Early Paleozoic terranes of New Zealand

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Abstract
Lower Paleozoic rocks of New Zealand comprise two major assemblages each with their own distinct sedimentary tectonic, metamorphic and igneous history; they thus represent two distinct tectono-stratigraphic terranes. In Nelson-Westland, the western, or Buller, terrane consists of the Western Sedimentary Belt, together with Ordovician paragneiss at Charleston and in Victoria Range. The sedimentary sequence, ranging in age from basal to Upper Ordovician, comprises continentderived quartz-rich turbidites with black shales inferred to have been deposited in submarine fans and slope basins. The eastern, Takaka terrane (Central and Eastern Sedimentary Belts) is much more varied in lithofacies, composition and age (Cambrian to Silurian) and itself comprises several tectonic, probably thrust, slices. Volcanics, volcaniclastics, siliceous and calcareous siltstone, conglomerate and turbidites dominate the Cambrian part of the sequence and indicate proximity to a Cambrian island arc. The oldest sediments are felsic volcanics and, possibly, melange and bedded chert (Floran, Middle Cambrian). Thick basinal limestone followed by quartz-rich turbidite span the Ordovician whereas a single thick quartzite represents the Silurian. Both terranes have undergone multi phase deformation. In the Buller terrane widespread folding and low grade metamorphism in the late Ordovician or Silurian (Greenland Event) was followed by reverse faulting and block rotation in Middle or Late Devonian time. The major deformational event in the Takaka terrane took place in the earliest Devonian (Pre-Baton tectonic event) and it too was followed by local faulting and tilting in the Middle to Late Devonian. A major intrusive episode in Buller Terrane rocks is represented by the S-type Karamea Suite granitoids, in contrast to the coeval mafic-ultramafic Riwaka Complex in the Takaka terrane. The two terranes are separated by the Anatoki Thrust, which can be traced from Paturau River south to the Alpine Fault at Springs Junction. The terranes and intervening fault have been displaced in a right-lateral sense by the Cenozoic Alpine Fault and are recognised by Ward in SW Fiordland. The most probable time of docking of the two terranes is earliest Devonian, but the contrast between them in Middle-Upper Devonian plutonic types suggests that final suturing may post-date the Upper Devonian (in which case Devonian sediments and igneous rocks in each terrane should be regarded as part of that terrane sequence).

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