Specified surface temperature and basal-heat flow.
Fluid flow occurs perpendicular to the isolines of hydraulic head.
The boundary conditions are impermeable boundaries at the bottom and the lateral sides. The whole overthrust zone is flushed at the speed of the overthrust. Watch the isotherms roll in and after stopping the overthrust, how they reequlibrate to match the geometry of the overthrust. Advection of heat due to the fluid flow cools the thrust sheet.