[S-IT14] Deep Earth Sciences

[SIT14-P08] Implications of Goethite and its polymorphs in the lower mantle: A first-principles approach

*Sparsh Sharma¹, Gaurav Shukla^1,2 (1.Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata, 2.National Centre for High Pressure Studies)

Keywords:Goethite, Lower Mantle, First Principles, Hydrous Mineral, High P-T Studies

Goethite (α-FeOOH) is one of the most common iron oxyhydroxides found on the surface of the Earth and inside the crust. It is an essential component of rust and bog-iron ores and a primary hydrous mineral. The study of hydrous minerals is of paramount relevance as they are crucial in transporting water into the Earth’s interior and affect the geophysical and geochemical processes. Recent studies have proposed that Goethite and its polymorphs might have the capability to transport water to the lowermost part of the mantle up until the core-mantle boundary and might contribute to the formation of seismic heterogeneities like the ULVZs. Thus, a study of Goethite and its polymorphs might play a pivotal role in understanding the water, hydrogen, and oxygen cycles inside the Earth and the role of iron in the deep Earth processes. Using the first principles studies, we tried to understand the structural changes associated with α-FeOOH, ε -FeOOH, and Py-Phase (FeOOH_x ) as they undergo the lower mantle pressures. The first principles calculations were performed using Density-functional Theory (DFT) as implemented in the Quantum Espresso package, and the thermodynamics, electronic, and thermoelastic properties of different phases of Goethite and their stability in the pressure-temperature conditions of the deep Earth have been studied.