Investigating hydrothermal processes offshore Japan and Portugal: A case for widespread fluid flow between continental and oceanic crust?

Rationale

Hydrothermalism is the main process promoting the exchange of heat, fluids and geochemical elements between the mantle, oceanic crust and sea water. Nonetheless, the complex physical and chemical interactions that occur between continental and oceanic crust are mostly unstudied. The existence of larger area on deep-water margins where fluids are prone to circulate beneath a veneer of sediment is still to be characterised in geophysical and mineralogical terms. This is a crucial limitation as a large part of fluids generated on continental crust can potentially migrate to deeper oceanic crust, leading to significant hydrothermalism and fluid accumulation in regions where such processes were thought to have ceased.

Methodology

Two-dimensional (2D seismic data, sidescan sonar data and basalt samples from the Mid-Ocean Ridge offshore the Azores will be compared with similar datasets from the Nankai Trough, Japan. We intend to investigate the physical and geochemical processes occurring in the two regions by comparing and contrasting the petrography, geochemistry and isotope signatures of hydrothermal minerals in selected samples from offshore Japan and the Azores. Using selected geophysical data and rock samples, we intend to investigate the processes behind any contrasts in mineralogy, isotopic and geochemical signatures in the two regions; Nankai being influenced by fluid circulation derived from the continental crust, and the Azores Islands comprising an isolated mid-ocean region.

Training

The University and Department provide an extensive skills training course for postgraduate students, including computing, bibliographic work, scientific writing, entrepreneurial skills and scientific ethics. The prospective student will also learn key principles in statistical and data analysis in geology. The student will present work at Departmental seminars, and national and international conferences, and to report it in journal papers. The student will join a vibrant research community with enormous scope for cross-disciplinary interaction with colleagues working on related generic and regional geological issues. Applicants are welcomed from any Earth Sciences discipline. Prior knowledge of geophysics and igneous petrography is not required, but it would be beneficial. Training will be provided in seismic interpretation using Unix workstations and state-of-the-art PCs. Cardiff houses one of the most advanced seismic interpretation laboratories in Europe and the student will have access to leading edge computational facilities.

Wider implications

The two study areas, Nankai and Azores, comprise some of the most important hydrothermal systems in the world. They are both known for their tectonic activity, seismicity and significant fluid exchange between the deep lithosphere and the ocean. This study will have wider implications to our present knowledge on how significant are fluid exchanges between continental and oceanic crust, and between oceanic crust and the overlying sediment.