AKLM-ALPHA - A PRE-EARTHSCOPE LITHOSPHERIC MODEL FOR ALASKA

Alaska sits at a complex and active corner of the North American plate. The southern margin of Alaska is bounded by a combined subduction/transcurrent plate boundary with the Pacific plate to the south, the North American plate to the north, and the colliding Yakutat micro plate wedged in-between. To the north and west the North American plate is separated from the Eurasian plate by a developing spreading center. The Alaskan lithosphere is caught in the middle of major dynamic action, much of it driven by the Yakutat indenter in the Gulf of Alaska, as reflected in the high topographic relief, large geoid anomaly, apparent high heat flow, and large GPS-determined crustal motions that reach far inland from the southern margin.

Alaska Lithosphere Model Alpha (AKLMα) is based on currently available constraints on the structure and thickness of the crust and upper mantle for Alaska. Crustal thickness is constrained by seismic refraction interpretation, limited receiver function interpretations, seismic tomography models in southern Alaska, and filled out for the rest of the state using gravity data. Crustal structure is based on regional geology, gravity, magnetic and very sparse drilling results. Beneath the Moho, Alaska lithospheric structure is very poorly constrained, but we have made an initial model based on heat flow, apparent elastic thickness (Te), global receiver function results, and other evidence.

Broadly speaking, the Alaskan lithosphere can be divided into 4 domains. The southern domain parallels the North American/Pacific plate boundary and is cold, stiff, and deep. The northern domain includes the so-called Arctic Alaska plate of the North Slope and is also relatively cold, stiff and thick, serving as an ultimate northern buttress to the “back-arc” stresses of central Alaska. Central Alaska has separate eastern and western domains. To the east, lithospheric deformation is concentrated on discrete faults, most notably the strike-slip Tintina and Denali, both overprinted by late-state compressional deformation, especially at the Cordilleran thrust front. To the west, GPS results show a broad rotational flow field that suggests more distributed motion. Both central domains are characterized by relatively thin crust, high heat flow, low Te, and thinner overall lithosphere.