Ignimbrites of the Sierra Madre Occidental and their relation to the tectonic history of western Mexico

Abstract

Igneous rocks of the Sierra Madre Occidental have been studied along two traverses across the range. One is at lat 24°N between Mazatlan and Durango City, where contiguous mapped areas extend across the Sierra; the other is near lat 28°N, where several separate areas west and north of Chihuahua City have been mapped. In these regions the Sierra contains two vast and largely coextensive igneous sequences, both calc-alkalic and both including ignimbrites. The older sequence of rocks, which ranges in age from 45 m.y. to at least 100 m.y., is characterized by abundant batholithic as well as volcanic rocks and is dominantly intermediate in composition. The younger sequence is dominated by rhyodacitic to rhyolitic ignimbrites erupted from large caldera complexes, generally accompanied by rhyolite flows and domes and small outpourings of mafic lavas. Intermediate rocks are rare, and volcanism was largely confined to the interval 34 to 27 m.y. ago, although some activity persisted until 23 m.y. ago.

Magmatismo y tectónica en la Sierra Madre Occidental y su relación con la evolución de la margen occidental de Norteamérica

“…En general se acepta que las rocas del CVI fueron producidas durante la actividad magmática cordillerana asociada a la orogenia Laramide. Sin embargo, en el trabajo de McDowell y Clabaugh (1979), el CVI incluye además a las rocas del batolito de las Sierras Peninsulares en Baja California y su extensión a Sinaloa, cuyas edades son relativamente más antiguas (~120-85 Ma).…”

“…A diferencia de lo que aparece en varios mapas geológicos regionales (e. g., Ortega-Gutiérrez et al, 1992;López-Ramos, 1995), no hay ignimbritas asignadas al Eoceno-Mioceno en el bloque Jalisco. Diferentes estudios geocronológicos han demostrado que las ignimbritas, expuestas ampliamente en la parte norte del bloque, tienen edades 40 Ar/ 39 Ar de 81 a 60 Ma (Wallace y Carmichael, 1989;Lange y Carmichael, 1991;Righter et al, 1995;Rosas-Elguera et al, 1997), por lo que se correlacionan más bien con el CVI estudiado en Sonora (McDowell et al, 2001 Clabaugh, 1979), el magmatismo se vuelve más heterogéneo y disperso en la SMO. El volcanismo es generalmente bimodal y discontinuo y tiende a migrar hacia el futuro Golfo de California.…”

Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

“…During the Late Cretaceous, arc magmatism migrated eastward from Baja California and coastal Sonora to eastern Sonora and Chihuahua, most likely as a result of flattening of the subducting slab during Laramide time. However, unlike in the United States, no magmatic gap developed in the Mexico and volcanism continued throughout the early Cenozoic, ultimately building the Sierra Madre Occidental ignimbrite plateau during the Eocene -early Oligocene [McDowell and Clabaugh, 1979;Cochemé and Demant, 1991]. During the Oligo-Miocene, the arc is thought to have migrated back westward to Baja California and coastal Sonora [Gastil et al, 1979;Sawlan, 1991], although the details and cause of this apparent migration are poorly known.…”

Reappraisal of the Geology and Geochemistry of Volcán Zamorano, Central Mexico: Implications for Discriminating the Sierra Madre Occidental and Mexican Volcanic Belt Provinces

“…The SMO is formally subdivided into lower and upper volcanic supergroups where the lower one is a volcano-plutonic complex with ages ranging from more than 100 Ma to the Eocene, and the upper supergroup comprising thick sequences (ranging from 200 to 2000 m, 1000 m on average) of mainly silicic ignimbrite with ages from 45 to 27 Ma (McDowell and Clabaugh, 1979) or up to about 23 Ma (McDowell and Keizer, 1977).…”