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

Prof Tim Minshull, Gaye Bayrakci (NOCS), Joonsang Park (NGI), Sebastian Hoelz (Geomar)
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. As part of the EU “Blue Mining” project, with international partners we acquired in summer 2016 a variety of geophysical and geological datasets, including controlled source electromagnetic (CSEM) data, from a small area of the Mid-Atlantic Ridge. The electromagnetic data 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 changes in rock type across a major detachment fault beneath the survey area. This project aims for the first time to apply a three-dimensional inversion 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

Methodology: 

The project will start with some familiarisation with the survey area and its geological context and with marine CSEM methods. The project will use signals from a towed electromagnetic source that is recorded on an array of seafloor instruments. An initial two-dimensional analysis will be completed using a subset of these instruments lying on a profile along which the source was towed, integrating the data from towed receivers that have been analysed previously to study near-seabed structure only. The resulting two-dimensional model will guide subsequent three-dimensional analysis, with some initial forward modelling followed by inversion of the full dataset. There may then be opportunities to compare the performance of different inversion codes and/or to incorporate constraints from passive electromagnetic (magnetotelluric) data from the same seafloor instruments. The resulting resistivity models will be combined with existing seismic velocity models from the same area and rock physics models to unravel the impacts of faulting and hydrothermal circulation on the oceanic crust in the survey area.

 

Location: 
NOC Southampton
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.

 

Eligibility & Funding Details: 
Background Reading: 

Humphris, S.E., Tivey, M.K. and M.A. Tivey, 2015. The Trans-Atlantic Geotraverse hydrothermal field: A hydrothermal system on an active detachment fault. Deep-Sea Res. 2. http://dx.doi.org/10.1016/j.dsr2.2015.02.015i

Gehrmann, R.A.S,, L.J. North, S. Graber, F. Szitkar, S. Peterson, T.A. Minshull and B.J. Murton, 2019. Marine mineral exploration with controlled-source electromagnetics at the TAG hydrothermal field, 26N Mid-Atlantic Ridge, Geophys. Res. Lett., 46, https://doi.org/10.1029/2019GL082928

Park, J., G. Sauvin and M. Vöge, 2017. 2.5D inversion and joint interpretation of CSEM data at Sleipner CO2 storage, Energy Procedia, 114, https://doi.org/10.1016/j.egypro.2017.03.1531

 

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