Does Kamaʻehu Volcano Sample a "Kea" or "Loa" Mantle Source Within the Hawaiian Plume?

Kamaʻehu Volcano (formerly Lōʻihi Seamount) lies along the geographical "Loa" (western) trend of Hawaiian volcanoes that includes Mauna Loa. Basalts from Kamaʻehu are thought to tap a Loa-type mantle source within the Hawaiian plume based on their relatively high 208Pb/204Pb ratios at a given 206Pb/204Pb (e.g., Abouchami et al., 2005; Weis et al., 2011). Here, we present new Pb-Sr-Nd isotope ratios and trace element abundances for a suite of tholeiitic to mildly alkalic Kamaʻehu basalts that erupted within the last ~8 kyr (based on the presence of 226Ra excesses), including a sample from the 1996 eruption. These Kamaʻehu basalts and recent lavas from Kīlauea and Mauna Loa provide a snapshot of the recent compositional heterogeneity of the Hawaiian plume. The isotopic and mantle-normalized trace element signatures of Kamaʻehu basalts are similar to lavas from Kīlauea (a Kea-trend volcano that aligns with Mauna Kea) except for their relatively high 208Pb/204Pb ratios. These similarities include positive Nb anomalies that are thought to related to the presence of ancient recycled oceanic crust (ROC) in the mantle source region. A mantle source and melting model (e.g., Pietruszka et al., 2013) based on the trace element abundances suggests that Kamaʻehu basalts were derived from a source with an average of ~13-14% ROC that experienced an average of ~7-9% dehydration in an ancient subduction zone. These results for Kamaʻehu basalts are similar to previous estimates for Kīlauea except that that the extent of dehydration is lower for the ROC in Kīlauea's source (~3-7%). In contrast, the Mauna Loa source is estimated to contain a larger amount ROC (~17%) that was less dehydrated (~2%). Overall, these observations suggest that Kamaʻehu basalts are derived from a Kea-type source, despite the location of this volcano on the geographical Loa trend. If this interpretation is correct, the Hawaiian plume currently has a NW-SE gradient in small-scale compositional heterogeneities. ***This presentation is dedicated to the memory of Professor Jasper Konter, Department of Earth Sciences, University of Hawaiʻi***