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The end of Midcontinent Rift magmatism and the paleogeography of Laurentia

Luke M. Fairchild, Nicholas L. Swanson-Hysell, Jahandar Ramezani, Courtney J. Sprain and Samuel A. Bowring
The end of Midcontinent Rift magmatism and the paleogeography of Laurentia
Lithosphere (February 2017) 9 (1): 117-133


Paleomagnetism of the North American Midcontinent Rift provides a robust paleogeographic record of Laurentia (cratonic North America) from ca. 1110 to 1070 Ma, revealing rapid equatorward motion of the continent throughout rift magmatism. Existing age and paleomagnetic constraints on the youngest rift volcanic and sedimentary rocks have been interpreted to record a slowdown of this motion as rifting waned. We present new paleomagnetic and geochronologic data from the ca. 1090-1083 Ma "late-stage" rift volcanic rocks exposed as the Lake Shore Traps (Michigan), the Schroeder-Lutsen basalts (Minnesota), and the Michipicoten Island Formation (Ontario). The paleomagnetic data allow for the development of paleomagnetic poles for the Schroeder-Lutsen basalts (187.8 degrees E, 27.1 degrees N; A (sub 95) = 3.0 degrees , N = 50) and the Michipicoten Island Formation (174.7 degrees E, 17.0 degrees N; A (sub 95) = 4.4 degrees , N = 23). Temporal constraints on late-stage paleomagnetic poles are provided by high-precision, (super 206) Pb- (super 238) U zircon dates from a Lake Shore Traps andesite (1085.57 + or - 0.25 Ma; 2sigma internal errors), a Michipicoten Island Formation tuff (1084.35 + or - 0.20 Ma) and rhyolite (1083.52 + or - 0.23 Ma), and a Silver Bay aplitic dike from the Beaver Bay Complex (1091.61 + or - 0.14 Ma), which is overlain by the Schroeder-Lutsen basalt flows. These Michipicoten Island Formation dates are the youngest yet obtained from Midcontinent Rift volcanic rocks and indicate that rift magmatism was active for at least 25 m.y. The addition of these late-stage paleomagnetic poles to the Laurentian apparent polar wander path suggests that rapid motion of Laurentia continued throughout the entirety of rift volcanism.

ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 9
Serial Issue: 1
Title: The end of Midcontinent Rift magmatism and the paleogeography of Laurentia
Affiliation: University of California at Berkeley, Department of Earth and Planetary Science, Berkeley, CA, United States
Pages: 117-133
Published: 201702
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 109
Accession Number: 2017-012071
Categories: Solid-earth geophysicsGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N47°25'50" - N47°25'50", W87°42'51" - W87°42'51"
N47°18'51" - N47°18'51", W91°13'41" - W91°13'41"
N47°30'30" - N47°32'10", W90°56'40" - W90°55'00"
N47°42'00" - N47°43'60", W85°58'00" - W85°35'60"
Secondary Affiliation: Massachusetts Institute of Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201709
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