CAREER: Experimental Investigation of the Transport Properties of Sulfide Melts at Upper Mantle Conditions

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

This CAREER award is designed as an experimental study to understand how molten iron sulfides percolate inside the Earth. Molten iron sulfides are crucial geochemical and geophysical components of our planet's interior. Their mobility inside the planet has shaped the structure and dynamics of the Earth, and thus, studying the behavior of sulfides at depth is key to understanding the Earth's evolution. The measurements of two properties, electrical conductivity and viscosity, will be conducted on iron sulfide melts over a wide range of pressure and temperature conditions that are relevant to the Earth's upper mantle. When combined with geophysical observations, these results have the potential to detect the presence of sulfide melts at depth and estimate their mobility at small (mm) and large (km) scales, which may lead to the reinterpretation of some geophysical anomalies that are measured on the Earth's surface. The experimental data set will also be relevant to the interior of other terrestrial planets. The research outcomes will be integrated with an extensive education initiative that consists of helping K-12 schoolteachers at the San Diego Unified School District promote earth science research into their courses. The investigator and her group will be working with science education leaders at Scripps Institute of Oceanography (SIO) and San Diego Unified School District (SDUSD) to design training workshops for the teachers around the experimental results from this project. Several undergraduate and graduate students, as well as one postdoc researcher will be supported as part of this project. The interconnectivity and mobility of sulfide melts seem to depend highly on the composition of the melt phase as well as on redox conditions, suggesting that there is a fundamental need to study the effect of melt chemistry and redox conditions on the transport properties of sulfide melts. High-pressure and high-temperature experiments will be conducted up to 10 GPa and up to 1700°C at UCSD-SIO and APS-GSECARS. Emphasis will be placed on two parameters affecting sulfide melts' mobility: chemistry and redox conditions. Sample compositions will be in the Fe-S-O-Ni-Cu system and oxygen fugacity will range from IW-1 to IW+4, corresponding to the Iron-Wüstite (IW) redox buffer. Experimental results will be applied to different tectonic contexts where the chemistry and redox conditions enhance sulfide melt interconnectivity and where geophysical (seismic, electromagnetic) observations indicate anomalies at different depths in the upper mantle. This investigation of the transport properties of sulfide compounds encompasses mineral physics and geophysics, and is relevant to economic geology (e.g., metal transport related to ore deposit formation), planetary science (e.g., metal-silicate differentiation), as well as metal industry (e.g., strength and plasticity of metal alloys). The education initiative that will be designed around the scientific outcomes of the project supports efforts that integrate next generation earth science standards into instructional practices at the K-12 level. This novel collaboration with science education specialists will have direct impact on the earth science education of SDUSD students. 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.