کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6428629 | 1634744 | 2015 | 10 صفحه PDF | دانلود رایگان |
- VS of coesite decreases monotonically with pressure.
- Coesite-stishovite transition exhibits enormous velocity and impedance contrasts.
- Phase transition of coesite to stishovite may explain the seismic X-discontinuity.
- A geophysical probe to track ancient subducted eclogitic material is proposed.
Compressional and shear wave velocities of coesite have been measured using ultrasonic interferometry in a multi-anvil apparatus up to 12.6 GPa at room temperature for the first time. While the P wave velocity increases continuously with pressure, the S wave exhibits an anomalous softening and the velocity decreases continuously with pressure. Finite strain analysis of the data yielded KS0=103.6(4)GPa, G0=61.6(2)GPa and K0â²=2.9(1), G0â²=0.3(1) for the bulk and shear moduli and their pressure derivatives, respectively. The anomalous elastic behavior of coesite results in large velocity and impedance contrasts across the coesite-stishovite transition, reaching â¼39% and â¼48% for P and S wave velocity contrasts, and â¼70% and 78% for P and S wave impedance contrasts, respectively, at pressure â¼8 GPa, with P and S wave velocity perturbations showing no apparent dependence on depths (i.e., dlnâ¡V(PorS)/dhâ¼0) within 8-12 GPa. These unusually large contrasts and depth independent characteristics render the transition between the two silica polymorphs one of the most plausible candidates for the cause of the seismically observed X-discontinuity. The current P and S wave velocity perturbation dependences on the SiO2 content, d(lnâ¡VP)/d(SiO2)â¼0.43(wt%)â1 and d(lnâ¡VS)/d(SiO2)â¼0.60(wt%)â1, can serve as a geophysical probe to track ancient subducted eclogite materials to gain insights on the geodynamics of the mantle.
Journal: Earth and Planetary Science Letters - Volume 412, 15 February 2015, Pages 42-51