[Rockhounds] The death of supercontinents brings diamonds to the surface

[Kreigh Tomaszewski]

Forged under extreme temperatures and pressures more than 150 kilometers
down in the mantle, diamonds ride rockets to reach Earth’s surface: narrow
pipes of magma called kimberlite that can erupt at the speed of sound.
Strangely, most kimberlite pipes are found in the quiet, ancient interiors
of continents. They are far from where most other eruptions occur: at the
edges of tectonic plates and near mantle plumes, broad upwellings that form
volcanic hot spots such as Hawaii or Yellowstone. “How on Earth did these
get here?” asks Thomas Gernon, a geologist at the University of
Southampton. “It was an elephant in the room that no one had a good
explanation for.”

Now, Gernon and his colleagues believe they do. They say the timing and
location of these diamond-bearing eruptions suggest they are aftereffects
of the breakup of supercontinents, which causes whirling turbulence in the
viscous mantle rock below. Like slow-motion tidal waves of rock, the
researchers say, these swells ripple beneath the continents, traveling
hundreds of kilometers over the course of millions of years—and
occasionally triggering kimberlite eruptions. “Kimberlites seem to be
responding to rhythms of supercontinents,” Gernon says.

The finding, published today in Nature
<https://www.nature.com/articles/s41586-023-06193-3>, is about more than
diamonds and kimberlites, says Folarin Kolawole, a structural geologist at
Columbia University who is unaffiliated with the study. It suggests that
tectonic action near Earth’s surface can influence the behavior of the
mantle on a broader scale than once thought. It also indicates that the
underground waves keep the margins of newly divided continents volcanically
active far longer than expected, possibly explaining other volcanic rocks
that had previously been chalked up to mantle plumes. “This gives us a way
forward—a hypothesis to test,” Kolawole says.

https://www.science.org/content/article/death-supercontinents-brings-diamonds-surface