Alteration, age, and emplacement of the Tangihua Complex Ophiolite, New Zealand

Abstract

The Tangihua Complex, New Zealand, represents an upper sequence of Late Cretaceous oceanic crustal material: massive basalt flows, pillow lavas, and dolerites. Three phases of alteration are preserved within the complex, each characterised by zeolite precipitation, which correlate to stratigraphic position. The mylonitised sole contains greenschist assemblages (c. 325°C) grading upwards into the initial phase of alteration (250–300°C), and is characterised by actinolite, epidote, albite, and Narich zeolites. This phase is cut by lower temperature veins of chlorite‐smectite and Carich zeolites. The final alteration phase (<50°C) precipitated K+and Ca2+‐rich minerals, including apophyllite and calcite. Disruption of Ar/Ar spectra around 50 Ma correlate with rifting in the Loyalty Basin and initiation of obduction along the Loyalty‐Three Kings Ridge system. We suggest that these events resulted in initial dismemberment, alteration, and movement of the ophiolite, whereas Ar/Ar plateaux at 25–35 Ma correspond to ophiolite emplacement and the last phases of alteration.