Numerical Simulations of Texture Development and Associated Rheological Anisotropy in Regions of Complex Mantle Flow
Abstract
The aim of this study is to compare the predictions of different micromechanical approaches that have been employed recently to study mineral alignment during flow in the upper mantle. Computational capabilities are reaching a point where the potential rheological effects of such lattice-preferred orientation (LPO) can be considered as an integral part of determining the flow pattern and evolution. But, in order to have confidence in taking this next step, the detailed behavior of the different micromechanical models needs to be understood. An important consequence of LPO development is the subsequent anisotropy of the mechanical properties. Curiously, most published geophysical studies only address the elastic anisotropy, probably because of its link with the observed seismic anisotropy. The viscoplastic (or rheological) anisotropy has received much less attention, although it may have a notable influence on regional and global convective flow pattern, which in turn controls the LPO development. Micromechanical approaches aim at linking the rheological behaviour at the grain scale, associated with the activate deformation mechanisms (dislocation glide and climb, diffusion creep, "), with the overall rheology at the sample scale, including also other mechanisms such as recrystallization. This is achieved by an evaluation of the internal stress generated by the (strong) mechanical interaction between neighbour grains. All models proposed in the literature (kinematic model, finite strain model, tangent self-consistent model, lower bound model, ") make simplifying assumptions, since the mechanical problem is very complicated. One can distinguish between rather simple models that allow some freedom in deformation of individual grains, and more advanced techniques (and generally more accurate) that require a minimum number (=4) of independent slip systems (or directional deformation mechanisms) for the plastic strain to occur. In respect to this, unlike all other models, the recent 'Second Order' self-consistent model has been shown to reproduce almost perfectly several exact solutions for olivine rheology, and this makes it a solid candidate for future applications on large scale convection in the deep Earth. We address in this presentation the predictive capability of these models with an eye toward their eventual use in coupled LPO-geodynamic flow simulations. We will focus on comparisons in the case of a complex flow pattern, rarely investigated in the literature, such as passively-driven upwelling zone beneath an oceanic spreading center.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMDI22A..06B
- Keywords:
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- 3902 Creep and deformation;
- 5112 Microstructure;
- 5120 Plasticity;
- diffusion;
- and creep;
- 8033 Rheology: mantle (8162)