New insights to temperature and pressure beneath the central Southern Alps, New Zealand

Abstract

Thermal modelling of the late Cenozoic compression in the area of maximum uplift of the Southern Alps, South Island, New Zealand, confirms that the recent uplift and erosion history is consistent with a surface temperature gradient of c. 60°C/km, and with paleo‐temperatures derived from zircon fission track ages of c. 250°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 exhumed rock at the surface because of the effects of crustal thickening. The hot springs scattered through the northern half of the Southern Alps are meteoric water which has equilibrated with rock at temperatures of 90–150°C, suggesting circulation to a depth of <3 km. The 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 temperatures of 200–350°C may be mostly from infrequent, possibly coseismic, fluid flow events at depths of 5–15 km.

Keywords:

• Southern Alps
• thermal modelling
• age dating
• fluid inclusions
• temperature
• pressure
• heat flow