Geology, Geochemistry and Magmatic Evolution of the Paleoproterozoic, Anorogenic Oxidized a-Type Redencao Granite of the Jamon Suite, Eastern Amazonian Craton, Brazil

Abstract

The anorogenic oxidized A-type Redenção granite, of Paleoproterozoic age, is located in the Amazonian Craton to the south of the Serra dos Carajás, in Brazil. The granitic pluton is comprised essentially of monzogranites disposed in near-concentric zones. Except for clinopyroxene-bearing monzogranites generated by accumulation of mafic minerals, the least-evolved facies is a coarse biotite-hornblende monzogranite that evolved by fractional crystallization to the dominant facies, a coarse (hornblende)-biotite monzogranite. The central portion of the pluton consists of leucogranites, which were probably derived from an independent magma. Seriate and porphyritic biotite monzogranite varieties cross-cut the coarse (hornblende)-biotite monzogranite, forming annular structures. The porphyritic monzogranites are at least in part generated by mingling between the magmas of the coarse biotite monzogranite and leucogranites. The mixing of magmas is probably more common in granitic plutons than generally admitted. The different varieties of the Redenção pluton are ferroan alkali-calcic A-type granites [FeO t /(FeO t + MgO) values of 0.83 to 0.94; K 2 O/Na 2 O 1 to 2]. The oxidized character of the Redenção pluton is revealed by the ubiquitous occurrence of magnetite and titanite, and relatively lower FeO t /(FeO t + MgO) values and higher magnetic susceptibility compared to those observed in typical reduced A-type granites.

IGCP Project 510 “A-type Granites and Related Rocks through Time”: Project vita, results, and contribution to granite research

“…They span the metaluminous/peraluminous boundary. Examples include granites from Carajas, Brazil (Dall'Agnol and Oliveira, 2007;Oliveira et al, 2009), which were interpreted to form by melting of quartzofeldspathic crust under relatively oxidizing conditions. Other examples from Australia have been attributed to partial melting of felsic granulite (Collins et al, 1982;King et al, 2001).…”

“…The latter has associated polymetallic tin deposits (Teixeira et al, 2002). The Jamon suite is poorly mineralized and only small tungsten deposits are associated with it (Dall'Agnol et al, 2005;Oliveira et al, 2009). Finally, the Serra dos Carajás suite has associated mineralization that resulted from original IOCG deposits of Archean age, modified and remobilized by Paleoproterozoic fluids related to the A-type granites (Botelho et al, 2005;Monteiro et al, 2008;Xavier et al, 2010).…”

“…2). In the Carajás province, in the southeastern Amazonian region, three distinct suites of 1.88 to 1.86 Ga A-type granites crosscut the Archean basement (Dall'Agnol and Oliveira, 2007;Dall'Agnol et al, 2005;Oliveira et al, 2008Oliveira et al, , 2009). In the Tapajós province, in the southern-central domain of the Amazonian craton (Lamarão et al, 2002), and in the southern part of the Guiana shield, near the border between Amazonas and Roraima states of Brazil Ferron et al, 2010;Valério et al, 2009), ca.…”

Geocronologia U-Pb, classificação e aspectos evolutivos do Granito Marajoara, Província Carajás

“…No entanto, as maiores razões Pl/Mc pertencem aos enclaves, as quais decrescem dos EMg (4,4) para os EGp (1,9), enquanto o conteúdo modal médio de Qz é significativamente inferior no primeiro (25,9%) em relação às demais variedades do GrMj (Tabela 2). Com tais variações, os dados das análises modais, quando plotados no diagrama Q-A-P (Streckeisen, 1976), demonstram que os EGp apresentam composição transicional entre o campo do granodiorito para aquele do monzogranito, enquanto os EMg são essencialmente granodiríticos (Figura 3), contrastando fortemente com a composição monzogranítica das duas fácies do GrMj e dos demais plútons da Suíte Jamon (Oliveira et al, 2009).…”

“…a albita (An 6 até An 0 ), nas bordas. Assemelha-se textural e composicionalmente ao plagioclásio (Pl 1 ) presente nas fácies menos evoluídas dos maciços Jamon (Dall'Agnol et al, 1999b), Musa (Gastal, 1987), Redenção (Oliveira et al, 2005(Oliveira et al, , 2009 e Bannach (Almeida et al, 2006), embora os agregados sejam menos frequentes. Os cristais de plagioclásio desses agregados frequentemente apresentam relações que podem ser interpretadas como feições de synneusis (Vance, 1965) ou de epitaxia (Dowty, 1980) Figura 6F, além daquelas do tipo rapakivi.…”