31 The western equatorial Pangea: Geological, geophysical, geochronological, and paleoecological insights on the youngest supercontinent assembly and breakup on Earth (Part 1)
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
8:00 AM - 12:00 PM
LMH, Isla Carmen
The roots of northeastern Mexico: A 1.3 Ga crustal block in the Novillo Complex.
Paper number: 31-1
Program: Technical Sessions
Time: 8:05 AM – 8:25 AM
Authors
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Eduardo Alemán-Gallardo Presenting AuthorInstituto de Ciencias Básicas e Ingeniería, Universidad Autónoma del Estado de Hidalgo, Mineral de la Reforma, Hidalgo
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Bodo WeberDivisión de Ciencias de la Tierra, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada , Baja California
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Juan Ramírez-FernándezFacultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León, Linares, Nuevo León
Abstract
The Novillo Complex, formerly referred to as the Novillo Gneiss, is an exposed unit in the eroded core of the Huizachal–Peregrina Anticlinorium in northeastern Mexico and represents part of the Precambrian basement of Oaxaquia.
Based on field relationships, petrography, whole-rock geochemistry, Nd isotopic data, and U–Pb zircon geochronology, the complex is subdivided into three main units: (1) the Álamos Unit, (2) the San Marcos AMCG Suite, and (3) the Risco Prieto Unit, together with post-orogenic intrusions. The Álamos Unit consists of felsic and mafic gneisses and metagranites related to arc magmatism. The San Marcos AMCG Suite comprises meta-anorthosites, banded gneisses sensu stricto, and metanelsonites that represent AMCG-type magmatism. The Risco Prieto Unit includes paragneisses, amphibolites, and magnesium-silicate marbles that record metasedimentary protoliths.
Geochronological data indicate that arc magmatism (Alamos unit) in the Novillo Complex occurred between 1334 and 1326 Ma. This unit also contains zircons dated at 1095 Ma, which may be interpreted as part of the Olmec Orogeny related to accretion of the Oaxaca insular arc to Amazonia. The San Marcos AMCG Suite records magmatic activity between 1038 and 1030 Ma that postdates the Olmec Orogeny and predates development of the Zapotec Orogeny, which in the Novillo Complex occurred about 975 Ma.
Following the Zapotec Orogeny, the Novillo Complex experienced orogenic collapse at 930 Ma, recorded by pegmatitic and metaferrodiorite dikes that cut the Zapotec fabric. The youngest zircons occur in migmatized zones of the Los Álamos Unit and yield ages of 607–596 Ma, slightly younger than mafic dikes that cut the complex, suggesting localized thermal overprinting and migmatization.
Geological Society of America Abstracts with Programs. Vol. 58, No. 3
doi: 10.1130/abs/2026CD-410974
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