SGER: Detailed Lava Surface Age Map and Pre-eruptive Magma Aging for the 2005-6 Volcanic Eruption at 9 46'-9 56'N EPR

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Abstract Observations made during NSF-funded rapid response expeditions to the East Pacific Rise 9N Integrated Studies Site of the Ridge2000 Program confirmed that one or more volcanic eruptions had taken place shortly before the expeditions of May and June, 2006. This is an ideal locale to attempt the first ever detailed lava surface age map from a deep submarine eruption. The collected rapid response effort included NSF funds to initiate a lava dating study using 210Po-210Pb radioactive disequilibrium. The rapid decay timescale (half life=138 days) allows for very high temporal resolution of lava ages if work is begun soon after a suspected eruption. The age resolution is diminished the longer one waits to initiate analyses since the natural, eruption-induced radioactive signature decays away in ~2 years. The present project will enable a large-scale dating study of what is now thought to be a multi-phase eruption during which a compound lava flow was emplaced over ~18 km of ridge axis and surrounding near-axis terrain. The work will provide nearly four times as many high resolution lava flow ages as any of five prior studies (and nearly twice as many as all of those studies combined). The project tests the hypothesis that this eruption occurred in stages, with attendant affects for heat and material flow through the crust, and that this will be reflected in discernable age difference in geographic sub-domains within the lava flow field. Furthermore, the similarity of 2005-2006 eruptives to those erupted in 1991-92 in this area suggests that much of the same magma was involved, which we can test for here. The dating has 2 components:a) 210Po-210Pb eruption dates on 10 Alvin-submersible-collected, spatially well-distributed lava samples. Along with the 6 samples funded with the prior SGER, this data will reveal details of the eruption sequence, feeding directly into on-going studies of lava emplacement and responses in local hydrothermalism and ecology by multiple research teams. The transformative potential of a high density lava flow surface age map caused the PI to begin dating analyses on all of the samples as soon as possible after collection (i.e., during the summer-fall of 2006), to obtain the highest possible age resolution with the hope that additional research funds would be forthcoming.b) 210Pb-226Ra radioactive disequilibrium dating of pre-eruptive magma age on 10-11 samples to determine the relative proportion of new and 1991-92 magma in the sub-ridge axial magma reservoir just prior to this eruption. This method also requires 230Th-238U-232Th analyses in the lavas. This component of the research is higher-risk as it proposes to use a newly discovered radioactive signature in mid-ocean ridge basalts in a new fashion, made possible by the uniquely documented repeat volcanism at this site. Coupled with underway lava volume estimate and lava composition studies by other collaborating investigators, we hope to estimate magma and heat fluxes into the melt reservoir before this eruption.Broader impacts This research addresses main goals of the of the Time Critical Studies and EPR Integrated Studies Site (ISS) components of the RIDGE2000 program and provides important, integrative data to other researchers studying the geology, geophysics and seismology, biology, and hydrology of the ISS; it also involves Postdoc training. Finally, the PI is involved in an Education and Outreach project in collaboration with the R2K office staff on submarine eruption forensics and related stories for their website as part of this project.