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

Date:
August 4, 2021
Source:
University of Wyoming
Summary:
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,
new research shows.



FULL STORY ==========================================================================
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 sediment 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 oceanic plate, where the sediments
were metamorphosed into a rock 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 continental crust 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." ========================================================================== Story Source: Materials provided by University_of_Wyoming. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. James B. Chapman. Diapiric relamination of the Orocopia Schist
(southwestern U.S.) during low-angle subduction. Geology, 2021;
49 (8): 983 DOI: 10.1130/G48647.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210804123559.htm

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