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 new densely-sampled ocean bottom seismic data across this margin (expected summer 2023). The student will integrate this dataset with pre-existing wide-angle seismic data and extensive pre-existing multichannel reflection data along the same profiles and nearby, some of which were newly acquired in 2021. Interpretation will be guided also by results from an electromagnetic survey carried out as part of the same project.
Following initial familiarisation with the techniques, the student will undertake standard data processing and quality control of the ocean bottom seismometer (OBS) data including determination of precise seafloor locations of instruments. Seismic velocities will be determined initially by tomography, incorporating travel-time picks both from the new dataset and from data acquired in the same location in 2000. The tomography will resolve velocity changes due to the onset of magmatic seafloor spreading, but may not resolve those associated with fault-controlled serpentinisation. A second step will involve the application of full-waveform inversion techniques to achieve higher resolution of fault-related structures and magmatic intrusions. In addition a technique called “mirror imaging” will be applied to the OBS data to create images analogous to seismic reflection profiles. Further constraints on velocity in the uppermost basement may come from downward continuation of available long-streamer multichannel seismic data. Finally the student will use an extensive seismic reflection dataset available in the area to extend constraints from OBS profiles into a regional geological interpretation, focused specifically on the interaction of magmatism and serpentinisation during the onset of seafloor spreading, and integrating results from a parallel project using electromagnetic data.
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 National Oceanography Centre Southampton. 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 wide-angle seismic data.
Seismic tomography and full waveform inversion, 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., Minshull, T. A., Sawyer, D. S., Reston, T. J., Klaeschen, D., Papenberg, C., ... & Morgan, J. K. (2016). Fault-controlled hydration of the upper mantle during continental rifting. Nature Geoscience, 9(5), 384-388.
Bullock, A. D., & Minshull, T. A. (2005). From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK. Geophysical Journal International, 163(2), 527-546.
Davy, R. G., Morgan, J. V., Minshull, T. A., Bayrakci, G., Bull, J. M., Klaeschen, D., ... & Cresswell, D. (2018). Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion. Geophysical Journal International, 212(1), 244-263.
