Relocation of the tectonic boundary between the Raukumara and Wairoa Domains (East Coast, North Island, New Zealand): Implications for the rotation history of the Hikurangi margin

Abstract

Paleomagnetic studies of Neogene marine sediments have documented large clockwise rotations of the Hikurangi margin (East Coast, North Island) during the Neogene, with the exception of the Raukumara Peninsula, which is unrotated with respect to the Australian plate. Immediately south of the Raukumara Peninsula, the Wairoa region has been rotated clockwise by 50-60°; the boundary between these domains is associated with a change in regional structural trends. However, a declination of 70 ± 14° reported from Otaian (19-22 Ma) sediments in the Rakauroa area is located to the north of this change. Characterisation of how differential rotations have been accommodated along the Hikurangi margin has been frustrated by this apparent mismatch between paleomagnetic and structural data. Paleomagnetic analysis of two new Rakauroa localities has yielded declinations of 16 ± 7° and 19 ± 9°, consistent with expected values for the Australian plate. This region is therefore not part of the Wairoa Domain. A strong viscous magnetic overprint was observed in many samples, the incomplete removal of which resulted in the misidentification of a large declination anomaly in the previous study. The paleomagnetically defined boundary between the Raukumara and Wairoa Domains now coincides with the area where regional structural trends alter. Reassignment of the Rakauroa area to the Raukumara Domain also results in a revised rotation history for the Wairoa Domain, suggesting rotation rates of 4-5°/m.y. since the late Miocene (5-10 Ma), and potentially no earlier rotation. No reliable record of early and middle Miocene vertical axis rotation on the Hikurangi margin now exists north of Marlborough; further studies are required to properly constrain the rotation history for this time interval.

Widespread remagnetizations and a new view of Neogene tectonic rotations within the Australia‐Pacific plate boundary zone, New Zealand

“…Mean paleomagnetic directions for type S and SO localities are listed in both geographic and tilt‐corrected coordinates in Table 2; tilt‐corrected ChRM data for these localities, along with representative great circle demagnetization paths where appropriate, are plotted in Figure 6. The reliability of the mean directions calculated for some type SO localities may be questionable due to the small amount of data available, which makes it difficult to assess whether the strong PDF overprint has been completely removed (e.g., FP, PC; see also discussion by Rowan et al [2005]).…”

“…These difficulties may, in part, be due to problems with existing paleomagnetic data. The strong present‐day field (PDF) overprints common in this region were often not completely removed by the blanket demagnetization techniques frequently used in early studies [ Rowan et al , 2005]. More significantly, the magnetization of New Zealand Neogene marine sediments is commonly carried by the authigenic iron sulfide, greigite (Fe 3 S 4 ) [ Roberts and Turner , 1993; Rowan and Roberts , 2005, 2006].…”

The kinematics of a transition from subduction to strike‐slip: An example from the central New Zealand plate boundary

“…The forearc of the Hikurangi subduction margin (the eastern North Island) rotates clockwise (∼3–4°/Myr) relative to the Australian and Pacific plates [ Walcott , 1984; Wright and Walcott , 1986; Lamb , 1988; Thornley , 1996; Wallace et al , 2004; Rowan et al , 2005]. Clockwise rotation of the margin leads to a dramatic northward increase in convergence rate (from 20 to 60 mm/yr) on the subduction thrust front (Figure 2) and also results in back‐arc rifting in the central North Island, and long‐term upper plate shortening in the southern half of the North Island.…”

“…It straddles the transition from subduction of the Pacific Plate at the Hikurangi Trough beneath the North Island, to the strike‐slip dominated Marlborough Fault System in the northeastern South Island. Moreover, paleomagnetic and geodetic data show that the forearc of the Hikurangi subduction margin in the North Island rotates rapidly (∼3–4°/Myr, clockwise) [ Walcott , 1984; Wright and Walcott , 1986; Lamb , 1988; Thornley , 1996; Wallace et al , 2004; Rowan et al , 2005; Nicol et al , 2007], while tectonic blocks in the strike‐slip portion of the plate boundary in the South Island undergo negligible vertical‐axis rotation relative to the bounding Pacific Plate [ Roberts , 1992; Little and Roberts , 1997; Wallace et al , 2007]. Although there is detailed knowledge of active faulting within the onshore plate boundary in the North and South Island (New Zealand Active Fault database: http://data.gns.cri.nz/af/; M. Stirling et al, National Seismic Hazard Model for New Zealand: 2010 update, submitted to Bulletin of the Seismological Society of America , 2012), until recently very little was known about how (and if) active faults in the North Island linked up to those in the South Island [ Carter et al , 1988].…”

Crustal structure of the Kermadec arc from MANGO seismic refraction profiles

“…[] interpret the basin stratigraphy as an east verging thrust wedge and suggest that the western part of Raukumara basin preserves the Cretaceous Gondwana trench slope. Paleomagnetic declination anomalies show that the Raukumara Peninsula has rotated with the Australian plate since 22–19 Ma [ Roberts , ; Rowan and Roberts , , ].…”