Thermal consequences of lithosphere extension over continental margins: the initial stretching phase

We compute the thermal evolution of a lithosphere submitted to stretching during a finite duration of time in order to discuss the initial stretching phase of future continental margins. The numerical method developed can handle 2-D laterally variable stretching as well as sedimentation. It is shown that lateral conduction is more important than vertical conduction over most continental margins during their formation by stretching. A simple way to evaluate the relative importance of lateral and vertical conduction effects at the axis of the zone of rifting just prior to oceanization is proposed. A simple way to evaluate the amplitude of the thermal uplift on the edges of the zone of rifting at the end of the stretching phase is also presented. For small width zones of rifting (< 70–100 km) lateral cooling becomes so large as to prevent large-scale melting and, presumably, prevent the transition to oceanization. The effect of high-sedimentation rates (100–500 m Myr−1) is to increase the surface temperature of the lithosphere and consequently significantly decrease the surface heat flow.