Abstract

Sanidine 40Ar/39Ar geochronology confirms that Silver Creek caldera, which straddles the eastern edge of the Colorado River extensional corridor near Oatman, Arizona (United States), is the source of the Peach Spring Tuff. Eight new dates (five from outflow, three from caldera fill) are analytically indistinguishable, and combined with the most precise previously published date give a weighted mean average age of 18.78 ± 0.02 Ma. A fragment of the caldera identified in the midst of the extensional corridor is structurally juxtaposed with mesozonal plutons of identical age. The implied extension direction (182°–225°) is compatible with abundant previously published structural data for the region.

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