Simultaneous high P-T measurements of ultrasonic compressional and shear wave velocities in Ichino-megata mafic xenoliths: Their bearings on seismic velocity perturbations in lower crust of northeast Japan arc

Soshi Nishimoto, Masahiro Ishikawa, Makoto Arima, Takeyoshi Yoshida, Junichi Nakajima

研究成果: Article査読

36 被引用数 (Scopus)

抄録

Simultaneous measurements of ultrasonic compressional (Vp) and shear wave velocities (Vs) were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast Japan arc crust. For comparison with the observed seismic heterogeneity of the lower crust of the northeast Japan arc, the velocity deviations (dVp and dVs) of the xenoliths were calculated using the average reference Vp (6.61 ± 0.1 km/s) and Vs (3.76 ± 0.1 km/s). The dVp and dVs values of the xenoliths at 700°C and 0.8 GPa are 0.8% and -1.2% for hornblende gabbro, 4.8% and 4.0% for hornblende-pyroxene gabbro, 0.9% and -1.5% for amphibolite, 2.5% and 1.7% for pyroxene amphibolite, and 0.9% and -5.6% for hornblendite, respectively. We compared the velocity perturbations in the lower crust determined by seismic tomography with dVp and dVs of the xenoliths using "Vp-Vs-Vp/Vs deviation diagrams." On the basis of our measurements, we suggest that (1) the seismically high-Vp and Vs regions beneath the Tobishima Basin consist of hornblende-pyroxene gabbro, (2) hornblende gabbro is a predominant rock type beneath the Dewa Hills and Ou Backbone Range, (3) the low-velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro, and (4) the low-Vp and high-Vs regions beneath the Kitakami Mountains consist of quartz-plagioclase-bearing rocks. Our data demonstrate that the seismic heterogeneity in the lower crust of the northeast Japan arc reflects variations in rock composition and temperature that are related to the regional geological history.

本文言語English
論文番号B12212
ジャーナルJournal of Geophysical Research: Solid Earth
113
12
DOI
出版ステータスPublished - 2008 12 4

ASJC Scopus subject areas

  • 地球物理学
  • 地球化学および岩石学
  • 地球惑星科学(その他)
  • 宇宙惑星科学

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