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

Thermal and fluid flow history in the Chicomuselo Fold and Thrust Belt during the final assembly and early breakup of Pangea

Paper number: 40-3
Program: Technical Sessions
Time: 2:15 PM – 2:35 PM

Authors

Abstract

The Chicomuselo Fold and Thrust Belt (CFTB) in Chiapas, located at a diffuse triple junction south of the North American Plate, is a critical record of tectonic events associated with the closure and subsequent breakup of Pangea, as well as of younger events that are overprinted in the rocks. This study integrates U-Pb geochronology, stable isotopes (δ18O and δ13C), clumped isotopes geothermometer (Δ47), and Raman spectroscopy (RSCM) to reconstruct the fluid trajectory and thermal history of the belt.

Our results indicate five distinct tectonic events (E1–E5). The first main shortening event (E1) is characterized by folding, thrusting faults, and tectonic stacking in the sedimentary-metasedimentary Carboniferous and Permian rocks, which gave rise to the CFTB. Geochemical data from calcite veins show that mobilized fluids during E1 originated from formational water trapped within the host rock and are in equilibrium with it. High temperatures recorded during the orogenic E1 are attributed to crustal thickening and stratigraphic triplication during the final pulse of Pangea's closure. The transition to the E2 event marks the early breakup of Pangea. This phase involved crustal thinning, lithospheric extension, and the formation of horst-and-graben structures. A significant influence of meteoric water is documented, as crustal uplift and erosion allowed surface fluids to infiltrate the system. Despite the influx of meteoric water, high-temperature calcite cements precipitated due to an elevated geothermal gradient associated with active magmatism and faulting. During the E3 event, corresponding to the continental-drifting phase and the opening of the Gulf of Mexico, the record shows mixing of formational and meteoric fluids. During E4, fluid-rock interactions occur only near regional faults, so calcite veins do not form; only bioclasts are recrystallized. Finally, the youngest E5 shows a progressive decrease in vein temperatures and limited fluid-rock interaction, suggesting that calcite precipitation occurred under increasingly shallow crustal conditions.

The integrated isotopic and spectroscopic data provide a robust framework for understanding the geodynamic transition from shortening to extension. The CFTB records the evolution from a thickened crustal setting during Pangea’s final assembly to the extensional regimes that eventually led to the opening of the Gulf of Mexico.

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

doi: 10.1130/abs/2026CD-410945

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