Study of heat flow at the earth's surface is an important discipline of geophysics. Prior to the present work, such studies were limited only to southern Iran. In this
paper, bottom-hole temperatures of oil and gas wells in north central Iran, Kopeh Dagh, Caspian coastal plain, and Moghan plain are used for the first time to calculate
geothermal gradients; and the results are compared with those reported from the Zagros-Persian Gulf area. The range and pattern of gradient variations in Iran is more
complicated than what is represented in the global heat flow map. This intricatensess is a reflection of diverse tectonic histories of the different structural zones. In most parts
of northern Iran including Kopeh Dagh, Moghan Plain, and north central Iran gradient values are 25 °Ckm-1 or higher. For Gilan area in the Caspian coastal plain a value of 19 °Ckm-1 is obtained. There is no data for the Alborz Mountain Range yet, but considering crustal and upper mantle partial melting in the Quaternary, thermal
gradient values are expected to be at the high side of the above mentioned range or even higher. There is no geothermal data for southern central Iran, the
Sanandaj-Sirjan metamorphic belt and the Zagros thrust
zone. However, a more
complete set of data is available for the folded Zagros-Persian Gulf. Geothermal gradient is highly variable in the Zagros and contours generally stretch parallel to
structural trend, with values increasing to the south as the Moho depth decreases. Average thermal gradient is considerably higher in the eastern Zagros-Persian Gulf
relative to the area situated to the west of the Qatar-Kazeroon lineament. The regional thermal anomaly in the east coincides with the closely spaced salt domes, either
exposed or still unbreached. Salt domes not only cause more effective heat conduction, but also in the case of the Hormoz series, they have a great potential of radioactive
heat generation due to their remarkable enrichment in uranium. The anomalously high geothermal gradients is the reason why gaseous hydrocarbons are dominant in the
eastern Zagros-Persian Gulf region.