Stokes magnetic anomaly system

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Abstract
The Stokes Magnetic Anomaly System is a zone of positive magnetic anomalies which extends for about 2400 km through the New Zealand region. The zone consists of a narrow (<10 km wide), Eastern Belt of linear magnetic anomalies associated with the Dun Mountain Ophiolite Belt, and a broader (10–100 km) Western Belt of numerous, discrete magnetic anomalies associated with the Rotoroa Igneous Complex. Over the New Zealand land mass, the Eastern Belt extends f10m Ahipara to Inchdutha and, apart from a 460 km dextral displacement by the Alpine Fault, it is offset only by a 6 km sinistral displacement near Auckland. The Western Belt lies 20–50 km west of the Eastern Belt, but cannot be traced north of Manaia. Wide variations in the direction and intensity of magnetisation in the source rocks preclude quantitative analysis of the System, but the continuity and shape of the System make it a valuable reference line and provide important constraints on reconstructions of the New Zealand region. The present configuration of the System was caused mainly by relative motion between the Australian and Pacific plates. This motion bent the rocks in a zone between the plates such that the System was bent in a recurved arc, the ends of which were at least 500 km apart, and the width reduced to a minimum in the centre of the zone. Later, the rocks in the zone became ruptured along the Alpine Fault and the two parts of the System were displaced dextrally about 460 km. Movement along the Campbell Fault resulted in an additional dextral displacement of about 330 km. The total displacement of the System across the New Zealand region is at least 1300 km.

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