Lead supervisor: Oliver Shorttle, Earth Sciences
Co-supervisor: John Maclennan, Earth Sciences; John Rudge, Earth Sciences
Brief summary:
Magma moves through hundreds of kilometres of nearly solid rock to eventually erupt at Earth’s surface; this project will combine data science and theory to investigate how this occurs.
Importance of the area of research concerned:
Mantle melting provides our primary window into the Earth’s interior, providing evidence for recycling of material from Earth’s surface into the deepest interior of the planet, for hidden geochemical reservoirs that have remained undisturbed since the planet’s formation, and for the modern temperature and geodynamic state of the mantle. However, the processes that give rise to a lava erupting at the surface of the Earth are poorly understood, requiring magmas to migrate through nearly 100 km of almost solid peridotite with potentially significant chemical modification along route. This is a key time in magma-genesis, during which the compositional and isotopic signatures of solid mantle domains are transferred into melts and possibly mixed and hybridised on their way to the surface. This transport processes therefore acts as a fundamental filter on all information we obtain from the mantle, which potentially biases our chemical and physical models of Earth’s formation, evolution, and present state. With a combination of new modelling and data analysis, this project will investigate what mantle-derived melts are telling us about the mantle.
Project summary :
What information do magmas contain on the mantle from which they formed and how does this vary by geodynamic setting? These are the key questions that will be addressed in this project. The approach taken will have three strands. First, new statistical models of mantle melting and melt transport will be developed. Second, existing magma-dynamics codes that model the physics of two-phase flow from the mantle will be exploited to investigate the topology and efficiency of melt transport from the mantle and used to inform the simple statistical modelling. Third, data science methods will interrogate large compositional datasets from a) magmas, and b) exhumed sections of peridotite to find the cryptic fingerprint of melt transport in basalt geochemistry. There is the opportunity for fieldwork to collect new samples of chemically diverse magmas from Iceland.
What will the student do?:
This project will combine theoretical work developing and applying models of mantle melting, statistical analysis of large geochemical datasets, and data generation to identify trends emerging from the physics of melt transport. The student will begin by developing statistical models of melt transport, investigating how transport histories affect the preservation of geochemical signals from different depths within the melting region. These results will be compared with the results of running magma-dynamics codes. Key parameters affecting the melt transport topology will be investigated through a series of novel simulations. In parallel, a new statistical analysis of geochemical data from a range of tectonic settings will be performed. This work will focus on quantifying the compositional variability of magmatic rocks, both intra-sample variability (via melt inclusion studies) and inter-eruption and temporal variability, employing spatial statistical methods to link basalt geochemistry to mantle structure. New measurements using the micro-analytical suite in Cambridge will augment existing melt inclusion data, providing major and trace element analyses.
References - references should provide further reading about the project:
Shorttle, 2015. Geochemical variability in MORB controlled by concurrent mixing and crystallisation. Earth and Planetary Science Letters 424 1-14. DOI: 10.1016/j.epsl.2015.04.035
Shorttle, Rudge, Maclennan and Rubin 2016. A Statistical Description of Concurrent Mixing and Crystallization during MORB Differentiation:Implications for Trace Element Enrichment. Journal of Petrology 57:11-12 2127-2162. DOI: 10.1093/petrology/egw056
Rudge, J.F., Maclennan, J. & Stracke, A.. 2013. The geochemical consequences of mixing melts from a heterogeneous mantle. Geochimica et Cosmochimica Acta, vol. 114. DOI:10.1016/j.gca.2013.03.042.
Applying
You can find out about applying for this project on the Department of Earth Sciences page.