geology of vancouver island

The Geology and Geological
History of Vancouver Island

Steven Earle, PhD
Department of Geology
Malaspina University-College
Nanaimo, British Columbia, Canada


Vancouver
Island is part
of the Insular
Superterrane
of western
B.C.


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).


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.


Myra Falls Mine

Dyke in pillow
basalt

Chert overlain by Cretaceous
conglomerate

Devonian
(Sicker Group)
Rocks


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


Karmutsen Formation
(Triassic) sea-floor
pillowed basalt

Quatsino Formation
limestone (with a
mafic dyke).

The Bonanza Fm. includes
volcanic rocks that erupted on
land, for the most part.


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.


Jurassic aged
Island Intrusion
granite with a
quartz-feldspar
vein


The rocks shown in
colour on this map
comprise the Wrangellia
Terrane, which collided
with North America at
around 100 m.y. ago.


The Nanaimo Group

sedimentary rocks were
deposited into the basin
between Wrangellia and
North America.
Nanaimo Group
(65-85 m.y.)


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.


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.



Nanaimo Group (Cretaceous)
Sandstone, mudstone, comglomerate


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


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.


Leech River
Complex (Pacific
Rim Terrane)
phyllite at

Niagara Falls


Crescent Terrane
Tertiary, Metchosin
Igneous Complex,
Sea-floor pillowed
basalt


These collisions led to compression of western North America
and the up-thrusting of Nanaimo Group and Wrangellia rocks
onto Vancouver Island


Sedimentary rocks
along the outermost
west coast (the
Carmanah Fm.)
were deposited
during the
Paleogene (up until
around 24 m.y.
ago.)


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.