Sequencing reelfoot extension based on relations from southeast Missouri and interpretations of the interplay between offset preexisting zones of weakness

Late Cambrian stratigraphic relations are used to reconstruct aspects of the structural architecture buried between the St. Francois Mountains and the Mississippi Embayment. Such reconstructions are possible because characteristics of units deposited during early thermal subsidence help document late Proterozoic‐Early Cambrian Catoctin extension in southeast Missouri. New observations of the Lamotte Sandstone and Bonneterre Formation (Dresbachian) show that a mismatched architecture is present and was buried by late Bonneterre Formation (early Franconian) sediments prior to the deposition of the Davis Formation (early‐middle Franconian). A structural map of the region was developed by integrating such new observations with published relations. Analysis of stratigraphic and structural relations reveal that two periods of brittle thinning of the crust resulted from Catoctin extension in southeast Missouri. Although structural architecture is partially masked, these distinct periods of thinning produced (1) a compartmentalized, tilt block terrane characterized by down‐to‐the‐southeast breakaways and (2) a number of linked, convergent halfgrabens. Late Cambrian stratigraphic relations provide evidence that the linked half‐grabens were superimposed asymmetrically on the tilt block terrane. A four‐stage tectonic sequence consisting of early mafic volcanism, two periods of brittle thinning, and late recurrent ultra‐mafic volcanism is interpreted with the application of models of tectonism controlled by preexisting zones of weakness. An interplay between offset, preexisting zones of weakness helps explain the timing of associated magmatism, faulting, and graben development. Changes in structural style resulting from such an interplay suggest that Catoctin extension in southeast Missouri was a protracted episode of polyphase deformation.