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Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America

Canadian Journal of Earth Sciences

By:
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DOI: 10.1139/cjes-2012-0139

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Abstract

The circular Bokan Mountain complex (BMC) on southern Prince of Wales Island, southernmost Alaska, is a Jurassic peralkaline granitic intrusion about 3 km in diameter that crosscuts igneous and metasedimentary rocks of the Alexander terrane. The BMC hosts significant rare metal (rare earth elements, Y, U, Th, Zr, and Nb) mineralization related to the last stage of BMC emplacement. U–Pb (zircon) and 40Ar/39Ar (amphibole and whole-rock) geochronology indicates the following sequence of intrusive activity: (i) a Paleozoic basement composed mainly of 469 ± 4 Ma granitic rocks; (ii) intrusion of the BMC at 177 ± 1 Ma followed by rapid cooling through ca. 550 °C at 176 ± 1 Ma that was synchronous with mineralization associated with vertical, WNW-trending pegmatites, felsic dikes, and aegirine–fluorite veins and late-stage, sinistral shear deformation; and (iii) intrusion of crosscutting lamprophyre dikes at >150 Ma and again at ca. 105 Ma. The peralkaline nature of the BMC and the WNW trend of associated dikes suggest intrusion during NE–SW rifting that was followed by NE–SW shortening during the waning stages of BMC emplacement. The 177 Ma BMC was synchronous with other magmatic centres in the Alexander terrane, such as (1) the Dora Bay peralkaline stock and (2) the bimodal Moffatt volcanic suite located ~30 km north and ~100 km SE of the BMC, respectively. This regional magmatism is interpreted to represent a regional extensional event that precedes deposition of the Late Jurassic – Cretaceous Gravina sequence that oversteps the Wrangellia and Alexander exotic accreted terranes and the Taku and Yukon–Tanana pericratonic terranes of the Canadian–Alaskan Cordillera.

Geospatial Extents

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America
Series title:
Canadian Journal of Earth Sciences
DOI:
10.1139/cjes-2012-0139
Volume
50
Year Published:
2013
Language:
English
Publisher:
NRC Research Press
Contributing office(s):
Alaska Science Center
Description:
14 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
678
Last page:
691
Country:
United States
State:
Alaska
Other Geospatial:
Bokan Mountain