CSEDI: Integrated Study of Water (H2O) in the Mantle: Processes and Signature

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

The CSEDI Science Plan identifies two broad themes in which HB2BO plays a critical role. First, CSEDI aims to understand cycling of water through the Earth?s deep interior. Second, it aims to understand melting and other phase transitions in the deep mantle. In recent years, the deep Earth community has concentrated a tremendous effort in order to determine the influence of HB2BO on mantle properties and processes, yet, key questions raised by the CSEDI Science Plan remain unanswered. There are still no strong constraints on the inventory of HB2BO in different layers of the deep Earth, nor are the fluxes of HB2BO between these layers or the locus of melting induced by HB2BO in the deep mantle known. Here a multidisciplinary effort is proposed between a theoretical mineral physicist (Wentzcovitch), an experimental petrologist (Hirschmann), an experimental rock physicist (Kohlstedt), and a seismologist (Revenaugh) to address some of the central outstanding issues regarding the role of HB2BO in the Earth?s mantle. Evidence regarding the thickness and structure of low velocity layers at the bottom of the upper mantle, as well as for links between the occurrence of such layers and tectonic environment will be searched for seismically. These results will be combined with experimental studies of the concentrations of HB2BO necessary to induce melting at these depths to understand the significance of these features for HB2BO storage and transport in the mantle. Experiments and ab initio calculations will be combined to examine the influence of minor element on OH substitution, on chemical diffusivity, and on creep rates of olivine and pyroxenes. Ab initio calculations will be use to determine the influence of HB2BO on the elasticity of the upper mantle and transition zone, and those results will be applied to search for seismological evidence of HB2BO. The proposed research represents a significant inter-departmental multi-disciplinary initiative at the University of Minnesota involving four faculty, two post-doctoral researchers, two graduate students, and one undergraduate. It is a major step in incorporating state-of-the-art materials theory to deeply seated geophysical problems related to the presence of water in the mantle. This effort will be facilitated by regular group meetings to ensure that our focus remains on multidisciplinary approaches and to promote interdisciplinary learning of all of the participants. For the three PIs in the Department of Geology and Geophysics, the proposed research dovetails well with the Geology and Geophysics REU undergraduate intern site (?Fluids in the Earth, from the Surface to the Core?) for which Hirschmann is the PI and Revenaugh and Kohlstedt are regular participants. In the past three years, these PIs have supervised thirteen interns. The Virtual Laboratory for Earth and Planetary Materials, VLab, directed by Wentzcovitch is deeply involved in communicating results and methods to the broader scientific community through workshops and tutorials, in the training of undergraduates through the summer internship program, and in the training of graduate students and post-docs which will also be exposed to this research. VLab?s organization will be used to promote and divulge outcomes of this project.