Crystal structure and thermoelastic properties of (Mg[subscript 0.91]Fe[subscript 0.09])SiO[subscript 3] postperovskite up to 135 GPa and 2,700 K

Journal Article · Wed Jul 02 04:00:00 EDT 2008 · Proc. Natl. Acad. Sci. USA

DOI:https://doi.org/10.1073/pnas.0711174105· OSTI ID:1006646

Shim, S -H; Catalli, K; Hustoft, J; Kubo, A; Prakapenka, V B; Caldwell, W A; Kunz, M ^[1]

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1. MIT

Intriguing seismic observations have been made for the bottom 400 km of Earth's mantle (the Dll 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) {yields} postperovskite (PPv), that may provide explanations for the seismic observations. Here, we report measurements of the crystal structure of (Mg{sub 0.91}Fe{sub 0.09})SiO{sub 3}-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{sub {phi}}) decreases by 2.4 {+-} 1.4% across the PPv transition. Combined with the predicted shear-wave velocity (V{sub S} ) increase, our measurements indicate that lateral variations in mineralogy between Pv and PPv may result in the anticorrelation between the V{sub {phi}} and V{sub S} anomalies at the D'' region. Also, density increases by 1.6 {+-} 0.4% and Grueneisen parameter decreases by 21 {+-} 15% across the PPv transition, which will dynamically stabilize the PPv lenses observed in recent seismic studies.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1006646
• Journal Information: Proc. Natl. Acad. Sci. USA, Journal Name: Proc. Natl. Acad. Sci. USA Journal Issue: (21) ; 05, 2008 Vol. 105; ISSN PNASA6; ISSN 0027-8424
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

58 GEOSCIENCES
CRYSTAL STRUCTURE
DENSITY
EARTH CORE
EARTH MANTLE
MINERALOGY
ORIGIN
PEROVSKITE
PHYSICAL PROPERTIES
PRESSURE DEPENDENCE
SOUND WAVES
TEMPERATURE DEPENDENCE
VARIATIONS
VELOCITY