PHASE-CHANGES AND THERMAL SUBSIDENCE IN INTRACONTINENTAL SEDIMENTARY BASINS

A model of tectonic subsidence is developed to explain the late acceleration of subsidence observed in some intracratonic sedimentary basins. The proposed mechanism combines the effect of thermal contraction of an initially hot lithosphere with the effect of a subcrustal phase transformation that moves under changing pressure and temperature conditions. The subsidence following a sudden change in temperature at the base of the lithosphere is calculated. The calculations show that: (1) phase changes, if present and activated, contribute substantially to the subsidence of sedimentary basins; (2) because the effect of phase change is delayed, subsidence accelerates after a time on the order of 20 Myr; and (3) the duration of the subsidence is on the order of 100 to 150 Myr. During the late stages of subsidence, the phase change is the dominating mechanism. An application to the Michigan basin is presented. The calculated sediment accumulation history fits the record well when the effect of sea-level changes is included in the model.