Effect of mineral phase transitions on sedimentary basin subsidence and uplift

Metamorphic phase transitions influence rock density, which is a major parameter affecting lithosphere dynamics and basin subsidence. To assess the importance of these effects, we have computed realistic density models for a range of crustal and mantle mineralogies from thermodynamic data by free-energy minimization. These density distributions are incorporated into one- and two-dimensional kinematic models of basin subsidence. The results demonstrate that, compared to models in which density is solely temperature dependent, phase transitions have the effect of increasing post-rift subsidence while decreasing syn-rift subsidence. Discrepancies between our model results and those obtained with the conventional uniform stretching models can be up to 95% for reasonable parameter choices. The models also predict up to 1 km of syn-rift uplift as a consequence of phase transitions. Mantle phase transitions, in particular the spinel–garnet–plagioclase–lherzolite transitions are responsible for the most significant effects on subsidence. Differences in mantle composition are shown to be a second-order effect. Parameterized density models are derived for crustal and mantle rocks, which reproduce the main effects of the phase transitions on subsidence.