Collaborative Research: Experimental Investigation of the Electrical Properties of Hydrous Silicate Melts in Subduction Context

Collaborative Research: Experimental Investigation of the Electrical Properties of Hydrous Silicate Melts in Subduction Context Collaborative Research: Experimental Investigation of the Electrical Properties of Hydrous Silicate Melts in Subduction Context Overview: Geophysical measurements in a variety of subduction zones indicate anomalous electrical and seismological behavior at depths where partial melting is expected. In particular, significant improvements of the electromagnetic technique over the past decade provide an increasingly precise image of subduction systems, highlighting the need for more detailed laboratory studies and modeling. Because it is sensitive to temperature, composition, and liquid phase geometry, electrical conductivity provides information about the chemistry and structure of rocks and fluids and helps identify melt migration pathways and storage conditions. Combined with electrical investigations in the laboratory, geophysical measurements across subduction zones are able to distinguish an integrated anomaly signature that can provide constraint on the nature and structure of anomalies. Intellectual Merit : The current electrical database of fluids does not cover the range of compositions observed and expected in subduction zones, requiring further laboratory investigations to remove any potential ambiguity in fluid characterization and proportion. In particular, the electrical conductivity of highly hydrous silicate melts (>10 wt % H2O) at mantle wedge conditions is still unknown. Electrical conductivity can also be used to probe unmixing processes between silicate melts and metal-bearing aqueous fluids that occur in the shallow part of subduction (<10 km depth) and lead to the formation of ore deposits. We propose a multi-disciplinary and multi-scale investigation of the electrical conductivity of hydrous silicate melts in subduction context, both at the depth of the mantle wedge and the shallow hydrothermal part of subduction zones, in order to characterize and model the electrical response of hydrous melts in subduction zones and to understand better melt interactions with metal-bearing fluids. In this project, two sets of electrical conductivity experiments are proposed and will be performed by a graduate student and PI Pommier at the University of California San Diego (SIO). Electrical conductivity cells will be developed by PI Pommier and co-PI Leinenweber. In Task 1, electrical measurements will be performed at 3 GPa on dry and hydrous silicate melts with compositions relevant to subduction zones, including water contents ranging from 5 to ~30 wt % H2O. In Task 2, electrical measurements of immiscible systems will be conducted at 150 MPa on granitic glasses with different amounts of NaCl+H2O. Representative amounts of Cu and Fe chloride salts will be added, of the order 1 wt % total, as observed in hydrothermal ore deposits. Collaborator Jon Blundy from the University of Bristol will help interpret the results in terms of immiscibility processes and apply them to ore deposit formation. PI Pommier and graduate student will also work with collaborator Kerry Key at UCSD, using the conductivity results from Tasks 1 and 2 and electromagnetic data across several subduction zones to provide constraints on subduction processes. Broader Impacts : This multi-disciplinary and multi-scale study will strengthen collaborations between the involved laboratories and with colleagues in associated fields and institutions (UCSD, ASU, University of Bristol). The project would be among the first studies carried out in the Planetary Experimental Petrology Laboratory developed by the PI at UCSD-SIO. The research will involve a graduate student who will be mentored by PI Pommier and will interact with all the participants. If funded, this proposal would allow a novel investigation of rock properties in subduction context with applications to petrology, volcanology, geophysics, and economic geology. The experimental data will be used to develop models for predicting conductivity of very hydrous melts as a function of physical and chemical parameters that are of interest to the geosciences community. It will also help investigate the formation of ore deposits, which is of interest to the economic geology community. The knowledge gained in this research will be incorporated into the undergraduate and graduate classes taught by the PI, and will be made available to other researchers in the field.