AN ALTERNATIVE RECONSTRUCTION OF PANGEA A FOR MIDDLE AMERICA WITH BOTH THE CHORTIS AND YUCATAN BLOCKS IN THE GULF OF MEXICO

Understanding Pangea breakup requires a robust reconstruction and this paper focuses on Middle America. Although most Pangean reconstructions locate the Yucatan block along the southern USA, the Chortis block is generally placed off southern Mexico (Pacific model) undergoing sinistral relative motion during the Mesozoic and Cenozoic. However, the Pacific model is inconsistent with the absence of a Cenozoic fault linking the Cayman Transforms and the Middle America Trench. We present an alternative Pangean reconstruction, where both the Yucatan and Chortis blocks are placed in the future Gulf of Mexico, and moving Mexico westwards along the Mojave/Sonora megashear to accommodate overlap with South America. Subsequent Mesozoic and Cenozoic evolution is inferred to have occurred in two-stages: (i) Jurassic clockwise rotation along the Mojave/Sonora and West Florida megashears, followed by (ii) anticlockwise rotation along the Sierra Madre Oriental and East Yucatan megashears. The first stage is linked to the breakup of Pangea where the Gulf of Mexico forms as a pull-apart basin. The second stage is related to the evolution of the Caribbean where the Chortis and Yucatan blocks are rotated into the trailing side of the Caribbean Plate (Pirate model). The new reconstruction is consistent with major parameters, such as: (a) gravity, magnetic and paleomagnetic data, (b) the northwest curvature of the northern Caribbean Plate boundary in Guatemala, (c) the 27-19 Ma removal of the southern Mexican forearc, (d) the offset of the Cretaceous volcanic arc (Guerrero-Suina); and (e) the continuity of Cretaceous platformal carbonates containing Caribbean fauna across Middle America.