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  • Title: Petrologic and geochronological constraints on the polymetamorphic evolution of the collisional granites, Araçuaí Orogen (SE Brazil).
    Author: Mauri S, Melo MG, Lana C, Marques RA.
    Journal: An Acad Bras Cienc; 2021; 93(3):e20200639. PubMed ID: 34730607.
    Abstract:
    Collisional granites of the Araçuaí Orogen, southeastern Brazil, record petrological and geochronological evidence for multiple crustal melting during the orogeny evolution. U-Pb zircon data indicate that these granites crystallized at 586 ± 2 M.y. High-grade metamorphism (M1) involved partial melting by fluid-absent reactions that produced the first generation of garnet in temperatures of approx. 750°C. Preservation of the mineral assemblage A1 (garnet-biotite-plagioclase-K-feldspar-quartz-ilmenite-melt) indicates that most of the generated melt was lost from these rocks at or near peak metamorphic conditions. A second metamorphic event (M2) is characterized by growth of a second generation of garnet in preserved A2 assemblage (garnet-sillimanite-biotite-plagioclase-K-feldspar-quartz-ilmenite-melt). Mineral equilibria modeling constrains conditions of M2 metamorphism to 713-729 °C and 6.2-7.3 kbar. Retrograde assemblage (A3) records equilibrium conditions at 610-660 °C. The Hf isotope composition indicates significant crustal contribution to the genesis of the collisional granites. The elevated geotherms in thickened crust provide enough heat for the M1 event at 562 ± 2 M.y. Subsequent heating probably associated to the transfer of mantle heat to the crust during the extensional thinning and gravitational collapse of the orogen lead to the M2 event at 526 ± 4 M.y. This event is concomitant to the emplacement of the post-collisional magmas in the orogen.
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