Ultramafic Mass in New Zealand — Malahoff 
149 
Te Anau volcanics, probably up to the base of 
the Maitai limestone. The peridotite, therefore, 
is younger than the volcanics and older than the 
Rangitoto (Maitai) limestone. The present 
shape of the ultramafic mass is that of a hori- 
zontal sheet with near-horizontal structures 
such as low-angle dipping bands. Hence, if 
the original dip of the Te Anau volcanics and 
the Maitai series was horizontal, the original 
dip of the Wairau ultramafic mass was proba- 
bly vertical. This suggests a vertical mode of 
emplacement for the Wairu ultramafic mass. 
The inferred relationship (Grindley, 1958: 
35) can be seen by turning Figure 7 sideways, 
so that the Maitai series are at the top. The 
peridotite of the ultramafic mass could have 
been intruded vertically after the extrusion of 
serpentinite lavas, the red and green volcanic 
breccia, and the spilite. After the intrusion of 
the peridotite, a period of erosion was followed 
by the deposition of the Rangitoto limestone 
and the rest of the Maitai series. Later, regional 
tilting and folding exposed the "roots” (Fig. 
7) of the ultramafic mass. The roots were sub- 
sequently destroyed by erosion. 
ACKNOWLEDGMENTS 
Field work for this paper was carried out in 
New Zealand during the period 1961-1962, 
as part of a thesis requirement for a Master 
of Science degree at the Victoria University 
of Wellington. The author is indebted to Pro- 
fessor H. W. Wellman of the Geology Depart- 
ment, Victoria University of Wellington, New 
Zealand, for guidance in the field and for criti- 
cism of manuscripts, and to Dr. E. I. Robert- 
son, director of the Geophysics Division, 
D.S.I.R., who made available the geophysical 
instruments used in this survey. Field work for 
this paper and analysis of the data were carried 
out while the author was employed by the Geo- 
physics Division, D.S.I.R. 
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