Bokan Mountain peralkaline granitic complex, Alexander Terrane (southeastern Alaska): Evidence for early Jurassic rifting prior to accretion with North America

Jaroslav Dosta, Susan M. Kar, J. Duncan Keppie, Daniel J. Kontak, J. Gregory Shellnutt

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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.

Original languageEnglish
Pages (from-to)678-691
Number of pages14
JournalCanadian Journal of Earth Sciences
Volume50
Issue number6
DOIs
Publication statusPublished - 2013 Jun 1

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rifting
terrane
Jurassic
accretion
mountain
dike
emplacement
mineralization
lamprophyre
aegirine
North America
metasedimentary rock
fluorite
cordillera
geochronology
rock
igneous rock
amphibole
magmatism
zircon

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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Bokan Mountain peralkaline granitic complex, Alexander Terrane (southeastern Alaska) : Evidence for early Jurassic rifting prior to accretion with North America. / Dosta, Jaroslav; Kar, Susan M.; Duncan Keppie, J.; Kontak, Daniel J.; Gregory Shellnutt, J.

In: Canadian Journal of Earth Sciences, Vol. 50, No. 6, 01.06.2013, p. 678-691.

Research output: Contribution to journalArticle

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