Lava lamp tectonics: How giant blobs of subducted sediment float up through deep Earth

Lava lamp tectonics: Research suggests giant blobs of subducted sediment float up through deep Earth
Numerical modeling of sediment subducted beneath North American crust suggests that the sediment may buoyantly rise up through the mantle, like a lava lamp blob, and become attached to the base of the crust. Credit: Jay Chapman

A University of Wyoming professor has used computer modeling to propose that sand and mud subducted off the coast of California around 75 million years ago returned to the Earth's crust by rising up through the mantle as enormous diapirs, like blobs in a lava lamp.

These blobs are now found at the surface of the Earth, far inland from the coast, in places including the Mojave Desert and western Arizona.

"These rocks aren't the prettiest to look at, but they went on an extraordinary journey and have an incredible story to tell," says Jay Chapman, an assistant professor in UW's Department of Geology and Geophysics who focuses on tectonics.

Chapman is the author of a new paper, titled "Diapiric relamination of the Orocopia Schist (southwestern U.S.) during low-angle subduction," which was published in the August issue of the journal Geology

"The rocks started their lives as eroded from the Sierra Nevada Mountains and carried by rivers and streams down to the ocean, where they ended up deposited in a subduction trench, similar to the modern-day Marianas trench," Chapman says. "Then, they were carried about 20 miles deep into the Earth by a subducting , where the sediments were metamorphosed into a called schist. That in and of itself is pretty amazing, but the truly special thing about these rocks is that they didn't stay subducted, but somehow made their way back up to the surface, where you can go stand on them today."

How the subducted sediments returned to the surface of the Earth and the distribution of the sediments in the subsurface are some of the questions Chapman is trying to answer with his research.

"The prevailing theory is that the sediments were smeared against and plastered to the base of the North American tectonic plate, forming a sheet-like layer," Chapman says. "However, the density of these sediments is much lower than rocks in the mantle or lower crust and, over millions of years, computer modeling predicts that the sediments will flow and buoyantly ascend, like hot wax in a lava lamp."

The research has implications for understanding subduction zone processes and the distribution of natural resources.

"Geoscientists around the world are working to understand what gives its unique composition, and subduction and reincorporation of sediment are a popular hypothesis," Chapman says. "In addition, many researchers are now wondering whether fluids and elements released from the subducted sediments may have contributed to the concentration of economically important minerals and metals."


Explore further

Scientists probe mysterious melting of Earth's crust in western North America

More information: James B. Chapman, Diapiric relamination of the Orocopia Schist (southwestern U.S.) during low-angle subduction, Geology (2021). DOI: 10.1130/G48647.1
Journal information: Geology

Citation: Lava lamp tectonics: How giant blobs of subducted sediment float up through deep Earth (2021, August 4) retrieved 25 September 2021 from https://phys.org/news/2021-08-lava-lamp-tectonics-giant-blobs.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
553 shares

Feedback to editors