Plutonic Rocks of Alaska-Aleutian Range Batholith1
Published:January 01, 1973
Abstract Potassium-argon mineral ages and reconnaissance mapping of the central and southern Alaska Range and Aleutian Range indicate that there were three major plutonic episodes during the Mesozoic and Cenozoic. The first began in the Early Jurassic about 180 m.y. ago and continued far about 25 m.y. Plufons of this age form an arcuate belt more than 500 mi (800 km) long that extends from Becharof Lake to the Talkeetna Mountains. The Jurassic plutonic rocks are largely diorite and quartz diorite with minor granodiorite. Late Cretaceous and Tertiary plutons occur locally within this belt but are largely confined to the northern part of the Alaska-Aleutian Range batholith, where they form north-trending belts transverse to the earlier tectonic elements and locally extend out into what was a more stable area bordering the earlier tectonic features. Composition of these plutons ranges from diorite through granite, but granodiorite and quartz monzonite predominate. Isolated granitic stocks intruded during the second episode also extend eastward into the central Alaska Range. The data suggest that this plutonic episode may be separated into Late Cretaceous (72-84 m.y.) and early Tertiary (50-65 m.y.) phases. The third episode is represented by middle Tertiary (34-40 m.y.) plutons that form a north-trending belt about 90 mi (145 km) long in the central part of the southern Alaska Range. These rocks are characteristically granites and quartz monzonites. Small plutons of middle Tertiary age are present locally in the Alaska Peninsula and the central Alaska Range. The chemical data that have thus far been accumulated on the rocks of these three plutonic episodes suggest progressive enrichment in alkali constituents with decreasing age.
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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.