Mantle Carbon Content Influences Plate Tectonics

New research by DCO scientists reconciles two models for maintaining a low-viscosity layer in Earth’s upper mantle, implicating mantle carbon as a key piece of the puzzle.

Earth’s mantle is not uniform. Different zones display distinct physical and chemical characteristics, a fact that is central for tectonic activity. Specifically, a low-viscosity layer in Earth’s upper mantle is essential for plate tectonics; however, exactly how this low viscosity is maintained has remained somewhat of a mystery. Some have suggested that it is due to water-related defects in the mineral olivine, whereas others point to significant volumes of melted rock. However, neither model is fully supported by observations.

New research by DCO scientists, published recently in Nature, reconciles these models, implicating mantle carbon as a key piece of the puzzle [1]. Seismic velocities and electrical conductivities provide insight regarding the physical properties of rocks constituting Earth’s interior. Geophysical surveys show that at 60 to 90 km depth, which corresponds to the transition from the lithosphere (rigid outer part of the mantle) to the asthenosphere (ductile inner part of the mantle), seismic velocities are considerably lowered and electrical conductivities are anomalously high. Fabrice Gaillard’s team, from the Institut des Sciences de la Terre d’Orléans (CNRS Orléans, France), performed high-temperature, high-pressure electrical conductivity measurements on volatile-rich (CO2 and H2O) melts, typically produced at the onset of mantle melting. They found that under such temperature and pressure conditions these melts are highly conductive, a small amount of which could explain observed electrical anomalies in the upper mantle. They further calculated electrical conductivity profiles across the asthenosphere for various tectonic plate ages.  The resulting model predicts several electrical discontinuities that replicate geophysical observations in a consistent petrological and geochemical framework.

This new model will now allow researchers to assess the role of CO2 in non-oceanic regions of the asthenosphere, and ultimately understand the precise relationship between CO2 and H2O concentration, asthenosphere mechanical strength, and tectonic plate motion.

Image credit: Sifré D. (CNRS Orléans, France)

Further Reading

Atlantis Massif Drillsites
DCO Research Subsurface Life in the Atlantis Massif: Just Add Water?

Researchers aboard IODP Expedition 357 collected cores from across the Atlantis Massif, a mountain…

DCO Research Did a Burst of Halogens Kick Off the End-Permian Extinction?

Directly following a massive and prolonged series of volcanic eruptions about 250 million years ago…

Earth rasterized
DCO Research Carbon Dioxide Stays Solid Under Deep Mantle Conditions

Researchers showed that under the intense temperatures and pressures that exist close to the core-…

blue boron-bearing diamond
DCO Research Origin of Blue Diamonds Discovered

DCO researchers analyzed dozens of rare, expensive blue diamonds to find the origin of these…

Back to top