Elasticity of single-crystal iron-bearing pyrope to 20 GPa and 750 K

Elastic properties of the major constituent minerals in the Earth’s upper mantle at relevant high pressure-temperature (P-T) conditions are crucial for understanding the composition and seismic velocity structures of the region. In this study, we have measured the single-crystal elasticity of natural Fe-bearing pyrope, Mg2.04Fe0.74Ca0.16Mn0.05Al2Si3O12, using in situ Brillouin spectroscopy and X-ray diffraction at simultaneous high P-T conditions up to 20 GPa and 750 K in an externally-heated diamond anvil cell. The derived aggregate adiabatic bulk and shear modulus (KS0, G0) at ambient conditions are 168.2 (±1.8) GPa and 92.1 (±1.1) GPa, respectively, consistent with literature results. Using the third-order Eulerian finite-strain equation to fit the high P-T data, the derived pressure derivative of the bulk and shear moduli at constant temperature are (∂KS/∂P)T=4.4 (±0.1) and (∂G/∂P)T=1.2 (±0.1), respectively. Applying these pressure derivatives, the temperature derivative of these moduli at constant pressure are also calculated, yielding (∂KS/∂T)P=-18.5(±1.3) MPa/K and (∂G/∂T)P=-5.2(±1.1) MPa/K, respectively. Compared to literature values, our results show that addition of 25% Fe in pyrope increases the pressure derivative of the bulk modulus by 7%, but has a negligible effect on other elastic parameters. Extrapolation of our results shows that Fe-bearing pyrope remains almost elastically isotropic at relevant P-T conditions of the upper mantle, indicating that it may not have a significant contribution to seismic Vp and Vs anisotropy in the upper mantle. Together with the elasticity of olivine and pyroxene minerals in the upper mantle, we have constructed new velocity profiles for two representative compositional models, pyrolite and piclogite, along Earth’s upper mantle geotherm. These velocity models show Vs profiles consistent with seismic observations, although Vp profiles are slightly lower than in seismic models.

Name thesis:degree_name

Master of Science in Geological Sciences

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Geological Sciences

Grantor

University of Texas at Austin

Year dc:date.issued

2012

Author dc:creator

• Lu, Chang

Advisor dc:contributor.advisor

• Lin, Jung-Fu

Committee members dc:contributor.committeemember

• Grand, Stephen P.
• Lassiter, John C.

• High pressure
• High temperature
• Diamond anvil cell
• Mineral physics
• Upper mantle
• Garnet
• Brillouin spectroscopy
• Iron-bearing pyrope

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/2152/ETD-UT-2012-05-5456

OAI identifier oai:identifier

oai:repositories.lib.utexas.edu:2152/ETD-UT-2012-05-5456