New laboratory constraints on the water content of the mantle

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

We have long known that the nominally anhydrous mantle minerals, such as can take substantial amounts of water into them (eg 3% for wadsleyite and ringwoodite). We also know that water has a drastic effect on the physical and chemical properties of these minerals, changing phase relations by hundreds of Kelvin and causing order-of-magnitude variations in viscosity, electrical conductivity and vacancy populations. This has created a whole genre of speculation about the water content in the mantle and its effects on mantle dynamics (eg; 'The mid-mantle water filter'; Bercovici and Karato 2003: 'Nine oceans of water in the transition zone'; Smyth et al 1994: 'No water in the transition zone'; Green at al 2010). We have, however, no firm understanding of the water content of the mantle deeper than about 100 km and these papers will remain speculative until we place firm constraints on the water content of the deep mantle. We can do this by combining geophysical inversions for electrical conductivity of the geomagnetic response function with laboratory measurements of the effect of water content on electrical conductivity. This is what the current project will do using cutting-edge designer-diamond anvil cell conductivity measurements with simultaneous infra-red measurements of water content. These new data will be used in Monte Carlo simulations of the geomagnetic response function which invert directly for water content.

Planned Impact

1. Who will benefit from this research?
a/ The main beneficiaries form this reaserch are academics as outlined in the academic beneficiaries section. Beyond the immediate area of reserach interest of the proposal (Solid Earth Geophysics) the results will provide constraints on the present water content of the Earth's mantle. This is important for informing the discussion regarding the long-term hydrological cycle: Currently we do not even know if the mantle is loosing water to the surface or if it is extracting water from the surface.

b/ We have identified an area of potential interest for schools outreach in demonstrating high-pressure synthesis and polymorphism: 'Diamonds from Dirt'. This outreach project links in with existing outreach by the Pi and colleagues from UCL Chemistry (Prof. Andrea Sella; EPSRC outreach professor).

2. How will they benefit from the research?
a/ The new constraints on the water content of the mantle will provide boundary conditions for geodynamical and hydrological models. They will also help to constrain the chemistry of the mantle for interpretations of geophysical observables such as seismic wave speed and attenuation. The best way to disseminate the results will be via conference presentations and publications in high-impact journals. In addition, the UCL ES website highlights important results as they are published.

b/ The 'Diamonds from Dirt' program will involve 2 components: 1) school visits to explain the concepts of polymorphism, high-pressure and materials synthesis. 2) this will be supplemented with experiments in which diamond will be grown from 'dirt' of various sorts and a web cast of the experiments and recovered diamond will be developed for use in the school visits.
 
Title Deepwaterblue pigment 
Description I am developing a new blue pigment for fine-art use based on the incorporation mechanism of ferric iron into the transition-zone mineral, ringwoodite. 
Type Of Art Artefact (including digital) 
Year Produced 2017 
Impact Working with Colart to investigate commercial possibilities 
 
Description We have investigated the incorporation mechanism of water (as protons) into the main mantle transition zone minerals using an innovative combined neuron and X-ray diffraction, and Moessbauer spectroscopy study. . Protons are incorporated into ringwoodite through two mechanisms - charge balancing ferric iron on the silicon site and charge balancing magnesium vacancies. The ferric iron mechanism means that it is not available to contribute to electrical conductivity by inter-valent charge transfer mechanisms, allowing us to attribute all of the change in conductivity associated with water incorporation to protonic conduction.
Exploitation Route I am developing a new blue pigment based around our findings about the incorporation mechanism of water in ringwoodite
Sectors Culture, Heritage, Museums and Collections,Other

 
Description Ringwoodite is a major potential water-bearing mineral in the Earth's transition zone. Protons can be incorporated as charge-balancing Fe3+ on the tetrahedral Si4+ site - Fe3+ in tetrahedral coordination causes a deep blue colour. After the Clearwell Caves Symposium where I talked about this it became clear thet blue pigmants are important for the art world and I am now working on developing a new blue pigment based around Fe3+(IV)-bearing oxide ceramics. Collart (AKA Windsor and Newton) are interested in exploring the commercial potential of any pigments which I develop.
First Year Of Impact 2016
Sector Culture, Heritage, Museums and Collections,Other
Impact Types Cultural,Economic

 
Description NERC fellowship scheme _ Simon Hunt my postdoc applied
Amount £711,084 (GBP)
Funding ID NE/P017525/1 
Organisation Natural Environment Research Council 
Department NERC Postdoctoral Fellowship
Sector Academic/University
Country United Kingdom
Start 08/2017 
End 08/2022
 
Description Japan deformation press 
Organisation Ehime University
Country Japan 
Sector Academic/University 
PI Contribution We have designed a new deformation press and provided access to the prototype, and help and support in performing experiments at UCL during August-November 2016. Dobson visied Japan during March 2016 to advise on the new press (based on our deformation design) being commissionned to go on a beamline at Photon Factory synchrotron in Tsukuba, Japan.
Collaborator Contribution A group of 4 researchers Visited UCL for 2 months in 2016 (August, November) to perform deformation experiments at the P-T conditions of the lower mantle. They provided all cells and hard anvils to reach the extreme pressures necessary. They have won a grant (approximately £200k) to install one of our (UCL design) presses on an existing multi-anvil beamline at the Photon Factory.
Impact The dfevelopment of a new high-pressure deformation beamline on Photon Factory synchrotron in Japan.
Start Year 2016
 
Description Art Symposium - UK 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact approximately 60 artists attended the 'Clearwell Caves Symposium' where I gave a lecture entitled 'The colours of Iron'
multiple URLs which are not allowed in the URL box:
http://www.vasw.org.uk/events/deep-material-encounters-symposium.php
http://hardwickgallery.org/event/deep-material-encounters/
Year(s) Of Engagement Activity 2016
URL http://www.ucl.ac.uk/slade/events/deep-material-encounters-clearwell-caves
 
Description New Scientist Article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact An article in New Scientist about the way water is incorporated into ringwoodite and how the crystal-chemical insights gained from our study is being used to make new blue pigments.
Year(s) Of Engagement Activity 2017
 
Description Seminar Zurich 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A general colloquium about my research into the deep Earth and viscoelastic effects in the mantle.
Year(s) Of Engagement Activity 2016