A Thermal Window in the Lithosphere Underneath North Anatolia and California

Abstract

The seismicity along major strike-slip plate boundaries like the San-Andreas or the North Anatolian fault zone is relatively shallow. It is restricted to depths not exceeding 15 or 20 km so that the lower crust and the mantle below it are sheared throughout the lithospheric thickness, say down to about 100 km. This ductile deformation generates heat by an amount equal to the product of the velocity across the plate boundary, say 5 cm/yr or 1 cm/yr, times the shear stress. This last quantity is not measurable and has to be estimated on the basis of laboratory creep data. This requires the knowledge of the exact temperature within the shear zone. Indeed creep laws are highly temperature sensitive. However, this temperature is likely to be strongly modified by the heat dissipated by the deformation itself. This brief argument illustrates the important feedback between thermal and mechanical quantities within the lithosphere. These can only be computed by solving doubled thermal and mechanical equations (Yuen et al., 1978; Fleitout and Froidevaux, 1980).