Structure and Uplift Rates in the North Canterbury Fold and Thrust Belt, New Zealand

David Oakley
Pennsylvania State University, Department of Geosciences
State College, Penns1ylvania, United States
[email protected]

The North Canterbury fold and thrust belt lies at the southern end of the Hikurangi subduction zone and is characterized by basement-involved fault-related folding, with a regionally extensive flight of marine terraces along the coast. My project aims to date these terraces and calculate uplift rates and to determine the structure of the anticlines on which uplift is occurring. This information is important in understanding how the region has developed in response to southward propagation of the subduction zone and to the transition between subduction and Alpine Fault transpression.

Seven shell samples have been radiocarbon dated and used with sea level curves and facies depths to calculate uplift rates. Samples range from recent to 44 ka and indicate uplift rates of about 1 to 3 mm/yr. Further samples for OSL and AAR dating have been collected and are awaiting results.

Bedding dips, measured in the field on multiple structures, are used to evaluate the range of possible fault propagation fold models, using trishear kinematics. The Haumuri Bluff anticline is one structure studied. A radiocarbon age of 3.3 ± 0.1 ka gives an uplift rate of 1.0 ± 0.5 mm/yr. Cross sections indicate that at 1 mm/yr, the anticline would be about 600 to 700 ka in age, slightly less than the 800 ka estimated from previous work for the thrust belt. The active growth of such anticlines, recorded by uplifted terraces and constrained by balanced cross sections, provides evidence of how the fold and thrust belt has developed over time.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects