LATE QUATERNARY EVOLUTION OF THE ALPINE FAULT ZONE AT PARINGA, SOUTH WESTLAND, NEW-ZEALAND

Recent mapping of the Alpine Fault trace in the Paringa region has revealed the existence of an extensive Haast Schist-derived thrust nappe resting on Western Province basement rock and moraine. Erosion of the nappe by the Paringa River and its tributaries, however, has resulted in eastward propagation of the active fault zone, forming southeast-dipping thrust faults linked by swarms of steeply dipping strike-slip faults. Late Quaternary sediments of the Paringa Formation have been intensely deformed along a newly developed zone of shortening and uplift on the northeast side of Paringa River. Marine, fluviatile, lacustrine, and terrestrial sediments record progressive uplift east of the Alpine Fault. The occurrence of lake deposits rhythmically interbedded with forest horizons may have resulted from damming of the Paringa River behind the zone of rapid uplift. The uplift rate for this region over the last 16 ka has been calculated at 13.7 +/- 1 mm/yr. After removing the effects of tilting due to localised uplift, a regional uplift rate of 7-8 +/- 1 mm/yr can be obtained. Estimated average uplift rates for the intervals between 16 ka and the present, and between 11 ka and the present are statistically indistinguishable.