Modes of range growth and faulting styles in the central Southern Alps, New Zealand

The ability to characterize crustal faulting on time scales ranging from the Holocene to Late Cenozoic is challenging on fault systems in high exhumation rate terrains, and where preservation of paleoseismic records is low due to high denudation rates. Fold and thrust belts are thus often physically and numerically modelled to obtain some constraint on structural evolution at the orogen scale over long periods of time. We present a field study of a single system, the Fox Peak Fault in the South Canterbury region of New Zealand, that documents several styles of faulting and range growth over the last ~2 million years. The South Canterbury fold and thrust belt marks a transition from oblique transpression in the NE South Island of New Zealand to almost pure thrusting at a shortening direction of ~110° near its center. In this region, doubly-plunging anticlinal ranges converge on each other due to thrust fault linkage and differential rates of advection toward the Main Divide. Using detailed mapping, surveying, GPR, and paleoseismic trenching of the Fox Peak Fault, we document three distinct styles of faulting that contribute to the production of topography in these areas: 1) Incipient and mature triangle zone development at the junction of oppositely-verging, range-bounding thrusts; 2) Spatiotemporally dense thrusting and associated subsidence; and 3) Orthogonal interference folding. Our observations also provide evidence that intra-catchment relief has developed not just by catchment incision due to base-level fall, but by basinward imbricate thrusting that has raised the heights of catchment walls. These observations have implications for both the long term structural interpretation of fold-and-thrust belts and the complex linkage of thrust fault dynamics to range growth. Recent large earthquakes in Canterbury provide contemporary evidence for aspects of these processes.