Pulsing Mantle Plumes: Causes and Geological Consequences

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Between Earth's crust and core lies the mantle, 2,900-km of hot rock that comprises 80% of Earth's volume. Carrying Earth's internal heat to the surface, the convecting mantle creeps like tar on a hot day. This overturning is the 'engine' that drives our dynamic Earth; all large-scale geological activity is driven by mantle convection. Mantle plumes are an important, but poorly understood, aspect of mantle convection. They are buoyant mantle upwellings that bring hot material from Earth's deep mantle to the surface, lifting Earth's surface as they rise and generating large volcanic provinces and volcanic islands, such as Iceland and Hawaii. There is increasing evidence that these upwelling plumes change in shape and strength through time; they pulse. Such pulses produce corresponding changes in surface topography, which has major implications for a range of surface processes. For example: (i) hydrocarbon generation - variations in sediment supply, which are driven by tectonic uplift and subsequent erosion, strongly influence the stratigraphy of sedimentary basins, which ultimately controls the distribution of hydrocarbons; and (ii) ocean circulation - the pulsing Icelandic mantle plume has played a central role in controlling regional uplift, which, in turn, has moderated overflow of cold North Atlantic Deep Water into the global ocean circulation system. This system transports both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. Consequently, pulsing mantle plumes have a direct influence on global climate. While the observational evidence for pulsing is increasing, the ultimate cause is unknown. Consequently, we cannot explain or predict the strength and frequency of pulses, or their signature at Earth's surface. Establishing a relationship between pulsing plumes and their surface manifestation is important if we are to understand Earth's geological history and the long-term evolution of Earth's mantle. To address these gaps in current understanding, the proposed research will use state-of-the-art numerical mantle convection models to investigate the mechanisms that cause pulsing in mantle plumes and to predict the surface response to these pulses. The cause of pulsing will be established by numerically testing a range of hypotheses; for example, that the rate of upwelling is controlled by changes in forcing from sinking slabs of cold crustal material. Each hypothesis will be validated by comparing model predictions of pulsing behavior with geological observations, predominantly from the North Atlantic Ocean. Models will also be used to predict how Earth's surface responds to these pulses; for example, when, where and by how much the surface is uplifted as the upwelling waxes and wanes. These predictions will be tested against observations of how the North Atlantic has responded to the pulsing Icelandic mantle plume. As well as solving a long-standing problem in Earth science, an important outcome of this research will be a predictive model of the response of Earth's surface to flow within Earth's interior. In other words, the model will show how Earth's 'engine' - mantle convection - drives surface deformation. Such a connection is vital for advancing the many fields of Earth sciences that examine the consequences of Earth's dynamic surface.