New insights into petrogenesis of Miocene magmatism associated with porphyry copper deposits of the Andean Pampean flat slab, Argentina

CARRASQUERO SILVIA I.; RUBINSTEIN NORA A.; GOMEZ ANABEL L. R.; CHIARADIA MASSIMO; FONTIGNIE DÉNIS; VALENCIA VICTOR A.

Geoscience Frontiers

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Lugar: Beijing; Año: 2018 p. 1565 - 1576

1674-9871

The Paramillos de Uspallata mining district located in the backarc region of the Pampean flat-slabsegment (28e33S) features porphyry-type deposits genetically associated with Middle Miocene volcanics.This mineralizing magmatism comprising hydrothermally altered (sodic-calcic, potassic andphyllic alteration) subvolcanic and pyroclastic rocks of andesite-basaltic andesite and dacite-rhyolitecomposition with a typical arc signature, represents the eastward broadening of the Farellones arc byw17 Ma. Its geochemistry also reveals a residual mineralogy of amphibole garnet with limitedplagioclase fractionation resulting in an adakitic signal; however, according to the isotopic data collectedin our study, the contributions of MASH (melting-assimilation-storage-homogenization) processes in theacquisition of this signal cannot be disregarded.Both the broadening of the Farellones arc and its residual mineralogy e typical of relatively deepmagmatic chambers e are consistent with a slab shallowing and outcoming crustal thickening setting.This tectonic scenario could be interpreted as a result of an early effect of the Juan Fernandez Ridgecollision that was further to the north by w17 Ma. Our findings suggest that magmas were fertile forporphyry type deposits during the early stages of the slab shallowing.