NSF-BSF: Composition and evolution of saline fluids in the upper mantle

Connections between the deep Earth and the surface environment where we live are crucial to maintaining the long-term habitability of the Earth. As an example, saline fluids inside the Earth in the upper mantle may play an important role in connecting subduction zones at depth and volcanism at the surface. How this happens is still mysterious.

One reason for this is that there are no experimental data for how such fluids interact chemically with upper mantle rocks, even though saline fluids are preserved in diamonds and rocks from the deep Earth. The proposed research seeks to understand the role of chloride in saline fluids. For example, the potential for chloride to transport metals under upper mantle conditions is highly intriguing.

How important is this process? What are the impacts on changing the upper mantle through time, the generation of melts, the long-term stability of continental roots, and the types of volcanism at the surface of Earth? Answering these questions will help unravel the reasons for the special features of Earth and its near-surface environment that contribute to Earth's habitability as well as helping to provide a basis for the prediction of the potential habitability of other planets.

This is a project jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF-GEO) and the Israel Binational Science Foundation (BSF) in accord with the language in the Memorandum of Understanding between the NSF and the BSF. This Agreement allows a single collaborative proposal, involving US and Israeli investigators, to be submitted and peer-reviewed by NSF.

Upon successful results of the NSF merit review and recommendation by the cognizant NSF Program of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.

The overall objective of this proposal is to understand the composition and evolution of saline fluids in the upper mantle. A unique combination of experimental, thermodynamic modeling, and observational studies are proposed to examine the origins and roles of Cl-rich fluids in diamond formation and mantle metasomatism. The Israeli participants bring two vital areas of expertise to the project, namely the experimental expertise needed to measure the solubilities of mantle rocks in chloride solutions and the expertise in analyzing fluid inclusions in diamonds.

These two areas of expertise are buttressed by the resources provided in the experimental laboratory for high pressure-temperature rock solubilities and the analytical laboratory for fluid inclusion analysis. Theoretical analysis of the experimental solubilities and published single mineral solubilities will be integrated with data from lower temperature and pressure experimental and spectroscopic studies to expand the calibration of metal-chloride complexes in the Deep Earth Water (DEW) model.

Integrating the results of these studies will enable chemical mass transfer predictions of fluid-rock interaction for comparison with the compositions of fluid and solid inclusions in natural diamonds to test alternate scenarios for the origin and evolution of saline fluids in the upper mantle.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.