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Abstract

This chapter summarizes the tectonic setting, geology, and tectonic evolution of the southern Alaska margin south of the Border Ranges fault system, which extends 2100 km from the Sanak Islands on the west to Chatham Strait on the east and seaward to the base of the continental slope (Fig. 1). Mesozoic and Cenozoic rocks that make up the southern Alaska continental margin record a complex history of subductionrelated underplating, offscraping, and metamorphism, as well as transform-related large-scale strike-slip displacements. The region discussed in this chapter has an area of about 328,000 km2, of which almost 30% is onshore. The land area includes parts or all of 26 1:250,000 scale quadrangles.

The mainland along the northern Gulf of Alaska margin consists of alluvium- and glacier-covered coastal lowlands, 0 to 40 km wide, backed by a belt as wide as 40 km of rugged foothills that rise to elevations of about 2000 m (Wahrhaftig, this volume). The foothills are bordered to the north by the exceedingly rugged Kenai, Chugach, and Saint Elias mountains. Average summit elevations are over 2000 m, and numerous peaks are over 5000 m; the highest peaks are Mt. Saint Elias in Alaska (5488 m) and nearby Mt Logan (5745 m) in Canada. All major drainages in the coastal mountains are occupied by glaciers except for the Alsek River, which drains across the Saint Elias Mountains from Canada, and the Copper River, which drains across the Chugach Mountains from the interior of Alaska. The Kodiak Islands group, the islands

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