Elastic wave velocities and Poisson’s ratios of amphibolite up to 900 ° C at 1.0 GPa: Effect of dehydration melting on Poisson’s ratio of mid- to lower crustal rock

HR: 0800h
AN: MR31C-0530 [Abstracts]
TI: Elastic wave velocities and Poisson’s ratios of amphibolite up to 900 ° C at 1.0 GPa: Effect of dehydration melting on Poisson’s ratio of mid- to lower crustal rock
AU: * Kojo, S
EM: shihoko_kojo@yahoo.co.jp
AF: Yokohama National University, Tokiwadai 79-7, Hodogaya-ku, Yokohama, 240-8501, Japan
AU: Arima, M
EM: arima@edhs.ynu.ac.jp
AF: Yokohama National University, Tokiwadai 79-7, Hodogaya-ku, Yokohama, 240-8501, Japan
AU: Ishikawa, M
EM: ishikawa@ynu.ac.jp
AF: Yokohama National University, Tokiwadai 79-7, Hodogaya-ku, Yokohama, 240-8501, Japan
AB: Vp and Vs measurements at high pressures and high temperatures (up to 900 ° C at 1.0 GPa) were carried out with piston-cylinder apparatus having a 34 mm inner diameter at high-pressure laboratory at Yokohama National University. The amphibolite was collected from Central Graben South, Mariana Trough by JAMSTEC cruise KR02-01. This rock is fine-grained homogeneous rock (grain size < 0.2 mm) without discernable oriented fabric. It consists mainly of hornblende (48.2 vol.%), plagioclase (44.4 vol.%), and substantial amount of magnetite (7.4 vol.%). Vp and Vs were measured using the pulse reflection method for a cylindrical rock sample having 5.7 mm diameter and ~5.0-5.5 mm length enclosed in a welded Pt capsule. Both Vp and Vs linearly decrease while Poisson's ratio increases from room temperature to ~500 ° C. The temperature derivative of Vp is -3.3 × 10^-4km s^-1 ° C ^-1and Vs is -2.6 × 10^-4 km s^-1 ° C ^-1 below 500 ° C. The temperature derivatives of Vp and Vs show a remarked change above ~500 ° C. The relatively lower Vp and Vs and higher Poisson's ratio at higher temperatures above 500 ° C are attributed to dehydration melting of amphibole-bearing assemblages. We identified substantial amounts of glass (4.1 wt.% at 700 ° C, 12.2 wt.% at 800 ° C and 20.3 wt.% at 900 ° C) in the quenched run products. The glass occurs as isolated pockets and/or pools among grain boundaries. Modal proportion of the glass linearly correlates with the increment of Poisson's ratio. The observed increments in Poisson's ratio with temperature are 0.02 at 700 ° C, 0.12 at 800 ° C, and 0.16 at 900 ° C, relative to the value at 500 ° C.
DE: 3630 Experimental mineralogy and petrology
DE: 3914 Electrical properties
DE: 7205 Continental crust (1219)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting