The Tablelands in Gros Morne National Park, Canada, is one of the few places on Earth where we can see our planet’s mantle. The mantle is the layer between the Earth’s core and the continental crust. It is the primary force behind tectonic plate movement. This layer makes up 84% of the Earth’s mass, yet it is exceptionally rare to see it on the surface.
Tectonic activity
The Earth’s mantle is a 2,900km thick layer of viscous, silicate rock. Convection currents in the mantle cause tectonic plates to converge, subduct, diverge, and glide past each other. The mantle is responsible for mountain ranges, volcanoes, earthquakes, and even island chains.
Aerial image of the Tablelands. Photo: Russ Heinl/Shutterstock
Gros Morne National Park is a 1,805 sq km testament to the raw power of plate tectonics. It became a UNESCO World Heritage Site in 1987 because “it provides a rare example of continental drift, where deep ocean crust and the rocks of the earth’s mantle are exposed”. Tectonic activity over half a billion years led to the formation of the park’s deep fiords, high cliffs, and the celebrated Tablelands.
The Tablelands plateau
The Tablelands is a plateau rising 700m above sea level. It began 500 million years ago during the formation of the Pangea supercontinent.
At the time, North America, Europe, and Africa joined together, and the ancient ocean, known as Iapetus, began to close. From 10km below the Iapetus ocean floor, the subduction of two tectonic plates pushed up pieces of the Earth’s crust and mantle. Scientists agree that the formation of the Tablelands proves that plate tectonics theory is accurate.
On the surface, pieces of the mantle form a desolate but colorful landscape. There are yellow, orange, red, and sometimes even green and blue rocks. These are mostly peridotite, a snakeskin-type rock called serpentinite, dunite, and pyroxenite. Tableland rocks are high in nickel, magnesium, chromite, iron, cobalt, olivine, clinopyroxene, and orthopyroxene. These are some of the oldest rocks on Earth.
A minor stream in the Tablelands. Photo: Windcoast/Shutterstock
But when mantle rock decomposes, it produces soil that is toxic to most plants. That, and not the cool Newfoundland climate, is why the Tableland is so bare. Yet some carnivorous plants have flourished, especially pitcher plants. They draw nutrients from unsuspecting insects that fall into their pitfall traps. Large wildlife struggles here, but microorganisms thrive. Astrobiologists believe that the Tablelands offer a similar environment to that of Mars.
Where else can you see the Earth’s mantle?
You can see the Earth’s mantle at a few other tectonic hotspots. Macquarie Island in Tasmania is the result of a collision between the Indo-Australian and Pacific Plates, creating land made entirely of crust and mantle. As with the Tablelands, tectonic activity pushed up pieces of the Earth’s crust and mantle from five kilometres below the ocean floor.
Another example is Saint Peter and Saint Paul Archipelago in Brazil. These micro islands show the sub-oceanic mantle.
Then there is Zabargad Island in Egypt, formed when continental plates converged and thrust the mantle to the surface.
Serpentinite rock. Photo: Chiyacat/Shutterstock
Recently, scientists have come across exposed mantle rock in Baltimore, Maryland. This happened during the formation of the Appalachian Mountains. Scientists believe that these ophiolite rocks are a remnant of the ancient Iapetus ocean floor, forced above sea level during that same process of subduction.
