Elasticity of olivine at high pressure and temperature, and effects of hydration and cations on the elasticity of several silicates

Li, Yingzhe

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https://hdl.handle.net/2142/121225 Copy

Description

Title

Elasticity of olivine at high pressure and temperature, and effects of hydration and cations on the elasticity of several silicates

Author(s)

Li, Yingzhe

Issue Date

2023-07-14

Director of Research (if dissertation) or Advisor (if thesis)

Bass, Jay D.

Doctoral Committee Chair(s)

Bass, Jay D.

Committee Member(s)

• Lundstrom, Craig C.
• Liu, Lijun
• Alp, Esen E.

Department of Study

Earth Sci & Environmental Chng

Discipline

Geology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Olivine
• Simultaneously High Pressure and High Temperature
• Elasticity
• Brillouin scattering
• CO2 laser-heating
• 410 km discontinuity

Abstract

An effective way to construct a mineralogical model for the Earth's interior is to compare laboratory data on acoustic velocities for candidate minerals at a specific pressure (P) and temperature (T) conditions with seismic velocity models. Such a mineralogical model provides valuable insights into understanding the Earth's composition and evolution. The observed seismic discontinuities define the boundaries of layers of the Earth. Despite the complexity of the upper mantle in many ways, the 410 km discontinuity in seismic velocities is generally agreed to be caused by the phase transition from olivine to wadsleyite. However, there is still no agreement on the volume proportion of olivine, which can be inferred from the velocity jump of the 410 km discontinuity. A solution to this debate is to directly measure the velocities of olivine and wadsleyite at the P-T conditions at 410 km depth. More broadly, the influence of water and cation substitution on the elastic properties of minerals must be investigated experimentally to explain seismic observations. A broader experimental database for studying elasticity trends among isostructural minerals with different water and chemical compositions can solve this problem. To address the issues mentioned above, my dissertation involves two main topics. For the first part, I studied the elasticity of willemite (ZnSiO4) at ambient conditions. Compared to literature results for the isostructural mineral phenakite (BeSiO4), we conclude that the relative magnitude of individual elastic constants is controlled by the orientation of the open channel crystal structure. We interpreted smaller on-diagonal and off-diagonal elastic constants for willemite compared to phenakite to be due to the more compliant and distorted Zn-tetrahedra in the crystal structure. Zn2+ cations lead to pronounced effects on the pure shear moduli and aggregate shear modulus. The prominent low VSH in willemite leads to a negative thermal expansion coefficient (NTE) at low temperatures due to its more flexible structure caused by the softer Zn tetrahedra. I have also studied the elasticity of natural hydrated beryllium and zinc silicates: bertrandite Be4Si2O7(OH)2 and hemimorphite Zn4Si2O7(OH)2H2O. We illustrate an approach that explains how the topology and chemical composition of these minerals affects their elastic properties. The hydrogen bonds in bertrandite and hemimorphite account for additional resistance against tetrahedral rotation, giving rise to a larger shear moduli in the plane of the hydrogen bonds. For the second part, I measured the thermal expansion coefficient of Kohistan-Pakistan (Koh) olivine (Mg# 95) up to 1000 K at 1 atm. We fitted the data with the Fei Equation of state (EoS) (Fei 1995), and the Kumar equation (Kumar 2003), respectively. The thermal expansion coefficient of Koh-olivine α (T)= 3.22 (9) ×10-5 K-1 +0.83(15) × 10-8 K-2×T -0.68(7) K× T-2. The thermal expansion coefficient of Koh-olivine at room temperature is 27.1(8) ×10-6 K-1. I then measured the sound velocities of Koh-olivine at simultaneous high P-T conditions in a diamond anvil cell. The pressure derivatives of Koh-olivine are KS′ = (∂KS/∂P) = 4.1(3), G′ = (∂G/∂P) = 2.0(3), G″ = (∂G2/∂P2) = 0.097(7). The temperature derivatives are ∂KS/∂T = -0.017(4) and ∂G/∂T = -0.009(2). Our studies show that the effect of adding a 5% iron content into olivine is equivalent to a temperature increase of up to 600K. We also synthesized wadsleyite at 13.9(7) GPa and 1525  50K. Our XRD data show that iron preferentially partitions into wadsleyite during this phase transition.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Yingzhe Li

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