Rock‐Matrix Porosity and Permeability of the Hydrothermally Altered, Upper Oceanic Crust, Oman Ophiolite

Porosity and permeability are key controls on hydrothermal circulation alteration in magmatically heated upper oceanic crust. However, the hydraulic properties of basalts altered above 200°C largely unknown, leaving their role high-temperature systems unclear. Here, we assess rock-matrix porosities permeabilities pervasively MORB-like from outcrops sheeted dikes axial lavas Semail ophiolite, Oman. The samples represent regional spilite (chlorite–albite–quartz ± actinolite; 150–440°C) localized epidosite (epidote–quartz; 255–435°C). spilitized rocks vary as follows: interpillow hyaloclastites (14–27 vol.%, 10−17–10−15 m2) > pillow cores (4–12 vol.%; ∼10−19–6 × 10−18 rims (4–11 ∼10−19–2 massive sheet flows (1–9 ∼10−19 ≥ (1–5 m2). Pillow values fall within ranges existing data fresh low-temperature situ hyaloclastite 1–4 orders magnitude higher clearly preferred flow paths. Epidosites have elevated porosity irrespective rock morphology (18–26 ∼10−16–10−14 stacks upscaled (∼104 m3) matrix ∼9 vol.% ∼10−17–10−16 m2 when 16 up to ∼10−14 epidotized. Upscaled spilites meet minimum requirements for observed heat fluid discharge seafloor even without fracture networks, reflect strong through rock-matrix.