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 and Geochemistry of a Miocene Syn-Extensional Plutonic Suite, central Sonora: Insights into Magma Chamber Processes from the Puerta del Sol Core Complex

Paper number: 25-7
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Puerta del Sol (PDS) range is one of the southernmost metamorphic core complexes of the North American Cordillera. Its footwall exposes a Miocene, syn-extensional plutonic suite. Using petrography and whole-rock geochemistry, this study investigates the petrogenesis of this suite, comprising the Garambullo (19.8±0.18 Ma) and Las Mayitas (21.8 Ma) plutons, their abundant mafic enclaves, and syn-magmatic dikes. The Garambullo pluton is a texturally heterogeneous monzodiorite to gabbro, while the Las Mayitas pluton is a medium-grained granodiorite. Both exhibit widespread magma mingling and disequilibrium textures (e.g., zoned, biotite-hornblende rimmed plagioclase). Enclaves and dikes range from gabbro to granite in composition. Geochemically, the suite is calc-alkaline and metaluminous (A/CNK = 0.6–1.0), with a broad silica range (44–74 wt.% SiO₂). Bi-variate diagrams show patterns of fractional crystallization of plagioclase, K-feldspar, and Fe-Mg minerals. Trace elements show arc signatures: high Ba/Nb (>82), moderate LREE/HREE enrichment ((La/Lu)ₙ = 6–13), and weak Eu anomalies (Eu/Eu* = 0.6–1.0). Published Sr-Nd-Pb isotopes (⁸⁷Sr/⁸⁶Srᵢ ≈ 0.707; εNdᵢ ≈ -4.3; 206Pb/204Pb = 19.1, 207Pb/204Pb = 15.6, 208Pb/204Pb = 38.8) reveal crustal assimilation of Paleoproterozoic (1.7 Ga) Caborca basement, similar to signatures in regional Laramide and mid-Tertiary magmas. Comparative analysis shows the strongest geochemical affinity is with regional mid-Tertiary magmas and lesser similarities to Laramide plutons and rift-related magmas. We conclude that the PDS Miocene suite represents late subduction-derived magmas undergoing a significant AFC process with the available Caborca basement during the Oligocene-Miocene. Their emplacement into the extending core complex footwall was facilitated by slab roll-back and lithospheric thinning, which is reflected in the less-evolved compositions within this syn-extensional arc setting.

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

doi: 10.1130/abs/2026CD-410780

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