Allison Fundis 1, Adam Soule 2, Dan Fornari 2, Michael Perfit 3

1 University of Washington, School of Oceanography

2 Woods Hole Oceanographic Institution, Department of Geology

3 University of Florida, Department of Geological Sciences

In order to understand the physical expressions of MOR events at various scales and thus the linkages between seafloor geology and crustal magmatism, it is important to be able to identify and study individual eruptions. By investigating lava morphologic characteristics associated with seafloor volcanic eruptions in conjunction with the geochemistry of the individual flows, we can begin to better understand how and why (i.e., erupted volumes, effusion rates, eruption processes and dynamics) they vary between MOR sites and ridge segments.

The 2005-2006 eruption at the EPR ISS marked the first observed repeat eruption at a mid-ocean ridge and provided a unique opportunity to deduce the emplacement dynamics of submarine lava flows.  Seafloor photography and high-resolution bathymetric profiles from deep-towed camera surveys have been used to produce a geologic map of the volcanic features associated with this eruption near 950N. Our analysis of the distribution of lava flow morphologies emplaced during 2005-2006 shows that seafloor lava morphology is primarily controlled by eruption rates at the vent and their variability along axis and with time. We also show that the dynamics of the 2005-2006 eruptions were substantially different than previous eruptions along this segment of the EPR.

In addition to our investigation of the geology of the 2005-2006 flows, we have also conducted geochemical analyses of basalts sampled by a ROV along the walls and floor of a flow channel created during the eruption. Our analyses show that despite the distance the flow covered (~3 km), little crystallization or chemical fractionation occurred – hence little cooling, which agrees with the rapid extrusion rates inferred from the surface morphology. This suggests that for rapidly emplaced axial-derived flows, post-eruptive crystal fractionation at fast-spreading MORs is not a prevalent petrogenetic process and is not responsible for geochemical heterogeneity on the crestal plateau. Other possibilities for creating across-axis geochemical heterogeneity include temporal variation in magma petrogenesis or off-axis eruptions sourced from distinct magma bodies.

Our study can be integrated and compared with data collected at other ISS and MOR sites in general, particularly where individual eruptions have been identified (i.e., Southern East Pacific Rise, Juan de Fuca Ridge, and Lau Spreading Center), to examine the primary controls on volcanic deposition at different sites and within the same sites over time.