Crustal block Structure of Brazil and associated ore deposits
Haralyi, Nicolau L.E.; Hasui, Yociteru
published: Jan 1, 1988
ArtNo. ESP136000302011, Price: 19.00 €
The integration of the available geophysical information, after adequate treatment taking into account the geologic, tectonic and radiometric data, allows one to identify the major structural features of Brazil. The regional structural framework leads to a more clear evaluation of the crustal evolution and, in consequence, to a better understanding of the distribution of the ore deposits. The more prominent structures correspond to discontinuities separating large crustal blocks. These discontinuities are clearly identified on gravity Bouguer maps as high lateral gradients separating linear lows and high gravity value regions, as well as on magnetic (airborne and Magsat) and rock density maps, and are related to heat flow anomalies and intraplate seismicity. They are recognized in the field as low-angle ductile shear zones to which imbrication, upthusting and allochtonism, recrystallization under upper amphibolite/lower greenschist facies conditions, and anatectic and hydrothermal remobilization are associated. The upthrusted block even exposes its lower level by granulite belt. The affected rocks are of Archeanage, and the referred horizontal tectonics occurred during late Archeantime. The ore deposits are mostly related to mafic-ultramafic complexes (Ni, Cu, V, asbestos), but some of them are linked to associated metasediments (Au) or gneisses (U). The crustal blocks (CB) are domains of granitegreenstone terrains of Archeanage.