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

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Abstract

The Paramillos de Uspallata mining district located in the backarc region of the Pampean flat-slab segment (28°–33°S) features porphyry-type deposits genetically associated with Middle Miocene volcanics. This mineralizing magmatism comprising hydrothermally altered (sodic-calcic, potassic and phyllic alteration) subvolcanic and pyroclastic rocks of andesite-basaltic andesite and dacite-rhyolite composition with a typical arc signature, represents the eastward broadening of the Farellones arc by ∼17 Ma. Its geochemistry also reveals a residual mineralogy of amphibole ± garnet with limited plagioclase fractionation resulting in an adakitic signal; however, according to the isotopic data collected in our study, the contributions of MASH (melting-assimilation-storage-homogenization) processes in the acquisition of this signal cannot be disregarded. Both the broadening of the Farellones arc and its residual mineralogy – typical of relatively deep magmatic chambers – 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 Ridge collision that was further to the north by ∼17 Ma. Our findings suggest that magmas were fertile for porphyry type deposits during the early stages of the slab shallowing.

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Carrasquero, S. I., Rubinstein, N. A., Gómez, A. L. R., Chiaradia, M., Fontignie, D., & Valencia, V. A. (2018). New insights into petrogenesis of Miocene magmatism associated with porphyry copper deposits of the Andean Pampean flat slab, Argentina. Geoscience Frontiers, 9(5), 1565–1576. https://doi.org/10.1016/j.gsf.2017.10.009

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