Ocorrência e Significado dos Septos do Embasamento Encontrados nas Suítes Graníticas do Batólito Pelotas, RS, Brasil

The Pelotas Batholith situated in the eastern part of Sul-rio-grandense Shield is NE oriented and has dimensions of about 400 x 120 km. It is a granitic belt with six main suites: Pinheiro Machado Suite, Erval Suite, Viamão Suite, Encruzilhada do Sul Suite, Cordilheira Suite and Dom Feliciano Suite. The development of a continental collision whose evolution started by the end of Neoproterozoic, 635-610Ma, and reached 550Ma, is registered in the granitic suites. Most granitoids are syn to late-collisional, which have their emplacement controlled initially by low- to mid-angle shear zones and lately by sub-vertical transcurrent shear zones. The last magmatic events produced alkaline and peralkaline granites and composite (acid and basic) dike swarms represent a postcollisional magmatism.During their ascension and emplacement these granitic units captured basement xenoliths sometimes with dimensions of several kilometers. Based upon petrographic, geochemical and structural data these xenoliths were compared with the metamorphic units that occur outside the batholith. Their similarity suggest that the batholith, in spite of being limited by shear zones, is very close to its original setting. The interaction of xenoliths with the granitic magma produced primary structures that reflect the conditions during the ascent and emplacement of granitic bodies and contribute to the understanding of the geotectonic evolution in the eastern part of Sul-rio-grandense Shield

Tectonic evolution of the Dom Feliciano Belt in Southern Brazil : geological relationships and U-Pb geochronology

O Cinturão Dom Feliciano, que se estende desde o leste do Uruguai até o sul do Brasil, representa um importante orógeno Neoproterozoico formado pela colagem de domínios oceânicos e fragmentos continentais entre os crátons Rio de La Plata, Congo e Kalahari. A integração de dados de mapeamento geológico e estrutural com resultados isotópicos permitu estabelecer uma melhor compreensão sobre as fontes de magmatismo e os processos de sedimentação. A evolução do Cinturão Dom Feliciano envolveu a superposição de três eventos orogênicos denominados Passinho (0.89 - 0.86 Ga), São Gabriel (0.77 - 0.68 Ga) e Dom Feliciano (0.65 - 0.54 Ga). Os dois primeiros eventos envolvem o fechamento do oceano Charrua com a geração inicial de um arco intra-oceânico (Passinho) e, posteriormente, de um arco continental (São Gabriel). Esse oceano separava as áreas continentais representadas pelo cráton Rio de La Plata e a microplaca continental Nico Perez. No terceiro evento ocorreu fechamento do oceano Adamastor em decorrência da colisão entre os crátons Rio de La Plata e Kalahari entre 650 - 620 Ma, envolvendo condições metamórficas de alta temperatura e pressão intermediária. Neste momento de grande espessamento crustal, a partição da deformação no cinturão controla a sua evolução final com a passagem para uma tectônica de escape, responsável pela nucleação de zonas de cisalhamento transcorrentes de escala crustal. Essas estruturas são profundas e promoveram a geração e a ascenção de magmas máficos, que, associados ao elevado gradiente térmico regional, induziram um extenso evento de retrabalhamento crustal, responsável pela formação do Batólito Pelotas. O colapso do orógeno é representado pelo magmatismo tardio do batólito e pela formação das sequências superiores da Bacia do Camaquã.The Dom Feliciano Belt is an important Neoproterozoic to Cambrian orogenic complex, extending from eastern Uruguay to southern Brazil. It comprises a collage of oceanic domains and continental fragments developed between 900 and 540 Ma between the Rio de La Plata, Congo and Kalahari cratons. The integration of field and structural data with recent isotopic results has introduced new insights on the sources of the magmatism and sedimentary processes. This paper presents a review of the geochronological results combined with stratigraphic, structural and geochemical data. The evolution of the Dom Feliciano Belt involved three orogenic events known as the Passinho (0.89 - 0.86 Ga), São Gabriel (0.77 - 0.68 Ga) and Dom Feliciano (0.65 - 0.54 Ga). The first two events involved the closure of the Charrua Ocean generating an intra-oceanic arc (Passinho) and, subsequently, an active continental margin arc (São Gabriel). This ocean separated the continental areas represented by the Rio de la Plata Craton and the Nico Perez continental microplate. Closure of the Adamastor ocean resulted in an important collisional event between the Nico Perez Microplate/Rio de La Plata Craton and Kalahari and Congo cratons between 650 and 620 Ma, involving high T/intermediate P metamorphism. At this time of crustal thickening, the partition of the deformation controled the final evolution of the belt with important escape tectonics, responsible for nucleating crustal-scale transcurrent shear zones. These structures were deep and promoted the rise of mafic magmas, which, associated with high regional thermal gradient, lead to an important event of crustal reworking, responsible for the formation of the Pelotas Batholith. The orogenic collapse is represented by late magmatism of Pelotas Batholith and deposition of upper section of the Camaquã Basin

Geology and tectonic significance of the metavulcano-sedimentary rocks of the Coxilha do Batovi Complex, Dom Feliciano Belt (São Gabriel, RS).

O Complexo Coxilha do Batovi (CCB) é uma sequência metavulcanossedimentar de idade pré-cambriana exposto em uma janela estrutural ao sul da cidade de São Gabriel.  Para entender a evolução estrutural do complexo foi realizado um estudo integrado de estratigrafia, sedimentologia, análise petrográfica, geologia estrutural e petrologia metamórfica. O CCB está situado no extremo sudoeste do limite do Terreno Taquarembó, sobre a Zona de Cisalhamento Ibaré de direção NW-SE.  É composto por meta-arenitos quartzíticos e arcoseanos finos a médios e metapelitos, com mármores, rochas metavulcânicas, formações ferríferas bandadas e metagranitos subordinados. As rochas do CCB registram uma complexa trama estrutural, resultante de uma história de deformação progressiva associada a um metamorfismo orogênico de baixo grau, na fácies Xistos Verdes. A espessura original do pacote sedimentar está multiplicada pela ação de dobras isoclinais e pela transposição da xistosidade principal. Em porções menos deformadas observa-se estratificação plano-paralela, cruzada acanalada e cruzada planar de baixo ângulo. Os perfis colunares levantados sugerem uma sequência de sedimentos progradantes caracterizados por sedimentos siliciclásticos quartzosos e carbonáticos depositados provavelmente em um ambiente deltaico em uma bacia intracratônica ou de margem passiva. A deformação do complexo resulta de um encurtamento regional de direção NE-SW, cuja máxima atuação da deformação gerou a Zona de Cisalhamento Ibaré.The Coxilha do Batovi Complex (CCB) is a Precambrian metavolcano-sedimentary sequence, exposed in a structural framework south of the town of São Gabriel. To understand the structural evolution of the complex, an integrated study of stratigraphy, sedimentology, petrographic analysis, structural geology and metamorphic petrology was carried out. The CCB is located at the southwestern end of the Taquarembó Terrane boundary, over the NW-SE direction Ibaré Shear Zone. The CCB is composed of fine to medium quartzitic and arkosean meta-sandstones and metapelites, with a subordinate occurrence of marbles, metavolcanic rocks, banded iron formations and metagranites. The rocks of the CCB record a complex structural fabric, resulting from a long history of progressive deformation associated to a low grade orogenic metamorphism, of greenschist facies conditions. The original thickness of the sedimentary package is multiplied by the action of isoclinal folds and by the crenulation and transposition of the main schistosity. In less deformed portions, are preserved primary structures such as plane-parallel stratification, trough cross-bedding, and low-angle planar cross-bedding. The measured and interpreted columnar profiles suggest a prograding sequence, composed of a thick package of meta-sandstones that grade to a rhythmic intercalation with metapelites superimposed by another thick package of meta-sandstones. The CCB rocks represent quartzitic and carbonate siliciclastic sediments likely deposited in a delta environment in an intracratonic or passive margin basin. The rocks of the complex are deformed by the action of a regional shortening of NE-SW direction, associated with the formation of foliations S1 and S2, whose maximum deformation performance generated the Ibaré Shear Zone

Contribuição ao magmatismo granítico brasiliano da região de Porto Alegre - RS

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Análise e Avaliação dos Problemas Existentes no Revestimento da Cúpula da Catedral Metropolitana de Porto Alegre, RS

The Metropolitan Cathedral of Porto Alegre, in Rio Grande do Sul state, was designed by roman architect João Batista Giovenalle. This construction was developed in a long time between 1921 and 1986. The external building design has a match of granite and marble. In the body of the church was used rose granite extracted from a quarry located in Porto Alegre. Its imposing dome has covering of siliceous dolomitic marble drew out from quarry of Espírito Santo state. Originally the author of the project planned to recover this architectural element with copper, but this material was replaced by marble due to financial difficulties. However it wasn’t planned the necessary suitableness structures to perfect operation of this new material and resulted in a series of pathologies that damaged its aesthetic satisfactory design and the own building.The Metropolitan Cathedral of Porto Alegre, in Rio Grande do Sul state, was designed by roman architect João Batista Giovenalle. This construction was developed in a long time between 1921 and 1986. The external building design has a match of granite and marble. In the body of the church was used rose granite extracted from a quarry located in Porto Alegre. Its imposing dome has covering of siliceous dolomitic marble drew out from quarry of Espírito Santo state. Originally the author of the project planned to recover this architectural element with copper, but this material was replaced by marble due to financial difficulties. However it wasn’t planned the necessary suitableness structures to perfect operation of this new material and resulted in a series of pathologies that damaged its aesthetic satisfactory design and the own building

Avaliação Tecnológica e Aproveitamento dos Granitos e Sienitos da Região de Encruzilhada do Sul e Cachoeira do Sul, RS - Brasil

The areas of Encruzilhada do Sul and southern part of Cachoeira do Sul are the main producers of ornamental rocks in the Rio Grande do Sul State, south Brazil. Granite and syenitic rocks are exploited in this region, being consumed by the national market and exported for countries such as Japan, Italy, Germany and United States. In spite of long tradition in the extraction of ornamental rocks, the knowledge about their quality is almost totally empiric. This work presents the first results of laboratory tests for the technological characterization of five types of granites and two types of syenites in the studied area. The studies involved petrography, determination of physicals indexes, impact resistance, flexural resistance, abrasive waste (AMSLER), thermal dilatation coefficient and brightness. The selected samples also exhibited with the range of values found for the granites and syenites extracted in others states of Brazil. The results of the technological characterization tests assure the quality of granites and syenites extracted in Rio Grande do Sul, stimulating the investments in an activity of crescent economic importance.

Reavaliação e novos dados Geocronológicos (Ar/Ar, Rb/Sr e Sm/Nd) do Batólito Pelotas no Rio Grande do Sul: implicações Petrogenéticas e Idade de Reativação das Zonas de Cisalhamento

SHRIMP and conventional U-Pb and Pb/Pb evaporation dating of zircon from the Pelotas batholith indicates one group of ages between 625 and 633 Ma for the Pinheiro Machado suite, and another group between 575 and 599 Ma for the Viamão, Encruzilhada do Sul and Dom Feliciano suites. Sr87/Sr86 isotopic ratios of 0.7060 - 0.7016, µNd values of -5 and -10, and Nd T DM model ages between 2200 and 1600 Ma suggest that the suites were mainly derived by melting of Paleoproterozoic crust formed during the Tranzamazonic Cycle. Basic magmatism and heterogeneous magma mixing in the Pinheiro Machado, Viamão, Encruzilhada do Sul and Dom Feliciano suite and the Piquiri alkaline magmatism, with Pb/Pb zircon evaporation ages between 610 and 615 Ma, suggest that a mantle component also contributed to the formation of the Pelotas batholith. 39Ar/40Ar determinations in micas from mylonitic rocks of high and low-dip shear zones showed ages between 540 and 530 Ma, which show that important tectonic events occurred after the emplacement of the batholith. This event developed in a tranpressive regime, was responsible for the reactivation of older shear zones, and was probably contemporaneous with the development of the Camaquã basin.O Batólito Pelotas é constituído por suítes graníticas com idades U/Pb (em zircão, Evaporação e SHRIMP) e Pb/Pb (em zircão, por evaporação) situadas no intervalo de 575 a 633 Ma, com um padrão de idade mais antigo entre 625 e 635 Ma (Suíte Pinheiro Machado) e outro mais novo entre 575 e 600 Ma (Suítes Viamão, Encruzilhada do Sul e Dom Feliciano). As razões isotópicas Sr87/Sr86 situadas entre 0,7060 a 0,7016, juntamente com valores de µNd fortemente negativos (em geral, entre -5 a -10) e idades modelos T DM (entre 1600 e 2200 Ma), indicam a predominância de processos de reciclagem de materiais de uma crosta provavelmente Paleoproterozóica (Ciclo Transamazônico). Por outro lado, a presença de magmatismo básico e feições de misturas de magmas nas Suítes Pinheiro Machado, Viamão, Encruzilhada e Dom Feliciano associados com magmatismo alcalino (Sienito Piquiri), com idade Pb/Pb (em zircão, por evaporação) entre 610 e 615 Ma, sugerem também contribuição mantélica na constituição do batólito. As idades Ar/Ar aqui obtidas a partir de rochas miloníticas de zonas de cisalhamento (de baixo e alto ângulo) que afetam o batólito sugerem a existência de um importante evento tectônico ocorrido entre 540 e 530 Ma. Este evento teria sido responsável pela reativação em regime transpressivo de zonas de cisalhamento mais antigas, relacionadas com a colocação das suítes graníticas do batólito, e geração de estruturas-em-flor positiva em vários domínios do mesmo. Esta tectônica parece se articular no espaço e no tempo com a tectônica extensional relacionada com a instalação da Bacia do Camaquã

Sandstone-filled normal faults : A case study from central California

We acknowledge the support of sponsoring companies of Phase 3 of the Sand Injection Research Group (SIRG). We would like to thank Chris Morley and another anonymous reviewer for constructive comments, and the editor for efficient handling of this paper. We also wish to thank and acknowledge the continuing help and access provided by the Bureau of Land Management and in particular Greg Middleton without whose enthusiasm and support our research would have been much more challenging.Peer reviewedPostprin

Análise tectônica e sedimentar da borda sudeste da Bacia do Paraná a partir de dados de estratigrafia de sequencia : Parte I - área de Candiota

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Multiple episodes of sand injection leading to accumulation and leakage of hydrocarbons along the San Andreas/San Gregorio fault system, California

Acknowledgements We acknowledge the reviews of three anonymous referees and are also very grateful to Andrew Hurst and David Iacopini for their critical comments of an earlier version of the paper. We also wish to thank Denis Bureau and Antonella Gatto for their support in the field.Peer reviewedPostprin