Investigating Fine‐Scale Permeability Structure and Its Control on Hydrothermal Activity Along a Fast‐Spreading Ridge (the East Pacific Rise, 9°43′–53′N) Using Seismic Velocity, Poroelastic Response, and Numerical Modeling

Milena Marjanović (1) , Thibaut Barreyre (2) , Fabrice Fontaine (1) , Javier Escartin (1)

1 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
2 UiB - Department of Earth Science [Bergen]

Along with the intracrustal heat source, crustal permeability is considered as the controlling factor for hydrothermal circulation within zero-age oceanic crust. To obtain fine-scale, 2-D models of upper crustal permeability along the East Pacific Rise 9°50′N, known for prolific hydrothermal activity, we use recently derived high-resolution seismic velocity and examine a number of the existing velocity-permeability relationships. To constrain our preferred permeability model, we compare thus derived permeability models with collocated permeability estimates from poroelastic response to tidal loading at L-vent. Furthermore, using the preferred permeability result, we model hydrothermal convection in 2-D and find that the distributions of recharge and discharge zones are in good agreement with seafloor observations, including locations of the vent fields. Our results suggest that seismic velocities can be used as a tool for deriving spatial variation of permeability, which must be considered in modeling of hydrothermal flow. Plain Language Summary Crustal permeability represents one of the main controlling factors for development and persistence of hydrothermal circulation at mid-ocean ridges. However, this parameter remains poorly constrained. Using recently obtained seismic velocity model and available velocity-permeability relationships, we calculate a number of permeability models for East Pacific Rise 9°50′ N region, known for vigorous venting sites, including L-vent. To narrow down a wide range of upper crustal permeabilities and constrain our preferred permeability model, we use measurements obtained from poroelastic response of crustal lithologies to tides at L-vent. Our results suggest that average permeability for the first~100 m of the upper oceanic crust is 10 −11.2 m 2 , whereas 10 −14 m 2 characterizes the remaining part. We further evaluate our results with numerical models of hydrothermal circulation. The model that uses our preferred permeability field predicts locations of hydrothermal fluid recharge and discharge zones that are consistent with seafloor observations. Our study suggests that a growing number of high-resolution seismic velocity models can be further used to provide first-order estimates of permeability that will help us to advance our understanding behind hydrothermal processes, fluid circulation, and associated exchanges along mid-ocean ridges.

Domaines: Géophysique [physics.geo-ph]

Milena Marjanović, Thibaut Barreyre, Fabrice Fontaine, Javier Escartin. Investigating Fine‐Scale Permeability Structure and Its Control on Hydrothermal Activity Along a Fast‐Spreading Ridge (the East Pacific Rise, 9°43′–53′N) Using Seismic Velocity, Poroelastic Response, and Numerical Modeling. Geophysical Research Letters, 2019, 46 (21), pp.11799-11810. ⟨10.1029/2019GL084040⟩. ⟨hal-02352659⟩