Implications for a Geothermal Reservoir at Abgarm, Mahallat, Iran: Magnetic and Magnetotelluric Signatures
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Original Paper
Implications for a Geothermal Reservoir at Abgarm, Mahallat, Iran: Magnetic and Magnetotelluric Signatures Seyed Hossein Hosseini,1 Banafsheh Habibian Dehkordi,1 Maysam Abedi,2,3 and Behrooz Oskooi1 Received 4 February 2020; accepted 29 August 2020
One of the well-known geothermal potential areas in Iran is the Abgarm in Mahallat region. Due to existence of several hot springs, the Abgarm area is of particular importance in geothermal studies. To investigate the geothermal mechanism at Abgarm, geophysical surveys of magnetometry and magnetotelluric (MT) were utilized near hot springs to image the geometry of all geological requisites for trapping a geothermal reservoir. The ground magnetic data were inverted in 3D to construct a magnetic susceptibility model, where a deep intrusive igneous rock (as a heat source) and a shallow magmatic lava were inferred from the physical model. Euler depth estimation also provided insight to a shallow granodiorite unit embedded in a thick sequence of sediments. Dimensionality and strike analysis of the MT data were performed through the phase tensor method to investigate the general geometry of the sought reservoir for running a 2D TE + TM mode inversion scheme. Through 2D inversion of the MT data along three profiles across the favorable zones, the electrical resistivity models were used to image sedimentary units (i.e., cap rock, top soil, bedrock and reservoir) and magmatic rocks. Considering both geophysical properties led to illustrate a plausible geothermal reservoir in the area. KEY WORDS: Abgarm, Geothermal, Magnetometry, Magnetotelluric, Mahallat.
INTRODUCTION Iran is a favorable region in terms of high geothermal potential due to its intimate link to tectonic activities and occurrence of large volcanic belts. Figure 1 indicates the volcanic belts and the distribution map of geothermal potential areas in Iran. The Mahallat region is one of the recognized geothermal fields in Iran, and several studies have been recently dedicated to investigate its potential
1 2
Institute of Geophysics, University of Tehran, Tehran, Iran. School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran. 3 To whom correspondence should be addressed; e-mail: [email protected]
for trapping geothermal reservoirs (e.g., Oskooi and Darijani 2014; Mohammadzadeh Moghaddam et al. 2016). The vast expanse of Mahallat and lack of exploratory information have made it difficult to evaluate precisely its geothermal favorability. However, the presence of hot springs within the Abgarm range has created a special exploratory indicator for the region. The name ‘‘Abgarm’’ in Persian means ‘‘hot water,’’ which indicates the originality and famousness of the hot springs in the region. The area surrounding the hot springs in Abgarm contains young volcanic rocks, altered units, extensive travertine outcrops and intrusive bodies, which are considered important key factors of potential geothermal fields. Hence, the hot springs in Abgarm have motivated geophysicists to
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