Tectonic significance of Upper Cambrian-Middle Ordovician Mafic volcanic rocks on the Alexander Terrane, Saint Elias Mountains, Northwestern Canada
journal contribution
posted on 2023-05-17, 15:52authored byBeranek, LP, van Staal, CR, Gordee, Sarah M, McClelland, WC, Israel, S, Mihalynuk, M
Upper Cambrian to Middle Ordovician mafic volcanic rocks of the Donjek assemblage comprise the oldest exposed units of the Alexander terrane in the Saint Elias Mountains of northwestern Canada. In this study, we use the geochemical and geological characteristics of these rocks to decipher their tectonic setting, petrogenetic history, and relationship to the early Paleozoic Descon arc system of the Alexander terrane in southeastern Alaska. Donjek assemblage volcanic rocks are subdivided into three geochemical types: transitional basalt (type I), light rare earth– enriched island-arc tholeiite to calc-alkaline basalt (type II), and enriched mid-ocean ridge basalt to ocean-island basalt (type III). Simple petrogenetic models illustrate that the basalts were generated by the decompressional partial melting of enriched asthenospheric mantle and variably mixed with depleted mantle and subduction-related components. Analogous geochemical signatures for modern Sumisu Rift and Okinawa Trough lavas imply that the Donjek assemblage basalts erupted during the rifting of the Descon arc. This model provides a new comparative framework for terranes of Siberian, Baltican, and Caledonian affinity in the North American Cordillera and, in particular, suggests a paleogeographic connection to rift-related magmatism in the Seward Peninsula region of the Arctic Alaska–Chukotka terrane.
History
Publication title
Journal of Geology
Volume
120
Pagination
293-314
ISSN
0022-1376
Department/School
School of Natural Sciences
Publisher
University of Chicago Press
Place of publication
1427 E 60th St, Chicago, IL, 60637 USA
Rights statement
No copyright is claimed for this article. It remains in the public domain.