Skip to main content

Advertisement

We’d like to understand how you use our websites in order to improve them. Register your interest.

Geoelectric structure beneath limestones of the Sao Francisco Basin, Brazil

Abstract

A reconnaissance MT survey was conducted in the southern portion of the Sao Francisco Sedimentary Basin, Brazil, for mapping the subsurface structure. The objective was to provide a regional model and in helping to select areas to be further surveyed with seismics. The data collected at seven EMAP-style spreads of 500 m, with an average spacing of 30 km. The field procedure allowed for the correction of statics and the production of 7 inverted models, smooth representations of the regional structure as seen below each site. A 2-D forward model tested and refined the regional structure revealed by the inversions and yielded an earth composed of 4 main geologic units. A 100 ohm.m limestone layer on the top of 20 ohm.m shales, followed by a 1000-200 ohm.m structured basement. Crustal resistivities do not change until reaching depths of more than 30 km. The model ends at a conductive half-space of 30 ohm.m. A suture zone between an orogenic belt and the Sao Francisco craton was modeled below the sedimentary section bringing its know limits 60 km to the east.

References

  1. Alkimin, F. F., B. B. B. Neves, and F. C. Alves, Arcabouco tectonico do craton de Sao Francisco, uma revisao, in III Simposio do Craton do Sao Francisco, pp. 45–62, Salvador, Brazil, 1993 (in Portuguese).

  2. Assumpcao, M., E. P. Fernandes, and J. O. Araujo Filho, Levantamento gravimetrico no Complexo de Barro Alto, GO, resultados preliminares, Revista Brasileira de Geofisica, 3, 17, 1984 (in Portuguese).

  3. Bahr, K.. Geological noise in magnetotelluric data: a classification of distortion types, Phys. Earth Planet. Inter., 66, 24–38, 1991.

  4. Beamish, D. and J. M. Travassos, Magnetotelluric imaging of basalt-covered sediments, First Break, 10, 345–357, 1992.

  5. Beamish, D. and J. M. Travassos, A study of magnetotelluric static distortion in the context of intrusive volcanism, Geophys. Prosp., 41, 61–82, 1993.

  6. Berrocal, J. A., S. Alarcon, and E. Pedreschi, Modelo preliminar da estrutura crusta na regiao proxima ao reservatorio de Sobradinho (BA) atraves do metodo de refracao sismica profunda, Anais CISBGf, Rio de Janeiro, 1, 109, 1989 (in Portuguese).

  7. Blitzkow, D., P. Gasparini, M. S. M. Mantovani, and N. C. Sa, Crustal structures of SE Minas Gerais, Brazil, deduced from gravity measurements, Revista Brasileira de Geociencias, 9, 39–43, 1979.

  8. Braun, O. P. G., Novas contribuicoes a estratigrafia do Grupo Bambui, XXXII Cong. Bras. Geol., Salvador, 1, 159–161, 1982 (in Portuguese).

  9. Braun, O. P. G., U. Mello, and H. D. Della Piazza, Bacias proterozoicas brasileiras com perspectivas exploratorias para hidrocarbonetos, in Origem e Evolucao de Bacias sedimentares, pp. 115–132, PETROBRAS, 1990 (in Portuguese).

  10. Brown, C., Tectonic interpretation of regional conductivity anomalies, Surv. Geophys., 15, 123–157, 1994.

  11. Chave, A. D. and D. J. Thomson, Some comments on magnetotelluric response function estimation, J. Geophys. Res., 94, 14,215–14,225, 1989.

  12. Chave, A. D. and D. J. Thomson, Robust, controlled leverage estimation of magnetotelluric response functions, in Proc. 11th Workshop on Electro-magnetic Induction in the Earth, Abstract 8.13, Victoria University, New Zealand, 1992.

  13. Chave, A. D., D. Thomson, and M. Ander, On the robust estimation of power spectra, coherences, and transfer functions, J. Geophys. Res., 92, 633–648, 1987.

  14. Chouteau, M., P. Zhang, D. J. Dion, B. Giroux, R. Morin, and S. Krivochieva, Delineating mineralization and imaging the regional structure with magnetotellurics in the region of Chibougamau (Canada), Geophys., 62, 730–748, 1997.

  15. Clarke, J., T. D. Gamble, W. M. Goubau, R. H. Koch, and R. F. Miracky, Remote reference magnetotellurics: equipment and procedures, Geophys. Prosp., 31, 149–170, 1983.

  16. CPRM, Mapa Geologico do Brasil e da area oceanica adjacente incluindo deposito minerais, C. Schobbenhaus, gen. coordinator, CPRM, 1995 (in Portuguese).

  17. D’Arrigo, H. B. P. and F. F. Alkmim, O Alto de Sete Lagoas e sua reativacao, Anais V Simposio Nacional de Estudos Tectonicos, Gramado (RS), Brazil, 21–22, 1995 (in Portuguese).

  18. Dey, A. and H. F. Morrison, Resistivity modeling for arbitrary shaped three-dimensional structures, Geophys., 44, 753–780, 1979.

  19. Egbert, G. D. and J. R. Booker, Robust estimation of geomagnetic transfer function, Geophys. J. R. astr. Soc., 87, 173–194, 1986.

  20. Gamble, T. D., W. M. Goubau, and J. Clarke, Magnetotelluric with a remote reference, Geophys., 44, 53–68, 1979.

  21. Groom, R. W. and K. Bahr, Corrections for the near-surface effects: decomposition of the magnetotelluric impedance tensor and scaling corrections for regional resistivities, Surv. Geophys., 13, 341–380, 1992.

  22. Groom, R. W. and R. C. Bailey, Decomposition of magnetotelluric impedance tensors in the presence of local three-dimensional galvanic distortion, J. Geophys. Res., 94, 1913–1925, 1989.

  23. Haak, V. and R. Hutton, Electrical resistivity in the continental lower crust, in Nature of the lower continental crust, Geol. Soc. Spec. Publ., 24, 34–49, 1986.

  24. Haak, V., M. Eisel, G. Nover, J. Stoll, A. Kontny, E. Huenges, U. Harms, and J. Kueck, KTB and the electrical conductivity of the crust, J. Geophys. Res., 102, 18,289–18,306, 1996.

  25. Hyndman, R. D. and P. M. Shearer, Water in the lower continental crust: modeling magnetotelluric and seismic reflection results, Geophys. J. Int., 98, 343–365, 1989.

  26. Jiracek, G. R., Nearsurface and topographic distortion in electromagnetic induction Surveys, Geophys., 11, 163–203, 1990.

  27. Jones, A. G., Static shift of magnetotelluric and its removal in a sedimentary basin environment, Geophys., 53, 967–978, 1988.

  28. Knize, S., J. A. Berrocal, and D. M. Oliveira, Modelo preliminar de velocidades sismicas de crosta atraves de explosoes locais registradas pela rede sismografica de sobradinho BA, Revista Brasileira de Geofisica, 2, 95–104, 1984 (in Portuguese).

  29. Larsen, J. C., Transfer functions: smooth robust estimates by least squares and remote reference methods, Geophys. J. Int., 99, 645–663, 1989.

  30. Larsen, J. C., R. L. Mackie, A. Manzella, A. Fiordelisi, and S. Rieven, Robust smooth MT transfer functions, Geophys. J. Int., 124, 801–819, 1996.

  31. Lesquer, A., F. F. M. Almeida, A. Davino, J. C. Lachaud, and P. Maillard, Signification structurale des anomalies gravimetriques de la partie sud du Craton Sao Francisco (Bresil), Tectonophysics, 76, 273–293, 1981.

  32. Mackie, R. L, T. R. Madden, and P. E. Wannamaker, Three-dimensional magnetotelluric modeling using difference equations theory and comparisons to integral equations, Geophys., 58, 215–226, 1993.

  33. Marchioreto, A. and M. Assumpcao, Inversao tomografica com ondas Rayleigh no sul do Craton do Sao Francisco e Faixa de dobramentos Brasilia-Uruacu, Anais 5 Cong. Int. Soc. Bras. Geofisica, 2, 983–986, 1997 (in Portuguese).

  34. Murray, G. E., M. J. Kaczor, and R. E. Macarthur, Indigenous pre-cambrian petroleum revisited, AAPG Bull., 64, 1681–1700, 1980.

  35. Ortu, J. C., Modelagem tectonofisica da porcao sul da Bacia do Sao Francisco, MG, M.Sc. Thesis, UFOP, 148 pp., Ouro Preto, 1990 (in Portuguese).

  36. Pellerin, L. and G. W. Hohmann, Transient electromagnetic inversion, a remedy for magnetotelluric static shifts, Geophys., 55, 1242–1250, 1990.

  37. Porsani, J. L., Estudo da estrutura geoeletrica da regiao do Jurua, M.Sc. Thesis, UFPa, 102 pp., 1991 (in Portuguese).

  38. Porsani, J. L. and S. L. Fontes, Estudo magnetotelurico na Bacia do Sao Francisco, Relatorio PETROBRAS/CENPES/SEGEF, 30 pp., 1993 (in Portuguese).

  39. Schwarz, G., Electrical condutivity of the earth’s crust and upper mantle, Surv. Geophys., 11, 133–161, 1990.

  40. Simpson, F., Stress and seismicity in the lower continental crust: a challenge to simple ductility and implications for electrical conductivity mechanim, in Anals of the 14th Workshop on Electromagnetic Induction in the Earth, pp. 215–228, Sinaia, 1998.

  41. Smith, J. T. and J. R. Booker, Rapid inversion of two and three-dimensional magnetotelluric data, J. Geophys. Res., 96, 3905–3922, 1991.

  42. Stanley, W. D., A. R. Saad, and W. Ohofugi, Regional magnetotelluric surveys in hydrocarbon exploration, Parana Basin, Brazil, Bull. AAPG, 69, 346–360, 1985.

  43. Sutarno, D. and K. Vozoff, Phase-smoothed robust M-estimation of magnetotelluric impedance functions, Geophys., 36, 938–942, 1991.

  44. Thomaz Filho, A., K. Kawashita, and U. G. Cordani, A origem do Grupo Bambui no contexto da evolucao geotectonica e idades radiometricas, Anais da Academia Brasileira de Ciencias, 78, 527–548, 1998 (in Portuguese).

  45. Torres-Verdin, C. and F. X. Bostick, Jr., Implications of the Born approximation for the magnetotelluric problem in three-dimensional environments, Geophys., 57, 587–602, 1992a.

  46. Torres-Verdin, C. and F. X. Bostick, Jr., Principles of spatial surface electric field filtering in magnetotellurics: electromagnetic array profiling (EMAP), Geophys., 57, 603–622, 1992b.

  47. Ussami, N., Interpretation of the gravity anomalies of Bahia state (Brazil), Ph.D. Thesis, University of Durham, 234 pp., 1986.

  48. Ussami, N., Estudos geofisicos no Craton do Sao Francisco: estagio atual e perspectivas futuras, in III Simposio do Craton do Sao Francisco, pp. 35–43, Salvador, Brazil, 1993 (in Portuguese).

  49. Valeriano, C. M., Evolucao tectonica da extremidade meridional da faixa Brasilia, regiao da represa de Furnas, sudoeste de Minas Gerais, Ph.D. Thesis, Instituto de Geociencias USP, 198 pp., Sao Paulo, Brazil, 1992 (in Portuguese).

  50. Wannamaker, P. E., Advances in three-dimensional magnetotelluric modeling using integral equations, Geophys., 56, 1716–1728, 1991.

  51. Wannamaker, P. E., G. W. Hohmann, and W. A. San Filipo, Electromagnetic modeling of 3-D bodies in layered earth using integral equations, Geophys., 49, 60–74, 1984.

  52. Wannamaker, P. E., J. A. Stodt, and L. Rijo, A stable finite element solution for two-dimensional magnetotelluric modeling, Geophys. J. R. astr. Soc., 88, 277–296, 1987.

  53. Wu, N., J. R. Booker, and T. Smith, Rapid two-dimensional inversion of Coprod2 data, J. Geomag. Geoelectr., 45, 1073–1087, 1993.

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to J. M. Travassos.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Travassos, J.M., Menezes, P.T.L. Geoelectric structure beneath limestones of the Sao Francisco Basin, Brazil. Earth Planet Sp 51, 1047–1058 (1999). https://doi.org/10.1186/BF03351578

Download citation

Keywords

  • Apparent Resistivity
  • Static Shift
  • Impedance Tensor
  • Lower Continental Crust
  • Resistive Rock