Tectonic plates weaker than previously thought

Tectonic plates weaker than previously thought

Experiments carried out at Oxford University have revealed that tectonic plates are weaker than previously thought. The finding explains an ambiguity in lab work that led scientists to believe these rocks were much stronger than they appeared to be in the natural world. This new knowledge will help us understand how tectonic plates can break to form new boundaries.

Study co-author Lars Hansen, Associate Professor of Rock and Mineral Physics in Oxford University's Department of Earth Sciences, said: 'The strength of tectonic plates has been a major target of research for the past four decades. For plate tectonics to work, plates must be able to break to form new plate boundaries. Significant effort has gone into measuring the strength of the key olivine-rich rocks that make up plates using laboratory experiments.

Unfortunately, those estimates of rock strength have been significantly greater than the apparent strength of plates as observed on Earth. Thus, there is a fundamental lack of understanding of how plates can actually break to form new boundaries. Furthermore, the estimates of rock strength from laboratory experiments exhibit considerable variability, reducing confidence in using experiments to estimate rock properties.

The new research, published in the journal Science Advances, uses a technique known as 'nanoindentation' to resolve this discrepancy and explain how the rocks that make up tectonic plates can be weak enough to break and form new plate boundaries.

"We have demonstrated that this variability among previous estimates of strength is a result of a special length-scale within the rocks - that is, the strength depends on the volume of material being tested. To determine this we used nanoindentation experiments in which a microscopic diamond stylus is pressed into the surface of an olivine crystal. These experiments reveal that the strength of the crystal depends on the size of the indentation," Dr. Hansen said.

This concept translates to large rock samples, for which the measured strength increases as the size of the constituent crystals decreases. Because most previous experiments have used synthetic rocks with crystal sizes much smaller than typically found in nature, they have drastically overestimated the strength of tectonic plates.

"Our results therefore both explain the wide range of previous estimates of rock strength and provide confirmation that the strength of the rocks that make up tectonic plates is low enough to form new plate boundaries," he said.

This result has implications beyond forming tectonic plate boundaries. Better predictions of the strength of rocks under these conditions will help inform us on many dynamic processes in plates.

For instance, we now know that the evolution of stresses on earthquake-generating faults likely depends on the size of the individual crystals that make up the rocks involved. In addition, flexing of plates under the weight of volcanoes or large ice sheets, a process intimately linked to sea level on Earth, will also ultimately depend on crystal size.

Source: University of Oxford

Featured image: Tectonic plates at þingvellir by Gamene (Flickr)

Comments

Whirled Publishing 4 days ago

This is an edit of the email I sent to Lars Hansen with my responses to three of his quotes:

" ... there is a fundamental lack of understanding of how plates can actually break to form new boundaries ... " You admit you don't understand when, why or how tectonic plates break to form new boundaries and you're saying - in public - that since you don't understand the forces that break and subduct tectonic plates, and since the most brilliant minds at Oxford, Cambridge and Stanford don't understand the forces that break and subduct tectonic plates, no one understands it ... no way could someone have figured this out ... is this what you're saying?

" ... tectonic plates can be weak enough to break and form new plate boundaries ... " Yes, tectonic plates break and form new boundaries - the subduction of tectonic plates is even more amazing, and the deep crevasses on the seafloor along the edges of some of the tectonic plates is even more spectacular. These clues are right in front of you - but you don't understand these forces that have broken and subducted the tectonic plates?

Lars, the forces that break and subduct the tectonic plates are already known and understood - including the exact date in history when the Cascadia subduction occurred, the exact date in history when the subduction beneath the South Sandwich Islands occurred, and the exact dates when dozens and dozens of other cataclysms have occurred.

Since you don't understand the forces that break and subduct tectonic plates, you assume it must be some long drawn-out geological process?

Lars, broken and subducted tectonic plates - and ocean trenches - are formed in minutes - not across millions of years.

Geologists are paid to be experts on these topics and yet they do not know ... while I am not paid to know and yet I know ... why? Because I was more interested in the truth rather than in a paycheck or in the status of being a professor - I taught at a private college - but I gave it up to pursue research.

Geologists don't understand the history or our Earth and the forces that have shaped the continents, the mountains, the glaciers, etc., because geologists cling to fake dates which have nothing to corroborate them - this attachment to unsubstantiated dates and the attachment to an unsubstantiated timeline results in you cheating yourselves out of knowing the true history of our Earth. You are also cheating your students and you are cheating the public out of knowing the true history of our Earth - while you assume you are an expert.

The forces that broke and subducted the tectonic plates - including the forces that formed the ocean trenches, the forces that formed the archipelago islands, the forces that formed the mountain ranges, the forces that formed the Pacific Ring of Fire, the forces responsible for the gold deposits along the subduction zones, etc. - are known and are thoroughly documented throughout hundreds of years of historic records but the most brilliant minds at Oxford, Cambridge, Stanford ... are unaware of all this?

" ... flexing of plates under the weight ... " You are on the right track with this brief quote, Lars, but your words suggest you have not yet grasped what has weighed down so heavily onto our Earth and onto our seafloors which has resulted in fracturing our Earth into dozens and dozens of pieces. So long as you cling to theories as if you have a grasp on reality, you'll never understand it.

R. Harrison (@Whirled Publishing) 1 day ago

You need to read some text books and actually comprehend what is said. Your comments are completely non-sensical.

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