Apatite as a quantitative tool for tephrochronology and magmatic evolution
Lead Research Organisation:
University of Oxford
Department Name: Earth Sciences
Abstract
Apatite is a calcium phosphate mineral that crystallises in small quantities from a wide variety of different magmas. It is particularly useful because it incorporates 'volatile' species such as water (H2O), carbon dioxide (CO2), chlorine, fluorine and sulphur, into its mineral structure. Volatiles are dissolved gases, which are an important component of many magmas. During magma ascent underneath a volcano the volatiles form bubbles, which expand and accelerate the magma upwards, fuelling explosive volcanic eruptions. Apatite has the potential to be a particularly reliable recorder of volatile concentrations in the magma before eruption, but in order to exploit the information it contains, we need independent measurements of the 'partition coefficients' for H2O and CO2 - the amount found in the mineral for a given concentration in the melt.
In the first part of the project, we will measure these partition coefficients in the laboratory, so that we can infer magmatic volatile contents from their concentrations in apatite. We will also measure partition coefficients for fluorine and chlorine. We will test the partition coefficients by using apatite to infer volatile concentrations in a magmatic system, known as the Laacher See Tuff, that has already been well characterised using alternative methods. This volcanic deposit was produced in a major explosive eruption nearly 13,000 year ago, with ash layers dispersed across central continental Europe up to 1100 km away from the volcanic vent.
In the second part of the project, we propose to develop apatite as a tool for correlating ash deposits from past explosive eruptions. Explosive volcanic eruptions inject large quantities of ash into the atmosphere, dispersing it over large areas, sometimes thousands of kilometres from the vent. These deposits are geologically instantaneous, and therefore widely used as time marker horizons for constraining age in studies ranging from past climate reconstructions to archaeology. It is therefore crucial to be able to identify a given eruption very precisely in sites that may be far apart. Usually volcanic glass compositions are used to identify different eruptions, but sometimes the deposits of different eruptions from the same volcano are similar: ash layers from these eruptions cannot be reliably used as marker horizons. We propose to use apatite crystals in place of glass chemistry to correlate between different ash layers. Apatite is an ideal candidate for this because it: (i) is common in a wide range of eruption deposits; (ii) is stable and insensitive to weathering, and (iii) has high concentrations of the elements of interest, which allows very precise measurements of chemical composition.
This development would facilitate the identification and correlation of ash layers and hence improve the robustness of correlations that are used in climate reconstructions and other fields. Better identification of ash layers would also help ash dispersal to be mapped and modelled accurately, which has clear implications for understanding the practical and economic outcomes of future explosive eruptions.
In the first part of the project, we will measure these partition coefficients in the laboratory, so that we can infer magmatic volatile contents from their concentrations in apatite. We will also measure partition coefficients for fluorine and chlorine. We will test the partition coefficients by using apatite to infer volatile concentrations in a magmatic system, known as the Laacher See Tuff, that has already been well characterised using alternative methods. This volcanic deposit was produced in a major explosive eruption nearly 13,000 year ago, with ash layers dispersed across central continental Europe up to 1100 km away from the volcanic vent.
In the second part of the project, we propose to develop apatite as a tool for correlating ash deposits from past explosive eruptions. Explosive volcanic eruptions inject large quantities of ash into the atmosphere, dispersing it over large areas, sometimes thousands of kilometres from the vent. These deposits are geologically instantaneous, and therefore widely used as time marker horizons for constraining age in studies ranging from past climate reconstructions to archaeology. It is therefore crucial to be able to identify a given eruption very precisely in sites that may be far apart. Usually volcanic glass compositions are used to identify different eruptions, but sometimes the deposits of different eruptions from the same volcano are similar: ash layers from these eruptions cannot be reliably used as marker horizons. We propose to use apatite crystals in place of glass chemistry to correlate between different ash layers. Apatite is an ideal candidate for this because it: (i) is common in a wide range of eruption deposits; (ii) is stable and insensitive to weathering, and (iii) has high concentrations of the elements of interest, which allows very precise measurements of chemical composition.
This development would facilitate the identification and correlation of ash layers and hence improve the robustness of correlations that are used in climate reconstructions and other fields. Better identification of ash layers would also help ash dispersal to be mapped and modelled accurately, which has clear implications for understanding the practical and economic outcomes of future explosive eruptions.
Planned Impact
The project is focused on developing a new tool for stratigraphic correlation and understanding pre-eruptive magmatic processes and as such, our primary means of communication of our results will be through the primary academic literature. Direct links to specific end users at this stage are tentative. However, we have identified a number of possible end users who may benefit from the research:
- We anticipate that specific end users of our research will include planners and policy makers involved with volcanic hazard and risk assessment and mitigation in central Italy, including the INGV (National Institute of Geophysics and Volcanology, Italy) and volcano observatories. They will benefit because our results will be relevant to understanding the dynamics of explosive volcanic eruptions at Campi Flegrei and similar systems.
- The results may also have indirect relevance for other agencies involved palaeoclimate research, that are investigating the rate of climate change and/or the response of humans and ecosystems to changes in climate. The chronology of many palaeo-enivronmental archives is constrained by tephra correlations. They will benefit through improved stratigraphic correlation.
- Others with wider, indirect interest in the results may include local residents in Italy, who would benefit indirectly from volcano hazard mitigation advice given by authorities, and the general public, who may be interested in general outcomes and future applications of the research. We will use traditional outreach activities to engage with these broader users (see Pathways to Impact).
- The PDRA employed on the project will benefit from training in a wide range of skills, from teaching, presentation and communication skills to experimental petrology, fieldwork and analytical techniques. The PDRA will be well-suited to a any career requiring a numerate employee with good communication skills, or to specific jobs involving microanalysis.
- We anticipate that specific end users of our research will include planners and policy makers involved with volcanic hazard and risk assessment and mitigation in central Italy, including the INGV (National Institute of Geophysics and Volcanology, Italy) and volcano observatories. They will benefit because our results will be relevant to understanding the dynamics of explosive volcanic eruptions at Campi Flegrei and similar systems.
- The results may also have indirect relevance for other agencies involved palaeoclimate research, that are investigating the rate of climate change and/or the response of humans and ecosystems to changes in climate. The chronology of many palaeo-enivronmental archives is constrained by tephra correlations. They will benefit through improved stratigraphic correlation.
- Others with wider, indirect interest in the results may include local residents in Italy, who would benefit indirectly from volcano hazard mitigation advice given by authorities, and the general public, who may be interested in general outcomes and future applications of the research. We will use traditional outreach activities to engage with these broader users (see Pathways to Impact).
- The PDRA employed on the project will benefit from training in a wide range of skills, from teaching, presentation and communication skills to experimental petrology, fieldwork and analytical techniques. The PDRA will be well-suited to a any career requiring a numerate employee with good communication skills, or to specific jobs involving microanalysis.
Organisations
- University of Oxford (Lead Research Organisation)
- UNIVERSITY OF OXFORD (Collaboration)
- National Institute for Geophysics and Volcanology (INGV) (Collaboration)
- UNIVERSITY OF EDINBURGH (Collaboration)
- Okayama University (Collaboration)
- Wesleyan University (Collaboration)
- Gottfried Wilhelm Leibniz Universität Hannover (Collaboration)
- INGV (Project Partner)
- University of Edinburgh (Project Partner)
- University of Tübingen (Project Partner)
Publications
Stock M
(2018)
Tracking Volatile Behaviour in Sub-volcanic Plumbing Systems Using Apatite and Glass: Insights into Pre-eruptive Processes at Campi Flegrei, Italy
in Journal of Petrology
Stock M
(2014)
New constraints on electron-beam induced halogen migration in apatite
in American Mineralogist
Stock M
(2016)
Late-stage volatile saturation as a potential trigger for explosive volcanic eruptions
in Nature Geoscience
Riker J
(2018)
First measurements of OH-C exchange and temperature-dependent partitioning of OH and halogens in the system apatite-silicate melt
in American Mineralogist
Humphreys M
(2021)
Rapid pre-eruptive mush reorganisation and atmospheric volatile emissions from the 12.9 ka Laacher See eruption, determined using apatite
in Earth and Planetary Science Letters
Description | 1. We have developed a well-constrained set of apatite volatile standards for use in various micro-analytical techniques, and a robust protocol for quantifying apatite volatile compositions and relating these to magmatic volatiles. 2. We have performed volatile-melt partitioning experiments between apatite and silicate melts from basaltic andesite to phonolite, and constrained exchange coefficients for OH, F, Cl and C, covering a range of temperature and pressure conditions, for comparison with thermodynamic modelling. We found fundamental changes in partitioning data with changing temperature conditions. 3. We have tested our new partitioning data using apatites from the Laacher See tephra, erupted at ~13 ka, and applied them to investigate pre-eruptive magmatic volatile compositions at the Campi Flegrei magma chamber. Importantly, apatite appears able to provide an otherwise relatively inaccessible record of volatile-undersaturated magma evolution. This is complementary to the information available from melt inclusions and gives new insights into the behaviour of the sub-volcanic magma system. This represents an important new avenue of petrological investigation that can be applied widely at other volcanic centres. At Campi Flegrei, there is no evidence that apatite microphenocrysts have started to re-equilibrate towards compositions that would be consistent with volatile saturation; this indicates that volatile saturation occurred only very shortly before eruption, and probably acted as a trigger by pressurising the magma chamber. At Laacher See, the accumulating crystal mush was dispersed rapidly throughout a heterogeneous melt body, again shortly before eruption. This lindicates that rapid mush reorganisation led to the explosive eruption. 4. We attempted to use apatite to investigate controls on eruption explosivity but found no clear links at Campi Flegrei. In likelihood, explosivity is controlled more by other extrinsic factors than pre-eruptive volatile concentrations or compositions. We have also evaluated the potential benefits and drawbacks of using apatite as a tool for tephrochronology. 5. We have developed a numerical model to explore the quantitative compositional variations in apatite composition during different volcanic scenarios. Using this code we can now successfully recreate observed apatite compositions for several different case studies. The model includes the ability to evaluate sensitivity to starting parameters and produces outputs that match well with independent estimates of starting compositions. |
Exploitation Route | - Aspects of our findings will be adopted by the volcano observatory staff (INGV) in the Campi Flegrei area and used to inform ongoing hazard assessment programmes in collaboration with local authorities. - Analytical protocols, standards and partitioning constraints will be used by researchers in ongoing work on magmatic and other apatites. In particular, our finding that apatites can record periods of volatile-undersaturated evolution will be widely applicable to research into other volcanic systems worldwide. - Our modelling will be of use for interpretation of apatite volatile compositions in rocks related to magmatic-hydrothermal mineralisation including porphyry deposits |
Sectors | Education Energy Environment Government Democracy and Justice Culture Heritage Museums and Collections |
URL | http://community.dur.ac.uk/madeleine.humphreys/Apatite%20for%20eruption/Welcome.html |
Description | - Increasing public engagement with research and related societal issues. One of the key findings from this grant was recently published in Nature Geoscience and received broad attention by online media. To date, the original article has been viewed >1100 times, prompting 16 general news articles and posts in scientific blogs and online magazines. - Providing training opportunities for undergraduate students - Significant academic impact has been achieved through generation of a new suite of apatite standards, which have underpinned several new studies in this area |
First Year Of Impact | 2016 |
Sector | Education,Culture, Heritage, Museums and Collections |
Impact Types | Cultural Societal |
Description | ERC Consolidator grant |
Amount | € 1,986,006 (EUR) |
Funding ID | 864923 STEMMS |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 04/2020 |
End | 04/2025 |
Description | NERC Standard grant |
Amount | £568,788 (GBP) |
Funding ID | NE/R011389/1 |
Organisation | Natural Environment Research Council |
Sector | Public |
Country | United Kingdom |
Start | 06/2018 |
End | 07/2021 |
Description | NERC ion microprobe facility |
Amount | £17,500 (GBP) |
Funding ID | IMF521/0514 |
Organisation | Natural Environment Research Council |
Department | NERC Ion Micro-Probe Facility |
Sector | Academic/University |
Country | United Kingdom |
Start | 04/2016 |
End | 01/2018 |
Title | Apatite standards |
Description | We characterised a suite of micro-analytical apatite standards that have now been loaned to several other research groups wishing to undertake similar work. The standards are comprehensively characterised using a number of different methods, representing an extremely robust and valuable resource that is helping to further research in this broad area. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2019 |
Provided To Others? | Yes |
Impact | The resource has created academic impact by facilitating a number of other research studies by independent research groups |
Title | Apatite EPMA protocol |
Description | Improved understanding of susceptibility of apatite to electron microprobe analysis; robust analytical protocol for apatite |
Type Of Material | Data analysis technique |
Year Produced | 2015 |
Provided To Others? | Yes |
Impact | Improved understanding of susceptibility of apatite to electron microprobe analysis; robust analytical protocol for apatite adopted by our research group in data collection |
Title | Apatite model |
Description | We created a new modelling method to quantify uncertainty related to interpretation of apatite volatile geochemistry. This will enable better use of apatite to interpret gas contents of volcanic liquids before eruptions and thus help to constrain volcanological processes in past eruptions. |
Type Of Material | Computer model/algorithm |
Year Produced | 2021 |
Provided To Others? | Yes |
Impact | No associated impacts yet |
Description | Hannover |
Organisation | Gottfried Wilhelm Leibniz Universität Hannover |
Country | Germany |
Sector | Academic/University |
PI Contribution | Intellectual and material input into joint development of analytical standards |
Collaborator Contribution | Access to C/S analysis for joint development of analytical standards |
Impact | Joint development of analytical standards |
Start Year | 2014 |
Description | INGV |
Organisation | National Institute for Geophysics and Volcanology (INGV) |
Country | Italy |
Sector | Public |
PI Contribution | Expertise and intellectual input; access to data and interpretations from samples collected jointly. |
Collaborator Contribution | Expertise and intellectual input; access to field knowledge and assistance with joint sample collection |
Impact | Stock et al. (2016). doi:10.1038/ngeo2639; Stock et al. (2018) in press |
Start Year | 2014 |
Description | Mike Cassidy IRF |
Organisation | University of Oxford |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Intellectual input, provision of standards, and contribution of analytical expertise for measurement of volatiles in apatite. |
Collaborator Contribution | Expertise in synthesis of experimental materials |
Impact | None yet |
Start Year | 2018 |
Description | Misasa manometry |
Organisation | Okayama University |
Country | Japan |
Sector | Academic/University |
PI Contribution | Collaborative work on measurement of OH in apatite by hydrogen manometry (hosted by University of Okayama, Misasa) |
Collaborator Contribution | Collaborative work on measurement of OH in apatite by hydrogen manometry (hosted by University of Okayama, Misasa) |
Impact | None yet |
Start Year | 2014 |
Description | TCEA Wesleyan Greenwood |
Organisation | Wesleyan University |
Department | Planetary Science |
Country | United States |
Sector | Academic/University |
PI Contribution | Provision of apatite standards for analysis; compilation of calibration curves |
Collaborator Contribution | Provision of thermo-chemical elemental analyser (TCEA) data for trace H2O contents of apatite crystals. |
Impact | Development of precise calibration curves for trace H2O concentrations in apatite standard matierals. |
Start Year | 2015 |
Description | deHoog |
Organisation | University of Edinburgh |
Department | School of Geosciences Edinburgh |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Intellectual input to joint development of standards and analytical protocol |
Collaborator Contribution | Intellectual input to joint development of standards and analytical protocol |
Impact | Development of standards and analytical protocols |
Start Year | 2014 |
Description | Nature Geoscience press release |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Press release for published paper |
Year(s) Of Engagement Activity | 2016 |
Description | Special interest group talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Gave a talk to regional special interest group, which prompted questions and discussion afterwards amongst audience, who reported a change in understanding and interest in research work |
Year(s) Of Engagement Activity | 2022 |