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New thermobarometric and U/Pb and 40Ar/ 39 Ar geochronologic data coupled with ages obtained from the Acatlán Complex, the basement of the Mixteco terrane of southern Mexico, reveal the existence of three distinctive high-pressure metamorphic events of early to middle Paleozoic age, each recorded in a separate lithological suite. Xayacatlán suite eclogites with oceanic affi nity underwent peak metamorphism at 609-491 °C and 13-12 kb during the Early Ordovician (ca. 490-477 Ma, U-Pb zircon), followed by a partial overprint at 600 °C and ~9.6 kb and then at 500 °C and ~6.7 kb. An overprinting event at 525-500 °C and ~9.5 kb is ascribed to the Devonian. The pressure-temperature (P-T) path of the Xayacatlán suite indicates a subduction-exhumation process followed by tectonically related reburial. Ixcamilpa suite blueschists with oceanic affi nity underwent epidote-blueschist metamorphism (T, 200-390 °C; P, 6-9 kb) and then epidoteamphibolite (T, 390-580 °C; P, 9-6 kb) events ascribed to the Late Ordovician-Early Silurian. Esperanza suite eclogites with continental affi nity underwent peak metamorphism at 830-730 °C and 17-15 kb. Amphibole from eclogite yields a 430 ± 5 Ma 40 Ar/ 39 Ar age, dating the high-pressure (HP) event. P-T paths of high-temperature (HT) eclogites like those of the Esperanza suite have been related to the collision of continental blocks. Partial overprinting occurred at 690-640 °C and 14-10 kb prior to 374 ± 2 Ma ( 40 Ar/ 39 Ar, phengite). The three HP suites were tectonically juxtaposed at different times before the Mississippian Period, resulting in the closure of the Iapetus Ocean. Phengite 40 Ar/ 39 Ar geochronology reveals the existence of a widespread tectonothermal event between 345 and 323 Ma, which may be related to the juxtaposition of the HP-composed block and the Gondwanan-affi nity Cosoltepec suite, causing the closure of the Rheic Ocean. The tectonothermal events in the Acatlán Complex coincide in time, physical conditions, and tectonic setting with events in the Appalachian-Caledonian orogen, suggesting their relation. On that basis the geology of the Acatlán Complex can lead to a more comprehensive understanding of the tectonic evolution of the Appalachian orogen and of the Gondwana-Laurentia interactions preceding the Pangean assembly.

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Correlation of deformational phases and thermal events in the Acatlán Complex permits definition of nine major tectonic events. Seven events are related to the evolution of the Iapetus and Rheic oceans. By the Early Ordovician, the Xayacatlán suite of Laurentian affinity was metamorphosed to eclogite facies and exhumed before colliding with the El Rodeo suite. From the Late Ordovician to Silurian, the Upper Ordovician Ixcamilpa suite with peri‐Gondwanan affinity was metamorphosed to blueschist facies, exhumed, and subsequently was overthrust by the Xayacatlán–El Rodeo block. Part of the Esperanza suite is an Early Silurian intra‐Iapetian continental arc that collided with and subducted beneath continental crust, generating a Silurian eclogitic event. By the Late Devonian, collision of the three high P/T suites closed the Iapetus Ocean. The resulting composite terrain was thrust over the Gondwana‐bordering Cosoltepec suite to close the Rheic Ocean. During the earliest Mississippian, the collision of the Acatlán Complex and the Oaxaca terrane uplifted and deformed the composite terrane. By the Early Permian, deposition of the Chazumba suite occurred in a pull‐apart basin. A latest Early Permian event produced thrust shear zones with N–S directed shortening. During the Middle Jurassic, plume rise caused regional doming, magmatism and amphibolite facies metamorphism. During the Late Cretaceous–Paleogene, folds and thrust faults overprint the Acatlán Complex. Most events in the Acatlán Complex correlate with events in the Appalachian chain, suggesting that the Acatlán Complex was located near the Appalachians until the Jurassic when it was displaced by the Gulf of Mexico opening.

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