The Proceedings of the Eighth International Conference on Creationism (2018)

perovskite. The overall mineralogical volume fraction map of the earth’s mantle is shown in Fig. 1. With this mineralogical structure of the mantle in view, the inelastic mechanical responses of rocks obviously depend on the different length scales of structures embedded within each of its constituent minerals. As already mentioned, a rock’s plastic response to stress depends on dislocation mobility and interaction, grain size and grain boundary-dislocation interactions, and crystallographic preferred orientations. These in turn depend on pressure, temperature, strain rate (deformation rate), stress state, and mineralogical composition. Representing these dependencies and processes in an accurate manner is key to realistic modeling of catastrophic mantle dynamics and the associated plate tectonics during the Genesis Flood. The following section addresses the relationships between crystalline microstructures and the primary mechanisms by which rocks deform. 2. Important deformational mechanisms The complex manner in which minerals deform, combined with extreme pressures and temperatures of the earth’s interior, together with the fact that mineral compositions vary with depth make modeling mantle dynamics in a realistic manner a daunting challenge. Compounding this challenge is the fact that mechanical properties of all the relevant minerals cannot be easily measured. With these challenges in mind this study focuses on several crucial rheological mechanisms that must have played key roles during the worldwide Flood cataclysm. A. Plasticity and creep In physics and materials science, plastic deformation refers to the irreversible changes of shape of a solid in response to applied forces. Elastic deformation, by contrast, refers to the changes in shape from applied forces that disappear entirely when the applied forces are removed. When plastic deformation occurs, dislocations nucleate and their interactions either hinder their mutual motions (hardening) or annihilate one another (recovery). When the dislocation density and their interactions increase, dislocation motion can be inhibited, such that a solid’s resistance to further deformation increases. This increased resistance arising from interactions among dislocations increases the work hardening. Work hardening typically increases as the strain rate and pressure increase but decreases as the temperature increases. On the other hand, more recovery can occur when the strain rate decreases, the pressure decreases, and the temperature increases (Karato 2012; Kirby 1983). In the case of the earth’s mantle, where there are persisting stresses and ongoing irreversible deformation of the rock material, both creation of new dislocations and annihilation of existing dislocations are continuously taking place. In the earth’s mantle, complicated thermal and mechanical states exist together. As the depth increases, the temperature and pressure simultaneously increase, and the competition between dislocation creation and annihilation determines the resulting rock strength at each depth. Because the strain rate during the Genesis Flood was dramatically greater than at present, the influences of strain rate on the strength of mantle rock at the time of the Flood are also of paramount importance. Cho et al. ◀ Strength-reducing mechanisms in mantle rock during the Flood ▶ 2018 ICC 709 Figure 1 . Constitutional map of important minerals in the Earth’s mantle. The volume fraction of each mineral has been obtained by observations from geochemistry, geophysics, and experimental studies at the mantle like pressure and temperature conditions (Karato, 2012; Ringwood, 1991; Stixrude and Lithgow-Bertelloni, 2011). The most dominant minerals are olivine (Ol), wadsleyite (Wd), ringwoodite (Rw), Mg-perovskite (MgPv), and post-perovskite (Ppv) at their corresponding depths. The abbreviations for the data references represent that K,2012 for Karato (2012), R,1991 for Ringwood (1991), and S,2011 for Stixrude and Lithgow-Bertelloni (2011). Ol, olivine; Opx, orthopyroxene; Cpx, clinopyroxene; HPCpx, high pressure clinopyroxene; Gt, garnet; Mj, majorite; Wd, wadsleyite; Rw, ringwoodite; Mw, magnesiowüstite; Fp, ferropericlase; MgPv, magnesium perovskite; Br, bridgmanite; CaPv, calcium perovskite; Ppv, post-perovskite.