Strike-slip faults in Alaska

Abstract

Long faults with large apparent right-lateral displacements and notably straight traces trend across Alaska from its south-eastern "panhandle" to the Bering Sea.They strike southeast in eastern Alaska and northeast in western Alaska, and several make up the Denali fault system, which crosses the State in a great arc that is convex to the north.These faults are a prominent feature of Alaska's geologic structure, and many are the loci of conspicuous rifts in its topography.Some have been active in Quaternary and historical times; most have a history of Tertiary displacement; and there is evidence that a few experienced Mesozoic and perhaps Paleozoic displacement.Left-lateral faults are less prominent, but a few important ones are known in southwestern Alaska.Their strike is north or north-northwest, and 'where numerous, they seem to have acted with the right-lateral faults to reshape broad terranes of the State.The position and trend of the known and suspected strike-slip faults, and the offsets along them, when viewed in relation to other geologic features, provide some support for a number of speculations about Alaska's tectonic evolution.These include the hypothesis (a modification of Carey's concept) that oroclinal bending deformed western Alaska during latest Cretaceous to early Tertiary time, that southwestern Alaska was shortened in mid-Tertiary time along an axis striking east-southeast, and that southeastern Alaska has been thrust against the Pacific Basin.If oroclinal bending did occur, its »Y .-,., .;.. " .characterhas major implications for the nature of relative movements (continental drift) between North America and Eurasia.Alaska.This mapping, presented in the appendix, includes all or r.ost