Banca de DEFESA: ALEXANDRE RANIER DANTAS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ALEXANDRE RANIER DANTAS
DATA : 10/02/2017
HORA: 15:00
LOCAL: Sala 1 (PPGG/UFRN)
TÍTULO:

PETROGRAPHY AND LITHOCHEMISTRY OF FERRIFEROUS ROCKS IN RIO GRANDE DO NORTE CENTRAL REGION (RIO PIRANHAS SERIDÓ DOMAIN, BORBOREMA PROVINCE NORTHEST)

PALAVRAS-CHAVES:

Iron formations, petrography, lithochemistry, Seridó Belt

PÁGINAS: 103
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

Ferriferous rocks occurrences in Rio Grande do Norte central region essentially correspond to small deposits without apparent economic potential. In contrast, during the last years, small deposits of this mineral has been well exploited in some areas of the region, especially within the Rio Piranhas-Seridó Domain. The iron formations occur as decimeters to tens of meters layers intercalated with the Jucurutu Formation gneiss, at the base of Seridó Group metavolcano-sedimentary sequence. They may be associated, but less frequently, with metamafic rocks hosted in the gneiss and possible orthoderived metamorphic rocks from Caico Complex. Systematic mapping at the scales of 1:100,000 (Lajes and Currais Novos geological maps) and mineral resources survey carried out by the Companhia de Pesquisa de Recursos Minerais (CPRM) identified a significant amount of mineral occurrences (registered 48 occurrences of ferriferous rocks). In this work will be performed a macroscopic and microscopic petrographic characterization of thin sections, bipolid and polished sections of banded iron rocks, besides the discussion of lithochemistry data by analyzing the major elements, trace signing and rare earth elements to defining protolith and tectonic environment, where appropriated, as well as the use of MEV-EDS to study the qualitative chemical composition of magnetites and amphiboles. Basically, these rocks are composed of quartz, iron oxides and hydroxides, amphibole (cummingtonite-grunerite and actinolite-tremolite series), fine- to medium grained and granonematoblastic texture, sometimes with compositional banding. They are formed by Fe2O3 content ranging between 46 and 59% and SiO2 content ranging between 33 and 50%. Petrographically it was identified two distinct groups: homogeneous ferriferous rocks and banded iron rocks. The lithochemistry permited to conclude that groups of homogeneous and banded iron rocks sometimes present a similar behavior, sometimes not. The bimodal rocks are mainly composed of Si and Fe, with small proportion of trace and rare earths elements. The chemical parameters indicate dominantly oxidant environment and groups of rocks at intermediate positions closest to the oceanic hydrothermal vents. As for the nature of the formation of the iron rocks, binary graphs with the relations between Th, Zr and Ti in ppm allowed to identify that they are chemically pure rocks, with few levels of terrigenous. While binary diagrams of SiO2 and Al2O3 in % of weight and Al-Fe-Mn ternaries indicate that all samples of ferriferous banded and granular formations form hydrothermal chemical-exhalation sediments. Specific diagrams for the identification of the tectonic environments for the formation of granular iron rocks and banded iron rocks studied in the Faixa Seridó indicate mainly oceanic chains located next to active continental margins transitional to island arches. The iron formation study is important not only because it is the most economical source of iron in the rocks, but is particularly essential to understanding the atmospheric evolution and to the oceanic chemical composition in the period of their deposition.

MEMBROS DA BANCA:
Presidente - 1513243 - MARCOS ANTONIO LEITE DO NASCIMENTO
Externo ao Programa - 1298966 - RAQUEL FRANCO DE SOUZA
Externo à Instituição - VLADIMIR CRUZ DE MEDEIROS - SGB