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Petrografia e geoquímica do batólito granítico São Gabriel da Cachoeira, Província Rio Negro (AM)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Souza, Antonio Gilmar Honorato |
| Copyright Year | 2009 |
| Abstract | The São Gabriel da Cachoeira granite is located on the northwest region of Amazonas State, and is a NE-SW trending elliptical batolith that outcrops along the Negro and Curicuriari rivers. The Granito São Gabriel da Cachoeira is part of the Rio Uapés Intrusive Suite that intrudes the Cauburi Complex, and belongs to Rio Negro/Rio Negro-Juruena Geochronological Province (1,52-1,80 Gy). Three facies were identified by petrographic studies: 1) São Gabriel: predominat between all facies, and composed by quartz-monzodiorite, granodiorites, monzogranites, mylonitic granites with NE oriented deformed mafic enclaves, and occasionaly xenoliths; 2) Ilha de Flores consists of porphyritic to mylonitic monzogranites and sienogranites, with medium matrix marked by NE oriented euhedral to subhedral feldspar phenocrysts aligned within the regional deformation trend, which possibly indicates magmatic flux in NE direction. Both groups are cross cutted by aplite dykes, pegmatites and ruptil-ductile to ductile shear zones; 3) Camanaus is a cross cutting dyke and pocket structure that intercepts both, the São Gabriel and Ilha de Flores. The intrusive rocks of the Camanaus facies are composed by biotite sienogranite to porphyritic monzogranite, with fine matrix and 1 cm long feldspar phenocrystals oriented to N70E. Random garnet rich leucogranite dykes may occur in the batolith. Chemical data points to a metaluminous composition as a general characteristic of the São Gabriel da Cachoeira granite, although it may presents a tendency to peraluminous in the more evoluted facies (Camanaus, and Ilha de Flores facies). Is a shoshonite granite, and geochemically enriched in REE (∑ REE = 339,15-775,06 ppm) with fractionation in LREE (LaN/SmN = 3,08-6,76) and trends to horizontal pattern when compared to HREE values. The São Gabriel da Cachoeira granite is classified as calci-alkaline to alkaline continental collision granite, when plotted in the discrimination diagram, or transitional between calc-alkalic to alkalic-calcic. Unlessone deformation event is registered in the São Gabriel da Cachoeira batolith rocks, with the main trend NE generated during the syntectonic batolith emplacement. The micro-textures such as minerals recrystallization, gneiss and milonite textures, grain reduction size due to tectonic grinding, followed by "augen" generation and "ribbon" textures, recrystalized plagioclase, recrystalized flakes in quartz, granoblastic polygonal texture subordinate, grain boundary area reduction (GBAR) and high-temperature grain boundary migration indicate temperatures up to 600C in batholith’s borders. The magma that generated the São Gabriel da Cacheoira batolith would be formed by a partial melting process, that took place within the crust Transamazonian age in wich fractional crystallization was the dominant process, through which this magma mass formed; and is well observed in the Harker diagrams (heavy, light, and rare earth elements, as well between the compatibility and incompatibility relationship) in 1.5 Gy continental colision environment. _______________________ |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://rigeo.cprm.gov.br/xmlui/bitstream/handle/doc/379/diss_gilmarsouza.pdf?isAllowed=y&sequence=1 |
| Alternate Webpage(s) | http://ppggeo.ufam.edu.br/images/assets/Documentos/DissertacaoGilmarHonorato2009compressed.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
