Stresses in a subducting slab in the presence of a metastable olivine wedge

Abstract

Abstract. The transformation of olivine to spinel in a subducting slab gives rise to thermal strain, transformation strain, and buoyancy forces inside the slab. We use a finite element method to solve the mechanical equation, and we follow the evolution of the stresses inside the slab during its descent. We use two different rheologies: elastic and viscoelastic with a viscosity that depends on pressure, temperature, and grain size. The stresses due to buoyancy are found to be negligible compared to the internal stresses due to the phase transformation. When the viscoelastic rheology is used, a zone of very high differential stress coincides with the olivine-spinel phase boundary. This zone is associated with large downdip compressire stresses inside the roetastable olivine wedge, and large downdip tensile stresses in the spinel region, along the wedge. If we assume that the failure criterion can be related to the differential stress, our model is in agreement with the patterns of deep seismicity. However, patterns of deep seismicity are unlikely to reflect buoyancy stresses, which in the presence of a roetastable olivine wedge, are negligible compared to the internal stresses.

Impact of phase change kinetics on the Mariana slab within the framework of 2-D mantle convection

“…and , it is considered that the phase boundary is uplifted 65 inside a low-temperature subducting oceanic plate. 66 However, according to high-pressure and high-temperature 67 experiments (e.g., Sung and Burns, 1976;Rubie et al, 1990) and 68 numerical modeling based on such experiments (Rubie and Ross,69 1994; Riedel and 70 Karato, , 1997Kirby et al, 1996;Yoshioka et al, 1997; 71 Devaux et al, 1997Devaux et al, , 2000Guest et al, 2004), because the phase 72 transformation reaction is slow, and phase transformation is 73 delayed in a low-temperature slab, a metastable olivine wedge 74 may exist in the deeper parts of slabs. Mosenfelder et al (2001) 75 calculated the metastable area of olivine using experimentally 76 determined kinetic data.…”

Quantifying the Effects of Non‐Hydrostatic Stress on Single‐Component Polymorphs

“…These models use constant pressures in their calculations. However, metastable olivine wedges may have differential stresses that exceed 1 GPa (Devaux et al., 2000). Such a large stress differential would lead to significantly different results for metastable olivine wedge models depending on what stress was used for the pressure term of the reaction kinetics.…”

“…Consequently, for a non-hydrostatically stressed solid, the equilibrium condition of each interface must be determined individually using HESS AND AGUE 10.1029/2020JB021594 Equation 9. Smaller stress variations of up to 0.1-0.2 GPa, which are common in some metamorphic systems (e.g., Andersen et al, 2008;Devaux et al, 2000;Little et al, 2007;Wheeler, 2014;Zulauf, 2001), would shift interface equilibrium temperatures by as much as 50-100°C (Figures 1b and 1d) on interfaces of the same mineral grain depending on its orientation. This suggests that non-hydrostatic stress can have a considerable impact on mineral stability.…”