Extrusive rhyolites and cogenetic granites of the Wichita province genetically related to the southern Oklahoma aulacogen are entirely sub-alkaline in character. Peralkaline granites occur in the province but are volumetrically minor and have been interpreted by earlier workers as differentiation products of subalkaline magma. The large volumes of sub-alkaline silicic magma in the southern Oklahoma aulacogen represent a style of magmatism which contrasts markedly with the alkaline igneous activity generally associated with intracontinental rifting.

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