Constraining the petrogenesis and timing of the late magmatic events in the British Palaeogene Igneous Province - NERC GW4+ DTP project

This project is one of a number that are in competition for funding from the NERC GW4+ DTP. The GW4+ DTP consists of the Great Western Four alliance of the University of Bath, University of Bristol, Cardiff University and the University of Exeter plus six Research Organisation partners. The partnership aims to provide a broad training in earth and environmental sciences, designed to train tomorrow’s leaders in earth and environmental science. For further details about the programme, please see http://nercgw4plus.ac.uk/.

Background

Modern geochemical techniques have greatly increased our understanding of the timing of the magmatism and nature of the mantle source region(s) during the earliest magmatic expressions of the Iceland plume, ca. 60 Ma, in the North Atlantic Igneous Province (NAIP).

Studies of the British part of the province (British Palaeogene Igneous Province - BPIP), consisting of a series of igneous centres along the west coast of Scotland and in Northern Ireland, have been instrumental in the formulation of these ideas. This project builds on substantial body of work, which has focused on the early stages of mantle plume volcanism as preserved in the lavas on Skye and Mull.

These studies have revealed that the magmatism in the province gradually changed from transitional tholeiitic-alkalic magma types to a tholeiitic magma type, which was much more depleted in incompatible trace elements than the earlier type.

Project aims and methods

Erosion has significantly reduced the thickness of the BPIP lava successions. Thus, although the geochemical nature of the early stages of magmatism are well preserved in the lavas, the youngest lavas have long-since been eroded away. The mid-to-late phases of activity in most of the igneous centres in the BPIP are preserved as a series of granitic to ultrabasic intrusions. The youngest major intrusion within these centres is commonly granitic in composition.

However, intruding these youngest granites in Skye, Ardnamurchan, Mull, Arran and the Mourne Mountains are a suite of basic dykes, representing a later phase of magmatism in the province. Preliminary geochemical data from these dykes show that some are more-enriched in incompatible trace elements than the youngest preserved lavas.

Previous studies have also found a temporal shift in the precious metal composition of NAIP lavas (Hughes et al., 2015), and directly related this to PGE enrichment recorded in mantle xenoliths from the underlying subcontinental lithospheric mantle and pre-dating the NAIP. All these features indicate a complex and evolving mantle geochemical system tapped by the Icelandic plume with variable lithospheric contamination. This project therefore aims to investigate the exact age, compositional variability and petrogenesis of these dykes.

Candidate

This project would suit a candidate who is interested in working on a classic igneous area in which many of the modern concepts of igneous petrology were formulated. You should have an interest in fieldwork, igneous petrography, geochemistry and petrogenesis, geochronology and the modelling of magma chamber processes and mantle melting.

CASE award

The NERC Isotope Geoscience Laboratory (Dr Ian Millar) has provisionally agreed (subject to a British Geological Survey application – decision due in November) to support this project as a CASE award. If successful, you will receive £1,000 per annum (£3,500 total) for expenses to facilitate visits to The NERC Isotope Geoscience Laboratory (NIGL) to discuss the project and undertake isotope and dating work (a separate NERC Isotope Geosciences Facilities Steering Committee application will be made if the project is successful).

The CASE supervisor may also accompany you in the field if time permits.

Training

This PhD will extend our knowledge of the temporal geochemical evolution of the BTIP by comparing earlier lava geochemistry with later magma compositions recorded by cross-cutting dykes.

The project will involve, and you will receive training in, careful field sampling, petrography, and geochemical analysis (major, trace, platinum group elements and radiogenic isotopes) in combination with high-precision Ar-Ar and U-Pb dating.

The results on these dyke suites will enable us to fully establish the magmatic evolution of the region. It is anticipated that this project will have major implications for the evolution of other large igneous provinces (LIPs).

You will be encouraged to undertake specific training courses as required by the needs of the project or your own specific interests.