Modelling spontaneous ductile (viscous) strain localisation on Earth

TL;DR

This paper introduces a stochastic modeling approach to simulate spontaneous viscous strain localization in Earth's mantle, successfully reproducing natural shear zones and advancing understanding of plate boundary formation.

Contribution

It presents a novel stochastic rheology model that captures strain localization in viscous rocks, addressing previous limitations in geodynamical simulations.

Findings

Successfully generates steady-state shear zones from random heterogeneity

Reproduces observed features of natural and experimental shear zones

Defines conditions and regimes for viscous strain localization

Abstract

A characteristic feature of the Earth is that diffuse thermal convection in the mantle produces localized deformation at the surface: Plate Tectonics. However, modelling this phenomenon remains a challenge, due to inability to simulate spontaneous strain localisation in the deep sections of the plates, where rocks deform by ductile processes and behave as highly viscous fluids. Analysis of shear zones - the main expression of strain localisation in nature - reveals that mechanical heterogeneity is key. Here we posit that the bottleneck for self-consistent generation of strain localisation in geodynamical models is poor representation of this heterogeneity and its evolution during deformation, in particular at small scales. To bypass this obstacle, we introduce a stochastic description of the mechanical properties of the rocks, which evolves as a function of the local work rate. This approach not only successfully generates steady-state shear zones from random rheological heterogeneity fields, but reproduces the full range of observations in nature and experiments. It allows defining the necessary conditions and a regime diagram for viscous strain localisation and quantifying the resulting bulk softening, paving the way for self-consistent modelling of the development of plate boundaries and initiation of Plate Tectonics on Earth.