Mantle volatiles: processes, reservoirs and fluxes

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences

Abstract

We have brought together a consortium of UK investigators and international partners with the key objective of providing a new process based understanding of volatile element (e.g. H2O, C, S, noble gases and halogens) fluxes into the deep mantle at subduction zones and out of the mantle at mid ocean ridges and ocean island settings. The mantle is by many orders of magnitude the largest silicate reservoir for carbon, nitrogen and sulphur on Earth and the input and output of volatiles (e.g., H2O, C, N, S, P, and halogens) at plate boundaries provides long-term controls on the climate and the biosphere. Nevertheless, our understanding of the deep-Earth volatile cycle is crude. In part because we have a very poor understanding of the relative contribution of recycled to primordial volatiles in the mantle system and how this might vary in different mantle reservoirs. In part this is because volatile elements are extensively lost during the eruptive process from many sample types making it hard to identify the controlling processes necessary to develop coherent models.
To address our objective the consortium combines several advances in new sample resources and analytical tools:
i) The recognition that rapidly quenched melt inclusions (MIs) within erupted material often preserve mantle-source volatile compositions;
ii) The ability to determine sulphur and boron isotopes in addition to major volatiles in the MIs;
iii) The discovery that boron isotopes can track the extent of volatile loss to the surface from subducting slabs and preserve this signal in the deeper mantle;
iv) The innovations in noble gas isotope determination that allow us to resolve recycled volatiles from those trapped during accretion and provide links to halogens, H2O and C;
v) The development of non-traditional stable isotopes such as Fe, Cu and Se to identify system oxidation state (a key variable in understanding sulphur) and chalcophile trace element determinations;
vi) The advances in computing power and techniques that allow better representation of mantle-like systems.

By coordinating the combined consortium expertise and analytical resources on the same sample suites in two thermally contrasting subduction regimes (Kamchatka (cool) and Southern Chile (hot)) we plan to investigate how both the processes and thermal setting control the efficiency and geochemical character (isotopic composition and relative abundance to other volatiles) of volatile subduction into the deep mantle. This allows us to take into consideration changes in subduction temperature as the Earth cools in the development of flux models that run for the age of the Earth. At mid ocean ridges and ocean island settings with different geochemical provenance (e.g. HIMU, EMI, EMII, FOZO) we will determine the proportion and character of volatile elements that have been recycled compared to those that were incorporated into the mantle during its formation (primitive volatiles). This is an essential component in building our understanding of the volatile flux into the mantle required to support the signals in the mantle today. New experimental partitioning developed within the consortium and our ability to track oxidation state will allow us to make a step change in understanding the sulphur cycle - barely understood to date but critical in understanding climate and commercial mineral deposit formation. Numerical simulations of mantle transport for suites of geochemical elements, iterating the geophysical parameters to approach matches for the geochemical observables, will allow us to identify the key geophysical processes in subduction zones and during whole mantle convection that control the geochemical distribution of subducted vs. primordial volatiles in the mantle. Together, these will lead to a significant advance in reconstructing the deep Earth volatile fluxes over Earth history - a grand science challenge.

Planned Impact

Specific beneficiaries
- The mineral resources industry: Sulphide minerals host a large fraction of the crustal budget of economically important elements, including many of the critical raw materials identified by both NERC ('Sustainable use of Natural Resources' theme) and the EU ('EU-14 critical raw materials') as those on which the European economy depends upon, but which might be at risk of supply disruptions. Fundamental understanding of partitioning control of S within arc and mid ocean ridge systems will be a key science output of the consortium changing our understanding of where and in what terrain S and related elements are deposited to form commercial resources.

- The instrumentation and analytical technique development industry: The development of new analytical skills and instrument capabilities is vital for both academia and industry as evidenced by collaborations between scientific instrument companies and universities (e.g. between Durham, Oxford and Bristol and Thermo Scientific) which aim to develop the capabilities of specific techniques or instruments, resulting in open access published technical reports and contributing to product development and sales growth.

- The education sector (e.g., schools): The cycling of volatiles in different tectonic settings is fundamental to planet habitability but is also important in terms of natural hazards, mineral resources and Earth processes. We believe there is an opportunity to use this research as the perfect tool for demonstrating the interconnectedness of Earth processes and how they can affect us.

We will deliver benefit by:
- The mineral resources industry: We will run a workshop in Y2 of the grant that brings key industry and consortium academics together with the objective of forming an industry/consortium advisory committee, defining a consortium mineral exploitation/exploration research program and developing the industry funding base. We will seek matching funds from industry for PDRA time to commercialise our research outputs relevant to the relationship between copper porphyry deposits and the fluxing of fluids through arc volcanoes.

- The instrumentation and analytical technique development industry: We will exploit existing collaborations and links with instrumentation companies as well as looking to develop new links to disseminate the new developments in analytical protocols and instrument capabilities that we will achieve. New data and techniques will be presented at international conferences, published in specialised online journals and also in open-access publications prepared by instrument companies (e.g. Thermo Scientific "Application Notes"), which are aimed at diverse target audiences in both academia and industry.

- The education sector: We are well placed to deliver this through structures within our institutions (e.g. the national online teaching tool Your Planet Earth - Bristol; Oxford Sparks, led by Co-I Pyle; the Scottish Earth Science Education Forum, Edinburgh). Via these we will provide resources for teachers delivering: (i) Educational activities for Key Stages 2-5 describing different aspects of the global volatile cycle, what its relevance is, and how they relate to the other topics in the National Curriculum (Natural Hazards, Plate Tectonics, Earthquakes, Volcanoes etc.); (ii) specific student exercises exploring the cycling of volatile elements, from chemical, geological and societal/natural hazard points of view. We plan to convene workshops for teachers to support integration of Earth Sciences into science teaching (e.g. the Earth Sciences Teaching Association Conference, Cardiff, Sept. 2015).

As a group we shall also continue and build upon our current activities engaging with the broader public, capitalising on the outreach frameworks in place at all 10 of our institutions. We will also develop new high profile activities specific to this TA such as participation in the Royal Society Summer Exhibition.

Publications


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Matthews S (2016) The temperature of the Icelandic mantle from olivine-spinel aluminum exchange thermometry in Geochemistry, Geophysics, Geosystems
 
Description The consortia has made significant advances in characterising the geochemical signals of volatiles that are sub ducted into the mantle and in understanding the processes that control the amount subducted; fieldwork has been completed to develop the database being used to inform the models being developed. Significant advances have also been made in identifying the processes that control how volatiles exhibit in mid ocean ridge and ocean island setting, developing the analytical techniques used to develop this data base and in acquiring samples to complete this portion of the work.
Exploitation Route The work will be used by many in the large community of scientists who study the deep Earth and its impact on the surface habitability of the planet over goelogical history. Techniques developed in the isotope geochemistry components of the study inform the mass spectrometer instrumentation industry in instrument upgrades and improvements - related instruments are used in many sectors of, for example, medicine and the semiconductor industry. Basic discoveries of how fluid migrate and how their associated chemistry changes and causes precipitation of sulpher bearing minerals improves the ability to predict and identify mineral bearing systems that provide society with metal ore resources,
Sectors Chemicals,Education,Environment,Other
 
Description Erik Hauri (Carnegie) 
Organisation Carnegie Institution for Science (CIS)
Department Observatories of the Carnegie Institution Washington
Country United States of America 
Sector Academic/University 
PI Contribution Collobaration on ion probe analysis
Collaborator Contribution Analytical access and expertise
Impact None yet
Start Year 2016
 
Description Modeling mantle convection 
Organisation Carnegie Institution for Science (CIS)
Department Department of Terrestrial Magnetism (DTM)
Country United States of America 
Sector Charity/Non Profit 
PI Contribution Isotope geochemistry expertise - providing model input parameters and assessing literature for range and quality of observed outputs.
Collaborator Contribution Training postdoc to input the geochemical parameters into mantle convection model built by collaborator and building and modifying input interface for project (Peter van Keken)
Impact Geophysics; fluid dynamics; isotope geochemistry
Start Year 2014
 
Description Volcanoes - an exhibition 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I curated a public exhibition to run at Oxford's Weston Library from 10 February 2017 - 21 May 2017. This event attracted a lot of media coverage (print, radio and television), and parallel activities, ranging from workshops to public talks.
Year(s) Of Engagement Activity 2017
URL http://www.bodleian.ox.ac.uk/whatson/whats-on/upcoming-events/2017/feb/volcanoes
 
Description blog on the Kamchatka fieldwork 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact blog on the Kamchatka fieldwork for the website - http://www.deepvolatiles.org/kamchatka-fieldtrip; articles on the Kamchatka fieldwork for the Deep Volatiles newsletter and VMSG news letter
Year(s) Of Engagement Activity 2016
URL http://www.deepvolatiles.org/kamchatka-fieldtrip
 
Description blog on the La Palma fieldtrip 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Walowski and Jones blog on the La Palma fieldtrip - http://www.deepvolatiles.org/canary-islands
Year(s) Of Engagement Activity 2016
URL http://www.deepvolatiles.org/canary-islands