Petrological model of the northern Izu-Bonin-Mariana arc crust: Constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan

Keigo Kitamura, M. Ishikawa, M. Arima

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Abstract

Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic-gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu-Bonin-Mariana (IBM) arc. The Vp values of the tonalitic-gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3-6.6 km/s for tonalites (56.4-71.1 wt.% SiO2), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO2), and 7.1-7.3 km/s for a hornblende gabbro (43.2-47.7 wt.% SiO2). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1-6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1-7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3-7.7 km/s at 15-22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.

Original languageEnglish
Pages (from-to)213-221
Number of pages9
JournalTectonophysics
Volume371
Issue number1-4
DOIs
Publication statusPublished - Aug 14 2003

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elastic wave
plutonic rock
pressure measurement
elastic waves
hornblende
wave velocity
crusts
Japan
arcs
gabbro
rocks
crust
rock
tonalite
velocity profile
acoustic impedance
lower crust
P-wave
low pressure
S-wave

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth-Surface Processes

Cite this

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title = "Petrological model of the northern Izu-Bonin-Mariana arc crust: Constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan",
abstract = "Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic-gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu-Bonin-Mariana (IBM) arc. The Vp values of the tonalitic-gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3-6.6 km/s for tonalites (56.4-71.1 wt.{\%} SiO2), 6.8 km/s for a quartz gabbro (53.8 wt.{\%} SiO2), and 7.1-7.3 km/s for a hornblende gabbro (43.2-47.7 wt.{\%} SiO2). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1-6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1-7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3-7.7 km/s at 15-22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.",
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T1 - Petrological model of the northern Izu-Bonin-Mariana arc crust

T2 - Constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan

AU - Kitamura, Keigo

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AU - Arima, M.

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N2 - Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic-gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu-Bonin-Mariana (IBM) arc. The Vp values of the tonalitic-gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3-6.6 km/s for tonalites (56.4-71.1 wt.% SiO2), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO2), and 7.1-7.3 km/s for a hornblende gabbro (43.2-47.7 wt.% SiO2). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1-6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1-7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3-7.7 km/s at 15-22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.

AB - Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic-gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu-Bonin-Mariana (IBM) arc. The Vp values of the tonalitic-gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3-6.6 km/s for tonalites (56.4-71.1 wt.% SiO2), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO2), and 7.1-7.3 km/s for a hornblende gabbro (43.2-47.7 wt.% SiO2). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1-6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1-7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3-7.7 km/s at 15-22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.

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