Some additional potassium-argon ages of Hawaiian rocks: the Mani volcanic complex of Molokai, Maui, Lanai and Kahoolawe

Potassium-argon (K-Ar) ages have been determined for rocks from the group of volcanoes vicinal to Maui, Hawaii, in an effort to fill gaps left by previous dating work. Ages for tholeiitic samples from the main shield-building stage of the volcanoes varied in sequence from 0.83 m.y. for Haleakala to 1.84 m.y. for West Molokai volcano. Some differ significantly from ages reported previously. For the volcanoes studied, ages agree with the general Hawaiian trend of volcanoes becoming progressively older to the north-west (Fig. 1B). New determinations of K-Ar ages were made for the late-stage, alkalic volcanism on Kahoolawe (1.03 m.y.), and for the later post-erosional phases at Kalaupapa, Molokai (1.24 m.y.) and from a vent of the Lahaina Series on West Maui (1.30 m.y.). These last two, when compared with the dates of the main shield-building stages of the respective volcanoes, show that very extensive erosion of these Hawaiian volcanoes has taken place in the surprisingly short period of a few hundred thousand years. This is substantiated by evidence of similar rapid erosion on the islands of Oahu and Hawaii. (orig.)