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Crustal recycling during subduction at the Eocene Cordilleran margin of North America; a petrogenetic study from the southwestern Yukon

George A. Morris and Robert A. Creaser
Crustal recycling during subduction at the Eocene Cordilleran margin of North America; a petrogenetic study from the southwestern Yukon
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (December 2003) 40 (12): 1805-1821

Abstract

The early Eocene (57.3-55.4 Ma) Bennett Lake and Mount Skukum Volcanic Complexes lie on the Coast Plutonic Complex and Intermontane Belt boundary of the Canadian Cordillera at the British Columbia-Yukon border, some 200 km east of the current and Eocene continental margin. Both complexes contain rock types from basaltic andesite to rhyolite in a series of lava and pyroclastic flows. The location relative to the continental margin, the rock types, and the presence of an enhanced LILE/HFSE (large-ion lithophile/high field strength element) signatures in all samples imply that contemporaneous subduction was the controlling factor in the formation of these complexes. The majority of samples, however, return unusually low compatible element concentrations for given rock types. We interpret this data to show that partial melting of the crust was the major source of erupted magmas. One formation of andesites at Mount Skukum and one late dyke at Bennett Lake do show higher concentrations of compatible trace elements, suggesting the presence of primitive magmas in the crust at the time of eruption, which contaminated and were erupted with the crustal melts. Sr-Nd isotopic data at both complexes are consistently primitive regardless of rock type and compatible element content, requiring a primitive crustal source for these magmas. We propose that the complexes were formed as a result of early Eocene subduction of the Kula Plate beneath the Canadian Cordillera. Intrusion of hot primitive melts caused partial melting of young crust to produce the majority of lavas observed. Contamination of these melts by primitive magmas is observed at both Mount Skukum and Bennett Lake.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 40
Serial Issue: 12
Title: Crustal recycling during subduction at the Eocene Cordilleran margin of North America; a petrogenetic study from the southwestern Yukon
Affiliation: Universite de Geneve, Departement de Mineraologie, Geneva, Switzerland
Pages: 1805-1821
Published: 200312
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 48
Accession Number: 2004-026588
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Lithoprobe Publ. No. 1332
Illustration Description: illus. incl. 2 tables, sketch maps
N60°00'00" - N60°30'00", W135°00'00" - W133°00'00"
Secondary Affiliation: University of Alberta, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200408
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