The Koloa Volcanic Suite of Kauai, Hawaii

The Koloa lavas of the post-erosional volcanic suite of Kauaivary in composition from melilitite to alkali olivine basalt.⁸⁷Sr/⁸⁶Sr varies from {small tilde}0.7030 to 0.7033, the rangebeing similar to that of other Hawaiian post-erosional suites.The chemical composition within single lava flows is variableand forms major-element trends that are different from the mainKoloa trend. The main trend can be related to increased degreesof partial melting during decreasing pressure. The combinedevidence from Sr and Nd isotopes and rare earth elements (REEs)could suggest that an ocean island basalt (OIB) plume was infiltratedby a carbonate-rich melt with a high concentration of Sr andREEs derived from the mid-ocean ridge basalt (MORB) source.However, the Pb-isotope systematics of the Hawaiian islandsdo not suggest that a MORB source was involved during the generationof the posterosional lavas. Instead, we suggest that the Hawaiiantholeiitic and nephelinitic magma suites are derived from azoned plume with a low ⁸⁷Sr/⁸⁶Sr core and a high ⁸⁷Sr/⁸⁶Sr concentricmargin. The trends of the single flows and their variation inisotope ratios suggest that they formed from magmas accumulatedmainly from the central core of the zoned plume.