DOI: http://dx.doi.org/10.5027/andgeoV22n2-a08

Middle Jurassic volcanism in the Northern and Central Andes

Natalie Romeuf, Luis Aguirre, Pierre Soler, Gilbert Feraud, Etienne Jaillard, Gilles Ruffet

Abstract


ABSTRACT. Stratigraphical, petrographical, geochronological and geochemical data available suggest that the various segments of the western margin of South America experienced a different geodynamic evolution throughout the Jurassic_ In the early Jurassic, the Northern Andes were characterized by an extensional tectonic regime whereas in the Central Andes subduction led to the emplacement of a calc-alkaline magmatism. During the middle Jurassic (Bathonian to Oxfordian), an active subduction, perpendicular to the continental margin, generated a magmatic arc (Misahualli/Colan arc) along the Northern Andes, The volcanic products are medium to high K calc-alkaline rocks composed of basaltic andesitic to rhyolitic lavas and acid pyroclastic rocks (ignimbrites, unwelded tuffs, volcanogenic sandstones and breccias). A new radiometric 40Ar-39Ar data gave an age of ca. 172 Ma for the Misahualli Formation of Ecuador, The Central Andes, in the southern coastal region of Peru, were characterized by an oblique convergence between the Phoenix oceanic plate and the continental margin of South America. This subduction produced a medium to high-K, calc-alkaline andesitic volcanic series (Rio Grande and Chala formations), comprising porphyritic basaltic andesites and emplaced as flows, intrusive rocks (dykes, 'silIs' and 'stocks') and acid pyroclastic rocks. New geochronological 40Ar-39Ar data confirm an age of ca. 165 Ma for the andesitic basalt flows of the Chala Formation. RESUMEN. Volcanismo del Jurasico Medio en los Andes del norte y centrales. Informacion estratigrafica, petrografica, geocronologica y geoquimica disponible sugiere que los diferentes segmentos del margen occidental de Sudamerica tuvieron una evolucion geodinamica diferente durante el Jurasico. En el Jurasico Inferior, los Andes del Norte se caracterizaron por un regimen tectonico extensional mientras que en los Andes Centrales procesos de subduccion generaron un magmatismo calcoalcalino. Durante el Jurasico medio (Batoniano a Oxfordiano) la subduccion ortogonal al margen continental genero un arco magmatico (Arco Misahualli-Colan) en los Andes del Norte. Los productos volcanicos de este arco son rocas calcoalcalinas de medio a alto K, que corresponden a andesitas basalticas y riolitas, y rocas piroclasticas acidas (ignimbritas, tobas, areniscas volcanogenicas y brechas). Se obtuvo una nueva edad radiometrica 40Ar-38Ar de ca. 172 Ma para la Formacion Misahualli en Ecuador. Los Andes Centrales, en la region costera meridional del Peru, estuvieron caracterizados por una convergencia oblicua entre la placa oceanica Phoenix y el margen continental de Sudamerica. Este proceso de subduccion produjo una serie volcanica andesitica calcoalcalina de medio a alto K (formaciones Rio Grande y Chala) que incluye andesitas basalticas porfiricas emplazadas como lavas, diques, 'sills' y 'stocks', y rocas piroclasticas acidas. Nuevas edades 40Ar-39Ar confirman una edad cercana a 165 Ma para los flujos de andesita basaltica de la Formacion Chala.

How to cite this article Romeuf, N., Aguirre, L., Soler, P., Feraud, G., Jaillard, E., and Ruffet, G., 1995, Middle Jurassic volcanism in the Northern and Central Andes: Revista Geológica de Chile v. 22, no. 2, p. 245-259., doi:http://dx.doi.org/10.5027/andgeoV22n2-a08