AGE OF SHIELD-BUILDING VOLCANISM OF KAUAI AND LINEAR MIGRATION OF VOLCANISM IN THE HAWAIIAN ISLAND CHAIN

Tholeiitic basalts of the Napali Formation comprise the bulk of the Kauai shield volcano. Potassium-argon ages measured on 16 samples from three separate areas in this formation lie in the range 5.14 ± 0.20 to 3.81 ± 0.06 m.y. The scatter in the measured ages in each area is greater than that expected from experimental error alone, and variable loss of radiogenic argon is regarded as at least partly responsible. Nevertheless an interval of eruption in the order of 0.8 m.y. is deduced for the Napali Formation. The results from the Napali Formation taken together with K-Ar ages measured earlier on basalts of the Makaweli Formation, the youngest formation of the dome-building phase, yield a mean age of 4.43 ± 0.45 m.y. for the construction of the main subaerial shield volcano of Kauai. When this result from Kauai is combined with estimates of the average age for the shield-building volcanism in 16 other volcanoes in the Hawaiian island chain, extending over a distance of more than 2800 km, the data are found to conform to migration of the centre of volcanism from north-northwest to south-southeast at a uniform rate of 9.4 (±0.3) cm/yr over the last 28 m.y. Non-linear models of propagation of volcanism in the Hawaiian chain are quite unnecessary, especially when uncertainties in the data base are taken into account. These results are consistent with an origin of the Hawaiian volcanic chain by eruption from a magma source situated below the Pacific lithospheric plate, as proposed under hot spot or plume models. Depending upon choice of the pole for the Pacific plate, rates of rotation about the pole of 0.9° to 1.0°/m.y. are derived. By extrapolation of the Hawaiian Island chain data an age estimate of 37.8 m.y. is derived for the Hawaiian-Emperor Seamount intersection. © 1979.