A Theory of Inter‐Granular Transient Dislocation Creep: Implications for the Geophysical Studies on Mantle Rheology

Abstract

Rheological properties of Earth's interior can be inferred from the analyses of some time-dependent deformation. They include post-glacial isostatic crustal uplift (e.g., Nakada & Lambeck, 1987;Peltier, 1998) and post-seismic deformation (e.g., Bürgmann & Dresen, 2008;Masuti et al., 2016). Although the depth extent to which rheological properties can be constrained from these observations is limited Mitrovica and Peltier (1991), these observations provide crucial data to place constraints on the rheological properties of relatively shallow regions of Earth's interior.However, the strain magnitude of these phenomena is small (on the order of elastic strain) and therefore influence of transient creep is potentially important. For example Peltier et al. (1980);Yuen et al. (1986) and Freed et al. (2010) (see also Masuti et al., 2016& Qiu et al., 2018 examined the role of transient creep in deformation associated with post-glacial and post-seismic deformation respectively and suggested that transient creep may play an important role in these phenomena. The role of transient creep in these time-dependent deformations is important if the effective viscosity is largely different between transient

Effects of initial velocity on the sinking of ilmenite-bearing cumulates in the early lunar mantle: Insight from the theory of Rayleigh-Taylor instability

“…For a single mineral, its deformation can take place in diffusion creep and dislocation creep at the same time. As these two deformation components relate to different imperfect structures on the crystal lattice, their strain rates are essentially additive (Karato 2008). For this reason, if the MPG mixing model is reliable in predicting the intermineralogical mixing, the total strain rate and total stress need to be partitioned based on…”

“…Diffusion creep is dominated by the migration of vacancies on the crystal lattice, which results in a linear relation between stress and strain rate. In contrast, dislocation creep, associated with the migration of dislocations on the crystal lattice, results in a nonlinear relation between stress and strain rate, which in turn causes a feedback between the mobility of mantle materials and the change of lunar mantle rheology (Schubert et al 2001;Karato 2008). The initial velocity at the IBC-mantle boundary can significantly affect the initial strain rate of IBC and, correspondingly, the dislocation creep components at the shallow lunar mantle.…”

Transient Creep of Quartz and Granulite at High Temperature Under Wet Conditions

“…What we know of the transient creep largely comes from studies on olivine (e.g., Chopra, 1997; S. Karato, 1998; Hansen et al., 2019; Masuti & Barbot, 2021; S.‐I. Karato, 2021). Although several studies have illuminated the transient microstructural development of crustal rocks imposed by sudden stress changes (e.g., C. A. Trepmann et al., 2007; C. Trepmann & Stöckhert, 2013), the detailed mechanical properties of transient creep of quartz and feldspar has not been explored yet.…”

“…What we know of the transient creep largely comes from studies on olivine (e.g., Chopra, 1997;S. Karato, 1998;Hansen et al, 2019;Masuti & Barbot, 2021;S.-I. Karato, 2021).…”

Identifying Geographical Patterns of Transient Deformation in the Geological Sea Level Record

“…Dislocation creep may lead to transients by interactions between different grains, or by non-steady state dislocation interactions inside grains. In the first case, interactions between grains deforming on either hard or soft slip systems (Karato, 1998(Karato, , 2021 could lead to a temporal change in material strength during deformation. Alternatively, interactions between dislocations inside grains, and the evolution of dislocation density, lead to gradual hardening of material and thus to transient behavior (Hansen et al, 2021;Wallis et al, 2021).…”