Intraplate deformation of oceanic crust near the Rio Grande Rise in the South Atlantic

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

“…Combined with our FWI image (Figure 2a), these results signify that crust near the RGR hosts levels of tectonic and hydrologic activity that are extraordinarily high for oceanic crust older than 65 Ma, which is generally thought to neither host sustained tectonic activity nor fluid exchange with the ocean (Johnson & Pruis, 2003;Stein & Stein, 1994). Estep et al (2020) imaged numerous extensional faults within the sedimentary cover along the same seismic line whose data we inverted for seismic velocity (Figure 2). Seafloor and shallow sediment offset along some of these faults served as evidence for recent extensional strain.…”

“…Figure 2 shows our FWI velocity model along with the associated uncertainty distribution. The FWI model includes several vertically elongated low-velocity zones in the upper crust, many of which (solid black lines) appear to link up with depth-converted fault interpretations previously made in the sedimentary section (white lines; Estep et al, 2020). We therefore interpret these anomalies as expressions of extensional crustal faults and let the sedimentary fault orientations guide our interpretations.…”

“…Recent acquisition of active-source seismic data at the eastern flank of the RGR offers an excellent opportunity to explore intraplate deformation and its effect on subsurface processes. Analyses of seismic images have already revealed a detailed distribution of extensional faults and their relative timing in the sediment section (Estep et al, 2020). Here, we present a combination of full-waveform inversion (FWI) seismic velocity and numerical hydrothermal models, providing evidence for large intraplate fault zones within ∼68 Ma upper oceanic crust, which elevate fluid fluxes adjacent to the RGR.…”

“…The Rio Grande Rise (RGR; Figure 1), an oceanic plateau formed in the late Cretaceous in the South Atlantic (Camboa & Rabinowitz, 1984;Ussami et al, 2013), appears to cause substantial intraplate deformation in its vicinity (Estep et al, 2020). This deformation has been attributed to the increased thickness and heat budget of RGR lithosphere, causing it to subside slower than the surrounding "normal" oceanic lithosphere since its formation.…”

“…The formation of oceanic plateaus and seamounts perturbs the seafloor and deforms the crust over short geologic timespans; these bathymetric features are generally not linked to sustained tectonic activity. However, recent seismic imaging has revealed large-offset extensional faults at the fringes of oceanic plateaus (Estep et al, 2020;Zhang et al, 2015Zhang et al, , 2016, some of which may have been active relatively recently due to ongoing differential subsidence between normal and thickened ocean lithosphere.…”