The average, or sometimes called normal, geothermal gradient in the upper part of the Earth is about 25oC/km.
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But, the geothermal gradient can vary from 200oC/km in areas where hot igneous bodies are intruding at shallow levels of the crust to 10oC/km, in areas like subduction zones where cold lithosphere descends back into the mantle.
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Geothermal gradients deeper in the earth become much lower than those near the surface.