The deep roots and internal structure of active and extinct seafloor massive sulphide deposits

Project Rationale:

Hydrothermal polymetallic seafloor massive sulphide (SMS) deposits form when seawater circulates within oceanic rocks driven by heat from below. This convection carries hot, metal-rich fluids upwards where they are expelled at the seafloor, and they react with cold seawater, resulting in mound-shaped structures that contain valuable mineral resources. SMS deposits are found at mid-ocean ridges and volcanic provinces. Their small size and the deep-water conditions where they usually occur make them a challenging target for surface seismic methods. In this project we aim at obtaining a complete knowledge of the internal structure and the deep plumbing of massive sulphide deposits. We will use novel ocean bottom seismic techniques to determine the seismic velocity structure of both active and inactive SMS deposits and the crust beneath them, providing new insights into their formation and development, and the three dimensional spatial extent of sub-seafloor sulphide mineralisation. The project will use signals recorded on ocean bottom seismometers (OBSs) from both surface seismic sources and from a seafloor drill, and will include the application of existing methods for the first time in deep-water setting and with the seabed rock drill, to analyse the signals generated by the drill.

Methodology:

The student will work on OBS datasets from the EU-funded Blue Mining and the NERC-funded ULTRA projects. The project will involve:

i) Defining the seismic structure within and beneath active and extinct SMS deposits in TAG area (~26oN on the Mid-Atlantic Ridge), using the Blue Mining dataset.
ii) Helping to design an inverse vertical seismic profile (IVSP) to make use of the drill bit as a seismic source at the Semyonov SMS deposits (~13o30’N on the Mid-Atlantic Ridge). Experiment design will include the generation of synthetic seismograms through a prior model created using the information from Blue Mining project and from the literature.
iii) Participation in the acquisition of surface seismic and IVSP data in Semyonov area (in 2020 or 2021).
iv) Development of approaches based on seismic interferometry, to process the IVSP data. The drill-bit noise will be recorded by 23 OBSs and the time during which waves travel between the drill-bit and the instruments will be calculated by cross-correlating the data recorded by the pilot instrument on top of the drill-rig, with other instruments located on and around the SMS deposit.
v) Integration of IVSP results with models derived from surface seismic and electromagnetic data and with observations from collected cores.

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 at the National Oceanography Centre Southampton. Specific training will include:

i) Seismic data processing, analysis and visualization;
ii) Scientific computational skills that can be transferred easily to a range of fields after graduation;
iii) Highly specialised methodology widely used in Oil & Gas industry (IVSP);
iv) Geophysical data acquisition at sea.

The student will participate in the broad ULTRA project and interact with several associated PhD students at different stages. They will have the opportunity to present their results to academic, government-funded and industrial specialists, and will be thoroughly coached in the skilful delivery of their methods and results to these audiences in both verbal and written form. The student will be rigorously trained in the art of scientific communication in the form of academic papers for international journals, and will have the opportunity to participate in seagoing scientific survey where various geophysical (seismic and electrical resistivity) and geochemical methods are applied.