Equation of State of Hemleyite: A Computational Approach

Lohani, Mohit (2022) Equation of State of Hemleyite: A Computational Approach. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Mohit Lohani (17MS005)) 17MS005_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

Exploring the Earth’s interior is one of the most challenging parts in the field of Geosciences. Seismic imaging of the Earth has been very useful to provide us the information on the physical properties of the deep Earth materials at different depths. To know about the composition of the deep Earth materials, mineral physics plays an important role. It helps us to know about the thermodynamic and thermoelastic properties of minerals and understand the composition and thermal structure of the Earth’s interior. Seismic imaging of the Earth shows many discontinuities which are likely due to the phase transitions of minerals at different depths inside the Earth. The possible phase transitions causing the major discontinuities have already been known by the application of mineral physics and seismology together. However, details of many discontinuities are yet to be explored. One of such discontinuity exists at the 660 km boundary of the mantle transition zone (MTZ) inside the Earth. The ideas of multiple seismic discontinuities near the 660 km boundary of the MTZ instead of a single and sharp one, continues to make this region a subject of further exploration. A recent study on a thin section of the heavily shocked Suizhou chondrite has discovered a new mineral hemleyite (FeSiO₃). This mineral has been suggested to form at the pressure and temperature conditions very similar to those of the 660 km boundary. A detailed study of thermodynamic and thermoelastic properties of hemleyite will help us enrich the knowledge of 660 km boundary. Study of equation of state of this mineral is the first and the crucial step towards exploring its thermodynamic and thermoelastic properties of this mineral. Hemleyite sample found in the meteorite existed as a solid solution with the other end member akimotoite (MgSiO₃). We have obtained the equation of state for this mineral system and found that, as more and more iron gets incorporated into the crystal structure of akimotoite, the bulk modulus of the system increases and the ambient volume of the unit cell decreases. The inclusion of 50% iron at the Mg site (Fe₀.₅Mg₀.₅SiO₃), has increased the value of bulk modulus by 17.94% and decreased the volume by 3.52%.

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