EARLY PALEOZOIC TERRANES IN NEW-ZEALAND AND THEIR RELATIONSHIP TO THE LACHLAN FOLD BELT

Two tectonostratigraphic terranes of Palaeozoic age are recognised in the Western Province of New Zealand, separated by the north-trending Anatoki Thrust. The Buller (western) terrane is composed largely of a relatively uniform suite of quartz-rich clastics (mainly turbiditic sandstone), siltstone and black shale and ranges from basal Ordovician to Late Ordovician in age. It is an equivalent of the Ballarat-Bendigo belt of Victoria. The Takaka (eastern) terrane contains a varied assemblage of Middle and Late Cambrian volcanics, volcaniclastics, carbonates and turbidites, Ordovician carbonate, shale and sandstone, and Silurian quartzite. The closest equivalent in Australia is Early Palaeozoic rocks of west Tasmania. The main deformational events, in the latest Ordovician or Silurian (Buller terrane), latest Silurian (Takaka terrane) and ?Middle Devonian (both terranes), can be equated with the Benambran, Bowning and Tabberabberan Orogenies of eastern Australia respectively. Palaeozoic granites are restricted to Buller terrane, and are spread over a belt 300-450 km wide. Age range (on sparse isotopic data) is 370-310 Ma (Late Devonian-Carboniferous), with the bulk in the Early Carboniferous. S-type granite predominates, with several A-type granites and a single I-type. The similarity in the nature and timing of the main events in the sedimentary, tectonic and volcanic history of New Zealand clearly link it with the Lachlan Fold Belt. On the other hand, the age and chemistry of the S-type New Zealand Palaeozoic granites make it unlikely that they are the direct equivalents of granite terranes of the Lachlan Fold Belt or Antarctica.