NEW INSIGHTS TO TEMPERATURE AND PRESSURE BENEATH THE CENTRAL SOUTHERNALPS, NEW-ZEALAND

Thermal modelling of the late Cenozoic compression in the area of maxi mum uplift of the Southern Alps, South Island, New Zealand, confirms t hat the recent uplift and erosion history is consistent with a surface temperature gradient of c. 60 degrees C/km, and with paleotemperature s derived from zircon fission track ages of c. 250 degrees C at 10 km depth. The present-day thermal regime at mid and lower crustal depths is cooler than that inferred from paleotemperatures preserved in the e xhumed rock at the surface because of the effects of crustal thickenin g. The hot springs scattered through the northern half of the Southern Alps are meteoric water which has equilibrated with rock at temperatu res of 90-150 degrees C, suggesting circulation to a depth of <3 km. T he hot springs constitute a minor component of the upper crustal heat flow, which appears to be predominantly conductive. Fluid pressure may approach lithostatic pressure below 3 km depth, implying a relatively weak crust. The fluid inclusion evidence for trapping of fluids at te mperatures of 200-350 degrees C may be mostly from infrequent, possibl y coseismic, fluid flow events at depths of 5-15 km.