upward currents in the Earth's mantle remained constant all the time, " says First-Instance Clint Conrad of the University of Hawaii. The circulating currents in the Earth's mantle are also the motor for plate tectonics and thus the drift of the continents: where hot semi-liquid rock rises and flows laterally under the crust, it also attracts the overlying plates with it. Elsewhere, crustal material is forced down and sinks into the deep mantle.

The researchers discovered the two stable sheath flows by accurately measuring and observing plate movements. "I was curious if there was a point to which all the tectonic plates in the northern hemisphere move, " Conrad explains. In fact, there are, as the measurements showed: He is in East Asia. Based on this finding, the scientists developed a mathematical model that identified two diverging points and two convergence points.

"Ghosts of Ancient Mantle Movements"

When they transferred this model to earlier and today's positions and motions of the earth plates, two points were found to have remained stable over more than 250 million years. "I was amazed that these places did not move in geological time, " said Conrad. They are located in the central Pacific Ocean and Africa and are among the areas where hot mantle material rises. "It was like seeing the ghosts of primeval mantle currents, " says the researcher.

The new discovery raises the question as to why these two sites have remained stable in a complex and dynamic system like the Earth's mantle. An indication could provide the composition of the shell, as the researchers explain. For under Africa and the Central Pacific, he deviates chemically from the rock elsewhere in the mantle. It is also unclear whether and how these two flow points influence the movements of the remaining shell material. display

"Answering these questions is important, because geological phenomena such as ocean basins, mountain ranges, earthquakes and volcanoes ultimately go back to the Earth's internal dynamics, " explains Conrad. To better understand what the surface of our home planet is, it is therefore important to research and understand the processes under the crust. (Nature, 2013; doi: 10.1038 / nature12203)

(University of Hawaii / German Research Center for Geosciences GFZ, 27.06.2013 - NPO)