Project

Back to overview

Thermo-chemical convection and the survival of reservoirs of dense material in the deep Earth's mantle

English title Thermo-chemical convection and the survival of reservoirs of dense material in the deep Earth's mantle
Applicant Deschamps Frédéric
Number 129510
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2010 - 30.09.2013
Approved amount 161'448.00
Show all

Keywords (6)

Mantle dynamics; Mantle structure; Mantle temperat; Earth's mantle structure; Earth's mantle dynamics; Convection

Lay Summary (English)

Lead
Lay summary
Inferring the mode of convection and the thermo-chemical structure of the Earth's mantle are key problems in geophysics. Both thermal and chemical sources contribute to lateral variations in density, and the mode of convection depends strongly on the relative strength of these two sources. Given a set of input parameters, numerical models of convection predict a mantle flow and structure that can be tested against geophysical observables, mainly seismic tomography maps. Because recent seismological observations suggest that reservoirs of dense material are present in the deep mantle, it is crucial to build and test models of thermo-chemical convection that can maintain large pools of dense material over a period of time comparable to the age of the Earth. Previous studies in 3D-Cartesian geometry have pointed out parameters that potentially play an important role in maintaining such reservoirs, but it is essential to check whether these findings are also valid in 3D-spherical geometry. This project aims to specify the influence of various parameters on the properties - stability and shape - of reservoirs of dense material in a spherical convective shell, and to apply these results to the dynamics and structure of the Earth's mantle. First, we will conduct preliminary studies to better understand the stability of a basal layer of dense material (influence of chemical viscosity contrast and layer thickness vs buoyancy ratio), and to map the topology of the reservoirs of dense material as a function of the thermal viscosity contrast and the chemical viscosity contrast. Second, we will explore the model space of thermo-chemical convection in a spherical shell and identify the ingredients that can maintain large thermo-chemical pools for a long period of time. In addition to the parameters we explored in our previous 3D-Cartesian studies, we will investigate the role played by the post-perovskite phase transition on the stability of these reservoirs. Finally, we will calculate models that include two sources of chemical heterogeneities, one modelling a primitive reservoir, and the other modelling the recycling of subducted MORB material. These two sources may be needed to explain the lack of correlation between the thermal and chemical signals observed by probabilistic tomography. Each model of thermo-chemical convection will be tested against existing seismic tomography models, including probabilistic tomography. These comparisons will point out which models of convection are the most likely for the Earth's mantle, and give new insights on the role played by specific ingredients, on the mantle dynamics and thermo-chemical structure.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
General assembly of the European Geosciences Union Poster 07.04.2013 Vienne, Austria Tackley Paul; Deschamps Frédéric;
General assembly of the European Geosciences Union Talk given at a conference 07.04.2013 Vienne, Austria Deschamps Frédéric; Tackley Paul; Li Yang;
AGU Fall meeting 2012 Poster 03.12.2012 San Francisco (USA), United States of America Deschamps Frédéric; Tackley Paul; Li Yang;
9th Geoscience Swiss Meeting Poster 11.11.2011 Zurich, Switzerland Li Yang; Deschamps Frédéric; Tackley Paul;


Associated projects

Number Title Start Funding scheme
149625 Thermo-chemical convection and the survival of reservoirs of dense material in the deep Earth's mantle 01.10.2013 Project funding
111870 The role of the post-perovskite phase transition in the mantle dynamics 01.05.2007 Project funding

Abstract

Inferring the mode of convection and the thermo-chemical structure of the Earth’s mantle are key problems in geophysics. Both thermal and chemical sources contribute to lateral variations in density, and the mode of convection depends strongly on the relative strength of these two sources. Given a set of input parameters, numerical models of convection predict a mantle flow and structure that can be tested against geophysical observables, mainly seismic tomography maps. Because recent seismological observations suggest that reservoirs of dense material are present in the deep mantle, it is crucial to build and test models of thermo-chemical convection that can maintain large pools of dense material over a period of time comparable to the age of the Earth. Previous studies in 3D-Cartesian geometry have pointed out parameters that potentially play an important role in maintaining such reservoirs, but it is essential to check whether these findings are also valid in 3D-spherical geometry. This project aims to specify the influence of various parameters on the properties - stability and shape - of reservoirs of dense material in a spherical convective shell, and to apply these results to the dynamics and structure of the Earth’s mantle. First, we will conduct preliminary studies to better understand the stability of a basal layer of dense material (influence of chemical viscosity contrast and layer thickness vs buoyancy ratio), and to map the topology of the reservoirs of dense material as a function of the thermal viscosity contrast and the chemical viscosity contrast. Second, we will explore the model space of thermo-chemical convection in a spherical shell and identify the ingredients that can maintain large thermo-chemical pools for a long period of time. In addition to the parameters we explored in our previous 3D-Cartesian studies, we will investigate the role played by the post-perovskite phase transition on the stability of these reservoirs. Finally, we will calculate models that include two sources of chemical heterogeneities, one modelling a primitive reservoir, and the other modelling the recycling of subducted MORB material. These two sources may be needed to explain the lack of correlation between the thermal and chemical signals observed by probabilistic tomography. Each model of thermo-chemical convection will be tested against existing seismic tomography models, including probabilistic tomography. These comparisons will point out which models of convection are the most likely for the Earth’s mantle, and give new insights on the role played by specific ingredients, on the mantle dynamics and thermo-chemical structure.This project will result in one Ph.D. dissertation. The two applicants, Dr. F. Deschamps and Prof. P.J. Tackley, both from ETH Zürich, combine the knowledge and expertise required in this project, mostly the numerical modelling of convection, the structure and dynamics of the Earth mantle, and the interpretation of seismic tomography.
-