Uplift history of South Westland using the fission-track dating technique

Abstract

Apatite and zircon fission-track ages have been determined for rocks at varying distances from the Alpine Fault in South Westland. Zircon ages between and within samples are widely scattered and are nowhere younger than Late Cretaceous, implying that burial has been no greater than about 7 km since that time. Apatite ages, particularly those close to the Alpine Fault, are dominantly Late Tertiary-Quaternary; such ages imply burial to depths >3 km prior to uplift. Three samples more than 10 km from the fault have mixed apatite ages; they most likely represent an uplifted, partially annealed zone from burial depths of <3 km. Uplift rates are maximum about 2 mm/a close to the fault and <1 mm/a along the coast. These rates are consistent with those previously determined from raised late Quaternary river-terrace levels.

Keywords:

• fission-track ages
• apatite
• zircon
• South Westland
• uplift
• Alpine Fault