Fault growth and landscape development rates in Otago, New Zealand, using in situ cosmogenic 10Be

Abstract

We use in situ cosmogenic 10Be measurements in quartzites to examine the growth and propagation rates of a Late Quaternary anticline forming above a blind reverse fault in Central Otago, New Zealand. We obtain average uplift and propagation rates of 0.10–0.15 mm yr −1 and 1.0–2.0 mm yr −1 respectively over the last 450 000 yr, though it is probable that growth occurred episodically, with more rapid development in the periods 600–400 kyr and 200–100 kyr and relative quiescence between about 400 and 200 kyr ago. These results quantify and confirm a qualitative analysis of the fault evolution based on geomorphology and drainage patterns. We obtain minimum 10Be exposure ages of up to 750 000 yr for the quartzites, some of the oldest ages obtained by this method outside Antarctica, which are made possible by the extremely low erosion rates of less than 0.6 mm kyr −1 in the resistant quartzites. These rocks consequently provide an opportunity to study geomorphic and tectonic processes in this region over unusually long time periods.