Radioelement concentrations and preliminary radiometric ages of rocks of the Kigluaik Mountains, Seward Peninsula, Alaska

A sequence of old metamorphic rocks including the Kigluaik and Nome Groups is exposed in the Kigluaik Mountains of the Seward Peninsula. The high-grade metasedimentary rocks give a whole-rock Rb-Sr age of 735 m.y. This late Precambrian age is believed to be the time of metamorphism. Orthogneisses, intrusive into the metasedimentary rocks, are probably also Precambrian in age; but many samples have had their ages disturbed by Cretaceous intrusions and thrusting.

Samples of Precambrian metagabbro are low in radioelements (U, Th, and K) typical of basalitc rocks. The Precambrian metasedimentary rocks have normal radioelement concentrations, but both the Precambrian orthogneisses and the Cretaceous granitic rocks are unusually rich in thorium.