The Distribution of Oxygen in Earth's Mantle

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

The exchange of oxygen between the mantle and surface environment is a key component of Earth's geochemical cycle. Oxygen plays a role in generation of magma within the earth and the transfer of volatile elements like sulfur, carbon and hydrogen from the solid earth into molten rock. When such magma rises towards the surface, volcanic gases are released, driving or regulating the composition of Earth's atmosphere. It is therefore increasingly accepted that variation in the oxygen content of Earth's mantle is closely linked to Earth's habitability as a planet.

Basaltic magma is generated by melting the mantle. Therefore, the composition of samples of basaltic volcanoes carries information about the composition of the underlying mantle. However, many processes modify the magma's composition from the point of generation at depth to eruption at the surface. The generation of the melt itself, its crystallisation in the shallow crust and the loss of volcanic gases near the surface all change the composition of magma. It is therefore necessary to account for these processes in order to understand the chemical characteristics of the mantle. Previous attempts to study variation in the oxygen content of the mantle have made simplifying assumptions about these processes. However, progress in theoretical understanding of elemental behaviour indicates that the correcting assumptions need to be revisited. One startling feature of the previous studies is that they come to very different conclusions about the distribution of oxygen in the mantle. The current uncertainty in the oxygen content of the upper mantle corresponds to a number of oxygen atoms that is about 100 times that present in the atmosphere!

We think that part of this discrepancy is caused by the sets of assumptions that previous investigators have made. A crucial component of our project is therefore to use new theoretical and observational constraints to understand how the processes in magmatic systems modify the chemistry of basalt. We have carefully chosen our target geologic setting: Iceland has plentiful basalts that are well studied in terms of traditional chemical compositions and therefore provide us with the extensive background information we need to underpin our models. Once we have improved models by adding our new observations, we can better focus our map of the variation in the oxidation state of the Earth's mantle.

In detail, our research will involve a great deal of painstaking geochemical work. We aim to use the isotopic composition of the element vanadium, because theoretical work and preliminary experimental studies indicate that the behaviour of vanadium and its isotopes is strongly controlled by mantle oxidation state. By combining new constraints from vanadium isotopes with other geochemical measurements that are thought to be sensitive to mantle oxygen, we can construct a model of oxidation state across the Iceland. The combination of several independent chemical constraints allows us to determine just how much variation in oxygen there is beneath this classic locality. Furthermore, it equips the community with a precise tool to extract global variations in mantle oxidation.

Planned Impact

Industrial Beneficiaries:
-FEI (high performance microscopy company) - Direct benefit;
-Mineral Resource and Energy companies - Indirect benefit.

FEI sells many QEMSCAN imaging systems to industry every year. The importance of quantifying the mineral compositions in ore rocks is clear for mining companies, and hydrocarbon companies use QEMSCAN for understanding reservoir quality. QEMSCAN converts EDS data into mineral-composition maps using a SIP file. We will develop a SIP file for mafic/ultramafic rocks and will share this with FEI. They may then use this file in combination with other companies to improve characteristion of ore-bearing rocks, with crucial global economic influence. We will also generate beautiful high resolution images that FEI may use in their marketing of the QEMSCAN system. The project PDRA and the summer students on the project will develop experience with QEMSCAN - a skill that will be very attractive to mining and hydrocarbon companies that use the software.

Educational Beneficiaries:
-Public/undergraduates/postgraduates via Imperial Rock Library -Direct;
-Industries requiring petrographic ability - Indirect.
-UK education via promotion of STEM subjects - Direct

The Imperial College London Rock Library is a database of rocks and minerals specifically designed as a university level training, evaluation and reference resource. Through easy access to thousands of examples of minerals, textures and rock types, straightforward online identification tools, training activities and evaluation tests the Rock Library provides a unique set of tools to ensure Earth Scientists obtain and maintain a high level of practical ability without requiring direct access to microscopes and hand specimens. The Rock Library and currently attracts 400,000 users per year from almost every country, most of which are undergraduates, postgraduates and industry geologists. However, there is a lack of basaltic examples in general and Icelandic examples specifically. Our work will address this by making high quality QEMSCAN images available to the Rock Library, thus expanding its technologic repertoire.

Encouraging the next generation of scientists is a fundamental responsibility of academia. We approach this by using 'student reporters' who will document the course of the work by participation in field work and subsequently following the samples they have witnessed being collected as they are converted into high quality, meaningful chemical data. Student reporters will inform both their peers and the general public through outreach including, but not limited to, the Imperial Festival, blogs, vlogs, and Imperial's Earth Class. Earth Class is specifically aimed at year 9 and 10 students who will be considering further education. We hope to generate excitement and enthusiams for STEM subjects in general, and our work in particular by portraying the journey of the work through the eyes of the young student reporters.

Publications

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Hopkins S (2019) The vanadium isotopic composition of lunar basalts in Earth and Planetary Science Letters

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Novella D (2020) A multi-proxy investigation of mantle oxygen fugacity along the Reykjanes Ridge in Earth and Planetary Science Letters

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/N009568/1 01/08/2016 31/03/2018 £66,251
NE/N009568/2 Transfer NE/N009568/1 01/04/2018 31/12/2019 £45,989
 
Description An improved method of analysis has been tested in the first 6 months of this award. Reproducible results with an order of magnitude less sample required has been achieved.
2017/2018:
All samples needed for the remainder of the work were collected.
We completed this initial dataset of Reykjanes Ridge analyses and established that V isotopes and Fe valence ratios do not co-vary.
PI Prytulak moved from Imperial College London to Durham University in April 2018. Grant Transfer took ~3 months to complete.

This grant was transferred - along with PI Prytulak - in April 2018 to Durham University.
Exploitation Route 2016: These are early days, but initial results are promising in fulfilling the aims of this grant. 2017/2018: We have completed the first task (glasses along Rekyjanes Ridge), have collected samples fro the remainder of the grant and are actively analysing those. Results of our initial Reykjanes Ridge work were presented at the international Goldschmidt 2017 conference in Paris by PDRA Dr. Davide Novella.
Sectors Chemicals,Education,Environment,Other

 
Description BGI Research Grant - Vanadium stable isotope fractionation in Earth's Interior
Amount € 2,000 (EUR)
Organisation German Research Foundation 
Sector Public
Country Germany
Start 02/2018 
End 02/2018
 
Description IAPETUS DTP PhD studentship to M. Stow
Amount £5,338,027 (GBP)
Funding ID NE/L002590/1 
Organisation Durham University 
Sector Academic/University
Country United Kingdom
Start 10/2018 
End 03/2021
 
Description SSCP DTP PhD studentship to S. Page
Amount £7,611,217 (GBP)
Funding ID NE/L002515/1 
Organisation Imperial College London 
Sector Academic/University
Country United Kingdom
Start 10/2017 
End 03/2020
 
Title Sample collection in Iceland - 2017 
Description PIs John Maclennan and Julie Prytulak, PDRA Davide Novella and undergraduate student 'reporters' Kev Wong and Xenia Boyes went to Iceland to collect material relevant to the project (basaltic lavas and picrites). Such samples are being prepared for geochemical analyses of major, minor and trace elements to be performed by EMPA, QUEMSCAN and LA-ICPMS, as well as stable isotopes with a MC-ICPMS. In one week of fieldwork we visited different sites throughout Iceland and collected samples from the following locations: -Borgarhraun -Vitis: Langaviti Pele's tears (65.895904 N, 16.845521 W) Theistareykir Picrites (65.931692 N, 17.071765 W) -Midfell: pillow lavas (64.174451 N, 21.047830 W) The collected samples contain also minerals (e.g. olivine, spinel, pyroxenes, plagioclase) that formed upon crystallization of the magmas. The combined study of glasses and minerals will allow us to investigate the effect of mineral crystallization on V isotope fractionation and the potential of V stable isotopes as redox sensor of the Earth's mantle. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? No  
Impact Successful collection of appropriate samples is key to the aims of the grant. They are actively being analysed. 
 
Description Cheltenham Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact PDRA Davide Novella participated in the GeoBus outreach research program at the 2017 Cheltenham Science Festival in collaboration with University College London.
Year(s) Of Engagement Activity 2017
 
Description Departmental Seminar, Hannover, Germany 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited departmental seminar at the Institute fur Mineralogie and Petrologie, Hannover, Germany. A 45 minute lecture with lively 20 minute discussion afterwards as part of a two-day visit to initiate and strengthen international collaboration.
Year(s) Of Engagement Activity 2016
 
Description Departmental seminar at Leeds University Earth Science Department 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Invited Departmental seminar as part of a two day visit to discuss further grant applications with colleagues at Leeds.
Year(s) Of Engagement Activity 2016
URL http://www.see.leeds.ac.uk/research/essi/geoscience-seminars/Event/?SemID=412
 
Description Undergraduate field work student reporters 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact As per our impact plan, we recruited two undergraduate students to join us for field work associated with this grant. The students, Xenia and Kevin, took video of our fieldwork, posted regular blog and twitter entries during the trip: (blog): https://lavatolab.wordpress.com (twitter) https://twitter.com/lavatolab. They will continue to be engaged with the grant progression, telling the story of how a collected lava can eventually tell us about the amount of oxygen in Earth's mantle.
Year(s) Of Engagement Activity 2016