The Spavinaw terrane is an occurrence of Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

 (1.40–1.35 Ga) intrusive and volcanic rocks in the mid-continent region of the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The terrane

Terrane

A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

 extends across southern Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

, southern Kansas

Kansas

Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

, northern Arkansas

Arkansas

Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

 and much of Oklahoma

Oklahoma

Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...

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

Spavinaw, Oklahoma

Spavinaw is a town in Mayes County, Oklahoma, United States. The population was 563 at the 2000 census. The town is best known as the birthplace of baseball player Mickey Mantle.-Geography:Spavinaw is located at ....

, Mayes County, Oklahoma

Mayes County, Oklahoma

Mayes County is a county located in the U.S. state of Oklahoma. It was named for Samuel Houston Mayes, Principal Chief of the Cherokee Nation from 1895 to 1899. According to the 2010 census the population was 41,259, a 7.5 percent increase from 2000, when the population was 38,369...

 and parts of the Saint Francois Mountains

Saint Francois Mountains

The St. Francois Mountains in southeast Missouri are a range of Precambrian igneous mountains rising over the Ozark Plateau. This range is one of the oldest exposures of igneous rock in North America....

 in Washington County, Missouri

Washington County, Missouri

Washington County is a county located in East Central Missouri in the United States. As of the 2010 U.S. Census, the county's population was 25,195. The largest city and county seat is Potosi...

. The terrane is composed almost exclusively of essentially unaltered intrusive granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

s and volcanic rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...

 and rhyolite tuff

Tuff

Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...

s.

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

Midcontinent Rift System

The Midcontinent Rift System 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, began to split apart during the Mesoproterozoic era of the...

.