The Spavinaw terrane is an occurrence of

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

(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 commonly defined as a vent or fissure 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 fo ...

rocks in the mid-continent region of the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. The

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...

extends across southern

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

, southern

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

, northern

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

and much of

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

. The rocks are almost entirely known from drill core and only exposed in outcrop near Spavinaw, Mayes County, Oklahoma 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 ...

Washington County, Missouri Washington County is a county 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 ...

. The terrane is composed almost exclusively of essentially unaltered intrusive

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

s and

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

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 co ...

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 basalts and rhyolites of Middle Proterozoic Midcontinent Rift System.

References

Cratons Proterozoic North America Terranes {{plate-tectonics-stub