Authigenic pumpellyite and other metamorphic effects in the Kyeburn formation, Central Otago

Abstract

Pumpellyite occurs as part of the metamorphic assemblage quartz-albite-pumpellyi-techlorite-sericite ± calcite ± ?stilpnomelane, in relatively shallow buried sandstones of the mid-Cretaceous Kyeburn Formation. In addition heulandite-clinoptilolite and montmorillonite occur in previously unrecorded tuff layers in the same formation, the former replacing both glassy matrix material and plagioclase feldspar. Coal rank and inferred depths of burial suggest that P-T conditions could have scarcely exceeded 50–130°c and 0 · 5–1 Kb.