AN INVERSE METHOD FOR DETERMINING LITHOSPHERIC STRAIN-RATE VARIATION ON GEOLOGICAL TIMESCALES

Inverse theory is used to calculate the strain rate variation as a function of time needed to fit observed subsidence patterns within extensional sedimentary basins. No a priori information concerning either the duration of rifting or the total strain is required. The method is one-dimensional but can be generalised for use with two- and three-dimensional data. Conventional kinematic modelling of such basins normally assumes that lithospheric stretching is instantaneous, or that the strain rate during a rifting period of known duration is constant. The scheme is tested on a variety of synthetic data and applied to subsidence data from the Dolomites, northern Italy. Linear error analysis, combined with random and systematic noise tests, show that variations in strain rate are significant and well resolved. In the Dolomites, inverse calculations produce good fits to the data, yielding total strains and durations of lithospheric stretching that are consistent with geological constraints. Calculated strain rates are not constant but vary between 10(-18)-10(-15) s-1. Information concerning spatial and temporal strain rate variation will provide important constraints for dynamic models of lithospheric deformation.