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

Abstract

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.

Hydrothermal Models Constrained by Fine‐Scale Seismic Velocities Confirm Hydrothermal Cooling of 7–63 Ma South Atlantic Crust

“…Techniques of seismic velocity analysis have evolved over time, with computationally expensive methods such as full-waveform inversion (FWI) becoming increasingly common, resulting in higher resolution velocity images. For example, Arnulf et al (2014) imaged subsurface features beneath a submarine volcano and Marjanović et al (2019) investigated the fine-scale permeability at a mid-ocean spreading center. However, to better understand the detailed nature of fluid and heat flow in oceanic crust and to potentially reconcile conflicting observations, it is important to address the issue by integrating multiple techniques.…”

“…(2014) imaged subsurface features beneath a submarine volcano and Marjanović et al. (2019) investigated the fine‐scale permeability at a mid‐ocean spreading center. However, to better understand the detailed nature of fluid and heat flow in oceanic crust and to potentially reconcile conflicting observations, it is important to address the issue by integrating multiple techniques.…”

“…Marjanović et al. (2019) integrate high‐resolution seismic velocity distributions, poroelastic response measurements, and numerical modeling to constrain upper crustal permeability and hydrothermal fluid flow at the East Pacific Rise. We use a similar approach for older crust in the western South Atlantic, while additionally computing conductive and advective heat fluxes at the seafloor.…”

“…Numerous studies have attempted to constrain the geometry of hydrothermal systems at mid‐ocean ridges using direct observations, borehole data, geophysical methods, analyses of ophiolites, and numerical models (e.g., Alt et al., 1986; Baker et al., 2016; Hasenclever et al., 2014; Mittelstaedt et al., 2012; Nicolas et al., 2003; Tolstoy et al., 2008). Recent advances have also been made in quantifying crustal permeability, which is an essential controlling factor for hydrothermal fluid flow (Barreyre & Sohn, 2017; Marjanović et al., 2019). Few hydrothermal studies have focused on older crust because the tectonic and thermal processes are less vigorous than at the spreading centers and thus more difficult to detect.…”

Tectonic Activity Near the Rio Grande Rise Increases Fluid Flux in Old Oceanic Crust

“…Gray line shows all data points; red line shows a 5 km moving average. largest interpreted faults are associated with local porosities (∼15%) and permeabilities (∼1 × 10 −12 m 2 ) typical of newly formed upper crust at midocean ridges (Barreyre & Sohn, 2017;Barreyre et al, 2018;Marjanović et al, 2019) rather than more mature upper crust (Carlson, 2010(Carlson, , 2011Fisher & Becker, 2000).…”