Prof Sally Gibson

Linking Earth's deep interior with its surface evolution

My research group is focused on both field and laboratory (petrological, experimental, geochemical and geophysical) investigations in order to understand melt generation in the Earth’s crust and mantle and how this relates to surface processes. Key questions that our current research seeks to address fall into 4 major fields:

1.  How does Earth's rigid outer shell modulate the release of volatiles from our planet's deep interior ?

On-going studies of fragments of deep-sourced mantle material (xenoliths) are providing important insights into the formation of the Earth’s lithosphere and how this large reservoir acts as a major sink and also a source for volatiles (CO2, H2O, S, F) released during volcanism. We have recently quantified the mass of the lithosphere beneath major tectonic settings and this has allowed us to calculate internally consistent estimates of multiple volatiles. Our studies reveal that the ancient cores of Earth's continents are a major sink in global volatile cycles. More work is now required to reduce the uncertainties in these estimates.

2. Ocean Islands: How do they form and what controls volcanism?

Ocean islands are sites of some of the world’s most active volcanism.

• Research on basaltic lavas from the islands of Tristan da Cuhna and Trindade in the South Atlantic has provided constraints on the role of recycled delaminated subcontinental lithosphere in the genesis of ocean-island basalts.
• Mid ocean ridges are anchored to mantle plumes by deep seated melt channels. Galapagos is an archetypal example of this type of interaction: our findings suggest that two-phase rather than solid-state flow is important (Gibson et al., 2015).
• A recent detailed investigation of alkaline and tholeiitic lavas from Santiago in the Galápagos has revealed that their compositions are as diverse as for any other island in the archipelago or indeed any other ocean island.
• By combining new geochemical data with published geophysical data our research has led to an understanding of the causes of widespread active volcanism throughout Galápagos: significant lithospheric thinning in the NE of the archipelago explains the generation of volcanism away from the main axis of the Galápagos plume (Gibson & Geist, 2010)

Research in Galápagos was initiated in 2007 in collaboration with D. Geist, G. Estes, T. Grant, D. Norman and S. Herbert. The main focus of this research was to establish Darwin’s route on Santiago -- formerly known as James Island -- in 1835 (Herbert et al., 2008). This is the island where Darwin made some of his most significant observations on volcanic rocks and led to his theory of gravitational settling as a cause of magmatic diversity (Gibson, 2009). 

3. Large Igneous Provinces: What processes are responsible for the most voluminous outpourings of magma in our planet's history?

These represent the most voluminous emplacements and outpourings of magma that have occurred on Earth’s during its 4.5 billion year evolution. They frequently coincide with the break-up of supercontinents (e.g. the Paraná-Etendeka and Deccan flood-basalt provinces) and are formed by the arrival of a large, up to 2000 km in diameter, thermal anomaly on the base of Earth’s lithosphere. These so-called mantle plumes are thought to be derived from thermal boundary layers deep within the Earth, such as the 2700 km core-mantle boundary.

• Our detailed and systematic geochemical studies, together with high pressure and temperature experiments, on high Fe-picrites (undertaken in collaboration with E. Takahashi, Tokyo; J. Tuff, Oxford) have shown that garnet pyroxenite, probably derived from subducted lithospheric mantle, is present within upwelling mantle plumes.
• Our research has also documented the longevity of volcanism associated with the initial impact of the Tristan mantle plume and its role in the opening of the South Atlantic.
• Studies of olivine-hosted melt inclusions reveal that primitive melts in flood basalt provinces are homogenised prior to cooling and crystallisation in deep-seated magma chambers in the Earth's crust (Jennings et al., 2017).

4. Remote sensing of rare-earth element deposits

An exciting collaboration with Dr Teal Riley (British Antarctic Survey) and Dr Graham Ferrier (University of Hull) examined how novel remote sensing techniques can be used to locate rare-earth element deposits. For an insight into some of our findings from this innovative new project click here. Some of our results on global carbonatite deposits can be found in a recent paper by Neave et al. (2016).

Current project: REE-LITH

Our exciting new NERC funded Pushing the Frontiers REE-LITH project has now started. Rare Earth Elements are critical to our green future and the overarching goal of the project is to reach a fundamental new understanding as to how lithospheric structure and mantle dynamics control the Archean to Recent origins of CO2-rich intraplate magmatism and associated rare-earth element (REE) deposits.The REE-LITH project involves a multi-disciplinary international team of Earth Scientists -- from the Universities of Cambridge (Gibson, Lebedev), Bowman, Sui), Exeter (Broom-Fendley), St Andrews (Hutchison), Madrid (Fullea) and Bergen (Rondenay).

Primary deposits of REEs are typically associated with carbonatites. By combing seismic tomography with global carbonatite locations we show there is a systematic relationship with the steep margins of ancient cratons, which does not always mirror surface geology. This is the first paper from the REE-LITH project  More to come..

Media coverage

March 21st 2025. Mapping Earth's minerals with seismic waves. Podcast https://www.thenakedscientists.com/articles/interviews/mapping-earths-minerals-seismic-waves

March 5th 2025. Why rare earths matter to Donald Trump and the west Financial Times. https://www.ft.com/content/65ee2baf-58ab-42e7-997b-7114c8920a91

March 2025. https://www.cam.ac.uk/research/news/new-global-map-promises-to-better-pinpoint-vital-rare-earth-deposits

July 2016. https://www.cam.ac.uk/research/features/fingerprinting-rare-earth-elements-from-the-air