A PALEOMAGNETIC STUDY OF THE EARLY JURASSIC TALKEETNA FORMATION, PENINSULAR TERRANE, ALASKA

Southern Alaska consists of an accretionary complex with over 50 terranes accreted over the past 200 million years. A paleomagnetic study was conducted in the Talkeetna Mountains to better define the poorly understood past movements of the Peninsular terrane and the sequence of accretion between the Peninsular and Wrangellia terranes. Early Jurassic basalts from the Talkeetna Formation were sampled from ten different sites. 8-14 cores were drilled from each site. Thermal and alternating field demagnetization studies were preformed to try to determine primary thermal remanent paleomagnetic directions from each site. Units sampled did not yield consistent inclinations and therefore did not indicate a consistent early Jurassic paleolatitude for the Peninsular terrane. Within-site scatter of paleomagnetic directions and inconsistent demagnetization behavior suggest hydrothermal alteration of magnetic minerals in the samples. A study of the magnetic mineralogy through reflected light microscopy will determine the extent of alteration and help constrain the alteration history of the early Jurassic Talkeetna Formation in the Talkeetna Mountains.