UNIVERSIDADE DE BRASÍLIA - INSTITUTO DE GEOCIÊNCIAS

DISSERTAÇÃO DE MESTRADO N^o 75

DATA DE DEFESA: 21/02/92
ÁREA DE CONCENTRAÇÃO: PROSPECÇÃO E GEOLOGIA ECONÔMICA
ORIENTADOR: PROF. REINHARDT ADOLFO FUCK (UnB)
EXAMINADORES: PROF. HARDY JOST (UnB)
PROF. MARIA ÂNGELA F. CANDIA (USP)

RESUMO

A sequência vulcano-sedimentar Juscelândia está localizada na parte central do Estado de Goiás, fazendo parte do Complexo Barro Alto.
Ela é constituída por metassedimentos (xistos pelíticos), metavulcânicas representantes de um vulcanismo bimodal, havendo predominância das rochas metabásicas (anfibolitos) e ortognaisses. Todas as rochas foram metamorfizadas na facies anfibolito.
Na área em estudo foram caracterizadas quatro fases de deformação. As duas primeiras fazem parte de um evento progressivo, enquanto as duas tardias estão relacionadas com a geração de dobras abertas associadas a retrometamorfismo xisto verde.
A litogeoquímica dos anfibolitos mostra que seus protolitos foram rochas subalcalinas, de filiação toleítica e com características de basaltos transicionais (MORBS tipo T.). É sugerida uma geração em ambiente de bacias de retro-arco (back-arc basin).

RENATO DE MORAES

METAMORPHISM AND DEFORMATION OF THE JUSCELÂNDIA VOLCANO-SEDIMENTARY SEQUENCE, GOIÁS STATE-BRAZIL, AND THE GEOCHEMISTRY OF ITS AMPHIBOLITES

DATE OF ORAL PRESENTATION: 21/02/92
TOPIC OF THE THESIS: PROSPECTION AND ECONOMIC GEOLOGY
SUPERVISOR: PROF. REINHARDT ADOLFO FUCK (UnB)
COMMITTEE MEMBERS: PROF. HARDY JOST (UnB)
PROF. MARIA ÂNGELA F. CANDIA (USP)

ABSTRACT

The ca. 1300 Ma Juscelândia volcano~sedimentary sequence is situated in the central part of Goiás, Brazil and is part of the Barro Alto Complex.
In a geological section.from the south to the north,the following tectonic-stratigraphic succecion is recognaized: i) fíne grained (garnet) amphibolites (metabasalts) with intercalations cherts and calcsilicate rocks, ii) alternation of fine grained (garnet) amphibolites and (garnet) biotite orthogneisses (metagranitoids), iii) Orthogneises, feldspathic schist, mica schist (felsic volcanics, tuff).iv) the top section comprises several kinds of metasediments (kyanite-staurolite-garnet-mica schist, muscovite-biotíte schist and philites) and metavolcanic (amphibolites and muscovite-biotite gneisses ), latter representative of bimodal volcanic activity.
In the study area, four phases of deformation were characterized. The first two phases of deformation were generated in one progressive event, while the later phases are related to the generation of open folds and associated retrometamorphic minerais of greenschist facies. The main foliation (Sn) is defined by amphibolite facies minerais. It has EW direction and dips 55^o to the N, and with direction stretching lineation associated. This relationship indicares that the structures were formed in a lateral ramp of a major thrust structures, with tectonic transport from the west to east.
Garnet, staurolite and kyanite overgrow the main foliation, indicating that peak of metamorphism post-dates the main deformatíon.
The geochemical composition of amphibolites shows that the origínal volcanics were subalkaline, tholeiitic rocks with transitional basalts (T MORB) characteristics. An origin in a back-arc basin is suggested.