New Zealand Journal of Geology and Geophysics abstracts
Northland Allochthon infolded into basement, Whangarei area, northern
New Zealand
K. B. Spörli
Rebecca E. Harrison
Department of Geology
University of Auckland
Private Bag 92 019
Auckland, New Zealand
email: kb.sporli@auckland.ac.nz
Abstract Northland Allochthon at Parua Bay and north
Ocean Beach, east of Whangarei, consists of Late Cretaceous-Oligocene Mangakahia
and Motatau Complex units. At both localities, deformed allochthon was emplaced
onto autochthonous early Miocene basal Waitemata Group (which rests unconformably
on Mesozoic Waipapa Terrane rocks) along a shear zone indicating westward
or southwestward transport. This contact was subsequently deformed by east-west-trending
folds, causing northward overturning of units at Parua Bay and tight infolding
between two blocks of autochthon at north Ocean Beach. At north Ocean Beach,
intrusion of a dike/sill related to the Miocene Kauri Mountain Pluton predated
the infolding. Other folds with similarly oriented axes and the same northward
vergence have been found south of Whangarei Harbour. These north-verging,
east-west-trending structures represent a north-south shortening after the
emplacement of the Northland Allochthon not previously recognised. They indicate
that the “autochthonous” blocks in the region were unusually mobile and may
in fact be parautochthonous. The significance of the northward vergence of
these late folds in the Whangarei area is not yet clear. Possibly equivalent
structures indicating similar late north-south shortening are distributed
throughout the northern North Island, but most commonly verge south.
Keywords Northland Allochthon; post-allochthon deformation;
infolding; basement; Whangarei; Parua Bay; north Ocean Beach; shortening
G03045; Received 12 May 2003; accepted 20 November 2003; Online publication
date 7 September 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 391-398
0028-8306/04/4703-0391 © The Royal Society of New Zealand 2004
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