geotherms

Geotherms are profiles that describe how temperature increases with depth inside the Earth. They are not universal curves but varying representations of the Earth’s thermal structure, reflecting how heat is produced, conducted, and convected in different tectonic settings.

Geotherms are inferred from borehole temperature measurements, surface heat-flow data, and knowledge of rock properties such as thermal conductivity and radiogenic heat production. By combining surface temperatures with depth and material properties, scientists estimate the temperature at depth. Geotherms differ between stable continental regions, active margins, oceanic crust, and the mantle due to variations in heat flow, crustal thickness, and internal heat generation.

In practice, continental crust geotherms typically show a relatively cool surface and a increasing temperature with depth that can be steeper than in oceanic settings, whereas oceanic crust geotherms generally reflect higher surface heat flow and thinner crust. A crustal geotherm may imply temperatures of several hundred degrees Celsius at depths of tens of kilometers, with exact values depending on local conditions. In the upper mantle, the gradient is smaller and can be approximated by the adiabatic gradient, about 0.3°C per kilometer, though actual temperatures are influenced by phase changes and mantle convection.

Geotherms have important implications for geology and engineering. They help predict mineral stability and metamorphic reactions, locate zones of partial melting, and inform geothermal energy assessments. Because the Earth is heterogeneous and dynamic, geotherms are simplified, regionally averaged representations rather than fixed universal curves.