40Ar/39Ar age of a young rejuvenation basalt flow: implications for the duration of volcanism and the timing of ancient limestone platform development during the Quaternary on Kaua i, Hawaiian Islands

Abstract

Remnants of an extensive carbonate platform crop out along, the southeast coast of Kaua'i, Hawaii. A basalt flow within this succession has a whole-rock Ar-40/Ar-39 step-heating plateau age of 375 +/- 4 ka. The plateau age, which we interpret as the eruption age, indicates that rejuvenation volcanism persisted on Kaua'i for considerably longer (c. 200 000 yr) than previously thought, and also that published whole-rock K-Ar determinations may not accurately reflect eruption ages. The succession of younger sedimentary deposits and age of the basalt imply that the eruption occurred near the end of marine isotope stage (MIS) 11. Preservation of limestone dune assemblages and extensive paleosols above present-day sea level indicates that Kaua'i underwent a period of emergence during the early and middle Pleistocene, probably due to passage over the lithospheric arch or forebulge created by crustal loading of Maui Nui. The presence of at least eight major limestone-soil "couplets", together with extrapolated ages from the Ar-40/Ar-39 dating, make this the oldest surficial record of limestone formation in the Hawaiian Islands. This work provides a framework for further interpretation of the stratigraphy and paleoecology of Kaua'i and the tropical Hawaiian Islands.