Gros Morne National Park


Most of the tablelike uplands on the Northern Peninsula are composed of Precambrian sedimentary rocks. But in a few places, like those shown above, the rocks are composed of igneous rocks from deep below the earth's surface. The type of rock seen here is a peridotite. It is composed of minerals such as olivene and pyroxene and has a lower silica content and higher magnesium and iron content than the granitic rocks we are more familiar with.

Normally this type of rock is only found in the upper layer of the earth's mantle and is buried beneath 10's of kilometers of the crust on the ocean floor or beneath 100's of kilometers of rock below the continental plate. Usually these rocks of the upper mantle are subducted deeper into the earth as the viscous rocks of the mantle circulate, but occasionally on the margins of the continents they can be pushed up through the mantle and reach the surface as they do here.

Fresh surfaces of peridotite are blackish green rock but when exposed to the atmosphere it very quickly hydrates and oxidizes to the yellow-rusty color seen in the photographs above. As these changes occur and the minerals transform into other minerals such as serpentine a number of chemicals are released into the soil.

Wherever these serpentine soils occur they are associated with unique plant communities that are able to tolerate the soil chemistry. On the Tablelands in Gros Morne National Park an exceptionally high concentration of the element chromium is present and this, combined with the harsh environmental conditions, precludes most plant life, leaving these almost barren slopes.

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