Análise estrutural da Falha da Lagartixa e arredores, Jacobina-BA
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Data
2019-07-23
Autores
Andrade, Cleberson Ernandes de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A Bacia de Jacobina (BA) possui longo histórico de exploração de ouro, sendo uma unidade Pré-Espinhaço inserida no contexto do Cráton do São Francisco correspondendo a uma bacia do extensional de idade arqueana, que inclui unidade de metaconglomerados (Formação Serra do Córrego) mineralizados em ouro, com pirita e uraninita detríticas, cuja mineralização é entendida como do tipo “paleoplacer” com influência hidrotermal. A evolução desta bacia é dividida em três etapas principais: sendo a primeira a abertura da bacia com sedimentação dando origem as unidades que compõem a Bacia de Jacobina e na continuidade da extensão do bacia, magmatismo ultrabásico alojado principalmente na forma de diques; já em uma segunda etapa tem-se a inversão da bacia com movimento compressivo (evento Dn) que deu origem aos cavalgamentos e foliação em alto ângulo; como terceira etapa compreende-se os eventos pós-Dn dentre eles se destacam a progressão do esforço compressivo e como último evento na região tem-se o colapso do orógeno. Tal evolução deu à área de estudo uma geometria complexa com descontinuidades tectônicas na direção N-S, e falhas transversais onde contatos litoestratigráficos são truncados. O objetivo principal deste trabalho é o estudo destas falhas transversais sendo elas a Falha da Lagartixa e outras duas falhas, uma a sul (Falha da Maricota), na região do Morro Serra do Córrego e outra a norte, na porção setentrional da área (Sistema de Falhas Sul-Viúva), através do levantamento estrutural de um polígono de 3,5 por 2,5 km. Como resultado desta pesquisa obteve-se que: 1) A Falha da Lagartixa tem atitude 152/55, tendo sua formação iniciada em evento pré- a sin-intrusão dos diques metaultramáficos (abertura da bacia) passando por reativações, com uma delas bem caracterizada, com evidências de movimentação normal; 2) Sistema de Falhas Sul-Viúva corresponde a um sistema com três falhas falhas principais, com planos sub-verticais (duas no Morro da Lagartixa e outra no Morro da Viúva), geradas em fase tardia, com movimentos destrais, sobrepostos por movimentos normais; 3)A Falha da Maricota tem atitude em torno de 160/75, com diques ultramáficos associado ao plano de falha, também correspondendo a uma falha formada na fase distensiva da Bacia de Jacobina com de reativação normal pós-Dn, tal qual é observado na Falha da Lagartixa.
The Jacobina Basin region has a long history of gold exploration, being inserted in the context of the São Francisco Craton (Pré-Espinhaço sequence). The Archean Jacobina Basin is characterized by an extensional basin which include metaconglomerates (Serra do Córrego Formation) mineralized in gold, with pyrite and detrital uraninite, whose mineralization is understood as the “paleoplacer” type with the hydrothermal influence. The evolution of this basin is divided in three main stages: (i) the first stage is related with the opening of the basin, with sedimentation giving rise to the units that compose the Jacobina Basin. This stage is followed by ultrabasic magmatism emplaced mainly in the form of the dykes; (ii) the second stage is characterized by the basin invertion with compressive movement (Dn event) that gave the origin to the thrust fault and foliation in high dip; (iii) the third and final stage comprises the post-Dn events, among them stand out the progression of the compressive effort and followed by the collapse of the orogen. Such evolution gave the study area a complex geometry with discontinuities in the N-S direction, and transverse faults where lithostratigraphic contacts are truncated. The main objective of this dissertation is to understand these transverse faults. We studied the Lagartixa Fault and other two faults: Maricota Fault (to the south; Serra do Córrego hill region), and the Sul-Viúva Fault System (northern region of the studied area). We performed this study through the structural survey of a polygon of 3.5 by 2.5 Km, encompassing the area of occurrence of these three faults. The Lagartixa Fault has NE-SW direction with attitude 152/55, dipping in high angle towards SE. The formation of this fault can be related with pre- to sin- metaultramafic dykes intrusions (basin opening stage). We also observed evidences of fault reactivations in the field and on petrographic scale analysis. The Sul-Viúva Fault System corresponds to system controlled be three faults with subvertical planes (two in Morro da Lagartixa and one in Morro da Viúva). These faults were generated in a later stage. The Maricota Fault has the attitude nearby to 160/75. We observed the occurrence of ultramafic dykes associated with the fault plans. This fault is formed in the distensive phase of the Jacobina Basin and has a history of reactivation, same pattern observed in the Lagartixa Fault.
The Jacobina Basin region has a long history of gold exploration, being inserted in the context of the São Francisco Craton (Pré-Espinhaço sequence). The Archean Jacobina Basin is characterized by an extensional basin which include metaconglomerates (Serra do Córrego Formation) mineralized in gold, with pyrite and detrital uraninite, whose mineralization is understood as the “paleoplacer” type with the hydrothermal influence. The evolution of this basin is divided in three main stages: (i) the first stage is related with the opening of the basin, with sedimentation giving rise to the units that compose the Jacobina Basin. This stage is followed by ultrabasic magmatism emplaced mainly in the form of the dykes; (ii) the second stage is characterized by the basin invertion with compressive movement (Dn event) that gave the origin to the thrust fault and foliation in high dip; (iii) the third and final stage comprises the post-Dn events, among them stand out the progression of the compressive effort and followed by the collapse of the orogen. Such evolution gave the study area a complex geometry with discontinuities in the N-S direction, and transverse faults where lithostratigraphic contacts are truncated. The main objective of this dissertation is to understand these transverse faults. We studied the Lagartixa Fault and other two faults: Maricota Fault (to the south; Serra do Córrego hill region), and the Sul-Viúva Fault System (northern region of the studied area). We performed this study through the structural survey of a polygon of 3.5 by 2.5 Km, encompassing the area of occurrence of these three faults. The Lagartixa Fault has NE-SW direction with attitude 152/55, dipping in high angle towards SE. The formation of this fault can be related with pre- to sin- metaultramafic dykes intrusions (basin opening stage). We also observed evidences of fault reactivations in the field and on petrographic scale analysis. The Sul-Viúva Fault System corresponds to system controlled be three faults with subvertical planes (two in Morro da Lagartixa and one in Morro da Viúva). These faults were generated in a later stage. The Maricota Fault has the attitude nearby to 160/75. We observed the occurrence of ultramafic dykes associated with the fault plans. This fault is formed in the distensive phase of the Jacobina Basin and has a history of reactivation, same pattern observed in the Lagartixa Fault.
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Palavras-chave
Geologia estrutural, Reativação de falhas, Magmatismo ultramáfico, Bacia Jacobina, Structural geology, Fault reactivation, Ultramafic magmatism, Jacobina basin