Cretaceous K‐Ar ages of volcanic rocks from the Musicians Seamounts and the Hawaiian Ridge

Abstract

K‐Ar conventional and 40Ar/39Ar ages on plagioclase from altered basalt samples show that Khatchaturian and Rachmaninoff Seamounts in the Musicians Seamounts, north‐central Pacific, are 65.2 ± 2.6 and 86.6 ± 5.2 m.y. old, respectively. The minimum age of Wentworth Seamount, located on the Hawaiian Ridge near Midway, is 71 ± 5 m.y. Wentworth appears to be a Cretaceous volcano that was incorporated into the Hawaiian volcanic chain. A single boulder of rhyolite dredged from the northern slope of the seamount underlying Necker Island has an age of 77.6 ± 1.7 m.y. Apparently Necker is a composite seamount constructed of both Cretaceous and late Tertiary volcanoes. With one possible exception, the ages of these and other Cretaceous seamounts in the north‐central Pacific are less than or equal to the age of the adjacent sea floor indicating that the seamounts formed at or near the crest of the East Pacific Rise.