Navegando por Assunto "Granito Tipo A"

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Cerro Porã Batholith: post-orogenic A-type granite from the Amoguijá Magmatic Arc - Rio ApaTerrane - South of the Amazonian Craton
(2013-09) PLENS, Dalila Pexe; RUIZ, Amarildo Salina; SOUSA, Maria Zélia Aguiar de; BATATA, Maria Elisa Fróes; LAFON, Jean Michel; BRITTES, Ana Flávia Nunes
The Cerro Porã Batholith has an approximately area of 30 km by 4 km, situated at the region of Porto Murtinho, Mato Grosso do Sul. It is located in Rio Apa Terrane, at the southern portion of the Amazonian Craton. It consists of Pink Syenogranitic Facies and Gray Monzogranitic Facies. The first facies is characterized by xenomorphic equigranular texture to essentially inequigranular texture with graphic and granophiric intergrowths. Both facies are composed of alkali feldspar, quartz, and plagioclase with biotite as the only primary mafic mineral. The Gray Monzogranitic Facies has porphyritic texture with graphic to granophiric fine-grained groundmass. It consists of quartz, plagioclase, alkali feldspar, and mafic aggregates (biotite and amphibole). Both facies were metamorphosed at greenschist facies and the Pink Syenogranitic Facies, which is milonytic in nature when it is in shear zones. One event of ductile–brittle deformation was identified, originated in a compressive system. It was responsible for the schistosity and mineral-stretching lineation. The development of the Esperança shear zone is related to this deformational phase and reflects the cinematic history of the reverse convergent system with top transport to NWW. Chemically, these rock types are classified as A2-type granitoids of range alkaline potassium saturated on silica. Geochronological data obtained by U-Pb (Sensitive High Resolution Ion Microprobe) method in zircon resulted in an age of 1749 ± 45 Ma, interpreted as crystallization age of the batholith. From the geotectonic point, the Cerro Porã Granite is considered to be the product of a magmatism associated with a magmatic arc developed in Statherian and emplaced in late-orogenic to post-orogenic stage.
Acesso aberto (Open Access)
Geologia, geocronologia e litoquímica dos granitos paleoproterozóicos do tipo A no setor setentrional da Província Tocantins
(2008-06) CHAVES, César Lisboa; GORAYEB, Paulo Sérgio de Sousa; MOURA, Candido Augusto Veloso
This work presents the geologic characterization of the Ipueiras Intrusive Suite, which comprises four granitic plutons, named do Carmo, Areias, Ipueiras and Itália, located in Goiás Massif, northern sector of the Tocantins Province. New petrographic, litogeochemical, geocronological and isotopic data had allowed to discriminate these plutons of other granites of the region. Lithochemical data showed that they are peraluminous subalkaline granites, with A-type affinity. Single zircon Pb-evaporation data indicate an age of 2,08 Ga for this magmatism. Sm-Nd (TDM) ages between 2,15 and 2,19 Ga, and positive εNd(2,08 Ga) values (+2,5 to +2,9) for the Areias and Ipueiras granites suggest an origin involving juvenile mantle components. This granitogenesis may be related to the last magmatic pulses of the Transamazonian thermotectonic event, well defined in the region.
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Geologia, petrografia e geoquímica e suscetibilidade magnética do Granito Paleoproterozoico São João, Sudeste do Cráton Amazônico, Província Carajás
(Universidade Federal do Pará, 2013-06-04) LIMA, Paulo Henrique Araújo; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The São João granite (SJG) is an anorogenic batholith of circular form, with an area of approximately 160 km2, which cuts Archean units of the Rio Maria Granite-Greenstone Terrain, southeastern Amazonian Craton. It consists of four distinct petrographic facies: biotite-amphibole monzogranite (BAMG), biotite-amphibole syenogranite (BASG), amphibole-biotite monzogranite to syenogranite (ABMSG) and biotite monzogranite to syenogranite (BMSG). The SJG has a metaluminous to weakly peraluminous nature, FeOt/(FeOt+MgO) ratios varying from 0.94 to 0.99 and K2O/Na2O from 1 to 2, shows geochemical affinities with the intraplate granites, A-type granites of A2 subtype and ferrous granites, suggesting a crustal source for its origin. The SJG has higher contents of LREE compared to HREE and a sub-horizontal pattern for the latter. The negative anomalies of Eu rising from less evolved towards more evolved rocks (BAMG → BASG→ ABMSG→ BMSG). Magnetic susceptibility data (MS) allowed the identification of six populations with different magnetic characteristics, where the highest values of MS relate to the less evolved facies and the lowest to the more evolved facies. The comparison between SJG and the granite suites of the Carajás Province shows that it displays strong geological, petrographic, geochemical and MS similarities with the granites of the Serra dos Carajás suite, and may be preliminarily included in the same.
Acesso aberto (Open Access)
Petrography, magnetic susceptibility and geochemistry of the Rio Branco Granite, Carajás Province, southeast of Pará, Brazil
(2013-03) SANTOS, Patrick Araujo dos; FEIO, Gilmara Regina Lima; DALL'AGNOL, Roberto; COSTI, Hilton Túlio; LAMARÃO, Cláudio Nery; GALARZA TORO, Marco Antônio
The Paleoproterozoic Rio Branco stock intrudes the Archean Cruzadão biotite monzogranite. It occurs west of the Canaã dos Carajás city, close to the Sossego copper mine in the Carajás Province. It is constituted by undeformed and isotropic, hololeucocratic syenogranites, showing equigranular texture. The granite is formed essentially by perthitic alkali feldspar, quartz, and plagioclase, with additional variable amounts of chloritized biotite. Fluorite, allanite, and zircon are common accessory minerals, whereas pyrite and chalcopyrite are scarces. Albitization and subordinate greisenization are the main alteration processes that affected the granite. The secondary mineralogy is represented by albite, fluorite, topaz, chlorite, muscovite, siderophyllite, and iron oxides. Magnetic susceptibility values are systematically low and vary between 1.3 x 10-5 a 6.9 x 10-4 (SI). The Rio Branco Granite is metaluminous to peraluminous and shows high FeOt/(FeOt + MgO). It has geochemical affinities with ferroan, reduced A2-subtype granites. The rare earth element (REE) patterns are flat with little heavy REE fractionation and show accentuated negative Eu anomalies (Eu/Eu* = 0.08 - 0.13). These characteristics are typical of evolved granites, derived from volatile-enriched liquids responsible by the intense subsolidus hydrothermal alteration. The dating of the Rio Branco granite did not give conclusive results, but the obtained data, associated with geological evidence, suggest that it is of Paleoproterozoic age. The comparison between the Rio Branco granite and Paleoproterozoic A-type suites of the Carajás Province suggests that the Rio Branco granite has more affinity with the Velho Guilherme suite and, in lesser degree, with the Serra dos Carajás suite. On the other hand, is clearly different from oxidized A-type granites of the Jamon suite. Despite its similarities with tin-specialized granites, the Rio Branco Granite is not associated with tin mineralizations.