Abstract

The well-known observation that permeability tends to decrease with depth has been invoked to explain and/or model the effects of fluid and heat flow within numerous societally relevant geological processes. However, this study finds that continental large igneous provinces may deviate from the classical permeability decay trend. We compile a new permeability database for the Columbia River Basalt Group (CRBG), United States, and show that average CRBG permeability (1) exhibits little depth dependence between 0 and 500 m; (2) systematically decays between ∼500 and 950 m depth; and (3) increases by 1.5 orders of magnitude between 950 and 1450 m depth. Further analysis indicates that CRBG permeability is spatially correlated with a 5:1 horizontal anisotropy ratio, and the direction of maximum horizontal spatial correlation is parallel to the longitudinal axis of the bedrock depression underlying the CRBG. To explain these observations, we hypothesize that rapid CRBG emplacement and subsequent lithospheric subsidence induces bending moment stresses within the CRBG that result in spatially correlated permeability at regional scales and increasing permeability at depth. Because continental large igneous provinces (LIPs) are characterized by rapid emplacement and subsequent subsidence, this study implies that that bending moment stresses may be a characteristic feature affecting the permeability structure of continental LIPs.

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