Collaborative Research: Water Concentration and Distribution in the Oceanic Lithosphere

Jacobs Technology Inc., Houston TX

Investigators

Abstract

The chemical compound H2O, which in its liquid state is called water, when it occurs bound in minerals and other solids, influences melting, rheology and plastic behavior of the mineral or material, and the material's thermal and electrical properties. In the case where H2O is bound in minerals deep in the ocean crust, this can result in enhanced generation of magmas, hence volcanic eruptions, and changes in the plasticity, deformation of the lithosphere. In areas where magmas rise to the surface, this H2O is released and forms an important part of the global cycle of H2O. Because most of the H2O on Earth is locked up in minerals in the crust and mantle, the concentration and distribution of H2O in various mantle and lithospheric reservoirs have been inferred primarily from analyses of undegassed glasses and melt inclusions in oceanic basalts through a comparison of their H2O content with incompatible rare earth elements like Cerium. This only provides a rough estimate of the H2O content of the Earth. This research builds off the results of a pilot study and uses a novel new approach to determine how much H2O is stored in minerals in the oceanic mantle and lithosphere, the mechanisms that fractionate H2O from other geochemical tracers in mantle lithologies, and the fate of the H2O and how it impacts the electrical conductivity and rheology of the oceanic lithosphere. Broader impacts of the work include support of a faculty member at an institution in South Carolina, an EPSCoR state (i.e., a state that does not receive significant federal funding), support of a researcher whose gender is under-represented in the sciences, and student training who will get trained on cutting-edge analytical instrumentation at NASA at the Johnson Space Center in Houston, TX. Impacts also include international collaboration with Belgian and Japanese scientists and making the data accessible to the public. Questions to be addressed by this research include seeing if H2O varies independently from lithophile elements in the lithosphere and if diffusion is responsible if decoupling is observed; looking to see if pyroxenes are typically a high-H2O, low-solidus reservoir; examine if H2O solubility in minerals under lithospheric pressures and temperatures put an upper limit on how much structurally bound H2O is held in the unaltered lithosphere; whether H2O concentrations are reflected in the H2O systematics of lithospheric samples; and whether there are systematic correlations between H2O distribution in the lithosphere and the degree of melting, depth, and lithology and metasomatic agents. To address these issues, Fourier Transform Infrared Spectroscopy (FTIR) will be used to determine the H2O concentrations in well-characterized, fresh (i.e., unaltered) peridotites and pyroxenites from a suite of locations and tectonic settings that include the Canary Islands in the Atlantic Ocean; the Kerguelen Plateau in the South Indian Ocean; the Hawaiian and Samoan Islands and the Ontong Java Plateau in the Pacific Ocean; and the Lena Trough in the Arctic Ocean. Additional geochemical indicators, such as trace element compositions of minerals and radiogenic isotopes of Sr, Hf, Nd, and Pb in minerals and rocks will be used to help determine if there is a link between process, mineralogy, and H2O content/behavior.