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Middle Jurassic Volcanism in the Northern and Central Andes

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Middle Jurassic Volcanism in the Northern and Central Andes Middle Jurassic volcanism in the Northern and Central Andes Natalie Romeuf Luis Aguirre Gilbert Féraud Gilles Ruffet SEPARATA REVISTA GEOLOGICA DE CHILE, Vol. 22,'No. 2 EDITADA POR EL SERVICIO NACIONAL DE GEOLOGIA Y MINERIA Avda. Santa Marla 0104, Casilla 10465 SANTIAGO - CHILE Diciembre 1995 Middle Jurassic volcanism in the Northern and Central Andes Natalie Romeuf Laboratoire de PBtrologie Magmatique, URA CNRS 1277, CEREGE, BP 80. Universite d' Aix-Marseille 111, 13545 Aix-en-Provence Cedex 04, France Luis Aguirre Laboratoire de PBtrologie Magmatique, URA CNRS 1277, CEREGE, BP 80, Universle d' Abc Marseille 111, 13545 Aix-en-Provence Cedex 04, France Present address: Departamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago Pierre Soler Orstom, UR1 H, DBparlement TOA, 213 rue Lafayette, 75480 Pans CBdex 10, France et Laboratoire de MinBralogie. URA CNRS 736. MNHM, 61 rue Buffon, 75005 Pans, France Gilbert Féraud Institut de GBodynamique, URA CNRS 1279,UniversitB de Nice-Sofia Antipolis, Parc Valrose, 06034 Nice CMex, France Etienne Jaillard MlsMn Orstom, Apartado 17-11-06596, Qulo. Ecuador and Orstom. URlH, DBpartement TOA, 213 rue Lafayette. 75480 Paris CBdex 10. France Gilles Ruffet institut de G6odynamique. URA CNRS 1279,UniversitB de Nice-SofiaAntipolis, Parc Valrose, 06034 Nice CBdex, France ABSTRACT -- I; FI; . Stratigraphical, petrographical, geochronological and geochemical data available suggest that the various segments of k.1 the westem margin of South America experienced a different geodynamic evolution throughout the Jurassic. In the early I Jurassic, the Northem Andeswerecharacterized by anextensional tectonic regime whereasin the Central Andessubduction 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/Colán arc) along the Noithem Andes. The volcanic products are medium to high K calc-alkaline rocks composed of basaltic andesitic to rhyolitic lavas and acid pyroclastic rocks (ignimbrites, unweldedtuff s, volcanogenic sandstones and breccias). A new radiometric 'OArJBAr data gave an age of ca. 172 Ma forthe MisahuallíFormationof Ecuador. The Central Andes, in the southem 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 (Río Grande and Chala 5 formations), comprising porphyritic basaltic andesites and emplaced as flows, intrusive rocks (dykes, 'sills' and 'stocks') and a acid pyroclastic rocks. Newgeochronological'OArJ@Ardata confirm an age of ca. 165 Ma for the andesitic basalt flows of the Chala Formation. Key words :Andes, Peru, Ecuador, Jurassic. Volcanism,Petrology, Geochemistry, Geochronology, Geodynamics,Active continental margins. 1 RESUMEN r- tE Volcanismo del Jurásico Medio en los Andes del norte y centrales. Información estratigráfica, petrogrilfica, geocronológgica y geoquímica disponible sugiere que los diferentes segmentos del margen Occidental de Sudamerica tuvieron una evolución geodinámica diferente durante el Jurásico. En el Jurásico Inferior, los Andes del Norte p. ßevtsfa Geol6gEa de Chile, Vol. 22, No. 2, 245-259,O F,gs..'3~bl&s,,Pp&"~ íg$? ?" L , * a5,j Middle Jurassic volcanism in the Northern and Central Andes Natalie Romeuf Laboratoire de PBtrologie Magmatique, URA CNRS 1277, CEREGE, BP 80, Universi16 d' Aix-Marseille 111, 13545 Aix-en-Provence CBdex 04,France Luis Aguirre Laboratoire de PBtrologie Magmatique, UFIA CNRS 1277. CEREGE, BP 80, Universfit5 d' Abc Marseille 111. 13545 Aix-en-Provence CBdex 04,France Present address: Departamento de Geologla. Universidadde Chile, Casilla 13518, Correo 21, Santiago Pierre Soler Orstom, UR1 H. DBpartement TOA, 213 fue Lafayette, 75480 Paris CBdex 10. France el Laboratoire de MinBrabgie, URA CNRS 736, MNHM, 61 rue Bullon. 75005 Pans, France Gilbert Féraud institut de GBodynamique. URA CNRS 1279,UniversBB de Nice-Solia Antipolis, Parc Valrose, 06034 Nice CBdex. France Etienne Jaillard MisMn Orstom. Apartado 17-11-06596, Quilo. Ecuador and Orstom, URlH, DBpartement TOA, 213 rue Lalayette. 75480 Paris Cedex 10. France Gilles Ruffet Institut de GBodynamique, URA CNRS 1279.Universil6 de Nice-Sofia Antipolis, Parc Vairose, 06034 Nice CBdex. France ABSTRACT Stratigraphical,petrographical, geochronological and geochemical data available suggest that the various segments of the westem margin of South America experienced a different geodynamic evolution throughout the Jurassic. In the early Jurassic,the Northem Andeswerecharacterizedby an extensionaltectonic regime whereasin the Central Andessubduction led to the emplacement of a calc-alkaline magmatism. During the middle Jurassic (Bathonian to Oxfordian), an active subduction, perpendicularto the continental margin, generated a magmatic arc (Misahualli/Colán arc) along the Northem 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 radiometric4oAr-38Ardata gave an aga of ca. 172 Ma forthe MisahuaIliFormation of Ecuador. The Central Andes, in the southerncoastal regionof 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 (Río Grande and Chala formations), comprisingporphyritic basaltic andesites and emplaced as flows, intrusive rocks (dykes, 'sills' and 'stocks') and acid pyroclastic rocks. New geochronological'OArJ@Ardata confirm an age of ca. 165 Ma for the andesitic basalt flows of the Chala Formation. Key Words :Andes, Pew, Ecuador, Jurassic. Volcanism, Petrology, Geochemistry, Geochronology, Geodynamics, Active continental malgins. RESUMEN Volcanismo del Jurásico Medio en los Andes del norte y centrales. Información estratigrdfica, petrogrdfica, geocronológica y geoquímica disponible sugiere que los diferentes segmentos del margen occidental de Sudamérica tuvieron una evolución geodinámica diferente durante el Jurásico. En el Jurásico Inferior, los Andes del Norte No. p. ßevlsfs Geoldgica de Chile, Vol. 22, 2, 245-259, 9 Figs., 3 fablas. Daoember 1995. 246 MIDDLEJURASSIC VOLCANISM IN THE NORTHERNANO CENTRAL 1 ANDES Ijf I se caracterizaron por un régimen tectónico extensional mientras que en los Andes Centrales procesos de subducción l generaran un magmatisma calcoalcalino. Durante el Jurásico medio (Batoniano a Oxfordiano) la subducción ortogonal al margen continental generó un arco magmático (Arco Misahuallí-Colán) en los Andes del Norte. Los productos volcánicos de este arco son rocas calcoalcalinas de medio a alto K, que corresponden a andesitas badlticas y riolitas, y rocas j piroclásticas ácidas (ignimbritas, tobas, areniscas volcanogénicas y brechas). Se obtuvo una nueva edad radiométnca '"Ar 1 3gArdeca. 172 Ma para la Formación Misahuallíen Ecuador. Los Andescentrales, en la región costera meridional del Perú, estuvieron caracterizados por una convergencia oblicua entre la placa oceánica Phoenix y el margen continental de Sudamérica. Este proceso de subducción produjo una sene volcánica andesítica calcoalcalina de medio a alto K (formaciones Río Grande y Chala) que incluye andesitas basálticas porfincas emplazadas como lavas, diques, 'sills' y 'stocks', y rocas piroclásticas ácidas. Nuevas edades 4'1Ar-39Arconfirman una edad cercana a 165 Ma para los flujos de andesita basáltica de la Formación Chala. Palabras claves:Andes, Pen]., Ecuador,Jurdsico. Volcanismo,P efrologla, Geoqulmica, Geocronologla,Geodinámica, Márgenes continen- fales activos. INTRODUCTION Accordingto several geodynamic reconstructions, perpendicular to the continental margin was active the Andean margin was the site of a major plate along the Northern Andes, whereas the Central An- reorganizationduring the latest Triassic-earliestJuras- des were dominated by transform faulting with F sic (Aspden etal., 1987; Mourier, 1988; Jaillard etal. restricted subduction. In the latest Jurassic, a major 1990). According to these reconstructions, during the reorganization of the plate motion took place. A new middle Jurassic (Bathonian-Bajocian), a subduction southwest-northeast convergence direction induced I the accretion of continental and arc terranes in the Northern Andes in northern Peru, Ecuador and Co- ~ lombia and the emplacement of subduction-related calc-alkaline volcanism in the Central Andes of Peru (Aspden etal., 1987; Jaillard etal., 1990). The authors present new petrological, mineralogical, geochro- nologicaland geochemicaldataconcerningfour Middle c tl Jurassic volcanic formations located in these two C different segments of the Andean margin (Figs. 1 and tl 2). Two of these formations crop out in the northern S segment and are located in Ecuador (Misahuallí For- 1 z mation, Fig. 1) and Northern Peru (Colán Formation, , F Fig. 1), whereas the othertwo (RíoGrande and Chala fl Formations, Fig. 2) are located in the centralsegment i! and crop out along the southern coast of Peru. S These data place new constraints on the geo- ! f dynamic interpretation of the Jurassic evolution of the E Northern and Central Andes. C E 7 t h / II I I I I h of FIG. 1. Location Jurassic outcrops of the Northern Andes in Y Juasslc balholihs Mbahuallland
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