Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)

BARRADAS, João Augusto da Silva

Dissertação

Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)

The studied area is located along the BR-010 Highway (Belém-Brasília) between the cities of Açailândia (MA) and Ligação do Pará (PA), in the southern part of the Bauxiti-bearing Province of Paragominas and has an extension of about 115 km. In it, two surfaces were distinguished, each one supported b...

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Autor principal:	BARRADAS, João Augusto da Silva
Grau:	Dissertação
Idioma:	por
Publicado em:	Universidade Federal do Pará 2022
Assuntos:	Rb-Sr Pb-Pb Galenas CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA GEOCRONOLOGIA E GEOQUÍMICA ISOTÓPICA GEOQUÍMICA E PETROLOGIA
Acesso em linha:	http://repositorio.ufpa.br:8080/jspui/handle/2011/14823

id	ir-2011-14823
recordtype	dspace
spelling	ir-2011-148232022-09-30T11:45:40Z Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo) BARRADAS, João Augusto da Silva LAFON, Jean Michel http://lattes.cnpq.br/4507815620234645 Rb-Sr Pb-Pb Galenas CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA GEOCRONOLOGIA E GEOQUÍMICA ISOTÓPICA GEOQUÍMICA E PETROLOGIA The studied area is located along the BR-010 Highway (Belém-Brasília) between the cities of Açailândia (MA) and Ligação do Pará (PA), in the southern part of the Bauxiti-bearing Province of Paragominas and has an extension of about 115 km. In it, two surfaces were distinguished, each one supported by a specific alteritic-sedimentary sequence. The highest surface corresponds to the tops of vast residual plateaus from 360 to 220 m in altitude and presents a slight slope to the north. The other surface, embedded in the first, culminates between 210 m, to the south, and 150 m, to the north, and shows a slight swell. The old lateritic-bauxitic cover supports the higher surface is constituted by a saprolitic horizon originating from the alteration of clayey or archosean sandstones and claystones from the “Itapecurú Deposits” of Cretaceous. On the saprolite rests a powerful armor, essentially ferruginous in the extreme south, which, towards the north, is progressively enriched in gibbsite. The first signs of bauxitic levels, still diffuse, are found about 40 km north of Açailândia. This trend is confirmed to the north with the presence of increasingly clear and consistent bauxitic horizons, above and at the base of the ferruginous horizon. Superimposed on this cover and in extremely sharp contact, there is a thick clay capping, the Belterra Clay. The lateritic-bauxitic cover developed in three phases. During the first phase, the ferruginous armor was formed through the ferruginization of the Itapecurú sediments, during the Lower Tertiary. Afterwards, the armor was affected by partial degradation and physical reworking of its products. Remains of older alterites may have also been involved in this process that resulted in deposition of nodular to pseudopisolithic gravel and sandy clay. The third phase, essentially chemical, consisted of the generation of bauxite in areas that presented more favorable climatic and geomorphological conditions. This event probably occurred at the end of the Eocene. The exclusively ferruginous lateritic armor that supports the lower surface has as substrate a reddish clayey sandstone containing small lateritic fragments and quartz pebbles. The cuirass itself has a massive, columnar or nodular structure, and the degraded stone-layer can be found in several places. Its cap is formed by a yellowish clayey-sandy material, rich in quartz grains and disseminated letheritic fragments. This laterite probably formed in the late Pliocene – early Pleistocene. Its substrate can be correlated with the Barreiras Group, while its capping would correspond to the unit called Post-Barreiras further north, in the Ipixuna-Aurora region. The stone-layers quite frequent in the area are located in the same stratigraphic position as the most recent lateritic armor and resulted from in situ degradation of this armor, without significant physical rework. However, locally, colluvial deposits of the glacis type or pediments composed of fragments of ancient armor were identified. The following stages characterized the evolution of the two alteritic-sedimentary sequences: 1- formation of a ferruginous armor from the Itapecurú Deposits; 2- partial degradation of the armor; 3- Bauxitization in the Paleogene; 4- deposition of sediments that later change to Belterra clay; 5- major erosive phase and individualization of vast plateaus; 6- filling of the valleys and lowered areas separating the plateaus by sandy-clay sediments correlated with the Barreiras Group and degradation products of the old armor; 7- ferruginization of the sediments from step 6; 8- more or less accentuated degradation of the ferruginous crust from stage 7, giving rise to stone-layers; 9- deposition of clayey-sandy sediments correlated with the Post-Barreiras on the armoring of stage 7 and the stone-layers; 10- dissection and establishment of the current drainage network. Climatic variations and periodic tectonic (epirogenetic) reactivations throughout the Cenozoic were the main factors responsible for this evolution. CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Este trabalho apresenta os resultados geocronológicos obtidos em rochas ígneas e mineralizações sulfetadas e auríferas da área de Monte do Carmo – Porto Nacional, centro-sul do Estado de Tocantins. Foram estudados o Granito Matança, o Granito Lajeado e um conjunto de rochas vulcânicas ácidas, até então sem denominação formal, através das metodologias Rb-Sr e Pb-Pb. A metodologia Pb-Pb também foi empregada na análise das galenas contidas em veios de quartzo auríferos. O Granito Matança forneceu uma idade Rb-Sr de 510 ± 15 Ma, com razão inicial de 0,71286 ± 59 (MSWD = 5,4). Este resultado pode ser interpretado seja como indicativo da época de cristalização do corpo granítico, caracterizando um magmatismo contemporâneo ao Evento Brasiliano, seja como a idade de reomogeneização isotópica durante este Evento. As razões isotópicas encontradas para o chumbo foram baixas e as pequenas variações entre elas favorecem a hipótese de uma idade do Proterozóico Superior para este corpo. Os pontos experimentais obtidos em rocha total e minerais de Granito Lajeado mostram-se fortemente dispersos no diagrama Rb-Sr, refletindo os processos de deformação cisalhante e de alteração hidrotermal ocorridos na região. O melhor indicativo de idade, obtido com as amostras mais preservadas, corresponde a 1741 ± 54 Ma, com razão inicial de 0,72184 ± 249 (MSWD = 6). Pelo método Pb-Pb foram analisadas amostras de rocha total e feldspato, resultando em uma idade isocrônica de 1999 ± 32 Ma (MSWD = 1,5), interpretada como a idade de cristalização do Granito Lajeado. As rochas vulcânicas ácidas mostram um comportamento similar ao do Granito Lajeado. Os dados Rb-Sr são marcados por forte dispersão no diagrama isocrônico devido aos processos deformacionais e hidrotermais tardios. O método Pb-Pb, por outro lado, permitiu determinar a idade de cristalização dessas rochas em 2028 ± 103 Ma (MSWD = 2,5). A similaridade entre os resultados Pb-Pb do Granito Lajeado e das rochas vulcânicas ácidas permite supor que estas unidades litológicas são geneticamente relacionadas. As galenas da área de Monte do Carmo foram analisadas pelo método Pb-Pb. Oito amostras alinharam-se em um diagrama 207Pb/204Pb versus 206Pb/204Pb com uma inclinação de 0,151301 ± 4186 (MSWD = 1,1). Esses dados foram interpretados como uma equação de mistura e a combinação da linha das galenas com a curva de crescimento de CUMMING & RICHARDS (1975) permitiu definir a idade de mineralização em 550 Ma e a sua origem de um material fonte com idade em torno de 2,1 Ga. 2022-09-30T11:45:21Z 2022-09-30T11:45:21Z 1994-05-10 Dissertação BARRADAS. João Augusto da Silva. Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo). Orientador: Jean Michel Lafon. 1993. 69 f. Dissertação (Mestrado em Geoquímica e Petrologia) - Programa de Pós-Graduação em Geologia e Geoquímica. Centro de Geociências, Universidade Federal do Pará, Belém, 1993. Disponível em: http://repositorio.ufpa.br:8080/jspui/handle/2011/14823. Acesso em:. http://repositorio.ufpa.br:8080/jspui/handle/2011/14823 por Acesso Aberto Attribution-NonCommercial-NoDerivs 3.0 Brazil http://creativecommons.org/licenses/by-nc-nd/3.0/br/ application/pdf Universidade Federal do Pará Brasil Instituto de Geociências UFPA Programa de Pós-Graduação em Geologia e Geoquímica 1 CD-ROM
institution	Repositório Institucional - Universidade Federal do Pará
collection	RI-UFPA
language	por
topic	Rb-Sr Pb-Pb Galenas CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA GEOCRONOLOGIA E GEOQUÍMICA ISOTÓPICA GEOQUÍMICA E PETROLOGIA
spellingShingle	Rb-Sr Pb-Pb Galenas CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA GEOCRONOLOGIA E GEOQUÍMICA ISOTÓPICA GEOQUÍMICA E PETROLOGIA BARRADAS, João Augusto da Silva Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
topic_facet	Rb-Sr Pb-Pb Galenas CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA GEOCRONOLOGIA E GEOQUÍMICA ISOTÓPICA GEOQUÍMICA E PETROLOGIA
description	The studied area is located along the BR-010 Highway (Belém-Brasília) between the cities of Açailândia (MA) and Ligação do Pará (PA), in the southern part of the Bauxiti-bearing Province of Paragominas and has an extension of about 115 km. In it, two surfaces were distinguished, each one supported by a specific alteritic-sedimentary sequence. The highest surface corresponds to the tops of vast residual plateaus from 360 to 220 m in altitude and presents a slight slope to the north. The other surface, embedded in the first, culminates between 210 m, to the south, and 150 m, to the north, and shows a slight swell. The old lateritic-bauxitic cover supports the higher surface is constituted by a saprolitic horizon originating from the alteration of clayey or archosean sandstones and claystones from the “Itapecurú Deposits” of Cretaceous. On the saprolite rests a powerful armor, essentially ferruginous in the extreme south, which, towards the north, is progressively enriched in gibbsite. The first signs of bauxitic levels, still diffuse, are found about 40 km north of Açailândia. This trend is confirmed to the north with the presence of increasingly clear and consistent bauxitic horizons, above and at the base of the ferruginous horizon. Superimposed on this cover and in extremely sharp contact, there is a thick clay capping, the Belterra Clay. The lateritic-bauxitic cover developed in three phases. During the first phase, the ferruginous armor was formed through the ferruginization of the Itapecurú sediments, during the Lower Tertiary. Afterwards, the armor was affected by partial degradation and physical reworking of its products. Remains of older alterites may have also been involved in this process that resulted in deposition of nodular to pseudopisolithic gravel and sandy clay. The third phase, essentially chemical, consisted of the generation of bauxite in areas that presented more favorable climatic and geomorphological conditions. This event probably occurred at the end of the Eocene. The exclusively ferruginous lateritic armor that supports the lower surface has as substrate a reddish clayey sandstone containing small lateritic fragments and quartz pebbles. The cuirass itself has a massive, columnar or nodular structure, and the degraded stone-layer can be found in several places. Its cap is formed by a yellowish clayey-sandy material, rich in quartz grains and disseminated letheritic fragments. This laterite probably formed in the late Pliocene – early Pleistocene. Its substrate can be correlated with the Barreiras Group, while its capping would correspond to the unit called Post-Barreiras further north, in the Ipixuna-Aurora region. The stone-layers quite frequent in the area are located in the same stratigraphic position as the most recent lateritic armor and resulted from in situ degradation of this armor, without significant physical rework. However, locally, colluvial deposits of the glacis type or pediments composed of fragments of ancient armor were identified. The following stages characterized the evolution of the two alteritic-sedimentary sequences: 1- formation of a ferruginous armor from the Itapecurú Deposits; 2- partial degradation of the armor; 3- Bauxitization in the Paleogene; 4- deposition of sediments that later change to Belterra clay; 5- major erosive phase and individualization of vast plateaus; 6- filling of the valleys and lowered areas separating the plateaus by sandy-clay sediments correlated with the Barreiras Group and degradation products of the old armor; 7- ferruginization of the sediments from step 6; 8- more or less accentuated degradation of the ferruginous crust from stage 7, giving rise to stone-layers; 9- deposition of clayey-sandy sediments correlated with the Post-Barreiras on the armoring of stage 7 and the stone-layers; 10- dissection and establishment of the current drainage network. Climatic variations and periodic tectonic (epirogenetic) reactivations throughout the Cenozoic were the main factors responsible for this evolution.
author_additional	LAFON, Jean Michel
author_additionalStr	LAFON, Jean Michel
format	Dissertação
author	BARRADAS, João Augusto da Silva
title	Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
title_short	Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
title_full	Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
title_fullStr	Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
title_full_unstemmed	Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)
title_sort	geocronologia das rochas ígneas e mineralizações auríferas associadas da porção centro sul do estado de tocantins (região de porto nacional – monte do carmo)
publisher	Universidade Federal do Pará
publishDate	2022
url	http://repositorio.ufpa.br:8080/jspui/handle/2011/14823
_version_	1787148569079185408
score	11.653393

Geocronologia das rochas ígneas e mineralizações auríferas associadas da porção Centro Sul do Estado de Tocantins (Região de Porto Nacional – Monte do Carmo)

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