The rheology of the subducting slab and manle (euroSLAB) (FP 07)
Final Report Abstract
A major emphasis during the funding period was placed on gaining a better understanding of the deformation behaviour of post perovskite (ppv). The ppv phase is a recently discovered (Mg,Fe)SiO3 polymorph that is stable at pressures greater than ~120 GPa and is thought to form a major component of the D’’ layer in the lowermost mantle. The deformation behaviour of ppv is thought to play an important part in the great seismic complexity of the D’’ layer. On a larger scale, flow in the D’’ layer also influences large scale mantle convection and possibly convective heat transfer from the outer core into the mantle. However, due to the high stability pressure of ppv it is very difficult to conduct controlled deformation experiments with (Mg,Fe)SiO3 ppv. We used the analogue substance CaIrO3 that displays a ppv structure at ambient pressure. Deformation experiments were performed with the deformation-DIA, a cubic multianvil device that enables controlled deformation to be performed at confining pressures of up to 10 GPa. Our studies revealed that CaIrO3 forms a deformation lattice preferred orientation (LPO) that can explain the observed seismic anisotropy of the D’’ layer. In a follow up study we showed that CaIrO3 additionally develops a transformation LPO when deformed during the phase transformation from pv to ppv structure that differs from the deformation LPO and is rotated into the deformation LPO by further deformation in the ppv field. These results helped to explain early diamond anvil studies that suggested LPOs, which were not compatible with the observed seismic anisotropy. Further studies were conducted to better constrain the viscosity differences between the Pv and the pPv, which is an important parameter for geodynamic modelling and to investigate the deformation behaviour of CaPtO3, which is another ppv analogue substance. Another field of research was an investigation of the dislocation microstructures of the high pressure minerals coesite and omphacite that are important minerals in subducting oceanic crust and therefore determine rheology during subduction. Samples were deformed in the d-DIA and analysed by electron backscatter diffraction and transmission electron microscopy. Interdisciplinary collaboration with other research groups of the EuroMinScI network let to studies on the role of partial melts in static and deforming rocks.
Publications
- (2007). Liquid-distribution and attainment of textural equilibrium in a partially-molten crystalline system with a high-dihedral-angle liquid phase. Earth and Planetary Science Letters, 262, 517-532
Walte, N. P., J. K. Becker, P. D. Bons, D. C. Rubie, and D. J. Frost
- (2007). Texture development and TEM analysis of deformed CaIrO3: Implications for the D '' layer at the core-mantle boundary. Geophysical Research Letters, 34(8)
Walte, N., F. Heidelbach, N. Miyajima, and D. Frost
- (2008). Dislocations and plasticity of experimentally deformed coesite. European Journal of Mineralogy, 20(4), 665-671
Idrissi, H., P. Cordier, D. Jacob, and N. Walte
- (2008). Experimental deformation of ordered natural omphacite: a study by transmission electron microscopy. European Journal of Mineralogy, 20(5), 835- 844
Müller, W. F., N. Walte, and N. Miyajima
- (2009). Burgers vector determination in deformed perovskite and postperovskite of CaIrO3 using thickness fringes in weak-beam dark-field images. Ultramicroscopy, 109, 683-692
Miyajima, N., and N. P. Walte
- (2009). Phase-field simulations of partial melts in geological materials. Computers & Geosciences, 35(9), 1907-1916
Wendler, F., J. K. Becker, B. Nestler, P. D. Bons, and N. P. Walte
- (2009). Transformation textures in post-perovskite: Understanding mantle flow in the D '' layer of the Earth. Geophysical Research Letters, 36
Walte, N. P., F. Heidelbach, N. Miyajima, D. J. Frost, D. C. Rubie, and D. P. Dobson
- (2009). Weakening of calcium iridate during its transformation from perovskite to post-perovskite. Nature Geoscience, 2, 794 – 797
Hunt, S., Weidner, D. J., Li Li, L. Wang, N. P. Walte, J. P. Brodholt, and D. P. Dobson
