5 results on '"Gu, Jesse T."'
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2. Composition of Earth's initial atmosphere and fate of accreted volatiles set by core formation and magma ocean redox evolution
- Author
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Gu, Jesse T., Peng, Bo, Ji, Xuan, Zhang, Jisheng, Yang, Hong, Hoyos, Susana, Hirschmann, Marc M., Kite, Edwin S., and Fischer, Rebecca A.
- Published
- 2024
- Full Text
- View/download PDF
3. 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
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SPEED of sound , *FUSED silica , *CONDENSED matter physics , *EXPLOSIVE volcanic eruptions , *SCIENTIFIC apparatus & instruments , *URANIUM-lead dating - Abstract
Acoustic compressional and shear wave velocities (VP, 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 H2O 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 (H2Om) while HRG-6 contains 1.67 (10) wt% OH- and 4.23 (17) wt% H2Om where the numbers in parentheses are ±1s. With increasing pressure, very little H2Om, if any, converts to OH- within uncertainties in hydrous rhyolitic glasses such that HRG-6 contains much more H2Om than HRG-3 at all experimental pressures. We observe a nonlinear relationship between high-pressure sound velocities and H2Ot, 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% H2Om 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
- Full Text
- View/download PDF
4. Plate tectonic cycling modulates Earth's 3 He/ 22 Ne ratio
- Author
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Dygert, Nick, Jackson, Colin R.M., Hesse, Marc A., Tremblay, Marissa M., Shuster, David L., and Gu, Jesse T.
- Abstract
The ratio of 3He and 22Ne varies throughout the mantle. This observation is surprising because 3He and 22Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3He/22Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3He/22Ne of OIB mantle approaches planetary precursor 3He/22Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3He/22Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3He/22Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3He/22Ne. Subduction of high 3He/22Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3He/22Ne. Mixing models suggest that to preserve a high 3He/22Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3He/22Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing.
- Published
- 2018
5. Plate tectonic cycling modulates Earth's 3He/22Ne ratio.
- Author
-
Dygert, Nick, Jackson, Colin R.M., Hesse, Marc A., Tremblay, Marissa M., Shuster, David L., and Gu, Jesse T.
- Subjects
- *
PLATE tectonics , *HELIUM isotopes , *GEODETIC observations , *GEOLOGICAL time scales , *RADIOACTIVE decay ,PLANETARY crusts - Abstract
The ratio of 3 He and 22 Ne varies throughout the mantle. This observation is surprising because 3 He and 22 Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3 He/ 22 Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3 He/ 22 Ne of OIB mantle approaches planetary precursor 3 He/ 22 Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3 He/ 22 Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3 He/ 22 Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3 He/ 22 Ne. Subduction of high 3 He/ 22 Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3 He/ 22 Ne. Mixing models suggest that to preserve a high 3 He/ 22 Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3 He/ 22 Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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