DYNAMICS OF PACIFIC PLATE CRUST IN THE SOUTH ISLAND (NEW-ZEALAND) ZONE OF OBLIQUE CONTINENT-CONTINENT CONVERGENCE

Here we analyze topographic and fission track data to quantify the response of the surface of the Pacific plate in South Island, New Zealand, to late Cenozoic oblique continental convergence across the Alpine fault. Over the central 350 km length of the Southern Alps mountain chain we derive and map the rates of mean surface uplift, the rates of working associated with mean surface uplift during the late Cenozoic mountain building, the amounts and rates of denudation and consequent isostatic rebound, and the tectonic component of rock uplift. The rate of mean surface uplift ranges from <0.1 mm/yr adjacent to the Alpine fault to >0.3 mm/yr over most of the area east of the Main Divide. The highest rates of mean surface uplift occur to the southeast of the regions of highest mean elevation and relief. The rate of working against gravity during uplift of the mean surface ranges from approximately 2.5 mW m-2 in the southwest to approximately 10 mW m-2 in the central eastern parts of the Alps. Areas of lower mean elevation uplifted most recently have received rates of energy input similar to that of areas of higher mean elevation where uplift started earlier. The amount of denudation is large compared with the mean surface uplift and ranges from approximately 18 km adjacent to the Alpine fault to approximately 2 km along the southeast margin of the Southern Alps. The rate of denudation ranges from approximately 2.5 to approximately 0.5 mm/yr with increasing distance from the Alpine fault across the Alps to the southeast. The amount of isostatic uplift ranges from a maximum of 14 km adjacent to the Alpine fault to approximately 2 km along the southeast margin of the Alps. The tectonic component of uplift varies from approximately 4 km along the Alpine fault to approximately 1 km along the eastern margin of the Alps.