New Zealand Journal of Geology
and Geophysics abstracts
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
C. J. Rowan
A.
P. Roberts
Southampton Oceanography
Centre
European Way
Southampton SO14 3ZH, United Kingdom
G. J. Rait
Talisman Energy Inc.
3400, 888 3rd St SW
Calgary, Alberta T2P 5C5, Canada
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.
Keywords Hikurangi
margin; paleomagnetism; Neogene; rotation; Raukumara Domain; Wairoa
Domain
G03071; Received 10 December
2003; accepted 20 April 2004; Online publication date 23 March 2005
New Zealand Journal of Geology
& Geophysics, 2005, Vol. 48:
185–196
0028–8306/05/4801–0185 © The Royal Society of New Zealand 2005
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