EGU24-11588, updated on 09 Mar 2024
https://doi.org/10.5194/egusphere-egu24-11588
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modelling the global geodynamic and seismological consequences of different phase boundary morphologies. 

Gwynfor Morgan1, J. Huw Davies1, Bob Myhill2, James Wookey2, and James Panton1
Gwynfor Morgan et al.
  • 1School of Earth and Environmental Sciences, Cardiff University, Cardiff, Wales, United Kingdom of Great Britain and Northern Ireland (morgangt2@cardiff.ac.uk)
  • 2School of Earth Sciences, University of Bristol, Bristol, England, United Kingdom of Great Britain and Northern Ireland

Throughout Earth’s mantle, several significant phase transitions occur, with the Ol→Wd and Rw→Brm+Pc reactions (exothermic and endothermic respectively) producing large discontinuities in Earth’s seismic velocity structure at 410 and 660km depth respectively (‘410’ & ‘660’). The equilibrium depth of these reactions is sensitive to temperature, and the resulting topography has been observed with various seismic phases. Numerical modelling from the 1980s onwards has suggested that the topography on endothermic phase transitions can stagnate downwellings and even layer mantle convection for extreme Clapeyron slopes or density changes. The thermodynamic properties of the post-spinel reaction make it unlikely that slabs would stagnate due to effects associated with phase transitions. At cooler temperatures the post-spinel reaction splits into two reactions (Rw + Ak → Ak + Pc → Brm + Pc) which seems to explain well aspects of the observed topography of the ‘660’ discontinuity. It has been suggested that this second reaction (which has a more extreme Clapeyron slope than the post-spinel reaction) could stagnate downwellings. Recently, Ishii et al (2023) suggested that the post-garnet reaction (Gt → Brm + Cor [+ St]) is in fact univariant, producing a sharp reaction that is endothermic for cooler temperatures and exothermic at higher temperatures – and that this may contribute to slab stagnation. Here, we test these slab stagnation mechanisms using realistic mineral physics and whole-mantle convection models (MCMs).

The lack of anti-correlation between the topography of the ‘410’ and ‘660’ discontinuities does not match simple theory if they are controlled solely by temperature variations across the post-olivine and post-spinel reactions respectively. Previous work has shown that the calculated topography on the discontinuities can be markedly different for various single-composition mantles generated from MCMs (Papanagnou et al, 2022). Here we will explore the impact of laterally varying chemistry generated in thermochemical MCMs on global discontinuity topography.

How to cite: Morgan, G., Davies, J. H., Myhill, B., Wookey, J., and Panton, J.: Modelling the global geodynamic and seismological consequences of different phase boundary morphologies. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11588, https://doi.org/10.5194/egusphere-egu24-11588, 2024.

Comments on the supplementary material

AC: Author Comment | CC: Community Comment | Report abuse

supplementary materials version 1 – uploaded on 13 Apr 2024, no comments