Establishing the P-T path for Alpine Schist, Southern Alps near Hokitika, New Zealand

Abstract

Pressure-temperature pseudosections for 'greyschist' (metamorphosed greywacke and argillite) from the Alpine Schist (Haast Schist group) near Hokitika (Southern Alps, New Zealand) are used to gain new insights into its metamorphic history. The rocks were metamorphosed at relatively low-grade conditions associated with the first appearance and initial growth of garnet in the stability field of albite. The measured and predicted garnet compositional zoning data are used to construct an overall P-T path by combining P-T path results from nearby rocks that have a range of MnO contents. The P-T path obtained is steep from ∼380 °C/2.5 kbar up to ∼490 °C/8.5 kbar, then recurves sharply with garnet ..