1. Nonlinear effects of hydration on high-pressure sound velocities of rhyolitic glasses.
- Author
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Gu, Jesse T., Suyu Fu, Gardner, James E., Shigeru Yamashita, Takuo Okuchi, and Jung-Fu Lin
- Subjects
SPEED of sound ,FUSED silica ,CONDENSED matter physics ,EXPLOSIVE volcanic eruptions ,SCIENTIFIC apparatus & instruments ,URANIUM-lead dating - Abstract
Acoustic compressional and shear wave velocities (V
P , VS ) of anhydrous (AHRG) and hydrous rhyolitic glasses (HRG) containing 3.28 wt% (HRG-3) and 5.90 wt% (HRG-6) total water concentration (H[sub 2]O[sub t]) have been measured using Brillouin light scattering (BLS) spectroscopy up to 3 GPa in a diamond-anvil cell at ambient temperature. In addition, Fourier-transform infrared (FTIR) spectroscopy was used to measure the speciation of H2 O in the glasses up to 3 GPa. At ambient pressure, HRG-3 contains 1.58 (6) wt% hydroxyl groups (OH- ) and 1.70 (7) wt% molecular water (H2 Om ) while HRG-6 contains 1.67 (10) wt% OH- and 4.23 (17) wt% H2 Om where the numbers in parentheses are ±1s. With increasing pressure, very little H2 Om , if any, converts to OH- within uncertainties in hydrous rhyolitic glasses such that HRG-6 contains much more H2 Om than HRG-3 at all experimental pressures. We observe a nonlinear relationship between high-pressure sound velocities and H2 Ot , which is attributed to the distinct effects of each water species on acoustic velocities and elastic moduli of hydrous glasses. Near ambient pressure, depolymerization due to OH[sup -] reduces VS and G more than VP and KS . VP and KS in both anhydrous and hydrous glasses decrease with increasing pressure up to ~1-2 GPa before increasing with pressure. Above ~1-2 GPa, VP and KS in both hydrous glasses converge with those in AHRG. In particular, VP in HRG-6 crosses over and becomes higher than VP in AHRG. HRG-6 displays lower VS and G than HRG-3 near ambient pressure, but VS and G in these glasses converge above ~2 GPa. Our results show that hydrous rhyolitic glasses with ~2-4 wt% H2 Om can be as incompressible as their anhydrous counterpart above ~1.5 GPa. The nonlinear effects of hydration on high-pressure acoustic velocities and elastic moduli of rhyolitic glasses observed here may provide some insight into the behavior of hydrous silicate melts in felsic magma chambers at depth. [ABSTRACT FROM AUTHOR]- Published
- 2021
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