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Relationships between plate motions and Late Cretaceous to Paleogene magmatism in southwestern Alaska
Author(s) -
Wallace Wesley K.,
Engebretson David C.
Publication year - 1984
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc003i002p00295
Subject(s) - geology , cretaceous , terrane , paleogene , forearc , paleontology , back arc basin , fault (geology) , pacific plate , clockwise , magmatism , plate tectonics , tectonics , rotation (mathematics) , subduction , geometry , mathematics
Four major Late Cretaceous to Paleogene magmatic belts have been recognized in southwestern Alaska, and tentative boundaries have been drawn for each. The belts indicate minimum ages by which the tectonostratigraphic terranes they overprint must have been linked together, though there has been significant postmagmatic tectonism. The Kuskokwim Mountains belt (73–60 m.y. B.P.), the Alaska Range belt (74–55 m,y. B.P.), and the Gulf of Alaska belt (62–57 m.y. B.P.) all may have been related to a period of rapid north‐northeastward motion of the KuIa plate from about 74 to 56 m.y. B.P. The angle of convergence was low with respect to the present orientation of the belts, suggesting the possibility of postmagmatic rotation of the belts. A higher angle of convergence may have existed with respect to the Alaska Range belt, a probable arc, if postmagmatic rotation resulted from 300–400 km of right‐lateral displacement on the Denali fault. The Gulf of Alaska belt is in an anomalous forearc position with respect to the Alaska Range belt, but probably formed by a convergence‐related mechanism. The Kuskokwim Mountains belt is in an apparent back arc position, but the mechanism of its origin is uncertain. It may have been part of an unusually broad Alaska Range arc or, less likely, it may have been a separate arc. Magmatic quiescence occurred throughout south‐western Alaska during a period of plate reorganization from about 56 to 43 m.y. B.P., a period which began with extremely rapid northward motion of the KuIa plate. Magmatism resumed when the present period of rather slow northwestward Pacific plate motion began at about 43 m.y. B.P. The Aleutian arc probably formed at this time, and has been episodically active in about the same location ever since.