GEOCHEMISTRY OF THE KARAMEA BATHOLITH, NEW-ZEALAND AND COMPARISONS WITH THE LACHLAN FOLD BELT GRANITES OF SE AUSTRALIA

The Karamea Batholith in the Buller terrane of the South Island New Ze aland forms part of an extensive Middle-Late Devonian belt of magmatic activity along, or close to, the Paleo-Pacific margin of Gondwana, Th e belt includes the I- and S-type granites of the Lachlan Fold Belt in SE Australia and coeval rocks in Antarctica. The northern half of the Karamea Batholith comprises five main intrusive phases: Zetland Diori te, Whale Creek Granite, Karamea Granite, O'Sullivans Granite and Dunp hy Granite. To the east of the Karamea Batholith in the Takaka terrane , ultramafic-mafic Devonian igneous rocks are represented by the Riwak a Complex. The rocks forming the Karamea Batholith are a high-K calc-a lkaline suite ranging in composition from metaluminous (ASI for Zetlan d Diorite = 0.8) to strongly peraluminous (ASI for Dunphy Granite = 1. 2-1.3). Initial Sr-87/Sr-86 ratios exhibit a large range from 0.705 in the Zetland Diorite to 0.719 in the Dunphy Granite. The corresponding values for epsilon(Nd) are -0.3 and -9.2. There is a strong inverse c orrelation between epsilon(Nd) and initial Sr-87/Sr-86, which suggests that the Karamea rocks were generated by a simple mixing process. The mafic end-member (with epsilon(Nd) = 0), which is itself probably der ived from a mixed lithospheric source, is taken to be the Zetland Dior ite/Riwaka Complex, and the crustal end-member is represented by Ordov ician Greenland Group greywackes that form the country rocks to the ba tholith. Mixing is also supported by recent U-Pb zircon studies. The i nherited zircon population in the granites matches the detrital zircon population in the Greenland Group greywackes. The Whale Creek Granite , Karamea Granite and O'Sullivans Granite can be modelled by 20-30% cr ustal material, whereas the Dunphy Granite appears to represent 65-85% crustal material. In terms of the I-S classification scheme developed for the Lachlan Fold Belt granites in SE Australia, both types are pr esent in the Karamea Batholith. However, in New Zealand there appears to be a continuum from one extreme to the other, which is consistent w ith the mixing model presented here.