TEMPORAL VARIATIONS OF THE OLDEST EMPEROR-HAWAIIAN PLUME SIGNATURE INFLUENCED BY INTERACTIONS BETWEEN BOTH DEEP AND SHALLOW MANTLE SOURCES

The Emperor-Hawaii plume is one of the most extensively studied large mantle plumes active today. Although numerous petrological, geophysical and geochemical studies exist for the Hawaiian Islands (i.e., those <~ 6 Ma), much less is known about the ancestral Hawaii plume—the Emperor Seamount chain. Here we present trace element and Sr-Nd-Pb-Hf isotope data for samples from seamounts along the length of the Emperor Seamount chain ranging from > 80 Ma (Meijii and Detroit Seamounts) to ~50 Ma (Koko Seamount), i.e., near the change in orientation of the Hawaii-Emperor plume track at ~ 47 Ma. Isotopic data form linear arrays in Hf-Nd and Sr-Nd isotope space that suggest involvement of at least two, and probably three, distinct mantle end members in the source of the Emperor lavas. The enriched component predominates in the younger seamounts and their compositions form trends that extend toward the field of Kea-trend Hawaiian volcanics today, although most do not overlap the Kea field. The depleted component is most prominent in the older Detroit Seamount (~ 80 Ma), which exhibits a range in εNd similar to that of MORB. Some Detroit volcanics, however, are distinguished from MORB by their higher εHf value for a given εNd, suggesting involvement of a depleted component with a distinct high εHf composition. Plate reconstruction models show that a major ridge jump at ~ 83 Ma brought the spreading center separating the Pacific and Kula plates in close proximity to the location of the Emperor plume when Detroit volcanism was active, facilitating melting of a high εHf depleted sheath surrounding the plume. We will also present new data on the backtracked locations of the Emperor Seamounts, i.e., the position of the deep mantle that would have been directly beneath the seamount at its time of emplacement, to assess whether proximity to the Pacific Large Low Shear Velocity Province (LLSVP) has an observable impact on the composition of volcanism along the Emperor portion of the chain as has been proposed for the younger Hawaiian Islands.