40 The western equatorial Pangea: Geological, geophysical, geochronological, and paleoecological insights on the youngest supercontinent assembly and breakup on Earth (Part 2)
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
1:30 PM - 5:30 PM
LMH, Isla Carmen
Late Paleozoic magmatism in the Chiapas Massif Complex, southern Mexico: A register of arc and postcollisional magmatism during the amalgamation of western equatorial Pangea
Paper number: 40-1
Program: Technical Sessions
Time: 1:35 PM – 1:55 PM
Authors
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Yuly Tatiana Valencia Morales Presenting AuthorUniversidad Nacional Autónoma de México, Mexico, Ciudad de México
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Bodo WeberCentro de Investigación Científica y de Educación Superior de Ensenada, Baja California, Ensenada, Baja California
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Juan Quintana-DelgadoCentro de Investigación Científica y de Educación Superior de Ensenada, Baja California, Ensenada, Baja California
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Dirk FreiUniversity of the Western Cape, Stellenbosch, Western Cape
Abstract
During the final assembly of western equatorial Pangea in the late Paleozoic, many crustal blocks located at the periphery of northwestern Gondwana were trapped between Gondwana and Laurentia as these continental landmasses collided diachronously, and the Rheic Ocean was closed. While some authors favor the idea of the concomitant subduction of the paleo-Pacific and the Rheic oceanic lithospheres, others suggest that the onset of convergence beneath the paleo-Pacific continental margin occurred either immediately after western Pangea was configured or much later in the middle Jurassic. The peri-Gondwanan blocks that currently compose eastern and southern Mexico keep a Carboniferous to Permo-Triassic magmatic record whose understanding can provide important clues about the timing and sequence of these tectonic events. Fieldwork, new geochronological analyses (zircon U-Pb LA-ICPMS), and previously obtained data revealed that the basement of the Chiapas Massif Complex (CMC) in the southern Maya Block recorded three Late Paleozoic magmatic episodes. The first igneous pulse is documented by the ~307 – 271 Ma magmatic protoliths of now intermediate to felsic orthogneisses. The Custepec Unit (CU), which was redefined here as composed of amphibolite and amphibolitic gneiss with igneous precursors, corresponds to the second pulse, which most probably occurred during the late Permian. The last magmatic episode, and the most voluminous, is represented by ~255 – 249 Ma undeformed granites whose emplacement was coeval with a high-grade tectonothermal event that caused the metamorphism and migmatization of the early Permian granites, the CU, and other basement rocks from the CMC. Geochemical and Sm-Nd isotope analyses, along with inherited zircon cores, indicate that reworking and rejuvenation of a Proterozoic crust occurred during the three magmatic pulses, in the presence of the lithospheric mantle in the early Permian and the asthenospheric mantle since the late Permian. These results are interpreted in terms of the transition from: (1) a volcanic arc established along the NW margin of Gondwana in the Carboniferous-early Permian as a consequence of the subduction of the Rheic oceanic plate, followed by (2) slab break-off in the late Permian, after Laurentia and northwestern Gondwana had collided, to (3) a post-collisional environment coeval with a high-grade tectonothermal event during the Permo-Triassic.
Geological Society of America Abstracts with Programs. Vol. 58, No. 3
doi: 10.1130/abs/2026CD-410846
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