Zircon in emplacement borders of post-collisional plutons compared to country rocks: A study on morphology, internal texture, U-Th-Pb geochronology and Hf isotopes (Aracuai orogen, SE Brazil)

Zircon is a powerful tool to study the internal evolution of igneous bodies and their interactions with country rocks. At pluton borders, zircon may record the emplacement history from the crystallization onset to deuteric processes, as well as inheritance from country rocks. We present a detailed morphology and internal structure study coupled with isotopic analyses (U-Th-Pb and Lu-Hf) on a great number of zircon grains extracted from samples collected at the borders of three distinct post-collisional intrusions of the Aracuai orogen: granites from the Arace - Pedra Azul and Vitoria plutons, and a tonalite from the Mestre Alvaro pluton. For comparison, we also present mineral and bulk-rock chemistry data from these samples of post-collisional intrusions, as well as zircon U-Pb-Hf data from their country rocks (the Nova Venecia migmatitic paragneisses and Ataleia granites) and a wide dataset compilation. Zircon saturation geothermometry suggests igneous temperatures above 800 degrees C for pluton borders. Zircon geochronology resulted in crystallization ages for borders of the plutons at 523 +/- 2 Ma (Arace - Pedra Azul), 505 +/- 1 Ma (Vitoria), and 527 +/- 2 Ma (Mestre Alvaro). Lu-Hf data (Arace - Pedra Azul pluton: epsilon Hf-(t) -18.6 to -23.8, T-DM ages from 2.25 to 2.47 Ga; Vitoria pluton: epsilon Hf-(t) -7.4 to -10.3, Tom ages from 1.58 to 1.71 Ga; Mestre Alvaro pluton: epsilon Hf-(t) -0.7 to -8.8, T-DM ages from 1.27 to 1.66 Ga; Nova Venecia migmatitic paragneiss: epsilon Hf-(t) +4.1 to -39.2, Tom ages from 1.20 to 3.47 Ga; and Ataldia granite: epsilon Hf-(t) -3.2 to -8.1, T-DM ages from 1.42 to 1.64 Ga) indicate involvement of country rocks in the petrogenesis of post-collisional intrusions. Together, new and compiled data suggest: i) magma hybridization at high temperature, involving country rocks; ii) rapid growth of zircon crystals probably at rapid cooling rates; and iii) in situ dissolution-recrystallization and overgrowth processes in zircon crystals in response to interactions with residual (late-stage) melts and/or deuteric fluids. (C) 2019 Elsevier B.V. All rights reserved.