Effect of water on the sound velocities of ringwoodite in the transition zone

Steven Dollard Jacobsen, Joseph R. Smyth

Research output: Chapter in Book/Report/Conference proceedingChapter

20 Scopus citations

Abstract

High-pressure elasticity studies will play a central role in efforts to constrain the potential hydration state of the Earth’s mantle from seismic observations. Here we report the effects of 1 wt% H2O (as structurally bound OH) on the sound velocities and elastic moduli of single-crystal ringwoodite of Fo90 composition, thought to be the dominant phase in the deeper part of the transition zone between 520 and 660-km depth. The experiments were made possible through development of a GHz-ultrasonic interferometer used to monitor P and S-wave travel times through micro-samples (30-50 µm thickness) under hydrostatic compression in the diamond- anvil cell. The velocity data to ~10 GPa indicate that hydrous ringwoodite supports 1-2% lower shear-wave velocities than anhydrous ringwoodite at transition zone pressures, though elevated pressure derivatives (K’ = 5.3 ± 0.4 and G’ = 2.0 ± 0.2) bring calculated hydrous P-velocities close to anhydrous values within their mutual uncertainties above ~12 GPa. Corresponding VP/VS ratios are elevated by ~2.3% and not strongly dependent on pressure. Velocities for hydrous ringwoodite are calculated along a 1673 K adiabat using finite-strain theory and compared with existing data on anhydrous ringwoodite and various radial seismic models. It may be possible to distinguish hydration from temperature anomalies by low S-velocities associated with "normal" P-velocities and accompanying high VP/VS ratios. The presence of a broadened and elevated 410-km discontinuity, together with depressed 660-km discontinuities and intervening low S-wave anomalies along with high VP/ VS ratios are the most seismologically diagnostic features of hydration considering the available information from mineral physics.

Original languageEnglish (US)
Title of host publicationEarth?s Deep Water Cycle, 2006
EditorsSuzan Van Der Lee, Steven D. Jacobsen
PublisherBlackwell Publishing Ltd
Pages131-145
Number of pages15
ISBN (Electronic)9781118666487
ISBN (Print)9780875904337
DOIs
StatePublished - Jan 1 2006

Publication series

NameGeophysical Monograph Series
Volume168
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

ASJC Scopus subject areas

  • Geophysics

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    Jacobsen, S. D., & Smyth, J. R. (2006). Effect of water on the sound velocities of ringwoodite in the transition zone. In S. Van Der Lee, & S. D. Jacobsen (Eds.), Earth?s Deep Water Cycle, 2006 (pp. 131-145). (Geophysical Monograph Series; Vol. 168). Blackwell Publishing Ltd. https://doi.org/10.1029/168GM09