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The Whale Mountain allochthon: A relic of the Iapetus Ocean preserved in the northeastern Brooks Range of Alaska and Yukon

By
Benjamin G. Johnson
Benjamin G. Johnson
Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506, USA
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Justin V. Strauss
Justin V. Strauss
Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA
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John F. Taylor
John F. Taylor
Department of Geoscience, Indiana University of Pennsylvania, Indiana, Pennsylvania 15705, USA
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William P. Ward
William P. Ward
Department of Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA
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Maurice Colpron
Maurice Colpron
Yukon Geological Survey, Whitehorse, Yukon YIA 2C6, Canada
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William C. McClelland
William C. McClelland
Department of Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA
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Jaime Toro
Jaime Toro
Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506, USA
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Publication history
08 May 201821 December 2018

ABSTRACT

The Whale Mountain allochthon is a structural complex composed of lower Paleozoic mafic volcanic and marine sedimentary rocks that are exposed within three fault-bounded, east–west-trending belts in the northeastern Brooks Range of Alaska and Yukon. Each belt is characterized by a unique structural and stratigraphic architecture. Trace-element systematics from the volcanic rocks define distinctive suites that are geographically restricted to each belt. The volcanic rocks of the southern belt (the Marsh Fork volcanic rocks) have a tholeiitic character and rare earth element trends that resemble modern mid-ocean-ridge basalt. The volcanic rocks of the central belt (the Whale Mountain volcanic rocks) and northern belt (Ekaluakat formation; new name) both have an alkaline character, but the northern belt rocks are significantly more enriched in the incompatible trace elements. New zircon U-Pb data from two volcaniclastic rock units, one from the southern belt and another from central belt, yield unimodal age populations that range from ca. 567 to 474 Ma, with weighted averages of 504 ± 11 and 512 ± 1.4 Ma for each sample. In the central and southern belts of the allochthon, basalt flows are interbedded with discontinuous limestone and dolostone units that contain trilobites and agnostoid arthropods. Three distinct trilobite faunas of late Cambrian (Furongian) age were recovered from widely separated localities. The scarcity of uniquely Laurentian genera, coupled with an abundance of distinctive species that could not be assigned to any established Furongian genus, argues against models that invoke extrusion of these volcanic rocks onto the autochthonous Laurentian shelf or slope. It is thus proposed that the Whale Mountain allochthon formed in a peri-Laurentian setting, possibly as disparate fragments of the northern Iapetus Ocean that were assembled in an ancient accretionary wedge and subsequently accreted to the northern margin of Laurentia during the early Paleozoic.

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Contents

GSA Special Papers

Circum-Arctic Structural Events: Tectonic Evolution of the Arctic Margins and Trans-Arctic Links with Adjacent Orogens

Geological Society of America
Volume
541
ISBN electronic:
9780813795416

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