Class Note 21
The craton may have a relatively thin (<2000m) cover of generally undeformed sediments, or it may be free of sedimentary cover and known as a shield.
Examples of continental shields occur in eastern Canada, Scandinavia, southern Africa, and western Australia.
An eposode of mountain building is known as an orogeny, and the range of mountains as an orogenic belt.
An orogeny results in the formation of a major mountain (orogenic) belt, such as the Alps, the Himalayas, and the western Cordillera (Rocky Mountains).
A major mountian belt s composed of several mountain ranges, such as the Front Range, Gore Range, Ten Mile Range, and the Sangre de Cristo Range here in Colorado.
Major mountain belts tend to have thick sequences (>5km) of sedimentary rocks.
Continents have grown through geologic time with the addition of new, exotic terranes, accreted onto the margins as accretionary wedges or prisms.
Continental crust is made up of blocks or terranes of high grade metamorphic rocks that are roughly the same age. The block we are on here is about 1.8 Billion years old for the age of metamorphism. This block extends from the Colordao-Wyoming border south over New Mexico and Arizona and Western Texas and west to Utah.
To the north the Wyoming terrane give an age of about 2.2 BY.
British Columbia and Alaska are a complex of young accreted terranes.