THE ROLE OF FAULTING IN ROCK UPLIFT IN THE SOUTHERN ALPS, NEW-ZEALAND

Fission track data for a suite of basement rock samples from the Southern Alps is used to assess the role of faulting in the late Cenozoic rock uplift of the Pacific plate. The amount of rock uplift derived from sites on both sides of the Moonlight, Ostler, Harper, Torlesse, Porters Pass, and Hope Faults shows that for all faults the vertical offset lies within the uncertainty of the data, typically +/ -2 km, and is <30% of the surrounding uplift. Major faults are conspicuously absent in die zone of greatest uplift. Over a scale of kilometres, die pattern of rock uplift across the Southern Alps is continuous and regular. The amount of rock uplift increases nearly exponentially with increasing proximity to the Alpine Fault, and the pattern is maintained with little variation over the central 350 lan long segment of the Southern Alps. This pattern is primarily the result of southeastward tilting of the middle and upper crust of the Pacific plate, which has ramped up the Alpine Fault in response to oblique convergence and crustal shortening. The geometry of the rock uplift implies that at least part of the Alpine Fault has a listric profile at depth.