期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 105, 期 21, 页码 7382-7386出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0711174105
关键词
equation of state; mantle; phase transition; bulk sound speed; Gruneisen parameter
Intriguing seismic observations have been made for the bottom 400 km of Earth's mantle(the D region) over the past few decades, yet the origin of these seismic structures has not. been well understood. Recent theoretical calculations have predicted many unusual changes in physical properties across the postperovskite transition, perovskite (Pv) -> postperovskite (PPv), that may provide explanations for the seismic observations. Here, we report measurements of the crystal structure of (Mg0.91Fe0.09)SiO3-PPV under quasi-hydrostatic conditions up to the pressure (P)-temperature (T) conditions expected for the core-mantle boundary (CMB). The measured crystal structure is in excellent agreement with the first-principles calculations. We found that bulk sound speed (V-Phi) decreases by 2.4 +/- 1.4% across the PPv transition. Combined with the predicted shear-wave velocity (Vs) increase, our measurements indicate that lateral variations in mineralogy between Pv and PPv may result in the anticorrelation between the V(D and Vs anomalies at the W region. Also, density increases by 1.6 +/- 0.4% and Gruneisen parameter decreases by 21 +/- 15% across the PPv transition, which will dynamically stabilize the PPv lenses observed in recent seismic studies.
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