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

Cho, N., J. Baumgardner, J.A. Sherburn, and M.F. Horstemeyer. 2018. Numerical investigation of strength-reducing mechanisms of mantle rock during the Genesis Flood. In Proceedings of the Eighth International Conference on Creationism , ed. J.H. Whitmore, pp. 707–730. Pittsburgh, Pennsylvania: Creation Science Fellowship. NUMERICAL INVESTIGATION OF STRENGTH-REDUCING MECHANISMS OF MANTLE ROCK DURING THE GENESIS FLOOD Noah Cho , 61 Nicklaus Ln., Starkville, MS 39759, USA HeechenECho@gmail.com John Baumgardner , 24515 Novato Place, Ramona, CA 92065, USA Jesse A. Sherburn , 3909 Halls Ferry Rd, Vicksburg, MS 39180, USA Mark F. Horstemeyer , 1292 Chapel Hill Rd, Starkville, MS 39759, USA ABSTRACT This paper reports our efforts to model the effects of grain size, recrystallization, creep, and texture on overall rock strength within the Earth’s mantle during the Genesis Flood. Our study uses experimental rheological data obtained from the mineralogical literature for olivine, which is an important mantle mineral. We apply an Internal State Variable (ISV) constitutive model within the framework of the TERRA finite element code to capture the subscale structures and their associated dynamics, strength, and viscosity effects during the Flood episode. Our numerical investigations, in both 2D and 3D, that include the improved deformation model reveal even more clearly that the potential for mantle instability enabled an episode of catastrophic plate tectonics to occur. This mantle instability arises from the extreme weakening behavior resulting from the relationship between microstructural features (herein texture, recrystallization, and grain size) and thermomechanical properties (e.g., stress and viscosity) under the conditions of temperature, pressure, and strain rate within the mantle during the Genesis Flood. It is our conviction that such an episode played a major role in the global Flood described in Genesis 7-8. KEY WORDS mantle rheology, Internal State Variable model, catastrophic plate tectonics, Genesis Flood, TERRA earth model Copyright 2018 Creation Science Fellowship, Inc., Pittsburgh, Pennsylvania, USA www.creationicc.org 707 INTRODUCTION The deformational behavior of rock under stress, that is, its rheology, plays a central role in the internal dynamics of the earth. Rock deformation is determined by the thermomechanical properties (e.g., elasticity, plasticity, viscosity, creep, and damage) of the minerals comprising the rock. Thermomechanical properties, in turn, are influenced profoundly by microstructural features such as grain size, phase transformations, dislocations, and texture (crystallographic orientation). Interestingly, many of these microstructural features can result in orders-of-magnitude reductions in rock strength, such that the mantle as a whole deforms in a catastrophic manner (Baumgardner 1994). Because mantle rocks are polycrystalline and microstructural properties of individual constituent minerals play important roles, a comprehensive deformation model (Horstemeyer 1998) capable of handling all these microstructural variations is needed to explore the weakening mechanisms with scientific rigor (Horstemeyer et al. 2002). A central focus of this paper is a description of such a comprehensive deformation model that may be applied to the runaway dynamics and catastrophic plate tectonics of the Genesis Flood. The concept of Catastrophic Plate Tectonics (CPT) was introduced in Baumgardner (1986) and has been developed and refined over the past three decades (Austin et al. 1994). Numerical simulations, both in 2D and 3D, have provided deeper insights into the weakening mechanisms that physically allow a runaway process to occur (Baumgardner 2003). However, previous simulations have employed simple deformation models based on thermally activated diffusional and strain-rate creep and a constant yield stress that assume no interactions among mineral phases. Sherburn et al. (2011) showed that the creep models widely used in the geophysics community typically do not capture elasticity, work hardening, and damage (e.g., faulting), even though these deformation mechanisms play significant roles. However, today more realistic models exist, especially within the metallurgical and engineering communities that do include these phenomena. Sherburn et al. (2011) presented a new constitutive model for the earth’s mantle, called an Internal State Variable (ISV) constitutive model that includes elasticity, plasticity, and creep regimes. Later, Sherburn et al. (2013) applied this ISV model to evaluate candidate weakening mechanisms related to static and dynamic recovery of dislocations in the mineral olivine. Despite that progress, many important features such as multiple mineral phases, variable grain size, and elastic stress limit (yield surface) models with pressure and temperature dependence had not yet been studied. This paper reports results of investigations that apply the ISVmodel with structure-property relations calibrated against experimental mineral data from the literature for olivine, which is the most important upper-mantle mineral in the framework of the TERRA finite element code. We explore the effects of grain size, creep, and texture (arising from plastic spin) on overall rock strength under possible conditions that existed in the mantle during the Genesis Flood. This study provides crucial new understanding on how the subscale heterogeneous structures and thermomechanical properties cooperatively act together to produce the extreme weakening that allowed the global Flood cataclysm to unfold as it did. MATERIALS AND METHODS 1. Dependence of mechanical properties on microstructure Themechanical properties of solids suchas strengthandviscosityare significantly influenced by their hierarchical multiscale structures,