EAR-PF: Hydrogen in the Earth's transition zone: Merging experimental and theoretical approaches

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Dr. Elizabeth C. Thompson has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education plans at Northwestern University. The investigation will determine the pressure and temperature stability field for aluminum-bearing super hydrous magnesium silicates minerals. The results of this study will help constrain the quantity and location of water in the Earth's transition zone and mantle (410-660 Km depth), a region of the Earth ~100 times more massive than the Earth's crust. The education plan will focus on mentoring, developing teaching materials and lectures, and outreach. Dr. Thompson will also collaborate with scientists at Ehime University in Japan.This project evaluates aluminum substitution in high-pressure superhydrous phase B, using several complementary techniques, including: (1) first-principles calculations, (2)synchrotron-based infrared spectroscopy, (3) Raman spectroscopy and (4) single crystal diffraction. These findings will impact deep Earth geochemistry in a wide-ranging sense, as Al-rich superhydrous phase B either ushers hydrogen through the transition zone and into the lower mantle or decomposes, releasing H2O depending on its P-T stability. Fluxed melts resulting from the decomposition of superhydrous phase B would produce chemical heterogeneities in the mantle. Additionally, dehydration melts may potentially influence plate tectonics due to the effect of hydrogen on melting temperatures and viscosity. This study will also explore the effect of Al-substitution on pressure-induced hydrogen bond symmetrization in superhydrous phase B, a phenomenon previously reported to have a significant influence on a mineral's bulk material properties including bulk modulus and its pressure derivative.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.