Geologia Da Porção Norte Do Greenstone Belt De Guarinos, Goiás

Abstract

The Guarinos greenstone belt is one of the three Archaean volcano-sedimentary rock assemblages of Crixás, Goiás, and its northern half was maped by the authors in 1992. The belt was intruded by a tonalite of the Caiamar Complex in the west, has a transcurrent fault contact with gneisses of the Moquém Block in the east and north, and is tectonically covered by Late Proterozoic metassedimentary rocks of the Araxá Group in the south. Its northeastern portion was intruded by a trondhjemite. Rocks of the belt (Guarinos Group) are grouped, from base to top, into the Serra do Cotovelo Formation (metakomatiites), Serra Azul Formation (tholeiitic metabasalts), São Patricinho Formation (detrital metassedimentary rocks), Aimbé Formation (banded iron formations, metaconglomerates and metahydrothermalites), and the Cabaçal Formation, which is further subdivided into a lower sub-unit (carbonaceous phyllites, locally metachert and banded iron and manganese formations), and an upper sub-unit (rythmic metashales and metasiltites). The supracrustais are folded into a normal and horizontal antiform in the south, which gives place to westerly dipping inverse antiforms in the north and east. The trondhjemite intrusion in the northeastern portion of the belt deformed the supracrustal rocks into a dome. Primary structures in metavolcanic and metasedimentary rocks indicate that the stratigraphic sequence of the greenstone belt is overturned, due to early northward verging nappes, followed by Late Proterozoic, easterly verging folding. Regional metamorphism took place under greenschist facies conditions. Contact metamorphic parageneses formed under hornblende hornfels and albite-epidote hornfels facies, respectively in contact with the western tonalite and the northeastern trondhjemite. Mylonites are of greenschist to lower amphibolite facies. Mineral resources in the area comprise gold and banded iron and manganese formations, under several modes of occurrence.RESUMO O greenstone belt de Guarinos é uma das três faixas de rochas supracrustais arqueanas da região de Crixás, Goiás, cuja metade norte foi mapeada pelos autores em 1992. As supracrustais limitam-se com um tonalito intrusive do Complexo Caiamar a oeste, por falha transcorrente com gnaisses do Bloco do Moquém a leste e norte, com rochas metassedimentares neoproterozóicas a sul. Na sua porção nordeste, a seqüência foi intrudida por um corpo de trondhjemito. As supracrustais (Grupo Guarinos) foram divididas, da base para o topo, nas formações Serra do Cotovelo (metakomatiitos), Serra Azul (metabasaltos toleifticos), São Patricinho (rochas metassedimentares detríticas rítmicas), Aimbé (formações ferríferas, metaconglpmerados e metahidrotermalitos) e Cabaçal, a qual contem uma subunidade inferior (filhos carbonosos, subordinadamente metachert e formações ferríferas e manganesíferas) e uma superior (metafolhelhos, metassiltitos e metarenitos finos e rítmicos). A estrutura regional do greenstone belt de Guarinos é, a sul, um antiforme normal e horizontal que grada, para norte e leste,...

U–Pb SHRIMP and Sm–Nd geochronology of granite–gneiss complexes and implications for the evolution of the Central Brazil Archean Terrain

“…Since the paper by Danni and Ribeiro (1978), when the region was characterized as a typical Archean granite-greenstone belt association, for about two decades the gneiss complexes were interpreted as basement of the greenstone belts. This interpretation was widely accepted until Jost et al (1995) and Resende et al (1998) describe the first evidence that at least some of the granitoids were either uplifted within or intruded into the supracrustal rocks. At that time, only imprecise Rb-Sr and Pb-Pb reference isochrons for a few of the gneisses of the studied area (Tassinari and Montalvão, 1980;Montalvão, 1985;Vargas, 1992), as well as Pb-Pb and Sm-Nd isochrons data for the komatiites of the Crixás greenstone belt (Arndt et al, 1989) were available.…”

GRAVITY INVERSION ON GRANITE-GREENSTONE BELT AREAS: CRIXÁS, GUARINOS AND PILAR DE GOlÁS, BRAZIL

“…The geologic section of the Fig. 4 was based on Resende & Jost (1995), Jost et al (1995Jost et al ( , 1998, besides Lacerda's map (1997). The format and the positioning of most of the geologic formations and the thrust faults are interpretative based in the geophysical model of the section (Fig.…”

Low- and high-alumina komatiites of Goiás, Central Brazil

“…As indicated by detailed 1:25,000 mapping of the Pilar de Goiás (Danni et al, 1986;Jost et al, 2001), Guarinos (Jost and Ferreira Filho, 1987), Faina, and Santa Rita (Resende, 1998) belts and observations in the Crixás belt, the frequency and thickness of these intercalations vary from one belt to another. In the northern three belts, the frequency and thickness increase from Crixás to Guarinos and Pilar, whereas in the southern two belts, these rocks are rare and rarely exceed 1 m in thickness.…”

“…The major contributions include those by Teixeira (1981), Kuyumjian (1981), Saboia and Teixeira (1983), Tomazzoli (1985), Tomazzoli and Nilson (1986), Danni et al (1986), Jost and Ferreira Filho (1987), Danni (1988), Jost and Oliveira (1991), and Jost et al (1995).…”