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

Geochemical and whole-rock isotopic analysis of Lu-Hf and Sm-Nd in Triassic and Jurassic rocks of the Sonobari Complex, El Fuerte Region, Sinaloa, Mexico.

Paper number: 25-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Sonobari Complex, in northwestern Mexico, is a block composed of igneous and metasedimentary rocks ranging in age from Ordovician to Late Cretaceous. This complex is composed of rocks of North and South American origin and thus played an important role in the interaction between Laurencia and Gondwana during the consolidation of Pangaea. It has been proposed in some studies as the basement of the Middle Jurassic-Late Cretaceous Guerrero Terrane; however, its relationship to the Jurassic oceanic-arc terranes of northwestern Mexico remains unknown. This work integrates petrology, geochemistry, and whole-rock Lu-Hf and Sm-Nd isotope analyses of Triassic and Jurassic orthogneisses and Ordovician metasedimentary rocks. Geochemically, the protoliths of the Triassic and Jurassic orthogneisses of the Sonobari Complex are Cordilleran-type, primarily peraluminous, and exhibit fractional crystallization trends. These orthogneisses show trace-element compositions suggesting a subducted-related origin, interpreted to reflect a volcanic arc setting. Most Triassic and Jurassic orthogneisses show slightly fractionated rare-earth element patterns, with negative Eu anomalies, suggesting crystallization under the influence of plagioclase. Late Triassic orthogneisses (n = 6) have an average initial epsilon Hf (εHfi) values ​of +3.3 and εNdi of -1.7; Late Jurassic orthogneisses (n = 5) have average εHfi of +3.8 and εNdi of -2.5, while two analyzed Late Jurassic intrusive rocks have average εHfi of +2.1 and εNdi of -1.0. Ordovician basement rocks exhibit the most evolved isotopic compositions (εHfi of -16.1 and -10.9; εNdi of -11.1 and -10.5). The results suggest that juvenile magmas sourced the protoliths of the Late Triassic and Jurassic orthogneisses and Late Jurassic rocks, which interacted with an isotopically evolved component, probably the continental crust. This could be associated with a Triassic-Jurassic continental arc, probably the southernmost continuation of the Southern California Triassic-Jurassic Cordilleran arc.

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

doi: 10.1130/abs/2026CD-410954

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