New Zealand Journal of Geology and Geophysics abstracts

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Late Pliocene stratigraphic succession and volcanic evolution of Karioi volcano, western North Island, New Zealand

G. G. GOLES

Department of Geological Sciences
1272 University of Oregon
Eugene, Oregon 97403-1272, U.S.A.

R. M. BRIGGS

Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand

M. D. ROSENBERG

Institute of Geological & Nuclear Sciences
Wairakei Research Centre
Private Bag 2000
Taupo, New Zealand

Abstract  Karioi, in western North Island, New Zealand, is the northwesternmost volcano of the Alexandra Volcanic Lineament. Active from c. 2.48 to 2.28 +/- 0.07 Ma (unmodified chronology), its products comprise the Karioi Formation. That formation is here subdivided into the basal Te Toto Member (new) of basaltic lavas and breccias erupted from small central-vent volcanoes; the middle Whaanga Member (new) of shield-building basalts and basaltic andesites erupted from fissures; and the uppermost Wairake Member (new) of cone-building basalt, basaltic andesite, and andesite lavas, tuffs, vent breccias, dikes, and valley-filling lavas and laharic deposits on the surface of the Whaanga shield. Wairake units were erupted from at least two distinct central vents. Karioi is surrounded by small monogenetic volcanoes of the Okete Formation that erupted basanitic, alkali olivine basaltic, and hawaiitic magmas and formed scoria cones, lavas, and tuff rings. Okete Formation is subdivided into units that predate Karioi volcano (Pauaeke Member, new), and those that postdate Karioi volcano (Marumaruaitu Member, new). Pauaeke volcanism occurred between 2.58 +/- 0.06 and 2.48 Ma, and Marumaruaitu volcanism between 2.37 +/- 0.08 and 1.90 +/- 0.07 Ma. Early Okete and Karioi units erupted from vents close to sea level, onto a gently westward-sloping, mostly subaerial plain. This plain had been veneered by beds referred to as Ohuka Carbonaceous Sandstone. The Karioi area has experienced little or no net uplift during the late Pliocene and Pleistocene, as opposed to elsewhere along the west coast. Its stability may have been facilitated by fault-bounded detachment of the Karioi block and loading of the crust by the volcano itself.

Keywords  late Pliocene; stratigraphy; Karioi Formation; Okete Formation; Alexandra Volcanic Lineament; Te Toto Member (new); Whaanga Member (new); Wairake Member (new); Pauaeke Member (new); Marumaruaitu Member (new); Ohuka Carbonaceous Sandstone; Pliocene-Pleistocene; deformation; new stratigraphic names

New Zealand Journal of Geology and Geophysics, 1996, Vol. 39: 283-294

0028-8306/96/3902-0283 $2.50/0 (c) The Royal Society of New Zealand 1996

PDF file of entire paper: medium quality (1280K); (scanned from paper original: notes about this process)

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