Palaeomagnetism of the Pikes Peak Granite, Colorado

Samples collected from four sites over an area of 450 km2 in the 1020–1040 My Pikes Peak granite, Colorado are stable to thermal demagnetization above 500 °C. A reliable Precambrian palaeomagnetic pole is thus obtained at 179° W, 6° N. Alternating field demagnetization indicates that the granite has been partially remagnetized. Geological evidence suggests that this occurred during Laramide (early Tertiary) deformation of the Front Range: this is supported by the magnetic evidence from a fifth site. Titanomagnetite (moderately oxidized to ilmenite) is the main carrier of the primary NRM: hematite is responsible for the Laramide magnetization.