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Neoproterozoic kimberlite emplacement in the Front Range, Colorado

Alan P. Lester, Edwin E. Larson, G. Lang Farmer, Charles R. Stern and Jonathan A. Funk
Neoproterozoic kimberlite emplacement in the Front Range, Colorado
Rocky Mountain Geology (2001) 36 (1): 1-12


A paucity of isotopic age determinations for the more than 100 kimberlitic diatremes, dikes, and sills within the Colorado-Wyoming kimberlite province has fostered the prevailing notion that emplacement of these bodies occurred during a discrete interval of ultramafic magmatism spanning Early to Late Devonian time. However, new geochronologic data for two kimberlite bodies (Chicken Park and Green Mountain kimberlites) support a Neoproterozoic emplacement age for these bodies. (super 40) Ar/ (super 39) Ar analysis of fine-grained matrix phlogopite from the Chicken Park dike indicates emplacement between 620 and 640 Ma. (super 40) Ar/ (super 39) Ar dating of the Green Mountain diatreme, utilizing both phlogopite megacrysts and mineral separates from xenoliths, is somewhat equivocal because of excess Ar, but suggests emplacement between 500 and 800 Ma. A Sm-Nd isochron, based on megacrystic phases from the Green Mountain diatreme, yields an age of 572+ or -49 Ma. Neoproterozoic emplacement indicates that the Colorado-Wyoming kimberlite province apparently has undergone multiple intervals of kimberlitic magmatism, similar to other kimberlite provinces worldwide. The episodes of kimberlite emplacement coincide with periods of relative orogenic and magmatic quiescence in Colorado and Wyoming.

ISSN: 1555-7332
EISSN: 1555-7340
Serial Title: Rocky Mountain Geology
Serial Volume: 36
Serial Issue: 1
Title: Neoproterozoic kimberlite emplacement in the Front Range, Colorado
Affiliation: University of Colorado, Department of Geological Sciences, Boulder, CO, United States
Pages: 1-12
Published: 2001
Text Language: English
Publisher: University of Wyoming, Dept. of Geology and Geophysics, Laramie, WY, United States
References: 56
Accession Number: 2003-061924
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N40°15'00" - N41°00'00", W106°19'60" - W104°49'60"
N41°00'00" - N42°22'60", W106°19'60" - W105°16'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200320
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