High-pressure ammonium-bearing silicates: Implications for nitrogen and hydrogen storage in the Earth’s mantle
-
Anke Watenphul
,
Bernd Wunder
Abstract
The ammonium analogues of the high-pressure potassium-bearing silicate phases K-hollandite, K-Si-wadeite, K-cymrite, and phengite were synthesized in the system (NH4)2O(-MgO)-Al2O3-SiO2- H2O [N(M)ASH] using multi-anvil and piston-cylinder equipment. Syntheses included NH4-hollandite (NH4AlSi3O8) at 12.3 GPa, 700 °C; NH4-Si-wadeite [(NH4)2Si4O9] at 10 GPa, 700 °C; NH4-cymrite (NH4AlSi3O8⋅H2O) at 7.8 GPa, 800 °C; and NH4-phengite [NH4(Mg0.5Al1.5)(Al0.5Si3.5)O10(OH)2] at 4 GPa, 700 °C. Run products were characterized by SEM, FTIR, and powder XRD with Rietveld refinements. Cell parameters of the new NH4 end-members are: a = 9.4234(9) Å, c = 2.7244(3) Å, V = 241.93(5) Å3 (NH4-hollandite); a = 6.726(1) Å, c = 9.502(3) Å, V = 372.3(1) Å3 (NH4-Si-wadeite); a = 5.3595(3) Å, c = 7.835(1) Å, V = 194.93(5) Å3 (NH4-cymrite). NH4-phengite consisted of a mixture of 1M, 2M1, 2M2, 3T, and 2Or polytypes. The most abundant polytype, 2M1, has cell dimensions a = 5.2195(9) Å, b = 9.049(3) Å, c = 20.414(8) Å, β = 95.65(3)°, V = 959.5(5) Å3. All unit-cell volumes are enlarged in comparison to the potassium analogues. Substitution of NH4 for K does not cause changes in space group. NH4 incorporation was confirmed by the appearance of NH4-vibration modes ν4 and ν3 occurring in the ranges of 1397-1459 and 3223-3333 cm-1, respectively.
Ammonium in eclogite facies metasediments is mainly bound in micas and concentrations may reach up to a few thousand parts per million. It can be stored to greater depths in high-pressure potassium silicates during ongoing subduction. This possibly provides an important mechanism for nitrogen and hydrogen transport into the deeper mantle.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Determination of high-pressure phase equilibria of Fe2O3 using the Kawai-type apparatus equipped with sintered diamond anvils
- Suhailite, a new ammonium trioctahedral mica
- First record of K-cymrite in North Qaidam UHP eclogite, Western China
- Stability of uranium (VI) peroxide hydrates under ionizing radiation
- Heat capacities and thermodynamic functions of TiO2 anatase and rutile: Analysis of phase stability
- The behavior of Co and Ni in olivine in planetary basalts: An experimental investigation
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- The application of Lorentz transmission electron microscopy to the study of lamellar magnetism in hematite-ilmenite
- A Monte Carlo study of short- and long-range order of tetrahedral cations in sapphirine and khmaralite
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- Formation of aragonite mesocrystals and implication for biomineralization
- U-Pb age, trace-element, and Hf-isotope compositions of zircon in a quartz vein from eclogite in the western Dabie Mountains: Constraints on fluid flow during early exhumation of ultrahigh-pressure rocks
- Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4·2H2O) on the gypsum cleavage surface
- Fukalite: An example of an OD structure with two-dimensional disorder
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- Structure and carbonate orientation of vaterite (CaCO3)
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- Water speciation in hydrous silicate and aluminosilicate glasses: Direct evidence from 29Si-1H and 27Al-1H double-resonance NMR
- Acid production by FeSO4·nH2O dissolution and implications for terrestrial and martian aquatic systems
