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Basalt dike in orange-red Hakatai Shale along Colorado River at Hance Rapid, river mile 76.5, Grand Canyon. Isis Temple and Cheops Pyramid on a fault-block (horst), sitting on "island" of Shinumo Quartzite, of the Unkar Group. Bottom of the Unkar above Granite Gorge, and Vishnu Basement Rocks.
As in the case of the Grand Canyon asbestos deposits, dolomite and limestone reacted with silica-bearing fluids, heated by the basalt intrusions, forming the serpentine mineral chrysotile. Much like the Grand Canyon asbestos deposits, these basaltic sills and dikes range in age from 1,050 to 1,140 Ma.
The sills range in thickness from 23 m (75 ft) at Hance Rapids, eastern Grand Canyon, to 300 m (980 ft) in Hakatai Canyon in the Shinumo Creek area. The feeder dikes to these sills are not exposed. However, the feeder dikes for the Cardenas Basalt can be traced, discontinuously, to within a few meters of its base.
The Cardenas Basalt and Dox Formation are found mostly in the eastern region of Grand Canyon. The Shinumo Quartzite, Hakatai Shale, and Bass Formation are found in central Grand Canyon. The Unkar Group accumulated approximately between 1250 and 1104 Ma (1,104 million years ago, 1.1 billion).
Good exposures of the supergroup can be seen in eastern Grand Canyon in the Inner Gorge and from Desert View, Lipan Point and Moran point. [12] [note 1] The Cardenas Basalt was laid on top of the rest of the Grand Canyon Supergroup. The oldest section of the supergroup is the Unkar Group. It accumulated in a variety of fluvial, deltaic, tidal ...
The Grand Canyon Supergroup, of which the Unkar Group is the lowermost part, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks. [3] [5] [6] The Cardenas Basalt has also been called the Rama Formation.
The Apache Group near the bottom of the Grand Canyon, includes fluvial shale and sandstone, as well as limestone from a shallow sea, exposed in the Salt River Canyon. The limestone contains stromatolite remains, mounds of blue-green algae. The Apache Group was intruded with basalt and diabase between 1.05 and 1.14
The Uinkaret volcanic field is an area of monogenetic volcanoes in northwestern Arizona, United States, located on the north rim of the Grand Canyon. [2] Lava flows from the Uinkaret volcanic field that have cascaded down into the Grand Canyon, damming the Colorado River, have been used to date the canyon's carving. [3]
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