37 Cordilleran Margin Evolution and Supercontinent Tectonics: From Pangea Assembly to North American Orogenesis (Posters)

This session integrates tectonics, petrology, geochronology, stratigraphy, and paleontology to illuminate how Paleo-Pacific plates drove subduction dynamics, crustal evolution, and paleogeographic reconstructions across the complex geological architecture of the American Cordilleras.

Friday, 24 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Structural Evolution and Geometry of the Motozintla Shear Zone: A Multireactivated Suture in Southern Mexico

Paper number: 37-6
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Motozintla Shear Zone (MSZ) is a multireactivated suture at the southern margin of the North American plate. While its existence was proposed over two decades ago based on the contrasting crystalline basements of the southern Mexican peninsula, it has only recently been described in detail. The MSZ juxtaposes the Chiapas Massif Complex (Precambrian–Permian igneous and metamorphic rocks) with the Yucatán Peninsula granitoids (Pan-African plutons). However, the nature of this suture—particularly the subduction vergence—remains poorly defined. This study presents structural data aimed at clarifying the geometry and tectonic evolution of the MSZ.

 

Our methodology integrated geological mapping, detailed outcrop-scale structural analysis, stereographic projection of trends, and microstructural/kinematic analysis of oriented thin sections. We further synthesized available literature to construct 3D models representing the MSZ’s configuration across four stages: the Ordovician, Permian–Triassic, Early Jurassic, and Cenozoic.

 

The structural evolution indicates that during the Ordovician, the Motozintla plutonic suite intruded the Candelaria and Jocote orthogneisses and paragneisses. This was contemporaneous with anatexis and tight folding of the metamorphic units, and syntectonic mylonitization of the plutons; these structures predominantly dip to the SW. Subsequently, this rigid basement and the Yucatán plutons were covered by a marine succession (Santa Rosa, Grupera, and Paso Hondo formations), which were later involved in the Huastecan orogeny during the assembly of Pangea. This event produced the Chicomuselo fold-and-thrust belt. The SW-dipping structures and NE-verging folds suggest a SW-dipping subduction zone, likely within a doubly vergent orogenic configuration, allowing the Chiapas Massif Complex to thrust over the Pan-African plutons.

 

During the breakup of Pangea, the MSZ was reactivated as a normal fault zone, facilitating the exhumation of crystalline rocks, magma channeling, the deposition of Jurassic continental syntectonic sequences, and the kinking of MSZ-related foliation. Finally, brittle faulting associated with the migration of the Chortis Block and the recent activity of the Polochic Fault dismembered the MSZ, resulting in its current complex architecture. These representations highlight the inherent difficulty in interpreting plate boundaries that have undergone numerous overprinting deformation events.

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

doi: 10.1130/abs/2026CD-410891

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