U-Pb geochronologic analyses have been conducted on 135 detrital zircon grains from Paleozoic strata of the Oaxaca terrane of southern Mexico. The grains are mainly mid-Proterozoic in age (age probability peak of 993 Ma), with subordinate clusters of ∼358 and ∼472 Ma. The mid-Proterozoic ages can be used to evaluate three possible paleopositions for the Oaxaca terrane during mid-Proterozoic time. Formation in proximity to northwest South America appears most likely, as southwestern portions of the Amazon craton (and perhaps basement massifs in the northern Andes) contain igneous rocks of the appropriate age. A more specific test of ties to these regions is not yet possible due to the limited number of U-Pb determinations from the region. Formation in proximity to Grenville-age rocks in northeast North America is less likely, as detrital zircons shed from these rocks are mostly older than 993 Ma. Previously proposed links with Grenville-age rocks in southwestern North America are not supported by our data, as there is little overlap of ages from the Oaxaca terrane and from Grenville-derived detrital zircons in southwestern US and northwestern Mexico. The presence of Paleozoic grains in our samples does not help constrain the Late Proterozoic-early Paleozoic displacement of the Oaxaca terrane, as magmatism of this age was apparently widespread within and adjacent to the Iapetus and Rheic ocean basins.
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