25-8 Petrology and Geochemistry of a Miocene Syn-Extensional Plutonic Suite, central Sonora: Insights into Magma Chamber Processes from the Puerta del Sol Core Complex

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

Poster Booth No.: 52

Presenting Author:

Elizard Gonzalez-Becuar

Authors:

Gonzalez-Becuar, Elizard¹, Lopez Acuña, Erick², Luis Alonso, Velderrain-Rojas³, López Bejarano, Raquel⁴, Vega García, Fabiola⁵

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.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.