Abstract

Preliminary examination of space images of Alaska reveals numerous linears which can be conveniently considered in three groups based on length — 10 to about 200 km, about 200 to 1000 km and > 1000 km. The shortest linears are most abundant, most varied in trend, and seem to represent the most recent tectonic structures. Linears of intermediate length are less abundant, less varied in trend and seem to reflect structures concealed by younger tectonic movements. Giant linears are of two types, straight, somewhat obscure ones that represent old, deeply buried structures, possibly crustal fractures, and arcuate, sharply expressed linears that coincide with relatively young great faults whose trace has followed one and then another of a nearly orthogonal set of old crustal fractures. Three clearly defined sets of straight northwest- and northeast-trending giant linears are recognized, as well as a group of linears trending nearly east.

In the Umiat and Yukon-Tanana Upland areas, a direct correlation of short and intermediate linears with subsurface geology and/or geophysics is apparent. Deeply buried or obscured regional geologic or geophysical features also mark many giant linears, substantiating their geologic origin. Similar giant linears, with trends comparable to those of Alaska and to concealed Precambrian structures in Canada, occur throughout the North American Cordillera. The understanding of these linears is critical to reconciling the deformation of the continental blocks with the concepts of plate tectonics.

East-trending linears north and east of Umiat correlate with subsurface geophysical data and suggest concealed structures of possible potential for oil or gas accumulation. Northeast- and northwest-trending giant linears may have guided the localization of mineralized belts in Alaska; this hypothesis has been substantiated by the independent location of porphyry copper-molybdenum deposits at the intersection of northwest- and northeast-trending faults in an area predictable by the hypothesis, but not by the conventional metallogenic concept.