A fracture zone in the south west Pacific basin south of New Zealand and its implications for sea floor spreading

Abstract

Offsets in the total magnetic field anomalies between longitudes 170°E and 180°E and latitudes 50°S and 60°S mark a fracture zone (named the Endeavour Fracture Zone) having a left lateral displacement striking north 5° west and terminating to the north at the edge of the Campbell Plateau, near the Antipodes Islands. The maximum displacement is 230 km at 52°S and decreases to the south, becoming zero at 60°48′S. Identification of the anomalies shows that the transform fault formed during the Upper Cretaceous and either terminated or reversed its offset during the Palaeocene. The relative offsets of corresponding magnetic features across the fault zone are consistent with a model having the half spreading rates in constant proportion to each other for this time interval. The data suggest that the Palaeocene-Eocene boundary marks a major change in the pattern of ocean floor spreading south of New Zealand, and that the relative motions of the southwest Pacific and Antarctic plates differed significantly from the present. This change in spreading is probably directly associated with the commencement of spreading between Australia and Antarctica.