From the highway above Norris
Point, you can look across Bonne Bay and see
a piece of the earth's history rising before
you. These are the Tablelands, a striking 600
metre-high plateau of rock from the earth's
upper mantle, an anomaly on the landscape that
has given scientists valuable information about
the theory of Plate Tectonics, in which continents
do not stay put, but move about on the surface
of the earth's fiery liquid core.
During this ‘continental
movement’ over 450 million years ago, the
earth's crust split beneath the ocean and,
as the plates moved closer together, the oceanic
crust and mantle layer of the Eurasia/Africa
plate was thrust on top of the sedimentary rock
of the North American Continental Shelf. By
the time the plates had finished their collision
course, a huge chunk of the ocean floor and
the upper mantle rock, usually buried beneath
it, was exposed. When the continents broke apart
again, the rift was 500 kilometres further east,
leaving this piece of the Eurasian/African Plate
stuck to North America, and providing Gros Morne
National Park with a unique cross section of
the ocean floor.
The mantle rock is called
peridotite; a dark greenish brown in its natural
state, it becomes a golden tan as it oxidizes
or weathers. Under extreme heat and pressure,
water has altered some of this material to form
serpentine, a marbled green rock common to the
oceanic lithosphere. The rock is so rich in
magnesium and iron that it supports little vegetation;
however, botanists are discovering a fascinating
community of arctic alpine species that have
somehow managed to survive in isolated pockets
of the Serpentine Barrens.
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