Single-crystal elasticity of humite-group minerals by Brillouin scattering

Qingchun Zhang; Xinyue Zhang; Luo Li; Zhu Mao; Xiang Wu

doi:10.2138/am-2023-9067

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Research Article| August 01, 2024

Single-crystal elasticity of humite-group minerals by Brillouin scattering

Qingchun Zhang;

Qingchun Zhang

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

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Xinyue Zhang;

Xinyue Zhang

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

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Luo Li;

Luo Li

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

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Zhu Mao;

Zhu Mao

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui 230026, China

Frontiers Science Center for Planetary Exploration and Emerging Technologies, University of Science and Technology of China, Hefei, Anhui 230026, China

* Corresponding author E-mail: [email protected].

https://orcid.org/0000-0002-6469-6954

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Xiang Wu

State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China

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Author and Article Information

Qingchun Zhang

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Xinyue Zhang

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Luo Li

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Zhu Mao

https://orcid.org/0000-0002-6469-6954

Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui 230026, China

Frontiers Science Center for Planetary Exploration and Emerging Technologies, University of Science and Technology of China, Hefei, Anhui 230026, China

Xiang Wu

State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China

* Corresponding author E-mail: [email protected].

Publisher: Mineralogical Society of America

Received: 17 May 2023

Accepted: 10 Oct 2023

First Online: 01 Aug 2024

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (2024) 109 (8): 1348–1358.

https://doi.org/10.2138/am-2023-9067

Abstract

Humite-group minerals play a crucial role in transporting water and fluorine to the Earth’s deep mantle through slab sinking. In this study, we have used Brillouin scattering to determine the single-crystal elastic constants of four natural humite-group minerals with varying H₂O and fluorite contents under ambient conditions, including one chondrodite [Mg_4.88Si_1.94O₈(OH_0.78F_1.22)] (F₆₁-Chn), one humite [Mg_7.03Si_3.07O₁₂(OH_1.26F_0.74)] (F₃₇-Hu), and two clinohumite [Mg_8.85Ti_0.19Si_3.93O₁₆(OH_1.11F_0.89) and Mg_8.63Fe_0.10Ti_0.24Si_3.97O₁₆(OH_1.84F_0.16)] (F₄₅-Chu and F₈-Chu) samples. The adiabatic bulk (K_S0) and shear (G₀) moduli calculated from the elastic constants using Voigt-Reuss-Hill averages are: K_S0 = 120.4(3) GPa and G₀ = 74.1(5) GPa for F₆₁-Chn, K_S0 = 122.4(3) GPa and G₀ = 78.4(2) GPa for F₃₇-Hu, K_S0 = 126.2(3) GPa and G₀ = 79.7(2) GPa for F₄₅-Chu, and K_S0 = 120.5(3) GPa and G₀ = 76.8(2) GPa for F₈-Chu. Our results indicate that the addition of F leads to a noticeable increase in the elasticity of clinohumite and chondrodite, which is in contrast to the effect of H₂O. Although Fe has a negligible effect on the bulk modulus of clinohumite, it can produce a substantial decrease in the shear modulus. These results provide important insights into the influence of humite-group minerals on the mantle velocity structure. Furthermore, we have investigated the effects of composition on the elasticity and sound velocities of minerals along the forsterite-brucite join in the MgO-SiO₂-H₂O system, confirming previous observations. Increasing H₂O content along the forsterite-brucite join leads to apparent reductions in the elasticity and sound velocities. The influence of Fe on the elasticity and sound velocities of these minerals has also been evaluated.