A record of eruption and intrusion at a fast spreading ridge axis : axial summit trough of the East Pacific Rise at 9–10°N
Figure S1: SM2000 multibeam bathymetry over the AST at 9 degrees 50'N collected after the 2005–06 eruption [Soule et al., 2008] is gridded at 50-cm horizontal resolution. (1.487Mb)
Figure S2: Example of TowCam estimates of fault dip from a near-axis (600 m east of ridge axis at ~9 degrees 55′N) inward facing normal fault. (741.3Kb)
Figure S3: Example of TowCam estimates of fault dips crossing the AST (AT11-7_CT03 at ~9 degrees 50′N) shown at five times vertical exaggeration. (681.7Kb)
Figure S4: Example of TowCam estimates of fault dips crossing the AST (AT11-7_CT13 at ~9 degrees 32′N) shown at ten times vertical exaggeration. (716.8Kb)
Figure S5: Example of TowCam estimates of fault dips crossing the AST (AT11-10_CT13 at ~9 degrees 29′N) shown at two times vertical exaggeration. (575.8Kb)
Table S1: Picks of the AST boundary mapped from side-scan sonar data at 50 m intervals along the ridge axis. (62.11Kb)
Table S2: Picks of the AST centerline mapped from side-scan sonar data at 50 m intervals along the ridge axis. (31.26Kb)
Soule, Samuel A.
Fornari, Daniel J.
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High-resolution side-scan sonar, near-bottom multibeam bathymetry, and deep-sea photo and bathymetry traverses are used to map the axial summit trough (AST) at the East Pacific Rise between 9 and 10°N. We define three ridge axis morphologic types: no AST, narrow AST, and wide AST, which characterize distinct ridge crest domains spanning tens of kilometers along strike. Near-bottom observations, modeling of deformation above intruding dikes, and comparisons to the geologic and geophysical structure of the ridge crest are used to develop a revised model of AST genesis and evolution. This model helps constrain the record of intrusive and extrusive magmatism and styles of lava deposition along the ridge crest at time scales from hundreds to tens of thousands of years. The grabens in the narrow-AST domain (9°43′–53′N) are consistent with deformation above the most recent (<10) diking events beneath the ridge crest. Frequent high–effusion rate extrusive volcanism in this domain (several eruptions every ∼100 years) overprints near-axis deformation and maintains a consistent AST width. The most recent eruption at the ridge crest occurred in this area and did not significantly modify the physical characteristics of the AST. The grabens in the wide-AST domain (9°23′–43′N) originated with similar dimensions to the narrow AST. Spreading, driven primarily by the intrusion of shallow dikes within a narrow axial zone, causes the initial graben bounding faults to migrate away from the axis. Infrequent extrusive volcanism (several eruptions every ∼1000 years) fills a portion of the subsidence that accumulates over time but does not significantly modify the width of the AST. Outside of these domains, lower–effusion rate constructional volcanism without efficient drain-back fills and erases the signature of the AST. The relative frequency of intrusive versus extrusive magmatic events controls the morphology of the ridge crest and appears to remain constant over millennial time scales within the domains we have identified; however, over longer time scales (∼10–25 ka), domain-specific intrusive-to-extrusive ratios do not appear to be fixed in space, resulting in a fairly consistent volcanic accretion over the length scale of the second-order ridge segment between 9°N and 10°N.
Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q10T07, doi:10.1029/2008GC002354.