Isotopic studies of the Acatlan Complex, southern Mexico: implications for Paleozoic North American tectonics

The Paleozoic Acatlan Complex and Grenville-age Oaxaca terrane of southern Mexico have been suggested to be the southern continuation of North American orogenic systems. The Paleozoic Acatlan Complex consists of multiply deformed metasedimentary rocks, schists, granitoids, and eclogites and have been compared to rocks of the Appalachian belt. The northward extension of both the Oaxaca terrane and Acatlan Complex, however, are obscurred by younger rock cover as they enter central Mexico. Isotopic studies show that the Acatlan Complex records three tectonothermal events. Neodymium model ages of the Acatlan Complex are unlike those of some accreted crustal blocks of the Pacific margin, which have little signs of crustal recyling. It is suggested that the Devonian metamorphic event that affected these two areas was the result of a Laurentia-Gondwana collision. A later collision in late Carboniferous time caused deformation in the Acatlan Complex, plutonic activity in southern Mexico, and deformation in the Ouachita, Marathon, and Appalachian belts. Both the Acatlan and Oaxaca terranes would have been continuous with South America until the break-up of Pangea in the Mesozoic era. -from Authors