Abstract
Abstract Microphotometric methods of coal rank assessment have been applied to dispersed coal fragments (phytoclasts) in metasedimentary rocks of the central North Island Torlesse sequence. To the east (Kaweka Range), zeolite facies rocks have phytoclast mean maximum reflectances of <1%, increasing through the prehnite-pumpellyite and stilpnomelane zones in the west (Kaimanawa Mountains) to a maximum of 10% reflectance. Graphite has been found in rocks approaching greenschist grade, but faulting has complicated the pattern of mineral and reflectance isograds. Reaction kinetic models show that the duration of heating has a major influence on the rank attained by the coal and this must be taken into account when comparing data from different metamorphic terranes.
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