GEOPHYSICAL IDENTIFICATION AND GEOLOGICAL IMPLICATIONS OF THE SOUTHERN ALASKA MAGNETIC TROUGH

The southern Alaska magnetic trough (SAMT) is one of the fundamental, crustal-scale, magnetic features of Alaska recognized on 10 km upward-continued maps of state-scale aeromagnetic compilations. The arcuate SAMT ranges from 50 to 100 km wide and extends along the southern Alaska margin for more than 1200 km onshore (from near the Alaska/Canada border at about 60 degrees north latitude to the Bering Sea) and an additional 500 km or more offshore (in the southern Bering Sea). The SAMT is bordered to the south by the southern Alaska magnetic high (SAMH) produced by strongly magnetic crust and to the north by a magnetically quiet zone that reflects weakly magnetic interior Alaska crust. Geophysically, the SAMT is more than just the north-side dipole low associated with the SAMH. Several modes of analysis, including examination of magnetic potential (pseudogravity) and profile modeling, indicate that the source of this magnetic trough is a discrete, crustal-scale body. Geologically, the SAMT coincides to a large degree with collapsed Mesozoic flysch basins including those in the Hagemeister subterrane, the Kahiltna terrane, and the Gravina-Nutzotin belt. This poster presents our geophysical evidence for the extent and geometry of this magnetic feature as well as initial geological synthesis and combined geologic/geophysical modeling to examine the implications of this feature for the broad scale tectonic framework of southern Alaska.