| Vishnu Basement Rocks | |
|---|---|
| Stratigraphic range: Early Paleoproterozoic ~ | |
| Type | Geological formation |
| Sub-units | Granite Gorge Metamorphic Suite Zoroaster Plutonic Complex |
| Underlies | Unkar Group and, as part of the Great Unconformity, the Tapeats Sandstone |
| Thickness | unknown |
| Lithology | |
| Primary | schist and granite |
| Other | granodiorite, tonalite, pegmatite, and ultramafic rocks |
| Location | |
| Region | Arizona – (Grand Canyon) |
| Country | United States |
| Type section | |
| Named for | "Vishnu's Temple" butte |
| Named by | Charles Doolittle Walcott[1] |
| Year defined | 1894 |
The Vishnu Basement Rocks is the name recommended for all Early Proterozoic crystalline rocks (metamorphic and igneous) exposed in the Grand Canyon region. They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group. These basement rocks have also been called either the Vishnu Complex or Vishnu Metamorphic Complex. These Early Proterozoic crystalline rocks consist of metamorphic rocks that are collectively known as the Granite Gorge Metamorphic Suite; sections of the Vishnu Basement Rocks contain Early Paleoproterozoic granite, granitic pegmatite, aplite, and granodiorite that have intruded these metamorphic rocks, and also, intrusive Early Paleoproterozoic ultramafic rocks.[2][3]
The term Zoroaster Plutonic Complex is used for all Paleoproterozoic granitic and grandioritic plutonic rocks in the Grand Canyon. Specific names have been assigned to individual plutons and dike swarms because the plutons and swarms differ greatly in their age, origin, and tectonic significance. The oldest of these plutonic complexes, Elves Chasm Gneiss, likely represent a small fragment of basement upon which the metavolcanic rocks that comprise the Granite Gorge Metamorphic Suite accumulated. The remainder of the Early Paleoproterozoic granites, granitic pegmatites, aplites, and granodiorites – are parts of either younger plutons or dike swarms, that have intruded the Granite Gorge Metamorphic Suite, either contemporaneously with, or after they were metamorphosed.[4][5]
It was named after a natural rock structure in the Colorado River valley which was named "Temple of Vishnu" from its appearance.[6]
- ^ See:
- Walcott, Charles D. (1883) "Pre-Carboniferous strata in the Grand Cañon of the Colorado, Arizona," American Journal of Science, 3rd series, 26 : 437–42, 484.
- Walcott, Charles Doolittle (1894) "Pre-Cambrian igneous rocks of the Unkar terrane Grand Canyon of the Colorado, Arizona, with notes on the petrographic character of the lavas, by Joseph Paxson Iddings," Fourteenth Annual Report of the United States Geological Survey … , Part 2, pp. 497–519, 520–24. Reprinted as a pamphlet: Walcott, Charles Doolittle, "Pre-Cambrian igneous rocks of the Unkar terrane Grand Canyon of the Colorado, Arizona, with notes on the petrographic character of the lavas, by Joseph Paxson Iddings," (Washington, D.C.: U.S. Government Printing Office, 1895); see p. 507.
- Noble, L. F., "The Shinumo Quadrangle, Grand Canyon District, Arizona," Bulletin 549, United States Geological Survey, Dept. of the Interior, (Washington, D.C.: Government Printing Office, 1914), pp. 11–96 [32]. From p. 32: "Proterozoic Rocks. Archean System. Vishnu schist. Name." The name Vishnu terrane has been given by Walcott1 to the fundamental crystalline complex of the Grand Canyon region that underlies the unaltered sedimentary rocks of Algonkian age … The type of locality is on [the] Colorado River, 30 miles east of the mouth of Shinumo Creek, at the base of one of the great buttes called "Vishnu's Temple," from which Walcott derived the name."
- ^ Anonymous (nd) Vishnu Basement Rocks. U. S. Geological Survey, Reston, Virginia.
- ^ Karlstrom, KE, BR Ilg, Bradley, D Hawkins, ML Williams, G Dumond, KK. Mahan, and SA Bowring, Samuel (2012) Vishnu basement rocks of the Upper Granite Gorge: Continent formation 1.84 to 1.66 billion years ago. In JM Timmons and KE Karlstrom, eds., pp. 7–24, Grand Canyon geology: Two billion years of earth's history. Special Paper no 294, Geological Society of America, Boulder, Colorado.
- ^ Karlstrom, KE, BR Ilg, ML Williams, DP Hawkins, SA Bowring, and SJ Seaman (2003) Paleoproterozoic rocks of the Granite Gorges. In SS Beus and M Morales, eds., pp. 9–38, Grand Canyon Geology, 2nd ed. Oxford University Press, New York.
- ^ Ilg, BR, KE Karlstrom, and ML Williams (1996) Tectonic evolution of Paleoproterozoic rocks in the Grand Canyon – Insights into middle-crustal processes. Geological Society of America Bulletin. 108(9):1149–66.
- ^ Dutton, Clarence E. (1882). The Tertiary History of the Grand Cañon District. Tertiary history of the Grand Canyon Districtwith atlas. Washington, DC, USA: Government Printing Office. p. 148. ISBN 9780879050313. From p. 148: "The finest butte of the chasm is situated near the upper end of the Kaibab division; but it is not visible from Point Sublime. It is more than 5,000 feet high, and has a surprising resemblance to an Oriental pagoda. We named it Vishnu's temple."