Título:	Petrografia, geoquímica e geocronologia das rochas vulcânicas efusivas e piroclásticas da formação arraias, grupo araí, nordeste de Goiás
Autor(es):	Silva, Cleverton Correia
Orientador(es):	Souza, Valmir da Silva
Coorientador(es):	Botelho, Nilson Francisquini
Assunto:	Vulcanismo Rochas vulcânicas
Data de defesa:	13-mar-2020
Referência:	SILVA, Cleverton Correia. Petrografia, geoquímica e geocronologia das rochas vulcânicas efusivas e piroclásticas da formação arraias, grupo araí, nordeste de Goiás.119 f., il. 2020. Tese (Doutorado em Geologia)—Universidade de Brasília, Brasília, 2020.
Abstract:	Located in the northern portion of the Brasília Belt, the Araí Group presents in the Arraias Formation a voluminous register of volcanic rocks interbedded with quartzites, etasandstones, breccia, and metaconglomerates. The rocks of this group are located on the peraluminous granites of the Aurumina Suite and the schist of the Ticunzal Formation, and, together with the anorogenic granites of the Pedra Branca Province, they compose one of the most complete and well-preserved records of the development of a rift intracontinental, which started during the Estateriano, in the central region of Brazil. Due to the excellent degree of preservation of the original structures and textures, it was possible to recognize at least three distinct volcanic events: pyroclastic, felsic effusive and mafic effusive. The pyroclastic deposits occupy extensive areas of the Araí Group and are classified as flow pyroclastic deposits (ignimbrites) with thicknesses that reach up to 100 m. The felsic effusive rocks are porphyritic, as for the appearance of quartz and feldspar phenocrysts, with corrosion gulfs, immersed in their aphanitic matrix. These rocks are acidic (66.10% to 76.60% SiO2), and have varied contents of Al2O3 (10.79 wt.% to 14.25 wt.%), Ca (0.03 wt.% to 1.95 wt.%) and ΣK2O+Na2O (2.63 wt.% to 8.23 wt.%). They have affinities with the rocks of the alkaline and sub-alkaline series and are classified as peraluminous dacite, rhyolite, alkali rhyolite, and trachyte. In a diagram normalized by the chondrite, these acid rocks are enriched in LREE in relation to heavy HREE, with their expressive negative Eu anomalies (Eu/Eu * = 0.26 to 0.53) indicating an important fractionation of feldspars. In the diagrams for tectonic settings, for example, Rb versus Y + Nb, the set of acid volcanic rocks of the Araí Group exhibits affinities with those generated in a within-plate and/or post-collisional setting. Mafic volcanism, in turn, is composed of basic aphanitic rocks (49.72 wt.% to 54.70 wt.% SiO2), whose colorings vary from greenish-gray, dark gray to brownish-gray, and contain vesicles filled with silica. Classified as basalt, alkaline basalt, andesitic basalt and trachybasalt, these rocks are formed essentially by plagioclase and clinopyroxene, the latter being replaced by tremolite-actinolite. They have varied contents of MgO (5.29 wt.% to 7.17 wt.%) CaO (6.49 wt.% to 9.98 wt.%), K2O (0.60 wt.% to 2.53 wt.%), Na2O (1.88 wt.% to 3.59 wt.%), TiO2 (0.65 wt.% to 1.51 wt.%), Ni (68 to 140 ppm) and V (112 to 240 ppm). In the diagram for REE normalized by the chondrite, exhibit a strong enrichment of LREE compared to HREE, with little pronounced anomalies of Eu (0.80 to 0.99), when normalized by the primitive mantle, these rocks exhibit positive anomalies of Ba, Pb, Nd, and negative anomalies of Rb, Nb, Sr, and Ti. εNd (T) values, ranging from -6.78 to -4.89, for a crystallization age of 1.78 Ga, reinforce the importance of the contamination of the magmas responsible for the generation of basalts with continental crust rocks, common in regions attenuated continental crust, as in the case of the Araí Intracontinental Rift.
Unidade Acadêmica:	Instituto de Geociências (IG)
Informações adicionais:	Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2020.
Programa de pós-graduação:	Programa de Pós-Graduação em Geologia
Licença:	A concessão da licença deste item refere-se ao termo de autorização impresso assinado pelo autor com as seguintes condições: Na qualidade de titular dos direitos de autor da publicação, autorizo a Universidade de Brasília e o IBICT a disponibilizar por meio dos sites www.bce.unb.br, www.ibict.br, http://hercules.vtls.com/cgi-bin/ndltd/chameleon?lng=pt&skin=ndltd sem ressarcimento dos direitos autorais, de acordo com a Lei nº 9610/98, o texto integral da obra disponibilizada, conforme permissões assinaladas, para fins de leitura, impressão e/ou download, a título de divulgação da produção científica brasileira, a partir desta data.
Aparece nas coleções:	Teses, dissertações e produtos pós-doutorado

Os itens no repositório estão protegidos por copyright, com todos os direitos reservados, salvo quando é indicado o contrário.