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

Detrital Zircon Provenance Study in Metasedimentary Rocks from the Cuicateco Terrane (Oaxaca, Mexico) – From the Opening of the Iapetus to the Closure of the Rheic Ocean.

Paper number: 5-9
Program: Technical Sessions
Time: 10:45 AM – 11:05 AM

Authors

Abstract

The Cuicateco terrane is a fault-bounded crustal block exposed to the northeast of Oaxaca, constituted mainly but not exclusively, by metasedimentary rocks. Here we present the first zircon provenance study performed in metasedimentary samples collected along sections and outcrops in the southeastern part of the Cuicateco terrane, also known as the “Sierra Mixe”. The rocks in the study area comprise white-mica and two-mica ± chlorite schists and quartzites (occasionally with volcaniclastic layers), intercalated with or in tectonic contact with metagabbroic layers, slices or dykes. All these rocks metamorphosed under greenschist-to amphibolite-facies conditions and, notably, most if not all of them display mylonitic deformation and folding. The entire sequences are intruded by younger, undeformed felsic porphyries. Based on detrital zircon U–Pb age distributions, maximum depositional ages (MDA) and lithological characteristics, we distinguish four metasedimentary units with depositional ages ranging from Late Ediacaran to Early Jurassic. The units are here informally defined as follows: (1) The Villa Alta Paragneiss is a quartz-feldspathic, partly migmatized (?) unit containing mafic fragments and dikes. Zircons have Ordovician (~460 Ma) metamorphic rims, and the youngest detrital zircon cores are Ediacaran (~627 Ma), bracketing the time of deposition between these two ages. (2) The Zacatepec Schist is typically rich in white mica. The youngest  zircon grains (both igneous and metamorphic) have Ordovician ages (~450 Ma), defining the MDA. (3) The Cotzocón Schist is also rich in white mica and quartz, but locally contains plagioclase porphyroclasts. The youngest detrital zircons display Carboniferous ages (~350 Ma, MDA). The other age peaks are like those known from the Santa Rosa Formation. (4) the Totontepec Schist is characterized by layers of white-mica-rich and quartz-feldspar-rich horizons with feldspar porphyroclasts, and abundant chlorite. The zircon record is dominated by Permian ages (~300-270 Ma), suggesting Triassic MDA coeval with the lower Todos Santos Group. The data support a long-lasting depositional history for the Cuicateco terrane, starting with initial opening of the Iapetus Ocean after breakup of Rodinia, a possible back-arc basin related to the Ordovician Famatinian arc along the NW Gondwana margin, the typical hiatus during the Devonian (closure of Iapetus), resumption of deposition within the Rheic Ocean – peri-Gondwanan realm during the Carboniferous prior to the assemblage of Pangea, and, finally, the onset of extension during breakup of Pangea.

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

doi: 10.1130/abs/2026CD-410804

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