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Caracterização do hidrotermalismo “verde” em rochas siliciclásticas do Grupo Pajeú (Supergrupo Oliveira dos Brejinhos), Espinhaço Setentrional, Bahia

2010; Sociedade Brasileira de Geologia; Volume: 40; Issue: 4 Linguagem: Inglês

10.25249/0375-7536.2010404550560

2177-4382

André Danderfer, Newton Souza Gomes, Kelly Cristina de Lima Ramos Pinto Alves,

Geography and Environmental Studies

The Pajeú Group defines the upper interval of the Oliveira dos Brejinhos Supergroup, occurring along the eastern border of the Northern Espinhaço Range in Bahia State. This unit records the infilling of a typical rift basin, formed during one of the evolutionary events of the Espinhaço basin in the São Francisco Craton northern part. The basal succession (Riacho Fundo Formation) was deposited mainly through alluvial fans systems, braided river and “dry” eolic system. Subsequently this sequence was covered by a retrogradational delta-lacustrine system (Ipuçaba Formation). In the southern, the basin infilling is finalized by an intermediate to acid volcanism and associated clastic and volcanoclastic rocks (Bomba Formation) of Eocalymian age. Distinctly in the northern segment of the basin, the sedimentary sequence of the Pajeú Group was affected by a hydrothermal event that gave a green color to the epiclastic rocks, including sandstones and conglomerates of the Riacho Fundo Formation and sandstones, mudstones and diamictites of the Ipuçaba Formation. The oldest rocks of the basement (gneisses of the Paramirim Complex) were equally affected by this event, although the upper sedimentary successions do not show effects of hydrothermal alteration, except for the basal eolian sandstones of the Bom Retiro Formation which cover the full extent of the Pajeú Group. Microscopic and microprobe studies allowed the identification of a rare mineral paragenesis that includes garnet, amphibole, epidote, titanite, quartz and albite. The origin of hydrothermal event as well as the associated mineral paragenesis could be related to the final stage of Pajeú rift formation. The source of the fluid is probably the magmatism that gave rise to the volcanic rocks of the Bomba. Formation.