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

The Motozintla Shear Zone suture, its role in the last stages of equatorial Pangea’s assembly and later break up

Paper number: 204-12
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

A detailed analysis of the Motozintla Shear Zone (MSZ), located at the southern edge of North America, has revealed its complex tectonic history. The MSZ is a critical structure that not only represents the suture zone where the Southern Maya and Maya terranes collided during the final stages of Pangea's assembly, but also locally separates the Chicomuselo Fold-Thrust Belt (CFTB) from the Chiapas Massif block.

Our analysis of the MSZ's anatomy, kinematics, deformation mechanisms and gradient, and temperature conditions shows that the deformation in the MSZ correlates with the CFTB, which occurred between 250 and 220 million years ago. At this time, the MSZ acted as a reverse-lateral fault under lower greenschist facies conditions. Its great exposure and careful study allowed us to observe that it reactivated pre-Permian structures and was itself reactivated multiple times throughout its history—as a normal fault in the Early Jurassic and as a reverse and lateral fault in the Cenozoic.

On a regional scale, the MSZ is part of a series of major lithospheric faults in southern Mexico, which share a similar orientation and were formed around the same time, accommodating predominantly dextral displacement. Notable examples include the dextral reverse Caltepec fault (~276 Ma), the Oaxaca fault (unknown formation age; dextral reactivation at ~169 Ma), the Tamaulipas-Golden Lane-Chiapas system (~170 Ma), and the mylonitic fabric within the southern Chiapas Batholith (~265 Ma).

The specific arrangement of NW-SE oriented lithospheric blocks, bounded by these long-lived faults responsible for bringing them together during the Permian, is a defining characteristic of Mexican geology. The MSZ's detailed study provides crucial insights into the role of these tectonic boundaries, as it not only bounded important basins in the Jurassic but also channelized magma during the Permian, Jurassic, and Cenozoic. Ultimately, a deeper understanding of the MSZ allows us to better comprehend the geological evolution of the southern edge of North America.

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

doi: 10.1130/abs/2025AM-413568

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