Scientists decipher the role of carbon and the break-up of continents

June 03, 2020

University of New Mexico (UNM) Professor of Earth and Planetary Sciences, Dr. Tobias Fischer and Syracuse University research fellow (now University of Auckland Lecturer), Dr. James Muirhead led an international team of interdisciplinary researchers to investigate the role of carbon in the break-up of continents.

This work, much of which has been funded by grants from the National Science Foundation, is a culmination of research efforts that started with former students from UNM and other US, French, Tanzanian and Kenyan universities.

The collaboration, which also included scientists from New Mexico Tech, the University of Oregon, University of Dar Es Salaam, Seoul National University, University of Tokyo, University of Alberta, Macquarie University, Goethe University and Université de Montpellier II, led to new insights into the storage and dynamic transfer of carbon below thick and very old continental crust currently published in the journal Nature titled, Displacement of cratonic mantle and lithospheric channeling concentrates deep carbon during continental rifting.

It was first recognized by former UNM student, now assistant professor at Seoul National University, Dr. Hyunwoo Lee, that the East African Rift and continental rifts in general are significant sources of carbon degassed from the Earth's mantle to the atmosphere. While later work by other groups showed that CO2 emissions from the East African Rift are variable along its 3,000 km extent, the question remained "where does all this carbon come from and how is it so efficiently released?"

Subsequent work by Fischer and collaborator Professor Stephen Foley from Macquarie University, Australia, proposed a model in which the degassing CO2 is ultimately sourced from carbon that has accumulated over billions of years at the base of the thick old cratonic lithosphere located in the center and edge of the East African Rift.

"The model suggests that this accumulated carbon originates from subducting oceanic plates and deep mantle plumes," said Fischer. "These processes could deliver sufficient carbon to the bottom of very thick and billion year old continental lithosphere to explain the high CO2 fluxes observed in the actively deforming part of the rift."

However, the model proposed by Fischer and Foley could not explain how this deep CO2 managed to leak out from the actively extending part of the rift, which is exactly where the current work connects the dots.

Muirhead and Fischer together with Master's student Amani Laizer from University of Dar Es Salaam in Tanzania and geophysics Ph.D. student Sarah Jaye Oliva from Tulane University returned to Tanzania in 2018 and collected data and samples in locations where active rifting,

i.e. where the plates move apart, intersect the old thick craton that lies above a mantle plume. Gas samples were collected from hot springs in this region that have never been sampled before.

The analyses of these samples within the context of already existing data from the earlier work showed a striking difference in chemical composition of the gases that are released from the active rift and the craton. Craton gases are entirely crustal with no sign of any mantle gases, including CO2. Nitrogen and crustal helium dominate these craton gases. Rift gases on the other hand are stuffed with mantle CO2 and have a strong mantle helium isotope signature. Measured mantle CO2 fluxes are close to zero on the craton but surge in the adjacent actively extending rift.

"Right at the boundary between the craton and the deforming rift sits the world's only currently erupting carbonatite volcano, Oldoinyo Lengai," said Fischer. "This volcano erupts lavas that are so liquid they move like motor oil. The reason for this is that they are devoid of the silica that makes up most igneous rocks but contain about 30 percent carbon, a staggeringly high amount that gives the rock its name carbonatite. Looking back in geologic time, it turns out that there are many carbonatite volcanoes right at the edge of the Tanzania craton, but they are just not currently active."

This distribution of carbonatites led the team to propose a mechanism that causes the lateral migration of the deep cratonic lithosphere where all that stored solid carbon is located, into the mantle at the edges of the craton.

Geophysical data acquired and analyzed by Tulane University and Université de Montpellier II image a steep step in plate thickness at the craton edge. The geophysicists led by Professor Cindy Ebinger, Drs. Sarah Oliva and Professor Christel Tiberi proposed that this step enhances formation of melt and explains the concentration of magma that carries the excess CO2, as well as the spatial distribution of sometimes damaging earthquakes that open cracks for the CO2 to rise to the surface. This would explain the striking difference in CO2 release and source as documented by the surface measurements.

This conceptual model also fits into quantitative physical models developed by Dr. Jolante van Wjik, professor at New Mexico Tech and Dr. Claire Currie, professor at University of Alberta, which shows that unusually thick and low density mantle rocks beneath a craton will be swept laterally by mantle flow, moving toward the thinner plate beneath the continental rift.

This material transfer may enhance melt production. Therefore, the research team concluded, lateral migration of deep cratonic lithosphere soaked with ancient accumulated carbon is ultimately responsible for carbonatite volcanism and the on-going continental break-up in this region of East Africa.

University of New Mexico

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to