Basalt Pore Genesis and Its Effects on Hydro-physical Properties

The complex pore topology of basaltic rocks leads to a wide range of hydro-physical properties that affect subsurface processes, from hydrothermal circulation to marine geochemistry. Magma viscosity regulates the coexisting processes that give rise to the pore network topologies: gas diffusion into bubbles, film drainage between bubbles, coalescence and post‑coalescence relaxation, and bubble migration. In this study, we integrate datasets gathered for igneous rocks worldwide with numerical experiments to investigate genesis-dependent pore architectures on two key reactive transport properties: permeability and fluid accessible surface area. Pore size polydispersity and inter-pore overlap—arising from coalescence without relaxation—increase the porosity at percolation, i.e., the threshold for the onset of permeability in basaltic rocks. At high porosity and far from percolation, permeability is governed by the mean pore size and the extent of pore overlap, which together determine pore throat size and flow constriction. Below the percolation threshold, SEM images indicate that permeability in dense, low-porosity extrusive igneous rocks (Φ ≲ 0.3) is primarily controlled by microfractures. Reactive surface area scales linearly with connected porosity and is inversely proportional to mean pore size; pore size polydispersity and inter-pore overlap exert only minor influence on the accessible specific surface area. Our numerical experiments reproduce observed porosity–permeability trends in natural systems and serve as a predictive framework for subsurface processes that involve advective–reactive flow in igneous rocks, such as CO2 mineralization.