Intellectual Merit. This Accomplishment Based Renewal of the investigator's ongoing studies of Lau Basin will make use of gravity data, magnetic data and bathymetry to model the variations in thickness of the ocean crust for the Western Lau Spreading Center in the western Pacific. The project will also include efforts to identify lineations in seafloor magnetization, and to use these as well as the gravity and magnetics models to study the early evolution of Lau Basin. The Western Lau Spreading Center is older than Central and Eastern Lau Spreading Centers, and existing models suggest that it formed through tectonic rifting prior to the inception of active seafloor spreading. The central emphasis of this project is to question this origin for WLSC, pointing out that bathymetric data indicates that western basin morphologies are similar to those of the active Central and Eastern Lau Spreading Centers. At these newer centers, current understanding suggests that bathymetry and rock chemistry is determined strongly by proximity to the back-arc. CLSC is furthest from the back-arc, and is most mid-ocean ridge-like, whereas ELSC is nearest the arc and shows a gradient in rock types, ranging from basaltic to the north at points furthest from the back-arc, to andesitic to the south at points closest to the arc. Seafloor bathymetry also transitions along this transect, from deeper Mid Ocean Ridge-like (3000 m) to shallower (~1600m). There is also a preponderance of seismic magma lens reflectors as one moves closer to the arc and crustal thicknesses increase, whereas these are largely absent to the north. Given this backdrop, the question arises: Did the Western Lau basin morphology arise as the basin formed by changes in magmatic productivity of spreading centers as they migrated over a mantle wedge of variable composition? This is in contrast to the existing view of a purely tectonic rifting model for the formation of the Western Lau basin. The question may also be inverted to address the issue of how changes in crustal composition and other characteristics might provide information on the spatial patterns and the nature of the compositional variations in the mantle wedge. For instance, the release of volatiles and water into the mantle through subduction-related transport lowers mantle solidus temperatures, and should lead to production of a greater quantity of melt than expected for a dehydrated mantle.
Broader impacts. Broader Impacts include research and training experiences for a graduate student, and fundamental insights into crustal formation processes of wider interest both to Ridge 2000 and Margins communities.
