Study shows diamonds aren't forever
Date:
June 5, 2020
Source:
Tulane University
Summary:
Diamonds, those precious, sparkling jewels, are known as the hardest
materials on Earth. They are a high-pressure form of carbon and
found deep in the ground. While diamonds are commonly thought
of as hard and stable, carbon from about 100 miles beneath the
African plate is being brought to shallower levels where diamond
will become unstable. Molten rock (magma) brings the excess carbon
towards the surface, and earthquakes open cracks that allow the
carbon to be released into the air as carbon dioxide.
FULL STORY ========================================================================== Diamonds, those precious, sparkling jewels, are known as the hardest
materials on Earth. They are a high-pressure form of carbon and found
deep in the ground.
========================================================================== While diamonds are commonly thought of as hard and stable, carbon from
about 100 miles beneath the African plate is being brought to shallower
levels where diamond will become unstable. Molten rock (magma) brings
the excess carbon towards the surface, and earthquakes open cracks that
allow the carbon to be released into the air as carbon dioxide.
PhD student Sarah Jaye Oliva and Professor of Earth and Environmental
Sciences and Marshall-Heape Chair in Geology Cynthia Ebinger are among
a group of international researchers who co-authored a paper "Displaced cratonic mantle concentrates deep carbon during continental rifting,"
which was published in the journal Nature on June 3.
"Somewhat amusedly," Ebinger said, "the paper is evidence that Diamonds
Aren't Forever." The pair report on their findings about the African
continent splitting in two and the massive amounts of CO2 (carbon dioxide) being released into the atmosphere.
Ebinger said of her student, "Sarah Jaye contributed to the gas
measurements, and she analyzed the deep structure and state-of-stress
data that enabled us to deduce the process leading to the excess CO2 in
some rift zones." Oliva participated in a month-long campaign in 2018
to sample gases released diffusely through the soil and at springs that
dot the East African Rift System in Tanzania.
========================================================================== Through the sampling, Oliva and other researchers found that CO2 fluxes
[flows] and the number of earthquakes are highest where the rift
intersects the edge of the ancient, thick cratonic plate that is more
than 60 km (about 37 miles) thicker than the adjoining area.
Oliva said this made sense because the steep edge of the bottom of the
plate is "where we expect magmas (molten rock material within the Earth
that will cool to form igneous rock) to form and where faulting and
fracture networks should be most intense." "The resulting faults and
fissures, we think, act as conduits through the crust that concentrate
fluxes of CO2 sourced from beneath," said Oliva.
Modeling by the researchers also suggests that the mantle underneath
the study region may be enriched in carbon due to the local erosion of
the cratonic lithosphere that may even contain diamonds. (A craton is
an old and stable part of the continental lithosphere, which consists
of the Earth's two topmost layers, the crust and the uppermost mantle.)
"The eroded material could melt as it moves towards thinner lithosphere,
and this would be another factor in increasing the CO2 flux through the
rift valley margin," said Oliva.
She added, "Participating in this project was extremely rewarding for
me. We, as seismologists, geodynamicists, structural geologists and
geochemists all came together to understand how rifts help mobilize
CO2 that is sequestered in the deep Earth. This newly liberated CO2
ultimately influences Earth's climate over geologic time, temporarily contributing to global warming."
========================================================================== Story Source: Materials provided by Tulane_University. Note: Content
may be edited for style and length.
========================================================================== Journal Reference:
1. James D. Muirhead, Tobias P. Fischer, Sarah J. Oliva, Amani Laizer,
Jolante van Wijk, Claire A. Currie, Hyunwoo Lee, Emily J. Judd,
Emmanuel Kazimoto, Yuji Sano, Naoto Takahata, Christel Tiberi,
Stephen F. Foley, Josef Dufek, Miriam C. Reiss, Cynthia
J. Ebinger. Displaced cratonic mantle concentrates deep carbon
during continental rifting. Nature, 2020; 582 (7810): 67 DOI:
10.1038/s41586-020-2328-3 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2020/06/200605105414.htm
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