A destabilising dynamo? Tracing and explaining Earth’s magnetic field evolution through the Cenozoic
Prof Andy Biggin, University of Liverpool
Dr Richard Holme, University of Liverpool
Dr Greig Paterson, University of Liverpool
Dr Mimi Hill, University of Liverpool
- External Supervisors:
Prof Andy Biggin (University of Liverpool), firstname.lastname@example.org
- CASE Partner:
Application deadline: 10 January 2020
The Earth’s magnetic field provides geoscientists a window into the planetary core both today and deep into the geological past. It can be used to tell us about the turbulent convection of liquid iron in Earth’s outer core and how this has changed through geological time in response to inner core growth below it, and mantle convection above it.
100 million years ago, the Earth’s magnetic field was in a different state to today; it did not undergo polarity reversals and it was slightly stronger and less variable than today (Doubrovine et al., 2018; Kulakov et al., 2019). We do not presently understand how and why the Earth’s magnetic field has changed its state dramatically since then but we do know that the answers are likely to tell us exciting new things about the evolution of Earth’s planetary interior.
Published hypotheses state that the magnetic field destabilised because the core was rapidly cooled due to an increased flux of subducted slabs into the lower mantle (Hounslow et al., 2018) and/or increased release of catastrophic mantle plume heads from just above the core-mantle boundary (Biggin et al., 2012).
This studentship aims to answer exciting questions:
- How did the magnetic field change over the last 100 million years?
- Were these changes caused by enhanced cooling of the core by the mantle?
- What role did the breakup of Pangaea play in changing core cooling conditions?
This project will involve a combination of field, lab and modelling work in a ratio that the student will determine.
The student will perform palaeomagnetic sampling in at least one field area and use the igneous rocks they collect to measure the strength and variability of the magnetic field at the time and place that the rocks cooled (Biggin et al., 2011; Tauxe, 2010). The primary identified target is the large edifice of basaltic lava flows forming the 16 million year old Columbia River Basalt in north-western USA. The student will go there to collect samples early in their project.
The student will also collate other published data from the last 100 million years and combine these with their own measurements to construct a ground-breaking new record of how the Earth’s magnetic field evolved from a nonreversing “superchron” state in the Cretaceous to its present condition of apparent instability.
Armed with their improved records of magnetic variability in the last 65 million years, the student will test published and novel hypotheses of deep Earth evolution and interaction. They will learn techniques to model the global field and make quantitative comparisons with numerical dynamo model outputs. They will compare their observations to the magnetic field behaviour predicted by self-consistent models of the core operating under different boundary conditions representing competing mantle convection scenarios.
This project would suit a geophysics or geology graduate who is keen to combine field lab and modelling while working in the highly multidisciplinary DEEP (Determining Earth Evolution from Palaeomagnetism https://tinyurl.com/ybt9s9f6) group.References:
Biggin et al. (2011). “Palaeomagnetic Field Intensity”. In: Harsh K. Gupta (ed.), Encyclopaedia of Solid Earth Geophysics, Springer, DOI 10.1007/978-90-481-8702-7.
Biggin, A. J., et al. (2012). "Possible links between long-term geomagnetic variations and whole-mantle convection processes." Nature Geoscience 5(8): 526-533.
Doubrovine, P. V., et al. (2019). "Latitude dependence of geomagnetic paleosecular variation and its relation to the frequency of magnetic reversals: Observations from the Cretaceous and Jurassic." Geochemistry Geophysics Geosystems 20: 1240-1279.
Hounslow, M., et al. (2018). "Subduction flux modulates the geomagnetic polarity reversal rate." Tectonophysics 742-743: 34-49.
Kulakov, E. V., et al. (2019). "Analysis of an updated paleointensity database (QPI-PINT) for 65-200 Ma: Implications for the long-term history of dipole moment through the Mesozoic." Journal of Geophysical Research doi: 10.1029/2018JB017287.
Tauxe, L. (2010). Essentials of Paleomagnetism. Berkeley, UC Press.