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(super 40) Ar/ (super 39) Ar evidence for ca. 1800 Ma tectonothermal activity along the Great Falls tectonic zone, central Montana

Daniel Holm and David Schneider
(super 40) Ar/ (super 39) Ar evidence for ca. 1800 Ma tectonothermal activity along the Great Falls tectonic zone, central Montana
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (December 2002) 39 (12): 1719-1728

Abstract

Late Paleoproterozoic (1900-1600 Ma) tectonothermal activity on all borders of the Archean Wyoming Province has long been established by low-precision K-Ar and Rb-Sr studies. However, recent tectonic models advanced for supercontinent aggregation require improved constraints on the timing of tectonothermal activity along major boundaries. On its northwestern boundary, the Great Falls tectonic zone separates the Archean Wyoming and Hearne provinces. Recently published U/Pb ages and geochemical data reveal the presence of a Paleoproterozoic (ca. 1860 Ma) marginal-arc magmatic complex along a portion of the Great Falls tectonic zone in central Montana. We present nine new (super 40) Ar/ (super 39) Ar mineral ages (on hornblende and biotite) from these same arc rocks, which indicate ca. 1800 Ma thermal activity (>500 degrees C) and subsequent rapid cooling to below 300 degrees C by 1775 Ma. This new data set constrains the timing of Wyoming-Hearne collision to between 1860 and 1800 Ma and the timing of last significant tectonothermal activity of this portion of the Great Falls tectonic zone (1800-1775 Ma.) We note that our data add to a growing geochronologic database indicating ca. 1800 Ma tectonothermal activity (via either initial suturing or continued tectonic activity) associated with Paleoproterozoic docking of the Wyoming Province with Laurentia.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 39
Serial Issue: 12
Title: (super 40) Ar/ (super 39) Ar evidence for ca. 1800 Ma tectonothermal activity along the Great Falls tectonic zone, central Montana
Affiliation: Kent State University, Department of Geology, Kent, OH, United States
Pages: 1719-1728
Published: 200212
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 44
Accession Number: 2003-022463
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N46°55'60" - N46°55'60", W110°43'60" - W110°43'60"
Secondary Affiliation: Ohio University, USA, United States
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200309
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