ABSTRACT This presentation reports a numerical study to investigate the mechanical effects of dynamic recrystallization (DRX) and the grain size on the speed of flow of rock inside the earth’s solid mantle during the Genesis Flood. The strength, or viscosity, of its constituent minerals is key to understanding and modeling the dynamics of the mantle correctly. A mineral’s strength is strongly influenced by the crystal size, its lattice defects (vacancies and dislocations), and other microscale and crystal-scale phenomena. Since the viscosity difference of the earth’s deep mantle between the present day and during the Flood cataclysm is approximately 10 orders of magnitude, serious study is needed to understand the physically plausible subscale mechanisms that facilitated such a drastic strength reduction of the mantle. The dominant deformation mechanisms would be largely different in the days of the Flood relative to the present day. The present-day earth mantle’s strain rate is estimated to be about 10-15 s-1 based on geophysical observations such as isostatic rebound (Brennen, 1974). By contrast, the strain rate during the Flood was on the order of 10-5 s-1 based on the earlier Catastrophic Plate Tectonics (CPT) calculations (Baumgardner, 1994; Cho et al., 2018). At this strain rate range during the Flood, typical of most deformation experiments today, we know that the deformation is strongly controlled by grain size and DRX (Bystricky et al., 2000). Hence, it is logically important how these microstructural structures and mechanisms played a significant role in the strength reduction of the mantle during the Flood. For this work, we have performed a set of whole mantle numerical simulations that include an advanced material model (for determining the viscosity). In this study, we particularly focus on the weakening effect of an inelastic mechanism involved with dislocations and DRX that occurs due to stored plastic deformation energy (Cho et al., 2019). For realism we include representative minerals for each portion of the mantle: olivine for the upper mantle, spinel for the mantle transition zone, and bridgmanite-ferropericlase for the lower mantle. Upon crossing these zones (phase boundaries), the grain size , DRX, and other microstructural variables change as in the actual mantle. The results show that, under thermomechanical conditions that we expect during the Flood, the mantle deforms in a transient regime, with its viscosity reduced significantly compared to the present day. In particular, DRX weakens the mantle rock to enable the runaway process even more relative to the case without it (Baumgardner, 1994). This weakening by the DRX is particularly intense near the sinking slabs where the material is strongly deformed. The runaway mechanical instability enabled by this DRX-aided weakening produces a rapid overturn of the entire mantle. Due to these microstructural rearrangements, the rock strength (viscosity) is reduced by orders of magnitude, such that the mantle as a whole deforms in a catastrophic manner. KEYWORDS Mantle, Recrystallization, catastrophic plate tectonics, Genesis Flood Heechen Cho, John Baumgardner, Maria Lee, Caleb Miller, and Mark Horstemeyer. Liberty University, 1971 University Blvd., Lynchburg, Va 24515 heechenecho@gmail.com, jrbaumgardner@liberty.edu, mlee147@liberty.edu, cmiller353@liberty. edu, and mhorstemeyer@liberty.edu © Cedarville University International Conference on Creationism. The views expressed in this publication are those of the author(s) and do not necessarily represent those of Cedarville University. 9th 2023 663 Cho, H., J. Baumgardner, M. Lee, C. Miller, and M.F. Horstemeyer. 2023. Dynamic recrystallization and grain size effects on catastrophic motion of the earth’s mantle during the Flood: Advancement of material models [poster]. In J.H. Whitmore (editor), Proceedings of the Ninth International Conference on Creationism, p. 663. Cedarville, Ohio: Cedarville University International Conference on Creationism. DYNAMIC RECRYSTALLIZATION AND GRAIN SIZE EFFECTS ON CATASTROPHIC MOTION OF THE EARTH’S MANTLE DURING THE FLOOD: ADVANCEMENT OF MATERIAL MODELS
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