Recent eruptions on the CoAxial segment of the Juan de Fuca Ridge: Implications for mid-ocean ridge accretion processes

The 1993 seismic swarm and volcanic eruption on the CoAxial segment of the Juan de Fuca Ridge was the first verified mid-ocean ridge accretion event m onitored by the National Oceanic and Atmospheric Administration/U.S. Navy S ound Surveillance System (SOSUS). Ambiguity in the location of the initial seismicity resulted in an uncertainty as to whether the dike intruded from the summit and north rift zone of the adjacent Axial Volcano or whether it arose locally within the CoAxial segment. However, analyses of multibeam, s ide-scan sonar, towed camera, submersible, and geochemical data show that t he CoAxial segment is morphologically, structurally, and geochemically dist inct from the north rift zone of Axial Volcano. There is no geologic or geo chemical evidence that dike injections from Axial Volcano have extended nor th of 46 degrees 18'N in the past, whereas the 1993 eruption site is at 46 degrees 31'N. Furthermore, all seafloor manifestations of the 1993 dike inj ection lie along the central neovolcanic zone of the CoAxial segment. Analy ses of repeat SeaBeam surveys combined with seafloor observations show that two other eruptions of approximately the same volume as the 1993 eruption occurred along the CoAxial segment in the 1981-1991 interval. These three d iking events may have relieved decades of accumulated stress over similar t o 35 km or more of this segment. The spatial pattern and hydrothermal histo ry of the 1993 event is consistent with a dike with a significant lateral c omponent of injection.