(1990, 1994

No abstract

As características petrográficas e geoquímicas do leucogranito peraluminoso do Complexo de Gouveia (MG), sua relaçãogeológica a migmatitos deste complexo arqueano e a zonas de cisalhamento, bem como sua intensa milonitização, aproximam sua gêneseà dos granitos de ambiente de colisão continental ou da tectônica transcorrente a ela associada. Idades químicas U-Th-Pb em cristaishomogêneos de monazita inclusos em K-feldspato do leucogranito mostram valor médio em torno de 1811 +/- 32 Ma, que marca acristalização do magma leucogranítico derivado da anatexia dos migmatitos. Esta anatexia teria se dado em ambiente hidratado e emcondições de alto grau metamórfico (fácies anfibolito alto) atingidas em função do espessamento crustal e cisalhamentos regionaisrelacionados às fases sin- a tardi-colisionais do evento Transamazônico. Além disso, esta rocha foi submetida ao retrabalhamentoBrasiliano sob fácies xisto-verde, identificado pela cloritização da biotita e da granada e por processos de turmalinização. A monazitaassociada aos corpos tardios de turmalinitos apresenta idade química U-Th-Pb de 634 +/- 20 Ma.Palavras-chave: leucogranito peraluminoso, gouveia, tectônica colisional, transamazônico, brasiliano ABSTRACTThe petrographic and geochemical characteristics of the peraluminous leucogranite of the Gouveia Complex (MG), their association to migmatites of such archean complex and to shear zones and their intense mylonitization approach their genesis to thegranites of continental collision setting or linked transcurrent tectonics. U-Th-Pb chemical ages of 0monazite grains included in K-feldsparof the leucogranite show mean values around 1811 +/- 32 Ma, which reveal its magmatic crystallization from anatexis of the migmatites.The anatexis that generated the leucogranites has been given in hydrated environment and high-grade metamorphic conditions(amphibolite facies) reached during crustal thickening and regional shear related to the syn- to late-collisional phases of theTransamazonian event. However, this rock has been subjected to Brasiliano reworking under green-schist facies, identified by chloritizationof biotite and garnet and by tourmalinization processes. Monazite associated with late tourmalinite bodies has U-Th-Pb chemical age of634 +/- 20 Ma.Keywords: peraluminous leucogranite, gouveia, collisional tectonics, transamazonian, brasiliano.

No abstract

New evidence supported by petrography (including mineral chemistry), lithogeochemistry, U-Pb geochronology by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and physicochemical study of fluid and melt inclusions by LA-ICP-MS and microthermometry, point to an orogenic setting of Lagoa Real (BahiaBrazil) involving uraniferous mineralization . Unlike the previous models in which uraniferous albitites represent Na-metasomatised 1.75 Ga anorogenic granitic rocks, it is understood here that they correspond to metamorphosed sodium-rich and quartz-free 1.9 Ga late-orogenic syenitic rocks (Na-metasyenites). These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). The interpretation of geochemical data points to a petrogenetic connection between alkali-diorite (local amphibolite protolith) and sodic syenite by fractional crystallization through a transalkaline series. This magmatic differentiation occurred either before or during shear processes, which in turn led to albitite and amphibolite formation. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate at 1.87 Ga under Oxidation/Reduction control. A second population of uraninites was also generated by the reactivation of shear zones during the 0.6 Ga Brasiliano Orogeny. The geotectonic implications include the importance of the Orosirian event in the Paramirim Block during paleoproterozoic Sȃo Francisco Craton edification and the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes. The regional microcline-gneiss, whose protolith is a 2.0 Ga syn-collisional potassic granite, represents the albitite host rock. The microcilne-gneiss has no petrogenetic association to the syenite (albitite protolith) in magmatic evolutionary terms. Keywords