Abstract
ABSTRACT: The A-type Paleoproterozoic Bannach Granite belongs to the Jamon Suite and cross-cut the Archean units of the Rio Maria Domain in the Carajas Province. It comprises eight facies with varied mafic content and texture: even-grained cumulate granite (CG), even coarse-grained biotite-amphibole monzogranite (cBAMz), even coarse-grained amphibole-biotite monzogranite (cABMz), porphyritic biotite monzogranite (pBMz), even coarse-grained leucomonzogranite (cLMz), early even medium-grained leucomonzogranite (EmLMz), late even medium-grained leucomonzogranite (LmLMz) and even fine-grained leucomonzogranite (fLMz). In the less evolved facies, the dominant amphibole is Fe-hornblende passing to Fe-edenite or hastingsite, with associated cummingtonite/grunerite originated from the destabilization of clinopyroxene. Biotite has ferroan composition and approaches annite in the late-emplaced leucomonzogranite. Plagioclase varies from andesine to oligoclase or from oligoclase to albite. Titanite, magnetite, and ilmenite are found in all granite facies showing magmatic origin. The near liquidus temperatures vary between 943oC and 795oC and the estimated emplacement pressure is 300 ± 50 MPa (~11.1 ± 1.9 km). Amphibole Fe/(Fe + Mg) ratios together with magmatic magnetite and titanite indicate that these granites crystallized at moderately oxidizing conditions, similar to those admitted for the Jamon granite and magnetite series granites of Laurentia. However, the composition of biotite suggests a more reduced character close to NNO to NNO -0.5. The late leucomonzogranite facies is an exception because it displays high Fe/(Fe + Mg) ratios in biotite and approaches to the reduced granites of Carajas, Laurentia and Fennoscandia in this regard. It derived from a more reduced source than the other facies of Bannach Granite.
Highlights
At the end of Paleoproterozoic and during the Mesoproterozoic Era, an intense magmatic activity has been reported in several cratonic areas of the world
The objective of this work was to study the mineralogy of the main facies of Bannach Granite (Duarte 1992, Almeida et al 2006, 2007), a batholith hosted by Archaean granitoid rocks of Rio Maria Domain, southeast of Amazonian Craton
Seven representative samples of the main facies of the Bannach pluton were selected for mineral chemistry analysis based on previous studies (Almeida et al 2006): GC (ADR136i), coarse-grained biotite-amphibole monzogranite (cBAMz) (ADR-136C), coarse-grained amphibole-biotite monzogranite (cABMz) (ADR-55A), coarse-grained leucomonzogranite (cLMz) (ADR-32B and ADR-32B-1) and late even medium-grained leucomonzogranite (LmLMz) (ADR-140 and ADR-140-1)
Summary
At the end of Paleoproterozoic and during the Mesoproterozoic Era, an intense magmatic activity has been reported in several cratonic areas of the world. These magmatic events are remarkable in the Amazonian Craton, where they include a huge volume of granitic and subordinate mafic plutonic rocks, associated with felsic, intermediate, and mafic volcanic rocks (Dall’Agnol et al 1999a, and references therein). In the Carajas Province, the magmatism is Paleoproterozoic in age and has anorogenic character. It is represented by the Jamon, Velho Guilherme, and Serra dos Carajás suites (Dall’Agnol et al 2005) and the Seringa
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