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The Pliocene to Quaternary narrowing of the Southern Andean volcanic arc between 37° and 41°S latitude

Luis E. Lara
Luis E. Lara
Servicio Nacional de Geología y Minería (SERNAGEOMIN, Chile), Ave. Santa María 0104, Providencia, Santiago, Chile, and IRD-LMTG, Laboratoire des Mécanismes de Transfert en Géologie, Université Paul Sabatier-Toulouse III, 14 avenue Edouard Belin, 31400, Toulouse, France
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Andrés Folguera
Andrés Folguera
Laboratorio de Tectónica Andina, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
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January 01, 2006

A complex arc-backarc system developed at the western margin of the Neuquén Basin north of 37°S during the late Cenozoic. Both transpressional deformation on the western orogenic front (Liquiñe-Ofqui fault system) and contractional deformation of the eastern Andean foothills occurred during the middle to late Miocene. South of 38°S, a physiography dominated by uplifted blocks and elongated basins was the site of intense volcanism from the early Pliocene to the Holocene. A wide volcanic arc was established from the western orogenic front to the eastern foothills of the Andes during the Pliocene. This volcanic phase was coeval with both extended transpressional deformation along the frontal arc and transient extensional episodes in the inner retroarc. Arc-front geochemical signatures of the magmas occurred further east of the front showing an increased subduction input in the subarc mantle. A decrease in plate convergence velocity 2–3 m.y. ago, along with a stable arc front caused a progressive westward narrowing of the Quaternary volcanic arc, probably since ca. 1.6 Ma. From the middle to late Pleistocene, volcanism was mainly centered around the Liquiñe-Ofqui fault system with minor Holocene activity in the eastern Andean region. Arc-front geochemical signatures are now restricted to the present volcanic front. Morphologically, this has resulted in paired volcanic belts that reflect different stages of arc narrowing rather than separate arc fronts.

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