Provenance analysis of the Paparoa and Brunner Coal Measures using integrated SEM‐cathodoluminescence and optical microscopy

Abstract

An integrated approach using grain‐by‐grain comparison of SEM‐cathodoluminescence (CL) andpetrographic characteristics was applied to investigate the provenance of fluvial/lacustrine quartz‐rich lithic arenites deposited in the Late Cretaceous transtensional Paparoa Basin in New Zealand. Results show most quartz in the Paparoa Basin was derived from a relatively low grade metamorphic source, most likely the underlying metasedimentary Greenland Group. This interpretation is supported by the presence of sedimentary lithics and Greenland Group conglomerate clasts in the Paparoa members. The eastern part of the basin is characterised by the addition of detrital chlorite and muscovite, some clearly replacing potassium feldspar in retrograde metamorphic lithoclasts, the lack of plutonic quartz, and an increase in polycrystalline metamorphic quartz. All this indicates an increase in metamorphic grade of the source area to the east upward through the stratigraphic section followed by a decrease. Such a change in grain type most likely reflects the migration of the basin past the exposed metamorphic rocks of the Paparoa Metamorphic Core Complex to the northeast of the strike‐slip Paparoa Tectonic Zone. On the west side of the basin, c. 15% of quartz grains are also derived from a plutonic source, probably the Barrytown Granite pluton or similar intrusions. Our provenance information provides the first concrete evidence for sinistral strike‐slip fault movement as predicted by tectonic reconstructions.

Keywords:

• Paparoa Coal Measures
• Brunner Coal Measures
• SEM‐cathodoluminescence
• provenance
• Greymouth Coal Field
• sinistral strike slip