WHY FLORIDA IS STILL ATTACHED TO NORTH AMERICA: IT’S YUCATAN’S FAULT

As Africa and North America (NA) began to separate 230 Ma, N-NE trending rifts formed along the southeast margin of NA and most had evolved into the Mid-Atlantic ridge by 180 Ma. However, the South Georgia Rift (SGR) failed, despite forming at the same time, experiencing the same massive flood basalt eruptions (Central Atlantic Magmatic Province-CAMP) at ~200 Ma, and being parallel to sub-parallel to the Atlantic rifts. The SGR runs NNE to NE just south of the Appalachians from South Carolina to the Gulf of Mexico and is approximately coincident with the suture between the Florida terranes and NA. Thus, the stress regime that resulted in the rifting of NA from Africa at ~200 Ma would be expected to have rifted NA from Florida as well. However, while the ~200 Ma CAMP dikes in the mid-Atlantic region and further north parallel the rifts, dikes along the SGR are perpendicular to the rift. This suggests the stress field along the southeast margin of NA changed dramatically at or by 200 Ma, and that this is the reason for the failure of the SGR and why Florida remained with NA. Why the stress field changed at this time is unknown.

I used the program GPlates to analyze various paleographic reconstructions of the breakup of Pangea and input these motions into a finite element program to determine expected lithospheric deformation (e.g. Seton et al., 2012). None of the paleogeographic models used had motion between the plates until ~190 Ma at the earliest, thus, because of the deformation that occurred between 230-200 Ma, the relative motions of plates from 190-170 Ma were used as possible motions for 230-200 Ma. Changes to existing paleogeographic models were also made based on the results generated by the finite element program, i.e. stress fields generated by the plate motion must match the deformation observed. Only by placing the Yucatan (or another fragment) near Florida and commencing its motion at ~200 Ma can the observed deformation be modelled. Thus, I propose that the NNW trending diabase dikes along the SGR indicate that the Yucatan began moving to the SSW around 200 Ma and is responsible for Florida remaining attached to North America.

Seton, M., Müller, R. D., Zahirovic, S., Gaina, C., Torsvik, T., Shephard, G., ... & Chandler, M. (2012). Global continental and ocean basin reconstructions since 200Ma. Earth-Science Reviews, 113(3), 212-270.