OVERVIEW OF PROTEROZOIC-PALEOZOIC TECTONIC EVOLUTION OF MEXICO (Invited Presentation)

About 80% of Mexico is made up of a mosaic of tectonostratigraphic terranes that were assembled throughout the Phanerozoic. Precambrian metamorphic complexes that crop out in northern Sonora and Chihuahua states, are the only units linked to the North America craton (Laurentia), and make only about 20% of the country´s territory. Oaxaquia microcontinent is the largest Proterozoic terrane of Mexico. It is widely accepted that it formed as part of the northern Grenville metamorphic belt, near Avalonia. Oaxaquia remained linked to Gondwana during the break up of Rodinia, as evidenced by fossil marine invertebrates from overlying Tremadocian and Silurian sedimentary rocks.

Oaxaquia is surrounded by Paleozoic metamorphic terranes. The Acatlán Complex (Mixteca terrane) is exposed on the SW side of Oaxaquia, it was made up by multiple deformation/metamorphic events, and contains metasedimentary and metaigneous rocks of eclogite-blueschist, amphibolite and greenschist facies. At least three metamorphic events were recorded, of Ordovician, Devonian-Early Carboniferous, and Late Carboniferous-Permian ages. It is interpreted as a continent-continent collision zone. However, its paleogeographic evolution is under debate. Detrital zircon geochronology suggests Gondwanan provenance.

Other Paleozoic sedimentary units and metamorphic complexes to the N-NW have been interpreted as either the westward extension of the Ouachita-Marathon belt, or as displaced terranes of Cordilleran origin (Río Fuerte, San José de Gracia Fms, Pescadito Schist, Rara Fm). They are Ordovician, Devonian, and Carboniferous in age. They show both Gondwana and Laurentia-derived detrital zircon provenances.

Oaxaquia contains early-Mississippian fossil faunas of Laurentia (mid-continent) affinity, suggesting that it was accreted to the Laurentian margin previous to Pangea formation. Paleozoic metamorphic complexes of eastern Oaxaquia (Maya Terrane) are Late Carboniferous-Permian in age, and recorded the final assembling of Pangea.