New Zealand Journal of Geology and Geophysics abstracts

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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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