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

Oceanic plateau crust is thicker and hotter than the surrounding "normal" oceanic crust, causing differential subsidence and subsequent strain between the two domains. Here, we show that recently active sedimentary faults that have been imaged adjacent to the Rio Grande Rise, an oceanic plateau in the western South Atlantic, have extensions that can penetrate at least ∼1.5 km into the upper oceanic crust. Our high‐resolution seismic velocity model indicates that these fault zones significantly reduce seismic velocities and increase inferred porosity and permeability. We also present physical property‐constrained fluid flow models that predict substantially increased fluxes along these pathways compared to crust not affected by faulting. As these phenomena are effectively enabled by the proximity of an oceanic plateau, we suggest that similar geologic settings globally may also exhibit elevated levels of tectonic and hydrothermal activity, with implications for the hydration of mature oceanic crust and the oceanic crustal biosphere. Plain Language Summary: Oceanic crust slowly sinks as it cools after its formation at midocean spreading centers, but it does so more slowly than usual at oceanic plateaus, where anomalous magmatism has left it relatively thick and buoyant. The different rates of sinking can induce faults that rupture the transitionary crust between the plateau and the surrounding oceanic crust. The Rio Grande Rise, located in the western South Atlantic Ocean, is an oceanic plateau at whose fringes recently active faults have been imaged in the sediments that cover the crust. We trace those faults at least 1.5 km deep into the crust and provide additional evidence for recent fault activity. We also show that fluids likely flow along those pathways, spilling into the ocean in much larger volumes than in normal oceanic crust. Faulting and associated fluid flow is likely also very active in crust bordering other oceanic plateaus globally, affecting the composition of the crust and the habitat of living organisms. We estimate the affected area to make up close to 10% of all oceanic crust on Earth. Key Points: Recently, active extensional faults adjacent to the Rio Grande Rise penetrate at least ∼1.5 km into the crustThe imaged faults significantly increase fluid circulation within the upper crust and fluid exchange with the oceanCrust adjacent to oceanic plateaus and other major bathymetric features may release an estimated 43 km3 of fluid into the oceans globally [ABSTRACT FROM AUTHOR]