Diverse basalt types from Loihi seamount, Hawaii

Loihi seamount is the southeasternmost active volcano in the Hawaiian-Emperor volcanic chain. The seamount is considered representative of the early phase of Hawaiian volcanism because of its youth, small size, and location near the melting anomaly. Seventeen dredge stations recovered transitional basalt, alkalic basalt, and basanite, in addition to the expected tholeiitic basalt. Four flows of alkalic basalt contain common small dunite xenoliths. The recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces; we estimate that the lavas are less than about 4,000 yr old, and many are less than 1,000 yr old. Loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed (subaerial) tholeiitic eruptive phase, previously thought to dominate Hawaiian volcanism from inception until the postcaldera collapse, alkalic stage.