204 Paleozoic Tectonics of SW Laurentia Without Borders: Final Amalgamation of Pangea in the USA, Mexico, and South America

We invite contributions that explore the Paleozoic tectonic evolution of southwestern Laurentia during the final assembly of western Pangea. Research on Paleozoic tectonic belts in Gondwana, particularly from Mexico and South America, is especially welcome.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 217B

Structural-geochronological record of progressive deformation through U-Pb in tectonic calcite veins in the Chicomuselo Fold and Thrust Belt, SE Mexico: Evidence for the amalgamation and the breakup of Western Pangea

Paper number: 204-11
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

The Chicomuselo fold-thrust belt (CFTB), located southeast of Mexico, is one of the least studied thin-skinned orogens, formed during the assembly of western Pangea and currently exposed at the surface. This belt comprises Carboniferous and Permian metasedimentary, clastic, and carbonate rocks that were deformed at the Permo-Triassic boundary by a shortening event penetrative at a grain-scale. This event formed isoclinal folds in the underlying, finer-grained rocks, as well as open folds and thrusts with abundant calcite tectonic veins in the overlying carbonate rocks. The CFTB has been affected not only by shortening associated with the assembly of Pangea, but also by multiple tectonic events that impacted the evolution of the southern margin of the North American Plate, such as the early breakup of Pangaea and the drifting opening of the Gulf of Mexico.

We present a detailed high-resolution structural-geochronological analysis, utilizing the in-situ U-Pb method on carbonates via LA-ICP-MS for the first time in Mexico. We dated 121 cements from tectonic veins related to folds and faults, complex veins randomly oriented, and host rocks (fossil shells and matrix), of which only 99 cements provided reliable ages. Our ages constrain the record of the progressive deformation related to: 1) Layer Parallel Shortening (LPS, early folding stage, 2) Fold-growth stage, and 3) Late-Stage Fold-Tightening (LSFT), associated with the most significant shortening event that occurred at the Permo-Triassic boundary, related to the amalgamation of Pangea. The late stage has new ages that enable the CFTB to be placed within a spatial and tectonic context, bringing new insights regarding the last closure of Pangea, allowing for an understanding of its role during the formation of this supercontinent.

Our study demonstrates the effectiveness, sensitivity, and high spatial and temporal resolution of the method for solving structural problems based on punctual geochronology in tectonically complex areas and that calcite is a holistic, versatile, resilient, and reliable mineral for preserving the history of progressive brittle deformation imprinted in limestone, as well as its importance in the study of the tectonic evolution of supercontinents.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412053

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