Potassium-Argon Ages of Lavas from the Hawi and Pololu Volcanic Series, Kohala Volcano, Hawaii

Abstract

Kohala is regarded as the oldest major shield volcano on the island of Hawaii. Potassium-argon ages of nine lava flows from the predominantly tholeiitic Pololu Volcanic Series of Kohala Volcano range from about 0.33 m.y. o t about 0.45 m.y. These results suggest that the subaerial part of the shield was built over a period on the order of 0.1 m.y. in the late Pleistocene, and that much of the island of Hawaii is younger than 0.4 m.y. Mugeante lava flows from the younger Hawi Volcanic Series are between 0.06 and 0.25 m.y. old. These ages confirm that the hiatus between the basaltic shield-building phase of volcanism and the veneer of differentiated alkali lava on Kohala is less than 0.2 m.y. It is inferred that the Lualualei stand of the sea began less than 0.4 m.y. ago and ended before about 0.15 m.y. ago.