Volatile Recycling at the Lesser Antilles Arc: Processes and Consequences

Lead Research Organisation: Durham University
Department Name: Earth Sciences

Abstract

The Earth is unique in our solar system in having abundant liquid water, plate tectonics and life. These properties are not unconnected; The evolution of life has depended heavily on water, and water is pumped around the planet by the plate tectonic cycle. Plate tectonics in turn, and its capacity to generate the very continents on which we live, also depends on the existence of water.

Subduction zones are the most important "valve" in the plate tectonic system. They form where tectonic plates sink back into the mantle. Here water, along with other volatiles such as carbon dioxide and sulphur, are returned to the deep interior. However, the return is not wholesale. As the sinking plate is subjected to heat and pressure, a large fraction of the incoming volatiles is "sweated off" and added to the overlying mantle where it causes melting. These melts feed volcanoes at subduction zones which are characteristically dangerously explosive. When considered with the earthquakes triggered by the plates scraping past each other and the consequent tsunamis and landslides, it is clear that subduction zones are the most hazardous places on Earth. Yet, these regions also have benefits: the cocktail of fluids travelling with magmas at subduction zones is responsible for transporting and emplacing valuable metal deposits into the crust, and the fine ash distributed by the explosive volcanoes produces nutrient-rich, fertile soils.

The importance of cycling volatiles through subduction zones is self-evident. However we still don't really know how it works and what the budgets are of volatiles delivered to the subduction zone, versus those recycled into the lithosphere, hydrosphere and atmosphere compared with those sequestered back into the deep mantle.

We propose an innovative multidisciplinary experiment to track volatiles at a subduction zone. Questions to be answered include: How do volatiles influence the types and amounts of magmas generated? How do they control where volcanoes, such as Mt Pinatubo and Montserrat are located and how explosive they are? How do volatiles dictate where ore deposits are formed? How do volatiles mediate the seismogenic behaviour of subduction zones - whether there are large "megathrust" earthquakes like Japan and Sumatra or whether slip is less violent?

Our focus area is the Lesser Antilles Arc, which is a special case, because it is one of only two Atlantic subduction zones. Plate formation processes at the slowly-spreading mid-Atlantic ridge produce a much more pervasively hydrated plate than those in the extensively studied Pacific. Furthermore, a laterally varying capacity to carry water in the plate and sediments subducting below the Antillean arc are a likely culprit for the arc's highly variable style and intensity of seismic and volcanic activity. By mapping structural differences along the arc we will be able to pinpoint the effects of variable water input.

We plan to use novel seismic approaches complemented by geochemical analyses and integrated using numerical models to identify and quantify where volatiles are in the downgoing plate, where they are released at depth, and how they are transported from the subducting plate through the mantle wedge to the arc. We will use a unique suite of rocks from deep in the crust which have been carried up in volcanoes to help us understand how magmas evolve, and what allows them to concentrate ore metals. Mapped water pathways will be compared with seismic and volcanic activity, as well as with those inferred at other subduction zones.

This large research project will be "bookended' on the one hand by an enormous amount of resource; data, samples, expertise and results from previous studies that will provide excellent value for money, and on the other hand a special focus on the societal benefits; informing natural hazard planning, and a better appreciation of how and where economic deposits form.

Planned Impact

The proposed research is fundamental, and will deepen our understanding of plate tectonics, and the water cycle. Non-academic beneficiaries will include: [1] regional (Caribbean) agencies responsible for mitigating potential hazards such as earthquakes, volcanoes and tsunami. [2] Mining companies interested in understanding the genesis and distribution of subduction-related ore deposits; [3] Agencies, including government, involved in the development of policies on securing the future resource base and the sustainability of resource exploitation; [4] Host nation capacity building through education and training [5] The general public, specifically individuals and groups focused on geology and lay science, and school children.

To achieve this impact the project has set up partnerships with the Seismological Research Centre of the University of West Indies, who will use our new data and seismic velocity structures to improve their hazard maps, and with the NERC-funded STREVA project that focuses on volcanic hazard in the Antilles, and includes ties with the Montserrat Volcano Observatory and regional government agencies. A student from the University of West Indies will undertake a six-month study visit to the UK to receive training in seismological methods that will allow them to be involved in the analysis of the new data.

Co-I Wilkinson has various projects with mineral exploration companies and hosts an annual symposium to communicate new scientific results to representatives from UK industry. To further engage potential industrial users, we will publish our results in academic journals and present our work at both academically focused conferences such as the American Geophysical Union Fall Meeting, and also at industry focused conferences such as the Society of Exploration Geophysicists Meeting.

We will communicate to the wider public via several routes. We will set up a project web site with specialist as well as outreach components. In addition, all involved universities participate in outreach programs to schools as well as specialist-interest adult groups and the general public, including the Seismology-in-Schools effort (Imperial), the Discover Oceanography Program (Southampton), Nature Live at the London Natural History Museum (Imperial), Science Weeks of Imperial College and Royal Society, and the "Beacons of Engagement" public outreach project (Bristol, Durham). Several of us have experience with interviewing and presenting in the media and to public audiences.

The project will be wrapped up with a workshop in the Antilles to which international scientists as well as potential non-academic beneficiaries will be invited.

Publications

10 25 50
 
Description The team have been able to generate a range of geochemical and geophysical data that provide evidence for the distribution of fluids in the mantle beneath the Lesser Antilles Arc. These fluids original from the subducted Atlantic plate and have infiltrated the mantle from below. Correlations in the locations identified by these contrasting approaches allowed us to make firm links between fluid sources and the location of fluids in the north of the arc. In contrast, differences in the expected and actual locations of the fluid signature in the south of the arc suggest that (i) the configuration of subducted plates in the south is more complex than originally though, and (ii) the integrated history of all stages of subduction are important in understanding the current geophysical and geochemical signatures. Viewing the new, and published, data through these realisations has allowed us to better understand the importance of different processes in takling (ii), and to produce a new model to explain (i).
Exploitation Route The results of VoiLA are of interest to a wider range of scientists understanding volcanoes and earthquakes, particualrly those in subduction zones. The work is also helping inform Caribbean agencies with responsibility for hazard monitoring.
Sectors Communities and Social Services/Policy,Leisure Activities, including Sports, Recreation and Tourism,Culture, Heritage, Museums and Collections,Other

 
Description IAPETUS DTP studentship - The volcanic roots of the Lesser Antilles island arc: insights from mineral isotope stratigraphy
Amount £79,072 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2018 
End 03/2022
 
Description Goldschmidt Meeting 2019 GC 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Science presentation to annual international geochemistry meeting.
Goldschmidt Conference 2019, Barcelona:
Variations in the Supply of Fluids to the Lesser Antilles Subduction Zone

Cooper G, Macpherson C & Blundy J
Year(s) Of Engagement Activity 2019
 
Description Goldscmidt Meeting 2019 JB 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Science presentation to annual international geochemistry meeting. Brown J, Prytulak J, Cooper G, Macpherson C, Nowell G & Neill I (2019) Goldschmidt Abstracts, 2019 403
Year(s) Of Engagement Activity 2019
URL https://goldschmidtabstracts.info/2019/403.pdf
 
Description Presentation and Poster at SotA 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact International conference on subduction zone magmatism. George Cooper presented his own component of researchf rom the VoiLA project as a talk and also presented a poster, which was displayed for the full 5-day meeting, explaining the purpose, scope, and design of the wider VoiLA project.
Year(s) Of Engagement Activity 2018
URL https://www.sota7.org/
 
Description Presentation at International Workshop (GeoPRISMs) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation at a workshop from large US initiative which is also one of our partners
Year(s) Of Engagement Activity 2015
URL http://geoprisms.org/tei-scd-2015/
 
Description VMSG 2020 Presentation GC 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Science presentation at UK Special Interest Group meeting (VMSG)
VMSG meeting 2020, Plymouth:
Variations in the supply of fluids to the Lesser Antilles subduction zone
Cooper, G.F., Macpherson, C.G., Blundy, J.D., Goes, S. & the VoiLA Group.
Year(s) Of Engagement Activity 2020
 
Description VMSG 2020 Presentation JB 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Science presentation at UK Special Interest Group meeting (VMSG)
VMSG meeting 2020, Plymouth:
Unradiogenic 87Sr/86Sr plagioclase crystals in cumulate xenoliths from Martinique and St. Vincent, Lesser Antilles.
Brown, J.R., Prytulak, J., Cooper, G.F., Macpherson, C.G., Nowell, G.M. and Neill, I.
Year(s) Of Engagement Activity 2020
 
Description VoiLA Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact "End of grant" workshop held in Trinidad and Tobago. This involved most of the primary project participants but also attracted Caribbean researchers and practitioners in geoscience and harzard mitigation management, and international researchers interested in subduction-related processes. A workshop was held with local professional scientists and a fieldtrip run with local petroleum sector geoscientists.
Year(s) Of Engagement Activity 2019
URL http://www.voila.ac.uk/index.php/workshop-sept-2019/