Multiscale modeling of upper mantle plasticity: From single-crystal rheology to multiphase aggregate deformation

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. We report a first application of an improved second-order (SO) viscoplastic self-consistent model for multiphase aggregates, applied to an olivine + diopside aggregate as analogue for a dry upper mantle peridotite deformed at 10 À15 s À1 shear strain rate along a 20-Ma ocean geotherm. Beside known dislocation slip systems, this SO-model version accounts for an isotropic relaxation mechanism representing 'diffusionrelated' creep mechanisms in olivine. Slip-system critical resolved shear stress (CRSS) are evaluated in both phases -as functions of P, T, oxygen fugacity (fO 2 ) and strain rate -from previously reported experimental data obtained on single crystals and first-principle calculations coupled with the Peierls-Nabarro model for crystal plasticity; and the isotropic-mechanism dependence on T and P matches that of Si selfdiffusion in olivine, while its relative activity is constrained by reported data. The model reproduces well the olivine and diopside lattice preferred orientations (LPO) produced experimentally and observed in naturally deformed rocks, as well as observed sensitivities of multiphase aggregate strength to the volume fraction of the hard phase (here diopside). It shows a significant weakening of olivine LPO with increasing depth, which results from the combined effects of the P-induced

Effects of crystal preferred orientation on upper-mantle flow near plate boundaries: rheologic feedbacks and seismic anisotropy

“…The strength and types of CPO distributions that are produced when these other mechanisms (also) operate tend to basically follow alignment directions for polycrystals where dislocation glide is dominant (e.g. Lebensohn et al 2010) although fabric strength may be overestimated (Raterron et al 2014) and high strain or hydration can alter recrystallized grain orientation in some cases (Zhang et al 2000). Differences in rates of CPO evolution and precise orientations for these other mechanisms have been reported, as discussed in Section 2.1.…”

“…This model space includes the upwelling zone beneath a slow (10 km Myr −1 ) spreading centre, the flow 'corner', and the onset of plate-driven shearing, which dominates evolution of the off-axis CPO. The base of the model is set at a depth 150 km, restricting the region to conditions that Raterron et al (2014) indicate would have nearly constant critical resolved shear stress threshold for olivine slip systems; pressure (P) and temperature (T) influences are modest for this region underlying oceanic crust 0-20 Myr old. Hadjazian et al (2017) combine deformation and seismic anisotropy modelling to explore changes as a function of ocean lithosphere age.…”

“…We assume that CPO is random as polycrystals enter the base of the model. Inclusion of P/T effects on slip system activity and/or the impacts of pre-existing texture (Raterron et al 2014;Boneh et al 2015) should be addressed in the future with larger models, but first it is important to establish whether the scale of feedback even warrants additional effort. Intermediate coupling (first iteration) reference case showing flow lines (grey) and olivine CPO.…”

Modeling the effect of subgrain rotation recrystallization on the evolution of olivine crystal preferred orientations in simple shear

“…A variety of homogenization models, ranging from kinematic (Etchecopar, 1977;Etchecopar and Vasseur, 1987;Ribe, 1989;Kaminski and Ribe, 2001) to lower bound (Chastel et al, 1993), tangent viscoplastic self-consistent (TGT-VPSC; Wenk et al, 1991;Tommasi et al, 1999Tommasi et al, , 2000, and second order viscoplastic selfconsistent (SO) approaches (Castelnau et al, 2008;Raterron et al, 2014), have been used to calculate the evolution of olivine crystal preferred orientation and the resulting anisotropy of physical properties in the mantle. These models fail, however, in predicting the essential features of the olivine CPO evolution in simple shear:…”

Deformation of forsterite polycrystals at mantle pressure: Comparison with Fe-bearing olivine and the effect of iron on its plasticity

“…At the scale of a rock, other components such as pyroxenes (e.g., Bystricky et al, 2006;Raterron et al, 2014) or small melt fractions (e.g., Hirth and Kohlstedt, 1996;Mei et al, 2002;Holtzman et al, 2003) can affect significantly the mechanical properties. At the microscopic scale, the plastic response of olivine is sensitive to the oxygen fugacity (fO 2 ), crystal hydroxyl content [OH] (e.g., Girard et al, 2013), and iron content (Hitchings et al, 1989;Katayama and Karato, 2008;Zhao et al, 2009;Nishihara et al, 2014).…”