KEYNOTE: PLATE BOUNDARY CONTROL ON THE LINKED KINEMATIC HISTORIES OF THE MACUSPANA, AKAL-REFORMA, COMALCALCO, AND DEEP WATER CAMPECHE BASIN TECTONIC ELEMENTS, SOUTHERN GULF OF MEXICO

Chiapas Foldbelt, Akal-Reforma “Horst”, and deep Campeche Foldbelt comprise Mesozoic-Middle Miocene strata separated by the extensional NE-trending Macuspana (late Middle Miocene-younger) and Comalcalco (Pliocene-younger) extensional troughs. During Middle Miocene NE-directed shortening within greater “Chiapas-Akal-Reforma Foldbelt”, the continental “North Guatemalan backstop” was a foreland buttress bounding the more basinal and deformable strata. Chiapas Foldbelt strata were thrust against the NW-trending southwestern flank of the backstop, while the Akal-Reforma trend shortened less intensely over a broader area and bypassed the backstop by dextral lateral ramping along the backstop’s NE-trending northwest flank. By late Middle Miocene, the Akal-Reforma trend became gravitationally unstable under continued shortening, and the dextral lateral ramp collapsed transtensionally from the NW flank of the backstop, thus opening the Macuspana Basin. The detachment was Callovian salt; subsequently, Comalcalco Trough opened as a second extensional scar on salt, leaving Akal-Reforma trend as a floating, rootless “horst” between the two detachment basins. The NNW-directed extension within the two basins feeds into deep water Campeche foldbelt folds; age of NW-directed folding corresponds to times of opening in the two troughs (since Middle Miocene). However, folding related to initial NE-shortening may occur in some areas. The southern Gulf of Mexico petroleum system resides in the structures noted, which were further buried and matured by younger marine fill as extension continued. Looking to the Mexican Pacific margin for tectonic drivers for this deformation history, 2 fundamental controls are most feasible; 1) transpressional E-ward migration of Chortis Block as part of the Caribbean Plate, and 2) onset of NE-dipping subduction behind the migrating Cocos-Caribbean-North American triple junction. Analysis of Chortis migration history points to option 2; Chortis was east of Chiapas Massif and Foldbelt when folding began. We depict the Neogene deformation history of southern Mexico in a kinematic model set within the mantle reference frame, and highlight efforts to resolve remaining problems.