File:Grand Canyon National Park- Basement Rocks 0201 (7706671774).jpg
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| Description |
The sheer cliffs of the Basement Rocks (Vishnu Schist and Zoroaster Granite) rise in a notoriously narrow section of trail called "The Box" in Bright Angel Canyon. NPS Photo by Kristen M. Caldon Basement Rocks: thickness - unknown. Weathered and colorful, igneous and metamorphic cliffs rise steeply from the river in Lower Granite Gorge. These are the oldest rocks in the canyon, dating from the Precambrian. These rocks make up the bottom of the Grand Canyon. They were created 1840-1680 million years ago, during the Precambrian- Paleoproterozoic Era. Grand Canyon’s basement rocks include both the metamorphic rocks of the Granite Gorge Metamorphic Suite as well as the igneous rocks of the Zoroaster Plutonic Complex. The metamorphic suite was formed during the collision between a volcanic island arc and the North American continent. The sedimentary and volcanic rocks that were accumulating in an ocean basin between the continent and island chain were subducted. They were subjected to intense heat and pressure resulting in the metamorphic rocks that we see today- dark schists and gneisses. During the collision, some of the sedimentary and volcanic rocks were subducted deep enough to be melted. Molten rock rose up through weak spots in the rocks but did not break the surface. These intrusions of melted rock cooled to form the granites and pegmatites of the Zoroaster Plutonic Complex. The intrusions include plutons, dikes, and sills. |
| Date | |
| Source | Grand Canyon National Park- Basement Rocks_0201 |
| Author | Grand Canyon National Park |
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This image was originally posted to Flickr by Grand Canyon NPS at https://flickr.com/photos/50693818@N08/7706671774. It was reviewed on 20 April 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 18:26, 20 April 2020 | | 2,592 × 3,872 (2.66 MB) | Killarnee (talk | contribs) | Transferred from Flickr via #flickr2commons |
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