Crustal Growth During Continental Rifting: An Example from the Southern Oklahoma Aulacogen

Abstract

The Southern Oklahoma Aulacogen (SOA) is one of several aulacogens that formed within the North American craton during breakup of the Laurentian Supercontinent in Late Proterozoic to Cambrian time. Lithospheric extension that formed the SOA was accompanied by voluminous bimodal igneous activity. Following cessation of rift-related igneous activity, isostatic adjustment of the crust resulted in accumulation of 4-5 km of Paleozoic sediments within an intracratonic basin that developed over the subsiding aulacogen. Uplift by block faulting, accompanied by erosion, during the late Paleozoic Ouachita Orogeny, and again in the Cretaceous and late Cenozoic, exposed the Cambrian igneous basement. The absence of significant Mesozoic and Cenozoic deformation within the mid-continent ensure preservation of the rift assemblage. Subsequent erosion has exposed the volcanic and plutonic rocks that floored this aulacogen such that the present erosional surface is not far below the erosional surface in Cambrian time. Integrated petrologic and geophysical investigations of these igneous rocks and the underlying crust suggest a significant amount of new material can be added to the crust during periods of lithospheric extension.