Granitóides Brasilianos Precoces do Cinturão Dom Feliciano: Caracterização Geoquímica e Discussão Estratigráfica

Abstract

Neste trabalho é apresentada uma revisão geral das principais características geoquímicas dos granitoides cálcio-alcalinos precoces do Escudo Sul-rio-grandense e suas implicações na restrição de modelos de evolução geotectônica propostos para o Cinturão Dom Feliciano durante o Ciclo Brasiliano. Discussões acerca dos aspectos estratigráficos, estruturais e metamórficos dessas rochas são igualmente apresentadas, com o objetivo de estabelecer uma cronologia para o magmatismo granítico em relação aos principais eventos tectono-termais responsáveis pela estruturação deste cinturão durante o Proterozóico Superior.

Post-collisional subvolcanic rhyolites associated with the Neoproterozoic Pelotas Batholith, southern Brazil

“…Under this hypothesis, fractional crystallization that was potentially 15 L min À1 Ar Auxiliary gas flow rate 0.7 L min À1 Ar Sample gas flow rate 0.6 L min À1 Ar combined with crustal contamination or assimilation is responsible for evolution of the alkaline magmas, which are highly differentiated from the transitional basalts or moderately alkaline magma. Similar processes have been proposed by various authors (e.g., Verma, 1983Verma, , 1984Halliday et al, 1984;Novak and Mahood, 1986;Cameron and Cameron, 1986;Halliday et al, 1986;Ferriz and Mahood, 1987;Moll-Stalcup, 1987;Hildreth, 1987;Halliday et al, 1987) to explain the genesis of high-silica rhyolites in many environments, such as the Volcanic Center Sierra La Primavera (Pleistocene e Mexico, Mahood & Halliday, 1988). Recent studies (e.g., Hildreth, 2004;Bachmann and Bergantz, 2004;Lipman, 2007) propose that high-silica rhyolites originated from the separation of liquids derived from rhyolitic crystal mush linked to large granodioritic or granitic plutons.…”

Paleoproterozoic Magmatic Provenance of Detrital Zircons, Porongos Complex Quartzites, Southern Brazilian Shield

“…Correlation with the Brusque Complex situated 700 km to the northeast has also been attempted (Hasui et al, 1975;Jost and Bitencourt, 1980;Almeida et al, 2000;Shukowski et al, 1991;Hallinan and Mantovani, 1993), and these quartzites are now known to contain only Paleoproterozoic detrital zircon grains (Hartmann et al, 2003a). Although some of these Porongos quartzite units could correspond to compositionally modified granitic mylonites (Fragoso-César, 1991;Fernandes et al, 1992aFernandes et al, , 1992b, we have demonstrated that, according to zircon morphology, all the studied quartzites have a sedimentary origin.…”

“…Porongos Complex volcanic and sedimentary protoliths have been interpreted as a passive continental margin sequence deposited over a sialic basement constituted of the Encantadas Complex (Jost and Bitencourt, 1980). Backarc (Fragoso-César et al, 1982;Fernandes et al, 1992aFernandes et al, , 1992bFernandes et al, , 1995Fernandes et al, , 1998 and forearc (Issler, 1983) environments have also FIG. 4.…”

SHRIMP U/Pb Zircon Dating of Neoproterozoic Granitic Magmatism and Collision in the Pelotas Batholith, Southernmost Brazil

“…It contains quartz, plagioclase (An 40), and brown biotite. Minimum temperatures of 650°C and pressures of 4 kbar have been determined for this gneiss, which is part of the Gl granitic phase of the Arroio dos Ra tos gneisses (Fernandes, Tommasi, Porcher, Koester et al, 1992;Lima et al, 1998). Biotite marks a continuous and regular foliation parallel to a gneissic microbanding and is partly retrometamorphosed to chlorite.…”