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Testing the links between magmatic, tectonic and climate controls on hydrothermal activity at the Mid-Atlantic Ridge


   Ocean and Earth Science

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  Dr A Lichtschlag, Dr B Murton, Prof Rachael James, Dr Maxime Lesage  No more applications being accepted  Funded PhD Project (Students Worldwide)

Southampton United Kingdom Climate Science Geochemistry Marine Sciences Geology

About the Project

Project Rationale:

High temperature hydrothermal activity at mid-ocean ridges is driven mainly by magmatic heat and crystallization and responds to structural processes that open-up and maintain fluid pathways from the interior of the ocean crust to the seafloor. Project ULTRA seeks to understand the 3D structure and composition of ultramafic-hosted hydrothermal deposits. These deposits are unusual in that they form on the ridge flanks in areas of structural exhumation of mantle rock, by detachment faulting and with minimal volcanic expression. This phenomenon raises questions about the tectonic controls on hydrothermal activity. For example, there is evidence from other locations at mid-ocean ridges that hydrothermal activity responds to climate-forced sea-level changes [1, 2]. This project aims to explore the fourth dimension, the changes of hydrothermal activity over time, by using different geochemical approaches to identify the history and the evolution of the system during and after the hydrothermal activity for several ultramafic-hosted hydrothermal systems at 13°N, Mid-Atlantic Ridge (MAR). In addition, we aim to test if at the ultra-mafic and ultraslow-spreading setting we can use sediments as prospecting tools and as a way of determining the resource potential of the system through the history of hydrothermal activity.

 

Methodology:

This PhD project will work on sediment cores collected from above seafloor massive sulphides and across an oceanic core complex at 13°N, MAR during the two cruises of the project ULTRA. Both cruises will include gravity coring combined with push cores collected with a remotely-operated vehicle on the second cruise. Sediment porewaters will be extracted from specific depth intervals under oxygen-free conditions using Rhizon samplers. These fluids will be profiled for nutrients (NH4, NO3, PO4, Si) cations, anions, Sr isotopes, total alkalinity, REE, metal ratios and sulphide to study the geochemical environment and elucidate the role of specific process (e.g. metal dissolution/scavenging). The chemostratigraphy of the sediments will be determined with an X-Ray scanner (ITRAX core scanner) at the British Ocean Sediment Core Research Facility at NOC, and specific layers will be chosen for dating the age of the sediment with various methods (e.g. dO18 stratigraphy[3], C14 and paleomagnetism). These mineralogy, geochemistry and isotope studies of the collected sediments will allow us to identify and understand common processes of formation, changes in sub-surface minerals, and changes in metal composition and distribution, and their effects on the structural characteristics of the deposits.

 

Funding and training:

The PhD project is fully funded by Green Minerals (Norway) for 3.5 years. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre Southampton. As part of the PhD project the candidate will receive training on proficiency in sea survival techniques and will be trained in a number of analytical techniques (specifically sediment and pore fluid analyses by ICP-OES, ICP-MS, core logging, ITRAX (XRF) logging, optical and SEM mineralogy, oxygen isotope analyses, magnetic remanence and C14 dating). The candidate will have regular opportunities to engage and network with national and international project partners through project meetings and conferences. While based in Southampton the student will spend some time at the office of Green Minerals (Oslo) and their collaborating research institutes in Norway. Following the completion of the PhD programme the right candidate may be considered for a position at Green Minerals.

All doctoral candidates will enrol in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 180 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas).  

Application:

The PhD position is open to all students (UK and international). Applicants should have a Master or an Engineering degree in a field related to Earth Science and/or Mining, although exceptional BSc Honours graduates will also be considered. The candidate needs to have a strong interest in geochemistry and preferable has some background knowledge in geology. A willingness to learn new techniques and a proficiency in English are expected. 

To apply: Please use the University application portal. Details and requirements can be found at: https://noc.ac.uk/education/gsnocs/how-apply

General enquiries should be directed to the GSNOCS Admissions Team on [Email Address Removed]. To discuss project-specific aspects please contact Dr Anna Lichtschlag.

Closing date: 14th of May 2021.

Expected start date: no later than the 1st of October, 2021.


References

[1] Middleton J. L., Langmuir C. H., Mukhopadhyay S., McManus J. F. and Mitrovica J. X. (2016) Hydrothermal iron flux variability following rapid sea-level changes. Geophys. Res. Lett. Available at: http://doi.wiley.com/10.1002/2016GL068408.
[2] Lund D. C., Asimow P. D., Farley K. A., Rooney T. O., E S., Jackson E. W. and Durham Z. M. (2016) Enhanced East Pacific Rise hydrothermal activity during the last two glacial terminations. Science (80-. ). 351, 600–604.
[3] Cherkashov G. A. (1995) Hydrothermal input into sediments of the Mid-Atlantic Ridge. Geol. Soc. London, Spec. Publ. 87, 223–229. Available at: http://sp.lyellcollection.org/lookup/doi/10.1144/GSL.SP.1995.087.01.18.