Understanding hydrothermal processes and mineral deposits at mid-ocean ridges using geophysical data

Programme website: http://inspire-dtp.ac.uk

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 [e.g., 1]. 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, which can be assessed with geophysical methods. This project looks at hydrothermal alteration from the seafloor to 2 km depth using seismic and electromagnetic methods, as well as analysis of seafloor samples.

As part of the EU “Blue Mining” project, with international partners we acquired in summer 2016 a variety of geophysical and geological datasets from a small area of the Mid-Atlantic Ridge. The seismic and electromagnetic data are sensitive to the contrast in seismic velocity and electrical resistivity of the mineral deposits on the seafloor with the underlying oceanic crust. This project aims to use these data to image the deeper structure which has been altered by hydrothermal circulation, to enhance the understanding of the processes controlling the alteration of the oceanic crust and formation of mineral deposits.

Methodology:
The project comprises three parts. Firstly, wide-angle seismic data from ocean bottom instruments and sea surface sources will be analysed with existing algorithms to constrain the deeper (down to 2 km depth) structure of the oceanic crust. Secondly, electromagnetic data from ocean bottom instruments (OBEM data) will be analysed and a 2-D sub-seafloor resistivity distribution will be inferred using existing algorithms. A joint inversion of three-component towed-receiver data and two-component OBEM data will be performed to increase the lateral and vertical resolution [2]. Thirdly, the student will analyse existing seismic and EM measurements on rock samples, with an opportunity to collect further EM and elastic data in the NOC rock physics laboratory, and integrate the results into a model of controls on elastic and electrical properties at hydrothermal sites and mineral deposits [3].

Training:
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in the School of Ocean and Earth Science. Specific training will include: geophysical data acquisition at sea and in the laboratory, high-level training in controlled source electromagnetics, active source seismology, rock physics and geophysical data inversion techniques. In addition we anticipate that the student will travel to Kiel, Germany to work with our collaborators in this project, and will present his/her work at international conferences.