| Texto completo | |
| Autor(es): |
Gomes, Celso de Barros
;
Comin-Chiaramonti, Piero
;
Azzone, Rogerio Guitarrari
;
Ruberti, Excelso
;
Enrich Rojas, Gaston Eduardo
Número total de Autores: 5
|
| Tipo de documento: | Artigo Científico |
| Fonte: | BRAZILIAN JOURNAL OF GEOLOGY; v. 48, n. 2, p. 29-pg., 2018-04-01. |
| Resumo | |
This paper reviews general aspects of alkaline-carbonatitic rocks of Brazilian, Paraguayan and Bolivian terrains. Although 30 such occurrences are known in literature, only the major ones have been thoroughly investigated. The carbonatites are of Cretaceous age, with two well-defined Lower Cretaceous and Upper Cretaceous generation episodes. A clear tectonic control by ancient structural features such as archs, lineaments and faults characterizes most cases. The rocks exhibit a large compositional variation, in decreasing orders of abundance from calciocarbonatites to magnesiocar-bonatites to ferrocarbonatites. In some complexes, they form multistage intrusions. C-O isotopes indicate that, in general, the carbonatites were affected by post-magmatic processes associated with the topographic level of emplacement and low-temperature H2O-CO2 rich fluids responsible for the increased amount of heavy carbon and oxygen. Sr-Nd isotopic compositions similar to those of coeval alkaline silicate rocks, ranging from depleted to enriched mantle sources, have been influenced by two distinct metasomatic events in Proterozoic at 2,0-1.4 Ga and 1.0-0.5 Ga. Sr-Nd-Pb-Os data seem related to an isotopically enriched source, their chemical heterogeneities reflecting a depleted mantle that was metasomatized by small-volume melts and by fluids rich in incompatible elements. Fractional crystallization and liquid immiscibility are believed to be the most effective processes in the formation of the Cretaceous carbonatites, with minor contribution of crustal contamination. Pb isotopic ratios yield evidence that HIMU and EM I mantle components played an important role in the genesis of the carbonatitic magma. (AU) | |
| Processo FAPESP: | 16/23399-4 - O magmatismo alcalino: investigações petrológicas e geoquímicas |
| Beneficiário: | Celso de Barros Gomes |
| Modalidade de apoio: | Auxílio à Pesquisa - Regular |
| Processo FAPESP: | 12/06082-6 - A província magmática Paraná-Etendeka no Brasil: relações temporais e petrológicas entre o magmatismo toleítico e alcalino e suas implicações geodinâmicas |
| Beneficiário: | Excelso Ruberti |
| Modalidade de apoio: | Auxílio à Pesquisa - Temático |
| Processo FAPESP: | 17/03768-8 - A influência composicional de xenocristais e antecristais em magmas básicos a ultrabásicos alcalinos |
| Beneficiário: | Rogério Guitarrari Azzone |
| Modalidade de apoio: | Auxílio à Pesquisa - Regular |