Abstract
The Neoarchean Rio das Velhas greenstone belt (RVGB), southeast Brazil, contains major tectonic and stratigraphic discontinuities that allow its division into three fault-bound tectonostratigraphic blocks named Santa Barbara, Nova Lima-Caete and Sao Bartolomeu. Detailed 1:25,000 scale mapping of the RVGB northern part revealed that each block contains important particularities and were subdivided into different lithostratigraphic formal units. The Santa Barbara block comprises the basal ultrabasic rocks of the Quebra Osso Group, followed by metavolcano-sedimentary successions of the Nova Lima Group (Vigario da Vara, Santa Quiteria, and Corrego do Sitio formations), and metasedimentary rocks of the Maquine Group (Palmital and Casa Forte formations). The Nova Lima-Caete block comprises the basal ultrabasic/basic volcanism (Ouro Fino and Morro Vermelho formations), metavolcano-sedimentary sequences (Mestre Caetano and Ribeirao do Brumado formations) of the Nova Lima Group, and the upper clastic sedimentary rocks of the Maquine Group (Palmital and Casa Forte formations). The Sao Bartolomeu block has a distinct rock assemblage given by metasedimentary rocks of the Nova Lima Group (Fazenda Velha, Corrego da Paina, and Pau D'Oleo formations), and clastic sedimentary rocks of the Maquine Group (Andaimes Formation). Despite some remarkable differences between these blocks, it is possible to recognize stratigraphic correlations and similar depositional evolution. The authors suggest volcanic architecture and sedimentary depositional models for the studied area, which includes: i) fissure eruption of komatiite lavas of the Quebra Osso Group in the SB block with subordinate clasto-chemical sedimentation; ii) ultrabasic/basic volcanism related to multiple volcanic centers in a subaqueous environment, characteristic from the basal portion of the Nova Lima Group in the SB and NLC blocks; iii) intermediate to acid volcanic and volcaniclastic rocks from the Nova Lima Group, present only in the NLC block, related to explosive eruptions; iv) clasto-chemical sedimentation, well recorded in the SB block; v) thick sequence of clastic sediments recorded in the three blocks with a predominance of greywacke-argillite cycles, deposited by turbidity currents in tectonically active submarine basins; vi) metasediments formed in alluvial-fluvial, coastal and shallow marine environments of the Maquine Group.
Highlights
Greenstone belts are, in general, greenschist facies thick sequences of underwater-deposited volcanic and sedimentary rocks preserved in cratonic regions
Considering that the stratigraphic nomenclature of the Rio das Velhas greenstone belt (RVGB) has so far been considered informal in the literature, we aim to propose a formal nomenclature for each block (Table 1), in analogy with that proposed by Pinto and Silva (1996), and suggest possible correlations between them
The Ribeirão Comprido Member is restricted to the Nova Lima-Caeté (NLC) block and corresponds to the Mindá unit defined in the Santa Bárbara (SB) block by Zucchetti et al (2000c)
Summary
Greenstone belts are, in general, greenschist facies thick sequences of underwater-deposited volcanic and sedimentary rocks preserved in cratonic regions. The Rio das Velhas greenstone belt (RVGB), located at the southern edge of the São Francisco craton, in southeastern Brazil (Fig. 1A), is a part of the Quadrilátero Ferrífero (‘Iron Quadrangle’) region (Fig. 1B), an important metallogenic province (Dorr II et al 1957; Dorr II 1969; Lobato et al 2001a, b). Structurally repeated rock sequences, all related to a complex evolution In this sense, to better characterize the RVGB, we adopted Baltazar and Zucchetti (2007) proposal to subdivide it into three tectonostratigraphic blocks bound by major structural lineaments (Fig. 1C). To better characterize the RVGB, we adopted Baltazar and Zucchetti (2007) proposal to subdivide it into three tectonostratigraphic blocks bound by major structural lineaments (Fig. 1C) Once these blocks differ in their supracrustal rock record (Fig. 2), different stratigraphic columns (Fig. 3) will represent each one. Considering that the stratigraphic nomenclature of the RVGB has so far been considered informal in the literature, we aim to propose a formal nomenclature for each block (Table 1), in analogy with that proposed by Pinto and Silva (1996), and suggest possible correlations between them
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