Mesozoic Tectonics and Correlations in Yukon-Koyukuk Province, West-Central Alaska: ABSTRACT

Abstract

The Yukon-Koyukuk province of west-central Alaska is a broad, wedge-shaped depression of Mesozoic and early Cenozoic rocks bordered on the west, north, and southeast by metamorphic rocks of Paleozoic and possibly older age. The province is not a simple sedimentary basin, as formerly believed, but a highly mobile tract that was subjected to repeated volcanism and plutonism during Cretaceous and early Tertiary times. Sedimentation was largely volcanogenic in character and confined, mostly, to a relatively short interval in mid-Cretaceous. Recent mapping on St. Lawrence Island suggests that the Mesozoic and early Cenozoic rocks of the Yukon-Koyukuk province swing in a broad arc across the Bering Sea and western St. Lawrence Island to join the Okhotsk volcanic belt of northea tern Siberia. Three different structural trends are recognizable among the intensely deformed pre-Tertiary rocks of the Yukon-Koyukuk province: East-west trends in the northern part of the province and adjoining Brooks Range, north-south trends along the western edge of the province from the western Brooks Range to the Yukon delta, and northeast-southwest trends along the Yukon and Koyukuk valleys. The province is transected between Ruby and Unalakleet by the Kaltag fault, a major strike-slip fault with 40-80 mi of probable right-lateral offset. Major structural discontinuities also occur along the Kobuk fault zone at the northern edge of the province, but the evidence for large-scale strike-slip displacement is inconclusive. End_of_Article - Last_Page 2500------------