Carson et al. (1994) reprocessed GLORIA sidescan sonar data (removing the effect of slope) to map the distribution of authigenic carbonates and gas hydrates in the Hydrate Ridge region. Their results suggest a nearly continuous distribution of diagenetic deposits at or near the seafloor surface across the western flank and southern summit of Hydrate Ridge. Recent higher resolution deep-towed data, groundtruthed with seafloor observations and sampling, are consistent with their early work and add additional coverage across all of Hydrate Ridge and the surrounding region (Johnson et al., 2003). On Hydrate Ridge, these new data show fluid venting manifestations at NHR are more extensive compared to those at SHR (Fig. F5). The observed north-south variability in the underlying structure and history of deformation of the ridge may explain this distribution.
Although the results from the structural mapping and ODP coring reveal the core of Hydrate Ridge (Zone I deformation) was likely accreted to the margin at the same time at both NHR and SHR, more uplift and erosion at NHR has resulted in the exposure of older stratigraphy (>1.7–1.6 Ma) at the seafloor. The existence of duplexed SV thrust faults beneath NHR (Fig. F4) has likely aided not only in its uplift but also in providing multiple deep fluid migration pathways to facilitate the massive fluid expulsion observed at the crest. NHR is also the only location in the Hydrate Ridge region that has undergone deformation through repeated SV wedge building events (Fig. F4). Duplexing is likely more prevalent in SV portions of the wedge in the Hydrate Ridge region than LV ones because the detachment for SV thrusts typically lies several hundred meters above the basement/cover contact (MacKay, 1995). In the SV case, a portion of the incoming abyssal plain section is allowed to be incorporated into the wedge through duplexing from below (resulting in substantial vertical thickening of the accretionary wedge above the basal décollement). In contrast, LV detachments in this region usually lie closer to the basement/cover contact (MacKay, 1995), virtually offscraping all of the incoming section and incorporating it into the wedge dominantly through lateral accretion. At SHR, duplexing is less pervasive, as shortening there during Zone I and II deformation was accommodated on both SV thrust faults and the LV thrust faults and folds west of the crest (Fig. F4). This mixing of structural styles presumably results in less net uplift at SHR. Less uplift at SHR has also helped to preserve the cap of younger slope basin sediments that are preserved there and absent from NHR.