204 Paleozoic Tectonics of SW Laurentia Without Borders: Final Amalgamation of Pangea in the USA, Mexico, and South America

We invite contributions that explore the Paleozoic tectonic evolution of southwestern Laurentia during the final assembly of western Pangea. Research on Paleozoic tectonic belts in Gondwana, particularly from Mexico and South America, is especially welcome.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 217B

Provenance of Pennsylvanian turbidites from the Sonora allochthon, Sonora, northwestern Mexico: new insights into the westernmost end of the late Paleozoic trans-Pangean belt

Paper number: 204-9
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

The Pangea supercontinent was assembled during late Paleozoic time by closure of the Rheic Ocean and the consequent continental collision of Gondwana with Baltica and Laurentia, which progressed from east to west. Convergence culminated in the development of a trans-Pangean orogenic belt and associated complex foreland system, which accommodated thick clastic wedges instrumental in the formation of hydrocarbon reservoirs. The trans-Pangean belt includes the Late Mississippian–late Permian Ouachita-Marathon orogen in the southern USA and northern Mexico. Previous work has suggested that the youngest sector of the belt was the Sonora allochthon in northwestern Mexico, represented by a north-verging fold-thrust belt. However, a solid link between the Sonora allochthon and the trans-Pangean belt has not yet been documented. We use detrital modes and detrital-zircon U-Pb geochronologic data to provide insight into the provenance of the Rancho Nuevo Formation, a Middle-Upper Pennsylvanian foreland turbidite succession that is considered part of the Sonora allochthon, and assess its ties to the trans-Pangean belt.

Two samples are very disparate in detrital-zircon signature.  One bears strong similarity to approximately coeval units in southern Arizona, showing the characteristic presence of Yavapai-Mazatzal 1600–1700 Ma grains.  The other has a dominant signature at 500–750 Ma. Grains of this age range are largely missing from Laurentian Pennsylvanian deposits (e.g., southwestern USA), whereas they are ubiquitous in Gondwana-affinity basement, as well as in Pennsylvanian foreland deposits in the Marathon sector of the trans-Pangean belt. Sediment recycling of at least part of detritus that makes up the Rancho Nuevo Formation is supported by the high-quartz content (>90% of the total detrital grains) and the occurrence of ultra-stable heavy minerals such as zircon and tourmaline, many of which show a very high degree of roundness.

Our preliminary data indicate that Pennsylvanian foreland turbidites of the Sonora allochthon were sourced in rocks from both Laurentia and Gondwana.  We speculate that recycling of grains demonstrates that uplifted rocks to the east, which had already accumulated mixed-sources detritus, shed sediment into these advancing turbidites. Additional detritus came from uplifted bedrock in the two continental blocks. Distinct streams fed turbidites at different times, such that stratigraphic levels or adjacent lobes show distinctly different signatures.  These deposits are thus tied to the trans-Pangean orogenic belt and foreland system.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412621

© Copyright 2025 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.