Distribution of Isotherms in the Lithosphere

Distribution of isotherms, equal temperature curves (in °C), in the lithosphere: this diagram is an idealized situation of the upper part of the globe, in the context of Plate Tectonics. Do, the oceanic ridge is located at the vertical of the ascending parts of the convective mantle cells (arrows).The rise of the hot mantle and the associated transfer of basic magmas, at the origin of the oceanic lithosphere, generate a considerable heat transfer towards the surface: the isothermal curves are very tight.

Inside of the stable plates, the newly formed lithosphere cools down as it moves away from the rift and the isothermal curves become spaced.

In a subduction zone (Zs), the cold oceanic lithosphere sinks into the hot mantle, vertically to the descending parts of the convective cells. However, it heats up very slowly, as the rocks have poor thermal conductivity. As a result, the isotherms sink into the mantle.

At the boundaries of the plates (unstable zones), heat transfer is mainly advective; it is mainly conductive in the inside (stable zones).