LAUSR

Abstract Ordovician megacrystic granitoids intrude the Neoproterozoic-Paleozoic Acatlan Complex of southern Mexico, which consists of rift-passive margin, clastic rocks and rift-related igneous rocks. Most of the Neoproterozoic-Ordovician rocks were folded at greenschist-amphibolite facies metamorphism, however some rocks underwent polyphase deformation, underthrusting under high-pressure metamorphism followed by extrusion during the Late Devonian-Carboniferous (365–330 Ma). Most of our new Nd isotopic data for Ordovician granitoids have ƐNd(T) ranging between −4.5 and −7.2 with TDM ages of 1.3–1.6 Ga that are similar to most published data from such Ordovician plutons: ƐNd(T) of −0.2 to −6.6 and TDM ages of 1.2–1.8 Ga. These values are comparable to the range shown by the Oaxacan Complex, which confirms the conclusion reached using zircon U-Pb isotopic data indicating an Oaxacan source. One exception is the Ordovician Teticic granitoid that has ƐNd(T) of −4.8 to −5.8 and TDM ages of 2162–2946 Ma. The combination of ca. 1.5 and 2–3 Ga TDM ages is also recorded in northwestern Amazonia, which is consistent with previous correlations of Oaxaquia with Amazonia. The transfer of Oaxaquia from Amazonia to southern Laurentia occurred during the amalgamation and breakup of Pangea, where the suture was roughly parallel to their relative motion: this resulted in dextral strike-slip faulting generally attributed to the Mojave-Sonora megashear.