M-193 Bedrock Geology of the Cavity Lake Fire Area, Boundary Waters Canoe Area Wilderness, Northeastern Minnesota
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M-193 Bedrock Geology of the Cavity Lake Fire Area, Boundary Waters Canoe Area Wilderness, Northeastern Minnesota
Published Date
2017
Publisher
Minnesota Geological Survey
Type
Map
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Report
Abstract
The bedrock geology in this part of the Boundary Waters Canoe Area Wilderness
is extremely diverse and unusually well exposed (Fig. 1). Many parts of this area were
mapped to varied levels of detail in the 1930s, and more recently in the 1970s and 1980s
(see Index Map), with efforts focused primarily along waterways. A severe windstorm in
1999 blew down trees in much of the region, and a delayed result in 2006 was the Cavity
Lake forest fire. The fire exposed bedrock and allowed comparatively unencumbered
access to interior parts of the map area, creating a unique and time-sensitive opportunity
for mapping. Fieldwork and compilation of prior mapping was conducted in 2007 and
2008, and a preliminary map was produced (Jirsa and Starns, 2008). That map is revised
here to incorporate subsequent fieldwork and geochronologic analyses, including one new
date acquired by coauthor Schmitz.
The map portrays bedrock that represents crustal evolution spanning the Neoarchean to
Mesoproterozoic Eras (Fig. 2), with an emphasis on structural and stratigraphic relationships
in the Neoarchean portion. Neoarchean greenstone-granite terrane of the Wawa subprovince
of the Superior Province is represented by a succession of mostly mafic to ultramafic
metavolcanic rocks (circa [ca.] 2,700 Ma), unconformably overlain by calc-alkalic volcanic
and volcaniclastic rocks (ca. 2,690 Ma), and intruded by the Saganaga Tonalite (also ca.
2,690 Ma).
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Bedrock geology of the Cavity Lake Fire Area, Northeastern Minnesota, mapped after the fire of 2006.
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THE U.S. GEOLOGICAL SURVEY AS PART OF THE 2007 STATE GEOLOGIC MAPPING PROGRAM ELEMENT (STATEMAP)
OF THE NATIONAL COOPERATIVE GEOLOGIC MAPPING PROGRAM, AND
THE PRECAMBRIAN RESEARCH CENTER, UNIVERSITY OF MINNESOTA DULUTH
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Jirsa, Mark, A; Starns, Edward, C; Schmitz, Mark, D. (2017). M-193 Bedrock Geology of the Cavity Lake Fire Area, Boundary Waters Canoe Area Wilderness, Northeastern Minnesota. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/194191.
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