PhD Research Summary
My PhD investigated how seawater moves through the upper oceanic crust, and what that means for ore formation and regional recharge and discharge pathways in the upper crust. Working in the spectacular exposures of the Semail ophiolite in Oman, I mapped and sampled basalts altered by hydrothermal fluids, then combined new porosity and permeability measurements, high-pressure lab experiments, structural and hydrothermal mapping and fracture-network modelling to build a picture of how fluid pathways evolve from centimetre to kilometre scales.
Three papers came out of this body of PhD work thus far, with one in preparation:
Rock-Matrix Porosity and Permeability of the Hydrothermally Altered, Upper Oceanic Crust, Oman Ophiolite
Alannah C. Brett-Adams, Larryn W. Diamond, Samuel Weber, Samuel A. Gilgen. Journal of Geophysical Research: Solid Earth, 2023.
A database of porosity and permeability measurements across altered basalts, comparing widespread spilite alteration against localised epidosite alteration — epidotisation substantially increases both porosity and permeability.
Influence of in-situ temperatures and pressures on the permeability of hydrothermally altered basalts in the oceanic crust
Brett-Adams et al. Tectonophysics, 2021, vol. 815, article 228994.
First measurements of how permeability of spilites and epidosites changes under realistic in-situ pressure and temperature conditions.
Reaction Mechanism and Water/Rock Ratios Involved in Epidosite Alteration of the Oceanic Crust
Samuel Weber, Larryn W. Diamond, Peter Alt-Epping, Alannah C. Brett-Adams. Journal of Geophysical Research: Solid Earth, 126(6), 2021.
Shows the spilite-to-epidosite reaction requires enormous water/rock ratios, implying vast volumes of hydrothermal fluid flowed through each cubic kilometre of precursor rock.