New Zealand Journal of Geology and Geophysics abstracts

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The age, geology, and geochemistry of the Tapuaenuku Igneous Complex, Marlborough, New Zealand

J. A. BAKER*
J. A. GAMBLE

School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand

I. J. GRAHAM

Institute of Geological and Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

*Present address: Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 OEX, England.

Abstract  The Tapuaenuku Igneous Complex (TIC) is a mid-Cretaceous layered intrusion and dike swarm cropping out at the axis of the Inland Kaikoura Ranges, South Island, New Zealand. The TIC is part of an extensive, but poorly preserved, igneous province that formed during or after cessation of subduction along the margin of Gondwana c. 100 Ma ago.

The TIC is a complex, multiphase intrusion that is subdivided into eight units (in order of relative emplacement): (1) radial dike swarm--basanite, trachybasalt, and shoshonite/latite dikes; (2) Layered Series (LS)--basin-shaped mafic cumulate rocks; (3) Staircase Intrusives--noncumulate gabbro and monzogabbro enclosed by a discontinuous sheet of cumulate gabbro; (4) Lower Hodder Gabbro and minor gabbroic intrusives--small stocks of noncumulate gabbro, monzogabbro, and monzonite; (5) Red Hills Breccia Pipe--heterolithic breccia emplaced in a pipe or diatreme; (6) Hodder Intrusives--a monzonite and sodalite syenite laccolith intruding the LS; (7) monzonite, orthoclase syenite and quartz syenite sills and dikes, and; (8) highly alkaline lamprophyre, phonotephrite, tephriphonolite, and phonolite dikes.

The plethora of rock types in the TIC were produced by fractionation of different mineral assemblages from a trachybasalt or basanite parent magma. The parental magma had incompatible trace element and radiogenic isotopic characteristics similar to HIMU-type ocean island basalt and akin to that of the numerous Cenozoic intraplate volcanic provinces situated in southern New Zealand. However, elevated initial Sr isotope ratios of some of the intrusive units requires them to have assimilated Torlesse greywacke country rock.

Keywords  Cretaceous; Tapuaenuku Igneous Complex; layered intrusion; radial dike swarm; Lookout Volcanics; cumulate; pyroxenite; gabbro; syenite; lamprophyre; phonolite; trachybasalt; shoshonite; latite; ocean island basalt; crystal fractionation; crustal assimilation

New Zealand Journal of Geology and Geophysics, 1994, Vol. 37: 249-268

0028-8306/94/3703-0249 $2.50/0 (c) The Royal Society of New Zealand 1994

PDF file of entire paper: medium quality (5271K); (scanned from paper original: notes about this process)

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