New Zealand Journal of Geology and Geophysics abstracts

---

SHRIMP U-Pb geochronology of Cretaceous magmatism in northwest Nelson-Westland, South Island, New Zealand

R. J. MUIR^1*
T. R. IRELAND²⁺
S. D. WEAVER¹
J. D. BRADSHAW¹
T. E. WAIGHT^{1[[daggerdbl]]}
R. JONGENS¹
G. N. EBY³

1Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand

2Research School of Earth Sciences
The Australian National University
GPO Box 4
Canberra, ACT 0200, Australia

3Department of Earth Sciences
University of Massachusetts
Lowell, Massachusetts 01854, U.S.A.

Present addresses:

^*Isotope Geosciences Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, G75 0QF, U.K. and Department of Geology and Applied Geology, University of Glasgow, Lilybank Gardens, Glasgow, G12 8QQ, U.K.

⁺Department of Geological and Environmental Sciences, Stanford University, CA 94305-2215, U.S.A.

^{[[daggerdbl]]}Department of Geology, La Trobe University, Bundoora, Victoria 3083, Australia.

Abstract  Ion microprobe U-Pb zircon ages have been obtained from four samples of Cretaceous granitoid and two samples of volcanogenic sediment from the northwest Nelson-Westland region of the South Island of New Zealand. Crow Granite, which intrudes lower Paleozoic metasedimentary rocks in the Buller Terrane on the eastern side of the Karamea Batholith, has given a crystallisation age of 137 +/- 3 Ma (2[[sigma]]). This age is typical of the Jurassic-Early Cretaceous plutonic rocks that dominate the Median Tectonic Zone, and raises the possibility that the Western Province and the Median Tectonic Zone were linked some 20 m.y. earlier than previously proposed. The "Gouland granodiorite", which forms a large pluton at the northeastern margin of the Karamea Batholith, has a crystallisation age of 119 +/- 2 Ma (2[[sigma]]). This age is similar to the Separation Point Batholith (118 Ma), and the distinctive chemistry of the batholith (high Na, Al, Sr, and low Y) is also displayed by the Gouland granodiorite. The "Big Deep granite", which intrudes Devonian granites of the Karamea Batholith in the Upper Buller Gorge, has a crystallisation age of 110 +/- 3 Ma (2[[sigma]]), similar to the age of Buckland Granite (Rahu Suite) in the Paparoa Batholith. Berlins Porphyry in the Lower Buller Gorge also has a mid-Cretaceous age of 111 +/- 2 Ma (2[[sigma]]). Two samples of Stitts Tuff from the Lower Buller Gorge have given crystallisation ages of 101 +/- 2 Ma (2[[sigma]]) and 102 +/- 3 Ma (2[[sigma]]). These ages constrain the timing of initiation of fault-bounded sedimentary basins on the West Coast, related to a major period of crustal extension before the opening of the Tasman Sea Basin.

Keywords  Cretaceous; granite; geochronology; U-Pb isotopes; zircon; New Zealand

New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 453-463

0028-8306/97/4004-0453 $7.00/0 (c) The Royal Society of New Zealand 1997

PDF file of entire paper: medium quality (1026K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page