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Age, chemistry, and correlations of Neoproterozoic–Devonian igneous rocks of the Arctic Alaska–Chukotka terrane: An overview with new U-Pb ages

By
Jeffrey M. Amato
Jeffrey M. Amato
Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA
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John N. Aleinikoff
John N. Aleinikoff
U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225, USA
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Vyacheslav V. Akinin
Vyacheslav V. Akinin
North East Scientific Research Institute, Far East Branch, Russian Academy of Sciences, Magadan, Portovaya Ulitsa, 16, 685000, Russia
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William C. McClelland
William C. McClelland
Department of Geoscience, 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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Published:
July 01, 2014

The Arctic Alaska–Chukotka terrane is a microcontinent with an origin exotic to Laurentia. We used a sensitive high-resolution ion microprobe (SHRIMP) to date nine samples of Neoproterozoic rock and five samples of Devonian rock from the Brooks Range and Seward Peninsula of Alaska and from the Chukotka Peninsula of northeastern Russia. Felsic magmatism occurred at 968 Ma and 742 Ma in the Brooks Range and at 865 Ma and 670–666 Ma on Seward Peninsula. Felsic igneous rocks in Chukotka were dated at 656 Ma and 574 Ma. Devonian igneous rocks are found throughout the Arctic Alaska–Chukotka terrane, and we dated samples with ages of 391 Ma, 390 Ma, 385 Ma, 371 Ma, and 363 Ma. The felsic character of the Neoproterozoic rocks suggests formation at least in part through crustal melting. The age of the crustal source rocks that melted to form the Neoproterozoic rocks is inferred to be Mesoproterozoic based on Nd model ages ranging from 1.6 to 1.4 Ga. Rocks of this age range have been reported from the basement of Baltica but are rare in Laurentia. The 565 Ma orthogneisses on Seward Peninsula have ca. 1.1 Ga Nd model ages. Devonian igneous rocks have a wide range of model ages ranging from 1.6 to 0.8 Ga. The tectonic setting of the 968 Ma, 865 Ma, and 742 Ma rocks is unknown. The ca. 670 Ma magmatism on Seward Peninsula is interpreted to have occurred in an arc setting based on geochemistry and similarities in their ages to the Avalonian–Cadomian arc system peripheral to Gondwana. Latest Neoproterozoic magmatism is inferred to have occurred in a rift setting based on composition and the Paleozoic passive margin sequence that was deposited across the Arctic Alaska–Chukokta terrane. Devonian magmatism likely occurred in an arc and/or backarc rift setting. Significant uncertainties remain concerning the age of the Arctic Alaska–Chukotka terrane basement, particularly the age of the host rocks for Neoproterozoic intrusions.

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GSA Special Papers

Reconstruction of a Late Proterozoic to Devonian Continental Margin Sequence, Northern Alaska, Its Paleogeographic Significance, and Contained Base-Metal Sulfide Deposits

Julie A. Dumoulin
Julie A. Dumoulin
U.S. Geological Survey, 4210 University Drive, Anchorage, Alaska 99508, USA
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Alison B. Till
Alison B. Till
U.S. Geological Survey, 4210 University Drive, Anchorage, Alaska 99508, USA
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Geological Society of America
Volume
506
ISBN print:
9780813725062
Publication date:
July 01, 2014

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