SHIELD THROUGH REJUVENATED VOLCANISM OF A KEA-TREND VOLCANO AND THE CONTRIBUTION OF THE UPPER ASTHENOSPHERE TO <0.6 MA REJUVENATED HAWAIIAN MAGMAS

Within the Hawaiian Island Chain, the parallel Kea and Loa volcano trends have geochemical differences in shield compositions. Additionally, rejuvenated stage volcanism on both Kea and Loa trend islands have a long-lived depleted component, thus requiring numerous sources sampled during the evolution of Hawaiian volcanos. The shield of the West Maui volcano, at <1.2 Ma, is the youngest Hawaiian volcano to experience shield through rejuvenated volcanism, providing an excellent opportunity to observe source heterogeneities of a Kea-trend volcano. We present new major and trace element geochemistry and Sr-Nd-Pb-Hf isotope data from West Maui postshield and rejuvenated stage lavas to characterize the temporal changes in the source of a Kea-trend volcano and the Hawaiian plume geodynamics associated with rejuvenated melting. The West Maui postshield erupted highly evolved lavas (benmoreite to trachyte) that overlap in age with the end of shield stage tholeiites. These lavas are enriched in incompatible elements (La_N/Yb_N = 5.8 – 18.4) and have isotopic signatures that overlap with the youngest Mauna Kea and Kilauea shield lavas, suggesting a homogeneous source for Kea trend volcanoes. The West Maui postshield and late shield/postshield lavas of East Moloka’i, however, trend towards the highest ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb values of West Maui and other Kea-type shield lavas, suggesting these lower degree, alkaline melts sourced less depleted material at the end of shield building. Like other islands, the West Maui rejuvenated stage is geochemically characterized by high εNd and low ⁸⁷Sr/⁸⁶Sr relative to shield lavas. West Maui rejuvenated lavas have low ²⁰⁸Pb/²⁰⁴Pb, but at relatively high ²⁰⁶Pb/²⁰⁴Pb and trend closest towards ~90Ma Pacific MORB of any rejuvenated stage. This is also the case for rejuvenated lavas of East Moloka’i, Kaua’i, and the North Arch Volcanic Field. Additionally, West Maui rejuvenated lavas have low εHf (+14 to +15) at a given εNd (+8 to +9) compared to Ni’ihau and Ka’ula that have higher εHf (+16 to +17) relative to εNd (+9 to +10), the latter requiring a long-lived, deep mantle source with high Lu/Hf. This implies rejuvenation in Kea-trend islands (West Maui and East Moloka’i), and the northernmost portions of the chain (Kaua’i and North Arch) geodynamically favor melting of the upper asthenosphere.