Isotopic evolution of Mauna Loa and the chemical structure of the Hawaiianplume

New He isotopic data from the HSDP pilot hole core, lava accumulation rate models, and data from the literature are used to develop a 200,000 year iso topic record for the lava erupted from the Mauna Loa volcano. This record, coupled with an analogous record from Mauna Kea from the Hawaii Scientific Drilling Project (HSDP) pilot hole project and other literature data from t he GEOROC database, are used to construct a "map" of lava isotopic composit ions for the island of Hawaii. The isotopic map is converted to a map of th e He and Nd isotopic compositions of melts from the mantle plume, which can be compared with a published melt supply map derived from geodynamic model ing. The resulting map of the plume indicates that values of helium He-3/He -4 > 20 Ra are confined to the core of the plume (radius approximate to 20- 25 km) and correspond to potential temperatures >1565 degreesC, suggesting the He isotopic signal is derived from deep in the mantle. The He-3/He-4 ma p has closed contours down to 10 Ra; the contours are teardrop-shaped and e longated in the general direction of plate motion. The closed contours indi cate that most of the plume He signal is lost during the early stages of me lting, which is consistent with helium behaving as a strongly incompatible element (K-He less than or equal to 0.001). The epsilon (Nd) contours (and by inference the contours for Sr, Pb, Hf, and Os) do not all close on the s cale of the island of Hawaii but instead partially follow material flow lin es within the plume beneath the lithosphere. The plume signal for Nd extend s circa 100 km in the direction of plate motion, which is consistent with t he moderately incompatible behavior of Nd (K-Nd approximate to 0.02). Downs tream from the plume core epicenter, plume Nd occurs with asthenospheric He ; this could be mistaken for an additional plume component, whereas it may be only a manifestation of differing incompatibility. Data from Mauna Loa s uggest the presence of a low-He-3/He-4 plume component that has low epsilon (Nd) and high Sr-87/Sr-86. The plume map suggests that this component may be a blob (circa 20 km scale), located between Mauna Loa and Hualalai and s eparated from the main plume core by a zone of more asthenosphere-like mate rial. The HSDP data preclude a proposed model where this material represent s a ring of entrained material from the lower mantle. The orientation of th e elongation of contours on the plume He and Nd isotope maps (similar to N4 5 degreesW) does not match the modern plate motion as measured by GPS (N65 degreesW) nor does it match the trend of the ridge axis between Maui and Lo ihi (N30 degreesW). The geochemical evidence, as well as the locations and growth histories of the Hawaiian volcanoes, suggest that the plume, as well as the Pacific plate, has been moving at a velocity of several centimeters per year over the past 1 to 2 million years.