Project EARTH-16-STFC-BJW1: The crystallisation of the Moon.
Supervisors: Professor Bernard J Wood, Dr Jon Wade
The Earth and the Moon were both extensively melted during the giant impact
which is considered to have given rise to the Earth’s satellite. The
consequence for the Moon was extreme solid-liquid differentiation beginning
with separation of a small core and proceeding through extreme layering of
the mantle and flotation of the anorthositic crust. These differentiation
processes have resulted in an uncertain distribution of elements within the
Moon and apparent inconsistencies in elemental abundances between Earth
and Moon. For example, the Moon appears to be very strongly depleted in
almost all volatile elements relative to the Earth, yet some very volatile
elements (e.g. Te) are less depleted in the Moon than in Earth. Most
siderophile (metal-loving) elements are depleted in the Moon’s mantle relative
to that of the Earth, but Co is not. Given the close apparent chemical affinity
between the Moon and the Earth these differences are surprising.The object
of this project is to develop an understanding of how these geochemical
anomalies have arisen. This will be approached principally by determining the
partitioning of elements of widely different chemical properties between the
different lunar reservoirs, core, layered mantle and crust as the Moon
solidified from the molten state. Development of a crystallisation model based
on new experimental results and literature data will place stronger constraints
on the chemical relationships between the Earth and the Moon and the nature
of the Moon-forming impact.
The project will involve determination of the partitioning of a wide range of
minor and trace elements between crystals and melts under pressure
conditions relevant to the lunar interior. Experiments will be performed in one
atmosphere furnaces and the piston-cylinder high pressure apparatus.
Quenched samples will then be analysed by electron microprobe, electron
microscope and Laser-ICP-MS spectrometry. The results will be used to
develop numerical models of lunar differentiation.
This project would be suitable for a student with a background in Earth
Sciences, Chemistry or Materials Science who enjoys “hands-on” laboratory
work. The range of skills acquired by students working in this field makes
them very employable in the Earth and/or Materials Sciences.
Background Reference
Shearer, C.K., Papike, J.J (1999) Magmatic evolution of the Moon. American
Mineralogist v.84 p1469-1494
Project EARTH-16-STFC-JW1: Heavy Mantles – evaporating space rock?
Supervisors: Dr Jon Wade, Professor Bernard J Wood
Recent studies of the differentiated planetary bodies suggest they are isotopically
heavy with respect to Si, with some authors suggesting that HED parent body, for
instance, records sequestration of Si into its core during formation. Although there
has been significant disagreement in the literature as to the magnesium isotopic
content of the differentiated terrestrial bodies, there is a developing consensus that
they are all broadly isotopically heavy and elementally depleted in both Si and Mg.
However, the small, oxidised nature of the HED parent body make it unlikely that
core formation or high-pressure silicate phases are the culprit for the isotopic and
elemental depletions of both elements.
The other explanation is that of element volatility – under highly reducing conditions
such as those found in the proto-planetary disc, both magnesium and silicon are
volatile. The residual silicate will evolve to become depleted in both and, assuming
evaporation at low-pressures, isotopically heavy in both. Support for this process
occurring in nature is found in the calcium-aluminium inclusions (CAI’s) found in
primitive meteorites. These highly refractory components, thought to have been
processed in the early proto-planetary disc, are depleted in the both Si and Mg and
exhibit large variations in their respective isotopic contents. These observations
suggest an enticing hypothesis – is volatility under reducing conditions responsible
for both the isotopic and element depletion in the Earth? Does the Mg isotope
content of the Earth reflect addition of a reduced component during planetary
formation, rather than the presence of a so far un-sampled mantle component?
The project will use experiments to explore the role of silicate composition upon
elemental and isotopic fractionations, and compare these to CAI’s contained within
meteorites. The project will make extensive use of experimental techniques as well
as microbeam (electron probe, LA-ICPMS and nanoSIMS) together with high
precision isotopic analysis to characterise both experimental and natural samples.
Project EARTH-16-STFC-RK1: Tidally forced melting, magmatic
segregation, and planetary evolution of Jupiter’s moon Io.
Theory and computational models.
Supervisor: Professor Richard Katz
Io is a satellite of Jupiter and among the most volcanically active bodies in the
solar system. The internal dynamics of the planet are not yet well understood.
The aim of this project is to develop and adapt mathematical theory based on
conservation principles, obtain solutions using sophisticated numerical models,
and based on the results, interpret surficial observations of the planet in terms of
the dynamic processes happening at depth.
Io shows intense volcanic activity, high-temperature lavas (1700-2000 K), and an
average surface heat flux of 2.5 W m-2 (30x Earth value) (see review by Schubert
et al. 2004). The supply of heat required to sustain such conditions is believed to
come from tidal dissipation, presumably leading to partial melting throughout the
mantle. Proposed simulations of internally heated convection, melting and melt
segregation in Io’s mantle will help to resolve the thermal budget and chemical
evolution of the planet. They may also illuminate the distribution of magma and
temperature beneath the crust/lithosphere. This will address the paradox of Io’s
high global heat flux and apparently thick lithosphere.
The theory for such problems is a combination of the fluid dynamics of mantle
convection and magma percolation with the chemical thermodynamics of melting
and freezing (e.g. Katz 2010). The resulting system of PDEs is non-linear and
typically must be solved with advanced numerical algorithms on highperformance computers. Students applying for this project must have a training in
theoretical fluid dynamics and some exposure to thermodynamics and
computational modeling.
Katz, R. F. (2010); Porosity‐ driven convection and asymmetry beneath
mid‐ ocean ridges, Geochem. Geophys. Geosyst., doi:10.1029/2010GC003282.
Schubert, G., Anderson, J.D., Spohn, T. & McKinnon, W.B. (2004). In Jupiter: the
planet, satellites and magnetosphere, Cambridge University Press.
Project EARTH-16-STFC-TM1: Quantifying volcanic activity on Venus
through change detection
Supervisors: Professor Tamsin Mather & Professor David Pyle
Supervisors: Tamsin Mather (Oxford, Earth Sciences), David Pyle (Oxford, Earth
Sciences), Colin Wilson (Oxford, Physics), Richard Ghail (Imperial College
London) and Robbie Herrick (University of Alaska Fairbanks)
Venus should be volcanically active today. Hundreds of volcanoes have been
identified in radar maps of Venus’s surface, and its atmosphere exhibits high
abundances of sulphurous gases – but confirming ongoing volcanic activity is a key
outstanding question. Several observations from the Venus Express orbiter hint at
ongoing volcanism: falling SO2 abundances at Venus’s cloud tops punctuated by
episodic injections have provided strong evidence for a volcanic input to the
atmosphere (Marcq et al. 2012), thermal emissivity anomalies have been detected
around some volcanoes indicative of young relatively unweathered lava deposits
(Smrekar et al. 2010); and transient hot spot anomalies in infrared surface imaging
data all suggest current dynamic volcanic processes (Shalygin et al. 2015). However
the degree and extent of current volcanic activity on Venus remains a subject of
debate.
This project will aim to address these issues via change detection and by analogue
with Earth-based scenarios. It will include working with the Magellan radar datasets
to quantify upper limits for volcanic change in high-resolution imagery and developing
algorithms for automated sorting of Magellan stereo-processed orthorectified radar
data (e.g., Herrick and Rumpf, 2011). This will be useful in developing tools for future
high-resolution radar missions. The project will also focus on exploring further
constraints on volcanic processes based on radiometry of volcanic hotspots such as
analyses in nightside near-IR spectral windows (e.g. Shalygin et al. 2015), but also
from microwave radiometry from Magellan and from future radar sounders (e.g.,
Lorenz et al., in press). Earth-based analogues will be used to ‘ground-truth’ these
planetary signals in the case of both radar and radiometry data (Pyle et al., 2013).
Further reading
Herrick, R. R., and M. E. Rumpf, Postimpact modification by volcanic or tectonic
processes as the rule, not the exception, for Venusian craters, J. Geophys. Res 116,
E02004, doi:10.1029/2010JE003722, 2011.
Lorenz, R.D. et al. (in press 2015) Detecting volcanism on Titan and Venus with
microwave radiometry, Icarus, doi:10.1016/j.icarus.2015.07.023
Marcq, E. et al. (2012), Variations of sulphur dioxide at the cloud top of Venus’s
dynamic atmosphere, Nature Geoscience, doi:10.1038/NGEO1650.
D.M. Pyle, T.A. Mather and J. Biggs (eds). Remote-sensing of volcanoes and
volcanic processes: integrating observation and modelling. Geological Society
Special Publication 380, 2013. (doi:10.1144/SP380.14)
Shalygin, E. et al. (2015) Active volcanism on Venus in the Ganiki Chasma rift zone,
Geophysical Research Letters, 42, 4762-4769, doi:10.1002/2015GL064088.
Smrekar et al. (2010), Recent Hotspot Volcanism on Venus from VIRTIS Emissivity
Data, Science, 328, 605-8, doi:10.1126/science.1186785.