skip to primary navigationskip to content
 

E334: Multiscale 3D analysis of silicate-hosted magnetic inclusions (Lead Supervisor: Richard Harrison, Earth Sciences)

Supervisor: Richard Harrison (Earth Sciences)

Importance of the area of research:

Paleomagnetic measurements of single crystals of quartz containing nanoscale magnetic inclusions demonstrate that the geodynamo was active at least 3.5 billion years ago and that the intensity of the magnetic field was ~50-70% of the present day field (J. Tarduno et al., 2010). There are currently no paleomagnetic data that predate 3.5 Ga, meaning that the behaviour of the geodynamo for the first one billion years of Earth’s history remains unknown. Silicate-hosted magnetic inclusions have the potential to provide information about the early geodynamo (J. A. Tarduno & Cottrell, 2013). However little is know about their nature and origin. If they are primary magmatic inclusions then they may retain a thermoremanent magnetiation relating to the ancient geodynamo. If they are secondary inclusions formed through later processes (e.g. hydrothermal alteration), then this primary magnetic information may have been changed or lost completely. Understanding the nanoscale mineralogy and chemisty of silicate-hosted magnetic inclusions is a pressing issue that could help to unlock information about the earliest history of the geodynamo.

Project summary:

The proposed project will focus on the mineralogy of silicate-hosted magnetic inclusions from a range of rocks. Our chief aims are a) to understand the formation mechanism of magnetic inclusions in a range of silicate hosts and develop methods to distinguish between primary and secondary inclusions, b) to explore the potential of these inclusions as a paleomagnetic recorders, c) to constrain how and when they became magnetised, and to develop both experimental and computational methods to enable their paleomagnetic properties to be measured and interpreted. Primarily the work will focus on new correlative methods of 3D mineralogical analysis linking behaviour across multiple length scales (atomic to micrometre).

What the student will do:

The student will use a variety of cutting edge methods to explore the potential of silicate-hosted magnetic inclusions as paleomagnetic archives in ancient earth rocks. They will use slice-and-view tomography to determine the 3-dimensional chemical and crystallographic make up of the inclusions  at the nm-µm scale, and thereby determine their formation mechanism. This involves taking succesive ~20 nm slices through the crystals using a focussed ion beam (FIB), acquiring detailed chemical and crystallographic information from each slice using energy dispersive X-ray (EDX) spectroscopy and electron back scattered diffraction (EBSD) to build up a 3D reconstruction of the microstructure. The 3D structure will be explored at the atomic scale using atom-probe-tomography, whereby a 3D volume of the sample is reconstructed atom-by-atom(Valley et al., 2014). Finally, the 3D information will be used to create computer models that accurately describe the paleomagnetic behaviour of these intergrowths and determine how and when they became magnetised.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Tarduno, J. A., & Cottrell, R. D. (2013). Signals from the ancient geodynamo: A paleomagnetic field test on the Jack Hills metaconglomerate. Earth and Planetary Science Letters, 367, 123–132. doi:10.1016/j.epsl.2013.02.008

Tarduno, J., Cottrell, R., Watkeys, M., Hofmann, A., Doubrovine, P., Mamajek, E., … Usui, Y. (2010). Geodynamo, Solar Wind, and Magnetopause 3.4 to 3.45 Billion Years Ago. Science, 327(5970), 1238–1240.

Valley, J. W., Cavosie, A. J., Ushikubo, T., Reinhard, D. a., Lawrence, D. F., Larson, D. J., … Spicuzza, M. J. (2014). Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience, 7(3), 219–223. doi:10.1038/ngeo2075.

Follow this link to find out about applying for this project

Other projects involving the supervisor(s) listed can be viewed here:

Filed under: