Rheology and texture evolution of the lower mantle analogue CaGeO3+MgO
Abstract
Even using available state of the art techniques, getting insights into the lower mantle physical properties remains challenging because of the high pressures involved (>22 GPa). The use of CaGeO3 perovskite (GePv) as an analog material, stable at much lower pressure than the natural (Mg, Fe)SiO3 perovskite, allows us to study the rheology of the lower mantle. In a previous study on a two-phase composite GePv + MgO, Wang et al. (2013) showed that up to 15% total bulk strain, the samples remain a Load Bearing Framework (LBF) texture, with the GePv phase supporting the applied stress. In another analogue, FeNiS + dunite, the initial LBF texture was shown to undergo a drastic transition to an interconnected weak layer (IWL) texture under a shear strain of about 1 (Wang et al., 2011). In order to determine if such a behavior occurs in GePv + MgO, we deformed this lower-mantle analog material to larger strains, using the Deformation-DIA (DDIA) apparatus at sector 13 of the Advanced Photon Source. These experiments were carried out at pressures of ~10 GPa (using anvils with a truncated edge length of 3 mm) and temperatures of 1000 K. The samples were deformed at strain rates of 10-5 - 10-4 s-1, up to finite bulk strains of ~50%. Using a monochromatic incident beam, angle dispersive X-ray diffraction patterns were collected upon deformation. The full Debye diffraction rings were interpreted in terms of lattice d-spacing. In this manner, the strain of six lattice planes for GePv and two for MgO could be resolved and were used to determine the micro-stress evolution of each phase. The samples show a dramatic weakening above 20% of strain. The diffraction patterns also evidence significant lattice preferred orientation (i.e., texture) development in both phases upon deformation. Textural quantification is in progress and a microscopy study of the recovered samples will be conducted to determine whether the samples have experienced a transition from the initial LBF texture to an IWL texture. Further experiments will also be conducted at higher temperatures and larger strains. These data are important to better understand the rheology of the lower mantle since they allow us to determine how much strain is necessary to produce IWL textures and therefore promote shear localization. Wang, Y., C. Lesher, et al. (2011). In situ high-pressure and high-temperature X-ray microtomographic imaging during large deformation: A new technique for studying mechanical behavior of multiphase composites. Geosphere 7(1): 40-53. Wang, Y., N. Hilairet, et al. (2013) High-pressure, high-temperature deformation in CaGeO3 (perovskite)×MgO aggregates: implications for multi-phase rheology of the lower mantle. Geochemestry, Geophysics, Geosystems (In press).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMMR41A2343G
- Keywords:
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- 3630 MINERALOGY AND PETROLOGY Experimental mineralogy and petrology;
- 3924 MINERAL PHYSICS High-pressure behavior;
- 3902 MINERAL PHYSICS Creep and deformation;
- 3954 MINERAL PHYSICS X-ray;
- neutron;
- and electron spectroscopy and diffraction