Basement rocks in adjoining parts of Oklahoma, Kansas, Missouri, and Arkansas
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Samples from more than two hundred and twenty wells penetrating basement rock have been examined and described from a 61,000 square mile area in adjoining parts of Oklahoma, Kansas, Missouri, and Arkansas. Twenty-five isotopic age determinations were made on twenty samples of basement rock from wells and outcrop areas. Nine basement rock units can be defined within the study area on the basis of petrography and isotopic age. 1. "Older granite and gneiss" is a loose association of granitic rocks considered to be older than 1400 million years. The unit cannot be precisely defined within the study area. 2. The Lyon County Quartzite is a micaceous quartzite restricted to relatively small areas in the buried basement of Kansas. The age of deposition is unknown but preceded the 1400 million year age of metamorphism. 3. The Chase County Granite Group is composed largely of granite and gneissic granite. Rocks of this group underlie most of the Nemaha Uplift in Kansas and also occur considerably east and west of the Uplift. The rocks were intruded at about 1400 million years, probably as a composite batholith. At about 1200 million years, four petrographically related rock units were intruded or extruded. The age difference between these units cannot be distinguished by isotopic ages. The four units are assembled into the Northeast Oklahoma Province, a petrographic grouping of volcanic rocks and chemically equivalent hypersolvus type epizone granites. 4. The Washington County Volcanic Group is composed mostly of rhyolite but also contains andesite and metarhyolite. The majority of the rhyolites were probably extruded as welded tuffs. 5. The Spavinaw Granite Group is composed of generally micrographic granite porphyries. The intrusions are considered to be largely sills on textural evidence and by analogy with outcrop areas elsewhere. 6. The Woodson County Granite is texturally variable. Samples from drill holes in Kansas are petrographically identical to boulders found at Rose Dome in Woodson County, Kansas. 7. The Osage County Microgranite is the most uniform unit in the area. The microgranite occurs in a roughly circular area in Osage County, Oklahoma. The unit was probably intruded as a sill within rhyolite flows. Two other petrographic units are interpreted as being younger than parts of the Northeast Oklahoma Province, although in the same 1200 million years isotopic age range. 8. The Vernon County Metamorphic Group is composed mostly of low rank metamorphic rocks derived from clastic sediments. The grade of metamorphism is from incipient to middle greenschist facies. Rhyolite detritus occurs in some samples. 9. The Central Oklahoma Granite Group is composed of two feldspar mesozone type granites. The unit is not distinguishable from the Chase County Granite Group on the basis of petrography. Uplift and erosion followed the intrusion of the Central Oklahoma Granite Group. The main uplifts were along the present Nemaha Uplift and along a northeast-southwest axis from southwest Missouri to central Oklahoma. There is no evidence for any igneous or metamorphic activity between 1200 million years and the deposition of lower Paleozoic sediments.