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In this study, we have determined the single‐crystal elasticity of clinohumite [Mg8.85Ti0.19Si3.93O16(OH1.11F0.89)] using Brillouin measurement up to 21 GPa at 300 K and 1 bar at 750 K, respectively. The elasticity of clinohumite was determined to be KS0 = 126.2(3) GPa, G0 = 79.7(2) GPa with pressure derivatives KS′ = 4.2(1), G′ = 1.3(1), pressure derivatives ∂KS/∂T = −0.024(1) GPa/K, and ∂G/∂T = −0.011(1) GPa/K). We comprehensively examined the effects of varying H2O, fluorine content and thermal states, on the velocity and density structures of the subducted harzburgite layer. Assuming a typical H2O content of 2 wt.% within harzburgite, our modeling has shown that hydrous harzburgite with clinohumite as the decomposition product of serpentine along a hot slab geotherm even has the VP and VS 0.4–0.8(6)% greater than it dry counterpart at 250–380 km depth. Yet in the top transition zone, the addition of H2O and F can effectively lower the sound velocities and density. The F‐bearing hydrous harzburgite has the VP and VS 1.1(5)–1.3(3)% lower than its dry counterpart, and only 0.6(5)% and 2.3(5)% greater than the pyrolitic mantle. Along cold slab geotherm, phase A will replace clinohumite as the dominant hydrous phase in the harzburgite, the VP and VS are 4.8(5)–5.3(3)% and 5.9(5)–6.0(3)% greater than the pyrolitic mantle in the upper mantle. In the top transition zone, the difference is approximately 3% in VP and 5% in VS. Our results provide crucial experimental evidence for future assessments of the seismic signals of subducted slabs with different hydrous minerals and thermal states. Plain Language Summary: Subducted slab plays a crucial role in connecting the Earth's surface to the interior. Transportation of H2O and other important volatiles to the Earth's mantle via subducted slab can greatly influence a series of physical properties of mantle minerals. Clinohumite is one of the most important H2O and fluorine (F) carriers in the subducted slab. Here, we determined the single‐crystal elasticity of F‐bearing clinohumite at high pressures and temperatures. The obtained elasticity data were applied to model the velocity profiles of the hydrous harzburgite. Our results show that the addition of H2O and F can enhance the velocity difference between harzburgite and pyrolitic mantle at 250–380 km depth along the hot slab geotherm, and VP and VS of harzburgite with 2 wt.% H2O and clinohumite as the H2O‐bearing phase are 0.4–0.8(6)% greater than those of dry harzburgite. In the transition zone depth, addition of H2O and Fe lowers the sound velocities of harzburgite. Hydrous harzburgite has a lower VP and VS than its corresponding dry phase. These new velocity constraints can help us better understand the circulation of H2O and F within Earth's interior and identify the detected seismic observations of subducted slabs with different compositions and thermal states. Key Points: Single‐crystal elasticity of F‐bearing clinohumite was determined to 21 GPa and 750 K and shows strong dependence with F contentThe obtained results were used to model the velocity profiles of the hydrous harzburgite layer considering the thermal state and compositionH2O and F in clinohumite have significant influence on the velocity profile of subduction slab [ABSTRACT FROM AUTHOR]

Orthopyroxene is one of the dominant minerals in the Earth's upper mantle. In this study, we used Raman spectroscopy to investigate the lattice vibration and phase transition of orthopyroxene with four different compositions using diamond-anvil cells up to 34 GPa at 300 K. Our orthopyroxene samples contain 0 (En100), 9% (En91Fs9), 11% (En86Fs11), and 21% (En74Fs21) Fe. At ambient conditions, the Raman modes exhibit a negative dependence on the Fe content, with the exception of the modes at ~850 and 930 cm–1. In contrast, these two Raman modes increase with increasing the Fe content. The phase transition from metastable α- to β-phase was observed at 12.9–15 GPa for samples with <21 mol% Fe and varying Fe content has a minor effect on the phase transition pressure. Besides Fe, incorporation of 2–24 mol% Al can cause an increase in the phase transition pressure from 10–13 to 14–16 GPa. At 29–30.1 GPa, we observed the second apparent change in the Raman spectra for all four investigated samples. For Fe-bearing orthopyroxene, this change in the Raman spectra and frequency shift is associated with the phase transition from β- to γ-phase, whereas for En100, it should be caused by the change of coordination number of Si from 4 to 6 or the presence of α-popx phase. Using the obtained Raman frequency shifts, we calculated the Grüneisen parameters at high pressures. These parameters are useful for understanding the thermoelastic properties of orthopyroxene at high pressures. [ABSTRACT FROM AUTHOR]