Anisotropy development during dynamic recrystallisation of partially molten olivine

The processes of partial melting and subsequent melt transport are fundamental to Earth's differentiation, from the separation of the core and mantle to magma generation, evolution, segregation and ascent within mantle and crustal domains. Active volcanoes have as their source the partially molten areas of the upper mantle and crust. The possibility of a melt to ascend depends on its connectivity, where the melt percentage, dihedral angle between melt and solid, as well as recrystallisation processes, play a fundamental role (Llorens et al., 2016). The deformation of the upper mantle is primarily governed by the mechanical behavior of olivine (Karato et al., 1989). During mantle flow, olivine undergoes crystal-plastic deformation and dynamic recrystallisation, leading to the development of Crystallographic Preferred Orientations (CPOs) and associated mechanical and seismic anisotropy. While the influence of plastic deformation is well understood, the role of the presence of melt in the rheology and anisotropy of mantle rocks during dynamic recrystallization remains unclear.

This contribution presents microdynamic numerical simulations of olivine polycrystalline aggregates during dynamic recrystallisation (Yu et al., 2024), varying the melt content to predict the CPO and associated mechanical and seismic anisotropy. We combine the VPFFT approach (Lebensohn and Rollett, 2020) within the ELLE numerical simulation platform (http://www.elle.ws; Piazolo et al., 2019) to reproduce partially molten olivine under simple shear deformation. The numerical results allow us to understand how the percentage of melt and intensity of recrystallisation affects the connectivity of melt, and how they influence the evolving anisotropy, which have implications for different upper-mantle and crustal basaltic mush zones.