The origin and evolution of the South American Platform

The Serra da Graciosa region includes important occurrences of granites and syenites of the Graciosa A-type Province (formerly Serra do Mar Suite), southern Brazil. Using fieldwork, petrography, and remote sensing imagery, we characterize the geology of the plutons in the region. Five individual plutons were recognized. Two correspond to the previously defined Marumbi and Anhangava Plutons. We divide the former "Graciosa Pluton" into three new plutons: Capivari, Órgãos, and Farinha Seca. The plutons are elliptical with northeast-southwest orientation. Two petrographic associations can be recognized: an alkaline association that includes peralkaline and metaluminous hypersolvus alkalifeldspar granites and syenites (Anhangava, Farinha Seca, Órgãos), and an aluminous association composed of metaluminous and weakly peraluminous subsolvus granites (Capivari, Órgãos, Anhangava, Marumbi). Occurrences of each association are limited to one individual pluton or to portions of a pluton, and the age relationships are not well established. Monzodioritic rocks are found marginal to the Órgãos and Farinha Seca Plutons, and interaction with silicic magmas locally produced hybrid quartz syenites (Farinha Seca Pluton). Geothermobarometry indicates emplacement at shallow crustal levels (P = 2 ± 0.6 kbar), and crystallization temperatures within the interval 900-700 • C for the granitic and syenitic rocks, and 1000-750 • C for the monzodioritic rocks.

Section: Geological Overviewmentioning

confidence: 89%

The Serra da Graciosa A-type granites and syenites, southern Brazil. Part 1: regional setting and geological characterization

Gualda

Vlach

2007

“…The older ages identified in the sample correspond to the Trans-Amazonian Cycle (see Almeida et al 2000) of orogenies, known to range from 2.26 to 2.00 Ga in SouthAmerica (Hartmann andDelgado 2001, Santos et al 2003). The early Encantadas Orogeny -2.26-2.10 Ga produced the magmatic tonalite-granodiorite association of the Encantadas Complex at 2257 ± 12 Ma, including the pyroxenite or magnesian basalt protolith of the studied sample.…”

Section: Discussionmentioning

confidence: 87%

Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

Hartmann

Santos

Leite

et al. 2003

The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M 1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702 ± 21 Ma during a greenschist facies event M 2 ; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257 ± 12 Ma) and Camboriú Orogeny (∼ 1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702 ± 21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

“…Tectonics is another factor that was probably significant in the genesis of carbonates in the Pantanal region. This is suggested by the direct association between the carbonate deposits and tectonic structures, normal faults and folds originated in the Brasiliano tectonic cycle, in the Neoproterozoic (Almeida et al 2000), and reactivated with the Andean orogeny and the subsidence of the Pantanal (Ussami et al 1999). The tectonic activity could have modified the relief, generating scarps and depressed areas, which controlled the location of rivers and lakes.…”

Section: Factors Controlling the Continental Carbonates Genesis And Ementioning

confidence: 99%

Paleoenvironmental Evolution of Continental Carbonates in West-Central Brazil

Oliveira

Rossetti

Utida

2017

This paper presents a sedimentological and stratigraphical study of Quaternary (Middle to Late Pleistocene/ Holocene) continental carbonates outcrops inside Pantanal Basin and its surroundings, especially in Serra da Bodoquena, Pantanal do Miranda and Corumbá/Ladário plateau, in the state of Mato Grosso do Sul, as well as in Serra das Araras, in the state of Mato Grosso. The aim is to understand the depositional paleoenvironments and analyse climate and tectonic influences in their genesis and evolution. The results show that the deposition of these continental carbonates started in the Middle to Late Pleistocene and have continued, with some interruptions, until the present days. Sedimentary successions were identified in the different areas, without complete correlation. Two sedimentary successions separated by an erosional surface were described in Serra da Bodoquena and Serra das Araras. In Corumbá and Pantanal do Miranda, only one succession was described. These successions were deposited in elongated lakes parallel to fault planes; small lakes, related plains and plateaus; springs related to cliffs produced by faulting; rivers conditioned by topographic variation. The climatic interpretation, without proper temporal resolution, obtained by the stable-isotope composition and stratigraphic interpretation, indicates alternation of dry and wet periods. The Neoproterozoic faults with their neotectonics and the subsidence of the Pantanal Basin, are the major control for carbonated water flow and development of depositional areas, gradually turning plateaus into slight tilted areas, allowing the evolution of depositional systems from lakes to rivers.