Three-dimensional mapping of mid-ocean ridge hydrothermal systems from electromagnetic data

Project Rationale 

High-temperature hydrothermal circulation at mid-ocean ridges accounts for 30% of heat exchange between the Earth's interior and the deep ocean, controls global geochemical cycles, forms valuable seafloor mineral deposits and nourishes chemosynthetic life forms. Hydrothermal circulation involves fundamental processes of heat and element exchange and likely played a role in the development of life on Earth. Hydrothermal processes cause alteration of the oceanic crust and deposits of economically valuable mineral deposits on the seafloor. Electromagnetic data from hydrothermal sites are expected to be sensitive to the contrast in electrical resistivity of the mineral deposits on the seafloor with the underlying oceanic crust, to hydrothermal fluids feeding these deposits, and to the underlying heat source driving the circulation. This project aims for the first time to apply a three-dimensional inversion to controlled-source electromagnetic (CSEM) data from a mid-ocean ridge setting and thereby to enhance understanding of the processes controlling the alteration of the oceanic crust and formation of mineral deposits. Two CSEM datasets are available for the project, each covering a small area of the Mid-Atlantic Ridge where there is currently active or recent hydrothermal venting and where a variety of other geophysical data are available.

 Methodology

The project will start with some familiarisation with the geological context of the survey areas around the “Transatlantic Geotraverse” (TAG) and “Lucky Strike” vent sites, and with marine CSEM methods. The project will use signals from a towed electromagnetic source that is recorded on arrays of seafloor instruments. An initial two-dimensional analysis will be completed for each area using a subset of these instruments lying on a profile along which the source was towed. The resulting two-dimensional models will guide subsequent three-dimensional analysis, with some initial forward modelling followed by inversion of the full dataset. There will then be opportunities to compare the performance of different inversion strategies and/or to incorporate constraints from other geophysical data. The resulting resistivity models will be combined with existing seismic velocity models from the same areas and rock physics models to unravel the impacts of hydrothermal circulation on the oceanic crust in the survey areas.

 Training

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 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). Specific training will include:

geophysical data acquisition at sea, controlled source electromagnetic data processing and analysis, rock physics and geophysical data inversion techniques, including the use of parallel computing. The student will join the UK’s most active research group in marine geophysics and will have opportunities to learn about a variety of other techniques. In addition we anticipate that the student will spend some time with co-supervisor Park in Oslo, Norway, and will present his/her work at international conferences. This training and international experience will equip the student well for employment in academia or in the exploration industry.