Project Background
For over a century, igneous processes have been viewed through the prism of magma chambers: large, liquid vats of magma. Over the last few decades, it has become increasingly clear that this magma chamber concept may not hold: geophysical investigations find little evidence of liquid magma reservoirs, documenting predominantly melt-poor but crystal-rich magma reservoirs. This is consistent with petrological data, which indicate that many reservoirs have complex histories, including periods in which crystallinity is high. These data have led to a paradigm shift in which magma reservoirs are considered predominantly composed of crystal mush: a mixture of crystals and melt (Cashman et al., 2017). However, the mush paradigm has not been universally accepted, and a range of different magma reservoir architectures is currently proposed (Edmonds et al., 2019). The different models have very different implications for how melts evolve, how melts are transported and how long-lived magmatic systems are.
Mid-ocean ridges provide an ideal system in which to study magma reservoir evolution and so test the different models: they were the first system in which mush reservoirs were documented, and abundant modern high-resolution seismic data provide an excellent geophysical context. Critically, both the plutonic and volcanic rock record is available for study, providing an excellent opportunity to use the complementary nature of plutonic and volcanic rocks to constrain magmatic histories (Lissenberg et al., 2019). Critical questions that need to be answered include the following: What size were the magma reservoirs? Were they crystal-rich or melt-rich? How quickly did they cool?
This project seeks to answer these questions, applying a range of cutting-edge techniques in petrology and geochemistry to rocks recovered from the Mid-Atlantic Ridge.
Project Aims and Methods
The project aims to reconstruct the evolution of mid-ocean ridge magma reservoirs, using the Mid-Atlantic Ridge as a template. The studentship will capitalise on the unique opportunity provided by the upcoming (April-June 2023) IODP Expedition 399, on which lead supervisor Lissenberg will sail (http://iodp.tamu.edu/scienceops/expeditions/atlantis_massif_blocks_of_life.html). This expedition aims to recover an extensive (~600 m), high resolution record of plutonic rocks, providing direct access to the fossilised magma reservoirs of the Mid-Atlantic Ridge. The student will use these samples to characterise magma reservoirs beneath slow-spreading mid-ocean ridges.
Drill core observations and microscopic textural observations will be combined with mineral major- and trace element concentrations to reconstruct reservoir size, melt compositions and melt evolution, with a particular focus on the crystallinity of the magma reservoirs and melt transport mechanisms (Lissenberg & MacLeod, 2016; Boulanger et al., 2020). These data will also underpin a reconstruction of reservoir temperatures and cooling rates (Sun & Lissenberg, 2018). Finally, the student will employ a novel approach to fingerprinting parental magmas using isotopic analysis on the crystal scale (Lambart et al., 2019), which is uniquely suited to identify the scale of emplacement of individual melt batches. We encourage the student to be involved in developing the research direction of the project as it unfolds, and for them to bring in their own ideas to the project.
Candidate requirements
This project would appeal to students interested in using petrology and geochemistry to improve understanding of magmatism on Earth. An interest in igneous processes and an affinity for petrological/geochemical analytical techniques would be required.
Training
The student will receive an extensive training programme in petrology and geochemistry, with a particular focus on in-situ mineral analysis (WDS+EDS analysis major element analysis, LA ICP-MS trace element analysis, micromilling-TIMS isotopic analysis). In addition to project-specific training and the DTP training courses, the student will have access to the large range of Cardiff University Student Development courses, to maximise transferable skills. The student is also expected to present project results to national and international conferences, and will benefit from a large international network of scientists working on IODP Expedition 399. Finally, the student will have the opportunity to demonstrate both in the classroom and in the field. Combined, the training package of the project will give the student an excellent basis for a career in academia or industry.
Entry requirements
In order to be accepted you would need to have a first-class BSc degree or a second-class degree plus an MSc or good MSci. However, for international students, you would need to have a relevant degree in the subject area and have evidence of an English Language qualification. Further information on the English Language can be found here: https://www.cardiff.ac.uk/study/international/english-language-requirements/postgraduate
How to apply
In order to formally apply for the PhD you will need to go to the following web page: https://www.cardiff.ac.uk/study/postgraduate/research/programmes/programme/earth-sciences
In the black box on the right of the page please select the following options:
·Doctor of Philosophy
·Full Time
·1st October 2023
Click on ‘Apply now’.
Please ensure that you include the ‘Project Title’ you are applying for and supervisor and that you add ‘NERC DTP’ under the source of funding.
The application deadline is Monday 9 January 2023 at 2359 GMT. Interviews will take place from 22nd February to 8th March 2023. For more information about the NERC GW4+ Doctoral Training Partnership please visit https://www.nercgw4plus.ac.uk.
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