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Title: Comparative compressibility of hydrous wadsleyite and ringwoodite: Effect of H 2 O and implications for detecting water in the transition zone: EFFECT OF WATER ON D K /D P OF WADSLEYITE

Review of recent mineral physics literature shows consistent trends for the influence of Fe and H 2O on the bulk modulus (K0) of wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410–660 km). However, there is little consensus on the first pressure derivative, K0' = (dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0' in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H 2O on K0' for wadsleyite and ringwoodite by conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 wadsleyite containing 2.0 and 0.25 wt % H 2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4 wt % H 2O. By measuring their pressure-volume evolution simultaneously up to 32 GPa, we constrain the difference in K0' independent of the pressure scale, finding that H 2O has no effect on K0', whereas the effect of H 2O on K0 is significant. The fitted K0' values of hydrous wadsleyite (0.25 and 2.0 wt % H 2O) and hydrous ringwoodite (1.4 wt %more » H 2O) examined in this study were found to be identical within uncertainty, with K0' ~3.7(2). New secondary-ion mass spectrometry measurements of the H 2O content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7.0(5) GPa/wt % H 2O, independent of Fe content for upper mantle compositions. Because K0' is unaffected by H 2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high-resolution, regional seismology studies.« less
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Univ. of Nevada, Las Vegas, NV (United States)
  3. Univ. of Colorado, Boulder, CO (United States)
  4. Univ. of Bayreuth (Germany)
  5. Carnegie Inst. of Washington, Washington, DC (United States)
  6. Ehime Univ., Matsuyama (Japan)
  7. Department of Natural History Sciences, Hokkaido University, Sapporo Japan
  8. High-Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne Illinois USA
  9. Hawaii Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu Hawaii USA
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 120; Journal Issue: 12; Journal ID: ISSN 2169-9313
American Geophysical Union
Research Org:
Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab.
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
OSTI Identifier: