THE MEXICAN SEGMENT OF THE NORTH AMERICAN CORDILLERA: THE MEETING OF PACIFIC AND ATLANTIC TECTONICS DURING MESOZOIC TIME

Mexico remains a segment of the Mesozoic North American Cordilleran margin that is poorly understood. This is in part because, in contrast with the USA and Canada, where Pacific and Atlantic tectonics are geographically well separated, Mexico was a narrow continental neck. In this neck, tectonic processes related to Atlantic margin Pangea breakup and Pacific margin subduction converged and overprinted each other. In this configuration, it is difficult to determine whether any given extensional or transtensional episode was triggered by Pacific or Atlantic tectonics. In this contribution, we describe and test the two main groups of tectonic models that have been proposed for Mexico.

Group one tectonic models interpret the Triassic to Jurassic history of Mexico to have been dominated by the Pacific tectonics. In these models, eastward subduction of a hypothetical Mezcalera plate produced a continental extensional arc, the Jurassic Nazas arc, and westward subduction of the Mezcalera plate produced exotic intraoceanic arcs of the Guerrero-Alisitos-Vizcaino superterrane, accreted during Cretaceous time by closure of the Mezcalera plate. In these models, the manifestation of Pangea breakup in Mexico did not begin until latest Middle Jurassic time, with the opening of the Gulf of Mexico.

Group two tectonic models interpret the Triassic-Jurassic history of Mexico as a mix of Pacific and Atlantic processes. In these models, the “Nazas arc” is interpreted as continental rift basins related to Pangea breakup. These basins lay in the backarc region of extensional oceanic arcs that fringed the Pacific margin of Mexico (Guerrero-Alisitos-Vizcaino superterrane), formed by eastward subduction of the Farallon/Cocos plate. In this presentation, we summarize the evidence that the Nazas province represents continental rift basins. We also summarize the abundant detrital zircon and paleomagnetic data that support the interpretation that the Guerrero-Alisitos-Vizcaino superterrane is not exotic, but instead formed along the Mexican margin.

We conclude by listing unresolved questions for future research.