TY - JOUR
T1 - Sound velocity measurements of CaSiO 3 perovskite to 133GPa and implications for lowermost mantle seismic anomalies
AU - Kudo, Yuki
AU - Hirose, Kei
AU - Murakami, Motohiko
AU - Asahara, Yuki
AU - Ozawa, Haruka
AU - Ohishi, Yasuo
AU - Hirao, Naohisa
N1 - Funding Information:
We thank T. Komabayashi, E. Sugimura and N. Sata for their support in the Brillouin spectroscopy measurements and helpful discussions. The reviewers’ comments were very helpful to improve the manuscript. Experiments were conducted at SPring-8 (proposal nos. 2010A0087, 2010B0087, and 2011A0087). Y.K. was supported by the Global COE program “From the Earth to Earths”, MEXT, Japan.
PY - 2012/10/1
Y1 - 2012/10/1
N2 - We report the measurements of aggregate shear velocity (V S) of CaSiO 3 perovskite (CaPv) at high pressure (P) between 32 and 133GPa and room temperature (T) on the basis of Brillouin spectroscopy. The sample had a tetragonal perovskite structure throughout the experiments. The measured P-V S data show the shear modulus and its pressure derivative at ambient condition to be G 0=115.8GPa and G'=1.20, respectively. The zero-pressure shear velocity is determined to be V S0=5.23km/s, in good agreement with the previous estimate inferred from the ultrasonic measurements on Ca(Si,Ti)O 3 perovskite at 1bar. Our experimental results are broadly consistent with the earlier calculations on tetragonal CaPv but exhibit lower velocity at equivalent pressure. Such tetragonal CaPv is present in cold subducting slabs and possibly in wide areas of the lowermost mantle. While primitive mantle includes certain amount of CaPv, a depleted peridotite (former harzburgite) layer in subducted oceanic lithosphere is deficient in CaPv and enriched in ferropericlase in the lower mantle. Such harzburgite exhibits 0.9% faster V S and 0.7% slower bulk sound velocity (V Φ) at the lowermost mantle P-T conditions if CaPv is present in the tetragonal form in the surrounding mantle. The observed fast V S and slow V Φ anomalies in the D" layer underneath the circum-Pacific region might be attributed in large part in the presence of subducted harzburgitic materials.
AB - We report the measurements of aggregate shear velocity (V S) of CaSiO 3 perovskite (CaPv) at high pressure (P) between 32 and 133GPa and room temperature (T) on the basis of Brillouin spectroscopy. The sample had a tetragonal perovskite structure throughout the experiments. The measured P-V S data show the shear modulus and its pressure derivative at ambient condition to be G 0=115.8GPa and G'=1.20, respectively. The zero-pressure shear velocity is determined to be V S0=5.23km/s, in good agreement with the previous estimate inferred from the ultrasonic measurements on Ca(Si,Ti)O 3 perovskite at 1bar. Our experimental results are broadly consistent with the earlier calculations on tetragonal CaPv but exhibit lower velocity at equivalent pressure. Such tetragonal CaPv is present in cold subducting slabs and possibly in wide areas of the lowermost mantle. While primitive mantle includes certain amount of CaPv, a depleted peridotite (former harzburgite) layer in subducted oceanic lithosphere is deficient in CaPv and enriched in ferropericlase in the lower mantle. Such harzburgite exhibits 0.9% faster V S and 0.7% slower bulk sound velocity (V Φ) at the lowermost mantle P-T conditions if CaPv is present in the tetragonal form in the surrounding mantle. The observed fast V S and slow V Φ anomalies in the D" layer underneath the circum-Pacific region might be attributed in large part in the presence of subducted harzburgitic materials.
KW - Brillouin spectroscopy
KW - CaSiO perovskite
KW - Harzburgite
KW - Lower mantle
KW - Shear velocity
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U2 - 10.1016/j.epsl.2012.06.040
DO - 10.1016/j.epsl.2012.06.040
M3 - Article
AN - SCOPUS:84864406459
SN - 0012-821X
VL - 349-350
SP - 1
EP - 7
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
ER -