St. Francois Mountains
Saint Francois Mountains | |
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relief map of Missouri showing the St. Francois Mountain region (red)
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Country | United States |
State | Missouri |
Geology | |
Age of rock | Precambrian |
Type of rock | igneous |
The St. Francois Mountains in southeast
Name
The name of the range derives from the
Geology
The St. Francois Mountains were formed by
The intrusive rocks of the area are composed of three types:
The subvolcanic intrusives are similar in geochemistry to the associated
The ring intrusives are high silica bodies which were intruded along ring faults associated with caldera collapse. Rock types include trachyandesite, trachyte, syenite and amphibole - biotite granite. They are commonly porphyritic.[7]
The central plutons are highly evolved two
The exposed igneous rocks of the St. Francois are surrounded at depth by the slightly younger (~100 my) widely distributed igneous Spavinaw terrane. The Spavinaw rocks are intersected in drill core across southern Missouri, southern Illinois, northern Arkansas, southern Kansas and northeastern Oklahoma. The Spavinaw rocks occur in outcrop only near Spavinaw, Oklahoma. The rhyolites and ash flow tuffs of the Spavinaw are essentially identical to the volcanics of the St. Francois mountains (the Washington County volcanics).[7]
The Saint Francois Mountains were formed by igneous activity, whereas most of the surrounding Ozarks are developed on Paleozoic sedimentary rocks as a dissected plateau. The localized vertical relief was caused by erosion following uplift during the Pennsylvanian and Permian periods produced by the Ouachita orogeny to the south. Elevations and strata dips in the Ozark structural dome generally radiate downward and outward away from the Saint Francois mountains.
These ancient mountains may be the only area in the Midwestern United States never to have been submerged, (as evidenced by the lack of marine fossils) existing as an island archipelago in the Paleozoic seas. Fossilized coral, the remains of ancient reefs, can be found among the rocks around the flanks of the mountains. These ancient reef complexes formed the localizing structures for the mineralizing fluids that resulted in the rich ore deposits of the area.
The igneous rocks of the Saint Francois Mts. are interpreted to be a series of caldera complexes,
Mineral resources
The St. Francois Mountains are the center of the
Granite has been commercially quarried since 1869 in the vicinity of Elephant Rocks State Park, a tor with huge weathered granite boulders. The red architectural granite quarried in the area has been used in buildings in St. Louis and other areas in the country. It is currently marketed as Missouri Red monument stone.
Structural features
Hughes Mountain contains a good example of
. The columnar jointing in this area is called the Devil's Honeycomb.Peaks
Mountains in this range include; Taum Sauk Mountain, Bell Mountain, Buford Mountain, Proffit Mountain, Pilot Knob, Hughes Mountain, Goggin Mountain and Lead Hill Mountain. The elevations range from 500 to 1,772 feet (152 to 540 meters). Taum Sauk Mountain is the highest peak in the range, and the highest point in the state, with an elevation of 1,772 ft (540 m). In the southernmost reaches of the range is Clark's Mountain, elevation 1,450 ft (440 m), with the distinction of being the highest isolated point in the range and in the state; it reaches its top from surrounding terrain of about 900 ft (270 m) in less than two miles (3.2 km). Black Mountain, in Madison County, has the highest rise in elevation from its base, along the St. Francis River (540 feet above sea level) to its summit (1,502 feet above sea level), a rise of just under 1,000 feet in elevation.
Recreation
Five Missouri
The St. Francis River in this area is a whitewater stream in the spring when water levels are up, and it has hosted the Missouri Whitewater Championships annually since 1968.
See also
- Geography of Missouri
- Missouri National and State Parks
- Taum Sauk pumped storage plant
References
- ^ U.S. Geological Survey Geographic Names Information System: Saint Francois Mountains
- .
- ^ "U.S. Geological Survey Photographic Library". libraryphoto.cr.usgs.gov. Archived from the original on 2012-02-17.
- ^ "Landslide Overview Map of the Conterminous United States. Geological Survey Professional Paper 1183".
- ^ a b c St. Francois County, Missouri Place Names Archived 2011-07-20 at the Wayback Machine, Western Historical Manuscript Collection
- ^ Denison, Rodger E., et al., Geology and Geochemistry of the Precambrian Rocks in the Central Interior Region of the United States, Geological Survey Professional Paper 1241-C, 1984
- ^ a b c d e Sims, P. K., Eva B. Kisvarsanyi and G. B. Morey, 1987, Geology and Metallogeny of Archean and Proterozoic Basement Terranes in the Northern Midcontinent, U.S.A., USGS Bulletin 1819
- ^ Kisvarsanyi, Eva (1981). "Geology of the Precambrian St. Francois terrane, southeastern Missouri". Report of Investigations (Missouri Geological Survey) No. 64. Contribution to Precambrian geology.
- Unklesbay, A.G; & Vineyard, Jerry D. (1992). Missouri Geology — Three Billion Years of Volcanoes, Seas, Sediments, and Erosion. University of Missouri Press. ISBN 0-8262-0836-3.