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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 Tackley Paul
Number 149625
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2013 - 30.09.2014
Approved amount 62'740.00
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Keywords (3)

Mantle dynamics; Mantle structure; Mantle temperat

Lay Summary (French)

Lead
Déterminer le mode de convection et la structure thermo-chimique du manteau terrestre sont des problèmes clé en géophysique. Température et composition y varient fortement. Les modèles sismologiques récents suggèrent que des réservoirs de matériau dense sont présents dans le manteau profond. Une approche prometteuse est de simuler numériquement la convection du manteau, puis de comparer les structures prédites par ces modèles avec les structures obtenues par tomographie sismique.
Lay summary

Buts

Le but de ce projet est d'identifier les paramètres contrôlant la convection du manteau terrestre, et de préciser le rôle joué par la transition de phase vers la post-perovskite. Ce projet souhaite déterminer l'influence de plusieurs paramètres sur la stabilité et la forme de réservoirs de matériau dense dans des enveloppes sphériques animées de convection, et d'appliquer ces résultats à la dynamique et à la structure du manteau terrestre.

 

Portée

Nous allons d'abord simuler la convection thermo-chimique du manteau dans des enveloppes sphériques et identifier les paramètres permettant de maintenir des réservoirs thermo-chimiques pendant de longues périodes de temps. Puis nous calculerons des modèles incluant deux sources d'hétérogénéités chimiques, une pour modéliser un réservoir primitif, et l'autre pour modéliser le recyclage de la croûte océanique. Chaque modèle sera comparé à des modèles de tomographie sismique, et notamment à la tomographie probabiliste. Ces comparaisons permettront d'indiquer quels sont les modèles de convection les plus appropriés au cas du manteau terrestre. Ce projet apportera de nouvelles vues sur la structure et la dynamique du manteau, qui sont des sujets d'intérêts majeurs en science de la Terre.


Direct link to Lay Summary Last update: 06.10.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Effects of low-viscosity post-perovskite on the stability and structure of primitive reservoirs in the lower mantle
Li Yang, Deschamps Frederic, Tackley Paul (2014), Effects of low-viscosity post-perovskite on the stability and structure of primitive reservoirs in the lower mantle, in Geophysical Research Letters, 41, 7089-7097.
The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry
Li Yang, Deschamps Frederic, Tackley Paul (2014), The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry, in Geophysical Journal International, 199, 914-930.
Large-scale thermo-chemical structure of the deep mantle: observations and models
Deschamps Frederic, Li Yang and Tackley Paul, Large-scale thermo-chemical structure of the deep mantle: observations and models, in Khan Amir et al. (ed.), Springer, Berlin.

Collaboration

Group / person Country
Types of collaboration
Dr. Frédéric Deschamps, Institute of Earth Sciences, Academia Sinica Taiwan (Asia)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Associated projects

Number Title Start Funding scheme
129510 Thermo-chemical convection and the survival of reservoirs of dense material in the deep Earth's mantle 01.10.2010 Project funding

Abstract

We here request a fourth year of funding for an already funded three-year Ph.D. project. This PhD project explores the model space of thermo-chemical convection in spherical geometry, and aims to identify the parameters that play a key role in Earth's mantle convection and to specify the role played by the phase transition to post-perovskite. 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 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 more in details the role played by the post-perovskite phase transition. Second, 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.The knowledge and experience of the collaborative team, and the progress made to date, foretell that the goals of this project will be achieved. Furthermore, the numerical modeling tools are already developed and being used.This project will bring new insights on the dynamics and thermo-chemical structure of the Earth's mantle, which are currently topics of major interest to the communities in geodynamic and deep Earth studies. The results we expect to obtain regarding the dynamics and thermo-chemical structure of the mantle may be incorporated in future researches carried out in ETH Zürich or in other institutions, thus opening long-term local and international collaborations.
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