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 (Araçuaí orogen, SE Brazil).
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2020
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Resumo
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 (UeThePb and LueHf) on a great number of
zircon grains extracted from samples collected at the borders of three distinct post-collisional intrusions
of the Araçuaí orogen: granites from the Arace^ e 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 UePb-Hf data from their country rocks (the Nova
Venecia migmatitic paragneisses and Atal eia granites) and a wide dataset compilation. Zircon saturation
geothermometry suggests igneous temperatures above 800 C for pluton borders. Zircon geochronology
resulted in crystallization ages for borders of the plutons at 523 ± 2 Ma (Arace^ e Pedra Azul), 505 ± 1 Ma
(Vitoria), and 527 ± 2 Ma (Mestre Alvaro). Lu eHf data (Arace^ e Pedra Azul pluton: εHf(t) 18.6 to 23.8,
TDM ages from 2.25 to 2.47 Ga; Vitoria pluton: εHf(t) 7.4 to 10.3, TDM ages from 1.58 to 1.71 Ga; Mestre
Alvaro pluton: εHf(t) 0.7 to 8.8, TDM ages from 1.27 to 1.66 Ga; Nova Venecia migmatitic paragneiss:
εHf(t) þ4.1 to 39.2, TDM ages from 1.20 to 3.47 Ga; and Ataleia granite: εHf(t) 3.2 to 8.1, TDM 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
dissolutionerecrystallization and overgrowth processes in zircon crystals in response to interactions
with residual (late-stage) melts and/or deuteric fluids.
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Zircon morphology, U-Pb geochronology, Post-collisional granites
Citação
ARAUJO, C. S. et al. 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 (Araçuaí orogen, SE Brazil). Lithos, v. 352–353, p. 105252, jan. 2020. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0024493719304116>. Acesso em: 10 mar. 2020.