Читать книгу Mantle Convection and Surface Expressions - Группа авторов - Страница 45

Perhaps due to their stability at ambient conditions Per and Fp are most studied of the mantle phases (Heidelbach et al., 2003; Immoor et al., 2018; F. Lin et al., 2017; Long et al., 2006; Merkel et al., 2002; Stretton et al., 2001; Uchida et al., 2004; Yamazaki & Karato, 2002). For a detailed review of deformation mechanisms in Per the reader is referred to (Amodeo et al., 2018). Slip in Per and Fp occurs in the 〈110〉 direction on {110}, {100} and {111} planes (Amodeo et al., 2018). In both Per and Fp low temperature deformation is by dominant slip on {110}〈10〉 over a wide range of pressures (Table 2.1; F. Lin et al., 2017; J.‐F. Lin et al., 2009; Merkel et al., 2002; Paterson & Weaver, 1970; Tommaseo et al., 2006). High pressure compression studies at low temperatures show textures characterized by {100} at high angles to compression which is attributed to slip on {110}〈10〉 (Figure 2.4a, Table 2.1; Immoor et al., 2018; J.‐F. Lin et al., 2009; Marquardt & Miyagi, 2015; Merkel et al., 2002; Tommaseo et al., 2006). High‐temperature studies on Per show increased activity of the {100}〈011〉 slip system with elevated temperature (Appel & Wielke, 1985; Copley & Pask, 1965; Hulse et al., 1963; Paterson & Weaver, 1970; Sato & Sumino, 1980).

Theoretical calculations (Amodeo et al., 2012, 2016) and single crystal deformation experiments on Per to 8 GPa (Girard et al., 2012) suggest a possible transition to {100}〈011〉 slip at pressure somewhere between 23 and 40 GPa. High pressure DAC measurement on Fp documented an abrupt increase in yield strength between 20 and 60 GPa, which may be associated with this slip system transition (Marquardt & Miyagi, 2015). However for a transition from {110}〈10〉 slip to {100}〈011〉 one would expect a texture change from {100} planes oriented at high angles to compression to {110} planes at high angle to compression (Figure 2.4a, b). Texture changes associated with a pressure induced slip system changes have not been documented and this may be due to difficulty in overprinting the lower pressure textures (Amodeo et al., 2016).

In Fp, Fe content may play a role in controlling deformation mechanisms. Subtle change in textures observed in room temperature DAC experiments may be linked to reduced activity of {110}〈10〉 (Tommaseo et al., 2006). In low pressure, high‐temperature shear experiments (300 MPa and up to 1473K), changes in deformation mechanisms appear to be most pronounced in samples with Fe contents in excess of 50% (Long et al., 2006). During high‐temperature deformation of Fp to high shear strains, {111}〈10〉 slip may also be activated (Heidelbach et al., 2003; Long et al., 2006; Yamazaki & Karato, 2002). Recent resistive heated DAC experiments on Fp show a transition to a {110} maximum in IPFs of the compression direction (Figure 2.4b), and this is attributed to increased activity of {100}〈011〉 slip with temperature at mantle pressures (Table 1). At ~1400K and pressures of 30–60 GPa both {110}〈10〉 and {100}〈011〉 slip systems are ~equally active (Immoor et al., 2018). Based on current experimental data, it appears that {110}〈10〉 is typically dominant in Fp at lower pressure and temperature and at high pressure and temperature {100}〈011〉 becomes increasingly dominant (Table 2.1).

Figure 2.4 Summary of textures observed in ferropericlase (a) and (b), CaSiO₃ perovskite (c), and in bridgmanite (d–g). Textures are shown as equal area, upper hemisphere, projection inverse pole figures of the compression direction for (a–f). Due to the lower symmetry deformation geometry (shear) the texture data of Tsujino et al. (2016) are represented as pole figures of (100) (010), and (001). Black arrows indicate the sense of shear. The textures plotted in g) are those from the extended data figure 7 of Tsujino et al. (2016) which were obtained using the Materials Analysis Using Diffraction program (Lutterotti et al., 1997). Scale bar is in multiples of random distribution.