The thermal evolution of lithosphere extending on a low-angle detachment zone

Abstract Expressions are obtained for temperature as a function of depth, and for surface elevation and surface heat flow using a simplified model to represent lithosphere extending on a low-angle detachment surface. The geometry of the resulting basin is determined by the dip of the detachment surface φ and the original thickness of the crust, h. For small extension the width of the basin is h /tan φ and with increasing extension the width of the basin cannot exceed 2 h /tan φ before sea-floor spreading begins. The asymmetry of heat flow and subsidence profiles across the basin is described and the predictions of the model are compared with those of the model for uniform extension by pure shear. The amplitude of thermal subsidence for the detachment-zone model is typically half as great as for the pure-shear model with the same extension factor. As the total subsidence is the same for each model the initial subsidence is correspondingly greater for the detachment-zone model. The time-integrated anomalous heat flow in the detachment-zone model is also approximately half that in the pure-shear model.