Estudio petrográfico y geoquímico del Complejo Plutónico El Peñuelo (Cinturón de Intrusivos de Concepción del Oro), noreste de México

El presente estudio reporta información petrográfica y geoquímica del Complejo Plutónico El Peñuelo (CPEP), perteneciente al Cinturón de Intrusivos de Concepción del Oro (CICO, noreste de México). El CPEP es una estructura semi-circular, constituida por tres centros de emplazamiento, ubicada en el extremo oriental del CICO y en la extensión norte de la traza del sistema de fallas Taxco-San Miguel de Allende. Sin embargo, el complejo no fue deformado por la actividad de este sistema de fallas. El CPEP está constituido por rocas intrusivas que varían desde cuarzo monzodiorita a cuarzosienita, siendo ésta última la unidad que cubre la mayor parte de la superficie del complejo. El CPEP se emplazó en rocas sedimentarias marinas del Cretácico superior. La cuarzosienita es cortada por diques de cuarzomonzodiorita y mesosienita porfíritica. Además, esta unidad contiene enclaves microgranulares de monzodiorita distribuidos de forma irregular y diques pegmatíticos cortan al resto de las unidades litológicas. La asociación mineralógica en el CPEP presenta cantidades variables de plagioclasa + feldspato alcalino + cuarzo ± anfíbol + biotita ± ortopiroxeno + clinopiroxeno + óxidos de Fe-Ti. Las rocas intrusivas tienen una composición química en SiO2 = 45.7-72.0 %, Mg# = 39.2-60.2 y n-Fe = 0.54-0.73. Presentan patrones de tierras raras, normalizados a condrita, enriquecidos en elementos ligeros [(La/Yb)N = 6-11] sin anomalías de Eu. Los diagramas multielementos, normalizados a manto primordial, muestran patrones de enriquecimiento en elementos LILE en relación a los HFSE. Su geoquímica de elementos traza es similar a la de granitoides de alto Ba-Sr: (a) una alta concentración de Ba (= 594-2302 ppm) y Sr (= 444-2192 ppm); (b) una baja concentración de Y (= 10-46 ppm) y Nb (= 6-17 ppm); y (c) valores altos para las relaciones Sr/Y (= 25-85) y La/Yb (= 8.9-16.5). El origen del CPEP se ha relacionado a la fusión parcial de un manto litosférico enriquecido, en condiciones post-orogénicas, seguida de cristalización fraccionada acoplada con asimilación de material cortical

Generation of Arc-Like and OIB-Like Magmas Triggered by Slab Detachment in the Eastern Mexican Alkaline Province: Petrological Evidence from the Cenozoic Sierra de San Carlos-Cruillas Complex, Tamaulipas

The origin of the Eastern Mexican Alkaline Province has been explained by landward arc migration and subsequent asthenospheric upwelling after slab roll-back of the Farallon Plate. In this work, we present new petrographic, mineral chemical, geochemical, and geochronological data of the Sierra de San Carlos-Cruillas (SSCC), one of the most important complexes in the province. This information, together with published data, helped us to reinterpret the tectonic processes operating during the generation of this province, as well as the mantle sources involved in the partial melting process. Detailed geochemical analysis suggests the participation of two types of metasomatized mantle regions: a lithospheric source modified by past subduction processes and an asthenospheric source slightly affected by carbonatite-related metasomatism. Variations in the partial melting degrees controlled the extent of magma enrichment in the latter. Major and trace element geochemistry, together with geochronological data and field relations, evinced an older post-orogenic setting related to the arc-like rocks (Eocene) and a younger intraplate extensional environment associated with all enriched igneous rocks (Oligocene-Miocene). Bivariate diagrams of SiO2-trace element ratios and multi-element patterns indicate that magmas from the SSCC complex dominantly evolved through fractional crystallization with a limited crustal contribution. Petrographic and mineral chemistry features suggest that some of these magmas experienced open-system processes (e.g. recharge events) in a complex and dynamic magmatic feeding system. In contrast to the traditional petrotectonic model, we propound that the passage and subsequent foundering of the Hess conjugate under northeastern Mexico resulted in its eclogitization and triggered slab tearing and succeeding detachment. This latter process occasioned mantle upwelling and the partial melting of the two recognized metasomatized mantle sources, thus generating the San Carlos-Cruillas magmatism

Coeval Early Ediacaran Breakup of Amazonia, Baltica, and Laurentia: Evidence From Micro‐Baddeleyite Dating of Dykes From the Novillo Canyon, Mexico

Abstract Final Rodinia supercontinent breakup during the early Ediacaran is recorded by mafic dyke swarms in Baltica and Laurentia, but corresponding dykes have been elusive for Amazonia, the third craton involved. We report ages and compositions for plume‐related dykes intruded into Rodinia‐type basement of the Novillo Gneiss, part of a microcontinent placed between Amazonia and Baltica in Rodinia reconstructions. In situ U‐Pb micro‐baddeleyite dating with secondary ion mass spectrometry yielded dyke intrusion ages of 619 ± 9 Ma (95% c.i.), coeval with ages of similar dykes from Baltica and Laurentia. A younger age group is consistent with an earlier 40Ar‐39Ar age at ~545 Ma, reflecting Pb loss and recrystallization during hydrothermal alteration. The results indicate an Amazonia‐Baltica‐Laurentia connection prior to opening of the Iapetus Ocean and suggest a previously unrecognized superplume‐related large igneous province extending over all sides of the former triple point. Weathering of these large igneous province basalts may have contributed to Ediacaran Gaskiers glaciation