Water in Earth’s mantle is a supercritical fluid that influences many geological processes, including earthquakes and volcanic eruptions. It is also a key agent for transporting chemical elements, but how it behaves under the extreme conditions of Earth’s interior is poorly understood. DCO scientist Dimitri Sverjensky (Johns Hopkins University, Baltimore, MD, USA) and colleagues have made monumental progress in this field over the last few years, and in a ground-breaking move have released a new piece of software that can model water-rock interactions down to 200 km below Earth’s surface [1,2].
Similar models have been used to predict water-rock interactions to a depth of about 15 km for 40 years or more. These models have been extremely informative in terms of understanding the geochemistry of the crust, through predicting the creation and destruction of various minerals. But taking these models deeper, into Earth’s mantle, had been impossible until now. Such models require thermodynamic data and equations that describe the behavior of water and other molecules dissolved in it, but one particularly important parameter, the dielectric constant of water, was missing at the high temperatures and pressures of deep Earth.
In April 2013, Sverjensky’s group, in collaboration with fellow DCO scientist Giullia Galli, published theoretical calculations of the dielectric constant of water at high temperature and pressure . With this information in hand, Sverjensky set about applying it to the generation of a new Deep Earth Water (DEW) model, and, through collaboration with other DCO scientists, tested and calibrated the model against available high-pressure experimental results. Several applications of these new data are underway, and will be submitted for publication in the near future.
“This would not have come about if it weren’t for a conversation I had with Isabelle Daniel at the first Deep Carbon Workshop in 2008”, said Sverjensky. “At that time, her experimental results were way ahead of geochemical theory. Now they are on a par. I am making the DEW model available in the hope that new experiments and theory will provide an integrated approach to understanding the role of water deep in Earth”
The DEW model presents a new method of predicting the dielectric constant of water, together with new estimation procedures that enable prediction of the thermodynamic properties of chemical species dissolved in water. Dimitri Sverjensky will be presenting the model at the upcoming AGU Fall Meeting, at 11:05AM on Monday 9 December 2013 as part of session V12A (Room 306), and the model is now available for download.
Learn more about the Deep Earth Water Community here.
Photo: When water meets the ubiquitous mineral olivine under pressure, the rock absorbs oxygen, transforming olivine into serpentine — characterized by a scaly, green-brown surface appearance like snakeskin. Lizardite (pictured) is an example of serpentine. Photo courtesy of Robert Downs, University of Arizona, RRuff Project.