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

Late Paleozoic Alleghanian Amalgamation of Western Pangea

Paper number: 5-1
Program: Technical Sessions
Time: 8:10 AM – 8:30 AM

Authors

Abstract

We present an updated series of paleo-tectonic maps outlining the Alleghanian collision between Laurentia and Pangea that formed western Pangea 350–275 Ma. The new maps enhance the Alleghanian model of Dewey (1982) and Pindell and Dewey (1982), and are constrained by paleomagnetically determined paleo-latitudes (Scotese 2021); an average azimuth of closure determined by several intra-continental shear zones; and inter-continental (Laurentia–Gondwana) convergence rates as required to satisfy first arrival of non-Laurentian flysch on the Laurentian autochthon as determined by stratigraphic architecture and source-to-sink petrographic and detrital zircon analysis. The indicated rates from this assessment are 30 km/Myr for 350–335 Ma; 20 km/Myr for 335–320 Ma; 10 km/Myr for 320–290 Ma; and 7 km/Myr for 290–275 Ma. These are relatively slow rates for subduction and may explain the paucity of continental arc magmatism along the leading fringe of Gondwana. The model produces a final reconstruction for western Equatorial Pangea consistent with current pre-breakup reconstructions (Pindell et al. 2020). Six reconstructions at 15 Myr intervals in the North American reference frame with accurate crustal block outlines provide a standardized framework for future integration of mapping and data. The Alleghanian Orogeny involved dextral-oblique subduction of Rheic Ocean crust and east-to-west progressive collision. We show how the Sabine Block may have undergone a period of independent motion relative to either continent between 350–305 Ma, pulled into the Ouachita re-entrant by subduction roll back and intra-arc extension as a means of ensuring continuous suturing. We hypothesize that a Peru-Bolivia style compressive continental arc orogen developed along the Pacific margin, spanning the Laurentia and Gondwana suture, in Late Permian–Early Triassic time. The study provides a spatio-temporal framework for understanding the Penn-Perm interior sedimentary basins associated with Alleghanian orogenesis.

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

doi: 10.1130/abs/2026CD-410823

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