The breakup of continents is fundamental to the creation of the Earth’s surface and oceans but many aspects remain poorly understood. Breakup involves a complex interplay of extensional tectonics and magmatism, resulting in a range of rifted margin types, including a “magma-poor” end-member involving broad regions of exhumed and serpentinised (hydrated) mantle. Breakup at such margins is commonly followed by slow to ultra-slow seafloor spreading, which can also result in mantle exhumation and thus ambiguity about where seafloor spreading starts. Normal faulting plays a key role in supplying fluids driving serpentinisation beneath hyper-extended continental crust but its role in regions of exhumed mantle is less clear. To address these issues, we will image lateral variations in serpentinisation and magmatism at the Goban Spur margin southwest of the UK by acquiring the first controlled source electromagnetic (CSEM) dataset across a continent-ocean transition (expected summer 2023), using both towed and seabed receivers. We will also detect differences between underlying continental and oceanic mantle using passive electromagnetic (magnetotelluric) data. The student will analyse a subset of this dataset, guided by results from a wide-angle seismic survey acquired during the same cruise and extensive pre-existing multichannel reflection data along the same profiles and nearby.
Following some initial familiarisation with the techniques, the student will process the CSEM data from seafloor instruments and then use a state-of-the-art electromagnetic inversion code to determine the resistivity structure beneath the seabed, accounting also for possible differences between vertical and horizontal resistivity. This analysis will include higher-resolution inversion of portions of the transect where the sediment cover is thin enough that our towed Vulcan receivers provide constraints on basement resistivity variations. Magnetotelluric data will be incorporated to constrain deeper structures. Once a resistivity model has been obtained, the student will use rock physics models to relate resistivities and seismic velocities to degrees of serpentinisation and magmatic intrusion. A subset of our seafloor CSEM receivers will be fitted also with three-component geophone packages. A further component of the project will involve analysis of whether airgun signals recorded by these geophones are also detected by the coincident electrodes and magnetometers. The student will spend one or more extended periods working in the group of Prof. Constable at Scripps Institution of Oceanography in La Jolla, California.
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. The student will join the UK’s most active marine geophysics group and a project consortium that includes collaborators in California and Germany. Specific training will include:
Marine seismic and electromagnetic data acquisition (via participation in the associated research cruise).
Processing of marine electromagnetic data.
Inversion of marine electromagnetic data, including aspects of super-computing.
Seismic interpretation and rifted margin processes.
This background will leave the student well-equipped for a career in research, in consultancy or in the geophysical survey industry.
Please see https://inspire-dtp.ac.uk/how-apply for details.
Bayrakci, G., T. A. Minshull et al., 2016, Fault-controlled hydration of the upper mantle during continental rifting, Nature Geoscience, 9, 384-388, doi: 10.1038/ngeo2671
Bullock, A. D, and T. A. Minshull, 2005, From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK, Geophys. J. Int., 163, 527-546, doi:10.1111/j.1365-246X.2005.02726.x
Naif, S., K. Key, S. Constable and R. L. Evans, 2015, Water-rich bending faults at the Middle America Trench, Geochem. Geophys. Geosys., 16, 2582-2597, doi:10.1002/2015GC005927