Effective thermal expansivity of Maxwellian oceanic lithosphere

The thermal expansivity of oceanic lithosphere is a key mineral physics parameter that controls the rate of seafloor subsidence. Because of strongly temperature-dependent mantle rheology, effective expansivity for lithosphere as a whole could be substantially lower than indicated by mineral physics data. Viscoelastic modeling indicates that this reduction in expansivity could be as high as ∼ 15–30% for a plausible range of mantle viscosity. Though brittle relaxation by thermal cracking is likely to alleviate this reduction, tension cracking results in fractured lithosphere with finite crack porosity, thereby prohibiting the recovery of fully equilibrated density. Even with complete brittle relaxation, effective thermal expansivity could still be lower by up to ∼ 20%.