Mapping Volcanic Terrain at the East Pacific Rise 9° 28’-55’N

D.J. Fornari¹*, S.A. Soule¹, J. Escartin², M.R. Perfit³, A. Fundis³, & M. Tivey¹

Corresponding author: dfornari@whoi.edu
¹Woods Hole Oceanographic Institution, Geology & Geophysics Dept. Woods Hole, MA 02543
²CNRS & Institut de Physique du Globe de Paris, Paris Cedex05, France
³University of Florida, Dept. of Geological Sciences, Gainesville, FL 32611

Abstract:
We have mapped the volcanic and tectonic features of the East Pacific Rise (EPR) crestal terrain to ~4 km on either side of the EPR axis over a ~ 50 km-long section of this fast-spreading ridge using high-resolution DSL-120 sidescan sonar imagery. Prominent flow-fronts displayed in the sonar imagery and cross-cutting relationships between acoustic facies are used to estimate relative ages between the flows and faulting, in order to produce a geological map of the terrain. Alvin observations and TowCam imagery are used to ground truth specific seafloor features as well as their relative ages. Lava channels, many extending directly from one margin of the axial summit trough (AST), provide clues to relative ages between flows. Some older lava channels, buried by flows proximal to the AST are also observed and suggest this type of distribution mechanism is common for extending flows across the summit plateau and building layer 2. Most deformation structures are efficiently buried by the lava emplacement near the AST. In some cases, tectonic features, notably small throw normal faultswithin 1-2 km of the AST have dammed flows or channeled them along axis until the faults terminated or the flows were able to overtop the fault and continue to flow away from the axis. We plan to continue to complete our mapping work this fall and produce a geological map of the recent ~0-40ka volcanic history of this section of the EPR.

Contributions to Integration and Synthesis:
Detailed geological maps of the EPR ISS that portray both the relationships between volcanic features and their context within the tectonic framework of the axial terrain and locations of hydrothermal vent sites are key to properly understanding how the EPR has evolved morphologically and structurally over the past ~40ka. Specifically the maps help to establish relationships between volcanic flows, the AST and relative location of vent sites within the AST and along its margin. These data can help to establish conceptual models of hydrothermal circulation and how they are influenced by the volcanic and tectonic features, by extrapolating the spatial relationships and variations between volcanic features into the shallow crust.