5 The southern margin of the North American cordillera through time

This session deals with the geologic evolution of the southeastern Cordillera of the North American Plate, its role during ancient orogenic cycles, opening of the Gulf of Mexico, and its interaction with the Caribbean Plate.

Wednesday, 22 April 2026
8:00 AM - 12:00 PM
LMH, Meeting Room

The Neoproterozoic Record of Crustal Extension and Rifting in Eastern and Southern Mexico – Pinpoints in Support of an Amazonia-Oaxaquia-Baltica Connection

Paper number: 5-10
Program: Technical Sessions
Time: 11:05 AM – 11:25 AM

Authors

Abstract

Precambrian basement inliers in Mexico are traditionally combined into the Oaxaquia microcontinent, which is supposed to underlie most of eastern and southern Mexico. However, repeated crustal extension following the assembly of Rodinia and Pangea likely dismembered the Precambrian basement into smaller crustal slices. The most prominent feature identifying rocks from Oaxaquia is, besides the abundance of anorthosites and associated rocks, a granulite facies metamorphic event at ~990 Ma (Zapotecan orogeny). While the timing of the Zapotecan orogeny is consistent with the latest phase of the Grenville orogeny in Eastern Laurentia (Rigolet phase), differences in tectonic context and similarities to tectonic events in Sveconorwegian provinces have led to models that incorporate Oaxaquia into the Rodinia supercontinent between Baltica and Amazonia. Although some authors have questioned this model, alternative models are likewise questionable. Recently, previously unknown Precambrian rocks were discovered outside of the traditional Oaxaquia region. These crustal slices were found in the Sierra de Juárez Complex and the Cuicateco terrane (Oaxaca), the Chiapas Massif and El Triunfo complexes (Chiapas), and in Guatemala. All these regions experienced a post-Zapotecan, non-granulitic metamorphic event at ~950-900 Ma. This event was first documented in the El Triunfo Complex near the Guatemalan border. At this locality, low ∂18O  values in metamorphic zircon imply crystallization from precursors altered by meteoric or seawater. This indicates the existence of deep detachment faults during orogenic collapse. The breakup of Rodinia is widely accepted to have been triggered by a mantle superplume. The impact produced lithospheric extension, rifting, and the development of the Central Iapetus Magmatic Province (CIMP). The CIMP produced mafic dike swarms in eastern Laurentia (Long Range, Labrador), southwestern Baltica (Egersund, Norway), and Mexico (Novillo, El Triunfo, and Cuicateco) during the early Ediacaran (~620-600 Ma). Igneous activity during the initial stage of lithospheric extension in eastern Laurentia did not begin until the Cryogenican (~760 Ma), whereas the earliest dyke swarm in SW Baltica (Hunnedalen dykes) intruded around 850 Ma. Preliminary zircon U-Pb ages from metagabbroic crustal slices in strongly deformed metasedimentary rocks from the Cuicateco Terrane yielded ages identical to those of the Hunnedalen dykes. These new findings further support the Amazonia-Oaxaca-Baltica connection during the Neoproterozoic.

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

doi: 10.1130/abs/2026CD-410734

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