The Newfoundland Story
Rocks on the Island of Newfoundland are divided
into three zones - Western, Central and Eastern.
The Western Zone has been part of North America
for at least the last billion years (1000 million),
but the other two zones are relative newcomers.
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Geological Subdivisions of Newfoundland.
The bringing together of ancient oceans and continents has given
Newfoundland three geological zones: the Western, Central and Eastern
zones. Each of these zones has distinct rock types and geological
histories.
Illustration by Duleepa Wijayawardhana.
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About 600 million years ago, North America was part of a much
larger continent. Then this continent broke apart. A mid-ocean
ridge developed along the break and the Iapetus Ocean began to
open. By the Middle Cambrian (540 million years ago), the Western
Zone lay on the eastern edge of ancient North America, a continent
we now call Laurentia.
Newfoundland in the Middle Cambrian.
Opening of the Iapetus Ocean and the formation of a mid-ocean ridge 540 million
years ago during the Middle Cambrian period.
From Stephen Colman-Sadd and Susan A. Scott,
Newfoundland and Labrador: Travellers Guide to the Geology
(St. John's: Government of Newfoundland and Labrador, 1994).
with more information (40 kb).
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Then convection currents shifted and subduction began.
By Early Ordovician time (about 490 million years ago),
volcanic island arcs had grown above the subduction zones,
as the floor of the Iapetus Ocean sank back into the
mantle. Today, the remains of these island arcs are
preserved in the volcanic and intrusive rocks of
the Central Zone.
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Newfoundland 490 Million Years Ago and Today.
Closing of the Iapetus Ocean and collision of ancient continents
which took place 490 million years ago in the Early Ordovician.
From Stephen Colman-Sadd and Susan A. Scott,
Newfoundland and Labrador: Travellers Guide to the Geology
(St. John's: Government of Newfoundland and Labrador, 1994).
with more information (45 kb)
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Subduction of the Iapetus Ocean floor slowly pulled Laurentia
toward another continent, Gondwana, which lay to the east. As
the continents converged, pieces of ocean crust and the underlying
mantle were pushed onto the continental margin of Laurentia
about 470 million years ago.
Movement of the Old Ocean Floor.
Cross-sections showing the movement of the old ocean floor. When the Iapetus Ocean closed, slope deposits and giant slabs of the old ocean floor (ophiolite) were transported westward across the old continental margin.
From A. B. Ryan, Newfoundland Journal of Geological Education, Vol. 7,
No. 2, 1983. Adapted by Duleepa Wijayawardhana.
with more information (20 kb).
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These huge slabs of ocean floor (up to 40 x 10 km)
are preserved in the mountains of western Newfoundland as a
rock sequence called ophiolite. Table Mountain in Gros
Morne National Park and Blow-Me-Down Mountain near
Corner Brook are examples.
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Top: Moho Seismic Discontinuity.
Photo courtesy of Trevor Bell, © 1998.
with more information (45 kb).
Left: Tablelands.
View of the Tablelands, Gros Morne National Park.
Photo courtesy of Trevor Bell, © 1998.
with more information (45 kb).
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By the Early Devonian (410 million years ago),
Laurentia and Gondwana had collided, forming a huge,
new continent. Across the middle of the continent, where
the Iapetus Ocean had once been, there was a mountain range,
and halfway along this lay what is now Newfoundland.
Over time, these mountains were gradually eroded by wind and
rain. By the Carboniferous (360 million years ago), Newfoundland
was once again fairly low-lying and swampy valleys and lakes on the
west coast were filling with sand, mud, and plant debris.
These are now preserved as sandstone, shale and coal, respectively.
At the same time, parts of the sea were drying up, leaving
evaporite rocks (salt and gypsum) behind.
(57 kb)
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(43 kb)
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Hills of White Gypsum.
Hills underlain by white gypsum near Flat Bay, western Newfoundland. Gypsum is a
soft, white mineral consisting mainly of calcium sulphate formed in hot climates
during the evaporation of sea water. Gypsum from the Flat Bay deposit in western
Newfoundland is used in the manufacturing of gyproc wallboard and cement in Corner
Brook and is also exported to the United States.
From Geological Survey of Newfoundland and Labrador -
"Geology and Geological Features - Mineralization" and "Aspects of Mining in Newfoundland and Labrador: Production."
http://www.gov.nl.ca/mines&en/geosurvey/.
Courtesy of David Liverman, Government of Newfoundland and Labrador.
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The continents stayed welded together until Early Jurassic time,
200 million years ago. Then they broke apart to form the present
Atlantic Ocean, which continues to open today. But the break did
not occur exactly along the line of the old Iapetus Ocean.
In North America, it lay just to the east of it, leaving fragments
of Gondwana still attached to Laurentia. The Eastern Zone of Newfoundland
is one of these fragments. Others include Nova Scotia, and parts
of New Brunswick and the northeastern United States.
The southern half of the mountain range that marked the line of the
Iapetus Ocean now forms the Appalachian Mountains of eastern North
America, running from Alabama to Newfoundland. The northern half is
to be found across the Atlantic Ocean in Scotland and Scandinavia.
Gondwana, minus the Eastern Zone and the other pieces it left behind
in North America, has broken apart to form Africa, South America,
India, Australia and Antarctica.
© Trevor Bell and David Liverman
Adapted from Stephen Colman-Sadd and Susan A. Scott, 1994
(Newfoundland and Labrador: Traveller's Guide to the Geology)
