White Paper Title: 
Considering physical implications of petrological, geochemical, and seafloor morphology inferences on mantle heterogeneity and melting

Ridge 2000 studies of seafloor lava samples have produced petrological and geochemical results that have implications for mantle melting, scales of heterogeneity, and a sense of crustal magma distributions. Considering these results in light of existing mantle flow and melting models (10-200 km depths) may allow determination of the range of mantle physical parameters that would allow the observed scales of variability/delivery patterns.    In many cases, current models do not provide immediate tests, but discussions at this meeting should narrow the field of new numerical experiments that can produce predictions tied more directly to R2K data, such as the new results on H2O contents along the Lau spreading center. 2-D models of Lau mantle wedge flow that account for prescribed water content and distance between trench, arc and spreading center are available as a starting point for this ISS (Harmon and Blackman, accepted EPSL 2010). As results of the underway seismic imaging experiment along the ELSC become available, additional physical constraints can be combined with the current (and any future) geochemical constraints. Moving to a 3-D model will be key for more completely addressing system dynamics. Discussions at the workshop can guide the emphasis of the early 3-D numerical tests, where seismic anisotropy measurements will be linked to the flow modeling.

White papers on degassing and morphologic systematics in relation to mantle/melt properties also suggest an avenue to more closely tie seismic properties of the crust and uppermost mantle (2-15 km depths). Discussions during the workshop could focus on the quantitative measures already available in (active) seismic results from each ISS and whether there are additional steps with existing data that would bring this type of investigation to fruition. For example, what is the range of observed porosity variability along/across strike and in what depth intevals does it occur? How does this fit with degassing/compositional predictions?  Is there evidence for lower crustal/uppermost mantle structure (e.g complex Moho transition zone) that could contribute to some of the anisotropic signal that has been interpreted soley in terms of mantle flow pattern?

Finally, since my most active field work during the Ridge 2000 program up to now (about to change as the Lau OBSs are recovered this Fall!) has been at the Mid-Atlantic Ridge, I hope to bring recent perspectives on slow-spreading systems into our discussions at relevant points. If there are synthesis topics where a broader suite of spreading centers can be included, it could increase the impact of any integrative publications that are an outgrowth of the workshop.