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

The Triassic-Jurassic Transition from Collision to Transtension in the Chiapas Massif Complex: Its Role During the Breakup of Pangea and Its Relation to Other Crustal Blocks

Paper number: 40-5
Program: Technical Sessions
Time: 2:40 PM – 3:10 PM

Authors

Abstract

The Chiapas Massif Complex (CMC) is essential to understanding the tectonic processes that occurred in the middle crust during final Pangea assemblage and breakup. An Early Triassic (~255-245 Ma) medium- to high-grade metamorphic event in the CMC is indicative of the final stage of collision between Gondwana and Laurentia. Coeval, syn- to post-collisional intrusion of voluminous granitoids (Chiapas batholith) was triggered by anatexis in an overthickened crust. Back then, the CMC was probably positioned adjacent to the Ouachita-Marathon belt, likely somewhere between the Sabine terrane and the Coahuila block. The onset of inter-continental extension is evident in the CMC through Late Triassic (~220-205 Ma) leucogranite stocks (Laguna granites, Valencia-Morales et al., 2024). These stocks also formed through anatexis, evidenced by coeval migmatite that occurs locally, but they are likely related to crustal thinning. They intruded along former tectonic contacts in the central CMC that were presumably inverted into detachment faults. On the other hand, cooling ages in the northwestern CMC indicate mid-Triassic uplift, while the central CMC remained in the middle crust. Some discrete blocks remained at mid-crustal levels until the Early Jurassic when undeformed S-type granites intruded. Others were already exposed and covered by volcanic and sedimentary rocks. However, during the breakup of Pangea, crustal extension and rifting were not orthogonal, but rather transtensional and accompanied by non-coaxial deformation. Mylonite zones observed in the CMC are likely related to this transtension, but these have not yet been thoroughly investigated. Zircon rims and monazite from mylonitic rocks (Valencia-Morales et al., 2024) yield U-Pb ages between ~188 and 179 Ma that are interpreted as being related to the time of deformation. This interpretation can be confirmed by our preliminarily titanite dating approach. The results suggest that ductile deformation in the CMC ceased before the Gulf of Mexico (GoM) opened in the Middle Jurassic, when the CMC began to drift southeastward along the East Mexican Transform toward the Cuicateco block (CB). Our ongoing research in the CB, on the other hand, suggests that crustal thinning and transtension were much more intense and long-lasting in rocks in the CB than in the CMC. Preliminary ages lead us to hypothesize that ductile deformation switched from the CNB to the CB during the Middle Jurassic.

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

doi: 10.1130/abs/2026CD-410917

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