Abstract

Potassium-argon ages have been determined on fresh pyroxenes from three of five dikes in the Louis Lake quadrangle of the Wind River Range, Wyoming. They indicate a minimum apparent age of intrusion at 1880 m.y. This is older than published whole-rock ages from the same dikes, but is consistent with whole-rock ages of up to 2060 m.y. from other dikes in this area. The within-dike dispersion of the directions of natural remanent magnetization decreases during alternating field demagnetization up to 1400 oe. Thermal demagnetization, however, is not effective in removing secondary magnetizations. After structural correction according to overlying Cambrian sediments, an over-all mean paleomagnetic pole from four dikes is obtained at 121° W., 43° N., which is in agreement with poles from Canadian Shield rocks of similar age. There is evidence in two of the dikes for a remagnetization episode, and the equivalent pole positions suggest that this may have occurred at the time of deposition of the Cambrian Flathead Sandstone. Alteration has greatly influenced the magnetic and isotopic properties of the dikes.

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