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Luiz Da Silva, Geological Survey of Brazil (Brazil)
Antonio Carlos Pedrosa Soares, UFMG (Brazil)
Carlos Maurício Noce, UFMG (Brazil)
Claiton Piva Pinto, Geological Survey of Brazil (Brazil)
Alan Cardek Gomes, Geological Survey of Brazil (Brazil)
Orivaldo Ferreira Baltazar, Geological Survey of Brazil (Brazil)
Valter Salino Vieira, Geological Survey of Brazil (Brazil)
Glaucia Queiroga, UFMG (Brazil)
Richard Armstrong, ANU (Australia)
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The Neoproterozoic Araçuaí orogen, exposed for some 300,000 square kilometers eastward from the São Francisco Craton in southeastern Brazil, preserves most records of the magmatic stages expected for a Wilson Cycle evolution, as recorded in modern subduction- to collision-related orogens. Pre-orogenic, rift-related magmatism with A-type chemical signature encompasses small granitic-gabbroic plutons dated at ca. 900 Ma and is assigned to the breakup of the São Francisco-Congo paleocontinent. The pre-orogenic magmatic evolution culminated with the outpouring of oceanic-type tholeiitic magmas preserved as metamorphosed ophiolite slivers. The onset age of the oceanic spreading is unknown, but the zircon U-Pb magmatic age for metaplagiogranites suggested that it lasted until ca. 690 Ma. The pre-collisional stage (G1) lasted from ca. 630 to 585 Ma and is characterized mainly by foliated tonalite and granodiorite, representing an expanded calc-alkaline suite formed in a continental margin magmatic arc. The recent discovery of (meta)dacitic rocks, also dated at ca. 585 Ma, led to the delineation of an unsuspected, pre-collisional, calc-alkaline volcanic arc setting, coeval to the youngest G1 plutons. The syn-collisional magmatism (G2) lasted from ca. 585 to ca. 560 Ma and comprises dominantly S-type garnet-biotite leucogranites. In addition to the peraluminous granites, minor magmatic plutons of charno-enderbitic composition are also associated with the G2 stage. Available U-Pb ages suggest that the most important G2 episode of syn-collisional magmatism took place around 575 Ma, synchronously with the metamorphic peak of the collisional stage. U-Pb zircon results also allowed to place constraints on a, so far, not well defined late-collisional stage magmatism (G3), characterized by cordierite-garnet and 2 micas S-type leucogranites, but showing ages bracketed between ca. 550 to 530 Ma. The post-collisional stage lasted from ca. 530 to 490 Ma and comprises the G4 and G5 magmatism, related to the gravitational collapse of the orogen. G4 comprises two-mica granitic intrusions and represents the youngest S-type magmatism known within the orogen. The G5 magmatism includes coeval, but non-comagmatic, mostly zoned plutons with A- and I-type signatures. In addition to granites the G5 magmatism also embraces gabbroic, charno-enderbitic, mangeritic and minor anorthositic components, corresponding to a typical anorthosite-mangerite-granite-charnockite (AMGC) suite. From the very early pre-collisional stage to the last post-collisional manifestations, the Araçuaí orogen records almost 140 m.y. of orogenic magmatism, implying in a succession of different sources of heat and melting processes, some of them involving mantle components indicated by magma mingling and mixing features (G1 and G5), and others related to the major crustal thickening event (G2) followed by adiabatic partial melting episodes (G3 and G4).
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