27 Evolution of Cordilleran-type orogenic systems

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
1:30 PM - 5:30 PM
LMH, Isla Carmen

From the dusk of the Mexican Orogeny to the dawn of the Basin and Range Province: Eocene tectono-magmatic evolution of the Zacatecas Horst, Mexico.

Paper number: 27-1
Program: Technical Sessions
Time: 1:45 PM – 2:05 PM

Authors

Abstract

The Zacatecas Horst is an area of significant economic interest (Ag, Au, Pb, Zn) with a complex deformation history linked to the tectono-magmatic evolution of central Mexico. Two dominant fault systems, oriented ~N–S and NW–SE, are thought to have acted as conduits for the emplacement of (sub-)volcanic bodies and mineralized veins, forming low- and intermediate-sulfidation deposits. However, the cross-cutting relationships and kinematic evolution of these fault systems have been debated for nearly four decades.

This study integrates rock magnetism, anisotropy of magnetic susceptibility (AMS), paleomagnetism, petrographic analyses, and two U–Pb zircon ages from major (sub-)volcanic structures—including one rhyolitic dome and five rhyolitic dikes with different orientations in the south-central Zacatecas Horst. These data are used to constrain the tectono-magmatic evolution of the area and to propose a revised deformation model.

Petrographic analyses demonstrate that three of the studied (sub-)volcanic structures correspond to pyroclastic dikes. Most structures contain variable assemblages of ferromagnetic minerals, including (titano)magnetite, (titano)maghemite, and (titano)hematite. AMS results indicate that the dikes were emplaced under non-coaxial stress conditions, recording transtensional deformation with a strike-slip component that evolved from dextral to sinistral kinematics. U–Pb zircon ages from two pyroclastic dikes yield emplacement ages of 45.8 and 42.1 Ma, placing magmatism during the middle Eocene. Paleomagnetic data indicate negligible vertical-axis rotation but record a post-emplacement tilting event that affected the Zacatecas Horst during the late Eocene–early Oligocene.

At a regional scale, these results provide a record of Cenozoic plate-boundary reorganization along the western North American margin. The Zacatecas Horst occupies a key position within the Eocene tectonic reorganization of central-northern Mexico, when contractional deformation associated with the Mexican Orogeny progressively gave way to transtensional and extensional regimes. The kinematic evolution inferred from AMS fabrics suggests that magma ascent and emplacement were strongly controlled by reactivated fault systems, highlighting the role of inherited structures in localizing magmatism and hydrothermal fluid flow. These results provide new constraints on the structural controls of mineralization in the Zacatecas Horst.

Together, these results reconcile previously proposed tectono-magmatic models and demonstrate that the Zacatecas Horst records a progressive transition from the waning stages of the Mexican Orogeny to the onset of Basin and Range extension during the Eocene–early Oligocene.

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

doi: 10.1130/abs/2026CD-410740

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.