Simone Cerqueira Pereira Cruz

The Tectonic interaction between the Paramirim Aulacogen and the Araçuaí Belt, São Francisco craton region, Eastern Brazil

The Paramirim aulacogen, hosted in the northern part of the São Francisco craton, corresponds to two superimposed and partially inverted rifts of Paleo and Neoproterozoic ages. The Rio Pardo salient of the Araçuaí belt defines the local limit of the craton and interferes with the aulacogen structures. In order to understand the mechanism and timing of the tectonic interaction between these tectonic features during the inversion processes, a structural analysis was undertaken in the southern Paramirim aulacogen and along the Rio Pardo salient. The results obtained indicate that the Rio Pardo salient formed during an early stage of closure of the Neoproterozoic Macaúbas rift system and consequent initiation of the Araçuaí orogen. The orogenic front propagated further northwards into the craton, causing a first stage of inversion in the southern terminus of the aulacogen trough. Subsequently, the Paramirim aulacogen experienced the main stage of inversion, which led to the development of a NNW-oriented basement involved fold-thrust system. These fabric elements overprint the Rio Pardo salient, and the structures of both the first and second stages of inversion affect the Salitre Formation, the youngestNeoproterozoic unit of the area, clearly indicating a Late Neoproterozoic maximum age for all the inversion stages of the Paramirim aulacogen.

Inversão tectônica de estruturas compressionais da porção Sul do Corredor do Paramirim, Bahia

The Paramirim Corridor represents the maximum inversion zone of the Paramirim Aulacogen. Reverse-to-reverse dextral shear zones and various types of folds dominate such corridor. These structures reflect a stress field that is WSW-ENE oriented, developed in units of Aulacogen basement, as well as in the Lagoa Real Intrusive Suite, of Statherian age, in Espinhaco and Sao Francisco supergroups, of Statherian-Tonian and Cryogenian ages, respectively, and in the Macaubas-Santo Onofre Group, of Tonian age at the most. A rich collection of extensional structures truncate compressional structures of the Paramirim Corridor, characterized by normal shear zones and foliation, which is sometimes mylonitic, down-dip stretching lineation, drag folds, traction fractures and S/C structures. In these shear zones, quartz occurs truncated by the foliation, while feldspars are fractured and altered to white mica. Distribution of the quartz c-axes is at a maximum of 14° from the Z-axis. Thus, it suggests that the deformation activated mainly the basal glide planes in the direction. The paleostress study using the Win-Tensor software demonstrated that the regimen ranged between radial and pure distention. The S1 direction oscillated around a vertical trend, while s3 was sub-horizontal, with a predominant N230-050° direction. Ar-Ar ages in biotite obtained from the extensional shear zones ranged from 480 and 490 Ma. Together, data obtained for the structures associated with the late extensional regimen described in the present study suggest that its nucleation is associated with distal and brittle-ductile sectors of the gravitational collapse zone of Aracuai-West Congo Orogen.

Structural framework of rocks of the Lagoa D'anta mine area, iron-manganese Urandi-Caetité-Licínio de Almeida District, Bahia, Brasil

O Distrito Ferro-Manganesifero Urandi-Caetite-Licinio de Almeida congrega um total de 35 minas de manganes, a maioria exaurida, e 1 mina de ferro, em atividade, cujas rochas hospedeiras dos minerios estao associadas com a Sequencia MetavulcanossedimentarCaetite-Licinio de Almeida, de idade paleoproterozoica. Essas unidades encontram-se deformadas pelo Cinturao de Dobramentos e Cavalgamentos Serra do Espinhaco setentrional, na porcao norte do Orogeno Aracuai. Na mina Lagoa Danta, foram identificadas intercalacoes de itabirito, cummingtonita xistos, marmore calcitico e manganodolomitico, rochas calcissilicaticas e carbonato-silicaticas, metabasalto anfibolitico, alem de quartzo-jacobsita xisto, solo residual rico em manganes e brecha lateritica manganesifera. O arcabouco estrutural principal apresenta trend geral NE-SW, sendo constituido dominantemente por estruturas compressionais. Esse arcabouco esta associado com a evolucao de duas zonas de cisalhamento transpressionais destrais, de idade ediacarana, denominadas de Carrapato, a oeste, e Sao Timoteo, a leste. O arcabouco estrutural na mina Lagoa Danta reflete um maior grau de encurtamento no setor sul do Cinturao de Dobramentos e Cavalgamentos Serra do Espinhaco setentrional, na porcao norte do Orogeno Aracuai. As estruturas ducteis relacionadas com essas fases deformacionais foram geradas em condicoes de metamorfismo progressivo com temperatura minima de 550°C. Estruturas stockwork de quartzo, calcita, epidoto, grunerita e magnetita truncam as estruturas ducteis da mina. Fraturas foram os principais canais de circulacao de agua meteorica que culminou com a formacao de um minerio supergenico de alto teor na mina.

Geologia e arcabouço estrutural da Sequência Metavulcanossedimentar Urandi, Bahia

The Urandi Metavolcanosedimentary Sequence (UMS) is located in the northern portion of the Aracuai Orogen. Its basement consists of rocks from the Santa Isabel Complex. This unit represents one of the metavolcanosedimentary sequences of the southern portion of the Gaviao Block. The geological mapping, performed on a scale of 1:2,000, allowed the identification of amphibolitic metabasalts, itabirites, metapelites, queluzites, marbles, calcic-silicate rocks and quartzites. The structural survey allowed the identification of three deformational and compressional stages: Dn; Dn+1 (divided into Dn+1 and Dn+1), which were nucleated under an E-W to NE-SE orientated stress field; and Dn+2, whose structures reflect a WSW-ENE orientated stress field. The two most ancient stages are possibly related to the deformations of Rhyacian-Orosirian age, while the last deformational stage reflects the interactions between the substrate from the Paramirim Aulacogen and the Aracuai Orogen. The mineral paragenesis that was observed suggests amphibolite facies condition for the first two stages and greenschist for the last one.

The Paramirim Aulacogen

The Paramirim aulacogen occupies the region of the northern Sao Francisco craton that extends from the northern Espinhaco range to a large plateau known as the Chapada Diamantina in the northeastern Brazilian state Bahia. Corresponding to a long-lived and partially inverted rift-sag basin, the aulacogen hosts and exposes the most complete section of the cratonic cover complex accumulated between the Statherian and Edicaran periods. The sedimentary and volcanic rocks of the basin fill successions are grouped into two major lithostratigraphic units, the Espinhaco and Sao Francisco supergroups. Exhibiting remarkable facies differentiation between their occurrences in the northern Espinhaco range, on the west, and Chapada Diamantina, on the east, these units are associated with Statherian granitic rocks, as well as Statherian, Calymmian and Tonian mafic dykes and sills. The Espinhaco Supergroup comprises five unconformity bounded sequences, which record alternating mechanical and flexural subsidence pulses that took place between 1775 and 900 Ma. Frankly dominated by quartz-rich sandstones, deposited in alluvial, aeolian and shallow marine systems, the supergroup reflects continuous recycling of sediments in the large depocenters of the aulacogen. The Neoproterozoic Sao Francisco Supergroup is composed of three distinct sequences, deposited between 900 and 500 Ma, among them the glaciogenic Bebedouro Formation and the shallow marine carbonates and pelites of the Salitre Formation. The overall geologic architecture of the aulacogen is dominated by structures generated during its contractional inversion in the Edicaran/Cambrian boundary. The regional structure of the aulacogen corresponds to a NNW-trending basement cored uplift, flanked on both sides by systems of reverse faults, thrusts, folds, and strike-slip shear zones. Structures related to the basin generation processes are preserved only in a small area of the central segment of the aulacogen. The dominant NNW-oriented fabric elements interact or are overprinted by E–W-trending structures in the northern and southern ends of the aulacogen. These structures represent the Neoproterozoic Brasiliano orogenic fronts that propagated from the marginal belts toward the craton interior.

Lithogeochemistry and geochronology of the subalkaline felsic plutonism that marks the end of the Paleoproterozoic orogeny in the Salvador–Esplanada belt, São Francisco craton (Salvador, state of Bahia, Brazil)

Studies conducted over the last decade concerning the rocks that underlie the municipality of Salvador have shown a complex geological history with a great diversity of medium- to high-grade metamorphic lithotypes, deformed in several phases and frequently cut by tabular mafic dykes and irregular granitic bodies. The latter, which were the subject of this study, frequently outcrop along the coastline of Salvador and are classified petrographically as monzo-syenogranites. They are classified as subalkaline and peraluminous according to their geochemical data, and stand out for being enriched in light rare earth elements and having a strong negative Europium (Eu) anomaly. These rocks are produced from anatectic melts nor through the interaction of mantle-derived magmas with crustal materials. The negative values of eNd(t) (-6.08) corroborate with the crustal character and in the diagrams of tectonic ambience, they are plotted in the field of post-tectonic granites. The Sm-Nd model age (TDM) around 2.9 Ga indicates a neoarchean source for these lithotypes, whereas their U-Pb zircon age (LA-ICPMS) of 2,064 ± 36 Ma is similar to the U-Pb (SHRIMP) and Pb-Pb (evaporation) ages for late-tectonic granites of the Itabuna–Curaca–Salvador belt. Considering the results of recent studies in the area of Salvador, the monzo- syenogranites can be interpreted as late-tectonic intrusions, since they are affected by dextral shear zones correlated with the last stage of deformation registered in the granulites of Salvador.

Structural framework of Bananeira Mine, Miguel Calmon, Bahia: a contribution to study of the tectonic evolution of the Itabuna-Salvador-Curaçá Orogen

O Orogeno Salvador-Curaca posiciona-se na porcao nordeste do Craton do Sao Francisco e representa uma incisao orogenica paleoproterozoica gerada a partir da colisao entre os blocos Gaviao, Serrinha, Jequie e Itabuna-Salvador-Curaca. Este trabalho apresenta os resultados da analise estrutural realizada na Mina Bananeira, no Municipio de Miguel Calmon (BA), onde aflora uma sequencia supracrustal, de idade ainda controversa, rica em manganes. Duas familias de estruturas foram identificadas, uma compressional, constituida pelas estruturas das fases Dn-1, Dn, Dn+1 e Dn+2, que corresponde as fases tangencial e transpressional sinistral, respectivamente. Nesse contexto, pode ser encontrada uma foliacao Sn-1//Sn que foi dobrada (Fase Dn+1). Zonas de cisalhamento foram nucleadas na fase final de deformacao compressional (Fase Dn+2). O acervo mais jovem e marcado pela presenca de zonas de cisalhamento normais, ruptil-ducteis (Fase Dn+3) e de estruturas rupteis caracterizadas por zonas de cisalhamento cataclasticas e fraturas de extensao, nas quais ha remobilizacao de manganes.

Arcabouço estrutural da Mina Bananeira, Miguel Calmon, Bahia[/title]: [subtitle]uma contribuição ao estudo da evolução tectônica do Orógeno Itabuna-Salvador-Curaçá

O Orogeno Salvador-Curaca posiciona-se na porcao nordeste do Craton do Sao Francisco e representa uma incisao orogenica paleoproterozoica gerada a partir da colisao entre os blocos Gaviao, Serrinha, Jequie e Itabuna-Salvador-Curaca. Este trabalho apresenta os resultados da analise estrutural realizada na Mina Bananeira, no Municipio de Miguel Calmon (BA), onde aflora uma sequencia supracrustal, de idade ainda controversa, rica em manganes. Duas familias de estruturas foram identificadas, uma compressional, constituida pelas estruturas das fases Dn-1, Dn, Dn+1 e Dn+2, que corresponde as fases tangencial e transpressional sinistral, respectivamente. Nesse contexto, pode ser encontrada uma foliacao Sn-1//Sn que foi dobrada (Fase Dn+1). Zonas de cisalhamento foram nucleadas na fase final de deformacao compressional (Fase Dn+2). O acervo mais jovem e marcado pela presenca de zonas de cisalhamento normais, ruptil-ducteis (Fase Dn+3) e de estruturas rupteis caracterizadas por zonas de cisalhamento cataclasticas e fraturas de extensao, nas quais ha remobilizacao de manganes.

Arcabouço estrutural da Mina Bananeira, Miguel Calmon, Bahia: uma contribuição ao estudo da evolução tectônica do Orógeno Itabuna-Salvador-Curaçá

O Orogeno Salvador-Curaca posiciona-se na porcao nordeste do Craton do Sao Francisco e representa uma incisao orogenica paleoproterozoica gerada a partir da colisao entre os blocos Gaviao, Serrinha, Jequie e Itabuna-Salvador-Curaca. Este trabalho apresenta os resultados da analise estrutural realizada na Mina Bananeira, no Municipio de Miguel Calmon (BA), onde aflora uma sequencia supracrustal, de idade ainda controversa, rica em manganes. Duas familias de estruturas foram identificadas, uma compressional, constituida pelas estruturas das fases Dn-1, Dn, Dn+1 e Dn+2, que corresponde as fases tangencial e transpressional sinistral, respectivamente. Nesse contexto, pode ser encontrada uma foliacao Sn-1//Sn que foi dobrada (Fase Dn+1). Zonas de cisalhamento foram nucleadas na fase final de deformacao compressional (Fase Dn+2). O acervo mais jovem e marcado pela presenca de zonas de cisalhamento normais, ruptil-ducteis (Fase Dn+3) e de estruturas rupteis caracterizadas por zonas de cisalhamento cataclasticas e fraturas de extensao, nas quais ha remobilizacao de manganes.