Rock samples collected from a series of African mines during a recent expedition indicate that the process of subduction is at least 2 billion years old, even if plate tectonics appeared (in their current configuration) just 1 billion years ago.
Large-scale continental movements are a trademark of the tectonic forces acting under the surface of our planet. These motions inevitably lead to collisions between different plates, and the process of subduction takes place where one of these plates is driven underneath the other one.
It was until now believed that subduction was a direct consequence of current tectonic patterns, but the new study demonstrates that this is not the case. The new samples were absolutely essential to making the new discovery, which may very well change the way we understand Earth's evolution.
The European Synchrotron Radiation Facility (ESRF) was responsible for conducting the X-ray studies on this research. Scientists from the Brookhaven National Laboratory (BNL), Monash University, the Universities of Cambridge, Grenoble, Lausanne and Ouagadougou were also a part of the science team.
The group was led by investigator J. Ganne, of the University of Toulouse, in France. Details of the research appear in the November 20 issue of the top journal Nature Geoscience. Experts say that subduction takes place at a rate of a few millimeters per year, depending on the area.
Based on these estimates, experts calculated many years ago that all the continents we see today were organized as a single supercontinent some 250 million years ago. Called Pangaea, it was torn apart by tectonic forces, which ruptured it into several smaller portions.
The rocks researchers collected allowed them to investigate the distribution of chemical elements within, something that is related to the way subduction occurs as tectonic plates move away from each other. Experts used a study technique called X-ray absorption near-edge spectroscopy (XANES).
Interestingly, scientists discovered that subduction occurred in its current configuration between 2 and 2.2 billion years ago, as demonstrated by the spatial distribution of chemicals inside the tested samples.
What is so remarkable about these findings is that the phenomenon occurred even if the planet itself was a lot hotter at the time. The mantle – the layer between the outer core and the crust – was also considerably warmer, which means that the forces driving plate tectonics had different parameters.
Scientists now plan to conduct XANES measurements on rock samples aged between 2.5 and 3.8 billion years. If similar results occur, then it may be that our understanding of the way plate tectonics work is a bit misguided.