Читать книгу Mantle Convection and Surface Expressions - Группа авторов - Страница 55

Although considerable progress has been made toward rheology studies of lower mantle phases, high pressure and temperature deformation studies particularly at steady state deformation conditions remain sparse. Significant advances have been made in documenting texture development and slip system activities in lower mantle phases and some general trends are observed with respect to differential stress measurements in these phases. Based on the experimental body as a whole, at mantle pressure Fp appears to be significantly weaker that Brg; however, the strength contrast as a function of pressure, temperature, and strain remains poorly constrained. As would be expected the strength of both of these phases decreases with increased temperature and with decreased strain rates. Room‐temperature strengths of Brg and MgSiO₃ pPv seem to indicate that MgSiO₃ pPv is weaker than Brg, but there is a large pressure gap between measurements in these two phases. Texture development in two‐phase aggregates also exhibits complex behavior with high plastic anisotropy hard phases disrupting texture development in softer more highly strained phases. Bulk behavior of lower mantle polyphase aggregates (i.e., rocks) remains relatively unstudied but has important implications for mechanical properties and anisotropy development in the deep Earth. Challenges exist both to interpretation of bulk rheology of these materials and texture development in the various phases. Systematic studies of polyphase deformation documenting the effects of strength contrast, plastic anisotropy, and microstructure will be vital moving forward. Additional complications may occur at high temperatures where possibilities exist for phases to deform by different deformation mechanisms. Recent technical advances in experimental deformation as well as theoretical developments have provided new capabilities to tackle these problems in the near future.