RADIOMETRIC AND KINEMATIC EVIDENCE FOR MIDDLE JURASSIC STRIKE-SLIP FAULTING IN SOUTHERN MEXICO RELATED TO THE OPENING OF THE GULF-OF-MEXICO

One of the least-known aspects of the evolution of the Gulf of Mexico is the nature and location of shear zones along which the relevant con tinental fragments were displaced. The Sierra de Juarez mylonitic comp lex, located in southern Mexico, is a poly-orogenic north-northwest-tr ending structure. Here we report U-Pb mylonitization dates of 165 +/- 20 Ma for igneous zircon from the syntectonic San Felipe granite, and an integrated Ar-40/Ar-39 age of 169.3 +/- 1.7 Ma from synkinematic mu scovite, both of which indicate a Middle Jurassic age for the strike-s lip event along the Sierra de Juarez mylonitic complex. This event the refore occurred during the opening of the Gulf of Mexico, and we propo se that the shear zone was kinematically related to the southeast disp lacement of the Yucatan block.