Determining the Isotope Building Blocks of Terrestrial
Planets
Supervisor: Julie Prytulak (Imperial College London)
Co-supervisor: Andrew Walker (University of Leeds)
How the Earth formed and evolved fundamentally captures the imagination.
From Earth’s inception in a proto-planetary disk, to its accretion and
differentiation, punctuated by dramatic events such as the Moon-forming giant
impact, geochemistry remains arguably the most powerful tool to shed light on
the planet’s infancy.
One
classic
approach
to
investigate the composition of the
Earth to unravel events in the
early Solar system is comparative
geochemistry. A ‘Bulk Silicate
Earth’ value is determined (i.e.
the Earth without the core) is
compared to various classes of
meteorites.
But even when
treating
different
meteorite
classes as ingredients in a
cosmic recipe, it is very difficult to
get the finished product ‘just right’, and reconcile multiple chemical
characteristic. Differences between the terrestrial and extraterrestrial material
may indicate a role for core-formation, magma-ocean processes, addition of
material by a ‘late veneer’, or a variety of early solar system processes.
The stable isotope composition of vanadium shows one of the largest
disparities between the Earth and meteorites of any isotope system
investigated thus far, with meteorites ubiquitously offset to isotopically light
values compared to the best current estimate for the bulk silicate Earth
(Nielsen et al. 2014; Prytulak et al. 2013). The data has been challenging to
interpret, since 1) all classes of measured meteorites, including chondrites,
Martian and Vesta-derived material have similar isotope compositions and 2)
metal-silicate experiments show that V isotopes are unlikely to be affected by
core formation.
Thus new approaches are needed to explain the
observations.
AIMS
The main question of this project is straightforward: What causes the large
disparity between the stable V isotope composition of the bulk silicate Earth
and meteorites? Specifically, 1) is the current estimate for the Bulk Silicate
Earth robust? And 2) what magnitude of isotope fractionation might be caused
by internal Earth processes?
METHODS
This PhD has two routes of investigating and explaining the large terrestrialextraterrestrial V isotope offset. 1) The student will perform first principle
calculations to determine theoretical isotope fractionation factors for deep
mantle minerals (e.g., Javoy et al. 2012; Huang et al. 2013). 2) The student
will perform V isotope measurements to compare with theoretically calculated
fractionation factors (e.g., Prytulak et al. 2011). Thus, the project involves
close collaboration with co-supervisor Andrew Walker (Leeds) in the first
instance, to train the student in first principle calculations of isotope
fractionation. These calculations guide isotope measurement of natural
samples during the latter part of the PhD.
STUDENT PROFILE AND RESEARCH ENVIRONMENT
The combination of lab and computer based work requires a candidate with
strong interest in cutting edge analytical and theoretical stable isotope
geochemistry and possessing excellent organizational and time management
skills. Candidates should have a degree in Earth Science, Chemistry, Physics
or Maths. Previous laboratory and/or computational experience is not required
but is highly advantageous.
The successful candidate will join the vibrant MAGIC research group at
Imperial College London, which comprises PhD students, postdoctoral
researchers,
fellows
and
four
academic
members
of
staff.
https://www.imperial.ac.uk/engineering/departments/earthscience/research/research-groups/magic/
The student will also benefit from interaction with the Geodynamics Group,
https://www.imperial.ac.uk/engineering/departments/earthscience/research/research-groups/geodynamics/ and from collaborative links
with the neighboring Natural History Museum, which has a large collection of
meteorites.
Do not hesitate to contact us for further information and informal enquiries:
[email protected]
http://www.imperial.ac.uk/people/j.prytulak!
[email protected]!
http://www.see.leeds.ac.uk/people/a.walker
REFERENCES
Huang, F., Chen, L., Wu, Z., Wang, W. 2013. First principles calculations of equilbrium Mg
isotope fractionations between garnet, clinopyroxene, orthopyroxene, and olivine:
Implications for Mg isotope thermometry. Earth and Planetary Science Letters, 67, 6170.
Javoy. M., Balan, E., Meheut, M., Blanchard, M., Lazzeri, M. 2012. First principles
investigation of equilibrium isotope fractionation of O- and Si- isotopes between
refractory solids and gases in the solar nebula. Earth and Planetary Science Letters,
319, 118-127.
Nielsen, S.G., Prytulak, J., Wood, B.J., Halliday, A.N. 2014. Vanadium isotopic difference
between silicate Earth and meteorites. Earth and Planetary Science Letters, 389, 167175.
51 50
Prytulak, J., Nielsen, S.G., Halliday, A.N. 2011. Determination of precise and accurate V/ V
isotope ratios by MC-ICP-MS, Part 2: Isotopic composition of six reference materials
plus the Allende chondrite and verification tests. Geostandards and Geoanalytical
Research, 35, 307-318.
Prytulak et al. 2013. The stable vanadium isotope composition of the mantle and mafic lavas.
Earth and Planetary Science Letters, 365, 177-189.