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Abstract

The tectonic framework of Alaska in use through 1969 was based on Payne's map, “Mesozoic and Cenozoic Tectonic Elements of Alaska,” on which he showed and described positive structures (geanticlines) and negative linear areas (geosynclines) established by Mesozoic earth movements and basins containing Tertiary clastic rocks. King, on his 1969 “Tectonic Map of North America,” added Precambrian and Paleozoic data and stressed the nature of tectonic materials, reclassifying all deposits by type and age of orogeny. In the plethora of plate-tectonic speculations which have appeared since 1968, so bewildering an array of possible crustal movements has been postulated that the tectonic history has been confused rather than clarified.

The essential skeletal elements of the observable tectonic framework consist of (1) a Precambrian and early Paleozoic Arctic (Innuitian) fold belt in the Brooks Range and northward; (2) a Precambrian and early Paleozoic “Cordilleran” fold belt south of the Yukon River and along the front of the Alaska Range; (3) a late Paleozoic (Permian) and Mesozoic Yukon eugeosyncline between the older fold belts and beneath the southern Bering Sea, plus associated miogeosynclinal or shelf sedimentary strata over the Brooks Range and northward; (4) the western edge of the Yukon shelf, stable through Precambrian and Paleozoic time; and (5) the Seward Peninsula block, a stable shelf in Paleozoic time but the site of eugeosynclinal sedimentation and deformation in Precambrian time. Superimposed on these primary elements on land and on the continental shelf are Cretaceous and Tertiary basins containing the detritus of late Mesozoic, Laramide, and younger uplifts. The location and form of these basins are controlled by older structures which have been reactivated.

Two conclusions seem apparent: (1) Observable tectonic elements have inherited their form and position from Paleozoic and possibly Precambrian structures, and the history of their development shows a close relation between them and adjacent elements. (2) Alaska is not formed from segments which were rifted from other continents and drifted to a final resting place; instead, it is a continental mass formed by the accretion of fold belts caused by interaction between the Canadian and Siberian shields and the crust of the ancient Arctic and Pacific oceans in Precambrian and most of Paleozoic time, and between the resulting larger continental mass and the crust of an ancient Pacific ocean (including the present Bering Sea area) since late Paleozoic time.

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