Neogene Fault and Feeder Dike Patterns in the Western Ross Sea

In Antarctica, where much of the continent is covered by water and ice, geophysical data from the Antarctic submarine continental shelf is a fundamental part of reconstructing geological history. Multibeam sonar from the western Ross Sea has revealed elongate volcanic edifices and fields of elongate submarine hills on the seafloor. Origin of the submarine hills as carbonate mounds and drumlins have been proposed. The hills are up to ~8000m long and ~3500m wide, and rise 50-100m above the seafloor. Morphometric analysis of the hills shows they are elongate, with axial ratios ranging from 1.2:1 to 2:1, and some hills are linked to form elongate ridges. Seismic profiles show significant pull-ups directly below the hills, consistent with narrow, higher-density magmatic bodies; thus we favor an origin as volcanic seamounts above subsurface feeder dikes. If this volcanic hypothesis is correct, feeder dikes below the hills and elongate volcanic ridges may document magmatically-forced extension within the Terror Rift. The seamount field forms part of a regional en echelon array of volcanic ridges extending NNW from Beaufort Island toward Drygalski Ice Tongue. The ridges and elongate seamount cluster trend NNE, subparallel to mapped fault trends in this sector of the Terror Rift. This geometry is compatible with right-lateral transtension along this zone, as previously proposed for the Terror Rift as a whole. Volcanic islands and dredged volcanic ridges within the en echelon array are dated at ~7-4 Ma, implying Neogene deformation. We are completing a detailed analysis of orientation patterns and cross-cutting relations between faults and volcanic hills and their feeder systems to test this model for Neogene rift kinematics.