PALEOMAGNETISM AND GEOCHEMISTRY OF TERTIARY INTRUSIONS AND FLOWS ASSOCIATED WITH THE KOOTZNAHOO FORMATION NEAR KAKE, SOUTHEAST ALASKA, AND IMPLICATIONS FOR THE ALEXANDER TERRANE

Major and trace element geochemistry of basaltic sills, dikes, and flows from 16 sites associated with the Paleogene-Neogene Kootznahoo Formation near Kake, Alaska plot in the "within-plate" or "ocean-floor" fields on the Ti-Zr-Y diagram of Pearce and Cann (1973). The mean in-situ characteristic remnant magnetism (ChRM) of 50 cores from 8 sites with MAD <7.0° and A₉₅ <10° is D =331.3° ± 7.07°, I = 66.5° ± 3.1, A₉₅=3.1, k = 43.95. Applying a structural correction based on the local strike and dip of the Kootznahoo Formation, the mean corrected direction for all sites is D = 339.0° ± 10.7°, I =76° ± 2.4°, A₉₅ = 2.4°, k = 70.75, which suggests a moderate 20.6° ± 9.8° of vertical axis counterclockwise rotation and no displacement when compared with a North American pole at ~23 Ma, the approximate crystallization age of the gabbros and basalts (Haeussler et al., 1992). However, close inspection of the paleomagnetic results from this study combined with previously published paleomagnetic data from Haeussler et al. (1992) show systematic regional differences in directions that suggest local tilting and vertical-axis rotations vary across the region from no vertical axis rotation up to 46.3° ± 8.3° counterclockwise rotation at some locations. This suggests Neogene deformation in the Alexander terrane east of the Queen Charlotte and Clarence Strait faults could be locally significant and should be considered when determining paleomagnetic directions for older rocks in the region.