High-temperature Contact Metamorphism at the Red Hills Ultramafic Intrusion-Wairau Valley--New Zealand

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Abstract
High-temperature contact metamorphism at the contact of an alpine-type ultramafic intrusion is described. Permian spilitic volcanics and tuffs within a zone about 750 yards in width are converted to amphibolites and pyroxene hornfelses. In the amphibolites the colour of the amphibole changes from green to brown-green and finally to deep brown at the contact. Two-pyroxene hornfelses are developed at the contact, together with wollastonite, grossular, and hydrogrossular. Chemical changes in the amphiboles across the contact aureole are: increase in (Na+ K) and (Al(6) + Fe+3+ Ti) approaching the contact, and progressive decrease in the water content. Similar chemical changes are noted in a lens of country rock included within the main ultramafic intrusion.

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