Twenty million years of post-orogenic fluid production and hydrothermal mineralization across the external Araçuaí orogen and adjacent São Francisco craton, SE Brazil.
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Date
2019
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Abstract
The Araçuaí orogen (AO) is a hot orogenic system that is known for its widespread and long-lived magmatism
(630–480 Ma).Within the last c. 20 million years of its evolution, the AO saw the widespread development of hydrothermal systems in its lower-grade external fold-and-thrust belt and its Foreland Domain (eastern margin of
the adjoining São Francisco craton). U\\Pb crystallization ages for hydrothermal monazite, rutile, and xenotime
indicate that fluid circulation along the entire AO occurred between 515 to ca. 495 Ma, largely overlapping with
U\\Pb ages of hydrothermal systems and mineralized zones in the adjacent São Francisco craton. Titanium-inquartz thermometry suggests that most hydrothermal systems closed at temperatures of ca. 360 °C. The Sm\\Nd
isotope composition of the vein monazite samples ranges from εNd500Ma −16.8 to −17.8, and one less-evolved
sample with εNd500Ma of −5.9. The Sm\\Nd isotope compositions overlap with the bulk rock Sm\\Nd data for the
Espinhaço Supergroup, suggesting that the hydrothermal veins in this study are mainly related to metamorphic
fluids derived from the prograde dehydration of low-grade metasedimentary rocks. The U\\Pb ages, Sm\\Nd isotope composition, and vein mineralogy are all consistent with a 20 My period of channelized fluid flow, characterized by an oxidizing, low pH, REE-, P-, and Ti-bearing aqueous metamorphic fluid. The expression of
supercritical fluid flow in the core of the AO is given by the emplacement of large volumes of bare/mineralized
pegmatite bodies and regional resetting of monazite ages in host rocks. On a regional context, this widespread
fluid flow is associated with a high-T, low-P metamorphism that marks the beginning of the post-collisional decompression of the orogeny, which is associated with lithospheric mantle delamination. The reorganization of
mass and heat, due to extensional collapse, resulted in multi-sourced fluid production and mineralization from
deep to shallow crustal levels that affected an area of over 400.000 km2 along the eastern border of the São
Francisco Craton.
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Keywords
Hydrothermal minerals, Fluid flow
Citation
GONÇALVES, G. de O. et al. Twenty million years of post-orogenic fluid production and hydrothermal mineralization across the external Araçuaí orogen and adjacent São Francisco craton, SE Brazil. Lithos, v. 342-343, p. 557-572, out. 2019. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0024493719301719>. Acesso em: 10 mar. 2020.