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وحياه كل مصطلح جيولوجيا مابينا تساعدونى انا عندى بحث لازم يستلم يوم السبت يارت الى يقدر يجبهولى البحث عن


major tectoinc features of the earth(percambrain shield

ياريت بسرعه يبا جماعه

The Canadian Shield

The Canadian Shield, also known as the Precambrian Shield or Laurentian Plateau, covers about half of Canada as well as most of Greenland and part of the northern United States; an area of 4.4 million square kilometers (1.7 million square miles).

It is the oldest part of the North American crustal plate and contains fossils of bacteria and algae over 2 billion years old.

The shield is composed of granite and the earth's greatest area of exposed Precambrian rock (igneous and metamorphic rock formed in the Precambrian geological era 500 million years ago).

The shield was the first part of the continent to be permanently raised above sea-level. Subsequent rising and falling, folding, erosion and continental ice sheets have created its present topography. The reoccurring invasion and withdrawal of the ice sheets (1.6 million to 10,000 years ago) depressed the surface creating Hudson Bay, scraped out tens of thousands of lake basins, carried away much of the soil cover and redeposited glacial debris.

The shield plateau ranges from 305 to 610 meters (1000 to 2000 feet) above sea level. In northern Labrador and Baffin Island the crustal plate has tilted so much that it rises over 1,500 meters (5,000 feet) above sea level. There are a number of mountain ranges within the shield: the Adirondack (northeastern New York state), Superior Highlands (northern Minnesota, Wisconsin & Michigan states), Torngat and Laurentian.

The shield is a rich source of metallic minerals such as iron, nickel, copper, zinc, uranium, gold, silver, platinum and molybdenum.

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