Project

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Physico-Chemical Structure of the Earth's Mantle: Coupling Geophysical Data Analysis with Mineral Physics

Applicant Connolly James A. D.
Number 130411
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.05.2010 - 30.04.2013
Approved amount 371'267.00
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Keywords (11)

Geophysics; Seismology; Gravity; Geoelectromagnetism; Mineralogy; Petrology; Phase equilibria; Earth composition and temperature; geophysical inversion; mantle tomography; joint inversion

Lay Summary (English)

Lead
Lay summary
Geophysical inversion is the primary source of information on the composition, temperature, and structure of the Earth's deep interior. Typically, geophysical inversion is used to infer secondary geophysical properties, such as seismic velocity or electrical conductivity, from direct geophysical observations. These secondary geophysical properties are then compared with those of various rocks to constrain the composition of planetary interiors. The disadvantage of this classical strategy is that it is generally not possible to simultaneously consider different types of geophysical data, i.e., seismic data is largely independent of conductivity data. This study employs a distinctly different strategy in that inversion is done directly for composition and temperature. The virtue of this approach is that it permits simultaneous inversion of different types of geophysical data, e.g., both electrical conductivity and seismic velocity are directly dependent on rock mineralogy and temperature. The complication in this strategy is that it requires a complete model for the geophysical properties of rocks as a function of composition and temperature. This difficulty is resolved by using thermodynamic models to predict the mineralogy of rocks at high temperature and pressure.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
A Hydromechanical Model for Lower Crustal Fluid Flow
Connolly James A. D., Podladchikov Yuri Y. (2013), A Hydromechanical Model for Lower Crustal Fluid Flow, in Harlov D.E., Austrheim H. (ed.), Springer-Verlag, Berlin, 599-658.
A geophysical perspective on mantle water content and melting: Inverting electromagnetic sounding data using laboratory-based electrical conductivity profiles
Khan A., Shankland T. J. (2012), A geophysical perspective on mantle water content and melting: Inverting electromagnetic sounding data using laboratory-based electrical conductivity profiles, in EARTH AND PLANETARY SCIENCE LETTERS, 317, 27-43.
Mapping the Earth’s thermochemical and anisotropic structure using global surface wave data
Khan A. Boschi L. and Connolly J. A. D. (2011), Mapping the Earth’s thermochemical and anisotropic structure using global surface wave data, in Journal of Geophysical Research, 116, B01301.
On the Heterogeneous Electrical Conductivity Structure of the Earth's Mantle with Implications for Transition Zone Water Content
Khan A. Kuvshinov A. and Semenov A. (2011), On the Heterogeneous Electrical Conductivity Structure of the Earth's Mantle with Implications for Transition Zone Water Content, in Journal of Geophysical Research, 116, B01103.
Precalculated phase equilibrium models for geophysical properties of the crust and mantle as a function of composition
Zunino A., Connolly J. A. D., Khan A. (2011), Precalculated phase equilibrium models for geophysical properties of the crust and mantle as a function of composition, in GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 12, 1-1000.
The thermo-chemical and physical structure beneath the North American continent from Bayesian inversion of surface-wave phase velocities
Khan A., Zunino A., Deschamps F. (2011), The thermo-chemical and physical structure beneath the North American continent from Bayesian inversion of surface-wave phase velocities, in JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 116, 1-1000.
The internal structure of the Moon: A geophysical perspective
Khan A. Pommier A. Neumann G. A. and Mosegaard K., The internal structure of the Moon: A geophysical perspective, in Tectonophysics, 1.

Awards

Title Year
Bowen Award, VGP section, American Geophysical Union 2011

Abstract

The aim of the proposed project is to directly infer Earth's mantle composition and thermal state from a broad range of geophysical data, including seismic, gravity, geodetic and electromagnetic sounding data, that sense disparate physical rock properties. The present proposal results from recent advances in seismic tomography and mineral physics, particularly knowledge of elastic properties of mantle phases at high pressure and temperature, that have spurred an increased interest in the origins of the observed lateral variations in physical properties (seismic wave speeds, density and electrical conductivity) of mantle and crustal minerals. It is believed that much of the lateral variations seen in tomographic images are related to lateral variations in temperature and composition, although their relative contributions are yet to be ascertained.Rather than invert for the physical property to which a specific geophysical field gives rise to, we propose to jointly invert different geophysical fields for composition and thermal state. Compared to conventional geophysical inversion techniques, our strategy has the advantage of providing a natural way of integrating the widely different data sets. At the same time, it also allows us to obtain tighter constraints on the inverted parameters. These improved constraints are realized by combining thermodynamic modeling of mantle mineral phase equilibria with inversion of geophysical data using stochastic sampling methods, something which has not been undertaken previously. The approach is strongly interdisciplinary in that it seeks to integrate geophysics, geodynamics and geochemistry in order to understand how the Earth developed its chemical and physical structure. Our inverse analysis will generate of maps of mantle composition and temperature constrained directly by geophyiscal data, in the form of global P and S wave travel times, receiver functions, surface wave dispersion data, normal mode splitting functions, electromagnetic sounding and gravity data as well as geochemical data where available (in the form of prior constraints derived from analyses of mantle peridotites). These maps will provide us with the information that is crucial to unravel the relative importance of chemical and thermal contributions that are observed as variations in seismic wave speeds in tomographic images. In turn, this information will provide constraints on the dynamic evolution of the Earth.The technical nature and diversity of the problems to be addressed in this project require a dedicated researcher who is not only knowledgeable about inverse problems, but who is also a master of the forward problems to be solved, including short- and long-period seismology (travel times, receiver functions, surface waves and normal modes), gravity and geodetic modeling, as well as time and frequency domain electromagnetic depth sounding. As we propose to integrate information obtained from geochemical analyses of rocks (e.g. mantle peridotites), versatility with regard to petrological and mineralogical modeling is of equal importance. The primary purpose of this proposal is therefore to obtain funding for a post-doctoral researcher (Amir Khan, see attached CV and publication list) to fulfill this role.
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