Analise da deformação regional e mineral do complexo Pedra Branca (CE) e de seus depositos cromiferos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

This work is an analysis of the deformation and metallogenetic aspects of an are a in the central portion of Ceara State. The area is located in the Pedra Branca Complex and it consists of TTG-type sequences containing several metamafic and metaultramafic bodies, some of which contain chromitite with PGE.The microstructural studies have shown that the deformation of granitic composition rocks observed in minerals such as, quartz, micas and feldspars, do not have any record of preterit deformation. On the other hand, mainly because of their reological properties, metamafic rocks show evidence of prior deformation, as was seen in hornblendes and plagioclases. Based on the field work and optical microscopic observations, three deformational events have been established: the first (D1), is characterized by gneissic banding and mineral lineation (N90), probably of Archean age. The second (D2), and more important, is characterized by a tangencial tectonics that produced a low-angle foliation and mineral lineation (N1O) during the Proterozoic. Th_ third (D3), was pos-metamorphic and produced gentle folds and brittle-ductile structures. A number of chromite occurrences have been recorded in association with the ultramafic rocks of the Pedra Branca Complexo They occur as pods or lenses of variable dimensions. Textural and deformational features show that they were not affeted by the main tectonic events. The chemical results show that the chromitites of the two districts (Esbarro and Trapia) are generated in same magmatic condition. In the Esbarro district, the ore contains pt and Pd alloys and Pt-Pd-bearing sulphides. The obtained geochemical data and a comparision with other chromite deposits show that Pedra Branca chromites are of stratiform type. Neverthless, the pods of chromitites are parallel with the strike of the D2 mineral lineation, which plays an important role in the structural control of the mineralization

ASSUNTO(S)

rochas - deformação rochas metamorficas geologia estrutural

ACESSO AO ARTIGO

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