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Voyageurs National Park
This section highlights the map units (i.e., rocks and unconsolidated deposits) that occur
in Voyageurs National Park and puts them in a geologic context in terms of the
environment in which they were deposited and the timing of geologic events that created
the present landscape.
Some of the oldest rocks in the world are exposed in
Voyageurs National Park. About 2.5- 4.5 billion years ago
(Ba), plate- tectonic processes generated a number of
isolated areas of continental crust. In North America,
rocks formed by these early tectonic events are found in
Minnesota, Wyoming, parts of Canada, and Greenland.
These bedrock units were shaped and carved by at least
four periods of glaciation. The most recent continental
glaciation in North America ended about 10,000 years
ago. All evidence of the geologic history that has
occurred between these two widely separated periods is
missing from Voyageurs and most of the Canadian
Archean Eon (2.5-3.0 Ba)
Relatively little is known about the early Precambrian
since there were few fossils preserved and hard- bodied
organisms are not found prior to about 550 million years
ago at the beginning of the Cambrian Period (figure 2).
However, excellent exposures of Archean rocks in
northern Minnesota, including the Voyageurs area,
reveal a protracted and complex structural evolution
(Davis et al. 1994). The Archean basement complex of
intensely metamorphosed rocks of sedimentary,
volcanic, and intrusive igneous origin, dated at 2.6 Ba and
older, is commonly referred to as pre- Kenoran. The
earliest gneisses and schists, rich in mica, may have
originally been sandstones (Harris et al. 1995). Following
the emergence of the continental rocks of the Superior
Province about 2.7- 3.0 Ba, structural deformation
occurred over more than 100 million years.
In late Archean time (2.8- 2.5 Ba), repeated episodes of
continental collision and north- south directed
compression and subduction generated a mountainbuilding
episode known in North America as the
Algoman Orogeny. This orogeny formed the gneisses,
schists, and granites exposed today in Voyageurs
National Park (Miller et al. 1987; Kiver and Harris 1999).
Subduction of oceanic crust beneath the cratonic crust
generated volcanic islands in the Precambrian sea. Zones
of thick, basaltic lava accumulated in linear basins (backarc
basins) formed between the less- dense continental
crust and the volcanic islands. These lava- filled basins
created today's greenstone belts (Kiver and Harris 1999).
The oldest known rock in Minnesota, the Ely
greenstone, formed at this time.
During the Algoman Orogeny, a great number of tectonic
faulting and folding events deformed the rocks in the
north- central Minnesota part of the Superior Province.
Today, these event are seen in the three geologically
distinct subprovinces, Wabigoon ,Quetico, and Wawa
Major fault zones form the boundaries between the three
subprovinces. The northeast- southwest trending Rainy
Lake- Seine River fault zone separates the Quetico
subprovince from the Wabigoon subprovince to the
north. South of Voyageurs, the Vermillion fault zone
marks the boundary between the Quetico subprovince
and the Wawa subprovince (figure 3). The Quetico
subprovince has been interpreted as a classical
sedimentary basin (fore- arc or back- arc basin)
developed between two active volcanic island chains
(volcanic arcs) represented by the Wabigoon and Wawa
subprovinces (figure 4) (Davis et al. 1994).
These ancestral fault zones developed oblique,
northwesterly components of movement that caused
extensive strike- slip motion. Locally, segments on these
faults were displaced by more than 20 miles (32 km), with
the north side of faults displaced to the east (Davis et al.
At least three phases of deformation folded the bedrock
of Voyageurs (Day 1990). The first episode produced
southwest - plunging en echelon folds. The second phase
of deformation was the most intense in the area and is
recognized by small- scale folds, a strong schistosity in
the rocks, mineral lineations, and a progressive transition
in ductile deformation from the first phase to the second
phase. The third phase produced high- angle faults and
shear zones. Regional folding appears to have occurred
prior to, concurrent with, and after regional
Sedimentary units were complexly folded along eastwest
axes and commonly have very steep to vertical dips.
North- south directed compression generated regional,
arch- like convex folds, or flexures, in sedimentary strata
(antiformal syncline or anticlinoria) along eastnortheasterly
trends. Regional metamorphism
accompanied compressive north- south oriented
thrusting and folding.
Later in the orogeny, the granitic plutons found in
Voyageurs intruded into the area. Mineral- rich fluids
from these plutons produced dikes, pegmatites, and quartz veins that concentrated metallic minerals in parts
of the greenstone belts.
. A schematic drawing of subprovinces of the Superior Province. Contacts between subprovinces are fault zones.
Proterozoic Eon (2.5-0.5 Ba)
The Proterozoic Eon represents about 40 percent of all
geologic time. By 1.8 Ba, isolated regions had joined into a
single large craton that included what we see today as
Greenland, central Canada, and the north- central
United States. The Midcontinent Rift that forms the axis
of Lake Superior formed during this time and is likely the
surface expression of a rising plume of hot mantle
material (Hauser 1996). Faults and igneous dikes mark
the northwest arm of this rift. Lava flows poured from
long fissures to fill the axes of synclinal basins. Magma
that did not breach the surface crystallized into granitic
plutons that are now exposed in the park.
Deformation in the Voyageurs area seems to have
terminated by the time the northwest- trending diabase
dike swarm was emplaced around 2.12 Ba (Day 1990). The
Proterozoic diabase dikes of the Kabetogama- Kenora
Dike Swarm in Voyageurs formed in long, linear
fractures between 2.2 and 2.1 Ba. Proterozoic schistose
tectonite (fault rock) intrude the older Archean rocks.
Prolonged Erosion (570 Ma - 0.19 Ma)
By the end of the Precambrian, the long series of tectonic
events that created the basement complex of the
Canadian Shield was over. Millions of years of erosion
left only the roots of ancient mountains exposed (Harris
et al. 1995). Extensive seaways covered much of the
craton during the Early Paleozoic, but during the Late
Paleozoic, Mesozoic, and Cenozoic, the province stood
above sea level and was extensively eroded. The
topography was reduced to a flat rolling plain even
before the advance of the Pleistocene glaciers. The
glaciers removed most of the Cenozoic deposits and all
of the Paleozoic and Mesozoic record. When the first
continental glaciers advanced into the Voyageurs area,
the landscape was probably of low relief with a fairly
uniform soil cover supporting extensive forests (Harris et
. Massive Precambrian rocks, like those pictured above, are exposed throughout Voyageurs National Park.
Pleistocene Epoch (1.6-0.01 Ma)
Throughout the Ice Age, beginning perhaps 190,000
years ago and extending intermittently in the Voyageurs region to approximately 11,400 years B.P., continental
sheet glaciers covered north- central Minnesota, the
Great Lakes Region, and most of Eastern Canada (Davis
et al. 1994). The Illinoian stage (190,000 to 135,000 years
B.P.) was the first glacial event and was followed by a
warming period known as the Sangamonian Interglacial
(135,000 to 119,000 years B.P.) The Wisconsin stage
followed the Sangamonian Interglacial and advanced and
retreated across the region from 135,000 years B.P. to
10,000 years B.P. when the Holocene Epoch, or "Recent"
geological time period began (figure 2).
During the Pleistocene, glaciers scooped out Lake
Superior's basin along the trend of the Midcontinent
Rift. At the east end of Lake Superior, the bottom of the
lake is 1,302 feet (397 m) below the surface at an elevation
of 700 feet (213 m) below sea level (Kiver and Harris
To the west of Voyageurs, Lake Agassiz formed during
glacial retreat. Meltwater from the last continental
glacier, backed- up because the north- flowing rivers that
drained into Hudson Bay were blocked by ice. Water
began to collect in the Red River valley in western
Minnesota about 12,000 years ago and then spread over
eastern North Dakota and adjacent Canadian Provinces.
Lake Agassiz covered the Voyageurs area during glacial
retreat from about 11,400 to 9,500 years B.P. (Davis et al.
Today unconsolidated sediments and thin soils have
been superimposed on some of the oldest bedrock in
North America. Streams have been reworking and
sorting the glacial debris rather slowly due to the low
relief in the area. Large basins are now occupied by lakes,
ponds, bogs, wetlands, and interconnecting waterways.
The tremendous weight of the ice sheet depressed the
crust. When the ice melted, the crust rebounded and it is
still rising today. Glacial rebound has caused some lakes
to drain away and some lakes to become bogs and
swamps. In the Boundary Waters region, the lakes
occupy deeper parts of the basins once filled by Lake
Agassiz. The land is rising at a rate of about 1 foot (0.3 m)
per century (Kiver and Harris 1999).
Davis, S.R., Hite, A.G., and Larson, W.S., 1994, Mineral occurrences and development potential near Voyageurs National Park, Minnesota: U.S. Department of the Interior, Bureau of Mines, MLA 5- 94, Intermountain Field Operations Center, Denver, CO., 153 p.
Day, W.C., 1990, Bedrock geologic map of the Rainy Lake area, northern Minnesota: USGS Map I- 1927, scale 1:50,000.
Harris, A.G., Tuttle, E., Tuttle, S.D., 1995, Geology of National Parks: Kendall/Hunt Publishing Co., Dubuque, IA, p. 247- 258.
Kiver, E.P., and Harris, D.V., 1999, Geology of U.S. Parklands: John Wiley & Sons, Inc., New York, p. 177- 189.
Miller, J.D., Jr., Morey, G.B., and Weiblen, P.W., 1987, Seagull Lake- Gunflint Lake area; A classical Precambrian stratigraphic sequence in northeastern Minnesota, in D.L. Biggs, ed., North- Central Section of the Geological Society of America: Geological Society of America, Centennial Field Guide, v. 3, p. 47- 51.