The Geology and Geological History of Vancouver Island Steven Earle, PhD Department of Geology Malaspina University-College Nanaimo, British Columbia, Canada

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The Geology and Geological History of Vancouver
IslandSteven Earle, PhDDepartment of
GeologyMalaspina University-CollegeNanaimo,
British Columbia, Canada
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• Vancouver Island is part of the Insular
  Superterrane of western B.C.

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Most of Vancouver Island is made up of the
Wrangellia Terrane (part of the Insular Super
Terrane) shown here in shades of green. The
Wrangellia Terrane arrived on the west coast of
North America some time around 100 m.y. ago. The
Nanaimo Gp. Rocks were deposited on top of the
Wrangellia rocks (from 85 to 65 .y. ago), and the
rocks of the Pacific Rim and Crescent Terranes
arrived here later(at 55 and 42 m.y.
respectively).
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The oldest rocks of Vancouver Island are Devonian
in age (ca. 370 m.y.) and include sea-floor and
terrestrial volcanic rocks as well as some
limestone of the Sicker and Buttle Lake Groups.
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Myra Falls Mine
Dyke in pillow basalt
Devonian (Sicker Group) Rocks
Chert overlain by Cretaceous conglomerate
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The Karmutsen and Quatsino Formations are part of
the Vancouver Group. The Karmutsen is dominated
by sea-floor basalt , while the Quatsino is
primarily limestone. The Karmutsen is the most
common rock type exposed on Vancouver Island
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Karmutsen Formation (Triassic) sea-floor pillowed
basalt Quatsino Formation limestone (with a
mafic dyke).
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The Bonanza Fm. includes volcanic rocks that
erupted on land, for the most part.
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The Westcoast Crystalline complex (WCC) includes
granitic rocks that are the intrusive equivalents
of the Bonanza Fm.
The WCC also includes metamorphic rocks in the
Victoria region.
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Jurassic aged Island Intrusion granite with a
quartz-feldspar vein
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The rocks shown in colour on this map comprise
the Wrangellia Terrane, which collided with North
America at around 100 m.y. ago.
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The Nanaimo Group sedimentary rocks were
deposited into the basin between Wrangellia and
North America.
Nanaimo Group (65-85 m.y.)
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The total thickness is roughly 5000 m. The
oldest rocks may be as old as 92 m.y. but most
basal units are no more than 86 m.y. The
youngest rocks are probably more than 65 m.y. but
could be younger.
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Most, but by no means all, of the Nanaimo Gp.
sediments were deposited under marine conditions,
largely as submarine fans offshore from coastal
shelf deposits.
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Nanaimo Group (Cretaceous) Sandstone, mudstone,
comglomerate
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The City of Nanaimo exists because of coal
mining, which took place from around 1850 to
1950. It could be argued that this is also why
British Columbia is part of Canada.The only
coal mining at present is from the Quinsam mine
near to Campbell River. Exploration for coal bed
methane is currently underway in the area north
of Nanaimo
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The Pacific Rim and Crescent Terranes were
accreted onto Vancouver Island as a result of
plate movements.
Pacific Rim at 55 m.y. and Crescent at 42 m.y.
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Leech River Complex (Pacific Rim Terrane)
phyllite at Niagara Falls
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Crescent Terrane Tertiary, Metchosin Igneous
Complex, Sea-floor pillowed basalt
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These collisions led to compression of western
North America and the up-thrusting of Nanaimo
Group and Wrangellia rocks onto Vancouver Island
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Sedimentary rocks along the outermost west coast
(the Carmanah Fm.) were deposited during the
Paleogene (up until around 24 m.y. ago.)
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Cross-section from the edge of the North American
plate at the subduction front, across Vancouver
Island to the Strait of Georgia. This section
shows the Pacific Rim Terrane in brown and the
Crescent Terrane in red. Cretaceous and Tertiary
sedimentary rocks are shown in yellow.