Three Major Failed Rifts in Central North America: Similarities and Differences

The North American craton preserves nearly two billion years of geologic history, including three major rifts that failed rather than evolving to continental breakup and seafloor spreading. The Midcontinent Rift (MCR) and Southern Oklahoma Aulacogen (SOA) show prominent gravity anomalies due to large volumes of igneous rift-filling rock. The Reelfoot Rift (RR), though obscure in gravity data, is of interest due to its seismicity. The ca. 1.1 Ga MCR records aspects of the assembly of Rodinia, whereas the ca. 560 Ma SOA and RR initiated during the later breakup of Rodinia and were inverted during the assembly of Pangea. Comparative study of these rifts using geophysical and geological data shows intriguing similarities and differences. The rifts formed in similar tectonic settings and followed similar evolutionary paths of extension, magmatism, subsidence, and inversion by later compression, leading to similar width and architecture. Differences between the rifts reflect the extent to which these processes occurred. Further study of failed rifts would give additional insight into the final stages of continental rifting and early stages of seafloor spreading.