Abstract

The Paramirim Aulacogen was filled by the Espinhaço and São Francisco supergroups in the period from 1.75 to 0.69 Ga, and suffered partial inversion during the Ediacaran. In the northern sector of the intracontinental domain of the Araçuaí-WestCongo Orogen, six compressive deformational phases were interpreted and associated with the frontal inversion of the Paramirim Aulacogen. Three structural domains were identified: Jacaraci Fold-Thrust Belt, Caetité Nappe, and Transpressive Domain. The nucleation of deformational structures is related to a maximum stress field with general WSW-ENE orientation. The first deformational phase (D₁), found in the Jacaraci Fold-Thrust Belt and the Transpressional Domain, is related to the evolution of the Rio Pardo Salient. A dextral transpressional system nucleated the Caetité Nappe. This system also juxtaposed amphibolite facies rocks over lower temperature facies, as well as Statherian over Tonian rocks. Furthermore, this system was responsible for deformation in the transpressional domains and late deformation in the Jacaraci Fold-Thrust Belt. The region presents a variety of structures and is, therefore, an excellent natural laboratory for studying positive inversion in aulacogens.

KEYWORDS:
aulacogen; orogen; tectonic inversion; craton; deformational phases

INTRODUCTION

The Paramirim Aulacogen (Fig. 1) is one of the aborted arms of a superimposed rift system of Statherian-Cryogenian age, developed in the São Francisco-Congo paleocontinent (Brito-Neves et al. 1999Brito-Neves B.B., Campos-Neto M.C., Fuck R.A. 1999. From Rodinia to Western Gondwana: An approach to the Brasiliano-Pan African cycle and orogenic collage. Espisodes, 22(3):155-199. https://doi.org/10.18814/epiiugs/1999/v22i3/002
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https://doi.org/10.2475/ajs.278.1.24... ). In the collisional domains in which the aulacogens are located in the foreland region, they are connected and arranged at high angles to the former continental margin. Deformation tends to channel to the interior, generating complex tectonic arrangements.

The northern region of the intracontinental sector of the Araçuaí Orogen coincides with the zone of maximum Ediacaran inversion of the Paramirim Aulacogen. This NNW-oriented mega feature is limited to the north by the Queimada Nova shear zone (Cruz 2004Cruz S.C.P. 2004. A interação tectônica entre o Paramirim Aulacogen e o Orógeno Araçuaí. Tese de Doutorado, Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto. 503 p.) at 13°S. In this sector, the thick-skinned deformation juxtaposed Archean and Statherian rocks on the Tonian units (Bitencourt et al. 2019Bitencourt C.N., Cruz S.C.P., dos Anjos Cruz V., Pedrosa-Soares A.C., Paquette J.L., Alkmim A.R., Barbosa J.S.F. 2019. Rifting events in the southern sector of the Paramirim Aulacogen, NE Brazil: New geochronological data and correlations for the São Francisco – Congo paleocontinent. Precambrian Research, 326:417-446. https://doi.org/10.1016/J.PRECAMRES.2018.12.005
https://doi.org/10.1016/J.PRECAMRES.2018... ) of the Santo Onofre Group. Two fold-thrust belts with thick-skinned deformation were identified (Danderfer-Filho 1990Danderfer-Filho A. 1990. Análise estrutural descritiva e cinemática do Espinhaço Supergroup na região da Chapada Diamantina (BA). MSc. Thesis, Universidade Federal de Ouro Preto, Ouro Preto, 99 p., 2000Danderfer-Filho A. 2000. Geologia sedimentar e evolução tectônica do Espinhaço Setentrional, estado da Bahia. Thesis, Instituto de Geociências, Universidade Federal de Brasília, Brasília. 497 p., Cruz 2004Cruz S.C.P. 2004. A interação tectônica entre o Paramirim Aulacogen e o Orógeno Araçuaí. Tese de Doutorado, Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto. 503 p., Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... , Cruz et al. 2012aCruz S.C.P., Alkmim F.F., Pedreira A., Teixeira L., Pedrosa-Soares A.C., Gomes L.C.C., Souza J.S., Leal A.B.M. 2012a. O Orógeno Araçuaí. In: Barbosa J.S.F (ed.). Geologia da Bahia: Pesquisa e Atualização. Salvador: CBPM Série Publicações Especiais. p. 131-178.): the northern Serra do Espinhaço, to the west, whose western limit is the Santo Onofre Shear Zone; and the Chapada Diamantina, to the east, whose eastern limit is the João Correia-Barra do Mendes Shear Zone.

This study aimed to present the deformational structures associated with the tectonic inversion (Sensu Glennie and Boegner 1981Glennie K.W., Boegner P.L.E. 1981. Sole Pit inversion tectonics. In: Illings L.V., Hobson G.D. (eds.), Petroleum Geology of the Continental Shelf of North-West Europe. London: Institute of Petroleum. p. 110-120., Cooper and Williams 1989Cooper M.A., Williams G.D. 1989. Inversion Tectonics. Geological Society Special Publication. v. 44.) of the Paramirim Aulacogen and present an evolutionary model for part of the Serra do Espinhaço Fold-Thrust Belt, north of the intracontinental sector of the Araçuaí Orogen.

GEOLOGICAL CONTEXT

The basement of the Paramirim Aulacogen (Fig. 2) comprises the rocks of the southern portion of the Gavião Paleoplate (Cruz et al. 2016Cruz S.C.P., Barbosa J.S.F., Santos Pinto M., Peucat J.J., Paquette J.L., Souza J.S., Martins V.S., Chemale Júnior F., Carneiro M.A. 2016. The Siderian-Orosirian magmatism in the Gavião Paleoplate, Brazil: U-Pb geochronology, geochemistry and tectonic implications. Journal of South American Earth Sciences, 69:43-79. https://doi.org/10.1016/j.jsames.2016.02.007
https://doi.org/10.1016/j.jsames.2016.02... ), consisting mainly of metagranitoids of tonalitic-granodioritic composition with amphibolitic enclaves. Paleo and Mesoarchean ages are dominant. Neoarchean metagranitoids, metavolcano-sedimentary sequences of Mesoarchean ages, including Greenstone Belts, Neoarchean, Rhyacian, and Orosirian, intruded by Siderian-Rhyacian-Orosirian granitoids are also known (Cordani et al. 1985Cordani U.G., Sato K., Marinho M.M. 1985. The geologic evolution of the ancient granite-greenstone terrane of central-southern Bahia, Brazil. Precambrian Research, 27(1-3):187-213. https://doi.org/10.1016/0301-9268(85)90012-9
https://doi.org/10.1016/0301-9268(85)900... , 1992Cordani U.G., Iyer S.S., Taylor P.N., Kawashita K., Sato K., Mcreath I. 1992. Pb-Pb, Rb-Sr, and K-Ar sistematic of the Lagoa Real uranium province (south-central Bahia, Brazil) and the Espinhaço Cycle (ca. 1.5-1.0 Ga). Journal South American Earth Science, 5(1):33-46., Martin et al. 1991Martin H., Peucat J.J., Sabaté P., Cunha J.C. 1991. Um segment de croûte continentale d’Age archéean ancien (3.5 millards d'années): lê massif de Sete Voltas (Bahia, Brésil). C Comptes rendus de l’Académie des Sciences, 313(5):531-538., Marinho 1991Marinho M.M. 1991. Lê sequence Volcano-Sedimentaire de Contendas Mirante et la Bordure Ocidentale du Bloc de Jequié (Craton du São Francisco, Brésil): um example de transition Archeen-Proterozoic. Doctor of Philosophy Thesis, Universidade de Clemont-Ferrand. 257 p., Nutman and Cordani 1993Nutman A.P., Cordani U.G. 1993. SHRIMP U-Pb zircon geochronology of Archean granitoids from the Contendas Mirante area of the São Francisco Craton, Bahia, Brazil. Journal South American Earth Science, 15:97-107., Cunha et al. 2012Cunha J.C., Barbosa J.S.F., Mascarenhas J.F. 2012. Greenstones Belts e Sequências Similares. In: Barbosa J.S. (eds.). Geologia da Bahia: Pesquisa e Atualização. Salvador: CBPM Série Publicações especiais. p. 203-325., Santos-Pinto et al. 1998Santos-Pinto M.A., Peucat J.J., Martin H., Sabaté P. 1998. Recycling of the Archaean continental crust: the case study of the Gavião Block, Bahia, Brazil. Journal of South American Earth Science, 11(5):487-498. https://doi.org/10.1016/S0895-9811(98)00029-7
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https://doi.org/10.25249/0375-7536.19982... , 2000Bastos-Leal L.R., Teixeira W., Cunha J.C., Leal A.B.M., Macambira M.J.B., Rosa M.L.S. 2000. Isotopic signatures of paleoproterozoica granitoids of the Gavião block and implications for the evolution of the São Francisco craton, Bahia, Brazil. Revista Brasileira de Geociências, 30(1):66-69., Rosa et al. 2000Rosa A.M.L.S., Conceição H., Oberli F., Meier M., Martin H., Macambira M.B., Santos E.B., Paim M.M., Leahy G.A.S., Bastos Leal L.R. 2000. Geochronology (U-Pb/Pb-Pb) and isotopic signature (Rb-Sr/Sm-Nd) of the paleoproterozoic Guanambi Batholith, southwestern Bahia State (NE Brazil). Revista Brasileira de Geociências, 30(1):62-65., Peucat et al. 2002Peucat J.J., Mascarenhas J.F., Barbosa J.S., Souza F.S., Marinho M.M., Fanning C.M. Leite C.M.M. 2002. 3.3 Ga SHRIMP U-Pb zircon age of a felsic metavolcanic rock from the Mundo Novo greenstone belt in the São Francisco craton, Bahia (NE Brazil). Journal South American Earth Sciences, 15(3):363-373. https://doi.org/10.1016/S0895-9811(02)00044-5
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https://doi.org/10.1016/j.jsames.2011.11... , 2016Cruz S.C.P., Barbosa J.S.F., Santos Pinto M., Peucat J.J., Paquette J.L., Souza J.S., Martins V.S., Chemale Júnior F., Carneiro M.A. 2016. The Siderian-Orosirian magmatism in the Gavião Paleoplate, Brazil: U-Pb geochronology, geochemistry and tectonic implications. Journal of South American Earth Sciences, 69:43-79. https://doi.org/10.1016/j.jsames.2016.02.007
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https://doi.org/10.1016/j.precamres.2020... ). Locally, granulitic orthogneisses are present (Arcanjo et al. 2005Arcanjo J.B., Marques-Martins A.A., Loureiro H.S.C., Varela P.H.L. 2005. Projeto Vale do Paramirim, Bahia: geologia e recursos minerais. Salvador: CBPM. (Série Arquivos Abertos, 22, 82 p.), Santos 2018Santos E.N. 2018. Migmatitos do Complexo Santa Izabel na região de Riacho de Santana, BA: caracterização e controle estrutural. Undergraduate Thesis, Universidade Federal da Bahia, Salvador. 116 p., Guimarães 2019Guimarães J.T. 2019. Projeto Igaporã-Macaúbas: geologia e recursos minerais das Folhas Boquira - SD.23-X-B-V, Macaúbas - SD.23-X-D-II E, Riacho de Santana - SD.23-X-D-V. Escala 1:100.000. Salvador: CPRM. 126 p.). Anorogenic, felsic, alkaline, and plutonic magmatism are represented by the Lagoa Real Intrusive Suite (Arcanjo et al. 2005Arcanjo J.B., Marques-Martins A.A., Loureiro H.S.C., Varela P.H.L. 2005. Projeto Vale do Paramirim, Bahia: geologia e recursos minerais. Salvador: CBPM. (Série Arquivos Abertos, 22, 82 p.)) aged around 1.75 Ga (Turpin et al. 1988Turpin L., Maruèjol, P., Cuney M. 1988. U-Pb, Rb-Sr and Sm-Nd chronology of granitic basement, hydrotermal albitites and uranium mineralization, Lagoa Real, South Bahia, Brazil. Contribution Mineralogy Petrology, 98:139-147. https://doi.org/10.1007/BF00402107
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https://doi.org/10.1016/j.jsames.2014.12... ).

In the intracontinental sector of the Araçuaí Orogen, the Espinhaço and São Francisco supergroups fill the Paramirim Aulacogen. These units outcrop in the fold and thrust belts of the northern Serra do Espinhaço, to the west, and Chapada Diamantina, to the east. The Espinhaço Supergroup has a thickness of more than 5,000 m (Guimarães et al. 2012Guimarães J.T., Alkmim F.F., Cruz S.C.P. 2012. Supergrupo Espinhaço e São Francisco. In: Barbosa J.S.F. (ed.). Geologia da Bahia: Pesquisa e Atualização de dados. Salvador: CBPM. v. 2. p. 33-85.) and comprises predominantly siliciclastic rocks (metarenites, metapelites, and metaconglomerates) with subordinate acidic, alkaline, and anorogenic metavolcanic rocks. The age of deposition of the rocks of this supergroup is estimated between 1.75 and 0.9 Ga (Danderfer-Filho et al. 2015Danderfer-Filho A., Lana C.C., Nalini Júnior H.A., Costa A.F.O. 2015. Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton. Gondwana Research, 28(2):668-688. https://doi.org/10.1016/j.gr.2014.06.012
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https://doi.org/10.1016/j.gr.2013.10.009... ).

The São Francisco Supergroup comprises:

1. in the northern Serra do Espinhaço Fold-Thrust Belt, the Santo Onofre Group (2,040 meters thick; Guimarães et al. 2012Guimarães J.T., Alkmim F.F., Cruz S.C.P. 2012. Supergrupo Espinhaço e São Francisco. In: Barbosa J.S.F. (ed.). Geologia da Bahia: Pesquisa e Atualização de dados. Salvador: CBPM. v. 2. p. 33-85.), and with the Fazendinha, Serra da Vereda, Serra da Garapa formations, and Boqueirão, separated by very well-exposed depositional contacts north of Caetité. To the south of this town, the contact between the units of this group is defined by a dextral transpressional shear zone. Generally, it consists of feldspathic metarenites, lithic metarkoses, and metaquartzarenites, stratified and massive, with matrix-sustained oligomictic metaconglomerates (Guimarães et al. 2008Guimarães J.T., Santos R.A., Melo R.C. 2008. Geologia da Chapada Diamantina (Projeto Ibitiara-Rio de Contas). Salvador: CBPM, 68 p. CBPM Série Arquivos Abertos, 31.);

2. in the Chapada Diamantina Fold-Thrust Belt, the Bebedouro and Salitre formations. The Bebedouro Formation consists mainly of massive and stratified clast- and matrix-supported polymictic diamictites, pelites, arkoses, lithic subarkoses, graywackes, and quartz sandstones with subordinated carbonates, which were deposited into a glacial-marine environment (Guimarães et al. 2012Guimarães J.T., Alkmim F.F., Cruz S.C.P. 2012. Supergrupo Espinhaço e São Francisco. In: Barbosa J.S.F. (ed.). Geologia da Bahia: Pesquisa e Atualização de dados. Salvador: CBPM. v. 2. p. 33-85.). According to these authors, the Salitre Formation mainly comprises carbonates with calcarenites, dolarenites, and subordinated columnar stromatolites. Santana (2016)Santana A.V. 2016. Análise estratigráfica em alta resolução em rampa carbonática dominada por microbiolitos, Formação Salitre, Bacia de Irecê, Bahia. PhD Thesis, Universidade de Brasília, Brasília, 183 p. obtained an U-Pb age (zircon, LA-ICP MS) of 669 ± 14 Ma for a felsic metavolcanic rock intercalated with carbonates of this formation.

Dark-gray to greenish diorites and gabbros/diabases (Arcanjo et al. 2005Arcanjo J.B., Marques-Martins A.A., Loureiro H.S.C., Varela P.H.L. 2005. Projeto Vale do Paramirim, Bahia: geologia e recursos minerais. Salvador: CBPM. (Série Arquivos Abertos, 22, 82 p.), Menezes et al. 2012Menezes R.C.L., Conceição H., Rosa M.L.S., Macambira M.J.B., Galarza M.A., Rios D.C. 2012. Geoquímica e geocronologia de granitos anorogênicos tonianos (c.914–899 Ma) da Faixa Araçuaí no Sul do Estado da Bahia. Geonomos, 20(1):1-13. https://doi.org/10.18285/geonomos.v20i1.21
https://doi.org/10.18285/geonomos.v20i1.... and cited references) intrude the units of the Espinhaço Supergroup producing sills and dikes. According to these authors, these are tholeiitic rocks from a continental intraplate environment with substantial crustal contamination. Two crystallization age groups were obtained in zircon from these mafic rocks: the oldest group, located in the Eastern Basin, yielded ages of 1,514 ± 22 Ma (Babinski et al. 1999Babinski M., Pedreira A., Brito-Neves B.B., Van-Schmus W.R. 1999. Contribuição à geocronologia da Chapada Diamantina. In: Simpósio Nacional de Estudos Tectônicos, 7., 1999. Anais… p. 118-121., TIMS), 1,496 ± 3.2 Ma, 1,492 ± 16 Ma (Guimarães et al. 2008Guimarães J.T., Santos R.A., Melo R.C. 2008. Geologia da Chapada Diamantina (Projeto Ibitiara-Rio de Contas). Salvador: CBPM, 68 p. CBPM Série Arquivos Abertos, 31., Loureiro et al. 2009Loureiro H.S.C., Bahiense I.C., Neves J.P., Guimarães J.T., Teixeira L.R., Santos R.A., Melo R.C. 2009. Geologia e recursos minerais da parte norte do corredor de deformação do Paramirim (Projeto Barra – Oliveira dos Brejinhos). Salvador: CBPM. 113 p. Série Arquivos Abertos 33.), and 1,507 ± 7 Ma (Silveira et al. 2013Silveira E.P., Söderlund U., Oliveira E.P., Ernst R., Menezes Leal A.B. 2013. First precise U-Pb baddeleyite ages of 1500 Ma mafic dykes from the São Francisco Craton, Brazil, and tectonic implications. Lithos, 174:144-156. https://doi.org/10.1016/j.lithos.2012.06.004
https://doi.org/10.1016/j.lithos.2012.06... ). In turn, the youngest group, with representatives in both Western and Eastern basins, produced ages at 854 ± 23 Ma (Danderfer-Filho et al. 2009Danderfer-Filho A., De Waele B., Pedreira A.J., Nalini H.A. 2009. New geochronological constraints on the geological evolution of Espinhaco basin within the São Francisco Craton-Brazil. Precambrian Research, 170(1-2):116-128. https://doi.org/10.1016/j.precamres.2009.01.002
https://doi.org/10.1016/j.precamres.2009... , SHRIMP, zircon) and 934 ± 14 Ma (Loureiro et al. 2009Loureiro H.S.C., Bahiense I.C., Neves J.P., Guimarães J.T., Teixeira L.R., Santos R.A., Melo R.C. 2009. Geologia e recursos minerais da parte norte do corredor de deformação do Paramirim (Projeto Barra – Oliveira dos Brejinhos). Salvador: CBPM. 113 p. Série Arquivos Abertos 33., LA-ICPMS, zircon), respectively.

The positive inversion (Sensu Gillcrist et al. 1987Gillcrist R., Coward M., Mugnier J.-L. 1987. Structural inversion and its controls: examples from the Alpine foreland and the French Alps: Geodinamica Acta, 1(1):5-34. https://doi.org/10.1080/09853111.1987.11105122
https://doi.org/10.1080/09853111.1987.11... ) of the Paramirim Aulacogen occurred in the Ediacaran (Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... ), and two main structural domains can be identified (Danderfer-Filho 1990Danderfer-Filho A. 1990. Análise estrutural descritiva e cinemática do Espinhaço Supergroup na região da Chapada Diamantina (BA). MSc. Thesis, Universidade Federal de Ouro Preto, Ouro Preto, 99 p., 2000Danderfer-Filho A. 2000. Geologia sedimentar e evolução tectônica do Espinhaço Setentrional, estado da Bahia. Thesis, Instituto de Geociências, Universidade Federal de Brasília, Brasília. 497 p., Lagoeiro 1990Lagoeiro L.E. 1990. Estudo das deformações nas seqüências carbonáticas do Grupo Una na região de Irecê, BA. Dissertação de Mestrado, Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, 150 p., Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... , Cruz et al. 2007aCruz S.C.P., Alkmim F.F., Leite C.M.M., Evangelista H.J. Cunha J.C., Matos E.C., Noce C.M., Marinho M.M. 2007a. Geologia e arcabouço estrutural do Complexo Lagoa Real, Vale do Paramirim, Centro-West da Bahia. Revista Brasileira de Geociências, 37(4):28-146., 2007bCruz S.C.P., Dias V.M., Alkmim F.F. 2007b. A história de inversão do aulacógeno do Paramirim contada pela sinclinal de Ituaçu, extremo sul da Chapada Diamantina (BA). Revista Brasileira de Geociências, 37(4):92-110., 2007cCruz S.C.P., Dias V.M., Alkmim F.F. 2007c. A interação tectônica embasamento/cobertura em Aulacógenos invertidos: um exemplo da Chapada Diamantina Ocidental. Revista Brasileira de Geociências, 37(4):111-127., 2012aCruz S.C.P., Alkmim F.F., Pedreira A., Teixeira L., Pedrosa-Soares A.C., Gomes L.C.C., Souza J.S., Leal A.B.M. 2012a. O Orógeno Araçuaí. In: Barbosa J.S.F (ed.). Geologia da Bahia: Pesquisa e Atualização. Salvador: CBPM Série Publicações Especiais. p. 131-178.):

1. the domain of thin-skinned deformation, which nucleates a varied set of structures in the Espinhaço and São Francisco Supergroup rocks, described by Danderfer-Filho (1990Danderfer-Filho A. 1990. Análise estrutural descritiva e cinemática do Espinhaço Supergroup na região da Chapada Diamantina (BA). MSc. Thesis, Universidade Federal de Ouro Preto, Ouro Preto, 99 p., 2000Danderfer-Filho A. 2000. Geologia sedimentar e evolução tectônica do Espinhaço Setentrional, estado da Bahia. Thesis, Instituto de Geociências, Universidade Federal de Brasília, Brasília. 497 p.), Lagoeiro (1990)Lagoeiro L.E. 1990. Estudo das deformações nas seqüências carbonáticas do Grupo Una na região de Irecê, BA. Dissertação de Mestrado, Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, 150 p.;

2. the domain of thick-skinned deformation (Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
   https://doi.org/10.1590/S0001-3765200600... ), with the formation of the Rio Pardo Salient (Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
   https://doi.org/10.1590/S0001-3765200600... , Peixoto et al. 2018Peixoto E., Alkmim F.F., Pedrosa-Soares A.C., Lana C., Chaves A.O. 2018. Metamorphic record of collision and collapse in the Ediacaran-Cambrian Araçuaí orogen, SE-Brazil: Insights from P-T pseudosections and monazite dating. Journal of Metamorphic Geology, 36(2):147-172. https://doi.org/10.1111/jmg.12287
   https://doi.org/10.1111/jmg.12287... ), which is truncated by reverse to transpressional dextral shear zones that are anchored in the basement older than 1.75 Ga and that truncate the Espinhaço and San Francisco supergroups. In the northern Espinhaço Fold-Thrust Belt structures located north of Caetité were described by Danderfer-Filho (2000)Danderfer-Filho A. 2000. Geologia sedimentar e evolução tectônica do Espinhaço Setentrional, estado da Bahia. Thesis, Instituto de Geociências, Universidade Federal de Brasília, Brasília. 497 p. and Guimarães (2019)Guimarães J.T. 2019. Projeto Igaporã-Macaúbas: geologia e recursos minerais das Folhas Boquira - SD.23-X-B-V, Macaúbas - SD.23-X-D-II E, Riacho de Santana - SD.23-X-D-V. Escala 1:100.000. Salvador: CPRM. 126 p., and those located south of that town will be described in this study.

Typical shear zones that reactivate these structures are related to the collapse of the Araçuaí-West Congo Orogen (Cruz et al. 2015Cruz S.C.P., Alkmim F.F., Barbosa J.S.F., Dussin I., Gomes L.C.C. 2015. Tectonic inversion of compressional structures in the Southern portion of the Paramirim Corridor, Bahia, Brazil. Brazilian Journal of Geology, 45(4):541-567. https://doi.org/10.1590/2317-488920150030240
https://doi.org/10.1590/2317-48892015003... ).

GEOLOGY OF THE SOUTHERN SECTOR OF THE NORTHERN SERRA DO ESPINHAÇO FOLD BELT

Lithological units

Studies carried out by Bitencourt et al. (2019)Bitencourt C.N., Cruz S.C.P., dos Anjos Cruz V., Pedrosa-Soares A.C., Paquette J.L., Alkmim A.R., Barbosa J.S.F. 2019. Rifting events in the southern sector of the Paramirim Aulacogen, NE Brazil: New geochronological data and correlations for the São Francisco – Congo paleocontinent. Precambrian Research, 326:417-446. https://doi.org/10.1016/J.PRECAMRES.2018.12.005
https://doi.org/10.1016/J.PRECAMRES.2018... allowed us to identify (Figs. 3 and 4):

1. basement older than 1.75 Ga, comprising: (i) Mesoarchean rocks of the Santa Izabel Magmatic Suite, with tonalitic, granodioritic, quartz-monzodioritic, quartz-dioritic, and dioritic composition with crystallization ages between 3,091 ± 24 and 3,136 ± 8 Ma (LA-ICPMS, zircon, Medeiros et al. 2017Medeiros E.L.M., Cruz S.C.P., Barbosa J.S.F., Paquette J.L., Peucat J., Jesus S.S.G.P., Barbosa R.G., Brito R.S., Carneiro M.A. 2017. The Santa Izabel complex, Gavião Block, Brazil: Components, geocronology, regional correlations and tectonic implications. Journal of South American Earth Sciences, 80:66-94. https://doi.org/10.1016/j.jsames.2017.09.008
   https://doi.org/10.1016/j.jsames.2017.09... ). These rocks have been migmatized to varying degrees and have amphibolitic and metaultramafic enclaves; (ii) Leandrinho metavolcano-sedimentary sequence that intercalates aluminous schists (metapelite), metagraywackes, acid metatuffs, and metalapillites. The crystallization age of acid metatuffs is 2,550 ± 2 Ma (Vitoria et al. 2022Vitoria R.S., Cruz S.C.P., Conceição H. 2022. Geology of the Neoarchean-Rhyacian Supracrustals of the Northern Intracontinental Sector of the Araçuaí Orogen: Evidence for Overlapping Basins. Journal of South American Earth Sciences, 119:103943.); (iii) Guanambi-Urandi monzosyenitic batholith, with syenites and monzonites with subordinate granitic and mafic rocks (Rosa et al. 2000Rosa A.M.L.S., Conceição H., Oberli F., Meier M., Martin H., Macambira M.B., Santos E.B., Paim M.M., Leahy G.A.S., Bastos Leal L.R. 2000. Geochronology (U-Pb/Pb-Pb) and isotopic signature (Rb-Sr/Sm-Nd) of the paleoproterozoic Guanambi Batholith, southwestern Bahia State (NE Brazil). Revista Brasileira de Geociências, 30(1):62-65., Teixeira 2000Teixeira L.R. 2000. Projeto Vale do Paramirim. Relatório Temático de Litogeoquímica. Convênio CPRM/CBPM.). The crystallization ages range from 2,041 ± 2 Ma - 2,054 −6/+8 Ma (zircon, isotope dilution, Rosa et al. 2000Rosa A.M.L.S., Conceição H., Oberli F., Meier M., Martin H., Macambira M.B., Santos E.B., Paim M.M., Leahy G.A.S., Bastos Leal L.R. 2000. Geochronology (U-Pb/Pb-Pb) and isotopic signature (Rb-Sr/Sm-Nd) of the paleoproterozoic Guanambi Batholith, southwestern Bahia State (NE Brazil). Revista Brasileira de Geociências, 30(1):62-65.);

2. Undeterminated age metavolcano-sedimentary sequence that comprises metarkose, metagraywacke, quartzite, aluminum and manganese schists, graphite-rich phyllites, felsic and mafic schists (metavolcanic rocks), itabirite, marble (some of which are manganese rich), and a carbonate-silicate rock (Cruz et al. 2009Cruz S.C.P. Barbosa J.S.F., Alves J.E., Damasceno G.C., Machado G.S., Borges J.O., Gomes A.M., Mesquita L., Pimentel I., Leal A.B.M., Palmeiras D. 2009. Folha Caetité, 1:100.000: Mapeamento geológico e cadastramento de ocorrências minerais. Convênio UFBA-FAPEX-CPRM. 180 p., Borges et al. 2015Borges J.O., Cruz S.C.P., Barbosa J.S.F., Santos E.S. 2015. Structural framework of the the Lagoa D’Anta mine area, iron-manganese Urandi-Caetité- Licínio de Almeida District, Bahia, Brasil. Brazilian Journal of Geology, 45(2):173-192. https://doi.org/10.1590/23174889201500020002
   https://doi.org/10.1590/2317488920150002... );

3. Algodão Formation (Espinhaço Supergroup) consists of alternating quartz to feldspathic metasandstones, sericitic metasandstones, oligomictic metaconglomerates, metasandstones and quartzites, laminated metapelites, metarhythmites and metasiltites, and quartzites. The youngest age is 1,958 ± 18 Ma (Bitencourt et al. 2019Bitencourt C.N., Cruz S.C.P., dos Anjos Cruz V., Pedrosa-Soares A.C., Paquette J.L., Alkmim A.R., Barbosa J.S.F. 2019. Rifting events in the southern sector of the Paramirim Aulacogen, NE Brazil: New geochronological data and correlations for the São Francisco – Congo paleocontinent. Precambrian Research, 326:417-446. https://doi.org/10.1016/J.PRECAMRES.2018.12.005
   https://doi.org/10.1016/J.PRECAMRES.2018... ). North of Caetité, Danderfer-Filho et al. (2015)Danderfer-Filho A., Lana C.C., Nalini Júnior H.A., Costa A.F.O. 2015. Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton. Gondwana Research, 28(2):668-688. https://doi.org/10.1016/j.gr.2014.06.012
   https://doi.org/10.1016/j.gr.2014.06.012... dated metavolcanic rocks of the Algodão Formation crystallized at 1,775 ± 26 Ma (U-Pb, LA-ICPMS, zircon).

4. Lagoa Real intrusive suite, with metasyenites and metasienogranites, mylonitized to varying degrees, with crystallization age of ca. 1.7 Ga (Turpin et al. 1988Turpin L., Maruèjol, P., Cuney M. 1988. U-Pb, Rb-Sr and Sm-Nd chronology of granitic basement, hydrotermal albitites and uranium mineralization, Lagoa Real, South Bahia, Brazil. Contribution Mineralogy Petrology, 98:139-147. https://doi.org/10.1007/BF00402107
   https://doi.org/10.1007/BF00402107... , Cordani et al. 1992Cordani U.G., Iyer S.S., Taylor P.N., Kawashita K., Sato K., Mcreath I. 1992. Pb-Pb, Rb-Sr, and K-Ar sistematic of the Lagoa Real uranium province (south-central Bahia, Brazil) and the Espinhaço Cycle (ca. 1.5-1.0 Ga). Journal South American Earth Science, 5(1):33-46., Lobato et al. 2015Lobato L.M., Pimentel M., Cruz S.C.P., Machado N., Noce C.M., Alkmim F.F. 2015. U-Pb Geochronology of the Lagoa Real Uranium District, Brazil: Implications for the age of the uranium mineralization. Journal of South American Earth Sciences, 58:129-140. https://doi.org/10.1016/j.jsames.2014.12.005
   https://doi.org/10.1016/j.jsames.2014.12... ).

5. Santo Onofre Group (São Francisco Supergroup), with Serra da Guarapa and Boqueirão formations. The Serra da Garapa Formation was subdivided into two lithofacies associations. The first is composed predominantly of quartzites, hematite-rich, graphite-rich, or manganese-rich metapelites and phyllites. The second lithofacies association comprises staurolite-garnet-quartz-biotite aluminous schist and quartzites. The Boqueirão Formation predominate metasubarkoses, lithic metasandstones, and metasiltites besides oligomictic metamicroconglomerates. The youngest ages obtained are 894 ± 38 and 899 ± 79 Ma, respectively (Bitencourt et al. 2019Bitencourt C.N., Cruz S.C.P., dos Anjos Cruz V., Pedrosa-Soares A.C., Paquette J.L., Alkmim A.R., Barbosa J.S.F. 2019. Rifting events in the southern sector of the Paramirim Aulacogen, NE Brazil: New geochronological data and correlations for the São Francisco – Congo paleocontinent. Precambrian Research, 326:417-446. https://doi.org/10.1016/J.PRECAMRES.2018.12.005
   https://doi.org/10.1016/J.PRECAMRES.2018... ).

Structural framework

From south to north, three structural domains were identified: Jacaraci Fold-Thrust Belt, Caetité Nappe, and Transpressional Domain (Fig. 5). The connection between Jacaraci Fold-Thrust Belt and the Transpressional Domain is made by a sinistral transcurrent shear zone (Fig. 3).

Jacaraci Fold-Thrust Belt

In this compartment, the Algodão Formation predominates (Figs. 3 and 6), with medium- to large-sized parallel and cross stratifications. The attitudes of the primary bedding planes (S₀) have strong data dispersion (Fig. 7A). Along the basal contact of the Espinhaço Supergroup rocks with the Aulacogen basement, the oldest deformational structures in the area and associated with basal detachment are found, which are the S₀//S₁ schistosity (Fig. 7B) and the stretching lineation (L_x1) (Fig. 8A). Both structures also show strong dispersion (Figs. 7B and 7C). Internally to the S₀//S₁ schistosity, isocline and intrafolial folds can be found, as well as symmetrical and asymmetrical boudins. Although dispersed, the stretching lineation mainly occupies the SW and SE quadrants. S/C structures suggest, in general, top to NW movement. Moving upward, away from the basal detachment, deformation gradually decreases and the primary bedding (S₀) predominates again. In this case, faults and reverse and thrust shear zones are observed less frequently.

Caetité Nappe

This structure was mapped southwest of the town of Caetité (Figs. 3, 5 and 9), where the rocks of lithofacies association 2 of the Serra da Garapa Formation outcrop. The S₀//S₁ foliation is observed in intrafolial isoclinal folds, being transposed by the S₀//S₁//S₂ foliation (Fig. 8B). Both structures comprise a compositional banding and schistosity. In the compositional banding of the S₀//S₁//S₂ foliation, there is an alternation of aluminous schists, with varying proportions of quartz, muscovite, garnet, staurolite, chlorite, pyrite, hematite and graphite, and quartzites. The schistosity is marked by the muscovite orientation. In Fig. 7E, the S₀//S₁//S₂ foliation shows strong dispersion. Associated with the S₀//S₁//S₂ foliation occur the following microstructures:

1. granoblastic, sometimes polygonal, porphyroclastic and core-mantle, all associated with quartz. New polygonal grains are observed around quartz porphyroclasts;

2. porphyroblastic, poikiloblastic, helicitic, and pressure shadow, associated with garnet and staurolite₁;

3. lepidoblastic, by the preferential orientation of muscovite;

4. decussate, by the radial arrangement of staurolite₂ grains;

5. nematoblastic, associated with elongated quartz grains.

The stretching lineation (L_x2) (Fig. 8C) is marked by the preferential orientation of quartz. This structure is paralleled with a muscovite-oriented mineral lineation (L_m2). The general orientation of these structures is NE (Fig. 7F). Both lineations are paralleled with crenulation fold hinges (L_b2) (Figs. 7G and 8D). The axial plane foliation of the crenulation folds has strong dispersion in the diagram of Fig. 7H.

An interference fold pattern and superimposed fold (type III of Ramsay and Huber 1987Ramsay J.G., Huber M.I. 1987. The Techniques of Modern Structural Geology, 2; Folds and Fractures. London: Academic Press. 278 p.) is interpreted for the northern sector of Caetité Nappe (Fig. 9). The oldest folds (F₃) are open to smooth and harmonic (Sensu Ramsay and Huber 1987Ramsay J.G., Huber M.I. 1987. The Techniques of Modern Structural Geology, 2; Folds and Fractures. London: Academic Press. 278 p.). The second folding phase's structures are horizontal normal (Sensu Fleuty 1964Fleuty M.J. 1964. The descriptions of folds. Proceedings of the Geologist’ Association, 75:461-492. https://doi.org/10.1016/S0016-7878(64)80023-7
https://doi.org/10.1016/S0016-7878(64)80... ), open, and disharmonious (Sensu Ramsay and Huber 1987Ramsay J.G., Huber M.I. 1987. The Techniques of Modern Structural Geology, 2; Folds and Fractures. London: Academic Press. 278 p.). These structures are truncated by dextral transpressional shear zones (Fig. 7F) that structure the contacts of the Serra da Garapa Formation with the Algodão Formation and of this formation with the basement of the Paramirim Aulacogen.

Transpressive Domain

In this domain are outcrop units of the Algodão Formation, the Santo Onofre Group (Serra da Garapa and Boqueirão Formations), and the Macaúbas Group (Nova Aurora Formation) (Figs. 3 and 5), in addition to the basement rocks of the Paramirim Aulacogen and the Lagoa Real intrusive suite. Plane-parallel and crossed primary bedding are observed in metarenites of the Algodão Formation, especially in outcrops further away from the shear zones that structure the contacts of these units. The distribution of these primary structures has a maximum plane at 097°/50° (Fig. 10A). WNW dips are also observed. Predominantly south of the 14°30’ parallel (Fig. 5), an S₀//S₁ schistosity can be observed, which is positioned parallel to the compositional banding. The microstructures associated with this foliation are:

1. granoblastic, predominantly polygonal, in addition to porphyroclastic, core-mantle, mylonitic, pressure shadow, ribbons, σ-type mantled porphyroclast, all related to quartz grains;

2. lepidoblastic, by the preferential orientation of muscovite. The S₀//S₁ schistosity, in general, is oriented along NS to NE-SW, with dips between 30° and 78° to E (Fig. 10B).

In siliciclastic rocks, metamorphic paragenesis, when present, is mainly made up by quartz, muscovite, and chlorite.

The stretching lineation (L_x1) is marked by the preferential orientation of quartz and clasts in metaconglomerates and occupies the SE quadrants mainly and the NW quadrants subordinately (Fig. 10C). S/C/C’ structures suggest structural top to NW, and intrafolial isoclinal folds (F₁) are present. A mineral lineation L_m1 is positioned parallel to the stretching lineation L_x1, revealed by the orientation of phyllosilicates. Compressional and frontal overlapping duplexes and fans are found in the western contact between the Boqueirão Formation (Santo Onofre Group) and the basement rocks of the Paramirim Aulacogen in the Santo Onofre Shear Zone (Figs. 5 and 11A). The distributions of the S₀//S₁ foliation and the L_x1 stretching lineation in Figs. 10B and 10C diagrams suggest that these structures are folded (F₂) with a NE-SW hinge.

Primary bedding S₀ and metamorphic foliation S₁ are folded by the second generation of these structures (F₃) (Figs. 11B-11D). This generation's folds with asymmetrical, disharmonious, acylindrical, open, and closed envelopes predominate (Sensu Ramsay and Huber 1987Ramsay J.G., Huber M.I. 1987. The Techniques of Modern Structural Geology, 2; Folds and Fractures. London: Academic Press. 278 p.), from normal-horizontal, predominant, to reclined fold (Sensu Fleuty 1964Fleuty M.J. 1964. The descriptions of folds. Proceedings of the Geologist’ Association, 75:461-492. https://doi.org/10.1016/S0016-7878(64)80023-7
https://doi.org/10.1016/S0016-7878(64)80... ). The general vergence is to the west, and the reclined folds are located in the vicinity of dextral transpressional shear zones that limit the units of the Santo Onofre Group (Fig. 5). Parasitic in S, Z, M, or W and chevron folds are part of the framework. Especially in phyllites and metapelites, the folds develop axial plane foliation (S₃), spaced, and discontinuous (Sensu Passchier and Trouw 2005Passchier C.W., Trouw R.A.J. 2005. Microtectonics. 2. Ed. Berlin: Springer, 366 p.), with a NE-SW trend.

The reverse-dextral shear zones (Fig. 11E) have a general orientation NNE-SSW with inflection to NS and are mainly located in the contacts between the units of the Santo Onofre Group with the Algodão Formation, as well as in the contact of the rocks of this Formation with the basement rocks of the Paramirim Aulacogen (Fig. 5). The schistosity S₀//S₁//S₂//S₄ is found in these structures. The stretching lineation (L_x4) is marked by the preferential orientation of quartz, being medium to high rake and preferentially positioned in the NE-SW direction. A positive flower structure associated with a dextral transcurrent shear zone oriented according to NNE-SSW was interpreted E-SE of the town of Caetité and involves the basement units of the Aulacogen, the Lagoa Real Intrusive Suite, the Algodão Formation, and the Santo Onofre Group (Fig. 6). The kinematic indicators are S/C structures (Fig. 11F).

Related to these shear zones, a set of folds, less penetrative, asymmetrical in Z with a hinge of medium to a high angle of dip (Fig. 10G), later rotated the F₂ folds. This asymmetry can be observed on a map (Fig. 5).

The later structures of these domains are normal shear zones and negative flower structures described by Cruz et al. (2015)Cruz S.C.P., Alkmim F.F., Barbosa J.S.F., Dussin I., Gomes L.C.C. 2015. Tectonic inversion of compressional structures in the Southern portion of the Paramirim Corridor, Bahia, Brazil. Brazilian Journal of Geology, 45(4):541-567. https://doi.org/10.1590/2317-488920150030240
https://doi.org/10.1590/2317-48892015003... and interpreted as related to the orogenetic collapse of this sector of the Intracontinental Orogen.

DISCUSSION: DEFORMATIONAL EVOLUTION

The structural framework of the studied area is complex and each structural domain individualized in this study presents a distinct deformational history, but with the following structural relationships:

1. the Jacaraci Fold-Thrust Belt has deformational structures whose kinematic indicators suggest mass transport generically to the NW;

2. the similarity of the structural framework and the vergence of this belt with what was defined for the western sector of the Rio Pardo Salient by Cruz and Alkmim (2006)Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
   https://doi.org/10.1590/S0001-3765200600... ;

3. the oldest structures verified in the Transpressional Domain, specifically the S₀//S₁ foliation and the first-generation folds, have similar geometry and vergence to those found in the Jacaraci Fold-Thrust Belt, defined in this study, and in the Rio Pardo Salient;

4. the structures of the Rio Pardo Salient are the oldest structures related to the inversion of the Paramirim Aulacogen and that are regionally truncated by a dextral transpressional system related to the frontal to transpressional inversion phase of the Paramirim Aulacogen (Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
   https://doi.org/10.1590/S0001-3765200600... ). These structures have geometric and kinematic similarities, as well as physical continuity with the transpressional domain defined in this study;

5. the structures of Caetité Nappe, and their interference features, are associated with the late regional transpressional system with the inversion of the Paramirim Aulacogen (Phase Dp de Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
   https://doi.org/10.1590/S0001-3765200600... ), which truncates the structures of the Rio Pardo Salient.

From the identified structural relationships and their regional relationships, a total of six compressive deformation phases (D₁, D₂, D₃, D₄, D₅, and D₆) were interpreted for the study area. The correlations between the three structural domains defined in this study are shown in Table 1. These deformations were developed under a maximum regional stress field oriented according to WSW-ENE, which reactivated and inverted the extensional structures related to the long evolution of the Paramirim Aulacogen and the precursor basins of the Araçuaí-West Congo Orogen (Fig. 12A).

The first phase of compressional deformation (D₁) (Fig. 12B) was responsible for the formation of the Jacaraci Fold-Thrust Belt and the oldest structures (Foliation S₀//S₁) described in the Transpressional Domain. These structures were folded by the D₂ phase (Fig. 12C). D₁ and D₂ deformational phases are correlated with the D_a generation of Cruz and Alkmim (2006)Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... . They are associated with the development of the Rio Pardo Salient, whose nucleation, under the WSW-ENE stress field, is related to the counterclockwise rotation of the São Francisco-Congo Plate and the interaction between the Araçuaí Orogen and the Paramirim Aulacogen. In the Rio Pardo Salient, tectonic transport varies from SE to NW in its western region, from N to S in its central region, and from SW to NE in its eastern region (Cruz and Alkmim 2006Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... ). The deformational structures D₁ and D₂ of this study are positioned in the western sector of this salient and reflect the structural top to the NW.

Despite being interpreted as related to a fold-thrust belt, considering the geometry of the structures present in the Jacaraci region, a hypothesis that still needs to be tested is that this belt is a klippe associated with a nappe structure with movement directed to the NW. This nappe would have been amalgamated to the Transpressional Domain through a sinistral shear zone (Fig. 5).

The third, fourth, and fifth deformational phases (D₃, D₄, and D₅) (Fig. 12D) are related to the evolution of Caetité Nappe. In the third phase, the nucleation of foliation S₀//S₁ was observed in isoclinal folds intrafolial to foliation S₀//S₁//S₂.

In the fourth deformation phase (D₄), there was the development of locally hierarchical foliation in the nappe as S₀//S₁//S₂, as well as stretching lineation (L_x2), intrafolial isoclinal folds (F₂) and boudins. The vergence interpreted for this phase is toward SW. A relevant aspect is the presence of paragenesis with garnet and staurolite in lithofacies 2 rocks of the Serra da Garapa Formation, suggesting metamorphic conditions of amphibolite facies, with temperatures between 550 and 650°C and pressures between 250 and 750 MPa (Bucher and Grapes 2011Bucher K., Grapes R. 2011. Petrogenesis of metamorphic rocks. Berlin: Springer-Verlag, 441 p.). The metamorphic contrast between the rocks of lithofacies associations 1 and 2, as well as lithofacies association 2 of this formation with the Algodão Formation, in which sedimentary structures are still preserved, suggests that a high-angle structure associated with a transpressional system was responsible for stratigraphic inversions:

1. by the juxtaposition of aluminous schists with garnet and staurolite and quartzites from the Serra da Garapa Formation (lithofacies association 2) over graphitic phyllites with chlorite and metarenites from the lithofacies association 1 of this formation, of greenschist facies metamorphism;

2. by thrusting the Algodão Formation, of Statherian age, over the rocks of these Tonian units;

3. by thrusting the rocks of the Lagoa Real Intrusive Suite over the rocks of the Algodão Formation;

4. for the riding of this Estaterian suite by the basement of the Paramirim Aulacogen.

The nucleation of dextral transpressional system is related to the frontal to transpressional deformation of the Paramirim Aulacogen described by Cruz and Alkmim (2006)Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... . This deformation reactivates and inverts the extensional structures of the basin evolution phase and leads to the juxtaposition of rocks of higher metamorphic grade, of amphibolite facies (Bitencourt 2014Bitencourt C.N. 2014. Petrologia e análise estrutural multiescalar da Formação Serra da Garapa (Grupo Santo Onofre) na porção sul do Cinturão de Dobramentos e Cavalgamentos Espinhaço Setentrional. Corredor do Paramirim, Caetité, Bahia. Undergraduate Thesis, Universidade Federal da Bahia, Salvador, 118 p.), of lithofacies association 2 of the Serra da Garapa Formation on rocks of lithofacies association 1 of this formation, of greenschist facies. The nucleation of the high-angle structure responsible for stratigraphic inversions and for juxtaposing rocks of higher metamorphic grade on rocks of lower metamorphic grade is possibly related to reactivations of extensional structures of the aulacogen or structures older than 1.8 Ga from its basement. The importance of the structural inheritance of the basement of sedimentary basins in controlling the geometries of nucleated structures during their inversion has been demonstrated by several works (Carrera and Munoz 2013Carrera N., Munoz J.A. 2013. Thick-skinned tectonic style resulting from the inversion of previous structures in the southern Cordillera Oriental (NW Argentine Andes). In: Nemcok M., Mora A.R., Cosgrove J.W. (eds.). Thick-Skin-Dominated Orogens: From Initial Inversion to Full Accretion. London: Geological Society, Special Publications. 377 p. https://doi.org/10.1144/SP377.2
https://doi.org/10.1144/SP377.2... , Deng et al. 2017Deng C., Fossen H., Gawthorpe R., Rotevatn A., Jackson C.A.-.L., FazliKhani H. 2017. Influence of fault reactivation during multiphase rifting: the Oseberg area, northern North Sea rift. Marine and Petroleum Geology, 86:1252-1272. https://doi.org/10.1016/j.marpetgeo.2017.07.025
https://doi.org/10.1016/j.marpetgeo.2017... , Nepomuceno et al. 2021Nepomuceno F., Ribeiro A., Silva D.R., Pires G.L.C., Trouw R.A.J., Araújo M.C.N., Mafia M. 2021. Meso to Neoproterozoic polyphase rifting and tectonic inversion: The example of the São João del Rei region at the southern border of the São Francisco Craton, Brazil. Journal of South American Earth Science, 109:103294. https://doi.org/10.1016/j.jsames.2021.103294
https://doi.org/10.1016/j.jsames.2021.10... , among others).

In Caetité Nappe, the foliation S₀//S₁//S₂ was folded (F₃ fold) during the fifth deformational phase (D₅). The sixth and last deformational phase (D₆) (Fig. 12E) was observed in all three individualized compartments (Table 1), being responsible for the development of:

1. dextral transpressional reverse shear zones that structure the contacts between the units of the Santo Onfre Group with the Algodão Formation, as well as those units with the basement of the Paramirim Aulacogen, in this case inverting and reactivating the Santo Onofre and Borda Leste shear zones, located at west and east, respectively (Fig. 5);

2. F₃ folds with a general NS trend, null general vergence to WSW observed in the Jacaraci Fold-Thrust Belt, in the Transpressional Domain and in the Caetité Nappe;

3. F₄ folds with general NW-SE trend and fold interference structure (type III, sensu Ramsay and Huber 1987Ramsay J.G., Huber M.I. 1987. The Techniques of Modern Structural Geology, 2; Folds and Fractures. London: Academic Press. 278 p.) in Caetité Nappe;

4. F₃ folds, axial plane foliation (S₃), reverse to dextral transpressional shear zones, foliation S₀//S₁//S₃, mineral stretching lineation (L_x3), as well as positive flower and pop-up structures (Borges et al. 2015Borges J.O., Cruz S.C.P., Barbosa J.S.F., Santos E.S. 2015. Structural framework of the the Lagoa D’Anta mine area, iron-manganese Urandi-Caetité- Licínio de Almeida District, Bahia, Brasil. Brazilian Journal of Geology, 45(2):173-192. https://doi.org/10.1590/23174889201500020002
   https://doi.org/10.1590/2317488920150002... ) in the Transpressional Domain.

Later, there was the development of asymmetrical Z-folds with high-angle hinges, which reflect the dextral component of the regional transpression. The deformational phases D₃ to D₆ are correlated with the D_p phase of Cruz and Alkmim (2006)Cruz S.C.P., Alkmim F.F. 2006. The tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco Craton region, Easter Brazil. Anais da Academia Brasileira de Ciências, 78(1):151-173. https://doi.org/10.1590/S0001-37652006000100014
https://doi.org/10.1590/S0001-3765200600... and with the D_n-1 and D_n phases of Borges et al. (2015)Borges J.O., Cruz S.C.P., Barbosa J.S.F., Santos E.S. 2015. Structural framework of the the Lagoa D’Anta mine area, iron-manganese Urandi-Caetité- Licínio de Almeida District, Bahia, Brasil. Brazilian Journal of Geology, 45(2):173-192. https://doi.org/10.1590/23174889201500020002
https://doi.org/10.1590/2317488920150002... , which were nucleated under thick-skinned deformation conditions.

The last deformational phase is reported in the literature by Cruz et al. (2015)Cruz S.C.P., Alkmim F.F., Barbosa J.S.F., Dussin I., Gomes L.C.C. 2015. Tectonic inversion of compressional structures in the Southern portion of the Paramirim Corridor, Bahia, Brazil. Brazilian Journal of Geology, 45(4):541-567. https://doi.org/10.1590/2317-488920150030240
https://doi.org/10.1590/2317-48892015003... and described by those authors in the transpressional domain of this study. This phase nucleated extensional shear zones associated with the orogenetic collapse of the northern sector of the Araçuaí Intracontinental Orogen.

CONCLUSION

Three structural domains were identified in the study area: Jacaraci Fold-Thrust Belt, Caetité Nappe, and Transpressional Domain. The deformational evolution of these domains is complex, comprising six compressional and progressive phases. These phases are related to a maximum stress field, of Ediacaran age, with general orientation of WSW-ENE and are associated with structuring the Araçuaí-West Congo Orogen. The first phase (D₁), found in the Jacaraci Fold-Thrust Belt and the Transpressional Domain, is related to the evolution of the Rio Pardo Salient. The dextral transpressional system was responsible for the nucleation of the Caetité Nappe, for the deformations in the transpressional domains, with the development of a positive flower structure, and in the Jacaraci Fold-Thrust Belt, as well as for larger-scale structures. Regionally, this system is related to the frontal inversion of the Paramirim Aulacogen. At Caetité Nappe, there was a juxtaposition of:

1. rocks metamorphosed into amphibolite facies over lower temperature rocks;

2. basement rocks older than 1.8 Ga over the Statherian rocks of the Lagoa Real Intrusive Suite;

3. Lagoa Real Intrusive Suite and Algodão Formation (Espinhaço Supergroup) over Tonian rocks of the Santo Onofre Group (San Francisco Supergroup).

ACKNOWLEDGMENTS

This study was supported by the CAPES (Finance Code 001). The authors thank the FAPESB for the scholarship granted for Caroline Novais Bitencourt and the CNPq for the research fellowship grant provided to Simone Cerqueira Pereira Cruz (grant no. 306502/2018-6 and 309050/2021-9). The authors also thank the anonymous reviewers and editor of the article for their contributions to the improvement of this study.

REFERENCES

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