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Magnetization age from paleomagnetism of the Copper Harbor red beds, northern Michigan, USA, and its Keweenawan geologic consequences

David T. A. Symons, Kazuo Kawasaki and Jimmy F. Diehl
Magnetization age from paleomagnetism of the Copper Harbor red beds, northern Michigan, USA, and its Keweenawan geologic consequences
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (January 2019) 56 (1): 1-15

Abstract

The Copper Harbor Formation on Lake Superior's Keweenaw Peninsula records the transition from volcanic to sedimentary infilling of North America's 1.1 Ga Keweenawan rift. Radiometric dating shows that the formation's primary mafic sediments and interbedded "Lake Shore" flows were deposited between approximately 1092 and approximately 1082 Ma. Our regional paleomagnetic results for the Copper Harbor's red beds yield a dominantly prefolding normal-polarity secondary chemical characteristic remanent magnetization in hematite at 18 of 21 sites with a mean direction of declination=274.9 degrees , inclination=+10.9 degrees (k=69.5, alpha (sub 95) =4.2 degrees ), and a paleopole at 7.4 degrees N, 181.7 degrees E (A (sub 95) =3.3 degrees ). Using paleopoles from Keweenawan volcanic rocks with U-Pb zircon age dates, an apparent polar wander path is constructed from 1106+ or -2 to 1087+ or -2 Ma. Extrapolation of this path dates oxidation of the Copper Harbor's primary gray beds to red beds at 1060+ or -5 Ma. The path implies an apparent polar wander rate of approximately 18 cm per year from approximately 1108 to 1096 Ma and of 6.8 cm per year from 1096 to 1087 Ma, along with a consistent clockwise rotation of 0.30+ or -0.05 degrees per million years for the Laurentian Shield from approximately 1108 to approximately 1160 Ma. Further, most Keweenawan volcanic rocks around the Lake Superior region carry an endemic approximately 1060 Ma normal-polarity hematite remanence overprint, acquired during the initial stages of Grenvillian tectonic uplift, that has caused asymmetry in a unit's normal and reverse paleopoles. Also, the Copper Harbor paleopole dates emplacement of the White Pine stratiform sedimentary copper mineralization more precisely at 1060+ or -5 Ma.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 56
Serial Issue: 1
Title: Magnetization age from paleomagnetism of the Copper Harbor red beds, northern Michigan, USA, and its Keweenawan geologic consequences
Affiliation: University of Windsor, Windsor, ON, Canada
Pages: 1-15
Published: 201901
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 75
Accession Number: 2019-014651
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables, geol. sketch maps
N46°45'00" - N47°28'00", W89°00'00" - W87°42'00"
Secondary Affiliation: University of Toyama, JPN, JapanMichigan Technological University, USA, United States
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from Canadian Science Publishing, NRC Research Press, Ottawa, ON, Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201910
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