The Alpine dyke swarm of western South Island, New Zealand comprises a suite of highly alkaline lamprophyres with associated tinguaite, trachyte and carbonatite differentiates (Cooper 1986) . Intrusion of dykes, sills and diatremes occurred in late Oligocene-early Miocene times along tension joints and shears related to the propagation of the Alpine Fault plate boundary through southern New Zealand. In an area centred on Haast River, felsic and carbonatitic differentiates occur, and many dykes

more »

... arry nodules of gabbro, and varieties of syenite. Seismic profiling suggests a subjacent shallow magma chamber. Elsewhere lamprophyres carry mantle-derived nodules and have risen directly from the melt zone without appreciable crustal fractionation. High pressure nodule-bearing lamprophyres range between end-member feldspar-free ouachitite and feldspar-bearing camptonite. Mineralogically they are composed of olivine ' titansalite, kaersutite, titanphlogopite or titan-biotite, titanomagmetite or ilmenite, apatite, calcite and occasional perovskite with minor interstitial analcime, sodalite or alkali feldspar in ouachitite and plagioclase in camptonite. Chemically both lamprophyre types are highly alkaline ultrabasic rocks with marked degrees of undersaturation expressed normatively by high n^, common ]x, and, when calculated on a volatile-free basis, c£. Nodule-bearing dykes have high Cr, Ni and Mg^ values suggesting near primitive melts. As with other members of the swarm lamprophyres exhibit highly fractionated REE patterns with (La/Yb)^^ in the range 14.8 to 46.2. Enrichment in large ion lithophile (Th, Ba, Rb, Sr) and high field strength (Ti, Ta, Nb) incompatible elements, together with the REE data, indicates similarity to within-plate alkaline rocks. Lamprophyres are thus chemically equivalent to hydrated and carbonated nephelinites with ouachitites approaching melilite-nephelinite and camptonite transitional to nepheline basanite. Nodules of inferred high pressure origin in ouachitites and camptonites can be divided into three main types: Cr-diopside series, Al-augite series, and amphiboleapatite series. Megacrysts of pargasite-kaersutite, clinopyroxene (ranging from endiopside, through titanaugite and titansalite, to sodian ferrosalite), olivine, biotite, and titanomagnetite occur in many dykes, but it is often unclear as to whether such crystals are comagmatic or xenocrystic. Cr-diopside series nodules have a textural variation ranging from coarse equant to porphyroclastic, with minerals typically showing effects of deformation in the kink banding of olivine and orthopyroxene. In order of abundance nodules comprise spinel harzburgite, spinel Iherzolite and wehrlite. Typically olivine ^ Ca-Al enstatite (EnQQ_Q") dominate, with minor chrome diopside and Cr-spinel or chromite (Cr/Cr + Ai^O.55 to 0.80). Cr-diopside occurs as discrete grains and as a component of intergrowths with spinel. The symplectites being interpreted as forming by exsolution from orthopyroxene. Titanian chromian magnesio-hastingsite (dissimilar in composition to the amphibole of the host ouachitite) and phlogopite occur by partial replacement of Cr-diopside, indicating metasomatic alteration of Iherzolite at depth. One composite nodule shows a phlogopite-Tr-Cr-magnesio-hastingsite-bearing Iherzolite intruded by a vein of pargasite-diopside-phlogopite-apatite-calcite. Lherzolite phases show a progressive decrease in ^ towards the vein over a distance of 1.5cm (e.g. olivine Foq, .is replaced by Fog^). Vein mineral chemistry is totally dissimilar to that of the host ouachitite suggesting an episode of diffusion, related to magma intrusion, postdating the pargasite-phlogopite metasomatic alteration of Iherzolite, but predating entrainment of the nodule. Comparison of amphibole-and phlogopite-free Cr-diopside series nodules with similar examples worldwide (Frey and Green 1974; Frey and Prinz 1978) shows typical enrichment in MgO, Cr, Ni and Cu and low concentrations of Al20g,