The Kinematics Of Fault Related Folding PDF Download

Here we investigate fault-propagation fold kinematics in North Canterbury, New Zealand, addressing questions of how kinematic model parameters can be constrained and different models distinguished and how marine terrace uplift rates reflect fold kinematics. Kinematic models are powerful tools in the study of fault-related folding, but they are subject to problems of non-uniqueness and uncertainty. The North Canterbury fold and thrust belt provides a location where actively growing basement-involved fault-propagation folds can be studied, where uplifted marine terraces provide critical information on fold growth rates, and where the results of kinematic models can inform understanding of deformation in a seismically active and tectonically complex region. We begin by developing methods to fit trishear kinematic models to data and to estimate model uncertainty using Markov chain Monte Carlo (MCMC) methods. We then use amino acid racemization, infrared stimulated luminescence, and radiocarbon dating to provide new age dates for marine terraces uplifted by folding and faulting in North Canterbury, where ages were poorly known before. Using the new ages, we calculate uplift rates for the marine terraces, which reveal significant temporal and spatial variations. We use two anticlines along the North Canterbury coast as examples to show that marine terraces can be used to constrain fault-propagation fold kinematic models, both by serving as originally horizontal surfaces to be restored and by facilitating comparison of uplift rates at different structural positions. These approaches allow us to distinguish between trishear and kink-band kinematic models and to constrain the values of trishear parameters, eliminating models that are consistent with the geologic evidence but not the terrace uplift. By incorporating terrace uplift into MCMC simulations, we are also able to provide estimates of fault slip rate and age of folding. Ages are consistent with previous estimates, while fault slip rates are likely somewhat higher than previously thought. Finally, we test models for fault-propagation folding in North Canterbury that incorporate listric faults, we consider the implications of recent earthquake sequences and of the reactivation of inherited normal faults for understanding fault geometry at depth, and we construct a regional cross section to estimate shortening across the North Canterbury fold and thrust belt. We find that models of rigid basement block rotation on listric faults, although often used to explain basement-involved folding, are not consistent with the style of faulting and folding seen in North Canterbury. Instead, we develop a model combining trishear with simple shear on steep listric faults, which serves to explain the regional characteristics of faulting and folding in North Canterbury. We also compare this model to the simpler fault geometries tested previously and consider the possibility that not all faults in North Canterbury fit the same model. Depth to detachment is poorly constrained by our kinematic models, but a mid-crustal detachment as proposed by previous authors is consistent with our results. Total shortening estimated from our regional cross section is consistent with the low end of estimates from the geodetic shortening rate across the fold belt and the expected age at which folding began.