Abstract
This study attempts to estimate the Curie point depth (CPD) using the centroid and forward modelling of the spectral peak methods in the Sabalan geothermal field in Ardabil, NW of Iran. The reduced-to-pole aeromagnetic data were divided into 18 overlapping blocks of the sizes of 100 × 100 km. In the centroid method, the average depth to the top of the deepest crustal block, Z t, was first computed by linear fitting to the second longest wavelength segment of the power spectrum of aeromagnetic data. Then, depth to the centroid of the deepest crustal block, Z 0, was computed by linear fitting to the longest wavelength segment of the power spectrum of the aeromagnetic data. The depth to the magnetic bottom was obtained from Z b = 2Z 0 − Z t. In the forward modelling of the spectral peak method, the modelled spectra fitted to the observed spectrum iteratively and Z t and Z b were finally estimated. According to the obtained results, the CPD varies from 10 to 18.6 km. The Curie temperature of magnetite was used to determine the thermal gradient and the heat flow in the area. The study area is found to have a great energy potential in the west, northwest and the southwest of the Sabalan with shallow CPD, high geothermal gradient and heat flow.
Highlights
The Curie point is the temperature at which the spontaneous magnetization vanishes and magnetic minerals show paramagnetic susceptibility
This is the first time that spectral analysis of the aeromagnetic data is being used to assess the thermal structure of the crust in Ardebil province and mainly around Mt
An attempt has been made to calculate the depth to bottom of the magnetic sources from the aeromagnetic data in the Ardebil province in NW of Iran using spectral methods
Summary
The Curie point (approximately 580 °C for magnetite at atmospheric pressure) is the temperature at which the spontaneous magnetization vanishes and magnetic minerals show paramagnetic susceptibility. Based on the fit of modelled spectra with the observed, one may accept or reject the results more confidently in this overall subjective process of fitting specific parts of the spectra In both of these methods, CPD is computed in three steps: (1) dividing the total magnetic field map into overlapping subregions, (2) calculating the logarithm of power spectrum for each region and (3) considering Zb = 2Z0 − Zt equation for centroid method and calculating the basal depth or fit of the modelled spectra with the observed spectrum and calculating Zt and Zb. Having found the CPD, the heat flow values of the region can be calculated using the following equation (Turcotte and Schubert 1982): q k. The biggest advantage of 2D power spectrum is that the depth of sources is determined by measuring the slope of the power spectrum when the centroid method is used (Saleh et al 2012)
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