
geothermal system at a depth beneath the area of Greece by
constructing the Curie isotherms. The results of his investiga-
tions revealed that the CPD varies considerably beneath
Greece, reaching 20 km towards western Greece and about
10 km beneath the Aegean. In East and Southeast Asia, CPD
was determined based on the spectral analysis of magnetic
anomaly data by Tanaka et al. (1999). In this study, they used
many heat flow data from the boreholes. The estimated CPD
for this area using centroid method varied from 9 to 46 km. In
addition, they predicted CPD from heat flow data. The CPD
estimated from the heat flow data were very similar to the
results of the CPD analysis of magnetic data. Dolmaz et al.
(2005) concluded that the study of earth crust’s thermal struc-
ture in SW of Turkey is useful to determine modes of defor-
mation, depths of brittle and ductile deformation zones and
regional heat flow variations. Karastathis et al. (2010)found
the deep origin of the geothermal fields and volcanic centres in
central Greece, by combining a trav el-time inversion of a
micro-seismic dataset together with a CPD analysis based on
the aeromagnetic data. They also found that a possible magma
chamber can be presumed by detecting a low seismic velocity
volume at depths below 8 km and the CPD estimation at about
7–8-km depth as well.
Bansal et al. (2011) estimated the bottom depth of magnetic
sources in Germany using aeromagnetic data. At first, they
proposed a modified centroid method to estimate the depth
to the bottom of magnetic sources. To assess the calculated
bottom depth of magnetic sources, the results were then com-
pared with the heat flow density data. Saleh et al. (2012)
estimated CPD and heat flow map for Northern Red Sea rift
of Egypt. Their aim was to map the CPD based on the spectral
analysis of the aeromagnetic data. The CPD varied from 5 to
20 km. The shallowest CPD of 5 km (associated with the high
heat flow) was suggested a promising area for geothermal
exploration. Eletta and Udensi (2012) investigated the CPD
isotherm from the aeromagnetic data to prepare a preliminary
potential map of geothermal resources in the Eastern Sector of
Central Nigeria. They showed that the high prospect areas are
located in the south-west parts of the study area. Obande et al.
(2014) applied spectral analysis of aeromagnetic data for geo-
thermal prospecting in the north-east Nigeria. They estimated
the top and the centroid depths of magnetic source from the
power spectrum. The obtained results were subsequently used
to estimate the bottom depth. The range of CPD varies from 6
to 12 km according to the heat flow and CPD values of the
study area wherein the highest heat flow value and the
shallowest CPD occurred near the thermal springs. The
Wikki warm spring area was found to have a great energy
potential with a shallow CPD and very high heat flow values.
The geological and geophysical evidences together with
the presence of several hot water springs in Ardebil province
in the NW of Iran indicate that the area could have a high
geothermal energy potential. Besides, the review of the
published materials shows that no comprehensive aeromag-
netic data analysis exists to prove the geothermal potential of
the region. So, any study regarding to locate geothermal po-
tential zones in such a vast region is highly important in the
early stage of a geothermal exploration program. Therefore,
this paper attempts to apply Centroid depth and forward
modelling of the spectral peak methods of the aeromagnetic
data to determine CPD in the main part of the Ardebil prov-
ince particularly around the Sabalan mountain area. The heat
flow values are then estimated and mapped to assess further
geothermal zones.
Geological settings
Ardabil province is a famous tourist destination in Iran. Its
pleasant climate especially in spring and summer seasons is
always worthy for most visitors and residents. Several hot
springs, with temperatures varied between 20 and 85 °C, exist
in Ardabil, which there are mostly around the Sabalan
Mountain (Mt. Sabalan). The Sabalan geothermal area
(Figs. 1 and 2) which is now under investigation for geother-
mal electric power generation lies at the NW of the Mt.
Sabalan (Ghaedrahmati et al. 2013). The area has been under
geoscientific exploration studies since 1978 (Fotouhi 1995).
Ardebil geology is diverse and complicated and has a long
evolution history. These features discriminate the area from
the other part of Iran. North of Ardabil is covered with older
alluvial, Clay, Marl and tuff intercalations. Surrounding region
around Mt. Sabalan is characterized by the predominance of
Quaternary terrace deposits (Dizu Formation); altered post-
caldera Pleistocene trachyandesitic domes, flows and lahars
(Kasra Formation); unaltered syn-caldera Pleistocene
trachydacite to trachyandesitic flows, domes and l ahars
(Toas Formation); and pre-caldera trachyandesitic lavas, tuffs
and pyroclastics (Valhazir Formation) (Fig. 2). The geologic
study of the Northwest of Sabalan confirmed that there are
two major types of structural setting: a set of linear faults
and several inferred faults (SKM, Sinclair Knight Merz
2005); the faults strike predominantly towards the northwest
and northeast (KML 1998). A northeast-southwest structural
trend is dominant in the south of Ardebil city. The main geo-
logical units exposed in this area include Miocene’saltered
tuff, tuff breccia, pumice, travertine, sandstone, shale, marl
and conglomerate and Eocene’s olivine basalt and
trachybasalt which overlay volcanic breccia and
trachyandesite of Eocene age.
However, the structural trend changes to northwest-
southeast direction in the further southern parts. This area
geologically contains a sedimentary sequence including
Cretaceous limestone, Jurassic’s shale and sandstone with in-
tercalation of dolomite which overlain by Eocene’svolcanic
383 Page 2 of 11 Arab J Geosci (2016) 9: 383