Relative strength of olivine and wadsleyite using Mn2GeO4 structural analog
Abstract
One of the key questions of modern geophysics is the rheological contrast between the upper mantle and the transition zone and its influence in the mantle convection. As a first approximation this contrast can be addressed through the relative strength of olivine, wadselyite and ringwoodite. Although olivine has been and is still extensively studied, our knowledge about the rheological properties of wadsleyite and ringwoodite are lacking because quantitative deformation experiments under pressure and temperature ranges of these phases are technically limited. Structural analogs of (Fe,Mg)2SiO4 has then to be used as first approximation. Mn2GeO4 has been used in many previous studies as a good analog material since it presents alpha and beta phases at pressures lower enough (4-5 GPa) to allow quantitative measurement using Deformation-DIA press. This study investigates the strength contrast between olivine and wadsleyite structured Mn2GeO4. The samples are composed of two layers, one of olivine or wadsleyite structured Mn2GeO4 and the other of a reference material (MgO or forsterite). In conjunction with a synchrotron x-ray source, sample strains and strain rates are determined from sample length markers in recorded radiographic images. Stresses are measured from energy dispersive and angle dispersive X-ray diffraction spectra. The experiments have been performed at 1000°C in the pressure stability field of each polymorph and similar strain rate or stress has been applied on the standard material. Relative strength of olivine and wadsleyite structured Mn2GeO4 is determined in comparing strain rate and stress of each sample to its reference and to the other polymorphs. The results show that olivine structured Mn2GeO4 is weaker than wadsleyite structured Mn2GeO4 to about one order of magnitude.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2008
- Bibcode:
- 2008AGUSM.U51A..07C
- Keywords:
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- 3900 MINERAL PHYSICS;
- 3924 High-pressure behavior;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction