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The Spavinaw terrane is an occurrence of Proterozoic (1.40–1.35 Ga)Age of 1370 ±20 Ma for samples from Spavinaw Creek outcrop in: Bickford, M. E. and Richard D. Lewis, U-Pb geochronology of exposed basement rocks in Oklahoma, Geological Society of America Bulletin, 1979;90;540-544 intrusive and
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...
rocks in the mid-continent region of the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
. The
terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a tectonic plate (or broken off from it) and Accretion (geology), accreted or "Suture (geology), sutured" to crust lying on another pla ...
extends across southern
Missouri Missouri is a state in the Midwestern region of the United States. Ranking 21st in land area, it is bordered by eight states (tied for the most with Tennessee): Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas t ...
, southern
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to th ...
, northern
Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the O ...
and much of Oklahoma. The rocks are almost entirely known from drill core and only exposed in outcrop near Spavinaw,
Mayes County, Oklahoma Mayes County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 41,259. Its county seat is Pryor Creek. Named for Samuel Houston Mayes, Principal Chief of the Cherokee Nation from 1895 to 1899, it wa ...
and parts of the
Saint Francois Mountains The St. Francois Mountains in southeast Missouri are a mountain range of Precambrian igneous mountains rising over the Ozark Plateau. This range is one of the oldest exposures of igneous rock in North America. The name of the range is spelled out ...
in
Washington County, Missouri Washington County is located in the southeastern part of the U.S. state of Missouri. As of the 2020 United States census, the population was 23,514. The county seat and largest city is Potosi. The county was officially organized on August ...
. The terrane is composed almost exclusively of essentially unaltered intrusive
granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...
s and
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...
rhyolite and rhyolite
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
s.Sims, P.K., Kisvarsanyi, E.B., and Morey, G.B., 1987, ''Geology and metallogeny of Archean and Proterozoic basement terranes in the northern Midcontinent, U.S.A.'' U.S. Geological Survey Bulletin, 1815 The terrane is 100 m.y. younger than the Saint Francois terrane of southeast Missouri, but older than
tholeiitic basalt The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...
s and rhyolites of Middle Proterozoic
Midcontinent Rift System The Midcontinent Rift System (MRS) or Keweenawan Rift is a long geological rift in the center of the North American continent and south-central part of the North American plate. It formed when the continent's core, the North American craton, ...
.


References

{{Reflist Cratons Proterozoic North America Terranes