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A IMPORTÂNCIA DA GRANITOGÊNESE TARDI-ARQUEANA (2.5 Ga) NA EVOLUÇÃO TECTONO-METAMÓRFICA DA PROVÍNCIA MINERAL DE CARAJÁS-O COMPLEXO GRANÍTICO ESTRELA E SUA AURÉOLA DE CONTATO

1998; Sociedade Brasileira de Geologia; Volume: 28; Issue: 4 Linguagem: Inglês

10.25249/0375-7536.19985135222

2177-4382

Carlos Eduardo de Mesquita Barros, Pierre Barbey,

Minerals Flotation and Separation Techniques

AUREOLE An important magmatic event giving rise to moderately alkaline granitoids (Old Salobo Granite and Estrela Granite Complex) occurred in the Carajas Mining Province in Late-Archean times (~2.56 Ga).Moderately alkaline granite (A type) genesis is generally thought to be due to partial melting of either granulites or metaigneous rocks.These melts are considered to have very high temperatures and very low viscosity, promoting epizonal emplacement.These Late-Archean granite bodies have imposed significant increase of thermal gradients, changes of the rheology of the metavolcanosedimentary country rocks (Salobo, Pojuca and Grão-Pará groups) and broadly overprinted the Rb-Sr isotopic systems in the Carajas region.Three domains have been discriminated in the Estrela Granite Complex host rocks: an external contact aureole (~ 450-550°C), an internal aureole (-550-650°C), and the xenolith domains (-650-850°C).The rocks of the external contact aureole are very slightly deformed, and affected by a discrete (S 1m ) foliation which is parallel to the primary regional lithological banding (S 0 ).In the internal aureole the host rocks show a very well developed sub vertical foliation (S 2 ) and/or lineation.In the metabasites of the internal aureole as well as from the xenoliths amphibole-bearing veins are very frequent.Petrographic facies spatial distribution confirmed by geochemical, structural and aerogeophysical data show that the Estrela Granite Complex is built up by several plutons.The structural behavior of the complex is outlined by a magmatic layering (S 0 ), that is flat on the central domains and subvertical on the peripheral zones of each pluton.The spatial disposition of the magmatic layering (S 0 ) indicates that the Estrela Granite Complex emplacement was mainly controlled by ballooning.Subvertical magmatic layering and foliation (S 1 ) of E-W orientation have been developed as a response of both emplacement forces (ballooning) and regional coaxial horizontal shortening of N-S direction.Late mylonite zones (S 1m ) are due to the formation of mechanical instabilities at the end of the cooling history.Such structural evolution within progressive deformation and decreasing-thermal regimes is typical of syntectonic granites.