A geophysical study of Nelson — Cook Strait region, New Zealand

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Abstract
Recent magnetic and gravity surveys in the Nelson region permit a fuller discussion of the nature of the long major magnetic anomaly associated with the trend of the Nelson Syncline. The previous view that the anomaly is due to buried Upper Paleozoic igneous rocks such as the Brook Street Volcanics and Rotoroa Igneous Complex is held to be incompatible in some ways with the relationships between gravity and magnetic force values and with the physical properties of these rocks. It is suggested that a buried serpentinised ultramafic system might be the most appropriate geological model to explain the anomalies; and that the Dun Mountain Ultramafics may either have been emplaced directly from this system, or may be the surface expression of these anomalies displaced to the east as part of a sheet-type movement.