Papers by Martin Valencia
EPISTEMUS, 2022
Las firmas de REE en muestras de rocas plutónicas en cinco sistemas de pórfido de cobre en Sonora... more Las firmas de REE en muestras de rocas plutónicas en cinco sistemas de pórfido de cobre en Sonora, sugieren que existe un proceso petrogenético a partir del enfriamiento de un plutón principal que genera columnas de magma de textura porfídica emplazada en niveles más someros de la corteza. Esto es revelado por una aparente inversión en la polaridad de la anomalía de europio en los patrones normalizados de REE. En general, los patrones muestran una pendiente enriquecida en LREE, con una anomalía negativa de europio bien desarrollada en el caso del plutón principal. Las firmas de los intrusivos asociados con la mineralización son muy similares, a excepción de que la anomalía de europio se hace menos negativa e incluso positiva. De acuerdo con los modelos existentes, esto puede explicarse considerando que hay un fraccionamiento importante de hornblenda durante la generación del stock porfídico, tal vez en condiciones magmáticas más reductoras.
Revista mexicana de …, 2008
... Ernesto RamosVelázquez 1,2, *, Thierry Calmus 1 , Victor Valencia 3 , Alexander Iriondo 4,5 ... more ... Ernesto RamosVelázquez 1,2, *, Thierry Calmus 1 , Victor Valencia 3 , Alexander Iriondo 4,5 , Martín ValenciaMoreno 1 ... mainly on their geochemical characteristics (RoldánQuintana, 1991; ValenciaMoreno et al, 1999, 2001,2003; VargasNavarro, 2002), geochronology ...
Micropaleontology
Conodont associations found in a carbonate succession cropping out in the Sierra AguaVerde (centr... more Conodont associations found in a carbonate succession cropping out in the Sierra AguaVerde (central Sonora, northwestern Mexico) indicate that the studied section spans the mid-Carboniferous Boundary. Declinognathodus noduliferus s.l., the index conodont for the base of the Pennsylvanian, is here reported for the first time in the studied area. The conodont fauna found in the lower part of the section is dominated by Taphrognathus varians, Gnathodus texanus, and Bispathodus n. sp. A., and also contains shallow-water conodonts such as Cloghergnathus sp., Hindeodus cristula, Cavusgnathus unicornis, Rhachistognathus prolixus, and Rhachistognathus muricatus. Pennsylvanian conodont fauna contains both cavusgnathids and gnathodonthids, including Adetognathus spathus, Adetognathus lautus, Adetognathus inflexus, and species of the Declinognathodus noduliferus group. Conodont associations found in Sonora are similar to those reported in other areas of North America, indicating that the shall...
Boletín de la Sociedad Geológica Mexicana, 2006
La abundante actividad magmática ocurrida durante el fi n del Mesozoico y el inicio del Cenozoico... more La abundante actividad magmática ocurrida durante el fi n del Mesozoico y el inicio del Cenozoico a lo largo de la Cordillera oeste de Norte América, produjo el emplazamiento de numerosos centros de mineralización de tipo pórfi do de cobre. Esta actividad se extendió también por todo el occidente de México, particularmente por la región noroeste del país. Esta región junto a las regiones aledañas de Arizona y New Mexico, en el suroeste de los Estados Unidos, constituye uno de los centros con mineralización de cobre más importantes en el mundo, que puede competir en tamaño con los famosos depósitos de la Cordillera oeste de Sur América. La mayor parte de los depósitos de cobre en México se localizan en la porción oriental del cinturón magmático Laramide (90-40 Ma) y predominantemente tienen edades entre 75 y 50 Ma. Los depósitos más grandes y mejor preservados se localizan en el noreste de Sonora, en la parte norte del cinturón, donde Cananea (~30 Mt Cu) y La Caridad (~8 Mt Cu) contienen acumulaciones de metal de gran relevancia a escala mundial. La mineralización de cobre está comúnmente acompañada por concentraciones localmente importantes de molibdeno, tungsteno y oro. La distribución de estos metales está aparentemente asociada a cambios regionales en el tipo de basamento en el cual se emplazó la mineralización. En general se distinguen tres dominios principales: el dominio norte caracterizado por un basamento cristalino proterozoico asociado a los terrenos Norte América y Caborca; un dominio central compuesto por rocas paleozoicas de cuenca marina profunda subyacidas por las rocas cristalinas del terreno Caborca, también defi nido como el terreno Cortés; y un dominio sur representado por secuencias mesozoicas de arco de islas del Terreno Guerrero. Los datos isotópicos de Sr y Nd disponibles muestran que los plutones laramídicos en los dominios norte y central tienen fi rmas más evolucionadas en comparación con las del dominio sur, lo cual sugiere que el tipo de basamento intrusionado tuvo una infl uencia importante en la composición fi nal de los magmas laramídicos, y pudo haber actuado también como un importante control en la distribución espacial de los metales asociados a los sistemas de tipo pórfi do cuprífero del noroeste de México. En general, aunque los metales no están limitados geográfi camente, se puede apreciar una predominancia de depósitos de Cu-MoW en la parte norte y central del cinturón subyacida por rocas antiguas de afi nidad norteamericana, la cual hospeda los depósitos más importantes. Además, existen varias chimeneas brechoides con altas leyes de molibdeno en esta misma porción del cinturón, justo al sur de la región de Cananea y La Caridad, lo cual sugiere un levantamiento tectónico y erosión relativamente mayor. Más hacia el sur, el cinturón está subyacido por rocas más jóvenes de afi nidad oceánica, caracterizadas por el Terreno Guerrero. La mineralización es típicamente de Cu-Au y se encuentra bien distribuida en esta parte del cinturón; sin embargo, las dimensiones de los centros mineralizados conocidos hasta ahora son relativamente pequeñas, siendo los depósitos de El Arco en Baja California (~3.6 Mt Cu) y Santo M E X IC ANA A .C .
The data provided in this database were used to establish the temporality, composition and petrog... more The data provided in this database were used to establish the temporality, composition and petrogenetic aspects of the so-called Cretaceous-Eocene Mexican Magmatic Arc (CEMMA). This magmatic arc is continuous throughout western Mexico and its understanding is critical to elucidating the tectonics of southwestern North America. The data were carefully compiled from the literature, including published articles, thesis, internal reports from mining companies, and to a large extent come from unpublished information generated by the working group (CONACYT Research Grant 49528-F). Unreliable data in relation to the methodology used and those where the information was inconsistent were not included. The Cretaceous-Eocene Mexican Magmatic Arc: Conceptual framework from geochemical and geochronological data of plutonic rocks
Boletín de la Sociedad Geológica Mexicana, 2011
El presente estudio reporta información petrográfica y geoquímica del Complejo Plutónico El Peñue... more 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 SiO 2 = 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. Palabras clave: Noreste de México, granitoides de alto Ba-Sr, magmatismo post-orogénico.
Boletín de la Sociedad Geológica Mexicana, 2005
The Sierra Madre Occidental (SMO) is the result of Cretaceous-Cenozoic magmatic and tectonic epis... more The Sierra Madre Occidental (SMO) is the result of Cretaceous-Cenozoic magmatic and tectonic episodes related to the subduction of the Farallon plate beneath North America and to the opening of the Gulf of California. The stratigraphy of the SMO consists of fi ve main igneous complexes: (1) Late Cretaceous to Paleocene plutonic and volcanic rocks and (2) Eocene andesites and lesser rhyolites, traditionally grouped into the so-called "Lower Volcanic Complex" (LVC); (3) silicic ignimbrites mainly emplaced during two pulses of Oligocene (~32-28 Ma) and early Miocene (~24-20 Ma) ages and grouped into the "Upper Volcanic Supergroup"; 4) transitional basaltic-andesitic lavas that erupted after each ignimbritic pulse and correlated with the Southern Cordillera Basaltic-Andesite (SCORBA) of the southwestern USA; and 5) postsubduction volcanism consisting of alkaline basalts and ignimbrites emplaced in the late Miocene, Pliocene and Pleistocene, directly related to the separation of Baja California from the Mexican mainland. The products of all these magmatic episodes, partially overlapped, cover a poorly exposed, heterogeneous basement with Precambrian to Paleozoic ages in the northern part (Sonora and Chihuahua) and Mesozoic ages beneath the rest of the SMO. The oldest rocks of the LVC (~101 to ~89 Ma) in Sinaloa, and Maastrichtian volcanics of the LVC in central Chihuahua are affected by moderate contractile deformation ascribed to the Laramide orogeny. In the fi nal stages of this deformation cycle, during the Paleocene and Early Eocene, ~E-W to ENE-WSW-trending tension fractures formed within the LVC, along which world-class porphyry copper deposits of the SMO were emplaced. Extensional tectonics began as early as the Oligocene in the whole eastern half of the SMO, forming grabens bounded by high-angle normal faults, traditionally referred to as the southern (or Mexican) Basin and Range province. In the early to middle Miocene, extension migrated westward. In northern Sonora the deformation was suffi ciently intense to exhume lower crustal rocks, whereas in the rest of SMO crustal extension did not exceed 20%. In the late Miocene time, extension became focussed in the westernmost part of the SMO, adjacent to the Gulf of California, where NNW normal fault systems produced both ENE and WSW tilt domains separated by transverse accomodation zones. It is worth noting that most of the extension occurred when subduction of the Farallon was still active off Baja California. Geochemical data show that the SMO rocks form a typical calc-alkaline rhyolite suite with intermediate to high K and relatively low Fe content. late Eocene to Miocene volcanism is clearly bimodal, but silicic compositions are dominant. Initial 87 Sr/ 86 Sr ratios mostly range between 0.7041 and 0.7070, and initial εNd values are generally intermediate between crust and mantle values (+2.3 and-3.2). Based on isotopic data of volcanic rocks and crustal xenoliths from a few sites in the SMO, contrasting models for the genesis of the silicic volcanism have been proposed. A considerable body of work led by Ken Cameron and others considered the mid-Tertiary SMO silicic magmas to have formed by fractional crystallization of mantle-derived mafi c magmas with little (<15%) or no participation of the crust. In contrast, other workers have suggested the rhyolites, taken to the extreme case, could be entirely the result of partial melting of
La actividad orogénica asociada a la subducción sostenida de la placa oceánica Farallón, debajo d... more La actividad orogénica asociada a la subducción sostenida de la placa oceánica Farallón, debajo del borde occidental de América del Norte, dejó marcadas evidencias de su paso por el noroeste de México, especialmente durante el Cretácico y el Paleógeno. Entre éstas, destaca el emplazamiento de la porción sur del Batolito de las Sierras Peninsulares a través de Baja California y la porción occidental de Sinaloa, y del cinturón volcánico-plutónico laramídico en Sonora y Sinaloa. Comúnmente, se acepta la idea de que la orogenia Laramide se dio en respuesta a ajustes en la geometría de la subducción, como resultado de cambios importantes en la relación de convergencia de las placas. Dichos ajustes forzaron al eje del magmatismo asociado a moverse tierra adentro, en respuesta a la reducción progresiva del ángulo de subducción. A escala regional, la compresión de la orogenia Laramide deformó la corteza en dos estilos distintivos: uno que está caracterizado por deformación de piel delgada d...
Manganese oxide mineralization on the eastern coast of Baja California Sur is intimately related ... more Manganese oxide mineralization on the eastern coast of Baja California Sur is intimately related to the Neogene tectonic evolution of the Gulf of California. Manganese is closely associated with the Cu-Co-Zn mineralization of the Boleo district and nearby deposits of Santa Rosalía region and Concepción peninsula. Trace element and rare earth element geochemistry of the manganese oxides provides clear evidence of a hydrothermal origin and excludes the hydrogenous nature for these deposits. Lead isotope data suggest that metal sources for the manganese mineralization along the eastern coast Baja California Sur are mostly the Miocene Andesite of Sierra Santa Lucía volcanics and the Peninsular Ranges batholith rocks. The strontium isotope data indicate that the mineralizing fluids involved in the manganese mineralization from Boleo district resulted from the interaction of two end-members: (1) the Sierra Santa Lucía volcanic rocks and (2) the gypsum member of the Boleo Formation. The geological observations and the available isotope and geochronological data suggest a southward migration of the hydrothermal processes in response to the evolving tectonic context of the opening of the Gulf of California.
Geology of Me´xico: Celebrating the Centenary of the Geological Society of Me´xico, 2007
The Sierra Madre Occidental is the result of Cretaceous-Cenozoic magmatic and tectonic episodes r... more The Sierra Madre Occidental is the result of Cretaceous-Cenozoic magmatic and tectonic episodes related to the subduction of the Farallon plate beneath North America and to the opening of the Gulf of California. The stratigraphy of the Sierra Madre Occidental consists of fi ve main igneous complexes: (1) Late Cretaceous to Paleocene plutonic and volcanic rocks; (2) Eocene andesites and lesser rhyolites, traditionally grouped into the so-called Lower Volcanic Complex; (3) silicic ignimbrites mainly emplaced during two pulses in the Oligocene (ca. 32-28 Ma) and Early Miocene (ca. 24-20 Ma), and grouped into the "Upper Volcanic Supergroup"; (4) transitional basaltic-andesitic lavas that erupted toward the end of, and after, each ignimbrite pulse, which have been correlated with the Southern Cordillera Basaltic Andesite Province of the southwestern United States; and (5) postsubduction volcanism consisting of alkaline basalts and ignimbrites emplaced in the Late Miocene, Pliocene, and Pleistocene, directly related to the separation of Baja California from the Mexican mainland. The products of all these magmatic episodes, partially overlapping in space and time, cover a poorly exposed, heterogeneous basement with Precambrian to Paleozoic ages in the northern part (Sonora and Chihuahua) and Mesozoic ages beneath the rest of the Sierra Madre Occidental. The oldest intrusive rocks of the Lower Volcanic Complex (ca. 101 to ca. 89 Ma) in Sinaloa, and Maastrichtian volcanics of the Lower Volcanic Complex in central Chihuahua, were affected by moderate contractile deformation during the Laramide orogeny. In the fi nal stages of this deformation cycle, during the Paleocene and Early Eocene, ~E-W to ENE-WSW-trending extensional structures formed within the
Geology of Me´xico: Celebrating the Centenary of the Geological Society of Me´xico, 2007
... Navarrete 277, Hermosillo, Sonora 83170, México Joaquin Ruiz Department of Geosciences, Unive... more ... Navarrete 277, Hermosillo, Sonora 83170, México Joaquin Ruiz Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Efrén Pérez-Segura Departamento de Geología, Universidad de Sonora, Hermosillo, Sonora 83000, México ABSTRACT The ...
During most of the Mesozoic and Cenozoic, the locus of subduction related arc magmatism in northw... more During most of the Mesozoic and Cenozoic, the locus of subduction related arc magmatism in northwestern Mexico was relatively mobile, probably due to changes in the mechanical conditions of the Farallon-North America plate convergence. The older Mesozoic events recognized in this region occurred in the Late Triassic and Jurassic, but the associated rocks are poorly preserved. However, a belt of Late Cretaceous through Paleogene magmatic rocks is well exposed along Baja California, Sonora and Sinaloa. Since the late 70's, it was noted that during the Early Cretaceous the igneous activity along this belt remained relatively static in the westernmost part, but migrated eastward in the Late Cretaceous, penetrating more than 1000 km into the continent. The arc magmatism reached western Sonora at about 90 Ma, and then it started to move faster inland, presumably due to flattening of the subducted oceanic slab. Recent U-Pb zircon data revealed unexpected old ages (89-95 Ma) near the e...
Journal of South American Earth Sciences, 2003
Fe-Au skarn deposits related to intrusive centers, mostly of granodioritic composition, are wides... more Fe-Au skarn deposits related to intrusive centers, mostly of granodioritic composition, are widespread in southern Mexico's Guerrero state. These intrusive rocks are largely associated with the NW-SE-oriented Laramide magmatic belt that extends across most of western Mexico. The geochemical composition and ages of representative rocks from the Mezcala mining district in central Guerrero are studied to evaluate the petrogenetic aspects of the ore-related magmas. Some major and trace elements display nearly linear silica variation trends, which suggest a possible comagmatic origin. However, other elements have scattered distributions, possibly due to irregular mantle-to-crust magma mixing ratios, heterogeneities in the composition of the assimilated crustal material, or modifications during the emplacement or postemplacement processes. Major element chemistry indicates calc-alkalic metaluminous compositions, whereas trace element data suggest a volcanic arc tectonic setting, confirming that these rocks evolved from magmas generated above a subduction zone. Compared with the Laramide granites from the northern part of the belt in northwestern Mexico, which intruded a crust underlain by Proterozoic North American rocks, the studied samples are similar but relatively low in Nb and high in Sr, the middle rare earth elements (REE), P, and Zr. They also display minor Ti enrichments and a moderate depletion in the heavy REE. These characteristics may indicate a source of basaltic composition. New 40 Ar/ 39 Ar dating of granodiorites and dacite porphyries shows a north-to-south age progression from 66.2^0.8 Ma in the northern part of the belt to 62.2^0.7 Ma in the south. Moreover, the argon dates identify a younger postorogenic igneous event 35-30 Ma ago. This event is poorly documented and may have occurred after the extinction of the Laramide arc and prior to the mid-Tertiary Sierra Madre Occidental ignimbrite flare-up. On the basis of limited geochemical data, these rocks appear to be depleted in P 2 O 5 and Sr and enriched in U relative to the studied Laramide granites. A Fe skarn deposit located in Buena Vista de Cuéllar, in the north central part of Guerrero, suggests that this magmatic pulse took place after the ore development of the Mezcala district.
Geological Society of America Bulletin, 2001
Along the Laramide belt of northwestern Mexico, granitic rocks of similar bulk composition show i... more Along the Laramide belt of northwestern Mexico, granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the North American Precambrian basement. In the northern part, the Laramide plutons (the ''northern granites'') intruded Proterozoic crystalline rocks and a thick Late Proterozoic through Paleozoic miogeoclinal cover of North American affinity. In the central part, the granitic bodies (the ''central granites'') were emplaced into a sequence of Paleozoic eugeoclinal rocks overlain by Late Triassic clastic units. The southern part of the belt (the ''southern granites'') intruded a less-known crust characterized by middle to late Mesozoic island-arc-related volcanic and sedimentary rocks of the Guerrero terrane. Data from a suite of metaluminous to slightly peraluminous calc-alkalic granitic rocks along the belt display north-to-south geochemical and isotopic variations, which could correlate with the type of intruded basement. The northern and central granites are characterized by strongly fractionated, light rare earth element (REE)-enriched patterns, which display generally pronounced negative europium anomalies, whereas the southern granites have lower total REE enrichments and much flatter chondrite-normalized slopes displaying almost no europium anomalies. Isotopic results also suggest regional variations, as shown by the following initial Sr and ⑀ Nd ranges: 0.7070 to 0.7089 and؊4.2 to؊5.4, respectively, for the northern granites; 0.7060 to 0.7079 and؊3.4 to؊5.1 for the central granites; and 0.7026 to 0.7062 and؊0.9 to ؉4.2 for the southern granites. On the basis of their isotopic similarities, the Proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern Arizona and northern Mexico is interpreted as
Geological Society of America Bulletin, 2000
The Arizpe and Bacanuchi Quadrangles provide a geologic history representative of the north-centr... more The Arizpe and Bacanuchi Quadrangles provide a geologic history representative of the north-central part of Sonora, where lithologies are dominated by late Mesozoic and Cenozoic igneous rocks. In this study, new geologic mapping, 40 Ar/ 39 Ar dating, and geochemical analyses have been combined to provide a stratigraphic framework for this area. Ten lithostratigraphic units and several igneous and tectonic events can be recognized. The oldest outcropping rocks are Lower Cretaceous strata of the Bisbee Group, which along with the Picacho conglomerate record a middle Cretaceous compressive tectonic event and associated sedimentation. Laramide igneous activity is widespread and represented by (1) highly altered andesitic flows and volcaniclastic rocks (Arroyo Alcaparros andesitic rocks) of late Campanian to Maastrichtian age, (2) less altered andesitic and dacitic flows (Cerro Las Jarillas volcanic rocks) of late Paleocene age, and the intrusive bodies of (3) Sierra El Manzanal granodiorite and (4) Rancho Vaquería quartz monzonite. The Sierra El Manzanal granodiorite was emplaced at ca. 68 Ma on the basis of a 40 Ar/ 39 Ar biotite age (67.97 ± 0.19 Ma) and cooled relatively rapidly according to less precise 40 Ar/ 39 Ar hornblende and K-feldspar ages from the same sample (64.8 ± 1.0 Ma and 62.8 ± 0.3 Ma, respectively). The Cerro Las Jarillas volcanic rocks are slightly younger (40 Ar/ 39 Ar biotite age of 58.67 ± 0.17 Ma). The Rancho Vaquería quartz monzonite was emplaced at ca. 57 Ma (40 Ar/ 39 Ar biotite age of 56.73 ± 0.14 Ma and a less precise 40 Ar/ 39 Ar hornblende age of 55.0 ± 0.7 Ma); a protracted cooling history of this pluton is indicated by the age spectrum of K-feldspar from the same sample. A probable magmatic lull and denudation seem to have occurred between middle and late Eocene time and probably until the early Oligocene. Subsequently, rhyolitic to mafic volcanism began close to late Oligocene time and lasted until the early Miocene. Felsic volcanism is represented by the Cerro Cebadéhuachi volcanic rocks, from which 40 Ar/ 39 Ar hornblende ages of 27.25 ± 0.09 and 27.32 ± 0.06 Ma and a biotite age of 26.97 ± 0.06 Ma were obtained at three different localities. The Mesa Pedregosa volcanic rocks represent the transition to younger, mafic volcanic activity that occurred during the late Oligocene, as indicated by a sanidine 40 Ar/ 39 Ar age of 25.48 ± 0.05 Ma. This late Oligocene and early Miocene magmatism was paired by two episodes of extensional deformation. The first phase is characterized by northwest-striking normal faults and folds, which expose the deepest structural levels of the area, and by the related basin fill, the Bacanuchi conglomerate. The second phase is represented by north-striking normal faults and by the syntectonic basin fill, the Arizpe conglomerate. Basaltic andesite volcanic flows at the base of the Arizpe conglomerate yielded 40 Ar/ 39 Ar (whole-rock) ages of 23.52 ± 0.17 and 21 ± 0.20 Ma. The extensional deformation (27 to 23 Ma) in the study area is coeval with the development of metamorphic core complexes in neighboring areas of Sonora and with the onset of extension in southern Sonora. The mafic volcanic rocks and clastic sedimentary units associated with this extension resemble the basin fills that in other parts of Sonora are assigned to the Báucarit Formation. Geochemical information from samples representing each of the igneous events displayed high-K calc-alkalic and mostly metaluminous compositions. The older units including the Arroyo Alcaparros andesitic rocks, the Cerro Las Jarillas volcanic rocks, the Sierra El Manzanal granodiorite, and the Rancho Vaquería quartz monzonite are characterized by steep chondrite-normalized REE 600
Canadian Journal of Earth Sciences, 2003
New major- and trace-element and radiogenic Sr and Nd data from granitic rocks help to characteri... more New major- and trace-element and radiogenic Sr and Nd data from granitic rocks help to characterize the geochemical composition of the Coastal Sonora batholith, which represents the westernmost portion of the Laramide Magmatic arc (~8040 Ma) in Mexico. Compared with more inland-located regions of the arc in central and eastern Sonora (Inner Granites), the plutons within the coastal batholith have higher MgO, FeO, and CaO and lower K2O contents, and tend to be more depleted in Nb, U, and to a lesser extent Rb, but relatively enriched in Sr. These rocks display flatter slopes of rare-earth elements, with La abundances around 80 to 200 times chondrite values and smaller but well-developed negative Eu anomalies. Initial 87Sr/86Sr ratios and εNd values from a few studied samples of the Coastal Sonora batholith range from 0.70586 to 0.70679 and from 2.3 to 4.7, respectively. These isotopic signatures allow recognition of a more mantle-related magma source for this batholith as compared...
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Papers by Martin Valencia