Magma mixing, zircon U–Pb ages and Hf isotopes: Insights for the Miocene magmatic plumbing system in the Soroche Porphyry, Puna Argentina, Central Andes

Abstract

This research highlights the importance to study the magmatic plumbing systems in Southern Puna, NW Argentina, emphasizing the significance of understanding the genesis of sub-volcanic bodies and their implications for the crustal assimilation and recycling processes. In the southeastern edge of Ratones salar, Southern Puna, there is an intrusive body cropping out, named Soroche Porphyry. This intrusion is formed by porphyritic rhyodacitic, basaltic andesites, and porphyritic andesitic rocks, with magma mixing relations between the mentioned lithologies. The main features of the Soroche Porphyry are described to interpret the dynamic aspects of magma mixing, identify and define textural, mineralogical, and geochemical features, directly related to the mentioned process. Taking into account these features, the results showed that a hybrid magma (homogeneous porphyritic andesite) was produced by mixing processes between basaltic andesitic and rhyodacitic magmas, whereas, the heterogeneous porphyritic andesite represent mingling areas, whereby the end members are easily identified. Furthermore, we dated the main rocks of the porphyry using zircon U–Pb methodology by LA-MC-ICP-MS, complemented by Hf isotopes analyses. The geochronological data evidenced magmatic activity around ~15 Ma, allowing the correlation of the Soroche Porphyry with the Inca Viejo Formation. The basaltic andesites yielded a zircon U–Pb age of 15.63 ± 0.08 Ma, the heterogeneous porphyritic andesites displayed an age of 15.52 ± 0.16 Ma, and the rhyodacites showed an age of 15.13 ± 0.12 Ma. The isotopic ƐHf (15 Ma) values from the rhyodacite between −4.9 and −11.3, suggested a great amount of crustal components, evidencing that the rhyodacitic magmas derived from assimilating and recycling crustal rocks probably from the lower Paleozoic rocks.