Abstract

The results of rubidium-strontium, fission-track, and lead-alpha analyses are evaluated in terms of the regional and local geological framework of the Okanogan Range (in Washington and British Columbia). An Upper Cretaceous (81± m.y.) granodioritic-quartz monzomtic intrusive episode and a Middle Cretaceous (104± m.y.) period of isotopic homogemzation of a trondhjemitic batholith are defined. A period of Jurassic regional metamorphism and late-metamorphic quartz dioritic-granodioritic emplacement, although not established, is suggested; the minimum age of this orogenic phase is 129± m.y.

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