Mr. James Gaherty
Earth Institute Contact: Mr. James Gaherty
North Atlantic Ocean; Iceland Hotspot
Intellectual Merit. The Iceland hotspot fundamentally controls the geophysical and geochemical character of the adjacent Mid-Atlantic Ridge (MAR). This hotspot-ridge system offers an excellent opportunity to study the effect of an anomalous mantle source on melt generation and upper-mantle flow beneath a spreading center. Although the upper-mantle character of the Iceland hotspot is now relatively well studied [e.g., Wolfe et al., 1997, Allen et al., 1999], long-standing and fundamental questions remain about the nature of mantle flow and melt generation beneath the Reykjanes and Kolbeinsey Ridges and how they are affected by the hotspot. Models of ridge-hotspot interaction differ on how hotspot material is transported along the ridge. In one view, it is thought that the hotspot material is channeled down the ridge at shallow depth. In an opposing view, the plume expands at deeper levels in a radial manner from its source, without channeling. The importance of passive versus buoyant flow within the melt zone is also uncertain. These models predict distinct differences in the character of the partial-melt zone beneath the ridge, including its width, depth, and magnitude, and how these properties change with distance from the Iceland. They also predict differences in flow-induced mineral fabric within and beneath the Atlantic lithosphere. These models can be differentiated using accurate estimates of seismic velocities and anisotropy in the upper-mantle beneath and adjacent to the Reykjanes and other portions of the MAR.
This proposal has three overlapping seismological objectives that are motivated by our principle scientific goal to characterize the nature of mantle flow and melt supply beneath the Reykjanes and Kolbeinsey Ridges and to determine the influence of the Icelandic hotspot on the seafloor-spreading system. We propose to:
* Determine lithospheric thickness, thermal structure and melt distribution in the mantle and crust beneath the Reykjanes and Kolbeinsey Ridges through surface-wave analyses.
* Determine the nature of mantle upwelling beneath the Reykjanes and Kolbeinsey Ridges through surfacewave studies of seismic anisotropy.
* Evaluate the influence of Iceland on upwelling beneath these ridges by estimating fabric-induced anisotropy elsewhere in the Atlantic.
High quality data sets exist for our use, namely recordings of surface waves from broadband seismic stations located on Iceland, other Atlantic islands, and along the Atlantic margin, which are freely available from the IRIS DMC. At the heart of the dataset are seismograms from the MAR recorded by the ICEMELT and HOTSPOT experiments. These data provide surface-wave coverage of a hotspot-ridge region that is unsurpassed globally, and the proposed analyses greatly expand on the limited studies done to date.
Broader Impact. The proposed research will broadly impact the community by offering substantial undergraduate and graduate research opportunities at both Georgia Tech and Hawaii. New seismic imaging methods and resulting models will ultimately be distributed for use by others in the community, both via scientific publication and the PI's websites. The research furthers the return on previous data collection efforts funded by NSF. The results of the proposed work will have direct consequences for several NSF-sponsored programs including RIDGE, Ocean Mantle Dynamics, and MARGINS.
Cross Cutting Themes:
Climate and Society
National Science Foundation