New U/Pb Ages from Granite and Granite Gneiss in the Ruby Geanticline and Southern Brooks Range, Alaska

Abstract

New U/Pb zircon ages from the Ray Mountains of central Alaska clarify the plutonic history of the Ruby geanticline and support earlier suggestions that the Ruby geanticline and S Brooks Range were once parts of the same tectonostratigraphic terrane. U/Pb zircon ages of 109 to 112 Ma from the Ray Mountains pluton confirm previously reported mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid- Cretaceous. New U/Pb zircon ages from 4 granite gneiss samples in the Ray Mountains indicate a Devonian protolith age of 390+ or -12 Ma and suggest that the Ruby geanticline, like the S Brooks Range, underwent a major plutonic event in mid-Paleozoic time.-Authors