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

Paleontological and Geochronologic Constraints on the Paleogeographic Evolution of the Oaxaquia Microcontinent, Mexico

Paper number: 31-4
Program: Technical Sessions
Time: 9:05 AM – 9:25 AM

Authors

Abstract

Oaxaquia is a coherent block of Grenville-age metamorphic rocks that formed during the assembly of Rodinia, exposed in several inliers across Mexico, with the Oaxacan Complex as its largest outcrop. It underlies much of eastern and southern Mexico. It is overlain by Lower Paleozoic (Ordovician and Silurian) sedimentary rocks that contain trilobites, conodonts, and graptolites of Gondwana and Old Realm affinity.

Some authors suggest that Oaxaquia remained attached to Gondwana until the Permian assembly of Pangea, and that the southern extension of the Marathon-Ouachita orogenic belt in northern Mexico resulted from the collision of Oaxaquia with Gondwana. However, there is evidence indicating that Oaxaquia may have accreted to North America before the Mississippian, prior to the final collision of Pangea, such as:

1) Shallow marine invertebrate fossils found in Mississippian sedimentary rocks that overlie Oaxaquia show similarities to those in the mid-continent province of North America, indicating proximity and connection through shallow-sea environments between Oaxaquia and North America at that time. 2) Detrital zircon from the Permian Rara Formation, which overlies the North American craton in central Chihuahua, has clusters similar to those from pre-Permian metamorphic rocks (Rio Fuerte Formation, Granjeno Shist, and Teziutlán complex) with a cluster around 350 Ma, a major population between 430 and 550 Ma, and a wide range of Proterozoic ages. 3) Late Permian-Early Triassic arc volcanism overlaps all previous units, suggesting that a Pacific east-facing subduction zone developed on the western margin of Oaxaquia/Pangea. 4) The coexistence of Laurentian and Gondwanan fossil plant elements in Permian strata supports models of an early collision between Oaxaquia and Laurentia, followed by floristic exchanges after the consolidation of Pangea.

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

doi: 10.1130/abs/2026CD-411039

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