Abstract

Precambrian ages in the range 1200–1500 m.y. have been found by the Rb-Sr method for basement rocks in Arizona. The data extend the “1350 m.y.” orogeny to northwestern Arizona (Chloride granite) and southern Arizona (Oracle granite) near Tucson. Cretaceous-Tertiary ages were obtained from basement rocks in southern Arizona and northern Sonora, Mexico.

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