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 South ern Alps is used to assess the role of faulting in the late Cenozoic r ock uplift of the Pacific plate. The amount of rock uplift derived fro m sites on both sides of the Moonlight, Ostler, Harper, Torlesse, Port ers Pass, and Hope Faults shows that for all faults the vertical offse t 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 patter n of rock uplift across the Southern Alps is continuous and regular. T he amount of rock uplift increases nearly exponentially with increasin g proximity to the Alpine Fault, and the pattern is maintained with li ttle variation over the central 350 lan long segment of the Southern A lps. This pattern is primarily the result of southeastward tilting of the middle and upper crust of the Pacific plate, which has ramped up t he Alpine Fault in response to oblique convergence and crustal shorten ing. The geometry of the rock uplift implies that at least part of the Alpine Fault has a listric profile at depth.