New Zealand Journal of Geology and Geophysics abstracts

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Age relationships and tectonic implications of late Cenozoic basaltic volcanism in Northland, New Zealand

IAN E.M. SMITH

Department of Geology
University of Auckland
Private Bag 92 019
Auckland, New Zealand

T. OKADA T. ITAYA

Hiruzen Research Institute
Okayama University of Science
1-1 Ridai-cho Okayama, 700, Japan

PHILIPPA M. BLACK

Department of Geology
University of Auckland

Abstract An episode of late Miocene - Recent essentially basaltic volcanism is the latest in a sequence of magmatic events recognised in the tectonically complex geological development of the Northland Peninsula. New K-Ar dates together with an extensive collection of new major and trace element chemical analyses prompt a reassessment of the significance of these late Cenozoic basalts. The main time/ space groupings recognised are Tertiary volcanics in the Kaikohe - Bay of Islands, Puhipuhi, Ti Point, and Stony Batter areas and Quaternary basalts in the Kaikohe - Bay of Islands and Whangarei areas and at Tara. Basalts in the Kaikohe - Bay of Islands area are transitional to alkalic in character, while those in the south are transitional to tholeiitic, with the Ti Point and Stony Batter rocks being geochemically distinct. A consistent model for these observations is that the magmas originate from different levels of a layered mantle source in which the upper part carries a geochemical signature inherited from an earlier subduction event.

Keywords Kerikeri Volcanics; Ti Point Volcanics; late Cenozoic; basalts; K-Ar; geochemistry; Northland

Received 26 August 1992; published 14 September 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 385—393
0028Ð8306/06/3603—0385 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (848K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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