TY - JOUR
T1 - High hydrogen solubility in Al-rich stishovite and water transport in the lower mantle
AU - Litasov, Konstantin D.
AU - Kagi, Hiroyuki
AU - Shatskiy, Anton
AU - Ohtani, Eiji
AU - Lakshtanov, Dmitry L.
AU - Bass, Jay D.
AU - Ito, Eiji
N1 - Funding Information:
We thank two anonymous reviewers for helpful comments. This work was conducted as a part of the 21st Century Center-of-Excellence program at Tohoku and Okayama Universities and supported by the grants in Aid for Scientific Researches from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Nos 14102009 and 16075202) to EO and a grant in Aid for young scientists from Japanese Society for Promotion of Science (No 17740344) to KDL. Support was also provided by the US National Science Foundation under grants EAR 0135642 and 0003383 (to JDB).
PY - 2007/10/30
Y1 - 2007/10/30
N2 - Stishovite is an important phase in subducting oceanic crust. The post-garnet assemblage from a precursor eclogite lithology contains up to 25% stishovite at pressures above 25 GPa. This stishovite may contain up to 5 wt.% Al2O3. We measured the hydrogen contents of stishovite samples synthesized at 20-25 GPa and 1200-1800 °C from several starting materials containing up to 10 wt.% Al2O3. FTIR spectra of stishovite show major bands at 3111-3134 cm- 1, with the frequencies increasing as H2O and Al2O3 contents increase, and several minor bands at 2659-2667, 3240, 3261, 3312-3334, and 3351 cm- 1. The H2O content of Al-free stishovite is in the range of 16-30 wt. ppm. The maximum H2O content of Al-bearing stishovite (4.4 wt.% Al2O3) synthesized at 20 GPa and 1400 °C is 3010 ± 300 wt. ppm. Most hydrogen in stishovite is associated with Al3+ substitutional defects on the octahedral (Si4+) site. The hydrogen can occupy 40% of vacancies created by incorporation of Al3+ at 20 GPa. This observation along with some anomalies in the FTIR spectra may indicate an alternative mechanism of Al3+ incorporation into stishovite via the formation of oxygen vacancies or interstitial Ali{radical dot}{radical dot}{radical dot} defects. We report the highest H2O concentrations in Al-stishovite to date, and argue that it is the most important carrier of water into the lower mantle post-garnet eclogitic assemblages.
AB - Stishovite is an important phase in subducting oceanic crust. The post-garnet assemblage from a precursor eclogite lithology contains up to 25% stishovite at pressures above 25 GPa. This stishovite may contain up to 5 wt.% Al2O3. We measured the hydrogen contents of stishovite samples synthesized at 20-25 GPa and 1200-1800 °C from several starting materials containing up to 10 wt.% Al2O3. FTIR spectra of stishovite show major bands at 3111-3134 cm- 1, with the frequencies increasing as H2O and Al2O3 contents increase, and several minor bands at 2659-2667, 3240, 3261, 3312-3334, and 3351 cm- 1. The H2O content of Al-free stishovite is in the range of 16-30 wt. ppm. The maximum H2O content of Al-bearing stishovite (4.4 wt.% Al2O3) synthesized at 20 GPa and 1400 °C is 3010 ± 300 wt. ppm. Most hydrogen in stishovite is associated with Al3+ substitutional defects on the octahedral (Si4+) site. The hydrogen can occupy 40% of vacancies created by incorporation of Al3+ at 20 GPa. This observation along with some anomalies in the FTIR spectra may indicate an alternative mechanism of Al3+ incorporation into stishovite via the formation of oxygen vacancies or interstitial Ali{radical dot}{radical dot}{radical dot} defects. We report the highest H2O concentrations in Al-stishovite to date, and argue that it is the most important carrier of water into the lower mantle post-garnet eclogitic assemblages.
KW - eclogite
KW - hydrogen
KW - infrared spectroscopy
KW - lower mantle
KW - stishovite
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U2 - 10.1016/j.epsl.2007.08.015
DO - 10.1016/j.epsl.2007.08.015
M3 - Article
AN - SCOPUS:35148886396
SN - 0012-821X
VL - 262
SP - 620
EP - 634
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -