Paleontologic and paleomagnetic data demonstrate that the Alaska Peninsula lay far south of its present location relative to North America in the early Mesozoic. Paleomagnetic studies of Late Cretaceous-early Tertiary volcanic rocks inboard of the Alaska Peninsula indicate no major northward displacement. Outboard of the peninsular terrane,

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however, rocks of comparable age retain a paleomagnetic record of much lower paleolatitude. Geologic evidence bearing on the arrival time of the peninsular terrane are inconclusive and the implicated Tertiary tectonic boundary between indigenous and exotic components of Alaska is not known.

The paleomagnetism of a sequence of 30 Paleocene basalt flows just inboard of the peninsular terrane suggests a small amount of northward displacement and about 55° of counterclockwise rotation. Results from a nearby 44 Ma sequence suggest no displacement and no rotation. Collectively, our paleomagnetic data from seven volcanic sequences 30-40 Ma (about 70 flows), on the inboard part of the peninsular terrane, indicate that this region was in its present position with respect to North America when the lavas were extruded. The age of the unrotated localities indicates that the counterclockwise rotation of southern Alaska recorded by Late Cretaceous-early Tertiary rocks was completed about 44 Ma.

On the outboard side of the Alaska Peninsula, preliminary results from one sequence of Eocene or Oligocene volcanic rocks on the Kupreanof Peninsula also suggest no major latitudinal displacement or rotation. If this volcanic sequence adequately averages secular variation and if the Tertiary tectonic history of this region is representative of the rest of the outboard Alaska Peninsula, these paleomagnetic data preclude post-Eocene northward displacement of exotic southern Alaska along faults within the Alaska Peninsula. Additional data from other volcanic sequences in this region will test this hypothesis.

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