Campo DC | Valor | Idioma |
dc.contributor.author | Davison, Ian | - |
dc.contributor.author | Teixeira, João Batista Guimarães | - |
dc.contributor.author | Silva, Maria da Gloria da | - |
dc.contributor.author | Rocha Neto, Manoel Barreto da | - |
dc.contributor.author | Matos, Fernando Martins Vieira | - |
dc.creator | Davison, Ian | - |
dc.creator | Teixeira, João Batista Guimarães | - |
dc.creator | Silva, Maria da Gloria da | - |
dc.creator | Rocha Neto, Manoel Barreto da | - |
dc.creator | Matos, Fernando Martins Vieira | - |
dc.date.accessioned | 2013-02-06T13:42:20Z | - |
dc.date.available | 2013-02-06T13:42:20Z | - |
dc.date.issued | 1988 | - |
dc.identifier.issn | 0301-9268 | - |
dc.identifier.uri | http://www.repositorio.ufba.br/ri/handle/ri/8382 | - |
dc.description | p. 1 - 17 | pt_BR |
dc.description.abstract | The Rio Itapicuru greenstone belt is situated within the Silo Francisco craton, and is the largest of a series of N-S
trending volcanosedimentary sequences surrounded by gneisses and granitoids. Pb-Pb and Rb-Sr dating of andesitic
lavas within the supracrustal sequence yielded ages of 2.1 Ga, with late tectonic granitoids emplaced about the same
time. The succession appears to be developed on a sialic basement represented by the Santa Luz gneiss complex.
Although the actual contact between basement and supracrustals has not been observed, there is a sharp contrast in
strain and metamorphic conditions near to the contact zone. A 2.9 Ga U-Pb age obtained from a gneissic raft within
the intrusive Ambrosio dome is interpreted as a basement to the greenstone sequence and was plucked from a lower
crustal level by the ascending magma.
The Itapicuru River section provides good exposures along an E-W profile and has been used to attempt a reconstruction
of the lithostratigraphy in this area, where the supracrustals reach a maximum thickness of 9.5 km. Rare
stratigraphic facing and structural data indicate that the base of the sequence is marked by an intrusive granitoid.
Above this contact is a 5.0 km thick succession of tholeiitic subaqueous basalts with rare cherts, banded iron formation,
pelites, andesitic lavas and tufts. This mafic domain is overlain by a 3.5 km thick sequence of andesites, tufts and
volcanogenic sediments, with rare dacites and laminated cherts. A silica gap between 55% and 60% Si02 characterises
the lavas as a bimodal sequence. Two small ultramafic bodies with komatiitic chemistry also occur in the andesitic
volcanic domain. The uppermost 1.0 km consists of volcanogenic siltstones and shales with rare arkoses, tufts and
basalts.
Localised bedding-parallel shear zones are the earliest deformation features observed. The shear zones may be up
to 200 m thick and were important in controlling subsequent lode gold mineralisation. In the north central sector of
the greenstone belt these shear zones were deformed by N-S trending, east verging folds, with ~ 20 km wavelength.
The main greenstone sequence in the Itapicuru River section lies on the overturned limb of a syncline, and the Ambrosio
dome occupies the adjoining anticline.
In the southern part of the greenstone belt, the initial deformation produced a major shear zone striking E-W with
a 40 ° S dip and a subhorizontal E-W stretching lineation. North verging folds and thrusts produced the present
E-W trend. A late, upright, NE-SW trending fold phase terminated the ductile deformation.
Greenschist facies metamorphism affected the major part of the belt during deformation, with amphibolite facies
assemblages developed around the margins, and thermal aureoles developed around intrusions. Metamorphic fluids
transported gold to higher crustal levels via pre-existing, steeply dipping shear zones and faults and produced the large
Fazenda Brasileiro deposit, along with many smaller deposits. | pt_BR |
dc.language.iso | en | pt_BR |
dc.publisher | Precambrian Research | pt_BR |
dc.source | http://www.sciencedirect.com/science/article/pii/0301926888900071# | pt_BR |
dc.title | The rio Itapicuru greenstone belt, Bahia, Brazil: structure and stratigraphical outline | pt_BR |
dc.title.alternative | Precambrian Research | pt_BR |
dc.type | Artigo de Periódico | pt_BR |
dc.description.localpub | Salvador | pt_BR |
dc.identifier.number | v. 42, n. 1–2 | pt_BR |
Aparece nas coleções: | Artigo Publicado em Periódico (IGEO)
|