Paleomagnetism and Paleointensity of the 1.1 Ga Old Diabase Sheets from Central Arizona

Eighty-five oriented samples (33 sites) from diabase sheets (ca. 1100 Ma) were collected from Central Arizona. Detailed rock magnetic, petrological, paleomagnetic, and paleointensity analyses were performed. The rock magnetic studies, as well as thermal and alternating field demagnetization treatments of the specimens indicate that the primary natural remanent magnetization (NRM) is carried mainly by low-Ti magnetite. Other phases like maghemite are also present and are responsible for some of the secondary components. In general paleomagnetic measurements isolate two distinct magnetic polarities, which show a clear asymmetry consistent with previous studies performed in Central Arizona as well as in the Grand Canyon and in the Lake Superior regions. Two of the sites in the present study also reveal directions that appear to be consistent with two distinct symmetric events. The asymmetry, almost entirely in inclination, is of the same sense as the Lake Superior one, but appears larger with a very steep (upward) reversed inclination and a moderately shallow (downward) normal one. The normal component has a mean direction of D = 274.8°, I = 38.7 ° (N = 13 sites, k = 30.4 and α95 = 7.6°). The reversed AR2 component has a mean direction D = 193.7°, I =-78.7 ° (N = 5 sites,