Petrologic and geochronological constraints on the polymetamorphic evolution of the collisional granites, Araçuaí Orogen (SE Brazil).
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Date
2021
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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 fl uid-absent reactions that
produced the fi rst 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
signifi cant 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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Keywords
Partial melting, Pseudosection, U-Pb zircon, Collisional granite, Recycling
Citation
FERREIRA, S. L. M. et al. Petrologic and geochronological constraints on the polymetamorphic evolution of the collisional granites, Araçuaí Orogen (SE Brazil). Anais da Academia Brasileira de Ciências, v. 93, 2021. Disponível em: <http://old.scielo.br/scielo.php?pid=S0001-37652021000501104&script=sci_abstract>. Acesso em: 29 abr. 2022.