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U-Pb detrital zircon geochronology as evidence for the origin of the Nome Complex, northern Alaska, and implications for regional and trans-Arctic correlations

By
Alison B. Till
Alison B. Till
U.S. Geological Survey, 4210 University Drive, Anchorage, Alaska 99508, USA
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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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Heather A. Bleick
Heather A. Bleick
U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA
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Published:
July 01, 2014

Detrital zircons from the Nome Complex, a metamorphic terrane in northern Alaska, reveal important constraints on the early Paleozoic history of the Arctic Alaska–Chukotka terrane, a microcontinental block with an origin exotic to Laurentia.

Twenty-two samples (17 in this study, five previously published) produce three detrital zircon population patterns (called themes), indicating that at least three distinguishable source areas contributed to the metamorphic protolith. Detrital zircon populations from metamorphosed rift-related mafic volcaniclastic rocks, a lithologic subunit of the Nome Complex, contain a dominant population of 740–550 Ma zircons. Samples from three other lithologic units yielded populations dominated by early Paleozoic zircons and characterized by a large population of 450–420 Ma zircons. A few samples, taken from two different lithologic units, yielded populations dominated by Mesoproterozoic zircons (most around 1.25–0.9 Ga) and lacked zircons younger than 900 Ma. None of the 22 samples contained more than a few Archean zircons.

The ages of the youngest detrital zircon populations indicate that little of the protolith for the Nome Complex can be as old as Proterozoic, as previously thought. Further, a significant part of the protolith sequence is Devonian or younger; these rocks are likely correlative with Devonian or Mississippian units in the Brooks Range, specifically marine parts of the Endicott or Lisburne Groups.

Based on detrital zircon data, limiting factors can be placed on the paleogeographic history of the Nome Complex and associated parts of the Arctic Alaska–Chukotka terrane: (1) 740–550 Ma zircons were deposited in a rift-related basin formed on a continental margin in the early Paleozoic; at least some of those zircons may have been sourced from local basement; (2) a transition to new sediment sources is reflected in Devonian or younger protoliths with the appearance of 450–420 Ma and 1.25–0.9 Ga detrital zircons; and (3) 450–420 Ma and 1.25–0.9 Ga zircons may have been supplied from sources outside the Arctic Alaska–Chukotka terrane.

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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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