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Journal of the Geological Society

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Geochronology of very low-grade Mesozoic Andean metabasites; an approach through the K–Ar, ⁴⁰Ar/³⁹Ar and U–Pb LA-MC-ICP-MS methods

¹ Departamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile (e-mail: voliveros{at}udec.cl)
² Departamento Ciencias de la Tierra, Universidad de Concepción, Casilla 160-C, Concepción, Chile
³ Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta, Canada T6G 2E3

Multiple geochronological methods using different metamorphic minerals were combined to date the regional, very low-grade metamorphism affecting Upper Jurassic–Lower Cretaceous volcano-sedimentary successions in the Andes of central Chile. Early Late Cretaceous metamorphic ages (between 82 and 108 Ma) were obtained by the K–Ar and U–Pb methods for celadonite and titanite. A much younger thermal event is responsible for actinolite formation at 8 Ma, most probably related to the intrusion of proximal Miocene granitoids. Previous models for the metamorphism should be reinterpreted taking into account the absence of a greenschist-facies event. The combination of different metamorphic minerals and chronometers is regarded as a powerful analytical tool to date the very low-grade metamorphism associated with the Mesozoic extensional regime developed within the Andes.