Walcott, R.I.; Mumme, T.C. 1982 Paleomagnetic study of the Tertiary sedimentary rocks from the east coast of the North Island, New Zealand. [s.l.]: [s.n.]. Report / Geophysics Division 189 44 p.
Abstract: The remanent magnetisation of 550 cores of sedimentary rocks of Southland and Pareora Age (about 10 to 20 My BP) from the East Coast of the North Island of New Zealand has been measured before and during thermal demagnetisation. A secondary remanent magnetisation probably acquired during the drying of the specimens of sedimentary rock in the laboratory is apparent in all specimens. It is incompletely removed by thermal demagnetisation at temperatures as high as 250 deg. Three groups of rocks of contrasting magnetic properties are recognised. 1. Southern Group, from south of Hawke Bay for which no primary remanent magnetisation is identified. 2. Wairoa Group, for most of which a primary magnetisation is present but contaminated by the secondary magnetisation. 3. Hicks Bay Group, which is some two orders of magnitude stronger in magnetic intensity than the others and which has an excellent stable remanent magnetisation. A declination anomaly is identified in the Wairoa Group from which we deduce a tectonic rotation of the rocks at a rate of some 4 deg./My over the last 15 My. No significant declination anomaly is identified for the Hicks Bay Group. A model for the reconstruction of the North Island during the last 20 My is suggested that is consistent with sea-floor spreading information and the paleomagnetic data. It assumes the Hicks Bay region to be tectonically part of the Kermadec Ridge and to have moved about 70 km southeastwards without significant rotation in the last 5 My. The rocks extending from near East Cape to near Banks Peninsula on the South Island lie within the plate boundary zone between Pacific and Indian Plates and have experienced rotations of around 65 deg. at rates of 4 deg./My
