New findings reveal surprising behavior of minerals in the depths of the Earth

New findings reveal surprising behavior of minerals in the depths of the Earth

Boudinage in brecciated dolostone rocks of the Panamint Range (Wildrose Area, Death Valley National Park). New research shows that periclase is more powerful than bridgmanite in Earth’s lower mantle, and is analogous to pudynates developing in hard (“stronger”) rocks among less efficient (“weaker”) rocks. Credit: Jennifer M. Jackson, Caltech

As you read this, there is an enormous world of extreme temperatures and pressures that have been oscillating and developing for longer than humans have been on this planet over 400 miles away. Now, a new detailed model from Caltech researchers outlines the surprising behavior of minerals deep in the planet’s interior over millions of years and shows that processes do indeed occur in a completely opposite way than previously assumed.

The research was conducted by an international team of scientists, including Jennifer M. Jackson, William E. Leonhard Professor of Metallurgical Physics. A paper describing the study appears in the journal nature On January 11th.

“Despite the planet’s massive size, the deep parts are often overlooked because they’re literally out of reach — we can’t sample them,” says Jackson. “In addition, these processes are so slow that they seem imperceptible to us. But the flow in the lower mantle communicates with everything it touches; it is a deep engine that affects tectonic plates It may control volcanic activity.”

The planet’s lower mantle is solid rockbut over hundreds of millions of years it slowly exudes, like a thick caramel, carrying heat throughout the planet’s interior in a process called convection.

Many questions remain unanswered about the mechanisms that allow this convection to occur. the extreme heat And pressures on the lower mantle—up to 135 gigapascals and thousands of degrees Fahrenheit—make this difficult to simulate in the lab.

For reference, the pressure in the lower mantle is roughly a thousand times the pressure at the deepest point in the ocean. Thus, while many laboratory experiments on mineral physics have made hypotheses about the behavior of lower mantle rocks, the processes occurring on geologic time scales to drive the slow flow of lower mantle convection are uncertain.

the lower mantle It consists mostly of magnesium silicate called bridgmanite but also contains a small but significant amount of magnesium oxide called bridgmanite-mixed periclase as well as small amounts of other minerals. Laboratory experiments had previously shown that periclase is weaker than bridgmanite and deforms more easily, but these experiments did not take into account how the minerals behave on a time scale of millions of years. When these schedules are combined into a pool My account formJackson and his colleagues found that the periclase grains are actually stronger than the surrounding bridgmanite grains.

We can use the boudinage analogy in rock record [image at right]where boudins, which is French for sausage, develops in a “stronger” solid rock layer amidst less efficient, “weaker” rock, says Jackson.

“As another analogy, think of thick peanut butter,” Jackson explains. “We’ve thought for decades that periclase was the ‘oil’ in peanut butter, acting as a lubricant between the solid granules of bridgmanite. Based on this new study, it turns out that periclase granules act as the ‘nuts’ in chunky peanut butter. The granules go together. periclase with flow but does not affect the viscous behavior, except in conditions in which the grains are strongly concentrated.We show that under pressure the movement is much slower in periclase than in bridgmanite.There is a reversal in the behavior: no deformation occurs in periclase, while the main phase controls, Bridgemanite, in deformation in the Earth’s deep mantle.”

Understanding these extreme processes occurring far from our feet is important for creating an accurate 4D simulation of our own planet, and helps us understand more about other planets as well. Thousands of exoplanets (planets outside our group Solar System) Now, discover more about the physics of minerals under extreme conditions It gives new insights about evolution planets radically different from ours.

more information:
Patrick Cordier et al, Bridgmanite deforms slower than bridgmanite under mantle conditions, nature (2023). DOI: 10.1038/s41586-022-05410-9

the quote: New Results Reveal Surprising Behavior of Minerals Deep in the Earth (2023, January 12) Retrieved January 13, 2023 from

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