Reexamining the Honolulu Volcanics: Hawai'i's Classic Case of Rejuvenation Volcanism

Abstract Rejuvenated volcanism is a worldwide phenomenon occurring on many oceanic islands in all of the major ocean basins. This plume-related volcanism follows the main edifice-building stage after a hiatus of variable duration (e.g. 0.6–2 Myrs in Hawai'i). The Honolulu Volcanics (HV), the classic case of rejuvenated volcanism, involved monogenetic eruptions from at least 48 vent areas. Previous studies inferred these vents were aligned along 3 to 11 rifts oriented orthogonal to the propagation direction of the Hawaiian plume. HV basalts are known for having high MgO contents (>10 wt %) and upper mantle xenoliths. Thus, HV magmas are assumed to be relatively primitive and to have ascended rapidly (50 kyr) between some eruptions. Our comprehensive, whole-rock major and trace element database (63 XRF analyses, 57 ICPMS analyses) of basalts from 37 vents show remarkable compositional diversity with no obvious spatial pattern or temporal trends. The two most recent eruptive sequences have the greatest diversity (basanite and melilitite compositions). HV basanites show systematic trace element trends that may reflect mixing of multiple source components. The nephelinites and melilitites require a complex source history that may have involved residual accessory minerals during mantle melting and a metasomatic component that was not carbonatitic. The new ages and geochemical data show eruptions along most of the previously proposed rift systems were unrelated (except for the Koko Rift). Therefore, geodynamic models that relate HV volcanism to these rift systems are invalid. Lava volumes for two HV eruptions were estimated at 0.11 and 0.23 km3 using surface mapping and water well data. Similar size, recent monogenetic eruptions