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Studia Geophysica et Geodaetica

, Volume 60, Issue 1, pp 141–161 | Cite as

Integrated interpretation of the magnetotelluric and magnetic data from Mahallat geothermal field, Iran

  • Behrooz Oskooi
  • Mahmoud Mirzaei
  • Behnam Mohammadi
  • Mohammad Mohammadzadeh-Moghaddam
  • Feridon Ghadimi
Article

Abstract

Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km2 around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent.

Keywords

geothermal field inversion Iran magnetic magnetotelluric Mahallat 

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References

  1. Ander M.A., Gross R. and Strangway D.W., 1984. A detailed magnetotelluric/audiomagnetotelluric study of the Jemez Volcanic Zone, New Mexico. J. Geophys. Res., 89(B5) 3335–353, DOI: 0.1029/JB089iB05p03335.CrossRefGoogle Scholar
  2. Bartel L.C. and Obson R.D., 1987. Results of a controlled-source audio-frequency magnetotelluric survey at the Puhimau thermal area, Kilauea Volcano, Hawaii. Geophysics, 52, 665–77, DOI: 0.1190/1.1442334.CrossRefGoogle Scholar
  3. Beiki M., 2010. Analytic signals of gravity gradient tensor and their application to estimate source location. Geophysics, 75, I59–I74, DOI: 10.1190/1.3493639.CrossRefGoogle Scholar
  4. Beitollahi A., 1996. Travertine Formation and the Origin of the High Natural Radioactivity in the Region of Mahallat Hot Springs. M.Sc. Thesis. Islamic Azad University of Tehran, Iran, 120 pp.Google Scholar
  5. Berktold A., 1983. Electromagnetic studies in geothermal regions. Surv. Geophys., 6, 173–200.CrossRefGoogle Scholar
  6. Bhattacharyya B.K. and Leu L.K., 1975. Analysis of magnetic anomalies over Yellowstone National Park: Mapping of Curie point isothermal surface for geothermal reconnaissance. J. Geophys. Res., 80, 4461–4465, DOI: 10.1029/JB080i032p04461.CrossRefGoogle Scholar
  7. Bibby H.M., Dawson G.B., Rayner H.H., Bennie S.L. and Bromley C.J., 1992. Electrical resistivity and magnetic investigations of the geothermal systems in the Rotorua area, New Zealand. Geothermics, 21, 1–2, 43–64, DOI: 10.1016/0375-6505(92)90067-J.CrossRefGoogle Scholar
  8. Bournas N., Galdeano A., Hamoudi M. and Baker H., 2003. Interpretation of the aeromagnetic map of Eastern Hoggar (Algeria) using the Euler deconvolution, analytic signal and local wavenumber methods. J. Afr. Earth Sci., 37, 191–205. DOI: 10.1016/j.jafrearsci.2002.12.001.CrossRefGoogle Scholar
  9. Bruhn D., Manzella A., Vuataz F., Faulds J., Moeck I. and Erbas K., 2010. Exploration methods. In: Huenges E. (Ed.), Geothermal Energy Systems: Exploration, Development, and Utilization. Wiley-VCH Verlag, Weinheim, Germany, 78–79, DOI: 10.1002/9783527630479.ch2.Google Scholar
  10. Cagniard L., 1953. Basic theory of the magnetotelluric method in geophysical prospecting. Geophysics, 8, 605–635.CrossRefGoogle Scholar
  11. Caldwell T.G., Bibby H.M. and Brown C., 2004. The magnetotelluric phase tensor. Geophys. J. Int., 158, 457–469.CrossRefGoogle Scholar
  12. Cantwell T. and Madden T.R., 1960. Preliminary report on crustal magnetotelluric measurements. Geophysics, 65, 4202–4205, DOI: 10.1029/JZ065i012p04202.CrossRefGoogle Scholar
  13. Davy B.W. and Caldwell T.G., 1998. Gravity, magnetic and seismic surveys of the caldera complex, Lake Taupo, North Island, New Zealand. J. Volcanol. Geotherm. Res., 81, 69–89.CrossRefGoogle Scholar
  14. Dhanunjaya Naidu G., Manoj C., Patro P., Sreedhar S. and Harinarayana T., 2011. Deep electrical signatures across the Achankovil shear zone, southern Granulite Terrain inferred from magnetotellurics. J. Gondwana Res., 577, 367–389.Google Scholar
  15. Hermance J.F., 1985. Magnetotelluric measurements across the Eastern neovolcanic zone in south Iceland. J. Geophys Res., 90(B12), 10093–10103, DOI: 10.1029/JB090iB12p10093.CrossRefGoogle Scholar
  16. Johnston J. M., Pellerin L. and Hohmann G.W., 1992. Evaluation of electromagnetic methods for geothermal reservoir detection. Geotherm. Resour. Counc. Trans., 16, 241–245.Google Scholar
  17. Montahaei M., Brasse H. and Oskooi B., 2010. Crustal conductivity structure of a margin from magnetotelluric investigations. J. Earth Space Phys., 36, 21–32.Google Scholar
  18. Napoleone G., Poggiali G., Ripepe M. and Savino D., 1980. Magnetic survey in the Travale Geothermal Field, Italy. In: Strub A.S. and Ungemach P. (Eds), Advances in European Geothermal Research. D. Reidel Publishing Company, Dordrecht, The Netherlands, 875–883, DOI: 10.1007/978-94-009-9059-3_77.CrossRefGoogle Scholar
  19. National Geophysical Data Centre, 2010. GEOMAG Computer Program and the 1990 Coefficients for IGRF Model. World Data Centre-A for Solid Earth Geophysics, NOAA, E/GCI, 325 Broadway, Boulder, CO 80304, USA.Google Scholar
  20. Nunziata C. and Rapolla A., 1981. Interpretation of gravity and magnetic data in the Phlegrean Fields geothermal area, Naples, Italy. J. Volcanol. Geotherm. Res., 9, 209–225.CrossRefGoogle Scholar
  21. Okuma S., 1998, Magnetic constraints on the subsurface structure of Akita-Yakeyama volcano, northeast Japan. Earth Planets Space, 50, 153–163.CrossRefGoogle Scholar
  22. O’Leary D.W., Mankinen E.A., Blakely R.J., Langenheim V.E. and Ponce D.A., 2002. Aeromagnetic Expression of Buried Basaltic Volcanoes Near Yucca Mountain, Nevada. U.S. Geological Survey Open-File Report 02-020, Denver, CO, 48 pp.Google Scholar
  23. Oskooi B. and Darijani M., 2014. 2D inversion of the magnetotelluric data from Mahallat geothermal field in Iran using finite element approach. Arabian J. Geosci., 7, 2749–2759, DOI: 10.1007/s12517-013-0893-6.CrossRefGoogle Scholar
  24. Oskooi B., Pedersen L.B., Smirnov M., Arnasson K., Esteinsson H., Manzella A. and the DGP Working Group., 2005. The deep geothermal structure of The Mid-Atantic Rige deduced from MT data in SW Iceland. J. Phys. Earth Planet. Inter., 150, 183–195.CrossRefGoogle Scholar
  25. Paoletti V., Di Maio R., Cella F., Florio G., Motschka K., Roberti N., Secomandi M., Supper R., Fedi M. and Rapolla A., 2009. The Ischia volcanic island (Southern Italy): Inferences from potential field data interpretation. J. Volcanol. Geotherm. Res., 179, 69–86, DOI: 10.1016/j.jvolgeores.2008.10.008.CrossRefGoogle Scholar
  26. Pedersen L.B., 2004. Determination of the regularization level of truncated singular-value decomposition inversion: the case of 1D inversion of MT data. J. Geophys. Prospect., 52, 261–270.CrossRefGoogle Scholar
  27. Pedersen L.B. and Engels M., 2005. Routine 2D inversion of magnetotelluric data using the determinant of the impedance tensor. Geophysics, 70, G33–G41.CrossRefGoogle Scholar
  28. Reid A.B., Allsop J.M., Granser H., Millet A.J. and Somerton I.W., 1990. Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, 55, 80–91.CrossRefGoogle Scholar
  29. Roquemore G.R., 1984. Ground magnetic survey in the Coso Range, California. J. Geophys. Res., 89, 3309–3314.CrossRefGoogle Scholar
  30. Salem A. and Ravat D., 2003. A combined analytic signal and Euler method (AN-EUL) for automatic interpretation of magnetic data. Geophysics, 68, 1952–1961, DOI: 10.1190/1.1635049.CrossRefGoogle Scholar
  31. Schmidt A., Yarnold R., Hill M. and Ashmore M., 2005. Magnetic susceptibility as proxy for heavy metal pollution: a site study. J. Geochem. Explor., 85, 109–117, DOI: 10.1016/j.gexplo.2004.12.001.CrossRefGoogle Scholar
  32. Siripunvaraporn W. and Egbert G., 2000. An efficient data-subspace inversion method for 2-D magnetotelluric data. Geophysics, 65, 791–803.CrossRefGoogle Scholar
  33. Smirnov M., 2003. Magnetotelluric data processing with a robust statistical procedure having a high breakdown point. Geophys. J. Int., 152, 1–7.CrossRefGoogle Scholar
  34. Soengkono S., 2001. Interpretation of magnetic anomalies over the Waimangu geothermal area, Taupo Volcanic Zone, New Zealand. Geothermics, 30, 443–459.CrossRefGoogle Scholar
  35. Soengkono S. and Hochstein M.P., 1995. Application of magnetic method to assess the extent of high temperature geothermal reservoirs. In: Proceedings: Twentieth Workshop on Geothermal Reservoir Engineering. Stanford University, Stanford, CA, SGP-TR-150, 71–78 (http://www.geothermal-energy.org/pdf/IGAstandard/SGW/1995/Soengkono.pdf).Google Scholar
  36. Spichak V. and Manzella A., 2009. Electromagnetic sounding of geothermal zones. J. Appl. Geophys., 68, 459–478.CrossRefGoogle Scholar
  37. Spichak V.V., Schwartz Ya. and Nurmukhamedov A., 2007. Conceptual model of the Mutnovsky geothermal deposit (Kamchatka) based on electromagnetic, gravity and magnetic data. Expanded Abstract. EGM 2007 International Workshop: Innovation in EM, Grav. and Mag. Methods: a new Perspective for Exploration. Capri, Italy, April 15–18, 2007 (http://www.eageseg.org/data/egm2007/Sessione%20D/Poster%20papers/D_PP_02.pdf).Google Scholar
  38. Stavrev P. and A. Reid., 2007. Degrees of homogeneity of potential fields and structural indices of Euler deconvolution. Geophysics, 72, L1–L12, DOI: 10.1190/1.2400010.CrossRefGoogle Scholar
  39. SUNA, 1998. Country Geothermal Potential Survey. 1st Phase Report to the Renewable Energies Office, Ministry of Energy, Islamic Republic of Iran, 306 pp.Google Scholar
  40. Swift C.M., 1967. A Magnetotelluric Investigation of Electrical Conductivity Anomaly in the Southwestern United States. Ph.D. Thesis. Massachusetts Institute of Technology, Cambridge, MA, 211 pp.Google Scholar
  41. Thompson D.T., 1982. EULDPH a new technique for making computer-assisted depth estimates from magnetic data. Geophysics, 47, 31–37.CrossRefGoogle Scholar
  42. Tikhonov A.N., 1950. On determining electrical characteristics of the deep layers of the Earth’s crust. Doklady, 73, 281–285 (http://mtnet.dias.ie/papers/ClassicPapers/Tikhonov_1950_Doklady.pdf).Google Scholar
  43. Uchida T., 1995. Resistivity structure of Sumikawa geothermal field, northeastern Japan, obtained from magnetotelluric data. Proceedings, World Geothermal Congress, Florence, Italy, 921–925 (http://www.geothermal-energy.org/pdf/IGAstandard/WGC/1995/2-Uchida.pdf).Google Scholar
  44. Ushijima K., Mustopa E.J., Jotaki H. and Mizunaga H., 2005. Magnetotelluric soundings in the Takigami geothermal Aria, Japan. Proceedings, World Geothermal Congress, Antalia, Turkey (http://www.geothermal-energy.org/pdf/IGAstandard/WGC/2005/0718.pdf).Google Scholar

Copyright information

© Institute of Geophysics of the ASCR, v.v.i 2015

Authors and Affiliations

  • Behrooz Oskooi
    • 1
  • Mahmoud Mirzaei
    • 2
  • Behnam Mohammadi
    • 1
  • Mohammad Mohammadzadeh-Moghaddam
    • 3
  • Feridon Ghadimi
    • 4
  1. 1.Institute of GeophysicsUniversity of TehranTehranIran
  2. 2.Department of Physics, Faculty of SciencesUniversity of ArakTeheranIran
  3. 3.Research Institute of Applied SciencesTehranIran
  4. 4.Department of Mining EngineeringArak University of TechnologyArakIran

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