Volcanic and tectonic features on the seafloor provide one of the most readily accessible features of mid-ocean ridge crests that may provide detailed information on the 'state' of the underlying magmatic system (e.g., length scales of segmentation, geochemical heterogeneity between and within melt lenses, degrees of overpressure in magma bodies, stress conditions in the crust). The repose interval between eruptions, the volume of eruptions, the along- and across-axis extent of lava deposition, and the morphology and geochemistry of lavas, have been studied extensively at the EPR ISS, where we have benefited from observing a complete magmatic cycle culminating in the 2005-06 eruption. Comparable datasets are available for the Endeavor segment and the E. Lau spreading center.

The 2005-06 eruption of the EPR has provided a wealth of new information about how an individual magmatic event is manifest on the seafloor. Such information is crucial to understanding seafloor geologic features that integrate processes over 10s to 100s of such events. The along axis extent of the 2005-06 eruption was controlled by fine-scale segmentation of the ridge to a large degree, but in some cases extended through previously defined segment boundaries. In addition, the across-axis extents of the flows are variable, in some places reaching the edges of the neovolcanic zone and in others barely overtopping the AST [Soule et al., 2007]. The 2005-06 lava flows, which occurred at the predicted ~decadal repose interval for the EPR ISS, produced lavas at high-eruption rates generally, but with lower eruption rates towards the N. and S. ends of the eruption, presumably at segment boundaries [Fundis et al., 2010].  The eruptive vents within the AST resulted in remarkably little change to the dimensions of the trough, despite significant outpouring and accumulation of lava and possibly some amount of tectonic extension [Soule et al., 2009].

Of additional significance to the discussion of volcanic and tectonic processes at the ISSs are recent results (unpublished) from work I have conducted on the Mid-Atlantic Ridge where the style of volcanism (e.g., eruption rate and frequency) appears closely tied to the proximity to a centrally located mid-crustal magma body. Here the distribution of magma in the crust exhibits much sharper gradients than at most of the ISSs.

Based on observations from the ISSs and other MORs I am interested in exploring the following hypotheses and related questions linking seafloor geology and crustal magmatism:

1) Ridge crest morphology (in particular, axial summit troughs and axial valleys) reflects accumulated deformation due to magmatic dike injection balanced by varying degrees of volcanic accretion [e.g., Carbotte et al., 2006; Soule et al., 2009].

Does such a process include or preclude the occurrence of magmatic/tectonic cycles and at what time scale? What role does melt lens inflation/deflation play in shaping the ridge crest? What is the primary control on whether dike injection ultimately results in eruption on the seafloor and do those controlling parameters differ between ISSs, within ISSs, and between ridges of different spreading rate?

2) The style of eruption (low-eruption-rate, constructional volcanism vs. high-eruption rate, volcanic repaving) reflects the availability of melt in the crust and the proximity of eruptive vents to those melt sources. 

Does variability in eruptive style correlate with seismic imaging of melt distribution? Can we discern changes in melt supply through time by examination of the volcanic products? Is spreading rate an accurate predictor of volcanic processes or do local variations in melt supply and tectonic stress provide stronger controls?

There is an opportunity at this meeting to strengthen the link between seafloor geology and crustal-scale geophysical observations at all the ISSs, in order to evaluate and refine proposed models of ocean crust construction, in particular the link between volcanic accretion and melt supply/melt lens segmentation.

References:

Fundis, A.T., Soule, S.A., Fornari, D.J., Perfit, M.R. (2010) Paving the seafloor: volcanic emplacement processes during the 2005-06 eruptions at the fast spreading East Pacific Rise 9˚50'N, G-cubed, doi:10.1029/2010GC003058, in press.

Soule, S.A., Escartin, J., Fornari, D.J. (2009) A record of eruption and intrusion at a fast spreading ridge axis: axial summit trough of the East Pacific Rise at 9˚-10˚N, G-cubed, 10, doi:10.1029/2008GC002354.

Soule, S.A., Fornari, D.J., Perfit, M.R., Rubin, K.H. (2007) New insights into mid-ocean ridge volcanic processes from the 2005-2006 eruption of the East Pacific Rise, 9˚46'N-9˚56'N, Geology, 35, 1079-1082.

Carbotte, S.M, Detrick, R.S., Harding, A., Canales, J.P., et al. (2006) Rift topography linked to magmatism at the intermediate spreading Juan de Fuca Ridge, Geology, 34, 209-212.