Reproducing rheology of Morency and Doin, 2004#

This section was contributed by Jonathan Perry-Houts

Modeling interactions between the upper mantle and the lithosphere can be difficult because of the dynamic range of temperatures and pressures involved. Many simple material models will assign very high viscosities at low temperature thermal boundary layers. The pseudo-brittle rheology described in (Morency and Doin 2004) was developed to limit the strength of lithosphere at low temperature. The effective viscosity can be described as the harmonic mean of two non-Newtonian rheologies: $\(v_{\text{eff}} = \left(\frac{1}{v_{\text{eff}}^v}+\frac{1}{v_{\text{eff}}^p}\right)^{-1}\)\( where \)\(\begin{aligned} v_{\text{eff}}^v = B \left(\frac{\dot{\epsilon}}{\dot{\epsilon}_\text{ref}}\right)^{-1+1/n_v} \exp\left(\frac{E_a +V_a \rho_m g z}{n_v R T}\right), \\ v_{\text{eff}}^p = (\tau_0 + \gamma \rho_m g z) \left( \frac{\dot{\epsilon}^{-1+1/n_p}} {\dot{\epsilon}_\text{ref}^{1/n_p}} \right),\end{aligned}\)\( where \)B\( is a scaling constant; \)\dot{\epsilon}\( is defined as the quadratic sum of the second invariant of the strain rate tensor and a minimum strain rate, \)\dot{\epsilon}0\(; \)\dot{\epsilon}\text{ref}\( is a reference strain rate; \)n_v\(, and \)n_p\( are stress exponents; \)E_a\( is the activation energy; \)V_a\( is the activation volume; \)\rho_m\( is the mantle density; \)R\( is the gas constant; \)T\( is temperature; \)\tau_0\( is the cohesive strength of rocks at the surface; \)\gamma\( is a coefficient of yield stress increase with depth; and \)z$ is depth.

By limiting the strength of the lithosphere at low temperature, this rheology allows one to more realistically model processes like lithospheric delamination and foundering in the presence of weak crustal layers. A similar model setup to the one described in (Morency and Doin 2004) can be reproduced with the files in the directory cookbooks/morency_doin_2004. In particular, the following sections of the input file are important to reproduce the setup:


../../../../../_images/morency_doin_2004_fig1.svg

Fig. 92 Approximate reproduction of figure 1 from (Morency and Doin 2004) using the ‘morency doin’ material model with almost all default parameters. Note the low-viscosity Moho, enabled by the low activation energy of the crustal component.#

Morency, C., and M.-P. Doin. 2004. “Numerical Simulations of the Mantle Lithosphere Delamination.” Journal of Geophysical Research: Solid Earth (1978–2012) 109 (B3).