J.F. Moyen et al., Geology, 2012
Today's crustal plate (left) dives deep beneath the surface, whereas billions of years ago (right), a plate would have encountered very hot temperatures and simply broken off.
How Plate Tectonics Started
Post: July 12, 2012 11:30 am
Author: Laura Komor
The crust of our Earth is constantly in flux. It’s made up of huge plates that are regularly bumping into each other, diving down, and uplifting. But this wasn’t always the case. A recent study published in the journal Geology
shows that plate subduction was once an intermittent occurrence. Jeroen van Hunen from England’s Durham University and Jean-François Moyen of Jean Monnet University in France began this study by looking at rocks that appeared to be a mix of older and newer materials. These rocks, from Australia and Zimbabwe, were made up of rock that underwent alteration after being subjected to high temperatures, as well as newer rock. The altered rock was probably the result of a crustal plate that subducted underneath another plate, reaching the high temperatures of the mantle where it was changed. However, this rock is mixed with newer rock in the study samples, meaning that the subduction process must have stopped at some point. Moyen and van Hunen proposed a theory: maybe the plates stopped diving under others because billions of years ago, the Earth’s mantle was much hotter than it is now. Under such circumstances, the high temperatures could have caused the plates to break off and halt subduction until the rock cooled enough to begin diving under again. About 2.7 billion years ago, the temperature of the mantle cooled and stabilized, allowing plate subduction to become a permanent process.
Another recent study by Tomas Naeraa, a researcher at the Geological Survey of Denmark and Greenland, suggests that 3.2 billion years ago, rocks were formed primarily by plumes of boiling hot magma that ejected up from the mantle. Naeraa also showed that isotope patterns from before 3.2 billion years ago were significantly different than those of newer rocks, indicating that the mantle was cooling down at this time, allowing plate subduction to begin, although intermittently.
Discover more at ScienceNews
The original article is in the journal Geology
Read more about Naeraa’s study in the journal Nature