Читать книгу One Best Hike: Grand Canyon. Everything You Need to Know to Successfully Hike from the Rim to the River—and Back онлайн

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Collisions, 1.8 billion to 1.4 billion years ago: About 1.8 billion years ago the location that would become the Grand Canyon was an oceanic basin that lay between the incipient North American Plate (to the northwest) and a volcanic island chain (the Yavapai Arc to the southeast). By 1.7 billion years ago the oceanic crust that carried the Yavapai Arc was being pushed over the edge of the North American Plate. In the process, the sediment in the intervening ocean basin was buried, twisted, heated, and hence metamorphosed to form the Vishnu, Brahma, and Rama schists, collectively known as the Grand Canyon Metamorphic Suite, or colloquially as the Vishnu Schist or basement rocks. Meanwhile, deeper sediments were completely melted. The resultant magma rose through cracks in the schist and cooled to form the intermingled Zoroaster Granite (and related rocks), a light-colored, often pinkish rock. Later, there was a collision with a second volcanic island chain, the Mazatzal Arc. These collisions added much material to the edge of North America, moving its boundary well south of the Grand Canyon region.