PALEOMAGNETIC INVESTIGATION OF BASALTS OF THE TALKEETNA FORMATION, PENINSULAR TERRANE, ALASKA

Alaska is comprised of numerous accreted tectonostratigraphic terranes. In the summer of 2007, a paleomagnetic study of samples collected in the Talkeetna Mountains of southern Alaska was done to determine the paleolatitude of one of these, the Peninsular terrane. These data could be compared to similar aged paleomagnetic data from Wrangellia terrane to test whether the two terranes may have amalgamated prior to early Jurassic time. Cores were collected from basalt flows at 10 sites in the early Jurassic Talkeetna Formation. To obtain primary thermal remnant magnetic directions, both alternating field and thermal demagnetization were used on the samples. After structural corrections for layer tilt, magnetic inclinations from the cores produced very mixed results with some sites indicating a paleolatitude close to that of present day Alaska and mean magnetic directions varying greatly between sites. Within sites, magnetic directions from individual samples exhibit significant variation with high α95 values. For many of the sites, only a small number of the samples spun could be used to calculate the mean magnetic direction. While most of the basalts do not appear to be extensively weathered, thermal demagnetization of many cores suggests possible alteration of magnetic minerals. Analysis of polished sections using reflected light microscopy will be employed to determine what is causing such wide variation in the within-site directional data. Reflected light results may provide constraints on the hydrothermal alteration history of these early Jurassic basalt flows.