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Previous issue date: 2013-12-19 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Pyrometamorphism results from conditions of high temperatures and very low pressures provoked by the intrusion of hypabyssal basic bodies into sedimentary or metassedimentary hosting rocks. The onshore portion of the Potiguar Basin in NE Brazil offers examples of this type of metamorphism nearby the contacts of Paleogene to Neogene plugs, sills and dikes of diabases and basalts crosscutting sandstones, siltstones and shales of the A?u Formation (Albian-Cenomanian). The thermal effects over these rocks are reflected on textures and minerals assemblages that characterize the sanidinite facies of metamorphism, often with partial melting of the feldspathic and mica-rich matrix. The liquid formed is potassic and peraluminous, with variably colored rhyolitic glass (colorless, yellow, brown) comprising microcrystals of tridymite, sanidine and clinoenstatite, besides residual detrital clasts of quartz and rarely zircon, staurolite and garnet. Lenses of shale intercalated within the sandstones display crystallites of Fe-cordierite (sekaninaite), mullite, sanidine, armalcolite (Fe-Ti oxide) and brown spinel. The rocks formed due to the thermal effect of the intrusions are called buchites for which two types are herein described: a light one derived from feldspathic sandstone and siltstone protoliths; and a dark one derived from black shale protoliths. Textures indicating partial melting and minerals such as sanidine, mullite, tridymite and armalcolite strongly demonstrate that during the intrusion of the basic bodies the temperature reached 1,000-1,150?C, and was followed by quenching. Cooling of the interstitial melts has as consequences the closure of pores and decrease of the permeability of the protolith, which varies from about 17-11% in the unaffected rocks to zero in the thermally modified types. Although observed only at contacts and over small distances, the number of basic intrusions hosted within the Potiguar Basin in both onshore and offshore portions leaves opened the possibility of important implications of the thermal effects over the hydrocarbon exploration in this area as well in other Cretaceous and Paleozoic basins in Brazil / Pirometamorfismo ?gneo resulta de condi??es de altas temperaturas e baix?ssimas press?es provocadas pela coloca??o de corpos b?sicos hipabissais em encaixantes sedimentares ou metassedimentares. A Bacia Potiguar (NE do Brasil), em sua parte continental, oferece exemplos deste tipo de metamorfismo nas proximidades e contatos de plugs, soleiras e diques de diab?sios do Pale?geno e N?ogeno, intrusivos em arenitos e folhelhos da Forma??o A?u (Albiano-Cenomaniano). O efeito termal nestas rochas se reflete em texturas e associa??es minerais que caracterizam a f?cies sanidinito, com frequente fus?o parcial da matriz feldsp?tica a mic?cea. O l?quido formado pela fus?o ? pot?ssico e peraluminoso, formando um vidro riol?tico de cores variadas (incolor, amarelo, marrom) englobando microcristais de tridimita, clinoenstatita e sanidina, al?m de clastos de quartzo e raramente zirc?o, estaurolita e granada. Lentes de folhelho, intercaladas nos arenitos, cont?m cristalitos de Fe-cordierita (secanina?ta), mullita, sanidina, armalcolita (?xido de Fe e Ti) e espin?lio marrom. As rochas formadas devido ao efeito termal das intrus?es se chamam buchitos, sendo aqui descritos os tipos claros (prot?lito arenito e siltito feldsp?tico) e escuros (prot?lito folhelho escuro). Texturas indicativas de que houve fus?o parcial e minerais tais como sanidina, mullita, tridimita e armalcolita demonstram que foram atingidas temperaturas da ordem de 1000-1150?C, seguido por arrefecimento ultrarr?pido. O resfriamento do l?quido intersticial tem como consequ?ncia o fechamento de poros e a diminui??o da permeabilidade dos prot?litos, passando de 17-11% nas rochas n?o afetadas a zero naquelas mais transformadas. Apesar de essas rochas serem observadas apenas nos contatos ou a pouca dist?ncia dos mesmos, o grande n?mero de corpos b?sicos intrusivos na Bacia Potiguar, tanto na parte emersa como na por??o oce?nica, deixa em aberto a possibilidade de fortes implica??es do efeito termal na explora??o de hidrocarbonetos nesta ?rea como tamb?m em outras bacias cret?ceas e paleozoicas no Brasil
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/18840 |
| Date | 19 December 2013 |
| Creators | Santos, Larissa dos |
| Contributors | CPF:15603180404, http://lattes.cnpq.br/1259445348649589, Moraes, Renato de, CPF:06763320809, http://lattes.cnpq.br/3666520216687501, Souza, Zorano Sergio de |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Geodin?mica e Geof?sica, UFRN, BR, Geodin?mica; Geof?sica |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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