Abstract: Paleomagnetism and Paleogeographic Reconstruction of Southern Alaska

D. B. Stone

Paleomagnetic measurements have been made on rock samples collected from many sites spread over a wide geographic area in southern and southwestern Alaska. The Alaska results are very different from those obtained by similar measurement on rocks collected in other parts of North America.

Interpreting the Alaskan data using the usual assumptions of a dipolar geomagnetic field indicates that the area sampled had a much lower magnetic latitude during most of Jurassic and Cretaceous times, relative northward motion occurring in earliest Tertiary time. Comparing the paleomagnetic latitude of the area samples with that of the rest of North America leads to a model for the tectonic development of southern Alaska. This model involves relative northward motion of slivers of continental material, perhaps in a manner analogous to the motion of Baja California today. Certainly the Alaska Peninsula paleomagnetic data for Late Cretaceous time have a much closer affinity to paleomagnetic data from the Pacific plate than to data from continental North America. Trying to fit the paleo-magnetically derived model to the known geology produces a conflict as to the location of the Jurassic subduction zone. The paleomagnetic data would seem to require a fossil subduction zone on what is now the northwest side of the Aleutian batholith system, unless "Baja Alaska" was displaced significantly from the North American plate at that time.

AAPG Search and Discovery Article #90966©1977 Alaska Geological Society 1977 Symposium, Anchorage, Alaska