Abstract: Late Tertiary Gulf of Alaska Plate-Tectonic Model Based on Continental-Margin Geology

Roland Von Huene, Terry R. Bruns

In many diagrammatic illustrations of plate-tectonic models for the Gulf of Alaska, the boundaries are drawn at the base of continental slopes except along the Fairweather fault. These conceptual models indicate that relative motion between the Pacific and American plates is strike-slip along the eastern margin of the gulf, obliquely convergent along the central gulf, and normally convergent along the western gulf. Such general models provide overview insight, but a first approximation of a model more consistent with geophysical data acquired in the last few years along continental margins now can be constructed. Along the eastern margin the plate boundary is formed (1) by the Queen Charlotte fault zone on the continental slope in the south, (2) a largely inferred fault extending from this zone across the continental slope to approximately the shelf break off the south end of Baranof Island, and (3) a fault on the continental shelf that may join with the Fairweather fault system. There may be additional faulting under the continental slope off Baranof Island, for it has not been possible to discern structure under thick glacial debris on the slope. Along the central Gulf of Alaska, relative plate motion appears to be represented not only by local deformation along the continental slope but also by much more intense folding and thrusting across the continental shelf and in the coastal plains and foothills belt. Along the western margin, the structure of the subduction zone is more complex than a thrust fault extending from the Benioff zone to the trench. It appears that rapid deformation is concentrated along the lower continental slope in a zone 30 to 40 km wide and the intensity of tectonism diminishes upslope with mild deformation in upper Cenozoic sediment in the shelf basin. The plate boundary there begins at the lower or middle slope, whereas along the eastern and central regions of the Gulf of Alaska, plate boundaries do not always correspond to slopes. The gross sense of relative plate motion corresponds well to regional stress as deduced from structural trends with a few local exceptions.

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