Volatile cycling and oxygen fugacity of subduction zones using stable vanadium isotopes
Lead Research Organisation:
University of Oxford
Department Name: Earth Sciences
Abstract
The outer shell of the Earth that we live on is made up of brittle 'plates'. The migration of these plates across the surface of the planet is directly linked to major geologic events such as earthquakes and volcanic eruptions. In some regions, two plates collide, forcing one beneath the other in a process called 'subduction'. Subduction zones are responsible for much of the explosive volcanism on Earth, including the infamous Pacific 'Ring of Fire'. However, these zones are also critical for the exchange and cycling of chemical elements between the surface and interior of the planet. As an oceanic plate subducts, it is subjected to high pressures and temperatures. During this process, the plate looses chemical components through fluids, degassing, reactions, and sometimes melting. One of the key parameters controlling how much of which elements are lost, is the available oxygen. Geochemists refer to the amount of available oxygen as the 'oxygen fugacity' of a system, which can be simply thought of as the partial pressure of oxygen. Oxygen fugacity has a large affect on the way the carbon (C), hydrogen (H), and other 'volatile' elements behave in a subduction system. Volatiles species (e.g., H2O and CO2) are those that vaporize at low temperatures. Combined with other physical and chemical conditions of subduction, oxygen fugacity controls how much H and C is lost through degassing during explosive volcanism, and how much can be dragged deeper into the Earth. There has been a long-standing debate over how much more oxygenated subduction zones are compared with the rest of the interior of the Earth. The fugacity of samples from subduction zone volcanoes tells us about present day processes and volatile cycling. Furthermore, if subduction zones are significantly more oxygenated than the rest of the interior of the Earth, then they may provide an efficient means of recycling oxygen into the interior of the Earth. Therefore, it is critical to constrain the oxygen fugacity of subduction zones to evaluate the whole Earth cycling of volatile elements and how this may change through time. It is essential to find a robust way of determining oxygen fugacity. Unfortunately, previous studies used methods that can be easily 'reset' by later events, so that they do not give a true indication of the original source. Consequently, there is considerable uncertainty in what the 'real' amount of available oxygen is in subduction systems. My previous research and expertise focused on the novel application of isotopes of chemical elements to solving Earth problems. I have continued in this broad avenue of investigation by working on a precise analytical method for the measurement of vanadium stable isotope variations. The measurements are not trivial, however they are very valuable. The power of vanadium stable isotopes in particular, is that their fractionation should be directly and robustly linked to oxygen fugacity. This fellowship analyses vanadium stable isotope variations in lavas, sediments and deep Earth samples from the Mariana (southwest Pacific), Aleutian (Alaska) and Mexican subduction zones. Through this work, better constraint can be placed on oxygen fugacity and how the Earth system behaves in terms of the fluxes of volatile elements such as carbon and hydrogen between deep and surface reservoirs of the Earth. This will help us tackle far-reaching present day issues related to how the carbon cycle works, and also potentially provide a means of investigating how the amount of oxygen in the Earth has changed over time, its links to the evolution of the atmosphere and ultimately to how our planet became able to sustain life.
Organisations
Publications
Nielsen S
(2014)
Vanadium isotopic difference between the silicate Earth and meteorites
in Earth and Planetary Science Letters
Nielsen S
(2011)
Determination of Precise and Accurate 51V/50V Isotope Ratios by MC-ICP-MS, Part 1: Chemical Separation of Vanadium and Mass Spectrometric Protocols
in Geostandards and Geoanalytical Research
Prytulak J
(2013)
Assessing the utility of thallium and thallium isotopes for tracing subduction zone inputs to the Mariana arc
in Chemical Geology
Prytulak J
(2011)
Determination of Precise and Accurate 51V/50V Isotope Ratios by Multi-Collector ICP-MS, Part 2: Isotopic Composition of Six Reference Materials plus the Allende Chondrite and Verification Tests
in Geostandards and Geoanalytical Research
Prytulak J
(2013)
The stable vanadium isotope composition of the mantle and mafic lavas
in Earth and Planetary Science Letters
Prytulak J
(2014)
Melting versus contamination effects on 238U-230Th-226Ra and 235U-231Pa disequilibria in lavas from São Miguel, Azores
in Chemical Geology
Ventura G
(2015)
The stable isotope composition of vanadium, nickel, and molybdenum in crude oils
in Applied Geochemistry
Description | The initial year of my fellowship focussed on a refining measurement protocols of the isotopes of the element vanadium. Initial studies of lavas from different types of geologic settings on Earth revealed a larger than anticipated difference in the isotope chemistry of vanadium. This prompted further work for the remaining two years of the fellowship, which was transferred to Imperial. |
Exploitation Route | There has already been interest from oil companies (Petrobras, Shell) and mining contacts to adapt the type of isotope measurement developed as a possible exploration tool. The experimental petrology discipline is keen to try and calibrate isotope fractionation factors now that I have demonstrated the resolvable natural variations found. |
Sectors | Environment,Other |
Description | The initial time period of my fellowship produced preliminary analyses and refined chemical separation protocols. The analytical chemistry developed has subsequently been used in other national and international Earth Science Laboratories |
First Year Of Impact | 2011 |
Sector | Chemicals,Environment,Other |
Description | NERC standard grant (Discovery Science) |
Amount | £66,251 (GBP) |
Funding ID | NE/N009568/1 |
Organisation | Natural Environment Research Council |
Sector | Public |
Country | United Kingdom |
Start | 08/2016 |
End | 07/2019 |
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 |