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Title: Anomalous density and elastic properties of basalt at high pressure: Reevaluating of the effect of melt fraction on seismic velocity in the Earth's crust and upper mantle

Independent measurements of the volumetric and elastic properties of Columbia River basalt glass were made up to 5.5 GPa by high-pressure X-ray microtomography and GHz-ultrasonic interferometry, respectively. The Columbia River basalt displays P and S wave velocity minima at 4.5 and 5 GPa, respectively, violating Birch’s law. These data constrain the pressure dependence of the density and elastic moduli at high pressure, which cannot be modeled through usual equations of state nor determined by stepwise integrating the bulk sound velocity as is common practice. We propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network. Likewise, this behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for P wave velocities perhaps to depths of the transition zone. By modeling the effect of partial melt on P wave velocity reductions it is suggested that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle.
 [1] ;  [2] ;  [3] ;  [4]
  1. Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Univ. Pierre et Marie Curie, Paris (France). Inst. of Mineralogy, Physics of Materials and Cosmo-chemistry
  2. Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Aarhus Univ. (Denmark). Dept. of Geoscience
  3. Northwestern Univ., Evanston, IL (United States). Dept. of Earth and Planetary Sciences
  4. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources
Publication Date:
Grant/Contract Number:
NA0002006; FG02-94ER14466; AC02-06CH11357; EAR-1215714; EAR-1452344; EAR-1214376; EAR-1128799
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 121; Journal Issue: 6; 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); National Science Foundation (NSF)
Country of Publication:
United States
OSTI Identifier: