U-Pb measurements on zircons separated from Precambrian basement rocks from Oklahoma yield the following: (1) the Spavinaw Granite, which appears in outcrops in Mayes County, northeastern Oklahoma, is 1,370 ± 20 m.y. old; (2) the ages of rocks exposed in the eastern Arbuckle Mountains in southeastern Oklahoma are: Tishomingo Granite, 1,374 ± 15 m.y.; Troy Granite, 1,399 ± 95 m.y.; and Blue River Gneiss, 1,396 ± 40 m.y. The granophyric Spavinaw Granite is associated with rhyolitic volcanic rocks and was clearly emplaced in the shallow crust; rocks of similar age and petrography occur in the subsurface in southeastern Kansas. The rocks exposed in the eastern Arbuckles, although of similar age, have textures suggesting emplacement at deeper crustal levels.

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