TheSpavinaw terrane is an occurrence ofProterozoic (1.40–1.35 Ga)[1]intrusive andvolcanic rocks in the mid-continent region of theUnited States. Theterrane extends across southernMissouri, southernKansas, northernArkansas and much ofOklahoma. The rocks are almost entirely known from drill core and only exposed in outcrop nearSpavinaw,Mayes County, Oklahoma and parts of theSaint Francois Mountains inWashington County, Missouri. The terrane is composed almost exclusively of essentially unaltered intrusivegranites andvolcanicrhyolite and rhyolitetuffs.[2]
The terrane is 100 m.y. younger than the Saint Francois terrane of southeast Missouri, but older thantholeiitic basalts and rhyolites of Middle ProterozoicMidcontinent Rift System.[2]
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