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Tectonic elements of North America and location of LITHOPROBE transects.

Before looking at the largest recorded rift on earth, the Keweenawan Rift System or KRS (marked on this map in striped green as KR within the oddly shaped transect marked GL) we should have another look at the heartland of the Canadian Shield. This is the old craton of the Superior Province, which also is the largest of the world's Archean cratons (1.6 million km2). The reason is that we want to know more about the earliest stages of the formation of the first cratons which form the nuclei of the North American continent.
The Superior Province offers an unrivalled perspective on early crustal genesis. It received additions of juvenile material (new rock formed from magma) to Earth's lithosphere during the Mid to Late Archean (approximately 3,100 to 2,600 Ma). Farther on we shall discuss the Abitibi subprovince, which is the largest building block of this juvenile crust. Geochemical data indicate that it was derived directly from the Late Archean mantle.

Given the occurrence of these various, and very old, terranes within the most prominent old craton invites the study of their internal makeup, of how these various types of terranes came to be together, or accreted. Was the mechanism the same which we have been observing in more recent plate-tectonic processes?

This is the purpose of a new study area or transect now being activated by LITHOPROBE, the Western Superior Transect. It follows a detailed study of the Kapuskasing Structural Zone, a transect for one of the earliest LITHOPROBE studies. Note the transect areas for each as outlined on the map (slide # 37) .

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