31 The western equatorial Pangea: Geological, geophysical, geochronological, and paleoecological insights on the youngest supercontinent assembly and breakup on Earth (Part 1)

This session welcomes studies in Mexico, southwestern North America, and northwestern South America investigating the Pangea’s supercontinent cycle from tectonic, stratigraphic, paleoecologic, geophysical, geochronologic, and paleogeographic perspectives to offer insights into its assembly and breakup.

Friday, 24 April 2026
8:00 AM - 12:00 PM
LMH, Isla Carmen

Late Paleozoic Subduction Transition from the Rheic Ocean to the Paleo-Pacific in Eastern Mexico: Insights from U-Pb Ages and Hf Isotopes in zircons from Teziutlán and Altotonga, eastern Mexico.

Paper number: 31-5
Program: Technical Sessions
Time: 9:25 AM – 9:45 AM

Authors

Abstract

The final assembly of western Pangea involved a critical tectonic transition from the diachronous closure of the Rheic Ocean to the establishment of the Paleo-Pacific subduction system. Paleozoic basement rocks in eastern Mexico are exposed in tectonic windows and drill cores, preserve a fundamental record of these crustal processes. This study integrates new and existing datasets to unravel the complex evolution of this convergent margin.

The Carboniferous Teziutlán Metamorphic Complex (TMC) in Puebla (Sierra Madre Terrane) represents an early phase of this evolution. Comprises a metavolcanic-metavolcaniclastic sequence intruded by Mississippian felsic plutons. Its arc-tholeiite geochemical signature and U-Pb zircon ages (ca. 332–312 Ma) record an active back-arc setting during the final convergence of peri-Gondwanan terranes with Laurentia, directly linked to the closure of the Rheic Ocean.

In contrast, new U-Pb zircon geochronology from the Altotonga intrusive suite in Veracruz reveals a primary Permian magmatic pulse (~284–264 Ma) and a subsequent Early Triassic tectonothermal event (~255–247 Ma). Complementary  Lu-Hf isotopic analyses yield significantly negative ɛHf(t) values (-12.2 to -2.9) and Paleoproterozoic to Neoproterozoic model ages (1.74–0.97 Ga). These signatures indicate substantial recycling of an ancient, evolved crustal source correlative with the Chiapas Massif, suggesting a strong affinity with the Maya Terrane.

The juxtaposition of these basement blocks, presumably separated by the Tamaulipas-Tehuantepec Fault, provides a clear chronology of the tectonic regime shift. The Carboniferous TMC records the final vestiges of Rheic closure. Subsequently, the Permo-Triassic Altotonga plutons, characterized by recycled Proterozoic signatures, mark the formal establishment and propagation of a continental magmatic arc along Pangea’s newly formed western margin. This transition was driven by the onset of Paleo-Pacific long-lived subduction beneath peri-Gondwanan terranes with Precambrian crustal residence.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410841

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