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- Title
Granitos com epidoto magmático e clinopiroxênio: plútons Tamboril e Olho d'Água, Terreno Cachoeirinha-Salgueiro, Nordeste do Brasil.
- Authors
Siqueira, Renan; Nóbrega Sial, Alcides; Pinto Ferreira, Valderez
- Abstract
Calc-alkalic, alkalic and high-K calc-alkaline granites intruded into the Cachoeirinha-Salgueiro Terrane (CST) in the Transversal Zone Domain, northeastern Brazil. The Tamboril and Olho d'Água plutons have similar mineralogical assemblages, but distinct textures. The Olho d'Água pluton iscomposed by medium grained clinopyroxene-biotite tonalite, equigranular, containing amphibole and magmatic epidote; and the Tamboril pluton by medium to coarse-grained biotite granodiorite, porphyritic, containing clinopyroxene and plagioclase megacrysts. In these plutons, clinopyroxene is substantially less abundant when there is the presence of epidote, that is, the increase of modal clinopyroxene is directly proportional to the decrease of the modal epidote. Larger elements point to these plutons as high-K calc-alkalic, metaluminous, with characteristics of magnesium granites of the Cordilheirano type. These plutons have low magnetic susceptibility values (≈0.3 × 10-3 SI), which are typical of S-type granites. However, I-type granites with magmatic epitope in the Cachoeirinha-Salgueiro Terrane also have low values of magnetic susceptibility (<0.5 × 10-3 SI) because Fe+3 is bound to the epidote structure. Metaluminous mineralogy shows that it is unlikely that the magma of Tamboril and the Olho d'Água suffered crustal assimilation. Fine-scale oscillatory zonations and biotite and epitope inclusions common in megacrystals of plagioclase and K-feldspars suggest convection in the magma chamber or variation of physico-chemical conditions during crystallization. There seem to be two generations of clinopyroxenes: idiomorphic, without inclusions and hipidiomorphic, with inclusions of various minerals. The latter, full of inclusions, may be considered as residues from the original source of magma.
- Publication
Geochimica Brasiliensis, 2018, Vol 32, Issue 1, p20
- ISSN
0102-9800
- Publication type
Article
- DOI
10.21715/GB2358-2812.2018321020