Integrated magnetic and gravity surveys for geothermal exploration in Central Iran
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ORIGINAL PAPER
Integrated magnetic and gravity surveys for geothermal exploration in Central Iran M. Mohammadzadeh Moghaddam 1 & S. Mirzaei 1 & J. Nouraliee 2 & S. Porkhial 3
Received: 20 November 2015 / Accepted: 31 May 2016 # Saudi Society for Geosciences 2016
Abstract The Delijan region of Central Iran is a popular tourist spot due to the occurrence of hot springs and having the greatest geothermal fields in Iran. In the years 2011 and 2012, an integrated geophysical investigation, using magnetic and gravity methods, was conducted over the hot springs in order to characterize geophysical anomaly sources corresponding to the geothermal resources. The results of the geophysical investigations revealed the heat source and the reservoir of the Delijan geothermal system (DGS). Based on results of Euler depth estimation and 3D inversion of magnetic and gravity data, the depths and extension of the discovered structures were determined with a good correlation with the geological information. The results of magnetic interpretation show that the main source (heat source) of the geothermal system is located NE of the Delijan-Abgarm fault (DAf) zone at depths of 2500 to 5000 m, and the results of gravity interpretation show that the reservoir of the geothermal system is located along the DAf zone at depths of 1000 to 4000 m. Also, the horizontal gradients of gravity data reveal complex fault systems which are acting as the preferential paths to circulate the hydrothermal fluids.
Keywords Geothermal field . Inversion . Magnetic . Gravity . Delijan
* M. Mohammadzadeh Moghaddam [email protected]
1
Research Institute of Applied Sciences, Beheshti University, Tehran, Iran
2
Niroo Research Institute (NRI), Tehran, Iran
3
Islamic Azad University, Karaj Branch, Moazen Blvd, Karaj, Iran
Introduction In geothermal explorations, the integrated interpretation of gravity and magnetic surveys provided constrained interpretation results against interpreting each dataset independently. With each dataset mapping differing rock physical properties (magnetic susceptibility variations for magnetic data and density variations for gravity data), the integrated interpretation of the two datasets gave less ambiguous results. Magnetic susceptibility and density contrasts have been occurring in the Delijan geothermal area, Central Iran. The magnetic method has come into use for identifying and locating bodies of hot igneous rocks which have relatively high concentrations of magnetic minerals. The high-susceptibility magnetic rocks including mafic intrusive bodies can be associated with the heat source of a geothermal system (Mohammadzadeh et al. 2015). For example, a magnetic study in Yucca Mountain in Nevada revealed the isolated, small-volume, highly magnetic bodies embedded within the alluvium deposits of the geothermal area (O’Leary et al. 2002). The gravity studies in different places of the world have presented useful results for geothermal exploration, such as delineation of faults and fractured zones corresponding to the reservoi
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