New Zealand potassium‐argon age list—2

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Abstract
Developments and modifications to potassium‐argon dating methods at the Institute of Nuclear Sciences are described. Potassium is extracted from rocks by ion‐exchange separation from other elements and analysed flame spectrophotometrically against potassium hydrogen phthalate standard solutions. Argon is extracted from rocks by RF induction heating and purified by passing over liquid nitrogen cold traps and heated titanium. Argon concentrations are assessed by a 38 Ar isotope dilution/mass spectrometric method, which has previously been calibrated against the primary atmospheric argon standard and secondary international rock standards. Analytical data are summarised for 84 potassium‐argon age determinations produced in the period 1971–73 and are cross‐referenced against published reports. The majority of the ages presented relate to projects investigating: (a) Pliocene—Upper Miocene hydrothermal alteration in Lower Miocene volmnics in the Coromandel Peninsula; (b) Ordovician metamorphism of slates in the Greenland Group in Westland; (c) effects of Pliocene uplift on Jurassic—Cretaceous metamorphic age patterns in the Alpine Schists of SE Nelson; (d) Pliocene glauconitisation of detrital micas in Upper Tertiary sediments at Oamaru; and (e) Mid‐Jurassic metamorphism of the Chat ham Schist, Chatham Islands.

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