Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10121398 | Physics of the Earth and Planetary Interiors | 2005 | 12 Pages |
Abstract
In situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press at SPring-8 on majoritic garnet synthesized from natural mid-ocean ridge basalt (MORB), whose chemical composition is close to the average of oceanic crust, at 19Â GPa and 2200Â K. Pressure-volume-temperature data were collected using a newly developed high-pressure cell assembly to 21Â GPa and 1273Â K. Data were fit to the high-temperature Birch-Murnaghan equation of state, with fixed values for the ambient cell volume (V0 = 1574.14(4)Â Ã
3) and the pressure derivative of the isothermal bulk modulus (Kâ²T = 4). This yielded an isothermal bulk modulus of KT0 = 173(1) GPa, a temperature derivative of the bulk modulus (âKT/âT)P = â0.022(5) GPa Kâ1, and a volumetric coefficient of thermal expansivity α = a + bT with values of a = 2.0(3) à 10â5 Kâ1 and b = 1.0(5) à 10â8 Kâ2. The derived thermoelastic parameters are very similar to those of pyrope. The density of subducted oceanic crust compared to pyrolitic mantle at the conditions in Earth's transition zone (410-660 km depth) was calculated using these results and previously reported thermoelastic parameters for MORB and pyrolite mineral assembledges. These calculations show that oceanic crust is denser than pyrolitic mantle throughout the mantle transition zone along a normal geotherm, and the density difference is insensitive to temperature at the pressures in lower part of the transition zone.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geophysics
Authors
Yu Nishihara, Ichiro Aoki, Eiichi Takahashi, Kyoko N. Matsukage, Ken-ichi Funakoshi,