Navegando por Assunto "Granito tipo A"

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Estudo petrográfico, geoquímico e isotópico de granitos da porção Leste do Domínio Tapajós, nas folhas São Domingos e Jardim do Ouro, Pará
(Universidade Federal do Pará, 2015-10-07) SEMBLANO, Flávio Robson Dias; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Tapajós Domain, located in Brazil Central shield (southern portion of the Amazonian Craton) makes part of the Tapajós-Parima (or Ventuari-Tapajós), Province corresponding to a Paleoproterozoic orogenic belt of NW-SE direction, extending from southwestern Pará state to southern Venezuela. Some authors describe this province as been formed by development of two distinct orogenies that accreted four magmatic arcs, followed by a post-orogenic alkaline magmatism. This post-orogenic Orosirian magmatism, occurred around 1880 Ma, is represented by the Maloquinha Intrusive Suite (MIS) and Iriri Group that have occured postdating Tropas Orogeny which give rise to Parauari Intrusive Suite (PIS). The MIS comprises alkali granites generated in post-collisional anorogenic environment that is spatially associated with Iriri Group volcanic rocks. This suite consists of alkali feldspar granite, syenogranite and monzogranite leucocratic bodies with predominant pertitic orthoclase and rare microcline. These rocks crop out as elliptical to round stocks and batholiths along NW-SE regional lineaments in the Tapajós Domain. Many bodies belonging to SIM have been dated by both methods, Pb-evaporation and U-Pb on zircon, that yielded ages between 1882±4 and 1864±18 Ma. In the eastern portion of the Tapajós Domain, the Nd isotope signature for these suite granites suggests paleoproterozoic sources (TDM Nd of 2.28 to 2.23 Ga, and εNd(t) of -0.72 to -2.45). Many plutons of SIP were dated by zircon Pb-evaporation method, and the ages found were between 1891±3 e 1879±11 Ma, its isotopic signature of Nd are εNd(t) -5.21 to -1.82 and TDM Nd of 2.43 to 2.32 Ga. This work was carried out in the eastern part of the Tapajós Domain, in the SB.21-Z-A-II (São Domingos) and SB.21-Z-A-III (Jardim do Ouro) 1:100,000 sheets, where five granitic bodies were studied (Igarapé Tabuleiro, Dalpaiz, Mamoal, Serra Alta and Igarapé Salustiano). The Igarapé Salustiano body shows a calc-alkaline affinity, meta to peraluminous and syncolisional I-Type granites nature, showing close relationship with the Parauari Intrusive Suite rocks of this Domain. Other bodies could be related to MIS and they are basically represented by hololeucocratics alkali feldspar granites, syenogranites and monzogranites. These rocks have high SiO2 (>70%), FeOt/(FeOt+MgO) (>0.80) and K2O/Na2O, low CaO, Al2O3, MgO and Sr contents, and post-collisional granites affinity, alkalic-calcic to alkalic character and high REE content with Eu negative anomalies, own from A-type granites. This work, as others made in the Tapajós-Parima and Amazônia Central provinces, identified TDM Nd contradictory ages to the ones assigned these two provinces for geochronological subdivision between them.
Acesso aberto (Open Access)
Granito Porquinho, Domínio Tapajós: exemplo de magmatismo alcalino-peralcalino e considerações metalogenéticas preliminares
(Universidade Federal do Pará, 2018-08-27) SILVA, Joseanna dos Santos; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
Porquinho Granite (PG) is a subcircular batholith located at the Tapajós Domain, Amazonian Craton, petrographically composed of isotropic hypersolvus alkali feldspar granites, grouped In: Biotite alkali feldspar granite (BAFG), Amphibole alkali feldspar granite (AAFG) and greisenized rocks. Biotites are classified as annite, while amphiboles vary in composition, from calcic (hastingsite, ferro-edenite, ferro-actinolite and ferro-ferri-hornblende) to sodic-calcic (ferro-ferri-winchite, ferro-ferri-katophorite, ferro-richterite, potassic-ferro-ferri-katophorite and ferro-katophorite) to sodic (riebeckite). Geochemically, PG is metaluminous to peraluminous, locally peralkaline, shows K 2 O/ Na 2 O ratios between 1 and 2, and FeO t /(FeO t + MgO) very close to 1, which led it to be classified as a ferroan granite. It is a reduced granite, with geochemical characteristics of A-type granites of the A 2 -subtype and is similar to the Phanerozoic intraplate granites. AAFG rocks are slightly more enriched in REE than BAFG, but they all present similar comportment, and strong negative Eu anomaly, forming the typical gullwing-shaped pattern of the A-type and the Sn-Ta-Nb mineralized granites. BAFG also shows similar behavior with Europa Granite (EG, Madeira Intrusive Suite; Pitinga) and Velho Guilherme Intrusive Suite (VGIS; Xingu), both mineralized in Sn-Ta-Nb, while AAFG approaches, geochemically, more to Maloquinha Intrusive Suite (MIS; Tapajós), non-mineralized. In this work, PG presented a geochronological age of 1,889 ± 2 Ma, interpreted as the age of crystallization, which is about 100 Ma older than the former one (1,786 ± 14 Ma). The older geochronological age fits better with geological context in which Porquinho Granite is inserted, but also means more detailed investigations need to be done in this area in order to eliminate possible doubts about its crystallization age and find out if PG has a more complex history of evolution.