Regional Geology of Yukon-Tanana Upland, Alaska1
Published:January 01, 1973
The basic geologic framework of the Yukon-Tanana upland, Alaska, a mountainous region of about 30,000 sq mi (77,700 sq km) between the Yukon and Tanana Rivers, was delineated primarily by L. M. Prindle and J. B. Mertie, Jr., in the early part of this century. The subsequent recognition of large-scale offset along the Tintina fault, which bounds the eastern upland on the north, has required a reconsideration of the regional stratigraphic and structural relations.
The northwestern part of the upland is predominantly underlain by a sedimentary sequence consisting of rocks which range in age from Cambrian to Mississippian. Cretaceous and Tertiary sedimentary rocks unconformably overlie the older sequence. The Cambrian is apparently underlain by a thick section of grits, quartzites, phyllites, and quartz-mica schists. Pre-Silurian volcanic rocks, mafic and ultramafic rocks of probably Devonian age, and Permo-Triassic diabase and volcanic rocks are also present. These sedimentary and igneous rocks are cut by granitic plutons of Cretaceous and Tertiary age.
The central and eastern parts of the upland are underlain by a metamorphic complex of rocks which range from lower-greenschist to amphibolite facies. Fossils date the parent sediments of some greenschist-facies rocks as Paleozoic. Radiometric dates from several localities in the metamorphic complex indicate that Precambrian, Ordovician, and Jurassic-Cretaceous thermal events are recorded in the metamorphic history. Mesozoic granodiorite and quartz monzonite batholiths and smaller granitic plutons of Mesozoic and Tertiary age intrude the crystalline schists. Locally, unmetamorphosed Cretaceous and/or Tertiary sedimentary rocks are in unconformable or fault contact with the older rocks. Tertiary volcanic rocks ranging in composition from rhyolife to basalt overlie the older rocks in small but significant parts of the eastern upland. Ultramafic intrusions, mostly small and serpentinized, also occur.
Work has progressed to the point where the sedimentary rocks in the upland can reasonably be correlated with those in other parts of Alaska, but interregional correlation of the metamorphic terranes must await additional clarification of structural and petrologie relations.
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Following the discovery of Prudhoe Bay oil field in 1968, much attention was turned to the Arctic in the search for giant hydrocarbon accumulations. The Soviets had already proved giant reserves in their West Siberian Basin, and exploration was moving ahead quickly in the Canadian Arctic. Plans were drawn up for an AAPG Symposium on Arctic Geology and held in February 1971. Papers were selected from the Symposium for this publication and cover seven topical groupings: Regional Arctic Geology of Canada, Regional Arctic Geology of the Nordic Countries, Regional Arctic Geology of the USSR, Regional Arctic Geology of Alaska, Comparisons in the North Atlantic Borders, Evolution of the Arctic Ocean Basin, and Economics of Petroleum Exploration and Production in the Arctic.