We now realise our conceptual view of magma chambers as large melt bodies is outmoded: that they are instead predominantly melt-poor crystal mushes1. The processes that form and modify these mushes, and their effects on the melts entering and exiting the system are, however, very poorly understood. This is particularly true for lower ocean crust formed beneath mid-ocean ridges, where access to the gabbroic crystal mush end-product is restricted. From the limited ocean drilling of lower crust that has been performed2 it is evident that melt migration and melt-mush reaction are key processes both in creating the lower crust and modifying the magmas that are extracted to form the upper crust3, and that these processes are intimately linked to syn-magmatic deformation of the mush.
Project Aims and Methods
This project will look beyond the one-dimensional ocean drill core record to examine the nature of the interplay between deformation, magma transport and melt evolution in an exhumed analogue: the Bay of Islands ophiolite of Newfoundland (Canada), where evidence for these processes is exquisitely preserved in the rock record4,5.
Following fieldwork in Newfoundland, in collaboration with the Geological Survey of Canada, the student will use a combination of analytical approaches to reconstruct the role of deformation-driven melt transport in the lower oceanic crust. This will include full thin section scale element mapping and laser ablation ICP-MS mineral trace element analyses to determine the petrogenetic history of the section, coupled with EBSD analyses. The latter will enable the student to constrain and model the deformation history. Integrating all of these aspects will for the first time allow a rigorous assessment of the role of deformation in driving melt transport and evolution in formation of the ocean crust. This work will furthermore be of the highest impact in further our generic understanding of crystal mush processes in magmatic systems.
This project will be of interest to students keen on igneous petrology, geochemistry and structural geology. They should be keen on (helicopter-based) field geology and using observations to solve geological problems.
If you have a lower second class degree, you will be considered if you also have a master’s degree. If you have a minimum upper second class degree and significant relevant non-academic experience, you are encouraged to apply.
CASE or Collaborative Partner
The Geological Survey of Canada will be a Collaborative Partner in this project, providing helicopter-based logistical support in the field, and thereafter full access to all maps, samples and data collected by the GSC over decades of study at headquarters in Ottawa and Québec.
The student will take advantage of several of the generic training courses run on a regular basis by the GW4+ partners. Particularly appropriate will be the Geographical Information Systems & Spatial Analysis, Data Analysis and Science Communication courses.
We do however anticipate directing the student to external courses similar to those run on a national basis in recent years, specifically in digital field skills training (e.g. as done by the British Geological Survey) and in microanalytical geochemical techniques. Great benefit could also come from attending an ECORD (IODP) Summer School, held at MARUM in Bremen; in recent years a hard-rock geology school, based upon the examination of Solid Earth oceanic basement drill cores, has been run every few years and within the timescale of the studentship. These courses or similar would be appropriate use of the training credits budget.
How to apply:
You should submit an application for postgraduate study via the Cardiff University Online Application Service, including:
an upload of your CV
a personal statement/covering letter
two references (applicants are recommended to have a third academic referee, if the two academic referees are within the same department/school)
current academic transcripts.
You should apply to the Doctor of Philosophy in Earth and Ocean Sciences with a start date of October 2020.
In the research proposal section of your application, please specify the project title and supervisors of this project and copy the project description in the text box provided. In the funding section, please select ’I will be applying for a scholarship/grant’ and specify that you are applying for advertised funding from NERC GW4+ DTP.
If you wish to apply for more than one project please email [email protected]
The deadline for applications is 16:00 on 6 January 2020.
Shortlisting for interview will be conducted by 31 January 2020.
Shortlisted candidates will then be invited to an institutional interview. Interviews will be held in Cardiff University between 10 February and 21 February 2020
1.Cashman, KV et al., 2017. Vertically extensive and unstable magmatic systems: A unified view of igneous processes. Science 355, eaag3055.
2. Dick, HJB et al., 2000. A long in situ section of the lower ocean crust: results of ODP Leg 176 drilling at the Southwest Indian Ridge. EPSL 179, 31-51.
3. Lissenberg, CJ & MacLeod, CJ, 2016. A reactive porous flow control on mid-ocean ridge magmatic evolution. J. Pet., 57, 2195-2220. doi: 10.1093/petrology/egw074.
4. Bédard, JH, 1993. The oceanic crust as a reactive filter: multiple syn-kinematic intrusion, hybridization and assimilation in an ophiolitic magma chamber. Geology 21, 77-80.
5. Bédard, JH, & Hébert, R, 1996. The lower crust of the Bay of Islands ophiolite, Canada: petrology, mineralogy and the importance of syntexis in magmatic differentiation in ophiolites and at ocean ridges. Journal of Geophysical Research, 101, 25105-25124.