Single-crystal U-Pb zircon age determination of the Red Mountain Pluton, Laramie anorthosite complex, Wyoming

In order to provide a precise age for the Red Mountain pluton, the youngest of the syenitic bodies of the Laramie Anorthosite Complex, Wyoming, zircons were extracted and analyzed for U-Pb isotopes. Zircon grains were selected and individually analyzed in order to minimize potential complications of inherited components. No grains with inherited cores were identified, either by microscopic examination or from the isotopic data. On a concordia diagram, the U-Pb data form a slightly discordant array. A best-fit line intersectsc oncordia at $1439−6+7$ Ma and 102 ± 64 Ma (95% confidence level). The upper intercept is interpreted as the crystallization age of the Red Mountain pluton and provides a younger age limit for the rest of the Laramie Anorthosite Complex.