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EVENTOS MAGMÁTICOS ARQLIEANOS DE NATUREZA CÁLCIO-ALCALINA E THOLEIÍTICA NO QUADRILÁTERO FERRÍFERO E SUAS IMPLICAÇÕES TECTÔNICAS

1997; Sociedade Brasileira de Geologia; Volume: 27; Issue: 1 Linguagem: Inglês

10.25249/0375-7536.1997121128

2177-4382

Maurício Antônio Carneiro, Hanna Jordt-Evangelista, Wilson Teixeira,

Geological and Geochemical Analysis

QUADRILÁTERO FERRÍFERO, BRAZIL Mafic amphibolitic dikes cutting tonalitic rocks with little evidence of metamorphism are one of the singularities in the crusta, evolution of the Quadrilátero Ferrífero, in Minas Gerais.Petrographic, geochemical and geochronogical studies show that in the Bonfim Metamorphic Complex these rock types constitute two distinct magmatic series, one tholeiitic and the other calcalkaline.They were partially metamorphosed under the conditions of higher greenschist to lower amphibolite facies.In the calcalkaline tonalites the metamorphic reactions, which required the introduction of water, were difficulted by their massive structure.Therefore primary textures and mineralogy were mostly preserved.In the tholeiitic rocks of the dikes the metamorphism was more homogeneous because the primary igneous mineralogy, rich in pyroxenes, is more sensible to hydration reactions than the mineralogy of the tonalites.The access of the needed aqueous fluids certainly was more effective to the mafic rocks because fluids tend to be concentrated in zones of crustal weakness such as dikes.We conclude that the non-penetrative metamorphic recrystallization of the two rocks series under the conditions of the higher greenschist to lower amphibolite facies, and also the preservation of early Archean U/Pb ages in titanites of the tonalites, indicate that the studied region was not submitted to any penetrative tectonometamorphic event of higher metamorphic conditions than the lower amphibolite facies during the Proterozoic.Therefore we also conclude that the tectonometamorphic overprinting of the Transamazonian Event (2.2 My) in the Bonfim Metamorphic Complex and probably also in the rest of the Quadrilátero Ferrífero was heterogeneous, not affecting all áreas with the same intensity.