Geological Map of Canada (CD-ROM)
Map D1860A
About the Geology of Canada
The new Geological Map of Canada is the latest edition produced by the
Geological Survey of Canada. The last edition was in 1969 (Douglas, 1969).
Map Design
The map displays bedrock formations at or near the surface of the land,
on the sea floor above the continental crust that forms the Canadian
landmass, and oceanic crust surrounding the landmass. The bedrock units
are grouped and coloured according to geological age and composition. The
colours of offshore units and oceanic crust are paler and more generalized
than those on land, although the constituent units offshore are still
easily discernible from their dashed boundaries. This colour design,
coupled with the use of a white buffer zone at the coast allows the
coastline of Canada to be readily distinguished and still show the
grand geological architecture of the Canadian landmass.
The map also shows major faults that have disrupted the Earth's crust,
onshore and offshore, and a variety of special geological features such as
kimberlite pipes,
which locally contain diamonds,
impact structures
suspected to have been caused by meteorites, and extinct and active
spreading centres in the surrounding oceans.
Map Compilation
The map was compiled from published and unpublished maps and reports of
the Geological Survey of Canada, Provincial Geological Surveys, the Yukon
and Northwest Territories Geology Divisions of Indian and Northern
Affairs Canada. Parts of U.S.A. were derived from maps of the United
States Geological Survey. The resulting map is more intricate and complex
than that published in 1969. This reflects completion of the helicopter-
assisted reconnaissance mapping of Canada in 1978 and recent more detailed
geological mapping by the Geological Survey of Canada and Provincial and
Territorial surveys -- much of it under Mineral Development Agreements and
through the GSC's National Geoscience Mapping Program
(NATMAP).
The compilation also used data from extensive gravity surveys by the former
Earth Physics Branch, now part of the GSC, and from aeromagnetic surveys.
The quality and accuracy of the map has been increased as a result of
improved methods of dating geological units, notably from advances in
micropaleontology (conodonts and radiolarian) and in radioactive dating
methods employing the isotopes of uranium and lead. Altogether the new
map has benefitted from a more accurate depiction and correlation of
geological formations and better understanding of their natural relations.
Similarly, extensive
marine geoscience surveys
since 1969 by the GSC now allow the geology on land to be extended across
the Great Lakes and offshore, and to display the age, structure, and
patterns of oceanic crust surrounding Canada.
The Geological Architecture of Canada
The geological assembly of Canada has resulted from the convergence,
collision, and separation of distinctive continental and oceanic fragments
at various times over the last four billion years. Canada's geological
architecture is dominated by its central foundation - the Precambrian
shield -- the largest area of Archean rocks (>2.5 billion years) in the
world and containing its oldest rocks, dated at 4.0 billion years. The
shield consists of several Archean fragments comprising granitic rocks
and gneiss laced with sinuous greenstone volcanic belts and broader tracts
of sedimentary rocks. Orogenic belts between the Archean fragments, such as
those flanking the Superior Province or Slave Province, contain younger,
Paleoproterozoic (2.5 to 1.6 billion years) rocks representing continental,
oceanic, and collisional deposits and foreign or exotic fragments. Although
most of the Precambrian shield was consolidated by the end of Paleoproterozoic time (known as Laurentia), its southeast
portion (the Grenville Province) was stabilized about one billion years ago.
The addition of Mesoproterozoic (1.6 to 1.0 billion years) and older gneisses
and granitic rocks to Laurentia in the Grenville orogenic belt thus completed
the assembly of the Precambrian shield.
Three younger deformed belts, mainly of Phanerozoic rocks (>545 million
years), surround the shield. The Appalachian belt, in the southeast,
contains large tracts of continental and oceanic fragments that were
attached to ancestral North America in early- and mid-Paleozoic times,
about 475 and 375 million years ago, respectively. Similarly, in the
Cordillera of western Canada, large areas of continental and oceanic
fragments were added to ancestral North America in the Mesozoic era at
various times during the last 180 million years. By contrast, in the
Innuitian belt in the Arctic Islands, only a small foreign fragment was
attached in the mid-Paleozoic about 400 million years ago. After the belts
were deformed they were superimposed by extensive less deformed basins
dominated by sedimentary rocks in the Appalachian and Innuitian belts,
but by volcanic rocks in the Cordillera.
Large parts of the Precambrian shield are covered by a thin veneer of
undeformed sedimentary rocks which, except for Western Canada Basin east
of the Cordillera, are mainly of early Paleozoic age. Locally, where the
Paleozoic rocks are overlain by Cretaceous strata, they form basins, as
in Hudson Bay, and fault-bounded troughs in and near Hudson Strait and
north of Baffin Island, related to the rifting and opening of Labrador Sea
and Baffin Bay. Crustal spreading and ocean opening, east of the passive
eastern continental margin, ceased west of Greenland in the early Cenozoic,
nearly 40 million years ago, but still continues in the mid-Atlantic Ocean.
A westward-thickening wedge of Mesozoic and Cenozoic sediments was deposited
in Western Canada Basin. Its sediments were derived from elevated sources in
the mountains of the deforming ancestral eastern Cordillera.
The Pacific margin of Canada, by contrast with the passive Atlantic margin,
is active. The North American continent is overriding and sliding past the
Pacific Ocean crust, thereby generating
earthquakes
(largely offshore) and volcanoes in the western Cordillera.
Uses of the Map
The Geological Map of Canada has many uses, from an educational tool for
teaching the geology of Canada to a template from which other national
thematic maps can be derived. Examples of such thematic maps include: a
tectonic map depicting the geological building blocks and related
structures (faults and folds) that resulted in the assembly of the Canadian
landmass and a metallogenic map showing the distribution and nature of
important mineral deposits and their genetic relationships to their host
geological formations. The new Geological Map of Canada is also the
framework against which other
national maps and databases,
such as the
Gravity Map,
Magnetic Anomaly Map,
Seismicity
(earthquake risk),
and various kinds of
regional geochemical maps
may be compared and interpreted.
The digital version of the new Geological Map of Canada opens up new
frontiers for learning about Canada and the great wealth and potential
of its landmass and offshore regions. Not only will it provide the
opportunity for geological patterns and related geological relationships
to be studied at the scale of the Canadian landmass, but it will form the
foundation for the digital national geoscience information base.
J.O. Wheeler
November, 1996
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