Horizontal thermal contractional strain of oceanic lithosphere: The ultimate limit to the rigid plate hypothesis

Depth-averaged horizontal strain rates in oceanic lithosphere due to thermal contraction are determined. Calculated strain rates range from ≈10 -2 Myr-1 (near the mid-ocean ridge) to ≈10 -5 Myr-1 (for the oldest oceanic lithosphere). The average thermal contractional strain rate in oceanic lithosphere is ≈10 -4 Myr-1. Newly created lithosphere is displaced toward old ocean basins at a rate that is 1.35% of the half-rate of seafloor spreading, giving displacement rates of 0.1 to 1.1 km Myr-1. The bias in plate displacement rates estimated from marine magnetic anomalies, expressed as a percentage of the full spreading rate, is 0.60% or 0.85% depending on the age of the magnetic isochron used to estimate current plate velocity. The displacement rate due to thermal contraction parallel to a mid-ocean ridge could be as large as ≈10 mm/yr. Strain rates due to thermo-elastic stresses are an order of magnitude smaller than the strain rate calculated when these stresses are neglected.