Geochemistry of the Greenland Group (early Ordovician), New Zealand

Abstract

The Greenland Group is a uniform quartz-rich greywacke-argillite sequence, of early Ordovician age, characterised by the following geochemical features: K₂O >Na₂O, CaO < 1.5%, Rb ≫ Sr. These features reflect the distinctive mineralogy of the Greenland Group, which contains little feldspar or volcanic detritus and appears to consist of varying proportions of two end-members, quartz and clay, with little other clastic material. Lower Ordovician rocks elsewhere in New Zealand and south-east Australia are also reported to be distinctively quartzose, and can be expected to have similar geochemical characteristics. The mineralogical and geochemical maturity of the Greenland Group suggests that it is polycyclic (but derived originally from a plutonic source), and that: the parent rock for the final cycle was a widespread quartzose sedimentary or metasedimentary unit.