The koloa volcanic suite of Kauai, Hawaii

Abstract

The Koloa lavas of the post-erosional volcanic suite of Kauai vary in composition from melilitite to alkali olivine basalt. 87Sr/86Sr varies from ̃0.7030 to 0.7033, the range being similar to that of other Hawaiian post-erosional suites. The chemical composition within single lava flows is variable and forms major-element trends that are different from the main Koloa trend. The main trend can be related to increased degrees of partial melting during decreasing pressure. The combined evidence from Sr and Nd isotopes and rare earth elements (REEs) could suggest that an ocean island basalt (OIB) plume was infiltrated by a carbonate-rich melt with a high concentration of Sr and REEs derived from the mid-ocean ridge basalt (MORB) source. However, the Pb-isotope systematics of the Hawaiian Islands do not suggest that a MORB source was involved during the generation of the posterosional lavas. Instead, we suggest that the Hawaiian tholeiitic and nephelinitic magma suites are derived from a zoned plume with a low 87Sr/86Sr core and a high 87Sr/86Sr concentric margin. The trends of the single flows and their variation in isotope ratios suggest that they formed from magmas accumulated mainly from the central core of the zoned plume. © 1992 Oxford University Press.