UPLIFT RATES OF MARINE TERRACES AS CONSTRAINTS ON FAULT-PROPAGATION FOLD KINEMATICS: EXAMPLES FROM TWO ANTICLINES IN NORTH CANTERBURY, NEW ZEALAND

Uplift rates of marine terraces are used in combination with data from surface mapping and seismic reflection lines to fit fold kinematic models to fault propagation folds in North Canterbury, New Zealand using a Markov Chain Monte Carlo method. Fault propagation folds can be related to fold geometry by way of multiple kinematic models, of which trishear and kink-band models are the most common. Where data are limited, either model can sometimes be applied to a particular fold. Further, numerous independent parameters in the trishear model permit multiple possible solutions. Because kinematic models can be described in terms of velocity, different models predict different uplift rates as a function of structural position. Thus uplift rates can be used as a constraint on the model, where geologic data are insufficient. Numerical data inversion methods can be used to fit models to fold geometry, particularly for trishear, which cannot be solved analytically, and the same methods can be extended to uplift rates. We test trishear models in this method by restoring formation contacts, bedding dips, and uplifted terraces of known age. We consider examples from the Hawkswood and Kate anticlines in North Canterbury. Marine terraces uplifted on the anticlines were dated using a combination of optically stimulated luminescence and amino acid racemization. Uplift rates were calculated from terrace age, elevation, and paleo-sea level. At Haumuri Bluff, on the Hawkswood anticline, marine terraces in the forelimb allow us to distinguish between two possible trishear models. At the Kate Anticline, terraces on the backlimb and crest of the fold are used to constrain possible fault geometries and to argue for a trishear rather than kink-folding kinematic model.