Radiogenic argon in the Southern Alps — a geological viewpoint

Abstract

The K-Ar whole-rock analyses for the New Zealand Alpine Schist are set out in a table arranged, as far as possible, as five traverses from north to south, and for each traverse in order of increasing distance from the Alpine Fault. For the southern traverse (Haast Pass Road), with the largest number of analyses, the number was reduced by averaging.

What is needed geologically for comparison with schist rank and present-day uplift rate is a function of Ar and K that remains the same for each locality irrespective of K content. “Age” increases with K content and cannot be true age.

The Haast Pass Road samples were divided into 23 sets, each set having a minimum range of distance from the Alpine Fault and the maximum range of K content. The 23 sets provide an “S” function that is invariant at each locality.

The “S” values are then compared with the schist ranks (rank = metamorphic grade) and with the present-day uplift rates, all of which are given in the table.

Because there have been two periods of uplift and erosion at the south and only one, the Alpine, for the rest of the Alps, the schist rank is two ranks higher at the south than at the north.

Because the Marlborough faults have bypassed the Wairau Fault in the last few million years, the present-day uplift rates are anomalously low at the north.