25 Integrating metamorphism, mass transfer, and magmatism across the American Cordillera (Posters)

Subduction drive crustal evolution and element cycling between Earth’s surface and interior. This session highlights petrological research integrating field data, geochemistry, geochronology, and experimental or numerical modeling to illuminate subduction dynamics across the American Cordillera.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Petrology of Western Flanks of Miocene Volcanism in the Sierra Madre del Sur: San José del Progreso and San Jerónimo Taviche, Oaxaca

Paper number: 25-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Miocene volcanic rocks from the San Jerónimo Taviche area, in the Sierra Madre del Sur of Oaxaca, are part of arc-related magmatism associated with the subduction of the Cocos plate beneath southern Mexico. This region lies within a well-recognized regional magmatic hiatus between ~28 and 24 Ma; however, post-gap magmatism has received relatively little attention, particularly in central Oaxaca, where petrographic, geochemical, and geochronological data remain limited. This study presents an integrated characterization based on field observations, petrography, and whole-rock major, trace, and rare earth element geochemistry of Miocene andesites that crop out as subvolcanic bodies and lava flows interbedded with volcano-sedimentary sequences. These rocks yield ages between ~25 and 23 Ma, allowing the timing of the final stage of the regional magmatic hiatus to be constrained and documenting the early reactivation of arc magmatism during the Early Miocene. Petrographically, the andesites are predominantly porphyritic, with plagioclase ± clinopyroxene ± orthopyroxene phenocrysts, and display a calc-alkaline affinity. Trace element patterns, characterized by enrichment in LILE and depletion in HFSE, are consistent with arc magmas and suggest a mantle source modified by subduction-related fluids. Overall, these results provide new constraints on the evolution of post-gap magmatism in the Sierra Madre del Sur.

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

doi: 10.1130/abs/2026CD-410766

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