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Doctoral Thesis
DOI
10.11606/T.44.1986.tde-15072015-153916
Document
Author
Full name
Enio Soliani Junior
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1986
Supervisor
Committee
Jost, Hardy
Kawashita, Koji
Qualifik, Paul
Title in Portuguese
Os dados geocronológicos do escudo sul-rio-grandense e suas implicações de ordem geotectônica
Keywords in Portuguese
Geocronologia
Geotectônica
Abstract in Portuguese
Em base a 250 análises radiométricas pelos métodos K-Ar, Rb-Sr, Pb-Pb e Traços de Fissão, interpretadas em conjunto com o acervo geocronológico pré-existente, este trabalho subdivide o Escudo do Rio Grande do Sul em províncias tectônicas e procura estabelecer o posicionamento temporal dos grandes eventos geradores de rocha. Constata-se que o Ciclo Brasiliano parece ter perdurado por um intervalo de tempo maior do que o até então imaginado, tem do seus limites sido ampliados para 850 a 550 m.a., com eventos tardios de até 450 m.a.. Exposições de terrenos pré-brasilianos são conhecidas de forma restrita nos domínios do Escudo, sendo uma expressiva percentagem das áreas atribuídas ao Ciclo Brasiliano. Estas podem ser compartimentadas em duas entidades geotectônicas maiores: (1) o Batólito Pelotas, multi-intrusivo e polifásico, a leste, composto por suítes granitóides com idades de 850 a 550 m.a. e (2) sua Bacia Marginal, a oeste, representada por supracrustais dos tipos para e ortognaisses, metamáfica-ultramáficas e metavulcano-sedimentares, com idades K-Ar e Rb-Sr concentradas entre 760 e 640 m.a.. Intrusivas nesses termos litológicos, suítes graníticas polifásicas e seus correspondentes vulcânicos, às vezes intercalados a depósitos molassóides, desenvolveram-se no intervalo de 650 a 460 m.a.. Por fim, tenta-se o enquadramento do Escudo Sul-rio-grandense no contexto geológico do Brasil Meridional e Uruguai, sendo que o estabelecimento de um quadro cronoestratigráfico permite que se vislumbre um modelo de evolução regional segundo a Tectônica de Placas.
Title in English
Not available.
Keywords in English
Not available.
Abstract in English
Based om 250 new radiometric analyses using K-Ar, Rb-Sr, Pb-Pb and Fission Tracks methods, all of then interpreted with the eexisting geochronological data, this paper divides the Rio Grande do Sul Shield (Southern Brazil) into geotectonic provinces, as well as presents the ages that seem to be of the major rock generator events. It is suggested that the Brasiliano Cycle (Upper Precambrian) was active during a time interval greater than has been thought and its chronological limits could be extended fron 850 to 550 Ma with late and local magmatic episodes reaching the 450 Ma ago. Outcrops of Early Proterozoic or older terranes are rare, being the most areas related to the Late Proterozoic. These areas can be divided into two tectonic entities: (1) the Pelotas Batholit, a multi-intrusive and polyphase granitoid body, in the eastern shield, pointing out ages that range from 850 to 550 Ma and (2) its Marginal Basin in the west represented by supracrustal rocks such as gneisses, mafic-ultramafic and volcano-sedimentary equences showing a complex structural pattern and green schists to amphibolite metamorphic facies. Their K-Ar and Rb-Sr ages are mainly concentrated between 760 and 640 Ma, though values of 800 Ma may be found.Polyphase granitic suites and their volcanic correspondents, sometimes interbanded with molassoid sediments, are being attributed to the 650 - 450 Ma time interval.Finally, it tries to enclose the Rio Grande do Sul Shield in the regional geologic context (Southern Brazil and Uruguay), which is supposed to have developed in agreement with the Plate Tectonic concepts.
 
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Publishing Date
2015-07-20
 
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