RECONNAISSANCE SANDSTONE GEOCHEMISTRY, PROVENANCE, AND TECTONIC SETTING OF THE LOWER PALEOZOIC TERRANES OF THE WEST-COAST AND NELSON, NEW-ZEALAND

Broad chemical characteristics of sedimentary rocks from the Buller an d Takaka Terranes have been examined, and provenance and tectonic sett ing inferred, using whole-rock major and trace element data from 208 s amples. Buller Terrane rocks west of the Karamea Batholith (Greenland Group) have chemistry typical of turbidite sediments deposited at a we athered passive continental margin. Bulk chemical characteristics conf irm earlier work, except that a small spatial chemical variation is se en, consistent with the presence of a small volcanogenic component in the south, decreasing to the north. East of the batholith, composition s of the Webb and Roaring Lion Formations overlap with those of the we stern Buller rocks, supporting equivalence (at least in part) with the Greenland Group. Passive margin chemical characteristics are maintain ed throughout the succeeding Ordovician formations. Within the Takaka Terrane there are sharp contrasts in chemistry between the Cambrian an d post-Cambrian (Ordovician-Silurian) successions. Cambrian formations have low SiO2/Al2O3, K2O/Na2O, Chemical Index of Alteration (CIA), Th /Sc and Ce/Sc ratios, and high Ti/Zr and V/La ratios. These features, together with provenance discriminant scores and enrichments in elemen ts linked with mafic minerals, are compatible with deposition adjacent to an active volcanic are. In the post-Cambrian units, element abunda nces and indices change systematically up the column, consistent with cessation of are activity and influx of quartzose elastic detritus in a passive margin setting. Chemistry of samples in the Ordovician inter val common to both Buller and Takaka Terranes is similar, indicating t hat the rocks probably both had Gondwana sources. Small anomalies, how ever, suggest that the two terranes may have had discrete source regio ns at the Gondwana margin.