North-south Variability in the History of Deformation and Fluid Venting across Hydrate Ridge, Cascadia Margin

Hydrate Ridge is an accretionary thrust ridge located on the lower slope of the central Cascadia convergent margin. Structural mapping using 2-D and 3-D multichannel seismic reflection profiles and gridded bathymetry coupled with deep towed sidescan sonar data and ODP drilling biostratigraphy, suggest that seafloor fluid venting patterns are likely controlled by the seaward vergent structural style at the older (>1.6-1.7 Ma) crest of northern Hydrate Ridge (NHR) and by the dominantly landward vergent structural style at the younger (1.7 Ma to recent) crest of southern Hydrate Ridge (SHR). North-south structural variability across Hydrate Ridge is manifested on the seafloor as aerially extensive authigenic carbonate crusts on NHR and a minor focused occurrence of authigenic carbonate on SHR. The older stratigraphy exposed at the seafloor at NHR has likely been subjected to a longer history of sediment compaction, dewatering, and deformation than the younger slope basin strata preserved at SHR, suggesting the extent of carbonates at NHR may result from a more intense history of fluid flow through a more uplifted, lithified, and fractured NHR sequence. Furthermore, instead of abundant fault and fracture conduits as at NHR, recent work at SHR shows that the major seafloor fluid venting site there is fed by fluid flow through a volcanic ash bearing turbidite sequence. These observations suggest, stratigraphic conduits for fluid flow may be important in less uplifted, landward vergent dominated portions of Hydrate Ridge. In addition, the variability in structural style observed at Hydrate Ridge may have implications for the distributions and concentrations of fluids and gas hydrates in other accretionary settings and play a role in the susceptibility of accretionary ridges to slope failure.