DSL120 Mosaics of Superfast EPR Crustal Layers Exposed by Ultraslow Spreading near Pito Deep

WHOI DSL-120 (120 kHz deep-towed) side-scan sonar data were collected in two study areas in an attempt to identify outcrops of exposed layers of superfast oceanic crust for detailed studies using submersible Alvin and ROV Jason-II. Each area is several kilometers long and span a depth range of about 1500 m. These areas represent southwest dipping normal faults on the Nazca plate side of Pito Deep, which is about 400 km to the northwest of Easter Island in the Southeast Pacific. The ~6 km Deep was formed by ultraslow seafloor spreading (~10 mm/yr) associated with a nearby pole of rotation of the northwestward propagating Pito Rift. The propagation and ultraslow seafloor spreading has primarily resulted in the formation of several major normal faults that have exposed superfast crustal layers. Direct observations, imaging, and sampling (using Alvin and Jason-II) along with earlier Nautile dive observations are used to interpret the side-scan sonar records. As described in a companion abstract, four major rock units were mapped: a pelagic sedimentary layer, basaltic layer, a sheeted diabase dike layer, and a gabbroic layer. The overall distribution of these layers and the transitions between the layers, their estimated thickness, continuity, and localized zones of faulting and deformation, will be summarized in a final interpretation map.