The late Eocene–early Miocene El Maitén Belt evolution: Magmatic response to the changing subduction zone geodynamics

FERNÁNDEZ PAZ, LUCÍA; IANNELLI, SOFÍA B.; ECHAURREN, ANDRÉS; RAMOS, MIGUEL; BECHIS, FLORENCIA; LITVAK, VANESA D.; ENCINAS, ALFONSO; KASEMANN, SIMONE; LUCASSEN, FRIEDRICH; FOLGUERA, ANDRÉS

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 103

0895-9811

During Mid-Cenozoic times, voluminous and genetically heterogeneous volcanism took place across NorthPatagonia in response to a period of plate tectonic reorganization. One of these volcanic associations is representedby the El Maitén Belt, located to the east of the main Andes for over ~300 km. This volcanic belt reflectsthe evolution of a continental arc in an extensional setting with remarkable compositional variations between thelate Eocene and the early Miocene. We present new field and isotopic data that, together with lithological,geochronological and geochemical data compilations, suggest significant changes in the nature and location ofmagmatic sources. This evolution may be summarized in three stages: i) incipient arc magmatism, with atholeiitic basaltic-basaltic andesitic composition, which evolved to ii) a mature arc, characterized by calcalkalineandesitic-dacitic associations, and a final stage characterized by iii) a late Oligocene-early Miocenejuvenile, tholeiitic basaltic volcanism, interpreted as the result of a westward arc migration and extension in theback-arc. Therefore, considering the mid-Cenozoic tectonic configuration given by the eastward subduction ofthe Farallon and Nazca plates, we evaluate slab dynamics within a petrological framework that can reproduce thegeochemical-geochronological characteristics of this belt. In this sense, rollback of the Nazca plate is the mostsuitable scenario to explain the El Maitén Belt behavior during this protracted extensional regime of Andeanevolution.